Neuro toxic esterase

Clothier, B. and Johnson, M.K., Reactivation and aging of neuro-toxic esterase inhibited by a variety of OP esters, Biochem. J., 185, 739, 1980. 

The second type of test is the determination of neuro-toxic esterase activity (NTE), In its simplest form, this involves treatment of the adult hen with a single maximum tolerated dose of the test substance and sub-scquent assay of the brain enzyme after the time of peak inhibition but before substantial resynthesis of new enzyme has occurred (John.son, 1982). The time of peak inhibition, which can be from 3 to 48 hr postdosing (and is determined by the pharmacokinetics of the compound), can often be assessed by observation of the time of onset of cholinergic signs. The threshold level of NTE inhibition at this early stage, which correlates with delayed neurotoxicity, is approximately 80%. No clinical signs are associated with an inhibition of 60% or less. When multiple determinations of NTE are made during chronic exposures, plateau levels are observed after 2 or 3 weeks. If inhibition of NTE in the brain and spinal cord is Ies,s than 50%, delayed neuropathy doe.s not occur. 

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