Animal models for bipolar disorder: from bedside to the cage

MicroRNAs as potential diagnostic biomarkers for bipolar disorder

Abnormal expression of microRNAs is connected to brain development and disease and could provide novel biomarkers for the diagnosis and prognosis of bipolar disorder. We performed a PubMed search for microRNA biomarkers in bipolar disorder and found 18 original research articles on studies performed with human patients and published from January 2011 to June 2023. These studies included microRNA profiling in blood- and brain-based materials. From the studies that had validated the preliminary findings, potential candidate biomarkers for bipolar disorder in adults could be miR-140-3p, -30d-5p, -330-5p, -378a-5p, -21-3p, -330-3p, -345-5p in whole blood, miR-19b-3p, -1180-3p, -125a-5p, let-7e-5p in blood plasma, and miR-7-5p, -23b-5p, -142-3p, -221-5p, -370-3p in the blood serum. Two of the studies had investigated the changes in microRNA expression of patients with bipolar disorder receiving treatment. One showed a significant increase in plasma miR-134 compared to baseline after 4 weeks of treatment which included typical antipsychotics, atypical antipsychotics, and benzodiazepines. The other study had assessed the effects of prescribed medications which included neurotransmitter receptor-site binders (drug class B) and sedatives, hypnotics, anticonvulsants, and analgesics (drug class C) on microRNA results. The combined effects of the two drug classes increased the significance of the results for miR-219 and -29c with miR-30e-3p and -526b* acquiring significance. MicroRNAs were tested to see if they could serve as biomarkers of bipolar disorder at different clinical states of mania, depression, and euthymia. One study showed that upregulation in whole blood of miR-9-5p, -29a-3p, -106a-5p, -106b-5p, -107, -125a-3p, -125b-5p and of miR-107, -125a-3p occurred in manic and euthymic patients compared to controls, respectively, and that upregulation of miR-106a-5p, -107 was found for manic compared to euthymic patients. In two other studies using blood plasma, downregulation of miR-134 was observed in manic patients compared to controls, and dysregulation of miR-134, -152, -607, -633, -652, -155 occurred in euthymic patients compared to controls. Finally, microRNAs such as miR-34a, -34b, -34c, -137, and -140-3p, -21-3p, -30d-5p, -330-5p, -378a-5p, -134, -19b-3p were shown to have diagnostic potential in distinguishing bipolar disorder patients from schizophrenia or major depressive disorder patients, respectively. Further studies are warranted with adolescents and young adults having bipolar disorder and consideration should be given to using animal models of the disorder to investigate the effects of suppressing or overexpressing specific microRNAs.

The Balance in the Head: How Developmental Factors Explain Relationships Between Brain Asymmetries and Mental Diseases

Cerebral lateralisation is a core organising principle of the brain that is characterised by a complex pattern of hemispheric specialisations and interhemispheric interactions. In various mental disorders, functional and/or structural hemispheric asymmetries are changed compared to healthy controls, and these alterations may contribute to the primary symptoms and cognitive impairments of a specific disorder. Since multiple genetic and epigenetic factors influence both the pathogenesis of mental illness and the development of brain asymmetries, it is likely that the neural developmental pathways overlap or are even causally intertwined, although the timing, magnitude, and direction of interactions may vary depending on the specific disorder. However, the underlying developmental steps and neuronal mechanisms are still unclear. In this review article, we briefly summarise what we know about structural, functional, and developmental relationships and outline hypothetical connections, which could be investigated in appropriate animal models. Altered cerebral asymmetries may causally contribute to the development of the structural and/or functional features of a disorder, as neural mechanisms that trigger neuropathogenesis are embedded in the asymmetrical organisation of the developing brain. Therefore, the occurrence and severity of impairments in neural processing and cognition probably cannot be understood independently of the development of the lateralised organisation of intra- and interhemispheric neuronal networks. Conversely, impaired cellular processes can also hinder favourable asymmetry development and lead to cognitive deficits in particular.

Plausible therapeutic effects of melatonin and analogs in the dopamine-associated pathophysiology of bipolar disorder

Bipolar disorder (BD) is a significant neuropsychiatric condition characterized by marked psychological mood disturbances. Despite extensive research on the symptomatology of BD, the mechanisms underlying its development and presentation remain unknown. Consequently, potential treatments are limited, and existing medications often cause significant side effects, leading to treatment discontinuation. Dopamine (DA) has been implicated in behavioral regulation, reward systems, and mood, highlighting the importance of the dopaminergic system in BD. Elevated levels of DA and tyrosine hydroxylase are associated with the onset of manic episodes, whereas reduced levels are linked to the depressive phase. Additionally, endogenous melatonin (MEL) levels are considerably lower in patients with BD. When administered as a treatment, exogenous MEL and MEL agonists improve behavioral characteristics and significantly modulate DA-related pathophysiological pathways in BD, with minimal adverse effects achieved through MEL receptor activation. Moreover, MEL and MEL agonists offer neuroprotection by promoting physiological homeostasis during disruption. The aim of this review is to investigate and propose MEL receptors as potential novel therapeutic targets for BD. This review seeks to analyze the role of MEL and its agonists in modulating dopamine-related pathophysiological pathways, improving behavioral outcomes, and providing neuroprotection with minimal side effects.

The involvement of the microbiota-gut-brain axis in the pathophysiology of mood disorders and therapeutic implications

INTRODUCTION

There is a growing body of evidence implicating gut-brain axis dysfunction in the pathophysiology of mood disorders. Accordingly, gut microbiota has become a promising target for the development of biomarkers and novel therapeutics for bipolar and depressive disorders.

AREAS COVERED

We describe the observed changes in the gut microbiota of patients with mood disorders and discuss the available studies assessing microbiota-based strategies for their treatment.

EXPERT OPINION

Microbiota-targeted interventions, such as symbiotics, prebiotics, paraprobiotics, and fecal microbiota transplants seem to attenuate the severity of depressive symptoms. The available results must be seen as preliminary and need to be replicated and/or confirmed in larger and independent studies, also considering the pathophysiological and clinical heterogeneity of mood disorders.

Animal models of neuropsychiatric systemic lupus erythematosus: deciphering the complexity and guiding therapeutic development

Systemic lupus erythematosus (SLE) poses formidable challenges due to its multifaceted etiology while impacting multiple tissues and organs and displaying diverse clinical manifestations. Genetic and environmental factors contribute to SLE complexity, with relatively limited approved therapeutic options. Murine models offer insights into SLE pathogenesis but do not always replicate the nuances of human disease. This review critically evaluates spontaneous and induced animal models, emphasizing their validity and relevance to neuropsychiatric SLE (NPSLE). While these models undoubtedly contribute to understanding disease pathophysiology, discrepancies persist in mimicking some NPSLE intricacies. The lack of literature addressing this issue impedes therapeutic progress. We underscore the urgent need for refining models that truly reflect NPSLE complexities to enhance translational fidelity. We encourage a comprehensive, creative translational approach for targeted SLE interventions, balancing scientific progress with ethical considerations to eventually improve the management of NPSLE patients. A thorough grasp of these issues informs researchers in designing experiments, interpreting results, and exploring alternatives to advance NPSLE research.

A Selective Nuclear Factor-κB Inhibitor, JSH-23, Exhibits Antidepressant-like Effects and Reduces Brain Inflammation in Rats

BACKGROUND

Accumulating evidence suggests that nuclear factor (NF)-κB is involved in the pathophysiology of mood disorders.

OBJECTIVES AND METHODS

We conducted two experimental protocols in rats to investigate the effects of a selective NF-κB inhibitor (JSH-23) on (i) lipopolysaccharide (LPS)-induced inflammation and (ii) on behavioral phenotypes in rat models of depression (sucrose consumption test and forced swim test) and mania (amphetamine-induced hyperactivity test). Additionally, we tested the effects of JSH-23 on levels of inflammatory components (interleukin-6, prostaglandin E2, nuclear phospho-p65, and tumor necrosis factor-α) in the brain.

