# Erowid/BlueLight Neuropharmacology Text



## BilZ0r

I contacted erowid recently, with the proposal to write a text that would hopefully bring the laymen up to a reasonable standard, as far as neuropharmacology/neurophysiology goes, in regards to psychoactive drugs.

The erowid team replied, saying that they would love it.

What I'm now proposing to you guys, is that we write it. I suggest that a single person is asked to write a section/chaper (hopefully one you're familiar with). Erowid suggested using a Wiki, and I think that after we've written it up in posts in here, we can port it over to one, and link it all up.

The chapter layout I proposed to erowid basically looked like this

-What is a cell (BilZ0r)
---What is a Neuron? (ksi and BilZ0r)
-What is a Protein?
---How proteins are produced (crOOk and BilZ0r)
-----What is a receptor? (BilZ0r)
-----What is an Enzyme? BilZ0r)
-Electrical properties of the Neuron (BilZ0r)
---Ion Channels
-----Voltage Gated Ion channels (BilZ0r)
-----Ligand Gated Ion channels (BilZ0r)
-Chemical properties of the Neuron
---The synapse (BilZ0r)
---G-Protein Coupled Receptors, and signalling cascades (BilZ0r)
---Homeostasis in Neuronal Signalling (BilZ0r)

Special Topics
-Pharmacokinetics (BilZ0r)
-Learning, memory and addiction on a cellular level (BilZ0r)
-Monoamine transporters and the amphetamines (BilZ0r)
-GPCRs under the microscope (mitogen)

Drug Glossary

And then maybe some special topics, like neurotoxicity, or anything a particular contributor has a zest for (so long as its appropriate).

Right, so do I have any volunteers? Any suggestion on changing the chapter structure

Printable PDF available here
http://img208.imageshack.us/img208/489/bluelightneuropharmacolmk2.pdf


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## raybeez

BilZ0r said:
			
		

> *I contacted erowid recently, with the proposal to write a text that would hopefully bring the laymen up to a reasonable standard, as far as neuropharmacology/neurophysiology goes, in regards to psychoactive drugs.*



Sounds like a neat idea. I have a good background in neurophisiology, so I'd be up for doing a writeup about the electrical properties of a neuron. It shouldn't be too hard explaining action potentials, sodium/potassium current, membrane depolarization, etc in a simple, easy to understand way. 

My only worry is that some of those proposed chapter topics would be hard to conceptualize without some background in biochemistry (ie what is a protein/enzyme/lipid) and cell biology, (ie plasma membrane structure/function). Maybe there should be an introductory chapter on some of these basics, focusing on the aspects relevant to some of the subsequent chapters.


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## BilZ0r

Well those exact things are what hopefully is going to be covered in the first two chapters... With "what is a neuron", explaining what a cell is, what the important parts of a cell are... and what is a receptor, what is a protein, about protein production, about enzymes...

There, I edited the chapter structure, so that receptors and enzymes are both subchaters under a protein section.

What I'm really looking for is someone to write something about Voltage Gated Ion channels... Although I understand them (the concept is preety simple), I feel that it would still be better if someone who felt they really had a good grasp of it wrote it (sure we would be going into Hodgkin-Huxley kinetics or anything, but still...)


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## BilZ0r

Well you sound perfect to tackle a section on how proteins are produced... That shouldn't be a very big section.. transcription, translation... an explaination that the cell can traffic the protein either intracellular or to the membrane...

You think that sounds like it would be enough?


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## raybeez

BilZ0r said:
			
		

> *Well you sound perfect to tackle a section on how proteins are produced... That shouldn't be a very big section.. transcription, translation... an explaination that the cell can traffic the protein either intracellular or to the membrane...
> 
> You think that sounds like it would be enough? *



Sure, easily doable. I'll PM you with a question or two that I have.


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## mitogen

*exactly how complex do you intend to make this?*

writing a textbook is, as i am sure you am already aware bilZ0r, an incredibly large undertaking...
is it designed to be a general summary providing links and resources or a fully self-contained tome?

either way, i'd be happy to contribute.
protein structure (and its intergration with neuropharmacology) and general molecular cell bio is really my field. i know quite a lot about trafficking and mitogenesis etc.

this said, i'd have to be more than slightly conceited to think that i can write definitive articles on, say, the structure of connexin or something

-james


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## BilZ0r

*Writing a textbook is an incredibly large undertaking...
is it designed to be a general summary providing links and resources or a fully self-contained tome?*

Ah my man! I wondered when you'd show up...

...Well it's going to be neither I hope... not a list of links, or a tome... hopefully it will be the kind of thing you could read in a 2 to 3 sittings... I hope each chapter will be around 500-2000 words... Depending on the chapter, I don't you'd even references, just a bibliography...

So would you be down for writing a chapter? Maybe down regulation, and desensetization of receptors?


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## mitogen

i think it would be interesting to have two parts to each chapter: the first being a general intro, and the second being a collection of some of the latest research in the field.
just a link to an abstract, a couple sentences describing the paper, then a sentence saying why this particular piece of research is exciting.

receptor trafficking is good for me. signalling, transmodulation etc. and protein structure... 

we need a geneticist

damn my mum just found my pot of opium tea and chucked it :/ "what are you doing brewing up plants? youll poison yourself! you know your father just sprayed everything in the garden with Confidor?"
lol...
she thinks the opium poppies are poisonous...


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## BilZ0r

... well I hope to keep it pretty simple if someone wants to get advanced then they can go read neuropsychopharmacology the 5th generation or something...

I don't think we really need a geneticist, there isn't much genetics that is relevant to the pharmacology of recreational drugs... not in my opinion at least.

I wasn't really going to have much of a mention on receptor trafficking, as a) it's relavence to recreational drugs is limited b) it's pretty advanced and c) it's still pretty uncharted... Don't you think? But any of those chapters above apart from the one raybeez has taken, are still open.


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## ksi

Ive read neuropsychopharmacology one of the editions. I dont know much about it anymore. But Im sure I can assist a bit in writing up a bit.
Besides that we had a good dutch print of some of the most important chapters for our farmacotherapy course.


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## BilZ0r

Whats your educational background? Is there any chapter you're especailly skilled to tackle?


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## mitogen

*"-Chemical properties of the Neuron
---The synapse
---G-Protein Coupled Receptors, and signalling cascades
---Receptor downregulation"* 
sounds like me

also,
"what is tolerance and how do the mechanisms vary between drugs?"
molecular tolerance:
-desensitization
-downregulation
pharmacokinetic tolerance etc.

also,
perhaps a chapter on some psych experiments, like discriminative stimulus etc. would be good.
i know sweet FA about that sort of stuff. would be interesting to learn a bit more.

also, maybe a comment on how a little knowledge of the underlying pharmacology of recreational substances can enhance the safety or comfort of using that substance.
for instance (not the greatest example but i cant think of anything better right now,) MDMA induced hyperthermia, or the fact that tolerance develops to the majority of the effects of opioids, but that this does not include inhibition of gastric motility (constipation!)


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## BilZ0r

Well we'll put you down for downregulation and desensitization for the moment?


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## thinctwo

Maybe I am missing something here, but I do not see any drug-related material in the proposed chapter layout.  
Is this to serve simply as an introduction to the neural system, or are specific 'neurotoxins' going to be discussed?


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## BilZ0r

An introduction to the neural system, with the objective of helping people understand other research on recreational drugs.

Thats why we don't need to cover molecular biology, because that interaction isn't probably particularly important in regards to recreational drugs.

Hopefully, where appropriate, people will use recreational drugs as examples though.


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## Pander Bear

my high school/college bio/anat/phys should give me adequate background for what is a cell, and the important parts of a cell, and if anybody jumps ship on "how a neuron works", I could pick that up too. . Can we use copyrighted images. Lord knows most of these concepts are better expressed through diagrams.


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## Dope_User

atlas, it shouldn't be a problem using copyrighted images as long as they are identified as such and cited in a bibliography.


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## Sledge

I just finished the chapter in my school book about enzymes (I study biochemistry) so I can write about them. I could use common enzymes working in drug metabolism, inhibition by MAO's, and some other things. I really don't know what enzymes has to do with the neuropharmacology but if it needs to be explained I'll gladly do so. Since english isn't my primary language there might be some grammatical errors, hopefully some of you could fix them.


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## astarythe

i think creating an extensive glossary (preferably with a feeback page and refular updates) would be really helpful; i'd bookmark it. 
    i've only taken cog-neuro at an undergraduate level, and find that a major problem for me  is not knowing the shorthand for specific neurotransmitters that i only know the group name for. 

   Similarly a section on how abbreviations, acronyms, & other diction are conjoined would be helpful. 

   I'd be happy to collaborate with atlas on how a neuron functions. if i can find my notes/tests i have also have alot of drawings (some rather meticulously done). i can contribute those, and possibly do more drawings for other topics if needed.

   I'd also be willing to do some work for the vocab section.  This page might help for vocab if nothing more: http://www.neurotransmitter.net/drugmechanisms.html


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## BilZ0r

I think it would be best to create our own diagrams...

If you "don't know what enzymes has to do with the neuropharmacology", then it's probably best if you don't write the section specifically dealing with that question.


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## C10H12N20

This text is the best idea I have seen on Bluelight as of yet...


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## mitogen

Hmm, might I suggest that people only write things that they believe they have an extensive interest in.


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## BilZ0r

^^^ I hoped that was kind of implied... either interest or knowledge...

Anyways, heres my first attempt at a chapter, have fun hacking it to bits (Figures will come much later).

Electrical properties of the Neuron

As already mentioned, one of the most distinctive and functionally important property of a neuron is that it is electrically excitable. This excitability is an emergent property of the neurons ability to alter its *membrane potential* (the word potential can be used interchangeably with voltage). All cells have a membrane potential, and it is generated by the uneven distribution of charged atoms (ions) across the cells membrane, which is impermeable to these ions. The most important ions for generating and altering the membrane potential are the positively charged sodium (Na+) and potassium ions (K+), and the negatively charged chloride ions (Cl-). In general, Na+ and Cl- is found at a higher concentration outside the cell, while K+ is found at high concentration inside the cell. The distribution is found because a protein, usually called the Na+-K+ pump (or ATPase), swaps three intracellular Na+ ions for two extracellular K+ ions. Not only does this action produce a *chemical gradient* of high extracellular Na+ and intracellular K+, but it also produces a *electrical gradient* because it swaps three intracellular positive charges, for two extracellular positive charges i.e. a net movement of one positive charge out of the cell. The eventually leads to a difference of charges, i.e. a voltage, of somewhere around –50 to –80mV. This is called the *resting potential*

Because particles have a natural urge to equally distribute themselves (2nd law of thermodynamics), it can be said that there is a chemical driving force on these unevenly spread ions. Na+ wants to flow into the cell, and K+ wants to flow out of the cell (i.e. into the areas where the particular ion is at low concentration). Because charged particles are attracted to areas of opposite charge, there is also an electrical driving force on the ions. Na+ wants to flow into the negatively charged cell, which would make the cell more positive, and if this was allowed to happen, it would make the cell increasing positive until the cell became so positive it began to repel the positively charged Na+. Eventually, the electrical force pushing Na+ out would become equal to the chemical force drawing it in. The voltage at which a cell would usually reach this Na+ equilibrium is around +55mV (called the Na+ *equilibrium potential* or reversal potential).

K+ wishes to leave the cell because of its high intracellular concentration and if it did so, it would make the cell increasing negative, until the electrical force drawing K+ back into the cell caused K+ flow to reach equilibrium. This K+ equilibrium potential is around –75mV. Because Cl- is a negative ion, it is repelled from entering the negative cell, even though there is a chemical force drawing it in (because of the high extracellular concentration). So Cl- has its equilibrium potential around –60mV, or very close to the membrane potential. This means that if the cell at resting potential became permeable to Cl-, not much Cl- would flow. Ca2+ is another important ion, which is distributed nearly exclusively extracellularly, and has an equilibrium potential of around +60mV. Importantly, you can see that _the distribution of a particular ion, and the charge of the cell, dictates that ions equilibrium potential, which is the voltage that ion is trying to pull the cell towards_.

This brings us back to the important property of the neuron: it is excitable. A neuron’s cell membrane can rapidly change its permeability to particular ions, by opening *ion channels*. Ion channels are pores formed by proteins that allow the flow of ions (usually a particular kind). Usually, these ion channels are can be opened (i.e. gated), by chemicals or by the cells voltage, which leads these kinds of ion channels to be called ligand, or voltage gated ion channels respectively. These channels are explained in more detail in the next chapters. 

If the membrane of a cell were to suddenly become permeable to K+ ions due to potassium channels opening, potassium would flow out of the cell. This would make the cell more negative than its usual resting potential, down to a maximum of the K+ equilibrium potential of –75mV. When a cell becomes more negative than usual, it can be described as being *hyperpolarised*. If, on the other hand, the cell became permeable to Na+ ions, because of sodium channels opening, Na+ would flow into the cell, making the cell less negative, and up to a maximum of +55mV. When a cell becomes less negative than usual it can be described as being *depolarised*.

You can see that the neuron has a mechanism for changing its membrane potential. While it may not be obvious to you now why this is so important, it will be explained in the following chapters how this allows the neuron integrate as well as transmit information over long distances.


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## BilZ0r

Voltage gated ion channels

As already mentioned ion channels are pores in the membrane of a cell which allow ions to pass through the otherwise impermeable membrane. These channels can be gated (i.e. opened) by various things. In this chapter we will look at ion channels which can be gated by the voltage across the cells membrane itself, or *voltage-gated ion channels*.

There are many individual kinds of voltage-gated ion channels, but all we will be concerned about are three large families, voltage-gated sodium, potassium and calcium ion channels; channels, which when open pass sodium, potassium and calcium respectively.

The most important function of two of these voltage gated ion channels is to generate the *action potential*. The action potential is a often thought of as an electrical signal which passes down the axons of neurons, like current down a wire. In reality it is caused by a chain reaction of voltage gated ion channels opening. The third channel is responsible for converting the electrical nature of the action potential into chemical signals a neuron can deal with. 

If a part of a neuron expressing voltage gated sodium and potassium channels (usually the axon and cell body) became depolarized (less positive) to around –50mV, voltage gated ion channels start to become active i.e. they reach threshold. At the cell body, the fastest activating voltage gated ion channel is the sodium channel. The sodium channels start to open, allowing Na+ to enter the cell, further depolarizing the cell, encouraging more sodium channels to open. The Na+ passively diffuses down the axon of the neuron, causing neighboring areas of neurons to become depolarized, where further voltage gated sodium channels open. This causes a chain reaction of Na+ entering the cell, depolarizing close-by areas of cell, opening further sodium channels, causing more Na+ to pour into the cell etc… If this were to happen unabated, the neuron would fire one action potential, Na+ would reach its equilibrium potential and the cell would become electrically dead. But two things happen to stop this, 1) sodium channels *inactivate* and 2) slower activating potassium channels being to open.

Inactivation of sodium channels happens normally around 1 millisecond after they begin to open. Inactivation is a transient block of a channel, which in the case of voltage gated sodium channels is caused by a length of the protein which forms the channel, physically blocking the channel like a cork. This inactivation limits both the time and voltage of the action potential. As stated, inactivation is transient, and if the neuron wasn’t returned to its resting potential, or at least below threshold, as soon as inactivation passed, the sodium channels would open again. This is when voltage gated potassium channels began to play their part. As potassium channels take about 1-2ms to open after they reach threshold, they are beginning to become fully activated when sodium channel inactivation is in full swing. K+ ions being to flood out of the cell, rapidly making the neuron more negative (repolarizing). Potassium channels do not show inactivation, but as they act to repolarize the cell the pull it below the threshold for sodium and potassium channel activation, which closes the potassium channels.

Importantly the action potential is *all-or-none*, that is to say, the body can’t code information in the amplitude of the action potential, the action potential either happens or it doesn’t. The body codes information in the frequency of action potentials. For instance, in neurons which transmit pain, more painful stimuli causes the neurons to fire more frequently, but with the same amplitude. Cocaine, apart from its well-known action of increasing dopamine, also blocks voltage gated sodium channels, which stops the formation and propagation of the action potential. This is why it causes numbness, by blocking the transmission in sensory neurons.

Finally, when the action potential has travelled the whole length of the axon, it depolarizes the ends of the neuron, (usually -synaptic terminals-), here voltage gated calcium channels can open, causing Ca2+ to enter the cell. This Ca2+ influx causes neurotransmitter release (as described in *the synapse*). Although this Ca2+ influx shares many properties with the sodium/potassium action potential, it is not all-or-none. Alcohol is believed to inhibit Ca2+ channel function directly (Hendricson et al., 2003), and many common drugs effects Ca2+ channel indirectly. For instance, D9-THC from cannabis and yohimbine from Yohimbe. By effecting Ca2+ influx, these drugs effect neurotransmitter release (discussed further in *the synapse* and *G-Protein Coupled Receptors, and signalling cascades*).

References
Hendricson AW, Thomas MP, Lippmann MJ, Morrisett RA. Suppression of L-type voltage-gated calcium channel-dependent synaptic plasticity by ethanol: analysis of miniature synaptic currents and dendritic calcium transients. J Pharmacol Exp Ther. 2003;307(2):550-8


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## BilZ0r

Ligand gated ion channels

Ligand gated ion channels are, as their name suggests, channels in a cells membrane that are gated by ligands, i.e. drugs/chemicals. The physiological role of nearly all ligand gated ion channels is to receive chemical signals in the way of neurotransmitters (discussed further in *the synapse*), and to transduce them to electrical signals. In order for these ion channels to be gated by a neurotransmitter, they have a *receptor* for the specific neurotransmitter as part of the proteins that make up the receptors. Therefore the ion channel complex is often refereed to by the name of the neurotransmitter/chemical/drug which is has a receptor for, and for the rest of this chapter we will largely use this style.

The two most common types ligand gated ion channels (also called ionotropic receptors) are the ion channels that are opened by the neurotransmitters glutamate and GABA, or ionotropic glutamate and GABA receptors. The ionotropic glutamate receptors may be further divided up into AMPA, kainic acid and NMDA receptors (named after drugs that specifically activate these types). While it is possible to further subdivide these receptors based on the individual proteins that make them up, it is outside the scope of this text. AMPA and kainic acid receptors are generally similar; both are opened by glutamate and both are largely selective for the flow of Na+ ions, which in all physiological situations is into the neuron. This flow of Na+ depolarizes the cell, making it more positive and bringing it closer to the threshold for firing an action potential. Because of this, it can be said that AMPA and kainic acid receptors are “excitatory”. The NMDA receptor is an anomaly amongst ligand gated ion channels, in that it is also partially voltage gated. The channel of the NMDA receptor has a site in which Mg2+ ions can sit. This Mg2+ is much larger than the normal ions that flow through the NMDA receptor (Na+ and Ca2+) and hence blocks it. When the cell partially depolarized, positive Mg2+ ions begin to be pushed out of the NMDA receptor channel (presumably because of the positive charge inside the neuron repelling it). Also, because the NMDA receptor is very permeable to Ca2+ channels, not only does it depolarize (excite) the cell, it also can cause many of the chemical changes within the cell caused by Ca2+ (see *G-Protein Coupled Receptors, and signalling cascades*). Largely, it is the release of glutamate, and its action of ionotropic glutamate receptors that allow one cell to excite another cell into firing (although usually it requires 100s of cells to release glutamate onto a cell to cause this).

The most famous drugs which directly effect ionotropic glutamate receptors are the so called “anaesthetic dissociates”, e.g. ketamine, PCP and DXM. These drugs all block the NMDA receptors ion channel, i.e. they are NMDA channel antagonists. Alcohol's actions is thought to be at least in part due to its ability to block NMDA receptor channels (Woodward, 2000).

The ligand gated ion channel that is gated by GABA is called the GABA-A receptor (to distinguish it from the non-ion channel GABA-B receptor). This channel is largely selective for the transit of Cl- ions. As stated before, Cl- ions have a reversal potential of around -60mV, so if a cell has a resting membrane potential of around –60mV GABA-A receptors do not cause much of an effect on membrane potential i.e. they neither hyperpolarise nor depolarise the cell. But if the cell is being depolarised by the action of ionotropic glutamate receptors, then GABA-A receptors strongly oppose this, and hence its action is often referred to as inhibitory).

A wealth of drugs directly effect GABA-A receptors, specifically benzodiazepines and barbiturates which bind to sites apart from the GABA binding site or the channel, to increase channel opening only when GABA normally opens the receptor. This is an example of *allosteric modulation*, and is a common feature of ligand gated ionc channels. Muscimol is a direct agonist, acting like GABA. Alcohol is also though to stimulate GABA-A receptors, though whether this is a direct action is still debated (Aguaya et al., 2002)

There are other kinds of ligand gated ion channels, though the only ones which have much relevance to recreational drugs are the ionotropic acetylcholine and serotonin receptors, also called the nicotinic and 5-HT3 receptors. Both of these receptors are ligand gated sodium channels. Nicotine activates the nicotinic receptor, and serotonin, which could be released by the action of MDMA, can activate 5-HT3 receptors (which may cause MDMA-induced vomiting). There are also the glycine, P2X and VR1 ligand gated ion channels expressed in the central nervous system.

As you can see, ligand gated ion channels are an important (probably the most important) mechanism of neuron-to-neuron communication, and drugs acting on this form of chemical to electrical transmission have a powerful way to alter neuronal activity (discussed more in *Signalling properties of neurons*).

