Binding data for popular arylcyclohexamines.

[pharmakos]

If it made sense to reduce complex neural pathways to the specific chemicals that jump across the synapse, then dopamine would be a salience/motivation chemical. I don't know much about glutamate's role in the nucleus accumbens/VTA but I'm willing to bet it's intimately involved, being many many times more prevalent than the monoamines.

i know i'm getting OT, but this perhaps has something to do with why food with added MonoSodiumGlutamate (MSG) is more satisfying =p

also, in case anyone didn't realize, the NMDA receptor is a subtype of the MSG/glutamate receptor. =p

i've always wondered what effect large amounts of chinese food would have on a dissociative trip heh

 

[sekio]

I thought the reason pcp was so prone to wig outs was:
1. 10 mg is a wipe out dose
2. never standardised
3. ultra super lipophilic
3a. long ass half life 8h+
3b. reabsorbed from bladder walls(!)

not neccesarily because its a sigma receptor agonist. but thats a good theory.

msg does bind to a "gluatamate receptor" on the tongue as it were (+ the sodium stimulates Na+ channels for saltiness) both of which are "rewarding" inasmuch humans are trained to seek high calorie (sweet) protien rich (msg) or mineral rich (salt) foods to ensure their survival long term as these were traditionally scarce/seasonal (or so the theory goes)

unfortunately msg would not be a dissociative, it would be an excitotoxin if it ever made it into the grain in large enough amounts. glutamate is a glutamate receptor agonist not antagonist. (which the dissociatives are - glutamate receptor, nmda subtype antagonists)

maybe the nmda receptor has various binding modes (c.f. dopamine transporter, cocaine vs modafinil). maybe even mild dopaminergic action is potentiated downstream by nmdar antagonism. maybe the different subunits of nmdar (there are at least 3 i know of) interact differently or have unique splice variants.

that kI data was calculated as Ki = 10^(-pKi) - it is the same data in a more "common" format (im an idiot and didnt see the real values right there in front of me...)

Does this research negate [the possibility of MXE being a dopamine/DAT ligand]?

Well, it does and it doesn't. It doesn't explicitly show that there's no binding at all whatsoever, but it does show there's no binding at >50% of the receptor sites at a really high concentration of the drug (10uM = 10,000 nM).

5-HT: 1A 1B 1D 1E 2A 2B 2C 5 7
Dopamine: D1 D2 D3 D4
GLutamate: NMDA, mGlu5
GABA: A, B
Adrenoreceptors:alpha2a/b/c, beta1
Muscarinic: M1, M2, M3, M4
Opioid: mu, delta, kappa
Transporters: SERT NET DAT
Sigma: sigm1, sigm2
Histamine: H1, H2

If there's no data shown for the compound at one of those above listed receptors/protiens, then there is essentially no binding of phgarmacological importance at dose levels achievable safely by humans.

It may be also worth noting that some of thse studies could be using mouse/rat receptors and others using human or vice versa, or different radioligands, or it's possible that some of the papers are a total fucking fraud too. I think i trust the ucmd report though.

 

[pharmakos]

^^ of course. i always thought it was interesting that dissociatives in some way do the opposite of what MSG does.

 

[crOOk]

Central antinociception induced by ketamine is mediated by endogenous opioids and μ- and δ-opioid receptors.
Abstract
It is generally believed that NMDA receptor antagonism accounts for most of the anesthetic and analgesic effects of ketamine, however, it interacts at multiple sites in the central nervous system, including NMDA and non-NMDA glutamate receptors, nicotinic and muscarinic cholinergic receptors, and adrenergic and opioid receptors. Interestingly, it was shown that at supraspinal sites, ketamine interacts with the μ-opioid system and causes supraspinal antinociception. In this study, we investigated the involvement of endogenous opioids in ketamine-induced central antinociception. The nociceptive threshold for thermal stimulation was measured in Swiss mice using the tail-flick test. The drugs were administered via the intracerebroventricular route. Our results demonstrated that the opioid receptor antagonist naloxone, the μ-opioid receptor antagonist clocinnamox and the δ-opioid receptor antagonist naltrindole, but not the κ-opioid receptor antagonist nor-binaltorphimine, antagonized ketamine-induced central antinociception in a dose-dependent manner. Additionally, the administration of the aminopeptidase inhibitor bestatin significantly enhanced low-dose ketamine-induced central antinociception. These data provide evidence for the involvement of endogenous opioids and μ- and δ-opioid receptors in ketamine-induced central antinociception. In contrast, κ-opioid receptors not appear to be involved in this effect.

Source: Brain Res. 2014 Mar 24. pii: S0006-8993(14)00374-6. doi: 10.1016/j.brainres.2014.03.026.

