Background：

G-protein coupled receptor for 5-hydroxytryptamine. Also functions as a receptor for various drugs and psychoactive substances， including mescaline， psilocybin， 1-(2，5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and lysergic acid diethylamide (LSD). Ligand binding causes a conformation change that triggers signaling via guanine nucleotide-binding proteins (G proteins) and modulates the activity of down-stream effectors. Beta-arrestin family members inhibit signaling via G proteins and mediate activation of alternative signaling pathways. Signaling activates phospholipase C and a phosphatidylinositol-calcium second messenger system that modulates the activity of phosphatidylinositol 3-kinase and promotes the release of Ca2+ ions from intracellular stores. Affects neural activity， perception， cognition and mood. Plays a role in the regulation of behavior， including responses to anxiogenic situations and psychoactive substances. Plays a role in intestinal smooth muscle contraction， and may play