References
Woodward JJ. Ethanol and NMDA receptor signaling. Crit Rev Neurobiol. 2000;14(1):69-89.


Aguayo LG, Peoples RW, Yeh HH, Yevenes GE. GABA(A) receptors as molecular sites of ethanol action. Direct or indirect actions? Curr Top Med Chem. 2002; 2(8):869-85.


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## BilZ0r

^^^ 2400 words in a day, not bad... The bolded words are where I think we should have links to other chapters...


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## specialspack

Im sure there's plenty of people with adequate undergrad + cell biology and chemistry to make redundant anything i might have to offer, but id just like to say what a fantastic idea this is, and mad props to you all for undertaking such a piece of work.


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## hyperborea13

There is a FAQ on neuroanatomy right here on bluelight, 

http://www.bluelight.ru/vb/showthread.php?s=&threadid=100189&r=10

I think it would make this project more comprehensive if it was used as a sort of introduction.  Just throwing this out there.


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## BilZ0r

What is a Receptor?

Pharmacologically speaking, a receptor is a structure where a chemical/drug binds with some kind of specificity, and produces some kind of biological effect. A chemical that binds to a receptor is called a ligand. Receptors are usually locations on proteins where ligand binding can cause a change in the shape (conformation) and cause the protein to become ‘active’ in some way. Ligands basically come in two main types: ones that bind to a receptor and activate it, or ones that bind to the receptor and do not activate it, these are called agonists and antagonists respectively. Ligand binding also happens in two main ways, *reversibly* and *irreversibly*. Simply a ligand may either approach, bind to and dissociate from a receptor, in a fully reversibly manner, or when a ligand binds to a receptor chemical bonds (covalent) form between them, effectively locking the ligand onto the receptor. Most recreational drugs are reversible ligands, though there are some exceptions (deprenyl).

The reversible binding of ligands is caused by an electrostatic attraction between the ligand and the receptor. Parts of the ligand that may be positively charged might have corresponding negatively charged areas on the receptor, and the converse for negatively charged parts of the ligand to positively charged sections of the receptor. This is why ligands that bind to the same receptors often have similar structures: they must all fit into the same location.

Generally speaking, neurotransmitters and hormones are agonists at receptors. However many drugs are antagonists at receptors. Although strictly speaking a receptor is simply a location on a protein, with the exception of enzymes, often the entire protein is labeled as the receptor for its most famous ligand e.g. the entire protein which is activated by nicotine is called the nicotinic receptor. This double use of the word receptor can become confusing when a protein has many receptor sites on it e.g. the GABA-A receptor protein not only has a receptor for the neurotransmitter GABA, but it also has independent receptors for benzodiazepines, barbiturates and thujone. These different ligands alter the activity of the same protein, but do not compete for the same receptor, hence one can describe them as *non-competitive* ligands, e.g. thujone is a non-competitive antagonist of the GABA-A receptor. On the other hand many drugs are *competitive*, for instance most antipsychotic drugs compete for the same binding site as dopamine on dopamine receptors so it can be said they antipsychotives are competitive antagonists at the dopamine receptor. One can also have situations whether neither of these terms explain the drug in quesiton. The classical example of this are the benzodiazepines, drugs which bind to, and modulate the GABA-A receptor. These drugs are neither truely agonists nor antagonists, as they have no effect on the receptor themselves, however, they massively potentiate the activity of GABA. This is often called *allosteric modulation*, specifically positive allosteric modulation.

The situation gets more complicated still, when ligands can be not just agonists or antagonists, but somewhere in-between, or so called *partial agonists*. Partial agonists bind to and activate receptors, but not to the same extent as full agonists. This ability of a ligand to activate a receptors is called it' *efficacy*, and is usually given as a percentage of a full agonist, so an antagonist has 0% efficacy, while a full agonist has 100%, and a partial agonist has somewhere in-between. LSD and most other tryptamine and phenethylamine hallucinogens are partial agonists at a subtype of serotonin receptors called 5-HT2A receptors.

Ligands also can bind to receptors with varying affinities. The affinity for a receptor is a ratio of the rate at which a ligand binds to a receptor to the rate at which it unbinds, but it is usually thought of as just the attraction a ligand has for the receptor. One can think of a ligands affinity and efficacy like a key in a lock. A keys ability to fit into the lock is its affinity, but its ability to open the lock is its efficacy. A drugs affinity is also sometimes called its *potency*.


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## fastandbulbous

*One extra bit*

For the section "what is a receptor", I don't know if you wanted to include one extra bit, or whether you'd rather deal with it somewhere else; namely the area of agonists/antagonist/inverse agonists where a drug can modulate an ion channel (the benzodiazepine/flumazinil example is the one that springs to mind). Although it might seem that an inverse agonist is an antagonist, an antagonist will simply reverse the effect of an agonist, whereas the inverse agonist will have the opposite pharmacological effect.

Using the benzodiazepine  example, an agonist (your common benzos) are anticonvulsants; the antagonist flumazenil reverses the actions of the agonist, but it also reverses the actions of an inverse agonist (convulsant). On its own, in the absense of an agonist or inverse agonist, an antagonist has no physiological effect


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## BilZ0r

Well I talk about it a bit in the ligand gated ion channel section.. maybe I'll talk about it a bit more.


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## astarythe

*....*

As far as helping to compile a glossary goes, I've vocabulary is something that I'm intersted in as a hobby of late...  but I don't want to commit to taking on the whole thing.

That you arlready have key words in bold makes it easier, and if you want I could use those to begin.

If you'd rather someone with a stronger background tackle this, or if you don't think its important at this juncture, I won't take offense.

Also if i should go through my notes to see what i have for diagrams, let me know. (I should have some  relevent to the text you already have).


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## BilZ0r

Yeah, the bolded words are also words I'd like to have in a glossary/index.

When it comes to diagrams, I know they are vitaly important, unfortunatly I don't have Adobe Illustrator, and I'm not very skilled with it... so I'm really going to have to rely on others to create the images needed. Though next weekend, or perhaps sooner, I'm gonna go through and do some rough images...


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## ksi

2 |  The  neuron

The neuron is a type of cell that is located in your body. The brain is the part of your body where the most neurons are located. There are about 10 billion interconnected neurons. These cells function by biochemical reactions. Through these reactions they can receive, process and transmit data from one cell to another (see *the synaps* chapter).

So there are alot of interconnected neurons. They can all communicate with eachother. On one cell there are more neurons which communicate with that cell. A neuron first needs to get signals from other neurons before they can fire. That can happen through spatial and temporal summation. When alot of impulses are added together it's called a spatial summation. When there is a serie of weak impulses this can form a bigger one. That's called temporal summation. The input of these impulses will lead to the cell body. This cell body and his nucleus wont play any significant roll in the signaling between neurons. Their roll is to maintain the neuron so they can still signal eachother.

The part of the neuron that is important for the signal is called the axon hillock. If the threshold value is crossed, then the neuron will give an action potential (for details behind this mechanism see the chapter *Electrical properties of the neuron*). This signal will be passed down the axon 
and wil be converted to a biochemical signal instead of a voltage signal in *the synaps*. The strength of this signal is always the same. If the original impulses are one hundred times greater then the threshold, the axon hillock will still send a signal of the same strength. So the output of the signal down the axon in a neuron is always the same. 


(neuron  picture (axon/dendrite/soma))


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## BilZ0r

I was imagining less about the signalling properties of neurons (as that can get discussed more fully in the 'signalling properties of neurons' chapter), and more just about basic anatomy... the cell body, the dendrites, the axon...


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## BilZ0r

The synapse

As already mentioned in the “*What is a neuron*”, the synapse is junction between axonal terminals and another cell (nearly always a neuron, but sometimes a muscle, or a cell specialized hormone release cell) what has been modified for the release and effect of neurotransmitters. There are also so called “*electrical synapses*”, where neurons are electrically coupled by channels (gap junctions) that pass through both of the cells’ membranes and allow the passage of ions and small organic molecules, but these synapses are poorly understood and are outside the scope of this text.

The action at the synapse in its simplest form is easy to understand. When an action potential invades the axonal terminal, it causes voltage sensitive calcium channels to open (see *Voltage Gated Ion Channels*) and Ca2+ floods into the channel. The Ca2+ influx causes the neurotransmitter containing vesicles to fuse with the membrane of the cells, and to release their contents into the synapse. Here the neurotransmitter diffuses across the synapse and can interact with its appropriate receptor and depending on the neurotransmitter and the receptor, this can have any of the myriad of effects that receptors are capable of inducing in a cell (See *Ligand Gated Ion Channels* and *G-Protein Coupled Receptors*). The neurotransmitter could also diffuse back and activate presynaptic receptors. 

As stated above, the Ca2+ influx caused by the action potential invading the presynaptic terminal and opening voltage sensitive calcium channels is the signal for neurotransmitter release. Not only can drugs directly effect calcium channels, like alcohol, which inhibits them, and hence decrease Ca2+ influx and neurotransmitter release, but presynaptic receptors can effect their activity. For instance, when the CB1 receptor is activated, it causes the activation of a multi-subunit protein called a G-protein (discussed further in *G-protein coupled receptors and signalling networks*). The particular type of G-protein which CB1 receptors activates binds to and inhibits calcium channels, which inhibits the release of neurotransmitter. That G-protein also activates a potassium channel, which causes potassium to leave the presynaptic terminal that lowers the presynaptic depolarization and reduces the number of open Ca2+ channels, and neurotransmitter release.

You can see that the important role of the synapse is a place to release neurotransmitters in order to transmit signals from one cell to the other. However, just as important as the release of neurotransmitter is the termination of their action, because if neurotransmitters weren’t cleared they would continue to act indefinitely. Also, in order for any neuronal signals to have any degree of temporal, spatial or amplitudinal resolution they must be able to be discerned from each other, i.e. they can not ‘blur’ together. Neurotransmitters are cleared by the action of enzymes and/or by molecular carriers (generally called transporters). The enzymes metabolize the neurotransmitter to inactive compounds (i.e. they do not act at receptors) and the transporters carry the neurotransmitter from the extracellular fluid to the intracellular compartment, so that they can not act on receptors any more. Drugs that effect neurotransmitter transporters or enzymes that break down neurotransmitters increase the action of the appropriate neurotransmitter. Cocaine is the classic example of a transporter inhibitor (aka a reuptake inhibitor), it inhibits the uptake of dopamine by the dopamine transporter. The enzyme which breaks down monoamine neurotransmitters (dopamine, serotonin, noradrenaline and adrenaline) monoamine oxidase (MAO), is the target of many pharmaceutical drugs like the antidepressant, MAO inhibitors (MAOIs), and most amphetamines have some action as MAOIs.

So, the synapse is place where two neurons connect and signal to each other. By effect release, reuptake or degradation of neurotransmitters, drugs have a powerful way of modulating synaptic transmission. Indeed, it would be safe to say that the vast majority of psychoactive drugs act directly at the synapse.


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## BilZ0r

What is an enzyme? By Anonymous

Enzymes are proteins that could be simply described as molecular catalysts; that is to say, they massively increase the rate of specific chemical reactions. Enzymes generally have a small cleft or crevice in their surface where the chemicals they act on (substrates) can bind; this is referred to as the enzyme’s “*active site*”.  Importantly, the activity of most enzymes can be regulated, either by chemicals that reversibly bind to receptors on the enzyme, or by the action of other enzymes that can bond small chemicals to the enzyme. For instance, the dopamine precursor L-DOPA inhibits the enzyme that produces it, tyrosine hydroxylase. Also dopamine receptors alter the activity tyrosine hydroxylase by covalent bonding or removing of phosphate molecules through activating other enzymes call protein kinases or protein phosphatases respectively. In the case of tyrosine hydroxylase the addition of a phosphate (phosphorylation) increases the rate at which it forms L-DOPA, while dephosphorylation slows it down. This is not the case with all enzymes, but generally, phosphorylation/dephosphorylation alters the rate of enzymes and also effects the behavior of receptors (discussed further in *G-protein coupled receptors and signaling networks*). Indeed, this kinda of enzyme cascade, where one enzyme activates another enzyme, which activates another enzyme etc. is a very common theme in neurons and other cells in the body.

Enzymes are not a particularly common target for recreational drugs. Monoamine oxidase (MAO) is an enzyme that breaks down both natural (endogenous) neurotransmitters but also chemicals which are ingested. Several antidepressants block MAO that inhibits its normal function of breaking down dopamine, serotonin and norepinephrine (also called noradrenaline). Beta carbolines from Banisteriopsis caapi or syrian rue are also MAO inhibitors, and are vital components of ayahuasca, because they stop the breakdown of DMT caused by MAO in the gut.

The most important thing to appreciate about enzymes is that they cause a selected chemical process, and that their activity can be modulate in many ways.

For more information, the interested reader should consult: Campbell, N.A. & Reece, J.B. (2002). Biology. pp. 24-103. San Francisco: Benjamin Cummings.


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## ksi

there are still a bit of topics which arent in the planning of making.. (yet)
so if there are still volunteers i think bilz0r is glad to get some help on some of the topics.


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## mitogen

wanna talk about kinase cascades and phosphorylases in signalling, LTP and LTD?
otherwise, that was well written


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## BilZ0r

*What is a cell?*

What is a cell?

A cell is “the lowest level of structure capable of performing all the activities of life” (Campbell et al., 1996). Physically, a cell is a collection of molecules contained within a membrane of some kind, capable of reproducing itself, energy utilization and other hallmarks of life. While some forms of life exist as single cells, so-called “higher life forms” can only sustain life as a collection of cells; they are multi-cellular. In many multi-cellular life forms groups of cells have undergone some form of specialization and aggregated into tissue so that the individual cells (and hence the tissue) are well suited to a particular task. Hepatocytes are the primary cells of the liver, and contain a huge array of metabolic enzymes, allowing the liver to degrade potentially dangerous chemicals and create complex molecules. Myocytes are the primary cells of muscles, and contain specially produced protein fibers which can change their length, allowing the muscle to contract and produce movement. Neurons are the cells of the nervous system, these unique cells allow information to be quickly sent from one part of the body to another. Neurons make rapid sensation and reaction possible and allow animals to change and learn new behaviors so that they are better suited to their environment.


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## BilZ0r

*What is a neuron?*

What is a neuron?

The most important properties of a neuron is its ability to fire an action potential and to release neurotransmitters. Anatomically, a neuron is analogous to a tree: it has roots in the form of a huge number of of branching dendrites (the receiving end of a neuron), it has a trunk, in the form of an axon (the transmitting section of a neuron) and a branches, in the form of axonal arborizations or terminals (Fig 1 and 2). Generally, a neuron can be seen as an integrator and disseminator of information. Figure 2 shows a real image of a single neuron filled so it can be visualize independently of the hundreds of neurons surrounding it. This image shows the dendritic spines of a dendrite (the small dots along the length of many of the dendrites). Each of those these spines will make at least one connection (or synapses) with a neighboring neuron, there will also be many synapses which we can not see, this means that this neuron makes thousands of connections with other neurons. Although we can not see it’s axonal terminals, it is safe to assume that this cell then makes thousands of connections with other neurons. Hence a neuron both receives inputs from a huge number of neurons, as well as giving inputs to a large number of neurons.



> *Figure 1.* Schematic of a neuron





> *Figure 2.* Micrograph of a filled neuron, probably a hipocampal pyramidal cell. Neuron image thanks to www.lebenswissen.de/pix/ Dendritic spine image thanks to tonto.stanford.edu/~viktor/



Functionally, a neuron is similar to a piece of wire, with a few changes. For one, information is generally only sent in one direction. Neurotransmitters are chemicals that are released by neurons in order to send signals to other neurons. Neurotransmitters are released by the axonal terminals of one cell, and diffuse across the synapse to the dendrites of another cell. Here neurotransmitters can bind to “receptors” and effect the neuron in many ways, but importantly they can alter the probability of it firing an “action potential”, the electrical signal which neurons send over long distances. These principles are discussed further in the “electrical properties of the neuron” and the “chemical properties of the neuron” chapters.

Another difference between a neuron and a piece of wire, is that a neuron can alter the nature of the information it is going to transmit depending on previous signals it has received, that is to say, it is not a passive conductor but a small processor, capable of making decisions. There are some 100 billion neurons in the brains of humans. Each one making and receiving thousands of connections. This results in an unfathomable number of connections and pathways, signals can move through the brain in. Integrative processing allows the overwhelming depth of information received by the sensory organs to be processed into discrete, meaningful perceptions. Conversely, the dissemination of information allows for associative processes to occur. These principles are discussed further in the “signaling properties of neurons”


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## 5-HT2

I'll do both proposed sections on signaling properties of neurons.

Also, I will write brief sections on the functions of the major neurotransmitters in brain.  I think the learning and memory portion can perhaps be put in the section for glutamate, because anything but the simplest mechanistic discussion of synaptic plasticity is too technical for the layman.


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## BilZ0r

I don't think functional discussion of neurotransmitters is really that constructive... functionallity is a function of release style, location of release, and receptor function... as well as g-protein trafficing... still, if you've got time to get into learning and memory (which hopefully should entail how addiction is just an abarant learning process) and how neurons alter each others signalling mechanism, potentially getting into burting, versus tonic, versus exclusively evoked neuronal firing patterns... Sure man... write something... anyone, write something...


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## BilZ0r

G-protein coupled receptors and signalling pathways

G-protein coupled receptors (GPCRs) are found in all animals so far investigated and even many plants and make up the single largest gene family in the human genome, indicating their importance as mediators of cell signaling. GPCRs should be of great interest to anyone investigating recreational drugs, as, for instance all of the opioid receptors, all of the 5 dopamine receptors, all of the 9 adrenoreceptors and all but 1 of the 13 or more serotonin receptors are GPCRs. GPCRs are large proteins that exist in the outer membrane of cells, with part of their protein exposed to the extracellular side (so that ligands can bind) and part of the protein facing the intracellular side (so that the receptor can effect the cell). GPCRs gain their name from their ability to bind to and activate guanine nucleotide-binding protein (G-proteins). These G-proteins allow the receptor to amplify the initial signal and effect many intracellular systems.

G-proteins are a complex of three separate subunits, called alpha, beta and gamma. The alpha subunit of the G-protein binds a guanine nucleotide: guanosine triphosphate (GTP) when the subunit is active and guanosine diphosphate (GDP) when the subunit is inactive. When an GPCR is in it’s neutral, non-active, agonist free state, it is not associated with a G-protein, however, when the GPCR becomes active because of agonist binding, the conformation of the GPCR is such that a G-protein can bind to its intracellular side. Once a G-protein binds to a GPCR it enhances a conformational change in it alpha-subunit, which causes the G-protein to release its molecule of GDP and bind a molecule of GTP. Now the G-protein dissociates from the GPCR and splits in two: into the alpha subunit and a beta-gamma subunit complex. These activated subunits can now alter the activity of many “effector systems”, for instance the GTP containing alpha subunit can effect many enzymes and proteins, while the beta-gamma complex often directly effects the activity of many ion channels and enzymes (fig. 1). If a G-protein activated effector system produces a molecule which continues the signaling cascade, then the molecule is called a 2nd messanger. The alpha subunit catalyses the breakdown of GTP of GDP, when this occurs the alpha subunit rebinds to the beta-gamma complex, ceasing both of their abilities to activate effector systems.



> *Figure 1.* The cycle of G-protein coupled receptors and their assocaited G-proteins



When a GPCR is activated by an agonist, as mentioned, G-proteins can bind, but this process is not limited to a single G-protein, indeed, as long as an agonist remains bound to GPCR it can activate many G-proteins. Likewise, the active forms of the alpha and beta-gamma subunits of the G-protein can activate many effector proteins. Furthermore, if the effector protein is an enzyme, each enzyme can produce a huge number of products while it is being activated by the G-protein subunits. This means that for a single agonist binding, a huge amplification of the signal can be transduced into the intracellular environment.

G-proteins and hence GPCRs can effect a huge variety of proteins, but there is specificity in their actions. The alpha subunits of G-proteins are not always the exact same kind of protein, indeed, there are over 20 varieties of alpha subunit (and there is a growing body of literature about multiple subtypes of beta and gamma subunits). The alpha subunits are usually sorted into 4, functionally different families, with each family containing anywhere from 2 to 9 different alpha subtypes. The families are alpha-s, alpha-i, alpha-q and alpha-12. G-proteins are generally named after the alpha subunit they contain, so that a G protein containing alpha-s is called G-alpha-s, or just G-s. These alpha families generally effect the same effector systems, alpha-s subtypes generally stimulate the enzyme “adenylyl cyclase”, alpha-i subtypes inhibit adenylyl cyclase and inhibit presynaptic Ca2+ channels, alpha-q subtypes stimulate the enzyme phospholipase C and alpha-12 effects various novel intracellular targets.

Different GPCRs have different affinities for G-proteins made up of different alpha subunits, so that some GPCRs will only couple to a particular G-protein. On the other hand many GPCRs couple to several kinds of G-proteins. Furthermore, in receptors that couple to two or more kinds of G-proteins, different agonists can cause the GPCR to activate a particular G-protein over other kinds, a processes called “agonist-directed trafficking”. For instance the serotonin 5-HT2A receptor has been shown to couple to G-alpha-q, G-alpha-12 and possibly the novel G-alpha-13. When serotonin binds to the 5-HT2A receptor it causes a roughly even activation of G-alpha-q and G-alpha-12, but psilocin activates G-alpha-12 roughly 25 times more readily.

