RESUMO
The effect of methyl mercury [MeHg] on the neuropil of the molecular cell layer of the cerebellzrr cortex of the mouse embryo was studied by the electron microscope. Fifteen adult mice [12 females and 3 males] were used in this study. From the lSt day of gestation, the pregnant female mice were provided with drinking water containing 4% MeHg. The developing cerebellum of the foetal mice was examined on the 14th day of gestation. The neuropil showed swollen dendritic profiles with clear dendroplasm, axonal knobs with degenerated synaptic vesicles and axo-dendritic contact without synaptic thickening. After 17 days of gestation, the dendritic profiles appeared swollen with immature mitochondria and few free ribosomes, axonal knobs with defined synaptic vesicles and axo-dendritic contacts with synaptic thickening. After 20 days of gestation, the dendritic profiles were swollen with immature ribosomes. The axonal knobs were observed containing illdefined synaptic vesicles. The axo-dendritic and axo-somatic contacts were recognized. They were of symmetrical synaptic thickening. From the above-mentioned observations, it appeared that exposure to methyl mercury caused permanent marked damage to the cerebellum. So, exposure to methyl mercury should be avoided