Distribution of type A and B monamine oxidase activities in the central nervous system of rat and chick.

The distribution of type A and B monamine oxidase (MAO) activities in the central nervous system (CNS) of rat and chick was investigated using 5-hydroxytryptamine and beta-phenylethylamine as specific substrates. The distribution of type A MAO was similar to that of type B MAO in rat CNS, but quite different in chick CNS. This may be ascribed to the difference in animal species. The major part of MAO activity in the spinal cord was found to be type A.     

Effects of hypophysectomy, bilateral adrenalectomy and hormone replacement therapy upon organ monoamine oxidase activity.

Changes in MAO activity after hypophysectomy (HX) are not due to adrenal insufficiency. ACTH failed to reverse the effects of HX and enhanced the depression of cardiac and spleenic MAO. The data suggests both facilitatory and inhibitory effects of pituitary hormones on MAO activity.     

Monoamine oxidase activity of the brain of Locusta migratoria in normal conditions and after intoxication by two insecticides: chlordimeform and dieldrin]

Our investigations have shown up an MAO activity in locust brain, by the use of a radio-isotopic method, as much at larval as at adult stage. This MAO activity is in a sample of 34,3 dpm/mg of brain tissue (wet weight). Investigations have also been undertaken on effects of dieldrin and chlordimeform poisoning on this MAO activity. Even at sublethal dosages, chlordimeform causes a significant inhibition of MAO activity in vivo. This finding is in accordance with Beeman and Matsumura's work in vitro. Moreover, acute poisoning by dieldrin produces more than 60% of inhibition of MAO, 3 hours after administration of 115 microng of this insecticide by injection in the hoemocelian cavity.     

Monoamine oxidase activity of the hypothalamus and pituitary: alterations after pinealectomy, changes in photoperiod, or additions of melatonin in vitro.

Rat pituitary MAO activity was reduced by constant darkness and by additions of melatonin in vitro and was increased by constant light and by pinealectomy. Hypothalamic MAO activity followed the same pattern but was less dramatically affected. The data suggest that MAO may be a target enzyme for melatonin.     

In vivo degradation of noradrenaline by MAO A in locus coeruleus of the rat

Depletion of noradrenaline in locus coeruleus neurons after reserpinization was prevented by clorgyline, a selective inhibitor of MAO A, but not by deprenyl, a selective inhibitor of MAO B. Only MAO A is therefore responsible for the degradation of homoneuronal noradrenaline in locus coeruleus nerve cells.     

Effects of thyroidectomy on monoamine oxidase activities toward tyramine and serotonin in the circumventricular nuclei of the rat.

Following thyroidectomy, monoamine oxidase (MAO) activities toward tyramine decreased significantly by 20% in the nucleus periventricularis and the nucleus arcuatus among the 3 hypothalamic nuclei of the rat, while MAO activity toward serotonin decreased significantly by 10% only in the nucleus periventricularis. It is suggested that thyroidectomy induced selective changes on the multiple forms of MAO in the discrete circumventricular nuclei.     

Effects of thyroidectomy on monoamine oxidase activities toward tyramine and serotonin in the circumventricular nuclei of the rat

Summary Following thyroidectomy, monoamine oxidase (MAO) activities toward tyramine decreased significantly by 20% in the nucleus periventricularis and the nucleus arcuatus among the 3 hypothalamic nuclei of the rat, while MAO activity toward serotonin decreased significantly by 10% only in the nucleus periventricularis. It is suggested that thyroidectomy induced selective changes on the multiple forms of MAO in the discrete circumventricular nuclei.     

Distribution of monoamine oxidase in hippocampal region of the rat

The distribution and development of type A and type B monoamine oxidase (MAO) activities in the hippocampal region of the rat was investigated with biochemical microdetermination. Type A MAO is absolutely dominant and unevenly distributed in the hippocampus. The development of type A MAO in the hippocampus seems to be delayed and reachs adult levels by the 30th day after birth.     

Oxidation of synephrine by type A and type B monoamine oxidase.

Synephrine (SP) was found to be a substrate for monoamine oxidase (MAO) in rat brain mitochondria, showing the Km and Vmax values of 250 microM and 32.6 nmoles/mg of protein/30 min respectively. The inhibition studies showed that the SP oxidation was carried out by both type A and type B MAO and a major part of the activity was due to type A MAO.     

