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 G_i/G_o coupled, mediating cellular effects through decreasing cellular levels of cyclic adenosine monophosphate (cAMP).

• 5-HT₂ receptors are G_q/G₁₁ coupled, mediating cellular effects through increasing cellular levels of inositol trisphosphate (IP₃) and diacylglycerol (DAG). Three subtypes exist, namely 5-HT_2A, 5-HT_2B, and 5-HT_2C (formerly called 5-HT_1C).

• 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 G_s coupled, mediating cellular effects through increasing cellular levels of cAMP.

• The 5-HT₇ receptors is G_s 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-HT_1C 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-HT_2C receptor.

External links

• Serotonin Receptor Subtypes and Ligands
• 5-HT Receptors and their Ligands
• Basic Neurochemistry - Serotonin Receptors