Effects of 2-deoxy-D-glucose on methamphetamine-induced dopamine and serotonin neurotoxicity.

The mechanisms underlying the neurotoxic actions of methamphetamine (METH) and related substituted amphetamines are unknown. Previous studies with 2-deoxyglucose (2-DG) have suggested that METH-induced neurotoxicity may involve exhaustion of intracellular energy stores. However, because 2-DG also produces hypothermic effects, and because METH's neurotoxic actions are highly susceptible to thermoregulatory influence, previous findings with 2-DG are difficult to interpret. The present studies were undertaken to further examine the influence of 2-DG's glucoprivic and thermic effects in the context of METH-induced dopamine (DA) and serotonin (5-HT) neurotoxicity. 2-DG protected against METH-induced DA neurotoxicity in both rats and mice. In both species, 2-DG, alone or in combination with METH, produced hypothermic effects. METH's toxic effects on brain 5-HT neurons were either unaffected or exacerbated by 2-DG, depending on species, brain region, and dose of METH tested. These results indicate that different mechanisms may underlie METH-induced DA and 5-HT neurotoxicity, and suggest that, as compared with 5-HT neurons, DA neurons are more susceptible to temperature influence, whereas 5-HT neurons are more vulnerable than DA neurons to metabolic compromise. Additional studies are needed to further assess the role of energy stores in the neurotoxic effects of METH and related drugs.

Atypical antidepressants inhibit depolarization-induced calcium uptake in rat hippocampus synaptosomes.

The effect of the atypical antidepressants mianserin, iprindole, and fluoxetine on synaptosomal calcium uptake was tested under conditions where a selective action on voltage-dependent calcium channels can be documented. Synaptosomes from rat hippocampus were incubated with 45calcium either in choline-rich medium or in depolarizing (60 mM K+) choline-rich medium, and drug effects on calcium uptake in these two conditions, as well as on the net depolarization-induced calcium uptake, were studied in the range of concentrations 0.6-200 microM. A concentration-dependent marked inhibition of uptake in depolarizing choline medium was observed for the three antidepressants, whereas only a minor degree of inhibition of uptake in resting choline medium was present at the highest drug concentration; as a result, the concentration-effect relationships exhibited a strong concentration-dependent inhibition of net depolarization-induced calcium uptake. The IC50 values, calculated by interpolation of the last three or four points of the concentration-effect relationships, were 27, 39, and 68 microM for fluoxetine, iprindole, and mianserin, respectively. Significant degrees of calcium channel inhibition are not expected at brain concentrations of mianserin and iprindole that are likely to be encountered during clinical use; however, the fluoxetine concentration-effect relationship established in the present study, coupled with the published ratio of 20:1 for brain:plasma concentrations of fluoxetine-norfluoxetine in humans, suggests that brain calcium channel function could be appreciably reduced in some patients treated with this atypical antidepressant.

d-Amphetamine interaction with glutathione in freshly isolated rat hepatocytes.

Hepatocellular damage has been reported as a consequence of amphetamine intake for which little is known about the respective biological mechanisms involved. To give a better insight of cellular d-amphetamine effects, the present study was performed to evaluate d-amphetamine effects on glutathione homeostasis, in vitro, using freshly isolated rat hepatocytes. Cell viability and lipid peroxidation were also evaluated. Incubation of freshly isolated rat hepatocytes with d-amphetamine (0.08, 0.20, 0.40, and 2.00 mM) induced a concentration dependent glutathione depletion which was observed at all times (1, 2, and 3 h of incubation). After 3 h of incubation, cellular GSH decreased to 85%, 78%, 71% and 47% of control levels for the referred concentrations, respectively. At the third hour of incubation, GSSG levels were only slightly increased for the three higher concentrations of d-amphetamine. The mass spectral study of the methanolic supernatants obtained from hepatocytes incubated with all d-amphetamine concentrations revealed the presence of the p-hydroxyamphetamine glutathione adduct (glutathion-S-yl)-p-hydroxyamphetamine. Pretreatment of hepatocytes with the P450 inhibitors metyrapone (1 mM) and iprindole (10 microM) significantly prevented the glutathione depletion induced by d-amphetamine. This inhibition was more effective for iprindole than for metyrapone. Incubation of isolated hepatocytes with p-hydroxyamphetamine (0.10 mM) for 3 h did not result in any modification of cell viability or GSH or GSSG levels. Also, in the mass spectrum study performed on these samples, the characteristic adduct obtained for d-amphetamine incubations was not detected. The above data suggest that the observed glutathione depletion induced by d-amphetamine is at least in part due to the conversion of d-amphetamine into (glutathion-S-yl)-p-hydroxyamphetamine and that P450 2D seems to have an important role in this metabolism. In spite of the results obtained, showing glutathione homeostasis alterations, incubation of freshly isolated rat hepatocytes with d-amphetamine did not result in any modification of cell viability or lipid redox status.

