Identification of Melatonin Receptors in the Rat Suprachiasmatic 2.2 Cell Line: A Valid Model for Circadian Rhythm Studies
Luke, Kimberly A.
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Circadian rhythms are expressed by organisms across all Kingdoms of life. In vertebrates, melatonin is the neurohormone that marks periods of light and darkness. Melatonin has been shown to not only influence periods of rest and activity, but also to regulate other physiological functions such as reproduction and circulation. The suprachiasmatic nucleus (SCN) in the anterior hypothalamus of the brain has been shown to be the site of the master circadian clock. This area also contains a high density of putative melatonin binding sites as well expression of melatonin receptors, confirmed by pharmacological identification and characterization. Three melatonin receptors have currently been identified through various methods. Both the mt 1 and MT 2 receptors have been cloned from mammalian tissues, and pharmacologically characterized. The MT 3 receptor has been identified through pharmacological means, but has not yet been cloned. The study of melatonin receptor expression and function in native tissues such as the SCN is hampered by the great amount of tissue needed. The development of the SCN 2.2 cell line has the potential to become a very useful model in facilitating research of the role of melatonin in the circadian timing system. This study provides preliminary support for the use of the SCN 2.2 cell line as a viable model for circadian rhythm research, as well as elucidating the roles of melatonin signaling in the circadian timing system.