LIGHT-INDUCED RETINOPATHY IN THE ALBINO-RAT IN LONG-TERM STUDIES - ANIMMUNOHISTOCHEMICAL AND QUANTITATIVE APPROACH

Retinas from male Wistar rats which were housed during a long-term dru g safety study at short, medium and long distance from a fluorescent l ight source were examined. Retinal atrophy was pronounced in the centr al retina of rats housed closest to the light source, and was characte rized by a loss of photoreceptor cells and of S-antigen immunoreactivi ty in the outer nuclear layer (ONL), absence of synaptophysin immunore activity in the outer plexiform layer (OPL), decrease of the number of nuclei in the inner nuclear layer (INL), astrocytic proliferation, an d Muller cell activation. The peripheral retina of these rats had a la minated architecture, although the number of photoreceptor cells and n uclei in the INL was reduced. Retinas from rats housed a medium distan ce from the light source did not have any apparent histological or imm unohistochemical changes, except for a lower number of photoreceptor c ells and nuclei in the INL. The rats housed a long distance from the l ight source had the highest number of nuclei in the ONL and INL of the central and peripheral retina, and were used as control group. Our da ta indicate that retinal atrophy occurs in male Wistar rats maintained under light conditions currently used in long-term toxicity studies, and suggest that photoreceptor cell loss is followed by trans-synaptic anterograde degeneration of neurons in the INL, astrocytic proliferat ion and Muller cell activation.