Photic Regulation of Gene Expression and Cellular Activity in the SCN

摘要

On the basis of their putative role in the process of stimulus-transcriptioncoupling, immediate-early genes, such as c-fos and c-jun, have been implicated as important components of signal transduction programs by which environmental stimuli regulate long-term cellular events. To explore the possibility that immediate-early genes may play a similar role in the transduction of light signals mediating the entrainment of the circadian pacemaker in the suprachiasmatic nucleus (SCN), immediate-early gene expression in the SCN was examined in vivo and in vitro for evidence of circadian regulation by photic stimuli. Immunocytochemical and molecular analyses demonstrate that light has an inductive effect on the expression of c-fos mRNA and fos protein in the SCN, but only at critical times during the circadian cycle when light is capable of modulating the period of the circadian pacemaker and mediating its entrainment. In addition, this circadian-dependent induction of c-fos expression in the SCN by light was mainly localized in the retinorecipient or ventrolateral subfield of the nucleus within a substantial portion of the GRP-containing neurons located in this region. These data provide evidence for the correlative relations between the induction of c-fos gene expression in the SCN and the modulation of the SCN circadian pacemaker by light and suggest that immediate-early genes may be components of the signal transduction cascade by which light entrains circadian rhythms.