Psychedelics and Neuronal Signaling Systems

[LlewellynDrury]

This is the relevant parts of a discussion. It was originally posted in the general psychedelic section and was closed.

Cotcha Yankinov:
I think depression, PTSD and addiction can be treated with psychedelics. Downregulation of 5-HT2A is something that interests me, but from what I understand psychedelic assisted psychotherapy holds great promise for addicts, and if I remember correctly a study concerning 1000 alcoholics showed that almost 50% hadn't returned to the bottle by 1 year after psychedelic psychotherapy (LSD I believe it was).

TheBlackPirate:
I agree. Also, other receptors including 5HT1A are also implicated in the safety and effectiveness of psychedelics. Most of the chemicals hyper-selective at 5HT2 receptors (25X-NBOMe and DOX) caused potentially fatal adverse reactions in some.

Most of the psychedelics with superior therapeutic indexes (4-HO-DMT, DMT, and LSD) have strong binding at multiple 5HT receptor sub-types.

Cotcha Yankinov:
That's very interesting, it sounds like auto receptor activation is important for safety then? I guess its innately implied with serotonin releasing agents that you're going to get auto receptor activation but far from it with the ones that are really selective.

I remember hearing something about 5HT1A (I suppose it would have to be post synaptic) being important for oxytocin concerning MDMA, any thoughts on this?

LlewellynDrury:
LSD was used in the 1950s and 60s in psychiatric settings to cure alcoholism in Canada. Humphry Osmond and Abram Hoffer developed the protocol in Saskatchewan. They had amazing results, many therapists used LSD across Canada until about 1966 when Sandoz stopped supplying it and the authorities freaked out. Good abiding citizens thinking for themselves and questioning authorities was too much for the government.
When trying to figure out the action of psychedelics at the cellular level it is important to know that receptors are not only on/off switches. When a specific molecule bind on a receptor its shape is slightly modified in a unique way at the binding site and also inside the cell. That unique intracellular modification of the receptor will trigger specific metabolic actions. A different bunch of cellular metabolic pathways will be activated for each drug. This is very complex and still poorly understood. So trying to figure out the action of a given drug with only the binding affinity to receptors is pretty reductive, if so pharmacology would be quite straightforward and this is far from being the case.

Cotcha Yankinov:
Are you speaking of what I have heard referred to as ligand directed or biased signaling, where not all ligands have the same downstream effects (different G proteins or arachidonic acid metabolites and such?)?

I'm curious, does psilocybin and such have the same downstream effects as LSD after it binds to 5HT2A?

I've been told that differences in downstream signaling helps explain the subjective differences of psychedelics, but I'm sure there are medicinal implications as well.

LlewellynDrury:
Exactly, watch this: https://www.youtube.com/watch?v=2tN_L1bRq7Y.
My guess is that LSD have a different dowmstream action an don't forget that LSD also have affinity to many subtypes of 5HT and D receptors and even alpha receptor.
Cotcha Yankinov:
Thank you very much for linking that! I'm about to binge watch all those workshops, I'm surprised to see Dave Nichols in the flesh, I've always read his MDMA studies though...

Anyhow, if you have any questions or anything I would definitely head over to the neuroscience and pharmacology forum, in particular there is an individual named Serotonin2A that I would seek out, he is an extremely intelligent neuroscientist/chemist. He usually comments on even my dumb posts so I'm sure he would help answer any questions if you happen to have any.

Just curious, outside of depression, do you think NMDA antagonists might serve any medicinal purpose?

LlewellynDrury:
Can't really awnser your question about NMDA antagonists but here something that can shed light about the relation of psychedelics and genetic downstream regulation:
The first step in a complex signalling system involves the binding of specific ligands (LSD, psilocin, DMT…) at the cell surface to a G Protein Coupled Receptor, thereby activating the receptor. The signal is transmitted into the cell via a conformational change in the receptor, which results in the activation of the bound G protein. GPCRs act as guanine nucleotide exchange factors for the a subunit of the G protein, whereby activated receptor promotes the exchange of bound GDP (guanine diphosphate) for Guanine Tri Phosphate on the a subunit, which is the rate-limiting step in G protein activation. The binding of GTP changes the conformation of ‘switch’ regions within the a subunit, which allows the bound trimeric G protein (inactive) to be released from the receptor, and to dissociate into active a subunit (GTP-bound) and bg dimer. The a subunit and the bg dimer go on to activate distinct downstream effectors, such as adenylyl cyclase, phosphodiesterases, phospholipase C, Src, and ion channels. These effectors in turn regulate the intracellular concentrations of secondary messengers, such as cAMP, cGMP, diacylglycerol, IP3, DAG, arachidonic acid, sodium, potassium or calcium cations, which ultimately lead to a physiological response, usually via the downstream regulation of gene transcription. The cycle is completed by the hydrolysis of a subunit-bound GTP to GDP, resulting in the re-association of the a and bg subunits and their binding to the receptor, which terminates the signal.

