Chronic desipramine enhances the effect of locally applied amphetamine on interstitial concentrations of dopamine in the nucleus accumbens

Experimental confirmation of new drug-target interactions predicted by Drug Profile Matching

We recently introduced Drug Profile Matching (DPM), a novel affinity fingerprinting-based in silico drug repositioning approach. DPM is able to quantitatively predict the complete effect profiles of compounds via probability scores. In the present work, in order to investigate the predictive power of DPM, three effect categories, namely, angiotensin-converting enzyme inhibitor, cyclooxygenase inhibitor, and dopamine agent, were selected and predictions were verified by literature analysis as well as experimentally. A total of 72% of the newly predicted and tested dopaminergic compounds were confirmed by tests on D1 and D2 expressing cell cultures. 33% and 23% of the ACE and COX inhibitory predictions were confirmed by in vitro tests, respectively. Dose-dependent inhibition curves were measured for seven drugs, and their inhibitory constants (Ki) were determined. Our study overall demonstrates that DPM is an effective approach to reveal novel drug-target pairs that may result in repositioning these drugs.

Characteristics and clinical correlates of restless legs syndrome in schizophrenia

OBJECTIVE

The cause of restless legs syndrome (RLS) has not yet been ascertained, but one of the most promising theories involves dopaminergic deficiency. In accordance with this theory, we assumed that the prevalence of RLS would be higher among schizophrenics treated with antipsychotics than in the normal population. The purpose of this study was to establish the prevalence, characteristics, and clinical correlates of RLS in schizophrenic patients undergoing treatment with antipsychotics.

METHODS

A total of 182 hospitalized schizophrenic patients and 108 age- and sex-matched normal controls were enrolled. The presence of RLS and its severity were assessed using the International Restless Legs Syndrome Study Group (IRLSSG) diagnostic criteria and the IRLSSG rating scale, respectively. The Athens Insomnia Scale (AIS), Brief Psychiatric Rating Scale (BPRS), and Barnes Akathisia Rating Scale (BARS) were used to evaluate insomnia, global psychiatric symptoms, and akathisia, respectively, in schizophrenic patients.

RESULTS

Of the 182 schizophrenic patients, 39 (21.4%) were found to have RLS and 87 (47.8%) met at least one of the RLS diagnostic criteria. The prevalence of RLS was significantly higher in the schizophrenia group than in the control group (p=0.009), as were the RLS scores (p<0.001). The BPRS (p=0.001) and the AIS (p<0.001) scores were higher in the RLS group than in the group with no RLS symptoms.

CONCLUSION

We conclude that it is important to consider the diagnosis of RLS when schizophrenic patients complain of insomnia, and that RLS symptoms could be associated with more severe psychiatric symptoms and insomnia.

A metabotropic glutamate 2/3 receptor antagonist, MGS0039, increases extracellular dopamine levels in the nucleus accumbens shell

(1R,2R,3R,5R,6R)-2-Amino-3-(3,4-dichlorobenzyloxy)-6-fluorobicyclo[3.1.0]hexane-2,6-dicarboxylic acid (MGS0039), a potent and selective metabotropic glutamate 2/3 (mGlu 2/3) receptor antagonist, exhibits antidepressant-like activities in some animal models. In the present study, we examined the effect of MGS0039 on extracellular dopamine levels in the rat nucleus accumbens (NAc) shell using in vivo microdialysis evaluation because accumbal dopamine has been implicated in depression. Local application of MGS0039 into the NAc shell at 10 microM significantly increased extracellular dopamine levels in the NAc shell in freely moving rats. In contrast, local application of 10 microM of LY354740, an mGlu 2/3 receptor agonist, significantly decreased extracellular dopamine levels in the same brain region. These findings suggest that dopamine release in the NAc shell is regulated by mGlu 2/3 receptors, and that the effect on dopamine levels in the NAc shell may partially explain the antidepressant-like properties of mGlu 2/3 receptor antagonists.

