Within-strain variation in behavior differs consistently between common inbred strains of mice

Late development of OCD-like phenotypes in Dlgap1 knockout mice

RATIONALE

Despite variants in the Dlgap1 gene having the two lowest p-value in a genome-wide association study of obsessive compulsive disorder (OCD), previous studies reported the absence of OCD-like phenotypes in Dlgap1 knockout (KO) mice. Since these studies observed behavioral phenotypes only for a short period, development of OCD-like phenotypes in these mice at older ages was still plausible.

OBJECTIVE

To examine the presence or absence of development of OCD-like phenotypes in Dlgap1 KO mice and their responsiveness to fluvoxamine.

METHODS AND RESULTS

Newly produced Dlgap1 KO mice were observed for a year. Modified SHIRPA primary screen in 2-month-old homozygous mutant mice showed only weak signs of anxiety, stress conditions and aggression. At older ages, however, these mutant mice exhibited excessive self-grooming characterized by increased scratching which led to skin lesions. A significant sex difference was observed in this scratching behavior. The penetrance of skin lesions reached 50% at 6-7 months of age and 90% at 12 months of age. In the open-field test performed just after the appearance of these lesions, homozygous mutant mice spent significantly less time in the center, an anxiety-like behavior, than did their wild-type and heterozygous littermates, none and less than 10% of which showed skin lesions at 1 year, respectively. The skin lesions and excessive self-grooming were significantly alleviated by two-week treatment with fluvoxamine.

CONCLUSION

Usefulness of Dlgap1 KO mice as a tool for investigating the pathogenesis of OCD-like phenotypes and its translational relevance was suggested.

Sex-specific threat responding and neuronal engagement in carbon dioxide associated fear and extinction: Noradrenergic involvement in female mice

Difficulty in appropriately responding to threats is a key feature of psychiatric disorders, especially fear-related conditions such as panic disorder (PD) and posttraumatic stress disorder (PTSD). Most prior work on threat and fear regulation involves exposure to external threatful cues. However, fear can also be triggered by aversive, within-the-body, sensations. This interoceptive signaling of fear is highly relevant to PD and PTSD but is not well understood, especially in the context of sex. Using female and male mice, the current study investigated fear-associated spontaneous and conditioned behaviors to carbon dioxide (CO2) inhalation, a potent interoceptive threat that induces fear and panic. We also investigated whether behavioral sensitivity to CO2 is associated with delayed PTSD-relevant behaviors. CO2 evoked heterogenous freezing behaviors in both male and female animals. However, active, rearing behavior was significantly reduced in CO2-exposed male but not female mice. Interestingly, behavioral sensitivity to CO2 was associated with compromised fear extinction, independent of sex. However, in comparison to CO2-exposed males, females elicited less freezing and higher rearing during extinction suggesting an engagement of active versus passive defensive coping. Persistent neuronal activation marker ΔFosB immuno-mapping revealed attenuated engagement of infralimbic-prefrontal areas in both sexes but higher activation of brain stem locus coeruleus (LC) area in females. Inter-regional co-activation mapping revealed sex-independent disruptions in the infralimbic-amygdala associations but altered LC associations only in CO2-exposed female mice. Lastly, dopamine β hydroxylase positive (DβH + ve) noradrenergic neuronal cell counts in the LC correlated with freezing and rearing behaviors during CO2 inhalation and extinction only in female but not male mice. Collectively, these data provide evidence for higher active defensive responding to interoceptive threat CO2-associated fear in females that may stem from increased recruitment of the brainstem noradrenergic system. Our findings reveal distinct contributory mechanisms that may promote sex differences in fear and panic associated pathologies.

Clinicopathologic Dissociation: Robust Lafora Body Accumulation in Malin KO Mice Without Observable Changes in Home-cage Behavior

Lafora Disease (LD) is a syndrome of progressive myoclonic epilepsy and cumulative neurocognitive deterioration caused by recessively inherited genetic lesions of EPM2A (laforin) or NHLRC1 (malin). Neuropsychiatric symptomatology in LD is thought to be directly downstream of neuronal and astrocytic polyglucosan aggregates, termed Lafora bodies (LBs), which faithfully accumulate in an age-dependent manner in all mouse models of LD. In this study, we applied home-cage monitoring to examine the extent of neurobehavioral deterioration in a model of malin-deficient LD, as a means to identify robust preclinical endpoints that may guide the selection of novel genetic treatments. At 6 weeks, ~6-7 months and ~12 months of age, malin deficient mice ("KO") and wild type (WT) littermates underwent a standardized home-cage behavioral assessment designed to non-obtrusively appraise features of rest/arousal, consumptive behaviors, risk aversion and voluntary wheel-running. At all timepoints, and over a range of metrics that we report transparently, WT and KO mice were essentially indistinguishable. In contrast, within WT mice compared across timepoints, we identified age-related nocturnal hypoactivity, diminished sucrose preference and reduced wheel-running. Neuropathological examinations in subsets of the same mice revealed expected age dependent LB accumulation, gliosis and microglial activation in cortical and subcortical brain regions. At 12 months of age, despite the burden of neocortical LBs, we did not identify spontaneous seizures during an electroencephalographic (EEG) survey, and KO and WT mice exhibited similar spectral EEG features. Using an in vitro assay of neocortical function, paroxysmal increases in network activity (UP states) in KO slices were more prolonged at 3 and 6 months of age, but were similar to WT at 12 months. KO mice displayed a distinct response to pentylenetetrazole, with a greater incidence of clonic seizures and a more pronounced post-ictal suppression of movement, feeding and drinking behavior. Together, these results highlight a stark clinicopathologic dissociation in a mouse model of LD, where LBs accrue substantially without clinically meaningful changes in overall wellbeing. Our findings allude to a delay between LB accumulation and neurobehavioral decline: one that may provide a window for treatment, and whose precise duration may be difficult to ascertain within the typical lifespan of a laboratory mouse.

