Refining rodent husbandry: the mouse. Report of the Rodent Refinement Working Party

Comparing United States and European Union academic animal programs: Organization, operation, and services offered

The Yale Animal Resource Cost and Benchmarking survey©, conducted in US academic Animal Research/Resource Centers (ARC), was modified to capture similar thematic information in European Union (EU; including the non-EU countries Switzerland and the UK) academic ARCs, which are members of the League of European Research Universities (LERU). Participating institutions came from Denmark, England, Finland, France, Germany, Ireland, Italy, Netherlands, Scotland, Spain, and Switzerland. Survey data analysis suggests that: (a) in LERU programs, it is common to have more than one ARC under the umbrella of a single institution with organizational "lumping" of the financial, regulatory, and/or operational tasks under one administrative unit; (b) accreditation by an outside agency (e.g., the Association for the Assessment and Accreditation of Laboratory Animal Care) is more common in US than LERU ARCs; (c) LERU ARCs are responsible for murine breeding, which contrasts with US ARCs, where ∼40% of rodent breeding is managed by researchers; (d) cryopreservation is the most frequently requested fee-for-service offering among LERU participants (75% of participants) compared to 30% of US participants; (e) like US programs, almost all LERU programs have mice and rats, but fewer LERU programs have nonhuman primates (NHPs), and none have dogs on census; (f) LERU ARCs have about an equal amount of vivarium housing and procedure space, while US facilities have twice as much housing as procedure space; (g) a higher percentage of LERU colonies are free of Helicobacter and murine norovirus compared to US colonies; and (h) more LERU ARCs used environmental microbiologic monitoring of rodent colonies compared to US programs.

Models for Inducing Experimental Cryptococcosis in Mice

Cryptococcus neoformans and Cryptococcus gattii are the predominant etiological agents of cryptococcosis, a particularly problematic disease in immunocompromised individuals. The increased clinical use of immunosuppressive drugs, the inherent ability of Cryptococcus species to suppress and evade host immune responses, and the emergence of drug-resistant yeast support the need for model systems that facilitate the design of novel immunotherapies and antifungals to combat disease progression. The mouse model of cryptococcosis is a widely used system to study Cryptococcus pathogenesis and the efficacy of antifungal drugs in vivo. In this chapter, we describe three commonly used strategies to establish cryptococcosis in mice: intranasal, intratracheal, and intravenous inoculations. Also, we discuss the methodology for delivering drugs to mice via intraperitoneal injection.

Structural enrichment for laboratory mice: exploring the effects of novelty and complexity

Providing structural enrichment is a widespread refinement method for laboratory rodents and other animals in captivity. So far, animal welfare research has mostly focused on the effect of increased complexity either by accumulating or combining different enrichment items. However, increasing complexity is not the only possibility to refine housing conditions. Another refinement option is to increase novelty by regularly exchanging known enrichment items with new ones. In the present study, we used pair-housed non-breeding female C57BL/6J and DBA/2N mice to investigate the effect of novelty when applying structural enrichment. We used a double cage system, in which one cage served as home cage and the other as extra cage. While the home cage was furnished in the same way for all mice, in the extra cage we either provided only space with no additional enrichment items (space), a fixed set of enrichment items (complexity), or a changing set of enrichment items (novelty). Over 5  weeks, we assessed spontaneous behaviors, body weight, and extra cage usage as indicators of welfare and preference. Our main results showed that mice with access to structurally enriched extra cages (complexity and novelty) spent more time in their extra cages and complexity mice had lower latencies to enter their extra cages than mice with access to the extra cages without any structural enrichment (space). This indicates that the mice preferred the structurally enriched extra cages over the structurally non-enriched space cages. We found only one statistically significant difference between the novelty and complexity condition: during week 3, novelty mice spent more time in their extra cages than complexity mice. Although we did not detect any other significant differences between the novelty and complexity condition in the present study, more research is required to further explore the potential benefits of novelty beyond complexity.

Reversible suppression of circadian-driven locomotor rhythms in mice using a gradual fragmentation of the day-night cycle

Circadian rhythms are regulated by molecular clockwork and drive 24-h behaviors such as locomotor activity, which can be rendered non-functional through genetic knockouts of clock genes. Circadian rhythms are robust in constant darkness (DD) but are modulated to become exactly 24 h by the external day-night cycle. Whether ill-timed light and dark exposure can render circadian behaviors non-functional to the extent of genetic knockouts is less clear. In this study, we discovered an environmental approach that led to a reduction or lack in rhythmic 24-h-circadian wheel-running locomotor behavior in mice (referred to as arrhythmicity). We first observed behavioral circadian arrhythmicity when mice were gradually exposed to a previously published disruptive environment called the fragmented day-night cycle (FDN-G), while maintaining activity alignment with the four dispersed fragments of darkness. Remarkably, upon exposure to constant darkness (DD) or constant light (LL), FDN-G mice lost any resemblance to the FDN-G-only phenotype and instead, exhibited sporadic activity bursts. Circadian rhythms are maintained in control mice with sudden FDN exposure (FDN-S) and fully restored in FDN-G mice either spontaneously in DD or after 12 h:12 h light-dark exposure. This is the first study to generate a light-dark environment that induces reversible suppression of circadian locomotor rhythms in mice.

Environmental modifications to rehabilitate social behavior deficits after acquired brain injury: What is the evidence?

