Repeated rat exposure inhibits the circadian activity patterns of C57BL/6J mice in the home cage

Dairy Cow Behavior Is Affected by Period, Time of Day and Housing

Simple Summary

Many factors, such as the climate, period of the year, time of day and housing, are known to affect cow behavior. However, it is not yet clear what is the combined effect of these factors. For instance, it is unclear whether warmer weather only alters cow behavior during the day or also during the night. Therefore, a survey was performed on eight dairy cow farms in Northern Italy in three periods: summer, winter and a temperate season (spring or autumn). Sensors were installed to monitor the temperature and humidity. Cow behavior was monitored with cameras and with accelerometers that were placed on their legs. These methods allow us to determine how much time the cows spent lying, standing or feeding. We found that both daytime and nighttime behavior differed between the periods and that housing had an effect not only on the behavior itself but also on how it changed between the periods and from daytime to nighttime. These findings show the importance of measuring behavior during both daytime and nighttime and illustrate the influence of the barn structure and farm management on cow behavior and welfare.

Abstract

Dairy cow behavior is affected by external and endogenous factors, including time of year, barn microclimate, time of day and housing. However, little is known about the combined effects of these factors. Data were collected on eight farms in Northern Italy during summer, winter and a temperate season. The temperature-humidity index (THI) was recorded using environmental sensors, whereas cow behavior was monitored using leg accelerometers and cameras. Period, time of day and their interaction all significantly affected lying, standing and feeding behavior. However, although THI had a significant negative effect on lying and a positive effect on standing during daytime (all p < 0.001), during nighttime, it only had a significant negative effect on lying duration and mean lying bout duration (p < 0.001 for both). There was also significant variation between farms in all behavioral parameters, as well as interactions with period and time of day. For instance, farm differences in lying duration were more pronounced during daytime than during nighttime. These findings show how housing can interact with other factors, such as period of the year and time of day, and illustrate the influence of barn structure and farm management on cow behavior and, consequently, their welfare.

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.

Behavior Testing in Rodents: Highlighting Potential Confounds Affecting Variability and Reproducibility

Rodent models of brain disorders including neurodevelopmental, neuropsychiatric, and neurodegenerative diseases are essential for increasing our understanding of underlying pathology and for preclinical testing of potential treatments. Some of the most important outcome measures in such studies are behavioral. Unfortunately, reports from different labs are often conflicting, and preclinical studies in rodent models are not often corroborated in human trials. There are many well-established tests for assessing various behavioral readouts, but subtle aspects can influence measurements. Features such as housing conditions, conditions of testing, and the sex and strain of the animals can all have effects on tests of behavior. In the conduct of behavior testing, it is important to keep these features in mind to ensure the reliability and reproducibility of results. In this review, we highlight factors that we and others have encountered that can influence behavioral measures. Our goal is to increase awareness of factors that can affect behavior in rodents and to emphasize the need for detailed reporting of methods.

Sleep Duration and Behaviours: A Descriptive Analysis of a Cohort of Dogs up to 12 Months of Age

Sleep is a vital behaviour that can reflect an animal's adaptation to the environment and their welfare. However, a better understanding of normal age-specific sleep patterns is crucial. This study aims to provide population norms and descriptions of sleep-related behaviours for 16-week-old puppies and 12-month-old dogs living in domestic environments. Participants recruited to a longitudinal study answered questions relating to their dogs' sleep behaviours in surveys issued to them when their dogs reached 16 weeks (n = 2332) and 12 months of age (n = 1091). For the statistical analysis, subpopulations of dogs with data regarding sleep duration at both timepoints were used. Owners of 16-week-old puppies perceived their dogs to sleep longer during the day and over a 24 h period, but for less time during the night than owners of 12-month-old dogs. At both timepoints, dogs were most commonly settled to sleep by being left in a room/area without human company. However, of dogs that had access to people overnight, 86.7% and 86.8% chose to be around people at 16 weeks and 12 months of age, respectively. The most common sleeping place was in a kennel/crate at 16 weeks (49.1%), and a dog bed at 12 months (31.7%). Future research within this longitudinal study will investigate how sleep duration and behaviours change with age and impact on a dog's health and behaviour.

