Intranuclear differences in the response of Purkinje cell DNA of the rat cerebellum to bleomycin. A microphotometric and autoradiographic study.

A single dose of the DNA-binding cytostatic agent bleomycin (100 micrograms/g body weight, subcutaneously) was given to 10-day-old rats to study unscheduled repair DNA synthesis in nucleolar and in bulk nuclear chromatin of postmitotic Purkinje neurons. The Feulgen reaction and Hoechst 33342 staining were used for quantitative evaluation of nuclear DNA content and chromatin structure. The repair synthesis of DNA was detected by 3H-thymidine autoradiography. The data showed a lesser staining of Purkinje as well as granule cell DNA by Hoechst 33342 in bleomycin-treated animals than in controls, but there was no difference in staining with the Feulgen reaction. The mechanisms of DNA staining by both cytochemical methods suggest that bleomycin reacted preferentially with AT-rich and single stranded DNA in cerebellar cells in vivo. Weak 3H-thymidine labelling was found in Purkinje cells of both control and treated rats, but in the latter group the labelling was more pronounced near or over the nucleolus. The enhanced unscheduled DNA synthesis in the nucleolar region of Purkinje cells of treated animals may be due to greater damage of DNA in this region or may indicate a greater ability of the nucleolar chromatin to repair its DNA.