Social behavior deficits are a common, debilitating consequence of traumatic brain injury and stroke, particularly when sustained during childhood. Numerous factors influence the manifestation of social problems after acquired brain injuries, raising the question of whether environmental manipulations can minimize or prevent such deficits. Here, we examine both clinical and preclinical evidence addressing this question, with a particular focus on environmental enrichment paradigms and differing housing conditions. We aimed to understand whether environmental manipulations can ameliorate injury-induced social behavior deficits. In summary, promising data from experimental models supports a beneficial role of environmental enrichment on social behavior. However, limited studies have considered social outcomes in the chronic setting, and few studies have addressed the social context specifically as an important component of the post-injury environment. Clinically, limited high-caliber evidence supports the use of specific interventions for social deficits after acquired brain injuries. An improved understanding of how the post-injury environment interacts with the injured brain, particularly during development, is needed to validate the implementation of rehabilitative interventions that involve manipulating an individuals' environment.

Novel Husbandry Practices Result in Rapid Rates of Growth and Sexual Maturation Without Impacting Adult Behavior in the Blind Mexican Cavefish

Animal model systems are dependent on the standardization of husbandry protocols that maximize growth and reduce generation time. The Mexican tetra, Astyanax mexicanus, exists as eyed surface and blind cave dwelling populations. The opportunity for comparative approaches between independently evolved populations has led to the rapid growth of A. mexicanus as a model for evolution and biomedical research. However, a slow and inconsistent growth rate remains a major limitation to the expanded application of A. mexicanus. Fortunately, this temporal limitation can be addressed through husbandry changes that accelerate growth rates while maintaining optimal health outcomes. Here, we describe a husbandry protocol that produces rapid growth rates through changes in diet, feeding frequency, growth sorting and progressive changes in tank size. This protocol produced robust growth rates and decreased the age of sexual maturity in comparison to our previous protocol. To determine whether changes in feeding impacted behavior, we tested fish in exploration and schooling assays. We found no difference in behavior between the two groups, suggesting that increased feeding and rapid growth will not impact the natural variation in behavioral traits. Taken together, this standardized husbandry protocol will accelerate the development of A. mexicanus as a genetic model.

In the pursuit of new social neurons. Neurogenesis and social behavior in mice: A systematic review

Social behaviors have become more relevant to our understanding of the human nervous system because relationships with our peers may require and modulate adult neurogenesis. Here, we review the pieces of evidence we have to date for the divergence of social behaviors in mice by modulation of adult neurogenesis or if social behaviors and the social environment can drive a change in neurogenic processes. Social recognition and memory are deeply affected by antimitotic drugs and irradiation, while NSC transgenic mice may run with lower levels of social discrimination. Interestingly, social living conditions can create a big impact on neurogenesis. Social isolation and social defeat reduce the number of new neurons, while social dominance and enrichment of the social environment increase their number. These new “social neurons” trigger functional modifications with amazing transgenerational effects. All of these suggest that we are facing two bidirectional intertwined variables, and the great challenge now is to understand the cellular and genetic mechanisms that allow this relationship to be used therapeutically.

Assessing the effect of compounds from plantar foot sweat, nesting material, and urine on social behavior in male mice, Mus musculus

Home cage aggression causes poor welfare in male laboratory mice and reduces data quality. One of the few proven strategies to reduce aggression involves preserving used nesting material at cage change. Volatile organic compounds from the nesting material and several body fluids not only correlate with less home cage aggression, but with more affiliative allo-grooming behavior. To date, these compounds have not been tested for a direct influence on male mouse social behavior. This study aimed to determine if 4 previously identified volatile compounds impact home cage interactions. A factorial design was used with cages equally split between C57BL/6N and SJL male mice (N = 40). Treatments were randomly assigned across cages and administered by spraying one compound solution on each cage's nesting material. Treatments were refreshed after day 3 and during cage change on day 7. Home cage social behavior was observed throughout the study week and immediately after cage change. Several hours after cage change, feces were collected from individual mice to measure corticosterone metabolites as an index of social stress. Wound severity was also assessed after euthanasia. Measures were analyzed with mixed models. Compound treatments did not impact most study measures. For behavior, SJL mice performed more aggression and submission, and C57BL/6N mice performed more allo-grooming. Wound severity was highest in the posterior region of both strains, and the middle back region of C57BL/6N mice. Posterior wounding also increased with more observed aggression. Corticosterone metabolites were higher in C57BL/6N mice and in mice treated with 3,4-dimethyl-1,2-cyclopentanedione with more wounding. These data confirm previous strain patterns in social behavior and further validates wound assessment as a measure of escalated aggression. The lack of observed treatment effects could be due to limitations in the compound administration procedure and/or the previous correlation study, which is further discussed.

Cross-sectional survey of husbandry for pet guinea pigs (Cavia porcellus) in New Zealand

AIMS

To describe basic husbandry (veterinary care, substrate and bedding, toys, frequency of cleaning) provided to guinea pigs (Cavia porcellus) by a sample of owners in New Zealand.

METHODS

Respondents were invited to complete a survey disseminated through the social media channels of animal interest and advocacy groups (3 September 2020 to 3 November 2020). Respondents who agreed to participate were asked a range of questions regarding provision of husbandry to their oldest pet guinea pig. Descriptive statistics are reported here relating to husbandry, length of ownership, provision of substrate, bedding and toys, frequency of cleaning and veterinary care.

RESULTS

A total of 503 responses were received, of which 329 complete responses were analysed. Of these respondents, 208/329 (63.2%) had owned guinea pigs for more than 2 years. Most owners provided a cage with a wooden base as substrate (144/321, 44.9%), bedding (308/329; 93.6%) and toys (169/329; 51.1%). Half (176/329; 53.5%) of respondents reported taking their guinea pig to a veterinarian. Just over half of owners surveyed cleaned water (165/329; 50.1%) and food (181/329; 55.0%) bowls daily, and a third picked up droppings (109/329; 33.1%) daily.

