STUDIES ON THE PATHOGENESIS OF ORGANOPHOSPHORUS COMPOUND-INDUCED DELAYED NEUROTOXICITY (OPIDN)

This thesis project was aimed at studying the pathogenesis of organophosphorus compound-induced delayed neurotoxicity (OPIDN). Some organophosphorus compounds, including tri-o-cresyl phosphate (TOCP) and diisopropyl fluorophosphate (DFP) produced a central-peripheral distal axonopathy. Since organophosphorus compounds are good phosphorylating agents, the significance of protein phosphorylation in OPIDN was studied. Specifically, the phosphorylation of cytoskeletal proteins: microtubules and neurofilaments, was investigated.; Paralysis of hens 18-21 days after a single 750 mg/kg oral dose of TOCP appeared to confer {dollar}{lcub}rm Ca{rcub}sp{lcub}++{rcub}{dollar}-calmodulin-dependence on the endogenous phosphorylation of microtubule and neurofilament proteins. A striking increase in tubulin and MAP-2 phosphorylation by the addition of {dollar}{lcub}rm Ca{rcub}sp{lcub}++{rcub}{dollar} and calmodulin in TOCP-treated animals was observed. An increased neurofilament protein phosphorylation was also seen in spinal cord and sciatic nerve preparation. The enhancement in phosphorylation fit the time course criteria for the involvement in OPIDN.; The increase in phosphorylation of cytoskeletal proteins in TOCP-treated animals is not merely correlated with the development of OPIDN but it is mechanistically related. This hypothesis is confirmed by the finding that the increase in phosphorylation started at 1 day following treatment, when neither clinical signs nor pathological damage was observed. The increased phosphorylation of cytoskeletal proteins persisted till day 21, when the animals were paralyzed.; The increased phosphorylation of cytoskeletal proteins in TOCP-treated animals was mediated by calmodulin dependent protein kinase type II (CaM Kinase II). The effect of in vivo TOCP treatment on crude CaM Kinase II preparation was further investigated. TOCP was found to increase the autophosphorylation of the kinase as well as its activity towards exogenous substrates such as microtubule-associated-protein-2 (MAP-2). This effect was seen at 1 and 21 day TOCP-treated animals, which further supports the involvement of this kinase in the pathogenesis of OPIDN.; In vitro incubation of CaM Kinase II with DFP also resulted in the increase autophosphorylation of the kinase in a dose-dependent manner. Since high concentrations of ATP have been reported to cause conformational changes in the kinase, it is possible that DFP mimicked the action of ATP in this respect. (Abstract shortened with permission of author.)...