Effects of neonatal methylmercury exposure on development of nucleic acids and proteins in rat brain: regional specificity.

Exposure of neonatal rats to methylmercury (1 or 2.5 mg/kg SC daily) during the preweaning period caused regionally-specific alterations in DNA, RNA and protein content in brain. In midbrain + brainstem, where neuronal replication and differentiation conclude early, reduced DNA content was prominent at either dose and was apparent well before evidence of general body growth impairment; small deficits in protein content and brain region weight were seen. In contrast, cerebral cortex showed an elevation of DNA in the high dose group and a tendency toward supranormal RNA values at either dose. In cerebellum, where maturation occurs last, both DNA and RNA were markedly stimulated in pups receiving either 1 or 2.5 mg/kg and little effect was seen on proteins or region weight. These results indicate that the response of the developing central nervous system to cell loss caused by methylmercury is dependent upon the stage of development at which exposure occurs: whereas clear-cut reductions in cell number (DNA content) occur in fairly mature, post-replicative regions, those areas undergoing rapid replication and differentiation are likely to exhibit compensatory stimulation or replacement of cells.