QUANTITATIVE ELECTRON-PROBE MICROANALYSIS OF ACETYLCHOLINESTERASE ACTIVITY IN RAT-BRAIN SECTIONS

In this study we determined acetylcholinesterase (AChE) activity by el ectron probe microanalysis (EPMA). AChE was localized in rat brain sec tions by a histochemical reaction that produced a Cu-ferricyanide prec ipitate. This reaction is based on the hydrolysis of acetylcholine sub strate with AChE. The copper (iron) concentration in the deposit is pr oportional to acetylcholine involved in the hydrolysis reaction. Absol ute determination of the size of the reaction was calculated from EPMA measurements compared with those made from a dextran standard contain ing a known amount of Cu(Fe). Electron probe microanalysis allows AChE activity to be assayed quantitatively on thick brain sections with a spatial resolution of 10 mu m.