Increased tryptophan decarboxylase and monoamine oxidase activities induce Sekiguchi lesion formation in rice infected with Magnaporthe grisea.

Sekiguchi lesion (sl)-mutant rice infected with Magnaporthe grisea showed increased light-dependent tryptophan decarboxylase (TDC) and monoamine oxidase (MAO) activities. TDC and MAO activities were observed before the penetration of M. grisea to rice cells and maintained high levels even after Sekiguchi lesion formation. Light-dependent expression of TDC gene was observed in leaves inoculated with M. grisea before Sekiguchi lesion formation. Spore germination fluid (SGF) of M. grisea also induced Sekiguchi lesion formation accompanied by increased enzymes activities and tryptamine accumulation. Sekiguchi lesion was also induced by treatments with tryptamine and beta-phenylethylamine, which are substrates for MAO, but was not induced by non-substrates such as indole-3-propionic acid, (+/-)-phenylethylamine and tryptophan under light. Light-dependent induction of Sekiguchi lesion by tryptamine was significantly inhibited in the presence of MAO inhibitors, metalaxyl and semicarbazide, and H2O2-scavengers, ascorbic acid and catalase. H2O2 in M. grisea-infected leaves with and without Sekiguchi lesions was demonstrated directly in situ by strong 3,3'-diaminobenzidine (DAB) staining. On the other hand, H2O2 induced Sekiguchi lesions on leaves of cv. Sekiguchi-asahi under light, but not in darkness. This difference was associated with the decrease of catalase activity in infected leaves under light and the absence of decrease in darkness. We hypothesize that the H2O2-induced breakdown of cellular organelles such as chloroplasts and mitochondria in mesophyll cells may cause high TDC and MAO activities and the development of Sekiguchi lesion, and that the sl gene products in wild-type rice may function as a suppressor of organelle breakdown caused by chemical or environmental stress.

[The effect of electromagnetic radiation on the monoamine oxidase A activity in the rat brain]. / Vliianie élektromagnitnogo izlucheniia na aktivnost' monoaminooksidazy A v mozge krys.

The effect of the ultralow power pulse-modulated electromagnetic radiation (EMR, power density 10 microW/cm2; carrying frequency 915 MHz; modulating pulses with frequency 2, 4, 6, 8, 12, 16 and 20 Hz) on activity of monoamine oxidase (MAO-A), enzyme involved in the oxidative deamination of monoamines, was investigated. It was established that the increase of activity MAO in hypothalamus reached the maximal meaning at modulation frequency of 6 Hz that corresponded 160% (p < 0.01) of the control level; and at modulation frequency of 20 Hz the decrease of enzyme activity up to 74% (p < 0.01) was found. Mainly the action of ultralow power pulse-modulated EMR on activity of MAO in hippocamp was activating; and the maximal increase of enzyme activity up to 174% (p < 0.01) was registered at modulation frequency of 4 Hz.

Activities of monoamine oxidase-A and -B in adult rat cerebellum following neonatal X-irradiation.

The activities of monoamine oxidases, MAO-A and MAO-B, were separately determined in the cerebellum (CE) from adult rats neonatally exposed to 5 Gy X-irradiation. They were found to be markedly reduced: 58% and 66% of values from nonirradiated, littermate controls. Since the specific activities of both isoenzymes (per mg tissue weight) were not significantly different from controls, the reduction of activity per CE is basically explained by the irradiation-induced cerebellar atrophy. The unmodified MAO-A specific activity makes it highly improbable that the increase in the cerebellar noradrenaline content, characteristic of neonatally X-irradiated rats, could be due to a decreased neuronal metabolism of noradrenaline by this enzyme.

[Pyridoxal phosphate as an agent for normalizing the monoamine oxidase activity of the brain in radiation sickness]. / Piridoksal'fosfat kak sredstvo normalizatsii monoaminoksidaznoi aktivnosti golovnogo mozga pri luchevoi bolezni.

