Definition: Serotonin is a type of neurotransmitter that is found mainly in the central nervous system and the gastrointestinal (GI) tract. Much of the serotonin is located in the GI tract where it is used to regulate digestion. In the CNS, serotonin helps regulate mood, sleep, appetite, learning and memory. Learn more about serotonin.
Image courtesy Piotr Bizior