Serotonin (5HT) is synthesized in:
- Cells in the raphe nuclei of brainstem convert L-tryptophan by tryptophan hydroxylase (TPH) to 5-hydoxytryptamine (5-HTP), and furtherly, by amino acid decarboxylase (DDC) to serotonin (5-HT). This is broken down by monoamineoxidase (MAO) to 5-HIAA. Serotonin is released into the synapse in a similar fashion to norepinephrine. Two presynaptic serotonin receptors serve as both brakes and enhancers of serotonin release when blocked by serotonin or norepinephrine, while the postsynaptic receptors regulate the release of the serotonin signal into the neuron. Serotonin producing neurons extend to the cerebellum, basal ganglia, frontal cortex, amygdala, thalamus, hypothalamus and limbic system, and down the spinal cord. TPH1 is in several tissues, and TPH2, is a brain-specific isoform. Ovarian hormones can affect the expression of TPH (postpartum depression and premenstrual stress syndrome).
- Enterochromaffin cells in the gastrointestinal tract
- Platelets