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PubMed1977

[5-hydroxytryptophan decarboxylase (5-HTPD) and monoamine oxidase (MAO) activities in the embryonic pineal organ of Lacerta vivipara J. A qualitative and quantitative microscopic study of the uptake of 3H-5-HTP under experimental conditions and the histochemistry of MAO (author's transl)].

Experiments involving combined injections of a drogue (Ro4-4602 or nialmide) and precursor (3H-5-HTP) allowed to determine the best conditions for performing an experimental study of serotonin (5-HT) synthesis and metabolism in the embryonic pineal organ of Lacerta vivipara. Inhibition of 5-HT synthesis at the decarboxylation step using Ro4-4602 significantly reduces the tritiated indolamine rates in the pineal sensory epithelium of embryos of the stages 37-40. In contrast with the embryos of stages 36 to 40 which received injections of 3H-5-HTP only, the secretory rudimentary photoreceptor cells (SRP) of embryos of the same stages which were pretreated with Ro4-4602 do not show a selective radioautographic labeling. After inhibition of the monoamine oxidases with nialomide, the tritiated indolamine rates are significantly increased in the SRP of embryos of stages 35 to 40. Our radioautographic studies show indirectly the early presence of 5-HTPD and MAO in the SRP (stage 35) during the pineal embryogenesis of Lacerta. In the distal part of the pineal, monoamine oxidase activity is histochemically demonstrated at stage 34. During ontogenesis, the reaction becomes increasingly intensive in the apical part of the epithelial cells while it extends to the epithelium of the proximal part of the pineal organ.

5-Hydroxytryptophan↗
PubMed2003

Gene-gene interaction between the monoamine oxidase A gene and solute carrier family 6 (neurotransmitter transporter, noradrenalin) member 2 gene in anorexia nervosa (restrictive subtype).

We earlier found an association between anorexia nervosa (AN) restrictive subtype (AN-R) and an inserted sequence within the NETpPR, a polymorphic region located in the promoter of the solute carrier family 6 (neurotransmitter transporter, noradrenalin) member 2 (SLC6A2) gene. To further examine the noradrenergic system in AN-R we performed an association study with a functional polymorphism (MAOA-uVNTR) in the promoter of the monoamine oxidase A (MAOA) gene. Since monoamine oxidase A metabolises noradrenalin, a positive association with the MAOA gene would be biologically plausible. The transmission disequilibrium test and 95 trios/duos (AN-R females+biological parents) showed the main effect of the longer, more transcriptionally active form of the MAOA-uVNTR (MAOA-L) to be statistically non-significant (McNemar's chi(2)=1.4, df=1, P=0.238, odds ratio: 1.4, 95% CI 0.8-2.7). A case-control approach supported this finding. We then stratified the MAOA-uVNTR TDT data according to the (a) NETpPR genotype of the AN-R females, and (b) NETpPR allele transmitted from NETpPR-S4/L4 heterozygous mothers. In both cases, contingency table analysis revealed previously unreported gene-gene interaction between the MAOA and SLC6A2 genes (P=0.019 and 0.019, respectively). Receiving an MAOA-L allele more than doubles the risk for developing AN-R, conditional on an individual also being a NETpPR-L4 homozygote (stratum-specific odds ratio: 2.4, 95% CI 1.1-6.0). These results suggest important involvement of the noradrenergic system in the biological underpinnings of AN-R.

Anorexia Nervosa↗
PubMed1977

Effects of monoamine oxidase inhibitors on the borohydride stabilizable binding of serotonin and tryptamine in brain.

The in vivo and in vitro effects of various monoamine oxidase inhibitors (MAOI) on the borohydride stabilizable finding of serotonin (5-HT) or tryptamine in brain was investigated. A significant correlation between the extent of Mao inhibition and the amount of stabilized binding of the indolealkylamines was demonstrated. All hydrazine-type MAOI and harmine, a reversible nonhydrazine-type MAOI, employed in vitro, were shown to decrease the binding. beta-Phenylisopropylhydrazine apparently blocks the receptor carbonyl groups in the brain in vitro as well as in vivo.

