Analysis of acute and chronic effects of antidepressive agents in a learned helplessness model in mice

In experimental learned helplessness in mice determined by preliminary inavoidable aversive exposure, activity of tricyclic antidepressants (desipramine, chlorimipramine, amitryptyline), type A MAO inhibitors (pyrazidol), and atypical (zimelidine, trazodon, befuralin) antidepressants as well as that of potential antidepressants (LIS-30, DZK-153) were determined upon chronic administration. The tricyclic compounds, befuralin and DZK-153 removed learned helplessness only after 14 days of administration. The substances with a predominant serotoninomimetic action (zimelidin, trazodon in high doses, pyrazidol, LIS-30) showed high efficacy following 6 days of administration. Single administration of the substances under study did not make it possible to disclose their specific antidepressant activity.     

Antagonism between long acting Monoamine Oxidase Inhibitors (MAOI) and MD780515, a new specific and reversible MAOI

The inhibition of type A and B monoamine oxidase (MAO A and B) in rat brain, liver and heart by MD780515, 3-[4-(3 cyanophenylmethoxy) phenyl]-5-(methoxymethyl)-2-oxazolidinone, has been investigated ex vivo with 5-hydroxytryptamine (5-HT) and β-phenylethylamine (PEA) as substrates. MAO A was strongly inhibited for four hours after oral administration of 10 mg/kg MD780515 (maximum inhibition : 72%, 86% and 83% in brain, liver and heart respectively. In contrast, in heart where PEA is deaminated by type A MAO, the predominant form of MAO in that tissue, the inhibition was 68% 30 minutes after administration of the compound. In all cases, MAO activities reached control values 24 hours after drug administration (10 mg/kg), whereas some inhibitory activity was still present 24 hours after oral administration of higher doses. The strong MAO A inhibition (68 to 83%) remaining in the three tissues 24 hours after oral administration of clorgyline (5 mg/kg) was completely removed by pretreatment with MD780515 (10 mg/kg). In the same conditions, MD780515 protected against the inhibition (53%) by clorgyline of PEA deamination in heart. Oral pretreatment with increasing doses of MD780515 (2.6 to 84 mg/kg) gradually removed brain MAO A inhibition caused by clorgyline (92%, 28.2 mg/kg) or tranylcypromine (88%, 4.8 mg/kg), the complete removal being observed at the dose of 21 mg/kg of MD780515 for clorgyline, and at 42 mg/kg for tranylcypromine. Inhibition of brain MAO B by tranylcypromine (96%) was not modified by pretreatment with the same range of oral doses of MD780515. The results are consistent with a specific and reversible inhibition of MAO A activity by MD780515 which can protect against long acting MAO A inhibitory effects of clorgyline and tranylcypromine. MD780515 enhances the selectivity of tranylcypromine.     

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.     

Liquid chromatographic and tandem mass spectrometric assay for evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors: application of biomarkers in drug discovery

A simple and selective assay for the evaluation of in vivo inhibition of rat brain monoamine oxidases (MAO) A and B following a single dose of MAO inhibitors was developed through the simultaneous determination of endogenous 5-hydroxy tryptamine, 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophane, and 2-phenethylamine (PEA) in rat brain using liquid chromatography-tandem mass spectrometry (LC/MS/MS). These analytes were separated on a Zorbax SB-C18 column using a gradient elution with acetonitrile and 0.2% formic acid and detected on an electrospray ionization mass spectrometer in positive-ion multiple-reaction-monitoring mode. The susceptibility and variability of these analytes as potential biomarkers in response to MAO inhibition in vivo were evaluated after application to three MAO inhibitors, tranylcypromine, clorgyline, and pargyline. A dramatic increase (about 40-fold) in PEA brain level and a decrease in 5-HIAA by more than 90% were observed after administration of 15 mg/kg of the nonselective MAO inhibitor tranylcypromine. As expected, the brain level of PEA escalated to about 6-fold, while the 5-HIAA level remained unchanged following a dose of the MAO B inhibitor pargyline at 2mg/kg. In contrast, the brain level of 5-HIAA reduced by approximately 53%, but the PEA level was unaffected following the same dose of the MAO A inhibitor clorgyline. The results indicated that 5-HIAA and PEA were susceptible and effective biomarkers in the rat brain in response to MAO A and B inhibition, respectively. The LC/MS/MS method is useful not only for the determination of inhibitory potency but also for the differentiation of the selectivity of a MAO inhibitor against rat brain MAO A and B in vivo.     

