Antidepressants attenuate the dexamethasone-induced decrease in viability and proliferation of human neuroblastoma SH-SY5Y cells: A involvement of extracellular regulated kinase (ERK1/2)

Excessive glucocorticoid levels in depressed patients have been associated with atrophic changes in some brain regions, but only few studies suggest that some antidepressants can interfere with deleterious effect of glucocorticoids on neuronal cells. The aim of the present study was to examine the effect of dexamethasone (DEX), a synthetic glucocorticoid and some antidepressants from different chemical groups (imipramine, desipramine, amitriptyline, citalopram, fluoxetine, reboxetine and tianeptine) on SH-SY5Y cells cultured in the medium containing steroid-free serum. DEX in concentrations from 1 to 100 μM did not change LDH release but exposure to 10 μM and 100 μM DEX for 24, 48 and 72 h caused a significant reduction in cell viability and proliferation as confirmed by MTT reduction and BrdU ELISA assays, respectively. Twenty four-hour incubation of cells with antidepressants (0.05–10 μM) and DEX (10 μM) showed that imipramine, amitriptyline, desipramine, citalopram and fluoxetine at concentrations from 0.1 up to 1 μM, reboxetine (0.1 μM) and tianeptine (0.05 μM) prevented the DEX-induced decreases in cell viability and proliferation rate. The protective effects of antidepressants were ameliorated by inhibitors of MAPK/ERK1/2, but not PI3-K/Akt pathway as shown for imipramine, fluoxetine and reboxetine. Moreover, Western blot analysis showed the decrease in the activated form of ERK1/2 (p-ERK) after DEX treatment and this effect was inhibited by imipramine. Thus, the reduction in SH-SY5Y cell viability caused by DEX appears to be related to its antiproliferative activity and some antidepressant drugs in low concentrations attenuate this effect by mechanism which involves the activation of MAPK/ERK1/2 pathway.     

Analysis of eighteen antidepressants,four atypical antipsychotics and active metabolites in serum by liquid chromatography: a simple tool for therapeutic drug monitoring

Therapeutic drug monitoring necessitates efficient, fast and reliable analytical methods validated by external quality control. We therefore devised an isocratic reversed-phase HPLC method with ultraviolet detection and optimised this to quantify mirtazapine, reboxetine, moclobemide, venlafaxine, O-desmethylvenlafaxine, paroxetine, fluvoxamine, fluoxetine, norfluoxetine, sertraline, citalopram, amitriptyline, nortriptyline, imipramine, desipramine, doxepin, nordoxepin, clomipramine, norclomipramine, trimipramine, mianserine, maprotiline, normaprotiline, amisulpride, clozapine, norclozapine, quetiapine, risperidone and 9-OH-risperidone in human serum. After solid-phase extraction of the drugs and metabolites, the chromatographic separation was achieved on a Nucleosil 100-Protect 1 column with acetonitrile-potassium dihydrogenphosphate buffer as mobile phase. The method was validated for therapeutic and toxic serum ranges. A linear relationship (r>0.998) was obtained between the concentration and the detector signal. Recoveries were between 75 and 99% for the drugs and metabolites. The accuracy of the quality control samples, expressed as percent recovery, ranged from 91 to 118%; intra- and inter-assay-relative standard deviations were 0.9-10.2% and 0.9-9.7%, respectively. Additional external quality control is carried out since 3 years. This method is applicable to rapidly and effectively analyze serum or plasma samples for therapeutic drug monitoring of about 30 antidepressants and atypical antipsychotics.     

