Preliminary evaluation of oral anticonvulsant treatment in the quinpirole model of bipolar disorder

Common changes in rat cortical gene expression after valproate or lithium treatment particularly affect pre- and post-synaptic pathways that regulate four neurotransmitters systems

OBJECTIVES

We have postulated that common changes in gene expression after treatment with different therapeutic classes of psychotropic drugs contribute to their common therapeutic mechanisms of action.

METHODS

To test this hypothesis, we measured levels of cortical coding and non-coding RNA using GeneChip® Rat Exon 1.0 ST Array after treatment with vehicle (chow only), chow containing 1.8 g lithium carbonate/kg (n = 10) or chow containing 12 g sodium valproate/kg (n = 10) for 28 days. Differences in levels of RNA were identified using JMP Genomics 13 and the Panther Gene Ontology Classification System was used to identify potential consequences of RNA.

RESULTS

Compared to vehicle treatment, levels of cortical RNA for 543 and 583 coding and non-coding RNAs were different after treatment with valproate and lithium, respectively. Moreover, levels of 323 coding and non-coding RNAs were altered in a highly correlated way by treatment with valproate and lithium, changes that would impact on cholinergic, glutamatergic, serotonergic and dopaminergic neurotransmission as well as on voltage gated ion channels.

CONCLUSIONS

Our study suggests that treating with mood stabilisers cause many common changes in levels of RNA which will impact on CNS function, particularly affecting post-synaptic muscarinic receptor functioning and the release of multiple neurotransmitters.

Association of Polymorphism within the Putative miRNA Target Site in the 3'UTR Region of the DRD2 Gene with Neuroticism in Patients with Substance Use Disorder

The study aims at looking into associations between the polymorphism rs6276 that occurs in the putative miRNA target site in the 3'UTR region of the DRD2 gene in patients with substance use disorder (SUD) comorbid with a maniacal syndrome (SUD MANIA). In our study, we did not state any essential difference in DRD2 rs6276 genotype frequencies in the studied samples of SUD MANIA, SUD, and control subjects. A significant result was found for the SUD MANIA group vs. SUD vs. controls on the Neuroticism Scale of NEO FFI test, and DRD2 rs6276 (p = 0.0320) accounted for 1.7% of the variance. The G/G homozygous variants were linked with lower results on the neuroticism scale in the SUD MANIA group because G/G alleles may serve a protective role in the expression of neuroticism in patients with SUD MANIA. So far, there have been no data in the literature on the relationship between the miRSNP rs6276 region in the DRD2 gene and neuroticism (personal traits) in patients with a diagnosis of substance use disorder comorbid with the affective, maniacal type disturbances related to SUD. This is the first report on this topic.

Sex differences in the blood-brain barrier: Implications for mental health

Prevalence of mental disorders, including major depressive disorder (MDD), bipolar disorder (BD) and schizophrenia (SZ) are increasing at alarming rates in our societies. Growing evidence points toward major sex differences in these conditions, and high rates of treatment resistance support the need to consider novel biological mechanisms outside of neuronal function to gain mechanistic insights that could lead to innovative therapies. Blood-brain barrier alterations have been reported in MDD, BD and SZ. Here, we provide an overview of sex-specific immune, endocrine, vascular and transcriptional-mediated changes that could affect neurovascular integrity and possibly contribute to the pathogenesis of mental disorders. We also identify pitfalls in current literature and highlight promising vascular biomarkers. Better understanding of how these adaptations can contribute to mental health status is essential not only in the context of MDD, BD and SZ but also cardiovascular diseases and stroke which are associated with higher prevalence of these conditions.

Changes in striatal dopamine transporters in bipolar disorder and valproate treatment

Background

Previous studies suggested that a disturbance of the dopamine system underlies the pathophysiology of bipolar disorder (BD). In addition, the therapeutic action of medications for treating BD, such as valproate (VPA), might modulate dopamine system activity, but it remains unclear. Here, we aimed to investigate the role of the striatal dopamine transporter (DAT) in BD patients and in social defeat (SD) mice treated with VPA.

Methods

We enrolled community-dwelling controls (N = 18) and BD patients (N = 23) who were treated with VPA in a euthymic stage. The striatal DAT availabilities were approached by TRODAT-1 single photon emission computed tomography. We also established a chronic SD mouse model and treated mice with 350 mg/kg VPA for 3 weeks. Behavioral tests were administered, and striatal DAT expression levels were determined.

Results

In humans, the level of striatal DAT availability was significantly higher in euthymic BD patients (1.52 ± 0.17 and 1.37 ± 0.23, p = 0.015). Moreover, the level of striatal DAT availability was also negatively correlated with the VPA concentration in BD patients (r = −0.653, p = 0.003). In SD mice, the expression of striatal DAT significantly increased (p < 0.001), and the SD effect on DAT expression was rescued by VPA treatment.

Conclusions

The striatal DAT might play a role in the pathophysiology of BD and in the therapeutic mechanism of VPA. The homeostasis of DAT might represent a new therapeutic strategy for BD patients.

Changes in gut microbiota during development of compulsive checking and locomotor sensitization induced by chronic treatment with the dopamine agonist quinpirole

Long-term treatment of rats with the D2/D3 dopamine agonist quinpirole induces compulsive checking (proposed as animal model of obsessive-compulsive disorder) and locomotor sensitization. The mechanisms by which long-term use of quinpirole produces those behavioral transformations are not known. Here we examined whether changes in gut microbiota play a role in these behavioral phenomena, by monitoring the development of compulsive checking and locomotor sensitization at the same time as measuring the response of gut microbiota to chronic quinpirole injections. Two groups of rats received nine injections of saline (n=16) or quinpirole (n=15; 0.25 mg/kg), at weekly intervals for the first 5 weeks and then two injections per week until the end of treatment. After each injection, rats were placed on a large open field for 55 min, and their behavior was video recorded for subsequent analysis. Fecal matter was collected after each trial and frozen for bacterial community profiling of the 16S rRNA gene, using paired-end reads of the V3 region. The results indicated that the induction of locomotor sensitization and compulsive checking was accompanied by changes in several communities of bacteria belonging to the order Clostridiales (class Clostridia, phylum Firmicutes), and predominantly in Lachnospiraceae and Ruminococcaceae families of bacteria. It is suggested that changes in these microbes may serve to support the energy use requirements of compulsive checking and obsessive-compulsive disorder.