I've got the whole article. Just let me know if you want to read it.

Before anyone overinterpretes this or accuses me of doing so: It seems extremely unlikely (to put it mildly) that ketamine binds to opioid receptors at all.

 

[blueberries]

From recent use of 3-MeO-PCP and Hydroxyzine, I have reason to believe it has some affinity for 5-HT2a and possibly D2 as I
get some perception alteration from 3-MeO which is wiped once Hydroxyzine is introduced. If anyone has more data about 3-
MeO-PCP I'd love to hear about it as I've come into a fair bit of it recently.

I always knew MXE had a very wide binding profile and thought that 3-MeO would be similar minus some of it's opioid
activity (due to the lack of 2-Oxo). PCP certainly has to have some HT2a agonism as I noticed a great perception change on
it, so I figure 3-MeO wouldn't be too far off, only that it's DAT properties are increased and it's NET properties are
reduced.

I find the 3-MeO to be actually more a nootropic than a substance of abuse due to this, but I've been using AMPA agonists
too so I couldn't be totally sure. What I do know is that 3-MeO-PCP + PRL-8-53 + IDRA-21 is giving me possibly the most
increased neuroproactivity I've felt in a long while!

 

[adder]

It's the 4-oxo group that makes PCP analogues bind to opioid receptors. Look up J. Med. Chem 1980, 23, 424-430, the opioid activity was gone once the carbonyl group was gone (well, it doesn't necessarily have to be carbonyl, bromadol has a hydroxy group and a phenylethyl group there, that's why I'm guessing 6-alpha-alkylmorphines could be as good as orvinols or even better). I think that compounds like ketamine might not have direct opioid agonist properties as their affinity is too low, but in the presence of them other opioid agonists exert a stronger effect. Perhaps it's actually only related to NMDAR antagonist properties that boost opioid effects by lowering tolerance, but honestly speaking what we know now is too little for me and I'd love to dig deeper.

 

[clubcard]

http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50000662 //All PCP
http://toxnet.nlm.nih.gov/cgi-bin/sis/search/f?./temp/~IftJc7:1

http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50044140 //All Ketamine
http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+2180

http://www.bindingdb.org/bind/chemsearch/marvin/MolStructure.jsp?monomerid=50004107 //All TCP
http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+7637

When I say 'All', I mean all the places that had sets of information. IC50 & EC50 is also required to understand action (there is some IC50/EC50 data in there) as well as their activity (full,partial,silent,inverse).

Building up a full set for ALL of those out there would take an age and would stilll have lots of holes. I note that researchers seem to be going through the once popular RCs so
maybe, eventually, people will know the majority of information on all. It's a Great undertaking and I hope we helped a little.

If you wonder where I got this from, a friend is doing a degree so please, if I f**k up, please correct me.

 

[crOOk]

From recent use of 3-MeO-PCP and Hydroxyzine, I have reason to believe it has some affinity for 5-HT2a and possibly D2 as I get some perception alteration from 3-MeO which is wiped once Hydroxyzine is introduced.

This still does not mean that 3-MeO-PCP is the molecule that is binding to the receptors you mention, it's simply incorrect deductive reasoning.

 

[WSH]

Before anyone overinterpretes this or accuses me of doing so: It seems extremely unlikely (to put it mildly) that ketamine binds to opioid receptors at all.

Ketamine certainly binds to the mu opioid receptor at clinically relevant concentrations, it's just that it doesn't have any agonist activity:

http://www.ncbi.nlm.nih.gov/pubmed/14530949

 

[crOOk]

Ketamine certainly binds to the mu opioid receptor at clinically relevant concentrations, it's just that it doesn't have any agonist activity:

http://www.ncbi.nlm.nih.gov/pubmed/14530949

Interacts != binds
If you want to, I'll see if I can get the whole article for you, I am really not that interested in the subject personally. However there still is no evidence that ketamine binds to mu opioid receptors and I still would say it seems very unlikely.

 

[WSH]

Interacts != binds
If you want to, I'll see if I can get the whole article for you, I am really not that interested in the subject personally. However there still is no evidence that ketamine binds to mu opioid receptors and I still would say it seems very unlikely.

Ketamine displaced the hot ligand from the mu opioid receptor, how could it do that without binding to it?

 

[crOOk]

Ketamine displaced the hot ligand from the mu opioid receptor, how could it do that without binding to it?

If I had an answer to that, you would not need to ask this question now. But to give you an idea of what I'm thinking of, look at this:
http://www.youtube.com/watch?v=ARM42-eorzE

EDIT: There's another article on this and it does seem like ketamine actually binds to all opioid receptors. Neither of these two articles have been cited a whole lot and they're both written in 1999 without any word on this since then. I don't know if something might be methodologically wrong, since I really don't know that much about biochemistry, but I still find it weird this is an information that isn't found more easily.

http://www.ncbi.nlm.nih.gov/pubmed/9915326

Also, in both studies the same author is listed first. One has been cited 5 times, the other one 3 times. This is a bit puzzling to me, since ketamine is a very important and popular anesthetic.