Effects of neonatally administered iprindole on adult behaviors of rats.

In past studies, administration of the antidepressant drugs clorimipramine, zimeldine, or desipramine to neonatal rats produced abnormalities in adult rats that modeled some behavioral and/or REM sleep features of human endogenous depression. Although these three drugs affected different neurotransmitter systems, all caused REM sleep deprivation (RSD). This suggested the hypothesis that RSD of neonatal rats caused their adult depression. One prediction of this hypothesis is that neonatally administered iprindole, an antidepressant drug that does not produce RSD, will not produce adult rats that model depression. The present study tested this hypothesis. Iprindole was administered to neonatal experimental rats and saline was administered to neonatal control rats. When the rats matured, compared with control rats, experimental rats were not significantly different in aggressive behavior (shock induced fighting), sexual behaviors, open field locomotion, and REM sleep. In our previous studies on rats, all these adult behaviors were affected in a depressive-like way by neonatally administered clorimipramine. Because iprindole does not decrease REM sleep, the present results support the hypothesis that in rats neonatal RSD causes adult depression.

A new class of antiarrhythmic--defibrillatory compounds.

Ventricular fibrillation (VF) is a major cause of sudden cardiac death in humans. Currently used antiarrhythmic drugs are aimed at preventing initiation of VF by decreasing the incidence of arrhythmias which can lead to VF. This approach today seems to be insufficient. On the basis of reports that VF can terminate spontaneously in various mammals, and even in humans, we propose pharmaceutical enhancement of self-ventricular defibrillation as a new therapeutical approach. Data obtained over the last decade indicate that a high cardiac extraneuronal noepinephrine level during VF facilitates self-defibrillation. Dibenzazepines (tricyclic antidepressants) and phenothiazines elevate norepinephrine level by inhibiting norepinephrine reuptake and were found to exhibit defibrillatory activity. The relationship of chemical structure to defibrillatory activity was studied in a group of dibenzazepine and phenothiazine compounds.

The effects of desipramine and iprindole on levels of enantiomers of fluoxetine in rat brain and urine.

The antidepressant fluoxetine (FLU) and its N-demethylated metabolite, norfluoxetine (NFLU), each contains a chiral center. The combination of FLU and desipramine (DMI), another antidepressant, has been reported to be useful in treatment of depression, to dramatically increase plasma levels of DMI and also to produce more rapid beta-adrenergic receptor down-regulation in brain than caused by DMI alone. We have now begun studies on the effects of this drug combination on the levels of FLU and NFLU enantiomers in the rat. In addition, the combination of FLU and iprindole (IPR) was also investigated. Male Sprague-Dawley rats were treated intraperitoneally with either normal saline vehicle, DMI (5 mg/kg/day), (R,S)-FLU (10 mg/kg/day) or DMI (5 mg/kg/day) + (R,S)-FLU (10 mg/kg/day) for 4 days. Following the last treatment, 24 h urine samples were collected. Rats were sacrificed and brains were removed. For the IPR study, rats were pretreated with either saline or IPR-HCl (11.2 mg/kg) and then treated 1 h later with (R,S)-FLU. After 5 h, the rats were sacrificed and brains were removed. Brain and urine samples were analyzed by gas chromatography with electron-capture detection for free (R)-and (S)-FLU and (R)- and (S)-NFLU after extraction and reaction with (-)-(S)-N-(trifluoroacetyl)prolyl chloride. The results from the brains of the rats treated with DMI/FLU indicate that levels of enantiomers of both FLU and NFLU were significantly increased over those seen in the animals receiving (R,S)-FLU alone.(ABSTRACT TRUNCATED AT 250 WORDS)

[Iprindole: a functional link between serotonin and noradrenaline systems?]. / Iprindole: lien fonctionnel entre systèmes sérotoninergique et noradrénergique?