Adenylyl cyclase (AC) is a very common enzyme, which converts the ubiquitous energy currency of the cell “ATP” into the 2nd messanger cyclic adenosine monophosphate (cAMP). cAMP activates kinases (enzymes which phosphorylate proteins); kinases which are activated by cAMP are fall into the protein kinase A (PKA) family, and regulate the activity of a huge number of receptors and ion channels especially (fig. 2). The effect of PKA on ion-channels can have profound effects on neuronal activity, for instance when a neuron is strongly excited (depolarized) it will generally fire action potentials in rapid succession, but the rate of firing will slow and after about 2 seconds firing will stop completely. This “accommodation” is due to the Ca2+ which enters the cell due to depolarization, activating calcium-activated potassium channels and hence positively charged potassium will leave the cell and attempt to repolarize the cell, preventing action potential formation. In certain cells, noradrenaline binding to beta-adrenoreceptors actives G-alpha-s G-proteins, which activates AC, which causes cAMP build up and activates PKA. PKA phosphorylates calcium-activated potassium channels, preventing accommodation. This means that cells which are strongly depolarized and exposed to noradrenaline (for instance, released by arousal or amphetamines) will continue to fire at a high frequency for a long time, where normally, they would fall silent. 

Phospholipase C (PLC) is activated by G-alpha-q and it breaks down particular fats in the membranes of neurons into two 2nd messenger products: inositol triphosphate (IP3) and diacylglycerol (DAG). These two molecules effect two different, but often-complimentary systems, IP3 binds to intracellular IP3 receptors on compartments within the cell (i.e. endoplasmic reticulum) and cause them to release Ca2+. DAG on the other hand activates protein kinase C (PKC) a kind of Ca2+ dependent protein kinase. You can see then that the two signaling molecules produced by the action of G-alpha-q on PLC work synergistically to increase the activity of PKC, although the Ca2+ released by IP3 can have many other effects. PKC (and other Ca2+-dependent protein kinases) effect a huge number of protein targets, but of special interest to neuropharmacologists is their effects on ligand gated ion channels (fig. 2). One of the classical effects of PKC is to phosphorylate the NMDA glutamate receptor (See ligand gated ion channels), and this phosphorylation can enhance the effect of the NMDA receptor or paradoxically increase its rate of inactivation depending on the particular nature of the PKC cascade. PKC can also enhance or depress AMPA glutamate receptors and GABA-A receptors.



> *Figure 2.* The signaling casaced of the three classical G-alpha subunits



As mentioned, the beta-gamma subunit complex can directly effect ion channels, the classic target being the so-called G-protein-coupled inwardly rectifying potassium (GIRK) channel. This class of potassium channel only opens when the cell is held at below –70mV, which stabilize the membrane potential by canceling any depolarizing (excitatory) currents by the opposing flow of K+ ions. This means that small excitatory inputs have no effect, and that larger currents are needed to raise the cell above –70mV, at which point excitatory inputs are much more efficient at exciting the cell. When the beta-gamma subunit complex binds to the GIRK channel it massive increase the current which can flow through them, meaning that an even larger excitatory current is needed to get the cell above the –70mV threshold needed to close the GIRK. Both the cannabinoid CB1 and Mu opioid receptor activate GIRK, though as both receptors act presynaptically, their effect is to reduce the Ca2+ influx at presynaptic terminals which induce transmitter release. In combination with the fact that both of these receptors couple to G-alpha-i containing G-proteins that directly inhibit Ca2+ channels, the end result of activation of these receptors is to reduce the amount of neurotransmitter released.

GPCRs also have many mechanisms for signaling to the nucleus of a cell, and hence to control gene expression, this area is still poorly understood, but probably effects many properties of the brain, such as receptor expression, propensity for learning and memory and cell division.


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## mitogen

how about 'what is the function significance of a.) diffuse modulatory neurotransmitter systems, and b.) what is all this talk about dopamine? (with regard to addiction and pleasurable sensations?)

sorry long time no see bilz0r, i've been working my ass off.  i'm doing a paper this semester entitled 'the neurobiology of addiction' (set up as a conjunct between Michelle Glass and some people from the behavioural science department) its gonna be tight. ill start writing a bit for the book when i get some decent references and material from that.

(OT: i'm reading Céline's journey to the end of the night. its very much my style - i wish i could write like that)


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## BilZ0r

Yeah, it's a good book that one.... Though the first half is much better than the second half.

yeah, the dopamine thing I'd like to get covered in the Learning and Memory section.. the diffuse/volume transmission section is something I'd like to cover in a special topic I want to write on amphetamines....

So are you ever gonna get around to written the section of Down regulation? It's something I don't know a whole heap about.... but I suppose the actual mechanism of down-regulation aren't as important as the functional consequences, though something on mechanisms might be helpful to help people understand how NMDA antagonists and other drugs could possibley help reverse tolerance.


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## mitogen

*spoiler* (i'm not up to the second half yet...)

mm kappa antagonists reducing opoid tolerance etc..

i am uber busy at the moment. hopefully that will change soon - i only have classes 3 days a week this semester, but I will probably have quite a bit of ongoing work, so yeh hopefully i will get around to starting it within 3-4 weeks or so.


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## who mE?

I would be happy to write the chapter on pharmacokinetics, including discussion and graphs of half-lives, steady-state metabolism, induction, inducers, plasma concentrations, oil/water partition coefficients, and drug-distribution.

Does anybody have any other topics within this subject they suggest I write about?

There should also be a section on the basic enzymes which are responsible for many of the metabolic breakdown pathways... Like glucuronization, oxidation, hydroxylation, etc... somebody else should do this part, because while I could look up all the enzyme names, I really don't have time for that.

I also would be happy to volunteer Wiki-space and webhosting, I'm involved in the Wiki developer community and could help you find the Wiki software which would be easiest to write a Neuropharmacology text with.  Feel free to IM/email me about this.


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## BilZ0r

^ Yeah, that sounds great. If you covered the basics of pharmacokinetics, absorption (passive (oil/water, stomach contents) active (rare)), distribution(BBB permiability, plasma proteins), metabolism (enzymes(induction/inhibition) and excretion I think that would just be the best shit out.

I was thinking of putting the final thing on wikipedia... but I don't really know anything about that, I don't really like the idea of some punter coming along and fucking with it...


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## BilZ0r

14BD: A GHB pro-drug, largely devoid of intrinsic activity.

2C-X: Chemicals such as 2C-B, 2C-I, 2C-E and 2C-T-7. These substitued phenethylamine hallucinogens have had little research devoted to them and nothing is known about their binding properties, though it is almost certain that they will be potent 5-HT2A receptor agonists. There is one paper show that 2C-I/B/D/H are 5-HT2A receptor antagonists, but this was demonstrated in a system which has little relevance to the complex nature of 5-HT2A receptor activation in the brain.

5-MeO-DMT: A tryptamine hallucinogen. It's hallucinogenic properties are attributed to its 5-HT2A receptor agonist effects though it is also a potent 5-HT1A receptor agonist.

Alcohol: See ethanol

Amphetamine: Cause the noradrenaline, dopamine and serotonin reuptake transporters to work in reverse (in that order of potency). Theses transporters normally take their respective neurotransmitter out of the extracellular fluid surrounding neurons and prevent them from binding to receptors, amphetamines cause the transporters to work in reverse, and move their neurotransmitters out of the cell, into the extracellular fluid. The action of amphetamines is dependent on them amphetamine passing through the transporter, hence the action of amphetamine is blocked reuptake inhibitors (like some antidepressants)

Benzodiazepines: A collection of pharmacologically and chemically related compounds which bind to the GABA-A ion channel, but at a site seperate to the GABA binding site. Benzodiazepines increase the affinity of the GABA-A receptor for GABA, and hence potentiate GABAs action.

Cannabidiol: Although often refered to as "non-psychoactive", cannabindiol is definately active. It has been shown to inhibit the anxiety inducing effects of THC [1] and be neuroprotective in many models of neurodegeneration. It has been consistantly shown that cannabidiol does not act on the CB1 receptor. It has been shown that cannadidiol acts by inhibiting the uptake and breakdown of the endogenous cannabinoid anandamide, but even if this action is replicated in vitro, the excess anandamide can not be acting on CB1 receptors. It has been hypothesised that Cannabidiol acts on the as yet uncharacterised cannabinoid receptor(s) which are speculated to exsist.

Cannabinoids: Cannabinoids are any of the chemically unique components in cannabis, though generally refers to psychoactive components. The classical cannabinoids are Ä9-tetrahydrocannabinol (THC), cannabinol (CBN) and cannabadiol (CBD).

Cannabinol: Another so called "non-psychoactive" cannabinoid. Reports show that it has very little or no psychoactive effects, though it definately has some physiological effects through unknown, non-CB1 receptor mechanisms. One report indicates it potentiates some of the effects of THC in humans[2].

Cocaine: Inhibitor of Dopamine, Serotonin and noradrenaline reuptake transporters, probably in that order of potency, leading to a higher level of these neurotransmitters in the extracellular fluid. Also blocks voltage sensitive sodium channels at low potency, which causes its local anaethetic action.

Codiene: A metabolic precursor of morphine (see opioids), converted to morphine by the liver enzyme CYP2D6.

DMT: One of the simplest members of the hallucinogenic tryptamine family. It's hallucinogenic activity is due to its agonist activity at 5-HT2A receptors, though it also has high affinity actions at 5-HT1A/D and 5-HT6 receptors, though not 5-HT1B receptors. It may have actions at other receptors, but these have not been studied at this time.

Ethanol: Alters the function of several ligand gated and voltage gated ion channels, including potentiating certain GABA-A receptors, certain nicotinic receptors, 5-HT3 receptors and glycine receptors while inhibiting NMDA receptors, voltage gated Ca2+, Na+ and K+ channels and certain nicotinic receptors. The most potent (and hence probably most important) actions of ethanol are potentiation of GABA-A receptor actions, inhibition of NMDA receptors, inhibition of voltage gated calcium channels and possibley potentiation of Nicotinic receptors.

Dextromethorphan: Classically known for its NMDA-receptor antagonist effects, it is actually a more potent serotonin reuptake transporter inhibitor. It also has significant potency for the sigma receptor. It is converted in the body, into dextrophan, which has a significantly higher NMDA receptor affinity.

GHB: Both an endogenous neurotransmitter and a recreational drug. GHBs highest affinity action is as an agonist at the GHB receptor, while it has a lower affinity action as an agonist at the GABA-B receptor. A lot of experimental results have indicated that the GABA-B receptor is the pharmacologically important target of GHB, but this is generally because the experimenters have used high doses of GHB and have recorded GABA-B dependent measures. It is likely that low doses of GHB in humans act primarily via the GHB receptor while higher, hynotic doses act via GABA-B.

GBL: A GHB prodrug, but as well is a more potent GABA-B receptor agonist

Heroin: See opioids

LSD: A prototypic indole hallucinogen. It's recreational, hallucingenic effect is largley due to its 5-HT2A receptor (partial) agonist effect. It also has marked affinity for 5-HT1A/B/E/F, 5-HT2B/C, 5-HT5A/B, 5-HT6, 5-HT7, D1, D2, D3, D4, D5, and alpha1A/B receptors. These effects on other receptors may explain LSDs unique potency and nature.

Ketamine: A dissociative anaethetic best known for its potent non-competative NMDA receptor antagonist effects. It has also been shown to be a sigma, 5-HT2[3], D2[3,4] and a relatively very weak (~20µM) kappa opioid receptor agonist (PDSP data) 

MDMA: An amphetamine which is about ten times more specific for releasing serotonin and noradrenaline than dopamine, though it probably still causes significant dopamine release through the serotonin it releases activating 5-HT2 receptors on dopaminergic cells or cells which control the firing of dopaminergic cells. MDMA itself is relatively weak at the 5-HT2A receptor (100x weaker than its actions at monoamine transporters)[5] 

Methamphetamine: An amphetamine which causes the release of noradrenaline, dopamine and serotonin (in that order of potency). Methamphetamine is probably more potent that amphetamine because it is less suceptable to metabolism and more rapidly pentrates into the brain.

Morphine: See opioids

Nicotine: Active chemical in tobacco. Nicotinic  binds to a wide variety of nicotinic acetylcholine receptors (ligand gated Na+ channels). Nicotine binds with high affinity to α4β2 nicotinic receptor although evidence indicates that it is the (α4)2α5(β2)2 and α4α6α5(β2)2 nicotinic on dopaminergic neurons that causes the addictive profile of nicotine [6].

Nitrous Oxide: Like most gaseous anaethetics, it's actions are somewhat of a mystery. It is likely that nitrous oxide's analgesic effects are somehow caused by the release of endogenous opioids, though its dissociative action are probably a mix of actions on ion channels (like those mentioned for ethanol).

Opioids: Any drug which shares a significant pharmacological similarity with morphine. Distinguished from "opiates" which are chemicals found in opium. Pharmacologically, opioids which are used recreationally have potent Mu-opioid receptor agonist effects, however most are non-specific agonists are all opioid receptor subtypes. 

Oxymorphone/oxycodone: See opioids

Salvia/Salvinorin: Salvia is a plant containing a large number of alkaloids and non-alkaloids, the most famous of which is Salvinorin A, which is a selective Kappa opioid agonist. It is believed that this is the mechanism for salvias psychedelic action.

THC: The architypal cannabinoid. A potent agonist at CB1 and CB2 cannabinoid receptors as well as actions which can not be atributed to either of those receptors.

1. Zuardi AW, Cosme RA, Graeff FG, Guimaraes FS: Effects of
ipsapirone and cannabidiol on human experimental anxiety. J
Psychopharmacol 1993;7:82-88.

2. Karniol IG, Shirakawa I, Takahashi RN, Knobel E, Musty RE.
Effects of delta9-tetrahydrocannabinol and cannabinol in man.
Pharmacology. 1975;13(6):502-12.

3. Kapur S, Seeman P.
NMDA receptor antagonists ketamine and PCP have direct effects on the dopamine D(2) and serotonin 5-HT(2)receptors-implications for models of schizophrenia.
Mol Psychiatry. 2002;7(8):837-44

4.Seeman P, Ko F, Tallerico T.
Dopamine receptor contribution to the action of PCP, LSD and ketamine psychotomimetics.
Mol Psychiatry. 2005 (epub)

5. Nash JF, Roth BL, Brodkin JD, Nichols DE, Gudelsky GA.
Effect of the R(-) and S(+) isomers of MDA and MDMA on phosphatidyl inositol turnover in cultured cells expressing 5-HT2A or 5-HT2C receptors.
Neurosci Lett. 1994;177(1-2):111-5

6. Wonnacott S, Sidhpura N, Balfour DJ.
Nicotine: from molecular mechanisms to behaviour.
Curr Opin Pharmacol. 2005 Feb;5(1):53-9


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## YellowPurpleHills

who mE, i am very excited about the chapter you are writing.  I can't wait to read it.  It would answer many of my questions.


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## crOOk

_Hmm... can't believe this hasn't been finished yet. There's so many knowledgable people on bluelight...

I'll try to write a short chapter about proteins:_

-What is a Protein?
Proteins are a certain type of biopolymers/biomacromolecules (molecules that are made out of very many components and therefore have a large molecular weight). They consist of the following elements: Carbon, Hydrogen, Oxygen, Nitrogen and Sulfur.
Every cell is made out of proteins and proteins are made out of amino acids chains that are interconnected by so called peptid bonds (Carbon-Nitrogen bonds). Peptid bonds can be broken down by making the proteins react with water. Since this process is very slow it is usually accelerated by enzymes (which are in fact, also proteins).
There are 20 different amino acids that proteins can consist of. The length of those "polypeptid chains" can be as short as less than 20 amino acids or as long as several thousand amino acids. This enables the proteins to have a large variety of functions. To mention just a few of them, they can function as enzymes, enable the muscles to contract or control many body processes as hormones.

_Feel free to add or modify any information that you feel is missing or incorrect._


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## BilZ0r

^ Thanks for contributing crook, says pretty much everything... If any of you other lazy sods wants to edit it, or add something or whatever... go ahead.


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## crOOk

Thx, I was afraid I forgot sth. So get off your lazy asses and write another chapter, all you chemist or whatever bluelighters.

crOOk


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## who mE?

for everybody's info... I'm being lazy cause I've got lots of other crap to do like look for a job and an apartment and do homework and work on consulting gigs... but I'll do my pharmacokinetics chapter *eventually* (lets say... by sept 1!)

*edit* got even lazier


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## moracca

I'm new here, but I think this is an excellent idea.  I have a very limited background in cell bioliogy and very little knowledge of pharmokinetics and the like, but if needed, I might be able to help create a few diagrams here and there?

//Moracca


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## crOOk

W00T! Great first post moracca!!!

@who mE?
He, we're all busy dude, working, school, house work etc.  Can't wait for your chapter though. Btw are you coming to the voov or not?

crOOk


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## moracca

Thanks!  I just came across the site today when it was referenced on another forum, and it seems like there are some very intelligent discussions that go a little deeper into how drugs work, which is a topic i'm very eager to learn more about.  Anyhow, let me know if I can be of service in any way.  I look foreward to expanding my mind on the bluelight forums.

//Moracca


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## crOOk

W00T! Another member! Dude, check it out, bluelight is a whole community with journals, galleries and shit unlike other forums. It's the shit.

crOOk


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## illuminati boy

Two things.... 

1) the likely audience for this writing is probably people who are semi-educated... in the sense that they probably know a few things about cells, chemistry etc., but have never heard of the likes of allosteric modulation or don't know that an agonist and antognist are not really 'true opposites' etc.  In that vein, it might be a good idea to have some links and/or suggested reading that is not right out of discipline specific journals.  Two books spring to mind; one pretty much 5HT specific, and the other very broad and in-depth, but still primarily aimed at a lay audience.  "Trips: How Hallucinogens Work In Your Brain" by Cheryl Pellerin  &  "Essential Psychopharmacology: Neuroscientific Basis and Practical Applications" by Stephen M. Stahl, M.D., Ph.D.  I am sure there are others as well, but the Stahl book is pretty comprehensive considering it's target audience.

2) regarding receptor profiles; I know that the NIMH-PDSP (National Institute of Mental Health Psychoactive Drug Screening Program) recently screened 19 psychedelic drugs against a large panel of receptors etc.  Many of these were newer RCs.  This list was something along the lines of 2C-B, 2C-B-fly, DOB, DOI, DOM, 2C-E, 2C-T-2, ALEPH-2, Mescaline, MEM, MDA, MDMA, DMT, 5-MeO-DMT, 5-MeO-MIPT, DIPT, 5-MeO-DIPT, DPT, & Psilocin if I recall.  So there is actually quite comprehensive data out there on the likes of 2C-T-2 and even 2C-B-FLY regarding their receptor affinities and effects on transporters and ion-chanels.  I am just not sure where the nitty-gritty data has been published, if indeed it has.

OK that's it.  I hope this might be helpful in some way and I will get out of the way now.  Please dont feel the need to de-rail the thread flaming me if I have proved a hinderence.


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## BilZ0r

> in the sense that they probably know a few things about cells, chemistry etc., but have never heard of the likes of allosteric modulation or don't know that an agonist and antognist are not really 'true opposites


 Is that in reference to anything in particular, or just in general? If you have anything you think needs changing give us a specific rewrite...


In regards to the PDSP data, I remember seeing something on MAPs about some due paying for screening for a bunch of hallucinogens, and talking about "receptor space" well, either way, the data on the propylthio- PEAs were never published either in journals nor on the PDSP database.


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## illuminati boy

Just in general, it might be a good idea to have a 'suggested further reading' section and/or some links to maybe some introductory online academic resources.

Yea I believe the receptor data was part of the 'receptor space' project.  But I'll be darned if I can find it anywhere...  It would sure be interesting to see though.


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## BilZ0r

Amphetamines and the monoamine transporter

*Introduction*
“Amphetamine” is a term given to a structurally related class of compounds sharing the alpha-methyl phenethylamine backbone. Although the amphetamines contain an array of pharmacologically distinct molecules, the classical amphetamine action is to raise the extracellular concentration of monoamine neurotransmitters (dopamine, serotonin and noradrenaline). Exactly how amphetamines cause the increase in monoamines is a complex, probably multifactorial mechanism, which will be reviewed here. 

*Facilitated exchange diffusion*
Amphetamines cause a massive increase in extracellular monoamines. Unlike reuptake inhibitors such as cocaine, which might cause a 200-400% increase in free monoamines, amphetamines can cause increase up to and over 1000%. This increase seems largely to be dependent on a group of integral membrane proteins collectively called the monoamine transporters. The monoamine transporter comes in four flavors, the dopamine, serotonin, noradrenalin and vesicular monoamine transporters, which are selectively expressed on dopaminergic, serotonergic, noradrenergic neurons and monoamine containing vesicles selectively. Each transporter is relatively selective for the monoamine that it gets it name from, though not exclusively. Exactly how monoamine transporters take monoamines from the extracellular space and into the neuron is unclear. Monoamine transporters are 12 transmembrane spanning proteins which are believed to function a homomultimers, and as well as their neurotransmitter binding site, they have Na+ and Cl- ion binding sites (figure 1). They transporter is generally believed to function by Na+ and Cl- first binding to the extracellular face of the protein, and then the neurotransmitter binds extracellularly. This binding somehow causes the protein to change conformation so that the extracellular binding sites are facing into the cell, the ions and neurotransmitter dissociate and hence are transported into the cell (figure 2). 



