Radiation-induced DNA strand breaks and cell pycnosis in the developing rat cerebellum.

DNA strand breaks and cell pycnosis induced by 60Co gamma radiation were studied in the developing rat cerebellum. Rats 2, 5 or 12 days old were irradiated and the repair of DNA strand breaks was studied at various intervals up to seven hours. DNA strand breaks were repaired in 30 min and post-repair DNA degradation was observed about 90 min after irradiation in 12 day old rats and some time later in the younger ones. The pycnotic activity in the external granular layer of the cerebellar cortex seen in histological preparations developed in a similar way, the older rats showing earlier signs of cell pycnosis and a faster degradation of DNA. A correspondence was found between DNA degradation and cell pycnosis.