THE EFFECTS OF METOPIRONE AND ADRENALECTOMY ON THE REGULATION OF THE ENZYMES MONOAMINE OXIDASE AND CATECHOL-O-METHYL TRANSFERASE IN DIFFERENT BRAIN REGIONS

Abstract— The role of glucocorticoids in the regulation of the enzymes monoamine oxidase (MAO) and catechol- O -methyltransferase (COMT) in brain regions has been studied. Glucocorticoids were blocked by Metopirone. The activities of MAO and COMT were determined in the hypophysis, hypothalamus, pineal gland and in the rest of brain. All the cerebral tissues except the pineal gland demonstrated highest MAO activity 8 h after Metopirone administration, when glucocorticoids were at the lowest level. Prolonged treatment for 10 days significantly augmented MAO activity in brain, hypophysis and hypothalamus, and COMT in the hypophysis increased by 56 per cent. The COMT activity in the rest of the brain did not change significantly with either short or prolonged administration. Complete ablation of the adrenal cortex resulted in a 167 per cent rise in MAO activity of the hypophysis. Metopirone and hydrocortisone inhibit MAO and COMT in vitro. The results suggest that glucocorticoids in the circulation of normal animals inhibit the activities of MAO and COMT. The inhibition or ablation of these hormones removes this rate-limiting control of catecholamine degradation resulting in higher activities of MAO and COMT. Metopirone, an inhibitor of MAO and COMT in vitro , acts in the opposite direction in vivo due to its inhibitory effects on corticoid biosynthesis.     

Modification of Morphine-induced Hyperlocomotion and Antinociception in Mice by Clorgyline,a Monoamine Oxidase-A Inhibitor

We evaluated the effects of pretreatment with clorgyline, an irreversible monoamine oxidase (MAO)-A inhibitor, on morphine-induced hyperlocomotion and antinociception. A single administration of morphine (30 mg/kg, i.p.) to male ICR mice induced a hyperlocomotion. ANOVA analysis revealed the statistical significance of the morphine effect on horizontal locomotion and of the clorgyline pretreatment × morphine interaction effect, but not of the effect of clorgyline pretreatment. The initial (5 min after challenge) phase of morphine actions vs. saline challenge appeared as if morphine had a strong inhibitory effect on locomotor activity in combination with different doses of clorgyline. The mice administered with morphine in combination of clorgyline (1 and 10 mg/kg) did not show any stereotypic behaviors. Clorgyline at a dose of 0.1 mg/kg but not other doses tested significantly potentiated morphine-induced antinociception evaluated by tail flick but not hot plate test. During the measurements of locomotor activity and antinociception, clorgyline at doses of 1 and 10 mg/kg significantly inhibited monoamine metabolism through MAO. These results suggest that clorgyline showed an inhibitory effect on morphine-induced hyperlocomotion, but not antinociception, through MAO inhibition. There is not a possibility that clorgyline pretreatment enhanced morphine action on motor activity, resulting in the abnormal behavior from hyperlocomotion to stereotypic movements.     

Molecular structure--activity relationship of hydrazides inhibiting glutamic acid decarboxylase, GABA-alpha-oxoglutarate aminotransferase, and monoamine oxidase activities in chick brain.

Several aryl and heteroaryl hydrazides were synthesized and evaluated for their inhibitory effects on glutamic acid decarboxylase (GAD), GABA-alpha-oxoglutarate aminotransferase (GABA-T), and monoamine oxidase (MAO) enzyme systems in chick brain 24 h after their intramuscular administration (0.75 mmol/kg). All compounds produced a reduction in GAD, GABA-T, and MAO activity. Structure-activity relationships indicated that the ring structure had a greater influence on the degree of GAD and GABA-T inhibition than did the N'-terminal group. In contrast, structural requirements for MAO inhibition were much more restrictive. The intramuscular administration of benzoic acid hydrazide to chicks 24 h prior to their being exposed to oxygen at high pressure provided significant protection against the onset of the hyperbaric oxygen-induced seizures.     

