Handling method alters the hedonic value of reward in laboratory mice

Protocol to study dam-pup social transmission using a modified paradigm for transmission of food preference

The social transmission of food preference, a rudimentary form of social learning, has primarily been studied in pairs of adult rodents. Here, we present a protocol to explore the parent-offspring context in social learning using an adaptation of this classic paradigm for rodent dam-pup dyads. We describe steps for studying weanling mice from the same mother and present a worked example using weight-based (food consumption) and time-based (exploration) indices of social learning.

Effects of Home Cage Tunnels on Within-cage Behaviors of Mice with Cranial Implants

Keeping tunnels in the home cages of mice used in research appears to both reduce handling-related stress and provide environmental enrichment. However, for mice that have surgical implants that extend beyond their body, having tunnels in the home cages could engender concerns for their welfare, including the possibility of them becoming stuck in the tunnel. The goal of this study was to determine how mice with different sizes of cranial implants interacted with a tunnel in their home cage. We used male and female mice with a C57BL/6J background in this study. The mice underwent a either a craniotomy in which they received either no implant (sham), an indwelling cannula used for drug delivery, or a ferrule-type implant. The number of mouse interactions with tunnels was recorded over a 30-min period while the mouse was in its home cage with its tunnel. We found that sham mice interacted significantly more with the tunnels than did mice with either cannulae or ferrule implants. On average sham mice interacted more with the tunnel by walking through or over it whereas mice with either type of implant rarely even touched the tunnel with their heads. Our results indicate that mice with implants do not enter in the tunnels, and thus the tunnel reduces accessible cage-space rather than providing enrichment benefits. These results raise the question of whether tunnels should be routinely available for mice with cranial implants.

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.

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.

A computational analysis of mouse behavior in the sucrose preference test

The sucrose preference test (SPT) measures the relative preference of sucrose over water to assess hedonic behaviors in rodents. Yet, it remains uncertain to what extent the SPT reflects other behavioral components, such as learning, memory, motivation, and choice. Here, we conducted an experimental and computational decomposition of mouse behavior in the SPT and discovered previously unrecognized behavioral subcomponents associated with changes in sucrose preference. We show that acute and chronic stress have sex-dependent effects on sucrose preference, but anhedonia was observed only in response to chronic stress in male mice. Additionally, reduced sucrose preference induced by optogenetics is not always indicative of anhedonia but can also reflect learning deficits. Even small variations in experimental conditions influence behavior, task outcome and interpretation. Thus, an ostensibly simple behavioral task can entail high levels of complexity, demonstrating the need for careful dissection of behavior into its subcomponents when studying the underlying neurobiology.

Individualized Housing Modifies the Immune–Endocrine System in CD1 Adult Male Mice

In the last years, different research groups have made considerable efforts to improve the care and use of animals in research. Mice (Mus musculus) are the most widely used animal species in research in the European Union and are sociable and hierarchical creatures. During experiments, researchers tend to individualize males, but no consideration is given to whether this social isolation causes them stress. The aim of this study was, therefore, to explore whether 4 weeks of social isolation could induce changes in different physiological parameters in adult Crl:CD1(ICR) (CD1) males, which may interfere with experimental results. Body weight, blood cells, and fecal corticosterone metabolites levels were the analyzed parameters. Blood and fecal samples were collected at weeks 1 and 4 of the experimental procedure. Four weeks of single housing produced a significant time-dependent decrease in monocytes and granulocytes. Fecal corticosterone metabolite levels were higher in single-housed mice after 1 week and then normalized after 4 weeks of isolation. Body weight, red blood cells, and platelets remained unchanged in both groups during this period. We can, therefore, conclude that social isolation affects some immune and endocrine parameters, and that this should be taken into account in the interpretation of research data.

A mapping review of refinements to laboratory rat housing and husbandry

Refining the housing and husbandry of laboratory rats is an important goal, both for ethical reasons and to allow better quality research. We conducted a mapping review of 1,017 studies investigating potential refinements of housing and husbandry of the laboratory rat to assess what refinements have, and have not, been studied, and to briefly assess whether there is evidence to support any impact on rat welfare. Among the many refinements studied, the majority involve changes to the cage, but some also involve alterations to the wider environment. The effects of these refinements were assessed using a range of readouts, many of which are difficult to interpret from a welfare perspective. Preference studies, which are easier to interpret, provide evidence that rats prefer complex environments, including shelters and multiple objects, which offer different areas/resources allowing the rat to engage in diverse behaviors. The reporting of methodology in papers was often poor, indicating that studies were potentially subject to biases. Given that many refinements co-occurred, it was often difficult to tease apart which ones were most beneficial for rat welfare. Effects of refinements were also moderated by a number of factors including age, sex, strain and photoperiod. Altogether our findings show that a one-size-fits-all approach to refinements is not appropriate, because different refinements will impact different rats in different ways. Our review has also produced a database of >1,000 articles that can be used for further and more detailed analyses. Our findings have also highlighted areas where future research is likely to be valuable, including refinements to rat transport, handling and the use of training.

