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5-HT receptors
In the field of neurochemistry, 5-HT receptors are receptors for the neurotransmitter and peripheral signal mediator serotonin, also known as 5-hydroxytryptamine or 5-HT. 5-HT receptors are located on the cell membrane of nerve cells and other cell types in animals and mediate the effects of serotonin as the endogenous ligand and of a broad range of pharmaceutical and recreational drugs. With the exception of the 5-HT3 receptor, a ligand gated ion channel, all other 5-HT receptors are G_protein coupled seven transmembrane (or heptahelical) receptors that activate an intracellular second messenger cascade.
- 5-HT1 receptors are Gi/Go coupled, mediating cellular effects through decreasing cellular levels of cyclic adenosine monophosphate (cAMP).
- 5-HT2 receptors are Gq/G11 coupled, mediating cellular effects through increasing cellular levels of inositol trisphosphate (IP3) and diacylglycerol (DAG). Three subtypes exist, namely 5-HT2A, 5-HT2B, and 5-HT2C (formerly called 5-HT1C).
- The 5-HT3 receptor is a ligand-gated Na+ and K+ cation channel, resulting in a direct plasma membrane depolarization.
- The 5-HT4 receptor is Gs coupled, mediating cellular effects through increasing cellular levels of cAMP.
- The 5-HT7 receptors is Gs coupled, mediating cellular effects through increasing cellular levels of cAMP.
Characterised 5-HT receptors
Within these general classes of 5-HT receptors, a number of specific types have been characterized:
| Summary of characterised 5-HT receptors, with selected agonist/antagonist agents | |||
| receptor | actions | agonists | antagonists |
| 5-HT1A | CNS: neuronal inhibition, behavioural effects (sleep, feeding, thermoregulation, anxiety) | buspirone | spiperone, methiothepin, ergotamine, yohimbine |
| 5-HT1B | CNS: presynaptic inhibition, behavioural effects; vascular: pulmonary vasoconstriction | ergotamine, sumatriptan | methiothepin, yohimbine, metergoline |
| 5-HT1D | CNS: locomotion; vascular: cerebral vasoconstriction | sumatriptan | methiothepin, yohimbine, metergoline, ergotamine |
| 5-HT2A | CNS: neuronal excitation, behavioural effects; smooth muscle: contraction, vasoconstriction / dilatation; platelets: aggregation | α-methyl-5-HT, LSD (CNS) | ketanserin, cyproheptadine, pizotifen, LSD (PNS) |
| 5-HT2B | stomach: contraction | α-methyl-5-HT, LSD (CNS) | yohimbine, LSD (PNS) |
| 5-HT2C | CNS, choroid plexus: cerebrospinal fluid (CSF) secretion | α-methyl-5-HT, LSD (CNS) | mesulergine, LSD (PNS) |
| 5-HT3 | CNS, PNS: neuronal excitation, anxiety, emesis | 2-methyl-5-HT | metoclopramide (high doses), renzapride, ondansetron, alosetron |
| 5-HT4 | GIT, CNS: neuronal excitation, gastrointestinal motility | 5-methoxytryptamine, metoclopramide, renzapride, tegaserod | GR113808 |
| 5-ht5 | CNS: unknown | unknown | unknown |
| 5-ht6 | CNS: unknown | unknown | unknown |
| 5-HT7 | CNS, GIT, blood vessels: unknown | 5-carboxytryptamine, LSD | methiothepin |
Note that there is no 5-HT1C receptor since, after the receptor was cloned and further characterised, it was found to have more in common with the 5-HT2 family of receptors and was redesignated as the 5-HT2C receptor.
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