Inhibition of noradrenaline deamination by antidepressants

Anti-norepinephrine deaminative activity of some antidepressants of different structure was studied. Pyrazidol (10(-5) M) reduced considerably the rate of norepinephrine deamination in bovine brain (80% inhibition), the inhibitory effects of inkazan and imipramine were also apparent (50-60%). Zimelidine, viloxazine and norzimelidine were found to be less active: at 10(-4) M, they caused a not more than 50% inhibition of oxidative norepinephrine deamination. The difference was revealed between the influence of some drugs on deamination of two monoamine oxidase A substrates: norepinephrine and serotonin. Thus, pyrazidol, viloxazine, zimelidine and norzimelidine were more active in suppressing norepinephrine, than serotonin deamination. Inhibition of norepinephrine deamination in the brain seems to be an important component of the neurochemical spectrum of pyrazidol and imipramine.     

Effects of clomiphene citrate, a nonsteroidal antiestrogen, on brain monoaminergic mechanisms in female goldfish, Carassius auratus

The antiestrogen, clomiphene citrate ( Merrell -National Laboratories) was administered to female goldfish in order to test the hypothesis that this drug may act on brain monoaminergic mechanisms. Brain monoamine oxidase (MAO) activity and hypothalamic serotonin (5-HT) content were measured fluorometrically after i.p. administration of 0, 5 or 25 micrograms clomiphene citrate/g body wt. Brain MAO activity was significantly inhibited by the high dose of clomiphene citrate, whereas hypothalamic 5-HT content was significantly elevated by both low and high doses of the antiestrogen. These data support the idea that brain monoamines in teleost fish are influenced by estrogen feedback mechanisms which can be blocked by clomiphene citrate.     

The Novel Neuropsychotropic Agent Milacemide Is a Specific Enzyme-Activated Inhibitor of Brain Monoamine Oxidase B

The novel neuropsychotropic agent milacemide hydrochloride (2-n-pentylaminoacetamide HCl) is a highly selective substrate of the B form of monoamine oxidase (EC 1.4.3.4; MAO). Under the in vitro conditions used in the present study, milacemide acts as an enzyme-activated, partially reversible inhibitor of MAO-B. A reversible inhibition of MAO-A activity is also observed at high concentrations. The inhibitory activity of milacemide is significantly greater for MAO-B. In vivo, after single or repeated oral administration, a specific inhibition of MAO-B is apparent in brain and liver, with a lack of inhibition of the MAO-A activity. In contrast to the irreversible inhibitory action of L-deprenyl, the recovery of MAO-B activity in vivo after milacemide administration is significantly faster, a result suggesting that it is a partially reversible inhibitor. The selective inhibitory effect of milacemide for MAO-B in vivo is confirmed by its potentiation of phenylethylamine-induced stereotyped behavior, whereas vasopressor responses to tyramine were not affected. These observations suggest that milacemide could enhance dopaminergic activity in the brain and could be used as therapy for Parkinson's disease in association with L-3,4-dihydroxyphenylalanine.     

Effect of adafenoxate on different rat brain structures monoamine oxidase activity in vitro

1. The effect of the nootropic drug adafenoxate on monoamine oxidase (MAO) activity in rat brain cortex, striatum, hypothalamus and hippocampus has been studied using the following substrates: tyramine (total MAO), serotonin (MAO A) and beta-phenylethylamine (MAO B). 2. In a series of increased concentrations (from 5 x 10(-4) up to 1 x 10(-5) M) adafenoxate inhibits total MAO, MAO A and MAO B in the brain structures studied. 3. The adafenoxate IC50 values obtained illustrate its inhibitory properties and its lack of selectivity toward MAO in the brain structures isolated. 4. The results of our research prove the participation of MAO in the mechanisms through which adafenoxate affects the brain monoaminergic systems and realises its central effects.     

Role of monoamine oxidase-B in medroxyprogesterone acetate (17-acetoxy-6 alpha-methyl-4-pregnene-3, 20-dione) induced changes in brain dopamine levels of rats

The effect of medroxyprogesterone acetate (MPA) on brain monoamine levels and monoamine oxidase (MAO) activity was studied in adult, healthy, non-pregnant female rats. MpA was injected in a single dose of 100 mg/kg i.m. Dopamine (DA), noradrenaline (NA), 5-hydroxytryptamine (5-HT) levels and MAO activity were estimated fluorometrically in rat brian. No change in DA, NA, 5-HT or MAO activity was observed after 7 days of MPA treatment while a significant decrease in DA levels along with a significant increase in MAO activity was observed after 21 days of MPA treatment. However, there was no change in NA and 5-HT levels after 21 days of MPA administration. The selective reduction of DA by MPA could be due to an increase in MAO-B activity. MPA does not appear to increase MAO-A activity because neither of the specific substrates (NA and 5-HT) of MAO-A was found to be decreased inspite of the increase in MAO activity as estimated by the kynuramine method. These findings suggest the importance of MAO-B also in DA metabolism in rat brain.     