Characterization of excretory/secretory products of the Taenia crassiceps cysticercus involved in the induction of regulatory T cells in vivo

The ability to modulate the host immune response has allowed some parasites to establish themselves in the tissues of an immunocompetent organism. While some parasite excretion/secretion products (ESPs) were recently reported to induce differentiation of regulatory T cells (Tregs), their identity is not known. This work is aimed to identify and characterize ESPs of Taenia crassiceps cysticerci linked with Treg induction in vivo. ESPs were obtained from cultures of T. crassiceps cysticerci and inoculated in mice, measuring Treg levels by flow cytometry. Proteins in ESPs were analyzed by electrophoresis; then, ESPs were classified as either differential or conserved. Differentially included proteins were MS-sequenced and functionally characterized. Only 4 of 10 ESPs induced Tregs. Proteins with catalytic activity and those involved in immunological processes predominated, supporting the idea that these molecules could play an important role in the induction of Tregs.

The gut microbiome contributes to somatic morphine withdrawal behavior and implicates a TLR2 mediated mechanism

The ongoing opioid epidemic has left millions of people suffering from opioid use disorder due to the over-prescription of highly addictive substances. Chronic opioid exposure leads to dependence, where the absence of the drug results in negative symptoms of withdrawal, often driving patients to continue drug use; however, few therapeutic strategies are currently available to combat the cycle of addiction and the severity of morphine withdrawal. This study investigates the microbiome as a potential therapeutic target for morphine withdrawal, as gut dysbiosis caused by morphine use has been proven to contribute to other aspects of opioid use disorders, such as tolerance. Results show that although the microbiome during morphine withdrawal trends toward recovery from morphine-induced dysbiosis, there continues to be a disruption in the alpha and beta diversity as well as the abundance of gram-positive bacteria that may still contribute to the severity of morphine withdrawal symptoms. Germ-free mice lacking the microbiome did not develop somatic withdrawal symptoms, indicating that the microbiome is necessary for the development of somatic withdrawal behavior. Notably, only TLR2 but not TLR4 whole-body knockout models display less withdrawal severity, implicating that the microbiome, through a gram-positive, TLR2 mediated mechanism, drives opioid-induced somatic withdrawal behavior.

Interfering With Contextual Fear Memories by Post-reactivation Administration of Propranolol in Mice: A Series of Null Findings

Post-reactivation amnesia of contextual fear memories by blockade of noradrenergic signaling has been shown to have limited replicability in rodents. This is usually attributed to several boundary conditions that gate the destabilization of memory during its retrieval. How these boundary conditions can be overcome, and what neural mechanisms underlie post-reactivation changes in contextual fear memories remain largely unknown. Here, we report a series of experiments in a contextual fear-conditioning paradigm in mice, that were aimed at solving these issues. We first attempted to obtain a training paradigm that would consistently result in contextual fear memory that could be destabilized upon reactivation, enabling post-retrieval amnesia by the administration of propranolol. Unexpectedly, our attempts were unsuccessful to this end. Specifically, over a series of experiments in which we varied different parameters of the fear acquisition procedure, at best small and inconsistent effects were observed. Additionally, we found that propranolol did not alter retrieval-induced neural activity, as measured by the number of c-Fos⁺ cells in the hippocampal dentate gyrus. To determine whether propranolol was perhaps ineffective in interfering with reactivated contextual fear memories, we also included anisomycin (i.e., a potent and well-known amnesic drug) in several experiments, and measures of synaptic glutamate receptor subunit GluA2 (i.e., a marker of memory destabilization). No post-retrieval amnesia by anisomycin and no altered GluA2 expression by reactivation was observed, suggesting that the memories did not undergo destabilization. The null findings are surprising, given that the training paradigms we implemented were previously shown to result in memories that could be modified upon reactivation. Together, our observations illustrate the elusive nature of reactivation-dependent changes in non-human fear memory.

