<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 the largest cache of serotonin located within the body
the enterochromaffin cells in the GI tract