A Diazo Coupling Method for the Electron Microscopic Localization of Cholinesterase

The presence of cholinesterase at the myoneural junction of intercostal muscle has been demonstrated in both light and electron microscopic preparations. A new simultaneous diazo coupling technique using α-naphthyl acetate as substrate and "hexazonium pararosanilin" as coupler has been applied to cold formalin-fixed tissues. After postfixation in buffered osmium tetroxide the sites of esterase activity are faithfully demonstrated at a high level of resolution. The details of cholin-esterase distribution and some technical aspects of the procedure are discussed.