SLEEPINESS PROFILES IN MICE SUBMITTED TO ACUTE AND CHRONIC SLEEP DEPRIVATION

Sleepiness is a behavioural consequence of sleep pressure, which shows interindividual variation, a characteristic possibly related to central sleep mechanisms. However, there is a lack of evidence linking progressive sleep need and sleepiness with factors of individual variability, which could be tested by total acute and chronic sleep deprivation. Thus, the objective of the study was to investigate the development of sleepiness in sleep deprived mice. Male C57BL/6J mice were distributed in sleep deprivation, sleep rebound and control groups. Animals underwent acute sleep deprivation for 3, 6, 9 or 12hours or chronic sleep deprivation for 6hours for 5 consecutive days. Sleep rebound groups had a sleep opportunity for 1, 2, 3, or 4hours after acute sleep deprivation or 24hours after chronic sleep deprivation. During the protocols, sleep attempts were counted to calculate a sleepiness index. After euthanasia, blood was collected for corticosterone assessment. Using the average of group sleep attempts, it was possible to differentiate between sleepy (mean>group average) and resistant animals (mean<group average). Resistant mice were more frequent in all protocols. Individual variation accounted for 52% of sleepiness variance during chronic sleep deprivation and extended wakefulness explained 68% of sleepiness variance during acute sleep deprivation. A normal corticosterone peak was observed at the start of the dark phase, independent of sleep deprivation. Different profiles of sleepiness emerged in sleep deprived mice. Sleep deprivation was the main factor for sleepiness during acute sleep deprivation whereas in chronic deprivation individual variation was more relevant.

Dissociation of impulsive traits by subthalamic metabotropic glutamate receptor 4

Behavioral strategies require gating of premature responses to optimize outcomes. Several brain areas control impulsive actions, but the neuronal basis of natural variation in impulsivity between individuals remains largely unknown. Here, by combining a Go/No-Go behavioral assay with resting-state (rs) functional MRI in mice, we identified the subthalamic nucleus (STN), a known gate for motor control in the basal ganglia, as a major hotspot for trait impulsivity. In vivo recorded STN neural activity encoded impulsive action as a separable state from basic motor control, characterized by decoupled STN/substantia nigra pars reticulata (SNr) mesoscale networks. Optogenetic modulation of STN activity bidirectionally controlled impulsive behavior. Pharmacological and genetic manipulations showed that these impulsive actions are modulated by metabotropic glutamate receptor 4 (mGlu4) function in STN and its coupling to SNr in a behavioral trait-dependent manner, and independently of general motor function. In conclusion, STN circuitry multiplexes motor control and trait impulsivity, which are molecularly dissociated by mGlu4. This provides a potential mechanism for the genetic modulation of impulsive behavior, a clinically relevant predictor for developing psychiatric disorders associated with impulsivity.

Measuring Behavior in the Home Cage: Study Design, Applications, Challenges, and Perspectives

The reproducibility crisis (or replication crisis) in biomedical research is a particularly existential and under-addressed issue in the field of behavioral neuroscience, where, in spite of efforts to standardize testing and assay protocols, several known and unknown sources of confounding environmental factors add to variance. Human interference is a major contributor to variability both within and across laboratories, as well as novelty-induced anxiety. Attempts to reduce human interference and to measure more "natural" behaviors in subjects has led to the development of automated home-cage monitoring systems. These systems enable prolonged and longitudinal recordings, and provide large continuous measures of spontaneous behavior that can be analyzed across multiple time scales. In this review, a diverse team of neuroscientists and product developers share their experiences using such an automated monitoring system that combines Noldus PhenoTyper® home-cages and the video-based tracking software, EthoVision® XT, to extract digital biomarkers of motor, emotional, social and cognitive behavior. After presenting our working definition of a "home-cage", we compare home-cage testing with more conventional out-of-cage tests (e.g., the open field) and outline the various advantages of the former, including opportunities for within-subject analyses and assessments of circadian and ultradian activity. Next, we address technical issues pertaining to the acquisition of behavioral data, such as the fine-tuning of the tracking software and the potential for integration with biotelemetry and optogenetics. Finally, we provide guidance on which behavioral measures to emphasize, how to filter, segment, and analyze behavior, and how to use analysis scripts. We summarize how the PhenoTyper has applications to study neuropharmacology as well as animal models of neurodegenerative and neuropsychiatric illness. Looking forward, we examine current challenges and the impact of new developments. Examples include the automated recognition of specific behaviors, unambiguous tracking of individuals in a social context, the development of more animal-centered measures of behavior and ways of dealing with large datasets. Together, we advocate that by embracing standardized home-cage monitoring platforms like the PhenoTyper, we are poised to directly assess issues pertaining to reproducibility, and more importantly, measure features of rodent behavior under more ethologically relevant scenarios.

Activation of a hippocampal CREB-pCREB-miRNA-MEF2 axis modulates individual variation of spatial learning and memory capability

Phenotypic variation is a fundamental prerequisite for cell and organism evolution by natural selection. Whereas the role of stochastic gene expression in phenotypic diversity of genetically identical cells is well studied, not much is known regarding the relationship between stochastic gene expression and individual behavioral variation in animals. We demonstrate that a specific miRNA (miR-466f-3p) is upregulated in the hippocampus of a portion of individual inbred mice upon a Morris water maze task. Significantly, miR-466f-3p positively regulates the neuron morphology, function and spatial learning, and memory capability of mice. Mechanistically, miR-466f-3p represses translation of MEF2A, a negative regulator of learning/memory. Finally, we show that varied upregulation of hippocampal miR-466f-3p results from randomized phosphorylation of hippocampal cyclic AMP (cAMP)-response element binding (CREB) in individuals. This finding of modulation of spatial learning and memory via a randomized hippocampal signaling axis upon neuronal stimulation represents a demonstration of how variation in tissue gene expression lead to varied animal behavior.

