Dopamine dysregulation syndrome: implications for a dopamine hypothesis of bipolar disorder

The role of dopamine in bipolar disorder

OBJECTIVE

Despite effective pharmacological treatments for bipolar disorder, we still lack a comprehensive pathophysiological model of the illness. Recent neurobiological research has implicated a number of key brain regions and neuronal components in the behavioural and cognitive manifestations of bipolar disorder. Dopamine has previously been investigated in some depth in bipolar disorder, but of late has not been a primary focus of attention. This article examines the role of dopamine in bipolar disorder, incorporating recent advances into established models where possible.

METHODS

A critical evaluation of the literature was undertaken, including a review of behavioural, neurochemical, receptor, and imaging studies, as well as genetic studies focusing on dopamine receptors and related metabolic pathways. In addition, pharmacologic manipulation of the central dopaminergic pathways and comparisons with other disease states such as schizophrenia were considered, principally as a means of exploring the hypothesised models.

RESULTS

Multiple lines of evidence, including data from pharmacological interventions and structural and functional magnetic resonance imaging studies, suggest that the dopaminergic system may play a central role in bipolar disorder.

CONCLUSION

Future research into the pathophysiological mechanisms of bipolar disorder and the development of new treatments for bipolar disorder should focus on the dopaminergic system.

The role of lithium in modulation of brain genes: relevance for aetiology and treatment of bipolar disorder

Bipolar disorder is a debilitating disorder of the brain with a lifetime prevalence of 1.0% for bipolar I, 1.1% for bipolar II disorder and 2.4-4.7% for subthreshold bipolar disorder. Medications, including lithium, have demonstrated efficacy in the treatment of bipolar disorder, but their molecular targets and mode of action are largely unknown. A few studies have begun to shed light on potential targets of lithium treatment that may be involved in lithium's therapeutic effect. We have recently conducted a microarray study of rat frontal cortex following chronic treatment (21 days) with lithium. Chronic treatment with lithium led to a significant (at least 1.5-fold) down-regulation of 151 genes and up-regulation of 57 genes. We discuss our results in the context of previous microarray studies involving lithium and gene-association studies to identify key genes associated with chronic lithium treatment. A number of genes associated with bipolar disorder, including Comt (catechol-O-methyltransferase), Vapa (vesicle-associated membrane protein-associated protein A), Dtnb (dystrobrevin beta) and Pkd1 (polycystic kidney disease 1), were significantly altered in our microarray dataset along with genes associated with synaptic transmission, apoptosis and transport among other functions.

Dissociable brain structural changes associated with predisposition, resilience, and disease expression in bipolar disorder

Genetic factors are important in the etiology of bipolar disorder (BD). However, first-degree relatives of BD patients are at risk for a number of psychiatric conditions, most commonly major depressive disorder (MDD), although the majority remain well. The purpose of the present study was to identify potential brain structural correlates for risk and resilience to mood disorders in patients with BD, type I (BD-I) and their relatives. Structural magnetic resonance imaging scans were acquired from 30 patients with BD-I, 50 of their first-degree relatives (28 had no Axis I disorder, while 14 had MDD) and 52 controls. We used voxel-based morphometry, implemented in SPM5 to identify group differences in regional gray matter volume. From the identified clusters, potential differences were further examined based on diagnostic status (BD-I patients, MDD relatives, healthy relatives, controls). Whole-brain voxel-based analysis identified group differences in the left hemisphere in the insula, cerebellum, and substantia nigra. Increased left insula volume was associated with genetic preposition to BD-I independent of clinical phenotype. In contrast, increased left substantia nigra volume was observed in those with the clinical phenotype of BD-I. Changes uniquely associated with the absence of a clinical diagnosis in BD relatives were observed in the left cerebellum. Our data suggest that in BD, genetic and phenotype-related influences on brain structure are dissociable; if replicated, these findings may help with early identification of high-risk individuals who are more likely to transition to syndromal states.