Questioning the predictive validity of the amphetamine-induced hyperactivity model for screening mood stabilizing drugs

Animal models are critical for the study of disease mechanisms and the screening of potential novel treatments. In the context of bipolar disorder, amphetamine-induced hyperactivity (AIH) is a frequently used screening model for antimanic effects. Yet, the utility of screening models depends on their predictive (or pharmacological) validity and it is expected that such models will respond to effective treatments. Lithium is the prototypic mood stabilizer but previous data regarding the effects of lithium in the AIH model are not clear and most data comes from studies using acute lithium administration that is not relevant to the therapeutic regimen in patients. To evaluate the pharmacological validity of AIH as a model for mania-like behavior we tested the interaction between chronic oral administration of lithium and amphetamine in ICR (CD-1®) mice and in black Swiss mice. We conducted 4 different experiments where chronic lithium was followed by an acute injection of amphetamine and one experiment where chronic amphetamine was combined with chronic lithium. The results show that amphetamine result in hyperactivity (experiments 1-4) and that lithium has no effects. Moreover, chronic amphetamine (experiment 5) result in sensitization that is not attenuated by lithium. The results clearly show that the predictive validity of the AIH model in ICR or black Swiss mice is problematic and possibly cast doubt on the utilization of the AIH as a screening model for novel mood stabilizers in other strains of mice.

The dopamine hypothesis of bipolar affective disorder: the state of the art and implications for treatment

Bipolar affective disorder is a common neuropsychiatric disorder. Although its neurobiological underpinnings are incompletely understood, the dopamine hypothesis has been a key theory of the pathophysiology of both manic and depressive phases of the illness for over four decades. The increased use of antidopaminergics in the treatment of this disorder and new in vivo neuroimaging and post-mortem studies makes it timely to review this theory. To do this, we conducted a systematic search for post-mortem, pharmacological, functional magnetic resonance and molecular imaging studies of dopamine function in bipolar disorder. Converging findings from pharmacological and imaging studies support the hypothesis that a state of hyperdopaminergia, specifically elevations in D2/3 receptor availability and a hyperactive reward processing network, underlies mania. In bipolar depression imaging studies show increased dopamine transporter levels, but changes in other aspects of dopaminergic function are inconsistent. Puzzlingly, pharmacological evidence shows that both dopamine agonists and antidopaminergics can improve bipolar depressive symptoms and perhaps actions at other receptors may reconcile these findings. Tentatively, this evidence suggests a model where an elevation in striatal D2/3 receptor availability would lead to increased dopaminergic neurotransmission and mania, whilst increased striatal dopamine transporter (DAT) levels would lead to reduced dopaminergic function and depression. Thus, it can be speculated that a failure of dopamine receptor and transporter homoeostasis might underlie the pathophysiology of this disorder. The limitations of this model include its reliance on pharmacological evidence, as these studies could potentially affect other monoamines, and the scarcity of imaging evidence on dopaminergic function. This model, if confirmed, has implications for developing new treatment strategies such as reducing the dopamine synthesis and/or release in mania and DAT blockade in bipolar depression.

Neuroprotective effects of various doses of topiramate against methylphenidate-induced oxidative stress and inflammation in isolated rat amygdala: the possible role of CREB/BDNF signaling pathway

Methylphenidate (MPH) abuse damages brain cells. The neuroprotective effects of topiramate (TPM) have been reported previously, but its exact mechanism of action still remains unclear. This study investigated the in vivo role of various doses of TPM in the protection of rat amygdala cells against methylphenidate-induced oxidative stress and inflammation. Seventy adult male rats were divided into seven groups. Groups 1 and 2 received normal saline (0.7 ml/rat) and MPH (10 mg/kg), respectively, for 21 days. Groups 3, 4, 5, 6, and 7 were concurrently treated with MPH (10 mg/kg) and TPM (10, 30, 50, 70, and 100 mg/kg), respectively, for 21 days. elevated plus maze (EPM) was used to assess motor activity disturbances. In addition, oxidative, antioxidantand inflammatory factors and CREB, Ak1, CAMK4, MAPK3, PKA, BDNF, and c FOS gene levels were measured by RT-PCR, and also, CREB and BDNF protein levels were measured by WB in isolated amygdalae. MPH significantly disturbed motor activity and TPM (70 and 100 mg/kg) neutralized its effects. MPH significantly increased lipid peroxidation, mitochondrial GSSG levels and IL-1β and TNF-α level and CAMK4 gene expression in isolated amygdala cells. In contrast, superoxide dismutase, glutathione peroxidase, and glutathione reductase activities and CREB, BDNF Ak1, MAPK3, PKA, BDNF, and c FOS expression significantly decreased. The various doses of TPM attenuated these effects of MPH. It seems that TPM can be used as a neuroprotective agent and is a good candidate against MPH-induced neurodegeneration.

Modeling mania in preclinical settings: A comprehensive review

The current pathophysiological understanding of mechanisms leading to onset and progression of bipolar manic episodes remains limited. At the same time, available animal models for mania have limited face, construct, and predictive validities. Additionally, these models fail to encompass recent pathophysiological frameworks of bipolar disorder (BD), e.g. neuroprogression. Therefore, there is a need to search for novel preclinical models for mania that could comprehensively address these limitations. Herein we review the history, validity, and caveats of currently available animal models for mania. We also review new genetic models for mania, namely knockout mice for genes involved in neurotransmission, synapse formation, and intracellular signaling pathways. Furthermore, we review recent trends in preclinical models for mania that may aid in the comprehension of mechanisms underlying the neuroprogressive and recurring nature of BD. In conclusion, the validity of animal models for mania remains limited. Nevertheless, novel (e.g. genetic) animal models as well as adaptation of existing paradigms hold promise.

Modeling bipolar disorder in mice by increasing acetylcholine or dopamine: chronic lithium treats most, but not all features

RATIONALE

Bipolar disorder (BD) is a disabling and life-threatening disease characterized by states of depression and mania. New and efficacious treatments have not been forthcoming partly due to a lack of well-validated models representing both facets of BD.

OBJECTIVES

We hypothesized that cholinergic- and dopaminergic-pharmacological manipulations would model depression and mania respectively, each attenuated by lithium treatment.

METHODS

C57BL/6 J mice received the acetylcholinesterase inhibitor physostigmine or saline before testing for "behavioral despair" (immobility) in the tail suspension test (TST) and forced swim test (FST). Physostigmine effects on exploration and sensorimotor gating were assessed using the cross-species behavioral pattern monitor (BPM) and prepulse inhibition (PPI) paradigms. Other C57BL/6 J mice received chronic lithium drinking water (300, 600, or 1200 mg/l) before assessing their effects alone in the BPM or with physostigmine on FST performance. Another group was tested with acute GBR12909 (dopamine transporter inhibitor) and chronic lithium (1000 mg/l) in the BPM.

RESULTS

Physostigmine (0.03 mg/kg) increased immobility in the TST and FST without affecting activity, exploration, or PPI. Lithium (600 mg/l) resulted in low therapeutic serum concentrations and normalized the physostigmine-increased immobility in the FST. GBR12909 induced mania-like behavior in the BPM of which hyper-exploration was attenuated, though not reversed, after chronic lithium (1000 mg/ml).

CONCLUSIONS

Increased cholinergic levels induced depression-like behavior and hyperdopaminergia induced mania-like behavior in mice, while chronic lithium treated some, but not all, facets of these effects. These data support a cholinergic-monoaminergic mechanism for modeling BD aspects and provide a way to assess novel therapeutics.

