Attenuation of high sweet solution preference by mood stabilizers: a possible mouse model for the increased reward-seeking domain of mania

Does treatment with autophagy-enhancers and/or ROS-scavengers alleviate behavioral and neurochemical consequences of low-dose rotenone-induced mild mitochondrial dysfunction in mice?

Bipolar-disorder's pathophysiology and the mechanism by which medications exert their beneficial effect is yet unknown, but others' and our data implicate patients' brain mitochondrial-dysfunction and its amendment by mood-stabilizers. We recently designed a novel mouse bipolar-disorder-like model using chronic administration of a low-dose of the oxidative-phosphorylation complex I inhibitor, rotenone. Four and eight weeks rotenone treatment induced manic- and depressive-like behavior, respectively, accompanied by mood-related neurochemical changes. Here we aimed to investigate whether each of the autophagy-enhancers lithium (a mood-stabilizer), trehalose and resveratrol and/or each of the reactive oxygen species (ROS)-scavengers, resveratrol and N-acetylcystein and/or the combinations lithium+resveratrol or trehalose+N-acetylcystein, can ameliorate behavioral and neurochemical consequences of neuronal mild mitochondrial-dysfunction. We observed that lithium, trehalose and N-acetylcystein reversed rotenone-induced manic-like behavior as well as deviations in protein levels of mitochondrial complexes and the autophagy marker LC3-II. This raises the possibility that mild mitochondrial-dysfunction accompanied by impaired autophagy and a very mild increase in ROS levels are related to predisposition to manic-like behavior. On the other hand, although, as expected, most of the drugs tested eliminated the eight weeks rotenone-induced increase in protein levels of all hippocampal mitochondrial complexes, only lithium ubiquitously ameliorated the depressive-like behaviors. We cautiously deduce that aberrant autophagy and/or elevated ROS levels are not involved in predisposition to the depressive phase of bipolar-like behavior. Rather, that amending the depressive-like characteristics requires different mitochondria-related interventions. The latter might be antagonizing N-methyl-D-aspartate receptors (NMDARs), thus protecting from disruption of mitochondrial calcium homeostasis and its detrimental consequences. In conclusion, our findings suggest that by-and-large, among the autophagy-enhancers and ROS-scavengers tested, lithium is the most effective in counteracting rotenone-induced changes. Trehalose and N-acetylcystein may also be effective in attenuating manic-like behavior.

Exploring the Evidence Implicating the Renin-Angiotensin System (RAS) in the Physiopathology of Mood Disorders

Mood disorders include Major Depressive Disorder (MDD), Bipolar Disorder (BD) and variations of both. Mood disorders has a public health significance with high comorbidity, suicidal mortality and economic burden on the health system. Research related to mood disorders has evolved over the years to relate it with systemic conditions. The Renin Angiotensin System (RAS) has been noticed to play major physiological roles beyond renal and cardiovascular systems. Recent studies have linked RAS not only with neuro-immunological processes, but also with psychiatric conditions like mood and anxiety disorders. In this comprehensive review, we integrated basic and clinical studies showing the associations between RAS and mood disorders. Animal studies on mood disorders models - either depression or mania - were focused on the reversal of behavioral and/or cognitive symptoms through the inhibition of RAS components like the Angiotensin- Converting Enzyme (ACE), Angiotensin II Type 1 receptor (AT1) or Mas receptors. ACE polymorphisms, namely insertion-deletion (I/D), were linked to mood disorders and suicidal behavior. Hypertension was associated with neurocognitive deficits in mood disorders, which reversed with RAS inhibition. Low levels of RAS components (renin activity or aldosterone) and mood symptoms improvement with ACE inhibitors or AT1 blockers were also observed in mood disorders. Overall, this review reiterates the strong and under-researched connection between RAS and mood disorders.

Exploring test batteries for depression- and anxiety-like behaviours in female and male ICR and black Swiss mice

Objective and rationale: Animal models are critical for the study of mental disorders and their treatments but are repeatedly criticized for problems with validity and reproducibility. One approach to enhance validity and reproducibility of models is to use test batteries rather than single tests. Yet, a question regarding batteries is whether one can expect a consistent individual behavioural phenotype in mice across tests that can be presumed to be part of the same construct. This study was designed to explore the relationship between the behaviours of mice across tests in some variations of test batteries for depression- and anxiety-like behaviours. Methods: Female and male healthy, intact, and untreated mice from the ICR and black Swiss strains were used in four separate experiments. With some variations, mice were exposed to a battery of behavioural tests representing affective- and anxiety-like behaviours. Data were analysed for differences between sexes and for correlations between behaviours within and across the tests in the battery. Results: No differences were found between the sexes. With very few exceptions, we found correlations within tests (when one test has more than one measure or is repeated) but not across different tests within the battery. Conclusions: The results cast some doubt on the utility of behavioural test batteries to represent different facets of emotional behaviour in healthy intact outbred mice, without any interventions or treatments. Additional studies are designed to explore whether stronger relationship between the tests will appear after manipulations or drug treatments.

