Formation and Rejoining of DNA Strand Breaks in Irradiated Neurons: In vivo

The rejoining of the strand breaks formed by X- and -y-irradiation of the DNA in the internal granular layer neurons of the canine cerebellum was followed in vivo at the level of the 165S chromosomal subunit. Single-strand breaks were produced with an efficiency of 58 + 5 eV in the DNA of differentiated neurons, a value similar to that found for cultured dividingcell lines, e.g., Chinese hamster ovary cells and murine leukemic lymphoblasts. The expression of the strand-break rejoining in neuronal DNA in vivo differed from that observed in dividing cells in vitro because reconstituted 165S subunits were degraded into smaller molecules during the early repair period. Large molecular weight species similar to those observed in unirradiated neurons did not appear in significant quantities until 10 hr after irradiation. The exact mechanistic relationships of these events are not known at this time.