Animal models of bipolar mania: The past, present and future

Bipolar disorder (BD) is the sixth leading cause of disability in the world according to the World Health Organization and affects nearly six million (∼2.5% of the population) adults in the United State alone each year. BD is primarily characterized by mood cycling of depressive (e.g., helplessness, reduced energy and activity, and anhedonia) and manic (e.g., increased energy and hyperactivity, reduced need for sleep, impulsivity, reduced anxiety and depression), episodes. The following review describes several animal models of bipolar mania with a focus on more recent findings using genetically modified mice, including several with the potential of investigating the mechanisms underlying 'mood' cycling (or behavioral switching in rodents). We discuss whether each of these models satisfy criteria of validity (i.e., face, predictive, and construct), while highlighting their strengths and limitations. Animal models are helping to address critical questions related to pathophysiology of bipolar mania, in an effort to more clearly define necessary targets of first-line medications, lithium and valproic acid, and to discover novel mechanisms with the hope of developing more effective therapeutics. Future studies will leverage new technologies and strategies for integrating animal and human data to reveal important insights into the etiology, pathophysiology, and treatment of BD.

Applications of the Neonatal Quinpirole Model to Psychosis and Convergence upon the Dopamine D2 Receptor

This mini review focuses on the importance of the dopamine D₂-like receptor family and its importance in psychosis. Past findings from this laboratory along with collaborators have been that neonatal quinpirole (a dopamine D₂-like receptor agonist) results in increases in dopamine D₂ receptor sensitivity that persists throughout the animal's lifetime. Findings from this model have been shown to have particular application and validity to schizophrenia, but may have broader implications toward other psychoses, which is reviewed in the present manuscript. In the present review, we also highlight other models of psychoses that have been centered on the subchronic administration of quinpirole to rats in order to model certain psychoses, which has uncovered some interesting and valid behavioral findings. This review highlights the importance of the combination of behavioral findings and neurobiological mechanisms focusing on neural plasticity in discovering underlying pathologies in these disorders that may lead to treatment discoveries, as well as the value of animal models across all psychoses.

Delay in the recovery of normal sleep-wake cycle after disruption of the light-dark cycle in mice: a bipolar disorder-prone animal model?

OBJECTIVE

Disruption of the circadian rhythm is known as a provoking factor for manic episodes. Individual differences exist in the recovery rate from disruption in the general population. To develop a screening method to detect individuals vulnerable to bipolar disorder, the authors observed the relationship between the recovery of the normal sleep-wake cycle after switching the light-dark (LD) cycle and quinpirole-induced hyperactivity in mice.

METHODS

Sixteen male mice (age of 5 weeks, weight 28-29 gm) were subjected to a circadian rhythm disruption protocol. Sleep-wake behaviors were checked every 5 min for a total duration of 15 days, i.e., 2 days of baseline observations, 3 days of LD cycle changes, and 10 days of recovery. During the dark cycle on the 16th experimental day, their general locomotor activities were measured in an open field for 120 minutes after an injection of quinpirole (0.5 mg/kg, s.c.).

RESULTS

The individual differences in the recovery rate of the baseline sleep-wake cycle were noted after 3 days of switching the LD cycle. Fifty percent (n=8) of the mice returned to the baseline cycle within 6 days after normalizing the LD cycle (early recovery group). The locomotor activities of mice that failed to recover within 6 days (delayed recovery group) were significantly higher (mean rank=12.25) than those of the early recovery group (mean rank=4.75, u=62.0, p=0.001, Mann-Whitney U test).

CONCLUSION

Given that the quinpirole-induced hyperactivity is an animal model of bipolar disorder, our results suggest individuals who have difficulties in recovery from circadian rhythm disruption may be vulnerable to bipolar disorder.

The catecholaminergic-cholinergic balance hypothesis of bipolar disorder revisited

Bipolar disorder is a unique illness characterized by fluctuations between mood states of depression and mania. Originally, an adrenergic-cholinergic balance hypothesis was postulated to underlie these different affective states. In this review, we update this hypothesis with recent findings from human and animal studies, suggesting that a catecholaminergic-cholinergic hypothesis may be more relevant. Evidence from neuroimaging studies, neuropharmacological interventions, and genetic associations support the notion that increased cholinergic functioning underlies depression, whereas increased activations of the catecholamines (dopamine and norepinephrine) underlie mania. Elevated functional acetylcholine during depression may affect both muscarinic and nicotinic acetylcholine receptors in a compensatory fashion. Increased functional dopamine and norepinephrine during mania on the other hand may affect receptor expression and functioning of dopamine reuptake transporters. Despite increasing evidence supporting this hypothesis, a relationship between these two neurotransmitter systems that could explain cycling between states of depression and mania is missing. Future studies should focus on the influence of environmental stimuli and genetic susceptibilities that may affect the catecholaminergic-cholinergic balance underlying cycling between the affective states. Overall, observations from recent studies add important data to this revised balance theory of bipolar disorder, renewing interest in this field of research.

Chronic treatment with mood-stabilizers attenuates abnormal hyperlocomotion of GluA1-subunit deficient mice

Abnormal excitatory glutamate neurotransmission and plasticity have been implicated in schizophrenia and affective disorders. Gria1−/− mice lacking GluA1 subunit (encoded by Gria1 gene) of AMPA-type glutamate receptor show robust novelty-induced hyperactivity, social deficits and heightened approach features, suggesting that they could be used to test for anti-manic activity of drugs. Here, we tested the efficacy of chronic treatment with established anti-manic drugs on behavioural properties of the Gria1−/− mice. The mice received standard mood stabilizers (lithium and valproate) and novel ones (topiramate and lamotrigine, used more as anticonvulsants) as supplements in rodent chow for at least 4 weeks. All drugs attenuated novelty-induced locomotor hyperactivity of the Gria1−/− mice, especially by promoting the habituation, while none of them attenuated 2-mg/kg amphetamine-induced hyperactivity as compared to control diet. Treatment with lithium and valproate reversed the elevated exploratory activity of Gria1−/− mice. Valproate treatment also reduced struggling behaviour in tail suspension test and restored reciprocally-initiated social contacts of Gria1−/− mice to the level shown by the wild-type Gria1+/+ mice. Gria1−/− mice consumed slightly more sucrose during intermittent sucrose exposure than the wild-types, but ran similar distances on running wheels. These behaviours were not consistently affected by lithium and valproate in the Gria1−/− mice. The efficacy of various anti-manic drug treatments on novelty-induced hyperactivity suggests that the Gria1−/− mouse line can be utilized in screening for new therapeutics.

Tamoxifen use for the management of mania: a review of current preclinical evidence

RATIONALE

Preliminary data on the efficacy of tamoxifen in reducing manic symptoms of bipolar disorder (BD) suggest that this agent may be a potential treatment for the management of this psychiatric disorder. However, the antimanic properties of tamoxifen have not been fully elucidated, hampering the development and/or use of mood-stabilising drugs that may share its same therapeutic mechanisms of action. Notably, we may gain a greater understanding of the neurobiological and therapeutic properties of tamoxifen by using suitable animal models of mania.