Proposing the sweet solution preference test as a screening assay for anti-manic effects of mood stabilizers

BACKGROUND

There is a desperate need for in-vivo behavioral screening tests for anti-manic effects. The frequently used psychostimulant-induced hyperactivity test appears to have lower validity than previously described, but other quick, simple and high throughput tests are currently unavailable.

NEW METHOD

In the context of modeling the behavioral facets of mania, we previously suggested that the sweet solution preference test (SSP) in naive mice might have predictive validity for screening anti-manic effects. The current study further examined this proposal by testing the effects of lithium, valproate and imipramine on SSP in three strains of mice (male mice from the black Swiss, ICR and C57bl/6 strains) and an exploratory test in females (black Swiss strain).

RESULTS

Data demonstrate that lithium and valproate at appropriate dosing schedules significantly and reliably reduce SSP in all three strains (including in females) but that the antidepressant imipramine has no effects.

COMPARISON WITH EXISTING METHODS

The results support the utilization of the SSP as mice screening model for anti-manic effects of drugs with stronger predictive validity compared with other methods.

CONCLUSIONS

The SSP is not a comprehensive model for bipolar disorder but it has good predictive validity and strong practical value that can be applied towards simple and fast screening of large numbers of animals, without the need for specialized equipment or complicated/prolonged procedures. We therefore propose that the SSP is an advantageous screening assay for testing novel mood stabilizing drugs for anti-manic properties.

The neurobehavioral effects of the designer drug naphyrone - an experimental investigation with pharmacokinetics and concentration/effect relationship in mice

RATIONALE

The recreational use of naphyrone, a potent synthetic cathinone with a pyrovalerone structure, has raised questions about possible deleterious neurobehavioral consequences.

OBJECTIVE

To investigate naphyrone-induced neurobehavioral effects and alterations in brain monoamines using two patterns of abuse, i.e., single and repeated (binge) use.

METHODS

We studied naphyrone dose/induced locomotor activity relationship at 3, 10, 30, and 100 mg/kg in mice. We investigated the effects of single (30 mg/kg; acute injection) versus repeated (30 mg/kg ×3/day for 3 days; binge injection) intraperitoneal naphyrone administration on locomotor activity, anxiety-like behavior, spatial recognition memory, anhedonia, behavioral despair, and social interaction. We measured post-mortem prefrontal cortex levels of monoamines and modeled naphyrone pharmacokinetics and concentration/locomotor effect relationship.

RESULTS

Both naphyrone administration patterns induced time-dependent increases in locomotor activity (p < 0.001 and p < 0.0001, respectively) and social interaction (p < 0.05 and p < 0.001, respectively) but did not alter spatial recognition memory or anhedonia. Acute naphyrone injection induced anxiety-like behavior (p < 0.01) and reduced resignation (p < 0.01) whereas binge administration induced non-anxiety-like behavior (p < 0.05) and did not alter behavioral despair. Both patterns increased the prefrontal cortex dopamine (p < 0.0001) and norepinephrine (p < 0.05 and p < 0.01, respectively) but not serotonin content. Naphyrone pharmacokinetics followed a two-compartment model with an overall elimination half-life of 0.3 h. The naphyrone concentration/locomotor effect relationship was described by an additive E_max model with an EC₅₀ of 672 μg/L.

CONCLUSIONS

Single naphyrone administration increases locomotor activity according to a direct concentration/effect relationship. The neurobehavioral effects after binge differs from those after single administration and are not explained by drug accumulation given the relatively fast elimination.

Mania- and anxiety-like behavior and impaired maternal care in female diacylglycerol kinase eta and iota double knockout mice

Genome-wide association studies linked diacylglycerol kinase eta and iota to mood disorders, including bipolar disorder and schizophrenia, and both genes are expressed throughout the brain. Here, we generated and behaviorally characterized female mice lacking Dgkh alone, Dgki alone, and double Dgkh/Dgki-knockout (dKO) mice. We found that fewer than 30% of newborn pups raised by dKO females survived to weaning, while over 85% of pups survived to weaning when raised by wild-type (WT) females. Poor survival under the care of dKO mothers was unrelated to pup genotype. Moreover, pups from dKO dams survived when fostered by WT dams, suggesting the poor survival rate of dKO-raised litters was related to impaired maternal care by dKO dams. Nest building was similar between WT and dKO dams; however, some dKO females failed to retrieve any pups in a retrieval assay. Pups raised by dKO dams had smaller or absent milk spots and reduced weight, indicative of impaired nursing. Unlike WT females, postpartum dKO females showed erratic, panicked responses to cage disturbances. Virgin dKO females showed behavioral signs of anxiety and mania, which were not seen in mice lacking either Dgkh or Dgki alone. Our research indicates that combined deletion of Dgkh and Dgki impairs maternal behavior in the early postpartum period, and suggests female dKO mice model symptoms of mania and anxiety.

