Effect of antidepressant drugs administered repeatedly on the dopamine D3 receptors in the rat brain

Polyvinyl alcohol/citric acid/β-cyclodextrin/CuONP composite nanofibers as an effective and green absorbent for the simultaneous extraction of three antidepressant drugs in biological fluids prior to GC-FID analysis

Composite nanofibers, namely, polyvinyl alcohol (PVA), citric acid (CA), β-cyclodextrin (β-CD), and copper oxide nanoparticles (PVA/CA/β-cyclodextrin/CuO NPs), were developed as a novel, green, and efficient adsorbent in the pipette tip-micro-solid-phase extraction method (PT-µSPE), for the simultaneous extraction of three antidepressants drugs namely imipramine (IMP), citalopram (CIT), and clozapine (CLZ) in biological fluids before quantification by gas chromatography (GC-FID). Based on the obtained results from field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD), the successful synthesis of composite nanofibers was approved. Due to the presence of β-cyclodextrins and CuO NPs rich of functional groups on their surface, the nanofibers have high extraction efficiency. Under the optimal conditions, the linear range for imipramine, citalopram, and clozapine was 0.1 to 1000.0 ng mL^-1 with a determination coefficient ≥ 0.99. The limits of detection (LODs) were in the range 0.03 to 0.15 ng mL^-1. The relative standard deviation was 4.8 to 8.7% (within-day, n = 4) and 5.1 to 9.2% (between-day, n = 3) for 3 consecutive days. In addition, excellent clean-up was achieved which is a great advantage over other sample preparation methods. Finally, the ability of the developed method to extract the target analytes from the biological samples was evaluated.

Pramipexole regulates depression-like behavior via dopamine D3 receptor in a mouse model of Parkinson's disease

Depression is one of the strongest predictors of quality of life in patients with Parkinson's disease (PD). Despite the high prevalence of depression, there is no clear guidance for its treatment in PD because the evidence for the efficacy of most antidepressants remains insufficient. Pramipexole, a dopamine agonist, is one of the few drugs that has proven to be clinically useful. However, the underlying mechanisms of antidepressive effects of pramipexole are still unknown. A 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model, dopamine D2 receptor (DRD2) and D3 receptor (DRD3) knockout mice were used in our study. Compared with other dopamine D2-like receptor agonists and madopar, pramipexole improved depression-like behavior and alleviate bradykinesia in an MPTP-induced mouse model of PD. Pramipexole significantly improved depression-like behavior in DRD2^-/- mice but not in DRD3^-/- mice. These results demonstrate that the antidepressive effect of pramipexole is mediated by DRD3 but not DRD2. Our findings highlight the need to develop novel dopamine agonists specifically targeting DRD3 for the treatment of depression in PD in the future.

Cariprazine as a therapeutic option for schizophrenia: a drug evaluation

Introduction: Schizophrenia is a very disabling condition that may result in a significant impairment of individual, professional, and social adjustments. Antipsychotics (APs), the first-line treatment for schizophrenia, in many cases modify the course of the disease, by reducing the institutionalization risk, at the price of severe and invalidating side effects. Cariprazine is one of the latest second-generation APs (SGAs) acting as a partial agonist of type 2 and 3 dopamine receptors, which was recently approved for the treatment of adult schizophrenia.Areas covered: The authors provide a critical review and commentary on the currently available data on the effectiveness and tolerability of cariprazine in schizophrenic patients, with a particular focus on its specific target symptoms.Expert opinion: Cariprazine appears significantly effective on both acute and maintenance treatment of schizophrenia, and in improving positive, negative, and cognitive symptoms, slightly more than other SGAs. It shows a good safety and tolerability profile, with akathisia being its most common side effect. Although further independent studies are needed to clarify its precise advantages over other SGAs, cariprazine seems a promising compound not only in schizophrenia, but also in a broad range of psychiatric conditions, including perhaps bipolar and addictive disorders.

Type 3 adenylyl cyclase in the main olfactory epithelium participates in depression-like and anxiety-like behaviours

BACKGROUND

Deficiency of olfaction is thought to be associated with depression, and type 3 adenylyl cyclase (AC₃) genetic knockout and forebrain knockout mice show depression-like behaviours. AC₃ is expressed in the main olfactory epithelium (MOE) and hippocampus, which plays an important role in olfactory signal transduction. However, it is unclear whether AC₃ in the MOE also plays a role in the pathogenesis of depression. Thus, we aimed to study the relationship between AC₃ in the MOE and the pathogenesis of depression.

METHODS

We obtained anosmic mice by intranasal perfusion of zinc sulphate (ZnSO₄) (ZnSO₄ mice), and distinctively knocked down AC₃ in the MOE (AC_3KD/MOE mice) by CRISPR/cas9 technology. Behavioural tests related to depression and anxiety were employed to evaluate the depression- and anxiety-like behaviours of mice. The mRNA and protein expressions of tyrosine hydroxylase (TH), dopamine receptors (Drds), and N-Methyl D-aspartate receptor subunit 2B (GluN2B) in the hippocampus of mice were investigated by qPCR and western blotting to explore the mechanism of depression and anxiety caused by AC₃ in the MOE, preliminarily.

RESULTS

Compared with NaCl mice, ZnSO₄ mice exhibited depression-like behaviours in tail suspension tests (TST), forced swimming tests, and social (FST) interaction tests (SIT), but showed no anxiety-like behaviours in anxiety-related behavioural tests. The mRNA and protein expressions of Drd3 and GluN2B in the hippocampus of ZnSO₄ mice were significantly downregulated. Compared with the negative control mice (NC mice), AC_{3KD / MOE} mice showed depression-like behaviours in TST, FST, and SIT tests, anxiety-like behaviours in light/dark transition test, elevated-plus maze test, and novelty-suppressed feeding test. The protein expressions of Drd3, TH, and GluN2B were significantly downregulated in the hippocampus.

LIMITATIONS

We did not further demonstrate that AC₃ in the MOE causes depression through the dopaminergic nervous system with dopamine or dopamine receptor agonists.

CONCLUSIONS

Our data demonstrate that intranasal infusion of ZnSO₄ can cause depression-like behaviours and has no effect on anxiety-like behaviours. Specific knockdown of AC₃ in the MOE can cause depression-like and anxiety-like behaviours. The behavioural changes caused by intranasal ZnSO₄ and specific knockdown of AC₃ in the MOE can be related to the significant downregulation of dopaminergic system and GluN2B expressions in the hippocampus of mice.

Dopamine D3 receptor: A neglected participant in Parkinson Disease pathogenesis and treatment?

Parkinson disease (PD) is a neurodegenerative disorder characterized by motor and non-motor symptoms which relentlessly and progressively lead to substantial disability and economic burden. Pathologically, these symptoms follow the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) associated with abnormal α-synuclein (α-Syn) deposition as cytoplasmic inclusions called Lewy bodies in pigmented brainstem nuclei, and in dystrophic neurons in striatal and cortical regions (Lewy neurites). Pharmacotherapy for PD focuses on improving quality of life and primarily targets dopaminergic pathways. Dopamine acts through two families of receptors, dopamine D1-like and dopamine D2-like; dopamine D3 receptors (D3R) belong to dopamine D2 receptor (D2R) family. Although D3R's precise role in the pathophysiology and treatment of PD has not been determined, we present evidence suggesting an important role for D3R in the early development and occurrence of PD. Agonist activation of D3R increases dopamine concentration, decreases α-Syn accumulation, enhances secretion of brain derived neurotrophic factors (BDNF), ameliorates neuroinflammation, alleviates oxidative stress, promotes neurogenesis in the nigrostriatal pathway, interacts with D1R to reduce PD associated motor symptoms and ameliorates side effects of levodopa (L-DOPA) treatment. Furthermore, D3R mutations can predict PD age of onset and prognosis of PD treatment. The role of D3R in PD merits further research. This review elucidates the potential role of D3R in PD pathogenesis and therapy.