> Figure 1. Structure of the monoamine transporter, Red reflects negative region, and blue positive. Intracellular face at the bottom of the page from Ravna et al., 2003





> Figure 2. Model of monoamine transporter function



The first mechanism used to explain amphetamine function was the so-called “facilitated exchange diffusion” model by Paton, 1973. In this model, amphetamine binds to extracellular neurotransmitter binding site of the transporter, causing the transporter to move the amphetamine molecule into the intracellular space, leaving the neurotransmitter binding site open in the intracellular face (for at least as long as it takes the transporter to flip back to facing extracellularly). Over the entire cell, amphetamine should cause an increase in the proportion of intracellular facing transporters, and on the whole increase the rate of reverse transporter (that is transport of neurotransmitter out of the cell). The source of the monoamines which are susceptible to reverse transport is unclear. Obviously, these monoamines must be in the cytosol of the cell, and not contained in vesicles, however, whether these neurotransmitters must first be displaced from vesicles by facilitated exchange diffusion through the vesicular monoamine transporter, or whether free neurotransmitter levels inside the cell are enough to support reverse transporter is unknown.

Facilitated exchange diffusion is supported by a large number of relatively correlative observations. In order for the neurotransmitter to bind to the transporter, sodium must bind as well and in accordance with that amphetamine-induced reverse transport depends on both extracellular Na+ (so that amphetamine can be transported into the cell) and intracellular Na+ (so that the neurotransmitter can be transporter out) (Schmitz et al., 2001) and infact an increase in intracellular sodium is enough to cause reverse transport (Khoshbousie et al., 2003). Another observation that this author makes that at the very least doesn’t disprove facilitated exchange diffusion is that the affinity of various amphetamines for the extracellular binding site is tightly correlated with their ability to release monoamines (figure 3) (this seems to indicate that binding to the extracellular binding site, and hence probably transport into the cell, is all that is required to induce reverse transport). Another consequence of the facilitated exchange diffusion model is that amphetamines would compete for neurotransmitters at the transporter, and as a result inhibit monoamine uptake. Indeed, it is often sited that amphetamines work by inhibiting reuptake, but the actual contribution of amphetamine-induced reverse transport and reuptake inhibition in regards to the increase in free monoamines is hard to calculate but it has been estimated that the majority of the increase in monoamines is due to reverse transport (Schmitz et al., 2001). This conclusion can be easily seen to be true as the maximum increase in free monoamines in the brain caused by amphetamines is well over 1000%, while cocaine causes a maximum increase in extracellular dopamine around 500%. 



> Figure 3. A tight correlation between uptake inhibition and release between various amphetamines



There are however several observations that bring the simplicity of facilitated exchange diffusion, which have produced other theories, discussed below. 

*Channel Mode*
Interestingly, it has been shown, that under the right conditions, cells expressing monoamine transporters can display large current events which are blocked by drugs which block monoamine transporters and are coincident with very large effluxes of monoamine neurotransmitters. These channel like events have been shown to contain on the order of 10,000 molecules of neurotransmitter, released over a few milliseconds at the most (Kahlig et al., 2005). In order to give this number some scale, this is approximately the same number of neurotransmitter molecule inside a vesicle. Amphetamine drastically increases the rate of these channel like events. It is worth noting that Kahlig et al., reports that these events only happen when neurons are held at massively depolarized potentials (>+40mV), so these channel like events are only likely to happen during the peak of an action potential.


*2nd Messanger systems*
Monoamine transporters have numerous sites which can be phsophorylated and this phosphorylation seems to be play an important role in amphetamine-mediated reverse transport. Specifically the activity of protein kinase C (PKC) seems to regulate transporter activity, for instance activating PKC is enough to induce monoamine transporter-dependent monoamine release, and it has been reported that PKC inhibition blocks amphetamine mediated dopamine release (Kantor et al., 2001). Furthermore, removal of a small section of the N-terminus of the dopamine transporter, or modification of this sections of the amino acid sequence so that it can not be phsophorylated (serine residues replaced with alanine) reduced amphetamine mediated dopamine release by 80% while leaving dopamine uptake unchanged. (Khoshbouei et al., 2004). Exactly how amphetamine lead to an activation of PKC is unclear, but may revolve around an alteration of intracellular Na+ homeostasis (due to Na+/amphetamine co-transport) and an influx of Ca2+ through the Na+/Ca2+ co-transporter.

*Monoamine Oxidase Inhibition*
It is often claimed that amphetamines work, at least in part, by inhibiting monoamine oxidase (MAO), the intracellularly expressed enzyme responsible for the break down of the monoamine neurotransmitters. The importance of this effect in general is probably minimal at best, as MDMA, methamphetamine and amphetamine are usually reported to need a concentration of 10-100µM to inhibit MAO-A 50% (most amphetamines are relatively MAO-A selective). However these drugs need concentrations 1000x lower than that to significantly effect monoamine release. While some people suggest that as MAO is an intracellular enzyme, and amphetamines are probably highly concentrated inside cells due to their transport by the monoamine transporters (though this has never been directly measured), monoamine oxidase inhibitors only cause a modest increase in free monoamine levels (~200%), and hence at best it is the MAOI effects of amphetamines must be minimal.


*Other mechanisms*
Many other mechanisms have been used to explain amphetamine actions, such as the weak base effect. In this theory the accumulation of amphetamines (which are weak bases) in synaptic vesicles, increases the vesicular pH to a point where the vesicular matrix, which holds neurotransmitters in a stable state breaks down, and causes neurotransmitters to leak into the cytosol of the cell. This increase of free intracellular monoamines favors reverse transport and leads to monoamine release. Another idea is that inward amphetamine transport which is driven by Na+ leads to a substantial inward Na+ current, depolarizing the cell, and leading to classical vesicular release. The contribution of this effect is largely unknown, but seems unlikely as vesicular release has largely been disproved as a mechanism of amphetamine-induced monoamine release (amphetamine-induced release is independent of extracellular Ca2+ and is insensitive to toxins which disrupt vesicular exocytosis).

*Conclusion*
Exactly how amphetamines cause monoamine release is still not clear. It seems to be caused by a reversal of monoamine transport through monoamine transporters. This amphetamine-induced transporter-mediated reverse transport has been shown to be largely dependent on PKC-mediated phosphorylation of the N-terminus of the transporter, and facilitated exchange diffusion. Other effects, such as reuptake inhibition, MAO inhibition and a facilitation of the channel like mode of the transporter may play small roles in mediating amphetamine-induced increase in monoamine neurotransmitter levels.


*Further Reading*
An excellent, complete historic review:
Sulzer D, Sonders MS, Poulsen NW, Galli A.
Mechanisms of neurotransmitter release by amphetamines: a review.
Prog Neurobiol. 2005 Apr;75(6):406-33

*References*

K.M. Kahlig, F. Binda, H. Khoshbouei, R.D. Blakely, D.G. McMahon, J.A. Javitch and A. Galli.
Amphetamine induces dopamine efflux through a dopamine transporter channel
Proc. Natl. Acad. Sci. U.S.A. 102 (2005), pp. 3495–3500

L. Kantor, G.H. Hewlett, Y.H. Park, S.M. Richardson-Burns, M.J. Mellon and M.E. Gnegy.
Protein kinase C and intracellular calcium are required for amphetamine-mediated dopamine release via the norepinephrine transporter in undifferentiated PC12 cells
J. Pharmacol. Exp. Ther. 297 (2001), pp. 1016–1024

H. Khoshbouei, H. Wang, J.D. Lechleiter, J.A. Javitch and A. Galli.
Amphetamine-induced dopamine efflux. A voltage-sensitive and intracellular Na+-dependent mechanism
J. Biol. Chem. 278 (2003), pp. 12070–12077.

H. Khoshbouei, N. Sen, B. Guptaroy, L. Johnson, D. Lund, M.E. Gnegy, A. Galli and J.A. Javitch
N-terminal phosphorylation of the dopamine transporter is required for amphetamine-induced efflux
PLoS Biol. 2 (2004), p. E78

D.M. Paton
Mechanism of efflux of noradrenaline from adrenergic nerves in rabbit atria
Br. J. Pharmacol. 49 (1973), pp. 614–627

A. W. Ravna, I. Sylte, S. G. Dahl
Molecular model of the neural dopamine transporter
J Comp-Aid Mol Des 17: 367–382, 2003.

Y. Schmitz, C.J. Lee, C. Schmauss, F. Gonon and D. Sulzer
Amphetamine distorts synaptic dopamine overflow: effects on D2 autoreceptors, transporters, and synaptic vesicle stores
 J. Neurosci. 21 (2001), pp. 5916–5924.


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## BilZ0r

*What is a Protein?*
Proteins are a certain type of biopolymers/biomacromolecules (molecules that are made out of very many components and therefore have a large molecular weight). 

Proteins are made out of amino acids, joined together in a generally linear chain. There are 20 different amino acids that proteins can be made from. The length of those "polypeptid chains" can be as short as less than 20 amino acids or as long as tens of thousand amino acids. This enables the proteins to have a large variety of functions. To mention just a few of them, they can function as neurotransmitters, enzymes, receptors or ion channels, and in fact mediate and control near every function of the body.

Every amino acid has slightly different proterties: some are water soluble while others are hydrophobic, some easily function as catalytic centres (that is, they are places for chemical reactions to take place), some can easily be joined to other amino acids, forming bonds between distant places on the protein, or even other proteins. The sequence of amino acids which make up the protein are tightly regulated by messenger ribonucleic acid (mRNA), another biopolymer which is copied from, and is essentially a mirror image of DNA. If the body was a construction projection, DNA can be thought of as the manual, mRNA is a photocopy of the manual, and proteins are the finished projected.

The important thing about proteins is that they hold their shape. Although proteins are produced like long rope, they fold up as they are produced into shapes dictated by the amino acids that make them up, hence all proteins of the same structure should form into the same shape. Hydrophilic amino acids will form to face into the aqueous composition of the cell, while hydrophobic amino acids will stick next to other hydrophobic amino acids, often forming the interior of the protein. Some proteins are produced to be partially buried in, or transit the membrane, here, hyrdophobic amino acids will form the part of the protein which sit in the membrane.

While proteins are rigid, they can subtlety change their shape, or conformation. These changes may happen spontaneously, may be induced by chemical changes to the protein, or even by the distribution of electrical charge which surrounds the protein.


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## Black Octagon

Oh Christ, the joy I am getting out of seeing this text's slow and arduous birth. Can't wait till it's finished. Keep up the good work, BilZ0r and friends!


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## BilZ0r

Learning and Memory on a cellular level

Even some of the most simple animals with neural structures too small to call brains, can learn from their experiences. Sea snails (animals with only a few thousand neurons) can associate neutral stimuli (those which produce no response) with noxious ones, if they repeatedly happen together and learn to respond to the neutral one as if it were the noxious one. Importantly, they can also unlearn the response, if a previously neutral stimulus is no longer paired with the noxious stimulus. Brains can also learn to pair neutral stimuli with rewarding stimuli, the classical example being Pavlov’s dogs, who learned to pair the sound of Pavlov entering his lab, with the food he gave them (he was studying the effects of food on salivation, however to his annoyance, the dogs began to salivate BEFORE he gave them the food). Interestingly, this so called Pavlovian conditioning is dependent on how well the neutral stimulus predicts the rewarding stimuli. If Pavlov had entered his lab regularly without feeding the dogs, it is likely that the dogs would have never learned to salivate to the sound of his footsteps.

Believe it or not, these learning situations are the comparatively complicated one as far as the neuroscientists is concerned. Imagine the situation where an experimental animal is exposed to a light that consistently precedes (and hence predicts) a tone, this is called sensory preconditioning. Following a Pavlovian style learning situation, a puff of air into the eye produces a blink, and if the puff is consistently paired with a tone, the subject will learn to blink just to the tone. Now if the animal is exposed to the light, it will blink, even though the tone has never been paired with the puff. 

All of these experimental results may seem obvious, but they show some very important things. Firstly, it was proposed by Hebb that if a neuron A consistently takes part in firing (i.e. fires at the same time as, and is connected to) neuron B, then the connectivity between neuron A and B will increase. What is interesting about sensory preconditioning is that obvious connectivity between the two neutral sensory stimuli formed just by pairing them together, supporting Hebbs theory. Hebbian principles were further engrained when it was shown that simply by strongly exciting a set of neuronal inputs into a population of neurons, the neuronal inputs became more efficient at this excitation, importantly this potentiation lasts for extremely long period (recorded for over 1 year). This is due a series of changes in the synapse, both pre- and postsynaptically, including an increase in glutamate release and an increase in AMPA receptors in the post-synaptic membrane. This long term potentiation (LTP) has been used as a model for memory since it was discovered over 30 years ago, and has stood robustly against most challenges. Specifically drugs and genetic modulation which prevent the formation or maintenance of LTP also prevent learning.

Reward relating learning (like like a rat pressing a lever for food) also has interesting cellular mechanisms, animals will not learn to pair a neutral stimulus with a food reward if their dopamine receptors are blocked, likewise, if dopaminergic neurons are destroyed the association can not be made. Dopamine cells are active by natural and drug induced rewards. Interestingly, animals will learn to do almost anything for direct stimulation of dopamine neurons. Some people see this as evidence that dopamine directly mediates pleasure, but experiments in the 1960s where humans were given the ability to directly stimulate their own dopamine neurons didn’t report extreme pleasure, though the would constantly activate their dopaminergic neurons (Heath, 1972). Furthermore, if an animal is trained to press a lever to stimulate their dopaminergic neurons, and another animal receives dopaminergic stimulation when the first does, the second animal does not show signs of pleasure, and can even show signs on distress. If this leaves one a bit confused about the role of dopamine, consider this, there are many places in the brain where it has been reported that dopamine massively facilitates the induction of LTP, indeed, in projections from the cortex to the striatum, LTP style stimulation actually produces a suppression in the power of the input neurons from the cortex into the striatum except when dopamine is present . While in the presence of dopamine, a large increase in synaptic strength in generated (Reynolds et al., 2001). The striatum, and especially the ventral striatum (AKA the nucleus accumbens) has been highly associated with the “rewarding” (i.e. refinforcing) properties of natural stimuli and addicting drugs.

This allows us to construct a model of the plasticity of synapses (at least in the striatum), if neuron A (cortical) and neuron B (striatal) are active out of synchrony then there is no change in synaptic strength while if they are active together, without dopamine the synaptic strength decreases. Finally, if neuron A and B are active together in the presence of dopamine, the synaptic strength increases. Although the exact functional role of this corticostriatal dopamine-dependent synaptic plasticity is unclear one can form a reasonable hypothesis. The cortex is activated by sensory stimuli while the striatum (which receives the majority of it’s input from the cortex) is involved in, and active during, movement. Hence a particular sensory stimuli activates a particular area of cortex and cortico-striatal projections, while, a particular behaviour leads to certain striatal neurons being active. If this combination of cortical activity (stimuli input) and striatal activity (behavioral output) produces a reward (dopamine) then the corticostriatal system that was active during this state is strengthened. Addictive drugs, which cause an inappropriate release of striatal dopamine lead to an aberrant corticostriatal state, where cortical neurons which code for drug associate stimuli lead to drug taking behavior.

This becomes even more interesting when one more closely considers the activity of dopaminergic neurons in an awake behaving animal. While on the surface dopaminergic neurons seem to respond to rewarding stimuli, careful examination shows the more closesly reflect the expectancy (or lack thereof) of reward. Dopamine release is most strongly induced by unexpected primary rewards (e.g. food, water), however, if the reward is preceded by a predictive stimuli (e.g. a tone), dopamine release will be shifted to being released by the tone. However, if the tone continually predicts the reward, eventually dopamine release will wane. Likewise, if an unpredicted reward happens regularly, the animal will cease to release dopamine to it's presentation. You can see that if an animal expects a reward, dopamine will not heavily release. However, there is usually a basal level of dopamine being released and if an expected reward is denied, this basal level will drop to zero. Hence, you can see that dopamine release acts as prediction error signal, if the animal recieves an unexpected reward, a large increase in dopamine is induced while if it correctly or incorrectly predicts a reward, dopamine stays at the basal level or decreases respectively.

This shows us how reward related learning can be unlearned, that a pause in dopamine causes corticostriatal synapses to weaken, and the behaviour that was not rewarded is lessened. (theory reviewed by Contreras-Vidal and Schultz, 1999)

While these hypothesis is certainly a vast over simplification, the basic rules are probably true. It is worth noting that not all research groups show that dopamine increase the strength of synapases, and that it can also decrease them (probably dependent on which dopamine receptors are activated (Centonze et al., 2001). However still, dopamine is modulating synaptic plasticity in a reward dependent fashion. This dopamine-mediated synaptic remodelling helps associations form between stimuli and behavior that lead to reward. When this system is hijacked by addictive drugs an aberrant association which encourages drug taking is formed, and it is formed as concretely as any other memory.


References

Centonze D, Picconi B, Gubellini P, Bernardi G, Calabresi P. (2001)
Dopaminergic control of synaptic plasticity in the dorsal striatum.
Eur J Neurosci. 2001 Mar;13(6):1071-7.    


Contreras-Vidal JL, Schultz W. (1999)
A predictive reinforcement model of dopamine neurons for learning approach behavior.
J Comput Neurosci. 6(3):191-214

Heath, R. G. (1972). Pleasure and brain activity in man. Deep and surface electroencephalograms during orgasm. Journal of Nervous and Mental Disease, 154(1):3-18

Reynolds JN, Hyland BI, Wickens JR. (2001). A cellular mechanism of reward-related learning.
Nature. 413(6851):67-70


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## BilZ0r

Note: I need people to rip into that one extra hard, if you see any problem with it, please tell me.


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## mitogen

Hey Bil,  I'm not going to be able to make a dent in learning in memory - not my field. I'm gonna post my recent review on receptor signalling networks and the 'receptosome concept,' which you may edit to your heart's content for appropriate content. PS, what ever happened about submitting that article I wrote to Erowid?


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## mitogen

*“G-protein coupled receptors: part of a network of signalling machinery”*

Here it is, in all its glory. Its a little ugly, and the figures won't come through i don't think, so drop me a line ( the.hierarchy@gmail.com preferably) if you want to see the .doc

“G-protein coupled receptors: part of a network of signalling machinery”

The section on “G-protein coupled receptors” (GPCRs) in the popular undergraduate level text book “Pharmacology” by Rang, Dale, Ritter & Moore [1], presents a relatively one-dimensional view of GPCR signalling. A neat diagram sums up the events that occur on binding of a ligand to its cognate GPCR: ligand binding attracts a GTPase (‘g’-) protein to the receptor, and the GDP bound to the g-protein is swapped for a GTP. The now-activated subunits of this heterotrimeric g-protein then dissociate and activate another molecule in the signalling cascade, such as adenylyl cyclase, which subsequently produces ‘second messenger’ molecules. These second messengers are responsible for activation of other downstream effectors, and the signal that began with a ligand binding to the GPCR is propagated.
In contrast, even a cursory glance at any recent review [2,3,4] on the subject of GPCR signalling will reveal to the reader that the textbook model of GPCR signalling is woefully inadequate. Rather, these reviews present the concept that a whole network of interacting proteins and biomolecules nucleated around scaffolding proteins are involved in what was once thought to be a relatively simple, linear transduction process. These protein networks are involved with fine-tuning and regulation of every facet of GPCR function. The ‘receptosome’ concept, that whole networks of molecules are spatially compartmentalised into plasma membrane microdomains such as caveolae and other lipid rafts is integral to all recent models of how GPCR signalling is effected. 
In this review I will discuss how each receptosome exists as a self-contained, functional signalling unit, and the importance of spatial compartmentalisation of GPCR signalling machinery. Important experimental observations which lead to the invalidation of older GPCR signalling dogma and forced reconsideration of the whole signalling paradigm will be included. Attention will be paid to the roles that particular groups of proteins play in receptosomes, and the modality of their interactions with other receptosome proteins. Finally I will discuss some of the methodology that is currently being used to determine these interactions and their importance to aspects of GPCR signalling.

The old GPCR signalling dogma:

The older “1-dimensional” (meaning that signal transduction follows a defined, stepwise path, as opposed to three dimensional networks of interactions) model of GPCR signalling has been superceded by models like the ‘receptosome’ model described in this review. Essentially, too many contradictions of and paradoxes in the old model arose from experimental observations. Some of the observations that forced the creation of a newer more comprehensive model are detailed below.
Old dogma states that a specific ligand binds to its cognate GPCR, which then undergoes a conformational change, such that its cytosolic domain develops high affinity for one particular G-protein family and subtype, which it recruits. The activated GPCR activates the recruited G-protein by functioning as a guanine nucleotide exchange factor, exchanging G-protein bound GDP for GTP. The activated G-protein then splits into its alpha and beta-gamma subunit components, which activate secondary targets. G-alpha usually modulates the activity of a second messenger producing enzyme, such as activation of phospholipase C in the case of Gq-alpha, or activation of adenylyl cyclase by Gs-alpha. The second messenger activates second messenger dependent kinases which proliferate the signalling cascade. Additionally, there is room in the one-dimensional model for G-protein Receptor Kinase (GRK) mediated phosphorylation and arrestin mediated desensitisation, which is why although these molecules were discovered relatively early on, they did not push for creation of a new model. [1,3,4]

Organisation of GPCR signalling machinery

One of the fundamental concepts of biochemistry is that the proteins that comprise the majority of cellular machinery interact with each other as huge networks of multiprotein complexes, with specific chemical affinities determining the strengths of these interactions [1,5]. Thus when a ligand binds to its cognate GPCR, a conformational change is induced in the GPCR which creates a chemical site for which specific G-protein(s) have high affinity. Additionally, according to the laws of mass action, the magnitude and rate of chemical interactions and reactions are heavily dependent on the concentrations of the reactants. This raises a fundamental problem with the classical one-dimensional theory of GPCR signalling as can be found in most generic pharmacology textbooks: if one looks at the average concentration of each protein component involved in GPCR signalling, it is far too low to possibly account for the rapidity of the biochemical response to receptor agonism [5]. Kinetics of the protein-protein interactions required to form a signalling cascade must therefore be simply too unfavourable for any agonist directed response to occur if these proteins were randomly or even uniformly distributed across the plasma membrane or cytosol. This appears to be a massive flaw in the old model of GPCR signalling. 
Several more flaws can be identified when the old model is compared with recent observations about the characteristics of GPCR signalling. 

