Serotonin (5-hydroxytryptamine, 5-HT) was identified initially as the active substance from
brain extracts that produced peripheral vasoconstriction (Rapport et al 1948). This
substance was later shown to be identical to a contractile substance isolated earlier from the
enterochromaffin cells of the gastrointestinal mucosa called enteramine (Erspamer and
Asero 1952). Subsequent studies demonstrated the localized distribution of 5-HT neurons
throughout the brain (and gut) using fluorescence histochemistry and, later …