Quantitative histochemical study of monoamine oxidase in the rabbit hippocampus

The distribution of monoamine oxidase activity in the rabbit hippocampus was studied by quantitative histochemical analysis. The presence of monoamine oxidase activity was found in str. lacunosum-moleculare of areas CA₁ and CA₂ of the hippocampus and in str. moleculare of the dentate fascia. A strong positive reaction was found in layers containing many myelinated fibers (the alveus and Shaffer's collaterals). However, when the reaction was carried out without substrate, considerable deposition of diformazan was observed in these layers. These observations and the ability of myelin to reduce nitro-BT spontaneously, described in the literature, suggest that the positive Glenner's reaction in the alveus and Shaffer's collaterals is not specific. The deposition of diformazan in the layer of pyramidal and granular neurons likewise is nonspecific, as is confirmed by the results of experiments with preincubation in iproniazid and with incubation without substrate.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino-on-Oka. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 135–141, March–April, 1977.     

The reaction pathway of membrane-bound rat liver mitochondrial monoamine oxidase

1. A preparation of a partly purified mitochondrial outer-membrane fraction suitable for kinetic investigations of monoamine oxidase is described. 2. An apparatus suitable for varying the O(2) concentration in a spectrophotometer cuvette is described. 3. The reaction catalysed by the membrane-bound enzyme is shown to proceed by a double-displacement (Ping Pong) mechanism, and a formal mechanism is proposed. 4. KCN, NaN(3), benzyl cyanide and 4-cyanophenol are shown to be reversible inhibitors of the enzyme. 5. The non-linear reciprocal plot obtained with impure preparations of benzylamine, which is typical of high substrate inhibition, is shown to be due to aldehyde contamination of the substrate.     

On rat liver mitochondrial monoamine oxidase activity and lipids

Following earlier observations on the retention of 5-hydroxytryptamine oxidizing activity by a purified preparation of monoamine oxidase from rat liver mitochondria, this fraction has been obtained in a water-soluble form by Triton X-100 gradient gel filtration and DEAE-Bio-Gel A chromatography. The soluble fraction appears to depend on Triton X-100 and phospholipids for its activity. The results seem to implicate membrane lipid components in the expression of rat liver mitochondrial monoamine oxidase activity.     

The influence of respiratory state on monoamine oxidase activity in rat liver mitochondria.

Changes in the respiratory state of rat liver mitochondria caused significant changes (up to 10-fold) in the rates of oxidative deamination of tyramine, indicating interactions between the inner coupling membrane and the monoamine oxidase sites in the outer membrane, and suggesting the possibility that monoamine oxidase is regulated by the thermodynamic state of the mitochondria.     

A kinetic evaluation of monoamine oxidase activity in rat liver mitochondrial outer membranes

1. A preparation of mitochondrial outer membranes from rat liver can be shown to contain two kinetically distinct monoamine oxidase activities. These activities are distinguishable by their different sensitivities to the irreversible inhibitor clorgyline, and by the effect of the reversible inhibitors benzyl cyanide and 4-cyanophenol. 2. The substrate specificities of the preparation and the two enzyme species have been elucidated.     

Electron microscopic localization of monoamine oxidase in the rat liver

Summary Two methods have been employed to localize monoamine oxidase activity in the cells of rat liver, using either 2-(2′-benzothiazolyl)-5-stryl-3-(4′-phtalhydrazidyl) tetrazolium chloride (BSPT) or ferricyanide as electron acceptor. With both methods monoamine oxidase activity was found both in the inner and the outer mitochondral membrane, although the outer membrane appeared the most probable location. In addition the BSPT method but not the ferricyanide method, revealed monoamine oxidase activity in the endoplasmatic reticulum. The results obtained by the two methods have been compared and are discussed in view of available biochemical data on monoamine oxidase. Supported by research grants from the National Research Council of Canada (A 3651), The Swedish Medical Research Council (4145) and M. Bergwall's Foundation, Stockholm.     

Regional histochemical aspects of xanthine oxidase activity in ischemic and reperfused small intestine of the rat

The study describes regional changes of xanthine oxidase and succinate dehydrogenase activities as shown by the ischemic and reperfused small intestine of the rat. The results are obtained with enzyme histochemical methods, including densitometrical verifications, and are substantiated with biochemical enzyme determinations. The decrease of xanthine oxidase activity was best visible in the anoxic duodenum and jejunum, where the findings of histochemical enzyme determinations agreed with those achieved biochemically. The activities of succinate dehydrogenase as measured densitometrically may serve as a further control, considering also the typical intracellular distribution of the reaction products.     