Augmentation effect of combination therapy of aripiprazole and antidepressants on forced swimming test in mice

RATIONALE

A deficiency in brain monoamine systems (serotonin, dopamine, and/or norepinephrine) have long been hypothesized for the pathogenesis of depression. Drugs enhancing neurotransmission of those monoamines have been proven to have antidepressant effects. We hypothesized that aripiprazole, a partial D(2) agonist, could increase the activity of various antidepressants in the mice forced swimming test (FST), an animal model of depression.

OBJECTIVES

The scope of this study was to investigate the antidepressant-like effect of aripiprazole, when combined with conventional antidepressants drugs.

MATERIALS AND METHODS

This study assessed the effects of co-administration of aripiprazole with selective serotonin reuptake inhibitors (SSRIs; sertraline, paroxetine, and citalopram), selective serotonin-norepinephrine reuptake inhibitors (SNRIs; venlafaxine and minalcipran), selective norepinephrine reuptake inhibitor (NRI; desipramine), and the dual dopamine and norepinephrine reuptake inhibitor (bupropion), using the FST in mice. Subactive doses of aripiprazole and antidepressants sertraline, paroxetine, citalopram, venlafaxine, minalcipran, bupropion (4 and 8 mg/kg), and desipramine (2 and 4 mg/kg) were given i.p. 30 and 45 min, respectively, before the test.

RESULTS

Aripiprazole (0.03 and 0.06 mg/kg) combined with inactive doses of antidepressants, increased the activity of all antidepressants with the exception of bupropion and desipramine.

CONCLUSION

The augmentation effects of aripiprazole, in the present study, are in agreement with clinical evidence suggesting that aripiprazole may enhance the efficacy of therapeutic effect of SSRIs and SNRIs but not of NRI. These results suggest that augmentation effect of aripiprazole only appears when 5-HT system is activated and might implicate complex regulation between dopamine and 5-HT(1A) and 5-HT(2A) receptors.

Association study of clock gene (CLOCK) and schizophrenia and mood disorders in the Japanese population

Recently the clock genes have been reported to play some roles in neural transmitter systems, including the dopamine system, as well as to regulate circadian rhythms. Abnormalities in both of these mechanisms are thought to be involved in the pathophysiology of major mental illness such as schizophrenia and mood disorders including bipolar disorder (BP) and major depressive disorder (MDD). Recent genetic studies have reported that CLOCK, one of the clock genes, is associated with these psychiatric disorders. Therefore, we investigated the association between the six tagging SNPs in CLOCK and the risk of these psychiatric disorders in Japanese patients diagnosed with schizophrenia (733 patients), BP (149) and MDD (324), plus 795 Japanese controls. Only one association, with schizophrenia in females, was detected in the haplotype analysis (P = 0.0362). However, this significance did not remain after Bonferroni correction (P = 0.0724). No significant association was found with BP and MDD. In conclusion, we suggest that CLOCK may not play a major role in the pathophysiology of Japanese schizophrenia, BP and MDD patients. However, it will be important to replicate and confirm these findings in other independent studies using large samples.

Bipolar disorder and dopamine dysfunction: an indirect approach focusing on tardive movement syndromes in a naturalistic setting

BACKGROUND

It has been suggested that dopamine dysfunction may play a role in bipolar disorder (BD). An indirect approach to examine this issue was developed, focusing on associations between dopamine proxy measures observed in BD (dopamine-related clinical traits using tardive movement syndromes as dopamine proxy measure of reference).

METHODS

3459 eligible bipolar patients were enrolled in an observational study. Incidence rates of tardive movement syndromes (tardive dyskinesia and tardive dystonia; TDD) were examined. A priori hypothesized associations between incident TDD and other dopamine proxies (e.g. prolactin-related adverse effects, bipolar symptoms) were tested over a 2 year follow-up period.

RESULTS

The incidence rate of tardive syndromes was 4.1 %. Incident TDD was independently associated not only with use of antipsychotics, but also with more severe bipolar symptoms, other extrapyramidal symptoms and prolactin-related adverse effects of medication.

CONCLUSION

Apart from the well-known association with antipsychotics, development of TDD was associated with various other dopamine proxy measures, indirectly supporting the notion of generalised dopamine dysregulation in BD.

