Expression of c-fos and c-jun in rat retina following protracted illumination

Illumination produces degeneration of outer photoreceptor segments, a phenomenon that may be reversed after a period of darkness. Neuronal expression of the immediate early genes (IEGs) c-fos and c-jun, both recognized as proto-oncogenes, has been reported after stimulation of different regions in the central nervous system (CNS). We performed a sequential study on Fos and Jun immunoreactivity to investigate the role of IEGs following 8 days of continuous illumination in 30-35-day-old Wistar rats. Retinas were fixed by perfusion in 4% paraformaldehyde, after a period of illumination followed by 0, 2, 7, 10 and 20 days in total darkness. Cryostat sections were immunocytochemically stained using antibodies to Fos and Jun. Fos and Jun immunoreactivities were detected in all photoreceptors evaluated, peaking in nuclei of rats kept in total darkness for 2 days, and becoming negative as from 7 days. Increases in c-fos and c-jun products during the darkness period may play a role in triggering molecular events participating in plastic changes in photoreceptors and/or in the protection for oxidative damage cause by free radicals induced by light irradiation.