Gross morphological consequences of irradiation of the cerebellum in infant rats with repeated doses of low-level X-ray

Abstract

The cerebellum of rats was irradiated with daily doses of 50–200 r hard X-ray, on successive days following birth, total number of exposures ranging from 1 to 10. The purpose was to design a method of selectively eliminating a specifiable proportion of the postnatally proliferating and migrating precursor cells of cerebellar microneurons. In this study the gross morphological consequences of different irradiation schedules were determined. Mortality rate was not raised by localized cerebellar irradiation, except in rats that received ten successive daily doses, and the animals that survived through infancy, including those that received 10 × 200 r, showed normal body growth. Total brain weight was markedly reduced in the animals receiving more than 2 × 100–200 r; the highest reduction was seen in animals that received 10 × 200 r. The bulk of reduction in total brain weight could be attributed to weight loss in the intended area of irradiation. Areal measurements showed that cerebellar irradiation did not affect appreciably the growth with age in the width and length of the cerebrum, but increase in the length and height of the cerebellum was markedly retarded. With single or multiple doses of 200 r cerebellar length was greatly reduced by day 10. Reduction at 30 and 90 days was not evident with 1–2 × 200 r, but with 4–5 × 200 r cerebellar length was reduced to the level of control animals 10 days of age, and with 10 × 200 r to the level of neonates. The cytological bases of the drastic effects produced by radiation remain to be determined.