Nuclear, nucleolar repair, or turnover of DNA in adult rat brain.

Labeled thymidine administered to adult rats is incorporated at a low level into brain DNA as shown by biochemical and autoradiographic methods. This incorporation takes place in part into neuronal nuclei and nucleoli and also into glial nuclei. While incorporation into glial nuclei is interpreted to represent known glial cell proliferation, incorporation into neuronal nucleoli may be related to nucleolar DNA synthesis, which in turn is responsible for the regulation of nucleolar RNA synthesis. It could also be due to DNA repair synthesis. Assuming this latter phenomenon, our results suggest that nucleolar DNA is more sensitive than chromosomal DNA to ionizing radiations and other factors.