Experimental analysis of embryogenesis of cerebellum in rat. I. Subnormal growth following x-ray irradiation on day 15 of gestation.

Rat embryos of 15 days gestation were exposed in utero to 170 R of X-ray irradiation. Embryos collected 6 hours, 1, 2 and 3 days after irradiation, and animals of 2, 6, 15 and 30 days postnatal age were used for this study. Six hours after irradiation cells in the neuroepithelium and mantle layer along the roof of fourth ventricle were observed destroyed. Neuroepithelium showed only fragmentary regeneration during next two days, and it contributed to a small number of Purkinje cells. During postnatal development of cerebellum the external granular layer, the zone of proliferative cells that gives rise to neurons of postnatal origin, was found reduced. Other structures such as internal granular layer, molecular layer and medullary layer also were reduced. These multiple temporally sequenced developmental events resulted in a subnormal-sized cerebellum. Various quantitative measures helped establish that grossly the cerebellum in the X-ray irradiated animals was about half of that in the normal animals. Problems related to regeneration in the embryonic cerebellum, and to the factors determining the subnormal size of the adult cerebellum are discussed. Viewing this as an experimental approach to the study of neuroembryogenesis of cerebellum, the role of Purkinje cells in the regulation of development of cerebellum is brought out.