Neurobehavioral effects of lithium in the rat: Investigation of the effect/concentration relationships and the contribution of the poisoning pattern

Severity of lithium poisoning depends on the ingested dose, previous treatment duration and renal function. No animal study has investigated neurobehavioral differences in relation to the lithium poisoning pattern observed in humans, while differences in lithium pharmacokinetics have been reported in lithium-pretreated rats mimicking chronic poisonings with enhanced brain accumulation in rats with renal failure. Our objectives were: 1)-to investigate lithium-related effects in overdose on locomotor activity, anxiety-like behavior, spatial recognition memory and anhedonia in the rat; 2)-to model the relationships between lithium-induced effects on locomotion and plasma, erythrocyte, cerebrospinal fluid and brain concentrations previously obtained according to the poisoning pattern. Open-field, elevated plus-maze, Y-maze and sucrose consumption tests were used. In acutely lithium-poisoned rats, we observed horizontal (p<0.001) and vertical hypolocomotion (p<0.0001), increased anxiety-like behavior (p<0.05) and impaired memory (p<0.01) but no altered hedonic status. Horizontal (p<0.01) and vertical (p<0.001) hypolocomotion peaked more markedly 24h after lithium injection and was more prolonged in acute-on-chronically vs. acutely lithium-poisoned rats. Hypolocomotion in chronically lithium-poisoned rats with impaired renal function did not differ from acutely poisoned rats 24h after the last injection. Interestingly, hypolocomotion/concentration relationships best fitted a sigmoidal E_max model in acute poisoning and a linear regression model linked to brain lithium in acute-on-chronic poisoning. In conclusion, lithium overdose alters rat behavior and consistently induces hypolocomotion which is more marked and prolonged in repeatedly lithium-treated rats. Our data suggest that differences between poisoning patterns regarding lithium-induced hypolocomotion are better explained by the duration of lithium exposure than by its brain accumulation.

Unique Behavioral and Neurochemical Effects Induced by Repeated Adolescent Consumption of Caffeine-Mixed Alcohol in C57BL/6 Mice

The number of highly caffeinated products has increased dramatically in the past few years. Among these products, highly caffeinated energy drinks are the most heavily advertised and purchased, which has resulted in increased incidences of co-consumption of energy drinks with alcohol. Despite the growing number of adolescents and young adults reporting caffeine-mixed alcohol use, knowledge of the potential consequences associated with co-consumption has been limited to survey-based results and in-laboratory human behavioral testing. Here, we investigate the effect of repeated adolescent (post-natal days P35-61) exposure to caffeine-mixed alcohol in C57BL/6 mice on common drug-related behaviors such as locomotor sensitivity, drug reward and cross-sensitivity, and natural reward. To determine changes in neurological activity resulting from adolescent exposure, we monitored changes in expression of the transcription factor ΔFosB in the dopaminergic reward pathway as a sign of long-term increases in neuronal activity. Repeated adolescent exposure to caffeine-mixed alcohol exposure induced significant locomotor sensitization, desensitized cocaine conditioned place preference, decreased cocaine locomotor cross-sensitivity, and increased natural reward consumption. We also observed increased accumulation of ΔFosB in the nucleus accumbens following repeated adolescent caffeine-mixed alcohol exposure compared to alcohol or caffeine alone. Using our exposure model, we found that repeated exposure to caffeine-mixed alcohol during adolescence causes unique behavioral and neurochemical effects not observed in mice exposed to caffeine or alcohol alone. Based on similar findings for different substances of abuse, it is possible that repeated exposure to caffeine-mixed alcohol during adolescence could potentially alter or escalate future substance abuse as means to compensate for these behavioral and neurochemical alterations.

Predictive Validity of Some Common Animal Models of Bipolar Disorder Using Lithium and Lamotrigine Therapy: An Attempt towards a Battery-Based Approach for the Evaluation of Mood Stabilizers

OBJECTIVE

To determine the predictive validity of some of the commonly employed models of mania and depression using standard drugs i.e. lithium (70 mg/kg) and lamotrigine (5 mg/kg) in male Wistar rats.