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.     

Inhibition of monoamine oxidase activity by antidepressants and mood stabilizers

OBJECTIVE: Monoamine oxidase (MAO), the enzyme responsible for metabolism of monoamine neurotransmitters, has an important role in the brain development and function, and MAO inhibitors have a range of potential therapeutic uses. We investigated systematically in vitro effects of pharmacologically different antidepressants and mood stabilizers on MAO activity. Methods: Effects of drugs on the activity of MAO were measured in crude mitochondrial fraction isolated from cortex of pig brain, when radiolabeled serotonin (for MAO-A) or phenylethylamine (for MAO-B) was used as substrate. The several antidepressants and mood stabilizers were compared with effects of well known MAO inhibitors such as moclobemide, iproniazid, pargyline, and clorgyline. Results: In general, the effect of tested drugs was found to be inhibitory. The half maximal inhibitory concentration, parameters of enzyme kinetic, and mechanism of inhibition were determined. MAO-A was inhibited by the following drugs: pargyline > clorgyline > iproniazid > fluoxetine > desipramine > amitriptyline > imipramine > citalopram > venlafaxine > reboxetine > olanzapine > mirtazapine > tianeptine > moclobemide, cocaine > lithium, valproate. MAO-B was inhibited by the following drugs: pargyline > clorgyline > iproniazid > fluoxetine > venlafaxine > amitriptyline > olanzapine > citalopram > desipramine > reboxetine > imipramine > tianeptine > mirtazapine, cocaine > moclobemide, lithium, valproate. The mechanism of inhibition of MAOs by several antidepressants was found various. Conclusions: It was concluded that MAO activity is acutely affected by pharmacologically different antidepressants at relatively high drug concentrations; this effect is inhibitory. There are differences both in inhibitory potency and in mechanism of inhibition between both several drugs and the two MAO isoforms. While MAO inhibition is not primary biochemical effect related to their therapeutic action, it can be supposed that decrease of MAO activity may be concerned in some effects of these drugs on serotonergic, noradrenergic, and dopaminergic neurotransmission.     

2-Naphthylamine, a compound found in cigarette smoke, decreases both monoamine oxidase A and B catalytic activity

Cigarette smokers exhibit a lower monoamine oxidase (MAO; EC 1.4.3.4) activity than nonsmokers. MAO is located in the outer membrane of mitochondria and exists as two isoenzymes, MAO A and B. MAO A prefers 5-hydroxytryptamine (serotonin), and MAO B prefers phenylethylamine (PEA) as substrate. Dopamine is a substrate for both forms. 2-Naphthylamine is a carcinogen found in high concentrations in cigarette smoke. The results of this study show that 2-naphthylamine has the ability to inhibit mouse brain MAO A and B in vitro by mixed type inhibition (competitive and non-competitive). The Ki for MAO A was determined to be 52.0 microM and for MAO B 40.2 microM. The inhibitory effect of 2-naphthylamine on both MAO A and B catalytic activity, supports the hypothesis that smoking decreases MAO activity in vivo, instead that smokers with lower MAO activity are more prone to become a smoker.     

The effect of isatin (tribulin) on metabolism of indoles in the rat brain and pineal: In vitro and in vivo studies

Isatin (Tribulin) produced a dose-dependent inhibition of both MAO A and MAO B in broken cell preparations from rat brain and pineal. However, isatin administered in vivo (80–160 mg/kg) to the intact animal significantly increased brain, but not pineal, serotonin and did not affect 5HIAA or other indoles in either brain or pineal. Further, in vivo administration did not produce detectable MAO inhibition in either tissue. In pineal organ culture, addition of isatin up to 1mM had no influence on the concentrations of pineal indoles or the activities of monoamine oxidase or serotonin N-acetyltransferase. However, the diazepam augmentation of beta adrenergic induction of serotonin N-acetyltransferase activity was blocked by isatin. The results of these studies call into question the proposed role of isatin as an endogenous monoamine oxidase inhibitor but support a possible role as a benzodiazepine receptor blocker.     

