The 5-HT2A receptor is a subtype of the 5-HT2 receptor that belongs to the serotonin receptor family and is a G protein-coupled receptor (GPCR). The 5-HT2A receptor is a cell surface receptor, but has several intracellular locations. 5-HT is short for 5-hydroxy-tryptamine or serotonin. This is the main excitatory receptor subtype among the GPCRs for serotonin, although 5-HT2A may also have an inhibitory effect on certain areas such as the visual cortex and the orbitofrontal cortex. This receptor was first noted for its importance as a target of serotonergic psychedelic drugs such as LSD and psilocybin mushrooms. Later it came back to prominence because it was also found to be mediating, at least partly, the action of many antipsychotic drugs, especially the atypical ones.
Dimethoxy-4-amylamphetamine (DOAM) is a lesser-known psychedelic drug and a substituted amphetamine. DOAM was first synthesized by Alexander Shulgin. In his book PiHKAL (Phenethylamines i Have Known And Loved), the minimum dosage is listed as 10 mg, and the duration is unknown. DOAM produces a bare threshold and tenseness. As the 4-alkyl chain length is increased from shorter homologues such as DOM, DOET, DOPR, and DOBU which are all potent hallucinogens, the 5-HT2 binding affinity increases, rising to a maximum with the 4-(n-hexyl) derivative before falling again with even longer chains, but compounds with chain length longer than n-propyl, or with other bulky groups such as isopropyl, t-butyl or γ-phenylpropyl at the 4- position, fail to substitute for hallucinogens in animals or produce hallucinogenic effects in humans, suggesting these have low efficacy and are thus antagonists or weak partial agonists at the 5-HT2A receptor.
6-MeO-THH, or 6-methoxy-1,2,3,4-tetrahydroharman, is a β-carboline derivative and a structural isomer of tetrahydroharmine (7-MeO-THH). 6-MeO-THH is mentioned in Alexander Shulgin's book TiHKAL, stating that 6-MeO-THH is very similar to the other carbolines. Limited testing suggests that it possesses mild psychoactive effects at 1.5 mg/kg and is said to be about one-third as potent as 6-methoxyharmalan. It has been isolated from certain plants of the Virola family.
5-Hydroxytryptamine (serotonin) receptor 5A, also known as HTR5A, is a protein that in humans is encoded by the HTR5A gene. Agonists and antagonists for 5-HT receptors, as well as serotonin uptake inhibitors, present promnesic (memory-promoting) and/or anti-amnesic effects under different conditions, and 5-HT receptors are also associated with neural changes.
The 5HT6 receptor is a subtype of 5HT receptor that binds the endogenous neurotransmitter serotonin (5-hydroxytryptamine, 5HT). It is a G protein-coupled receptor (GPCR) that is coupled to Gs and mediates excitatory neurotransmission. HTR6 denotes the human gene encoding for the receptor.
LY-341495 is a research drug developed by the pharmaceutical company Eli Lilly, which acts as a potent and selective orthosteric antagonist for the group II metabotropic glutamate receptors (mGluR2/3).
5-Carboxamidotryptamine (5-CT) is a tryptamine derivative closely related to the neurotransmitter serotonin.
2-Ethyl-5-methoxy-N,N-dimethyltryptamine (EMDT) is a tryptamine derivative which is used in scientific research. It acts as a selective 5-HT6 receptor agonist, with a Ki of 16 nM, and was one of the first selective agonists developed for this receptor. EMDT inhibits both short- and long-term memory formation in animal studies, and this effect can be reversed by the selective 5-HT6 antagonist SB-399,885. Additionally, it is active in the tail suspension test, suggesting that it could be an effective antidepressant.
AMDA (9-Aminomethyl-9,10-dihydroanthracene) is an organic compound which acts as a potent and selective antagonist for the 5-HT2A receptor. It has been used to help study the shape of the 5-HT2A protein, and develop a large family of related derivatives with even higher potency and selectivity.