OBJECTIVES

Here, we review the preclinical studies that have evaluated the effects of tamoxifen to provide an overview of the current progress in our understanding of its antimanic actions, highlighting the critical role of protein kinase C (PKC) as a therapeutic target for the treatment of BD.

CONCLUSIONS

To date, this field has struggled to make significant progress, and the organisation of an explicit battery of tests is a valuable tool for assessing a number of prominent facets of BD, which may provide a greater understanding of the entire scope of this disease.

Chronic oral carbamazepine treatment elicits mood-stabilising effects in mice

OBJECTIVE

The underlying biology of bipolar disorder and the mechanisms by which effective medications induce their therapeutic effects are not clear. Appropriate use of animal models are essential to further understand biological mechanisms of disease and treatment, and further understanding the therapeutic mechanism of mood stabilisers requires that clinically relevant administration will be effective in animal models. The clinical regimens for mood-stabilising drugs include chronic oral administration; however, much of the work with animal models includes acute administration via injection. An effective chronic and oral administration of the prototypic mood stabiliser lithium was already established and the present study was designed to do the same for the mood stabiliser carbamazepine.

METHODS

Mice were treated for 3 weeks with carbamazepine in food. ICR mice were treated with 0.25%, 0.5% and 0.75%, and C57bl/6 mice with 0.5% and 0.75%, carbamazepine in food (w/w, namely, 2.5, 5.0 or 7.5 g/kg food). Mice were then tested for spontaneous activity, forced swim test (FST), tail suspension test (TST) and amphetamine-induced hyperactivity.

RESULTS

Oral carbamazepine administration resulted in dose-dependent blood levels reaching 3.65 μg/ml at the highest dose. In ICR mice, carbamazepine at the 0.5% dose had no effect on spontaneous activity, but significantly reduced immobility in the TST by 27% and amphetamine-induced hyperactivity by 28%. In C57bl/6 mice, carbamazepine at the 0.75% dose reduced immobility time in the FST by 26%.

CONCLUSIONS

These results demonstrate a behaviourally effective oral and chronic regimen for carbamazepine with mood stabilising-like activity in a standard model for mania-like behaviour and two standard models for depression-like behaviour.

Chronic valproate attenuates some, but not all, facets of mania-like behaviour in mice

Bipolar disorder (BD) mania is a psychiatric disorder with multifaceted symptoms. Development of targeted treatments for BD mania may benefit from animal models that mimic multiple symptoms, as opposed to hyperactivity alone. Using the reverse-translated multivariate exploratory paradigm, the behavioural pattern monitor (BPM), we reported that patients with BD mania exhibit hyperactivity as well as increased specific exploration and more linear movements through space. This abnormal profile is also observed in mice with reduced function of the dopamine transporter (DAT) through either constitutive genetic [knockdown (KD)] or acute pharmacological (GBR12909) means. Here, we assessed the pharmacological predictive validity of these models by administering the BD-treatment valproic acid (VPA) for 28 d. After 1.5% VPA- or regular-chow treatment for 28 d, C57BL/6J mice received GBR12909 (9 mg/kg) or saline and were tested in the BPM. Similarly, DAT KD and wild type (WT) littermates were treated with VPA-chow and tested in the BPM. GBR12909-treated and DAT KD mice on regular chow were hyperactive, exhibited increased specific exploration and moved in straighter patterns compared to saline-treated and WT mice respectively. Chronic 1.5% VPA-chow treatment resulted in therapeutic concentrations of VPA and ameliorated hyperactivity in both models, while specific exploration and behavioural organization remained unaffected. Hence, the mania-like profile of mice with reduced functional DAT was partially attenuated by chronic VPA treatment, consistent with the incomplete symptomatic effect of VPA treatment in BD patients. Both DAT models may help to identify therapeutics that impact the full spectrum of BD mania.

Rodent models for mania: practical approaches

The scarcity of good animal models for bipolar disorder (BPD) and especially for mania is repeatedly mentioned as one of the rate-limiting factors in the process of gaining a better understanding into its pathophysiology and of developing better treatments. Standard models of BPD have some value but usually represent only one facet of the disease and have partial validity. A number of new approaches for modeling BPD and specifically mania have been suggested in the last few years and can be combined to improve models. These approaches include targeted mutation models representing reverse translation, the identification of advantageous strains for components of the disorder, a search for the most homologous species to address specific human pathology, and the exploration of individual differences of response including the separation between susceptible and resilient animals. Additionally, recent efforts have identified and developed new tests to distinguish between "normal" and "BPD-like" animals including the different utilization of known tests and novel tests such as the female-urine-sniffing test and behavior pattern monitor analysis. Additional tests relating to further domains of BPD are still needed. An ideal model for BPD that will encompass the entire disease and be useful for every demand will probably not become available until we have a full understanding of the pathophysiology of the disorder. However, the current advances in modeling should lead to better comprehension of the disorder and therefore to the gradual development of increasingly improved models.

Predictive animal models of mania: hits, misses and future directions

Mania has long been recognized as aberrant behaviour indicative of mental illness. Manic states include a variety of complex and multifaceted symptoms that challenge clear clinical distinctions. Symptoms include over-activity, hypersexuality, irritability and reduced need for sleep, with cognitive deficits recently linked to functional outcome. Current treatments have arisen through serendipity or from other disorders. Hence, treatments are not efficacious for all patients, and there is an urgent need to develop targeted therapeutics. Part of the drug discovery process is the assessment of therapeutics in animal models. Here we review pharmacological, environmental and genetic manipulations developed to test the efficacy of therapeutics in animal models of mania. The merits of these models are discussed in terms of the manipulation used and the facet of mania measured. Moreover, the predictive validity of these models is discussed in the context of differentiating drugs that succeed or fail to meet criteria as approved mania treatments. The multifaceted symptomatology of mania has not been reflected in the majority of animal models, where locomotor activity remains the primary measure. This approach has resulted in numerous false positives for putative treatments. Recent work highlights the need to utilize multivariate strategies to enable comprehensive assessment of affective and cognitive dysfunction. Advances in therapeutic treatment may depend on novel models developed with an integrated approach that includes: (i) a comprehensive battery of tests for different aspects of mania, (ii) utilization of genetic information to establish aetiological validity and (iii) objective quantification of patient behaviour with translational cross-species paradigms.

Chronic valproate treatment blocks D2-like receptor-mediated brain signaling via arachidonic acid in rats

BACKGROUND AND OBJECTIVE

Hyperdopaminergic signaling and an upregulated brain arachidonic acid (AA) cascade may contribute to bipolar disorder (BD). Lithium and carbamazepine, FDA-approved for the treatment of BD, attenuate brain dopaminergic D(2)-like (D(2), D(3), and D(4)) receptor signaling involving AA when given chronically to awake rats. We hypothesized that valproate (VPA), with mood-stabilizing properties, would also reduce D(2)-like-mediated signaling via AA.