Inter-individual variability in habituation of anxiety-related responses within three mouse inbred strains

Inter-individual variability in behavioral and physiological response has become a well-established phenomenon in animal models of anxiety and other disorders. Such variability is even demonstrated within mouse inbred strains. A recent study showed that adaptive and non-adaptive anxiety phenotypes (measured as habituation and/or sensitization of anxiety responses) may differ within cohorts of 129 mice. This variability was expressed across both anxiety- and activity-related behavioral dimensions. These findings were based however on re-analysis of previously published data. The present study therefore aimed to empirically validate these findings in 129 mice. In addition, we assessed such inter-individuality in two other strains: BALB/c and C57BL/6. Males of three mouse inbred strains (BALB/c, C57BL/6 and 129S2) were behaviorally characterized through repeated exposure to a mild aversive stimulus (modified Hole Board, 4 consecutive trials). Behavioral observations were supplemented with assessment of circulating corticosterone levels. Clustering the individual response trajectories of behavioral and endocrine responses yielded two multidimensional response types of different adaptive value. Interestingly, these response types were displayed by individuals of all three strains. The response types differed significantly on anxiety and activity related behavioral dimensions but not on corticosterone concentrations. This study empirically confirms that adaptive capacities may differ within 129 cohorts. In addition, it extends this inter-individual variability in behavioral profiles to BALB/c and C57BL/6. Whether these two sub-types constitute differential anxiety phenotypes may differ per strain and requires further study.

A cross-species assessment of behavioral flexibility in compulsive disorders

Lack of behavioral flexibility has been proposed as one underlying cause of compulsions, defined as repetitive behaviors performed through rigid rituals. However, experimental evidence has proven inconsistent across human and animal models of compulsive-like behavior. In the present study, applying a similarly-designed reversal learning task in two different species, which share a common symptom of compulsivity (human OCD patients and Sapap3 KO mice), we found no consistent link between compulsive behaviors and lack of behavioral flexibility. However, we showed that a distinct subgroup of compulsive individuals of both species exhibit a behavioral flexibility deficit in reversal learning. This deficit was not due to perseverative, rigid behaviors as commonly hypothesized, but rather due to an increase in response lability. These cross-species results highlight the necessity to consider the heterogeneity of cognitive deficits in compulsive disorders and call for reconsidering the role of behavioral flexibility in the aetiology of compulsive behaviors.

Metallothionein 1 Overexpression Does Not Protect Against Mitochondrial Disease Pathology in Ndufs4 Knockout Mice

Mitochondrial diseases (MD), such as Leigh syndrome (LS), present with severe neurological and muscular phenotypes in patients, but have no known cure and limited treatment options. Based on their neuroprotective effects against other neurodegenerative diseases in vivo and their positive impact as an antioxidant against complex I deficiency in vitro, we investigated the potential protective effect of metallothioneins (MTs) in an Ndufs4 knockout mouse model (with a very similar phenotype to LS) crossed with an Mt1 overexpressing mouse model (TgMt1). Despite subtle reductions in the expression of neuroinflammatory markers GFAP and IBA1 in the vestibular nucleus and hippocampus, we found no improvement in survival, growth, locomotor activity, balance, or motor coordination in the Mt1 overexpressing Ndufs4-/- mice. Furthermore, at a cellular level, no differences were detected in the metabolomics profile or gene expression of selected one-carbon metabolism and oxidative stress genes, performed in the brain and quadriceps, nor in the ROS levels of macrophages derived from these mice. Considering these outcomes, we conclude that MT1, in general, does not protect against the impaired motor activity or improve survival in these complex I-deficient mice. The unexpected absence of increased oxidative stress and metabolic redox imbalance in this MD model may explain these observations. However, tissue-specific observations such as the mildly reduced inflammation in the hippocampus and vestibular nucleus, as well as differential MT1 expression in these tissues, may yet reveal a tissue- or cell-specific role for MTs in these mice.

Primary cilia safeguard cortical neurons in neonatal mouse forebrain from environmental stress-induced dendritic degeneration

The developing brain is under the risk of exposure to a multitude of environmental stressors. While perinatal exposure to excessive levels of environmental stress is responsible for a wide spectrum of neurological and psychiatric conditions, the developing brain is equipped with intrinsic cell protection, the mechanisms of which remain unknown. Here we show, using neonatal mouse as a model system, that primary cilia, hair-like protrusions from the neuronal cell body, play an essential role in protecting immature neurons from the negative impacts of exposure to environmental stress. More specifically, we found that primary cilia prevent the degeneration of dendritic arbors upon exposure to alcohol and ketamine, two major cell stressors, by activating cilia-localized insulin-like growth factor 1 receptor and downstream Akt signaling. We also found that activation of this pathway inhibits Caspase-3 activation and caspase-mediated cleavage/fragmentation of cytoskeletal proteins in stress-exposed neurons. These results indicate that primary cilia play an integral role in mitigating adverse impacts of environmental stressors such as drugs on perinatal brain development.

