THE HISTOCHEMICAL DEMONSTRATION OF MONOAMINE OXIDASE ACTIVITY BY TETRAZOLIUM SALTS

1. By the use of tryptamine as substrate in the presence of tetrazolium salts in a solution buffered to pH 7.6 histochemical localization of monoamine oxidase activity is achieved during a 45 minute incubation of tissue sections at 37°C. 2. Inhibition experiments implicate the postulated acetaldehyde product of monoamine oxidase action on tryptamine and serotonin in the reduction of the tetrazoles. It was not determined whether this reduction is nonenzymatic or mediated through a flavoprotein enzyme system. 3. Localization of the formazan to autonomic ganglia and fibers, chief cells of the gastric fundus, mucosal epithelium of the duodenum and certain specific zones of the renal tubules by means of the tryptamine-tetrazolium technique was confirmed as indicating monoamine oxidase activity by identical localization using the hydrazone precipitation technique of Koelle and Valk.