Animals↗
PubMed1985

Chronic administration of type A monoamine oxidase inhibitors increases duration of thiopentone anaesthesia in the rat.

Daily intraperitoneal administration for fifteen days of the mixed type A and type B monoamine oxidase inhibitors phenelzine, isocarboxazid, iproniazid and tranylcypromine caused a marked increase in the duration of thiopentone anaesthesia ('sleeping time') tested 48 hours after the last drug injection. This effect was not due to accumulation of drug or other carryover since it failed to occur after 5 days of daily administration. Similar prolongation of anaesthesia was seen after 15, but not 5 days of administration of the selective type A monoamine oxidase inhibitors clorgyline and LY 51641 but not with the type B inhibitors pargyline and deprenyl.

Anesthesia↗
PubMed1973

The oestrous cycle and monoamine oxidase activity.

1. During the oestrous cycle of the rat, monoamine oxidase (MAO) activity was studied in the uterus, the ovaries and the adrenal glands and also in 4 brain regions which are rich in monoamines. In all these structures the activity was lowest during the night between oestrus and metoestrus. High values were found in di-oestrus, with the exception of the uterus in which the MAO activity reached its peak during metoestrus.2. A stimulating effect of progesterone on uterine, ovarian and adrenal MAO activity was observed.3. An index for the cyclic variations in progesterone production was obtained by measuring the adrenal and ovarian progesterone content at the same stages of the cycle as MAO activity.4. The sum of the amounts of progesterone contained in the ovaries and adrenal glands was low in early oestrus but increased during late oestrus when MAO activity was at its minimum. Progesterone contents were high in met- and di-oestrus when MAO activity was also high.

Adrenal Glands↗
PubMed1990

Monoamine oxidase inhibition by moclobemide and 2-amino-ethyl carboxamide derivatives: mode of action and kinetic characteristics.

The selective, reversible inhibitors of monoamine oxidase (MAO) moclobemide and Ro 41-1049 (selective for MAO-A), as well as of Ro 16-6491 and Ro 19-6327 (selective for MAO-B) inhibited the enzyme with an initial competitive phase, followed by a time-dependent inhibition of MAO. Ro 41-1049, Ro 16-6491 and Ro 19-6327, being activated by MAO into reversible adducts, fit into the classification as mechanism-based inhibitors. Conversely, since no product formation was observed after incubation of tissue homogenates with moclobemide, this drug probably belongs to the class of the "slow-binding" MAO inhibitors.

Animals↗
PubMed1992

4-Methoxytranylcypromine, a monoamine oxidase inhibitor: effects on biogenic amines in rat brain following chronic administration.

4-Methoxytranylcypromine (MeOTCP), a ring-substituted analogue of the monoamine oxidase (MAO)-inhibiting antidepressant tranylcypromine (TCP), was investigated in the rat after chronic (28-day) administration and the results compared with those observed with TCP using equimolar doses of both drugs. At the dose tested, MeOTCP produced a greater inhibition of type A MAO in brain, liver, and heart than did TCP. Both drugs caused a reduction in the specific binding to beta-adrenergic and tryptamine receptors in cortex from brain. MeOTCP produced a marked increase in 5-hydroxytryptamine levels in pons-medulla, hypothalamus, and hippocampus relative to values in vehicle-treated rats and also produced a significant increase in these levels over those observed in the TCP-treated rats.

Animals↗
PubMed1997

Monoamine oxidase inhibitor sensitive site implicated in sensitization to quinpirole.

Clorgyline (1.0 mg/kg/day) administered via osmotic minipumps blocked the development of locomotor sensitization to the dopamine receptor agonist quinpirole (0.5 mg/kg every 3 days for 8 injections). In male rats already well sensitized to quinpirole, the continuous infusion of clorgyline (1.0 mg/kg/day for 28 days) produced a progressive decline in locomotor activity, despite a continued regimen of quinpirole injections (0.5 mg/kg every 3 days). It is suggested that the development, as well as the maintenance, of locomotor sensitization to quinpirole is modulated by the activation of an monoamine oxidase inhibitor-sensitive site. This site may be a dopamine D2 receptor-linked monoamine oxidase inhibitor-displaceable quinpirole binding site, the enzyme monoamine oxidase-A, or other clorgyline binding sites.