Lentiviral-mediated let-7d microRNA overexpression induced anxiolytic- and anti-depressant-like behaviors and impaired dopamine D3 receptor expression

Generalized anxiety and major depression disorders (MDD) are severe debilitating mood disorders whose etiology are not fully understood, but growing evidence indicates that microRNAs (miRNAs) might play a key role in their neuropathophysiological mechanisms. In the current study, we investigate the role of Lethal-7 (let-7d) miRNA, and its direct target dopamine D3 receptor (D3R) gain-of-function, in the hippocampus, in preclinical models of anxiety and depression in mice. For this purpose, we have constructed a lentiviral vector carrying let-7d miRNA and its anxiolytic effect was investigated by employing the open-field (OF) and the elevated plus maze (EPM) tests. The anti-depressant activity was evaluated using the tail suspension and the forced-swim tests (TST & FST). Our results show that let-7d overexpression significantly improved the measures of anxiety in the OF and EPM tests. In addition, let-7d increased the mobility time in the TST and FST. Interestingly, gene expression interaction analysis shows that the D3R mRNA negatively correlates with let-7d expression. In a different set of experiments, we used a tetracycline-inducible (tet-off) lentiviral vector to overexpress D3R to assess its gain-of-function in the hippocampus on anxiety- and depression-like behaviors. In line, we found that in the absence of doxycycline, D3R produced a significant anxiogenic and depressant-like response. Most importantly, these effects were abrogated when mice were fed doxycycline in drinking water. Our results provide the first evidence for an anxiolytic and anti-depressant-like action of let-7d through a potential D3R target-mediated mechanism which might open new avenues for anxiolytic and anti-depressant therapies.

The Dopamine Receptor D3 Regulates Lipopolysaccharide-Induced Depressive-Like Behavior in Mice

BACKGROUND

The altered expression and function of dopamine receptor D3 (D3R) in patients and animal models have been correlated with depression disease severity. However, the morphological alterations and biological effects of D3R in the brain after inflammation-induced depressive-like behavior remain elusive.

METHODS

In the present study, we ascertained the changes of D3R expression in the brain regions after depressive-like behavior induced by peripheral administration of lipopolysaccharide (LPS). Protein levels of proinflammatory cytokines, brain-derived neurotrophic factor (BDNF), and extracellular signal-regulated kinase (ERK1/2)-cAMP-response element-binding protein (CREB) signaling pathway after activation or inhibition of D3R in the brain of depressive mice were also investigated.

RESULTS

LPS caused a significant reduction of D3R in the ventral tegmental area (VTA), medial prefrontal cortex (mPFC), and nucleus accumbens (NAc), which are areas related to the mesolimbic dopaminergic system. Pretreatment with pramipexole (PPX), a preferential D3R agonist, showed antidepressant effects on LPS-induced depression-like behavior through preventing changes in LPS-induced proinflammatory cytokines (tumour necrosis factor-α, interleukin-1β, and interleukin-6), BDNF, and ERK1/2-CREB signaling pathway in the VTA and NAc. In opposition, treatment with a D3R selective antagonist NGB 2904 alone made mice susceptible to depression-like effects and caused changes in accordance with the LPS-induced alterations in proinflammatory cytokines, BDNF, and the ERK1/2-CREB signaling pathway in the mPFC and NAc.

CONCLUSIONS

These findings provide a relevant mechanism for D3R in LPS-induced depressive-like behavior via its mediation of proinflammatory cytokines and potential cross-effects between BDNF and the ERK1/2-CREB signaling pathway.

Cariprazine Exhibits Anxiolytic and Dopamine D3 Receptor-Dependent Antidepressant Effects in the Chronic Stress Model

Background

Cariprazine, a D3-preferring dopamine D2/D3 receptor partial agonist, is a new antipsychotic drug recently approved in the United States for the treatment of schizophrenia and bipolar mania. We recently demonstrated that cariprazine also has significant antianhedonic-like effects in rats subjected to chronic stress; however, the exact mechanism of action for cariprazine's antidepressant-like properties is not known. Thus, in this study we examined whether the effects of cariprazine are mediated by dopamine D3 receptors.

Methods

Wild-type and D3-knockout mice were exposed to chronic unpredictable stress for up to 26 days, treated daily with vehicle, imipramine (20 mg/kg), aripiprazole (1 and 5 mg/kg), or cariprazine (0.03, 0.1, 0.2, and 0.4 mg/kg), and tested in behavioral assays measuring anhedonia and anxiety-like behaviors.

Results

Results showed that cariprazine significantly attenuated chronic unpredictable stress-induced anhedonic-like behavior in wild-type mice, demonstrating potent antidepressant-like effects comparable with aripiprazole and the tricyclic antidepressant imipramine. This antianhedonic-like effect of cariprazine was not observed in D3-knockout mice, suggesting that the cariprazine antidepressant-like activity is mediated by dopamine D3 receptors. Moreover, cariprazine significantly reduced drinking latency in the novelty-induced hypophagia test in wild-type mice, further confirming its antianhedonic-like effect and showing that it also has anxiolytic-like activity.

Conclusions

In combination with previous studies, these results suggest that cariprazine has a unique pharmacological profile and distinct dopamine D3 receptor-dependent mechanism of action that may be beneficial in the treatment of schizophrenia, bipolar disorder, and major depressive disorder.

Dopaminergic mechanisms in memory consolidation and antidepressant reversal of a chronic mild stress-induced cognitive impairment`

Cognitive deficits in depression can be modelled using the novel object recognition (NOR) test, performance in which is impaired by chronic mild stress (CMS). We aimed to examine the involvement of mesocorticolimbic DA terminal regions, and to establish the substrate for CMS-induced impairment of NOR and its reversal by chronic antidepressant treatment. In experiments 1 and 2, we examined the effect of infusions into medial PFC, dorsal hippocampus (HPC), and nucleus accumbens (NAc) shell of D1 and D2 antagonists and D3 agonist, which were predicted to impair NOR with a short (1 h) delay, and of D1 and D2 agonists and D3 antagonist, which were predicted to facilitate NOR with a long (24 h) delay. Using optimal doses identified in experiment 2, in experiments 3 and 4, we examined effects on drug-stimulated NOR of CMS and chronic treatment with venlafaxine (VFX) or risperidone (RSP). We found a wide involvement of DA systems in memory for NOR: D1 receptors in PFC, HPC, and NAc; D3 receptors in PFC and HPC; and D2 receptors in PFC. CMS impaired D2- and D3-mediated effects in PFC and HPC; antidepressants rescued those effects in PFC but not HPC. The involvement of DA in NOR is multifaceted, but the effects of CMS and antidepressants are more discrete, involving D2 and D3 receptors in PFC specifically. While raising many difficult questions, these results suggest that the D2 and D3 receptors in the medial PFC may be an important substrate for cognitive deficits in depression and their remediation.

