title: Photic and circadian regulation of c-fos gene expression in the hamster suprachiasmatic nucleus.
abstract: Photic information entrains a circadian pacemaker located in the suprachiasmatic nucleus (SCN) of the mammalian hypothalamus to environmental light/dark cycles. To determine whether light regulates c-fos gene expression in the SCN, we have measured c-fos mRNA levels in the SCN of the golden hamster. We report that, during the subjective night, light causes a rapid increase in levels of c-fos mRNA in the SCN. Light pulses of 5 min duration are sufficient to induce c-fos mRNA, and the highest mRNA levels occur 30 min following the onset of light. The minimum level of illumination required to induce an increase in c-fos mRNA is indistinguishable from the minimum irradiance that produces a phase shift in the hamster's circadian rhythm of activity. In addition, the induction of c-fos mRNA in the SCN by light is itself under circadian regulation. Light induction of c-fos mRNA occurs only during the subjective night, at circadian times when photic phase shifting of activity occurs. Taken together, these data suggest that c-fos may be a molecular component of the photic pathway for entrainment of mammalian circadian rhythms.
authors.affiliation: Institute of Neuroscience, Northwestern University, Evanston, Illinois 60208.
authors.forename: J M
authors.initials: JM
authors.lastname: Kornhauser
authors.forename: D E
authors.initials: DE
authors.lastname: Nelson
authors.forename: K E
authors.initials: KE
authors.lastname: Mayo
authors.forename: J S
authors.initials: JS
authors.lastname: Takahashi
mesh_terms: D000818:Animals; D002940:Circadian Rhythm; D006224:Cricetinae; D005786:Gene Expression Regulation; D008027:Light; D008297:Male; D008647:Mesocricetus; D009693:Nucleic Acid Hybridization; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016760:Proto-Oncogene Proteins c-fos; D011519:Proto-Oncogenes; D012333:RNA, Messenger / Q000096:biosynthesis; D013493:Suprachiasmatic Nucleus / Q000378:metabolism*; D013997:Time Factors
chemical_list: D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D012333:RNA, Messenger