A study was made of the influence of the coenzyme pyridoxal phosphate on the activity of mitochondrial monoaminoxidase (MAO) catalyzing oxidative deamination of serotonin at the exacerbation of acute radiation disease (on the 6th day after radiation exposure) in different parts of the brain (cerebral hemisphere, stem and cerebellum). Experiments were staged on rabbits, irradiated by x-ray at a dose of 4.5 Gy with a dose rate of 0.33 Gy/min. The peak of radiation disease was characterized by considerable changes in MAO activity resulting in catalysis of oxidative deamination of serotonin in different parts of the brain and in different mitochondrial subfractions. Pyridoxal phosphate produced a positive effect on monoaminoxidase activity, catalyzing serotonin deamination, and as a coenzyme it can be incorporated in a complex of drugs used for normalization of metabolism of mediators of the nervous system as well as for therapy of radiation injuries.

Alterations in monoamine oxidase activity of the mouse brain and liver after mixed neutron-gamma irradiation.

Monoamine oxidase (MAO) plays an important role in the metabolism of neuro-transmitter biogenic amines. Its activity was determined in mouse brain and liver after exposure to different kinds of ionizing radiation and after pretreatment with a radioprotective agent. After a lethal dose of mixed neutron-gamma irradiation the MAO activity decreased in the brain and increased in the liver. In contrast, after a lethal dose of 60Co-gamma irradiation enzyme activity was considerably increased in the brain while in the liver it increased like after mixed neutron-gamma irradiation. AET (S2-aminoethyl-isothiuronium-Br X HBr), when administered in a radio-protective dose, inhibited MAO activity in the brain, while it increased in the liver. Even more marked changes of enzyme activity were observed in both brain and liver after AET pretreatment and mixed neutron-gamma irradiation. On the basis of the results it is suggested that different kinds of ionizing radiation lead to different types of lipid peroxidation in the lipid environment surrounding MAO, an event leading to altered enzyme activity. AET itself inhibited MAO in the brain and increased the activity in the liver but did not prevent the alterations caused by ionizing radiation in enzyme activity.

Free-radical-mediated fragmentation of monoamine oxidase in the mitochondrial membrane. Roles for lipid radicals.

A flux of hydroxyl radicals generated by gamma-irradiation can fragment monoamine oxidase in the membrane of submitochondrial particles. This fragmentation can be inhibited by mannitol and in addition is more extensive in monoamine oxidase preparations that have been depleted of lipid. This latter observation is consistent with the higher yields of fragmentation induced by hydroxyl radicals in soluble proteins in the absence of added lipids. In the absence of oxygen, gamma-irradiation of submitochondrial particles leads to cross-linking reactions. A flux of hydroperoxyl radicals also causes fragmentation, whereas one of superoxide is virtually inactive in this respect. The irradiation of submitochondrial particles leads in addition to the accumulation of products of lipid peroxidation. When these irradiated preparations are exposed to ferrous or cupric salts a further fragmentation of monoamine oxidase ensues, especially at acid pH. These transition-metal-catalysed reactions do not occur with irradiated preparations depleted of lipid, and the post-irradiation protein modifications are concomitant with further lipid peroxidation. The data indicate roles for lipid radicals in both fragmentation and cross-linking reactions of proteins in biological membranes. These reactions may have an important bearing on control of protein activity and of protein turnover in membranes.

The dopamine metabolite 3-methoxytyramine is not a suitable indicator of dopamine release in the rat brain.

It has been postulated that changes in the concentration of 3-methoxytyramine (3-MT) in the brain might reflect changes in the release of 3,4-dihydroxyphenylethylamine (DA, dopamine) and, therefore, might be used as an index of dopaminergic activity in the brain. 3-MT is known to accumulate rapidly after death. Killing by microwave irradiation (MWR) is considered to be the method of choice to obtain "undisturbed" 3-MT concentrations. We measured striatal 3-MT concentrations even lower than those following MWR when the brains were excised and frozen in dry ice very rapidly (typical time between decapitation and freezing of the brain 22 s). There was a linear increase in striatal 3-MT concentration when the time between decapitation and freezing was varied between 13 and 300 s. Extrapolation to time zero indicated negligible amounts of 3-MT at the time of decapitation. In addition, it was observed that DA, 3,4-dihydroxyphenylacetic acid, and homovanillic acid decompose during the cooling phase after heating the brain by microwave. It is concluded that MWR induces artifactual changes in the postmortem levels of DA and metabolites. Consequently 3-MT cannot be considered to be a reliable indicator of DA release in the rat brain.