Animals↗
PubMed1988

Alterations of serotonin neurotransmission and inhibition of mouse killing behavior: II. Effects of selective and reversible monoamine oxidase inhibitors of type A.

Three groups of rats were tested for mouse killing behavior after IP injection of selective and reversible type A monoamine oxidase inhibitors. The rats were either spontaneous killers, or non-killers which acquired killing behavior following para-chlorophenylalanine treatment or electrolytical destruction of dorsal and median raphe nuclei. Moclobemide (para-chloro-N-(2-morpholinoethyl)-benzamide), cimoxatone (3-(4-(3-cyanophenyl-methoxy)phenyl)-5-(methoxy-methyl)-2-oxazo lid inone, MD 780515), toloxatone (5-(hydroxymethyl)-3-(3-methylphenyl)-2-oxazolidinone) and amiflamine ((+)-4-dimethylamino-2, alpha-dimethylphenethyl amine, FLA 336 (+)) were used as selective and reversible monoamine oxidase inhibitors of type A. Cimoxatone, toloxatone and amiflamine inhibited mouse killing behavior of spontaneous killer rats without apparent sedation, whereas moclobemide was not efficient at doses which did not decrease locomotor activity. A similar inhibition of mouse killing behavior was obtained in spontaneous and serotonin depleted killer rats. The results are discussed in relation to the behavioral expression of serotoninergic supersensitivity in the three groups of killer rats described earlier using serotonin agonist and uptake inhibitors.

Aggression↗
PubMed1977

Monoamine oxidase in rat reticulocytes: subcellular localization and identification of isoenzymes.

After "chemically induced reticulocytosis" in rats by treatment with acetyl-phenylhydrazide, monoamine oxidase (MAO) activities were determined in erythrocyte preparations of these animals. Studies on subcellular fractions obtained by differential centrifugation showed that the enzyme activity of rat reticulocytes is a classical mitochondrial MAO. The patterns of inhibition produced by clorgyline (A-type MAO), deprenil (B-type MAO) and pargyline or tranylcypromine (both types of MAO) in reticulocytes were determined in vitro using tryptamine as a substrate for both types of MAO and phenylethylamine as a substrate for the B-type. The results indicate that both A-type (approximately 75%) and B-type (approximately 25%) MAO are present in rat reticulocytes; while tryptamine was mainly deaminated by the A-type enzyme, both types of MAO were shown to contribute to the deamination of phenylethylamine. These findings were confirmed in investigations on the thermostabilities of the tryptamine and phenylethylamine deaminating activities of rat reticulocyte MAO.

Animals↗
PubMed1991

Measurement of cerebral monoamine oxidase B activity using L-[11C]deprenyl and dynamic positron emission tomography.

A tracer kinetic procedure was developed for the measurement of monoamine oxidase type B (MAO-B) activity using L-[11C]deprenyl and positron emission tomography (PET). The kinetic model consisted of two tissue compartments with irreversible binding to the second compartment (three rate constants). In addition, a blood volume component was included. Special attention was given to the accurate measurement of the plasma and whole blood input functions. The method was applied to the measurement of the dose-response curve of a reversible MAO-B inhibitor (Ro 19-6327). From the results, it followed that the rate constant for irreversible binding (k3) appeared to be a better index of MAO-B activity than the net influx constant Ki. Furthermore, regional analysis demonstrated that Ki, but not k3, was flow dependent. This implies that full kinetic analysis is required for an accurate assessment of MAO-B activity.

Aged↗
PubMed1976

Metabolic interaction of secondary amines and tertiary amino propiophenones with monoamine oxidase systems.

The metabolic interaction of three secondary amines and three nitrogen-containing metabolites of safrole (tertiary amino propiophenones) with rat liver mitochondrial monoamine oxidase systems was studied in vitro employing [7-14C] benzylamine--HCl as a substrate. The two cyclic secondary amines, piperidine and pyrrolidine, showed hyperbolic competitive inhibition while pure competitive inhibition was observed in case of dimethylamine--HCl and three safrole metabolites. Inhibition characteristics for rat liver, kidney and brain mitochondrial monoamine oxidase with two cyclic secondary amines and tertiary amino with two cyclic secondary amines and tertiary amino propiophenones of safrole and elemicin were investigated manometrically using tyramine and serotonin as the substrates.