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.

Post Mortem Study on the Effects of Routine Handling and Manipulation of Laboratory Mice

Routine handling and manipulation of laboratory mice are integral components of most preclinical studies. Any type of handling and manipulation may cause stress and result in physical harm to mice, potentially leading to unintended consequences of experimental outcomes. Nevertheless, the pathological effects of these interventions are poorly documented and assumed to have a negligible effect on experimental variables. In that context, we provide a comprehensive post mortem overview of the main pathological changes associated with routine interventions (i.e., restraint, blood drawing, and intraperitoneal injections) of laboratory mice with an emphasis on presumed traumatic osteoarticular lesions. A total of 1000 mice from various studies were included, with 864 animals being heavily manipulated and 136 being handled for routine husbandry procedures only. The most common lesions observed were associated with blood collection or intraperitoneal injections, as well as a series of traumatic osteoarticular lesions likely resulting from restraint. Osteoarticular lesions were found in 62 animals (61 heavily manipulated; 1 unmanipulated) with rib fractures and avulsion of the dens of the axis being over-represented. Histopathology and micro-CT confirmed the traumatic nature of the rib fractures. While these lesions might be unavoidable if mice are manipulated according to the current standards, intentional training of research personnel on appropriate mouse handling and restraint techniques could help reduce their frequency and the impact on animal wellbeing as well as study reproducibility.

Chronic Unpredictable Mild Stress Model of Depression: Possible Sources of Poor Reproducibility and Latent Variables

Major depressive disorder (MDD) is one of the most common mood disorders worldwide. A lack of understanding of the exact neurobiological mechanisms of depression complicates the search for new effective drugs. Animal models are an important tool in the search for new approaches to the treatment of this disorder. All animal models of depression have certain advantages and disadvantages. We often hear that the main drawback of the chronic unpredictable mild stress (CUMS) model of depression is its poor reproducibility, but rarely does anyone try to find the real causes and sources of such poor reproducibility. Analyzing the articles available in the PubMed database, we tried to identify the factors that may be the sources of the poor reproducibility of CUMS. Among such factors, there may be chronic sleep deprivation, painful stressors, social stress, the difference in sex and age of animals, different stress susceptibility of different animal strains, handling quality, habituation to stressful factors, various combinations of physical and psychological stressors in the CUMS protocol, the influence of olfactory and auditory stimuli on animals, as well as the possible influence of various other factors that are rarely taken into account by researchers. We assume that careful inspection of these factors will increase the reproducibility of the CUMS model between laboratories and allow to make the interpretation of the obtained results and their comparison between laboratories to be more adequate.

Refinements to rodent head fixation and fluid/food control for neuroscience

The use of head fixation in mice is increasingly common in research, its use having initially been restricted to the field of sensory neuroscience. Head restraint has often been combined with fluid control, rather than food restriction, to motivate behaviour, but this too is now in use for both restrained and non-restrained animals. Despite this, there is little guidance on how best to employ these techniques to optimise both scientific outcomes and animal welfare. This article summarises current practices and provides recommendations to improve animal wellbeing and data quality, based on a survey of the community, literature reviews, and the expert opinion and practical experience of an international working group convened by the UK's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs). Topics covered include head fixation surgery and post-operative care, habituation to restraint, and the use of fluid/food control to motivate performance. We also discuss some recent developments that may offer alternative ways to collect data from large numbers of behavioural trials without the need for restraint. The aim is to provide support for researchers at all levels, animal care staff, and ethics committees to refine procedures and practices in line with the refinement principle of the 3Rs.