Mirtazapine prevents induction and expression of cocaine-induced behavioral sensitization in rats

Cocaine abuse is a major health problem worldwide. Treatment based on both 5-HT2A/C and 5-HT3 receptor antagonists attenuate not only the effects of cocaine abuse but also the incentive/motivational effect related to cocaine-paired cues. Mirtazapine, an antagonist of postsynaptic α2-adrenergic, 5-HT2A/C and 5HT3 receptors and inverse agonist of the 5-HT2C receptor, has been shown to effectively modify, at the preclinical and clinical levels, various behavioral alterations induced by drugs abuse. Therefore, it is important to assess whether chronic dosing of mirtazapine alters locomotor effects of cocaine as well as induction and expression of cocaine sensitization. Our results reveal that a daily mirtazapine regimen administered for 30days effectively induces a significant attenuation of cocaine-dependent locomotor activity and as well as the induction and expression of behavioral sensitization. These results suggest that mirtazapine may be used as a potentially effective therapy to attenuate induction and expression of cocaine-induced locomotor sensitization.

Citalopram-associated gambling: a case report

Pathological gambling behaviour is a side effect of dopaminergic drugs used in Parkinson's disease, but has seldom been reported with selective serotonin reuptake inhibitors. A 58-years-old woman with somatisation disorder since the age of 20 and recent-onset major depression (at 54 years) received 40 mg/day intravenous citalopram, thereafter switching to the same dose of oral citalopram to treat her comorbid psychiatric disorders after showing poor response to paroxetine for one year. Her anxious and depressive symptoms were moderately reduced after 7 months of oral citalopram, but simultaneously, the patient admitted gambling. We gradually discontinued citalopram and introduced pregabalin and alprazolam; this was followed by a reduction of gambling compulsions, but the somatisation and depressive symptoms did not further improve. Pathological gambling may be mediated by an interplay of 5-HT1A serotonergic and D2 dopaminergic mechanisms. Citalopram affects both these mechanisms in areas that were shown to be involved in gambling behaviour, but while dopaminergic effects of citalopram appear to be consistent with the induction of gambling, its serotonergic mechanisms are rather inconsistent. In our patient, mood destabilisation induced by citalopram may have contributed to the first onset of pathological gambling.

Antidepressant response to aripiprazole augmentation associated with enhanced FDOPA utilization in striatum: a preliminary PET study

Several double blind, prospective trials have demonstrated an antidepressant augmentation efficacy of aripiprazole in depressed patients unresponsive to standard antidepressant therapy. Although aripiprazole is now widely used for this indication, and much is known about its receptor-binding properties, the mechanism of its antidepressant augmentation remains ill-defined. In vivo animal studies and in vitro human studies using cloned dopamine dopamine D2 receptors suggest aripiprazole is a partial dopamine agonist; in this preliminary neuroimaging trial, we hypothesized that aripiprazole's antidepressant augmentation efficacy arises from dopamine partial agonist activity. To test this, we assessed the effects of aripiprazole augmentation on the cerebral utilization of 6-[(18)F]-fluoro-3,4-dihydroxy-l-phenylalanine (FDOPA) using positron emission tomography (PET). Fourteen depressed patients, who had failed 8 weeks of antidepressant therapy with selective serotonin reuptake inhibitors, underwent FDOPA PET scans before and after aripiprazole augmentation; 11 responded to augmentation. Whole brain, voxel-wise comparisons of pre- and post-aripiprazole scans revealed increased FDOPA trapping in the right medial caudate of augmentation responders. An exploratory analysis of depressive symptoms revealed that responders experienced large improvements only in putatively dopaminergic symptoms of lassitude and inability to feel. These preliminary findings suggest that augmentation of antidepressant response by aripiprazole may be associated with potentiation of dopaminergic activity.

Dopamine D₃ receptor gene variation: impact on electroconvulsive therapy response and ventral striatum responsiveness in depression

Dysfunction of dopamine D₃ receptors, particularly in the mesocorticolimbic system, has been linked to the pathogenesis of major depression. Preclinical data show enhanced D₃ receptor binding in the striatum upon antidepressant medication and electroconvulsive therapy (ECT). Thus, the potential impact of dopamine D₃ receptor gene (DRD3) variation on ECT outcome in treatment-resistant major depression was evaluated by applying a combined molecular and imaging genetic approach. Altogether, 10 representative variants covering 95.4% of DRD3 gene variation were investigated for association with response to ECT in a sample of 104 (71 female, 33 male) Caucasian patients with pharmacorefractory major depression. Additionally, ventral striatum responsiveness to happy faces was assessed in two independent samples of depressed patients (total N=54) by means of functional magnetic resonance imaging at 3 T. Significant association of DRD3 rs3732790, rs3773679 and rs9817063 variants with response (uncorrected p=0.02-0.03) and remission (uncorrected p=0.01) after ECT was discerned. Logistic regression analyses revealed association of rs3732790 (uncorrected p=0.009; corrected p=0.045) and rs3773679 (uncorrected p=0.009; corrected p=0.045) with remission when applying a recessive model of inheritance. The rs3732790T allele conferring a more favourable treatment response was furthermore found to be associated with stronger striatal responsiveness to happy facial expressions (sample 1: cluster-corrected p=0.002; sample 2: p=0.023). In summary, the present study suggests some impact of DRD3 gene variation on ECT response, potentially mediated by alteration of striatal engagement during the processing of emotionally rewarding stimuli.

Effects of immobilization stress on emotional behaviors in dopamine D3 receptor knockout mice

A central problem in understanding the dopamine system in anxiety and depression is to specify functions of different members of the dopamine receptor family. Recent studies have reported that the dopamine D2/D3 receptor agonist pramipexole exerts an antidepressant-like effect in the chronic mild stress model and in the behavioral despair model, suggesting dopamine D3 receptor may be an important target for antidepressant actions. The aim of the present study was to examine the role of dopamine D3 receptor on the anxiety-like and depression-like behaviors induced by immobilization stress. We subjected D3 receptor knockout (D3KO) mice to a series of behavioral paradigms after acute (1 h) or chronic (1 h a day for 14 days) immobilization stress. The results showed that immobilization stress significantly altered the anxiety-like behaviors (open field test and elevated plus maze) and depression-like behaviors (tail suspension test) in both D3KO mice and their wild-type littermates. Moreover, further analysis of the data indicated that the D3KO mice, but not their littermates, failed to show a change in immobility time in the tail suspension test after the acute and chronic stress as compared to intact controls, suggesting an increased resistance to the immobilization stress given before behavioral tests. Although our study did not suggest a significant role of D3 receptor in regulating basal anxiety-like and depression-like behaviors, it demonstrated the mice lacking D3 receptor might be more resistant to stressful procedure than their WT littermates.