Interleukin-1 inhibits stress-induced gastric erosion in rats

The effect of interleukin (IL)-1 on the occurrence of stress-induced gastric erosions was examined in rats. The intracerebroventricular (icv) administration of IL-1 beta significantly inhibited the occurrence of water-immersion restraint stress-induced gastric erosion at doses of 200 ng, 500 ng and 1 microgram, whereas the intravenous (iv) administration of IL-1 beta altered the occurrence of gastric erosion only at a dose of 1 microgram. The inhibitory effect of IL-1 alpha icv administered on the occurrence of gastric erosion was found only at a dose of 1 microgram. The inhibitory effect of IL-1 beta icv administered on the occurrence of stress-induced gastric erosion was not influenced by icv administration of alpha-helical CRF(9-41), a corticotropin-releasing factor (CRF) receptor antagonist. Indomethacin completely blocked the inhibitory action of IL-1 beta icv administered on stress-induced gastric erosion. It is concluded from these results that IL-1 acts mainly in the central nervous system to inhibit the occurrence of stress-induced gastric erosion and that the IL-1 beta-induced inhibition of gastric erosion is mediated by prostaglandin in a manner that is independent of brain CRF.     

Short and long term inhibitory actions of alpha-melanocyte stimulating hormone on lordosis in rats

The effects of 200 ng of intracerebroventricularly (ICV) and 20 micrograms of subcutaneously (SC) administered alpha-melanocyte stimulating hormone (MSH) on lordosis in rats were examined. Previous research, employing crossover designs, has revealed significant effects of MSH on lordosis. The results of Experiments 1a and 1b suggest that similar designs produce significant effects even in the absence of MSH. Thus, it is not clear that previous results were due exclusively to an action of MSH. Experiment 2 employed a modification of previous procedures and indicated that MSH administered either SC or ICV inhibited receptivity in subjects displaying high levels of responding. Moreover, MSH administered SC was also found to facilitate receptivity in subjects displaying low levels of responding. However, a possible long term inhibitory action of MSH on receptivity was also revealed. Because animals were tested repeatedly, this brought into question the results of Experiment 2. Procedures were revised accordingly and the effects of MSH re-examined. The results of Experiment 3 indicated that MSH administered SC facilitated receptivity while MSH administered ICV inhibited receptivity. In addition, MSH administered ICV exerted an inhibitory effect one week after administration. Therefore, MSH appears to exert both short and long-acting effects on sexual receptivity.     

Effects of L-DOPA administration upon monoamine oxidase activity in rat tissues

The effects of L-DOPA administration in various doses (250,500 and 1000 mg/kg for 7 days) upon type A and B MAO activities in rat tissues have been investigated using the substrates 5-HT, tyramine and benzylamine. The specific activities of MAO in heart, kidney and brain were significantly increased after L-DOPA, whereas liver and vas deferens MAO was unchanged. None of the observed changes was totally specific for either form of the enzyme, although some evidence for a slight selectivity on type A MAO of heart and type B MAO of kidney and brain was obtained. These results indicate that some tissues may respond to elevated intracellular catecholamine levels, resulting from L-DOPA administration, by increasing their capacity to deaminate those amines. However, at present, the exact mechanism by which these changes are brought about is unknown.     

Evidence for the Presence of Two Types of Monoamine Oxidase in Rabbit Choroid Plexus and Their Role in Breakdown of Amines Influencing Cerebrospinal Fluid Formation

Abstract: The presence of monoamine oxidase (MAO) in the choroid plexuses from all brain ventricles of rabbit was established radiornetrically. Histochemical staining of MAO revealed the enzyme to be present primarily in the secretory epithelium. The mode of inhibition by the selective inhibitors clorgyline and deprenyl showed that type A and B MAO are present in approximately equal proportions in the plexus, Intraventricular administration of nialamide markedly reduced CSF production measured by [¹⁴C]inulin dilution during ventriculocisternal perfusion. The nialamide effect was significantly diminished after sympathetic denervation of the plexus, indicating that neuronal MAO is also present in the plexus; it probably represents a small fraction of the total MAO A activity in the tissue. In addition, nialamide tended to potentiate the reduction in CSF formation obtained by intraventricular noradrenaline.