EFFECT OF VITAMIN "E" ON THE PERIPHERAL NEUROTOXICITY OF THE PYRETHROID ALLETHRIN IN ADULT MALE ALBINO RAT
Mohamed H.M. Wahdan
Anatomy Department, Faculty of Medicine, Cairo University
Allethrin is one of the most recent and widely used pyrethroid insecticides. Contamination of the environment with allethrin may negatively impact animal and human health through repeated exposure to small doses over a short time. The present work was planned with the aim to study the histological changes that might occur in the sciatic nerve of adult male albino rat following allethrin exposure and to throw more light on the protective role of vitamin "E" on the peripheral neurotoxicity induced by this insecticide. Fifty adult male albino rats, weighing 153-217 grams, were utilized in this work. The animals were divided into five groups; each of ten rats: animals of group I served as control, animals of group II received allethrin daily for five successive days, animals of group III received allethrin for the same duration then were left to recover for 15 days, animals of group IV administered allethrin and vitamin "E" daily for the same duration and those of group V were given allethrin for the same duration and vitamin "E" daily for 20 successive days, started from the first day of allethrin administration. Allethrin was given in a daily dose of 25 mg/kg body weight and vitamin "E" was administered in a daily dose of 300 mg/kg body weight. Both allethrin and vitamin "E" were given to the animals by gastric intubation. At the end of the experiment the rats were sacrificed by decapitation. The sciatic nerves of each rat were dissected and examined by light microscopy using osmic acid and toluidine blue stains, and electron microscopy. Morphometric study for the number of degenerated myelinated nerve fibres was performed in all specimens. This research revealed many histological changes in the sciatic nerve, following exposure to allethrin, including Wallerian degeneration in most myelinated nerve fibres with pleomorphic destruction, fragmentation, loss of normal lamination and rupture of myelin sheaths. The axoplasms of these nerve fibres were irregular, degenerated and contained myelin fragments with loss of neurofibrils. Obvious increase in endoneurium was also observed. After 15 days of allethrin cessation, few myelinated nerve fibres appeared regenerating in addition to variable degrees of degeneration in the remaining nerve fibres. Concomitant administration of vitamin "E" with allethrin for five successive days had minimized the peripheral neurotoxic effect of this insecticide. Moreover, continuous daily administration of vitamin "E" for 15 successive days after allethrin cessation resulted in more marked improvement in the histological changes observed in the sciatic nerve following allethrin intoxication. Following the intake of vitamin "E", this study revealed that most myelinated nerve fibres were either normal or regenerating, and only few fibres showed mild to moderate degrees of degeneration. Allover this study, the non-myelinated nerve fibres seemed to be not affected. In conclusion, the present study has demonstrated that continuous daily oral administration of allethrin for five successive days has hazardous toxic effects on the structure of the sciatic nerve of adult male albino rat. Furthermore, vitamin "E" administration greatly minimized the peripheral neurotoxic effect of allethrin and enhanced the process of regeneration of nerve fibres. It is recommended to avoid the use of allethrin in agriculture and insect control as much as possible, to prevent contamination of air, soil, water and food with this environmental toxin.