Mouse handling limits the impact of stress on metabolic endpoints

Gestational administration of Bifidobacterium dentium results in intergenerational modulation of inflammatory, metabolic, and social behavior

Prenatal stress (PNS) profoundly impacts maternal and offspring health, with enduring effects including microbiome alterations, neuroinflammation, and behavioral disturbances such as reductions in social behavior. Converging lines of evidence from preclinical and clinical studies suggest that PNS disrupts tryptophan (Trp) metabolic pathways and reduces gut Bifidobacteria, a known beneficial bacterial genus that metabolizes Trp. Specifically, previous work from our lab demonstrated that human prenatal mood disorders in mothers are associated with reduced Bifidobacterium dentium in infants at 13 months. Given that Bifidobacterium has been positively associated with neurodevelopmental and other health benefits and is depleted by PNS, we hypothesized that supplementing PNS-exposed pregnant dams with B. dentium would ameliorate PNS-induced health deficits. We measured inflammatory outputs, Trp metabolite levels and enzymatic gene expression in dams and fetal offspring, and social behavior in adult offspring. We determined that B. dentium reduced maternal systemic inflammation and fetal offspring neuroinflammation, while modulating tryptophan metabolism and increasing kynurenic acid and indole-3-propionic acid intergenerationally. Additional health benefits were demonstrated by the abrogation of PNS-induced reductions in litter weight. Finally, offspring of the B. dentium cohort demonstrated increased sociability in males primarily and increased social novelty primarily in females. Together these data illustrate that B. dentium can orchestrate interrelated host immune, metabolic and behavioral outcomes during and after gestation for both dam and offspring and may be a candidate for prevention of the negative sequelae of stress.

Metabolic and Skeletal Characterization of the KK/Ay Mouse Model-A Polygenic Mutation Model of Obese Type 2 Diabetes

Type 2 diabetes (T2D) increases fracture incidence and fracture-related mortality rates (KK.Cg-Ay/J. The Jackson Laboratory; Available from: https://www.jax.org/strain/002468 ). While numerous mouse models for T2D exist, few effectively stimulate persistent hyperglycemia in both sexes, and even fewer are suitable for bone studies. Commonly used models like db/db and ob/ob have altered leptin pathways, confounding bone-related findings since leptin regulates bone properties (Fajardo et al. in Journal of Bone and Mineral Research 29(5): 1025-1040, 2014). The Yellow Kuo Kondo (KK/Ay) mouse, a polygenic mutation model of T2D, is able to produce a consistent diabetic state in both sexes and addresses the lack of a suitable model of T2D for bone studies. The diabetic state of KK/Ay stems from a mutation in the agouti gene, responsible for coat color in mice. This mutation induces ectopic gene expression across various tissue types, resulting in diabetic mice with yellow fur coats (Moussa and Claycombe in Obesity Research 7(5): 506-514, 1999). Male and female KK/Ay mice exhibited persistent hyperglycemia, defining them as diabetic with blood glucose (BG) levels consistently exceeding 300 mg/dL. Notably, male control mice in this study were also diabetic, presenting a significant limitation. Nevertheless, male and female KK/Ay mice showed significantly elevated BG levels, HbA1c, and serum insulin concentration when compared to the non-diabetic female control mice. Early stages of T2D are characterized by hyperglycemia and hyperinsulinemia resulting from cellular insulin resistance, whereas later stages may feature hypoinsulinemia due to β-cell apoptosis (Banday et al. Avicenna Journal of Medicine 10(04): 174-188, 2020 and Klein et al. Cell Metabolism 34(1): 11-20, 2022). The observed hyperglycemia, hyperinsulinemia, and the absence of differences in β-cell mass suggest that KK/Ay mice in this study are modeling the earlier stages of T2D. While compromised bone microarchitecture was observed in this study, older KK/Ay mice, representing more advanced stages of T2D, might exhibit more pronounced skeletal manifestations. Compared to the control group, the femora of KK/Ay mice had higher cortical area and cortical thickness, and improved trabecular properties which would typically be indicative of greater bone strength. However, KK/Ay mice displayed lower cortical tissue mineral density in both sexes and increased cortical porosity in females. Fracture instability toughness of the femora was lower in KK/Ay mice overall compared to controls. These findings indicate that decreased mechanical integrity noted in the femora of KK/Ay mice was likely due to overall bone quality being compromised.

The implementation of tunnel handling in a mouse breeding facility revealed strain-specific behavioural responses

As a step towards implementing non-aversive handling techniques at a big mouse breeding facility in Germany, tunnel handling was introduced in a breeding unit comprising three inbred mouse strains. To assess whether tunnel handling would be feasible for the animal technicians in their everyday work and beneficial for the mice when being handled during weekly cage change only, the behaviour of tunnel- and tail-handled animals of both sexes was examined before, during and after the handling events over a period of nine weeks. Moreover, the time expenditure was compared between both handling techniques. It was possible to use the tunnel in all three mouse strains. However, the impact of the handling techniques on the behavioural parameters investigated in the present study were strain-specific. All behavioural parameters suggested that NZW mice benefited the most from tunnel handling. The results obtained from Hello Kitty and WNK mice were ambiguous, which may suggest that a brief handling session during the cage clean may have not been sufficient to habituate them to the process of handling. It took the animal technicians approximately 3 seconds longer per mouse when using a tunnel. The strain-specific results should encourage researchers to share their experiences with non-aversive handling techniques in different mouse strains, for example, along with their research articles.

Social isolation leads to mild social recognition impairment and losses in brain cellularity

Chronic social stress is a significant risk factor for several neuropsychiatric disorders, mainly major depressive disorder (MDD). In this way, patients with clinical depression may display many symptoms, including disrupted social behavior and anxiety. However, like many other psychiatric diseases, MDD has a very complex etiology and pathophysiology. Because social isolation is one of the multiple depression-inducing factors in humans, this study aims to understand better the link between social stress and MDD using an animal model based on social isolation after weaning, which is known to produce social stress in mice. We focused on cellular composition and white matter integrity to establish possible links with the abnormal social behavior that rodents isolated after weaning displayed in the three-chamber social approach and recognition tests. We used the isotropic fractionator method to assess brain cellularity, which allows us to robustly estimate the number of oligodendrocytes and neurons in dissected brain regions. In addition, diffusion tensor imaging (DTI) was employed to analyze white matter microstructure. Results have shown that post-weaning social isolation impairs social recognition and reduces the number of neurons and oligodendrocytes in important brain regions involved in social behavior, such as the anterior neocortex and the olfactory bulb. Despite the limitations of animal models of psychological traits, evidence suggests that behavioral impairments observed in patients might have similar biological underpinnings.

A systematic review of the development and application of home cage monitoring in laboratory mice and rats

BACKGROUND

Traditionally, in biomedical animal research, laboratory rodents are individually examined in test apparatuses outside of their home cages at selected time points. However, the outcome of such tests can be influenced by various factors and valuable information may be missed when the animals are only monitored for short periods. These issues can be overcome by longitudinally monitoring mice and rats in their home cages. To shed light on the development of home cage monitoring (HCM) and the current state-of-the-art, a systematic review was carried out on 521 publications retrieved through PubMed and Web of Science.

RESULTS

Both the absolute (~ × 26) and relative (~ × 7) number of HCM-related publications increased from 1974 to 2020. There was a clear bias towards males and individually housed animals, but during the past decade (2011-2020), an increasing number of studies used both sexes and group housing. In most studies, animals were kept for short (up to 4 weeks) time periods in the HCM systems; intermediate time periods (4-12 weeks) increased in frequency in the years between 2011 and 2020. Before the 2000s, HCM techniques were predominantly applied for less than 12 h, while 24-h measurements have been more frequent since the 2000s. The systematic review demonstrated that manual monitoring is decreasing in relation to automatic techniques but still relevant. Until (and including) the 1990s, most techniques were applied manually but have been progressively replaced by automation since the 2000s. Independent of the year of publication, the main behavioral parameters measured were locomotor activity, feeding, and social behaviors; the main physiological parameters were heart rate and electrocardiography. External appearance-related parameters were rarely examined in the home cages. Due to technological progress and application of artificial intelligence, more refined and detailed behavioral parameters have been investigated in the home cage more recently.

CONCLUSIONS

Over the period covered in this study, techniques for HCM of mice and rats have improved considerably. This development is ongoing and further progress as well as validation of HCM systems will extend the applications to allow for continuous, longitudinal, non-invasive monitoring of an increasing range of parameters in group-housed small rodents in their home cages.