Circadian wheel running behavior is altered in an APP/E4 mouse model of late onset Alzheimer's disease

Circadian rhythms are altered in several diseases associated with aging, one of which is Alzheimer's disease (AD). One example of a circadian rhythm is the rest-activity cycle, which can be measured in mice by monitoring their wheel-running. The present study sought to investigate differences in light phase/dark phase activity between a mouse model of late onset AD (APP/E4) and control (C57Bl6J) mice, in both the pre-plaque and post-plaques stages of the disease. To assess activity level, 24-h wheel running behavior was monitored at six months (pre-plaque) and twelve months (post-plaque) for a period of nine days. The following measures were analyzed: counts (wheel rotations) during the dark phase, counts during the light phase, hour of activity onset, and hour of activity offset. Key findings indicate that activity onset is delayed in APP/E4 mice at six and twelve months, and activity profiles for APP/E4 and C57Bl6J mice differ during the light and dark phase in such a way that APP/E4 mice run less in the early hours of the dark phase and more in the later hours of the dark phase compared to C57Bl6J mice. These findings imply that rest-activity cycle is altered in the pre-plaque stages of AD in APP/E4 mice, as they show impairments as early as six months of age.

Chronic Co-species Housing Mice and Rats Increased the Competitiveness of Male Mice

Rats are predators of mice in nature. Nevertheless, it is a common practice to house mice and rats in a same room in some laboratories. In this study, we investigated the behavioral and physiological responsively of mice in long-term co-species housing conditions. Twenty-four male mice were randomly assigned to their original raising room (control) or a rat room (co-species-housed) for more than 6 weeks. In the open-field and light-dark box tests, the behaviors of the co-species-housed mice and controls were not different. In a 2-choice test of paired urine odors [rabbit urine (as a novel odor) vs. rat urine, cat urine (as a natural predator-scent) vs. rabbit urine, and cat urine vs. rat urine], the co-species-housed mice were more ready to investigate the rat urine odor compared with the controls and may have adapted to it. In an encounter test, the rat-room-exposed mice exhibited increased aggression levels, and their urines were more attractive to females. Correspondingly, the levels of major urinary proteins were increased in the co-species-housed mouse urine, along with some volatile pheromones. The serum testosterone levels were also enhanced in the co-species-housed mice, whereas the corticosterone levels were not different. The norepinephrine, dopamine, and 5-HT levels in the right hippocampus and striatum were not different between the 2. Our findings indicate that chronic co-species housing results in adaptation in male mice; furthermore, it appears that long-term rat-odor stimuli enhance the competitiveness of mice, which suggests that appropriate predator-odor stimuli may be important to the fitness of prey animals.

Can Sleep and Resting Behaviours Be Used as Indicators of Welfare in Shelter Dogs (Canis lupus familiaris)?

Previous research on humans and animals suggests that the analysis of sleep patterns may reliably inform us about welfare status, but little research of this kind has been carried out for non-human animals in an applied context. This study explored the use of sleep and resting behaviour as indicators of welfare by describing the activity patterns of dogs (Canis lupus familiaris) housed in rescue shelters, and comparing their sleep patterns to other behavioural and cognitive measures of welfare. Sleep and activity patterns were observed over five non-consecutive days in a population of 15 dogs. Subsequently, the characteristics of sleep and resting behaviour were described and the impact of activity on patterns of sleep and resting behaviour analysed. Shelter dogs slept for 2.8% of the day, 14.3% less than previously reported and experienced less sleep fragmentation at night (32 sleep bouts). There were no statistically significant relationships between behaviours exhibited during the day and sleep behaviour. A higher proportion of daytime resting behaviour was significantly associated with a positive judgement bias, less repetitive behaviour and increased time spent coded as ‘relaxed’ across days by shelter staff. These results suggest that, in the context of a busy shelter environment, the ability to rest more during the day could be a sign of improved welfare. Considering the non-linear relationship between sleep and welfare in humans, the relationship between sleep and behavioural indicators of welfare, including judgement bias, in shelter dogs may be more complex than this study could detect.

