Continuous exposure to bright light upregulates bFGF and CNTF expression in the rat retina

Purpose. To examine mRNA expression of neurotrophic factors in the retina after exposure to bright light. Methods. Male adult Sprague-Dawley rats were exposed to light of 115-130 ft-c. Retinas were collected after 1, 2, 4 or 7 days of exposure. Northern blot analysis was performed to determine mRNA levels for the following factors and their receptors: basic fibroblast growth factor (bFGF), ciliary neurotrophic factor (CNTF), acidic fibroblast growth factor (aFGF), brain-derived neurotrophic factor (BDNF), insulinlike growth factor 1 (IGF-1) and glial fibrillary acidic protein (GFAP). Expression of bFGF, CNTF and GFAP was localized by in situ hybridization. Results. Exposure to light of 115-130 ft-c resulted in a substantial increase in bFGF and CNTF expression that persisted during the entire 7-day period of exposure. The peak expression of bFGF was almost 9-fold at day 2. The increase in CNTF mRNA reached a maximum of 6-fold at day 4. A small increase (50%) in IGF-1 mRNA was also seen at day 4. Among the receptors, an elevation of 3-fold in FGF receptor 1 (FGFR-1) was observed at day 2. There was also a small increase (70%) in IGF-1 receptor (IGF-IR) at day 2. In addition, the expression of GFAP showed a rapid elevation of about 8-fold by day 1 and 9-fold by day 2, and 18-fold by day 4. There was, however, no significant alteration in the expression of aFGF and BDNF In situ hybridizations showed that the elevation of bFGF, CNTF and GFAP occurred across the entire retina with especially prominent increases over specific layers for each gene. Conclusions. Continuous exposure to bright light upregulates bFGF, CNTF FGFR-1 and GFAP expression in the rat retina. The pattern of induced expression closely resembles that induced by mechanical injury, implying a common underlying mechanism.