Serotonin Agonists

A serotonin receptor agonist is an agonist of one or more serotonin receptors. They activate serotonin receptors in a manner similar to that of serotonin (5-hydroxytryptamine; 5-HT), a neurotransmitter and hormone and the endogenous ligand of the serotonin receptors.

Non-selective agonists

Serotonergic psychedelics such as tryptamines (e.g., psilocybin, psilocin, , 5-MeO-DMT, bufotenin), lysergamides (e.g., , ergine ()), phenethylamines (e.g., mescaline, 2C-B, 25I-NBOMe), and amphetamines (e.g., , ) are non-selective agonists of serotonin receptors. Their hallucinogenic effects are specifically mediated by activation of the 5-HT_2A receptor.

Drugs that increase extracellular serotonin levels such as serotonin reuptake inhibitors (e.g., fluoxetine, venlafaxine), serotonin releasing agents (e.g., fenfluramine, ), and monoamine oxidase inhibitors (e.g., phenelzine, moclobemide) are indirect non-selective serotonin receptor agonists. They are used variously as antidepressants, anxiolytics, antiobsessionals, appetite suppressants, and entactogens.

5-HT₁ receptor agonists

5-HT_1A receptor agonists

Azapirones such as buspirone, gepirone, and tandospirone are 5-HT_1A receptor partial agonists marketed primarily as anxiolytics, but also as antidepressants. The antidepressants vilazodone and vortioxetine are 5-HT_1A receptor partial agonists. Flibanserin, a drug used for female sexual dysfunction, is a 5-HT_1A receptor partial agonist. Many atypical antipsychotics, such as aripiprazole, asenapine, clozapine, lurasidone, quetiapine, and ziprasidone, are 5-HT_1A receptor partial agonists, and this action is thought to contribute to their beneficial effects on negative symptoms in schizophrenia.

5-HT_1B receptor agonists

Triptans such as sumatriptan, rizatriptan, and naratriptan are 5-HT_1B receptor agonists that are used to abort migraine and cluster headache attacks. The ergoline antimigraine agent ergotamine also acts on this receptor.

Serenics such as batoprazine, eltoprazine, and fluprazine are agonists of the 5-HT_1B receptor and other serotonin receptors, and have been found to produce antiaggressive effects in animals, but have not been marketed. Eltoprazine is under development for the treatment of aggression and for other indications.

5-HT_1D receptor agonists

In addition to being 5-HT_1B agonists, triptans (i.e. sumatriptan, almotriptan, zolmitriptan, naratriptan, eletriptan, frovatriptan and rizatriptan) are also agonists at the 5-HT_1D receptor, which contributes to their antimigraine effect caused by vasoconstriction of blood vessels in the brain. The same is true for ergotamine.

5-HT_1E receptor agonists

The triptan eletriptan is an agonist of the 5-HT_1E receptor. BRL-54443 is a selective 5-HT_1E and 5-HT_1F receptor agonist which is used in scientific research.

5-HT_1F receptor agonists

Triptans such as eletriptan, naratriptan, and sumatriptan are agonists of the 5-HT_1F receptor. Lasmiditan is a selective 5-HT_1F agonist that is under development by Eli Lilly and Company for the treatment of migraine.

5-HT₂ receptor agonists

5-HT_2A receptor agonists

Serotonergic psychedelics like psilocybin, LSD, and mescaline act as 5-HT_2A receptor agonists. Their actions at this receptor are thought to be responsible for their hallucinogenic effects. Most of these drugs also act as agonists of other serotonin receptors. Not all 5-HT_2A receptor agonists are psychoactive.

The 25-NB (NBOMe) series is a family of phenethylamine serotonergic psychedelics that, unlike other classes of serotonergic psychedelics, act as highly selective 5-HT_2A receptor agonists. The most well-known member of the 25-NB series is 25I-NBOMe. (2''S'',6''S'')-DMBMPP is an analogue of the 25-NB compounds and is the most highly selective agonist of the 5-HT_2A receptor that has been identified to date. O-4310 (1-isopropyl-6-fluoropsilocin) is a tryptamine derivative that is a highly selective agonist of the 5-HT_2A receptor.