The old dogma of “1 g-protein couples to one GPCR” has been comprehensively disproved – in fact GPCRs more often than not couple to more than one G-protein [6]. This has significant ramifications for the signalling pathways activated by a particular GPCR. One particularly illuminating example of this observation is that the thyrotropin receptor is able to couple to all four major G-protein families [6]. Other experiments have shown that the majority of GPCRs have at least some affinity for each type of G-protein: therefore the preference for activation of a particular G-protein subtype actually lies on a continuum. In light of this concept, it is possible to infer that it is possible to describe GPCR interactions with particular G-proteins statistically: for example, a particular GPCR may interact with G-protein X 90% of the time, G-protein Y 9.99% of the time and G-protein Z a biochemically negligible 0.01% of the time. These statistics would be based on the chemistry of the interaction sites on the GPCR and G-proteins X, Y & Z. Interaction of the GPCR with G-protein X is obviously the most thermodynamically favourable binding interaction in a mixture of the four proteins at equilibrium. 

A further observation that can not be integrated with the old model of GPCR signalling is that agonism by different ligands induces GPCRs to have different affinities for particular G-proteins. The paper “Opioid agonists differentially regulate Mu-opioid receptors and trafficking proteins in vivo” [7] is a good example of how different agonists can induce different biochemical responses in the cell. It is likely that the mechanism for this involves the two agonists used, morphine and etorphine, inducing different receptor conformations, and therefore recruiting different groups of G-proteins to the Mu-opioid receptor.
It is also possible, however, that this effect is not actually mediated by G-proteins at all, and involves direct interaction of other non-G-protein signalling machinery at the Mu receptor. Models have been suggested in which particular receptors may have a number of different conformations which they can assume, and different agonist ligands thermodynamically stabilise particular conformations, which each have a set of G-proteins they activate to different extents. This is a discrete model – there are a defined number of conformations that a receptor can take, and the potency of the agonist to induce that conformation and therefore the overall activity of the drug at the receptor, depends on the degree of thermodynamic stabilisation of that conformation [8]. Alternately, it is possible to imagine a continuous model, where each agonist induces an individual receptor conformation, which alters the G-protein coupling of the receptor and therefore the properties of the signal induced by that agonist. It is even possible to amalgamate these two theories, and conceptualise a model where each different agonist does continuously induce a different receptor conformation, but there are ‘peaks’ in agonist affinity and efficacy which correspond to stabilisation of particular, discrete conformations [9]. Needless to say, a “one GPCR binds to one G-protein” model is completely unable to account for any of these ideas.

Another observation that has forced progression from the older GPCR signalling dogma is that G-protein coupling is not necessarily required for biochemical responses to receptor agonism [10]. Following receptor activation and subsequent G-protein activation, the GPCR is often phosphorylated by a G-protein coupled receptor kinase (GRK,) [10] (or sometimes a by second messenger dependent kinases,) [11] and it is this chemical modification that creates a binding site on the GPCR for a group of proteins called arrestins, which attache to the GPCR and blocks any further coupling to G-proteins, in effect causing the cessation of G-protein mediated signalling [10]. It has been shown, however, that Beta-arrestin may act as a scaffolding molecule and serve to recruit other non-G-protein related signalling machinery. Experiments have shown that arrestin-2 can recruit the tyrosine kinase Src by binding to its SH3 domain, and can also activate MAP kinase pathways. Other experiments showed binding of JNK3 and ASK1, which is a JNK kinase kinase. Thus GPCRs can activate MAPK and tyrosine kinase pathways via their interaction with arrestin proteins [11]. Recent studies have shown an interaction between activated beta2adrenoreceptors (B2AR) and Src which is increased by overexpression of beta-arrestin. Additionally, inhibition of beta-arrestin binding to either B2AR or Src attenuates B2AR mediated activation of MAPK. [10]
Beta-arrestin has also been implicated in regulation of receptor trafficking and endocytosis by its interaction with the heavy chain of clathrin and the clathrin adaptor protein AP2 [10]. These observations of arrestin molecules as scaffolds that nucleate assembly of non-G-protein mediated signalling processes add further detract from old GPCR signalling dogma. 

Described above is a series of experimental observations that obligatorily invalidate the one-dimensional model of GPCR signalling, while at the same time building the concept of GPCR signalling as involving a whole network of interacting proteins, with some acting as nodes and scaffolds onto which other proteins nucleate, while others are involved in fine tuning and regulation of the signalling machinery, and still others involved in the trafficking and regulation of the receptors themselves. The most important feature of a newer model of GPCR signalling would have to incorporate the principles of biochemical kinetics and concepts such as collision theory. If all the protein components required for GPCR signalling were to be randomly or even uniformly distributed throughout the cytosol and plasma membrane, the observed rapid response of GPCRs to agonism could not possibly occur. Thus, a new model must include a spatial dimension. The components must be spatially organised such that the biochemistry is actually possible. In answer to this requirement, the literature is packed with reviews and papers documenting the existence of membrane microdomains, or lipid rafts, such as caveolae, in which many of the signalling components and receptors are often congregated. 

Caveolae are small (50-100nm) invaginations in the plasma membrane of cells, and are considered to be a subclass of lipid rafts. The lipid composition of caveolae includes characteristically high levels of cholesterol and sphingolipids, along with caveolins, a group of proteins which comprises three isoforms: cavelolin-1, caveolin-2 and caveolin-3. It is generally accepted that caveolae will form if a cell expresses caveolin-1, or in the case of striated muscle myocytes, caveolin-3. Thus, while the plasma membranes of most or all cells contain lipid rafts, only some cells contain caveolae. A 2003 paper in the Journal of Neurochemistry [12] gives a good example of a GPCR being localised to caveolin membrane fractions, and shows “molecular and functional association of mGluR1a receptors with caveolins.” The study demonstrates that agonistic activation of mGluR1a receptors increased ERK phosphorylation in low density caveolin enriched membrane fractions, but not in high density membrane fractions containing no caveolins. Also mentioned in the study was the observation that mGluR1 heterodimerizes with adenosine A1 receptor and calcium sensing receptor; all three of these proteins localise to caveolin rich membrane microdomains [12].
Another example of the role of localisation of receptors and signalling machinery to caveolae is the comparison of Beta1-adrenoreceptor (B1AR) and B2AR signalling in cardiac myocytes. B2ARs activate adenylyl cyclase 6 (AC6) with a lower efficacy than B1ARs, and it appears that this is due to rapid translocation of B2ARs out of caveolae and into clathrin coated pits after receptor activation. AC6 is localised strictly to caveolae, and as such when the B2AR is translocated, it can no longer physically contact AC6 to activate it [5]. 
A concept that is integral to the model of spatial compartmentalisation of signalling proteins into regions such as caveolae and other lipid rafts is the selective expression of certain isoforms of G-proteins and second messenger synthesising enzymes such as adenylyl cyclase (AC) to particular types of raft, or not to any raft at all. There are nine AC subtypes, but not all of them localise to lipid rafts [5]. Therefore, the fact that many different subtypes exist of G-proteins, second messenger synthesising enzymes and other signalling proteins such as Regulators of G-protein Signalling (RGS,) is a way of increasing the diversity of plasma membrane domains and microdomans.
Many proteins which associate with caveolin proteins contain a caveolin- or caveolin-like- binding motif [13]. Le Clerc et al. published a study in 2002 in the journal Endocrinology examining the effect of Angiotensin II Receptor Type 1’s (AIIR1) caveolin-like binding motif (CLBM) (_X_XXXX_XX_, where _ represents an aromatic amino acid residue) on AIIR1’s signalling and trafficking properties. They mutated this binding motif by replacing each aromatic residue with alanine, a small, sterically unintrusive molecule. The mutated receptor was shown to be four-fold less effective at activating phospholipase C, indicating that the functional CLBM is required for proper signalling. The authors proposed that the CLBM could be acting as a site for nucleation of proteins involved in the regulation of function of AIIR1 [13]. A similar study by Tomohiro Yamaguchi and colleagues [14] examined the effects of interaction of endothelin type A and B (ETaR & ETbR, respectively) receptors with caveolin-1. It was found that ETbR only interacted with caveolin-1 in the absence of an agonist, or bound to the antagonist RES-701-1. When endothelin-1 or another antagonist BQ788 were added, the complex dissociated. ETaR, however, bound to caveolin-1 irrespective of whether a ligand was bound or not. Additionally, overexpression of caveolin-1 dramatically increased the amount of ETbR localised to caveolae, while addition of endothelin-1 reduced caveolar localisation. Disruption of caveolae by filipin reduced the effect of endothelin-1 agonism on ERK1/2 phosphorylation [14].

Taken together, the concepts and experimental observations described here provide the framework for a GPCR signalling platform that is heavily based around spatial compartmentalization of a network of interacting components. This has been called a ‘receptosome’ in some publications [4], and it is quite possible that these receptosomes are the functional unit of plasma membrane receptor signalling, like a cell is the functional unit of a tissue. Agnati et al. in a review publication called “On the molecular basis of the receptor mosaic hypothesis of the engram,” suggest that signalling units such as receptosomes form mosaics on the pre- and post-synaptic membranes of synapses, and that these mosaics are the computational entity that actually decodes the neurochemical messages. They move on to suggest that the arrangement of these mosaics of receptosomes could form ‘supramolecular networks’ that store information about the previous activity patterns of the synapse. While it is important to note that not all GPCR related signalling machinery is congregated into lipid rafts, it is likely that the receptosome theory applies to the majority of GPCR signalling, principally because compartmentalisation of signalling proteins makes such good sense kinetically.
Figure 1. Shows the 5HT2c receptor and its interacting proteins forming a receptosome.


Figure 1. Proteins that interact with the 5HT2c receptor: an example of a synaptic receptosome.

Componentry and organisation of the receptosome: GPCRs & GPCR Interacting Proteins

Having identified general features of the receptosome and the logic behind organising signalling machinery this way, this section of the review will discuss the main groups of proteins that are likely to be part of the receptosome network and their functions.
I will address the questions of what these proteins are, where and how they interact with each other, and why these interactions are fundamental to GPCR / heptahelical transmembrane receptor signalling. Several protein-protein interaction domains such as PDZ, SH2 and SH3 domains are common in receptosome proteins, and the roles of these domains in protein interactions will be highlighted where appropriate.

G-protein Receptor Kinases:

It has been observed experimentally for decades that GPCRs undergo desensitisation and subsequent internalisation under repeated agonist stimulation. The first event in this process is usually phosphorylation of the receptor. There are at least two methods which the cell uses to perform this function: phosphorylation by second messenger activated kinases such as Protein Kinase A (PKA), and phosphorylation by non-second messenger dependent G-protein coupled Receptor Kinases, which are specific to activated GPCRs. The former is an example of ‘heterologous’ desensitisation, whereby agonism of one receptor can result in activation of PKA and subsequent phosphorylation and desensitisation of another receptor [1]. This effect is usually weak and short lasting, and the phospho-residue is not a target for arrestin binding. GRK mediated desensitisation is termed ‘homologous,’ since agonism of a receptor induces desensitisation of the same receptor [1]. Unlike phosphoresidues created by PKA or other second messenger activated kinases, GRK will phosphorylate different sites, and these phosphoresidues are targets for arrestin binding. Once arrestin is bound, various events occur, most importantly blockade of GPCR access to G-proteins. It is not the actual phosphorylation event that desensitises the GPCR in this case, but arrestin binding. GRK mediated phosphorylation was first discovered in the context of rhodopsin-dependent visual signalling, and later, beta2adrenergic receptor signalling. Since then, it has been established that the majority of GPCRs are desensitised in this way [15].

Arrestins:

Arrestins have been known to interact with GPCRs for a relatively long time, and their function was not particularly difficult to fit into the classical GPCR signalling dogma. Arrestins bind, as described previously, to GRK-phosphorylated GPCRs, and for a long time it was thought that arrestins were only involved in desensitisation and internalisation [4]. While some GPCRs internalise independent of arrestins, the usual scenario involves the bound arrestin attaching to clathrin – one of the major components of endocytotic machinery. Follow clathrin binding, arrestin acts as a scaffold protein and nucleates several other proteins to form the multiprotein complex that will effect receptor endocytosis. Other proteins identified in this complex include: AP2 (assembly particle-2,) a large (340kDa) protein that binds to the globular domain at the end of each clathrin heavy chain and function to promote clathrin triskelion formation and oligomerization into the cage that coats membrane invaginations to form clathrin coated pits [16], NSF (n-ethylamide sensitive factor), an intracellular trafficking protein, ARF6, an ADP-ribosylation factor and its exchange factor ARNO, which together regulate vesicle budding. Additionally, arrestin-2 can act as signalling intermediates, and attaches to multiple of the tyrosine kinase c-Src, including its SH3 and SH1 domains to activate MAPK pathways [11]. Arrestin-2 also has an ERK1/2 phosphorylation dependent regulation site at residue Ser-412 which modulates c-SRC and GPCR binding [11]. There are three beta-arrestin subtypes: arrestin-1, 2 & 3, each with different binding specificities and signalling functions. Arrestin-1 is specific to the visual GPCR rhodopsin, while arrestin-2 has a much wider GPCR specificity, and while arrestin-1 is dimeric, arrestin-2 exists as a monomer in solution [11]. These varying characteristics of arrestins add to the overall specificity and complexity of GPCR signalling.
Figure 2. shows a schematic of GPCR activation, arrestin mediated desensitisation, internalisation, and degradation or resensitisation. Some arrestin interacting proteins are shown.


Figure 2. The roles of arrestins in GPCR desensitisation, internalisation, degradation and resensitisation	[4]

RGS’s:

Regulators of G-protein Signalling, or ‘RGS’ proteins play a crucial role in regulating the function of G-proteins, and therefore in the signalling efficacy of the receptor system. There are, like many other GIPs examined in this review, a number of members of the RGS family, each with their own G-protein subunit specificity. The mammalian RGS family comprises several subfamilies, termed: Rz, R4, RA, R12 and R7, which are classified on the basis of structural and sequence homology. RGS proteins contain an RGS box which allows them to interact with activated G-alpha subunits and increase the rate that the G-alpha subunit hydrolyses GTP to GDP. The net effect of this interaction is to reduce the time that the G-alpha subunit actively signals to other proteins. As well as their characteristic RGS box domains, RGS proteins often contain other protein-protein interaction domains such as PDZ domains on RGS-R12 members. These protein-protein interaction domains make RGS proteins the target of considerable research efforts because of the implication that RGS proteins can, like arrestins, act as signalling intermediates as well as their role in regulating G-alpha signalling. For example, RGS proteins containing the RBD domain have been shown to initiate MAPK signalling [17]
The roles of RGS proteins in mu-opioid receptor signalling have been quite extensively studied, and examples of these studies are demonstrative of general RGS function. RGS2 and RGS3, for example, increase opioid agonist potency, while RGS4 and RGS16 reduce the potency of agonists. It is not known whether RGS2 and RGS3 actively reduce the rate of G-alpha GTP hydrolysis, or whether their effect is mediated by one of their other protein-protein interactions [18]. Experiments in which RGS9-2 is knocked out show increased response to Mu-opioid agonists and impaired desensitisation [18]. Garzon et al. in a 2004 paper [17] demonstrated that morphine “alters the selective association between mu-opioid receptors and specific RGS proteins in mouse periaqueductal gray matter,” and in pull-down assays, they noted that certain proteins increased or decreased in their association with mu opioid receptors. It is possible that this may be something to do with morphine altering the receptor conformation and subsequently the network of proteins, particularly G-proteins, which interact with it. RGS proteins have selectivity for specific G-proteins, and if the group of G-proteins present in the network changes, then the group of RGS proteins present would also be likely to change.

Homer:

Several metabotropic glutamate receptors, such as mGluR1a and mGluR5a & b, along with Ca++ permeable IP3 receptors, ryanodine receptors, TRP channels, dynamin II and shank proteins contain the sequence (-PPxxFR-) which is a binding sequence for ‘Homer’ proteins. These Homer proteins, contain an enabled “VASP homology-like” domain which binds to the Homer binding sequence, and a C-terminal coiled coil domain which allows them to homo- and heteromultimerise. It is Homer’s coiled coil interactions that allow the above proteins to form large complexes. A complex containing mGluR’s, Homer proteins, TRP channels, ryanodine receptors and P/Q Ca++ channels, according to Bockaert et al. [4] would “constitute an ideal machinery for intracellular Ca++ release.” Homer proteins act primarily as scaffolding for protein complex formation, but experiments inhibiting Homer activity by using Homer1a, which lacks the coiled coil domain and acts as a dominant negative form of Homer, have shown that Homer has regulatory effects on mGluR signalling and ryanodine channel function [4].

GPCR-GPCR Interactions:

GIPs are essential to the function of a receptosome, but it is important to note that GPCRs do not just interact with non-GPCR proteins: the recent literature [19] documents many experiments exploring GPCR-GPCR interactions, including homo- and hetero-oligomerisation. Oligomerisation of GPCRs can affect many properties of GPCR function or sometimes only one or none, depending on the particular oligomer. For example, heteromeric complexes of B2ARs and delta or kappa opioid receptors doesn’t affect the pharmacology of either the adrenergic or opioidergic units, but profoundly alters the trafficking properties of the heteromer [20]. Again a familiar concept can be found in the nature of GPCR oligomerisation: signalling specificity and complexity are increased by a further level.

RAMPs:

The discovery of Receptor Activity Modifying Proteins or RAMPs revolutionised the field of GPCR signalling, because it demonstrated that not only could GIPs fine tune GPCR signalling, modulate trafficking and activate secondary signalling pathways, they could also turn a receptor into a completely different entity, with a totally different cognate ligand. There are three members of the RAMP family that have been identified so far, designated RAMP1, 2 & 3. As an example of RAMP function, RAMP1 can bind to the calcitonin receptor-like receptor (CL,) and convert it into a ‘high affinity calcitonin gene-related peptide receptor.” Alternatively, interaction of CL with RAMP2 or 3 produces an adrenomedullin receptor. RAMPs are now known to interact with the majority of GPCR Class II receptors, and are regulated heavily by physiological and pathophysiological processes. For example, RAMP2 and adrenomedullin mRNA are elevated in models of cardiac hypotrophy, and during pregnancy, progesterone causes upregulation of all three RAMPs. It is also thought that many of the orphan ligands which have been found (i.e. no receptor has been identified,) are ligands to GPCR-RAMP complexes, when the GPCR already has a cognate ligand in its non-RAMP complexed state [20].

‘Magic tail’ interacting proteins & PDZ Domains:

The C-terminal tail of many GPCRs contains a PDZ ligand, to which proteins with the PDZ protein-protein interaction domain common to many proteins involved in receptor signalling bind [21]. The protein PICK1 (Protein Interacting with C-kinase 1) is one such protein: by binding to the PDZ ligand motif of mGluR7a, PICK1 induces clustering of these receptors at presynaptic terminals. It is also proposed that PICK1 interaction with mGluR7a receptors mediates coupling to Ca++ channels [22].
The protein NHERF (Na+/H+ exchange regulatory factor) also contains PDZ domains, and controls the signalling properties of parathyroid hormone receptor, which binds to NHERF by its PDZ ligand. PDZ-ligand mediated coupling of NHERF to B2AR’s and kappa opioid receptors is likely the way that NHERF controls the Na+/H+ exchanger protein [21,23].
PDZ-ligand interactions between the PDZ domain of cyclic nucleotide Ras guanine exchange factor and the PDZ ligand on B2A enables B2AR to activate Ras and the associated MAPK pathway [21].
PDZ-ligand interactions also play an important role in receptosome scaffolding. The protein Shank spatially organises receptors and ion channels and provides interaction between receptors and the cytoskeleton [21]

Methods: Proteomics and experimental determination of protein-protein interactions

The dawn of the new millennium has seen the development of high throughput methods which generate vast amounts of novel data on protein-protein interactions. A number of different methods have been used to generate this data, all with their respective advantages and limitations. Use of different methods, or even variations of conditions within methods, can produce conflicting data sets. Appropriate synthesis of data sets produced by different methods is required to produce a coherent ‘map’ of interactions.