So, is it clear at all how it induces opioidergic activity? Surely this would have something to do with it's affinity to the respective receptors. Again I've been to lazy to read any of the 3 studies.
http://www.ncbi.nlm.nih.gov/pubmed/24675031 Central antinociception induced by ketamine is mediated by endogenous opioids and μ- and δ-opioid receptors.
http://www.ncbi.nlm.nih.gov/pubmed/14530949 Interaction of ketamine with mu2 opioid receptors in SH-SY5Y human neuroblastoma cells.
http://www.ncbi.nlm.nih.gov/pubmed/9915326 Stereoselective interaction of ketamine with recombinant mu, kappa, and delta opioid receptors expressed in Chinese hamster ovary cells.

If anyone is really excited to read these, I'll gladly send them over as pdf via email. Maybe you could educate us afterwards.^^

 

[pharmakos]

that article does indeed make it sound like ketamine competitively binds to the mu opioid receptor.

 

[crOOk]

that article does indeed make it sound like ketamine competitively binds to the mu opioid receptor.

With my laziness it will for now remain a mystery what cascade of events leads to there being some opioidergic activity after ketamine administration, unless someone else feels up to the task IF it is even clear yet how exactly this happens.

Are there any known endogenous opioid receptor antagonists?

 

[WSH]

EDIT: There's another article on this and it does seem like ketamine actually binds to all opioid receptors. Neither of these two articles have been cited a whole lot and they're both written in 1999 without any word on this since then. I don't know if something might be methodologically wrong, since I really don't know that much about biochemistry, but I still find it weird this is an information that isn't found more easily.

I don't think that there is anything wrong with them, because they are peer-reviewed and a binding assay is a very easy and standard thing to do, ketamine displaced the hot ligand and as far as i know that implies that it binds to the receptor.

Are there any known endogenous opioid receptor antagonists?

Well, dynorphins have antagonistic effects, although they are not antagonists in the technical sense.

 

[endotropic]

With my laziness it will for now remain a mystery what cascade of events leads to there being some opioidergic activity after ketamine administration, unless someone else feels up to the task IF it is even clear yet how exactly this happens.

Are there any known endogenous opioid receptor antagonists?

Let's take the results from the first study WSH linked (http://www.ncbi.nlm.nih.gov/pubmed/14530949) at face value, and assume that Ketamine really does displacee [H3]DAMGO from mu receptor sites in SH-SY5Y cell membranes (those results could be due to some unreported methodological error, let's just assume that's not the case right now).

In binding assays like they use in that study, the cells membranes are torn to pieces, effectively destroying the cell and everything in it. What's left are small chunks of plasma membrane containing integral membrane proteins (like the mu-opioid receptor, associated g-proteins, etc.). The receptor is still functional, it can activate its g-protein, but that's essentially the end of the line as far as signaling goes. Everything else from inside the cell that could react with that g-protein is already washed away at that point.

That means there's no potential for endogenous transmitter release regardless of drug treatment. That's one of the main advantages of using a membrane based binding assay over a cellular one, you're left with only the direct effects of drug on receptor, with downstream events essentially eliminated.

Long story short, if the results from that study are accurate, ketamine binds competitively to the mu-opioid receptor in the ~10uM range. Then you have the adenylyl cyclase inhibition assay from the same paper, performed on whole cells this time. In that experiment they claim that ketamine doesn't have mu agonist activity until the ~700uM range, which is higher than physiological concentrations. So even if you believe the binding data, the rest of the paper suggests that it's not a functional mu agonist at a relevant range.

 

[crOOk]

Let's take the results from the first study WSH linked (http://www.ncbi.nlm.nih.gov/pubmed/14530949) at face value, and assume that Ketamine really does displacee [H3]DAMGO from mu receptor sites in SH-SY5Y cell membranes (those results could be due to some unreported methodological error, let's just assume that's not the case right now).

In binding assays like they use in that study, the cells membranes are torn to pieces, effectively destroying the cell and everything in it. What's left are small chunks of plasma membrane containing integral membrane proteins (like the mu-opioid receptor, associated g-proteins, etc.). The receptor is still functional, it can activate its g-protein, but that's essentially the end of the line as far as signaling goes. Everything else from inside the cell that could react with that g-protein is already washed away at that point.

That means there's no potential for endogenous transmitter release regardless of drug treatment. That's one of the main advantages of using a membrane based binding assay over a cellular one, you're left with only the direct effects of drug on receptor, with downstream events essentially eliminated.