The functional DRD3 Ser9Gly polymorphism (rs6280) is pleiotropic, affecting reward as well as movement

Abnormalities of motivation and behavior in the context of reward are a fundamental component of addiction and mood disorders. Here we test the effect of a functional missense mutation in the dopamine 3 receptor (DRD3) gene (ser9gly, rs6280) on reward-associated dopamine (DA) release in the striatum. Twenty-six healthy controls (HCs) and 10 unmedicated subjects with major depressive disorder (MDD) completed two positron emission tomography (PET) scans with [¹¹C]raclopride using the bolus plus constant infusion method. On one occasion subjects completed a sensorimotor task (control condition) and on another occasion subjects completed a gambling task (reward condition). A linear regression analysis controlling for age, sex, diagnosis, and self-reported anhedonia indicated that during receipt of unpredictable monetary reward the glycine allele was associated with a greater reduction in D2/3 receptor binding (i.e., increased reward-related DA release) in the middle (anterior) caudate (p<0.01) and the ventral striatum (p<0.05). The possible functional effect of the ser9gly polymorphism on DA release is consistent with previous work demonstrating that the glycine allele yields D3 autoreceptors that have a higher affinity for DA and display more robust intracellular signaling. Preclinical evidence indicates that chronic stress and aversive stimulation induce activation of the DA system, raising the possibility that the glycine allele, by virtue of its facilitatory effect on striatal DA release, increases susceptibility to hyperdopaminergic responses that have previously been associated with stress, addiction, and psychosis.

Pramipexole is active in depression tests and modulates monoaminergic transmission, but not brain levels of BDNF in mice

The dopamine D(2)/D(3) receptor agonist pramipexole exerts antidepressive capacities in patients with Parkinson's disease with little evidence for patients with affective diseases only. Little is known about the neurobiological basis of these antidepressive effects. In this study, C57BL/6N mice received acute or chronic (3 weeks) treatment with pramipexole in different dosages (0.1, 0.3, 1, and 3mg/kg b.w.) and imipramine or saline serving as positive and negative controls. To characterize antidepressant-like effects mice underwent behavioral characterization. In a second experiment dosages of pramipexole shown to be effective were used and candidate brain regions including hippocampus, frontal cortex and striatum were analyzed for levels of 5-hydroxytryptamine (5-HT), noradrenaline and dopamine and their metabolites as well as brain-derived neurotrophic factor (BDNF) to investigate possible neurochemical correlates of behavioral changes. Whereas acute treatment with pramipexole resulted in antidepressive-like effects in the Porsolt Forced Swim Test, Novel Cage Test, Openfield Test and Dark-light-Box Test and a tendency but insignificant effect in the Tail Suspension Test, chronic treatment did not show significant effects in any of the behavioral analyses. Neurochemical analyses revealed a highly significant effect on dopaminergic metabolites in the striatum as well as a moderate transient modulation of the serotonergic system in the hippocampus. BDNF levels were not affected by any dosage and treatment regime in any brain region investigated. In conclusion, the present data substantiate antidepressive effects of pramipexole and indicate a contribution of the dopaminergic and serotonergic metabolism in these effects, but argue against an eminent role of BDNF.

Effects of antidepressant drug treatment and psychotherapy on striatal and thalamic dopamine D2/3 receptors in major depressive disorder studied with [11C]raclopride PET

Antidepressant drug treatment and psychotherapy are both effective in treating major depression, but there are no published studies comparing the effects of these two treatments on the dopaminergic neurotransmitter system in major depression. We conducted a randomized comparative study on the effects of fluoxetine medication and short-term psychodynamic psychotherapy on striatal and thalamic dopamine D(2/3) receptors in patients with major depression. Duration of the treatment was 4 months, and dopamine D(2/3) receptor binding was quantified before and after treatment as the binding potential (BP (ND)) using [(11)C]raclopride and 3D positron emission tomography. Both treatments were clinically effective in treating major depression, as shown by substantial decreases in symptom ratings. Yet, there were no effects on D(2/3) receptor availability in the ventral striatum or other subdivisions of the striatum. Fluoxetine but not psychotherapy increased [(11)C]raclopride BP (ND) in lateral thalamus (+7.74%, p = 0.002) but this increase was not correlated with clinical improvement. In conclusion, this preliminary study does not support the involvement of ventral dopaminergic neurotransmission in the antidepressant effects of fluoxetine or psychodynamic psychotherapy. The effects of fluoxetine on thalamic dopamine systems need to be further explored.

Inhibition of specific adenylyl cyclase isoforms by lithium and carbamazepine, but not valproate, may be related to their antidepressant effect

OBJECTIVES

Lithium, valproate, and carbamazepine decrease stimulated brain cyclic-AMP (cAMP) levels. Adenylyl cyclase (AC), of which there are nine membrane-bound isoforms (AC1-AC9), catalyzes the formation of cAMP. We have recently demonstrated preferential inhibition of AC5 by lithium. We now sought to determine whether carbamazepine and valproate also preferentially inhibit specific AC isoforms or decrease cAMP levels via different mechanisms.

METHODS

COS7 cells were transfected with one of AC1-AC9, with or without D1-dopamine receptors. Carbamazepine's and valproate's effect on forskolin- or D1 agonist-stimulated ACs was studied. The effect of Mg(2+) on lithium's inhibition was studied in membrane-enriched fraction from COS7 cells co-expressing AC5 and D1 receptors. AC5 knockout mice were tested for a behavioral phenotype similar to that of lithium treatment.

RESULTS

Carbamazepine preferentially inhibited forskolin-stimulated AC5 and AC1 and all D1 agonist-stimulated ACs, with AC5 and AC7 being the most sensitive. When compared to 1 or 3 mM Mg(2+), 10 mM Mg(2+) reduced lithium-induced AC5 inhibition by 70%. In silico modeling suggests that among AC isoforms carbamazepine preferentially affects AC1 and AC5 by interacting with the catechol-estrogen site. Valproate did not affect any forskolin- or D1 receptor-stimulated AC. AC5 knockout mice responded similarly to antidepressant- or lithium-treated wild-types in the forced-swim test but not in the amphetamine-induced hyperactivity mania model.

CONCLUSIONS

Lithium and carbamazepine preferentially inhibit AC5, albeit via different mechanisms. Lithium competes with Mg(2+), which is essential for AC activity; carbamazepine competes for AC's catechol-estrogen site. Antidepressant-like behavior of AC5 knockout mice in the forced-swim test supports the notion that AC5 inhibition is involved in the antidepressant effect of lithium and carbamazepine. The effect of lithium and carbamazepine to lower cAMP formation in AC5-rich dopaminergic brain regions suggests that D1-dopamine receptors in these regions are involved in the antidepressant effect of mood stabilizers.

Repeated administration of imipramine attenuates glutamatergic transmission in rat frontal cortex

The effects of repeated administration of a tricyclic antidepressant, imipramine, lasting 14 days (10 mg/kg p.o., twice daily), were studied ex vivo in rat frontal cortex slices prepared 48 h after last dose of the drug. In slices prepared from imipramine-treated animals the mean frequency, and to a lesser degree the mean amplitude, of spontaneous excitatory postsynaptic currents recorded from layer II/III pyramidal neurons, were decreased. These effects were accompanied by a reduction of the initial slope ratio of pharmacologically isolated N-methyl-D-aspartate to AMPA/kainate receptor-mediated stimulation-evoked excitatory postsynaptic currents. Imipramine treatment also resulted in a decrease of extracellular field potentials evoked in layer II/III by stimulation of underlying sites in layer V. These results indicate that chronic treatment with imipramine results in an attenuation of the release of glutamate and an alteration in the postsynaptic reactivity of ionotropic glutamate receptors in rat cerebral cortex.