METHODS

An acute dose of quinpirole (1 mg/kg) or saline was administered to unanesthetized rats that had been treated for 30 days with a therapeutically relevant dose of VPA (200 mg/kg/day) or vehicle. Regional brain AA incorporation coefficients, k*, and incorporation rates, J(in), markers of AA signaling and metabolism, were measured by quantitative autoradiography after intravenous [1-(14)C]AA infusion. Whole brain concentrations of prostaglandin (PG)E(2) and thromboxane (TX)B(2) also were measured.

RESULTS

Quinpirole compared to saline significantly increased k* in 40 of 83 brain regions, and increased brain concentrations of PGE(2) in chronic vehicle-treated rats. VPA treatment by itself reduced concentrations of plasma unesterified AA and whole brain PGE(2) and TXB(2), and blocked the quinpirole-induced increments in k* and PGE(2).

CONCLUSION

These results further provide evidence that mood stabilizers downregulate brain dopaminergic D(2)-like receptor signaling involving AA.

The effects of neuropsychiatric drugs on glycogen synthase kinase-3 signaling

Glycogen synthase kinase-3 (GSK-3) has been implicated in the action of antipsychotics, mood stabilizers, and antidepressants. Given that only antipsychotics are able to alleviate the positive symptoms of schizophrenia, the regulation of GSK-3 by antipsychotics would be expected to differ from other neuropsychiatric drugs if GSK-3 is involved in the alleviation of psychosis. Consequently, the current study examined the effects of antipsychotics (haloperidol and clozapine), mood stabilizers (lithium and valproic acid), and antidepressants (imipramine and fluoxetine) on GSK-3, as well as Akt and Wnt in the prefrontal cortex and striatum. Western blotting and co-immunoprecipitation experiments showed that only antipsychotic treatment increased Dvl-3, GSK-3, and β-catenin levels and enhanced the association of GSK-3 at the dopamine D2 receptor (D₂DR) complex in the rat prefrontal cortex. In the striatum, haloperidol had the same effect on Wnt signaling as observed in the prefrontal cortex, whereas clozapine did not affect Dvl-3, GSK-3 or β-catenin levels. All three classes of drugs were able to activate Akt signaling as shown by the increased phosphorylated Akt and phosphorylated GSK-3 protein levels in the prefrontal cortex and/or striatum. In conclusion, regulation of the Wnt pathway is specific to antipsychotics, whereas antipsychotics, mood stabilizers, and antidepressants all affect Akt.

Convergent functional genomic studies of ω-3 fatty acids in stress reactivity, bipolar disorder and alcoholism

Omega-3 fatty acids have been proposed as an adjuvant treatment option in psychiatric disorders. Given their other health benefits and their relative lack of toxicity, teratogenicity and side effects, they may be particularly useful in children and in females of child-bearing age, especially during pregnancy and postpartum. A comprehensive mechanistic understanding of their effects is needed. Here we report translational studies demonstrating the phenotypic normalization and gene expression effects of dietary omega-3 fatty acids, specifically docosahexaenoic acid (DHA), in a stress-reactive knockout mouse model of bipolar disorder and co-morbid alcoholism, using a bioinformatic convergent functional genomics approach integrating animal model and human data to prioritize disease-relevant genes. Additionally, to validate at a behavioral level the novel observed effects on decreasing alcohol consumption, we also tested the effects of DHA in an independent animal model, alcohol-preferring (P) rats, a well-established animal model of alcoholism. Our studies uncover sex differences, brain region-specific effects and blood biomarkers that may underpin the effects of DHA. Of note, DHA modulates some of the same genes targeted by current psychotropic medications, as well as increases myelin-related gene expression. Myelin-related gene expression decrease is a common, if nonspecific, denominator of neuropsychiatric disorders. In conclusion, our work supports the potential utility of omega-3 fatty acids, specifically DHA, for a spectrum of psychiatric disorders such as stress disorders, bipolar disorder, alcoholism and beyond.

Strategies for the development of animal models for bipolar disorder: new opportunities and new challenges

The paucity of appropriate animal models for bipolar disorder is repeatedly mentioned as one of the critical factors hindering research into the pathophysiology of the disorder and the development of truly novel treatments. Recent advances in our understanding of the biological basis of bipolar disorder can be used to identify and develop better models. One possibility that is discussed in a separate chapter of this book is the use of molecular biology techniques to develop animals with targeted mutations related to genes implicated in the disorder. However, the development of such animals may not be enough for usable and helpful models. Additional strategies should, therefore, be combined with targeted mutation methodology to develop good model animals and good tests that will significantly impact our ability to further explore the underlying biology of bipolar disorder and to develop better drugs and treatments.The present chapter presents a short introduction related to commonly used models and discusses some of the possible strategies for advancement. These strategies include developing better tests, exploring separate tests for the different domains of the disease, creating test batteries, and developing models for endophenotypes. In addition, the chapter raises the possibility of identifying better model animals using comparative biology approaches. The chapter presents two different ways for identifying advantageous model animals using either specific strains of laboratory animals or using the natural diversity of nontraditional model animals.In summary, it is concluded that while each strategy offers significant contributions, it is important to combine the different approaches in order to be able to achieve novel, appropriate, and predictive models for bipolar disorder.

The neurobiology of the switch process in bipolar disorder: a review

OBJECTIVE

The singular phenomenon of switching from depression to its opposite state of mania or hypomania, and vice versa, distinguishes bipolar disorder from all other psychiatric disorders. Despite the fact that it is a core aspect of the clinical presentation of bipolar disorder, the neurobiology of the switch process is still poorly understood. In this review, we summarize the clinical evidence regarding somatic interventions associated with switching, with a particular focus on the biologic underpinnings presumably involved in the switch process.

DATA SOURCES

Literature for this review was obtained through a search of the MEDLINE database (1966-2008) using the following keywords and phrases: switch, bipolar disorder, bipolar depression, antidepressant, SSRIs, tricyclic antidepressants, norepinephrine, serotonin, treatment emergent affective switch, mania, hypomania, HPA-axis, glucocorticoids, amphetamine, dopamine, and sleep deprivation.

STUDY SELECTION

All English-language, peer-reviewed, published literature, including randomized controlled studies, naturalistic and open-label studies, and case reports, were eligible for inclusion.

DATA SYNTHESIS

Converging evidence suggests that certain pharmacologic and nonpharmacologic interventions with very different mechanisms of action, such as sleep deprivation, exogenous corticosteroids, and dopaminergic agonists, can trigger mood episode switches in patients with bipolar disorder. The switch-inducing potential of antidepressants is unclear, although tricyclic antidepressants, which confer higher risk of switching than other classes of antidepressants, are a possible exception. Several neurobiological factors appear to be associated with both spontaneous and treatment-emergent mood episode switches; these include abnormalities in catecholamine levels, up-regulation of neurotrophic and neuroplastic factors, hypothalamic-pituitary-adrenal axis hyperactivity, and circadian rhythms.

CONCLUSIONS

There is a clear need to improve our understanding of the neurobiology of the switch process; research in this field would benefit from the systematic and integrated assessment of variables associated with switching.

