Light treatment enhances photoreceptor survival in dystrophic retinas of Royal College of Surgeons rats

PURPOSE. TO determine whether treatment with bright light elicits a protect ive response that enhances photoreceptor survival in Royal College of Surge ons (RCS) rats with inherited retinal degeneration. METHODS. RCS rats Were illuminated for 10 to 12 hours with 130 foot-candles (fc) of white or green tight. Untreated littermates that were kept under l ow cyclic light levels were used as control subjects. Photoreceptor surviva l was determined by quantitative analysis of photoreceptor nuclei and ultra structural assessment of cellular organization. Basic fibroblast growth fac tor (bFGF) and ciliary neurotrophic factor (CNTF) gene expression Were dete rmined at the mRNA and protein levels. RESULTS. Treatments of RCS rats with a single dose of bright light on postn atal day 23 (P23) greatly enhanced photoreceptor survival. Ultrastructural analysis revealed intact inner segments in light-treated retinas, whereas i n untreated retinas only remnants of inner segments were observed. By P42, numerous viable nuclei were counted in the posterior retina of light-treate d rats, whereas most of the remaining nuclei in untreated RCS rat retinas w ere highly pyknotic. At 2.5 days after treatment with a single dose of brig ht light, bFGF gene expression was significantly higher than in untreated R CS rat retinas. By P42, bFGF protein levels were still significantly higher in the treated retinas. CONCLUSIONS. Exogenous bFGF has been shown to promote photoreceptor surviva l in the RCS rat retina. Thus, the increased bFGF expression that was measu red in the light-treated RCS rat retinas may be a protective response to li ght stress, which supports the observed rescue of photoreceptors in light-t reated RCS rat retinas.