Orexin A (human, rat, mouse) is an endogenous agonist at orexin receptors with Ki values of 20 and 38 nM for OX1 and OX2 receptors respectively. Orexin A stimulates feeding following central administration and is involved in other hypothalamic functions, influencing wakefulness by affecting dopamine, norepinephrine, histamine and acetylcholine systems to stabilize sleep cycles. An absence of orexin A causes narcolepsy, and in animal models, it can alleviate cognitive deficits caused by loss of sleep.