Mouse breeding facilities in Argentina: Current state, challenges, and strengths in relation to animal welfare

The science and technology of laboratory animals has come a long way worldwide, but for reasons related to the development of the countries, this journey started later in some Latin American countries, as is the case of Argentina. Without a specific legal framework to conduct animal experimentation, local strengths to promote animal welfare are based on professionals specifically trained in the care of laboratory animals as well as an extended network of ethics committees that ensures compliance with the ethical principles applied to animal experimentation. Nevertheless, there are no updated reports showing welfare indicators in rodent facilities. Therefore, we conducted a survey on mice breeding facilities enrolled in a national record elaborated by the National Ministry of Science. Questions related to four of the Five Domains Model of Mellor, concerning (1) nutrition, (2) physical environment, (3) health, and (4) behavioral interactions with the environment, other animals, and humans, were included as well as information concerning general aspects of the establishments. Data obtained from 25 mice breeder facilities localized all over the country were summarized, providing for the first time a clear picture of the national situation about the welfare of laboratory mice in these establishments. This data will be essential to design future policy as well as for deciding priorities aiming to improve the welfare of mice bred in Argentinian facilities.

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.

Determining Candidate Hypobaric Hypoxia Profiles for Humane Killing of Laboratory Mice

Millions of mice are used annually in scientific research and must be humanely killed. Despite significant welfare concerns, carbon dioxide exposure remains the most common killing method, primarily because there is no practical and humane alternative. We explored whether hypobaric hypoxia via gradual decompression could induce a non-recovery state in anesthetized male C57BL/6 and Balb/c laboratory mice. We aimed to determine if this was possible in a feasible timescale with minimal pathological consequences, as a proof-of-principle step. Systematic evaluation of two decompression rates (75, 150 ms−1) and three profile shapes (accelerated, linear, gradual) in a factorial design revealed that hypobaric hypoxia effectively induced a non-recovery state in anesthetized laboratory mice, irrespective of decompression rate and shape. Mice took longer to reach a non-recovery state with the 75 ms−1 decompression rate (75 ms−1: 257 ± 8.96 vs. 150 ms−1: 214 ± 7.26 s), with longer latencies in gradual and linear shaped profiles. Accelerated shaped profiles were least susceptible to meaningful refinement via rate. The only pathological changes of concern were moderate middle ear congestion and hemorrhage. These findings suggest that hypobaric hypoxia has potential, and subsequent work will evaluate the welfare consequences of gradual decompression in conscious mice, to identify decompression profiles that minimize welfare harms associated with ear barotrauma.

Environmental Enrichment for Rats and Mice Housed in Laboratories: A Metareview

Simple Summary

Environmental enrichment has been widely studied with laboratory rodents, but there is no consensus regarding what counts as enrichment or what it should achieve. Inconsistent use of the term “enrichment” creates challenges in drawing conclusions about the quality of an environment. We conducted a metareview to better understand the definitions and goals of enrichment, perceived risks or requirements of enrichment, and what forms of enrichment have previously been endorsed for use with rodents housed in laboratories. This may help researchers and animal care staff to better define their chosen approach and intended outcomes when providing environmental enrichment.

Abstract

Environmental enrichment has been widely studied in rodents, but there is no consensus on what enrichment should look like or what it should achieve. Inconsistent use of the term “enrichment” creates challenges in drawing conclusions about the quality of an environment, which may slow housing improvements for laboratory animals. Many review articles have addressed environmental enrichment for laboratory rats and mice (Rattus norvegicus and Mus musculus). We conducted a metareview of 29 review articles to assess how enrichment has been defined and what are commonly described as its goals or requirements. Recommendations from each article were summarised to illustrate the conditions generally considered suitable for laboratory rodents. While there is no consensus on alternative terminology, many articles acknowledged that the blanket use of the terms “enriched” and “enrichment” should be avoided. Environmental enrichment was most often conceptualised as a method to increase natural behaviour and improve animal welfare. Authors also commonly outlined perceived risks and requirements of environmental enrichment. We discuss these perceptions, make suggestions for future research, and advocate for the adoption of more specific and value-neutral terminology.

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.

Non-Invasive Assessment of Mild Stress-Induced Hyperthermia by Infrared Thermography in Laboratory Mice

