Response of the developing rat brain to varying doses and dose-rates of gamma-radiation.

Pregnant rats were irradiated on day 18 of gestation at doses of 40, 80, 160, 200 and 240 rads delivered at 1, 3, 10 and 47 rads/min. Postnatal growth patterns were followed by changes in weight, DNA, protein and RNA in the cerebral hemispheres (cortex) and rest-of-brain (RB) at birth, 21, 63 and 160 days of age. Reductions in the parameters studied were independent of dose-rate at 40 and 80 rads in both the cortex and RB. At the higher doses, as dose-rate increased, brain size decreased (1 greater than 3 greater than 10 and 47 rads/min). Comparisons are made between effects produced by prenatal irradiation in rat and man during a comparable developmental stage.