Cotcha Yankinov:
Very interesting, thanks for that Is there any sort of compiled reference as to what is known to signal through what out there?

Serotonin2A once said the following "5-HT2A is coupled to several G-proteins, PLC through Gq, apparently Gi/o, Rho, beta-arrestin. The activation of PLA2 involves both Gq and Gi/o (at least in certain cell types). Serotonin activates all of those pathways." - I thought it was very curious that endogenous serotonin was able to activate all of the pathways. But I wonder if this is a good thing or bad thing in the case of drugs that increase serotonin like MDMA/SSRIs? Do you think there might be more medicinal potential in some of the biased ligands, and that maybe some of the down stream effectors are better left untouched?
[h=2][/h]

 

[Cotcha Yankinov]

Hey Drury I see in the work shop you linked there are some references as to what signals through what pathway, but it sounds like there is not a whole lot of commercial incentive to figure out what's going on after something binds to the receptor regarding psychedelics.

Do you have interest in any particular psychedelics for any particular reasons?

 

[LlewellynDrury]

Pharmaceutical companies want to makes a fast buck. Cytoplasmic signalling is very complex and only a handful of pathways are well known. It involve too much research and work for commercial enterprises to figure it all. To a large extend we are left with the good old trial and error method to find useful novel psychoactive substances. For a long time only the structure-activity relationship could guide us. Now you can further select a substance that have an interesting receptors affinity profile and then you conduct laboratory animal trials. If it looks promising you go on with clinical trials on humans.

My favourite drug is 2C-E, and my interest is based entirely on its subjective effects. Almost nothing is known about its pharmacology. It is as powerfully analytical as LSD but it is warmer, friendlier.

In the second half of a 2C-E trip there are no thought loops, manic thinking and general overstimulation. You can relax, have a good meal, fuck with your lover and fall asleep easily in the midst of swirling paisley. I’d say it’s a more easy-going substance that has all the LSD qualities I’m seeking (furthermore it’s still 100% legal in Canada and easy to find).

2C-E holds great potential in psychotherapy, probably Shulgin’s greatest discovery.

 

[Skorpio]

If psychadelics become legal, pharmaceutical companies will invest in them. Pharmaceutical companies aren't making any cocaine analogs either, and it isn't because they don't know how to...
Tides are shifting, and the time of true purpose designed psychadelics will come.

I take a little objection to your last line: "2C-E holds great potential in psychotherapy, probably Shulgin’s greatest discovery," If only because it misses the place of the individual in psychotherapy. Psychadelics are the ultimate subjective experience, and for example I could dig up plenty of trip reports of 2CE being classified as cold, too confusing, and industrial strength. I think for the best results with psychadelic psychotherapy, a wide range of (safe) compounds should be able to be trialed, so that the subject could utilize what is most useful for them.

 

[Cotcha Yankinov]

I'll definitely have to look up some 2-CE trip reports. You can fall asleep on 2-CE? Does that imply it's maybe not as much of a typical 5-HT2A stimulator?

Also, I have heard this and wonder if you think it is true - do you think that some drugs that have full agonism at 5-HT2A might not be psychedelic because they have different downstream signaling? In other words, even if 2-CE came back as having high affinity to 5-HT2A, we still don't know whether it's responsible for its effects?

Or maybe because of specific downstream signaling after 5-HT2A it doesn't induce insomnia?

 

[LlewellynDrury]

Well Skorpio, really big pharma have pretty much stepped out of research about CNS active drugs because it’s getting too complicated and they just go on making money with the old ones they hold the patents for.

I truly wish psychedelic therapy will be widespread in the future, but consider the fact that cancer dying patients typically lower the amount of opioids they use after a single psilocybin session, this is not good news for pharmaceutical companies driven by drug sales profit…So in our global capitalist world who worship Holy Economic Growth psychedelics as medicine is likely to encounter a lot of resistance.

If you take 2C-E industrial doses, like 20+ mg, in shitty settings, poorly prepared or with the wrong persons you’re asking for problems. It is a very powerful substance. I can also dig up LSD or psilocybin bad ending hair raising trip reports. These are tools that shouldn’t be in the hands of ignorant and reckless persons.