Stress-induced hyperthermia (SIH) is a physiological response to acute stressors in mammals, shown as an increase in core body temperature, with redirection of blood flow from the periphery to vital organs. Typical temperature assessment methods for rodents are invasive and can themselves elicit SIH, affecting the readout. Infrared thermography (IRT) is a promising non-invasive alternative, if shown to accurately identify and quantify SIH. We used in-house developed software ThermoLabAnimal 2.0 to automatically detect and segment different body regions, to assess mean body (Tbody) and mean tail (Ttail) surface temperatures by IRT, along with temperature (Tsc) assessed by reading of subcutaneously implanted PIT-tags, during handling-induced stress of pair-housed C57BL/6J and BALB/cByJ mice of both sexes (N = 68). SIH was assessed during 10 days of daily handling (DH) performed twice per day, weekly voluntary interaction tests (VIT) and an elevated plus maze (EPM) at the end. To assess the discrimination value of IRT, we compared SIH between tail-picked and tunnel-handled animals, and between mice receiving an anxiolytic drug or vehicle prior to the EPM. During a 30 to 60 second stress exposure, Tsc and Tbody increased significantly (p < 0.001), while Ttail (p < 0.01) decreased. We did not find handling-related differences. Within each cage, mice tested last consistently showed significantly higher (p < 0.001) Tsc and Tbody and lower (p < 0.001) Ttail than mice tested first, possibly due to higher anticipatory stress in the latter. Diazepam-treated mice showed lower Tbody and Tsc, consistent with reduced anxiety. In conclusion, our results suggest that IRT can identify and quantify stress in mice, either as a stand-alone parameter or complementary to other methods.

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

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

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.

Reward-enhancing effects of d-amphetamine and its interactions with nicotine were greater in female rats and persisted across schedules of reinforcement

Nicotine enhances the value of environmental stimuli and rewards, and reward enhancement can maintain nicotine consumption. Stimulants such as d-amphetamine are misused more by women and are commonly co-used with nicotine. d-Amphetamine potentiates nicotine's effects in human and animal research. To date, there are no published studies examining this interaction in a reward-enhancement task. The current study sought to investigate the reward-enhancing effects of nicotine alongside and coadministered with d-amphetamine. Further, we evaluated the persistence of reward enhancement across ratio and temporal schedules of reinforcement. We used 10 male and 10 female Sprague-Dawley rats. Enhancement was assessed within subjects by examining active lever pressing for a visual stimulus reinforcer on variable ratio 3, variable interval 30 s and variable time 30 s - variable ratio 3 schedules. Before 1-h sessions, rats received one injection of saline, 0.1 or 0.3 mg/kg d-amphetamine and one of saline or 0.4 mg/kg nicotine, making six possible drug combinations (saline + saline, saline + nicotine, 0.1 d-amphetamine + aline, 0.1 d-amphetamine + nicotine, 0.3 d-amphetamine + saline and 0.3 d-amphetamine + nicotine) experienced in a randomized order by each rat. When d-amphetamine was coadministered with nicotine, we found an interaction effect on reward enhancement that persisted across schedules of reinforcement. Males and females exhibited reward enhancement by 0.3 d-amphetamine, while only females showed reward enhancement by 0.1 d-amphetamine. Further, females responded more for the visual stimulus than males in all d-amphetamine conditions. Future studies should assess how reward enhancement is involved in high nicotine-amphetamine comorbidity rates and enhanced amphetamine misuse in women.

Placental endocrine insufficiency programs anxiety, deficits in cognition and atypical social behaviour in offspring

Abnormally elevated expression of the imprinted PHLDA2 gene has been reported in the placenta of human babies that are growth restricted in utero in several studies. We previously modelled this gene alteration in mice and found that just 2-fold increased expression of Phlda2 resulted in placental endocrine insufficiency. In addition, elevated Phlda2 was found to drive fetal growth restriction (FGR) of transgenic offspring and impaired maternal care by their wildtype mothers. Being born small and being exposed to suboptimal maternal care have both been associated with the increased risk of mental health disorders in human populations. In the current study we probed behavioural consequences of elevated Phlda2 for the offspring. We discovered increased anxiety-like behaviours, deficits in cognition and atypical social behaviours, with the greatest impact on male offspring. Subsequent analysis revealed alterations in the transcriptome of the adult offspring hippocampus, hypothalamus and amygdala, regions consistent with these behavioural observations. The inclusion of a group of fully wildtype controls raised in a normal maternal environment allowed us to attribute behavioural and molecular alterations to the adverse maternal environment induced by placental endocrine insufficiency rather than the specific gene change of elevated Phlda2. Our work demonstrates that a highly common alteration reported in human FGR is associated with negative behavioural outcomes later in life. Importantly, we also establish the experimental paradigm that placental endocrine insufficiency can program atypical behaviour in offspring highlighting the under-appreciated role of placental endocrine insufficiency in driving disorders of later life behaviour.

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.

