Serotonin in the Nervous System: Few Neurons Regulating Many Functions

Serotonin is synthesized from tryptophan in small groups of neurons within the central nervous system. These neurons, however, branch profusely and innervate all the nervous system, where, by releasing serotonin in different manners, they regulate a myriad of functions, including many behaviors. This chapter reviews the main functions of serotonin in the nervous system of invertebrates and vertebrates, showing that many of these have been conserved throughout evolution. It also summarizes the current knowledge about the mechanisms that control and regulate serotonin secretion from different compartments of the same neurons, evidencing their differences, which enable small numbers of neurons to display a wide variety of functions, including the regulation of our mood states.