The opposite effect of isotype-selective monoamine oxidase inhibitors on adipogenesis in human bone marrow mesenchymal stem cells

Adiponectin production during adipocyte differentiation of human bone marrow mesenchymal stem cells (hBM-MSCs) can be used to evaluate the pharmacological activity of anti-diabetic drugs to improve insulin sensitivity. Monoamine oxidase (MAO) inhibitors such as phenelzine and pargyline inhibit adipogenesis in murine pre-adipocytes. In this study, however, we found that selective MAO-A inhibitors, moclobemide and Ro41-1049, and a selective MAO-B inhibitor, selegiline, promoted adiponectin production during adipocyte differentiation in hBM-MSCs, which suggested the anti-diabetic potential of these drugs. In contrast, non-selective MAO inhibitors, phenelzine and tranylcypromine, inhibited adipocyte differentiation of hBM-MSCs. Concomitant treatments of MAO-A and MAO-B selective inhibitors did not change the stimulatory effect on adiponectin production in hBM-MSCs. Taken together, the opposite effects of isotype-selective MAO inhibitors on adiponectin production during adipogenesis in hBM-MSCs may not be directly associated with the inhibitory effects of MAO, suggested that the structure of MAO inhibitors may contain a novel anti-diabetic pharmacophore.     

Differential Postnatal Development of Monoamine Oxidases A and B in the Blood-Brain Barrier of the Rat

Abstract: We studied the monoamine metabolizing mitochondrial enzyme, monoamine oxidase (MAO), in cerebral microvessels obtained from postnatally developing rats by measuring the specific binding of [³H]pargyline, an irreversible inhibitor of MAO, and the rate of oxidation of three known MAO substrates: benzylamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and tryptamine. MAO activity increased postnatally, with the greatest increase occurring in the second week and reaching a peak at 3 weeks of age. A concomitant increase in MAO of the cerebral cortex also occurred, but was several-fold less than that of cerebral microvessels. Using clorgyline and deprenyl, relatively specific inhibitors of MAO-A and MAO-B, we showed that cerebral microvessels contain both forms of MAO at all ages, but there was a major preponderance in the postnatal development of MAO-B. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of rat microvessels after [³H]pargyline binding also showed two distinct bands of radioactivity at all ages. These two bands corresponded to molecular weights of ∼6.5,000 for MAO-A and -60,000 for MAO-B. SDS-PAGE resuits of brain microvessels obtained from 1-, 14-, and 42-day-old rats confirm the differential postnatal development of MAO-B in rat brain microvessels.     

THE EFFECTS OF CHRONIC REGIMENS OF CLORGYLINE AND PARGYLINE ON MONOAMINE METABOLISM IN THE RAT BRAIN

The effects of chronic administration of clorgyline and pargyline on rat brain monoamine metabolism have been examined. The inhibitory selectivity of these drugs towards serotonin deamina-tion (MAO type A) and phenylethylamine deamination (MAO type B) can be maintained over a 21-day period by proper selection of low doses of these drugs (0.5-1.0 mg/kg/24h). The results are consistent with MAO type A catalyzing the deamination of serotonin and norepinephrine and with MAO type B having little effect on these monoamines. Dopamine appears to be dcaminated in vivo principally by MAO type A. Clorgyline administration during a 3-week period was accompanied by persistent elevations in brain norepinephrine concentrations; serotonin levels were also increased during the first 2 weeks, but returned towards control levels by the third week of treatment. Low doses of pargyline did not increase brain monoamine concentrations, but treatment with higher doses for 3 weeks led to elevations in brain norepinephrine and 5-hydroxytryptamine; at this time significant MAO-A inhibition had developed. The changes in monoamine metabolism seen at the end of the chronic clorgyline regimen are not due to alterations in tryptophan hydroxylase activity. At this time tyrosine hydroxylase activity was also unaffected.     