Researchers studying protein-protein interactions have a large toolbox of methodologies at their disposal. These include complementation assays, mass spectrometric approaches, chip based methods and bioinformatic analysis. The nature of the data produced by various methods differs: data can be qualitative or quantitative, and can describe pairwise interactions between two interaction partners, or can describe grouped interactions within a complex. The inability of most methods used to investigate large scale interactomes to measure quantitative information about interactions such as kinetics raises an important question: what exactly constitutes an interaction? Some biologically relevant interactions may occur on short timescales with very low affinity, but might be considered irrelevant by, or be below the sensitivity of such methods [25].

One issue that is particularly applicable to the study of protein-protein interactions occurring in receptosomes, and particularly interactions with membrane bound proteins, is the difficulty of resolving hydrophobic proteins in 2D gels [25,26]. Modern two-dimensional liquid chromatographic techniques have been able to provide improved resolution of hydrophobic proteins but preparation of pull-down assay experiments still proves difficult with membrane proteins [26]. One of the other important problems in GPCR and GIP interaction analysis is the low cellular concentrations of these proteins. If the experimenter chooses to overexpress a particular GPCR or GIP, they run the risk of ruining the stoichiometry of the interaction network [26]. 

One particularly effective method of analysing protein complexes is called SEAM, which stands for Sequential Epitope tagging, Affinity tagging and Mass spectrometry. In this process, a protein is selected and epitope tags such as Myc are fused to one of its termini. It is then overexpressed in a cellular system of choice and the cell lysate is run through an affinity column where anti-Myc antibodies are attached to the beads. A second mixture of proteins is then run through the column, and those proteins that are bound to the epitope tagged proteins are resolved by 2D liquid chromatography and fed into a mass spectrometer for identification. Subsequently, one of the MS identified proteins is then Myc tagged and the procedure run again. In this way, it is possible to build up complexes of proteins [27].

Obviously a vast amount of information has to be gathered regarding protein-protein interactions between components of signalling machinery before any kind of mathematical modelling process can be applied to these networks. First, it is necessary to determine the stoichiometry of each complex, and the precise interactions of each protein with each other. It would also be exceptionally useful to have the crystal or NMR structures of each protein involved. Additionally, having identified the qualitative aspects of the system, quantitative biophysical data would be needed concerning the strength and kinetics of interactions. This task will be a massive undertaking, but eventually researchers will be able to build these mathematical models of GPCR signalling and incorporate them into pre-existing models of human brain function, such as the Blue Brain project that is being run on IBM’s Blue Gene supercomputer (http://bluebrainproject.epfl.ch/). Once GPCR and GIP interactions can be comprehensively modelled, the potential for drug design targeted to, and therapeutic intervention of these systems will be unprescendented.



REFERENCES:

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Biochem Soc Trans. 2004 Nov;32(Pt 5):851-5.
4.)	Bockaert J, Fagni L, Dumuis A, Marin P. “GPCR interacting proteins (GIP).
Pharmacol Ther. 2004 Sep;103(3):203-21.” 
5.)	Ostrom RS, Insel PA. “The evolving role of lipid rafts and caveolae in G protein-coupled receptor signaling: implications for molecular pharmacology.”
Br J Pharmacol. 2004 Sep;143(2):235-45. Epub 2004 Aug 2. 
6.)	Kukkonen JP. “Regulation of receptor-coupling to (multiple) G proteins. A challenge for basic research and drug discovery.” Receptors Channels. 2004;10(5-6):167-83. 
7.)	Patel MB, Patel CN, Rajashekara V, Yoburn BC “Opioid agonists differentially regulate mu opioid receptors and trafficking proteins in vivo.” Mol Pharmacol. 2002 Dec;62(6):1464-70
8.)	Hermans E. “Biochemical and pharmacological control of the multiplicity of coupling at G-protein-coupled receptors.” Pharmacol Ther. 2003 Jul;99(1):25-44.
9.)	No reference: personal theory
10.) Hall RA, Premont RT, Lefkowitz RJ. “Heptahelical receptor signalling: beyond the G protein paradigm” J Cell Biol. 1999 May 31;145(5):927-32. 
11.) Milano SK, Pace HC, Kim YM, Brenner C, Benovic JL. “Scaffolding functions of arrestin-2 revealed by crystal structure and mutagenesis.” Biochemistry. 2002 Mar 12;41(10):3321-8. 
12.) Burgueno J, Enrich C, Canela EI, Mallol K, Lluis C, Franco R, Ciruela F “Metabotropic glutamate type 1 alpha receptor localizes in low-density caveolin-rich plasma membrane fractions” J Neurochem. 2003 Aug;86(4):785-91.
13.) Leclerc PC, Auger-Messier M, Lanctot PM, Escher E, Leduc R, Guillemette G. “A polyaromatic caveolin-binding-like motif in the cytoplasmic tail of the type 1 receptor for angiotensin II plays an important role in receptor trafficking and signaling.” Endocrinology. 2002 Dec;143(12):4702-10. 
14.) Yamaguchi T, Murata Y, Fujiyoshi Y, Doi T. “Regulated interaction of endothelin B receptor with caveolin-1.” Eur J Biochem. 2003 Apr;270(8):1816-27.
15.) Inglese J, Freedman NJ, Koch WJ, Lefkowitz RJ “Structure and mechanism of G protein-coupled receptor kinases” J Biol Chem. 1993 Nov 15;268(32):23735-8. 
16.) Lodish, Berk, Zipursky, Matsudaira, Baltimore, Darnell “Molecular Cell Biology” 4th Edition, p734-5 W.H. Freedman & Company 2000
17.) Garzon J, Rodriguez-Munoz M, Sanchez-Blazquez P. “Morphine alters the selective association between mu-opioid receptors and specific RGS proteins in mouse periaqueductal gray matter.” Neuropharmacology. 2005 May;48(6):853-68.
18.) Garzo n, J., Rodrıguez-Diaz, M., Lopez-Fando, A., Sanchez-
      Blazquez, P. “RGS9 proteins facilitate acute tolerance
      to mu-opioid effects.” European Journal of Neuroscience 13,
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19.) Maggio R, Novi F, Scarselli M, Corsini GU “The impact of G-protein-coupled receptor hetero-oligomerization on function and pharmacology” FEBS J. 2005 Jun;272(12):2939-46.
20.) Jordan BA, Trapaidze N, Gomes I, Nivarthi R, Devi LA “Oligomerization of opioid receptors with B2-adrenergic receptors: a role in trafficking and mitogen-activated protein kinase activation” PNAS Jan 2, 2002 vol.98(1)343-348
21.) Morfis M, Christopoulos A, Sexton PM. “RAMPs: 5 years on, where to now?” Trends Pharmacol Sci. 2003 Nov;24(11):596-601.
22.) Boudin H, Doan A, Yia I, Shigemoto R, Huganir RL, Worley P, Craig AM. “Presynaptic clustering of mGluR7a requires the PICK1 PDZ domain binding site.” Neuron. 2000 Nov;28(2):485-97.
23.) Hall RA, Premont RT, Chow CW, Blitzer JT, Pitcher JA, Claing A, Stoffel RH, Barak LS, Shenolikar S, Weinman EJ, Grinstein S, Lefkowitz RJ. “The beta2-adrenergic receptor interacts with the Na+/H+-exchanger regulatory factor to control Na+/H+ exchange.” Nature. 1998 Apr 9;392(6676):626-30.
24.) Doronin S, Malbon CC. “Functional proteomics of G-protein-coupled receptors: analysis of large scale signalling devices” Pharmaceutical News (2002) 9, 347-355.
25.) von Mering C, Krause R, Snel B, Cornell M, Oliver SG, Fields S, Bork P. “Comparative assessment of large-scale data sets of protein-protein interactions.”
Nature. 2002 May 23;417(6887):399-403. Epub 2002 May 8.
26.) Wu CC, Yates Jr. III “The application of mass spectrometry to membrane proteomics” Nat Biotechnol. 2003 Mar;21(3):262-7.
27.) Deshaies RJ, Seol JH, McDonald WH, Cope G, Lyapina S, Shevchenko A, Shevchenko A, Verma R, Yates JR 3rd. “Charting the protein complexome in yeast by mass spectrometry.” Mol Cell Proteomics. 2002 Jan;1(1):3-10. 


This could use some proof-reading. I submitted it for marking about 10 minutes after I finished it late on a Sunday night (was due by the time Michelle got to work on Monday morning.) She's actually letting me proof it and resubmit it because its kinda ugly.


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## BilZ0r

Homeostatis in neuronal signalling

*Homeostatis* is the body’s tendency to keep everything the same, like a thermostat, but not just for temperature, but nearly every physiological parameter. Simple homeostatic controls exist for things like hormones, for instance the adrenal medullary cells which releases adrenaline, will have receptors for adrenaline, which slow adrenal release. This process is known as negative feedback. More complicated homeostatic controls exist for things such as body weight, blood pressure and water intake, however the general theme is the same, if a change takes the body away from its homeostatic set point, then negative feedback will try and restore this.

Nearly all aspects of signaling in the synapse are homeostatically controlled. The release of nearly all neurotransmitters are controlled by an *autoreceptor*, a presynaptic receptor which receives the type of neurotransmitter which the neuron it is located on releases, and feedbacks to inhibit the release of this neurotransmitter. Noradrenaline release is controlled by the alpha2 adrenoreceptor, GABA by the GABAB receptor, serotonin by the 5HT1A/B receptor, dopamine by the D2 receptor, glutamate by mGluRIII. When neurotransmitters bind to their autoreceptors, they usually activate a G-protein coupled cascade which leads to the inhibition of calcium channels and/or activation of potassium channels, which leads to a reduction in neurotransmitter release and presynaptic depolarization respectively. Many autoreceptors also inhibit the synthesis of their respective neurotransmitter. For instance the dopamine D2 receptor leads to phosphorylation and inhibition of tyrosine hydroxylase, the rate limiting enzyme in dopamine production. It is worth noting that these receptors are usually expressed in non-presynaptic locations, on other neuronal types, where they have a different function. Though sometimes they maintain their function as inhibitors of neurotransmitter release, for instance the histamine autoreceptor, the H3 receptor, is found presynaptically on nearly every type on neuron, and has been shown to inhibit the release of every neurotransmitter so far investigated. When a receptor is acting like this it is referred to as *heteroreceptor*, the 5-HT1A is another common heteroreceptor. In most native systems, neurotransmitters are being released most of the time, and hence the autoreceptors are tonically (i.e. continuously) active, constantly damping the release of neurotransmitter. Therefore, drugs which block autoreceptors, (e.g. yohimbine, and alpha2 adrenoreceptor antagonist) lead to a large increase in released neurotransmitter.

Autoreceptor action is exclusively a presynaptic method of homeostastis. Receptors themselves are capable of gating hyperactivity. Many ligand gated ion channels *desensitize* (i.e. they enter a state of low efficacy) in response to the application of an agonist, often on an extremely rapid time scale, the AMPA glutamate receptor desensitizes to 10% of maximum current within 10ms of saturating concentrations of agonist. Benzodiazepines rapidly induce tolerance to their behavioural effects. These drugs, which potentiate the action of GABA at the GABA-A receptor, produce molecular changes which mirror this tolerance. The exact mechanism remains unclear, but evidence shows that it is likely that prolonged benzodiazepine treatment renders GABA-A receptors insensitive to benzodiazepine modulation. It seems likely that this is primarily due to the receptor being pulled into an intracellular vesicle (*internalization*), presumabley after the action of a kinase. The receptor is then modulated in some way, possibly by removing benzodiazepine sensitive subunits, so that it is insensitive to benzodiazepines and returned to the membrane surface. It seems that only very high doses or very long treatments with benzodiazepines lead to a total decrease in GABA-A receptor number, and this may be through reduction in GABA-A receptor subunit mRNA expression[1].

G-protein coupled receptors (GPCR) are also subject to desensitization. Activation of GPCRs increases the activity of G-protein receptor kinases, which phosphorylate the receptor and decrease their signaling efficacy (usually through a decrease in ligand or G-protein affinity). This phosphorylation is reversible, but also allows the binding of proteins called arrestins to the intracellular side of the GPCR. Arrestins not only completely cut the GPCR off from activating G-proteins but they also allows the binding of other molecules, classical the clathrins, which internalize the receptor. Once internalized, (where receptor is separated from interactions with ligands) it awaits one of two fates, reinsertion back into the membrane, or degradation by protiolytic enzymes. Hence long term treatment with agonists lead to a long-term depletion in receptor number (*down-regulation*), which only the synthesis of new receptors can resolve. It is worth noting that GPCRs can also interact with genes, altering expression and after chronic agonist application sufficient to induces internalization it is common to note a decrease in the production no that receptors mRNA, which will also reduce receptor numbers and further slow recovery times. 



> *Figure 1.* Downregulation of a receptor. If a receptor is occupied by an agonist (A), then it may be phosphorylated (P) by GPCR Kinase (GPK), which can lead to arrestin binding, and internalization.



References

[1] Bateson AN.	Basic pharmacologic mechanisms involved in benzodiazepine tolerance and withdrawal. Curr Pharm Des. 2002;8(1):5-21


----------



## 5-HT2

BilZ0r said:
			
		

> Note: I need people to rip into that one extra hard, if you see any problem with it, please tell me.



It's pretty good, except when you start talking about synaptic plasticity in the mesocorticolimbic dopamine system.  It seems as if you have based your assertions mainly on the work of Reynolds, Hyland, and Wickens, but a lot of other people have looked at this, and it's safe to say there is absolutely NO consensus in the field.  Despite valiant efforts by many labs, the role of dopamine in corticostriatal synaptic plasticity is still very mysterious.  Some goups have observed LTD upon application of dopamine or dopamine agonists, and some groups have observed LTP.  Adding another wrinkle to the confusion, the plasticity observed can be highly dependent on the stimulation protocol utilized.  However, the role of striatal medium spiny neuron UP and DOWN states has not been fully explored.  There are some tantalizing unpublished results from my old lab that take UP/DOWN acivity states into account and seem to explain some of other peoples' results, but they are still only a start.  A grad student in my old lab is devoting all her energy to looking at this problem, but is constantly bitching about the inconsistency of her results.  For an introductory text like this, I would avoid going into details and just say that dopamine appears to be involved in corticostriatal synaptic plasticity, which in turn seems to be important for reward-related learning, but nobody knows just HOW.


----------



## Ataxia

One suggestion:

This would be PERFECT in .pdf format when it's done. It could easily be distributed and shared amongst the community online. When this is done, it will be a major reference for all those with an amateur interest in pharmacology!


----------



## BilZ0r

I think the in vivo evidence it pretty good, and I think that as a hypothesis it is undoubtabley the best. Meanwhile, as I say "While these hypothesis is certainly a vast over simplification, the basic rules are probably true. Dopamine increase synaptic plasticity, and so helps associations form between stimuli and behavior that lead to reward. When this system is hijacked by addictive drugs an aberrant association which encourages drug taking is formed."


----------



## 5-HT2

^^^yeah, but does it promote LTP, or LTD???  You're making a HUGE stretch when you say there is "convincing" evidence that dopamine increases corticostriatal LTP.  I would definitely agree that the evidence suggests that it promotes synaptic plasticity, but the direction, and the other necessary conditions under which plasticity in either direction can occur, are controversial to say the least.  Probably dopamine can facilitate synaptic plasticity in either direction, depending on variables such as the activity state of the neuron and network and the presence of other neuromodulators.  Again, I would advise you to avoid making definitive statments about such a thorny issue.  Just "there is evidence that DA promotes synaptic plasticity" should be enough for an introductory treatment of the topic.  

Also, what _in vivo_ evidence are you referring to?  Are you talking about slice work, or actual _in vivo_ recordings in the intact brain?


----------



## BilZ0r

Of course I'm talking about in vivo, as in, in vivo... whole alive animal.. Show me a paper which shows that dopamine premotes LTD in vivo... Sure, i'm relying heavily on the evidence from one group, but that's cause they're about the only people doing it.... as far as I am awear.


----------



## Synapse999

From newsweek, to even CNN.  lately.
Even though they rarely use the term "Synapse" and its important role.
More and more, people are understanding finally the key roles that play into the how and why of the neuron. 


Glad to see, there was a thread, to include this frequently overlooked and assumed function.


-Synapses, the spaces between neurons, are the channels through which we think, act, imagine, feel, and remember, and also the means by which our most fundamental traits, preferences, and beliefs are encoded. In short, they enable each of us to function as a single, integrated individual - a synaptic self - from moment to moment, from year to year-


Synaptic-Self - Joseph E. LeDoux


----------



## 5-HT2

BilZ0r said:
			
		

> Of course I'm talking about in vivo, as in, in vivo... whole alive animal..



Sorry, there are people who misuse _in vivo_ to describe slice work, when that should really be called _ex vivo_.  Also, I haven't read the Reynolds et al. Nature paper in about a year, so I was rusty on the details (just skimmed it again).  



			
				Bilz0r said:
			
		

> Show me a paper which shows that dopamine premotes LTD in vivo... Sure, i'm relying heavily on the evidence from one group, but that's cause they're about the only people doing it.... as far as I am awear



There is none.  As far as I know, Reynolds et al., 2001 is the only one where they look at _synaptic_ plasticity induced by dopamine neuron stimulation (as opposed to addictive drugs).  To my knowledge, nobody has replicated that finding, and word on the street is that other people are trying or have tried (however, this is second hand information from a prominent investigator in the field who may not believe the results in that paper).  

On the other hand, it has been reported that repeated passive cocaine administration induces  LTD in the nucleus accumbens (Thomas MJ, Beurrier C, Malenka RC, Nat. Neurosci 2001).  There are also unpublished results from another lab that cocaine self-administration also induces LTD in the NAc.  So there may be differences between the plasticity induced by ICSS and addictive drugs.  These other results may show, albeit indirectly, that you can not unequivocally say that dopamine always promotes corticostriatal LTP.


----------



## BilZ0r

Yeah... but thats paper isn't looking at dopamines modulation of LTP or LTD, it's just looking at generaly glutamatergic tone... I don't find the results all together surprising, though interesting... no change in minature rates, indicating that there has been no change in total synapse number.... but changes in the electrically evoked signal caused by a decrease in quantal size.... that's pretty fucked up.... but yeah, that papers is looking at the effect of long term dopamine on glutamatergic signalling, not on the second to second effect of dopamine on synaptic plasticity.

I've said before that people should look to see the effect of dopamine (From SNc stimulation) on place cell activity... burst the dopamine when they're in the location of the place cell firing, and see whether the cells tonic or max firing changes...

And if they can only find goal cells in the Prefrontal cortex, then a study like that could get reallly interesting....


----------



## 5-HT2

BilZ0r said:
			
		

> And if they can only find goal cells in the Prefrontal cortex, then a study like that could get reallly interesting....



One group has, and here is the reference!


----------



## BilZ0r

Awsome, I knew they'd be in there someone... Further evidence that the anterior cingulate is massively different from prelimbic and infralimbic cortices.

But I'll consider your advise and try and make it sounds a little less conclusive.


----------



## EN21

A question from a stupid lay person:
BilZOr, it´s really great to read your summaries in neuropharmacology -This helps much in understanding. But I have a little question. You wrote: 
 "Therefore, drugs which block autoreceptors, (e.g. yohimbine, and alpha2 adrenoreceptor antagonist) lead to a large increase in released neurotransmitter."
Concerning the D2 receptor this would mean that D2 antagonists lead to an increased dopamine release, (right?)
But I always thought that antipsychotic agents are used to decrease the overall dopamine levels in brain. 
Those two sentences do not really fit. Why?


----------



## BilZ0r

Although that seems like a reasonable way fo thinking, it's flawed for a couple of reasons. One, dopamine doesn't have a clear autoreceptor, D2 and D1 like receptors both participate in negative feedback...
2) Antipsychotics aren't designed to stop dopamine release, they're just made to stop 'crazy people acting crazy'. Infact, both typical and antipsychotics increase dopamine release, at least in acute treatments[1, 2]. but importantly, at least the typical ones are blocking ALL D2 receptors at the 50-80% range, so the released dopamine aint acting there.


----------



## EN21

Thank you!
This really helps understanding. But this also would mean that there is a lot of dopamine released, that cannot act. Can this dopamine excess be responsible for the long term side effects, since it can be oxidized to the ortho-quinone, which can further react.
Do you know what I mean?


----------



## BilZ0r

Well the excess dopamine could be responsible for some of the extrapyramidal effects, though I don't know. I would worry about dopamine-oxidative products route though.


----------



## 5-HT2

BilZ0r said:
			
		

> One, dopamine doesn't have a clear autoreceptor, D2 and D1 like receptors both participate in negative feedback...



Well, the D2 receptor, specifically the short isoform, is considered by most people in the field to function in the manner of a classical autoreceptor, i.e. presynaptically localized on dopamine neurons and inhibits dopamine release.


----------



## BilZ0r

*PHARMACOKINETICS*

Pharmacokinetics is often differentiated from the rest of pharmacology, as it is the study of what the body does to drugs as opposed to what drugs do to the body. For the aid of pharmacology students, it is usually broken down into four stages, mirroring the drugs passage through the human body: absorption, distribution, metabolism and excretion.

