Protective effects of vitamin E on methylmercury toxicity in the dorsal root ganglia

Abstract

The protective potential of Vitamin E against methylmercury neurotoxicity was investigated by means of both light and electron microscopy. Rats were treated with a daily dosage of methylmercury (2.0 mg McHg/kg body wt), Vitamin E (50 mg Vit. E/kg body wt), both methylmercury and Vitamin E, or saline solution for 8 weeks. All animals were sacrificed by intracardial perfusion of fixative and the dorsal root ganglia (L 1-L 4) (DRG) were sampled for examination. No remarkable pathological changes were observed in animals treated with Vit. E alone. McHg-treated animals showed toxic neurological signs at 8 weeks of exposure. Both light and electron microscopy demonstrated morphological changes in the neuronal cell bodies (extensive lysosomal accumulation and destruction of Nissl substance—rough endoplasmic reticulum and polyribosomal clusters) and in the dorsal root fibers (axoplasmic degradation and myelin sheath degeneration). In contrast, the McHg/Vit. E-treated animals displayed no observable neurological signs after the same duration of McHg exposure. Pathological examination revealed full protection of the DRG neurons which showed no significant degenerative changes as did those observed in McHg-alone animals. Degenerative changes, however, were still observed in the dorsal root fibers, showing moderate changes (lysosomal and axoplasmic debris accumulation) in some axons, particularly at the regions of the Nodes of Ranvier, and destruction of the myelin sheaths. It is shown in this investigation that Vitamin E can offer significant protection against methylmercury toxicity. Under our present experimental conditions, the protective effectiveness appears to be neuronal cell body > axoplasm > myelin sheaths.