Continuous deep brain stimulation of the nucleus accumbens reduces food intake but does not affect body weight in mice fed a high-fat diet

Obesity is an enormous health problem, and many patients do not respond to any of the available therapies. Deep brain stimulation (DBS) is currently investigated as a potential treatment for morbid obesity. In this study, we tested the hypothesis that high-frequency DBS targeting the nucleus accumbens (NAc) shell region reduces food intake and weight gain in mice fed a high-fat diet. We implanted male C57BL/6J mice with bilateral electrodes and a head-mounted microstimulator enabling continuous stimulation for up to 5 weeks. In successfully operated animals (n = 9 per group, high-frequency vs. sham stimulation), we investigated immediate and long-term stimulation effects on metabolic and behavioral phenotypes. Here we show that stimulation acutely induced a transient reduction in energy expenditure and locomotor activity but did not significantly affect spontaneous food intake, social interaction, anxiety or exploratory behaviors. In contrast, continuous stimulation over 5 weeks led to a decrease in food intake and thigmotaxis (the tendency to stay near walls in an open lit arena). However, chronic stimulation did not substantially change weight gain in mice fed a high-fat diet. Our results do not support the use of continuous high-frequency NAc shell DBS as a treatment for obesity. However, DBS can alter obesity-related parameters with differing short and long-term effects. Therefore, future research should employ time and context-sensitive experimental designs to assess the potential of DBS for clinical translation in this area.

FELASA recommendations for the rehoming of animals used for scientific and educational purposes

Directive 2010/63/EU of the European Parliament and the Council of 22 September 2010 states that at the end of a procedure, the most appropriate decision on the future of an animal previously used or intended for use in scientific procedures should be taken on the basis of animal welfare and potential risks to the environment. Member States may allow animals to be rehomed provided the health of the animal allows it, there is no danger to public health, animal health or the environment and if appropriate measures have been taken to safeguard the wellbeing of the animal. In countries where rehoming is permitted, it is the responsibility of the Animal Welfare Body to advise on a rehoming scheme which must include appropriate socialization in order to help facilitate successful rehoming, avoid unnecessary distress to the animals and guarantee public safety. This paper reviews the EU legislation, existing guidance, current literature and best practice to define rehoming, sets out general considerations for rehoming laboratory animals including socialization and provides practical advice on the steps required in a rehoming scheme. For those species most frequently rehomed, more detailed species-specific sections are included.

Using refined methods to pick up mice: A survey benchmarking prevalence & beliefs about tunnel and cup handling

Refined handling improves laboratory mouse welfare and research outcomes when compared to traditional tail handling, yet implementation does not seem to be widespread. Refined handling includes picking up a mouse using a tunnel or cupped hands. The aim of this study was to determine the current prevalence of and beliefs towards refined handling using the theory of planned behavior. It was predicted that refined handling prevalence is low compared to traditional handling methods, and its implementation is determined by individual and institutional beliefs. Research personnel were recruited via online convenience sampling through email listservs and social media. A total of 261 participants in diverse roles (e.g. veterinarians, managers, caretakers, researchers, etc.) responded primarily from the USA (79%) and academic institutions (61%) Participants were surveyed about their current use, knowledge, and beliefs about refined handling. Quantitative data were analyzed via descriptive statistics and generalised regression. Qualitative data were analyzed by theme. Research personnel reported low levels of refined handling implementation, with only 10% of participants using it exclusively and a median estimate of only 10% of institutional mice being handled with refined methods. Individually, participants had positive attitudes, neutral norms, and positive control beliefs about refined handling. Participants' intention to provide refined handling in the future was strongly associated with their attitudes, norms, and control beliefs (p<0.01). Participants believed barriers included jumpy mice, perceived incompatibility with restraint, lack of time, and other personnel. However, participants also believed refined handling was advantageous to mouse welfare, handling ease, personnel, and research. Although results from this survey indicate that current refined handling prevalence is low in this sample, personnel believe it has important benefits, and future use is associated with their beliefs about the practice. People who believed refined handling was good, felt pressure to use it, and were confident in their use reported higher implementation. Increased refined handling could be encouraged through education on misconceptions, highlighting advantages, and addressing important barriers.

Acclimation and Blood Sampling: Effects on Stress Markers in C57Bl/6J Mice

Blood sampling in rodents is common practice in scientific studies. Some of the refined methods widely used are the puncture of the saphenous vein or tail vein, or even tail docking. The handling needs of these different blood sampling methods are different and can directly affect stress, increasing the variability of the study. Moreover, there is less aversion and stress if the animal is accustomed to the environment, handling and technique. Therefore, our study aimed to assess the influence of these three blood sampling techniques (saphenous puncture, tail vein puncture and tail vein docking) and the use of previous acclimation on different indicators of animal stress, assessing blood glucose concentrations and faecal corticosterone metabolites (FCMs). Twenty-four young adult male and female C57Bl6/J mice were divided in three groups by sampling method: tail docking (TD), saphenous vein puncture (SV) and caudal vein puncture (CV) groups. All mice were studied with and without acclimation, which was performed during 9 consecutive days. The results showed that both males and females present very similar responses to the different handling and sampling methods without significant differences. Nevertheless, acclimation in all sampling methods decreased glucose and FCM levels significantly. The method that obtained the lowest glucose and FCM levels with significance was saphenous vein puncture. Therefore, we can say that it causes less stress when performing prior acclimation, even when this involves greater handling of the animal. Our results contribute to refinement within the 3R concept and could serve researchers to programme and select a good handling technique and a welfare-friendly blood sampling method for their experiments.

Research Animal Behavioral Management Programs for the 21st Century

Behavioral management programs have been developed commonly for research dogs and primates but rarely has program consideration been expanded to include all research species worked with. This is necessary to reduce animal stress and promote natural behaviors, which can promote good animal welfare and result in more robust and reproducible scientific data. We describe the evolution of consideration for research animal needs and define an umbrella-based model of research animal behavioral management programs, which may be used for all research species. In addition to developing a more comprehensive program, we emphasize the need for regular welfare assessments to determine whether the program is working cohesively and whether any aspects require modification.

Mice learn from the predator-attack experience to accelerate flight behavior via optimizing the strategy of environment exploration

Efficiently avoiding predators is critical for animal survival. However, little is known about how the experience of predator attack affects behaviors in predator defense. Here, we caught mice by tail to simulate a predator attack. We found that the experienced mice accelerated the flight in response to the visual threaten cue. Single predator attack didn't induce anxiety but increased the activity of innate fear or learning related nucleus. The predator attack induced acceleration of flight was partly rescued when we used drug to block protein synthesis which is critical in the learning process. The experienced mice significantly reduced the focused exploration on the floor during the environment exploration, which might facilitate the discovery of predator. These results suggest that mice could learn from the experience of predator attack to optimize their behavioral pattern to detect the predator cue immediately and response intensely, and therefore increase the probability of survival.

Experimenter familiarization is a crucial prerequisite for assessing behavioral outcomes and reduces stress in mice not only under chronic pain conditions

Rodent behavior is affected by different environmental conditions. These do not only comprise experimental and housing conditions but also familiarization with the experimenter. However, specific effects on pain-related behavior and chronic pain conditions have not been examined. Therefore, we aimed to investigate the impact of different housing conditions, using individually ventilated and standard open top cages, inverted day-night cycles, and experimenter familiarization on male mice following peripheral neuropathy using the spared nerve injury (SNI) model. Using a multimodal approach, we evaluated evoked pain-related- using von Frey hair filaments, measured gait pattern with the CatWalk system, assessed anxiety- and depression-like behavior with the Elevated plus maze and tail suspension test, measured corticosterone metabolite levels in feces and utilized an integrative approach for relative-severity-assessment. Mechanical sensitivity differed between the cage systems and experimenter familiarization and was affected in both sham and SNI mice. Experimenter familiarization and an inverted day-night cycle reduced mechanical hypersensitivity in SNI and sham mice. SNI mice of the inverted day-night group displayed the slightest pronounced alterations in gait pattern in the Catwalk test. Anxiety-related behavior was only found in SNI mice of experimenter-familiarized mice compared to the sham controls. In addition, familiarization reduced the stress level measured by fecal corticosteroid metabolites caused by the pain and the behavioral tests. Although no environmental condition significantly modulated the severity in SNI mice, it influenced pain-affected phenotypes and is, therefore, crucial for designing and interpreting preclinical pain studies. Moreover, environmental conditions should be considered more in the reporting guidelines, described in more detail, and discussed as a potential influence on pain phenotypes.