Intraaccumbens dopaminergic lesion suppresses desipramine effects in the forced swim test but not in the neuronal activity of lateral septal nucleus

The nucleus accumbens (NAcc) function is related to locomotor activity, while the lateral septal nucleus (LSN) is related to the motivational aspects of behavior. Thus, a dopaminergic lesion of the NAcc blocks the antiimmobility effect of desipramine (DMI) and this tricyclic increases the firing rate of the LSN; however, it is unknown whether a relation exists between a dopaminergic lesion of the NAcc and the response of LSN neurons to DMI treatment. Therefore, we conducted a longitudinal study to further explore the participation of NAcc dopaminergic terminals in the immobility reduction exerted by DMI in the forced swim test and its relation to the firing rate of the LSN, at the same time exploring motor and motivational aspects of DMI-dopaminergic relationships in the animals. A dopaminergic lesion was bilaterally produced by 6-hydroxydopamine (6-OHDA) injection into the NAcc of adult ovariectomized Wistar rats pretreated with DMI (25 mg/kg ip, 30 min before lesion to protect NA terminals but to destroy DA endings). Treatments with DMI or saline began 24 h after stereotaxic surgery. The results showed that DMI once a day during 9 days (10 mg/kg) reduced immobility in the forced swim test in the sham-lesion group (P<.02); however, in the dopaminergic lesion group submitted to DMI treatment, immobility remained at control level in agreement with other reports. DMI increased the firing rate of the LSN (P<.001) independently of the 6-OHDA lesion. In conclusion, the dopaminergic terminals of the NAcc seem to be essential for the motor manifestation associated with motivation induced by DMI in the forced swim test, given that the antiimmobility actions of DMI are blocked after a dopaminergic NAcc lesion; however, the effect on the firing rate of LSN neurons is still present.

Do antidepressants affect motivation in conditioned place preference?

The positive motivational effects of a range of antidepressants/neurotransmitter reuptake inhibitor compounds were studied using conditioned place preference. These agents included amitriptyline (2.5-10 mg/kg), venlafaxine (5 and 10 mg/kg), sibutramine (5 and 10 mg/kg), fluoxetine (2.5-10 mg/kg), paroxetine (5-15 mg/kg) and sertraline (2.5-10 mg/kg). Male Wistar rats were place conditioned in a three-compartment box to vehicle or drug alternately for 8 days using a 30-min pretreatment time. Control animals received vehicle only. Cocaine (5 mg/kg) was used as a positive control for the procedure. Significant place preference (P<0.05) was observed with paroxetine (15 mg/kg), fluoxetine (5 and 10 mg/kg), sertraline (2.5-10 mg/kg) and cocaine. Venlafaxine and sibutramine, serotonin/noradrenaline reuptake inhibitors, produced no place conditioning, while the highest dose of the tricyclic antidepressant, amitriptyline (10 mg/kg), produced signs of place aversion. The role of serotonin in reward pathways and differences in serotonin, noradrenaline and dopamine reuptake-inhibiting properties of these compounds may explain why only the serotonin-selective reuptake inhibitors produced place preference in this study.

The role of dopamine in the mechanism of action of antidepressant drugs

The present paper reviews evidence on the effect of antidepressant treatments on dopamine transmission. Chronic treatment with antidepressant drugs potentiates the behavioural stimulant responses elicited by the stimulation of dopamine receptors, including reward-related behaviours. Moreover, antidepressants affect dopamine release in several brain areas. The reviewed literature is discussed in terms of the possible mechanisms underlying antidepressant-induced supersensitivity to dopamine-mediated behavioural responses, and of the possible implications for the therapeutic effect of these drugs. It is concluded that the potentiation of dopaminergic neurotransmission induced by chronic antidepressant treatments might contribute to their therapeutic effect.

Selective increase of dopamine D3 receptor gene expression as a common effect of chronic antidepressant treatments

The mesolimbic dopaminergic system is a neuroanatomical key structure for reward and motivation upon which previous studies indicated that antidepressant drugs exert a stimulatory influence, via still unknown neurobiological mechanisms. Here we examined the effects of chronic administration of antidepressants of several classes (amitriptyline, desipramine, imipramine, fluoxetine and tranylcypromine) and repeated electroconvulsive shock treatments (ECT) on dopamine D3 receptor expression in the shell of the nucleus accumbens, a major projection area of the mesolimbic dopaminergic system. Short-term drug treatments had variable effects on D3 receptor mRNA expression. In contrast, treatments for 21 days (with all drugs except fluoxetine) significantly increased D3 receptor mRNA expression in the shell of nucleus accumbens; D3 receptor binding was also significantly increased by amitriptyline or fluoxetine after a 42-day treatment. ECT for 10 days increased D3 receptor mRNA and binding in the shell of nucleus accumbens. D1 receptor and D2 receptor mRNAs were increased by imipramine and amitriptyline, but not by the other treatments. The time-course of altered D3 receptor expression, in line with the delayed clinical efficiency of antidepressant treatment, and the fact that various antidepressant drugs and ECT treatments eventually produced the same effects, suggest that increased expression of the D3 receptor in the shell of nucleus accumbens is a common neurobiological mechanism of antidepressant treatments, resulting in enhanced responsiveness to the mesolimbic dopaminergic system.