Absence of tissue-bound semicarbazide-sensitive amine oxidase activity in carp tissues

We have previously reported that carp (Cyprinus carpio) tissue mitochondria contain a novel form of monoamine oxidase (MAO), which belongs neither to MAO-A nor to MAO-B of the mammalian enzyme. This conclusion results from the findings that the carp MAO was equally sensitive to a selective MAO-A inhibitor clorgyline and to the MAO-B selective inhibitor l-deprenyl, when tyramine, a substrate for both forms, serotonin or beta-phenylethylamine, a substrate for either A or B-form of mammalian MAO, was used. In the present study, we tried to detect another amine oxidase, termed tissue-bound semicarbazide-sensitive amine oxidase (SSAO), activity in carp tissues. As definition of SSAO was used, such as insensitivity to inhibition of the kynuramine oxidizing activity by an MAO inhibitor pargyline and high sensitivity to the SSAO inhibitor semicarbazide. The results indicated that the oxidizing activity was selectively and almost completely inhibited by 0.1 mM pargyline alone or a combination of 0.1 mM pargyline plus 0.1 mM semicarbazide, but not by 0.1 mM semicarbazide alone. We also tried to detect any SSAO activity by changing experimental conditions, such as lower incubation temperature, higher enzyme protein concentration, a lower substrate concentration and different pH's in the reaction, as the enzyme source. However, still no SSAO activity could be detected in the tissues. These results conclusively indicate that carp tissues so far examined do not contain SSAO activity.     

Deamination of Aliphatic Amines by Monoamine Oxidase A and B Studied Using a Bioluminescence Technique

Deamination of n-octylamine and n-decylamine has been studied in various tissues using a new bioluminescence technique. Selectivity of n-octylamine and n-decylamine as substrates for monoamine oxidase (MAO) A or B has been determined using both clorgyline and (-)-deprenyl inhibition curves and kinetic parameters. Homogenates of rat brain, liver and heart containing predominantly MAO-A or -B were prepared by preincubation for 60 min with (-)-deprenyl or clorgyline (30 nM), respectively. Human placenta (MAO-A) and platelet (MAO-B) were used as reference tissues containing only one MAO form. In tissues (rat liver, brain) containing both MAO forms in equal proportion, inhibition curve studies showed a preference of both substrates for the B form of the enzyme; however, where MAO-A was the major form (rat heart, human placenta), clorgyline was the more effective inhibitor. In the beef brain cortex n-octylamine showed marked preference for MAO-B, whereas n-decylamine was selective toward-MAO-A. Kinetic studies in general supported the picture of greater selectivity of the aliphatic amine substrates for deamination by MAO-B, as reflected by lower Km values for this enzyme type. However, n-octylamine was more selective for MAO-B than n-decylamine in both kinetic and inhibition curve studies. The deamination of these aliphatic amine substrates cannot be explained only by reference to the binary classification of MAO into types A and B.     

Serotonin Metabolism by Monoamine Oxidase in Rat Primary Astrocyte Cultures

The oxidative deamination of serotonin (5-HT) to 5-hydroxyindoleacetic acid (5-HIAA) by rat primary astrocyte cultures was investigated in intact cells using HPLC. All detectable 5-HIAA accumulated in the extracellular medium, and its rate of production was proportional to the 5-HT concentration over the tested range of 5 x 10(-7) to 10(-4) M. At 5 x 10(-7) M 5-HT, intracellular 5-HT was detectable only in astrocytes treated with monoamine oxidase (MAO) inhibitors. These findings are consistent with the idea that 5-HT taken up into astrocytes is not stored for re-release, but is rapidly metabolized to 5-HIAA, which is then extruded from the cell. At 5 x 10(-7) M 5-HT, 5-HIAA formation in intact cells was blocked 63% by the selective high-affinity 5-HT uptake inhibitor fluoxetine. 5-HT oxidation to 5-HIAA is carried out principally by MAO-A, because clorgyline was more effective at inhibiting the production of 5-HIAA than was pargyline. Radioenzymatic determinations of MAO activity in cell homogenates supported these findings, because under these conditions clorgyline was 1,000-fold more effective than pargyline at inhibiting MAO activity toward 14C-labelled 5-HT. However, the relatively selective MAO-B substrate beta-phenylethylamine (PEA) was also oxidized, showing that these cultures also contained MAO-B activity; the Km values for MAO-A oxidation of 5-HT and MAO-B oxidation of PEA were 135 and 45 microM, and Vmax values were 88 and 91 nmol/mg of total cell protein/h, respectively. Higher concentrations of PEA (greater than 20 microM) were oxidized by both MAO-A and MAO-B isozymes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Antioxidant and Amine Oxidase Inhibitory Activities of Hydroxyurea