RESULTS

Acute treatment with JSH-23 (10 mg/kg, intraperitoneally [ip]) led to potent anti-inflammatory effects in LPS-treated rats, including a diminished hypothermic response to LPS and a reduction in pro-inflammatory mediators' levels in the brain. Chronic treatment with JSH-23 (3 mg/kg, ip, once daily, for 14 days) resulted in robust antidepressant-like effects (increased sucrose consumption and decreased immobility time). The antidepressant-like effects of JSH-23 were mostly accompanied by a reduction in levels of pro-inflammatory mediators in the brain. On the other hand, JSH-23 did not reduce amphetamine-induced hyperactivity.

CONCLUSIONS

Altogether, these data suggest that NF-κB may be a potential therapeutic target for pharmacological interventions for depression.

Transitional photoperiod induces a mania-like behavior in male mice

This study aimed to investigate the behavioral responses and circadian rhythms of mice to both rapid and gradual increases in photoperiod, mimicking the transition from winter to summer, which is associated with a heightened prevalence of hospitalizations for mania and suicidal behavior. Behavioral tests were performed in C57BL/6 male mice exposed to a transitional photoperiod, from short to long durations. To determine if circadian rhythms are affected, we measured spontaneous locomotor activity and body temperature. Mice exhibited heightened exploratory and risk-taking behaviors compared with equatorial and static long (16:8 h of light-dark cycle for several days) groups. These behaviors were prevented by lithium. Spontaneous locomotor activity and body temperature rhythms persisted and were effectively synchronized; however, the relative amplitude of activity and interdaily stability were diminished. Additionally, the animals displayed increased activity during the light phase. Photoperiodic transition modulates behavior and circadian rhythms, mirroring certain features observed in bipolar disorder patients. This study introduces an animal model for investigating mania-like behavior induced by photoperiodic changes, offering potential insights for suicide prevention strategies and the management of mood disorders.

The emerging neuroimmune hypothesis of bipolar disorder: An updated overview of neuroimmune and microglial findings

Bipolar disorder (BD) is a severe and multifactorial disease, with onset usually in young adulthood, which follows a progressive course throughout life. Replicated epidemiological studies have suggested inflammatory mechanisms and neuroimmune risk factors as primary contributors to the onset and development of BD. While not all patients display overt markers of inflammation, significant evidence suggests that aberrant immune signaling contributes to all stages of the disease and seems to be mood phase dependent, likely explaining the heterogeneity of findings observed in this population. As the brain's immune cells, microglia orchestrate the brain's immune response and play a critical role in maintaining the brain's health across the lifespan. Microglia are also highly sensitive to environmental changes and respond to physiological and pathological events by adapting their functions, structure, and molecular expression. Recently, it has been highlighted that instead of a single population of cells, microglia comprise a heterogeneous community with specialized states adjusted according to the local molecular cues and intercellular interactions. Early evidence has highlighted the contribution of microglia to BD neuropathology, notably for severe outcomes, such as suicidality. However, the roles and diversity of microglial states in this disease are still largely undermined. This review brings an updated overview of current literature on the contribution of neuroimmune risk factors for the onset and progression of BD, the most prominent neuroimmune abnormalities (including biomarker, neuroimaging, ex vivo studies) and the most recent findings of microglial involvement in BD neuropathology. Combining these different shreds of evidence, we aim to propose a unifying hypothesis for BD pathophysiology centered on neuroimmune abnormalities and microglia. Also, we highlight the urgent need to apply novel multi-system biology approaches to characterize the diversity of microglial states and functions involved in this enigmatic disorder, which can open bright perspectives for novel biomarkers and therapeutic discoveries.

Crocin (bioactive compound of Crocus sativus L.) potently restores REM sleep deprivation-induced manic- and obsessive-compulsive-like behaviors in female rats

Rapid-eye movement (REM) sleep deprivation (SD) can induce manic-like behaviors including hyperlocomotion. On the other hand, crocin (one of the main compounds of Crocus sativus L. or Saffron) may be beneficial in the improvement of mental and cognitive dysfunctions. Also, crocin can restore the deleterious effects of SD on mental and cognitive processes. In this study, we investigated the effect of REM SD on female rats' behaviors including depression- and anxiety-like behaviors, locomotion, pain perception, and obsessive-compulsive-like behavior, and also, the potential effect of crocin on REM SD effects. We used female rats because evidence on the role of REM SD in modulating psychological and behavioral functions of female (but not male) rats is limited. REM SD was induced for 14 days (6h/day), and crocin (25, 50, and 75 mg/kg) was injected intraperitoneally. Open field test, forced swim test, hot plate test, and marble burying test were used to assess rats' behaviors. The results showed REM SD-induced manic-like behavior (hyperlocomotion). Also, REM SD rats showed decreased anxiety- and depression-like behavior, pain subthreshold (the duration it takes for the rat to feel pain), and showed obsessive compulsive-like behavior. However, crocin at all doses partially or fully reversed REM SD-induced behavioral changes. In conclusion, our results suggested the possible comorbidity of OCD and REM SD-induced manic-like behavior in female rats or the potential role of REM SD in the etiology of OCD, although more studies are needed. In contrast, crocin can be a possible therapeutic choice for decreasing manic-like behaviors.

Mice with deficiency in Pcdh15, a gene associated with bipolar disorders, exhibit significantly elevated diurnal amplitudes of locomotion and body temperature

Genetic factors significantly affect the pathogenesis of psychiatric disorders. However, the specific pathogenic mechanisms underlying these effects are not fully understood. Recent extensive genomic studies have implicated the protocadherin-related 15 (PCDH15) gene in the onset of psychiatric disorders, such as bipolar disorder (BD). To further investigate the pathogenesis of these psychiatric disorders, we developed a mouse model lacking Pcdh15. Notably, although PCDH15 is primarily identified as the causative gene of Usher syndrome, which presents with visual and auditory impairments, our mice with Pcdh15 homozygous deletion (Pcdh15-null) did not exhibit observable structural abnormalities in either the retina or the inner ear. The Pcdh15-null mice showed very high levels of spontaneous motor activity which was too disturbed to perform standard behavioral testing. However, the Pcdh15 heterozygous deletion mice (Pcdh15-het) exhibited enhanced spontaneous locomotor activity, reduced prepulse inhibition, and diminished cliff avoidance behavior. These observations agreed with the symptoms observed in patients with various psychiatric disorders and several mouse models of psychiatric diseases. Specifically, the hyperactivity may mirror the manic episodes in BD. To obtain a more physiological, long-term quantification of the hyperactive phenotype, we implanted nano tag® sensor chips in the animals, to enable the continuous monitoring of both activity and body temperature. During the light-off period, Pcdh15-null exhibited elevated activity and body temperature compared with wild-type (WT) mice. However, we observed a decreased body temperature during the light-on period. Comprehensive brain activity was visualized using c-Fos mapping, which was assessed during the activity and temperature peak and trough. There was a stark contrast between the distribution of c-Fos expression in Pcdh15-null and WT brains during both the light-on and light-off periods. These results provide valuable insights into the neural basis of the behavioral and thermal characteristics of Pcdh15-deletion mice. Therefore, Pcdh15-deletion mice can be a novel model for BD with mania and other psychiatric disorders, with a strong genetic component that satisfies both construct and surface validity.

Targeting inflammasome complexes as a novel therapeutic strategy for mood disorders

INTRODUCTION

Inflammasome complexes, especially NLRP3, have gained great attention as a potential therapeutic target in mood disorders. NLRP3 triggers a caspase 1-dependent release of the inflammatory cytokines IL-1β and IL-18, and seems to interact with purinergic and kynurenine pathways, all of which are implicated in mood disorders development and progression.

AREAS COVERED

Emerging evidence supports NLRP3 inflammasome as a promising pharmacological target for mood disorders. We discussed the available evidence from animal models and human studies and provided a reflection on drawbacks and perspectives for this novel target.