Piplartine, an amide alkaloid from Piper tuberculatum, presents anxiolytic and antidepressant effects in mice

In the present work, we studied the effects of piplartine (PIP), an amide alkaloid isolated from the roots of Piper tuberculatum (Piperaceae), in the elevated plus maze, open field, rota rod, pentylenetetrazole (PTZ)-induced seizures, and forced swimming tests, in mice (Swiss, male, 25 g) to assess anxiolytic, sedative, muscle relaxant, anticonvulsant and antidepressant effects, respectively. Results showed that PIP (50 and 100 mg/kg, i.p.), similarly to diazepam, significantly increased not only the number of entrances (100% and 66%, respectively) but also the time of permanence in the open arms (104% and 199%, respectively), indicating that PIP presents an anxiolytic activity. Both effects were completely blocked by the previous administration of flumazenil what suggests the involvement of benzodiazepine type receptors. In the open field test, although PIP did not alter the number of crossings, it significantly increased grooming (103% and 119%) and rearing (60% and 23%), at the doses of 50 and 100 mg/kg respectively, as compared to controls. However, in the rota rod test, PIP was devoid of effect. Although in the PTZ-induced convulsion test, PIP did not alter the latency time for the onset of the first convulsion, as compared to controls, it significantly reduced in 58% and 60%, respectively, the animal's latency time to death. Furthermore, a significant and dose-dependent decrease in the immobility time, as evaluated by the forced swimming test, was observed after PIP administration (41% and 75% decrease, at the doses of 50 and 100 mg/kg, respectively), suggesting an antidepressant effect, similarly to that observed with imipramine, a classical antidepressant drug used as standard. In conclusion, we showed that PIP presents significant anxiolytic and antidepressant activities, making this drug potentially useful in anxiety and depression.

Dopamine D2-like receptors and the antidepressant response

Converging lines of evidence suggest a role for the mesolimbic dopamine system in the response to somatic antidepressant therapies. Here, we review evidence suggesting that antidepressant treatments of different types share the effect of increasing the sensitivity of dopamine D2-like receptors in the nucleus accumbens, clinical studies suggesting that activation of these receptors has antidepressant efficacy, as well as relevant imaging and genetic data on the role of this system in the antidepressant response. We then attempt to reconcile this data with evidence of a common target of antidepressant drugs in the cyclic adenosine monophosphate (cAMP) response element binding protein-brain-derived neurotrophic factor (CREB-BDNF) pathway in a model that suggests potential directions for future inquiry.

Dopamine D3 receptor antisense oligodeoxynucleotide potentiates imipramine-induced dopaminergic behavioural supersensitivity

Chronic antidepressant treatments result in the potentiation of dopaminergic transmission in the mesolimbic dopamine system revealed as an increased motor response to dopamine D2-like agonists. On the basis of the involvement of this system in the control of motivation and reward-related behaviour, which are impaired in depression, it has been suggested that such supersensitivity might play an important role in the mechanism of action of these drugs. Several studies have provided evidence suggesting a role of dopamine D3 receptors in mediating antidepressant-induced increased motor response to dopamine agonists. To test this hypothesis, we studied the effect of the intracerebroventricular infusion of a dopamine D3 receptor antisense oligodeoxynucleotide (10 microg/3 microl, 2-3 daily injections) on the expression of imipramine-induced supersensitivity (20 mg/kg daily intraperitoneal injections for 21 days) to the motor effect of the dopamine D2-like receptor agonist quinpirole (a single 0.3 mg/kg subcutaneous injection 24-48 h after imipramine withdrawal). The results show that a treatment previously shown to reduce the synthesis of dopamine D3 receptors, rather than resulting in an inhibitory effect, potentiated the ability of imipramine to induce dopaminergic motor supersensitivity. The present results suggest that increased dopamine D3 receptor expression following antidepressant treatments is not involved in the mechanism of dopaminergic supersensitivity, and are consistent with evidence supporting an inhibitory role for dopamine D3 receptors in motor activity, both in normal and in sensitized subjects.

Antidepressant-like properties of the anti-Parkinson agent, piribedil, in rodents: mediation by dopamine D2 receptors

The dopamine D2/D3 receptor agonist and alpha2 adrenergic receptor antagonist, piribedil, is used clinically as monotherapy and as an adjunct to L-3,4-dihydroxyphenylalanine in the treatment of Parkinson's disease. As it appears to improve mood, we examined its actions in rodent models of antidepressant properties, in comparison with the prototypical anti-Parkinson agent, apomorphine, the D2/D3 receptor agonist, quinpirole, and the antidepressants, imipramine and fluvoxamine. In the mouse forced-swim test, acute administration of imipramine, fluvoxamine, apomorphine or quinpirole decreased immobility time, actions dose dependently mimicked by piribedil (2.5-10.0 mg/kg, subcutaneously). In rats, acute and subchronic administration of piribedil similarly reduced immobility (0.63-10.0 mg/kg, subcutaneously) and apomorphine, quinpirole and imipramine were also active in this test, whereas fluvoxamine was inactive. Both in mice and in rats, the D2/D3 receptor antagonist, raclopride, and the D2 receptor antagonist, L741,626, dose dependently blocked the antidepressant properties of piribedil, whereas the selective D3 receptor antagonists, S33084 and SB277,011, were ineffective. In a chronic mild stress model in rats, piribedil (2.5-40.0 mg/kg, subcutaneously) restored sucrose intake in stressed animals exerting its actions more rapidly (by week 1) than imipramine. Imipramine, fluvoxamine, apomorphine, quinpirole and piribedil dose dependently (0.63-10.0 mg/kg, subcutaneously) suppressed aggressive and marble-burying behaviour in mice. In the latter procedure, raclopride and L741,626, but not S33084, attenuated the actions of piribedil. Over a dose range (0.63-10.0 mg/kg, subcutaneously) equivalent to those active in models of antidepressant activity, piribedil did not stimulate locomotor behaviour. In conclusion, principally via recruitment of D2 receptors, piribedil exerts robust and specific antidepressant-like actions in diverse rodent models.

Psychopharmacology of maternal separation anxiety in vervet monkeys

Maternal separation in non-human primates has been proposed as a model of early adversity. The symptoms of separation anxiety were studied in vervet monkeys, during the weaning period, when psychotropic medications were administered. The control group received a normal diet and treatment groups received citalopram, reboxetine or lamotrigine in their food daily. Treatment was given for 7 weeks starting 1 month prior to weaning. Behavior was recorded twice weekly for 8 weeks, and was rated for anxiety and depression. Cerebrospinal fluid was collected at the beginning and end of the trial and analyzed for monoamines and metabolites using High Performance Liquid Chromatography. Citalopram pretreatment prevented the reduction of affiliation behavior and reduced stereotypies after weaning, and both citalopram and reboxetine abolished the increase in activity seen in control monkeys after weaning, but no statistically significant differences were found between groups. Citalopram pretreatment also significantly increased noradrenaline and 5-hydroxyindolacetic acid (5-HIAA) levels and reboxetine significantly decreased dopamine levels over time. The 5-HIAA levels of reboxetine and lamotrigine treated monkeys were significantly lower than that of the control group at the end of the trial. Although limited by a small sample size, this study demonstrates the possibility of investigating the psychopharmacology of early adversity in a non-human primate model.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Acute and repeated administration of fluoxetine, citalopram, and paroxetine significantly alters the activity of midbrain dopamine neurons in rats: An in vivo electrophysiological study

We examined the effect of the administration of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine, citalopram, and paroxetine on the activity of spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and ventral tegmental area (VTA) in anesthetized adult male Sprague-Dawley rats. This was accomplished using the technique of in vivo extracellular recording. A single injection of 2.5 mg/kg (i.p.) of fluoxetine significantly increased the number of spontaneously active SNC and VTA DA neurons. In contrast, a single injection of either 1 mg/kg (i.p.) of paroxetine or 5 mg/kg of fluoxetine significantly increased the number of spontaneously active VTA DA neurons. The repeated administration (one injection per day for 21 days) of all of the SSRIs produced a significant increase in the number of spontaneously active VTA DA neurons. Overall, our results indicate that the systemic administration of SSRI alters the activity of midbrain DA neurons with differential effects on VTA compared with SNC DA neurons.