Rat exposure in mice with neuropathic pain induces fear and antinociception that is not reversed by 5-HT2C receptor activation in the dorsal periaqueductal gray

Previous studies have demonstrated that serotonin 5-HT2C receptors in the dorsal periaqueductal gray (dPAG) mediate both anxiety and antinociception in mice submitted to the elevated plus maze. The present study examined the effects of intra-dPAG infusion of the serotonin 5-HT2C receptor agonist (MK-212) in the defensive reactions and antinociception in mice with neurophatic pain confronted by a predator. Neuropathic pain was induced by chronic constriction injury (CCI) of the sciatic nerve, and predator confrontation was performed using the rat exposure test (RET). Our results demonstrated that both sham-operated and CCI mice exhibited intense defensive reactions when confronted by rats. However, rat-exposed CCI mice showed reduced pain reactivity in comparison to CCI mice exposed to a toy rat. Intra-dPAG infusion of MK-212 prior to predator exposure did not significantly alter defensive or antinociceptive responses. To our knowledge, our results represent the first evidence of RET-induced antinociception in mice. Moreover, the results of the present study suggest that 5-HT2C receptor activation in the dPAG is not critically involved in the control of predator-evoked fearful or antinociceptive responses.

Strain differences in fatigue and depression after experimental stroke

Fatigue and depression are common symptoms after stroke. Animal models of poststroke fatigue (PSF) and poststroke depression (PSD) would facilitate the study of these symptoms. Spontaneous locomotor activity is as an objective measure of fatigue and learned helplessness an accepted correlate of depression. We used different rat strains to evaluate stroke-induced changes in behavior in hopes that interstrain differences would provide insights into the biological basis of these symptoms. Male Lewis, Wistar, and Sprague-Dawley (SD) rats underwent experimental stroke. Spontaneous activity was assessed continually after stroke (for up to 50 days). In a subset of animals, the forced swim test was performed prior to and 1 month after stroke to assess learned helplessness; blood was obtained at sacrifice for cytokine assay. Stroke induced strain-related differences in activity; Lewis rats increased spontaneous activity during the dark cycle, while Wistar and SD rats increased activity during the light cycle. The velocity of movement decreased during the dark cycle in Wistar and SD rats and during the light cycle in Lewis rats. Stroke also led to an increase in learned helplessness in Lewis rats. In summary, different patterns of behaviors emerge in different rat strains after stroke. Lewis rats displayed behavior consistent with depression but not fatigue, while Wistar and SD rats displayed behavior consistent with fatigue but not depression. These data argue that PSF and PSD are different biological constructs and suggest that analysis of strain-related differences may provide insight into symptom pathophysiology.

Reproducibility and relevance of future behavioral sciences should benefit from a cross fertilization of past recommendations and today's technology: "Back to the future"

Thanks to the discovery of novel technologies and sophisticated analysis tools we can now 'see' molecules, genes and even patterns of gene expression, which have resulted in major advances in many areas of biology. Recently, similar technologies have been developed for behavioral studies. However, the wide implementation of such technological progress in behavioral research remains behind, as if there are inhibiting factors for accepting and adopting available innovations. The methods of the majority of studies measuring and interpreting behavior of laboratory animals seem to have frozen in time somewhere in the last century. As an example of the so-called classical tests, we will present the history and shortcomings of one of the most frequently used tests, the open field. Similar objections and critical remarks, however, can be made with regard to the elevated plus maze, light-dark box, various other mazes, object recognition tests, etc. Possible solutions and recommendations on how progress in behavioral neuroscience can be achieved and accelerated will be discussed in the second part of this review.

Scheduled exercise phase shifts the circadian clock in skeletal muscle

PURPOSE

It has been well established in mammals that circadian behavior as well as the molecular clockwork can be synchronized to the light-dark cycle via the suprachiasmatic nucleus of the hypothalamus (SCN). In addition to light, it has been demonstrated that nonphotic time cues, such as restricting the time of food availability, can alter circadian behavior and clock gene expression in selected peripheral tissues such as the liver. Studies have also suggested that scheduled physical activity (exercise) can alter circadian rhythms in behavior and clock gene expression; however, currently, the effects of exercise alone are largely unknown and have not been explored in skeletal muscle.

METHODS

Period2::Luciferase (Per2::Luc) mice were maintained under 12 h of light followed by 12 h of darkness then exposed to 2 h of voluntary or involuntary exercise during the light phase for 4 wk. Control mice were left in home cages or moved to the exercise environment (sham). A second group of mice had restricted access to food (4 h · d(-1) for 2 wk) to compare the effects of two nonphotic cues on PER2::LUC bioluminescence. Skeletal muscle, lung, and SCN tissue explants were cultured for 5-6 d to study molecular rhythms.

RESULTS

In the exercised mice, the phase of peak PER2::LUC bioluminescence was shifted in the skeletal muscle and lung explants but not in the SCN suggesting a specific synchronizing effect of exercise on the molecular clockwork in peripheral tissues.