EXPERT OPINION

Several studies have supported the involvement of NLRP3 inflammasome in MDD. However, most of the evidence comes from animal models. The role of NLRP3 inflammasome in BD as well as its anti-manic properties is not very clear and requires further exploration. There is evidence of anti-manic effects of P2×R7 antagonists associated with reduction in the brain levels of IL-1β and TNF-α in a murine model of mania. The involvement of other NLRP3 inflammasome expressing cells besides microglia, like astrocytes, and of other inflammasome complexes in mood disorders also deserves further investigation. Preclinical and clinical characterization of NLRP3 and other inflammasomes in mood disorders is needed before considering translational approaches, including clinical trials.

Dopamine pathways mediating affective state transitions after sleep loss

The pathophysiology of affective disorders-particularly circuit-level mechanisms underlying bidirectional, periodic affective state transitions-remains poorly understood. In patients, disruptions of sleep and circadian rhythm can trigger transitions to manic episodes, whereas depressive states are reversed. Here, we introduce a hybrid automated sleep deprivation platform to induce transitions of affective states in mice. Acute sleep loss causes mixed behavioral states, featuring hyperactivity, elevated social and sexual behaviors, and diminished depressive-like behaviors, where transitions depend on dopamine (DA). Using DA sensor photometry and projection-targeted chemogenetics, we reveal that elevated DA release in specific brain regions mediates distinct behavioral changes in affective state transitions. Acute sleep loss induces DA-dependent enhancement in dendritic spine density and uncaging-evoked dendritic spinogenesis in the medial prefrontal cortex, whereas optically mediated disassembly of enhanced plasticity reverses the antidepressant effects of sleep deprivation on learned helplessness. These findings demonstrate that brain-wide dopaminergic pathways control sleep-loss-induced polymodal affective state transitions.

The engagement of autophagy in maniac disease

AIMS

Mania is a prevalent psychiatric disorder with undefined pathological mechanism. Here, we reviewed current knowledge indicating the potential involvement of autophagy dysregulation in mania and further discussed whether targeting autophagy could be a promising strategy for mania therapy.

DISCUSSIONS

Accumulating evidence indicated the involvement of autophagy in the pathology of mania. One of the most well-accepted mechanisms underlying mania, circadian dysregulation, showed mutual interaction with autophagy dysfunction. In addition, several first-line drugs for mania therapy were found to regulate neuronal autophagy. Besides, deficiencies in mitochondrial quality control, neurotransmission, and ion channel, which showed causal links to mania, were intimately associated with autophagy dysfunction.

CONCLUSIONS

Although more efforts should be made to either identify the key pathology of mania, the current evidence supported that autophagy dysregulation may act as a possible mechanism involved in the onset of mania-like symptoms. It is therefore a potential strategy to treat manic disorder by correting autophagy.

Rodent models for mood disorders - understanding molecular changes by investigating social behavior

Mood disorders, including depressive and bipolar disorders, are the group of psychiatric disorders with the highest prevalence and disease burden. However, their pathophysiology remains poorly understood. Animal models are an extremely useful tool for the investigation of molecular mechanisms underlying these disorders. For psychiatric symptom assessment in animals, a meaningful behavioral phenotype is needed. Social behaviors constitute naturally occurring complex behaviors in rodents and can therefore serve as such a phenotype, contributing to insights into disorder related molecular changes. In this narrative review, we give a fundamental overview of social behaviors in laboratory rodents, as well as their underlying neuronal mechanisms and their assessment. Relevant behavioral and molecular changes in models for mood disorders are presented and an outlook on promising future directions is given.

Ketogenic diet for mood disorders from animal models to clinical application

Mood disorders such as major depressive disorder (MDD) and bipolar disorder (BD) are often resistant to current pharmacological treatment. Therefore, various alternative therapeutic approaches including diets are, therefore, under investigation. Ketogenic diet (KD) is effective for treatment-resistant epilepsy and metabolic diseases, however, only a few clinical studies suggest its beneficial effect also for mental disorders. Animal models are a useful tool to uncover the underlying mechanisms of therapeutic effects. Women have a twice-higher prevalence of mood disorders but very little is known about sex differences in nutritional psychiatry. In this review, we aim to summarize current knowledge of the sex-specific effects of KD in mood disorders. Ketone bodies improve mitochondrial functions and suppress oxidative stress, inducing neuroprotective and anti-inflammatory effects which are both beneficial for mental health. Limited data also suggest KD-induced improvement of monoaminergic circuits and hypothalamus-pituitary-adrenal axis-the key pathophysiological pathways of mood disorders. Gut microbiome is an important mediator of the beneficial and detrimental effects of diet on brain functioning and mental health. Gut microbiota composition is affected in mood disorders but its role in the therapeutic effects of different diets, including KD, remains poorly understood. Still little is known about sex differences in the effects of KD on mental health as well as on metabolism and body weight. Some animal studies used both sexes but did not find differences in behavior, body weight loss or gut microbiota composition. More studies, both on a preclinical and clinical level, are needed to better understand sex-specific effects of KD on mental health.

GWAS-identified bipolar disorder risk allele in the FADS1/2 gene region links mood episodes and unsaturated fatty acid metabolism in mutant mice

Large-scale genome-wide association studies (GWASs) on bipolar disorder (BD) have implicated the involvement of the fatty acid desaturase (FADS) locus. These enzymes (FADS1 and FADS2) are involved in the metabolism of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which are thought to potentially benefit patients with mood disorders. To model reductions in the activity of FADS1/2 affected by the susceptibility alleles, we generated mutant mice heterozygously lacking both Fads1/2 genes. We measured wheel-running activity over six months and observed bipolar swings in activity, including hyperactivity and hypoactivity. The hyperactivity episodes, in which activity was far above the norm, usually lasted half a day; mice manifested significantly shorter immobility times on the behavioral despair test performed during these episodes. The hypoactivity episodes, which lasted for several weeks, were accompanied by abnormal circadian rhythms and a marked decrease in wheel running, a spontaneous behavior associated with motivation and reward systems. We comprehensively examined lipid composition in the brain and found that levels of certain lipids were significantly altered between wild-type and the heterozygous mutant mice, but no changes were consistent with both sexes and either DHA or EPA was not altered. However, supplementation with DHA or a mixture of DHA and EPA prevented these episodic behavioral changes. Here we propose that heterozygous Fads1/2 knockout mice are a model of BD with robust constitutive, face, and predictive validity, as administration of the mood stabilizer lithium was also effective. This GWAS-based model helps to clarify how lipids and their metabolisms are involved in the pathogenesis and treatment of BD.

Neurite outgrowth deficits caused by rare PLXNB1 mutation in pediatric bipolar disorder

Pediatric bipolar disorder (PBD) is a severe mood dysregulation condition that affects 0.5-1% of children and teens in the United States. It is associated with recurrent episodes of mania and depression and an increased risk of suicidality. However, the genetics and neuropathology of PBD are largely unknown. Here, we used a combinatorial family-based approach to characterize cellular, molecular, genetic, and network-level deficits associated with PBD. We recruited a PBD patient and three unaffected family members from a family with a history of psychiatric illnesses. Using resting-state functional magnetic resonance imaging (rs-fMRI), we detected altered resting-state functional connectivity in the patient as compared to an unaffected sibling. Using transcriptomic profiling of patient and control induced pluripotent stem cell (iPSC)-derived telencephalic organoids, we found aberrant signaling in the molecular pathways related to neurite outgrowth. We corroborated the presence of neurite outgrowth deficits in patient iPSC-derived cortical neurons and identified a rare homozygous loss-of-function PLXNB1 variant (c.1360C>C; p.Ser454Arg) responsible for the deficits in the patient. Expression of wild-type PLXNB1, but not the variant, rescued neurite outgrowth in patient neurons, and expression of the variant caused the neurite outgrowth deficits in cortical neurons from PlxnB1 knockout mice. These results indicate that dysregulated PLXNB1 signaling may contribute to an increased risk of PBD and other mood dysregulation-related disorders by disrupting neurite outgrowth and functional brain connectivity. Overall, this study established and validated a novel family-based combinatorial approach for studying cellular and molecular deficits in psychiatric disorders and identified dysfunctional PLXNB1 signaling and neurite outgrowth as potential risk factors for PBD.

