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.     

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.     

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.     

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.     

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.     

Effect of adrenalectomy and dexamethasone treatment on the monoamine oxidase activity in the thyroid gland of the rat

Summary Adrenalectomy increased MAO activity in the thyroid gland of rats. The administration (200 g/100 g daily for 7 days) to adrenalectomized rats decreased MAO activity below levels of intact controls.     

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.     

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.     

Chlorodimeform and its effect on monoamine oxidase activity in the cattle tick, Boophilus microplus.

The action of the acaricide, chlorodimeform and its metabolite. N-desmethylchlorodimeform, on the activity monoamine oxidase (MAO) from the cattle tick, Boophilus microplus, were studied. Both compounds were found to be potent in vitro and in vivo inhibitors of the enzyme. However the inhibition of MAO does not seem to be related to the toxic action of the acaricide.     

Chlorodimeform and its effect on monoamine oxidase activity in the cattle tickBoophilus microplus

Summary The action of the acaricide, chlorodimeform and its metabolite, N-desmethylchlorodimeform, on the activity monoamine oxidase (MAO) from the cattle tick,Boophilus microplus, were studied, Both compounds were found to be potent in vitro and in vivo inhibitors of the enzyme. However the inhibition of MAO does not seem to be related to the toxic action of the acaricide.     

Genotype dependence of monoamine oxidase in inbred strains of mice

Summary MAO activity was found to be influenced by the genotype or strain of mouse up to 20 days of age. The strain differences observed may derive from different rates of brain development. A number of neurological mutations comprizing three pathological classes had no effect on MAO.This work was supported in part by NIH grant No. NS06448 from the National Institute of Neurological Disease and Stroke.     

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.     

Platelet monoamine oxidase B: Use and misuse

The human platelet in addition to having serotonin (5-HT) receptors, uptake carriers (receptor) and transmitter storage vesicles, primarily possesses mitochondrial monoamine oxidase (MAO) type B. Similar to the major form of MAO in the human brain, this enzyme actively oxidizes A-B and B substrates (tyramine, dopamine, phenylethylamine) as well as the novel secondary amine anticonvulsant, milacemide and dopaminergic neurotoxin, MPTP. 5-HT oxidation is hardly affected by the platelet enzyme and MAO inhibitors have no net effect on its accumulation. MAO-B is selectively inhibited by 1-deprenyl and thus the platelet enzyme may be useful to monitor the anti-Parkinson activity of such drugs, as related to their ability to inhibit brain MAO-B. The oxidation of the anticonvulsant, milacemide, to glycine in vitro and in vivo by MAO-B, may herald new prospects for the development of inert prodrugs capable of being metabolized to neuroactive substances by MAO-B. The plasma levels of their metabolites may be an index of MAO-B activity found in the platelet and brain.     

Platelet monoamine oxidase B: use and misuse

The human platelet in addition to having serotonin (5-HT) receptors, uptake carriers (receptor) and transmitter storage vesicles, primarily possesses mitochondrial monoamine oxidase (MAO) type B. Similar to the major form of MAO in the human brain, this enzyme actively oxidizes A-B and B substrates (tyramine, dopamine, phenylethylamine) as well as the novel secondary amine anticonvulsant, milacemide and dopaminergic neurotoxin, MPTP. 5-HT oxidation is hardly affected by the platelet enzyme and MAO inhibitors have no net effect on its accumulation. MAO-B is selectively inhibited by 1-deprenyl and thus the platelet enzyme may be useful to monitor the anti-Parkinson activity of such drugs, as related to their ability to inhibit brain MAO-B. The oxidation of the anticonvulsant, milacemide, to glycine in vitro and in vivo by MAO-B, may herald new prospects for the development of inert prodrugs capable of being metabolized to neuroactive substances by MAO-B. The plasma levels of their metabolites may be an index of MAO-B activity found in the platelet and brain.     

The discovery of antidepressants: a winding path

Modern treatment of mental depression started with the availability of monoamine oxidase (MAO) inhibitors and tricyclic antidepressants. These drugs also contributed to the early development of psychopharmacology. Attempts to improve the anti-tuberculous action of the hydrazine derivative isoniazid by developing derivatives thereof led to the synthesis of iproniazid. Its introduction as the first modern antidepressant was based on three unexpected actions of the drug: MAO-inhibition, 'reversal' of reserpine-induced sedation, and the presence of psychostimulation as a clinical side effect in man. However, the initial success of iproniazid and other MAO inhibitors, hydrazides and non-hydrazides, was curtailed by the occurrence of undesirable side effects such as potentiation of the blood-pressure elevating action of food amines. The tricyclic antidepressants were a development of the class of antihistamines, one of which, chlorpromazine, showed neuroleptic activity. A congener of this compound, imipramine, was discovered by clinical observation to have unexpected antidepressant effects. The clinical success of this drug (which is still in use) led to the development of a successful series of other tricyclic and non-tricyclic antidepressants. Progress in the elucidation of possible mechanisms of the action of the tricyclic compounds has helped this development. Recent advances in basic research have also induced a revival of MAO-inhibitors since, due to the discovery of MAO-subtypes, inhibitors with higher specificity and fewer undesirable side effects are now available.     

Monoamine oxidase inhibition by d-amphetamine in ganglia and nerve endings

Summary The inhibition of monoamine oxidase (MAO) activity by d-amphetamine was measured in homogenates of cat superior cervical ganglion and nictitating membrane, using tyramine (TM) and noradrenaline (NA) as substrates. In both tissues, d-amphetamine was shown to be a competitive inhibitor of the oxidation of TM. The Ki for d-amphetamine, as a MAO inhibitor, was lower in the ganglia than in the peripheral nerve endings.Supported by a Contract from the National Research Council of Argentina (CONICET) (Res. 67/79).     

Occurrence of mitochondrial monoamine oxidase in human semen

Summary Mitochondrial monoamine oxidase (MAO) was found in human semen, showing its K_m and V_max values of 91.7 M 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.     

Ontogenesis of monoamine oxidase in the thyroid gland of rats

Summary During postnatal development, MAO activity in the thyroid gland of male rats increases until day 16, when adult values are reached.