CONCLUSIONS AND CLINICAL RELEVANCE

While owners provided an array of toys, and a range of bedding and substrate types to their guinea pigs, cages were cleaned out less frequently than recommended, and it was common for guinea pig cages to be cleaned out less frequently than recommended. Future research is required to provide robust and evidence-based links between husbandry and the welfare of pet guinea pigs.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

Expert workshop summary: Advancing toward a standardized murine model to evaluate treatments for antimicrobial resistance lung infections

The rise in antimicrobial resistance (AMR), and increase in treatment-refractory AMR infections, generates an urgent need to accelerate the discovery and development of novel anti-infectives. Preclinical animal models play a crucial role in assessing the efficacy of novel drugs, informing human dosing regimens and progressing drug candidates into the clinic. The Innovative Medicines Initiative-funded “Collaboration for prevention and treatment of MDR bacterial infections” (COMBINE) consortium is establishing a validated and globally harmonized preclinical model to increase reproducibility and more reliably translate results from animals to humans. Toward this goal, in April 2021, COMBINE organized the expert workshop “Advancing toward a standardized murine model to evaluate treatments for AMR lung infections”. This workshop explored the conduct and interpretation of mouse infection models, with presentations on PK/PD and efficacy studies of small molecule antibiotics, combination treatments (β-lactam/β-lactamase inhibitor), bacteriophage therapy, monoclonal antibodies and iron sequestering molecules, with a focus on the major Gram-negative AMR respiratory pathogens Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Here we summarize the factors of variability that we identified in murine lung infection models used for antimicrobial efficacy testing, as well as the workshop presentations, panel discussions and the survey results for the harmonization of key experimental parameters. The resulting recommendations for standard design parameters are presented in this document and will provide the basis for the development of a harmonized and bench-marked efficacy studies in preclinical murine pneumonia model.

Fragmented day-night cycle induces reduced light avoidance, excessive weight gain during early development, and binge-like eating during adulthood in mice

Fragmented day-night (FDN) cycles are environments in which multiple periods of light and dark alternate across a 24 h period. Exposure to FDN cycles disrupts circadian rhythms, resulting in period lengthening and alterations to mood in mice. A constant light environment, which also induces period lengthening, is linked to mood and metabolic disturbances and disruption to the development of the circadian clock. This study aims to determine how exposure to the FDN cycle impacts development in mice, with the hypothesis that there would be similar and adverse effects as observed in constant light conditions. Our study used CD-1 mice reared under the FDN cycle compared to the commonly used 12 h light: 12 h dark consolidated day-night cycle. During the first week of development, mouse pups reared under the FDN cycle gained bodyweight at a faster rate and did not avoid aberrant light exposure in comparison to 12:12 LD reared mouse pups. Developmental exposure to the FDN cycle lasted two weeks, and then mice were transferred to the 12:12 LD cycle, where after 2 weeks, bodyweight was similar between FDN reared and 12:12 LD reared mice at 1-month and 2-months old. When re-exposed to the FDN cycle during adulthood, FDN reared pups exhibited binge-like eating behaviors and reduced light avoidance. This study shows that the unnatural distribution of light and dark across the 24 h day can cause disruptions during early development that can reappear during adulthood when placed in the same stressful light-dark environment as adults.

Protein profiles from used nesting material, saliva, and urine correspond with social behavior in group housed male mice, Mus musculus

Current understanding of how odors impact intra-sex social behavior is based on those that increase intermale aggression. Yet, odors are often promoted to reduce fighting among male laboratory mice. It has been shown that a cage of male mice contains many proteins used for identification purposes. However, it is unknown if these proteins relate to social behavior or if they are uniformly produced across strains. This study aimed to compare proteomes from used nesting material and three sources (sweat, saliva, and urine) from three strains and compare levels of known protein odors with rates of social behavior. Used nesting material samples from each cage were analyzed using LC-MS/MS. Sweat, saliva, and urine samples from each cage's dominant and subordinate mouse were also analyzed. Proteomes were assessed using principal component analyses and compared to behavior by calculating correlation coefficients between PC scores and behavior proportions. Twenty-one proteins from nesting material either correlated with affiliative behavior or negatively correlated with aggression. Notably, proteins from the major urinary protein family, odorant binding protein family, and secretoglobin family displayed at least one of these patterns, making them candidates for future work. These findings provide preliminary information about how proteins can influence male mouse behavior. SIGNIFICANCE: Research on how olfactory signals influence same sex social behavior is primarily limited to those that promote intermale aggression. However, exploring how olfaction modulates a more diverse behavioral repertoire will improve our foundational understanding of this sensory modality. In this proteome analysis we identified a short list of protein signals that correspond to lower rates of aggression and higher rates of socio-positive behavior. While this study is only correlational, it sets a foundation for future work that can identify protein signals that directly influence social behavior and potentially identify new murine pheromones.

Compounds from plantar foot sweat, nesting material, and urine show strain patterns associated with agonistic and affiliative behaviors in group housed male mice, Mus musculus

Excessive home cage aggression often results in severe injury and subsequent premature euthanasia of male laboratory mice. Aggression can be reduced by transferring used nesting material during cage cleaning, which is thought to contain aggression appeasing odors from the plantar sweat glands. However, neither the composition of plantar sweat nor the deposits on used nesting material have been evaluated. The aims of this study were to (1) identify and quantify volatile compounds deposited in the nest site and (2) determine if nest and sweat compounds correlate with social behavior. Home cage aggression and affiliative behavior were evaluated in 3 strains: SJL, C57BL/6N, and A/J. Individual social rank was assessed via the tube test, because ranking may influence compound levels. Sweat and urine from the dominant and subordinate mouse in each cage, plus cage level nest samples were analyzed for volatile compound content using gas chromatography-mass spectrometry. Behavior data and odors from the nest, sweat, and urine were statistically analyzed with separate principal component analyses (PCA). Significant components, from each sample analysis, and strain were run in mixed models to test if odors were associated with behavior. Aggressive and affiliative behaviors were primarily impacted by strain. However, compound PCs were also impacted by strain, showing that strain accounts for any relationship between odors and behavior. C57BL/6N cages displayed the most allo-grooming behavior and had high scores on sweat PC1. SJL cages displayed the most aggression, with high scores on urine PC2 and low scores on nest PC1. These data show that certain compounds in nesting material, urine, and sweat display strain specific patterns which match strain specific behavior patterns. These results provide preliminary information about the connection between home cage compounds and behavior. Salient compounds will be candidates for future controlled studies to determine their direct effect on mouse social behavior.

