Cranial irradiation of young rats impairs later learning and growth

Young rats (26 days) were exposed to ionizing radiation of the head of 0, 1200, 2400, or 3000 rads total in 200 rads/day doses. The subsequent growth of irradiated rats was permanently impaired: such impairment was positively related to amount of irradiation. Beginning in adolescence, rats were trained on a horizontal/vertical visual discrimination in a runway task, and although all four groups mastered the discrimination, they differed in their patterns of acquisition. These results indicate long term effects are associated with a cranial irradiation regimen similar to that given to children suffering acute lymphocytic leukemia (ALL).