Serotonin, or 5-hydroxytryptamine (5-HT), is a neurotransmitter with an integral physiological role in the human body; it regulates various activities, including behavior, mood, memory, and gastrointestinal homeostasis. Serotonin is synthesized in the raphe nuclei of the brainstem and the enterochromaffin cells of the intestinal mucosa. More @Wikipedia
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