Breaking News!! Another Research Update!!
Alright guys... I think the rules just changed. We're playing ball in a new court now.
This is going to open a whole new realm of possibilities for things to research. 
A-type GABA receptor as a central targe - PubMed Mobile
 Originally Posted by A-type GABA receptor as a central target of TRPM8 agonist menthol.
Abstract
Menthol is a widely-used cooling and flavoring agent derived from mint leaves. In the peripheral nervous system, menthol regulates sensory transduction by activating TRPM8 channels residing specifically in primary sensory neurons. Although behavioral studies have implicated menthol actions in the brain, no direct central target of menthol has been identified. Here we show that menthol reduces the excitation of rat hippocampal neurons in culture and suppresses the epileptic activity induced by pentylenetetrazole injection and electrical kindling in vivo. We found menthol not only enhanced the currents induced by low concentrations of GABA but also directly activated GABA(A) receptor (GABA(A)R) in hippocampal neurons in culture. Furthermore, in the CA1 region of rat hippocampal slices, menthol enhanced tonic GABAergic inhibition although phasic GABAergic inhibition was unaffected. Finally, the structure-effect relationship of menthol indicated that hydroxyl plays a critical role in menthol enhancement of tonic GABA(A)R. Our results thus reveal a novel cellular mechanism that may underlie the ambivalent perception and psychophysical effects of menthol and underscore the importance of tonic inhibition by GABA(A)Rs in regulating neuronal activity.
So yes, this thing is saying that menthol seems to not only be a positive allosteric modulator of GABA(A) receptors but also a direct agonist, and this was verified specifically for the hippocampus. In case you're wondering what type of PAM it is, it seems to be fairly unique. This next study claims that it's unlike the typicals like benzos and barbiturates and actually shares some properties with the very obscure and particularly euphoric anesthetic propofol, one of the drugs implicated in contributing to Michael Jackson's overdose.
Menthol shares general anesthetic activ - PubMed Mobile
 Originally Posted by Menthol shares general anesthetic activity and sites of action on the GABA(A) receptor with the intravenous agent, propofol.
Abstract
Menthol and related compounds were investigated for modulation of recombinant human gamma-aminobutyric acid type A (GABA(A), alpha(1)beta(2)gamma(2s)) receptor currents expressed in Xenopus oocytes. Sub-maximal (EC(20)) GABA currents were typically enhanced by co-applications of 3-300 microM (+)-menthol (e.g. by approximately 2-fold at 50 microM) > isopulegol > isomenthol> alpha-terpineol >> cyclohexanol. We studied menthol's actions on GABA(A) receptors compared to sedatives (benzodiazepines) and intravenous anesthetics (barbiturates, steroids, etomidate and propofol). Flumazenil (a benzodiazepine antagonist) did not inhibit menthol enhancements while currents directly activated by 50 microM propofol were significantly inhibited (by 26+/-3%) by 50 microM (+)-menthol. GABA(A) receptors containing beta(2) subunits with either a point mutation in a methionine residue to a tryptophan at the 286 position (in transmembrane domain 3, TM-3) or a tyrosine to a tryptophan at the 444 position (TM-4) are insensitive to modulation by propofol. Enhancements of GABA EC(20) currents by menthol were equally abolished in GABA(A) alpha(1)beta(2)(M286W)gamma(2s) and alpha(1)beta(2)(Y444W)gamma(2s) receptors while positive modulations by benzodiazepines, barbiturates and steroids were unaffected. Menthol may therefore exert its actions on GABA(A) receptors via sites distinct from benzodiazepines, steroids and barbiturates, and via sites important for modulation by propofol. Finally, using an in vivo tadpole assay, addition of (+)-menthol resulted in a loss of righting reflex with an EC(50) of 23.5+/-4.7 microM (approximately10-fold less potent anesthesia than propofol). Thus, menthol and analogs share general anesthetic action with propofol, possibly via action at similar sites on the GABA(A) receptor.
Now where does this leave us? Well damn... there are a lot of things I could say, but I think I'll hold off on too much for now. But some immediate observations....
First, there's the link with propofol. This makes it pretty unique, and it looks like it's still not exactly the same receptor site. But just as a quick overview, propofol is supposed to be one of the much more euphoric GABAergics and maybe mildly hallucinogenic, and I have actually heard about sexual effects from it before. However, it's also been found to have multiple mechanisms of action, with some belief that the endocannabinoid system may be playing a role, so it's probably best not to speculate there.
What really interests me is the direct agonist effect.... That alone could make it have hallucinations, though I would expect it to from the kappa-opioid agonism by the time it was a high enough dose for that. Makes me wonder what the effects would be like from a strong trip, though.... But anyway, here's what comes to mind. GABA has been reported by people to induce vivid and lucid dreams, which is interesting considering the effects that drugs like benzos have on dreams, but it could just be that they effect memory and REM-related functions too specifically. It's easy to see with them at lower doses, and drugs like alcohol, that GABA can positively effect dreams, so maybe a direct agonist like GABA itself can more easily get these effects. The other big thing is muscimol, the main desired active chemical in Amanita muscaria and Amanita pantherina mushrooms. Just like how salvia is unique in that it's really the only commonly used hallucinogen that binds to the kappa-opioid receptors for a significant effect, the amanita mushrooms are basically in the same situation but for GABA(A) receptors. Muscimol binds directly to GABA(A) and has powerful hallucinogenic effects at high doses. One thing it's also pretty well-known for is inducing bizarre dreams. There are actually many users of it who claim that it's one of its most desirable effects, saying that the way it works is that first you can take them and then sleep into a deep sleep of powerful or meaningful but very psychedelic dreams that are usually extremely vivid and often lucid, and then if you took enough you'll trip later when you wake up. But the dream effects can be gotten even at a lower dose, and I know people have used teas to that end before. I can't help but wonder if higher doses of menthol may be drawing from these kinds of effects as well....
There are so many new things to consider now!!
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