*Absorption*
The classical route of drug administration is orally. There are many factors altering the absorption of orally administered drugs: gastric contents, intestinal pH and most importantly, the physiochemistry of the drug. Drugs which are most rapidly absorbed are drugs which can easily pass through the membrane of cells which make up the drug wall. This means the drug needs to be partially lipophillic, that is, soluble in fats, to be rapidly absorbed. Drugs also can pass between cells, as opposed to through them, so lipophobic chemcails can also be absorbed though this is a limited pathway. Conversely, the drug also needs to be partially hydrophilic, because it needs to be able to dissolve in the watery (aqueous) environment of both the gut and the blood. That means drugs like ethanol are very rapidly absorbed from the gut (it rapidly passes through cell membranes, being both lipophillic, hydrophilic and physically small) while hydrophobic benzodiazpines often take hours to reach the maximum plasma concentration after a single dose (though the water soluble benzodiazepine midazolam is absorbed over twice as fast as it’s more hydrophobic cousins, such as diazepam and alprazolam).

The lipophillicity of drugs can also be effected by the pH of the gastric contents. Chemicals which are either basic (like amphetamines) or acidic (like barbiturates) become more fat soluble (and hence more easily absorbed) in acidic or basic solutions. So theoretically, once could eat something acidic or basic and enhance the absorption of drugs from the gut (though in practice this has an equal an opposite reaction in regards to excretion). Also, most absorption happens in the small intestine, where pH is kept below 7 (~pH 5) by bile secretions, and hence any attempts to manipulate gastric pH are probably pointless.

As any drinker knows, one can also alter the absorption of drugs by filling the stomach with food, which slows the movement of drugs form the stomach, to the small intestine. However, one can find reports of fatty foods increasing the absorption of drugs, specifically highly lipophillic compounds or compounds where are extended release formulations (XR). This is because these drugs do not dissolve in aqueous environments, and essentially stay in a big clump, slowing their transit out of the gut and into the blood, and increasing the fat content of the gastric canal allows them to dissolve. There is evidence that some benzodiazepines may be fat soluble enough for this effect to come into play.

*Distribution*
Once drugs are absorbed, either through oral, intravenous or any other way, they are distributed throughout the body via the blood. Orally administered drugs are absorbed through the intestinal wall, where they dissolve into the blood in the hepatic-portal vein which travels directly to the liver. From there the blood travels to the heart and is pumped around the body. What is of most interest to the users of recreational drugs is getting the drug distributed into the brain. The brain is unlike any other organ in the body, and it uniquely protected by the “blood-brain-barrier” (BBB) which is a conceptual term for the nature of the blood vessels which permeate the brain. The cells which make up these blood vessels are tightly bound together, so that drugs can not move in between cells as they can in other tissue types, and must pass through the cells. They are also bristling with so-called “multi-drug transporters” (like P-glycoprotein), molecular pumps which actively extrude drugs back into the blood. While these transporters can not pump all drugs out of the brain, they can certainly effect the brain permeation of a lot of chemicals. 

Because drugs MUST be lipophillic to pass through the BBB some drugs are excluded from the brain. The classical example of BBB impermeable drugs are the new generate of “non-sedating antihistamines”. Old antihistamines were fat soluble, and could enter the brain, blocking histamine receptors, and causing sleeplyness. 2nd generation antihistamines were generally made by adding lipophobic groups such carboxycylic acids and alcohols to the structure of first generation antihistamines, making the whole molecule fat insoluble and preventing their passage into the brain; stopping them causing sedation. Another example which frustrates some recreational drug users is the potent opioid loperamide, which although fat-soluble, is a high affinity substrate for P-glycoprotein transporter, and is essentially excluded from the brain (indeed, P-glycoprotein transporters in the gut wall prevent it from getting much further than the intestines). Cannabinoids are also distributed in an interesting way. They are in generally, extremely fat soluble and water insoluble, which lends them to dissolving in fat tissue in the body. Because of this cannabinoids can take weeks to clear from the body after a single dose, while most, more water soluble drugs, are nearly completely cleared from the body after 3-5 days, 

*Metabolism*
Drugs which are taken orally are taken directly to the liver via the hepatic portal vein. The liver is a densely infused with blood vessels, and metabolic enzymes for various classes. Because nearly all chemicals absorbed from the gut needs to pass through the liver, the metabolism that takes place there, before the chemical enters the rest of the body is called “first pass metabolism”. Metabolism in the liver can be broadly split into two catagories, phase I and phase II metabolism. Phase I metabolism envolves breaking down chemicals. The classical phase I enzymes are the super family of enzymes know as the cytochrome P450 enzymes (CYP), which has about 50 subtypes, in 17 families, each with several subfamilies. Each enzyme has a name like CYP2D6, which means it’s the 6th subtype in the D subfamily in the 2 family. Most drugs are metabolised by drugs in the 1,2 and 3 family, specifically, CYP1A2, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4 and CYP3A5. Furthermore, drugs can be metabolized by a whole range of hepatic enzymes, like monoamine oxidase, alcohol dehydrogenase, flavin-containing monooxygenases and many others. It is worth noting that the majority of these enzymes are expressed in the gut wall, and begin to metabolize drugs well before they get into the blood stream.

Phase II enzymes add things to the drugs, usually to make them highly water soluble, so they are excreted by the kidneys into the urine. Phase II enzymes conjugate large molecules like glutathione and glucuronide or small sulphate molecules to drugs. Phase II reactions are generally subsequent to phase I reactions, though not exclusively.

The activity and quantity of phase I enzymes are plastic, that is to say, the amount of enzymes and the speed at which the break down drugs can be increased by chemicals known as “inducers” and decreased by drugs called “inhibitors”. This means that coadministration of drugs with enzyme inhibitors leads to an increased amount of drug which make it into the systemic blood supply and ultimately to the brain. Conversely, coadministration of inducers with a drug means that less of the drug gets into the brain. Enzyme inhibitors and inducers usually only effect a small number of enzymes. Enzyme inhibitors can work via a number of mechanisms. Suicide inhibitors work by being a substrate for the enzyme, but undergo an irreversible reaction once in contact with enzyme, covalently binding to the active site of the enzyme, rendering it useless. Other inhibitors bind to allosteric sites on the enzyme, slowing it’s activity. One needs to be careful about mixing drugs and chemicals which inhibit their metabolic enzymes. More than one death is attributed to mixing MDMA and the anti-HIV drug ritonavir which potently inhibits CYP2D6, the primary enzyme responsible for MDMA metabolism. The danger appears because it adds two more levels of variablitity. Drugs are absorbed variabley from person to person, and enzyme inhibitors act to varying amounts from people to people. Hence a dose of inhibitor which might reduce the activity of an enzyme by 20% in one person, might reduce it by 80% in another, making a normally safe dose of drug lethal. One can also essentially inhibit an enzyme by taking two drugs at the same time which are metabolized by the same enzyme. Here you get “enzyme competition”. For enzyme competition to work, one needs to nearly saturate the metabolic capacity of an enzyme, and this can usually only be achieved when there is only a limited amount of the enzyme. For instance administering two drugs which are metabolized by CYP3A4 are unlikely to compete, because CYP3A enzymes make up 40-60% of the total amount of CYP450 in the liver, however two drugs which are metabolized by CYP2D6 are likely to compete as they make up only 2% of liver CYP450s. Hence it can be dangerous to mix drugs which use the same metabolic enzymes.

Administering drug via routes other than oral skips first pass metabolism, though of course, the drug will pass through the liver eventually, where metabolism will begin. The differences in metabolism and distribution between intravenous and oral administration produces some interesting effects. If a drug is administer intravenously (IV) one measures the plasma concentration of the drug over time, you get will a graph as shown in figure 1. If one administers the same dose of the drug orally and measures the same properties, you will get a similar curve, though shifted to the right and far more squat. This should be obvious to anyone who has used intravenous drugs. The peak of the drug effect, which corresponds (roughly) to the plasma peak happens essentially instantaneously with IV administration, though when the same amount of drug is administered orally, the maximum effect (and plasma peak) happens much later and is much less. If one measures the area under the curve (AUC) of the plasma concentration x time graph one can judge the amount of metabolism a drug undergoes in the body. For example, if a drug is in no way metabolized during oral administration, then the AUC is equal to the AUC during intravenous use. However, if the drug is metabolized, the AUC decreases below than of the IV graph. If one takes the AUC of the oral dose and divide it by the AUC of the intravenous dose, you get a value known as the “bioavailability” which is essentially the percentage of the drug which escapes first pass metabolism, e.g. a non metabolized drug has a bioavailability of 100% while an extremely metabolized drug would have a bioavailability of 1%. Not only do different drugs have different bioavailabilties but so do different routes of administration, e.g. smoking has 100% bioavailability but intramuscular or subcutaneous administration usually have bioavailabilties below 100% as there are metabolic enzymes in the skin and muscle.



> *Figure 1.* Blood concentration vs time of a hypothetical drug given IV (red) or orally. If the drug is not subject to first pass metabolism it will have an area under the curve (AUC) equal to the IV graph (dark blue). If the drug is subject to first pass metabolism it will have an AUC less than the IV curve (light blue)​



Metabolism doesn’t always reduce the effectiveness of drugs. Many drugs need to be metabolized to work, these drugs are called “pro-drugs”. A classical pro-drug is codeine, it is metabolized by CYP2D6 into morphine. Codeine itself it virtually inactive at any of the opioid receptors, how morphine is a potent mu-opioid receptor agonist (it is worth noting that the phase II metabolite of morphine, morphine-6-glucuronide, is far more potent than morphine, and there has been considerable debate as to whether morphine is a morphine-6-glucoronide prodrug). Because codeine needs hepatic enzymes to be active, it is most potent via oral administration, as it the case with all prodrugs dependent on hepatic enzymes. The CYP2D6 mediated conversion of codeine to morphine can be saturated by codeine doses of 200-400mg, and hence doses higher than this have no effect.

*Excretion*
The final pathway for nearly all drugs is excretion via the kidneys. The kidneys work by essentially filtering all components of the blood out apart from very large very large molecules and blood cells, and then transporting all the useful components back into the blood, like salts, water, glucose, amino acids etc. As the kidney is designed to remove noxious chemicals, this is a cleaver system; as the body can’t know what poisons it could face, a system designed to actively remove toxins wouldn’t work, so the system instead removes everything, then keeps only that what it needs.

Unfortunately for the kidney, this system is not fool proof, as the kidney has difficulty excreting lipophilic chemicals, as they can permeate back through the walls of the kidney (you now see why phase II enzymes are important, by making noxious chemicals water soluble chemicals from escaping the kidney). As already mentioned certain chemicals can change their fat solubility depending on the pH of the solution they are dissolved in. Basic chemicals like amphetamines become fat soluble in basic environments and water soluble in acidic environments. Indeed, it has been shown that in subjects who have had treatments to make their urine more basic, they excrete amphetamine at a rate 10x slower than subjects who were treated to produce hyper-acidic urine.



> *Figure 2.* The main metabolic enzymes or clearance mechanisms for common recreational drugs​


----------



## Black Octagon

Does this mean that the body of the text is more or less finished? I want MORE!


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## BilZ0r

Yeah, I'm just waiting for some text, from someone... but yeah... more or less... done. Maybe you can think of something more that needs discussing?


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## Black Octagon

BilZ0r said:
			
		

> Yeah, I'm just waiting for some text, from someone... but yeah... more or less... done. Maybe you can think of something more that needs discussing?



Excellent! That was quite an achievement. Well done.

The only thing I could think of adding, if this were to truly be a 'text,' is an Introduction and Conclusion which explain the importance of understanding neuropharmacology when discussing drugs and drug use. It could follow the vein of Bluelight and Erowid by taking a harm reduction spin, or it could focus on the politics of drug use, or could just remain science-focused.

One other possibility would be maybe a case-study or two which explain the neuropharmacology of specific drugs and thereby synthesise the important elements from each chapter. Though I have no idea if this is practical, seeing how some case-studies (e.g. your 'Neuropharmacology of Hallucinogens' article) require an understanding of other areas (in this case, brain science) in order to understand properly.

Also, I'm gonna read through everything again to see if a layman like myself would find an extra diagram or twelve useful.


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## BilZ0r

[EDIT] Sorry PDF version is lost to the either [/EDIT]


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## Black Octagon MK 2

A delightful addition to our online arsenal!

So, what now? The thread title mentions that this is an Erowid/BlueLight text. Does that mean it will be featured on Erowid? Have they contributed to it in any major way?


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## BilZ0r

^ Yes, hopefully, erowid will both host it, and help editing it. Give it time, it's quite long.


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## Smyth

Ok ivew had an opportunity to look at it now. On the whole is very good but there are still some typos which you may want to revise and also consider inputting page numbering.

The stuff by Bilz0r is very comprehensive and logical even if it might seem a bit oversimplified. However the more in depth coverage by mitogen is quite difficult for me to understand.


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## Psychedelics_r_best

Fantastic biology. I'd love to write something, but I probably wouldnt be too fantastic at it as my knowledge is not that extensive in terms of neuropharmacology. Those questions aren't really very complex if you are only trying to convey the basic information. What would be most helpful is how all that information regarding basic cell functions relates and is effected by drug consumption. Well, you already got a good deal of that.

What I would really like to see in addition is some general little index on how different groups of drugs act on cells, and their toxicity/ neurotoxic potential. Just general groups like alcohol, dissociative NMDA agonists, serotonergic indoles, phenethylamine/ amphetamine based drugs, THC.


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## BilZ0r

Mmmm... Yeah, I think I tried to bug theDEA into writting something on MDMA, talking about THC is kinda pointless, either you say "THC probably isn't neurotoxic" or you try and sum up like 500 papers which all say different things..

Yeah, maybe I'll try and make the drug dictionary/glossary thing more comprehensive...


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## mepat1111

I downloaded the pdf and have grasped the initial chapters with no problems, taking the middle-later sections a bit slower to make sure all is absorbed into my drug-riddled brain ahaha!

Very well written thus far, very impressed with your abilities to simplify rather complex ideas into simple terms for the layman such as myself...


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## Matt the Raver

I only just stumbled on this site the other day. I have to admit I'm very impressed. Normally literature on psychoactive chemicals revolves around emphasising how bad they are and their addictive properties, which has the unfortunate effect of stifling honest and open minded debate. 

Have you considered a detailed review of specific receptor functions? 

One thing I noticed,  was that you've said that MDMA promotes dopamine release via 5HT2A receptors present on dopaminergic neurones. 

However, one important aspect is the inhibitory effect 5HT2C plays on dopamine release. 

5HT2C receptors are expressed on GABAergic neurones in the substantia nigra and ventral tegmental area, which synapse with dopaminergic neurones, thereby inhibiting their activity. (See Neuropharmacology 38 1083-1152 (1999) Barnes & Sharp) (This is quite an extensive review, which I'ld describe as  the meaning of serotonin) 

MDMA seems to work by desensitising 5HT2C thereby causing dopamine release by disinhibition.


----------



## Xildo

Psychedelics_r_best said:
			
		

> Fantastic biology. I'd love to write something, but I probably wouldnt be too fantastic at it as my knowledge is not that extensive in terms of neuropharmacology. Those questions aren't really very complex if you are only trying to convey the basic information. What would be most helpful is how all that information regarding basic cell functions relates and is effected by drug consumption. Well, you already got a good deal of that.
> 
> What I would really like to see in addition is some general little index on how different groups of drugs act on cells, and their toxicity/ neurotoxic potential. Just general groups like alcohol, dissociative NMDA agonists, serotonergic indoles, phenethylamine/ amphetamine based drugs, THC.



of course you would include opiates in that description

i think this is a superb idea, when is the wiki coming?


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## servalis

This is really amazing! Thankyou so much for posting this I am absolutely in love with reading this. There are a few typos I have noticed though. I hope it doesn't seem pompous if I point them out. 

Under the what is a protein section, aqueous, buried, and subtly are misspelled.

Under what is a receptor, near the bottom of paragraph 3 question and receptor are misspelled. 

That's as far as I have gotten. I hope this helps!


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## BilZ0r

Oh yeah, I didn't pay for my bilz0r.com domain. I'll look into it.


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## marquee

I pretty familiar with NMDA receptor antagonists (ketamine, phencyclidine, dextromethorphan), especially ketamine, if a writeup would be useful.


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## ziddy

Could someone please rehost the PDF?


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## lost_pdf

I joined just for this. Is there a torrent? Do i have to pm someone?

Could someone host the pdf please!


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## lost_pdf

Bump!


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## bigmac74

The file is too large to upload as an attachment here, so I uploaded it to YouSendIt...

http://download.yousendit.com/EF5DD85F20CCF77D


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## lost_pdf

Thank you brother. From the depths of our collective being: light.


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## ziddy

The yousendit link has expired. Could someone else host it?


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## bigmac74

*Reuploaded*

http://www.comteche.com/free-image-hosting/images/1Tm02047.pdf

This link should be permanent.


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## Black Octagon MK 2

Um, it's broken again...


----------



## bantaren

Black Octagon MK 2 said:
			
		

> Um, it's broken again...




Yes, confirmed. Couldn't someone please upload it? Really want that PDF...


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## ziddy

http://www.abolishsuffering.com/misc/bluelight_neuropharmacology.pdf


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## gethigh

i can add a little bit that i know about 2 opiates, you can add more if you know.
oxy/hydrocodone converts into two metabolites, noroxy/hydrocodone and oxy/hydromorphone, norooxy/hydrocodone is useless for analgesia and for recreational value, you can slow down the metabolization by drinking grapefruit juice. oxy/hydromorphone is a minor metabolite and is much more potent then the precursors but is minimal in effect, the high received from oxy/hydrocodone is produced by oxy/hydrocodone it self and possibly helped by oxy/hydromorphone.


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## gethigh

sorry i was high and wasnt thinking disreguard that post


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## johnnyb420

oh my god gethigh you are way over your head in this thread 

i applaud your interest but for gods sake just read it you are nowhere near being ready to ad to this

keep up your hunger for knowledge man someday you will be one smart dude if pay attention


----------



## t4exanadu

I'm wondering what the status of this document is. Is the original author planning on adding new content or accepting new content from others? There are a number of areas I would like to contribute to such as a section on the biogenic amines and the role of glutamate receptors in the action of some hallucinogenic substances. I am quite impressed with the results of the text thus far. Thanks for all of your hard work.


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## Mugz

Has anyone got a link to the PDF that works???


----------



## t4exanadu

mugabe said:
			
		

> Has anyone got a link to the PDF that works???



http://www.abolishsuffering.com/misc...armacology.pdf


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## Mugz

^just tried it and it doesnt work


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## melange

man I'm gonna have to eat some ritalin to study and remember and retain this info


or get high or something


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## Mugz

bump again, is there any news on a link that works for the PDF???


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## adrian89987

where could I upload it to?

I have a copy.

Yousendit.com?


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## adrian89987

http://www.yousendit.com/transfer.php?action=batch_download&batch_id=bVlERE9naFJsMHhjR0E9PQ


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## Mugz

thanks


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## Mugz

ive lost it again when i had to restart my system. could someone put a link up again please because the last one has expired.
thanks


----------



## NeuroSoup

I am from www.NeuroSoup.com. We would like to host a free version of your Neuropharmacology Text on the site so users could download it. Would this be alright with you? If so, please contact me at: http://www.neurosoup.com/contact_kcole.htm


----------



## dylmeister007

how do you guys know all this stuff?

do you study it


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## MurphyClox

...there are indeed a lot of persons with academic background here at ADD. See here: http://www.bluelight.ru/vb/showthread.php?t=402239

- _Murphy_


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## psychedelicious

Bluelight Neuropharmacology PDF

not going anywhere for a while, imageshack'd


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## bcuzZ

thank you !


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## silentscience

wow.


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## Mycelium

How about we all work on editing it on Wikibooks? I'm sure it'll take off from there.

BTW I can run a server and can grant (reputable) members an account for hosting and whatnot. I'm sure I have some drug related domains laying around, too.


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## Yopreacher

This is impressive stuff. In have only looked at it briefly but it seems to be quite accessible yet not to simple. It makes me happy to see that the community can cooperate and produce such quality work.

I take it that you want to see it spread?

Can I post a link to the pdf on other forums or is it better to link to this thread?


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## ZeuZzZ

Man this is gonna put me ahead of the class when I start my pharmacology course at uni next year.  to everyone who made this, truly invaluable information.


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## CRICKETBEE

thanks for this!


Funny...i just posted a thread asking people to recommend me a bunch of books on how the brain works and how psychedelics, stims and opiates work in the brain.

i think there is a real need for stuff like this

It sounds like more people wanted to add to it....is it still an ongoing project?

thanks


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## eatcod

This is fantastic, thank you to everyone involved in it.

Is this project still in progress?

I'd like to offer to help proofreading and editing to clean it up too.  I don't know much at all about the science but am a bit obsessive with spelling and grammar so would like to have an edited copy just for my own ease of reading!


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## hybridweb

This is a really cool idea! If you guys are looking for updates or additions in a few years still, I'd be way down to contribute. I'm currently working on a BS in Behavioral Neuroscience, so after that I'll have a good background in biochem, MCD biology, neurophysiology, genetics, and some psychology; I'm down to try to pass some of that on! I'm also tired of all the crazy drug misinformation floating around, it'd be cool to try to dispel that. In the mean time, I'll be working my way through the current version. Great project!


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## O-P-M Dream's

ummmm what???


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## Altmed

raybeez said:


> Sounds like a neat idea. I have a good background in neurophisiology, so I'd be up for doing a writeup about the electrical properties of a neuron. It shouldn't be too hard explaining action potentials, sodium/potassium current, membrane depolarization, etc in a simple, easy to understand way.
> 
> Wow! I just found this...
> http://img208.imageshack.us/img208/489/bluelightneuropharmacolmk2.pdf
> 
> Should be a sticky!
> 
> TY to all the contributors!