Iprindole is an active antidepressant in clinical practice but its mechanism of action has never been clearly defined. Serotoninergic regulation of noradrenergic neurons of locus coeruleus depends on 5-HT2 receptors. This regulatory action of the 5-HT system appears to facilitate the down-regulation of beta receptors. In behavioural tests involving the noradrenergic system, the role of iprindole, administered in subactive doses, was evaluated in the presence of subactive doses of fluvoxamine, a serotonin uptake inhibitor. Yohimbine is an alpha2 antagonist, inducing a dose-dependent toxicity. This test allows a rapid and selective screening of antidepressants with direct and indirect beta-agonist properties. Administration of iprindole displayed a toxicity of fluvoxamine in the presence of yohimbine. A 5-day pre-treatment of iprindole antagonized this potentiation unmasked after acute administration of iprindole. The down-regulation of beta receptors induced by a chronic treatment by iprindole could prevent the adrenergic expression of yohimbine's toxicity. But the down-regulation of 5-HT2 receptors also obtained with chronic treatment by iprindole, can explain this antagonism preventing fluvoxamine's action. Hypothermia induced by a high dose of apomorphine, depends on an activation of the noradrenergic system. During the interaction with fluvoxamine, iprindole unmasked an antagonism of this hypothermia due to apomorphine. The activity of a subactive dose of salbutamol, a direct beta-agonist, was evaluated in the presence of fluvoxamine on hypothermia induced by a high dose of apomorphine. The aim of this interaction was to define the beta-adrenergic property of iprindole more precisely.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of D-amphetamine on the extracellular concentrations of glutamate and dopamine in iprindole-treated rats.

A single administration of D-amphetamine and iprindole has been reported to produce selective, long-lasting decreases in brain dopamine (DA) content because of axon terminal degeneration. It has been found that the noncompetitive glutamate (GLU) antagonist, MK 801, blocks D-amphetamine-induced DA depletion in iprindole-treated rats. In the present study, the effect of D-amphetamine (9.2 mg/kg) and iprindole (10 mg/kg) on the extracellular concentrations of DA and GLU was determined in the striatum of awake, freely moving rats by the use of in vivo microdialysis. D-Amphetamine significantly increased DA and GLU efflux in the striatum of iprindole-treated rats as compared to the vehicle-treated group. The increase in the extracellular concentration of GLU occurred 4-6 hr following drug administration. The concentration of DA was decreased significantly in the striatum of D-amphetamine and iprindole-treated rats 7 days following administration as compared to the vehicle-treated group. Inhibition of tyrosine hydroxylase after alpha-methylparatyrosine (150 mg/kg) administration attenuated D-amphetamine-induced DA and GLU release. The DA antagonist, haloperidol (1 mg/kg), blocked D-amphetamine-induced GLU release without affecting the increase in the extracellular concentration of DA produced by the combination of D-amphetamine and iprindole. Both alpha-methylparatyrosine and haloperidol blocked the depletion of DA in the striatum 7 days after D-amphetamine and iprindole as compared to the vehicle group. In addition, administration of MK-801 (2 mg/kg) 2 hr after D-amphetamine significantly attenuated the long-term (7 day) decrease in striatal DA content produced by the combination of D-amphetamine and iprindole.2+

[Current views of the mechanism of action of antidepressants]. / Aktualne poglady na mechanizm dzialania leków przeciwdepresyjnych.

Considering the ever growing number of new discoveries and changes in ideas in the field of psychopharmacology, the authors present the actual state of knowledge about the mechanism of action of antidepressant drugs. Three periods characterize the research and the development of antidepressants. In the first period the presynaptic monoamine neuron was considered as the target structure both with respect to the search for the origin of depression and the mechanism of action of antidepressants. Two types of antidepressants, monoamine uptake inhibitors and monoamine oxidase inhibitors (IMAO) are representative of this period. In the second period, the research focused its interest primarily on monoaminergic receptors, anticipating that they were critically involved in the pathophysiology of depression. Such research sought to explain the antidepressant properties of iprindole and mianserine which are neither monoamine uptake inhibitors nor inhibitors of MAO. The onset of the third period is recent and it is characterized by the shift in research emphasis to intracellular transmission events. This period started with the discovery of the antidepressant properties of the phosphodiesterase inhibitor rolipram.

