Behavioral effects of ventilated micro-environment housing in three inbred mouse strains

Effects of housing conditions on stress, depressive like behavior and sensory-motor performances of C57BL/6 mice

BACKGROUND

The effects of housing conditions on animal physiology, behavior or stress are still debated. The aim of this study was to investigate the effects of three different housing systems, individually ventilated cages (IVC), classical small cages with floor surface area of 500 cm2 (CC500) and classical large cages with floor surface area of 800 cm2 (CC800) on body weight, sensory-motor performances, depression-like behavior, plasma corticosterone and brain oxidative stress parameters in C57BL/6 mice. The mice housed in one of the cages from birth to 6 months of age. Hang wire and adhesive removal tests were performed to evaluate somatosensory and motor performances. The extent of depression was determined by the forced swim test. Blood corticosterone levels were measured. In addition, brain malondialdehyde (MDA), total antioxidant status (TAS) and total oxidant status (TOS) levels were analyzed.

RESULTS

The depression-like behavior of the groups was similar. Although there were no significant differences in hang wire test among groups, CC500 group required longer durations in adhesive removal test. The body weight and plasma corticosterone levels of CC800 group were significantly higher than other groups. The oxidative stress parameters were highest in CC500 cage.

CONCLUSIONS

Our study showed that the least stressful housing condition was IVC cage systems. Interestingly, the number of mice in the classical cages had a significant effect on stress levels and sensory-motor performance.

'Invisible actors'-How poor methodology reporting compromises mouse models of oncology: A cross-sectional survey

The laboratory mouse is a key player in preclinical oncology research. However, emphasis of techniques reporting at the expense of critical animal-related detail compromises research integrity, animal welfare, and, ultimately, the translation potential of mouse-based oncology models. To evaluate current reporting practices, we performed a cross-sectional survey of 400 preclinical oncology studies using mouse solid-tumour models. Articles published in 2020 were selected from 20 journals that specifically endorsed the ARRIVE (Animal Research: Reporting of In Vivo Experiments) preclinical reporting guidelines. We assessed reporting compliance for 22 items in five domains: ethical oversight assurance, animal signalment, husbandry, welfare, and euthanasia. Data were analysed using hierarchical generalised random-intercept models, clustered on journal. Overall, reporting of animal-related items was poor. Median compliance over all categories was 23%. There was little or no association between extent of reporting compliance and journal or journal impact factor. Age, sex, and source were reported most frequently, but verifiable strain information was reported for <10% of studies. Animal husbandry, housing environment, and welfare items were reported by <5% of studies. Fewer than one in four studies reported analgesia use, humane endpoints, or an identifiable method of euthanasia. Of concern was the poor documentation of ethical oversight information. Fewer than one in four provided verifiable approval information, and almost one in ten reported no information, or information that was demonstrably false. Mice are the "invisible actors" in preclinical oncology research. In spite of widespread endorsement of reporting guidelines, adherence to reporting guidelines on the part of authors is poor and journals fail to enforce guideline reporting standards. In particular, the inadequate reporting of key animal-related items severely restricts the utility and translation potential of mouse models, and results in research waste. Both investigators and journals have the ethical responsibility to ensure animals are not wasted in uninformative research.

Role of Environment and Experimenter in Reproducibility of Behavioral Studies With Laboratory Mice

Behavioral phenotyping of mice has received a great deal of attention during the past three decades. However, there is still a pressing need to understand the variability caused by environmental and biological factors, human interference, and poorly standardized experimental protocols. The inconsistency of results is often attributed to the inter-individual difference between the experimenters and environmental conditions. The present work aims to dissect the combined influence of the experimenter and the environment on the detection of behavioral traits in two inbred strains most commonly used in behavioral genetics due to their contrasting phenotypes, the C57BL/6J and DBA/2J mice. To this purpose, the elevated O-maze, the open field with object, the accelerating rotarod and the Barnes maze tests were performed by two experimenters in two diverse laboratory environments. Our findings confirm the well-characterized behavioral differences between these strains in exploratory behavior, motor performance, learning and memory. Moreover, the results demonstrate how the experimenter and the environment influence the behavioral tests with a variable-dependent effect, often with mutually exclusive contributions. In this context, our study highlights how both the experimenter and the environment can have an impact on the strain effect size without altering the direction of the conclusions. Importantly, the general agreement on the results is reached by converging evidence from multiple measures addressing the same trait. In conclusion, the present work elucidates the contribution of both the experimenter and the laboratory environment in the intricate field of reproducibility in mouse behavioral phenotyping.

