[Orexin, sleep and appetite regulation: a review]

Since 1998, two research groups independently reported the discovery of two novel hypothalamic neuropeptides, called hypocretin-1 and hypocretin-2, respectively many studies have been carried out about their possible functions. One group named these new peptides orexins (A and B) after the Greek word for appetite, since they found that central administration of orexins potently increased food intake in rats. However hypocretins/ orexins are involved in various hypothalamic mechanisms, such as energy homeostasis, neuroendocrine functions, appetite and satiety regulation, vigilance and defence behaviour, sleep and wake regulation. Here is a review of the recent literature, showing some recent discoveries about the link between orexin system, sleep regulation and appetite regulation.