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Orexin
Neuropeptide that regulates arousal, wakefulness, and appetite. / From Wikipedia, the free encyclopedia
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Orexin (/ɒˈrɛksɪn/), also known as hypocretin, is a neuropeptide that regulates arousal, wakefulness, and appetite.[5] It exists in the forms of orexin-A and orexin-B. The most common form of narcolepsy, type 1, in which the individual experiences brief losses of muscle tone ("drop attacks" or cataplexy), is caused by a lack of orexin in the brain due to destruction of the cells that produce it.[6][7]
There are 50,000–80,000 orexin-producing neurons in the human brain,[8] located predominantly in the perifornical area and lateral hypothalamus.[5][9] They project widely throughout the central nervous system, regulating wakefulness, feeding, and other behaviours.[5] There are two types of orexin peptide and two types of orexin receptor.[10][9]
Orexin was discovered in 1998 almost simultaneously by two independent groups of researchers working on the rat brain.[11][12][13] One group named it orexin, from orexis, meaning "appetite" in Greek; the other group named it hypocretin, because it is produced in the hypothalamus and bears a weak resemblance to secretin, another peptide.[6] Officially, hypocretin (HCRT) is used to refer to the genes and transcripts, while orexin is used to refer to the encoded peptides.[14] There is considerable similarity between the orexin system in the rat brain and that in the human brain.[10]