Quantitative electron probe microanalysis of acetylcholinesterase activity in rat brain sections.

In this study we determined acetylcholinesterase (AChE) activity by electron probe microanalysis (EPMA). AChE was localized in rat brain sections by a histochemical reaction that produced a Cu-ferricyanide precipitate. This reaction is based on the hydrolysis of acetylcholine substrate with AChE. The copper (iron) concentration in the deposit is proportional to acetylcholine involved in the hydrolysis reaction. Absolute determination of the size of the reaction was calculated from EPMA measurements compared with those made from a dextran standard containing 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 microns.