On the Digital Psychopharmacology of Valproic Acid in Mice

Antiepileptic drugs (AEDs) require daily ingestion for maximal seizure prophylaxis. Adverse psychiatric consequences of AEDs present as: (i) reversible changes in mood, anxiety, anger and/or irritability that often necessitate drug discontinuation, and (ii) autism and/or cognitive/psychomotor delays following fetal exposure. Technical advances in quantifying naturalistic rodent behaviors may provide sensitive preclinical estimates of AED psychiatric tolerability and neuropsychiatric teratogenicity. In this study, we applied instrumented home-cage monitoring to assess how valproic acid (VPA, dissolved in sweetened drinking water) alters home-cage behavior in adult C57BL/6J mice and in the adult offspring of VPA-exposed breeder pairs. Through a pup open field assay, we also examined how prenatal VPA exposure impacts early spontaneous exploratory behavior. At 500-600 mg/kg/d, chronic VPA produced hyperphagia and increased wheel-running without impacting sleep, activity and measures of risk aversion. When applied to breeder pairs of mice throughout gestation, VPA prolonged the latency to viable litters without affecting litter size. Two-weeks old VPA-exposed pups displayed open field hypoactivity without alterations in thigmotaxis. As adults, prenatal VPA-exposed mice displayed active state fragmentation, hypophagia and increased wheel running, together with subtle alterations in home-cage dyadic behavior. Together, these data illustrate how automated home-cage assessments of spontaneous behavior capture an ethologically centered psychopharmacological profile of enterally administered VPA that is aligned with human clinical experience. By characterizing the effects of pangestational VPA exposure, we discover novel murine expressions of pervasive neurodevelopment. Incorporating such rigorous assessments of psychological tolerability may inform the design of future AEDs with improved neuropsychiatric safety profiles, both for patients and their offspring.

Schizophrenia: Developmental Variability Interacts with Risk Factors to Cause the Disorder: Nonspecific Variability-Enhancing Factors Combine with Specific Risk Factors to Cause Schizophrenia

A new etiological model is proposed for schizophrenia that combines variability-enhancing nonspecific factors acting during development with more specific risk factors. This model is better suited than the current etiological models of schizophrenia, based on the risk factors paradigm, for predicting and/or explaining several important findings about schizophrenia: high co-morbidity rates, low specificity of many risk factors, and persistence in the population of the associated genetic polymorphisms. Compared with similar models, e.g., de-canalization, common psychopathology factor, sexual-selection, or differential sensitivity to the environment, this proposal is more general and integrative. Recently developed research methods have proven the existence of genetic and environmental factors that enhance developmental variability. Applying such methods to newly collected or already available data can allow for testing the hypotheses upon which this model is built. If validated, this model may change the understanding of the etiology of schizophrenia, the research models, and preventionbrk paradigms.

The Impact of Social and Behavioral Factors on Reproducibility in Terrestrial Vertebrate Models

The use of animal models remains critical in preclinical and translational research. The reliability of the animal models and aspects of their validity is likely key to effective translation of findings to medicine. However, despite considerable uniformity in animal models brought about by control of genetics, there remain a number of social as well as innate and acquired behavioral characteristics of laboratory animals that may impact on research outcomes. These include the effects of strain and genetics, age and development, sex, personality and affective states, and social factors largely brought about by housing and husbandry. In addition, aspects of the testing environment may also influence research findings. A number of considerations resulting from the animals' innate and acquired behavioral characteristics as well as their social structures are described. Suggestions for minimizing the impact of these factors on research are provided.

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.

An individual based, multidimensional approach to identify emotional reactivity profiles in inbred mice

BACKGROUND

Despite extensive environmental standardization and the use of genetically and microbiologically defined mice of similar age and sex, individuals of the same mouse inbred strain commonly differ in quantitative traits. This is a major issue as it affects the quality of experimental results. Standard analysis practices summarize numerical data by means and associated measures of dispersion, while individual values are ignored. Perhaps taking individual values into account in statistical analysis may improve the quality of results.

NEW METHOD

The present study re-inspected existing data on emotional reactivity profiles in 125 BALB/cJ and 129 mice, which displayed contrasting patterns of habituation and sensitization when repeatedly exposed to a novel environment (modified Hole Board). Behaviors were re-analyzed on an individual level, using a multivariate approach, in order to explore whether this yielded new information regarding subtypes of response, and their expression between and within strains.

RESULTS

Clustering individual mice across multiple behavioral dimensions identified two response profiles: a habituation and a sensitization cluster.

COMPARISON WITH EXISTING METHOD(S)

These retrospect analyses identified habituation and sensitization profiles that were similar to those observed in the original data but also yielded new information such as a more pronounced sensitization response. Also, it allowed for the identification of individuals that deviated from the predominant response profile within a strain.

CONCLUSIONS

The present approach allows for the behavioral characterization of experimental animals on an individual level and as such provides a valuable contribution to existing approaches that take individual variation into account in statistical analysis.