Paralemmin interacts with D3 dopamine receptors: implications for membrane localization and cAMP signaling

Paralemmin is a novel lipid-anchored protein, which is highly expressed in neuronal plasma membranes. In this study, we demonstrate that paralemmin specifically interacts with the third intracellular loop of the D3 dopamine receptor. Utilizing co-immunoprecipitation and glutathione-S-transferase (GST) pulldown strategies, we demonstrate that paralemmin interacts exclusively with D3, but not D2 or D4 dopamine receptors or beta-adrenergic receptors. Immunocytochemistry demonstrated co-localization of paralemmin and D3 receptor in vivo in hippocampus and cerebellum and in vitro in glial and neuronal cultures. Deletion mutational analysis indicates that amino acids 154-230 of paralemmin strongly interacted with amino acids 211-227 and 281-330 of the third intracellular loop of D3 receptor. The consequences of these interactions were investigated by co-expression in HEK293 cells. Cell surface biotinylation experiments demonstrate that paralemmin decreased D3 receptor concentration at the plasma membrane. Consistent with this observation, paralemmin expression decreased dopamine-stimulated adenylate cyclase activity. However, paralemmin also decreased basal, isoproterenol and forskolin-stimulated adenylate cyclase activity, suggesting a more general cellular function for paralemmin. Taken together, paralemmin has been implicated as a potent modulator of cellular cAMP signaling within the brain.

Antidepressant-like effect of D(2/3) receptor-, but not D(4) receptor-activation in the rat forced swim test

Dopamine plays a role in the pathophysiology of depression and therapeutic effects of antidepressants but the contribution of individual D(2)-like receptor subtypes (D(2), D(3), D(4)) to depression is not known. We present evidence that activation of D(2)/D(3), but not D(4) receptors, can affect the outcome in the rat forced swim test (FST). Nomifensine, a dopamine uptake inhibitor (7, 14, and 28 micromol/kg); quinpirole, a D(2)-like receptor and agonist (0.4, 1.0, and 2.0 micromol/kg); PD 12,8907, a preferential D(3) receptor agonist (0.17, 0.35, and 0.7 micromol/kg); PD 168077 (0.1, 0.3, and 1.0 micromol/kg) and CP 226269 (0.3, 1.0, and 3.0 micromol/kg), both selective D(4) receptor agonists, were administered s.c. 24, 5, and 0.5/1 h before testing. Nomifensine, quinpirole at all doses and PD 128907 at the highest dose decreased immobility time in FST. PD 168077 and CP 226269 had no effect on the model. To further clarify what type of dopamine receptors were involved in the anti-immobility effect of quinpirole, we tested different antagonists. Haloperidol, a D(2)-like receptor antagonist (0.27 micromol/kg), completely blocked the effect of quinpirole; A-437203 (LU-201640), a selective D(3) receptor antagonist (17.46 micromol/kg), showed a nonsignificant trend to attenuate the effect of the low dose of quinpirole, and L-745,870, a selective D(4) receptor antagonist (1.15 micromol/kg), had no effect. The pharmacological selectivity of the compounds tested suggests that the antidepressant-like effects of quinpirole are most likely mediated mainly by D(2) and to a lesser extent by D(3) but not D(4) receptors.

Tritium labelling of dopaminergic ligands domperidone and (+/−)-7-hydroxy DPAT

Methods are presented for tritiating the D2 specific dopaminergic antagonist domperidone and D3 specific dopaminergic agonist (+/-)-7-hydroxy DPAT. Techniques to characterize the products of the tritiation are also given.

Long-term exposure of rats to tramadol alters brain dopamine and α1-adrenoceptor function that may be related to antidepressant potency

The aim of the present study was to determine whether tramadol, which has a potential antidepressant efficacy, evokes, when administered repeatedly, changes similar to the alterations induced by conventional antidepressant drugs. Repeated administration of tramadol (20 mg/kg i.p. for 21 days) enhanced the d-amphetamine-induced locomotor hyperactivity and increased the density of alpha(1)-adrenoceptors in the rat brain cortex, as measured by saturation analysis of [(3)H]prazosin binding. Autoradiographic analysis of [(3)H]7-OH-DPAT and [(3)H]raclopride binding revealed a significant up-regulation of dopamine D2 and D3 receptors in the rat nucleus accumbens upon repeated treatment with tramadol. All the above-mentioned effects induced by repeated administration of tramadol resemble the effects induced by conventional antidepressants. However, tramadol when administered repeatedly did not increase the levels of mRNA encoding for brain-derived neurotrophic factor (BDNF) and its receptor, TrkB. This is what differs tramadol from conventional antidepressants, since neurotrophic effects of these drugs have recently been postulated.

Invited review: the evolution of antidepressant mechanisms

Present antidepressants are all descendents of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. The identification of their mechanism of action, and those of reserpine and amphetamine, in the 1960s, led to the monoamine theories of depression being postulated; first, with noradrenaline then 5-hydroxytryptamine being considered the more important amine. These monoamine theories of depression predominated both industrial and academic research for four decades. Recently, in attempts to design new drugs with faster onsets of action and more universal therapeutic action, downstream alterations common to current antidepressants are being examined as potential antidepressants. Additionally, the use of animal models has identified a number of novel targets some of which have been subjected to clinical trials in humans. However, monoamine antidepressants remain the best current medications and it may be some time before they are dislodged as the market leaders.

Neuronal cell lines transfected with the dopamine D2 receptor gene promoter as a model for studying the effects of antidepressant drugs

The present study investigated the effect of three antidepressant drugs (ADs), desipramine (DMI, a noradrenaline reuptake inhibitor), citalopram (CIT, a selective serotonin reuptake inhibitor) and mianserin (MIA, thought to act as an antagonist of pre-synaptic alpha2 adrenoceptor) on the transcriptional activity of the dopamine D2 receptor gene promoter. The fragment of dopamine D2 receptor gene promoter (-850 to +133) was subcloned into pGL3 vector (Promega), which has an insert coding for luciferase used as a reporter gene. Such construct (pGL3-D2R) was used to transiently transfect the neuroblastoma cell lines, Neuro 2a, SH-SY5Y and NB41A3, which endogenously express the dopamine D2 receptor protein. The obtained results indicate that transcriptional activity of dopamine D2 receptor gene promoter was dose-dependently increased by retinoic acid, forskolin, rolipram and phorbol 12 myristate 13-acetate, as well as by DMI, CIT and MIA. In the Neuro 2a cells, the most significant increase was observed after the ADs were present in the incubation medium at a doses of 0.1-1 microM for 72 h. In the SH-SY5Y cells, the significant increase in the transcriptional activity of D2 receptor gene promoter was observed already after 24-h exposure to DMI. Incubation of the Neuro 2a cells in the presence of forskolin (1 microM) or rolipram (50 microM) (but not phorbol 12-myristate 13-acetate at 0.1 microM) in combination with DMI resulted in the further increase in transcriptional activity of the studied promoter, indicating the involvement of protein kinase A pathway in these effects.