An automated homecage system for multiwhisker detection and discrimination learning in mice

Automated, homecage behavioral training for rodents has many advantages: it is low stress, requires little interaction with the experimenter, and can be easily manipulated to adapt to different experimental conditions. We have developed an inexpensive, Arduino-based, homecage training apparatus for sensory association training in freely-moving mice using multiwhisker air current stimulation coupled to a water reward. Animals learn this task readily, within 1–2 days of training, and performance progressively improves with training. We examined the parameters that regulate task acquisition using different stimulus intensities, directions, and reward valence. Learning was assessed by comparing anticipatory licking for the stimulus compared to the no-stimulus (blank) trials. At high stimulus intensities (>9 psi), animals showed markedly less participation in the task. Conversely, very weak air current intensities (1–2 psi) were not sufficient to generate rapid learning behavior. At intermediate stimulus intensities (5–6 psi), a majority of mice learned that the multiwhisker stimulus predicted the water reward after 24–48 hrs of training. Both exposure to isoflurane and lack of whiskers decreased animals’ ability to learn the task. Following training at an intermediate stimulus intensity, mice were able to transfer learning behavior when exposed to a lower stimulus intensity, an indicator of perceptual learning. Mice learned to discriminate between two directions of stimulation rapidly and accurately, even when the angular distance between the stimuli was <15 degrees. Switching the reward to a more desirable reward, aspartame, had little effect on learning trajectory. Our results show that a tactile association task in an automated homecage environment can be monitored by anticipatory licking to reveal rapid and progressive behavioral change. These Arduino-based, automated mouse cages enable high-throughput training that facilitate analysis of large numbers of genetically modified mice with targeted manipulations of neural activity.

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.

Sex and Strain Variation in Initial Sensitivity and Rapid Tolerance to Δ9-Tetrahydrocannabinol

Background and Objectives: For cannabis and other drugs of abuse, initial response and/or tolerance to drug effects can predict later dependence and problematic use. Our objective is to identify sex and genetic (strain) differences in initial response and rapid tolerance to Δ9–tetrahydrocannabinol (THC), the main psychoactive ingredient in cannabis, between highly genetically divergent inbred mouse strains—C57BL/6J (B6) and DBA/2J (D2).

Experimental Approach: Sex and strain responses relative to baseline were quantified following daily exposure (i.p.) to 10 mg/kg THC or vehicle (VEH) over the course of 5 days. Dependent measures included hypothermia (decreased body temperature) and ataxia (decreased spontaneous activity in the open field), and antinociception (increase in tail withdrawal latency to a thermal stimulus). Initial sensitivity to THC was defined as the difference in response between baseline and day 1. Rapid tolerance to THC was defined as the difference in response between days 1 and 2.

Results: B6 exhibited greater THC-induced motor activity suppression and initial sensitivity to ataxia relative to the D2 strain. Females demonstrated greater levels of THC-induced hypothermia and initial sensitivity relative to males. Higher levels of THC-induced antinociception and initial sensitivity were observed for D2 relative to B6. Rapid tolerance to THC was observed for hypothermia and antinociception. Much less tolerance was observed for THC-induced ataxia. D2 exhibited rapid tolerance to THC-induced hypothermia and antinociception at time points associated with peak THC initial response. Likewise, at the peak initial THC response time point, females demonstrated greater levels of rapid tolerance to hypothermic effects relative to males.

Conclusions: Both sex and genetic factors drive variation in initial response and rapid tolerance to the ataxic, antinociceptive, and hypothermic effects of THC. As these traits directly result from THC activation of the cannabinoid receptor 1, gene variants between B6 and D2 in cannabinoid signaling pathways are likely to mediate strain differences in response to THC.

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.

Reporting animal research: Explanation and elaboration for the ARRIVE guidelines 2.0

Improving the reproducibility of biomedical research is a major challenge. Transparent and accurate reporting is vital to this process; it allows readers to assess the reliability of the findings and repeat or build upon the work of other researchers. The ARRIVE guidelines (Animal Research: Reporting In Vivo Experiments) were developed in 2010 to help authors and journals identify the minimum information necessary to report in publications describing in vivo experiments. Despite widespread endorsement by the scientific community, the impact of ARRIVE on the transparency of reporting in animal research publications has been limited. We have revised the ARRIVE guidelines to update them and facilitate their use in practice. The revised guidelines are published alongside this paper. This explanation and elaboration document was developed as part of the revision. It provides further information about each of the 21 items in ARRIVE 2.0, including the rationale and supporting evidence for their inclusion in the guidelines, elaboration of details to report, and examples of good reporting from the published literature. This document also covers advice and best practice in the design and conduct of animal studies to support researchers in improving standards from the start of the experimental design process through to publication.