Hydroxyurea (HU, NH₂CONHOH), or hydroxycarbamide, is a hydroxamic acid derivative used as a drug for anti-neoplasm and sickle-cell disease. In this study, HU was found to have antioxidant activities against 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals and dose-dependent inhibitory activities against monoamine oxidase (MAO)-A, MAO-B, and semicarbazide-sensitive amine oxidase (SSAO) as compared to controls of clorgyline, deprenyl, and semicarbazide respectively. HU showed mixed-type, competitive-type, and competitive-type inhibition, respectively, with respect to substrates of MAO-A, MAO-B, and SSAO with apparent inhibition constants (Ki) of 19.46, 5.38, and 1.84 μM.     

Quantitative determination of forty-eight antidepressants and antipsychotics in human serum by HPLC tandem mass spectrometry: a multi-level, single-sample approach

This method describes the simultaneous determination of amisulpride, amitriptyline, aripiprazole, benperidol, chlorpromazine, chlorprothixene, citalopram, clomipramine, clozapine, desipramine, doxepin, fluoxetine, flupentixol, fluphenazine, fluvoxamine, haloperidol, hydroxyrisperidone, imipramine, levomepromazine, maprotiline, mianserine, mirtazapine, moclobemide, norclomipramine, nordoxepin, norfluoxetine, nortriptyline, O-desmethylvenlafaxine, olanzapine, opipramol, paroxetine, perazine, perphenazine, pimozide, pipamperone, quetiapine, reboxetine, risperidone, sertraline, sulpiride, thioridazine, trazodone, trimipramine, venlafaxine, viloxazine, ziprasidone, zotepine and zuclopenthixol with a single sample/triple injection approach. Drugs were assigned to subgroups covering low, medium and high concentrations (overall range of therapeutic levels to be considered: 0.5-2000 ng/mL) by further dilution of the supernatant obtained after the first protein precipitation. Chromatographic separation was necessary for isobaric mass fragments and performed on a monolithic C18 column (50mmx4.6mm) with methanol gradient and 5mM acetate buffer at pH 3.9. The injection interval was 8 min. A set of three internal standards was used for quantification of drugs with widely varying hydrophobicity. After electrospray ionization positive ion fragments were detected in the multiple reaction monitoring (MRM) mode with an API 4000 tandem mass spectrometer. Regression parameters of calibration curves and limits of quantification showed good covering of therapeutic and subtherapeutic ranges with an average correlation coefficient of 0.9988. Imprecision and inaccuracy measures were prepared for intra- and inter-assay comparisons at three concentration ranges in all subgroups. Average coefficients of variation were 6.1% for intra-assay and 7.4% for inter-assay comparisons, while average deviations from spiked concentrations were 4.8% for intra-assay and 4.2% for inter-assay comparisons, respectively. Recovery rates, measured as the percent recoveries of spiked serum samples against standard solutions without serum matrix, varied between 92 and 111%, with an average of 101%. As the only exception, the olanzapine response was much higher (185%) in serum matrix than in matrix-free controls.     