Decreased levels of discomfort in repeatedly handled mice during experimental procedures, assessed by facial expressions

Mice are the most commonly used laboratory animal, yet there are limited studies which investigate the effects of repeated handling on their welfare and scientific outcomes. Furthermore, simple methods to evaluate distress in mice are lacking, and specialized behavioral or biochemical tests are often required. Here, two groups of CD1 mice were exposed to either traditional laboratory handling methods or a training protocol with cup lifting for 3 and 5 weeks. The training protocol was designed to habituate the mice to the procedures involved in subcutaneous injection, e.g., removal from the cage, skin pinch. This protocol was followed by two common research procedures: subcutaneous injection and tail vein blood sampling. Two training sessions and the procedures (subcutaneous injection and blood sampling) were video recorded. The mouse facial expressions were then scored, focusing on the ear and eye categories of the mouse grimace scale. Using this assessment method, trained mice expressed less distress than the control mice during subcutaneous injection. Mice trained for subcutaneous injection also had reduced facial scores during blood sampling. We found a clear sex difference as female mice responded to training faster than the male mice, they also had lower facial scores than the male mice when trained. The ear score appeared to be a more sensitive measure of distress than the eye score, which may be more indicative of pain. In conclusion, training is an important refinement method to reduce distress in mice during common laboratory procedures and this can best be assessed using the ear score of the mouse grimace scale.

Pain Recognition in Rodents

Available methods for recognizing and assessing pain in rodents have increased over the last 10 years, including the development of validated pain assessment scales. Much of this work has been driven by the needs of biomedical research, and there are specific challenges to applying these scales in the clinical environment. This article provides an introduction to pain assessment scale validation, reviews current methods of pain assessment, highlighting their strengths and weaknesses, and makes recommendations for assessing pain in a clinical environment.

Use of nonaversive handling and training procedures for laboratory mice and rats: Attitudes of American and Canadian laboratory animal professionals

Nonaversive or low stress handling techniques can reduce fear and stress in research rodents, ultimately improving study data quality. Uptake of low stress handling has been slow in the USA and Canada. In this study we explored the understanding, experience, and attitudes toward low stress handling of rats and mice in laboratory animal professionals from the USA (US) and Canada (CA). Participants (n = 40) were recruited for a standardized interview and job categories were divided into veterinary/PhD level roles (doctoral level; DL) and non-veterinary/non-PhD level roles (non-doctoral level, NDL) (US: 23, DL: 9, NDL: 14; CA: 17, DL: 8, and NDL: 9). Interviews were transcribed and analyzed using NVIVO. Two research assistants independently coded themes for each question and consolidated responses based on commonality. Laboratory animal professionals understood the benefits of low stress handling and training techniques with rats and mice, stating reduced stress, better data, and improved welfare, with CA participants more likely to mention animal welfare as a benefit, and DL more likely to mention improved research data and reduced stress. Participants across demographic groups indicated improved job satisfaction and decreased stress as the positive impacts low stress handling would have on their positions. The primary perceived barriers to low stress handling implementation were researcher attitudes, the time needed to implement and use these techniques, and training personnel to use the techniques properly and consistently. To promote refinement of handling of rats and mice, more educational opportunities on the benefits and implementation of low stress handling techniques need to be provided to laboratory animal professionals, as well as to researchers.

Handling method affects measures of anxiety, but not chronic stress in mice

Studies in mice have shown that less aversive handling methods (e.g. tunnel or cup handling) can reduce behavioural measures of anxiety in comparison to picking mice up by their tail. Despite such evidence, tail handling continues to be used routinely. Besides resistance to change accustomed procedures, this may also be due to the fact that current evidence in support of less aversive handling is mostly restricted to effects of extensive daily handling, which may not apply to routine husbandry practices. The aim of our study was to assess whether, and to what extent, different handling methods during routine husbandry induce differences in behavioural and physiological measures of stress in laboratory mice. To put the effects of handling method in perspective with chronic stress, we compared handling methods to a validated paradigm of unpredictable chronic mild stress (UCMS). We housed mice of two strains (Balb/c and C57BL/6) and both sexes either under standard laboratory conditions (CTRL) or under UCMS. Half of the animals from each housing condition were tail handled and half were tunnel handled twice per week, once during a cage change and once for a routine health check. We found strain dependent effects of handling method on behavioural measures of anxiety: tunnel handled Balb/c mice interacted with the handler more than tail handled conspecifics, and tunnel handled CTRL mice showed increased open arm exploration in the elevated plus-maze. Mice undergoing UCMS showed increased plasma corticosterone levels and reduced sucrose preference. However, we found no effect of handling method on these stress-associated measures. Our results therefore indicate that routine tail handling can affect behavioural measures of anxiety, but may not be a significant source of chronic husbandry stress. Our results also highlight strain dependent responses to handling methods.

Impact of Refinements to Handling and Restraint Methods in Mice

There is increasing evidence that, compared to non-aversive handling methods (i.e., tunnel and cupping), tail handling has a negative impact on mouse welfare. Despite this evidence, there are still research organisations that continue to use tail handling. Here, we investigated handling for routine husbandry by three different methods: tail, cupping and tube in a relevant real-world scenario involving mice bred off-site. After transfer to the destination unit, mice were assessed for overt behaviours associated with anxiety and fear. Mice that experienced tail handling were less easy to handle, were more responsive to the box opening, and scored lower in a hand approach test. One barrier to non-tail handling methods is the current practice of restraining mice by the tail for procedures. We therefore next assessed whether a modified method for restraint that takes the animal from cupping to restraint without the use of the tail was associated with better welfare. This refined restraint method reduced overt signs of distress although we did not find any differences in corticosterone levels or anxiety-related behaviours. These findings suggest that avoiding tail handling throughout the animal’s laboratory experience, including during restraint, benefits their welfare.

Effects of separated pair housing of female C57BL/6JRj mice on well-being

In laboratory animal facilities, it is a common code of practice to house female mice in groups. However, some experimental conditions require to house them individually, even though social isolation may impair their well-being. Therefore, we introduced a separated pair housing system and investigated whether it can refine single housing of adult female C57BL/6JRj mice. Individually ventilated cages (IVC) were divided by perforated transparent walls to separate two mice within a cage. The cage divider allowed visual, acoustic, and olfactory contact between the mice but prevented interindividual body-contact or food sharing. Short- and long-term effects of the separated pair housing system on the well-being of the mice were compared with single and group housing using a range of behavioral and physiological parameters: Nest building behavior was assessed based on the complexity of nests, the burrowing performance was measured by the amount of food pellets removed from a bottle, and trait anxiety-related behavior was tested in the free exploratory paradigm. For the evaluation of the ease of handling, interaction with the experimenter's hand was monitored. Social interaction with unknown conspecifics and locomotor activity were investigated in a test arena. Moreover, body weight and stress hormone (metabolites) were measured in feces and hair. After the mice spent a day under the respective housing conditions, concentrations of fecal corticosterone metabolites were higher in separated pair-housed mice, and they built nests of a higher complexity when compared to single-housed mice. The latter effect was still observable eight weeks later. In week 8, separated pair-housed mice showed less locomotor activity in the social interaction arena compared to mice from the other housing systems, i.e., single and group housing. Regardless of the time of testing, pair housing improved the burrowing performance. Separated pair-housed mice were more difficult to catch than group-housed mice. Hair corticosterone, progesterone, and dehydroepiandrosterone concentrations changed with increasing age independently of the housing system. There were no effects of the housing systems on trait anxiety-related behavior in the free exploratory paradigm, voluntary interaction with the experimenter's hand, and body weight. Overall, the transfer to the separated pair housing system caused short-term stress responses in female C57BL/6JRj mice. Long-term effects of separated pair housing were ambiguous. On one hand, separated pair housing increased nesting and burrowing behavior and may therefore be beneficial compared to single housing. But on the other hand, locomotor activity decreased. The study underlined that the effects of the housing conditions on physiological and behavioral parameters should be considered when analyzing and reporting animal experiments.

