Teratogenicity and neurotoxicity effects induced by methomyl insecticide on the developmental stages of Bufo arabicus

Methomyl (MET) is a carbamate insecticide that has been widely used to protect the crop against insects as an alternative for organophosphorus insecticide. Thus the present study aims to evaluate the potential toxic effects of MET on the developmental stages of Bufo arabicus. Tadpoles were classified into three stages (25, 37, 40). Every stage was divided into two groups, control and MET-treated group (10 ppm for two weeks) after LC50 determination in acute toxicity test for 96 h. Control and MET-treated larvae were examined at the level of morphological, histological, skeleton deformities and immunohistochemical labeling of alpha-synuclein in the spinal cord and dorsal root ganglion. MET-exposed larvae showed hyperactivity, extreme agitation, abnormal swimming and kinking tail as compared to control. Alizarin Red S-Alcian blue staining showed scoliosis in MET treated tadpoles at 25 and 37 stages; kyphosis, retarded tail regression and reduced ossification of the phalanges of digits for both fore-and hind limbs were noted in MET-exposed tadpoles at 40 stage as compared to control. Histopathological changes in myotomes, notochord and spinal cord were shown in MET-exposed tadpoles as compared to control. Immunohistochemical examination showed an over expression of alpha-synuclein either in the neurons of the spinal cord or in the dorsal root ganglion of MET-exposed tadpoles at stage 40 as compared to control. The present study concluded that MET insecticide induces malformation and teratogenicity effects which were accompanied by neurodegenerative effects for the neurons either in the spinal cord or in the dorsal root ganglion.