Proteomic Analysis of Myocardia Containing the Obscurin R4344Q Mutation Linked to Hypertrophic Cardiomyopathy

Obscurin is a giant cytoskeletal protein with structural and regulatory roles encoded by the OBSCN gene. Recently, mutations in OBSCN were associated with the development of different forms of cardiomyopathies, including hypertrophic cardiomyopathy (HCM). We previously reported that homozygous mice carrying the HCM-linked R4344Q obscurin mutation develop arrhythmia by 1-year of age under sedentary conditions characterized by increased heart rate, frequent incidents of premature ventricular contractions, and episodes of spontaneous ventricular tachycardia. In an effort to delineate the molecular mechanisms that contribute to the observed arrhythmic phenotype, we subjected protein lysates prepared from left ventricles of 1-year old R4344Q and wild-type mice to comparative proteomics analysis using tandem mass spectrometry; raw data are available via ProteomeXchange with identifier PXD017314. We found that the expression levels of proteins involved in cardiac function and disease, cytoskeletal organization, electropotential regulation, molecular transport and metabolism were significantly altered. Moreover, phospho-proteomic evaluation revealed changes in the phosphorylation profile of Ca²⁺ cycling proteins, including sAnk1.5, a major binding partner of obscurin localized in the sarcoplasmic reticulum; notably, this is the first report indicating that sAnk1 undergoes phosphorylation. Taken together, our findings implicate obscurin in diverse cellular processes within the myocardium, which is consistent with its multiple binding partners, localization in different subcellular compartments, and disease association.

Reproducibility of animal research in light of biological variation

Context-dependent biological variation presents a unique challenge to the reproducibility of results in experimental animal research, because organisms' responses to experimental treatments can vary with both genotype and environmental conditions. In March 2019, experts in animal biology, experimental design and statistics convened in Blonay, Switzerland, to discuss strategies addressing this challenge. In contrast to the current gold standard of rigorous standardization in experimental animal research, we recommend the use of systematic heterogenization of study samples and conditions by actively incorporating biological variation into study design through diversifying study samples and conditions. Here we provide the scientific rationale for this approach in the hope that researchers, regulators, funders and editors can embrace this paradigm shift. We also present a road map towards better practices in view of improving the reproducibility of animal research.

The Life of Behavior

Neuroscience needs behavior. However, it is daunting to render the behavior of organisms intelligible without suppressing most, if not all, references to life. When animals are treated as passive stimulus-response, disembodied and identical machines, the life of behavior perishes. Here, we distill three biological principles (materiality, agency, and historicity), spell out their consequences for the study of animal behavior, and illustrate them with various examples from the literature. We propose to put behavior back into context, with the brain in a species-typical body and with the animal's body situated in the world; stamp Newtonian time with nested ontogenetic and phylogenetic processes that give rise to individuals with their own histories; and supplement linear cause-and-effect chains and information processing with circular loops of purpose and meaning. We believe that conceiving behavior in these ways is imperative for neuroscience.

High Behavioral Sensitivity to Carbon Dioxide Associates with Enhanced Fear Memory and Altered Forebrain Neuronal Activation

There is considerable interest in pre-trauma individual differences that may contribute to increased risk for developing post-traumatic stress disorder (PTSD). Identification of underlying vulnerability factors that predict differential responses to traumatic experiences is important. Recently, the relevance of homeostatic perturbations in shaping long-term behavior has been recognized. Sensitivity to CO₂ inhalation, a homeostatic threat to survival, was shown to associate with the later development of PTSD symptoms in veterans. Here, we investigated whether behavioral sensitivity to CO₂ associates with PTSD-relevant behaviors and alters forebrain fear circuitry in mice. Mice were exposed to 5% CO₂ or air inhalation and tested one week later on acoustic startle and footshock contextual fear conditioning, extinction and reinstatement. CO₂ inhalation evoked heterogenous freezing behaviors (high freezing CO₂-H and low freezing CO₂-L) that significantly associated with fear conditioning and extinction behaviors. CO₂-H mice elicited potentiated conditioned fear and delayed extinction while behavioral responses in CO₂-L mice were similar to the air group. Persistent neuronal activation marker ΔFosB immunostaining revealed altered regional neuronal activation within the hippocampus, amygdala and medial pre-frontal cortex that correlated with conditioned fear and extinction. Inter-regional co-activation mapping revealed disruptions in the coordinated activity of hippocampal dentate-amygdala-infralimbic regions and infralimbic-prelimbic associations in CO₂-H mice that may explain their enhanced fear phenotype. In conclusion, our data support an association of behavioral sensitivity to interoceptive threats such as CO₂ with altered fear responding to exteroceptive threats and suggest that "CO₂-sensitive" individuals may be susceptible to developing PTSD.

Animal models of liability to post-traumatic stress disorder: going beyond fear memory

In this review, we advocate a dimensional approach on the basis of candidate endophenotypes to the development of animal models of post-traumatic stress disorder (PTSD) capable of including genetic liability factors, variations in symptoms profile and underlying neurobiological mechanisms, and specific comorbidities. Results from the clinical literature pointed to two candidate endophenotypes of PTSD: low sensory gating and high waiting impulsivity. Findings of comparative studies in mice of two inbred strains characterized by different expressions of the two candidate endophenotypes showed different strain-specific neural and behavioral effects of stress experiences. Thus, mice of the standard C57BL/6J strain show stress-induced helplessness, stress-learned helplessness, and stress-extinction-resistant conditioned freezing. Instead, mice of the genetically unrelated DBA/2J strain, expressing both candidate endophenotypes, show stress-induced extinction-resistant avoidance and neural and behavioral phenotypes promoted by prolonged exposure to addictive drugs. These strain differences are in line with evidence of associations between genetic variants and specific stress-promoted pathological profiles in PTSD, support a role of genotype in determining different PTSD comorbidities, and offer the means to investigate specific pathogenic processes.