Increased serum neurotrophin-4/5 levels in bipolar disorder

Neurotrophins are central to several aspects of central nervous system function, and emerging evidence links these growth factors to mood disorders. The purpose of this study was to investigate serum neurotrophin-4/5 (NT-4/5) levels in patients with bipolar disorder, both within mood episodes and in euthymia. Patients with bipolar I disorder (n=154) and controls (n=30) had their NT-4/5 serum levels assayed using an ELISA. Levels of NT-4/5 levels were significantly higher in bipolar disorder patients than in controls; NT-4/5 levels were increased in mania, depression and euthymia, but not significantly different between BD mood states. As far as are aware, this is the first study showing NT-4/5 immunocontent alterations in bipolar disorder. A tentative explanation would be that NT-4/5 increases is compensating for ongoing oxidative damage in dopaminergic neurons.

Circadian polymorphisms associated with affective disorders

BACKGROUND

Clinical symptoms of affective disorders, their response to light treatment, and sensitivity to other circadian interventions indicate that the circadian system has a role in mood disorders. Possibly the mechanisms involve circadian seasonal and photoperiodic mechanisms. Since genetic susceptibilities contribute a strong component to affective disorders, we explored whether circadian gene polymorphisms were associated with affective disorders in four complementary studies.

METHODS

Four groups of subjects were recruited from several sources: 1) bipolar proband-parent trios or sib-pair-parent nuclear families, 2) unrelated bipolar participants who had completed the BALM morningness-eveningness questionnaire, 3) sib pairs from the GenRed Project having at least one sib with early-onset recurrent unipolar depression, and 4) a sleep clinic patient group who frequently suffered from depression. Working mainly with the SNPlex assay system, from 2 to 198 polymorphisms in genes related to circadian function were genotyped in the participant groups. Associations with affective disorders were examined with TDT statistics for within-family comparisons. Quantitative trait associations were examined within the unrelated samples.

RESULTS

In NR1D1, rs2314339 was associated with bipolar disorder (P = 0.0005). Among the unrelated bipolar participants, 3 SNPs in PER3 and CSNK1E were associated with the BALM score. A PPARGC1B coding SNP, rs7732671, was associated with affective disorder with nominal significance in bipolar family groups and independently in unipolar sib pairs. In TEF, rs738499 was associated with unipolar depression; in a replication study, rs738499 was also associated with the QIDS-SR depression scale in the sleep clinic patient sample.

CONCLUSION

Along with anti-manic effects of lithium and the antidepressant effects of bright light, these findings suggest that perturbations of the circadian gene network at several levels may influence mood disorders, perhaps ultimately through regulation of MAOA and its modulation of dopamine transmission. Twenty-three associations of circadian polymorphisms with affective symptoms met nominal significance criteria (P < 0.05), whereas 15 would be expected by chance, indicating that many represented false discoveries (Type II errors). Some evidence of replication has been gathered, but more studies are needed to ascertain if circadian gene polymorphisms contribute to susceptibility to affective disorders.

Oxidative stress markers in bipolar disorder: a meta-analysis

BACKGROUND

Oxidative stress is thought to mediate neuropathological processes of a number of neuropsychiatric disorders and recent data suggest that oxidative stress may be involved in the pathophysiology of bipolar disorder (BD). In the present investigation, we conducted a meta-analysis of studies that evaluated markers of oxidative stress in individuals with BD, as compared to healthy controls.

METHODS

A Medline search was conducted to identify studies that measured peripheral markers of oxidative stress in bipolar disorder. Data were subjected to meta-analysis using a random effects model to examine the effect sizes of the pooled results. Bias assessment (Egger's test) and assessment of heterogeneity (I(2)) were also carried out.

RESULTS

Thiobarbituric acidic reactive substances (TBARS) (p = 0.001) as well as NO activity (p = 0.02) were significantly increased in BD with a large effect size for TBARS and a moderate effect size for increase in NO. No significant effect sizes were observed for the antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase (all p>0.05).

LIMITATIONS

Some caution is warranted in interpreting these results: (1) Egger's test was positive for SOD, suggesting that SOD results may have been influenced by a publication bias. (2) We analyzed the absolute values of each antioxidant enzyme separately and the literature suggests that an imbalance between the antioxidant enzymes is a better indication of the presence of oxidative stress.