Distribution of monoamine oxidase in hippocampal region of the rat

Summary The distribution and development of type A and type B monoamine oxidase (MAO) activities in the hippocampal region of the rat was investigated with biochemical microdetermination. Type A MAO is absolutely dominant and unevenly distributed in the hippocampus. The development of type A MAO in the hippocampus seems to be delayed and reachs adult levels by the 30th day after birth.     

Distribution of type A and B monoamine oxidase activities in the central nervous system of rat and chick

Summary The distribution of type A and B monoamine oxidase (MAO) activities in the central nervous system (CNS) of rat and chick was investigated using 5-hydroxytryptamine and -phenylethylamine as specific substrates. The distribution of type A MAO was similar to that of type B MAO in rat CNS, but quite different in chick CNS. This may be ascribed to the difference in animal species. The major part of MAO activity in the spinal cord was found to be type A.     

Monoamine oxidase activity in tissues of spontaneously hypertensive rats

Summary Monoamine oxidase (MAO) activity was assayed both in central and peripheral blood vessels of spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar Kyoto rats (WKR). The activity of MAO in the brain and peripheral vasculature was essentially the same in both SHR and WKR. It can therefore be concluded that central and peripheral vascular MAO activity is not altered in the genetically hypertensive animals.     

Methoxyphenylethylamines as substrates for type A and type B monoamine oxidase

Summary 4-Methoxyphenylethylamine was found to be a specific substrate for type B monoamine oxidase (MAO) in rat brain mitochondria, whereas 3,4-dimethoxyphenylethylamine was common for both types of MAO. These results suggest that O-methylation in the para-position increases the preference of the substrate for type B MAO, while a methoxy-group in the meta-position contributes to the substance being a type A substrate.     

Monoamine oxidase activity in single nerve cell bodies from substantia nigra of rat and man

Summary In single nerve cell bodies isolated from the substantia nigra of man and rat the active forms of MAO A and MAO B were found by the use of the microdiver technique and specific inhibitors.     

Monoamine oxidase inhibitors and histamine metabolism

In rat, histamine metabolism is altered by some nonspecific inhibitors of monoamine oxidase (MAO) such as iproniazid, and, to a lesser extent, tranylcypromine. Type A MAO inhibitors, such as clorgyline and MD780515, do not seem to interfere with the metabolism of histamine. Deprenyl, a type B MAO inhibitor, shows some inhibition which is, however, much lower than that observed with iproniazid. The strong effect of iproniazid is probably due to its DAO inhibiting properties.     

Monoamine oxidase activity in Helix pomatia.

The distribution and characterization of MAO in various tissues of the snail were analyzed. Only low amounts of the enzyme exist in the different tissues and data suggest that there is more than one type of MAO.     

Multiplicity of monoamine oxidase in chick brain.

The substrate- and inhibitor-related characteristics of monoamine oxidase (MAO) were studied on chick brain mitochondria. It was found that neither 5-hydroxytryptamine nor beta-phenylethylamine is the specific substrate for type A and type B MAO in chick brain.     

Monoamine oxidases in development

Monoamine oxidases (MAOs) are flavoproteins of the outer mitochondrial membrane that catalyze the oxidative deamination of biogenic and xenobiotic amines. In mammals there are two isoforms (MAO-A and MAO-B) that can be distinguished on the basis of their substrate specificity and their sensitivity towards specific inhibitors. Both isoforms are expressed in most tissues, but their expression in the central nervous system and their ability to metabolize monoaminergic neurotransmitters have focused MAO research on the functionality of the mature brain. MAO activities have been related to neurodegenerative diseases as well as to neurological and psychiatric disorders. More recently evidence has been accumulating indicating that MAO isoforms are expressed not only in adult mammals, but also before birth, and that defective MAO expression induces developmental abnormalities in particular of the brain. This review is aimed at summarizing and critically evaluating the new findings on the developmental functions of MAO isoforms during embryogenesis.     

Occurrence of mitochondrial monoamine oxidase in human semen.

Mitochondrial monoamine oxidase (MAO) was found in human semen, showing its Km and Vmax values of 91.7 microM and 290 pmoles/mg of protein/60 min, respectively, with kynuramine as substrate. A major part of the activity was due to type A MAO.     

Oxidation of synephrine by type A and type B monoamine oxidase

Summary Synephrine (SP) was found to be a substrate for monoamine oxidase (MAO) in rat brain mitochondria, showing the K_m and V_max values of 250 M and 32.6 nmoles/mg of protein/30 min respectively. The inhibition studies showed that the SP oxidation was carried out by both type A and type B MAO and a major part of the activity was due to type A MAO.