Enzymatic detection of x-ray-induced strand breaks in nuclear DNA on sections of mouse tissue

An enzyme-histochemical method was used to detect X-ray-induced strand breaks in the DNA of mammalian tissue cells. Paraffin sections of ethanol-fixed mouse brain and liver were incubated with three kinds of exogenous DNA polymerizing enzymes, and the amount of in situ incorporation of 3H-deoxyribonucleotides into nuclear DNA was examined by autoradiography. No increase in labelling intensity was observed over nuclei of neurons and astrocytes in cerebral cortex, or over hepatocytes in liver immediately after X-irradiation when compared with unirradiated specimens. In liver Kupffer cells, heavily-labelled nuclei appeared from 30 min to 6 hours after, but were not observed immediately after X-irradiation. This method cannot, therefore, be applied to detect the strand breaks directly induced by X-rays, but it is useful in detecting secondary DNA degradation occurring as a result of nuclear degradation.