The suprachiasmatic nucleus or nuclei (SCN) is a small region of the brain in the hypothalamus, situated directly above the optic chiasm. It is the principal circadian pacemaker in mammals, responsible for generating circadian rhythms.[1][2] Reception of light inputs from photosensitive retinal ganglion cells allow it to coordinate the subordinate cellular clocks of the body and entrain to the environment.[1][3] The neuronal and hormonal activities it generates regulate many different body functions in an approximately 24-hour cycle.
The idea that the SCN is the main circadian pacemaker in mammals was proposed by Robert Moore, who conducted experiments using radioactive amino acids to find where the termination of the retinohypothalamic projection occurs in rodents.[4][5] Early lesioning experiments in mouse, guinea pig, cat, and opossum established how removal of the SCN results in ablation of circadian rhythm in mammals.[4]
Moreover, the SCN interacts with many other regions of the brain. It contains several cell types and several different peptides (including vasopressin and vasoactive intestinal peptide) and neurotransmitters.
Disruptions or damage to the SCN has been associated with different mood disorders and sleep disorders, suggesting the significance of the SCN in regulating circadian timing[6]
^ abHastings, Michael H.; Maywood, Elizabeth S.; Brancaccio, Marco (August 2018). "Generation of circadian rhythms in the suprachiasmatic nucleus". Nature Reviews Neuroscience. 19 (8): 453–469. doi:10.1038/s41583-018-0026-z. ISSN 1471-0048. PMID 29934559. S2CID 256745076.
^Hastings, MH; Maywood, ES; Brancaccio, M (11 March 2019). "The Mammalian Circadian Timing System and the Suprachiasmatic Nucleus as Its Pacemaker". Biology. 8 (1). doi:10.3390/biology8010013. PMC 6466121. PMID 30862123.
^Weaver, David R.; Emery, Patrick (2013-01-01), Squire, Larry R.; Berg, Darwin; Bloom, Floyd E.; du Lac, Sascha (eds.), "Chapter 39 - Circadian Timekeeping", Fundamental Neuroscience (Fourth Edition), San Diego: Academic Press, pp. 819–845, ISBN 978-0-12-385870-2, retrieved 2023-04-25
^ abKlein, David C.; Moore, Robert Y.; Reppert, Steven M. (1991). Suprachiasmatic Nucleus: The Mind's Clock. Oxford University Press. ISBN 978-0-19-506250-2.
^Moore, Robert Y. (2013-01-01), Gillette, Martha U. (ed.), "Chapter One - The Suprachiasmatic Nucleus and the Circadian Timing System", Progress in Molecular Biology and Translational Science, Chronobiology: Biological Timing in Health and Disease, 119, Academic Press: 1–28, doi:10.1016/B978-0-12-396971-2.00001-4, PMID 23899592, retrieved 2023-04-25
^Ma, Melinda A.; Morrison, Elizabeth H. (2023), "Neuroanatomy, Nucleus Suprachiasmatic", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 31536270, retrieved 2023-04-25
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