Animals↗
PubMed1987

Salicylate and mitochondrial monoamine oxidase function in Reye's syndrome.

The main objective of this investigation was to study the effect of salicylate on platelet mitochondrial monoamine oxidase (MAO) activity isolated from blood of two patients with Reye's syndrome. Comparative studies were made with hospitalized children without Reye's syndrome (n = 27) and healthy children (n = 19) serving as controls. Platelet MAO was measured by a radioenzymatic technique with [14C]tyramine as a substrate. The results of this study showed that salicylate (1.0 mM) caused an appreciable inhibition of the platelet MAO activity of patients with Reye's syndrome at the onset of the illness. This was demonstrated by a greater than 50% reduction in enzyme maximum velocity (Vmax) value. The salicylate MAO-inhibitory effect was maintained throughout the duration of the illness. Salicylate had only a minimal MAO-inhibitory effect on platelets isolated from blood of recovered Reye's syndrome patients, healthy controls, and non-Reye's hospitalized children, and no apparent effect on enzyme Vmax values. These preliminary findings suggest that salicylate-induced mitochondrial injury may affect MAO function in children with Reye's syndrome.

Adolescent↗
PubMed1986

MD 240928 and harmaline: opposite selectivity in antagonism of the inactivation of types A and B monoamine oxidase by pargyline in mice.

In mice treated 24 hrs earlier with pargyline (20 mg/kg i.p), both type A and type B monoamine oxidase (MAO-A and MAO-B) were partially inactivated in brain, heart and liver. The abilities of two short-acting, reversible inhibitors of MAO to antagonize that inactivation were compared. Pretreatment with MD 240928 at doses of 10, 20 or 30 mg/kg i.p. antagonized the inactivation of type B MAO but did not alter the inactivation of type A MAO in all three tissues. In contrast, pretreatment with harmaline at a dose of 10 mg/kg i.p. antagonized the inactivation of type A MAO but did not alter the inactivation of type B MAO. Antagonism of the pargyline-induced inactivation is interpreted as being due to the transient selective inhibition of MAO-A by harmaline and of MAO-B by MD 240928, preventing the mechanism-based inactivation of those enzymes by pargyline. The selective protection by harmaline is in agreement with earlier results with that compound in rats; the selective protection by MD 240928 is the first report of selective protection against MAO-B inactivation.

Alkaloids↗
PubMed1983

Effect of selective monoamine oxidase inhibition by clorgyline and deprenyl on the norepinephrine receptor-coupled adenylate cyclase system in rat cortex.

The consequences of selective monoamine oxidase (MAO) inhibition on the norepinephrine(NE)-sensitive adenylate cyclase system were determined in slices of rat cerebral cortex. The chronic administration of clorgyline, which selectively inhibited the activity of MAO-A, caused a significant decrease in the responsiveness of the noradrenergic cyclic AMP-generating system. The noradrenergic subsensitivity was accompanied by a significant decrease in the density of beta-adrenoceptors, as measured by 3H-dihydroalprenolol (DHA) binding, without altering the Kd value. However, selective inhibition of MAO-B by deprenyl did not alter the sensitivity of the cyclic AMP-generating system to NE or the specific DHA binding. The basal levels of cyclic AMP in the cortex were unaltered by the drugs. Since inhibition of MAO-A, but not MAO-B, increases the availability of NE, the results support the hypothesis that a persistent NE-receptor interaction is one of the prerequisites for the in vivo densitization of the NE-sensitive adenylate cyclase and the concomitant down-regulation of the number of beta-adrenoceptors in brain.

Adenylyl Cyclases↗
PubMed1989

Inhibition of monoamine oxidase within monoaminergic neurons in the rat brain by (E)-beta-fluoromethylene-m-tyrosine (MDL 72394).

