QUANTITATIVE, VIDEO-BASED HISTOCHEMISTRY TO MEASURE REGIONAL EFFECTS OF ANTICHOLINESTERASE PESTICIDES IN RAT-BRAIN

Acetylcholinesterase histochemistry was coupled to inexpensive and wid ely available apparatus for video microscopy and densitometry to study enzyme activity and inhibition in different parts of the rat brain. Q uantitative histochemistry, under properly defined conditions, yielded an output that increased linearly with incubation time and section th ickness and was a smooth hyperbolic function of substrate concentratio n. The time-course of staining after in vivo exposure to eserine revea led no sign that carbamate-induced cholinesterase inhibition was readi ly reversed in vitro. Brains from rats treated either with a carbamate or an organophosphate anticholinesterase pesticide showed significant regional variation in cholinesterase inhibition. The histochemical da ta corresponded well. with data from bio chemical as says of acetylcho linesterase activity (overall correlation coefficient of absolute valu es, r = 0.95). Also, a comparison of assay types by two-way analysis o f variance showed no significant main effect. These results support th e conclusion that video based histochemistry is suitable for detailed studies of developmental and toxicological influences on cholinesteras es in multiple microscopic regions of the rat brain. (C) 1996 Academic Press, Inc.