KML-010 is a drug derived from spiperone. It functions as a highly selective 5-HT2A receptor antagonist, with negligible affinity for the 5-HT1A or 5-HT2C receptors, and over 400-fold lower affinity for the D2 receptor in comparison to spiperone.
5-Benzyloxytryptamine (5-BT), is a tryptamine derivative which acts as an agonist at the 5-HT1D, 5-HT2 and 5-HT6 serotonin receptors, and an antagonist of TRPM8.
7,N,N-trimethyltryptamine (7-methyl-DMT, 7-TMT), is a tryptamine derivative which acts as an agonist of 5-HT2 receptors. In animal tests, both 7-TMT and its 5-methoxy derivative 5-MeO-7-TMT produced behavioural responses similar to those of psychedelic drugs such as DMT, but the larger 7-ethyl and 7-bromo derivatives of DMT did not produce psychedelic responses despite having higher 5-HT2 receptor affinity in vitro (cf. DOBU, DOAM). 7-TMT also weakly inhibits reuptake of serotonin but with little effect on dopamine or noradrenaline reuptake.
4-Fluoro-5-Methoxy-N,N-dimethyltryptamine (4-F-5-MeO-DMT) was first described by David E. Nichols team in 2000. It is a potent 5-HT1A agonist. Substitution with the 4-fluorine markedly increased 5-HT1A selectivity over 5-HT2A/2C receptors with potency greater than that of the 5-HT1A agonist 8-OH-DPAT.
5-Ethyl-N,N-dimethyltryptamine is a tryptamine derivative which acts as an agonist at the 5-HT1A and 5-HT1D serotonin receptors, with around 3x selectivity for 5-HT1D.
5-(Nonyloxy)tryptamine is a tryptamine derivative which acts as a selective agonist at the 5-HT1B receptor. Increasing the O-alkoxy chain length in this series gives generally increasing potency and selectivity for 5-HT1B, with highest activity found for the nonyloxy derivative, having a 5-HT1B binding affinity of 1.0 nM, and around 300-fold selectivity over the related 5-HT1A receptor.
SB-206553 is a drug which acts as a mixed antagonist for the 5-HT2B and 5-HT2C serotonin receptors. It has anxiolytic properties in animal studies and interacts with a range of other drugs. It has also been shown to act as a positive allosteric modulator of α7 nicotinic acetylcholine receptors. Modified derivatives of SB-206553 have been used to probe the structure of the 5-HT2B receptor.
Substituted tryptamines, or serotonin analogues, are organic compounds which may be thought of as being derived from tryptamine itself. The molecular structures of all tryptamines contain an indole ring, joined to an amino (NH2) group via an ethyl (−CH2–CH2−) sidechain. In substituted tryptamines, the indole ring, sidechain, and/or amino group are modified by substituting another group for one of the hydrogen (H) atoms.
5-MeO-NBpBrT is a N-substituted member of the methoxytryptamine family of compounds. Like other such compounds it acts as an antagonist for the 5-HT2A receptor, with a claimed 100x selectivity over the closely related 5-HT2C receptor. While N-benzyl substitution of psychedelic phenethylamines often results in potent 5-HT2A agonists, it had been thought that N-benzyl tryptamines show much lower efficacy and are either very weak partial agonists or antagonists at 5-HT2A, though more recent research has shown stronger agonist activity for 3-substituted benzyl derivatives. Extending the benzyl group to a substituted phenethyl can also recover agonist activity in certain cases.
6-Chloronicotine is a drug which acts as an agonist at neural nicotinic acetylcholine receptors. It substitutes for nicotine in animal studies with around twice the potency, and shows antinociceptive effects.
O-Acetylbufotenine is a tryptamine derivative which produces psychedelic-appropriate responding in animal studies. It is an acylated derivative of bufotenine with higher lipophilicity that allows it to cross the blood-brain barrier; once inside the brain, it is metabolised to bufotenine. It also acts directly as an agonist at 5-HT1A and 5-HT1D receptors.
