Serotonin receptors are found in almost all animals and are even known to regulate longevity and behavioral aging in the primitive nematode, Caenorhabditis elegans.[5][6]
5-hydroxytryptamine receptors or 5-HT receptors, or serotonin receptors are found in the central and peripheral nervous systems.[1][2]
They can be divided into 7 families of G protein-coupled receptors which activate an intracellular second messenger cascade to produce an excitatory or inhibitory response. The exception to this is the 5-HT3 receptor which is a ligand-gated ion channel.
In 2014, a novel 5-HT receptor was isolated from the small white butterfly, Pieris rapae, and named pr5-HT8. It does not occur in mammals and shares relatively low similarity to the known 5-HT receptor classes.[7]
The 7 general serotonin receptor classes include a total of 14 known serotonin receptors.[9] The 15th receptor 5-HT1P has been distinguished on the basis of functional and radioligand binding studies, its existence has never been definitely affirmed or refuted.[10][11] The specific types have been characterized as follows:[12][13][14]
Information on serotonin receptors (human isoforms if nothing else is stated)
Note that there is no 5-HT1C receptor since, after the receptor was cloned and further characterized, it was found to have more in common with the 5-HT2 family of receptors and was redesignated as the 5-HT2C receptor.[106]
Very nonselective agonists of 5-HT receptor subtypes include ergotamine (an antimigraine), which activates 5-HT1A, 5-HT1D, 5-HT1B, D2 and norepinephrine receptors.[38] LSD (a psychedelic) is a 5-HT1A, 5-HT2A, 5-HT2C, 5-HT5A and 5-HT6 agonist.[38]
Expression patterns
The genes coding for serotonin receptors are expressed across the mammalian brain. Genes coding for different receptors types follow different developmental curves. Specifically, there is a developmental increase of HTR5A expression in several subregions of the human cortex, paralleled by a decreased expression of HTR1A from the embryonic period to the post-natal one.
[107]
5-HT1-like
A number of receptors were classed as "5-HT1-like" - by 1998 it was being argued that, since these receptors were "a heterogeneous population of 5-HT1B, 5-HT1D and 5-HT7" receptors the classification was redundant.[108]
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↑Molecular Neuropharmacology: A Foundation for Clinical Neuroscience (2nd ed.). New York: McGraw-Hill Medical. 2009. p. 4. ISBN9780071481274. "Similarly, little is known about which of serotonin's 14 known receptors must be activated to achieve an antidepressant response."
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↑Annaházi, Anita; Berger, Thomas Erwin; Demir, Ihsan Ekin; Zeller, Florian; Müller, Michael; Anneser, Markus; Skerra, Arne; Michel, Klaus et al. (April 2022). "Metabotropic 5‐HT receptor‐mediated effects in the human submucous plexus" (in en). Neurogastroenterology & Motility34 (10): e14380. doi:10.1111/nmo.14380. ISSN1350-1925. PMID35438222.
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