CONCLUSIONS

The present meta-analysis suggests that oxidative stress markers are increased in BD and that oxidative stress may play a role in the pathophysiology of BD.

Electrophysiological correlates of sleep disturbance induced by acute and chronic administration of D-amphetamine

Sleep disturbance is the strongest predictor of manic relapse and is considered one of the most important objective measures of treatment response in bipolar disorder (BD). However, the neurobiological mechanisms underlying sleep disturbance in BD are poorly understood. The administration of psychostimulants to rodents can trigger a number of manic-like behaviors. Therefore, the present study aims to investigate the effects of single and repeated D-amphetamine (AMPH) administration on sleep patterns in rats. Sleep was continuously monitored during light periods after single and repeated (7 days) injections of AMPH (2 mg/kg, i.p.) or saline in adult Wistar rats using electrocorticogram and electromyographic recordings. Acute injections of AMPH suppressed sleep for the first 2 h, and were followed by a gradual increase in the amount of sleep. Both slow wave sleep (SWS) and paradoxical sleep (PS) were compromised. Repeated exposure to AMPH led to a drastic disruption of the sleep-wake cycle that was mainly characterized by a decrease of PS during all time-points recorded in comparison to the saline group. Furthermore, both acute and chronic AMPH administration induced longer latencies to both SWS and PS. These findings suggest that AMPH produces profound sleep disturbances and decreases PS sleep. Given that some of these abnormalities are observed in individuals with BD, this animal model can provide a means to investigate neurobiological aspects of sleep disturbance in BD, as well as their response to mood stabilizers.

Going up in smoke: tobacco smoking is associated with worse treatment outcomes in mania

BACKGROUND

This study aimed to compare the treatment responses between smokers and non-smokers in bipolar mania clinical trials.

METHODS

Post-hoc analysis was conducted on data collected from three double-blind, randomised controlled trials in bipolar mania that had similar inclusion criteria. Patients were randomised to olanzapine (N=70) or placebo (N=69) for 3 weeks in Trial 1, olanzapine (N=234) or haloperidol (N=216) for 12 weeks in Trial 2, and olanzapine (N=125) or divalproex (N=126) for 47 weeks in Trial 3. This study analysed the Young Mania Rating Scale (YMRS) total scores and Clinical Global Impressions scale for bipolar disorder (CGI-BP) mania severity scores between smokers and non-smokers for each trial and for the pooled data from all three trials, using a mixed-effects model repeated measures approach.

RESULTS

For the pooled data, non-smokers showed superior treatment outcomes on both the YMRS (P=0.002) and CGI-BP (P<0.001), as well as longer time to discontinuation for any cause utilising Kaplan-Meier survival curves. For the individual trials, non-smokers showed greater improvement than smokers on both CGI-BP and YMRS in both treatment arms of Trial 2 (CGI-BP: haloperidol P=0.011, olanzapine P=0.042; YMRS: haloperidol P=0.010, olanzapine P=0.019), and in the olanzapine arm of Trial 3 (CGI-BP: P=0.002; YMRS: P=0.006). No significant difference in outcomes was found between smokers and non-smokers in Trial 1.

LIMITATIONS

Post-hoc design, categorical definition of smoking status, unavailable antipsychotic drug levels, confounding effects of trial medications and substance abuse.

CONCLUSIONS

Smoking appears to be associated with worse treatment outcomes in mania.

Euthymic patients with bipolar disorder show decreased reward learning in a probabilistic reward task

BACKGROUND

Bipolar disorder (BPD) features cycling mood states ranging from depression to mania with intermittent phases of euthymia. Bipolar disorder subjects often show excessive goal-directed and pleasure-seeking behavior during manic episodes and reduced hedonic capacity during depressive episodes, indicating that BPD might involve altered reward processing. Our goal was to test the hypothesis that BPD is characterized by impairments in adjusting behavior as a function of prior reinforcement history, particularly in the presence of residual anhedonic symptoms.

METHODS

Eighteen medicated BPD subjects and 25 demographically matched comparison subjects performed a probabilistic reward task. To identify putative dysfunctions in reward processing irrespective of mood state, primary analyses focused on euthymic BPD subjects (n = 13). With signal-detection methodologies, response bias toward a more frequently rewarded stimulus was used to objectively assess the participants' propensity to modulate behavior as a function of reinforcement history.