Home-cage monitoring ascertains signatures of ictal and interictal behavior in mouse models of generalized seizures

Epilepsy is a significant contributor to worldwide disability. In epilepsy, disability can be broadly divided into two components: ictal (pertaining to the burden of unpredictable seizures and associated medical complications including death) and interictal (pertaining to more pervasive debilitating changes in cognitive and emotional behavior). In this study, we objectively and noninvasively appraise aspects of ictal and interictal behavior in mice using instrumented home-cage chambers designed to assay kinematic and appetitive behavioral measures. Through daily intraperitoneal injections of the chemoconvulsant pentylenetetrazole (PTZ) applied to C57BL/6J mice, we coordinately measure how “behavioral severity” (complex dynamic changes in movement and sheltering behavior) and convulsive severity (latency and occurrence of convulsive seizures) evolve or kindle with repeated injections. By closely studying long epochs between PTZ injections, we identify an interictal syndrome of nocturnal hypoactivity and increased sheltering behavior which remits with the cessation of seizure induction. We observe elements of this interictal behavioral syndrome in seizure-prone DBA/2J mice and in mice with a pathogenic Scn1a mutation (modeling Dravet syndrome). Through analyzing their responses to PTZ, we illustrate how convulsive severity and “behavioral” severity are distinct and independent aspects of the overall severity of a PTZ-induced seizure. Our results illustrate the utility of an ethologically centered automated approach to quantitatively appraise murine expressions of disability in mouse models of seizures and epilepsy. In doing so, this study highlights the very unique psychopharmacological profile of PTZ.

Towards large scale automated cage monitoring - Diurnal rhythm and impact of interventions on in-cage activity of C57BL/6J mice recorded 24/7 with a non-disrupting capacitive-based technique

BACKGROUND AND AIMS

Automated recording of laboratory animal's home cage behavior is receiving increasing attention since such non-intruding surveillance will aid in the unbiased understanding of animal cage behavior potentially improving animal experimental reproducibility.

MATERIAL AND METHODS

Here we investigate activity of group held female C57BL/6J mice (mus musculus) housed in standard Individually Ventilated Cages across three test-sites: Consiglio Nazionale delle Ricerche (CNR, Rome, Italy), The Jackson Laboratory (JAX, Bar Harbor, USA) and Karolinska Insititutet (KI, Stockholm, Sweden). Additionally, comparison of female and male C57BL/6J mice was done at KI. Activity was recorded using a capacitive-based sensor placed non-intrusively on the cage rack under the home cage collecting activity data every 250 msec, 24/7. The data collection was analyzed using non-parametric analysis of variance for longitudinal data comparing sites, weekdays and sex.

RESULTS

The system detected an increase in activity preceding and peaking around lights-on followed by a decrease to a rest pattern. At lights off, activity increased substantially displaying a distinct temporal variation across this period. We also documented impact on mouse activity that standard animal handling procedures have, e.g. cage-changes, and show that such procedures are stressors impacting in-cage activity. These key observations replicated across the three test-sites, however, it is also clear that, apparently minor local environmental differences generate significant behavioral variances between the sites and within sites across weeks. Comparison of gender revealed differences in activity in the response to cage-change lasting for days in male but not female mice; and apparently also impacting the response to other events such as lights-on in males. Females but not males showed a larger tendency for week-to-week variance in activity possibly reflecting estrous cycling.

CONCLUSIONS

These data demonstrate that home cage monitoring is scalable and run in real time, providing complementary information for animal welfare measures, experimental design and phenotype characterization.

Simultaneous assessment of cognitive function, circadian rhythm, and spontaneous activity in aging mice

Cognitive function declines substantially with age in both humans and animal models. In humans, this decline is associated with decreases in independence and quality of life. Although the methodology for analysis of cognitive function in human models is relatively well established, similar analyses in animal models have many technical issues (e.g., unintended experimenter bias, motivational issues, stress, and testing during the light phase of the light dark cycle) that limit interpretation of the results. These caveats, and others, potentially bias the interpretation of studies in rodents and prevent the application of current tests of learning and memory as part of an overall healthspan assessment in rodent models of aging. The goal of this study was to establish the methodology to assess cognitive function in aging animals that addresses many of these concerns. Here, we use a food reward-based discrimination procedure with minimal stress in C57Bl/6J male mice at 6, 21, and 27 months of age, followed by a reversal task to assess behavioral flexibility. Importantly, the procedures minimize issues related to between-experimenter confounds and are conducted during both the dark and light phases of the light dark cycle in a home-cage setting. During cognitive testing, we were able to assess multiple measures of spontaneous movement and diurnal activity in young and aged mice including, distance moved, velocity, and acceleration over a 90-h period. Both initial discrimination and reversal learning significantly decreased with age and, similar to rats and humans, not all old mice demonstrated impairments in learning with age. These results permitted classification of animals based on their cognitive status. Analysis of movement parameters indicated decreases in distance moved as well as velocity and acceleration with increasing age. Based on these data, we developed preliminary models indicating, as in humans, a close relationship exists between age-related movement parameters and cognitive ability. Our results provide a reliable method for assessing cognitive performance with minimal stress and simultaneously provide key information on movement and diurnal activity. These methods represent a novel approach to developing non-invasive healthspan measures in rodent models that allow standardization across laboratories.