METHODS

The depression facet of bipolar disorder was evaluated using forced swim test, tail suspension test, and chronic mild stress test. The models used to evaluate the mania facet of bipolar disorder were isolation-induced aggression test, saccharine preference test, and morphine-sensitized hyperlocomotion test.

RESULTS

The immobility time was significantly (p<0.05) reduced by lamotrigine in the tail suspension test and the forced swim test, while lithium caused significant (p<0.05) reduction only in the tail suspension test. Rats exposed to chronic mild stress showed the maximal increment of 1% sucrose consumption at the 3rd week of treatment in both the lithium (p<0.001) and lamotrigine (p<0.01) groups. In the isolation-induced aggression test, the aggressive behaviour of rats was significantly reduced by both lithium [approach (p<0.001), attack (p<0.01), and bite (p<0.01)] and lamotrigine [approach (p<0.001), and attack (p<0.05)]. Neither of the drugs were effective in the saccharine preference test. Only lithium was able to significantly (p<0.05) reduce the crossing parameter in morphine-sensitized rats.

CONCLUSION

Our study identifies the chronic mild stress test and isolation-induced aggression test of having the highest predictive validity in the depression and mania facets of bipolar disorder, respectively, and should be a part of a battery of tests used to evaluate novel mood stabilizers.

Toward a Valid Animal Model of Bipolar Disorder: How the Research Domain Criteria Help Bridge the Clinical-Basic Science Divide

Bipolar disorder is a diagnostically heterogeneous disorder, although mania emerges as a distinct phenotype characterized by elevated mood and increased activity or energy. While bipolar disorder's cyclicity is difficult to represent in animals, models of mania have begun to decode its fundamental underlying neurobiology. When psychostimulants such as amphetamine or cocaine are administered to rodents, a resulting upsurge of motor activity is thought to share face and predictive validity with mania in humans. Studying black Swiss mice, which inherently exhibit proclivity for reward seeking and risk taking, also has yielded some insight. Further, translating the biology of bipolar disorder in humans into animal models has led to greater understanding of roles for candidate biological systems such as the GRIK2 and CLOCK genes, as well as the extracellular signal-related kinase pathway involved in the pathophysiology of the illness. The National Institute of Mental Health Research Domain Criteria initiative seeks to identify building blocks of complex illnesses like bipolar disorder in hopes of uncovering the neurobiology of each, as well as how each fits together to produce syndromes like bipolar disorder or why so many mental illnesses co-occur together. Research Domain Criteria-driven preclinical models of isolated behaviors and domains involved in mania and bipolar disorder will ultimately inform movement toward nosology supported by neurobiology.

Chronic treatment with mood stabilizer lithium inhibits amphetamine-induced risk-taking manic-like behaviors

A lack of behavioral tests and animal models for manic-depressive bipolar disorder is recognized as an important factor limiting development of novel pharmaceutical treatments for the disorder. Repeated amphetamine-induced hyperactivity is a commonly used animal model for mania. However, hyperactivity represents only one facet of mania and is also seen in other disorders. Increased engagement in risk taking behavior is frequently observed in the manic phase of bipolar disorder. In the present study, we analyzed the effect of the most commonly used mood stabilizer lithium on repeated amphetamine treatment-induced risk-taking behaviors in rats using elevated plus maze and wire-beam bridge tests. We found that repeated amphetamine treatment not only increased locomotor activity, but also increased risk taking behaviors in rats, and further that chronic lithium treatment inhibited the amphetamine-increased risk taking behavior. Our studies suggest that these tests may be useful tools to analyze the pharmacological validity of new and improved anti-manic drugs in animals.

Effect of lithium on behavioral disinhibition induced by electrolytic lesion of the median raphe nucleus

RATIONALE

Alterations in brainstem circuits have been proposed as a possible mechanism underlying the etiology of mood disorders. Projections from the median raphe nucleus (MnR) modulate dopaminergic activity in the forebrain and are also part of a behavioral disinhibition/inhibition system that produces phenotypes resembling behavioral variations manifested during manic and depressive phases of bipolar disorder.

OBJECTIVE

The aim of this study is to assess the effect of chronic lithium treatment on behavioral disinhibition induced by MnR lesions.

METHODS

MnR electrolytic lesions were performed in C57BL/6J mice, with sham-operated and intact animals as control groups. Following recovery, mice were chronically treated with lithium (LiCl, added in chow) followed by behavioral testing.

