Oral administrations of methamidophos and TOCP have different effects on in vitro protein phosphorylation levels from subcellular fractions of hen brain

The effects of methamidophos and tri-o-cresyl phosphate (TOCP) on the endogenous phosphorylation of specific brain proteins were studied in Beijing white laying hens during the early stage of delayed neurotoxicity. Phosphorylation of mitochondrial and synaptosomal proteins was assayed in vitro by using [γ-32P]ATP as phosphate donor. Tri-o-cresyl phosphate (TOCP) administration enhanced the phosphorylation of synaptosomal proteins with molecular weight of 40 and 55 kDa by as much as 36% and 65%, respectively, and decreased the phosphorylation of mitochondrial protein (35 kDa) by 33%. A single dose of methamidophos enhanced the phosphorylation of 32-kDa synaptosomal protein by 44%; however, it had no effect on brain mitochondrial proteins. The activity of neuropathy target esterase (NTE) in dosed hens’ brain and spinal cord was assayed for the effects of methamidophos and TOCP. These results showed that methamidophos inhibited brain NTE by 41% compared with that of control after 7-day exposure, while TOCP inhibited brain NTE by 66%. Moreover, NTE activity from spinal cord in treated hens also exhibited a similar trend of activity inhibition. Together, these results suggested that methamidophos and TOCP induced changes of protein phosphorylation level from hen brain and resulted in different kinds of neurotoxicity.