Subchronic fluoxetine treatment induces a transient potentiation of amphetamine-induced hyperlocomotion: possible pharmacokinetic interaction

The results of the present study show that 5 days of systemic treatment with fluoxetine (5 mg/kg) resulted in an augmented locomotor response to amphetamine (0.5 mg/kg). This augmented response to amphetamine was observed 24 and 48 h, but not 5 days, after the cessation of fluoxetine treatment. Subchronic fluoxetine treatment also produced an increase in the brain concentration of amphetamine when rats were challenged with amphetamine 48 h, but not 5 days, after the cessation of fluoxetine treatment. Thus, the effect of subchronic fluoxetine in augmenting amphetamine-induced hyperactivity was consistent with the effect of subchronic fluoxetine in augmenting the amphetamine concentration in the brain. This pattern of results indicates that subchronic fluoxetine potentiates the response to amphetamine within a limited time-window, and that this potentiating effect is likely to be due to the reduced metabolism of amphetamine via the inhibition of cytochrome P450 by fluoxetine and/or its metabolite norfluoxetine.

Chronic clomipramine administration reverses NMDA-evoked decreases in dopamine release in the raphe nuclei

The effect of acute or chronic treatment with the antidepressant clomipramine (CIM) on basal and N-methyl-d-aspartate (NMDA) evoked release of dopamine (DA) in rat raphe has been studied using microdialysis. Acute injection of CIM (10 or 20 mg/kg) caused a decrease in raphe DA release, as did infusion of NMDA (25-100 microM) into this region. When NMDA infusion was preceded by a single acute injection of CIM no differences between NMDA and NMDA plus CIM treated groups was observed. Chronic (15 day) treatment with CIM caused a dose-dependent increase in basal extracellular DA. In addition the effect of infusing NMDA into the raphe on DA release was markedly reduced or abolished. This suggests that adaptive changes occur in NMDA receptor function during treatment with CIM.

Chronic but not acute clomipramine alters the effect of NMDA receptor regulation of dopamine release in rat frontal cortex

The effect of acute or chronic treatment with the antidepressant clomipramine (CIM) on N-methyl-D-aspartate (NMDA) evoked release of dopamine (DA) in the frontal cortex of the rat has been studied using microdialysis. Acute injection of CIM (10 or 20 mg/kg) caused a decrease in dialysate DA in the frontal cortex. Infusion of 25-100 microM NMDA into the frontal cortex decreased DA release in this region. When NMDA infusion was preceded by a single injection of CIM no marked differences between NMDA and NMDA + CIM treated groups were observed. Chronic (15 day) treatment with CIM (10 or 20 mg/kg) caused a dose-dependent increase in basal extracellular DA. In these animals, however, the effects of infusion of NMDA on DA release in the cortex were greatly attenuated or abolished. This suggests that adaptive changes occur in NMDA receptor function during treatment with an antidepressant. The possible significance of this in the aetiology and treatment of depression is discussed.

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Chronic administration of l-sulpiride at low doses reduces A10 but not A9 somatodentritic dopamine autoreceptor sensitivity

The effect of chronic treatment (twice daily for 21 days) with low doses of l-sulpiride (2 mg/kg i.p.) on the apomorphine-induced inhibition of A10 and A9 dopaminergic neurons was compared with the effect of chronic administration of the classic antidepressant desipramine (20 mg/kg i.p. daily for 21 days). Intravenous administration of apomorphine (0.01-0.04 mg/kg), to rats treated chronically with l-sulpiride, produced a reduction of the spontaneous firing rate of A9 dopaminergic neurons not significantly different from that observed in control (saline-treated) rats. In contrast, apomorphine at the same doses was more potent in inhibiting A10 firing in control rats than in l-sulpiride-treated subjects. On the other hand, desipramine-treated rats were found normosensitive (as compared to saline-treated rats) to the inhibitory properties of apomorphine in both A9 and A10 dopaminergic neurons. It is suggested that chronic l-sulpiride-induced reduction of autoreceptor sensitivity in the A10 region may contribute to its clinical antidepressant effect.