Evaluation of Various IVC Systems According to Mouse Reproductive Performance and Husbandry and Environmental Parameters

IVC systems are marketed for improving the health and management of mouse colonies. The current study compared mouse reproductive performance and husbandry and environmental parameters among 3 high-density (HD) IVC rack systems (RS1, RS2, and RS3), which were present in separate but comparable rooms. Three breeding trios each of Swiss Webster (CFW) and BALB/c mice were placed in each rack (n = 36 female, n = 18 male). Reproductive indices were measured for 3 breeding cycles over 2 generations; indices included time to parturition, litter size and pup weight, survivability, and interbirth interval. Over 18 wk, personnel used scoring systems to evaluate each RS daily to every other week according to cage dirtiness, need for spot changing, ease of cage changing, daily health checks, and cage wash processing. Macroenvironmental parameters (temperature, relative humidity, noise, total particulate matter) were measured weekly over 14 wks. Microenvironmental parameters (temperature, relative humidity, NH₃, CO₂, O₂) of 2 cages each of male and female CFW mice (4 mice/cage) on each RS were measured at 6 time points over 2 wks. RS1 had significantly smaller mean litter sizes of CFW mice (mean ± 1 SD, 6.5 ± 2.9 pups) as compared with both RS2 (9.5 ± 1.7 pups) and RS3 (9.3 ± 3.8 pups). RS1 scored as being significantly easier to process through the cage wash. RS2 had significantly lower room noise levels (46.0 ± 5.0 dBA) but higher humidity (58.6% ± 8.9%) as compared with both RS1 (43.7% ± 9.9%) and RS3 (46.0% ± 12.0%) over the 2-wk cycle, particularly at 8 and 12 d after cage change. In conclusion, in terms of mouse reproductive performance and husbandry and environmental parameters, each system had at least 1 advantage over the other 2. Therefore, various factors should be considered when choosing an IVC system for mice.

Behavioural effects of cage systems on the G93A Superoxide Dismutase 1 transgenic mouse model for amyotrophic lateral sclerosis

Environmental factors inherent to animal facilities can impact on the neuro-behavioural phenotype of laboratory mice and genetic mouse models for human diseases. Many facilities have upgraded from traditional 'open filter top' cages (FT) to individually ventilated cage (IVC) systems, which have been shown to modify various behavioural responses of laboratory mice. Importantly, the impact of IVC housing on the G93A superoxide dismutase 1 mouse model of amyotrophic lateral sclerosis (ALS) is currently unknown. Male and female wild type-like (WT) and heterozygous SOD1^G93A mice were group-housed in FT or IVC systems from PND 30 ± 5 onwards. Body weight and motor function were assessed weekly from 15 weeks onward. Mice were also tested for cognitive abilities (i.e., fear conditioning and social recognition memory) and sensorimotor gating (i.e., prepulse inhibition: PPI). SOD1^G93A mice lost body weight, and their motor function degenerated over time compared with control littermates. Motor impairments developed faster when SOD1^G93A females were housed in IVCs. Context and cue freezing were increased in SOD1^G93A females compared with controls, whereas all SOD1^G93A mice exhibited lower acoustic startle and PPI than WT mice. IVC housing led to an increase in cue freezing in males and reduced the severity of PPI deficits in SOD1^G93A females. Overall, IVC housing impacted moderately on the SOD1^G93A phenotype but central behavioural deficits were still evident across housing conditions. Nonetheless, our findings indicate the importance of assessing the effect of cage system in genetic mouse models as these systems can modulate the magnitude and onset of genotypic differences.

