The Kinetic of Light–induced Retinopathy in Adult and Juvenile Rats

Abstract

Abstract: : Purpose: We have previously shown that prior to eyelid opening, the retina of newborn Sprague Dawley (SD) rats was more resistant than adult retina to bright light exposure. The purpose of this study was to further explore the extent of this neonatal protection. Methods: Juvenile SD rats were exposed to a bright luminous environment (10000 lux; 12 hours/day) from P₁₄–P₁₅, P₁₄–P₁₇, P₁₄–P₂₀, P₁₄–P₂₈ or P₂₈–P₃₄. Results were compared with those obtained from adult SD rats exposed to the same light intensity for 1, 3, 6 or 14 consecutive days. Electroretinograms (ERGs) and retinal histology were performed one month after the end of light exposure. Results: For all rats, we characterized the time course of light damage using a sigmoidal curve. Analysis of the latter revealed that half of maximal light–induced damages, as measured with the scotopic ERG, occurred after 3.24 ± 1.01 days of exposure in adult rats and 5.75 ± 0.33 days in juveniles, the difference between the two being significant (p<0.05). A similar analysis using the photopic ERGs also revealed a significant difference (P<0.05) between adults (3.60 ± 0.88 days) and juveniles (6.25 ± 0.12 days). Of particular interest, the scotopic and photopic ERG attenuation exhibited by juvenile rats exposed for more than 14 days was equivalent to that of adult rats exposed for less than 3 days. The latter was also verified histologically where juvenile retinas exposed for 14 days led to similar thinning of the outer nuclear layer as adult retinas exposed for 3 days (5 vs 3 rows of photoreceptor nuclei). Conclusions: Like adults, juvenile rats exposed to a bright light environment will eventually develop a retinopathy. However, the exposure must occur following eyelid opening and its duration must significantly exceed that necessary to induce a similar retinopathy in adults. Of interest, the photopic (cone) system appears to be slightly (but not significantly) more resistant than the scotopic (rod) system to intense light damage. Our data suggest that the underlying mechanisms leading to light–induced retinopathy in juveniles versus adult rats may be different. Supported by CIHR and Réseau Vision du FRSQ.

Keywords: radiation damage: light/UV • photoreceptors • electroretinography: non-clinical