Effect of undernutrition on DNA and RNA synthesis in subcellular fractions from different regions of the developing rat brain.

The effect of undernutrition on the incorporation of [methyl-3H] thymidine into DNA and of 5-[3H] uridine into RNA of cerebral hemispheres, cerebellum, and brain stem was studied in vivo and in vitro in rats. The labeling of DNA from nuclei and mitochondria and of RNA from nuclei, mitochondria, microsomes, and soluble fractions, was also measured in vitro. The results demonstrate that nucleic acid synthesis is impaired and delayed during undernutrition. Specific effects were observed for the different brain regions and subcellular fractions: at 10 days nuclear and mitochondrial DNA and RNA synthesis was impaired, whereas at 30 days only the mitochondrial nucleic acid synthesis was affected. The delay of DNA and RNA labeling, caused by undernutrition, was most evident in the cerebellum, probably due to its intense cell proliferation during postnatal development. The specific sensitivity of mitochondria as compared to other subcellular fractions, may by due to the intense biogenesis and/or turnover of nucleic acids in brain mitochondria not only during postnatal development, but also in the adult animal.