Optimising the structure and function of the adult P23H-3 retina by light management in the juvenile and adult

This study tests the potential of light restriction to optimise retinal structure and function in adulthood, using the P23H-3 rhodopsin-mutant transgenic rat as a model. P23H-3 rats were reared in scotopic (5 lux) or mesopic (40–60 lux) cyclic (12 h/12 h light/dark) light. A further 2 groups were reared in one of these light conditions to P(postnatal day)30, and then were transferred to the other condition. Retinae were examined at P30-365. Rod and cone function were assessed by the dark-adapted flash electroretinogram. The rate of photoreceptor death was assessed with the TUNEL technique, and photoreceptor survival by the thickness of the outer nuclear layer (ONL). Photoreceptor structural changes were assessed by immunohistochemistry. Mesopic rearing severely reduced the number, function and outer segment (OS) length of photoreceptors. Light restriction in the adult (achieved by moving mesopic-reared animals to scotopic conditions at P30) slowed photoreceptor death, induced recovery of the ERG and of OS length in survivors, resulting in an adult retina that matched the scotopic-reared in function, photoreceptor survival (stability) and structure. Conversely, light exposure in the adult (achieved by moving scotopic-reared animals to mesopic conditions at P30) accelerated photoreceptor death, shortened OSs and reduced the ERG, resulting in a retina that was as damaged and dysfunctional as a mesopic-reared retina, and showed greater photoreceptor instability. Present observations suggest, that the stability and function of adult photoreceptors are determined by both early and adult ambient light experience. Light restriction in the adult was effective in inducing the self-repair of photoreceptors, and the recovery of their function and stability. Light restriction in the juvenile (before P30) improved early photoreceptor survival but made adult photoreceptors vulnerable to brighter light experienced in adulthood. For comparable human dystrophies, these results suggest that light restriction begun after retinal maturation may be effective in optimising the structure, function and stability of the adult retina.