LIGHT-INDUCED C-FOS MESSENGER-RNA EXPRESSION IN THE SUPRACHIASMATIC NUCLEUS AND THE RETINA OF C3H HEN MICE/

Light-induced expression of c-fos mRNA was studied over a circadian pe riod (similar to 24 h) in C3H/HeN mice maintained in constant dark. Th is 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) a fter a light pulse (300 lux) was determined by in-situ hybridization a utoradiography using a S-35-labeled c-fos riboprobe. Light induced the expression of c-Sos mRNA in retino-recipient areas of the SCN. This r esponse 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 extende d 1 h over the period of photosensitivity for phase shifts in circadia n behavior. In the retina of C3H/HeN mice, light-induced c-fos mRNA ex pression was observed in a small number of cells in the ganglion cell layer (similar to 0.2%) which may represent ganglion cells projecting to the SCN. A dependence of c-fos expression with the circadian time w as observed in retinal ganglion cells, suggesting that retinal photose nsitivity may also be controlled by a circadian oscillator. In conclus ion, we demonstrated light-induced expression of the immediate early g ene c-fas mRNA in both the retina and SCN of C3H/HeN mice expressing t he rd mutation.