has primary input serotonin(1+) serotonin secretion GO:0001820 5-hydroxytryptamine secretion The regulated release of serotonin by a cell. Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine synthesized in serotonergic neurons in the central nervous system, enterochromaffin cells in the gastrointestinal tract and some immune system cells. serotonin release 5-HT secretion serotonin transport signal release secretion