Monoamine oxidase activity of rat brain under cold exposure

Cold stress and cold adaptation were studied for their effect on the activity and substrate specificity of the monoamine oxidase A and B and on the Km of serotonin deamination in the rat brain mitochondria and supernatant. Mitochondrial monoamine oxidase Km with serotonin is established to increase more than twice under cold stress and decrease considerably in cold adapted rats. The lowering of the mitochondrial monoamine oxidase A activity is accompanied by the appearance of serotonin and the glucosamine deaminating activity in supernatant. The data suggest that decrease in the monoamine oxidase activity under cold stress may be caused by both release of the enzyme from mitochondrial membrane and changes in its catalytic property alteration.     

Monoamine oxidase -A and -B activity in the rat brain after hemitransection

The activity of MAO-A and MAO-B in four different brain regions (striatum, limbic system, occipito-temporal cortex and hemispheres) was determined after hemitransection of the left side. There was no difference in the MAO-A activities of either the left or right sides of the brain in either control or hemitransected rats. The activity of MAO-B was the same for both sides in control rats, but there was an increased MAO-B activity in the left side of the hemitransected rats with respect to the right side in all brain regions investigated, with the possible exception of the limbic system. The increase was due to a change in the V_max rather than to a changed K_m of the MAO-B. The interaction of the MAO-B with oxygen was unchanged after hemitransection.     

Monoamine oxidase activity in rabbit brain nuclei in experimental acute emotional stress

Activity of monoamine oxidase in the neurons of catecholamine-synthesizing nuclei of hypothalamic and brainstem of rabbits with different resistance of cardiovascular functions to emotional stress was studied by the Glenner et al. method. An acute experimental emotional stress was induced by non-periodic electric stimulation of the hypothalamic ventromedial nucleus and the skin in immobilized adult chinchilla rabbits. It was found that monoamine oxidase activity in the neurons of groups A5, A6, A7 and A14 under acute experimental emotional stress increased in rabbits "resistant"to stress and remained unchanged in rabbits "predisposed" to stress. The activity of monoamine oxidase in the neurons of group A12 remained unchanged in the rabbits "resistant"to stress and decreased in the rabbit "predisposed" to stress.     

Monoamine oxidase activity in the hypothalamus and various other brain areas and in some endocrine glands of the rat during the estrus cycle

—The activity of monoamine oxidase (MAO, EC 1.4.3.4) was measured in the entire hypothalamus and different hypothalamic regions, in the amygdala, frontal and lateral cerebral cortex, in the pituitary, adrenals and genital organs of male rats and of female rats during the estrus cycle. Activity of MAO changed cyclically in the hypothalamus, amygdala, adrenals and ovaries. The highest levels in the hypothalamus occurred at 10 a.m. on the day of proestrus and during estrus. The lowest levels occurred at 6 p.m. on the day of proestrus, of metestrus and during diestrus. Cyclical variations similar to those found in the whole hypothalamus were also observed in anterior, posterior and lateral portions and the median eminence of the hypothalamus. Activity in the median eminence was greater than that of the whole hypothalamus or its various other portions. The amygdala exhibited less marked cyclical activity which followed the pattern of the hypothalamus by increasing at 10 a.m. and peaking at 3 p.m. on the day of proestrus. At the‘post-critical’period of proestrus, when the activity of MAO in the hypothalamus and amygdala decreased, the activity of MAO in the ovaries and adrenals rose. During the estrus cycle much lower levels of activity of MAO were demonstrated in other regions of the brain (frontal and lateral cerebral cortex), in the pituitary and in the uterus, none of which showed cyclical changes. The changes in activity of MAO in cerebral tissues, endocrine glands and genital organs have been discussed in relation to the probable participation of monoamines in the mechanism(s) of secretion of gonadotrophins by the hypothalamus.     

