Light-induced c- fos mRNA expression in the suprachiasmatic nucleus and the retina of C3H/HeN mice

Abstract

Light-induced expression of c- fos mRNA was studied over a circadian period (∼ 24 h) in C3H/HeN mice maintained in constant dark. This mouse strain expresses an rd mutation (retinal degeneration) which does not affect light-induced phase shifts of circadian rhythms. c -fos mRNA expression in the retina and the suprachiasmatic nucleus (SCN) after a light pulse (300 lux) was determined by in-situ hybridization autoradiography using a 35S-labeled c- fos riboprobe. Light induced the expression of c- fos mRNA in retino-recipient areas of the SCN. This response was dependent on the circadian time (CT) and was observed only during the subjective night (CT14–CT22) and early subjective day (CT2). However, the period of photosensitivity for c- fos induction extended 1 h over the period of photosensitivity for phase shifts in circadian behavior. In the retina of C3H/HeN mice, light-induced c -fos mRNA expression was observed in a small number of cells in the ganglion cell layer (∼ 0.2%) which may represent ganglion cells projecting to the SCN. A dependence of c -fos expression with the circadian time was observed in retinal ganglion cells, suggesting that retinal photosensitivity may also be controlled by a circadian oscillator. In conclusion, we demonstrated light-induced expression of the immediate early gene c -fos mRNA in both the retina and SCN of C3H/HeN mice expressing the rd mutation.