CONCLUSIONS

These data provide evidence that the molecular circadian clock in peripheral tissues can respond to the time of exercise suggesting that physical activity contributes important timing information for synchronization of circadian clocks throughout the body.

Japanese quail's genetic background modulates effects of chronic stress on emotional reactivity but not spatial learning

Chronic stress is known to enhance mammals' emotional reactivity and alters several of their cognitive functions, especially spatial learning. Few studies have investigated such effects in birds. We investigated the impact of a two-week stress on Japanese quail's emotional reactivity and spatial learning. Quail is an avian model widely used in laboratory studies and for extrapolation of data to other poultry species. As sensitivity to chronic stress can be modulated by intrinsic factors, we tested juvenile female Japanese quail from three lines, two of them divergently selected on tonic immobility duration, an indicator of general fearfulness. The different emotional reactivity levels of quail belonging to these lines can be revealed by a large variety of tests. Half of the birds were submitted to repeated unpredictable aversive events for two weeks, whereas the other half were left undisturbed. After this procedure, two tests (open field and emergence tests) evaluated the emotional reactivity of treated and control quails. They were then trained in a T-maze for seven days and their spatial learning was tested. The chronic stress protocol had an impact on resting, preening and foraging in the home cage. As predicted, the emotional reactivity of treated quails, especially those selected for long tonic immobility duration, was higher. Our spatial learning data showed that the treatment enhanced acquisition but not memorization. However, intrinsic fearfulness did not seem to interact with the treatment in this test. According to an inverted U-shaped relationship between stress and cognition, chronic stress can improve the adaptability of birds to a stressful environment. We discussed the mechanisms possibly implied in the increase of emotional reactivity and spatial abilities.

Post-training reward partially restores chronic stress induced effects in mice

Reduced responsiveness to positive stimuli is a core symptom of depression, known as anhedonia. In the present study, we assessed the expression of anhedonia in our chronic stress mouse model using a subset of read-out parameters. In line with this, we investigated in how far chronic stress would affect the facilitating effect of post-training self-administration of sugar, as we previously observed in naïve mice. Male C57BL/6J mice were repeatedly and at unpredictable times exposed to rats (no physical contact) over the course of two weeks. Following novelty exploration, (non-) spatial learning and memory processes with and without post-training sugar acting as reinforcer, emotionality, reward sensitivity and corticosterone levels were determined. We found that (1) the effects of chronic stress persisted beyond the period of the actual rat exposure. (2) Post-training self-administration of sugar as reinforcer improved spatial performance in naïve mice, whereas (3) in stressed mice sugar partially “normalized” the impaired performance to the level of controls without sugar. Chronic stress (4) increased behavioral inhibition in response to novelty; (5) induced dynamic changes in the pattern of circadian corticosterone secretion during the first week after rat stress and (6) increased the intake of sucrose and water. (7) Chronic stress and sugar consumed during spatial training facilitated the memory for the location of the sucrose bottle weeks later. Concluding, our chronic stress paradigm induces the expression of anhedonia in mice, at different levels of behavior. The behavioral inhibition appears to be long lasting in stressed mice. Interestingly, sugar consumed in close context with spatial learning partially rescued the stress-induced emotional and cognitive impairments. This suggests that reward can ameliorate part of the negative consequences of chronic stress on memory.

Distinctive effects of unpredictable subchronic stress on memory, serum corticosterone and hippocampal BDNF levels in high and low exploratory mice

Stress affects learning and memory processes and sensitivity to stress greatly varies between individuals. We studied behavioral and neurobiological effects of unpredictable subchronic stress (USCS) in two behavioral extremes of mice from the same strain (CF1) selected by their exploratory behavior of the central arena of an open field. The top and bottom 25% explorers were classified as low exploratory (LE) and high exploratory (HE) mice, respectively. The open field task, the novel object recognition task (NOR), sucrose intake and tail suspension task were evaluated in LE and HE groups exposed to USCS for two weeks or control conditions. Also serum corticosterone and hippocampal BDNF and S100B levels were analyzed. Both stressed groups exhibited less exploratory activity when submitted to USCS, but their difference in exploratory behavior remained. This short stress protocol did not induce changes in sucrose intake or immobility in the tail suspension task. Also, LE mice exhibited impaired NOR performance after USCS, whereas HE mice changed their pattern of exploration towards less exploration of the familiar object. HE had lower corticosterone levels than LE mice, but corticosterone levels increased after stress only in HE mice. Hippocampal BDNF in LE was lower than in HE but decreased after USCS only in HE mice, whereas S100B levels were not different between groups and did not change with USCS. In conclusion, our results suggest that individual differences in exploratory behavior in rodents from the same strain influence cognitive and biochemical response to stress.