The epidemiology of fighting in group-housed laboratory mice

Injurious home-cage aggression (fighting) in mice affects both animal welfare and scientific validity. It is arguably the most common potentially preventable morbidity in mouse facilities. Existing literature on mouse aggression almost exclusively examines territorial aggression induced by introducing a stimulus mouse into the home-cage of a singly housed mouse (i.e. the resident/intruder test). However, fighting occurring in mice living together in long-term groups under standard laboratory housing conditions has barely been studied. We performed a point-prevalence epidemiological survey of fighting at a research institution with an approximate 60,000 cage census. A subset of cages was sampled over the course of a year and factors potentially influencing home-cage fighting were recorded. Fighting was almost exclusively seen in group-housed male mice. Approximately 14% of group-housed male cages were observed with fighting animals in brief behavioral observations, but only 14% of those cages with fighting had skin injuries observable from cage-side. Thus simple cage-side checks may be missing the majority of fighting mice. Housing system (the combination of cage ventilation and bedding type), genetic background, time of year, cage location on the rack, and rack orientation in the room were significant risk factors predicting fighting. Of these predictors, only bedding type is easily manipulated to mitigate fighting. Cage ventilation and rack orientation often cannot be changed in modern vivaria, as they are baked in by cookie-cutter architectural approaches to facility design. This study emphasizes the need to invest in assessing the welfare costs of new housing and husbandry systems before implementing them.

Comparative Effects of 1/4-inch and 1/8-inch Corncob Bedding on Cage Ammonia Levels, Behavior, and Respiratory Pathology of Male C57BL/6 and 129S1/Svlm Mice

Corncob is a common bedding material used in laboratory rodents, but little is known about differences in the effects of the 2 available sizes on rodent models and health. This study compared the effects of these 2 corncob bedding sizes on cage ammonia levels, behavior, and respiratory pathology in mice. We hypothesized that the beddings would not differ significantly in their effects on these parameters. Two strains of male mice (C57BL/6 and 129S1/Svlm) were housed in static, filter-top cages containing 1 of the 2 bedding types for the duration of the study (12 wk). Intracage ammonia was measured during 1 wk of the study on days 0, 3, 5, and 7. Behavior was evaluated by using circadian rhythm, open field, and Morris water-maze tests. Animals were euthanized with injectable euthanasia solution to collect respiratory and ocular tissues for histopathologic lesion scoring. Animals that were euthanized immediately upon arrival from the vendor served as negative controls. Bedding size did not significantly affect behavior or ammonia levels. Average intracage ammonia levels on day 7 were 525 ppm for 1/4-in. bedding and 533 ppm for 1/8-in. bedding. Regardless of the bedding size, lesions noted in both strains of mice were of similar incidence and severity, were limited to the nose, and consisted of minimal to mild suppurative rhinitis. The eyes, trachea, and lungs were not affected. In conclusion, 1/4-in. and 1/8-in. corncob beddings have comparable effects on cage ammonia levels and the behavior and respiratory pathology in male mice of the strains tested.

Housing mice in the individually ventilated or open cages-Does it matter for behavioral phenotype?

Individually ventilated caging (IVC) systems for rodents are increasingly common in laboratory animal facilities. However, the impact of such substantial change in housing conditions on animal physiology and behavior is still debated. Most importantly, there arise the questions regarding reproducibility and comparison of previous or new phenotypes between the IVC and open cages. The present study was set up for detailed and systematic comparison of behavioral phenotypes in male and female mice of three widely used inbred strains (C57BL/6JRccHsd, DBA/2JRccHsd, 129S2/SvHSd) after being kept in two housing environments (IVC and open cages) for 6 weeks (since 4 weeks of age) before behavioral testing. The tests addressed exploratory, anxiety-like and stress-related behavior (light-dark box, open field, forced swim test, stress-induced hyperthermia), social approach and species-specific behavior (nest building, marble burying). In all tests, large and expected strain differences were found. Somewhat surprisingly, the most striking effect of environment was found for basal body temperature and weight loss after one night of single housing in respective cages. In addition, the performance in light-dark box and open field was affected by environment. Several parameters in different tests showed significant interaction between housing and genetic background. In summary, the IVC housing did not invalidate the well-known differences between the mouse strains which have been established by previous studies. However, within the strains the results can be influenced by sex and housing system depending on the behavioral tasks applied. The bottom-line is that the environmental conditions should be described explicitly in all publications.