Inhibition of monoamine oxidase by phenyl azides.

We had previously shown that 4-fluoro-3-nitrophenyl azide (FNPA) is a competitive inhibitor of both types of monoamine oxidase (MAO) in the dark, but it is a preferential photoaffinity label for only the type B MAO (MAO-B). Recently we synthesized a number of arylazido compounds with structures related to FNPA and determined the effects of these compounds on the two types of MAO in rat brain cortex. We found that the fluoro group of FNPA was not required for the inhibition of MAO activities because neither the presence nor the position of the fluoro group affected its inhibition of MAO. On the other hand, both the nitro and the azido groups of FNPA were shown to be important for FNPA inactivation of two types of MAO. The inhibitory potency was significantly lower for compounds without either group. Furthermore, we found that all nitrophenyl azide isomers except 2-nitrophenyl azide were photodependent inhibitors of MAO-B. Under the same experimental conditions none of the compounds photoinactivated MAO-A. On the basis of these findings, mechanisms for FNPA inhibition of the two types of MAO are discussed.

[Monoamine oxidase (MAO) activity in the liver and brain of guinea pigs exposed to an electric field of industrial frequency]. / Zachowanie sie monoaminooksydazy (MAO) w watrobie i mózgu swinek morskich poddanych ekspozycji pola elektrycznego o czestotliwosci przemyslowej.

The activity of MAO has been determined in the brain and liver of 36 male guinea-pigs. The animals have been exposed to electric fields of 50 Hz and 100 kV/m frequency. The guinea-pigs have been divided into the following groups (12 animals each): group I--every day 4 hrs' exposure to electric fields (total dose--100 hours), group II--4 hrs' exposure every other day (total dose--100 hours), group III--4 hrs' exposure every third day (total dose--100 hours). The control group consisted of 8 animals. Enzymatic determinations of MAO have been performed by McEven and Cohen's technique, using benzylamine as substrate. A statistically significant increase of MAO activity in brain homogenates of group I and slow decrease in groups II and III, to the control value, has been shown. No changes of the test enzyme have been found in the liver tissue.

The activity of monoamine oxidases A and B in gamma-irradiated rabbit brains.

The activities of monoamine oxidases A and B towards 5-hydroxytryptamine and beta-phenethylamine, respectively, were compared in the left and right caudatus, hippocampus, parietal cortex, cerebellum and frontal cortex 6 months after gamma-irradiation (single dose of 23 Gy) of either the right hemisphere or of the whole rabbit brain (in which case, a dose of l6 Gy). No difference in monoamine oxidase A or B activities were found in any of the brain regions.

Rapid microwave fixation of rat brain.

A new microwave device which inactivates brain enzymes rapidly and uniformly is described. From the results obtained with microwave irradiation at two power levels (0.8 kW and 4.5 kW), it has been demonstrated that the high power microwave irradiation has several advantages over the low power irradiation. In its application to neurochemical studies, significant increase in the DOPAC level was found in the irradiated brain, while there were no statistical differences in the levels of NE, DA, 5-HT and 5-HIAA between microwave irradiation and decapitation. Significant increase in the Ach level and marked reduction of the choline level were observed after microwave irradiation. There were no significant differences in the level of cyclic GMP in the brain between the two methods of sacrifice, while significant reduction of the cyclic AMP level was observed in the irradiated brain.

Serotonin and proteolytic enzymes in brain of irradiated animals.

Early and late irradiation effects on biogenic amines (5-HT and NA) contents, intracellular hydrolytic enzyme activity and MAO in brain tissue was studied on mice and rats. In mice in the majority of cases (irradiated on the first day after birth) there occurs a remote effect of irradiation in the form of the increase in 5-HT content and different, species-dependent, changes in hydrolytic activity. Among early effects (24 hrs following the irradiation) the decrease in 5-HT and NA contents was stated in rats. These changes were accompanied by the increase in MAO and hydrolytic (proteolytic) activities.