Selective 5-HT_2A receptor agonists like the 25-NB compounds, specifically those which can behave as full agonists at this receptor, can cause serotonin syndrome-like adverse effects such as hyperthermia, hyperpyrexia, tachycardia, hypertension, clonus, seizures, agitation, aggression, and hallucinations which has ended in death on numerous occasions despite these particular drugs only being available to drug users for about 2–3 years, being widely in use mostly in the period from 2010-2012. Bans were put in place around 2012-2013 by countries where they had risen to popularity. They quickly and often accidentally lead to overdose. In contrast to the aforementioned drugs's potent, selective, and most importantly, full agonism (meaning the drug can fully activate the receptor to 100% of its activation potential, and does so even with minuscule amounts due to high potency, LSD, like the other "safe" psychedelics which are almost impossible to overdose fatally on, is a partial agonist, and this means it has a limit of how much it can activate the receptor, a limit which is basically impossible to exceed even with exponentially larger amounts of the drug. These partial agonists have proven relatively safe after having seen widespread abuse by drug users for many decades. Activation of the 5-HT_2A receptor is also implicated in serotonin syndrome caused by indirect serotonin receptor agonists like serotonin reuptake inhibitors, serotonin releasing agents, and monoamine oxidase inhibitors. Antagonists of the 5-HT_2A receptor like cyproheptadine and chlorpromazine are able to reverse and mediate recovery from serotonin syndrome.

5-HT_2B receptor agonists

Agonists of the 5-HT_2B receptor are implicated in the development of cardiac fibrosis.Hutcheson, J. D., Setola, V., Roth, B. L., & Merryman, W. D. (2011). Serotonin receptors and heart valve disease—it was meant 2B. Pharmacology & Therapeutics, 132(2), 146-157. Fenfluramine, pergolide, and cabergoline have been withdrawn from some markets for this reason. Many serotonergic psychedelics, such as LSD and psilocin, have been shown to activate this receptor directly. MDMA has been reported to be both a potent direct agonist and have an indirect effect by increasing plasma serotonin levels.Zolkowska, D., Rothman, R. B., & Baumann, M. H. (2006). Amphetamine analogs increase plasma serotonin: implications for cardiac and pulmonary disease. Journal of Pharmacology and Experimental Therapeutics, 318(2), 604-610.

5-HT_2C receptor agonists

Lorcaserin is an appetite suppressant and anti-obesity drug which acts as a selective 5-HT_2C receptor agonist. ''meta''-Chlorophenylpiperazine (mCPP) is a 5-HT_2C-preferring serotonin receptor agonist that induces anxiety and depression and can cause panic attacks in susceptible individuals.

5-HT₃ receptor agonists

2-Methyl-5-hydroxytryptamine (2-methylserotonin) and quipazine are moderately selective agonists of the 5-HT₃ receptor that are used in scientific research. Agonists of this receptor are known to induce nausea and vomiting, and are not used medically.

5-HT₄ receptor agonists

Cisapride and tegaserod are 5-HT₄ receptor partial agonists that were used to treat disorders of gastrointestinal motility. Prucalopride is a highly selective 5-HT₄ receptor agonist that can be used to treat certain disorders of gastrointestinal motility. Other 5-HT₄ receptor agonists have shown potential to be nootropic and antidepressant drugs, but have not been marketed for such indications.

5-HT_5A receptor agonists

Valerenic acid, a constituent of valerian root, has been found to act as a 5-HT_5A receptor agonist, and this action could be involved in the sleep-promoting effects of valerian.

5-HT₆ receptor agonists

No selective agonists of the 5-HT₆ receptor have been approved for medical use. Selective 5-HT₆ receptor agonists like E-6801, E-6837, EMDT, WAY-181,187, and WAY-208,466 show antidepressant, anxiolytic, antiobsessional, and appetite suppressant effects in animals, but also impair cognition and memory.

5-HT₇ receptor agonists

AS-19 is a 5-HT₇ receptor agonist that has been used in scientific research.

See also

* Serotonin receptor antagonist

References

External links

IUPHAR GPCR Database - 5-HT receptor family
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{{Serotonin receptor modulators