A role of color vision in emmetropization in C57BL/6J mice

Spectral composition affects emmetropization in both humans and animal models. Because color vision interacts the effects of chromatic defocus, we developed a method to bypass the effects of longitudinal chromatic aberration by placing a spectral filter behind the optics of the eye, using genetic tools. Newborn C57BL/6J (B6) mice were reared in quasi-monochromatic red (585–660 nm) or blue (410–510 nm) light beginning before eye-opening. Refractive states and ocular dimensions were compared at 4, 6, 8, and 10 weeks with mice reared in normal white light. Cre recombinase-dependent Ai9 reporter mice were crossed with Chx10-Cre to obtain Chx10-Cre;Ai9 mice, expressing red fluorescent protein in retinal Cre-positive cells. Ai9 offsprings, with and without Cre, were reared under a normal visual environment. Refraction and axial components were measured as described above. Expression levels of M and S opsin were quantified by western blotting at 10 weeks. Compared with those reared in white light, B6 mice reared in red light developed relative hyperopia, principally characterized by flattening of corneal curvature. Emmetropization was not affected by blue light, possibly because the reduction in vitreous chamber depth compensated for the increase in corneal curvature. Compared with Cre-negative littermates, the refraction and axial dimensions of Chx10-Cre;Ai9 mice were not significantly different at the follow-up timepoints. M opsin levels were higher in Chx10-Cre;Ai9 mice at 10 weeks while S opsin levels were not different. Red light induced a hyperopic shift in mouse refractive development. Emmetropization was not impacted in mice with perturbed color vision caused by intrinsic red-fluorescent protein, suggesting that color vision may not be necessary in mouse emmetropization when other mechanisms are present.

Reproducibility and Comparative aspects of Terrestrial Housing Systems and Husbandry Procedures in Animal Research Facilities on Study Data

As mentioned in other chapters, reproducibility of research data is very complicated and has numerous contributors for concerns. This chapter will discuss the animal housing systems and corresponding husbandry practices in regard to current practices and known and potential confounders in the research environment. This area has a very high impact for reproducibility and comparability of study data outcomes.

Physiologic Stress of Ear Punch Identification Compared with Restraint Only in Mice

Social housing of laboratory rodents is recommended whenever possible to encourage natural behavior and social dynamics. Several identification methods are used to distinguish rodents from one another. One of the most common means of identifying mice is ear punching. The effect of ear punching for identification or genotyping on the welfare of mice remains a concern, because this method negatively affects welfare in other species. To assess the influence of ear punching on the welfare of mice, we implanted telemetry units in 6 female Swiss-Webster mice and monitored heart rate, body temperature, and activity after various routine procedures. The physiologic and behavioral responses to restraint (by scruffing) only, restraint and ear punching, and routine handling for husbandry were evaluated. The mean heart rate of mice after receiving an ear punch was significantly higher than baseline values at 30 min after the procedure, and the mean body temperature was significantly increased over baseline for at least 1 h. The heart rate, body temperature, and activity levels of mice after scruffing only and routine handling did not differ from baseline values. The proportion of time mice spent head grooming, a potentially nocifensive behavior, was increased immediately after ear punching and began to decline by 60 min. We show that the physiologic stress of mice receiving an ear punch was greater than that from restraint (scruffing) alone, whereas behavioral indices of pain were unchanged, suggesting that ear punching causes a transient response in mice.

Implementing strategies to reduce singly housed male mice

There are different husbandry situations that lead to social isolation of male mice. Besides legal considerations, single housing has a negative impact on behavioural and molecular studies. We have implemented two strategies, the 'companion mouse' and just-weaned male grouping, to reduce the number of male mice housed singly in our facility. We have achieved a progressive reduction (42% in three years) without an increase in aggression.

Refinement and Reduction in the Production of Genetically Modified Mice

This paper introduces the sixth report of the BVAAWF/FRAME/RSPCA/UFAW Joint Working Group on Refinement (JWGR), which addresses reduction and refinement in the generation, management and care of genetically modified (GM) mice. The report provides a comprehensive review of the potential for reduction and refinement at all stages of the generation and maintenance of GM animals. The issues covered include scientific, procedural and practical issues. The need for good training in all of these areas is emphasised. The report concludes with a section on the need to develop comprehensive criteria for welfare assessments for GM mice and a preliminary list of criteria is provided. The full report has been publisheded in Laboratory Animals.