RESULTS

MnR lesion induced manic-like behavioral alterations including hyperactivity in the open field (OF), stereotyped circling, anxiolytic/risk taking in the elevated plus maze (EPM) and light/dark box (LDB) tests, and increased basal body temperature. Lithium was specifically effective in reducing OF hyperactivity and stereotypy but did not reverse (EPM) or had a nonspecific effect (LDB) on anxiety/risk-taking measures. Additionally, lithium decreased saccharin preference and prevented weight loss during single housing.

CONCLUSIONS

Our data support electrolytic lesions of the MnR as an experimental model of a hyper-excitable/disinhibited phenotype consistent with some aspects of mania that are attenuated by the mood stabilizer lithium. Given lithium's relatively specific efficacy in treating mania, these data support the hypothesis that manic symptoms derive not only from the stimulation of excitatory systems but also from inactivation or decreased activity of inhibitory mechanisms.

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.

Inhibition of protein translation by the DISC1-Boymaw fusion gene from a Scottish family with major psychiatric disorders

The t(1; 11) translocation appears to be the causal genetic lesion with 70% penetrance for schizophrenia, major depression and other psychiatric disorders in a Scottish family. Molecular studies identified the disruption of the disrupted-in-schizophrenia 1 (DISC1) gene by chromosome translocation at chromosome 1q42. Our previous studies, however, revealed that the translocation also disrupted another gene, Boymaw (also termed DISC1FP1), on chromosome 11. After translocation, two fusion genes [the DISC1-Boymaw (DB7) and the Boymaw-DISC1 (BD13)] are generated between the DISC1 and Boymaw genes. In the present study, we report that expression of the DB7 fusion gene inhibits both intracellular NADH oxidoreductase activities and protein translation. We generated humanized DISC1-Boymaw mice with gene targeting to examine the in vivo functions of the fusion genes. Consistent with the in vitro studies on the DB7 fusion gene, protein translation activity is decreased in the hippocampus and in cultured primary neurons from the brains of the humanized mice. Expression of Gad67, Nmdar1 and Psd95 proteins are also reduced. The humanized mice display prolonged and increased responses to the NMDA receptor antagonist, ketamine, on various mouse genetic backgrounds. Abnormal information processing of acoustic startle and depressive-like behaviors are also observed. In addition, the humanized mice display abnormal erythropoiesis, which was reported to associate with depression in humans. Expression of the DB7 fusion gene may reduce protein translation to impair brain functions and thereby contribute to the pathogenesis of major psychiatric disorders.

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.

Diurnal rodents as an advantageous model for affective disorders: novel data from diurnal degu (Octodon degus)

Circadian rhythms are strongly associated with affective disorders and recent studies have suggested utilization of diurnal rodents as model animal for circadian rhythms-related domains of these disorders. Previous work with the diurnal fat sand rat and Nile grass rat demonstrated that short photoperiod conditions result in behavioral changes including anxiety- and depression-like behavior. The present study examined the effect of manipulating day length on activity rhythms and behavior of the diurnal degu. Animals were housed for 3 weeks under either a short photoperiod (5-h:19-h LD) or a neutral photoperiod (12-h:12-h LD) and then evaluated by sweet solution test and the forced swim test for depression-like behavior, and in the light/dark box and open field for anxiety-like behavior. Results indicate that short photoperiod induced depression-like behavior in the forced swim test and the sweet solution preference test and anxiety-like behavior in the open field compared with animals maintained in a neutral photoperiod. No effects were shown in the light/dark box. Short photoperiod-acclimated degu showed reduced total activity duration and activity was not restricted to the light phase. The present study further supports the utilization of diurnal rodents to model circadian rhythms-related affective change. Beyond the possible diversity in the mechanisms underlying diurnality in different animals, there are now evidences that in three different diurnal species, the fat sand rat, the grass Nile rat and the degu, shortening of photoperiod results in the appearance of anxiety- and depression-like behaviors.

Trehalose induced antidepressant-like effects and autophagy enhancement in mice

RATIONALE

The disaccharide trehalose protects cells from hypoxic and anoxic injury and suppresses protein aggregation. In vivo studies with trehalose show cellular and behavioral beneficial effects in animal models of neurodegenerative diseases. Moreover, trehalose was shown to enhance autophagy, a process that had been recently suggested to be involved in the therapeutic action of antidepressant and mood-stabilizing drugs.

OBJECTIVE

The present study was therefore designed to explore antidepressant and mood-stabilizing activity of trehalose in animal models for depression and mania.

METHODS

Trehalose 1 or 2% was administered for 3 weeks as a drinking solution to Black Swiss mice (a model of manic-like behaviors) or 2% to ICR mice and their behavior evaluated in a number of tests related to depression or mania. The effects of trehalose were compared with similar chronic administration of the disaccharide maltose as well as with a vehicle (water) control.