The Role of the Gut Microbiome in Bipolar Disorder and its Common Comorbidities

Bipolar disorder is a decidedly heterogeneous and multifactorial disease, with significant psychosocial and medical disease burden. Much difficulty has been encountered in developing novel therapeutics and objective biomarkers for clinical use in this population. In that regard, gut-microbial homeostasis appears to modulate several key pathways relevant to a variety of psychiatric, metabolic, and inflammatory disorders. Microbial impact on immune, endocrine, endocannabinoid, kynurenine, and other pathways are discussed throughout this review. Emphasis is placed on this system's relevance to current pharmacology, diet, and comorbid illness in bipolar disorder. Despite the high level of optimism promoted in many reviews on this topic, substantial obstacles exist before any microbiome-related findings can provide meaningful clinical utility. Beyond a comprehensive overview of pathophysiology, this review hopes to highlight several key areas where progress is needed. As well, novel microbiome-associated suggestions are presented for future research.

Bipolar Chronobiology in Men and Mice: A Narrative Review

In patients with bipolar disorder, we do not only see a cycling of mood episodes, but also a shift in circadian rhythm. In the present overview, the circadian rhythm, the "internal clock", and their disruptions are briefly described. In addition, influences on circadian rhythms such as sleep, genetics, and environment are discussed. This description is conducted with a translational focus covering human patients as well as animal models. Concluding the current knowledge on chronobiology and bipolar disorder, implications for specificity and the course of bipolar disorder and treatment options are given at the end of this article. Taken together, circadian rhythm disruption and bipolar disorder are strongly correlated; the exact causation, however, is still unclear.

Montelukast induces beneficial behavioral outcomes and reduces inflammation in male and female rats

Background

Accumulative data links inflammation and immune dysregulation to the pathophysiology of mental disorders; little is known regarding leukotrienes’ (LTs) involvement in this process. Circumstantial evidence suggests that treatment with leukotriene modifying agents (LTMAs) such as montelukast (MTK) may induce adverse neuropsychiatric events. Further methodic evaluation is warranted.

Objective

This study aims to examine behavioral effects, as well as inflammatory mediator levels of chronic MTK treatment in male and female rats.

Methods

Depression-like phenotypes were induced by exposing male and female rats to a chronic unpredictable mild stress (CUMS) protocol for four weeks. Thereafter, rats were treated (intraperitoneally) once daily, for two weeks, with either vehicle (dimethyl sulfoxide 0.2 ml/rat) or 20 mg/kg MTK. Following treatment protocols, behavioral tests were conducted and brain regions were evaluated for inflammatory mediators including tumor necrosis factor (TNF)-α, interleukin (IL)-6 and prostaglandin (PG) E2.

Results

Overall, MTK did not invoke negative behavioral phenotypes (except for an aggression-inducing effect in males). Numerous positive behavioral outcomes were observed, including reduction in aggressive behavior in females and reduced manic/hyperactive-like behavior and increased sucrose consumption (suggestive of antidepressant-like effect) in males. Furthermore, in control males, MTK increased IL-6 levels in the hypothalamus and TNF-α in the frontal cortex, while in control females it generated a robust anti-inflammatory effect. In females that were subjected to CUMS, MTK caused a prominent reduction in TNF-α and IL-6 in brain regions, whereas in CUMS-subjected males its effects were inconsistent.

Conclusion

Contrary to prior postulations, MTK may be associated with select beneficial behavioral outcomes. Additionally, MTK differentially affects male vs. female rats in respect to brain inflammatory mediators, plausibly explaining the dissimilar behavioral phenotypes of sexes under MTK treatment.

Mitochondrial Impairment: A Common Motif in Neuropsychiatric Presentation? The Link to the Tryptophan-Kynurenine Metabolic System

Nearly half a century has passed since the discovery of cytoplasmic inheritance of human chloramphenicol resistance. The inheritance was then revealed to take place maternally by mitochondrial DNA (mtDNA). Later, a number of mutations in mtDNA were identified as a cause of severe inheritable metabolic diseases with neurological manifestation, and the impairment of mitochondrial functions has been probed in the pathogenesis of a wide range of illnesses including neurodegenerative diseases. Recently, a growing number of preclinical studies have revealed that animal behaviors are influenced by the impairment of mitochondrial functions and possibly by the loss of mitochondrial stress resilience. Indeed, as high as 54% of patients with one of the most common primary mitochondrial diseases, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome, present psychiatric symptoms including cognitive impairment, mood disorder, anxiety, and psychosis. Mitochondria are multifunctional organelles which produce cellular energy and play a major role in other cellular functions including homeostasis, cellular signaling, and gene expression, among others. Mitochondrial functions are observed to be compromised and to become less resilient under continuous stress. Meanwhile, stress and inflammation have been linked to the activation of the tryptophan (Trp)-kynurenine (KYN) metabolic system, which observably contributes to the development of pathological conditions including neurological and psychiatric disorders. This review discusses the functions of mitochondria and the Trp-KYN system, the interaction of the Trp-KYN system with mitochondria, and the current understanding of the involvement of mitochondria and the Trp-KYN system in preclinical and clinical studies of major neurological and psychiatric diseases.

Zebrafish as a potential non-traditional model organism in translational bipolar disorder research: Genetic and behavioral insights

Bipolar disorder (BD) is a severe and debilitating illness that affects 1-2% of the population worldwide. BD is characterized by recurrent and extreme mood swings, including mania/hypomania and depression. Animal experimental models have been used to elucidate the mechanisms underlying BD and different strategies have been proposed to assess BD-like symptoms. The zebrafish (Danio rerio) has been considered a suitable vertebrate system for modeling BD-like responses, due to the genetic tractability, molecular/physiological conservation, and well-characterized behavioral responses. In this review, we discuss how zebrafish-based models can be successfully used to understand molecular, biochemical, and behavioral alterations paralleling those found in BD. We also outline some advantages and limitations of this aquatic species to examine BD-like phenotypes in translational neurobehavioral research. Overall, we reinforce the use of zebrafish as a promising tool to investigate the neural basis associated with BD-like behaviors, which may foster the discovery of novel pharmacological therapies.

Low-Dose Aspirin Augments the Anti-Inflammatory Effects of Low-Dose Lithium in Lipopolysaccharide-Treated Rats

Mounting evidence suggests that immune-system dysfunction and inflammation play a role in the pathophysiology and treatment of mood-disorders in general and of bipolar disorder in particular. The current study examined the effects of chronic low-dose aspirin and low-dose lithium (Li) treatment on plasma and brain interleukin-6 and tumor necrosis factor-α production in lipopolysaccharide (LPS)-treated rats. Rats were fed regular or Li-containing food (0.1%) for six weeks. Low-dose aspirin (1 mg/kg) was administered alone or together with Li. On days 21 and 42 rats were injected with 1 mg/kg LPS or saline. Two h later body temperature was measured and rats were sacrificed. Blood samples, the frontal-cortex, hippocampus, and the hypothalamus were extracted. To assess the therapeutic potential of the combined treatment, rats were administered the same Li + aspirin protocol without LPS. We found that the chronic combined treatment attenuated LPS-induced hypothermia and significantly reduced plasma and brain cytokine level elevation, implicating the potential neuroinflammatory diminution purportedly present among the mentally ill. The combined treatment also significantly decreased immobility time and increased struggling time in the forced swim test, suggestive of an antidepressant-like effect. This preclinical evidence provides a potential approach for treating inflammation-related mental illness.

Neurobehavioral Differences of Valproate and Risperidone on MK-801 Inducing Acute Hyperlocomotion in Mice

Objective

The glutamate system plays a major role in the development of neuropsychiatric disorders such as addiction, epilepsy, dementia, and psychosis. MK-801 (dizocilpine), an uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, could increase locomotor activity and stereotyped neurobehaviors mimicking schizophrenic-like features in the mouse model. The study would explore the neuropharmacological differences of risperidone and valproic acid on the MK-801-induced neurobehavioral changes.

Methods

The subjects were male C57BL/6J mice obtained from the National Laboratory Animal Center. Drug effects were assessed using the open field with a video-tracking system and gaiting tests. After habitation, risperidone (0, 0.1 mg/kg) or valproic acid (0, 200 mg/kg) was injected and ran locomotion for 30 mins. Sequentially, mice were followed by intraperitoneal injection (i.p.) with MK-801 (0, 0.2 mg/kg) and ran locomotion for 60 mins. Gaiting behaviors such as step angles, stride lengths, and stance widths were measured following the study drugs.