Juvenile handling rescues autism-related effects of prenatal exposure to valproic acid

Environmental factors acting on young animals affect neurodevelopmental trajectories and impact adult brain function and behavior. Psychiatric disorders may be caused or worsen by environmental factors, but early interventions can improve performance. Understanding the possible mechanisms acting upon the developing brain could help identify etiological factors of psychiatric disorders and enable advancement of effective therapies. Research has focused on the long-lasting effects of environmental factors acting during the perinatal period, therefore little is known about the impact of these factors at later ages when neurodevelopmental pathologies such as autism spectrum disorder (ASD) are usually diagnosed. Here we show that handling mice during the juvenile period can rescue a range of behavioral and cellular effects of prenatal valproic acid (VPA) exposure. VPA-exposed animals show reduced sociability and increased repetitive behaviors, along with other autism-related endophenotypes such as increased immobility in the forced swim test and increased neuronal activity in the piriform cortex (Pir). Our results demonstrate that briefly handling mice every other day between postnatal days 22 and 34 can largely rescue these phenotypes. This effect can also be observed when animals are analyzed across tests using an “autism” factor, which also discriminates between animals with high and low Pir neuron activity. Thus, we identified a juvenile developmental window when environmental factors can determine adult autism-related behavior. In addition, our results have broader implications on behavioral neuroscience, as they highlight the importance of adequate experimental design and control of behavioral experiments involving treating or testing young animals.

Effects of non-aversive versus tail-lift handling on breeding productivity in a C57BL/6J mouse colony

Non-aversive handling is a well-documented refinement measure for improving rodent welfare. Because maternal stress is related to reduced productivity, we hypothesized that welfare benefits associated with non-aversive handling would translate to higher production and fewer litters lost in a laboratory mouse breeding colony. We performed a randomized controlled trial to examine the effects of a standard method of handling (tail-lift with forceps) versus non-aversive handling with transfer tunnels ('tunnel-handled') on breeding performance in 59 C57BL/6J mouse pairs. Intervention assignments could not be concealed from technicians, but were concealed from assessors and data analyst. An operationally significant effect of tunnel-handling (large enough differences to warrant programmatic change) was defined before study initiation as a 5% increase in productivity, or one extra pup over the reproductive lifetime of each pair. Pairs were randomly allocated to handling intervention and cage rack location, and monitored over an entire 6-month breeding cycle. For each group, we measured number of pups born and weaned, and number of entire litters lost prior to weaning. Differences between transfer methods were estimated by two-level hierarchical mixed models adjusted for parental effects and parity. Compared to tail-lift mice, tunnel-handled mice averaged one extra pup per pair born (+1.0; 95% CI 0.9, 1.1; P = 0.41) and weaned (+1.1, 95% CI 0.9, 1.2; P = 0.33). More tunnel-handled pairs successfully weaned all litters produced (13/29 pairs, 45% vs 4/30 pairs, 13%; P = 0.015), averaged fewer litter losses prior to weaning (11/29 pairs [38%] vs 26/30 pairs [87%]; P <0.001), and had a 20% lower risk of recurrent litter loss. The increase in numbers of pups produced and weaned with tunnel handling met threshold requirement for operational significance. These data and projected cost savings persuaded management to incorporate tunnel handling as standard of care across the institution. These data also suggest that overlooked husbandry practices such as cage transfer may be major confounders in studies of mouse models.

Stress-induced body weight loss and improvements in cardiometabolic risk factors do not translate to improved myocardial ischemic tolerance in western diet-fed mice

Although both diet-induced obesity and psychological stress are recognized as significant independent contributors to cardiometabolic and behavioral disorders, our understanding of how these two disorders interact and influence cardiometabolic risk and myocardial ischemic tolerance is limited. The aim of this study was to assess the combined effects of an obesogenic diet and psychological stress on cardiometabolic risk factors (body weight, dyslipidemia, insulin sensitivity) and postischemic cardiovascular outcomes. C57Bl/6J mice (n = 48) were subject to a combination of 22 weeks of western diet (WD) feeding and chronic restraint stress (CRS) for the last 4 weeks. Metabolic and behavioral changes were assessed using glucose tolerance tests and open field tests (OFTs), respectively. After 22 weeks, cardiac function and ischemic tolerance were assessed in Langendorff perfused hearts. WD feeding increased body weight and worsened blood lipids and insulin sensitivity. WD-fed mice also exhibited reduced exploratory behavior within the OFT. CRS reduced body weight and increased locomotion in both dietary groups and had differential effects on fasting glucose metabolism in the two dietary groups while not impacting non-fasting insulin. Although the WD only marginally reduced reperfusion left ventricular developed pressure recovery, CRS worsened reperfusion diastolic dysfunction in both dietary groups. Interestingly, despite WD+CRS animals exhibiting improved cardiometabolic parameters compared to the WD group, these changes did not translate to marked improvements to postischemic cardiac outcomes. In conclusion, in this study, combined WD feeding and CRS did not act synergistically to worsen cardiometabolic risk factors but instead improved them. Despite these cardiometabolic improvements, WD+CRS increased reperfusion end diastolic pressure which may be indicative of worsened ischemia/reperfusion injury.

Comparison of Gelatin Flavors for Oral Dosing of C57BL/6J and FVB/N Mice

Precise oral dosing in rodents is usually achieved by intragastric gavage. If performed incorrectly due to technical difficulties, inexperience, or animal resistance, oral gavage may have animal welfare implications such as esophageal and gastric rupture and aspiration. The stress that is induced by this procedure can also lead to confounding results. In several animal models, drug vehicles must be sugar-free, deliver drugs in a specific formulation, and sometimes supply water. Gelatin has all of these properties. The current study aimed to evaluate the use of gelatin vehicles with different sensory features as an alternative to oral gavage. We investigated the time taken by 2 different inbred mouse strains, FVB/N and C57BL/6J, to ingest sugar-free gelatin pellets of varying flavors. Results showed that FVB/N mice took more time to eat the unflavored, strawberry and diet-flavored gelatin pellets than did C57BL/6J mice. Both strains showed low preference for lemon flavor, with the same ingestion times after the second day. This study showed that the C57BL/6J mice are more likely to eat gelatin than are FVB/N mice, and that the 2 strains of mice show a lower preference for lemon flavoring as compared with other flavors. This method of voluntarily oral administration offers an alternative to gavage for studies that use oral dosing studies.

Welfare Assessment, End-Point Refinement and the Effects of Non-Aversive Handling in C57BL/6 Mice with Lewis Lung Cancer

Cancer-bearing mice are at risk of developing anxiety, pain, or malaise. These conditions may not only harm welfare but could also undermine data quality and translational validity in studies to develop therapeutic interventions. We aimed to establish whether, or at what point mice developing lung cancer show these symptoms, what measures can best detect their onset, and if data quality and animal welfare can be enhanced by using non-aversive handling (NAH). Welfare was monitored using various daily methods. At the beginning and end of the study, we also scored behaviour for general welfare evaluation, recorded nociceptive thresholds, and applied the mouse grimace scale (MGS). Cancer caused a decline in daily welfare parameters (body weight, and food and water consumption) beginning at around 4 days prior to euthanasia. As cancer progressed, rearing and walking declined to a greater extent in cancer-bearing versus control mice, while grooming, inactive periods, and MGS scores increased. A decline in nest building capability and food consumption provided a particularly effective means of detecting deteriorating welfare. These changes suggested a welfare problem arose as cancer developed, so similar studies would benefit from refinement, with mice being removed from the study at least 4 days earlier. However, the problem of highly varied tumour growth made it difficult to determine this time-point accurately. There were no detectable beneficial effects of NAH on either data quality or in terms of enhanced welfare.

Neuroinflammation, body temperature and behavioural changes in CD1 male mice undergoing acute restraint stress: An exploratory study

BACKGROUND

Animal models used to study pathologies requiring rehabilitation therapy, such as cardiovascular and neurologic disorders or oncologic disease, must be as refined and translationally relevant as possible. Sometimes, however, experimental procedures such as those involving restraint may generate undesired effects which may act as a source of bias. However, the extent to which potentially confounding effects derive from such routine procedures is currently unknown. Our study was therefore aimed at exploring possible undesirable effects of acute restraint stress, whereby animals were exposed to a brightly lit enclosed chamber (R&L) similar to those that are commonly used for substance injection. We hypothesised that this would induce a range of unwanted physiological alterations [such as neuroinflammatory response and changes in body weight and in brown adipose tissue (BAT)] and behavioural modification, and that these might be mitigated via the use of non-aversive handling methods: Tunnel Handling (NAH-T) and Mechanoceptive Handling (NAH-M)) as compared to standard Tail Handling (TH).

