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Chemical (5-hydroxytryptamine, or 5-HT) derived from the amino acid tryptophan. It occurs in brain and intestinal tissue, platelets, and certain connective-tissue cells and is a component of many animal venoms (e.g., wasp, toad). A strong stimulator of blood-vessel constriction and a neurotransmitter, serotonin concentrates in certain brain areas, especially the midbrain and hypothalamus. Some cases of depression are apparently caused by reduced amounts or activity of serotonin in the brain; many antidepressants counteract that condition. Excessive brain serotonin activity may cause migraine headaches and nausea. LSD may act by inhibiting the action of serotonin.
This entry comes from Encyclopædia Britannica Concise. For the full entry on serotonin, visit Britannica.com.