Regeneration and recovery in the fetal nervous system after radiation injury

Abstract

Previous studies showed that recovery from destructive injury in 12-day fetal rats (23 to 34 somite pairs) exposed to 150 R appeared to be remarkably good except for minor abnormalities of the brain and spinal cord in some animals and occasionally microphthalmia. Nothing more was known of the morphogenesis of this restitution. A series of rats irradiated on the 12th fetal day was studied histologically and in other ways from a few hours after exposure to adulthood. Five to eight hours after 150 R there was widespread necrosis of certain classes of primitive proliferative cells in the nervous system and other tissues, but residual cells had resumed proliferative activity. By 24 h regeneration of the proliferative cells was advanced and most necrotic cells had disappeared, and at 48 h the irradiated fetus closely resembled the normal. There were very few residual dead cells, and minute foci of proliferative cell rosettes were present in the midline of the ventral spinal cord and brain stem. Seventy-two and ninety-six hours after irradiation the fetuses looked like their normal counterparts except for persistent or resolving minute rosettes. At later stages to adulthood, effects of the rosette formation were not visible. In some individuals the spinal cords were reduced slightly in overall cross-sectional area and the pallium was shorter than normal. Other irradiated animals could not be distinguished from normals.