Results

The results showed that risperidone and valproic acid alone could not alter the locomotor activities. Following the MK-801 injection, the travelled distance and speed in the entire open field dramatically increased. The dose 0.1 mg/kg of risperidone could totally inhibit the MK-801-induced hyperlocomotion compared with that of the saline-injected group (p < 0.001). The valproic acid (200 mg/kg) partially suppressed the hyperlocomotion which is induced by MK801.

Conclusion

The more dominant effect of risperidone to rescue MK-801 induced hyperlocomotion compared with that of valproic acid. The partial suppression of valproic acid may imply the psychopharmacological evidence as adjuvant effect to treat psychotic patients through tuning glutamatergic neurotransmission.

A New NF-κB Inhibitor, MEDS-23, Reduces the Severity of Adverse Post-Ischemic Stroke Outcomes in Rats

Aim: Nuclear factor kappa B (NF-κB) is known to play an important role in the inflammatory process which takes place after ischemic stroke. The major objective of the present study was to examine the effects of MEDS-23, a potent inhibitor of NF-κB, on clinical outcomes and brain inflammatory markers in post-ischemic stroke rats. Main methods: Initially, a Toxicity Experiment was performed to determine the appropriate dose of MEDS-23 for use in animals, as MEDS-23 was analyzed in vivo for the first time. We used the middle cerebral artery occlusion (MCAO) model for inducing ischemic stroke in rats. The effects of MEDS-23 (at 10 mg/kg, ip) on post-stroke outcomes (brain inflammation, fever, neurological deficits, mortality, and depression- and anxiety-like behaviours) was tested in several efficacy experiments. Key findings: MEDS-23 was found to be safe and significantly reduced the severity of some adverse post-stroke outcomes such as fever and neurological deficits. Moreover, MEDS-23 significantly decreased prostaglandin E2 levels in the hypothalamus and hippocampus of post-stroke rats, but did not prominently alter the levels of interleukin-6 and tumor necrosis factor-α. Significance: These results suggest that NF-κB inhibition is a potential therapeutic strategy for the treatment of ischemic stroke.

Therapeutic approaches employing natural compounds and derivatives for treating bipolar disorder: emphasis on experimental models of the manic phase

Bipolar disorder (BD) is a complex psychiatric disease characterized by mood swings that include episodes of mania and depression. Given its cyclical nature, BD is especially hard to model; however, the standard practice has been to mimic manic episodes in animal models. Despite scientific advances, the pathophysiology of BD is not fully understood, and treatment remains limited. In the last years, natural products have emerged as potential neuroprotective agents for the treatment of psychiatric diseases. Thus, the aim of this review was to explore the therapeutic potential of natural compounds and derivatives against BD, taking into account preclinical and clinical studies. Reliable articles indexed in databases such as PubMed, Web of Science and Science Direct were used. In clinical studies, treatment with herbal plants extracts, omega-3, inositol, n-acetylcysteine and vitamin D has been associated with a clinical improvement in symptoms of mania and depression in BD patients. In animal models, it has been shown that red fruits extracts, curcumin, quercetin, gallic acid, alpha-lipoic acid and carvone can modulate many neurochemical pathways involved in the pathophysiology of manic episodes. Thus, this review appointed the advances in the consumption of natural compounds and derivatives as an important therapeutic strategy to mitigate the symptoms of BD.

Adult Neural Stem Cells as Promising Targets in Psychiatric Disorders

The development of new therapies for psychiatric disorders is of utmost importance, given the enormous toll these disorders pose to society nowadays. This should be based on the identification of neural substrates and mechanisms that underlie disease etiopathophysiology. Adult neural stem cells (NSCs) have been emerging as a promising platform to counteract brain damage. In this perspective article, we put forth a detailed view of how NSCs operate in the adult brain and influence brain homeostasis, having profound implications at both behavioral and functional levels. We appraise evidence suggesting that adult NSCs play important roles in regulating several forms of brain plasticity, particularly emotional and cognitive flexibility, and that NSC dynamics are altered upon brain pathology. Furthermore, we discuss the potential therapeutic value of utilizing adult endogenous NSCs as vessels for regeneration, highlighting their importance as targets for the treatment of multiple mental illnesses, such as affective disorders, schizophrenia, and addiction. Finally, we speculate on strategies to surpass current challenges in neuropsychiatric disease modeling and brain repair.

Enlightened: addressing circadian and seasonal changes in photoperiod in animal models of bipolar disorder

Bipolar disorders (BDs) exhibit high heritability and symptoms typically first occur during late adolescence or early adulthood. Affected individuals may experience alternating bouts of mania/hypomania and depression, with euthymic periods of varying lengths interspersed between these extremes of mood. Clinical research studies have consistently demonstrated that BD patients have disturbances in circadian and seasonal rhythms, even when they are free of symptoms. In addition, some BD patients display seasonal patterns in the occurrence of manic/hypomanic and depressive episodes as well as the time of year when symptoms initially occur. Finally, the age of onset of BD symptoms is strongly influenced by the distance one lives from the equator. With few exceptions, animal models useful in the study of BD have not capitalized on these clinical findings regarding seasonal patterns in BD to explore molecular mechanisms associated with the expression of mania- and depression-like behaviors in laboratory animals. In particular, animal models would be especially useful in studying how rates of change in photoperiod that occur during early spring and fall interact with risk genes to increase the occurrence of mania- and depression-like phenotypes, respectively. Another unanswered question relates to the ways in which seasonally relevant changes in photoperiod affect responses to acute and chronic stressors in animal models. Going forward, we suggest ways in which translational research with animal models of BD could be strengthened through carefully controlled manipulations of photoperiod to enhance our understanding of mechanisms underlying seasonal patterns of BD symptoms in humans. In addition, we emphasize the value of incorporating diurnal rodent species as more appropriate animal models to study the effects of seasonal changes in light on symptoms of depression and mania that are characteristic of BD in humans.

MicroRNA-dependent control of neuroplasticity in affective disorders

Affective disorders are a group of neuropsychiatric disorders characterized by severe mood dysregulations accompanied by sleep, eating, cognitive, and attention disturbances, as well as recurring thoughts of suicide. Clinical studies consistently show that affective disorders are associated with reduced size of brain regions critical for mood and cognition, neuronal atrophy, and synaptic loss in these regions. However, the molecular mechanisms that mediate these changes and thereby increase the susceptibility to develop affective disorders remain poorly understood. MicroRNAs (miRNAs or miRs) are small regulatory RNAs that repress gene expression by binding to the 3'UTR of mRNAs. They have the ability to bind to hundreds of target mRNAs and to regulate entire gene networks and cellular pathways implicated in brain function and plasticity, many of them conserved in humans and other animals. In rodents, miRNAs regulate synaptic plasticity by controlling the morphology of dendrites and spines and the expression of neurotransmitter receptors. Furthermore, dysregulated miRNA expression is frequently observed in patients suffering from affective disorders. Together, multiple lines of evidence suggest a link between miRNA dysfunction and affective disorder pathology, providing a rationale to consider miRNAs as therapeutic tools or molecular biomarkers. This review aims to highlight the most recent and functionally relevant studies that contributed to a better understanding of miRNA function in the development and pathogenesis of affective disorders. We focused on in vivo functional studies, which demonstrate that miRNAs control higher brain functions, including mood and cognition, in rodents, and that their dysregulation causes disease-related behaviors.