Monoamine Oxidase (MAO)-A but Not MAO-B Inhibitors Potentiate Tyramine-Induced Catecholamine Release from PC12 Cells

The previous report that PC12 (pheochromocytoma) cells have a K(+)-induced, as well as a tyramine-induced, catecholamine release mechanism has been confirmed. Selective monoamine oxidase (MAO)-A (clorgyline and moclobemide) and not MAO-B inhibitors (l-deprenyl, AGN 1135, and Ro 16-6491) potentiate the catecholamine-releasing action of tyramine significantly more than that of K+. The potentiation of tyramine-induced [3H]noradrenaline release from PC12 cells by MAO-A inhibitors has been linked to the presence of MAO-A in these cells, for which tyramine and noradrenaline are substrates. In the above respects, it is the PC12 cell that resembles more closely the peripheral adrenergic neuron, rather than the chromaffin cell, which is endowed with MAO-B and lacks the tyramine-releasable pool of catecholamines.     

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.     

Multiple forms of monoamine oxidase in rabbit platelets.

Rabbit platelets were found to contain both types A and B MAO activities. The specific enzymatic activity of rabbit platelet MAO was higher for the substrate serotonin than for phenylethylamine. The K_m's for rabbit platelet MAO indicated that the MAO-B enzyme was similar to human platelet MAO and that both MAO-A and MAO-B enzymes in the rabbit platelet are similar to the corresponding forms in the rabbit brain. The drugs clorgyline and deprenyl confirmed the existence of types A and B MAO in the platelet and furthermore indicated that the type A form accounted for approximately 90% of the total enzymatic activity. Amitriptyline at low (micromolar) concentrations selectively inhibited MAO-B activity in both rabbit platelets and brain.     

Formation of the Neurotransmitter Glycine from the Anticonvulsant Milacemide Is Mediated by Brain Monoamine Oxidase B

Milacemide (2-n-pentylaminoacetamide) is a secondary monoamine that in the brain is converted to glycinamide and glycine. This oxidative reaction was suspected to involve the reaction of monoamine oxidase (MAO). Using mitochondrial preparations from tissues that contain MAO-A and -B (rat brain and liver), MAO-A (human placenta), and MAO-B (human platelet and bovine adrenal chromaffin cell), it has been established that mitochondria containing MAO-B rather than MAO-A oxidize (H2O2 production and glycinamide formation) milacemide. The apparent Km (30-90 microM) for milacemide oxidation by mitochondrial MAO-B preparations is significantly lower than that for milacemide oxidation by mitochondrial MAO-A (approximately 1,300 microM). In vitro MAO-B (l-deprenyl and AGN 1135) rather than MAO-A (clorgyline) selectively inhibited the oxidation of milacemide. These in vitro data are matched by ex vivo experiments where milacemide oxidation was compared to oxidation of serotonin (MAO-A) and beta-phenylethylamine (MAO-B) by brain mitochondria prepared from rats pretreated with clorgyline (0.5-10 mg/kg) and l-deprenyl (0.5-10 mg/kg). Furthermore, in vivo experiment demonstrated that l-deprenyl selectively increased the urinary excretion of [14C]milacemide and the total radioactivity with a concomitant decrease of [14C]glycinamide. Such changes were not observed after clorgyline treatment, but were evident only at doses beyond clorgyline selectivity. The present data therefore demonstrate that milacemide is a substrate for brain MAO-B, and its conversion to glycinamide, further transformed to the inhibitory neurotransmitter, glycine, mediated by this enzyme may contribute to its pharmacological activities.     

Monoamine oxidase A and B inhibiting effect and molecular modeling of some synthesized coumarin derivatives

New series of bioactive 7-oxycoumarin derivatives were synthesized and tested for their in vitro and in vivo monoamine oxidase (MAO) A and B inhibitory effect. In vitro studies revealed exceptionally potent and selective MAO-A inhibitors with K_i values on a picomolar range. The acetohydrazide (3b) and the dioxopyrrolidine derivative (7b) showed the most potent in vitro and in vivo MAO inhibition activity. Moreover, molecular modeling study of the synthesized compounds into MAO-A (PDB: 2Z5X) and MAO-B (PDB: 2XFN) binding sites exhibited direct correlation between AutoDock binding affinity and% inhibition MAO-A (pM) and MAO-B (μM). In addition, the results of in vivo MAO inhibiting properties (ED₅₀) of the tested compounds revealed better direct correlation.     