Effect of antidepressants on striatal and accumbens extracellular dopamine levels

The effect of the selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor, fluoxetine (10 mg/kg s.c.), two tricyclic antidepressants, clomipramine (10 mg/kg s.c.) and imipramine (10 mg/kg s.c.), and vehicle on extracellular dopamine levels was studied in rat nucleus accumbens and striatum by in vivo microdialysis. Fluoxetine produced significant decreases in extracellular dopamine levels in both the nucleus accumbens and striatum (mean maximum percentage decrease: 58% and 57% of pre-drug baseline, respectively). In contrast, imipramine and clomipramine significantly increased extracellular dopamine in the striatum (148% and 150%, respectively) compared to the effect of vehicle alone (118%). These results suggest that the selective serotonin reuptake inhibitor, fluoxetine, and the tricyclic antidepressants, clomipramine and imipramine, affect dopaminergic activity in diverse ways and in a region-specific manner. Thus, the antidepressant effect of these drugs is unlikely to be related to their acute effects on dopaminergic neurotransmission. The differential effects of the selective serotonin reuptake inhibitor and tricyclic antidepressants on extracellular dopamine could account for other differences in their clinical and side effect profiles. Further studies of the chronic effects of the selective serotonin reuptake inhibitor and the tricyclic antidepressants on dopaminergic activity are required to elucidate the role of dopamine in the antidepressant effect.

Chronic variable stress enhances the stimulatory action of a low dose of morphine: reversal by desipramine

Adult male rats were exposed to a chronic variable stress treatment, an animal model of depression, with or without concurrent daily administration of desipramine. Animals given chronic and variable stress were submitted daily to a different stressor following an injection of either saline or desipramine (5 mg/kg, i.p.), whereas control animals were unmanipulated except for the injection process. One day after the last event of the chronic procedure, control and stressed animals were administered saline or morphine (0.75 or 1.5 mg/kg, i.p.) and their locomotion assessed for 90 min. In an additional experiment, 24 h after the last stressor, stressed and control rats were challenged with either saline or one of two higher doses (behaviorally suppressant) of morphine (5 and 10 mg/kg, i.p.). A significantly greater increase in locomotor activity following a low dose (1.5 mg/kg) of morphine was observed in chronically stressed rats as compared to control rats. This potentiated locomotor response to morphine in stressed rats was prevented by desipramine pretreatment. The chronic and variable stress treatment did not modify the sedative response to the high doses of morphine. These data support the suggestion that a chronic and variable stress procedure results in sensitization to the stimulant effect of opioid stimulation, and that pretreatment with the antidepressant agent desipramine blocks the development of this sensitization.

Local effects of ibogaine on extracellular levels of dopamine and its metabolites in nucleus accumbens and striatum: interactions with D-amphetamine

Systemic administration of ibogaine (40 mg/kg, i.p.) has been reported to induce both acute (1-3 h) and persistent (19-20 h) changes in extracellular levels of dopamine and its metabolites in the nucleus accumbens and striatum. In the present study, local administration of ibogaine to the striatum and nucleus accumbens produced effects that mimicked both the acute and persistent effects of systemic administration: perfusion with high concentrations (200 and 400 microM) of ibogaine mimicked the acute effects (decreased extracellular dopamine levels and increased extracellular metabolite levels) whereas perfusion with a low concentration (10 microM) of ibogaine mimicked the persistent effects (decreased extracellular levels of DOPAC). These results indicate that ibogaine acts directly in brain regions containing dopaminergic nerve terminals and that long-lasting effects of systemically administered ibogaine might be mediated by persisting low levels of ibogaine. Locally administered ibogaine (10 microM) was also found to enhance the effects of systemically administered D-amphetamine (1.25 mg/kg, i.p.) on extracellular dopamine levels, and conversely, systemically administered ibogaine (40 mg/kg, i.p.; 19 h pretreatment) enhanced the effects of locally administered D-amphetamine (1-10 microM). These results indicate that, in addition to a metabolic mechanism implicated previously, a pharmacodynamic mechanism contributes to the interaction between ibogaine and D-amphetamine. The relevance of such mechanisms to claims regarding ibogaine's anti-addictive properties is unclear.