Attenuated dopamine signaling after aversive learning is restored by ketamine to rescue escape actions

Escaping aversive stimuli is essential for complex organisms, but prolonged exposure to stress leads to maladaptive learning. Stress alters neuronal activity and neuromodulatory signaling in distributed networks, modifying behavior. Here, we describe changes in dopaminergic neuron activity and signaling following aversive learning in a learned helplessness paradigm in mice. A single dose of ketamine suffices to restore escape behavior after aversive learning. Dopaminergic neuron activity in the ventral tegmental area (VTA) systematically varies across learning, correlating with future sensitivity to ketamine treatment. Ketamine’s effects are blocked by chemogenetic inhibition of dopamine signaling. Rather than directly altering the activity of dopaminergic neurons, ketamine appears to rescue dopamine dynamics through actions in the medial prefrontal cortex (mPFC). Chemogenetic activation of Drd1 receptor positive mPFC neurons mimics ketamine’s effects on behavior. Together, our data link neuromodulatory dynamics in mPFC-VTA circuits, aversive learning, and the effects of ketamine.

Over 264 million people around the world suffer from depression, according to the World Health Organization (WHO). Depression can be debilitating, and while anti-depressant drugs are available, they do not always work. A small molecule drug mainly used for anesthesia called ketamine has recently been shown to ameliorate depressive symptoms within hours, much faster than most anti-depressants. However, the molecular mechanisms behind this effect are still largely unknown.

Most anti-depressant drugs work by restoring the normal balance of dopamine and other chemical messengers in the brain. Dopamine is released by a specialized group of cells called dopaminergic neurons, and helps us make decisions by influencing a wide range of other cells in the brain. In a healthy brain, dopamine directs us to rewarding choices, while avoiding actions with negative outcomes. During depression, these dopamine signals are perturbed, resulting in reduced motivation and pleasure. But it remained unclear whether ketamine’s anti-depressant activity also relied on dopamine.

To investigate this, Wu et al. used a behavioral study called “learned helplessness” which simulates depression by putting mice in unavoidable stressful situations. Over time the mice learn that their actions do not change the outcome and eventually stop trying to escape from unpleasant situations, even if they are avoidable. The experiment showed that dopaminergic neurons in an area of the brain that is an important part of the “reward and aversion” system became less sensitive to unpleasant stimuli following learned helplessness. When the mice received ketamine, these neurons recovered after a few hours.

Individual mice also responded differently to ketamine. The most ‘resilient’, stress-resistant mice, which had distinct patterns of dopamine signaling, also responded most strongly to the drug. Genetic and chemical manipulation of dopaminergic neurons confirmed that ketamine needed intact dopamine signals to work, and revealed that it acted indirectly on dopamine dynamics via another brain region called the medial prefrontal cortex.

These results shed new light on how a promising new anti-depressant works. In the future, they may also explain why drugs like ketamine work better for some people than others, ultimately helping clinicians select the most effective treatment for individual patients.

Prefrontal dopamine D1 receptor manipulation influences anxiety behavior and induces neuroinflammation within the hippocampus

Background

Prefrontal dopamine D1 receptor (D1R) mediates behavior related to anxiety, reward and memory, and is involved in inflammatory processes, all of which are affected in bipolar disorder. Interleukin-6 (IL-6), a pro-inflammatory cytokine, is increased in patients with bipolar disorder in plasma samples, imaging studies and postmortem tissue and is an indicator for an inflammatory state. We could previously show that lentiviral overexpression of D1R in the medial prefrontal cortex (mPFC) of male adult rats and its termination induces bipolar disorder-like behavior. The purpose of this study was to investigate anxiety and the role of the immune system, specifically IL-6 positive neurons in this animal model. Due to its high density of inflammatory mediator receptors and therewith sensibility to immune activation, the hippocampus was investigated.

Methods

Expression of the gene for D1R in glutamatergic neurons within the mPFC of male, adult rats was manipulated through an inducible lentiviral vector. Animals over-expressing the gene (mania-like state), after termination of the expression (depressive-like) and their respective control groups were investigated. Anxiety behavior was studied in the elevated plus maze and marble burying test. Furthermore, IL-6-positive cells were counted within several subregions of the hippocampus.

Results

D1R manipulation in the mPFC had only mild effects on anxiety behavior in the elevated plus maze. However, subjects after termination buried more marbles compared to D1R over-expressing animals and their respective control animals indicating elevated anxiety behavior. In addition, animals in the depressive-like state showed higher numbers of IL-6 positive cells reflecting an elevated pro-inflammatory state in the hippocampus, in the CA3 and dentate gyrus. Consistently, inflammatory state in the whole hippocampus and anxiety behavior correlated positively, indicating a connection between anxiety and inflammatory state of the hippocampus.

Conclusions

Behavioral and neurobiological findings support the association of manipulation of the D1R in the mPFC on anxiety and inflammation in the hippocampus. In addition, by confirming changes in the inflammatory state, the proposed animal model for bipolar disorder has been further validated.

Transcriptome Changes in Three Brain Regions during Chronic Lithium Administration in the Rat Models of Mania and Depression

Lithium has been the most important mood stabilizer used for the treatment of bipolar disorder and prophylaxis of manic and depressive episodes. Despite long use in clinical practice, the exact molecular mechanisms of lithium are still not well identified. Previous experimental studies produced inconsistent results due to different duration of lithium treatment and using animals without manic-like or depressive-like symptoms. Therefore, we aimed to analyze the gene expression profile in three brain regions (amygdala, frontal cortex and hippocampus) in the rat model of mania and depression during chronic lithium administration (2 and 4 weeks). Behavioral changes were verified by the forced swim test, open field test and elevated maze test. After the experiment, nucleic acid was extracted from the frontal cortex, hippocampus and amygdala. Gene expression profile was done using SurePrint G3 Rat Gene Expression whole transcriptome microarrays. Data were analyzed using Gene Spring 14.9 software. We found that chronic lithium treatment significantly influenced gene expression profile in both mania and depression models. In manic rats, chronic lithium treatment significantly influenced the expression of the genes enriched in olfactory and taste transduction pathway and long non-coding RNAs in all three brain regions. We report here for the first time that genes regulating olfactory and taste receptor pathways and long non-coding RNAs may be targeted by chronic lithium treatment in the animal model of mania.

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.

Risky decision-making following prefrontal D1 receptor manipulation

The prefrontal dopamine D1 receptor (D1R) is involved in cognitive processes. Viral overexpression of this receptor in rats further increases the reward-related behaviors and even its termination induces anhedonia and helplessness. In this study, we investigated the risky decision-making during D1R overexpression and its termination. Rats conducted the rodent version of the Iowa gambling task daily. In addition, the methyl CpG–binding protein-2 (MeCP2), one regulator connecting the dopaminergic system, cognitive processes, and mood-related behavior, was investigated after completion of the behavioral tasks. D1R overexpressing subjects exhibited maladaptive risky decision-making and risky decisions returned to control levels following termination of D1R overexpression; however, after termination, animals earned less reward compared to control subjects. In this phase, MeCP2-positive cells were elevated in the right amygdala. Our results extend the previously reported behavioral changes in the D1R-manipulated animal model to increased risk-taking and revealed differential MeCP2 expression adding further evidence for a bipolar disorder-like phenotype of this model.

Role of epigenetic regulatory enzymes in animal models of mania induced by amphetamine and paradoxical sleep deprivation

It is known that bipolar disorder has a multifactorial aetiology where the interaction between genetic and environmental factors is responsible for its development. Because of this, epigenetics has been largely studied in psychiatric disorders. The present study aims to evaluate the effects of histone deacetylase inhibitors on epigenetic enzyme alterations in rats or mice submitted to animal models of mania induced by dextro-amphetamine or sleep deprivation, respectively. Adult male Wistar rats were subjected to 14 days of dextro-amphetamine administration, and from the eighth to the fourteenth day, the animals were treated with valproate and sodium butyrate in addition to dextro-amphetamine injections. Adult C57BL/6 mice received 7 days of valproate or sodium butyrate administration, being sleep deprived at the last 36 hr of the protocol. Locomotor and exploratory activities of rats and mice were evaluated in the open-field test, and histone deacetylase, DNA methyltransferase, and histone acetyltransferase activities were assessed in the frontal cortex, hippocampus, and striatum. Dextro-amphetamine and sleep deprivation induced hyperactivity and increased histone deacetylase and DNA methyltransferase activities in the animal's brain. Valproate and sodium butyrate were able to reverse hyperlocomotion induced by both animal models, as well as the alterations on histone deacetylase and DNA methyltransferase activities. There was a positive correlation between enzyme activities and number of crossings for both models. Histone deacetylase and DNA methyltransferase activities also presented a positive correlation between theirselves. These results suggest that epigenetics can play an important role in BD pathophysiology as well as in its treatment.

