Arches. Photo by Daniel Chia
HOPES: Huntington's Outreach Project for Education, at Stanford
Nov
15
2010

serotonin

A neurotransmitter that affects mood, appetite, and sleep. It is a powerful vasoconstrictor (constricts the blood vessels) and is found especially in the brain, blood serum, and gastric mucous membrane of mammals; also called 5-HT or 5-hydroxytryptamine.