I agree 2C-E is not a panacea, but Shulgin itself (and his group) considered it as a very special substance that stood out. Of course 2C-T-2, 2C-T-7, LSD or psilocybin may be a better choice for some. 2C-E is my favourite but I still use other phenethylamines (typtamines and ergolines too) at different dosage for specific goals.

 

[serotonin2A]

Most people would find it difficult to sleep on 2C-E. It is a 5-HT2A agonist and that is almost certainly the mechanism for its psychedelic effects.

 

[Cotcha Yankinov]

Hey Serotonin so we were discussing the whole biased ligand thing, and I'm wondering if you had any thoughts on how the heck serotonin can signal through all the cascades... I mean I understand evolutionarily it makes sense that no signaling cascade goes unused but how does serotonin set off one signal one time and a different signal another time?

Functionally, what is the difference between one receptor conformation change and another? Does the G protein disassociate in a different way or something?

 

[LlewellynDrury]

I'm not talking sleeping during the peak but at night on the comedown, this is somthing I find very difficult with LSD.

 

[Cotcha Yankinov]

I'm not talking sleeping during the peak but at night on the comedown, this is somthing I find very difficult with LSD.

Ohhh okay sorry I misunderstood. Same, I find sleeping on psychedelics impossible, while all the studies have shown the selective 5HT2A inverse agonists are great sleeping meds (though suspiciously never made it to market seeing as they threatened the current GABA drugs that dominate the market). Alas, there is still Risperidone...

How the heck is 2-CE still legal in Canada? You would think they would just ban all PiHKAL substances.

 

[LlewellynDrury]

We are Lucky bastards, there is no unspecific analog provision in our law, only the amphetamine like molecules (similar to the DOX series) are banned, the 2Cs are left unregulated.

 

[serotonin2A]

Hey Serotonin so we were discussing the whole biased ligand thing, and I'm wondering if you had any thoughts on how the heck serotonin can signal through all the cascades... I mean I understand evolutionarily it makes sense that no signaling cascade goes unused but how does serotonin set off one signal one time and a different signal another time?

I guess a more basic question is why would it make sense for a receptor to only couple to a single signaling cascade? Apparently some cell responses require simultaneous activation of multiple signaling cascades.

Receptor activation often induces multiple cellular effects. Monoamine receptor activation usually causes a change in cellular excitability, but there are often other effects as well, such as changes in gene expression and cell structure. The receptor also has to regulate its own signaling, to keep it in homeostasis, either by (1) phosphorylating itself or its downstream signaling targets, resulting to changes in signaling efficacy or internalization, or (2) by changing its expression level.

On the other hand, just because serotonin can drive signaling through multiple signaling pathways doesn't mean that always happens in every cell. Receptors and other proteins are usually segregated in specific regions of the cell membrane and in particular compartments in the cell, meaning that in any given cell type the 5-HT2A receptor may only activate a subset of the pathways that is can potentially be coupled to.

Functionally, what is the difference between one receptor conformation change and another? Does the G protein disassociate in a different way or something?

The 3rd intracellular loop of GPCRs is responsible for most signaling effects. The receptor binds to a G-protein because part of its 3rd intracellular loop is complementary to the structure of the G protein. Agonist binding changes the conformation of the 3rd intracellular loop, which increases the affinity of the receptor for the G-proteins; once the G-protein binds to the receptor, the conformation of the G-protein changes, causing the alpha and beta-gamma subunits to separate, which initiates downstream signaling.

The 3rd intracellular loop is rather big and contains binding sites for multiple different G-proteins etc. So for example one agonist may induce a receptor conformation that has high affinity for effector proteins A and B whereas another agonist may induce a conformation that has high affinity for effector proteins A and C...

 

[Cotcha Yankinov]

Ohhhh so depending on the receptor's confirmation different G proteins will have more or less affinity for it?? Are there any receptor conformations where no G proteins may bind or where it's extremely unlikely?

When someone says a ligand is "unbiased", do they mean that it signals through the default G proteins for that particular cell type (likelihood of signaling through a particular cascade that is proportional to the different levels of expression of those different G proteins) and therefore might signal similar to the endogenous ligand? I mean it sounds like different cell types can have different G proteins so it's sorta up to chance which one binds if it's an unbiased ligand?

 

[LlewellynDrury]

Hi serotonin2A,

Can you recommend a good textbook about neural signaling with detailed sections covering intracellular signal transduction? I’m just starting to dust my knowledge about the matter and realize that my basic neuroscience textbooks from the early 2000s aged badly and don’t tell much about it. I dropped out of academic world 10 years ago and access to literature is not as easy nowadays. My academic background is biochemistry so I can understand highly technical publications.