The effect of combined treatment with imipramine and amantadine on the behavioral reactivity of central ??1-adrenergic system in rats

The problem of drug-resistant depression implies a strong need for alternative antidepressant therapies. Recently, it has been shown that joint administration of a tricyclic antidepressant, imipramine (IMI), with amantadine (AMA), a drug already approved for clinical use in the treatment of other diseases, induces a stronger 'antidepressant' effect in the forced swimming test in rats than treatment with either drug given separately. Combined treatment with IMI and AMA also induces up-regulation of dopamine D2 and D3 receptors in the rat brain, and appears to be effective in the treatment of patients with drug-resistant unipolar depression. In the present study, we examined the effect of IMI (5 or 10 mg/kg p.o.) and AMA (10 mg/kg p.o.) given separately or jointly, either as a single dose or repeatedly (twice daily for 14 days) on the development of adaptive changes in the behavioral reactivity of the central alpha1-adrenergic system. Following repeated administration of the higher dose of IMI together with AMA, we observed an increase in clonidine-induced aggression in mice, and significant enhancement of D-amphetamine-induced locomotor hyperactivity, as well as phenylephrine-induced exploratory behavior, in rats. In binding studies using [3H]prazosin, no changes in the density (Bmax) or affinity (Kd) of alpha1-adrenergic receptors were observed in rat brain cortex. However, competition analysis allowed us to observe an increase in the affinity of alpha1-adrenergic receptors (Ki) for an agonist (phenylephrine) upon repeated treatment with IMI, given alone or in combination with AMA. AMA appears to act through several pharmacological mechanisms, none of which has been identified as the chief mode of action. In the light of data obtained in the present study, one can supplement the postulated mechanisms of antidepressant action of AMA by adaptive changes in the reactivity of alpha1-adrenergic receptors, which develop upon repeated combined treatment with IMI.

S32504, a Novel Naphtoxazine Agonist at Dopamine D3/D2 Receptors: III. Actions in Models of Potential Antidepressive and Anxiolytic Activity in Comparison with Ropinirole

In forced-swim tests in mice and rats, the novel D(3)/D(2) receptor agonist S32504 [(+)-trans-3,4,4a,5,6,10b-hexahydro-9-carbamoyl-4-propyl-2H-naphth[1,2-b]-1,4-oxazine] dose-dependently (0.04-2.5 mg/kg) and stereospecifically suppressed immobility compared with its enantiomer S32601 [(-)-trans-3,4,4a,5,6,10b-hexahydro-9-carbamoyl-4-propyl-2H-naphth-[1,2-b]-1,4-oxazine]. Ropinirole was less potent than S32504 in this procedure, and it was likewise less potent than S32504 (0.04-2.5 mg/kg) in attenuating motor-suppressant properties of the alpha(2)-adrenoceptor agonist S18616 [(S)-spiro[(1-oxa-2-amino-3-azacyclopent-2-ene)-4,2'-(1',2',3',4'-tetrahydronaphthalene)]]. In a learned helplessness paradigm, S32504 (0.08-2.5 mg/kg) suppressed escape failures. Furthermore, in a chronic mild stress model of anhedonia, S32504 (0.16-2.5 mg/kg) rapidly restored the suppression of sucrose consumption. S32504 inhibited marble-burying behavior in mice (0.04-0.16 mg/kg) and aggressive behavior in isolated mice (0.04-2.5 mg/kg): only higher doses of ropinirole mimicked these actions of S32504. In tests of anxiolytic activity, S32504 was more potent (0.0025-0.16 mg/kg) than ropinirole in suppressing fear-induced ultrasonic vocalizations, and S32601 was inactive. Furthermore, in contrast to ropinirole, S32504 modestly enhanced punished responses in a Vogel conflict procedure and increased open-arm entries in a plus-maze. At doses active in the above-described procedures, S32504 did not elicit hyperlocomotion. In the forced-swim, marble-burying, and ultrasonic vocalization models, actions of S32504 were blocked by the D(2)/D(3) antagonists haloperidol and raclopride and by the D(2) antagonist L741,626 [4-(4-chlorophenyl)-1-(1H-indol-3-ylmethyl)piperidin-4-ol], but not by the D(3) receptor antagonist S33084 [(3aR,9bS)-N-[4-(8-cyano-1,3a,4,9b-tetrahydro-3H-benzopyrano[3,4-c]pyrrole-2-yl)-butyl]-(4-phenyl)benzamide. Finally, chronic administration of S32504 did not, in contrast to venlafaxine, modify corticolimbic levels of serotonin(2A) receptors or brain-derived neurotrophic factor. In conclusion, S32504 displays a broad and distinctive profile of activity in models of potential antidepressive and anxiolytic properties. Its actions are more pronounced than those of ropinirole and principally involve engagement of D(2) receptors.

A potential antidepressant activity of SA4503, a selective sigma 1 receptor agonist

The aim of the present study was to examine SA4503 [1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride], a novel selective receptor agonist, in respect of its potential antidepressant action. To this end we used a forced swimming test in rats to study SA4503 alone, as well as its interaction with imipramine, a classic tricyclic antidepressant. SA4503 decreased the immobility time in the forced swimming test in rats (although only at one of the three doses used); at the same time it did not change the locomotor activity recorded under the same experimental conditions. Moreover, SA4503 showed a synergistic effect with imipramine in the forced swimming test (both those compounds given jointly decreased the immobility time, but were ineffective when administered separately). It had previously been shown that repeated administration of antidepressants with different pharmacological profiles enhanced the action of D-amphetamine, quinpirole and other dopamine stimulants. SA4503 administered repeatedly increased the locomotor hyperactivity induced by D-amphetamine and quinpirole (a dopamine D /D receptor agonist), but not by (+/-)-7-hydroxy-dipropyloamino-tetralin hydrobromide [(+/-)-7-OH-DPAT; a dopamine D receptor agonist]. The results presented in this paper support the suggestion that SA4503 may have potential antidepressive properties.

Effect of repeated treatment with tianeptine and fluoxetine on central dopamine D(2) /D(3) receptors

Tianeptine (TIA) is an antidepressant drug that has been shown to decrease extracellular serotonin level and reveals no affinity for neurotransmitter receptors. The present study was aimed at determining whether repeated TIA treatment induced any adaptive changes in the central dopamine D(2)/D(3) system (behavioural and biochemical) similar to those reported earlier for tricyclic antidepressants. Experiments were carried out on male Wistar rats. TIA was administered at a dose of 5 and 10 mg/kg once or repeatedly (twice daily for 14 days). Fluoxetine (FLU), used as a reference compound, was also administered at a dose of 10 mg/kg. The results obtained showed that TIA or FLU administered repeatedly increased the hyperlocomotion induced by D-amphetamine and 7-hydroxy-dipropylaminotetralin (7-OH-DPAT). Biochemical study revealed a decrease in the [(3)H]7-OH-DPAT binding sites after acute and repeated treatment with TIA or FLU in the islands of Calleja minor, as well as in the shell part of nucleus accumbens septi. On the other hand, both TIA and FLU administered repeatedly increased the binding of [(3)H]quinpirole (a D(2)/D(3) receptor agonist) in the nucleus caudatus as well as in the core part of the nucleus accumbens septi. Similar effects have been observed when dopamine D(2)/D(3) receptors were visualized with the use of [3H]raclopride, a dopamine D(2)/D(3) receptor antagonist. However, TIA and FLU induced a decrease in the level of mRNA encoding for dopamine D(2) receptors, not only after repeated but also after acute treatment. These results indicate that repeated TIA and FLU administration induces adaptive changes in the dopaminergic D(2)/D(3) system and especially enhances the functional responsiveness of dopamine D(2) and D(3) receptors. However, the question of whether this increased responsiveness is important for clinical antidepressant efficacy remains open.

