Serotonin is a monoamine neurotransmitter that is primarily found in the gastrointestinal (GI) tract and central nervous system (CNS).
Approximately 80 percent of the human body's total serotonin is located in the enterochromaffin cells in the gut, where it is used to regulate intestinal movements.
The remainder is synthesized in serotonergic neurons in the CNS where it has various functions, including the regulation of mood, appetite, sleep, muscle contraction, and some cognitive functions including memory and learning; and in blood platelets where it helps to regulate hemostasis and blood clotting.
In addition to humans and animals, serotonin is also found in fungi and plants.
Serotonin is used by a variety of single-cell organisms for various purposes. Selective serotonin re-uptake inhibitors (SSRIs) have been found to be toxic to algae. The gastrointestinal parasite ''Entamoeba histolytica'' secretes serotonin, causing a sustained secretory diarrhea in some patients.
Patients infected with ''Entamoeba histolytica'' have been found to have highly elevated serum serotonin levels which returned to normal following resolution of the infection. ''Entamoeba histolytica'' also responds to the presence of serotonin by becoming more virulent.
Serotonin was originally discovered by Italian Vittorio Erspamer in Rome in 1935 and American scientists in the late 1940s. Isolated and named in 1948 by Maurice M. Rapport, Arda Green, and Irvine Page of the Cleveland Clinic, the name ''serotonin'' is something of a misnomer and reflects the circumstances of the compound's discovery. It was initially identified as a vasoconstrictor substance in blood serum – hence ''serotonin'', a serum agent affecting vascular tone. This agent was later chemically identified as 5-hydroxytryptamine (5-HT) by Rapport, and, as the broad range of physiological roles were elucidated, 5-HT became the preferred name in the pharmacological field.
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