Biosynthesis of DNA and RNA in neuronal and glial cells from various regions of developing rat brain.

Slices of cerebral hemispheres, brain stem, and cerebellum from rats 5-30 days old were used for in vitro incorporation of [methyl-3H]thymidine and [6-14C]orotic acid into DNA and RNA, respectively. The rates of DNA and RNA synthesis decreased markedly during development, with the most marked decrease observed for DNA. The different brain regions showed specific patterns of decline of DNA and RNA synthesis. Following incubation of slices, the tissues were fractionated to obtain fractions enriched in neuronal cells and in glial cells. In cerebellum, the granule neurons were separated from the Purkinje neurons. The glial:neuronal ratio of DNA specific activity was different in the three regions examined: in cortex it decreased from 6 at 10 days to 3 at 20-30 days; in brain stem it was 3 throughout 10-30 days; in the cerebellum (glia:granule neuron ratio) it was also 3 at 30 days but only 0.3 at 10 days. Concerning the RNA incorporation, small differences were found between neuronal and glial cells.