Orexin-B

Orexin-B is a neuropeptide that plays a significant role in the regulation of sleep-wake cycle, appetite, and energy homeostasis. It is one of the two orexin peptides produced in the hypothalamus, the other being Orexin-A.

Structure and Function

Orexin-B is a 28-amino acid peptide that is produced in the lateral hypothalamus. It is encoded by the HCRT gene, which also encodes Orexin-A. Orexin-B is less potent than Orexin-A, but it has a longer half-life.

Orexin-B binds to the Orexin receptor 2 (OX2R), which is a G-protein coupled receptor. This binding triggers a series of intracellular events that lead to increased neuronal activity and wakefulness.

Role in Sleep-Wake Cycle

Orexin-B, along with Orexin-A, is crucial for the maintenance of wakefulness. It is involved in the promotion of REM sleep and the suppression of non-REM sleep. Deficiency in orexin peptides can lead to narcolepsy, a neurological disorder characterized by excessive daytime sleepiness and sudden attacks of sleep.

Role in Appetite and Energy Homeostasis

Orexin-B is involved in the regulation of feeding behavior and energy balance. It stimulates appetite and increases food intake. It also plays a role in the regulation of energy expenditure, contributing to the maintenance of body weight.

Clinical Significance

Alterations in the orexin system, including changes in the levels of Orexin-B, have been implicated in a number of disorders, including sleep disorders, obesity, and metabolic syndrome.