Orexin-A

Also known as: Hypocretin-1

Orexin-A (hypocretin-1) is a 33-amino-acid hypothalamic neuropeptide that exerts its effects primarily through binding to two G-protein-coupled receptors, OX1 and OX2. Activation of OX1 receptors is associated with increased intracellular calcium via phospholipase C signaling, while OX2 receptor activation couples to both calcium and cyclic AMP pathways. This dual signaling promotes neuronal excitation in wake-promoting brain regions, including the locus coeruleus, tuberomammillary nucleus, and raphe nuclei, thereby stabilizing arousal and suppressing rapid eye movement (REM) sleep. Preclinical research, including a 2006 study, has demonstrated that central administration of orexin-A in rodents significantly increases wakefulness and reduces both non-REM and REM sleep durations. These effects are dose-dependent and reversible with selective orexin receptor antagonists. Additional studies have linked orexin-A to the regulation of feeding behavior, energy homeostasis, and reward processing, though its primary role remains the maintenance of arousal and vigilance states. Clinically, orexin-A deficiency is a hallmark of narcolepsy type 1, characterized by excessive daytime sleepiness and cataplexy. While synthetic orexin-A analogs and receptor agonists are under investigation for treating narcolepsy and other hypersomnias, orexin-A itself remains in preclinical stages due to challenges with blood-brain barrier permeability and metabolic stability. For research purposes only — not medical advice.

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