Orexin B (also known as hypocretin-2) is an excitatory neuropeptide produced in the hypothalamus that works alongside Orexin A to promote arousal, maintain wakefulness, and regulate feeding behaviors. Together, these critical peptides are essential for normal sleep-wake cycles and overall energy homeostasis. [1, 2, 3, 4, 5]

Key Characteristics and Function

• Origins: Both Orexin A and Orexin B are created by cleaving a single precursor protein called prepro-orexin. While Orexin A is a 33-amino-acid peptide with structural disulfide bonds, Orexin B is a 28-amino-acid linear peptide. [1, 2]

• Receptors: Orexin B primarily binds to the OX2 receptor (with which it has high affinity) and to a lesser extent the OX1 receptor. Orexin A binds equally to both. [1]

• Wakefulness: The orexin system acts as an energetic "on-switch" for the brain. It stimulates the neurons responsible for keeping you awake and alert. [1, 2, 3, 4]

• Regulation: Beyond sleep, orexins modulate metabolism, reward-seeking behaviors, and stress responses. [1, 2]

Medical and Neurological Relevance

• Narcolepsy: The degeneration of orexin-producing neurons leads to narcolepsy, a disorder characterized by excessive daytime sleepiness and sudden losses of muscle tone (cataplexy). [1, 2, 3, 4, 5]

• Insomnia: Because orexins drive arousal, pharmaceutical companies target this system to treat insomnia. Drugs like dual orexin receptor antagonists (DORAs) block orexin receptors to artificially promote sleep. [1]

• Parkinson's Disease: Emerging research suggests Orexin B may help excite nigral dopaminergic neurons, potentially offering neuroprotective effects and alleviating certain motor symptoms. [1, 2]