RESULTS

Chronic administration of trehalose resulted in a reduction of frontal cortex p62/beclin-1 ratio suggesting enhancement of autophagy. Trehalose had no mood-stabilizing effects on manic-like behavior in Black Swiss mice but instead augmented amphetamine-induced hyperactivity, an effect similar to antidepressant drugs. In ICR mice, trehalose did not alter spontaneous activity or amphetamine-induced hyperactivity but in two separate experiments had a significant effect to reduce immobility in the forced swim test, a standard screening test for antidepressant-like effects.

CONCLUSIONS

The results suggest that trehalose may have antidepressant-like properties. It is hypothesized that these behavioral changes could be related to trehalose effects to enhance autophagy.

Further evidence for ClockΔ19 mice as a model for bipolar disorder mania using cross-species tests of exploration and sensorimotor gating

Bipolar disorder (BD) is a pervasive neuropsychiatric disorder characterized by episodes of mania and depression. The switch between mania and depression may reflect seasonal changes and certainly can be affected by alterations in sleep and circadian control. The circadian locomotor output cycles kaput (CLOCK) protein is a key component of the cellular circadian clock. Mutation of the Clock gene encoding this protein in ClockΔ19 mutant mice leads to behavioral abnormalities reminiscent of BD mania. To date, however, these mice have not been assessed in behavioral paradigms that have cross-species translational validity. In the present studies of ClockΔ19 and wildtype (WT) littermate mice, we quantified exploratory behavior and sensorimotor gating, which are abnormal in BD manic patients. We also examined the saccharin preference of these mice and their circadian control in different photoperiods. ClockΔ19 mice exhibited behavioral alterations that are consistent with BD manic patients tested in comparable tasks, including hyperactivity, increased specific exploration, and reduced sensorimotor gating. Moreover, compared to WT mice, ClockΔ19 mice exhibited a greater preference for sweetened solutions and greater sensitivity to altered photoperiod. In contrast with BD manic patients however, ClockΔ19 mice exhibited more circumscribed movements during exploration. Future studies will extend the characterization of these mice in measures with cross-species translational relevance to human testing.

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.

Differential effects of dopamine transporter inhibitors in the rodent Iowa gambling task: relevance to mania

RATIONALE

The Iowa Gambling Task (IGT) can be used to quantify impulsive and risky choice behaviors in psychiatric patients, e.g., bipolar disorder (BD) sufferers. Although developing treatments for these behaviors is important, few predictive animal models exist. Inhibition of the dopamine transporter (DAT) can model profiles of altered motor activity and exploration seen in patients with BD. The effect of DAT inhibition on impulsive choices related to BD has received limited study however. We used a rodent IGT to elucidate the effects of similarly acting drugs on risky choice behavior.

OBJECTIVES

We hypothesized that (1) C57BL/6 mice could adopt the "safe" choice options in the IGT and (2) DAT inhibition would alter risk preference.

METHODS

Mice were trained in the IGT to a stable risk-preference and then administered the norepinephrine/DAT inhibitor amphetamine, or the more selective DAT inhibitors modafinil or GBR12909.

RESULTS

Mice developed a preference for the "safe" option, which was potentiated by amphetamine administration. GBR12909 or modafinil administration increased motor impulsivity, motivation significantly, and risk preference subtly.

CONCLUSIONS

The rodent IGT can measure different impulse-related behaviors and differentiate similarly acting BD-related drugs. The contrasting effects of amphetamine and modafinil in mice are similar to effects in rats and humans in corresponding IGT tasks, supporting the translational validity of the task. GBR12909 and modafinil elicited similar behaviors in the IGT, likely through a shared mechanism. Future studies using a within-session IGT are warranted to confirm the suitability of DAT inhibitors to model risk-preference in BD.

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.

Evidence for antimanic efficacy of glycogen synthase kinase-3 (GSK3) inhibitors in a strain-specific model of acute mania

