Orexin B is a hypothalamic neuropeptide that regulates feeding behavior, wakefulness, and behavior under situations of high motivational relevance. It is an agonist of orexin (OX) receptors with IC50 values of 420 and 36 nM for human recombinant OX1 and OX2 receptors, respectively, expressed in CHO cells. It induces transient increases in intracellular calcium in CHO cells stably expressing OX1 and OX2 (EC50s = 2,500 and 60 nM, respectively) and in primary rat ventral tegmental area (VTA) dopaminergic neurons. Orexin B stimulates arachidonic acid release from CHO cells expressing human recombinant OX1 (EC50 = 4.17 nM). It also stimulates food intake in freely feeding mice and goldfish when administered at intracerebroventricular doses of 30 nmol and 10 ng/g, respectively.
