FURTHER-STUDIES OF BRAIN CHOLINESTERASE - CHOLINERGIC RECEPTOR RATIOSIN THE DIAGNOSIS OF ACUTE LETHAL POISONING OF BIRDS BY ANTICHOLINESTERASE PESTICIDES

Cholinesterase (ChE) and the muscarinic (mAChR) and nicotinic (nAChR) cholinergic receptors were measured in the brains of 86 birds of 20 di fferent species collected in Saskatchewan, Canada during 1991 and 1992 . There was a strong correlation between ChE and mAChR, and the ratio of ChE: mAChR was 38% less variable than was ChE alone. In a hypotheti cal test for minimal acute lethal poisoning of all birds based on a re duction by 50% of the normal ChE measured in each, the use of a single diagnostic threshold value of the ChE : mAChR ratio had a diagnostic sensitivity of 98% and a specificity of 99%, thus making theoretically possible the diagnosis of acute lethal poisoning by anticholinesteras e chemicals without the use of reference control values for ChE. Both ChE and mAChR were highly stable during 12 days of postmortem decompos ition under several different daily temperature regimes. Substantial c hanges in these molecules occurred only under conditions of constant h igh temperature (36 C). Acute lethal poisoning by the organophosphate chlorpyrifos did not affect the density of mAChR. Postmortem decomposi tion did not appear to be an important confounding factor in the diagn ostic interpretation of either ChE or the ChE:mAChR ratio except under hot climatic conditions.