RESULTS

Relative to comparison subjects, euthymic BPD subjects showed a reduced and delayed acquisition of response bias toward the more frequently rewarded stimulus, which was partially due to increased sensitivity to single rewards of the disadvantageous stimulus. Analyses considering the entire BPD sample revealed that reduced reward learning correlated with self-reported anhedonic symptoms, even after adjusting for residual manic and anxious symptoms and general distress.

CONCLUSIONS

The present study provides preliminary evidence indicating that BPD, even during euthymic states, is characterized by dysfunctional reward learning in situations requiring integration of reinforcement information over time and thus offers initial insights about the potential source of dysfunctional reward processing in this disorder.

Is co-administration of bupropion with SSRIs and SNRIs in forced swimming test in mice, predictive of efficacy in resistant depression?

The monoamine hypothesis based on the deficiency of one or several monoamines is commonly evoked to explain the physiopathology of depression. This hypothesis initially based on noradrenalin and serotonin deficiency has been extended to dopamine. The animal models of depression also suggest an implication of dopamine in the physiopathology of depression. The forced swimming test is an animal model used to predict the antidepressant activity of drugs.

OBJECTIVES

The scope of this study was to investigate the antidepressant-like effect of a dopamine re-uptake inhibitor, bupropion, when combined with conventional antidepressants drugs SSRIs (selective serotonin re-uptake inhibitors), SNRI (selective serotonin-noradrenalin re-uptake inhibitors) and a NRI (selective noradrenalin inhibitor).

METHODS

This study assessed the effects of co-administration of bupropion with SSRIs: sertraline, paroxetine, citalopram, fluvoxamine, SNRIs: venlafaxine and milnacipran and NRI: desipramine, using an animal model of depression, the forced swimming test in mice. Subactive doses of bupropion (4 and 8mg/kg) and antidepressants: sertraline (2mg/kg), paroxetine, citalopram, fluvoxamine, venlafaxine, milnacipran and desipramine (4mg/kg) were given i.p. 45 and 30min, respectively, before the test.

RESULTS

Bupropion (4 and 8mg/kg) combined with inactive doses of antidepressants, decreased immobility time in the mice FST except with sertraline and desipramine. In conclusion, the antidepressant-enhancing effects of bupropion, in the present study, are in agreement with preliminary clinical evidence suggesting that bupropion may enhance the efficacy of therapeutic effect of SSRIs and SNRIs but not the therapeutic effect of NRI. These results suggest that bupropion enhances only the serotonergic system.

Chronic carbamazepine administration attenuates dopamine D2-like receptor-initiated signaling via arachidonic acid in rat brain

Observations that dopaminergic antagonists are beneficial in bipolar disorder and that dopaminergic agonists can produce mania suggest that bipolar disorder involves excessive dopaminergic transmission. Thus, mood stabilizers used to treat the disease might act in part by downregulating dopaminergic transmission. In agreement, we reported that dopamine D2-like receptor mediated signaling involving arachidonic acid (AA, 20:4n-6) was downregulated in rats chronically treated with lithium. To see whether chronic carbamazepine, another mood stabilizer, did this as well, we injected i.p. saline or the D2-like receptor agonist, quinpirole (1 mg/kg), into unanesthetized rats that had been pretreated for 30 days with i.p. carbamazepine (25 mg/kg/day) or vehicle, and used quantitative autoradiography to measure regional brain incorporation coefficients (k*) for AA, markers of signaling. We also measured brain prostaglandin E2 (PGE2), an AA metabolite. In vehicle-treated rats, quinpirole compared with saline significantly increased k* for AA in 35 of 82 brain regions examined, as well as brain PGE2 concentration. Affected regions belong to dopaminergic circuits and have high D2-like receptor densities. Chronic carbamazepine pretreatment prevented the quinpirole-induced increments in k* and in PGE2. These findings are consistent with the hypothesis that effective mood stabilizers generally downregulate brain AA signaling via D2-like receptors, and that this signaling is upregulated in bipolar disorder.