Different effects of monoamine oxidase inhibition on MPTP depletion of heart and brain catecholamines in mice

Pargyline, an inhibitor of monoamine oxidase type B (MAO-B), did not prevent the depletion of heart norepinephrine 24 hr after a single dose of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) in mice. In mice killed 24 hr after the last of 4 daily doses of MPTP, the depletion of dopamine in the striatum and of norepinephrine in the frontal cortex was completely prevented by pargyline, but the depletion of heart norepinephrine was not prevented. These results with pargyline are the same as results obtained earlier with deprenyl, another selective inhibitor of MAO-B. The doses of pargyline and of deprenyl that were used resulted in almost complete inhibition of MAO-B activity (phenylethylamine as substrate) in brain, heart and liver of mice. Deprenyl did not inhibit MAO-A activity (serotonin as substrate) in brain, but pargyline caused some inhibition of MAO-A in brain. In heart and liver, serotonin was oxidized only at about 1/10 the rate of phenylethylamine oxidation, suggesting that MAO-B predominates in these tissues. Both pargyline and deprenyl caused some inhibition of serotonin deamination in heart and liver, suggesting that the oxidation may have been due partly to MAO-B. Experiments with selective MAO inhibitors in vitro showed that only about 20% of the oxidation of serotonin was occurring via MAO-B in heart and liver. The in vitro oxidation of MPTP by MAO in mouse brain, heart and liver was almost completely inhibited by pretreatment with either pargyline or deprenyl. Neither pargyline nor deprenyl had any significant effect on the concentrations of MPTP in brain or heart one-half hr after injection of MPTP into mice. The concentrations of the metabolite, MPP+ (1-methyl-4-phenyl-pyridinium), were markedly reduced in brain and in heart by pretreatment with either pargyline or deprenyl. The data suggest that MPP+ formation, which is necessary for the depletion of brain catecholamines after MPTP injection, may not be necessary for depletion of norepinephrine in heart. Since the oxidation of MPTP in vitro was inhibited more by pargyline or deprenyl pretreatment than was the appearance of MPP+ in vivo, the possibility exists that some MPP+ formation might occur by an enzyme other than MAO.     

A new type of mitochondrial monamine oxidase distinct from type-A and type-B

The characteristics of mitochondrial monoamine oxidase (MAO) in carp liver were studied with MAO inhibitors and substrates. This enzyme was thermolabile, but was stabilized in the presence of bovine serum albumin. With clorgyline and deprenyl, single-sigmoidal curves for inhibition of the activity towards tyramine or 5-hydroxytryptamine were obtained; the sensitivities to the two inhibitors were identical. The activity towards β-phenylethylamine was not completely inhibited by clorgyline or deprenyl, but the remaining activity was inhibited by semicarbazide and the inhibition curves by either clorgyline or deprenyl and semicarbazide were also identical to the curves with the other two substrates. These results suggest that carp liver mitochondria contain “classical” MAO and a clorgyline- and deprenyl-resistant amine oxidase and that the classical MAO does not seem to be MAO-A or MAO-B, which are present in mitochondria of most mammalian tissues.     

Effect of long-term administration of antidepressants on the lipid composition of brain plasma membranes