Increased corticosterone levels in mice subjected to the rat exposure test

In recent years, there has been a notable interest in studying prey-predator relationships to develop rodent-based models for the neurobehavioral aspects of stress and emotion. However, despite the growing use of transgenic mice and results showing important differences in the behavioral responses of rats and mice, little research has been conducted regarding the responses of mice to predators. The rat exposure test (RET), a recently developed and behaviorally validated prey-predator (mouse-rat)-based model, has proven to be a useful tool in evaluating the defensive responses of mice facing rats. To further validate the RET, we investigated the endocrine and behavioral responses of mice exposed to this apparatus. We first constructed a plasma corticosterone secretion curve in mice exposed to a rat or to an empty cage (control). Rat-exposed mice showed a pronounced rise in corticosterone levels that peaked 15 min from the beginning of the predator exposure. The corticosterone levels and behavioral responses of mice exposed to a rat or to a toy in the RET apparatus were then measured. We observed high plasma corticosterone levels along with clear avoidance behaviors represented by decreases in tunnel and surface area exploration and increases in risk assessment behaviors and freezing. This strongly suggests that the test elicits a repertoire of behavioral responses compatible with an aversion state and indicates that it is a promising model for the evaluation of prey-predator interactions. However, more physiological, neurochemical, and pharmacological studies are needed to further validate the test.

Brain development under stress: hypotheses of glucocorticoid actions revisited

One of the conundrums in today's stress research is why some individuals flourish and others perish under similar stressful conditions. It is recognized that this individual variability in adaptation to stress depends on the outcome of the interaction of genetic and cognitive/emotional inputs in which glucocorticoid hormones and receptors play a crucial role. Hence one approach towards understanding individual variation in stress coping is how glucocorticoid actions can change from protective to harmful. To address this question we focus on four hypotheses that are connected and not mutual exclusive. First, the classical Glucocorticoid Cascade Hypothesis, in which the inability to cope with chronic stress causes a vicious cycle of excess glucocorticoid and downregulation of glucocorticoid receptors (GR) in the hippocampus triggering a feed-forward cascade of degeneration and disease. Second, the Balance Hypothesis, which takes also the limbic mineralocorticoid receptors (MR) into account and proposes that an integral limbic MR:GR imbalance is causal to altered processing of information in circuits underlying fear, reward, social behaviour and resilience, dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis and impairment of behavioural adaptation. The MR:GR balance is altered by gene variants of these receptor complexes and experience-related factors, which can induce lasting epigenetic changes in the expression of these receptors. A particular potent epigenetic stimulus is the maternal environment which is fundamental for the Maternal Mediation Hypothesis. The outcome of perinatal gene x environment interaction, and thus of MR:GR-mediated functions depends however, on the degree of 'matching' with environmental demands in later life. The Predictive Adaptation Hypothesis therefore presents a conceptual framework to examine the role of glucocorticoids in understanding individual phenotypic differences in stress-related behaviours over the lifespan.

Automated scoring of fear-related behavior using EthoVision software

Fear conditioning is a frequently used paradigm for assessing learning and memory in rodents. Traditionally researchers have relied upon scoring of fear-related behavior by human observation, which can be difficult and subjective and thus vary among investigators. The goal of this study was to evaluate the ability of EthoVision tracking software (Noldus Information Technology Inc.) to reliably and accurately score fear-related behavior in mice. Specifically, we were interested in its ability to accurately track mice and score immobility as a fear-related behavior during contextual and cued fear conditioning. Contextual and cued fear conditioning were performed in modified PhenoTyper chambers (Noldus Information Technology Inc.) fitted with grid floors to deliver a scrambled foot shock. Our results demonstrate that we have identified parameters in EthoVision that can accurately track mice and be used for automated scoring of immobility that is nearly identical to scoring by human observation. Together, EthoVision software and the modified PhenoTyper chambers provide an excellent system for the reliable and accurate measurement of fear-related behavior in a high-throughput manner.