Degenerative changes in the developing nervous system as a result of in utero exposure to methylmercury

Tissue samples from the cerebral and cerebellar cortex of neonatal rats which had been prenatally exposed to low doses of methylmercury were examined by electron microscopy. Although all these neonates appeared to be physically normal, ultrastructural examination revealed various degenerative changes in their nervous systems. The most prominent pathological findings, including disruption and myelin-figure formation of the nuclear membranes and large areas of focal degradation and endothelial damage, were found in both the cerebellum and cerebral cortex of the animals. The present study provides evidence that minute amounts of methylmercury, which by itself may produce no significant injury to the maternal tissues nor any observable gross teratology of the neonate, may still be hazardous to the developing nervous system.