A Physiological Instability Displayed in Hippocampal Neurons Derived From Lithium-Nonresponsive Bipolar Disorder Patients

BACKGROUND

We recently reported a hyperexcitability phenotype displayed in dentate gyrus granule neurons derived from patients with bipolar disorder (BD) as well as a hyperexcitability that appeared only in CA3 pyramidal hippocampal neurons that were derived from patients with BD who responded to lithium treatment (lithium responders) and not in CA3 pyramidal hippocampal neurons that were derived from patients with BD who did not respond to lithium (nonresponders).

METHODS

Here we used our measurements of currents in neurons derived from 4 control subjects, 3 patients with BD who were lithium responders, and 3 patients with BD who were nonresponders. We changed the conductances of simulated dentate gyrus and CA3 hippocampal neurons according to our measurements to derive a numerical simulation for BD neurons.

RESULTS

The computationally simulated BD dentate gyrus neurons had a hyperexcitability phenotype similar to the experimental results. Only the simulated BD CA3 neurons derived from lithium responder patients were hyperexcitable. Interestingly, our computational model captured a physiological instability intrinsic to hippocampal neurons that were derived from nonresponder patients that we also observed when re-examining our experimental results. This instability was caused by a drastic reduction in the sodium current, accompanied by an increase in the amplitude of several potassium currents. These baseline alterations caused nonresponder BD hippocampal neurons to drastically shift their excitability with small changes to their sodium currents, alternating between hyperexcitable and hypoexcitable states.

CONCLUSIONS

Our computational model of BD hippocampal neurons that was based on our measurements reproduced the experimental phenotypes of hyperexcitability and physiological instability. We hypothesize that the physiological instability phenotype strongly contributes to affective lability in patients with BD.

Protein kinase C isoforms as a target for manic-like behaviors and oxidative stress in a dopaminergic animal model of mania

Bipolar disorder (BD) is a chronic condition characterized by severe mood swings alternating between episodes of mania and depression. Evidence indicates that protein kinase C (PKC) and oxidative stress are important therapeutic targets for BD. However, what PKC isoforms that are precisely involved in this effect are unknown. Therefore, we evaluated the effects of the intracerebroventricular (ICV) injection of PKC inhibitors (lithium (Li), tamoxifen (TMX), PKCα inhibitor (iPKCα), PKCγ inhibitor (iPKCγ), and PKCε inhibitor (iPKCε)) on the manic-like behaviors and oxidative stress parameters (4-hydroxy-2-nonenal (4-HNE), 8-isoprostane (8-ISO), carbonyl groups, 3-nitrotyrosine (3-NT), glutathione peroxidase (GPx) and glutathione reductase (GR)) in the brains of rats submitted to the model of mania induced by methamphetamine (m-AMPH). Animals received a single ICV infusion of artificial cerebrospinal fluid, Li, TMX, iPKCα, iPKCγ or iPKCε followed by an intraperitoneal injection of saline or m-AMPH before the behavioral analysis (open-field task). Oxidative stress was evaluated in the striatum, frontal cortex, and hippocampus. ICV injection of Li, TMX or iPKCε blocked the m-AMPH-induced increase in the manic-like behaviors - crossings, rearings, visits to the center, sniffing, and grooming. ICV infusion of iPKCα triggered a decrease in these behaviors induced by m-AMPH. Besides, the iPKCε administration significantly prevented the oxidative damage to lipids and proteins, as well as disturbances in the activity of antioxidant enzymes induced by m-AMPH. The findings of the present study suggest that PKCε isoform is strongly implied in the antimanic and antioxidant effects of Li, TMX, and the other PKC inhibitors in the model of mania.

Behavioral tests assessing neuropsychiatric phenotypes in adolescent mice reveal strain- and sex-specific effects

In humans, infancy and adolescence are associated with major changes in synaptic functions and ongoing maturation of neural networks, which underlie the major behavioral changes during these periods. Among adult cases with neuropsychiatric disorders including autism spectrum disorder, schizophrenia, attention deficit hyperactivity, and bipolar disorders, 50% have developed behavioral symptoms and received a diagnosis before 15 years of age. However, most of the behavioral studies in mice modeling neuropsychiatric phenotypes are performed in adult animals, missing valuable phenotypic information related to the effect of synaptic maturation during development. Here, we explored which behavioral experiments assessing neuropsychiatric phenotypes can be performed during a specific window of development in adolescent male and female C57BL/6N, DBA/2, and FVB/N mice that are typically used as background strains for generating genetically-modified mouse models. The three wild-type strains were evaluated across anxiety, social behaviors, and cognitive functions in order to cover the main behavioral impairments that occur in neuropsychiatric disorders. During adolescence, the three strains displayed significant differences under certain behavioral paradigms. In addition, C57BL/6N and FVB/N, but not DBA/2 mice revealed some sex-related differences. Our results provide new insights into discrete behaviors during development and emphasize the crucial importance of the genetic background, sex, and experimental settings in the age-dependent regulation of different behaviors.

Long non-coding RNA Neat1 regulates adaptive behavioural response to stress in mice

NEAT1 is a highly and ubiquitously expressed long non-coding RNA (lncRNA) which serves as an important regulator of cellular stress response. However, the physiological role of NEAT1 in the central nervous system (CNS) is still poorly understood. In the current study, we addressed this by characterising the CNS function of the Neat1 knockout mouse model (Neat1-/- mice), using a combination of behavioural phenotyping, electrophysiology and expression analysis. RNAscope® in situ hybridisation revealed that in wild-type mice, Neat1 is expressed across the CNS regions, with high expression in glial cells and low expression in neurons. Loss of Neat1 in mice results in an inadequate reaction to physiological stress manifested as hyperlocomotion and panic escape response. In addition, Neat1-/- mice display deficits in social interaction and rhythmic patterns of activity but retain normal motor function and memory. Neat1-/- mice do not present with neuronal loss, overt neuroinflammation or gross synaptic dysfunction in the brain. However, cultured Neat1-/- neurons are characterised by hyperexcitability and dysregulated calcium homoeostasis, and stress-induced neuronal activity is also augmented in Neat1-/- mice in vivo. Gene expression analysis showed that Neat1 may act as a weak positive regulator of multiple genes in the brain. Furthermore, loss of Neat1 affects alternative splicing of genes important for the CNS function and implicated in neurological diseases. Overall, our data suggest that Neat1 is involved in stress signalling in the brain and fine-tunes the CNS functions to enable adaptive behaviour in response to physiological stress.

Differential effects of lithium isotopes in a ketamine-induced hyperactivity model of mania

Sub-anesthetic doses of ketamine produce an increase in rodent ambulation that is attenuated by co-administration of naturally-occurring lithium (LiN), the drug most commonly employed in the treatment of bipolar illness. As a consequence, ketamine-induced hyperactivity has been proposed as an animal model of manic behavior. The current study employed a modified version of this model to compare the potency of LiN to that of each of its two stable isotopes - lithium-6 (Li-6) and lithium-7 (Li-7). Since Li-7 constitutes 92.4% of the parent compound it was hypothesized to produce comparable behavioral effects to that of LiN. The current study was devised to determine whether Li-6 might be more, less, or equally effective at tempering hyperactivity relative to Li-7 or to LiN in an animal model of manic behavior. Male rats were maintained on a restricted but high-incentive diet containing a daily dose of 2.0 mEq/kg of lithium (LiN), Li-6 or Li-7 for 30 days. A control group consumed a diet infused with sodium chloride (NaCl) in place of lithium to control for the salty taste of the food. On day 30, baseline testing revealed no differences in the locomotor behavior among the four treatment groups. Animals then continued their Li/NaCl diets for an additional 11 days during which every subject received a single IP injection of either ketamine (25 mg/kg) or 0.9% physiological saline. On the final four days of this regimen, locomotor activity was assessed during 60 min sessions each beginning immediately after ketamine injection. While all three lithium groups produced comparable decreases in ketamine-induced hyperactivity on the first trial, by the fourth trial Li-6 animals exhibited significantly greater and more prolonged reductions in hyperactivity compared to either Li-7 and Li. These results suggest that Li-6 may be more effective at treating mania than its parent compound.