Maternal immune activation: reporting guidelines to improve the rigor, reproducibility, and transparency of the model

The 2017 American College of Neuropychopharmacology (ACNP) conference hosted a Study Group on 4 December 2017, Establishing best practice guidelines to improve the rigor, reproducibility, and transparency of the maternal immune activation (MIA) animal model of neurodevelopmental abnormalities. The goals of this session were to (a) evaluate the current literature and establish a consensus on best practices to be implemented in MIA studies, (b) identify remaining research gaps warranting additional data collection and lend to the development of evidence-based best practice design, and (c) inform the MIA research community of these findings. During this session, there was a detailed discussion on the importance of validating immunogen doses and standardizing the general design (e.g., species, immunogenic compound used, housing) of our MIA models both within and across laboratories. The consensus of the study group was that data does not currently exist to support specific evidence-based model selection or methodological recommendations due to lack of consistency in reporting, and that this issue extends to other inflammatory models of neurodevelopmental abnormalities. This launched a call to establish a reporting checklist focusing on validation, implementation, and transparency modeled on the ARRIVE Guidelines and CONSORT (scientific reporting guidelines for animal and clinical research, respectively). Here we provide a summary of the discussions in addition to a suggested checklist of reporting guidelines needed to improve the rigor and reproducibility of this valuable translational model, which can be adapted and applied to other animal models as well.

Mouse models of maternal immune activation: Mind your caging system!

Rodent models of maternal immune activation (MIA) are increasingly used as experimental tools to study neuronal and behavioral dysfunctions in relation to infection-mediated neurodevelopmental disorders. One of the most widely used MIA models is based on gestational administration of poly(I:C) (= polyriboinosinic-polyribocytdilic acid), a synthetic analog of double-stranded RNA that induces a cytokine-associated viral-like acute phase response. The effects of poly(I:C)-induced MIA on phenotypic changes in the offspring are known to be influenced by various factors, including the precise prenatal timing, genetic background, and immune stimulus intensity. Thus far, however, it has been largely ignored whether differences in the basic type of laboratory housing can similarly affect the outcomes of MIA models. Here, we examined this possibility by comparing the poly(I:C)-based MIA model in two housing systems that are commonly used in preclinical mouse research, namely the open cage (OC) and individually ventilated cage (IVC) systems. Pregnant C57BL6/N mice were kept in OCs or IVCs and treated with a low (1 mg/kg, i.v.) or high (5 mg/kg, i.v.) dose of poly(I:C), or with control vehicle solution. MIA or control treatment was induced on gestation day (GD) 9 or 12, and the resulting offspring were raised and maintained in OCs or IVCs until adulthood for behavioral testing. An additional cohort of dams was used to assess the influence of the different caging systems on poly(I:C)-induced cytokine and stress responses in the maternal plasma. Maternal poly(I:C) administration on GD9 caused a dose-dependent increase in spontaneous abortion in IVCs but not in OCs, whereas MIA in IVC systems during a later gestational time-point (GD12) did not affect pregnancy outcomes. Moreover, the precise type of caging system markedly affected maternal cytokines and chemokines at basal states and in response to poly(I:C) and further influenced the maternal levels of the stress hormone, corticosterone. The efficacy of MIA to induce deficits in working memory, social interaction, and sensorimotor gating in the adult offspring was influenced by the different housing conditions, the dosing of poly(I:C), and the precise prenatal timing. Taken together, the present study identifies the basic type of caging system as a novel factor that can confound the outcomes of MIA in mice. Our findings thus urge the need to consider and report the kind of laboratory housing systems used to implement MIA models. Providing this information seems pivotal to yield reproducible results in these models.

A behavioral test battery for mouse models of Angelman syndrome: a powerful tool for testing drugs and novel Ube3a mutants

Background

Angelman syndrome (AS) is a neurodevelopmental disorder caused by mutations affecting UBE3A function. AS is characterized by intellectual disability, impaired motor coordination, epilepsy, and behavioral abnormalities including autism spectrum disorder features. The development of treatments for AS heavily relies on the ability to test the efficacy of drugs in mouse models that show reliable, and preferably clinically relevant, phenotypes. We previously described a number of behavioral paradigms that assess phenotypes in the domains of motor performance, repetitive behavior, anxiety, and seizure susceptibility. Here, we set out to evaluate the robustness of these phenotypes when tested in a standardized test battery. We then used this behavioral test battery to assess the efficacy of minocycline and levodopa, which were recently tested in clinical trials of AS.