There is a growing body of evidence suggesting that animal models can be developed to probe the specific domains of bipolar disorder (BD) using the endophenotype approach. Here we tested clinically active antimanic drugs to validate amphetamine-induced hyperactivity in Black Swiss mice as a putative model of the manic phase of BD. We also co-administered a mood stabilizer and an atypical antipsychotic drug in a manner akin to the clinical treatment regimens. Since lithium has been shown to potentially act through glycogen synthase kinase-3 (GSK3) inhibition, we evaluated the efficacy of selective GSK3 inhibitors in this model. Habituated animals were pretreated with a compound of interest before being challenged with amphetamine (2.0 mg/kg) and returned to activity cages for an additional 1.5 h. We tested lithium, sodium valproate, carbamazepine, olanzapine, ziprasidone as well as co-administered lithium and olanzapine at sub-efficacious doses. The GSK3 inhibitors tested included indirubin, alsterpaullone, TDZD-8, AR-A014418, SB-216763, and SB-627772. All mood stabilizers and antipsychotic drugs reduced hyperactivity without affecting spontaneous locomotion. While subactive doses of lithium and olanzapine were without effect, their co-administration produced robust reductions in hyperactivity. All GSK3 inhibitors were active in the model, producing selective inhibition of rearing hyperactivity. These data support the predictive validity of the model for the acute manic phase of BD and may have utility as an in-vivo model for identifying novel antimanic therapeutics.

Glycogen synthase kinase-3 in the etiology and treatment of mood disorders

The mood disorders major depressive disorder and bipolar disorder are prevalent, are inadequately treated, and little is known about their etiologies. A better understanding of the causes of mood disorders would benefit from improved animal models of mood disorders, which now rely on behavioral measurements. This review considers the limitations in relating measures of rodent behaviors to mood disorders, and the evidence from behavioral assessments indicating that glycogen synthase kinase-3 (GSK3) dysregulation promotes mood disorders and is a potential target for treating mood disorders. The classical mood stabilizer lithium was identified by studying animal behaviors and later was discovered to be an inhibitor of GSK3. Several mood-relevant behavioral effects of lithium in rodents have been identified, and most have now been shown to be due to its inhibition of GSK3. An extensive variety of pharmacological and molecular approaches for manipulating GSK3 are discussed, the results of which strongly support the proposal that inhibition of GSK3 reduces both depression-like and manic-like behaviors. Studies in human postmortem brain and peripheral cells also have identified correlations between alterations in GSK3 and mood disorders. Evidence is reviewed that depression may be associated with impaired inhibitory control of GSK3, and mania by hyper-stimulation of GSK3. Taken together, these studies provide substantial support for the hypothesis that inhibition of GSK3 activity is therapeutic for mood disorders. Future research should identify the causes of dysregulated GSK3 in mood disorders and the actions of GSK3 that contribute to these diseases.

Antidepressants reverse short-photoperiod-induced, forced swim test depression-like behavior in the diurnal fat sand rat: further support for the utilization of diurnal rodents for modeling affective disorders

Recent findings demonstrate strong links between abnormalities in circadian rhythms and sleep and the etiology, pathophysiology and treatment of major affective disorders. Further exploration of these interactions requires the development, identification and utilization of good and predictive animal models. The biology and behavior related to circadian rhythms are significantly different in diurnal and nocturnal rodents. Accordingly, it is possible that exploring the interactions between these mechanisms and affective change in diurnal animals may be advantageous. Recent studies demonstrate that diurnal fat sand rats and Nile grass rats show depression-like behavior when maintained under short-photoperiod (SP) conditions compared with animals maintained under neutral photoperiod (NP) conditions. Moreover, these behaviors were ameliorated after treatment with bright light. The present study further explores the possible utility of sand rats as animal models by testing the effects of antidepressants on the SP-induced depression-like behaviors of sand rats. Sand rats maintained in SP or NP conditions for 3 weeks were treated subchronically (5 injections) with the clinically effective antidepressant bupropion, and their behavior was tested in a number of depression-related tests. Results show that antidepressant treatment reverses the effects of SP conditions in the forced swim test, but that neither SP conditions nor antidepressants influenced sweet solution preference. These results partly support the validity of the sand rat model, but suggest that not all tests that were validated in nocturnal laboratory rodents can be applied to other rodent species and that additional tests should be applied to further explore the validity of the model.

Modeling mania: Further validation for Black Swiss mice as model animals

The paucity of appropriate animal models for bipolar disorder hinders the research of the disorder and its treatments. Previous work suggests that Black Swiss (BS) mice may be a suitable model animal for behavioral domains of mania including reward-seeking, risk-taking, vigor, aggression and sensitivity to psychostimulants. These behaviors are high in BS mice compared with other strains and are responsive to the mood stabilizers lithium and valproate but not to the antidepressant imipramine. The current study evaluated the etiological validity of this model by assessing brain expression of two proteins implicated in affective disorders, β-catenin and BDNF, in BS mice versus C57bl/6, A/J and CBA/J mice. Additionally, pharmacological validity was further tested by assessing the effects of risperidone in a behavioral battery of tests. β-catenin and BDNF expression were evaluated in the frontal cortex and hippocampus of untreated BS, CBA/J, A/J and C57bl/6 mice by western blot. Subchronic 0.1 and 0.3mg/kg doses of risperidone were tested in a battery of behavioral tests for domains of mania. Expression of β-catenin was found to be lower in the hippocampus of BS mice compared with the other strains. Reduced β-catenin expression was not observed in the frontal cortex. BDNF expression levels were similar between strains in both the hippocampus and frontal cortex. In the behavioral tests, risperidone ameliorated amphetamine-induced hyperactivity without affecting other tests in the battery. These results offer additional pharmacological and possible etiological validity supporting the utilization of Black Swiss mice as a model for domains of mania.