Effects of Cage Enrichment on Behavior, Welfare and Outcome Variability in Female Mice

The manner in which laboratory rodents are housed is driven by economics (minimal use of space and resources), ergonomics (ease of handling and visibility of animals), hygiene, and standardization (reduction of variation). This has resulted in housing conditions that lack sensory and motor stimulation and restrict the expression of species-typical behavior. In mice, such housing conditions have been associated with indicators of impaired welfare, including abnormal repetitive behavior (stereotypies, compulsive behavior), enhanced anxiety and stress reactivity, and thermal stress. However, due to concerns that more complex environmental conditions might increase variation in experimental results, there has been considerable resistance to the implementation of environmental enrichment beyond the provision of nesting material. Here, using 96 C57BL/6 and SWISS female mice, respectively, we systematically varied environmental enrichment across four levels spanning the range of common enrichment strategies: (1) bedding alone; (2) bedding + nesting material; (3) deeper bedding + nesting material + shelter + increased vertical space; and (4) semi-naturalistic conditions, including weekly changes of enrichment items. We studied how these different forms of environmental enrichment affected measures of animal welfare, including home-cage behavior (time–budget and stereotypic behavior), anxiety (open field behavior, elevated plus-maze behavior), growth (food and water intake, body mass), stress physiology (glucocorticoid metabolites in fecal boluses and adrenal mass), brain function (recurrent perseveration in a two-choice guessing task) and emotional valence (judgment bias). Our results highlight the difficulty in making general recommendations across common strains of mice and for selecting enrichment strategies within specific strains. Overall, the greatest benefit was observed in animals housed with the greatest degree of enrichment. Thus, in the super-enriched housing condition, stereotypic behavior, behavioral measures of anxiety, growth and stress physiology varied in a manner consistent with improved animal welfare compared to the other housing conditions with less enrichment. Similar to other studies, we found no evidence, in the measures assessed here, that environmental enrichment increased variation in experimental results.

Environmental enrichment and mouse models: Current perspectives

The provision of environmental enrichment to numerous species of laboratory animals is generally considered routine husbandry. However, mouse enrichment has proven to be very complex due to the often contradictory outcomes (animal health and welfare, variability in scientific data, etc.) associated with strain, age of the animal when enrichment is provided, gender of the animal, scientific use of the animal, and other housing attributes. While this has led to some suggesting that mice should not be provided enrichment, more recently opinion is trending toward acknowledging that enrichment actually normalizes the animal and data obtained from a mouse living in a barren environment are likely not to be representative or even reliable. This article offers an overview of the types of impact enrichment can have on various strains of mice and demonstrates that enrichment not only has a role in mouse husbandry, but also can lead to new areas of scientific enquiry in a number of different fields.

Coping with Stress During Aging: The Importance of a Resilient Brain

BACKGROUND

Resilience is the ability to achieve a positive outcome when we are in the face of adversity. It supposes an active resistance to adversity by coping mechanisms in which genetic, molecular, neural and environmental factors are involved. Resilience has been usually studied in early ages and few is known about it during aging.

METHODS

In this review, we will address the age-related changes in the brain mechanisms involved in regulating the stress response. Furthermore, using the EE paradigm, we analyse the resilient potential of this intervention and its neurobiological basis. In this case, we will focus on identifying the characteristics of a resilient brain (modifications in HPA structure and function, neurogenesis, specific neuron types, glia, neurotrophic factors, nitric oxide synthase or microRNAs, among others).

RESULTS

The evidence suggests that a healthy lifestyle has a crucial role to promote a resilient brain during aging. Along with the behavioral changes described, a better regulation of HPA axis, enhanced levels of postmitotic type-3 cells or changes in GABAergic neurotransmission are some of the brain mechanisms involved in resilience.

CONCLUSION

Future research should identify different biomarkers that increase the resistance to develop mood disorders and based on this knowledge, develop new potential therapeutic targets.

Evaluation of the effects of space allowance on measures of animal welfare in laboratory mice

We studied how space allowance affects measures of animal welfare in mice by systematically varying group size and cage type across three levels each in both males and females of two strains of mice (C57BL/6ByJ and BALB/cByJ; n = 216 cages, a total of 1152 mice). This allowed us to disentangle the effects of total floor area, group size, stocking density, and individual space allocation on a broad range of measures of welfare, including growth (food and water intake, body mass); stress physiology (glucocorticoid metabolites in faecal boli); emotionality (open field behaviour); brain function (recurrent perseveration in a two-choice guessing task); and home-cage behaviour (activity, stereotypic behaviour). While increasing group size was associated with a decrease in food and water intake in general, and more specifically with increased attrition due to escalated aggression in male BALB mice, no other consistent effects of any aspect of space allowance were found with respect to the measures studied here. Our results indicate that within the range of conditions commonly found in laboratory mouse housing, space allowance as such has little impact on measures of welfare, except for group size which may be a risk factor for escalating aggression in males of some strains.

Mouse Testing Methods in Psychoneuroimmunology 2.0: Measuring Behavioral Responses

The field of psychoneuroimmunology (PNI) aims to uncover the processes and consequences of nervous, immune, and endocrine system relationships. Behavior is a consequence of such interactions and manifests from a complex interweave of factors including immune-to-neural and neural-to-immune communication. Often the signaling molecules involved during a particular episode of neuroimmune activation are not known but behavioral response provides evidence that bioactives such as neurotransmitters and cytokines are perturbed. Immunobehavioral phenotyping is a first-line approach when examining the neuroimmune system and its reaction to immune stimulation or suppression. Behavioral response is significantly more sensitive than direct measurement of a single specific bioactive and can quickly and efficiently rule in or out relevance of a particular immune challenge or therapeutic to neuroimmunity. Classically, immunobehavioral research was focused on sickness symptoms related to bacterial infection but neuroimmune activation is now a recognized complication of diseases and disorders ranging from cancer to diabesity to Alzheimer's. Immunobehaviors include lethargy, loss of appetite, and disinterest in social activity/surrounding environment. In addition, neuroimmune activation can diminish physical activity, precipitate feelings of depression and anxiety, and impair cognitive and executive function. Provided is a detailed overview of behavioral tests frequently used to examine neuroimmune activation in mice with a special emphasis on pre-experimental conditions that can confound or prevent successful immunobehavioral experimentation.

