Ultracytochemical demonstration of monoamine oxidase activity in nervous and non-nervous tissue of the rat.

Abstract

A method is described for the ultrastructural localization of the enzyme monoamine oxidase based on the formation of an osmiophilic formazan from the tetrazolium salt (2-(2'-benzothiazolyl)-5-styrl-3-(4'-phthalhydrazidyl) tetrazolium chloride) (BSPT) and using tryptamine as substrate. It was tested in rat heart, liver, adrenal cortex and medulla, kidney, pineal gland, cerebral cortex and cerebellar cortex and was found to provide good ultrastructural preservation, high contrast of the specific, enzyme-dependent precipitate and improved sensitivity. Monoamine oxidase activity was found in the mitochondrial outer compartment, nuclear envelope and endoplasmic reticulum in all organs studied; it was also seen occasionally in plasma membranes of liver and heart. Similar localizations were observed in interstitial cells and capillary endothelial cells. The enzyme-dependent nature of the observed precipitate was verified by control experiments consisting of incubation of overfixed tissue, omission of substrate from the incubation medium, and incubation in the presence of a specific, nonreversible inhibitor, pargyline. These studies confirm and extend the results of cell fractionation studies using liver, demonstrate the widespread distribution of monoamine oxidase in tissues, and suggest that monoamine oxidase plays important functional roles in extraneuronal cells.

Immunocytochemical localization of monoamine oxidase type B in rat liver

“…When examined under transmission electron microscopy, MAOB was localized to the mitochondrial outer membrane of hepatocytes.These results are in general agreement with those of Shannon et al (1974) and Muller and Lage (1977). By…”

“…For the first time, using a double-labeling immunofluorescence histochemical method for laser microscopy, we reported that in rat liver, no MAOB immunoreactivity was found in endothelial cells, hepatic stellate cells, or in Kupffer's cells. Though there were reports that MAOB is localized on capillary endothelial cells of rat tongue (Xu et al, 2002), hepatic stellate cells of rat liver (Muller and Lage., 1977), and Kupffer's cells of human peripheral blood (Seiler et al, 1995). In fact, at electron microscopic level, we also found no MAOB was expressed in endothelial cells, hepatic stellate cells, or in Kupffer's cells (data not show).…”

“…Original Paper enzyme histochemistry, Shannon et al (1974) found MAO reaction products in mitochondrial outer compartment, the rough endoplasmic reticulum, and the nuclear membrane of unfixed guinea pig liver, Muller and Lage (1977) described that MAO was localized to the mitochondrial outer membrane, the rough endoplasmic reticulum, the crystal membrane of mitochondria, the nuclear envelope, and the plasma membrane of rat hepatocytes and hepatic stellate cells. Whereas, we did not find any apparent localization of MAOB in the rough endoplasmic reticulum, the crystal membrane of mitochondria, the nuclear envelope, nor the plasma membrane.…”

Immunohistochemical Localization of Monoamine Oxidase Type B in Pancreatic Islets of the Rat

“…There were two kinds of mitochondria in pancreatic islet B cells: one contained MAOB on their outer membranes, but a substantial proportion of them lacked this enzyme. This finding may be attributable to one or more of the following factors (Shannon et al 1974;Muller and Lage 1977): (a) different physiologic regions or states of the outer membranes, in which case the observed activity represents the true distribution of active MAOB; (b) uneven fixation that destroys some active enzyme sites; or (c) artificial, which was made by cutting. Further research is needed to understand the exact reasons for these differences.…”

Monoamine Oxidase Type B is Localized to Mitochondrial Outer Membranes in Mast Cells, Schwann Cells, Endothelial Cells and Fibroblasts of the Rat Tongue.

“…In peripheral organs, MAOB activity has been shown to be far more abundant in the outer membrane fraction of rat liver mitochondria than in the inner membrane fraction [28]. Using an enzyme histochemical method employing a substrate common to both MAOA and MAOB, subcellular localization of MAO activity has been examined in the heart, liver, adrenal cortex and medulla, and kidney of rats [9,24]. However, to our knowledge, no previous study has examined, by immunohistochemistry, the individual subcellular localization of MAOA or MAOB enzyme in peripheral tissues.…”