Wistar Kyoto Rats Display Anhedonia In Consumption but Retain Some Sensitivity to the Anticipation of Palatable Solutions

The Wistar Kyoto (WKY) rat has been proposed as a model of depression-like symptoms. However, anhedonia—a reduction in the response to normatively rewarding events—as a central depression symptom has yet to be fully assessed in this model. We compared WKY rats and Wistar controls, with stress-susceptibility examined by applying mild unpredictable stress to a subset of each group. Anhedonia-like behavior was assessed using microstructural analysis of licking behavior, where mean lick cluster size reflects hedonic responses. This was combined with tests of anticipatory contrast, where the consumption of a moderately palatable solution (4% sucrose) is suppressed in anticipation of a more palatable solution (32% sucrose). WKY rats displayed greatly attenuated hedonic reactions to sucrose overall, although their reactions retained some sensitivity to differences in sucrose concentration. They displayed normal reductions in consumption in anticipatory contrast, although the effect of contrast on hedonic reactions was greatly blunted. Mild stress produced overall reductions in sucrose consumption, but this was not exacerbated in WKY rats. Moreover, mild stress did not affect hedonic reactions or the effects of contrast. These results confirm that the WKY substrain expresses a direct behavioral analog of anhedonia, which may have utility for increasing mechanistic understanding of depression symptoms.

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.

Unified Behavioral Scoring for Preclinical Models

Preclinical mental health research relies upon animal models, and whilst many encouraging advances are being made, reproducibility and translational relevance may be limited by sub-optimal testing or model choices. Animal behaviors are complex and test batteries should be designed to include their multifaceted nature. However, multiple behavioral testing is often avoided due to cost, availability or statistical rigor. Additionally, despite the disparity in the incidence of mental health problems between the sexes, a move toward reducing animal numbers could be a deterrent to including both male and female animals. The current study introduces a unified scoring system for specific behavioral traits with the aim of maximizing the use of all data generated whilst reducing the incidence of statistical errors. Female and male mice from two common background strains were tested on behavior batteries designed to probe multiple aspects of anxiety-related and social behavioral traits. Results for every outcome measure were normalized to generate scores for each test and combined to give each mouse a single unified score for each behavioral trait. The unified behavioral scores revealed clear differences in the anxiety and stress-related, and sociability traits of mice. Principle component analysis of data demonstrated significant clustering of animals into their experimental groups. In contrast, individual tests returned an ambiguous mixture of non-significant trends and significant effects for various outcome measures. Utilizing a range of behavioral measures and combining all outcome measure data to produce unified scores provides a useful tool for detecting subtle behavioral traits in preclinical models.

Impulse for animal welfare outside the experiment

Animal welfare is a growing societal concern and the well-being of animals used for experimental purposes is under particular scrutiny. The vast majority of laboratory animals are mice living in small cages that do not offer very much variety. Moreover, the experimental procedure often takes very little time compared to the time these animals have been bred to the desired age or are being held available for animal experimentation. However, for the assessment of animal welfare, the time spent waiting for an experiment or the time spent after finishing an experiment has also to be taken into account. In addition to experimental animals, many additional animals (e.g. for breeding and maintenance of genetic lines, surplus animals) are related to animal experimentation and usually face similar living conditions. Therefore, in terms of improving the overall welfare of laboratory animals, there is not only a need for refinement of experimental conditions but especially for improving living conditions outside the experiment. The improvement of animal welfare thus depends to a large extent on the housing and maintenance conditions of all animals related to experimentation. Given the current state of animal welfare research there is indeed a great potential for improving the overall welfare of laboratory animals.

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.

Measuring affect-related cognitive bias: Do mice in opposite affective states react differently to negative and positive stimuli?

Affect-driven cognitive biases can be used as an indicator of affective (emotional) state. Since humans in negative affective states demonstrate greater responses to negatively-valenced stimuli, we investigated putative affect-related bias in mice by monitoring their response to unexpected, task-irrelevant stimuli of different valence. Thirty-one C57BL/6J and 31 DBA/2J females were individually trained to return to their home-cage in a runway. Mice then underwent an affective manipulation acutely inducing a negative (NegAff) or a comparatively less negative (CompLessNeg) affective state before immediately being tested in the runway with either an ‘attractive’ (familiar food) or ‘threatening’ (flashing light) stimulus. Mice were subsequently trained and tested again (same affective manipulation) with the alternative stimulus. As predicted, mice were slower to approach the light and spent more time with the food. DBA/2J mice were slower than C57BL/6J overall. Contrary to predictions, NegAff mice tended to approach both stimuli more readily than CompLessNeg mice, especially the light, and even more so for DBA/2Js. Although the stimuli successfully differentiated the response of mice to unexpected, task-irrelevant stimuli, further refinement may be required to disentangle the effects of affect manipulation and arousal on the response to valenced stimuli. The results also highlight the significant importance of considering strain differences when developing cognitive tasks.

