Light microscopic visualization of monoamine oxidase using a cerium method.

H2O2-generating monoamine oxidase can be visualized in the light microscope with tetrazolium, metal salt (ferricyanide) and coupled peroxidatic oxidation methods. Due to methodological draw-backs these procedures do no allow satisfactory results. In search for an alternative method a light microscopic cerium procedure was designed in which the primary reaction product, cerium perhydroxide, serves for the generation of amplified and intensified diaminobenzidine brown. With this cerium-diaminobenzidine-H2O2-Co method monoamine oxidase was visualized more easily and reliably and with higher sensitivity and more precise localization than with the other techniques. At present this method is considered to be the procedure of choice and was used to re-investigate and investigate the distribution of monoamine oxidase in rats, mice, gerbils, guinea-pigs, marmosets, monkeys and man. In these species many cells and tissues showed monoamine oxidase activity where the enzyme has not yet been found before and the structures with already known monoamine oxidase activity showed an improved localization.