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Serotonin

Monoamine neurotransmitter / From Wikipedia, the free encyclopedia

Serotonin (/ˌsɛrəˈtnɪn, ˌsɪərə-/[6][7][8]) or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vasoconstriction.[9] Approximately 90% of the serotonin that the body produces is in the intestinal tract.[10]

Quick facts: Clinical data, Other names, Physiological dat...
Serotonin
Clinical data
Other names5-HT, 5-Hydroxytryptamine, Enteramine, Thrombocytin, 3-(β-Aminoethyl)-5-hydroxyindole, Thrombotonin
Physiological data
Source tissuesraphe nuclei, enterochromaffin cells
Target tissuessystem-wide
Receptors5-HT1, 5-HT2, 5-HT3, 5-HT4, 5-HT5, 5-HT6, 5-HT7
AgonistsIndirectly: SSRIs, MAOIs
Precursor5-HTP
BiosynthesisAromatic L-amino acid decarboxylase
MetabolismMAO
Identifiers
  • 3-(2-Aminoethyl)-1H-indol-5-ol
CAS Number
PubChem CID
IUPHAR/BPS
ChemSpider
KEGG
PDB ligand
CompTox Dashboard (EPA)
ECHA InfoCard100.000.054
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Quick facts: Names, Identifiers, Properties, Hazards...
Serotonin
Names
IUPAC name
5-Hydroxytryptamine
Preferred IUPAC name
3-(2-Aminoethyl)-1H-indol-5-ol
Other names
5-Hydroxytryptamine, 5-HT, Enteramine; Thrombocytin, 3-(β-Aminoethyl)-5-hydroxyindole, 3-(2-Aminoethyl)indol-5-ol, Thrombotonin
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.054
KEGG
MeSH Serotonin
UNII
  • InChI=1S/C10H12N2O/c11-4-3-7-6-12-10-2-1-8(13)5-9(7)10/h1-2,5-6,12-13H,3-4,11H2 Y
    Key: QZAYGJVTTNCVMB-UHFFFAOYSA-N Y
  • InChI=1/C10H12N2O/c11-4-3-7-6-12-10-2-1-8(13)5-9(7)10/h1-2,5-6,12-13H,3-4,11H2
    Key: QZAYGJVTTNCVMB-UHFFFAOYAX
  • C1=CC2=C(C=C1O)C(=CN2)CCN
Properties
C10H12N2O
Molar mass 176.215 g/mol
Appearance White powder
Melting point 167.7 °C (333.9 °F; 440.8 K) 121–122 °C (ligroin)[1]
Boiling point 416 ± 30 °C (at 760 Torr)[2]
slightly soluble
Acidity (pKa) 10.16 in water at 23.5 °C[3]
2.98 D
Hazards
Lethal dose or concentration (LD, LC):
750 mg/kg (subcutaneous, rat),[4] 4500 mg/kg (intraperitoneal, rat),[5] 60 mg/kg (oral, rat)
Safety data sheet (SDS) External MSDS
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Biochemically, the indoleamine molecule derives from the amino acid tryptophan, via the (rate-limiting) hydroxylation of the 5 position on the ring (forming the intermediate 5-hydroxytryptophan), and then decarboxylation to produce serotonin.[11] Serotonin is primarily found in the enteric nervous system located in the gastrointestinal tract (GI tract). However, it is also produced in the central nervous system (CNS), specifically in the raphe nuclei located in the brainstem, Merkel cells located in the skin, pulmonary neuroendocrine cells and taste receptor cells in the tongue. Additionally, serotonin is stored in blood platelets and is released during agitation and vasoconstriction, where it then acts as an agonist to other platelets.[12]

Approximately 90% of the human body's total serotonin is located in the enterochromaffin cells in the GI tract, where it regulates intestinal movements.[13][14] About 8% is found in platelets and 1–2% in the CNS.[15] The serotonin is secreted luminally and basolaterally, which leads to increased serotonin uptake by circulating platelets and activation after stimulation, which gives increased stimulation of myenteric neurons and gastrointestinal motility.[16] The remainder is synthesized in serotonergic neurons of the CNS, where it has various functions. These include the regulation of mood, appetite, and sleep. Serotonin also has some cognitive functions, including memory and learning.

Several classes of antidepressants, such as the SSRIs and the SNRIs among others, interfere with the normal reabsorption of serotonin after it is done with the transmission of the signal, therefore augmenting the neurotransmitter levels in the synapses.

Serotonin secreted from the enterochromaffin cells eventually finds its way out of tissues into the blood. There, it is actively taken up by blood platelets, which store it. When the platelets bind to a clot, they release serotonin, where it can serve as a vasoconstrictor or a vasodilator while regulating hemostasis and blood clotting. In high concentrations, serotonin acts as a vasoconstrictor by contracting endothelial smooth muscle directly or by potentiating the effects of other vasoconstrictors (e.g. angiotensin II, norepinephrine). The vasoconstrictive property is mostly seen in pathologic states affecting the endothelium  such as atherosclerosis or chronic hypertension. In physiologic states, vasodilation occurs through the serotonin mediated release of nitric oxide from endothelial cells. Additionally, it inhibits the release of norepinephrine from adrenergic nerves.[17] Serotonin is also a growth factor for some types of cells, which may give it a role in wound healing. There are various serotonin receptors.

Serotonin is metabolized mainly to 5-HIAA, chiefly by the liver. Metabolism involves first oxidation by monoamine oxidase to the corresponding aldehyde. The rate-limiting step is hydride transfer from serotonin to the flavin cofactor.[18] There follows oxidation by aldehyde dehydrogenase to 5-HIAA, the indole acetic-acid derivative. The latter is then excreted by the kidneys.

Besides mammals, serotonin is found in all bilateral animals including worms and insects,[19] as well as in fungi and in plants.[20] Serotonin's presence in insect venoms and plant spines serves to cause pain, which is a side-effect of serotonin injection.[21][22] Serotonin is produced by pathogenic amoebae, and its effect in the human gut is diarrhea.[23] Its widespread presence in many seeds and fruits may serve to stimulate the digestive tract into expelling the seeds.[24]