Chronic imipramine but not bupropion increases arachidonic acid signaling in rat brain: is this related to 'switching' in bipolar disorder?

Agents effective against mania in bipolar disorder are reported to decrease turnover of arachidonic acid (AA) in phospholipids and expression of calcium-dependent AA-selective cytosolic phospholipase A(2) (cPLA(2)) in rat brain. In contrast, fluoxetine, an antidepressant that is reported to switch bipolar depressed patients to mania, increases cPLA(2) expression and AA turnover in rat brain. We therefore hypothesized that antidepressants that increase switching to mania generally increase cPLA(2) and AA turnover in brain. To test this hypothesis, adult male CDF-344 rats were administered imipramine and bupropion, with reported high and low switching rates, respectively, at daily doses of 10 and 30 mg kg(-1) i.p., respectively, or i.p. saline (control) for 21 days. Frontal cortex expression of different PLA(2) enzymes and AA turnover rates in brain when the rats were unanesthetized were measured. Compared with chronic saline, chronic imipramine but not bupropion significantly increased cortex cPLA(2) mRNA activity, protein and phosphorylation, expression of the cPLA(2) transcription factor, activator protein-2alpha (AP-2alpha) and AA turnover in phospholipids. Protein levels of secretory phospholipase A(2), calcium-independent phospholipase A(2), cyclooxygenase (COX)-1 and COX-2 were unchanged, and prostaglandin E(2) was unaffected. These results, taken with prior data on chronic fluoxetine in rats, suggest that antidepressants that increase the switching tendency of bipolar depressed patients to mania do so by increasing AA recycling and metabolism in brain. Mania in bipolar disorder thus may involve upregulated brain AA metabolism.

Cross-species assessments of motor and exploratory behavior related to bipolar disorder

Alterations in exploratory behavior are a fundamental feature of bipolar mania, typically characterized as motor hyperactivity and increased goal-directed behavior in response to environmental cues. In contrast, abnormal exploration associated with schizophrenia and depression can manifest as prominent withdrawal, limited motor activity, and inattention to the environment. While motor abnormalities are cited frequently as clinical manifestations of these disorders, relatively few empirical studies have quantified human exploratory behavior. This article reviews the literature characterizing motor and exploratory behavior associated with bipolar disorder and genetic and pharmacological animal models of the illness. Despite sophisticated assessment of exploratory behavior in rodents, objective quantification of human motor activity has been limited primarily to actigraphy studies with poor cross-species translational value. Furthermore, symptoms that reflect the cardinal features of bipolar disorder have proven difficult to establish in putative animal models of this illness. Recently, however, novel tools such as the human behavioral pattern monitor provide multivariate translational measures of motor and exploratory activity, enabling improved understanding of the neurobiology underlying psychiatric disorders.

Brain arachidonic acid uptake and turnover: implications for signaling and bipolar disorder

PURPOSE OF REVIEW

Arachidonic acid was first detected in the brain in 1922. Although earlier work examined the role of arachidonic acid in growth and development, more recent advancements have elucidated roles for arachidonic acid in brain health and disease.

RECENT FINDINGS

In this review, we summarize evidence demonstrating that unesterified arachidonic acid in the plasma pool, which is supplied in part from adipose, is readily taken up and incorporated into brain phospholipids. By labeling plasma unesterified arachidonic acid, it is possible to trace the subsequent release of arachidonic acid from brain phospholipids upon neuroreceptor-mediated release by phospholipase A2 in response to drugs and neuroinflammation in rodents. With the synthesis of 11C labeled fatty acids, brain arachidonic acid signaling can now be measured in humans with position emission tomography. Arachidonic acid signals are known to regulate important biological functions, including neuroinflammation and excitotoxicity, and we focus on how the brain arachidonic acid cascade is a common target of drugs used to treat bipolar disorder (e.g. lithium, carbamazepine and valproate).

SUMMARY

A better understanding of the regulation of arachidonic acid uptake into the brain and the brain arachidonic acid cascade could lead to new imaging techniques and the identification of novel therapeutic targets in excitotoxicity, neuroinflammation and bipolar disorder.

Is the brain arachidonic acid cascade a common target of drugs used to manage bipolar disorder?

Although lithium has been used therapeutically to treat patients with bipolar disorder for over 50 years, its mechanism of action, as well as that of other drugs used to treat bipolar disorder, is not agreed upon. In the present paper, I review studies in unanaesthetized rats using a neuropharmacological approach, combined with kinetic, biochemical and molecular biology techniques, demonstrating that chronic administration of three commonly used mood stabilizers (lithium, valproic acid and carbamazepine), at therapeutically relevant doses, selectively target the brain arachidonic acid cascade. Upon chronic administration, lithium and carbamazepine decrease the binding activity of activator protein-2 and, in turn, the transcription, translation and activity of its arachidonic acid-selective calcium-dependent phospholipase A2 gene product, whereas chronic valproic acid non-competitively inhibits long-chain acyl-CoA synthetase. The net overlapping effects of the three mood stabilizers are decreased turnover of arachidonic acid, but not of docosahexaenoic acid, in rat brain phospholipids, as well as decreased brain cyclo-oxygenase-2 and prostaglandin E2. As an extension of this theory, drugs that are thought to induce switching to mania, especially when administered during bipolar depression (fluoxetine and imipramine), up-regulate enzymes of the arachidonic acid cascade and turnover of arachidonic acid in rat brain phospholipids. Future basic and clinical studies on the arachidonic acid hypothesis of bipolar disorder are warranted.

Pharmacological validation of a chronic social stress model of depression in rats: effects of reboxetine, haloperidol and diazepam

Chronic social stress is one of the most important factors responsible for precipitation of depressive disorder in humans. In recent years, the impact of social stress on the development of psychopathologies has been thoroughly investigated in preclinical animal studies. We have shown recently that behavioural effects of chronic social stress in rats can be reversed by citalopram and fluoxetine. This study has been designed for further pharmacological validation of the chronic social stress paradigm as a model of depressive symptoms in rats. For this, rats were subjected to 5 weeks of daily social defeat and were in parallel treatment for a clinically relevant period of 4 weeks with the antidepressant drug reboxetine (40 mg/kg/day) and the neuroleptic drug haloperidol (2 mg/kg/day). The anxiolytic diazepam (1 mg/kg) was administered acutely at the end of the stress period. Stress caused decreased locomotor and exploratory behaviours, decreased sucrose preference and increased immobility in the forced swim test, but did not affect behaviour in the elevated plus maze. Four weeks of oral treatment with reboxetine ameliorated the adverse effects of social stress and normalized behaviours related to motivation and reward sensitivity. The treatment with haloperidol worsened the adverse effects of chronic social stress having effects similar to stress on reward and motivation-related behaviours. Diazepam reduced anxiety-related behaviours as measured in elevated plus maze in control animals having no effects on socially stressed individuals. Neither sucrose preference nor performance in forced swim test was affected by diazepam. The effectiveness and selectivity of the treatment with the antidepressant reboxetine in ameliorating socially induced behavioural disturbances supports the validity of the chronic social stress as a model of depressive-like symptoms in rats.

