Effects of methylmercury on neuroepithelial germinal cells in the developing telencephalic vesicles of mice

Methylmercury (MeHg) poisoning (20 mg/kg body weight) in embryonic mice resulted in significant reductions of mitotic indices in the neuroepithelial germinal cells of the telencephalon at the ventricular surface 4 to 12 h following intoxication. After 24 h, no significant difference in the mitotic indices was observed as compared to controls. However, after 48 h there was an increase in mitotic indices of MeHg group as compared to controls. Analysis of the mitotic figures revealed features suggestive of early-phase mitotic arrest in MeHg-exposed animals. Radioautographic studies suggest a disturbance in the interkinetic nuclear migration of proliferating ventricular cells in the MeHg group. Acute degenerative changes in scattered ventricular cells characterized by edema and spongy changes of cytoplasm associated with dissolution of ribosomes, clearing of the cytoplasmic matrix and loss of organelles including microtubules were observed by electron microscopy. Loss of microtubules was also evident within mitotic figures in MeHg-poisoned animals. It is suggested that reduction and arrest of mitotic activity and disturbances in the interkinetic nuclear migration of neuroepithelial germinal cells are related to cytotoxic effects of MeHg on ventricular cells, including effects on microtubules. These findings suggest in that MeHg severely affects proliferating neuroepithelial germinal cells during the acute phases of MeHg poisoning, and that these changes may eventually affect the architectonic makeup of the cortical plate as the brain matures.