Orexin A (OXA, hypocretin-1) is a hypothalamic neuropeptide regulating the feeding behavior. Central administration of orexin A to rats stimulated food consumption in a dose-dependent manner. The effect persisted at 4 h after injection, as orexin A seems to be resistant to peptidases. Orexin A specifically binds a G protein-coupled receptor, OX₁R (IC₅₀ = 20 nM to displace 50 % of radiolabeled orexin A bound to this receptor). Orexin A produced in the amygdala induces wakefulness and plays a role in the induction of human emotions. Narcolepsy has been associated with orexin deficiency. The peptide also corresponds to bovine, canine, ovine, and porcine orexin A.