Early changes in mitochondrial monoamine oxidase activity of rat liver during 2-acetylaminofluorene feeding

The activities of mitochondrial type A and B monoamine oxidase were determined in the liver of rats fed a diet containing 2-acetylaminofluorene (AAF). Three days after the initiation of AAF-feeding, there was a significant decrease of type B monoamine oxidase activity without affect on type A enzyme. The decreased activity of type B monoamine oxidase, which reached a minimum after three weeks, was sustained for as long as AAF-feeding was continued. Sex-related difference in response to AAF was seen in the rat with respect to the onset and the intensity of the decreased type B monoamine oxidase activity, male rats being more sensitive to the carcinogen than female rats. In contrast to the in vivo effect, AAF showed a potent inhibitory effect on type A monoamine oxidase, rather than on type B enzyme, when added in vitro. The pI₅₀ values were estimated to be 7.5 against type A monoamine oxidase and 4.1 against type B enzyme, respectively. The in vitro inhibition of both types of monoamine oxidase by AAF was competitive. The K_i values for AAF were calculated to be 9.51 · 10^?9 M for type A monoamine oxidase and 1.30 · 10^?5 M for type B enzyme, respectively. In accordance with the potent inhibitory effect of AAF on type A monoamine oxidase in vitro, a single administration of the carcinogen, at a dose of 50 mg/kg, resulted in a marked and temporal decrease of the enzyme activity in the mitochondria of male rat liver. Recovery of the decreased type B monoamine oxidase activity was slow, and the enzyme activity did not return to control levels, even if rats were fed the basal diet for 2 or 4 weeks after the cessation of AAF-feeding.     

Electron microscopic localization of monoamine oxidase in the rat liver.

Two methods have been employed to localize monoamine oxidase activity in the cells of rat liver, using either 2-(2'-benzothiazolyl)-5-stryl-3-(4'-phtalhydrazidyl) tetrazolium chloride (BSPT) or ferricyanide as electron acceptor. With both methods monoamine oxidase activity was found both in the inner and the outer mitochondral membrane, although the outer membrane appeared the most probable location. In addition the BSPT method but not the ferricyanide method, revealed monoamine oxidase activity in the endoplasmatic reticulum. The results obtained by the two methods have been compared and are discussed in view of available biochemical data on monoamine oxidase.     

Immunocytochemical localization of monoamine oxidase type B in rat liver

We used an immunohistochemical method to examine the localization of monoamine oxidase type B (MAOB) in rat liver. At the light microscopic level, MAOB was highly expressed in rat liver. It was intense around portal area, and weak around central area. All the hepatocytes examined had MAOB immunoreactivity. For the first time, using a double-labeling immunofluorescence histochemical method for laser microscopy, we report that no MAOB is found in endothelial cells, hepatic stellate cells, or Kupffer's cells. When examined under transmission electron microscopy, MAOB was localized to the mitochondrial outer membrane of hepatocytes. No apparent localization of MAOB was found in the rough endoplasmic reticulum, the crystal membrane of mitochondria, the nuclear envelope, or the plasma membrane.     

Imipramine inhibits monoamine oxidase activity in hyperglycemic rat brain

The effect of the chronic treatment of tricyclic antidepressants like Imipramine on the catecholamine metabolism of rat brain, in normal and hyperglycemic conditions was investigated. Imipramine was found to elevate the catecholamine levels in controls, while chronic treatment of hyperglycemic animals with the drug, failed to cause any change other than seen as a result of hyperglycemia. The activities of Monoamine oxidase on the other hand, decreases significantly as a result of the treatment, both in controls and in the hyperglycemic state. The results suggest that the drug apart from acting as an antidepressant, assumes the role of a monoamine oxidase inhibitor under pathological conditions.     

Histochemical study of monoamine oxidase latency in the liver of the rat

Summary In a histochemical test system with adrenaline as substrate and nitroblue tetrazolium (NBT) as electron acceptor, an increase of NBT reduction in rat liver sections was found microspectrophotometrically following short hypotonic treatment. Investigations with iproniazide, a monoamine oxidase inhibitor, and non-enzymatic NBT reduction showed that the increased formazan formation was related to the presence of monoamine oxidase. It is suggested that the reason for the observed increase of formazan formation is due to increased permeability of the inner mitochondrial membrane to NBT. Consequently, the increase of monoamine oxidase observed in the histochemical test system does not represent mobilization of a latent activity, but rather complete assessment of activity that is normally present.