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 female urine sniffing test: a novel approach for assessing reward-seeking behavior in rodents

BACKGROUND

Abnormal hedonic behavior is a key feature of many psychiatric disorders. Several paradigms measure reward-seeking behavior in rodents, but each has limitations. We describe a novel approach for monitoring reward-seeking behavior in rodents: sniffing of estrus female urine by male mice, along with number of ultrasonic vocalizations (USVs) emitted during the test.

METHODS

The female urine sniffing test (FUST) was designed to monitor reward-seeking activity in rodents together with tests of helplessness and sweet solution preference. USVs and dopamine release from the nucleus accumbens (NAc) were recorded. Sniffing activity was measured in 1) manipulation-naive C57BL/6J and 129S1/SVImJ mice and Wistar-Kyoto rats; 2) stressed mice; 3) two groups of mice that underwent the learned helplessness paradigm-one untreated, and one treated with the SSRI citalopram; and 4) GluR6 knockout mice, known to display lithium-responsive, mania-related behaviors.

RESULTS

Males from all three strains spent significantly longer sniffing female urine than sniffing water. Males emitted USVs and showed significantly elevated NAc dopamine levels while sniffing urine. Foot-shock stress significantly reduced female urine sniffing time. Compared with mice that did not undergo the LH paradigm, LH males spent less time sniffing female urine, and citalopram treatment alleviated this reduction. Compared with their wildtype littermates, GluR6KO males sniffed female urine longer and showed enhanced saccharin preference.

CONCLUSIONS

In rodents, sniffing female urine is a preferred activity accompanied by biological changes previously linked to reward-seeking activities. The FUST is sensitive to behavioral and genetic manipulation and to relevant drug treatment.

Strain-specific battery of tests for domains of mania: effects of valproate, lithium and imipramine

The lack of efficient animal models for bipolar disorder (BPD), especially for the manic pole, is a major factor hindering the research of its pathophysiology and the development of improved drug treatments. The present study was designed to identify an appropriate mouse strain for modeling some behavioral domains of mania and to evaluate the effects of drugs using this strain. The study compared the behavior of four strains: Black Swiss, C57Bl/6, CBA/J and A/J mice in a battery of tests that included spontaneous activity; sweet solution preference; light/dark box; resident-intruder; forced-swim and amphetamine-induced hyperactivity. Based on the 'manic-like' behavior demonstrated by the Black Swiss strain, the study evaluated the effects of the mood stabilizers valproate and lithium and of the antidepressant imipramine in the same tests using this strain. Results indicated that lithium and valproate attenuate the 'manic-like' behavior of Black Swiss mice whereas imipramine had no effects. These findings suggest that Black Swiss mice might be a good choice for modeling several domains of mania and distinguishing the effects of drugs on these specific domains. However, the relevance of the behavioral phenotype of Black Swiss mice to the biology of BPD is unknown at this time and future studies will investigate molecular differences between Black Swiss mice and other strains and asess the interaction between strain and mood stabilizing treatment.

It is darkness and not light: Depression-like behaviors of diurnal unstriped Nile grass rats maintained under a short photoperiod schedule

Circadian rhythms are strongly implicated in affective disorders and some recent studies suggested that diurnal rodents might be advantageous model animals for them. In line with this possibility, previous work demonstrated that in the diurnal fat sand rat, short photoperiod conditions result in depression- and anxiety-like behavioral phenotype that is relieved with bright light treatment. To further explore the possibility of using diurnal species as model animals for affective disorders, the present study examined the effects of short photoperiod schedule in an additional diurnal rodent, the unstriped Nile grass rat. Results indicate that 6 weeks short photoperiod (5 h light/19 h dark) regimen induced depression-like behavior in the forced swim test and the saccharin preference test compared with animals maintained in a neutral photoperiod regimen (12 h light/12 h dark). No effects were shown in the light/dark box model of anxiety or in a test for spontaneous activity. These results demonstrate that photoperiod manipulations in diurnal rodents induce affective-like behavioral change and support the possibility that diurnal rodents might provide a good potential as model animals for depression spectrum disorders.