<Tr> <Td_colspan="2"> Infobox references </Td> </Tr> <Tr> <Td> </Td> <Td> </Td> </Tr> <P> Serotonin (/ ˌsɛrəˈtoʊnɪn, ˌsɪərə - /) or 5 - hydroxytryptamine (5 - HT) is a monoamine neurotransmitter . Biochemically the indoleamine molecule is derived from the amino acid tryptophan . 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 . Additionally, serotonin is stored in blood platelets and is released during agitation and vasoconstriction, where it then acts as an agonist to other platelets . Serotonin is popularly thought to be a contributor to feelings of well - being and happiness . </P> <P> Approximately 90% of the human body's total serotonin is located in the enterochromaffin cells in the GI tract, where it is used to regulate intestinal movements . 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 . 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 . Modulation of serotonin at synapses is thought to be a major action of several classes of pharmacological antidepressants . </P>

Where is most of the body's serotonin located