The irreversible inhibition of the monoamine oxidase (MAO) activity within monoaminergic neurons in the rat brain 24 h after single or repeated administration of (E)-beta-fluoromethylene-m-tyrosine (FMMT, MDL 72394) was examined. The enzyme activity was determined by incubating synaptosome-rich homogenates of hypothalamus or striatum with low concentrations of 5-[14C]hydroxytryptamine (5-HT), [14C]noradrenaline (NA), or [14C]dopamine (DA) in the absence and presence of the selective amine uptake inhibitors citalopram (5-HT), maprotiline (NA), and GBR 12909 (DA). After a single subcutaneous injection of FMMT, the inhibition of MAO within the noradrenergic and dopaminergic neurons was significant but only slightly greater than that outside these neurons. The opposite relationship was observed for the serotonergic neurons. After 7 days' treatment of rats with carbidopa, 20 mg/kg p.o., + FMMT once daily, the preference for the inhibition of MAO within the noradrenergic and dopaminergic neurons was accentuated further. The inhibition outside the serotonergic neurons was still greater than within these neurons. The NA uptake inhibitor CPP 199 antagonized the selective inhibition of MAO within the noradrenergic neurons, which indicates that this preference is due to the accumulation of the active metabolite (E)-beta-fluoromethylene-m-tyramine by the NA transporter.

Animals↗
PubMed2003

Attenuation of MPTP-induced dopaminergic neurotoxicity by TV3326, a cholinesterase-monoamine oxidase inhibitor.

(R)-[(N-propargyl-(3R) aminoindan-5-yl) ethyl methyl carbamate] (TV3326) is a novel cholinesterase and brain-selective monoamine oxidase (MAO)-A/-B inhibitor. It was developed for the treatment of dementia co-morbid with extra pyramidal disorders (parkinsonism), and depression. On chronic treatment in mice it attenuated striatal dopamine depletion induced by MPTP and prevented the reduction in striatal tyrosine hydroxylase activity, like selective B and non-selective MAO inhibitors. TV3326 preferentially inhibits MAO-B in the striatum and hippocampus, and the degree of MAO-B inhibition correlates with the prevention of MPTP-induced dopamine depletion. Complete inhibition of MAO-B is not necessary for full protection from MPTP neurotoxicity. Unlike that seen after treatment with other MAO-A and -B inhibitors, recovery of striatal and hippocampal MAO-A and -B activities from inhibition by TV3326 did not show first-order kinetics. This has been attributed to the generation of a number of metabolites by TV3326 that cause differential inhibition of these enzymes. Inhibition of brain MAO-A and -B by TV3326 resulted in significant elevations of dopamine, noradrenaline and serotonin in the striatum and hippocampus. This may explain its antidepressant-like activity, resembling that of moclobemide in the forced-swim test in rats.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1993

Effect of structural modification of alkyl N-propargylamines on the selective inhibition of monoamine oxidase B activity.

A series of alkyl N-methyl-propargylamine derivatives has been discovered recently to be very potent selective irreversible monoamine oxidase B inhibitors (MAO-B). In the present study, we used a simple compound in this series, namely N-2-butyl-N-methylpropargylamine.HCl (2-BuMP), as the basic structure to investigate the effect of structural modification on the effectiveness and selectivity of the inhibition of MAO activities. When the N-methyl group was replaced by a hydrogen atom, an ethyl group or a propargyl group, MAO inhibitory activity was abolished. The modification of the propargyl group, e.g. to 3-butynyl, N-cyanomethyl or to allyl groups, also destroyed the inhibitory activity. The potency of the inhibitors was related to the carbon chain length of the alkyl group as well as to the substitution of the alpha or the terminal carbon atoms. Substitution of hydroxyl, carboxyl or carboethoxyl groups on the terminal carbon of the alkyl chain drastically reduced the inhibitory activity. More potent MAO inhibitory activity was observed for molecules with a single methyl group substitution on the alpha carbon in comparison with those substituted with two hydrogen or two methyl groups. Other branched alkyl N-methylpropargylamines, e.g. N-methyl-N-(3-pentyl)propargylamine, appeared to be slightly less selective in the inhibition of MAO-B activity. Some of these alkyl propargylamine MAO-B inhibitors, which do not possess the amphetamine-like moiety of L-deprenyl, may have significant neuropsychopharmacological implications.

Alkylation↗