Metabolomics in Psychiatric Disorders: What We Learn from Animal Models

Biomarkers are a recent research target within biological factors of psychiatric disorders. There is growing evidence for deriving biomarkers within psychiatric disorders in serum or urine samples in humans, however, few studies have investigated this differentiation in brain or cerebral fluid samples in psychiatric disorders. As brain samples from humans are only available at autopsy, animal models are commonly applied to determine the pathogenesis of psychiatric diseases and to test treatment strategies. The aim of this review is to summarize studies on biomarkers in animal models for psychiatric disorders. For depression, anxiety and addiction disorders studies, biomarkers in animal brains are available. Furthermore, several studies have investigated psychiatric medication, e.g., antipsychotics, antidepressants, or mood stabilizers, in animals. The most notable changes in biomarkers in depressed animal models were related to the glutamate-γ-aminobutyric acid-glutamine-cycle. In anxiety models, alterations in amino acid and energy metabolism (i.e., mitochondrial regulation) were observed. Addicted animals showed several biomarkers according to the induced drugs. In summary, animal models provide some direct insights into the cellular metabolites that are produced during psychiatric processes. In addition, the influence on biomarkers due to short- or long-term medication is a noticeable finding. Further studies should combine representative animal models and human studies on cerebral fluid to improve insight into mental disorders and advance the development of novel treatment strategies.

Efficacy of folic acid as an adjunct to lithium therapy on manic-like behaviors, oxidative stress and inflammatory parameters in an animal model of mania

Evaluate the efficacy of folic acid (FA) as a therapeutic adjunct to lithium (Li) on the manic-like behaviors as well as parameters of oxidative stress and inflammation in an animal model of mania induced by m-amphetamine (m-AMPH). Wistar rats first received m-AMPH or saline (NaCl 0.9%, Sal) for 14 days. Between the 8th and 14th day, rats were treated with water, Li, FA or a combination of thereof drugs (Li + FA). Manic-like behaviors were assessed in the open-field test. Oxidative stress and inflammation parameters were assessed in the frontal cortex, striatum, and hippocampus. Administration of m-AMPH in rats significantly enhanced the exploratory and locomotor behaviors, as well as the risk-taking and stereotypic behaviors. Li + FA reversed these behavioral alterations elicited by m-AMPH. Administration of this psychostimulant also increased oxidative damage to lipids and proteins, whereas Li + FA reversed these oxidative damages. m-AMPH also induced an increase in the glutathione peroxidase (GPx) activity and a decrease in the glutathione reductase (GR) activity. Li + FA reversed the alteration in GR activity, but not in GPx activity. In addition, m-AMPH increased the IL-1β and TNF-α levels in the rat brain; Li + FA combined therapy reversed the alterations on these inflammatory parameters. FA administration per se reduced the increased TNF-α content induced by m-AMPH. Present study provides evidence that FA is effective as an adjunct to Li standard therapy on manic-like behaviors, oxidative stress and inflammatory parameters in a model of mania induced by m-AMPH.

A new inbred strain of Fawn-Hooded rats demonstrates mania-like behavioural and monoaminergic abnormalities

The Fawn-Hooded (FH) rat carries a gene mutation that results in a dysfunctional serotoninergic system. However, previous studies have reported differing features between the FH/Wjd and FH/Har strains. We aimed to compare the behavioural and neurobiological features of FH/HamSlc rats with those of Fischer 344 rats. We performed the open field, elevated minus-maze, Y-maze spontaneous alternation, and forced swim tests to investigate behavioural alterations. We also assessed neurobiological characteristics by quantifying monoamines and their related compounds in the prefrontal cortex, hippocampus, and striatum using high-performance liquid chromatography with an electrochemical detection system. FH/HamSlc rats showed hyperactivity and a high impulsivity tendency in the open field and the elevated minus maze test, but no cognitive dysfunction. In addition, the hyperactivity was suppressed immediately after the forced swim test. FH/HamSlc rats showed low dopamine levels, but high dopamine turnover in the striatum. Serotonin and noradrenaline levels were low in the prefrontal cortex and the hippocampus of FH/HamSlc rats, but high serotonin turnover was observed in the prefrontal cortex, hippocampus, and striatum. FH/HamSlc rats show (1) mania-like behavioural characteristics that are different from those of other strains of FH rats; (2) stimulus dependent suppression of hyperactivity similar to the clinical findings that exercise alleviates the symptoms of bipolar disorder; and (3) monoaminergic dysregulation such as monoamine imbalance and hyperturnover that may be associated with mania-related behavioural characteristics. Thus, the FH/HamSlc rat is a new animal model for mania including bipolar disorder.

Lithium and glutamine synthetase: Protective effects following stress

Even though lithium is widely used as treatment for mood disorders, the exact mechanisms of lithium in the brain remain unknown. A potential mechanism affects the downstream target of the Wnt/β-catenin signaling pathway, specifically glutamine synthetase (GS). Here, we investigate the effect of lithium on GS-promoter activity in the brain. Over seven days, B6C3H-Glultm^(T2A-LacZ) mice that carry LacZ as a reporter gene fused to the GS-promotor received either daily intraperitoneal injections of lithium carbonate (25 mg/kg) or NaCl, or no treatment. Following histochemical staining of β-galactosidase relative GS-promotor activity was measured by analyzing the intensity of the staining. Furthermore cell counts were conducted. GS-promotor activity was significantly decreased in female compared to male mice. Treatment group differences were only found in male hippocampi, with increased activity after NaCl treatment compared to both the lithium treatment and no treatment. Lithium treatment increased the overall number of cells in the CA1 region in males. Daily injections of NaCl might have been sufficient to induce stress-related GS-promotor activity changes in male mice; however, lithium was able to reverse the effect. Taken together, the current study indicates that lithium acts to prevent stress, rather affecting general GS-promoter activity.

Review of animal models of bipolar disorder that alter ion regulation

BACKGROUND

Accurate modeling of psychiatric disorders in animals is essential for advancement in our understanding and treatment of the severe mental illnesses. Of the multiple models available for bipolar illness, the ones that disrupt ion flux are currently the only ones that meet the three criteria for validity: face validity, construct validity, and predictive validity.

METHODS

A directed review was performed to evaluate animal models for mania in which ion dysregulation was the key intervention.

RESULTS

Three models are identified. All focus on disruption of the sodium potassium pump. One is pharmacologic and requires surgical insertion of an intracerebroventricular (ICV) cannula and subsequent administration of ouabain. Two are genetic and are based on heterozygote knockout (KO) of the alpha2 or alpha3 subunits of the sodium pump. Alpha2 KOs are believed to have altered glial function, and they do not appear to have a full array of manic symptoms. Alpha3 KOs appear to be the best characterized animal model for bipolar disorder currently available.

CONCLUSION

Animal models that disrupt ion regulation are more inclined to model both mania and depression; and are thus the most promising models available. However, other models are important for demonstrating mechanisms in important pathophysiologic aspect of bipolar disorder.

Bipolar Disorder: Its Etiology and How to Model in Rodents

Characterized by the switch of manic and depressive phases, bipolar disorder was described as early as the fifth century BC. Nevertheless up to date, the underlying neurobiology is still largely unclear, assuming a multifactor genesis with both biological-genetic and psychosocial factors. Significant process has been achieved in recent years in researching the causes of bipolar disorder with modern molecular biological (e.g., genetic and epigenetic studies) and imaging techniques (e.g., positron emission tomography (PET) and functional magnetic resonance imaging (fMRI)). In this chapter we will first summarize our recent knowledge on the etiology of bipolar disorder. We then discuss how several factors observed to contribute to bipolar disorder in human patients can be manipulated to generate rodent models for bipolar disorder. Finally, we will give an overview on behavioral test that can be used to assess bipolar-disorder-like behavior in rodents.