Has iprindole an alpha adrenergic activity?

1. Acute administration of iprindole potentiated the toxicity of 1-norepinephrine and increased the intensity of oxotremorine-induced tremors. 2. On the forced swimming test combination iprindole with imipramine reduced the duration of immobility. 3. The action of yohimbine on the locomotor activity was antagonized by a pre-injection of iprindole. 4. Iprindole increased and prolonged exophthalmia and loss of righting reflex induced by xylazine. 5 All these results seems indicate that iprindole has an indirect alpha 1 and alpha 2 adrenergic activity.

A gas chromatographic procedure for separation and quantitation of the enantiomers of the antidepressant tranylcypromine.

A novel assay procedure has been developed that allows for the separation and quantification of the enantiomers of the monoamine oxidase inhibitor tranylcypromine (TCP) in brain and liver of rats. The analytical method involves extraction of the drug from rat tissue with an organic solvent. TCP is then derivatized with S-(-)-N-(trifluoroacetyl)-prolyl chloride to allow gas chromatographic analysis of the resulting diastereoisomers. Conditions for analysis by a gas chromatograph equipped with a nitrogen-phosphorus detector and a capillary column are described. The method has been applied to the separation and quantification of the enantiomers of TCP in samples of brain and liver of rats that had been injected with this drug alone and after pretreatment with iprindole, a drug known to block aromatic ring hydroxylation.

Protection against amphetamine-induced neurotoxicity toward striatal dopamine neurons in rodents by LY274614, an excitatory amino acid antagonist.

LY274614, 3SR,4aRS,6SR,8aRS-6-[phosphonomethyl]decahydr oisoquinoline-3- carboxylic acid, has been described as a potent antagonist of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Here its ability to antagonize the prolonged depletion of dopamine in the striatum by amphetamine in iprindole-treated rats is reported. A single 18.4 mg/kg (i.p.) dose of (+/-)-amphetamine hemisulfate, given to rats pretreated with iprindole, resulted in persistent depletion of dopamine in the striatum 1 week later. This prolonged depletion of dopamine in the striatum was antagonized by dizocilpine (MK-801, a non-competitive antagonist of NMDA receptors) or by LY274614 (a competitive antagonist of NMDA receptors). The protective effect of LY274614 was dose-dependent, being maximum at 10-40 mgkg (i.p.). A 10 mg/kg dose of LY274614 was effective in antagonizing the depletion of dopamine in the striatum, when given as long as 8 hr prior to amphetamine but not when given 24 hr prior to amphetamine. Depletion of dopamine in the striatum was also antagonized when LY274614 was given after the injection of amphetamine; LY274614 protected when given up to 4 hr after but not when given 8 or 24 hr after amphetamine. The prolonged depletion of dopamine in the striatum in mice, given multiple injections of methamphetamine, was also antagonized dose-dependently and completely by LY274614. The data strengthen the evidence that the neurotoxic effect of amphetamine and related compounds toward nigrostriatal dopamine neurons involves NMDA receptors and that LY274614 is an NMDA receptor antagonist with long-lasting in vivo effects in rats.

MK801 antagonism of the prolonged depletion of striatal dopamine by amphetamine in iprindole-treated rats.

The administration of amphetamine to rats pretreated with iprindole to inhibit the metabolism of amphetamine results in a long-lasting depletion of striatal dopamine and its metabolites, DOPAC and HVA. Pretreatment with MK801, a noncompetitive antagonist of the NMDA (N-methyl-D-aspartate) subclass of excitatory amino acid receptors, antagonized the depletion of striatal dopamine, DOPAC and HVA 3 days after a single dose of amphetamine in iprindole-treated rats. MK801 pretreatment was effective up to 4 hours but not at 8 or 24 hours in preventing amphetamine effects on striatal dopamine, DOPAC and HVA.

Effect of iprindole on the metabolism of trimipramine in the rat.

