Evidence of cell loss from the rat retina during senescence

Abstract

In order to determine whether neuronal cell death in the retina accompanies senescence, retinas from pigmented ACI rats of various ages were analysed for changes in dimensions, cell densities, DNA content, and rhodopsin levels. Between the ages of 4 and 30 months, there were significant declines in the densities of nuclei in all three nuclear layers of the retina. Over this age span, nuclear density in the outer nuclear layer (ONL) declined by 32–41 %, depending on the region of the retina examined, while inner nuclear layer (INL) nuclear density decreased by 25–34 %. Over the same age range, the nuclear density in the ganglion cell layer (GCL) declined by 25–28 %. The eye increased in size over the 4–30 month age span, particularly between 4 and 12 months. The retinal stretching that resulted from this growth could only partially account for the age-related decline in retinal cell densities. Depending on the region of the retina examined, decreases in nuclear density of 17–26 % for the ONL, 9–17 % for the INL, and 16–20 % for the GCL were apparently due to cell death. Measurements of retinal DNA content support the conclusion that significant cell loss from the retina occurs during senescence; between 4 and 30 months of age retinal DNA content decreased by about 13 %. Age-related changes in retinal rhodopsin content did not parallel apparent changes in photoreceptor number. Between 4 and 11 months of age, rhodopsin levels rose by about 10 %, and then remained constant up to 26 months. Over this same age span, there was an apparent decrease in photoreceptor number of about 15 %. These findings suggest that the amount of rhodopsin per photoreceptor cell increased by up to 25 % between 4 and 26 months of age. Beyond 26 months, rhodopsin levels fell in parallel with photoreceptor cell numbers.