[Page 3074]Known by its biochemical name 5-hydroxytryptamine (5-HT), serotonin is a monoamine neurotransmitter (i.e., a chemical substance that transmits nerve impulses across a synapse) derived from the amino acid l-tryptophan. Primarily clustered within the gastrointestinal tract of humans and animals, 5-HT is found in smaller concentrations spread across the nine ridges of the dorsal and median raphe nuclei located within the brain stem. Governed by the diffuse modulatory systems of the brain, 5-HT is released and slowly diffused across the extracellular fluid of the cell, as opposed to the relatively close confines of the synaptic cleft, thereby remaining outside the cell for a longer period of time. Acting as a neuromodulator, increases or decreases in the availability of 5-HT affect the functionality served by the ...