Studies on the delayed neurotoxicity of organophosphorus compounds- (I).

Delayed neurotoxicity experiments of an organophosphorus compound, TOCP, on hens and quails were carried out. The animals were orally exposed with TOCP in dose of 400 mg/kg, and maintained for 25 and 50 days under observation, respectively. They were sacrificed and dissected at different periods after the exposure, and the histopathological examinations were made on those animals. During the periods of 50 days, no abnormal symptoms except for acute poisoning were noted in the quails. As to the hens, neurological disorders were observed from around 12 days of the experiment. In hens, the morphological alteration in the earlier stage of the experiment was perivascular cuffing of small round cells seen in the cerebrum, cerebellum and spinal cord. The major alteration was degeneration of axons and myelin in the white matter of the spinal cord. A minimal degree of these changes was found even in the hens in which the clinical signs of neurotoxicity had not yet been observed. Later the process expanded to the whole spinal cord as well as the sciatic nerve. The electron microscopy performed after 15 days revealed moderate change of myelin and axons. From these results, it was concluded that the clinical signs as well as the morphological changes were closely related to the exposure of the compound, TOCP.