Biochemical characterization of dichlorvos-induced delayed neurotoxicity in rat.

In vitro and in vivo studies were carried out to assess the delayed neurotoxicity potential of dichlorvos. In vitro, dichlorvos caused a concentration and time-dependent decrease in the activity of neuropathy target esterase (NTE). The Ki of dichlorvos for NTE was calculated to be 1.28 x 10(3) M-1 min-1. In vitro reactivation and ageing studies revealed that dichlorvos-inhibited NTE became refractory to activation by potassium fluoride after 5 min in the ageing medium, thus indicating the formation of an aged complex between dichlorvos and NTE. In vivo also, dichlorvos (200 mg/kg body wt) given as a single subcutaneous dose inhibited NTE in brain at various intervals after exposure (24 h, 10 days, and 21 days). The delayed neurotoxicity potential of dichlorvos was finally confirmed by the rota rod test, which revealed severe motor deficit in all the exposed animals.