Possible role of enhanced microtubule phosphorylation in dichlorvos induced delayed neurotoxicity in rat.

The effect of a single subcutaneous dose of 200 mg/kg body weight dichlorvos on neuronal microtubule phosphorylation has been studied in rat following the development of organophosphate induced delayed neurotoxicity (OPIDN). Microtubule associated Ca2+/calmodulin dependent as well as cAMP dependent protein kinases were assayed. Dichlorvos administration led to a consistent increase in the activity of both the kinases at all post exposure intervals (7th, 15th and 21st day) as compared to that of controls. After in vitro phosphorylation using [gamma-32P]ATP, various proteins were resolved on one-dimensional 8% SDS-PAGE, stained with Coomassie Blue and autoradiographed. The amount of 32P incorporated was quantified by microdensitometry. Dichlorvos enhanced the phosphorylation of 55- and 280-kDa proteins. These two proteins were identified as tubulin and microtubule associated protein-2 (MAP-2) by immunoblotting. This study showed that dichlorvos induced hyperphosphorylation of tubulin and MAP-2 which in turn destabilizes microtubule assembly, and may ultimately result in axonal degeneration leading to dichlorvos induced delayed neurotoxicity.