The IMPROVE Guidelines (Ischaemia Models: Procedural Refinements Of in Vivo Experiments)

Most in vivo models of ischaemic stroke target the middle cerebral artery and a spectrum of stroke severities, from mild to substantial, can be achieved. This review describes opportunities to improve the in vivo modelling of ischaemic stroke and animal welfare. It provides a number of recommendations to minimise the level of severity in the most common rodent models of middle cerebral artery occlusion, while sustaining or improving the scientific outcomes. The recommendations cover basic requirements pre-surgery, selecting the most appropriate anaesthetic and analgesic regimen, as well as intraoperative and post-operative care. The aim is to provide support for researchers and animal care staff to refine their procedures and practices, and implement small incremental changes to improve the welfare of the animals used and to answer the scientific question under investigation. All recommendations are recapitulated in a summary poster (see supplementary information).

Light and the laboratory mouse

Light exerts widespread effects on physiology and behaviour. As well as the widely-appreciated role of light in vision, light also plays a critical role in many non-visual responses, including regulating circadian rhythms, sleep, pupil constriction, heart rate, hormone release and learning and memory. In mammals, responses to light are all mediated via retinal photoreceptors, including the classical rods and cones involved in vision as well as the recently identified melanopsin-expressing photoreceptive retinal ganglion cells (pRGCs). Understanding the effects of light on the laboratory mouse therefore depends upon an appreciation of the physiology of these retinal photoreceptors, including their differing sens itivities to absolute light levels and wavelengths. The signals from these photoreceptors are often integrated, with different responses involving distinct retinal projections, making generalisations challenging. Furthermore, many commonly used laboratory mouse strains carry mutations that affect visual or non-visual physiology, ranging from inherited retinal degeneration to genetic differences in sleep and circadian rhythms. Here we provide an overview of the visual and non-visual systems before discussing practical considerations for the use of light for researchers and animal facility staff working with laboratory mice.

Severity assessment and scoring for neurosurgical models in rodents

The most important acute neurological diseases seen at neurosurgery departments are traumatic brain injuries (TBI) and subarachnoid hemorrhages (SAH). In both diseases the pathophysiological sequela are complex and have not been fully understood up to now, and rodent models using rats and mice are most suitable for the investigation of the pathophysiological details. In both models, surgery is performed under anesthesia, followed by assessment of their functional outcome and behavioral testing before brain tissue analysis after euthanasia. Postoperative analgesia is mandatory, and supplementary care is highly recommended for refinement purposes. Pain and stress assessment is mainly based on clinical and behavioral signs, and further research is needed to improve the evaluation of severity in these models.

Effects of natural enrichment materials on stress, memory and exploratory behavior in mice

Environmental enrichment is an essential component of laboratory animal housing that allows animals to engage in natural behaviors in an otherwise artificial setting. Previous research by the authors suggested that, compared with synthetic enrichment materials, natural materials were associated with lower stress levels in mice. Here, the authors compare the effects of different enrichment materials on stress, memory and exploratory behavior in Swiss Webster mice. Mice that were provided with natural enrichment materials had lower stress levels, better memory and greater exploratory behavior than did mice provided with synthetic enrichment materials or with no enrichment materials. These findings suggest that provision of natural enrichment materials can improve well-being of laboratory mice.

The vest-collar as a rodent collar to prevent licking and scratching during experiments

Various types of restraint collars have been used for research animals, and the Elizabethan collar (E-collar) is the most commonly used. However, animals can be choked by the E-collar or they tend to remove it; furthermore, repeated rubbing and scratching of the collar may chafe the neck. We developed a new restraint collar with a vest to overcome these limitations. The vest-collar (V-collar) can be worn similarly to a vest, in contrast to the E-collar, which is fixed around the neck. A cone-shaped collar is attached to the vest in the V-collar and is made of Eva foam to surround the chest softly, accompanied by a transparent polyvinyl chloride (PVC) film for visibility. To evaluate the performance of the V-collar, we conducted experiments with mice wearing the V-collar and the E-collar. Both groups showed normal weight gain and food intake. Glucose and stress hormone levels showed no significant differences, and no stress-associated leukocyte profiles were observed during the experiments. However, despite the short experimental duration, more than half of the mice in the E-collar group showed injury to the skin on the neck, with increased thickness of the epidermal and keratin layers. Moreover, inflammatory cell counts were higher in the E-collar group than in the V-collar group. In conclusion, the V-collar, in contrast to the E-collar, does not cause skin injuries in animals and is thus beneficial for animals and investigators. Investigators can effectively use the V-collar to enhance laboratory animal welfare.

The Mouse Grimace Scale: A Clinically Useful Tool?

Medical research has a heavy and continuing demand for rodent models across a range of disciplines. Behavioural assessment of pain in such models is highly time consuming, thus limiting the number of models and analgesics that can be studied. Facial expressions are widely used to assess pain in human infants. Recently the mouse grimace scale (MGS) has been developed and shown to be accurate and reliable, requiring only a short amount of training for the observer. This system therefore has the potential to become a highly useful tool both in pain research and clinical assessment of mouse pain. To date, the MGS has only been used as a research tool, however there is increasing interest in its use in cage-side clinical assessment. It is often wrongly assumed that MGS scores of animals not in pain (i.e. at baseline) are zero. Here, we aimed to assess the variability in baseline MGS scores between cohorts, sexes and strains of mice. Establishing the presence of a consistent baseline MGS score could lead to a valuable clinical pain assessment tool for mice when baseline information from the individual mouse may not be available as a comparator. Results demonstrated a significant difference in baseline MGS scores between both sexes (males > females) and strains of mice. The method used to score the facial action units (Live vs. retrospectively from still images) demonstrated significant differences in scores with live scores being significantly lower than retrospective scoring from images. The level of variation shown demonstrates the need for further research to be undertaken with regard to establishing baseline MGS scores for specific strains and sexes of mice, taking into account the method of scoring, prior to considering clinical implementation of this method in pain assessment.

