SR-5B, also designated 5-hydroxytryptamine (serotonin) receptor 5B (5-HT5B) and G protein-coupled receptor 134 (GPR134), is a receptor for the monoamine ligand serotonin (5-hydroxytryptamine, 5-HT). Serotonin is a neurotransmitter derived from serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract. Serotonin actions are mediated by receptors that influence the biochemistry of depression, anxiety, sexuality and appetite. Rat SR-5B is present in serotonergic neurons in dorsal raphe (DR) and central superior nucleus (CS, median raphe nucleus). DR cell bodies showing SR-5B mRNA expression are abundant in the medial portions of the nucleus. CS coexpression of SR-5B receptor mRNA with serotonin transporter mRNA is high in the intermediate portions of the nucleus. Serotonin receptors include SR-1-7 (5-HT1-7). Subtypes within the SR-1 group include SR-1A, -1B, -1D, -1E and -1F. Subtypes within the SR-2 group include SR-2A, -2B and -2C. Subtypes within the SR-5 group include SR-5A and -5B. SR receptors can couple to G proteins that act on either adenylate cyclase or phospholipase C (PLC). The SR-3 class of receptors are ion channels.