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.

Mode of action of mood stabilizers: is the arachidonic acid cascade a common target?

Bipolar disorder is a major medical, social and economic burden worldwide. However, the mechanisms of action of effective antibipolar disorder drugs remain elusive. In this paper, we review studies using a neuropharmacological approach in unanesthetized rats, combined with kinetic, biochemical and molecular biology techniques, showing that chronic administration of three Food and Drug Administration-approved mood stabilizers (lithium, valproate and carbamazepine) at therapeutically relevant doses, selectively target the brain arachidonic acid (AA) cascade. Whereas chronic lithium and carbamazepine decrease the binding activity of activator protein-2 and in turn the transcription, translation and activity of its AA-selective calcium-dependent phospholipase A(2) gene product, valproate appears to be a non-competitive inhibitor of long-chain acyl-CoA synthetase. The net overlapping effects of the three drugs are decreased turnover of AA but not of docosahexaenoic acid in rat brain phospholipids, and decreased brain cyclooxygenase-2 and prostaglandin E(2). Although these observations support the hypothesis proposed by Rapoport and colleagues that the AA cascade is a common target of mood stabilizers, this hypothesis is not necessarily exclusive of other targets. Targeting the AA cascade with drugs or diet may be a useful therapeutic approach in bipolar disorder, and examining the AA cascade in patients might help in better understanding the disease.

Phenomic, convergent functional genomic, and biomarker studies in a stress-reactive genetic animal model of bipolar disorder and co-morbid alcoholism

We had previously identified the clock gene D-box binding protein (Dbp) as a potential candidate gene for bipolar disorder and for alcoholism, using a Convergent Functional Genomics (CFG) approach. Here we report that mice with a homozygous deletion of DBP have lower locomotor activity, blunted responses to stimulants, and gain less weight over time. In response to a chronic stress paradigm, these mice exhibit a diametric switch in these phenotypes. DBP knockout mice are also activated by sleep deprivation, similar to bipolar patients, and that activation is prevented by treatment with the mood stabilizer drug valproate. Moreover, these mice show increased alcohol intake following exposure to stress. Microarray studies of brain and blood reveal a pattern of gene expression changes that may explain the observed phenotypes. CFG analysis of the gene expression changes identified a series of novel candidate genes and blood biomarkers for bipolar disorder, alcoholism, and stress reactivity.

Antimanic therapies target brain arachidonic acid signaling: lessons learned about the regulation of brain fatty acid metabolism

Bipolar disorder is a major medical, social and economic burden worldwide. However, the biochemical basis of the disorder and the mechanisms of action of effective antibipolar disorder drugs remain elusive. In this paper, we review how combining a kinetic approach to studying the turnover of fatty acids within brain phospholipids of unanesthetized rats along with chronic administration of antimanic drugs (lithium, valproate and carbamazepine) at therapeutically relevant doses, shows that the brain arachidonic acid cascade is a common target of these drugs. The overlapping effects of the three drugs are decreased turnover of arachidonic acid but not of docosahexaenoic acid in rat brain phospholipids, and decreased brain cyclooxygenase-2 and prostaglandin E(2). Whereas lithium and carbamazepine target the transcription of the arachidonic acid-selective calcium-dependent cytosolic phospholipase A(2), valproate is a non-competitive inhibitor of an arachidonic acid-selective acyl-CoA synthetase. Two potential models of bipolar disorder, chronic N-methyl-d-aspartate and n-3 polyunsaturated fatty acid deprivation, opposite to the antimanic drugs, increase the turnover and markers of the arachidonic acid cascade in rat brain. These observations support the hypothesis proposed by Rapoport and colleagues that the arachidonic acid cascade is a common target of mood stabilizers and that by targeting substrate-specific enzymes the turnover of individual fatty acids can be regulated within the brain.

Effects of topiramate on the prepulse inhibition of the acoustic startle in rats

The anticonvulsant topiramate (TPM) has been recently proposed as a novel adjuvant therapy for bipolar disorder and schizophrenia, yet its efficacy remains controversial. As both disorders are characterized by gating deficits, we tested the effects of TPM on the behavioral paradigm of prepulse inhibition (PPI) of the acoustic startle response, a validated animal model of sensorimotor gating. TPM (10, 18, 32, 58, 100 mg/kg, intraperitoneal, i.p.) enhanced PPI in rats in a dose-dependent fashion, prevented the PPI reduction mediated by the dopaminergic agonist apomorphine (0.25 mg/kg, subcutaneous, s.c.) and potentiated the effects of the antipsychotic drugs haloperidol (0.05, 0.1 mg/kg, i.p.) and clozapine (2.5, 5 mg/kg, i.p.). Conversely, TPM elicited no significant effect on the PPI disruption mediated by the NMDA receptor antagonist dizocilpine (0.05, 0.1 mg/kg, s.c.) and surprisingly antagonized the attenuation of dizocilpine-induced PPI disruption mediated by clozapine (5 mg/kg, i.p.). Our results suggest that TPM may exert diverse actions on the neural substrates of sensorimotor gating. While the pharmacological mechanisms of such effects are still elusive, our findings might contribute to shed light on some controversies on the therapeutic action of TPM, and point to this drug as a putative novel adjuvant therapy for some clusters of gating disturbances.

Animal models of bipolar disorder

Animal models of human diseases should meet three sets of criteria: construct validity, face validity, and predictive validity. To date, several putative animal models of bipolar disorder have been reported. They are classified into various categories: pharmacological models, nutritional models, environmental models, and genetic models. None of them, however, totally fulfills the three validity criteria, and thus may not be useful for drug development. Mounting evidence suggests that mitochondrial dysfunction has a role in bipolar disorder. To test whether accumulation of mtDNA deletions in the brain can cause bipolar disorder, we generated transgenic mice with neuron-specific expression of mutant Polg (D181A). These mice showed altered diurnal activity rhythm and periodic activity change associated with the estrous cycle. These phenotypes were worsened by administration of a tricyclic antidepressant, but improved after lithium treatment. This mouse model of bipolar disorder potentially fulfills the three validity criteria, and therefore might be used for future drug development studies.

Modelling facets of mania--new directions related to the notion of endophenotypes

The lack of appropriate animal models is a major limitation in research of bipolar disorder (BPD): at this time there are very few models for this devastating disease. Whereas limited attempts have been made to develop comprehensive models for BPD, the new notion of endophenotypes encourages us to explore the possibility of developing separate models for separate facets of the disorder. Since more models are available for depression, there is a dire need for models for mania that will be relatively easy and simple to induce and test and will therefore be practical for purposes of screening possible new drugs or mutant mice that are developed based on novel molecular theories. Such models may already be tentatively available as they were developed in the context of other disorders, but there is a need to validate them for mania. The present paper proposes such models for most of the facets of mania including: increased energy, activity or restlessness; extreme irritability; reduced sleep; provocative, intrusive or aggressive behaviour; increased sexual drive; abuse of drugs; distractibility, reduced ability to concentrate; and unrealistic beliefs in one's abilities and powers resulting in poor judgement. Validating these models may demand a major research effort but it may be worthy as validated models for the different facets of mania could then be used efficiently and may be utilized to construct a standard battery of tests that can serve to explore the various components of manic-like behaviour in rodents.