What's wrong with my mouse cage? Methodological considerations for modeling lifestyle factors and gene-environment interactions in mice

The mechanistic understanding of lifestyle contributions to disease has been largely driven by work in laboratory rodent models using environmental interventions. These interventions show an array of methodologies and sometimes unclear collective conclusions, hampering clinical interpretations. Here we discuss environmental enrichment, exercise and stress interventions to illustrate how different protocols can affect the interpretations of environmental factors in disease. We use Huntington's disease (HD) as an example because its mouse models exhibit excellent validity and HD was the first genetic animal model in which environmental stimulation was found to be beneficial. We make a number of observations and recommendations. Firstly, environmental enrichment and voluntary exercise generally show benefits across laboratories and mouse models. However, the extent to which these environmental interventions have beneficial effects depends on parameters such as the structural complexity of the cage in the case of enrichment, the timing of the intervention and the nature of the control conditions. In particular, clinical interpretations should consider deprived control living conditions and the ethological relevance of the enrichment. Secondly, stress can have negative effects on the phenotype in mouse models of HD and other brain disorders. When modeling stress, the effects of more than one type of experimental stressor should be investigated due to the heterogeneity and complexity of stress responses. With stress in particular, but ideally in all studies, both sexes should be used and the randomized group sizes need to be sufficiently powered to detect any sex effects. Opportunities for clinical translation will be guided by the 'environmental construct validity' of the preclinical data, including the culmination of complementary protocols across multiple animal models. Environmental interventions in mouse models of HD provide illustrative examples of how valid preclinical studies can lead to conclusions relevant to clinical populations.

The amount of cage bedding preferred by female BALB/c and C57BL/6 mice

In order to improve the welfare of laboratory mice, a number of different environmental enrichment strategies have been developed to provide opportunities for mice to engage in naturalistic behaviors. Providing sufficient cage bedding for mice to use as a burrowing substrate could be considered an environmental enrichment strategy, but few studies have considered the welfare aspects of cage bedding amount. The authors compared the preferences of group-housed female BALB/c and C57BL/6 mice for three different volumes of cage bedding (0.5 l, 1.5 l and 6 l). Mice of both strains but especially C57BL/6 mice showed strong preferences for cages with more bedding. The results highlight the importance of providing a sufficient amount of cage bedding to laboratory mice.

Using the mouse grimace scale to assess pain associated with routine ear notching and the effect of analgesia in laboratory mice

Social housing is recommended where possible for laboratory mice. In order to achieve this, mice must be individually identifiable. Although, various methods are available, permanent identification is often required, such as ear notching. This method is likely to be painful and to date there is limited literature on pain assessment and alleviation for this routine husbandry practice. Here we aimed to determine if the mouse grimace scale (MGS) could be used to assess pain in C57BL/6 mice following routine ear notching. Langford et al. found that very acute noxious stimuli (i.e. < 10 min in duration) did not produce a change in MGS score in comparison to baseline. Here, no significant difference was found between MGS scores at baseline and immediately post ear notching, potentially indicating that the pain associated with ear notching is either too acute to assess using the MGS tool or the practice is not painful. Studies in other species indicate that ear notching is painful, therefore, unless we can confidently conclude that the process of ear notching is not painful, we should err on the side of caution and assume it is painful due to the large number of mice ear-notched and potential welfare consequences. Alternative methods of assessing pain following this routine practice should be used in order to assess both the potential pain in mice, and the effectiveness of analgesics or local anaesthetics to relieve any associated pain.

Mouse short- and long-term locomotor activity analyzed by video tracking software

Locomotor activity (LMA) is a simple and easily performed measurement of behavior in mice and other rodents. Improvements in video tracking software (VTS) have allowed it to be coupled to LMA testing, dramatically improving specificity and sensitivity when compared to the line crossings method with manual scoring. In addition, VTS enables high-throughput experimentation. While similar to automated video tracking used for the open field test (OFT), LMA testing is unique in that it allows mice to remain in their home cage and does not utilize the anxiogenic stimulus of bright lighting during the active phase of the light-dark cycle. Traditionally, LMA has been used for short periods of time (mins), while longer movement studies (hrs-days) have often used implanted transmitters and biotelemetry. With the option of real-time tracking, long-, like short-term LMA testing, can now be conducted using videography. Long-term LMA testing requires a specialized, but easily constructed, cage so that food and water (which is usually positioned on the cage top) does not obstruct videography. Importantly, videography and VTS allows for the quantification of parameters, such as path of mouse movement, that are difficult or unfeasible to measure with line crossing and/or biotelemetry. In sum, LMA testing coupled to VTS affords a more complete description of mouse movement and the ability to examine locomotion over an extended period of time.

Environmental enrichment and gut inflammation modify stress-induced c-Fos expression in the mouse corticolimbic system

Environmental enrichment (EE) has a beneficial effect on rodent behaviour, neuronal plasticity and brain function. Although it may also improve stress coping, it is not known whether EE influences the brain response to an external (psychological) stressor such as water avoidance stress (WAS) or an internal (systemic) stressor such as gastrointestinal inflammation. This study hence explored whether EE modifies WAS-induced activation of the mouse corticolimbic system and whether this stress response is altered by gastritis or colitis. Male C67BL/6N mice were housed under standard or enriched environment for 9 weeks, after which they were subjected to a 1-week treatment with oral iodoacetamide to induce gastritis or oral dextran sulfate sodium to induce colitis. Following exposure to WAS the expression of c-Fos, a marker of neuronal activation, was measured by immunocytochemistry. EE aggravated experimentally induced colitis, but not gastritis, as shown by an increase in the disease activity score and the colonic myeloperoxidase content. In the brain, EE enhanced the WAS-induced activation of the dentate gyrus and unmasked an inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression within this part of the hippocampus. Conversely, EE inhibited the WAS-evoked activation of the central amygdala and prevented the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this region. EE, in addition, blunted the WAS-induced activation of the infralimbic cortex and attenuated the inhibitory effect of gastritis and colitis on WAS-evoked c-Fos expression in this area. These data reveal that EE has a region-specific effect on stress-induced c-Fos expression in the corticolimbic system, which is likely to improve stress resilience. The response of the prefrontal cortex – amygdala – hippocampus circuitry to psychological stress is also modified by the systemic stress of gut inflammation, and this interaction between external and internal stressors is modulated by the housing environment.

