This is one of the several different receptors for 5-hydroxytryptamine (serotonin), a biogenic hormone that functions as a neurotransmitter, a hormone, and a mitogen. The activity of this receptor is mediated by G proteins that stimulate adenylate cyclase. Isoform A and isoform B appear to be expressed at higher levels. Isoform A is the predominant isoform in spleen, caudate and hippocampus. Isoform B is expressed at lower levels. Isoform D is a minor isoform in terms of expression. Belongs to the G-protein coupled receptor 1 family.