Depression as a spreading adjustment disorder of monoaminergic neurons: a case for primary implication of the locus coeruleus

A model for the pathophysiology of depression is discussed in the context of other existing theories. The classic monoamine theory of depression suggests that a deficit in monoamine neurotransmitters in the synaptic cleft is the primary cause of depression. More recent elaborations of the classic theory also implicitly include this postulate, other theories of depression frequently prefer to depart from the monoamine-based model altogether. We suggest that the primary defect emerges in the regulation of firing rates in brainstem monoaminergic neurons, which brings about a decrease in the tonic release of neurotransmitters in their projection areas, an increase in postsynaptic sensitivity, and concomitantly, exaggerated responses to acute increases in the presynaptic firing rate and transmitter release. It is proposed that the initial defect involves, in particular, the noradrenergic innervation from the locus coeruleus (LC). Dysregulation of the LC projection activities may lead in turn to dysregulation of serotonergic and dopaminergic neurotransmission. Failure of the LC function could explain the basic impairments in the processing of novel information, intensive processing of irrational beliefs, and anxiety. Concomitant impairments in the serotonergic neurotransmission may contribute to the mood changes and reduction in the mesotelencephalic dopaminergic activity to loss of motivation, and anhedonia. Dysregulation of CRF and other neuropeptides such as neuropeptide Y, galanin and substance P may reinforce the LC dysfunction and thus further weaken the adaptivity to stressful stimuli.

The novel long PDE4A10 cyclic AMP phosphodiesterase shows a pattern of expression within brain that is distinct from the long PDE4A5 and short PDE4A1 isoforms

In situ hybridisation methods were used to map the distribution of the novel long PDE4A10 isoform in the brain. PDE4A10 distribution was compared to that of the long PDE4A5 isoform and the short PDE4A1 isoform using probes specific for unique sequences within each of these isoforms. Coronal sections of the brain, taken at the level of the olfactory bulb, prefrontal cortex, striatum, thalamus, hippocampus and cerebellum, were analysed. Strongest expression of PDE4A isoforms was found in the olfactory bulb granular layer with high signals also in the piriform cortex, the dentate gyrus and the CA1 and CA2 pyramidal cells. For the two long forms, level general staining was noted throughout the striatum, thalamus and hippocampus but no signal was evident in the cerebellum. The long PDE4A10 and PDE4A5 isoforms localised to essentially the same regions throughout the brain, although PDE4A10 was uniquely expressed in the major island of Calleja. A signal for the short PDE4A1 isoform was found in regions in which the two long isoforms were both expressed, with the exception of the medial nucleus of the amygdala where weak signals for PDE4A5 and PDE4A10 were detected but PDE4A1 was absent. Uniquely, strong signals for PDE4A1 were detected in the glomerular layer of the olfactory bulb, the CA3 pyramidal cell region and the cerebellum; areas where signals for the two long forms were not evident. PDE4A transcripts for both PDE4A5 and PDE4A10 were not apparent in the brain stem and those for PDE4A1 were low. PDE4A isoforms are present in several key areas of the brain and therefore present valid targets for therapeutic interventions. Whilst the two long PDE4A isoforms show a remarkably similar distribution, in at least three regions there is clear segregation between their pattern of expression and that of the PDE4A1 short form. This identifies differential regulation of the expression of PDE4A long and short isoforms. We suggest that specific PDE4A isoforms may have distinct functional roles in the brain, indicating that PDE4A isoform-selective inhibitors may have specific therapeutic and pharmacologic properties.

Some behavioural effects of antidepressant drugs are time-dependent

1. The effects of repeated administration of antidepressant drugs (imipramine, IMI and citalopram, CIT) on the beta- and alpha2-adrenergic as well as dopaminergic D3 receptors were compared with time-dependent changes in the receptor responsiveness after acute treatment. 2. Repeated treatment with IMI or CIT (administered at a dose of 10 mg/kg p.o. twice a day for 14 days) induced down-regulation of beta-adrenergic receptors, demonstrated by behavioural experiment using salbutamol-induced hypoactivity and by binding studies using [3H]CGP12177. The changes in alpha2-adrenergic receptors were studied using clonidine-induced hypoactivity, which was attenuated by repeated treatment with IMI or CIT. Behavioural responsiveness of dopamine D3 receptors was investigated using two doses of 7-OH-DPAT. This drug at a dose of 0.05 mg/kg s.c. induced locomotor hypoactivity (interpreted as a result of stimulation of presynaptic dopamine D3 receptors), which was reversed by repeated administration of IMI or CIT, while 7-OH-DPAT at a dose of 3 mg/kg s.c. (which stimulated postsynaptic dopamine D3 receptors) induced significant hyperactivity, which was markedly enhanced by repeated administration of antidepressant drugs. 3. The effect of acute administration of IMI or CIT measured 14 days after drug treatment were similar to the described above alterations at the level of alpha2 adrenoreceptors and presynaptic dopamine D3 receptors, i.e. the drugs attenuated clonidine-induced hypoactivity and reversed locomotor hypoactivity evoked by low dose of 7-OH-DPAT. To induce the down-regulation of beta-adrenergic receptors or up-regulation of the behavioural responsiveness of dopaminergic D3 postsynaptic receptors, the repeated administration of IMI or CIT was necessary. 4. Therefore it has been concluded that presynaptic dopaminergic D3 and alpha2-adrenergic receptors are more sensitive to the acute treatment with antidepressant drugs than postsynaptic D3 and beta-adrenergic receptors.

Antidepressants: past, present and future

Since the discovery of first antidepressants in mid-1950's, the field has been intensively studied. Several new classes of compounds emerged and several hypotheses on the mechanism of their action were proposed. The novel antidepressants are either selective and reversible monoamine oxidase inhibitors, (e.g., moclobemide), or selective serotonin reuptake inhibitors (e.g., citalopram or paroxetine), or serotonin and noradrenaline reuptake inhibitors (e.g. , venlafaxine). Recently neuropeptides (e.g., thyrotropin-releasing hormone,TRH) or antagonists of neuropeptide receptors (e.g., tachykinin NK(1) receptor) undergo clinical tests. Several hypotheses proposed the predominant involvement of one or few neurotransmitter receptors in the mechanism of antidepressant action, but it is now assumed that several distinct receptor mechanisms' trigger different but converging intracellular signal cascades that activate transcription factors, which, in turn, promote the expression of genes encoding for proteins, that play a crucial role in restoring of neuronal functions involved in mood regulation.

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.