METHODS

Two indicators of physiological alterations and three potentially stress sensitive behavioural parameters were assessed. Physiological alterations were recorded via body weight changes and assessing the temperature of Brown Adipose Tissue (BAT) using infra-red thermography (IRT), and at the end of the experiment we determined the concentration of cytokines CXCL12 and CCL2 in bone marrow (BM) and activated microglia in the brain. Nest complexity scoring, automated home-cage behaviour analysis (HCS) and Elevated Plus Maze testing (EPM) were used to detect any behavioural alterations. Recordings were made before and after a 15-minute period of R&L in groups of mice handled via TH, NAH-T or NAH-M.

RESULTS

BAT temperature significantly decreased in all handling groups following R&L regardless of handling method. There was a difference, at the limit of significance (p = 0.06), in CXCL12 BM content among groups. CXCL12 content in BM of NAH-T animals was similar to that found in Sentinels, the less stressed group of animals. After R&L, mice undergoing NAH-T and NAH-M showed improved body-weight maintenance compared to those exposed to TH. Mice handled via NAH-M spent a significantly longer time on the open arms of the EPM. The HCS results showed that in all mice, regardless of handling method, R&L resulted in a significant reduction in walking and rearing, but not in total distance travelled. All mice also groomed more. No difference among the groups was found in Nest Score, in CCL2 BM content or in brain activated microglia.

CONCLUSIONS

Stress induced by a common restraint procedure caused metabolic and behavioural changes that might increase the risk of unexpected bias. In particular, the significant decrease in BAT temperature could affect the important metabolic pathways controlled by this tissue. R&L lowered the normal frequency of walking and rearing, increased grooming and probably carried a risk of low-grade neuro-inflammation. Some of the observed alterations can be mitigated by Non-aversive handlings.

Glucoregulation and coping behavior after chronic stress in rats: Sex differences across the lifespan

The purpose of the current study was to determine how biological sex shapes behavioral coping and metabolic health across the lifespan after chronic stress. We hypothesized that examining chronic stress-induced behavioral and endocrine outcomes would reveal sex differences in the biological basis of susceptibility. During late adolescence, male and female Sprague-Dawley rats experienced chronic variable stress (CVS). Following completion of CVS, all rats experienced a forced swim test (FST) followed 3 days later by a fasted glucose tolerance test (GTT). The FST was used to determine coping in response to a stressor. Endocrine metabolic function was evaluated in the GTT by measuring glucose and corticosterone, the primary rodent glucocorticoid. Rats then aged to 15 months when the FST and GTT were repeated. In young rats, chronically stressed females exhibited more passive coping and corticosterone release in the FST. Additionally, chronically stressed females had elevated corticosterone and impaired glucose clearance in the GTT. Aging affected all measurements as behavioral and endocrine outcomes were sex specific. Furthermore, regression analysis between hormonal and behavioral responses identified associations depending on sex and stress. Collectively, these data indicate increased female susceptibility to the effects of chronic stress during adolescence. Further, translational investigation of coping style and glucose homeostasis may identify biomarkers for stress-related disorders.

A Good Life for Laboratory Rodents?

Most would agree that animals in research should be spared "unnecessary" harm, pain, or distress, and there is also growing interest in providing animals with some form of environmental enrichment. But is this the standard of care that we should aspire to? We argue that we need to work towards a higher standard-specifically, that providing research animals with a "good life" should be a prerequisite for their use. The aims of this paper are to illustrate our vision of a "good life" for laboratory rats and mice and to provide a roadmap for achieving this vision. We recognize that several research procedures are clearly incompatible with a good life but describe here what we consider to be the minimum day-to-day living conditions to be met when using rodents in research. A good life requires that animals can express a rich behavioral repertoire, use their abilities, and fulfill their potential through active engagement with their environment. In the first section, we describe how animals could be housed for these requirements to be fulfilled, from simple modifications to standard housing through to better cage designs and free-ranging options. In the second section, we review the types of interactions with laboratory rodents that are compatible with a good life. In the third section, we address the potential for the animals to have a life outside of research, including the use of pets in clinical trials (the animal-as-patient model) and the adoption of research animals to new homes when they are no longer needed in research. We conclude with a few suggestions for achieving our vision.

Lifetime Observation of Cognition and Physiological Parameters in Male Mice

Laboratory mice are predominantly used for one experiment only, i.e., new mice are ordered or bred for every new experiment. Moreover, most experiments use relatively young mice in the range of late adolescence to early adulthood. As a consequence, little is known about the day-to-day life of adult and aged laboratory mice. Here we present a long-term data set with three consecutive phases conducted with the same male mice over their lifetime in order to shed light on possible long-term effects of repeated cognitive stimulation. One third of the animals was trained by a variety of learning tasks conducted up to an age of 606 days. The mice were housed in four cages with 12 animals per cage; only four mice per cage had to repeatedly solve cognitive tasks for getting access to water using the IntelliCage system. In addition, these learner mice were tested in standard cognitive tests outside their home-cage. The other eight mice served as two control groups living in the same environment but without having to solve tasks for getting access to water. One control group was additionally placed on the test set-ups without having to learn the tasks. Next to the cognitive tasks, we took physiological measures (body mass, resting metabolic rate) and tested for dominance behavior, and attractivity in a female choice experiment. Overall, the mice were under surveillance until they died a natural death, providing a unique data set over the course of virtually their entire lives. Our data showed treatment differences during the first phase of our lifetime data set. Young learner mice showed a higher activity, less growth and resting metabolic rate, and were less attractive for female mice. These effects, however, were not preserved over the long-term. We also did not find differences in dominance or effects on longevity. However, we generated a unique and valuable set of long-term behavioral and physiological data from a single group of male mice and note that our long-term data contribute to a better understanding of the behavioral and physiological processes in male C57Bl/6J mice.

Oral anserine supplementation does not attenuate type-2 diabetes or diabetic nephropathy in BTBR ob/ob mice

Carnosine, a naturally occurring dipeptide present in an omnivorous diet, has been shown to ameliorate the development of metabolic syndrome, type-2 diabetes (T2D) and early- and advanced-stage diabetic nephropathy in different rodent models. Anserine, its methylated analogue, is more bio-available in humans upon supplementation without affecting its functionality. In this work, we investigated the effect of oral supplementation with anserine or carnosine on circulating and tissue anserine and carnosine levels and on the development of T2D and diabetic nephropathy in BTBR ob/ob mice. BTBR ob/ob mice were either supplemented with carnosine or anserine in drinking water (4 mM) for 18 weeks and compared with non-supplemented BTBR ob/ob and wild-type (WT) mice. Circulating and kidney, but not muscle, carnosine, and anserine levels were enhanced by supplementation with the respective dipeptides in ob/ob mice compared to non-treated ob/ob mice. The evolution of fasting blood glucose, insulin, fructosamine, triglycerides, and cholesterol was not affected by the supplementation regimens. The albumin/creatine ratio, glomerular hypertrophy, and mesangial matrix expansion were aggravated in ob/ob vs. WT mice, but not alleviated by supplementation. To conclude, long-term supplementation with anserine elevates circulating and kidney anserine levels in diabetic mice. However, anserine supplementation was not able to attenuate the development of T2D or diabetic nephropathy in BTBR ob/ob mice. Further research will have to elucidate whether anserine can attenuate milder forms of T2D or metabolic syndrome.

Light affects behavioral despair involving the clock gene Period 1

Light at night has strong effects on physiology and behavior of mammals. It affects mood in humans, which is exploited as light therapy, and has been shown to reset the circadian clock in the suprachiasmatic nuclei (SCN). This resetting is paramount to align physiological and biochemical timing to the environmental light-dark cycle. Here we provide evidence that light at zeitgeber time (ZT) 22 affects mood-related behaviors also in mice by activating the clock gene Period1 (Per1) in the lateral habenula (LHb), a brain region known to modulate mood-related behaviors. We show that complete deletion of Per1 in mice led to depressive-like behavior and loss of the beneficial effects of light on this behavior. In contrast, specific deletion of Per1 in the region of the LHb did not affect mood-related behavior, but suppressed the beneficial effects of light. RNA sequence analysis in the mesolimbic dopaminergic system revealed profound changes of gene expression after a light pulse at ZT22. In the nucleus accumbens (NAc), sensory perception of smell and G-protein coupled receptor signaling were affected the most. Interestingly, most of these genes were not affected in Per1 knock-out animals, indicating that induction of Per1 by light serves as a filter for light-mediated gene expression in the brain. Taken together we show that light affects mood-related behavior in mice at least in part via induction of Per1 in the LHb with consequences on mood-related behavior and signaling mechanisms in the mesolimbic dopaminergic system.

