G-protein coupled receptor for 5-hydroxytryptamine (serotonin). Also functions as a receptor for ergot alkaloid derivatives, various anxiolytic and antidepressant drugs and other psychoactive substances, such as 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, such as adenylate cyclase. Signaling inhibits adenylate cyclase activity. Arrestin family members inhibit signaling via G proteins and mediate activation of alternative signaling pathways. Regulates the release of 5-hydroxytryptamine, dopamine and acetylcholine in the brain, and thereby affects neural activity, nociceptive processing, pain perception, mood and behavior. Besides, plays a role in vasoconstriction of cerebral arteries. Homodimer. Heterodimer with HTR1D. Detected in cerebral artery smooth muscle cells (at protein level). Detected in brain cortex, striatum, amygdala, medulla, hippocampus, caudate nucleus and putamen. Ligands are bound in a hydrophobic pocket formed by the transmembrane helices. Phosphorylated. Desensitization of the receptor may be mediated by its phosphorylation. Palmitoylated. A residue in the 7th transmembrane region (Thr-355 in human, 'Asn-351' in mouse and rat) is important for species-specific sensitivity to various agonists. Belongs to the G-protein coupled receptor 1 family.