orexin

(hypocretin)

A neuropeptide that regulates arousal, wakefulness, and appetite.
Produced by a cluster of orexin-producing neurons in the hypothalamus that encircles the fornix and extends across the lateral hypothalamus, projecting widely throughout the central nervous system. Orexin's circuits originate from the hypothalamus and project to various brain areas, including the locus coeruleus, thalamus, basal forebrain, tuberomammillary nucleus, cortex and others.

(Functions)
• Promotes wakefulness.
• Stimulates food intake (appetite), craving for food.
• Regulates brown adipose tissue activity via the sympathetic nervous system to enhance energy expenditure. Orexin-producing neurons have been shown to be inhibited by leptin but to be activated by ghrelin and hypoglycemia.
- - leptin: Inhibits hunger and regulate energy balance as a long-term factor. Produced by adipocytes.
- - ghrelin: Strongly promotes food intake just before an expected meal as a short-term factor. Secreted by the stomach.

(Types)
• orexin-A (hypocretin-1): Associated with happiness. It can be used for treatment of depression in the future.
• orexin-B (hypocretin-2)

(Diseases caused by orexin system dysfunction)
• type 1 narcolepsy: Brief losses of muscle tone ("drop attacks" or cataplexy), caused by a lack of orexin in the brain due to destruction of the orexin-producing neurons.
• takotsubo cardiomyopathy: A non-ischemic cardiomyopathy with a sudden temporary weakening of the myocardium. It usually appears after a significant stressor, either physical or emotional. Orexins are cardiovascular neuropeptides, and lack of orexin may influence various pathophysiological mechanisms of cardiovascular diseases.
• ESSENCE (early symptomatic syndromes eliciting neurodevelopmental clinical examinations)

Orexin antagonist inhibits the effect of orexin by acting as a receptor antagonist of one or both of the orexin receptors, OX1 and OX2.
(Orexin receptor antagonists to treat insomnia)
• suvorexant
• lemborexant
• daridorexant