Quantitative flux analysis in mammals

Altered metabolic activity contributes to the pathogenesis of a number of diseases, including diabetes, heart failure, cancer, fibrosis and neurodegeneration. These diseases, and organismal metabolism more generally, are only partially recapitulated by cell culture models. Accordingly, it is important to measure metabolism in vivo. Over the past century, researchers studying glucose homeostasis have developed strategies for the measurement of tissue-specific and whole-body metabolic activity (pathway fluxes). The power of these strategies has been augmented by recent advances in metabolomics technologies. Here, we review techniques for measuring metabolic fluxes in intact mammals and discuss how to analyse and interpret the results. In tandem, we describe important findings from these techniques, and suggest promising avenues for their future application. Given the broad importance of metabolism to health and disease, more widespread application of these methods holds the potential to accelerate biomedical progress.

Translating glucose tolerance data from mice to humans: Insights from stable isotope labelled glucose tolerance tests

Objective

The glucose tolerance test (GTT) is widely used in human and animal biomedical and pharmaceutical research. Despite its prevalent use, particularly in mouse metabolic phenotyping, to the best of our knowledge we are not aware of any studies that have attempted to qualitatively compare the metabolic events during a GTT in mice with those performed in humans.

Methods

Stable isotope labelled oral glucose tolerance tests (siOGTTs; [6,6-²H₂]glucose) were performed in both human and mouse cohorts to provide greater resolution into postprandial glucose kinetics. The siOGTT allows for the partitioning of circulating glucose into that derived from exogenous and endogenous sources. Young adults spanning the spectrum of normal glucose tolerance (n = 221), impaired fasting (n = 14), and impaired glucose tolerance (n = 19) underwent a 75g siOGTT, whereas a 50 mg siOGTT was performed on chow (n = 43) and high-fat high-sucrose fed C57Bl6 male mice (n = 46).

Results

During the siOGTT in humans, there is a long period (>3hr) of glucose absorption and, accordingly, a large, sustained insulin response and robust suppression of lipolysis and endogenous glucose production (EGP), even in the presence of glucose intolerance. In contrast, mice appear to be highly reliant on glucose effectiveness to clear exogenous glucose and experience only modest, transient insulin responses with little, if any, suppression of EGP. In addition to the impaired stimulation of glucose uptake, mice with the worst glucose tolerance appear to have a paradoxical and persistent rise in EGP during the OGTT, likely related to handling stress.

Conclusions

The metabolic response to the OGTT in mice and humans is highly divergent. The potential reasons for these differences and their impact on the interpretation of mouse glucose tolerance data and their translation to humans are discussed.

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We compared the mechanisms governing glucose handling in humans and mice.

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Humans and mice underwent stable isotope labelled oral glucose tolerance tests.

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Metabolic responses between humans and mice were highly divergent.

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Unlike humans, most mice exhibit little EGP suppression or insulin response.

Monitoring daytime differences in moderate intensity exercise capacity using treadmill test and muscle dissection

There is growing interest in medicine and sports in uncovering exercise modifiers that enhance or limit exercise capacity. Here, we detail a protocol for testing the daytime effect on running capacity in mice using a moderate intensity treadmill effort test. Instructions for dissecting soleus, gastrocnemius plantaris, and quadriceps muscles for further analysis are provided as well. This experimental setup is optimized for addressing questions regarding the involvement of daytime and circadian clocks in regulating exercise capacity.

For complete details on the use and execution of this protocol, please refer to Ezagouri et al. (2019).

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Exercise capacity is influenced by the time of day

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Protocol for determining moderate intensity exercise capacity using treadmill test

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Instructions for muscle dissection

Group housing and social dominance hierarchy affect circadian activity patterns in mice

In this study, we investigated the effect of social environment on circadian patterns in activity by group housing either six male or six female mice together in a cage, under regular light-dark cycles. Based on the interactions among the animals, the social dominance rank of individual mice was quantitatively established by calculating Elo ratings. Our results indicated that, during our experiment, the social dominance hierarchy was rapidly established, stable yet complex, often showing more than one dominant mouse and several subordinate mice. Moreover, we found that especially dominant male mice, but not female mice, displayed a significantly higher fraction of their activity during daytime. This resulted in reduced rhythm amplitude in dominant males. After division into separate cages, male mice showed an enhancement of their 24 h rhythm, due to lower daytime activity. Recordings of several physiological parameters showed no evidence for reduced health as a potential consequence of reduced rhythm amplitude. For female mice, transfer to individual housing did not affect their daily activity pattern. We conclude that 24 h rhythms under light-dark cycles are influenced by the social environment in males but not in females, and lead to a decrement in behavioural rhythm amplitude that is larger in dominant mice.

Effects of handling on the behavioural phenotype of the neuregulin 1 type III transgenic mouse model for schizophrenia

Handling of laboratory mice affects animal wellbeing and behavioural test outcomes. However, present research has focused on handling effects in common strains of laboratory mice despite the knowledge that environmental factors can modify established phenotypes of genetic mouse models. Thus, we examined the impact of handling on the face validity of a transgenic mouse model for the schizophrenia risk gene neuregulin 1 (i.e. Nrg1 type III overexpression). Nrg1 III tg and wild type-like (WT) control mice of both sexes underwent tail or tunnel handling before being assessed in the open field (OF), elevated plus maze (EPM), social preference/novelty, prepulse inhibition, and fear conditioning tests. Tunnel-handling reduced the startle response in all mice, increased OF locomotion and exploration in males and reduced anxiety in males (OF) and females (EPM) compared to tail-handling. Importantly, tunnel handling induced a more pronounced startle response to increasing startle stimuli in Nrg1 III tg females compared to respective controls, a phenomenon absent in tail-handled females. Finally, Nrg1 III tg males displayed reduced OF exploration and centre locomotion and Nrg1 III tg females displayed increased cue freezing over time compared to controls. In conclusion, handling methods have a significant impact on a variety of behavioural domains thus the impact of routine handling procedures need be considered when testing behavioural phenotypes. Handling did not change the main schizophrenia-relevant characteristics of Nrg1 III tg mice but affected the acoustic startle-response in a genotype- and sex-specific manner. Future research should evaluate the effect of handling on other genetic models.

Comparison of in vivo and in situ detection of hippocampal metabolites in mouse brain using 1 H-MRS

The study of cerebral metabolites relies heavily on detection methods and sample preparation. Animal experiments in vivo require anesthetic agents that can alter brain metabolism, whereas ex vivo experiments demand appropriate fixation methods to preserve the tissue from rapid postmortem degradation. In this study, the metabolic profiles of mouse hippocampi using proton magnetic resonance spectroscopy (¹ H-MRS) were compared in vivo and in situ with or without focused beam microwave irradiation (FBMI) fixation. Ten major brain metabolites, including lactate (Lac), N-acetylaspartate (NAA), total choline (tCho), myo-inositol (mIns), glutamine (Gln), glutamate (Glu), aminobutyric acid (GABA), glutathione (GSH), total creatine (tCr) and taurine (Tau), were analyzed using LCModel. After FBMI fixation, the concentrations of Lac, tCho and mIns were comparable with those obtained in vivo under isoflurane, whereas other metabolites were significantly lower. Except for a decrease in NAA and an increase in Tau, all the other metabolites remained stable over 41 hours in FBMI-fixed brains. Without FBMI, the concentrations of mIns (before 2 hours), tCho and GABA were close to those measured in vivo. However, higher Lac (P < .01) and lower NAA, Gln, Glu, GSH, tCr and Tau were observed (P < .01). NAA, Gln, Glu, GSH, tCr and Tau exhibited good temporal stability for at least 20 hours in the unfixed brain, whereas a linear increase of tCho, mIns and GABA was observed. Possible mechanisms of postmortem degradation are discussed. Our results indicate that a proper fixation method is required for in situ detection depending on the targeted metabolites of specific interests in the brain.