The connection between changes in lipid pattern in brain plasma membranes and long-term administration of therapeutically effective doses of antidepressants has not been sufficiently demonstrated so far. Therefore, we analyzed effect of antidepressants that differ in pharmacological selectivity on membrane lipid composition in the rat brain tissue. Laboratory rats were given desipramine, maprotiline, citalopram, moclobemide or lithium for a 4-week period. We observed a significant decrease in phosphatidylethanolamine representation after administration of maprotiline, citalopram and moclobemide when compared with controls. Membrane cholesterol content was decreased after desipramine administration and increased after citalopram or lithium treatment. Electroneutral phospholipids were decreased after the administration of all tested antidepressants except for desipramine. Decrease in phosphatidylserine was found following long-term administration of maprotiline or desipramine; relative representation of phosphatidylinositol was reduced after lithium treatment. Statistically significant negative correlation between cholesterol and electroneutral phospholipids was discovered. Membrane microviscosity evaluated by fluorescence anisotropy of membrane probes was only slightly decreased after desipramine and increased after citalopram administration. Hypothesis was supported that changes in brain neurotransmission produced by antidepressants could be, at least partially, associated with adaptive changes in membrane cholesterol and phospholipids.     

Effects of Selective Monoamine Oxidase Inhibitors on the In Vivo Release and Metabolism of Dopamine in the Rat Striatum

Brain microdialysis was used to examine the in vivo efflux and metabolism of dopamine (DA) in the rat striatum following monoamine oxidase (MAO) inhibition. Relevant catecholamines and indoleamines were quantified by HPLC coupled with a electrochemical detection system. The MAO-B inhibitor selegiline only affected DA deamination at a dose shown to inhibit partially type A MAO. Alterations in DA and metabolite efflux were not observed when using the MAO-B-selective dose of 1 mg/kg of selegiline. At 10 mg/kg, selegiline reduced the efflux of DA metabolites to approximately 70% of basal values without affecting DA efflux. K(+)- and veratrine-stimulated DA efflux was not affected by selegiline. Experiments using amphetamine and the DA uptake inhibitor nomifensine demonstrated that the effect of selegiline on DA metabolism was unlikely to be mediated either by inhibition of DA uptake or by an indirect effect of its metabolite amphetamine. The possibility that the effect of selegiline is mediated via a nonspecific inhibition of MAO is discussed. In contrast, the MAO-A inhibitor clorgyline inhibited basal DA metabolism and increased basal and depolarisation-induced DA efflux. A 1 mg/kg dose of clorgyline reduced basal DA metabolite efflux (40-60% of control values) without affecting DA efflux. At 10 mg/kg of clorgyline, DA efflux increased to 253 +/- 19% of basal values, whereas efflux of DA metabolites was reduced to between 15 and 26% of control values. The release of DA induced by K+ and veratrine was not affected by 1 mg/kg of clorgyline but was increased by approximately 200% following pretreatment with 10 mg/kg of clorgyline. The nonselective MAO inhibitor pargyline caused similar but more pronounced alterations in these parameters.(ABSTRACT TRUNCATED AT 250 WORDS)     

Gonadal Influences on the Sexual Differentiation of Monoamine Oxidase Type A and B Activities in the Rat Brain

Abstract: The sex-dependent differentiation of monoamine oxidase (MAO) in the hypothalamus of 60-day-old, Charles River rats was found to involve only type A (MAO-A), and not type B (MAO-B) enzyme. In vivo inhibition of type A by clorgyline, and type B by (−)deprenyl, however, tended to decrease the specific activity of both types of MAO to a smaller extent in the female than in the male hypothalamus. When masculinization was prevented by neonatal administration of estradiol (E) to males, hypothalamic MAO-A and MAO-B activities increased in both control and MAO-inhibited rats. Androgenization of females, however, had little effect on the MAO activity. Whereas the effects of neonatal estrogenization were attributable neither to a direct influence of E nor to a sexual difference in the peripheral clearance of the MAO-inhibitor used, single, high doses of steroids to adult, but not to newborn rats, did acutely affect the kinetics of MAO-A. The activity of MAO-A was also decreased by high concentrations of E or TS in vitro. The imprinting for patterns of hypothalamic MAO-A and MAO-B in the two sexes results, probably, from genetic predetermination. Neonatal changes in the homeostasis of gonadal hormones may result in type-MAO nonspecific effects in adulthood, whereas the short-term effects of high concentrations of steroids may be selective for the A form.