Here’s a very interesting research article titled “Psychedelics and the Human Receptorome” by Thomas S Ray: http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0009019 . Fortunately the whole article is freely available. Do you work in an institution where you can have easy access to relevant journals and can order single articles? If so, would you be willing to share these? By the way MAPS offer a good selection of articles you can download for free from their website.

Thanx

 

[serotonin2A]

Ohhhh so depending on the receptor's confirmation different G proteins will have more or less affinity for it?? Are there any receptor conformations where no G proteins may bind or where it's extremely unlikely?

Yes, that is the state that inverse agonists bind to.

When someone says a ligand is "unbiased", do they mean that it signals through the default G proteins for that particular cell type (likelihood of signaling through a particular cascade that is proportional to the different levels of expression of those different G proteins) and therefore might signal similar to the endogenous ligand? I mean it sounds like different cell types can have different G proteins so it's sorta up to chance which one binds if it's an unbiased ligand?

"Unbiased" agonists activate the second messengers coupled to a receptor non-selectively.

I wouldn't describe the situation as a cell having a "default" set of G proteins. My point wasn't that a cell doesn't have a particular type of G protein. Rather the 5-HT2A receptor may not colocalize with some G proteins even if they are expressed by the cell and it can bind to them. The distribution of G proteins over the surface of the cell is not homogeneous.

There are at least two mechanisms controlling this: 1. Membrane proteins can be segregated in regions called lipid rafts. 2. The intracellular portion of receptors (and often other proteins) contain sequences that effectively control where they will be localized on the cell surface. So the "zone" where 5-HT2A is found only overlaps with the "zone" of some G proteins.

 

[Cotcha Yankinov]

So I'm wondering how inverse agonists/antagonists affect receptor regulation - if the mechanism of receptor homeostasis lies after the step of G protein association (beta arrestin?) then won't more receptors keep popping up since there isn't any G protein activity, assuming there isn't a proportional amount of beta arrestin or what have you being triggered by an agonist that makes it through antagonist blockade and causing receptors to disappear faster than they are popping up?

 

[serotonin2A]

The mechanism that drives 5-HT2A internalization occurs in parallel with G protein activation. Almost every antagonist/inverse agonist tested induces internalization, suggesting they really act as agonists that are selective for the pathway driving internalization. But they are still classified as antagonists because they block the effects of serotonin.

 

[Cotcha Yankinov]

Very interesting... I was under the impression that antagonists/inverse agonists caused receptor upregulation. I guess that might still be true of agonists that bind to a different site than the agonist?

So for some reason it seems like every drug with 5-HT1A affinity is a partial agonist, I was wondering if you thought that these partial agonists might have a fair degree of selectivity for the pathway that induces receptor internalization, because then maybe a partial agonist at 5-HT1A auto receptors would decrease the amount of receptors and increase serotonin concentrations because there is less genuine auto receptor activation?

 

[serotonin2A]

Very interesting... I was under the impression that antagonists/inverse agonists caused receptor upregulation. I guess that might still be true of agonists that bind to a different site than the agonist?

That is generally true for most receptors but not for 5-HT2A.

So for some reason it seems like every drug with 5-HT1A affinity is a partial agonist, I was wondering if you thought that these partial agonists might have a fair degree of selectivity for the pathway that induces receptor internalization, because then maybe a partial agonist at 5-HT1A auto receptors would decrease the amount of receptors and increase serotonin concentrations because there is less genuine auto receptor activation?

I think you are thinking of buspirone and analogs. That is just one structural class of 5-HT1A agonists. There are many other classes and some of them are full agonists. One example is 8-OH-DPAT, which still is the prototypical 5-HT1A agonist (it was originally thought to be selective but that is now known to be incorrect).

 

[Cotcha Yankinov]

That is generally true for most receptors but not for 5-HT2A.

So I ask the blunt question - what's so special about 5-HT2A?

Currently I am on Risperidone, with it's almighty 5-HT2A inverse agonism. Here I was expecting 5-HT2A rebound (and resulting insomnia) when I decide to taper off, but is it likely that I will just experience a return of the same levels of 5-HT2A that I had before Risperidone?

Regarding the 5-HT1A pondering, will a 5-HT1A inverse agonist reduce the amount of auto receptors available (via signaling internalization), therefore increasing serotonin concentrations and acting as an anti-depressant?