The L-type calcium channel blocker nimodipine mitigates cytoskeletal proteins phosphorylation in dichlorvos-induced delayed neurotoxicity in rats

The present investigation was carried out to assess the protective efficacy of nimodipine against dichlorvos-induced organophosphate induced delayed neurotoxicity (OPIDN). Single subcutaneous dose of dichlorvos (200 mg/kg body weight) led to a consistent increase in the activity of both microtubule associated protein kinases viz. Ca²⁺/Calmodulin-dependent and cAMP dependent protein kinases, at all post exposure intervals (day 7, 15 and 21) as compared to that of controls. Autoradiography followed by microdensitometric studies demonstrated enhanced phosphorylation of 55 kDa and 280 kDa proteins in dichlorvos-exposed animals. These two proteins were confirmed to be tubulin and microtubule associated protein-2 (MAP-2) by western blotting. The hyperphosphorylation of these two proteins was shown to interfere with the assembly of neuronal microtubules as shown by electron microscopic studies that may eventually lead to possible disruption of neuronal cytoarchtecture resulting in axonal degeneration. Administration of nimodipine along with dichlorvos brought about a significant reduction in the activities of both the kinases as well as the extent of microtubule associated protein phosphorylation. This indicates that nimodipine, a centrally acting calcium channel blocker, may contribute to the amelioration of dichlorvos induced neurotoxicity by attenuation of calcium mediated disruption of cytoskeletal proteins and hence, calcium channel blockers like nimodipine have great future as new therapeutic agents for OPIDN.