Production

Serotonin is produced from dietary tryptophan by the action of tryptophan hydroxylase and dopa decarboxylase in chromaffin cells and neurons. Platelets acquire serotonin on passage through the gut where the local concentration is high.

The degradation pathway of serotonin is important from the view of carcinoid syndrome. Monoamine oxidase and aldehyde dehydrogenase convert serotonin to 5-hydroxy-indoleacetic acid - 5HIAA. 5HIAA is excreted in the urine and thus provides a ready means of assessing serotonin turnover.

Serotonin is found in:

• the stomach and small intestine: in chromaffin, neural crest-derived cells
• platelets
• the central nervous system: 5HT acts as a central transmitter from the cells of the raphe nucleus in the pons and upper medulla; these project widely to the spinal cord and the cerebral hemispheres