Methods

We combined data of eight independent experiments involving 111 Ube3a mice and 120 wild-type littermate control mice. Using a meta-analysis, we determined the statistical power of the subtests and the effect of putative confounding factors, such as the effect of sex and of animal weight on rotarod performance. We further assessed the robustness of these phenotypes by comparing Ube3a mutants in different genetic backgrounds and by comparing the behavioral phenotypes of independently derived Ube3a-mutant lines. In addition, we investigated if the test battery allowed re-testing the same animals, which would allow a within-subject testing design.

Results

We find that the test battery is robust across different Ube3a-mutant lines, but confirm and extend earlier studies that several phenotypes are very sensitive to genetic background. We further found that the audiogenic seizure susceptibility phenotype is fully reversible upon pharmacological treatment and highly suitable for dose-finding studies. In agreement with the clinical trial results, we found that minocycline and levodopa treatment of Ube3a mice did not show any sign of improved performance in our test battery.

Conclusions

Our study provides a useful tool for preclinical drug testing to identify treatments for Angelman syndrome. Since the phenotypes are observed in several independently derived Ube3a lines, the test battery can also be employed to investigate the effect of specific Ube3a mutations on these phenotypes.

Effect of a change in housing conditions on body weight, behavior and brain neurotransmitters in male C57BL/6J mice

The development of modern housing regimes such as individually ventilated cage (IVC) systems has become very popular and attractive in order to reduce spreading of pathogenic organisms and to lower the risk to develop a laboratory animal allergy for staff members. Additionally, optimal housing of laboratory animals contributes to improve animal health status and ensures high and comparable experimental and animal welfare standards. However, it has not been clearly elucidated whether 1) a change to IVC systems have an impact on various physiological phenotypic parameters of mice when compared to conventional, standard cages and 2) if this is further affected by changing from social to single housing. Therefore, we investigated the influence of a change in housing conditions (standard cages with social housing changed to standard or IVC cages combined with social or single housing) on body weight, behavior and a neurochemical fingerprint of male C57BL/6J mice. Body weight progression was significantly reduced when changing mice to single or social IVC cages as well as in single standard cages when compared to social standard housing. Automated motor activity measurement in the open field showed that mice maintained in social husbandry with standard cages displayed the lowest exploratory behavior but the highest activity difference upon amphetamine treatment. Elevated plus maze test revealed that a change to IVC single and social housing as well as single standard housing produced anxiety-related behavior when compared to maintenance in social standard housing. Additionally, postmortem neurochemical analysis of the striatum using high-performance liquid chromatography coupled to electrochemical detection showed significant differences in striatal dopamine and serotonin turnover levels. In summary, our data indicate a crucial influence of a change in housing conditions on several mouse phenotype parameters. We propose that the maintenance of well-defined housing conditions is mandatory to ensure reproducible and comparable results and contributes to the application of the 3R refinement principle in animal studies by contributing to welfare and hygienical standards.

Olfaction variation in mouse husbandry and its implications for refinement and standardization: UK survey of animal scents

Olfaction plays a crucial role in mouse communication, providing information about genetic identity, physiological status of conspecifics and alerting mice to potential predators. Scents of animal origin can trigger physiological and behavioural responses that could affect experimental responses and impact positively or negatively on mouse welfare. Additionally, differing olfactory profiles could help explain variation in results between laboratories. A survey was sent to animal research units in the UK to investigate potential transfer of scents of animal origin during routine husbandry procedures, and responses were obtained from animal care workers and researchers using mice in 51 institutions. The results reveal great diversity between animal units regarding the relevant husbandry routines covered. Most [71%] reported housing non-breeding male and female mice in the same room, with 76% reporting that hands were not washed and gloves not changed between handling male and female mice. The most commonly reported species housed in the same facility as mice was the rat (91%), and 41% of respondents were aware that scents from rats could affect mice. Changing of gloves between handling mice and other species was reported by 79% of respondents. Depending on the aspect considered, between 18 and 33% of respondents believed human and non-human animal odours would strongly affect mouse physiology, behaviour or standardization, while approximately 32–54% believed these effects would be weak. This indicates uncertainty regarding the significance of these factors. Understanding and controlling these practices could reduce unwanted variability in experimental results and maximize welfare.

