[Hypothalamic neuropeptides implicated in the regulation of sleep/wakefulness states].
ABSTRACT Several neuropeptides, including galanin, orexin, melanin-concentrating hormone (MCH), urocortin-2, pituitary adenylate cyclase activating protein, and vasoactive intestinal peptide, have been implicated in the regulation of sleep/wakefulness states. In particular, neuropeptides produced in the hypothalamus, including galanin, orexin, and MCH, have been shown to play crucial roles. Galanin is localized to the prepotic area of the hypothalamus and is likely to be involved in the promotion and maintenance of sleep. MCH, which is expressed by neurons in the lateral hypothalamic area (LHA), seems to be implicated in rapid eye movement sleep regulation. Orexins are also localized in the LHA and have been established as one of the most important factors in the regulation of sleep/wakefulness states. A series of studies have suggested that orexin deficiency causes narcolepsy in humans and other mammalian species, highlighting the roles of this hypothalamic neuropeptide in the regulation of sleep and wakefulness. Studies of efferent and afferent systems of orexin-producing neurons have shown that the orexin neuronal system has close interactions with the systems that regulate emotion, energy homeostasis, reward, and arousal. These observations suggest that orexin neurons are involved in sensing the body's external and internal environments and regulate vigilance states accordingly.