LIGHT–INDUCED RETINOPATHY: FROM THE NEWBORN TO THE ADULT RATS.

Abstract

Abstract: : Purpose:To characterize the light–induced retinopathy (LIR) from newborn to adulthood in Sprague–Dawley rats. Methods: Female Sprague–Dawley rats with their litters were maintained under bright cyclic light (10000 lux; 12D: 12L) from birth to postnatal day 14 (P₀– P₁₄), from P₁₄ to P₂₀ or from P₁₄ to P₂₈. Electroretinograms (ERGs) and retinal histology were obtained at one month of age. Results: After less than 6 days of light exposure, the mother’s ERGs were nearly abolished. In contrast, there was no evidence of LIR in the P₀– P₁₄ rats, while the ERGs were significantly attenuated in the P₁₄– P₂₀ (a–wave: 50%; b–wave: 65% of control amplitude; P<0.01) and even more in the P₁₄– P₂₈ group (a–wave: 16%; b–wave: 43% of control amplitude; P<0.01). Histological analysis of the mother’s retinas revealed the complete disappearance of the Outer Nuclear Layer (ONL) and Outer Plexiform Layer (OPL). In contrast, newborn rats exposed from P₀– P₁₄ showed little effect on ONL thickness, while exposure from P₁₄– P₂₈ led to a 60% decrease of the ONL thickness. In contrast the OPL was already 68% thinner than normal in P₀– P₁₄ group and further attenuated to 29 % of normal in the P₁₄– P₂₈ group. Conclusions: Perinatal exposure to an intense luminous environment does not yield the severe retinopathy observed in adult rats subjected to an identical environmental insult. Our demonstration of the lack of an adult–like retinopathy even at an age when the eyelids are open (P₁₄– P₂₈ group) rules out the protective effect of the eyelids as an explanation for the near absence of an LIR in the P₀– P₁₄ group. Our results would thus support the claim of a relative perinatal retinal immunity to environmental toxic stresses previously shown to exist in our oxygen–induced retinopathy model. Funded by CIHR and Réseau Vision.

Keywords: radiation damage: light/UV • electroretinography: non–clinical • retina: distal (photoreceptors, horizontal cells, bipolar cells)