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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]
- ^ a b c GRCh38: Ensembl release 89: ENSG00000161610 – Ensembl, May 2017
- ^ a b c GRCm38: Ensembl release 89: ENSMUSG00000045471 – Ensembl, May 2017
- ^ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
- ^ a b c Davis JF, Choi DL, Benoit SC (2011). "24. Orexigenic Hypothalamic Peptides Behavior and Feeding - 24.5 Orexin". In Preedy VR, Watson RR, Martin CR (eds.). Handbook of Behavior, Food and Nutrition. Springer. pp. 361–2. ISBN 9780387922713.
- ^ a b Stanford Center for Narcolepsy FAQ (retrieved 27-Mar-2012)
- ^ Sutcliffe JG, de Lecea L (October 2000). "The hypocretins: excitatory neuromodulatory peptides for multiple homeostatic systems, including sleep and feeding". Journal of Neuroscience Research. 62 (2): 161–168. doi:10.1002/1097-4547(20001015)62:2<161::AID-JNR1>3.0.CO;2-1. PMID 11020209. S2CID 33215844.
- ^ Scammell TE, Winrow CJ (2011-02-10). "Orexin receptors: pharmacology and therapeutic opportunities". Annual Review of Pharmacology and Toxicology. 51: 243–266. doi:10.1146/annurev-pharmtox-010510-100528. PMC 3058259. PMID 21034217.
- ^ a b Marcus JN, Elmquist JK (2006). "3. Orexin Projections and Localization of Orexin Receptors". In Nishino S, Sakurai T (eds.). The Orexin/Hypocretin System: Physiology and Pathophysiology. Springer. p. 195. ISBN 9781592599509.
- ^ a b Boss C, Roch C (August 2015). "Recent trends in orexin research--2010 to 2015". Bioorganic & Medicinal Chemistry Letters. 25 (15): 2875–2887. doi:10.1016/j.bmcl.2015.05.012. PMID 26045032.
- ^ Sakurai T, Amemiya A, Ishii M, Matsuzaki I, Chemelli RM, Tanaka H, et al. (February 1998). "Orexins and orexin receptors: a family of hypothalamic neuropeptides and G protein-coupled receptors that regulate feeding behavior". Cell. 92 (4): 573–585. doi:10.1016/S0092-8674(00)80949-6. PMID 9491897. S2CID 16294729.
- ^ de Lecea L, Kilduff TS, Peyron C, Gao X, Foye PE, Danielson PE, et al. (January 1998). "The hypocretins: hypothalamus-specific peptides with neuroexcitatory activity". Proceedings of the National Academy of Sciences of the United States of America. 95 (1): 322–327. Bibcode:1998PNAS...95..322D. doi:10.1073/pnas.95.1.322. PMC 18213. PMID 9419374.
- ^ Extance A (2022-11-07). "The brain chemicals that control what we enjoy". chemistryworld.com. Royal Society of Chemistry. Retrieved 2023-04-04.
- ^ Gotter AL, Webber AL, Coleman PJ, Renger JJ, Winrow CJ (July 2012). "International Union of Basic and Clinical Pharmacology. LXXXVI. Orexin receptor function, nomenclature and pharmacology". Pharmacological Reviews. 64 (3): 389–420. doi:10.1124/pr.111.005546. PMID 22759794. S2CID 2038246.