Brain-Body Control of Glucose Homeostasis-Insights From Model Organisms

Tight regulation of blood glucose is essential for long term health. Blood glucose levels are defended by the correct function of, and communication between, internal organs including the gastrointestinal tract, pancreas, liver, and brain. Critically, the brain is sensitive to acute changes in blood glucose level and can modulate peripheral processes to defend against these deviations. In this mini-review we highlight select key findings showcasing the utility, strengths, and limitations of model organisms to study brain-body interactions that sense and control blood glucose levels. First, we discuss the large platform of genetic tools available to investigators studying mice and how this field may yet reveal new modes of communication between peripheral organs and the brain. Second, we discuss how rats, by virtue of their size, have unique advantages for the study of CNS control of glucose homeostasis and note that they may more closely model some aspects of human (patho)physiology. Third, we discuss the nascent field of studying the CNS control of blood glucose in the zebrafish which permits ease of genetic modification, large-scale measurements of neural activity and live imaging in addition to high-throughput screening. Finally, we briefly discuss glucose homeostasis in drosophila, which have a distinct physiology and glucoregulatory systems to vertebrates.

There's no place like home? Return to the home cage triggers dopamine release in the mouse nucleus accumbens

Various stimuli have been employed as reinforcers in preclinical rodent models to elucidate the underpinnings of reward at a molecular and circuit level, with the release of dopamine (DA) in the nucleus accumbens (NAc) as a well-replicated, physiological correlate. Many factors, however, including strain differences, sex, prior stress, and reinforcer administration protocols can influence reward responding and DA release. Although previous evidence indicates that access to the home cage can be an effective reinforcer in behavioral tasks, whether this simple environmental manipulation can trigger DA release in the NAc has not been demonstrated. Here, using fiber photometric recordings of in vivo NAc dopamine release from a genetically-encoded DA sensor, we show that the movement of animals from the home cage to a clear, polycarbonate recording chamber evokes little to no DA release following initial exposure whereas returning animals from the recording chamber to a clean, home-like cage or to the home cage robustly triggers the release of DA, comparable in size to that observed with a 10 mg/kg i.p. Cocaine injection in the recording chamber. Although DA release can be evoked in moving mice to a clean cage, this release was significantly augmented when moving animals from the clean cage to the home cage. Our data provide direct evidence that home cage return from a foreign environment results in a biochemical change consistent with that of a rewarding stimulus. This simple environmental manipulation provides a minimally invasive approach to study the reward circuitry underlying an ethologically relevant reinforcer, return to the safe confines of "home". The home cage - DA release paradigm may also represent a biomarker-driven paradigm for the evaluation of genetic and experiential events that underlie anhedonic states, characteristic of major mood disorders, and to present new opportunities to identify their treatments.

Frequent exposure to varied home cage sizes alters pain sensitivity and some key inflammation-related biomarkers

BACKGROUND

Nature and size of rodent cages vary from one laboratory or country to another. Little is however known about the physiological implications of exposure to diverse cage sizes in animal-based experiments.

METHOD

Here, two groups of male Swiss mice (Control group - Cage stationed, and Test group - Cage migrated) were used for this study. The cage-migrated mice were exposed daily to various cage sizes used across laboratories in Nigeria while the cage-stationed mice exposed daily to different but the same cage size and shape. At the end of the 30 days exposure, top-rated paradigms were used to profile changes in physiological behaviours, and this was followed by evaluation of histological and biochemical metrics.

RESULTS

The study showed a significant (p < 0.05) decrease in blood glucose levels (at 60 and 120 min of oral glucose tolerance test) in the cage-migrated mice compared to cage-stationed mice. Strikingly, peripheral oxidative stress (plasma malondialdehyde) and pain sensitivity (formalin test, hot-and-cold plate test, and von Frey test) decreased significantly in cage-migrated mice compared to cage-stationed animals. Also, the pro-inflammation mediators (IL-6 and NF-κB) increased significantly in cage-migrated mice compared to cage-stationed mice. However, emotion-linked behaviours, neurotransmitters (serotonin, noradrenaline and GABA), brain and plasma electrolytes were not significantly difference in cage-migrated animals compared to cage-stationed mice.

CONCLUSION

Taken together, these results suggest that varied size cage-to-cage exposure of experimental mice could affect targeted behavioural and biomolecular parameters of pain and inflammation, thus diminishing research reproducibility, precipitating false negative/positive results and leading to poor translational outcomes.

Moving Beyond the Absence of Pain and Distress: Focusing on Positive Animal Welfare

For many years, researchers, veterinarians, animal ethics committees, and regulators have focused on minimizing pain and distress as a primary goal of refinement when working with animals in science. More recent publications as well as a shift in animal ethics and public opinion have emphasized promotion of positive affective states, culminating in the concept of positive animal welfare. Robust measures are required to know when positive animal welfare states are occurring, and a number of measures are proposed and discussed. Regardless of whether there are newer methods available that focus exclusively on measuring positive affective states, consistent consideration of research animal behavioral programs, refinement, and adopting periodic stand-alone animal welfare assessments for all species involved will help to push the care and practices of research animals towards an increased focus on positive animal welfare.

The impact of handling technique and handling frequency on laboratory mouse welfare is sex-specific

Handling is a well-known source of stress to laboratory animals and can affect variability of results and even compromise animal welfare. The conventional tail handling in mice has been shown to induce aversion and anxiety-like behaviour. Recent findings demonstrate that the use of alternative handling techniques, e.g. tunnel handling, can mitigate negative handling-induced effects. Here, we show that technique and frequency of handling influence affective behaviour and stress hormone release of subjects in a sex-dependent manner. While frequent tail handling led to a reduction of wellbeing-associated burrowing and increased despair-like behaviour in male mice, females seemed unaffected. Instead, they displayed a stress response to a low handling frequency, which was not detectable in males. This could suggest that in terms of refinement, the impact in handling could differ between the sexes. Independently from this observation, both sexes preferred to interact with the tunnel. Mice generally explored the tunnel more often than the tail-handling hands of the experimenter and showed more positively rated approaches, e.g. touching or climbing, and at the same time, less defensive burrowing, indicating a strong preference for the tunnel.

Benefits of tunnel handling persist after repeated restraint, injection and anaesthesia

Millions of mice are used every year for scientific research, representing the majority of scientific procedures conducted on animals. The standard method used to pick up laboratory mice for general husbandry and experimental procedures is known as tail handling and involves the capture, elevation and restraint of mice via their tails. There is growing evidence that, compared to non-aversive handling methods (i.e. tunnel and cup), tail handling increases behavioural signs of anxiety and induces anhedonia. Hence tail handling has a negative impact on mouse welfare. Here, we investigated whether repeated scruff restraint, intraperitoneal (IP) injections and anaesthesia negated the reduction in anxiety-related behaviour in tunnel compared with tail handled BALB/c mice. We found that mice which experienced repeated restraint spent less time interacting with a handler compared to mice that were handled only. However, after repeated restraint, tunnel handled mice showed increased willingness to interact with a handler, and reduced anxiety in standard behavioural tests compared with tail handled mice. The type of procedure experienced (IP injection or anaesthesia), and the duration after which behaviour was measured after a procedure affected the willingness of mice to interact with a handler. Despite this, compared with tail handling, tunnel handling reduced anxiety in standard behavioural tests and increased willingness to interact with a handler within hours after procedures. This suggests that the welfare benefits of tunnel handling are widely applicable and not diminished by the use of other putatively more invasive procedures that are frequently used in the laboratory. Therefore, the simple refinement of replacing tail with tunnel handling for routine husbandry and procedures will deliver a substantial improvement for mouse welfare and has the potential for improving scientific outcomes.

Negative mood affects the expression of negative but not positive emotions in mice

Whether and to what extent animals experience emotions is crucial for understanding their decisions and behaviour, and underpins a range of scientific fields, including animal behaviour, neuroscience, evolutionary biology and animal welfare science. However, research has predominantly focused on alleviating negative emotions in animals, with the expression of positive emotions left largely unexplored. Therefore, little is known about positive emotions in animals and how their expression is mediated. We used tail handling to induce a negative mood in laboratory mice and found that while being more anxious and depressed increased their expression of a discrete negative emotion (disappointment), meaning that they were less resilient to negative events, their capacity to express a discrete positive emotion (elation) was unaffected relative to control mice. Therefore, we show not only that mice have discrete positive emotions, but that they do so regardless of their current mood state. Our findings are the first to suggest that the expression of discrete positive and negative emotions in animals is not equally affected by long-term mood state. Our results also demonstrate that repeated negative events can have a cumulative effect to reduce resilience in laboratory animals, which has significant implications for animal welfare.