Functional Dissociation of Group III Metabotropic Glutamate Receptors Revealed by Direct Comparison between the Behavioral Profiles of Knockout Mouse Lines

BACKGROUND

Group III metabotropic glutamate receptors (mGlu4, mGlu7, mGlu8) display differential brain distribution, which suggests different behavioral functions. However, comparison across the available animal studies remains methodologically hazardous and controversial. The present report directly compares knockouts for each group III receptor subtype using a single behavioral test battery and multivariate analysis.

METHODS

The behavioral phenotypes of C57BL/6J mice lacking mGlu4, mGlu7, or mGlu8 and their respective littermates were examined using a multimetric test battery, which included elements of neuromotor performance, exploratory behavior, and learning and memory. Multivariate statistical methods were used to identify subtype-specific behavioral profiles and variables that distinguished between these mouse lines.

RESULTS

It generally appears that mGlu7 plays a significant role in hippocampus-dependent spatial learning and in some fear-related behaviors, whereas mGlu4 is most clearly involved in startle and motivational processes. Excepting its influence on body weight, the effect of mGlu8 deletion on behavior appears more subtle than that of the other group III receptors. These receptors have been proposed as potential drug targets for a variety of psychopathological conditions.

CONCLUSION

On the basis of these controlled comparisons, we presently conclude that the different group III receptors indeed have quite distinct behavioral functions.

Individually ventilated cages cause chronic low-grade hypoxia impacting mice hematologically and behaviorally

Use of individually ventilated caging (IVC) systems for mouse-based laboratory investigation has dramatically increased. We found that without mice present, intra-cage oxygen concentration was comparable (21%) between IVC housing and ambient environment caging (AEC) that used wire top lids. However, when mice were housed 4-to-a-cage for 1week, intra-cage oxygen dropped to 20.5% in IVC housing as compared to 21% for AEC housing. IVC intra-cage humidity was also elevated relative to AEC housing. Mice raised in IVC housing as compared to mice raised in AEC housing had higher RBC mass, hematocrit and hemoglobin concentrations. They also had elevated platelet counts but lower white blood cell counts. IVC mice, relative to AEC mice, had increased saccharin preference and increased fluid consumption but similar locomotion, food intake, social exploration and novel object recognition when tested in an AEC environment. Taken together, these data indicate that ventilated caging systems can have a 0.5% reduction from ambient oxygen concentration that is coupled to mouse red blood cell indices indicative of chronic exposure to a hypoxia. Importantly, IVC housing can impact behavioral testing for depressive-like behavior.

Environmental stress alters genetic regulation of novelty seeking in vervet monkeys

Considerable attention has been paid to identifying genetic influences and gene–environment interactions that increase vulnerability to environmental stressors, with promising but inconsistent results. A nonhuman primate model is presented here that allows assessment of genetic influences in response to a stressful life event for a behavioural trait with relevance for psychopathology. Genetic and environmental influences on free-choice novelty seeking behaviour were assessed in a pedigreed colony of vervet monkeys before and after relocation from a low stress to a higher stress environment. Heritability of novelty seeking scores, and genetic correlations within and between environments were conducted using variance components analysis. The results showed that novelty seeking was markedly inhibited in the higher stress environment, with effects persisting across a 2-year period for adults but not for juveniles. There were significant genetic contributions to novelty seeking scores in each year (h² = 0.35–0.43), with high genetic correlations within each environment (rhoG > 0.80) and a lower genetic correlation (rhoG = 0.35, non-significant) between environments. There were also significant genetic contributions to individual change scores from before to after the move (h² = 0.48). These results indicate that genetic regulation of novelty seeking was modified by the level of environmental stress, and they support a role for gene–environment interactions in a behavioural trait with relevance for mental health.