Effects of acute and chronic stress on the neural retina of young, mid-age, and aged Fischer-344 rats.

Male Fischer-344 rats at 5 (young), 11 (mid-age) and 18 (aged) months of age were exposed either to a single, 1-h period of acute stress, or to daily 4-h periods (chronic) of escapable footshock stress for 6 months, and subsequently allowed a one month interval without stress. The influence of age and exposure to stress on the neural retina was examined by histopathologic and morphometric methods. Age changes in the retina of unstressed control animals included reduction in the thickness of the outer nuclear layer (ONL; photoreceptor nuclei) and of the retina, especially in the peripheral areas. The superior hemisphere was more severely affected than the inferior retina. Exposure to acute stress did not influence retinal histopathology. However, in mid-age and aged rats exposed to chronic stress, the ONL and retinal thicknesses were reduced significantly. Our results indicate for the first time that exposure of rats to chronic stress produces changes in retinal morphology that are associated commonly with aging, such as extensive loss of peripheral photoreceptor cells. In addition, the results show that the effects of chronic stress exposure are greatest in aged rats. The effect of light exposure on the aging retina was not investigated since all rats were exposed to the same total photoperiod.