Histochemical demonstration of neurotoxic esterase

We developed a histochemical method for localizing neurotoxic esterase (NTE), defined as the phenylvalerate (PV)-hydrolyzing esterase that is resistant to 40 microM paraoxon (A) but inactivated by paraoxon plus 50 microM mipafox (B). NTE is considered to be the target enzyme in the production of organophosphorus ester-induced delayed neurotoxicity (OPIDN). Cryostat sections were incubated in a medium containing alpha-naphthyl valerate and 6-benzamido-4-methoxy-m-toluidine diazonium chloride (fast violet B) after treatment with the above-mentioned inhibitors, leading to formation of an aqueous insoluble precipitate at sites of enzymatic activity. NTE activity was estimated as staining detectable in A but not in B. In the central nervous system (CNS) of chicken, NTE appeared to be present primarily in the somata of most neurons, but at sites indistinguishable from those of the other inhibitor-resistant and -sensitive alpha-naphthyl valerate-hydrolyzing esterases. It could not be distinguished in the CNS of cat, probably because it constitutes less than 3% of the total PV-hydrolyzing activity in the CNS of that species.