Establishment of a battery of simple models for facets of bipolar disorder: a practical approach to achieve increased validity, better screening and possible insights into endophenotypes of disease

The lack of appropriate animal models for bipolar disorder (BPD) hinders the translation of novel molecular and genetic findings into the development of new more efficient treatments. Attempts to develop a comprehensive model for BPD did not result in a practical and valid model and at present most studies utilize a limited number of models for specific components of the disorder. Whereas there is a higher availability of models for the depression pole of BPD, only a few models represent the manic pole with the most frequently used being psychostimulant-induced hyperactivity. This last model had been important in studies of the disease and has some validity but it is clear that by itself cannot be considered to represent mania. Additional models for facets of BPD are needed to allow better screening of new drugs and new mutant mice. Such models may also support the exploration of endophenotypes of BPD and the mechanisms of the disease. An advantage of a battery approach is that each model can be only partially valid when used alone but the combination of a few models may result in strong validity. The present study suggests that such a battery can be based on existing models previously developed in the context of studying normal behavior or other disorders after an initial validation in the context of BPD. An example for this idea is described using the resident-intruder test for aggression. Present results show that 3 weeks oral treatment with 1.2-2.4% lithium (increasing doses), or 20 g/kg daily dose of valproate, significantly reduced aggressive behavior in resident mice without affecting non-aggressive social interactions. Accordingly, it is suggested that the simplified resident-intruder paradigm may model the aggression related to mania as part of a test battery for facets of BPD. It is further speculated that, pending further research, this paradigm can be combined with additional methods to explore changes in the LHPA axis that may be linked to an important endophenotype of BPD.

Citalopram counteracts depressive-like symptoms evoked by chronic social stress in rats

Recently, we have described a new model of chronic social stress in rats, based on the resident-intruder paradigm. In this model, rats show behavioural changes that may be considered correlates of depressive symptoms, such as anhedonia and motivational deficits. The present study was designed for pharmacological validation of this model. Animals were socially stressed for 5 weeks and, in parallel, after the first week of stress, they were subjected to chronic (4 weeks) treatment with the antidepressant drug citalopram. The drug was administered via drinking water (30 mg/kg). The optimal dose of citalopram was determined in a pilot study. After 4 weeks of treatment, plasma levels of citalopram and its metabolite were found to be within the human therapeutic range. The effects of social stress and citalopram treatment were assessed by behavioural tests. Chronically stressed rats showed reduced locomotor and exploratory activity, reduced sucrose preference and increased immobility time in the forced swimming test. Chronic oral administration of citalopram abolished those effects and normalized behaviours related to motivation and reward sensitivity. These observations provide evidence for the predictive validity of the chronic social stress paradigm as a model of depressive symptoms in rats.

Topiramate augments the antipsychotic-like effect and cortical dopamine output of raclopride

Recent clinical studies have shown that the anticonvulsant drug topiramate may improve negative symptoms in schizophrenia when added to a stable regimen of neuroleptic medication. It has also been shown that addition of topiramate to neuroleptics might be beneficial in treatment-resistant schizophrenia. Clinically effective doses of antipsychotic drugs (APDs) have been found to suppress conditioned avoidance response behavior (CAR), a preclinical test of antipsychotic activity with high predictive validity, in rats. Therefore, we investigated the putative antipsychotic-like activity of topiramate when added to the selective dopamine (DA) D2 receptor antagonist raclopride, using the CAR model in the rat. Extrapyramidal side effect liability of the drug combination was evaluated in parallel by means of the catalepsy test. We also examined the effect of this drug treatment on DA release in the medial prefrontal cortex (mPFC) and the nucleus accumbens (NAC), using in vivo microdialysis in freely moving animals. Topiramate (40 mg/kg), while ineffective when given alone, significantly augmented the antipsychotic-like effect of raclopride (0.075 mg/kg) on CAR without any concomitant catalepsy. Addition of topiramate to rats treated with raclopride generated a large increase in DA output in the mPFC, whereas no additional effect on the raclopride-induced DA release in the NAC was obtained. These data support the adjunctive use of topiramate in schizophrenia to ameliorate negative symptoms and suggest that this treatment may increase the efficacy, but not the extrapyramidal side effect liability, of the APDs used.

Topiramate does not alter expression in rat brain of enzymes of arachidonic acid metabolism

RATIONALE

When administered chronically to rats, drugs that are effective in bipolar disorder-lithium and the anticonvulsants, valproic acid and carbamazepine-have been shown to downregulate the expression of certain enzymes involved in brain arachidonic acid (AA) release and cyclooxygenase (COX)-mediated metabolism. Phase II clinical trials with the anticonvulsant topiramate [2,3:4,5-bis-O-(1-methylethylidene)-beta-D-fructopyranose sulfamate] suggest that this drug may also be effective for bipolar disorder.

OBJECTIVES

To see if topiramate has effects similar to those of the other three drugs, we administered topiramate to rats for 14 days at 20 mg/kg, p.o. twice daily.

RESULTS

Compared with p.o. vehicle, topiramate treatment did not significantly affect the brain activity or protein level of cytosolic phospholipase A2, secretory PLA2, or Ca2+-independent iPLA2. Additionally, brain protein levels of COX-1, COX-2, 5-lipoxygenase, and cytochrome P450 epoxygenase were unchanged.

CONCLUSIONS

These results suggest that topiramate does not modify expression of the enzymes involved in brain AA metabolism that have been shown to be targeted by lithium, valproic acid, or carbamazepine. If topiramate proves effective in bipolar disorder, it may not act by modulating brain AA metabolism. In view of the proven anticonvulsant effect of topiramate, our results also suggest that the AA cascade is not involved in the anti-seizure properties of the drug.

Topiramate does not Alter the Kinetics of Arachidonic or Docosahexaenoic Acid in Brain Phospholipids of the Unanesthetized Rat

Interest in the potential therapeutic utility of topiramate for treating bipolar disorder was stimulated by published reports of investigator-initiated open label clinical studies. Because chronic lithium, carbamazepine and valproate decrease the turnover of arachidonic acid (AA) but not docosahexaenoic acid (DHA) in brain phospholipids of the awake rat, we tested if topiramate would produce similar results. Rats received either topiramate (20 mg/kg twice per day) or vehicle for 14 days and then while unanesthetized were infused intravenously with either [1-(14)C] AA or [1-(14)C] DHA for 5 min while blood was collected from the femoral artery at fixed times. Topiramate did not alter the incorporation rate of AA or DHA from their respective brain acyl-CoA pool into brain phospholipids, nor the turnover of AA and DHA in brain phospholipids. The results of our study indicate that topiramate does not possess a pharmacological property that three drugs with proven efficacy in treating bipolar disorder have in common.