Where are we heading? Challenges in evidence-based severity assessment

Evidence-based severity assessment in laboratory animals is, apart from the ethical responsibility, imperative to generate reproducible, standardized and valid data. However, the path towards a valid study design determining the degree of pain, distress and suffering experienced by the animal is lined with pitfalls and obstacles as we will elucidate in this review. Furthermore, we will ponder on the genesis of a holistic concept relying on multifactorial composite scales. These have to combine robust and reliable parameters to measure the multidimensional aspects that define the severity of animal experiments, generating a basis for the substantiation of the refinement principle.

Effects of early life and current housing on sensitivity to reward loss in a successive negative contrast test in pigs

Animals in a negative affective state seem to be more sensitive to reward loss, i.e. an unexpected decrease in reward size. The aim of this study was to investigate whether early-life and current enriched vs. barren housing conditions affect the sensitivity to reward loss in pigs using a successive negative contrast test. Pigs (n = 64 from 32 pens) were housed in barren or enriched conditions from birth onwards, and at 7 weeks of age experienced either a switch in housing conditions (from barren to enriched or vice versa) or not. Allotting pigs to the different treatments was balanced for coping style (proactive vs. reactive). One pig per pen was trained to run for a large reward and one for a small reward. Reward loss was introduced for pigs receiving the large reward after 11 days (reward downshift), i.e. from then onwards, they received the small reward. Pigs housed in barren conditions throughout life generally had a lower probability and higher latency to get the reward than other pigs. Proactive pigs ran overall slower than reactive pigs. After the reward downshift, all pigs ran slower. Nevertheless, reward downshift increased the latency and reduced the probability to get to the reward, but only in pigs exposed to barren conditions in early life, which thus were more sensitive to reward loss than pigs from enriched early life housing. In conclusion, barren housed pigs seemed overall less motivated for the reward, and early life housing conditions had long-term effects on the sensitivity to reward loss.

Enrichment with Lucerne Hay Improves Sow Maternal Behaviour and Improves Piglet Survival

This study investigated the effects of providing lucerne hay on the behaviour and the performance of sows housed in farrowing crates during farrowing and lactation. Seventy-two mixed parity sows received either 1 kg lucerne hay daily from entry into the farrowing crate (-2 d from expected farrowing date) until weaning at 17 d (lucerne group, n = 36), or received no additional enrichment (control group, n = 36). In the 18 h prior to farrowing, the sows in the lucerne treatment spent more time performing nest-building behaviour (14.8% lucerne vs 11.1% control, p = 0.0009) and less time sham-chewing (1.0% lucerne vs 1.9% control, p = 0.01) than control sows, and gave birth to fewer stillborn piglets/litter (0.1 lucerne vs 0.4 control, p = 0.027). After farrowing (Day 3), the control sows spent less time lying than the lucerne sows (26% control vs 43% lucerne, p < 0.05). The control sows also spent less time interacting with their piglets during early lactation compared to late lactation (25.5% Day 5 vs 47.3% Day 12, p < 0.05), suggesting reduced maternal behaviour in this group. The lucerne sows continued to interact with the lucerne throughout lactation, indicating that they still found the enrichment rewarding after the nesting period had ceased. Based on these results, lucerne enrichment was considered to improve sow welfare during farrowing and lactation and reduce the number of stillborn piglets.

Stress transforms lateral habenula reward responses into punishment signals

Neuronal activity in the lateral habenula (LHb), a brain region implicated in depression [C. D. Proulx, O. Hikosaka, R. Malinow, Nat. Neurosci. 17, 1146-1152 (2014)], decreases during reward and increases during punishment or reward omission [M. Matsumoto, O. Hikosaka, Nature 447, 1111-1115 (2007)]. While stress is a major risk factor for depression and strongly impacts the LHb, its effect on LHb reward signals is unknown. Here we image LHb neuronal activity in behaving mice and find that acute stress transforms LHb reward responses into punishment-like neural signals; punishment-like responses to reward omission also increase. These neural changes matched the onset of anhedonic behavior and were specific to LHb neurons that distinguished reward and its omission. Thus, stress distorts LHb responsivity to positive and negative feedback, which could bias individuals toward negative expectations, a key aspect of the proposed pathogenesis of depression [A. T. Beck, Depression: Clinical, Experimental, and Theoretical Aspects, sixth Ed (1967)].