Laboratory mouse housing conditions can be improved using common environmental enrichment without compromising data

Animal welfare requires the adequate housing of animals to ensure health and well-being. The application of environmental enrichment is a way to improve the well-being of laboratory animals. However, it is important to know whether these enrichment items can be incorporated in experimental mouse husbandry without creating a divide between past and future experimental results. Previous small-scale studies have been inconsistent throughout the literature, and it is not yet completely understood whether and how enrichment might endanger comparability of results of scientific experiments. Here, we measured the effect on means and variability of 164 physiological parameters in 3 conditions: with nesting material with or without a shelter, comparing these 2 conditions to a “barren” regime without any enrichments. We studied a total of 360 mice from each of 2 mouse strains (C57BL/6NTac and DBA/2NCrl) and both sexes for each of the 3 conditions. Our study indicates that enrichment affects the mean values of some of the 164 parameters with no consistent effects on variability. However, the influence of enrichment appears negligible compared to the effects of other influencing factors. Therefore, nesting material and shelters may be used to improve animal welfare without impairment of experimental outcome or loss of comparability to previous data collected under barren housing conditions.

Adequate housing of laboratory animals is essential to guarantee their well-being. From a scientific perspective, physically and mentally healthy animals also contribute to increased validity and reproducibility of experimental results. The choice of nesting material or shelter type, referred to as environmental enrichment, may influence how laboratory animals perform species-specific behaviors. Consequently, changes in these nesting and shelter materials could influence scientific results by, for example, increasing variability in measured characteristics. Whether studies using different environmental enrichment materials can be compared is currently questioned. Our study shows that simple, species-specific environmental enrichment in the form of nesting material alone or in combination with a shelter did not consistently increase variability of physiological parameters in mice. Differences in parameter average values appeared to be of minor biological relevance when compared to the effects of other environmental factors. These simple environmental enrichment devices may therefore be applied to improve the housing environment of laboratory mice without compromising data validity or comparability.

Introducing Clicker Training as a Cognitive Enrichment for Laboratory Mice

Establishing new refinement strategies in laboratory animal science is a central goal in fulfilling the requirements of Directive 2010/63/EU. Previous research determined a profound impact of gentle handling protocols on the well-being of laboratory mice. By introducing clicker training to the keeping of mice, not only do we promote the amicable treatment of mice, but we also enable them to experience cognitive enrichment. Clicker training is a form of positive reinforcement training using a conditioned secondary reinforcer, the "click" sound of a clicker, which serves as a time bridge between the strengthened behavior and an upcoming reward. The effective implementation of the clicker training protocol with a cohort of 12 BALB/c inbred mice of each sex proved to be uncomplicated. The mice learned rather quickly when challenged with tasks of the clicker training protocol, and almost all trained mice overcame the challenges they were given (100% of female mice and 83% of male mice). This study has identified that clicker training for mice strongly correlates with reduced fear in the mice during human-mice interactions, as shown by reduced anxiety-related behaviors (e.g., defecation, vocalization, and urination) and fewer depression-like behaviors (e.g., floating). By developing a reliable protocol that can be easily integrated into the daily routine of the keeping of laboratory mice, the lifetime experience of welfare in the mice can be improved substantially.

A murine model of peripheral irradiation-induced fatigue

PURPOSE

Fatigue is the most ubiquitous side effect of cancer treatment, but its etiology remains elusive. Further investigations into cancer-related fatigue pathobiology necessitate the expanded use of animal models. This study describes the development of a murine model of radiation-induced fatigue.

METHODS

Voluntary wheel running activity measured fatigue in 5-8 week-old, male C57BL/6 mice before and after γ irradiation totaling 2400cGy (3 consecutive days×800cGy daily fractionated doses) to the lower abdominal areas. Three trials confirmed fatigue behavior at this dose. Anhedonia, body weight, and hemoglobin were also measured. Gastrointestinal, skeletal muscle, and bone marrow tissue samples were evaluated for signs of damage.

RESULTS

In two validation trials, irradiated mice (trial 1, n=8; trial 2, n=8) covered less cumulative distance in kilometers post-irradiation (trial 1, mean=115.3±12.3; trial 2, mean=113.6±21.8) than sham controls (trial 1, n=5, mean=126.3±5.7, p=0.05; trial 2, n=8, mean=140.9±25.4, p=0.02). Decreased mean daily running distance and speed were observed during the last four hours of the dark cycle in irradiated mice compared to controls for two weeks post-irradiation. There were no differences in saccharin preference or hemoglobin levels between groups, no effect of changes in body weight or hemoglobin on wheel running distance, additionally, histology showed no damage to muscle, bone marrow, or gastrointestinal integrity, with the latter confirmed by ELISA.

CONCLUSION

We characterized a novel mouse model of fatigue caused by peripheral radiation and not associated with anemia, weight changes, or anhedonia. This model provides opportunities for detailed study of the mechanisms of radiation-induced fatigue.