Synthesis of the catecholamines from tyrosine. Once synthesized, dopamine, norepinephrine and epinephrine are packaged in granulated vesicles. Within these vesicles, norepinephrine and epinephrine are bound to ATP and a protein called chromogranin A . Both of these enzymes are widley distributed throughout the body. The hydroxylase is normally not saturated and as a result, an increased uptake of tryptophan in the diet will lead to increased brain serotonin content.
Serotonin is present at highest concentrations in platelets and in the gastrointestinal tract.
Lesser amounts are found in the brain and the retina. Serotonin containing neurons have their cell bodies in the midline raphe nuclei of the brain stem and project to portions of the hypothalamus, the limbic system, the neocortex and the spinal cord. After release from serotonergic neurons, most of the released serotonin is recaptured by an active reuptake mechanism. The function of the antidepressant, Prozac is to inhibit this reuptake process, thereby, resulting in prolonged serotonin presence in the synaptic cleft. The function of serotonin is exerted upon its interaction with specific receptors.