Visual Deficit in Albino Rats following Fetal X Irradiation

To investigate the effect of radiation on visual ability, five groups of rats on the 15th day of gestation received x irradiation in doses of 0, 50, 75, 100, or 150 r at 50 r/ min. Two-thirds of the newborn rats died or were killed and eaten during the first postnatal week. The 75- and 50-r groups were lost entirely. The cannibalism occurred in all groups, so that its cause was uncertain. The remaining rats, which as fetuses had received 0, 100, and 150 r, were tested for visual discrimination in a water-flooded T. All 3 groups discriminated a lighted escape ladder from the unlighted arm of the T with near- equal facility. Thereafter, as the light was dimmed progressively, performance declined in relation to dose. With the light turned off, but the bulb and ladder visible in ambient illumination, the 150-r group performed at chance, the 100-r group reliably better, and the control group better still. Thus, in the more precise task the irradiated animals failed. Since irradiation on the 15th day primarily damages the cortex, central blindness seems the most likely explanation. All animals had previously demonstrated their ability to solve the problem conceptually; hence a conclusion ofmore » visual deficiency seems justified. The similar performances of all groups during the easiest light discrimination test showed that the heavily irradiated and severely injured animals of the 150-r group were nonetheless able to learn readily. Finally, contrary to earlier studies in which irradiated rats were retarded in discriminating a light in a Skinner box, present tests reveal impairment neither in learning rate nor light discrimination.« less