Acclimation Prior to an Intraperitoneal Insulin Tolerance Test to Mitigate Stress-Induced Hyperglycemia in Conscious Mice

The insulin tolerance test is commonly used in metabolic studies to assess whole body insulin sensitivity in rodents. It is a relatively simple test that involves measurement of blood glucose levels over time following a single intraperitoneal injection of insulin. Given that it is performed in the conscious state and blood is often collected via a tail snip, it has the potential to elicit a stress response from animals due to anxiety associated with handling and blood collection. As such, a stress-induced rise in blood glucose can occur, making it difficult to detect and interpret the primary endpoint measure, namely an insulin-mediated reduction in blood glucose. This has been seen in many mouse strains, and is quite common in diabetic db/db mice, where glucose levels can increase, rather than decrease, after insulin administration. Here, we describe a method of acclimating mice to handling, injections and blood sampling prior to performing the insulin tolerance test. We find that this lowers stress-induced hyperglycemia and results in data that more accurately reflects whole body insulin sensitivity.

Identifying obstacles preventing the uptake of tunnel handling methods for laboratory mice: An international thematic survey

Handling of laboratory mice is essential for experiments and husbandry, but handling can increase anxiety in mice, compromising their welfare and potentially reducing replicability between studies. The use of non-aversive handling (e.g., tunnel handling or cupping), rather than the standard method of picking mice up by the tail, has been shown to enhance interaction with a handler, reduce anxiety-like behaviours, and increase exploration and performance in standard behavioural tests. Despite this, some labs continue to use tail handling for routine husbandry, and the extent to which non-aversive methods are being used is currently unknown. Here we conducted an international online survey targeting individuals that work with and/or conduct research using laboratory mice. The survey aimed to identify the handling methods currently being used, and to determine common obstacles that may be preventing the wider uptake of non-aversive handling. We also surveyed opinions concerning the current data in support of non-aversive handling for mouse welfare and scientific outcomes. 390 complete responses were received and analysed quantitatively and thematically. We found that 35% report using tail handling only, and 43% use a combination of tail and non-aversive methods. 18% of respondents reported exclusively using non-aversive methods. The vast majority of participants were convinced that non-aversive handling improves animal welfare and scientific outcomes. However, the survey indicated that researchers were significantly less likely to have heard of non-aversive handling and more likely to use tail handling compared with animal care staff. Thematic analysis revealed there were concerns regarding the time required for non-aversive methods compared with tail handling, and that there was a perceived incompatibility of tunnel handling with restraint, health checks and other routine procedures. Respondents also highlighted a need for additional research into the impact of handling method that is representative of experimental protocols and physiological indicators used in the biomedical fields. This survey highlights where targeted research, outreach, training and funding may have the greatest impact on increasing uptake of non-aversive handling methods for laboratory mice.

Practical Considerations when Using Mouse Models of Diabetes

Mouse models of diabetes are important tools used in preclinical diabetes research. However, when working with these models, it is important to consider factors that could influence experimental outcome. This is particularly important given the wide variety of models available, each with specific characteristics that could be influenced by extrinsic or intrinsic factors. Blood glucose concentrations, a commonly used and valid endpoint in these models, are particularly susceptible to manipulation by these factors. These include potential effects of intrinsic factors such as strain, sex, and age and extrinsic factors such as husbandry practices and experimental protocols. These variables should therefore be taken into consideration when the model is chosen and the experiments are designed. This chapter outlines common variables that can impact the phenotype of a model, as well as describes the methods used for assessing onset of diabetes and monitoring diabetic mice.

Guidelines and Considerations for Metabolic Tolerance Tests in Mice

The epidemic of the century, Diabetes Mellitus (DM) is continuously rising. Intensive research is urgently needed whereby experimental models represent an essential tool to optimise the diagnostic strategy and to improve therapy. In this review, we describe the central principles of the metabolic tests available in order to study glucose and insulin homeostasis in mice, focusing on the most widely used - the glucose and insulin tolerance tests. We provide detailed experimental procedures as well as the practical implementation of these methods and discuss the main factors that should be taken into account when using this methodology.

Improving the practicality of using non-aversive handling methods to reduce background stress and anxiety in laboratory mice

Handling can stimulate stress and anxiety in laboratory animals that negatively impacts welfare and introduces a confounding factor in many areas of research. Picking up mice by the tail is a major source of handling stress that results in strong aversion to the handler, while mice familiarised with being picked up in a tunnel or cupped on the open hand show low stress and anxiety, and actively seek interaction with their handlers. Here we investigate the duration and frequency of handling required for effective familiarisation with these non-aversive handling methods, and test whether this is sufficient to prevent aversion and anxiety when animals then experience immobilisation and a mild procedure (subcutaneous injection). Very brief handling (2 s) was sufficient to familiarise mice with tunnel handling, even when experienced only during cage cleaning. Brief but more frequent handling was needed for familiarisation with cup handling, while pick up by tail induced strong aversion even when handling was brief and infrequent. Experience of repeated immobilisation and subcutaneous injection did not reverse the positive effects of tunnel handling. Our findings demonstrate that replacing tail with tunnel handling during routine cage cleaning and procedures provides a major refinement with little if any cost for familiarisation.

Assessment of Mouse Handling Techniques During Cage Changing

Mouse handling during cage changing and health evaluation has traditionally been performed by using forceps. This method was adopted as a biosecurity measure but can adversely affect employee ergonomics and rodent behavior. In this study, we evaluated alternative methods of rodent handling and their potential implications for efficiency, biosecurity, and animal welfare. Study groups included plastic cups, gloved hands, 2 methods of tunnel handling, and forceps. Evaluations included speed of cage change, ATP-based assessment of sanitization, and retrospective analysis of colony health and breeding data. The time to change 14 cages was significantly faster at each time point for the gloved hands and forceps groups as compared with the other methods. Overall speed did not increase significantly with each subsequent study week for any group. ATP levels after sanitization with hydrogen peroxide-peracetic acid mixture differed significantly between gloves and forceps. When ATP level was evaluated on a per-cm² basis, no significant difference between gloves and forceps was detected. Although tunnel and cup handling both increased the time for cage-changing, the tunnel served as both an indirect handling method and a shelter when left within the cage. Retrospective analysis revealed that breeding performance and colony health were similar among groups. Although efficiency is a concern for large-scale implementation of novel handling methods, the tunnel method may prove beneficial for sensitive strains or studies requiring indirect handling. In addition, using gloved hands to directly handle mice during cage changing is efficient and avoids the ergonomic strain associated with forceps. Precautions should be taken when handling mice with gloves, given that the increased contact area carries an increased load of organic debris. Changing gloves between rack sides or before proceeding to the animals belonging to a different investigator minimizes the potential for cross-contamination.

Reporting and analysis of repeated measurements in preclinical animals experiments

A common feature of preclinical animal experiments is repeated measurement of the outcome, e.g., body weight measured in mice pups weekly for 20 weeks. Separate time point analysis or repeated measures analysis approaches can be used to analyze such data. Each approach requires assumptions about the underlying data and violations of these assumptions have implications for estimation of precision, and type I and type II error rates. Given the ethical responsibilities to maximize valid results obtained from animals used in research, our objective was to evaluate approaches to reporting repeated measures design used by investigators and to assess how assumptions about variation in the outcome over time impact type I and II error rates and precision of estimates. We assessed the reporting of repeated measures designs of 58 studies in preclinical animal experiments. We used simulation modelling to evaluate three approaches to statistical analysis of repeated measurement data. In particular, we assessed the impact of (a) repeated measure analysis assuming that the outcome had non-constant variation at all time points (heterogeneous variance) (b) repeated measure analysis assuming constant variation in the outcome (homogeneous variance), (c) separate ANOVA at individual time point in repeated measures designs. The evaluation of the three model fitting was based on comparing the p-values distributions, the type I and type II error rates and by implication, the shrinkage or inflation of standard error estimates from 1000 simulated dataset. Of 58 studies with repeated measures design, three provided a rationale for repeated measurement and 23 studies reported using a repeated-measures analysis approach. Of the 35 studies that did not use repeated-measures analysis, fourteen studies used only two time points to calculate weight change which potentially means collected data was not fully utilized. Other studies reported only select time points (n = 12) raising the issue of selective reporting. Simulation studies showed that an incorrect assumption about the variance structure resulted in modified error rates and precision estimates. The reporting of the validity of assumptions for repeated measurement data is very poor. The homogeneous variation assumption, which is often invalid for body weight measurements, should be confirmed prior to conducting the repeated-measures analysis using homogeneous covariance structure and adjusting the analysis using corrections or model specifications if this is not met.