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## Altmed

CRICKETBEE said:


> thanks for this!
> 
> 
> Funny...i just posted a thread asking people to recommend me a bunch of books on how the brain works and how psychedelics, stims and opiates work in the brain.
> 
> i think there is a real need for stuff like this
> 
> It sounds like more people wanted to add to it....is it still an ongoing project?
> 
> thanks



I'm glad to see this out there! I was going to ask for the same/similar, so it seems we think alike.

I's love to find a bit more advanced great text on opiate, CYP450  & Cox-2 inhibitor metabolism through the liver, kidneys and then to the blood/ brain barrier, safety of taking these & genetics. It seems to me that with some research on what's already out there, this could help those with different types of chronic pain.

There are natural ways to do these things as well, yet would be great to see them in print, including avoiding &/or controlling the adverse effects of steroids, both anabolic & glucocorticoids, as both can have equally nasty adverse effects.


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## Hyperthesis

Are there any efforts by Bluelight to continue resp. extend *BilZ0r*'s fantastic work?


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## Symposion

I hope so.
This is a really well developed idea, as long as he only wanted something that anyone can read easily.

And he did it. 
I wish some material like this would be enlarged.


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## DooMMooD

Hey, GREAT posts and great information.  A lot of it most (i hope) will know from their biology and chemistry classes, but quite a large portion is much more detailed and slightly more advanced than ANY of those basic classes will get into, specifically (and obviously) when it comes to drugs.  

Great info, thanks for the posts, it has helped me learn a few extra things and to solidify and clear up my existing questions and knowledge quite a good bit.  So thank you for the information, and teaching me a few things.

*Now my question: not to be a nagger, but can someone please fix the figures and graphs in the PHARMACOKINETICS section? * 

I understand it all, it just helps me to see the figures that are supposed to be shown, because it helps solidify my understanding of these things quite a bit 

Basically: i "get it", but i'll "get it" permanently if i see the graphs described.  The graph and thinking in actual concentrations and saturation is easier for my brain because i can see things mathematically sometimes easier than reading the words, and it translates in my head to the written info if i see how these #s function.  

I do a lotta math and #s and graphs and flow graphs and flow figures and charts my brain immediately understands and translates into whats actually happening well in my brain.  Sorry for the rant, about this, just kinda explaining it to myself so that the reasoning makes sense to, well, me.


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## MasterOfDeception

The first post contains great stuff , it also happens that I am interested in neuroscience this period. I have also found this neuroscience page which is a good start for beginners : 

http://faculty.washington.edu/chudler/introb.html

Any more specific info on the neuopharmacology of psychoactive substances(with enough details, analysis and explanation) ? Mostly interested in psychedelics, mdma and antipsychotics. Thanx!
Wikipedia provides some info but it's not explanatory enough.

Btw, http://www.bilz0r.com/Neuropharm-phis text.pdf  this pdf doesn't work. Anyone that has another link or that can upload it?


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## ebola?

Bilz0r's text is really good: it's accessible like a text for a survey work, but it also contains more specifics to 'bluelight-type interests' than one could expect in a text of that sort.

It needs to be publicized more widely. 

ebola


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## MasterOfDeception

ebola? said:


> Bilz0r's text is really good: it's accessible like a text for a survey work, but it also contains more specifics to 'bluelight-type interests' than one could expect in a text of that sort.
> 
> It needs to be publicized more widely.
> 
> ebola



Exactly
Also mitrogen's last article apo G-protein Coupled Receptors seems rather advanced
Too bad he has stopped posting here?


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## specialspack

Is Bilz0r still out there?


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## Hyperthesis

specialspack said:


> Is Bilz0r still out there?


According to his profile he seems to log in once in a while, but is only very rarely posting. His factual absence is one of the biggest losses for Bluelight in years (IMHO).



Hyperthesis said:


> Are there any efforts by Bluelight to continue resp. extend *BilZ0r*'s fantastic work?


... I never received an answer to that question.  Obviously it was primarily directed to the admins/mods, which may have their reasons not to respond. I guess they simply don't know, as this was BilZ0r's project and he announced his abstence some time agon IIRC.

Hence, let me rephrase the question, now rather adressing the users of this forum: What would be suggested improvements or extensions to BilZ0r's text? Which topics does the crowd wish to read most?


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## TZR

Cool topic.. learned this all my freshman year of school.


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## alkap555

BilZ0r...awesome writeup man. Coming from a neuropharmacology bkgrnd myself I have to say thats some good shit.


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## Jabberwocky

BilZ0r said:


> Printable PDF available here
> http://www.bilz0r.com/Neuropharm-phis text.pdf



Do you happen to have link to this that is still good? I really appreciate all the work the contributors have put into this. Much thanks!


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## SNR

I wish I could see it! It is not loading, can you upload it to a different site?


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## Molecular_Man

Thank you.. Very interesting. If it expands a lot, it can be a good popular book.


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## sekio

I'll go through and typeset this in a few days, and make another pdf

edit:
http://img208.imageshack.us/img208/489/bluelightneuropharmacolmk2.pdf


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## Sebastians_ghost

What an impressive project!  Is this an ongoing work?  In any case, very nice job, everyone.


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## petebog

Looks interesting, thanks to everyone involved in this.

Link in first post is dead and the OP last logged in 5 months ago, maybe a mod could update it with the link above?


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## jeah

to blizor and everyone.. two words.. THANK YOU.  coming from someone who got back into school.  a potential great new resource/always new ways and formats to learn/BL is the perspective.  thanks.


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## buffalobillygoat

Thank you to everyone involved in this project.  I had been searching for a while for something _exactly_ like this, and was about to post a thread.  So glad I saw the sticky first.  This is a really valuable and accessible resource - great work, thanks again.


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## Letshavefun

I think we should carry this on. Write a full text exploring organic chemistry, and make this one chapter. Perhaps release it free to the internet to educate?


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## ifeedonsouls

Both the original source and the imageshack one seems to be down. 
Could anyone upload it anywhere? 

Thanks in advance,
Ifeedonsouls


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## endotropic

ifeedonsouls said:


> Both the original source and the imageshack one seems to be down.
> Could anyone upload it anywhere?
> 
> Thanks in advance,
> Ifeedonsouls



Hmm strange, I'll make sure sekio knows the imageshack link isn't working.  In the meantime you can access the text by clicking through the links in the original post on this thread.


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## ifeedonsouls

endotropic said:


> Hmm strange, I'll make sure sekio knows the imageshack link isn't working.  In the meantime you can access the text by clicking through the links in the original post on this thread.



Why didn't I try that? I must have been really tired...
Thanks!


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## PetalToTheMetal

Letshavefun said:


> I think we should carry this on. Write a full text exploring organic chemistry, and make this one chapter. Perhaps release it free to the internet to educate?


That seems like a great idea.  Another forum has a similar resource thread. http://wayback.archive.org/web/20140908205902/https://www.zoklet.net/bbs/showthread.php?t=242589


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## Pharmokinetictal

*Cognocyclopedia*

So I have a MS in neuropsychopharm and do neuro research as a career. I'm an expert in cell signaling, molecular bio, addiction, drugs (of many types), pharmacology, proteomics (protein interactions), structural and organic chemistry, etc.

I'd love to help contribute to this 'organic' reference mine of real knowledge from people who don't prescribe or advertise molecules, but actually have experience with them. I've always believed patients know more about their conditions, their drug, and their Brody than the doctor does, and especially the govt.

There are corrections in some of the postings, though, I'd like to make. The definition of a protein is incorrect and more akin to an enzyme. A protein is one of ~22 amino acids that contain a NH2 amine end and a COOH carboxylic end. Tyrosine, phenethylamine, tryptophan, histidine, serine, asparagine...those are small molecule proteins. They can bind together at the N terminal of one and the C terminal of another to form a peptide bond. The order in which they are assembled is encoded in our DNA and so, too, our mRNA. When created, methionine is always the first to be made, and there can be hundreds-thousands of polypeptide bonds. The structures form grooves, helices, and sheets. They always have an active site now that they are enzymes. All enzymes are proteins, but not the other way around. Enzymes serve a catalytic purpose in all cellular functions. The majority add phosphate groups to molecules and other enzymes or macroproteins. A simple protein, however, is generally no more than 8 carbons and 1 nitrogen with some hydrogens and occasionally 1-2 oxygens or 1 sulfur.

Proteins are building blocks for either enzymes, vitamins, or neurotransmitters. Drugs, too, are made from proteins or based on their structure. For example, amphetamine is an acronym. aLPHA-mETHYL-phENetHTYL amine.
Look at amphetamine and phenethylamine and you'll understand why adderall affects the dopaminergic pathway how it does.

It's important to know the epinephrine and adrenaline are the same molecule, but have different names depending on how our body uses them. Adrenaline is a hormone whereas epinephrine is a neurotransmitter.

I'd love to have s chapter in misnomers and misunderstandings--i.e. Oxy is NOT synthetic heroin. Firstly...they are two different molecules made from different molecules. Secondly, 'synthetic' in this sense does not apply to chemistry. If THC was made in a lab or grown on the plant, it is still THC. 'Synthetic' can only be used in terms of how a molecule is made rather than its resemblance to another drugs effect (sorry, but peeve of mine).

Other examples would be separating adderall from meth stigma. I think it's important to talk about race if mixtures as well. A lot of people think that Dexedrine is significantly stronger than adderall. But adderall is actually 75% d-amphetamine...not 50% like some people think. Ritalin is also more similar to cocaine than adderall regarding its mechanism of action. Heroin is not bad (or any worse than any other potent opioid). It's street heroin that's dangerous and our laws that make H 'bad.' When norco or Percocet say 10/325...that means 10mg of drug, 325 Tylenol. So many people tell me they have the '500mg kind of vicodin.' Also...opiates are only the naturally occurring compounds like morphine, thebaine, and codeine. Opioids are any drug that binds to the delta/kappa/mu-opioid receptors. Mm benzodiazepines are f'ing dangerous. Don't take them unless you need to. Do not get dependent (it would be cool to define addiction, tolerance and dependence from a cellular modification perspective). BZD withdrawal is unbearable. GABA (along with glycine) is our only inhibitory compensatory mechanism in our brain. Don't mess with it or your brain will be repleted with excitotoxic NMDA-mediated glutamatergic transmission which will lead to apoptosis/cell death. Alcohol too. Finally for now, be your own advocate. Doctors truly are poorly educated on pain mgmt or psych disorders. Research your meds, if you want to change them, find an intelligent way of communicating why. For example, despite it being a recognized beneficial practice, docs don't do it because they don't like change and because the dea might think something is wrong--if you are on a long term treatment (i.e. Narcs or BZDs), you can mitigate tolerance and delay/avoid severe dependence if you frequently alternate your med with one similar to it. Switch from klonopin to Ativan to Valium or Xanax and back to klonopin. Each of these drugs binds to a different GABAa subtype, so you will never down-regulate one receptor through over stimulation for more than a month before switching. The same goes for roxi/perc, zohydro, dilaudid, morphine (oral BA sucks), or Opana. Stay away from bup or methadone unless it's for maintenance/detox. Talk with your doc. Save your receptors!

Uh so yeah. Hit me up or reply. Let me know if I can help craft this thing  Salúd, friends


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## Pharmokinetictal

Ps-the advice i offer was only for educational and harm reduction purposes. I do not encourage the misuse or specific use of any substance in particular.


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## JohnBoy2000

The link don't work for me.
Just links to imageshack - no book.

Anyone have an updated link?


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## JK25

BilZ0r said:


> I contacted erowid recently, with the proposal to write a text that would hopefully bring the laymen up to a reasonable standard, as far as neuropharmacology/neurophysiology goes, in regards to psychoactive drugs.
> 
> The erowid team replied, saying that they would love it.
> 
> What I'm now proposing to you guys, is that we write it. I suggest that a single person is asked to write a section/chaper (hopefully one you're familiar with). Erowid suggested using a Wiki, and I think that after we've written it up in posts in here, we can port it over to one, and link it all up.
> 
> The chapter layout I proposed to erowid basically looked like this
> 
> -What is a cell (BilZ0r)
> ---What is a Neuron? (ksi and BilZ0r)
> -What is a Protein?
> ---How proteins are produced (crOOk and BilZ0r)
> -----What is a receptor? (BilZ0r)
> -----What is an Enzyme? BilZ0r)
> -Electrical properties of the Neuron (BilZ0r)
> ---Ion Channels
> -----Voltage Gated Ion channels (BilZ0r)
> -----Ligand Gated Ion channels (BilZ0r)
> -Chemical properties of the Neuron
> ---The synapse (BilZ0r)
> ---G-Protein Coupled Receptors, and signalling cascades (BilZ0r)
> ---Homeostasis in Neuronal Signalling (BilZ0r)
> 
> Special Topics
> -Pharmacokinetics (BilZ0r)
> -Learning, memory and addiction on a cellular level (BilZ0r)
> -Monoamine transporters and the amphetamines (BilZ0r)
> -GPCRs under the microscope (mitogen)
> 
> Drug Glossary
> 
> And then maybe some special topics, like neurotoxicity, or anything a particular contributor has a zest for (so long as its appropriate).
> 
> Right, so do I have any volunteers? Any suggestion on changing the chapter structure
> 
> Printable PDF available here
> http://img208.imageshack.us/img208/489/bluelightneuropharmacolmk2.pdf




I'm doing my dissertation for my Masters in Neuro-Psychopharmacology this year.  I have to hand it in in November.  When I do I will also forward it through to you or reply to you via private message or the likes.  

It will be worth your perusal.


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## NeVeRGiViNUP

*Severe depression was I born that way?*



BilZ0r said:


> Ligand gated ion channels
> 
> Ligand gated ion channels are, as their name suggests, channels in a cells membrane that are gated by ligands, i.e. drugs/chemicals. The physiological role of nearly all ligand gated ion channels is to receive chemical signals in the way of neurotransmitters (discussed further in *the synapse*), and to transduce them to electrical signals. In order for these ion channels to be gated by a neurotransmitter, they have a *receptor* for the specific neurotransmitter as part of the proteins that make up the receptors. Therefore the ion channel complex is often refereed to by the name of the neurotransmitter/chemical/drug which is has a receptor for, and for the rest of this chapter we will largely use this style.
> 
> The two most common types ligand gated ion channels (also called ionotropic receptors) are the ion channels that are opened by the neurotransmitters glutamate and GABA, or ionotropic glutamate and GABA receptors. The ionotropic glutamate receptors may be further divided up into AMPA, kainic acid and NMDA receptors (named after drugs that specifically activate these types). While it is possible to further subdivide these receptors based on the individual proteins that make them up, it is outside the scope of this text. AMPA and kainic acid receptors are generally similar; both are opened by glutamate and both are largely selective for the flow of Na+ ions, which in all physiological situations is into the neuron. This flow of Na+ depolarizes the cell, making it more positive and bringing it closer to the threshold for firing an action potential. Because of this, it can be said that AMPA and kainic acid receptors are “excitatory”. The NMDA receptor is an anomaly amongst ligand gated ion channels, in that it is also partially voltage gated. The channel of the NMDA receptor has a site in which Mg2+ ions can sit. This Mg2+ is much larger than the normal ions that flow through the NMDA receptor (Na+ and Ca2+) and hence blocks it. When the cell partially depolarized, positive Mg2+ ions begin to be pushed out of the NMDA receptor channel (presumably because of the positive charge inside the neuron repelling it). Also, because the NMDA receptor is very permeable to Ca2+ channels, not only does it depolarize (excite) the cell, it also can cause many of the chemical changes within the cell caused by Ca2+ (see *G-Protein Coupled Receptors, and signalling cascades*). Largely, it is the release of glutamate, and its action of ionotropic glutamate receptors that allow one cell to excite another cell into firing (although usually it requires 100s of cells to release glutamate onto a cell to cause this).
> 
> The most famous drugs which directly effect ionotropic glutamate receptors are the so called “anaesthetic dissociates”, e.g. ketamine, PCP and DXM. These drugs all block the NMDA receptors ion channel, i.e. they are NMDA channel antagonists. Alcohol's actions is thought to be at least in part due to its ability to block NMDA receptor channels (Woodward, 2000).
> 
> The ligand gated ion channel that is gated by GABA is called the GABA-A receptor (to distinguish it from the non-ion channel GABA-B receptor). This channel is largely selective for the transit of Cl- ions. As stated before, Cl- ions have a reversal potential of around -60mV, so if a cell has a resting membrane potential of around –60mV GABA-A receptors do not cause much of an effect on membrane potential i.e. they neither hyperpolarise nor depolarise the cell. But if the cell is being depolarised by the action of ionotropic glutamate receptors, then GABA-A receptors strongly oppose this, and hence its action is often referred to as inhibitory).
> 
> A wealth of drugs directly effect GABA-A receptors, specifically benzodiazepines and barbiturates which bind to sites apart from the GABA binding site or the channel, to increase channel opening only when GABA normally opens the receptor. This is an example of *allosteric modulation*, and is a common feature of ligand gated ionc channels. Muscimol is a direct agonist, acting like GABA. Alcohol is also though to stimulate GABA-A receptors, though whether this is a direct action is still debated (Aguaya et al., 2002)
> 
> There are other kinds of ligand gated ion channels, though the only ones which have much relevance to recreational drugs are the ionotropic acetylcholine and serotonin receptors, also called the nicotinic and 5-HT3 receptors. Both of these receptors are ligand gated sodium channels. Nicotine activates the nicotinic receptor, and serotonin, which could be released by the action of MDMA, can activate 5-HT3 receptors (which may cause MDMA-induced vomiting). There are also the glycine, P2X and VR1 ligand gated ion channels expressed in the central nervous system.
> 
> As you can see, ligand gated ion channels are an important (probably the most important) mechanism of neuron-to-neuron communication, and drugs acting on this form of chemical to electrical transmission have a powerful way to alter neuronal activity (discussed more in *Signalling properties of neurons*).
> 
> References
> Woodward JJ. Ethanol and NMDA receptor signaling. Crit Rev Neurobiol. 2000;14(1):69-89.
> 
> 
> Aguayo LG, Peoples RW, Yeh HH, Yevenes GE. GABA(A) receptors as molecular sites of ethanol action. Direct or indirect actions? Curr Top Med Chem. 2002; 2(8):869-85.


 great stuff I have severe depression and do remember being a tad depressed as a child before use question is did my drug use make it worse and how without a substance can I make my electricical grid fire and just be able to get out of my own way of thinking. I am scared I have destroyed my neroulogical circuit what natural none mind altering route to the happy life do I have?


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## [éS]Infinite

It's sort of crazy, a few years ago I was reading this thread, trying to better understand the processes that take place in the brain that give rise to the vast psychoactive and psychological states that we experience. I was lost in a sea of unfamiliar words and novel concepts.
This week I will be attending my graduation from uni in neuroscience, and I know a lot of the topics like the back of my hand.
Amazing how life comes full circle.


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## bindingaffinity

Wow, congratulations!

I'm jealous, wish I had studied this stuff in university instead of dicking around with short exact sequences and inner models. I wonder if it's still feasible for me to get a degree in it now that I'm working a full time job... probably not.


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## breadwitch

JohnBoy2000 said:


> The link don't work for me.
> Just links to imageshack - no book.
> 
> Anyone have an updated link?



I made a mega link if anyone's interested








						MEGA
					

MEGA provides free cloud storage with convenient and powerful always-on privacy. Claim your free 20GB now




					mega.nz


----------



## Winter666

BilZ0r said:


> I contacted erowid recently, with the proposal to write a text that would hopefully bring the laymen up to a reasonable standard, as far as neuropharmacology/neurophysiology goes, in regards to psychoactive drugs.
> 
> The erowid team replied, saying that they would love it.
> 
> What I'm now proposing to you guys, is that we write it. I suggest that a single person is asked to write a section/chaper (hopefully one you're familiar with). Erowid suggested using a Wiki, and I think that after we've written it up in posts in here, we can port it over to one, and link it all up.
> 
> The chapter layout I proposed to erowid basically looked like this
> 
> -What is a cell (BilZ0r)
> ---What is a Neuron? (ksi and BilZ0r)
> -What is a Protein?
> ---How proteins are produced (crOOk and BilZ0r)
> -----What is a receptor? (BilZ0r)
> -----What is an Enzyme? BilZ0r)
> -Electrical properties of the Neuron (BilZ0r)
> ---Ion Channels
> -----Voltage Gated Ion channels (BilZ0r)
> -----Ligand Gated Ion channels (BilZ0r)
> -Chemical properties of the Neuron
> ---The synapse (BilZ0r)
> ---G-Protein Coupled Receptors, and signalling cascades (BilZ0r)
> ---Homeostasis in Neuronal Signalling (BilZ0r)
> 
> Special Topics
> -Pharmacokinetics (BilZ0r)
> -Learning, memory and addiction on a cellular level (BilZ0r)
> -Monoamine transporters and the amphetamines (BilZ0r)
> -GPCRs under the microscope (mitogen)
> 
> Drug Glossary
> 
> And then maybe some special topics, like neurotoxicity, or anything a particular contributor has a zest for (so long as its appropriate).
> 
> Right, so do I have any volunteers? Any suggestion on changing the chapter structure
> 
> Printable PDF available here
> http://img208.imageshack.us/img208/489/bluelightneuropharmacolmk2.pdf


Please add "Psychopharmacology ".


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## Gaffy

Ask m'y sister


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## Winter666

Don't get it.


----------