Welfare and Scientific Considerations of Tattooing and Ear Tagging for Mouse Identification

Ear tagging is perceived as less painful or stressful than tattooing and therefore is generally considered less harmful or costly to welfare. However, ear tags are more difficult to read than tattoos and can fall out, and mice usually require restraint for the tag numbers to be read accurately. We assessed the welfare and scientific implications of tattooing by using a commercial device compared with restraint in a device versus ear tagging. Male and female BALB/c mice (n = 32) underwent procedures after 1 wk of tail or nonaversive (tunnel) handling to determine whether tunnel handling reduced anxiety. Pain was evaluated using both the Mouse Grimace Scale (MGS) and manual and automated behavior analyses; light-dark preference testing and voluntary interaction with the handler's hand were used to assess anxiety. Tail inflammation after tattooing was quantified using bioluminescent imaging, and ear tag and tattoo misidentification rates were estimated from volunteer staff records. Tunnel handling reduced anxiety compared with tail handling. According to the MGS, tattooing was not more painful than ear tagging but caused significant tail inflammation and more agitation and anxiety. However, all tattoos were read correctly without handling, whereas all ear tagged mice needed restraint, and at least 25% of the tag codes were misread. Handling stress together with identification errors at this rate represent potentially serious concerns regarding the scientific integrity of data from studies using ear tagging. These concerns are unlikely to arise with tattooing. Although tattooing was stressful, so were restraint and ear tagging. However, considering the other major advantages of tattooing, the total costs associated with tattooing were not substantially greater than for ear tagging.

Gentle Handling Attenuates Innate Defensive Responses to Visual Threats

Innate defensive responses to threats are essential for animal survival. The complexity and variability of innate defensive behaviors can be due to individual experiences, environmental factors, and internal states. However, it is not completely understood if the gentle handling involved in sensory processing affects innate defensive responses to visual threats. Here, we report attenuation of innate defensive responses after gentle handling accompanied by de-excitation of the intermediate layer (IL) and deep layer (DL) of the superior colliculus (SC) but not of the superficial layer (SL). Our theoretical analysis of the c-Fos network revealed an increased correlation in module 1, which maybe generally functionally associated with fear emotional, a decreased correlation in module 2, which maybe generally functionally associated with sensory processing. The IL of the SC appeared to have the highest correlation with the two modules. We verified the dynamic activities of the IL of SC in response to overhead looming stimulus using fiber photometry. Retrograde labeling of 18 regions of interest (ROIs) showed that the IL received significant inputs from the cortical areas, thalamus, hypothalamus, and brainstem. These data suggest the sensory processing involved in the modulatory roles of the SC in innate fear processing.

Communicating through scents: an interview with Jane Hurst

Jane Hurst is a William Prescott Professor of Animal Science at the University of Liverpool, UK, studying scent communication in mammals and its role in behaviours. In this interview, Jane discusses how scents encode complex information in rodents, driving behaviours such as kinship interactions and choosing a mate, how understanding natural behaviours of animals can inform experimental designs, and what is the connection between Jane Austin and pheromones.

Making Sense of Rodent Models of Anhedonia

A markedly reduced interest or pleasure in activities previously considered pleasurable is a main symptom in mood disorder and psychosis and is often present in other psychiatric disorders and neurodegenerative diseases. This condition can be labeled as "anhedonia," although in its most rigorous connotation the term refers to the lost capacity to feel pleasure that is one aspect of the complex phenomenon of processing and responding to reward. The responses to rewarding stimuli are relatively easy to study in rodents, and the experimental conditions that consistently and persistently impair these responses are used to model anhedonia. To this end, long-term exposure to environmental aversive conditions is primarily used, and the resulting deficits in reward responses are often accompanied by other deficits that are mainly reminiscent of clinical depressive symptoms. The different components of impaired reward responses induced by environmental aversive events can be assessed by different tests or protocols that require different degrees of time allocation, technical resources, and equipment. Rodent models of anhedonia are valuable tools in the study of the neurobiological mechanisms underpinning impaired behavioral responses and in the screening and characterization of drugs that may reverse these behavioral deficits. In particular, the antianhedonic or promotivational effects are relevant features in the spectrum of activities of drugs used in mood disorders or psychosis. Thus, more than the model, it is the choice of tests that is crucial since it influences which facets of anhedonia will be detected and should be tuned to the purpose of the study.