Role of dominance-submission relationships in shock-induced fighting of mice

Modeling mania in preclinical settings: A comprehensive review

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

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

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

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.

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

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

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

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

Dominance behavior: a phylogenetic analysis in the mouse

Tube-dominance behavior differed significantly in C57BL/6By and BALB/cBy mice. Evaluation of these two inbred strains, and their recently developed recombinant inbred strains permitted the derivation of an hypothesis regarding possible genetic control of this behavior in mice. The results were analyzed by means of patristic matrices with accompanying phylogenetic tree analysis that marks the first occasion that such analysis has been used for a behavioral trait. Based on the data obtained and the statistical analyses and groupings of the various strains, the most satisfactory hypothesis that can be proposed at this time is one which assumes that dominance behavior, as measured in this experiment, is influenced genetically by at least 3 loci. Attempts to link these loci were not successful.