aromatic compound metabolism L-tryptophan degradation aromatic compound biosynthesis serotonin biosynthesis GO:0042427 pathway 5-hydroxytryptamine biosynthesis Biosynthesis of serotonin (5-hydroxytryptamine, or 5-HT), a monoamine neurotransmitter. Serotonin is synthesized in serotonergic neurons in the central nervous system (CNS) and enterochromaffin cells in the gastrointestinal tract of animals including humans. Serotonin is also found in many mushrooms and plants, including fruits and vegetables. In plants, serotonin is implicated in several physiological roles such as flowering, morphogenesis, and adaptation to environmental changes. UPa:UPA00846 KEGG:map01100 5-HT biosynthesis KEGG:map00380