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

TOCP (Tri-orthocresyl phosphate), an organophosphorus compound, has been implicated in producing neuropathy in the male S. D. rats. Repeated subcutaneous doses of TOCP (600 mg/kg) for up to 6 weeks produced ataxia, most striking at 50 days after final injection, followed by gradual recovery. Ultrastructurally, the internal structure of affected nerve fibers was primarily composed of altered smooth endoplasmic reticulum, tubular membrane system, and mitochondria, although myelin sheath was found to be essentially normal. In the histopathological examination, axonal and myelin degeneration was disclosed in the gracile nucleus and in the gracile fasciculus of the cords as well as in the sciatic nerves. The localization and degree of these changes were considered to be "dying back", showing systemic neuropathy. In addition, muscular lesion showed small group atrophy, corresponding to Type I fiber atrophy.