Major metabolites of trimipramine in young male Sprague-Dawley rats are the result of alicyclic and aromatic ring oxidation. The four major urinary metabolites have been identified as 10-oxotrimipramine, 2-hydroxytrimipramine, 2-hydroxynortrimipramine, and 2-hydroxy-10-oxotrimipramine. When iprindole was administered to rats prior to trimipramine, the effect on trimipramine metabolism was profound. The formation of both 10-oxo metabolites was virtually completely inhibited; the production of 2-hydroxytrimipramine was significantly reduced while the metabolic formation of 2-hydroxynortrimipramine was increased. It is apparent from these preliminary results that metabolic alicyclic and aromatic hydroxylations are catalyzed by different cytochrome P450 isozymes and more than one P450 isozyme is involved in the aromatic ring oxidation of trimipramine and nortrimipramine.

Acute or chronic antidepressants do not modify [125I]cyanopindolol binding to 5-HT1B receptors in rat brain.

Acute or chronic treatment of young or adult rats with chlorimipramine, tianeptine or iprindole, antidepressants with different effects on 5-HT uptake mechanisms, did not modify the density or the affinity of 5-HT1B receptors of the frontal cortex. No significant receptor change was found after prenatal exposure to these antidepressants. The lack of effect of the antidepressants was not related to the density of 5-HT1B receptors, which was significantly lower in younger animals.

Interactions of iprindole with fenfluramine metabolism in rat brain and liver.

An assay procedure utilizing electron-capture gas chromatography was developed for simultaneous analysis of fenfluramine and norfenfluramine. This method was applied to brain and liver samples from rats which had been injected with fenfluramine with or without pretreatment with iprindole. The tissues from rats treated with fenfluramine showed extensive formation of norfenfluramine, consistent with findings reported previously in the literature. Pretreatment with iprindole led to an increase in brain and liver levels of fenfluramine, and, unexpectedly, to a marked decrease in levels of norfenfluramine in these tissues. These findings suggest that iprindole blocks N-deethylation and that it may be a useful tool with which to study the effects of fenfluramine in the absence of norfenfluramine. The results also emphasize the importance of considering drug-drug interactions in future research on fenfluramine.

Chronic electroconvulsive treatment augments coupling of the GTP-binding protein Gs to the catalytic moiety of adenylyl cyclase in a manner similar to that seen with chronic antidepressant drugs.

A significant increase of guanylylimidodiphosphate (GppNHp)-, fluoride-, and forskolin-stimulated adenylyl cyclase was observed in synaptic membrane preparations from rat cerebral cortex subsequent to chronic electroconvulsive shock (ECS) treatment. This effect required at least five treatments over a course of 10 days. The inhibition of adenylyl cyclase induced by GppNHp was not affected by these treatments. The dissociation constant (KD) and maximal binding for the photoaffinity GTP analog, [32P]P3-(4-azidoanilido)-P1-5'-GTP [( 32P]AAGTP), to each of the synaptic membrane G proteins also were unchanged after ECS treatment. Nonetheless, the transfer of [32P]AAGTP from Gi to Gs, which we suggest is indicative of the coupling between Gs and the adenylyl cyclase catalytic moiety, was accelerated by chronic ECS treatment but not by acute or sham treatment. Furthermore, chemical uncoupling of Gs from adenylyl cyclase rendered membranes from treated animals indistinguishable from controls. Finally, in all cases tested, membranes prepared from animals subjected to chronic treatment with amitriptyline or iprindole showed similar changes in the Gs-mediated activation of adenylyl cyclase. Acute treatments produced effects similar to controls, and liver and kidney membranes from animals receiving chronic treatment showed no changes in adenylyl cyclase despite the marked changes seen in brain. These results suggest that chronic administration of ECS enhances coupling between Gs and adenylyl cyclase enzyme and modifies interactions between Gs and Gi.

Molecular aspects of the neuronal noradrenaline transporter.

The neuronal noradrenaline transporter was partially purified by means of low and high pressure liquid chromatography using anion exchange, gel filtration and lectin affinity columns. A protein characterized by a molecular weight of 50-53 kilodalton was enriched; it may represent the transporter or a component of it. In addition, a RNA fraction characterized by a mean size of 2 kilobases was isolated from PC12 rat phaeochromocytoma cells and from bovine adrenal medulla; this RNA fraction caused expression of the noradrenaline transporter after microinjection into Xenopus laevis oocytes.