Long story short, if the results from that study are accurate, ketamine binds competitively to the mu-opioid receptor in the ~10uM range. Then you have the adenylyl cyclase inhibition assay from the same paper, performed on whole cells this time. In that experiment they claim that ketamine doesn't have mu agonist activity until the ~700uM range, which is higher than physiological concentrations. So even if you believe the binding data, the rest of the paper suggests that it's not a functional mu agonist at a relevant range.

Thank you very much for the explanation, that all makes perfect sense. The broken cells would explain why they found no opioidergic activity despite ketamine binding to the respective receptors. I am pretty weak on these biochemical assays. I am still a bit puzzled by the factor 70 difference in dissociation constants, but that might not be relevant.

And there's the third study which claims there IS in fact opioidergic activity caused by ketamine which was successfully blocked by various other competitive ligands (which when using the right antagonists in vivo should give a better idea of the Kd, right?). Not sure if they used physiological concentrations, but they claim the antinociceptive effects ARE due to ketamine's interaction with mu opioid receptors, so if they don't want to render their study completely invalid, they should have been using the right dosage for ketamine to not surpass therapeutical level of activity (using the term physiological somehow doesn't quite sound right when referring to ketamine lol).

On a sidenote, I think it'd be interesting to know what ketamines effects are like at "hole doses" with a proper amount of naloxone preadministered.

 

[sekio]

It's important to differentiate "total effects" from the direct effects of ketamine itself. It may indeed produce opioidergic activity in a biological system like a human or rat, but that doesn't mean it has to be a mu-opioid ligand itself. Some other downstream pathway could be triggering endorphin release.

I wonder what sort of binding happens to receptor heterodimers.

 

[WSH]

I am still a bit puzzled by the factor 70 difference in dissociation constants, but that might not be relevant.

Only the 12.1 µM value is a dissociation constant, the 700 µM value is an IC50, that means that ketamine BINDS to the mu opioid receptor @ 12.1 µM and it ACTIVATES it @ 700 µM.

On a sidenote, I think it'd be interesting to know what ketamines effects are like at "hole doses" with a proper amount of naloxone preadministered.

Kappa antagonists definitely block some of the ketamine effects in rats:

http://www.ncbi.nlm.nih.gov/pubmed/20358363

So yeah, mu antagonists would also be interesting, but i also would like to know what serotonin antagonists would do.

 

[crOOk]

It may indeed produce opioidergic activity in a biological system like a human or rat, but that doesn't mean it has to be a mu-opioid ligand itself. Some other downstream pathway could be triggering endorphin release.

Precisely what I had been thinking and the reason for posting those dominos a few posts up. It seems that these articles are speaking a pretty clear language about ketamine indeed being a ligand itself. That in turn doesn't mean ketamine couldn't trigger some sort of cascade of events when it binds to another target that eventually causes opioidergic activity itself.

Only the 12.1 µM value is a dissociation constant, the 700 µM value is an IC50, that means that ketamine BINDS to the mu opioid receptor @ 12.1 µM and it ACTIVATES it @ 700 µM.

Oh ok I didn't read carefully enough. Thank you.

Kappa antagonists definitely block some of the ketamine effects in rats:

Wow that is news to me. It always seemed odd that both kappa and nmda receptor antagonists would lead to such similar effects.
May I ask, why block serotonine receptors? This would be a pretty easy experiment and I've actually done it before, but the dose of my serotonine antagonist might not have been high enough or it's affinity too low. It was quetiapine at 150mg and s-ketamine was used intravenously and intramuscularly both at 100mg. I did not notice any difference, but I might've very well used too little.
Quetiapine binding data according to wiki: 5-HT1A (IC50 = 717nM) partial agonist, 5-HT2A (IC50 = 148nM), 5-HT2C, and 5-HT7 receptor antagonist
If you explain why this would be interesting and whether the binding profile of quetiapine would get the job done, I could try it again next time I have some ketamine, but with a much higher quetiapine dose. I wouldn't do this unless it really seems like an interesting observation could be made because I will be experiencing some considerable akathisia on higher doses.
Also, quetiapine will block endogenous serotonin and to a small degree dopamine, so any euphoria will most definitely be attenuated even if ketamine doesn't interact with serotonin receptors at all.


Another thing I'm wondering, if there is clinically relevant opioidergic activity (which judging by the subjective effects is definitely not the case for me btw), then why are there no classical withdrawls to be observed in people with massive ketamine habits? I've known people who took upwards of a gram a day (and often up to 10g, at least when k was still dirt cheap on the street), but they have never complained about any major physical withdrawls. I have never seen any constipation from ketamine either personally.