Intrinsic, light-independent, regional differences in photoreceptor cell degeneration in vitamin A-deficient rat retinas.

The retinas of retinol-deficient rats reared in darkness or cyclic light were examined to determine whether regional degeneration of photoreceptor cells was induced by environmental lighting or resulted from intrinsic differences between ocular hemispheres. Weanling male Sprague-Dawley rats were fed a retinol-adequate or retinol-deficient diet and were reared in either cyclic light or darkness through 29 weeks. The nasal retinal quadrants were examined by light microscopy and the number of photoreceptor nuclei was counted in a 630 micron segment beginning 200 micron from the optic nerve. Retinol-deficient rats reared in darkness for 29 weeks lost 24% of their photoreceptors in the inferior nasal quadrant but only 11% in the superior nasal quadrant. Deficient rats reared in cyclic light for 29 weeks lost 39% of their photoreceptor cells in the inferior nasal quadrant and only 16% in the superior nasal quadrant. Photoreceptor cells degenerated faster in the inferior nasal quadrant than in the superior nasal quadrant in darkness or cyclic light. These results indicate that regional differences in rate of photoreceptor cell loss in retinol-deficient rats are not induced by the lighting conditions but occur as a result of intrinsic differences between the ocular hemispheres.