Monoamine oxidase activity in hepatopancreas of Octopus vulgaris

1. Monoamine oxidase activity has been studied in hepatopancreas of Octopus vulgaris using 5-HT and PEA as substrates.2. Time courses of MAO activity against 5-HT and PEA show that the enzyme has higher affinity for PEA than for 5-HT.3. MAO activity against 5-HT appears more sensitive than MAO activity against PEA, to variations of the temperature (range 17–67°C).4. The inhibition curves obtained with clorgyline and deprenyl indicate that MAO activity is due to a single form of the enzyme, not corresponding to type A and type B MAO.5. Semicarbazide 10⁻⁴ M does not affect the deamination of 5-HT and PEA, demonstrating that a semicarbazide-sensitive amine oxidase is not involved in this process.     

Monoamine oxidase and catechol-O-methyl transferase activity in Tetrahymena.

Tetrahymena pyriformis strain HSM was found to have monomine oxidase (MAO) and a catechol-3-methyl transferase-like (COMT) activity. As in mammalian tissues, the MAO activity is predominantly localized in the mitochondrial pellet and COMT in the cytosol. The COMT-like activity was present in amounts comparable to several mouse tissues and was inhibited by tropolone. MAO activity was much lower than in any of the mouse tissues tested, and its activity varied greatly from preparation to preparation. The substrate preference of Tetrahymena MAO was tryptamine greater than serotonin greater than dopamine, and activity increased with increasing pH from pH 6.5 to pH 7.8, as does that of mouse liver MAO. Teh Km of Tetrahymena MAO for tryptamine was approximately 4 micrometer, an order of magnitude lower than that of mouse liver MAO. Sensitivity of inhibition by MAO inhibitors was variable. In some preparations, no inhibition was observed. In others clear inhibition was obtained, harmine and clorgyline being among the most potent inhibitors.     

Monoamine oxidase types A and B in the vertebrate brain

1. Monoamine oxidase (MAO) activity was measured in brains of teleosts, amphibians a reptile, birds and mammals. Selective inhibitors were used to determine the relative proportion of MAO type A and MAO type B. 2. Brain homogenates of all tetrapods showed double sigmoid inhibition curves, indicating the presence of both forms of MAO. 3. Brain homogenates of all teleosts showed single sigmoid inhibition curves, with greater sensitivity to type A inhibitors. 4. These results indicate that tetrapod brains contain both type A and type B MAO activity, whereas teleost brains contain only a type A-like enzyme. 5. It is possible that the presence of two forms of MAO in brain may confer an advantage to a terrestrial lifestyle.     

Monoamine oxidase activity measurements using radioactive substrates

The use of Amberlite CG-50, Dowex 50 and solvent extraction for separation of the oxidation products of the biogenic amines are compared, and measurements of monoamine oxidase activity using ¹⁴C-labeled biogenic amines are described. K_m data for tyramine, dopamine, tryptamine, and serotonin for monoamine oxidase activity of rabbit brain mitochondria are reported. Rates of product formation from [¹⁴C]tyramine are compared with polarographic measurements of oxygen utilization using purified MAO and intact mitochondria from rabbit liver and brain. Difficulties in comparative measurements of monoamine oxidase activity and some reasons for wide variations in published data are discussed.     

Monoamine oxidase B activity is increased in human gliomas

Glial tumours are the most common type of brain neoplasm in humans. Tumour classification and grading represent key factors for patient management. However, current grading schemes are still limited by subjective histological criteria. In this context, gliosis has been linked to increases in monoamine oxidase B (MAO-B) activity. Thus, in the present study, MAO-B activity in membranes of glial tumours (n=20), meningiomas (n=12) and non-pathological human brains (n=15) was quantified by [14C]PEA oxidation. MAO-B activity was significantly greater in glioblastoma multiformes than in postmortem control brains (p<0.01) or meningiomas (p<0.001). There were no significant differences in MAO-B activity between glioblastoma multiformes (n=11) and low-grade astrocytomas (n=3) or anaplastic astrocytomas (n=6). In conclusion, the present results demonstrate a significant and selective increase in MAO-B activity in human gliomas when compared with meningiomas or non-tumoural tissue. These results suggest that the quantification of MAO-B activity may be a useful diagnostic tool for differentiating glial tumours from other types of brain tumours or surrounding normal brain tissue.