Routine habitat change: a source of unrecognized transient alteration of intestinal microbiota in laboratory mice

The mammalian intestine harbors a vast, complex and dynamic microbial population, which has profound effects on host nutrition, intestinal function and immune response, as well as influence on physiology outside of the alimentary tract. Imbalance in the composition of the dense colonizing bacterial population can increase susceptibility to various acute and chronic diseases. Valuable insights on the association of the microbiota with disease critically depend on investigation of mouse models. Like in humans, the microbial community in the mouse intestine is relatively stable and resilient, yet can be influenced by environmental factors. An often-overlooked variable in research is basic animal husbandry, which can potentially alter mouse physiology and experimental outcomes. This study examined the effects of common husbandry practices, including food and bedding alterations, as well as facility and cage changes, on the gut microbiota over a short time course of five days using three culture-independent techniques, quantitative PCR, terminal restriction fragment length polymorphism (TRFLP) and next generation sequencing (NGS). This study detected a substantial transient alteration in microbiota after the common practice of a short cross-campus facility transfer, but found no comparable alterations in microbiota within 5 days of switches in common laboratory food or bedding, or following an isolated cage change in mice acclimated to their housing facility. Our results highlight the importance of an acclimation period following even simple transfer of mice between campus facilities, and highlights that occult changes in microbiota should be considered when imposing husbandry variables on laboratory animals.

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.

Mouse testing methods in psychoneuroimmunology: an overview of how to measure sickness, depressive/anxietal, cognitive, and physical activity behaviors

The field of psychoneuroimmunology (PNI) aims to uncover the processes and consequences of nervous, immune, and endocrine system relationships. Behavior is a consequence of such interactions and manifests from a complex interweave of factors including immune-to-neural and neural-to-immune communication. Often the signaling molecules involved during a particular episode of neuroimmune activation are not known but behavioral response provides evidence that bioactives such as neurotransmitters and cytokines are perturbed. Immunobehavioral phenotyping is a first-line approach when examining the neuroimmune system and its reaction to immune stimulation or suppression. Behavioral response is significantly more sensitive than direct measurement of a single specific bioactive and can quickly and efficiently rule in or out relevance of a particular immune challenge or therapeutic to neuroimmunity. Classically, immunobehavioral research was focused on sickness symptoms related to bacterial infection but neuroimmune activation is now a recognized complication of diseases and disorders ranging from cancer to diabesity. Immunobehaviors include lethargy, loss of appetite, and disinterest in social activity and the surrounding environment. In addition, neuroimmune activation can precipitate feelings of depression and anxiety while negatively impacting cognitive function and physical activity. Provided is a detailed overview of behavioral tests frequently used to examine neuroimmune activation in mice with a special emphasis on preexperimental conditions that can confound or prevent successful immunobehavioral experimentation.

Effects of space allocation and housing density on measures of wellbeing in laboratory mice: a review

In the majority of countries where there are legislative requirements pertaining to the use of animals in research, figures are quoted for minimum cage sizes or space allocation to be provided per animal. These figures are generally based on professional judgement and are in common usage. However, there is a growing trend and expectation that welfare science should inform regulatory decision-making. Given the importance of the potential welfare influences of cage size on the animals themselves, this paper presents the latest scientific knowledge on this topic in one of the most commonly used animals in research, the mouse. A comprehensive review of studies in laboratory mice was undertaken, examining the effects of space allocation per animal and animal density on established welfare indicators. To date, animal density studies have predominated, and the effects of space allocation per se are still relatively unclear. This information will guide those involved in facility management or legislative review, and provide a more solid foundation for further studies into the effects of routine husbandry practices on animal welfare.

The effects of enriching laboratory cages using various physical structures on multiple measures of welfare in singly-housed rats

The single housing of laboratory rats may be recommended in some situations such as hypothesis-driven or test-specific studies, during electroencephalogram recording of phases of sleep and after surgical procedures. However, as single housing of laboratory rats has been shown to be stressful, modification of the housing environment is needed to improve the welfare of these animals. This experiment was carried out to investigate the long-term effects of environmental enrichment on some behavioural, physiological, pathological and psychological measures of welfare. With two batches of animals, 24 rats were housed singly in either enriched cages (EC) (n = 12 cages) or unenriched cages (UC) (n = 12 cages). Behaviour was sampled every week and so was body weight and weight gain over a six-week observation period. Behaviours of the rats in the elevated plus-maze were recorded on the seventh week, whereas organ weights were recorded postmortem. The results revealed that long-term single housing of rats in super-enriched cages increased levels of indicators of good welfare including sleep, exploration, movement and feeding behaviour, body weights, weight gains and the relative weights of the thymus gland and spleen, and decreased levels of indicators of poor welfare such as stationary behaviour and the relative weight of adrenal glands. Thus, enrichment of conventional cages of newly weaned singly-housed laboratory rats with multiple physical structures appeared to improve their ability to control the environment and to promote their species-specific behaviour; changes that can ultimately result in good welfare.