title: Circadian photic regulation of melatonin receptor density in rat suprachiasmatic nuclei: comparison with light induction of fos-related protein.
abstract: High-affinity melatonin receptors are present in rat suprachiasmatic nuclei (SCN), and their density exhibits a daily rhythm regulated by the light/dark cycle. In this study we demonstrate that the light regulation of these receptors depends on a circadian mechanism. Pinealectomized rats kept in constant darkness were subjected to 1-hr light pulses delivered across the circadian cycle. The density of melatonin receptors was significantly increased when photic exposure was performed during subjective night, and not different from control animals kept in darkness when the light pulse was applied during subjective day. The protein product (Fos) of the immediate early gene c-fos studied in the same paradigm showed globally the same circadian sensitivity phase. These results clearly show that, although the rhythmic appearance of melatonin receptor density in SCN follows and is directly regulated by the standard light/dark cycle, this light regulation is not passive. As is the case with Fos-like protein, it is only during a precise phase of the circadian cycle that light is able to regulate the density of melatonin receptors in SCN.
authors.affiliation: "Neurobiologie des Fonctions Rhythmiques et Saisonnieres", Universite Louis Pasteur, Strasbourg, France.
authors.forename: M
authors.initials: M
authors.lastname: Masson-Pevet
authors.forename: L
authors.initials: L
authors.lastname: Bianchi
authors.forename: P
authors.initials: P
authors.lastname: Pevet
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D003624:Darkness; D007150:Immunohistochemistry; D008027:Light; D008297:Male; D010870:Pineal Gland / Q000502:physiology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011956:Receptors, Cell Surface / Q000378:metabolism* / Q000528:radiation effects*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism* / Q000528:radiation effects*; D044094:Receptors, Melatonin; D013493:Suprachiasmatic Nucleus / Q000378:metabolism* / Q000528:radiation effects*
chemical_list: D016760:Proto-Oncogene Proteins c-fos; D011956:Receptors, Cell Surface; D018160:Receptors, Cytoplasmic and Nuclear; D044094:Receptors, Melatonin