Locomotor activity rhythm in inbred strains of mice: implications for behavioural studies

Chronic jet lag reduces motivation and affects other mood-related behaviors in male mice

Introduction: The circadian system regulates various physiological processes such as sleep-wake cycles, hormone secretion, metabolism, and the reaction to both natural and drug-based rewards. Chronic disruption of the circadian system caused by unsteady synchronization with light-dark (LD) schedules, such as advancing chronic jet lag (CJL), leads to adverse physiological effects and pathologies, and is linked with changes in mood and depressive behaviors in humans and rodent models. Methods: C57BL/6J male mice were subjected to circadian disruption through phase advances of 6 h every 2 days (CJL +6/2). Mice under 12:12-h LD cycle were used as controls. After 8 weeks under these conditions, a battery of behavioral tests was performed to assess if mood-related behaviors were affected. Results: Compared to controls under 24 h LD cycles, mice under CJL presented desynchronization of activity-rest rhythms that led to several behavioral impairments, including a decrease in motivation for food reward, and an increase in anxiety, anhedonia, and depressive-like behavior. Conclusion: Chronic circadian disruption, caused by an experimental CJL protocol, affects mood-related and reward-related behaviors in mice. Understanding the importance of the circadian system and its potential role for disruption due to CJL is important for maintaining good health and well-being.

Female dominance hierarchies influence responses to psychosocial stressors

Social species form dominance hierarchies to ensure survival and promote reproductive success. Traditionally studied in males, rodent hierarchies are considered despotic, and dominant social rank results from a history of winning agonistic encounters. By contrast, female hierarchies are thought to be less despotic, and rank is conferred by intrinsic traits. Both social buffering and elevated social status confer resilience to depression, anxiety, and other consequences of chronic stress. Here, we investigate whether female social hierarchies and individual traits related to social rank likewise influence stress resilience. We observe the formation of dyadic female hierarchies under varying conditions of ambient light and circadian phase and subject mice to two forms of chronic psychosocial stress: social isolation or social instability. We find that stable female hierarchies emerge rapidly in dyads. Individual behavioral and endocrinological traits are characteristic of rank, some of which are circadian phase dependent. Further, female social rank is predicted by behavior and stress status prior to social introduction. Other behavioral characteristics suggest that rank is motivation-based, indicating that female rank identity serves an evolutionarily relevant purpose. Rank is associated with alterations in behavior in response to social instability stress and prolonged social isolation, but the different forms of stress produce disparate rank responses in endocrine status. Histological examination of c-Fos protein expression identified brain regions that respond to social novelty or social reunion following chronic isolation in a rank-specific manner. Collectively, female rank is linked to neurobiology, and hierarchies exert context-specific influence upon stress outcomes.

Cannabidiol (CBD) drives sex-dependent impairments in omission, but has no effect on reinforcer devaluation

Habits are inflexible behaviors that persist despite changes in outcome value. While habits allow for efficient responding, neuropsychiatric diseases such as drug addiction and obsessive-compulsive disorder are characterized by overreliance on habits. Recently, the commercially popular drug cannabidiol (CBD) has emerged as a potential treatment for addictive behaviors, though it is not entirely clear how it exerts this therapeutic effect. As brain endocannabinoids play a key role in habit formation, we sought to determine how CBD modifies goal-directed behaviors and habit formation. To explore this, mice were administered CBD (20mg/kg i.p.) or vehicle as a control and trained on random interval (RI30/60) or random ratio (RR10/20) schedules designed to elicit habitual or goal-directed lever pressing, respectively. Mice were tested for habitual responding using probe trials following reinforcer-specific devaluation as well as omission trials, where mice had to withhold responding to earn rewards. We found that while CBD had little effect on operant behaviors or reward devaluation, CBD inhibited goal-directed behavior in a sex-specific and contextdependent manner during the omission task. Beyond drug treatment, we found an effect of sex throughout training, reward devaluation, and omission. This work provides evidence that CBD has no effect on habit formation in a reward devaluation paradigm. However, the omission results suggest that CBD may slow learning of novel actionoutcome contingencies or decrease goal-directed behavior. This work calls for further examination of sex-dependent outcomes of CBD treatment and highlights the importance of investigating sex effects in habit-related experiments.

Muskelin regulates actin-dependent synaptic changes and intrinsic brain activity relevant to behavioral and cognitive processes

Muskelin (Mkln1) is implicated in neuronal function, regulating plasma membrane receptor trafficking. However, its influence on intrinsic brain activity and corresponding behavioral processes remains unclear. Here we show that murine Mkln1 knockout causes non-habituating locomotor activity, increased exploratory drive, and decreased locomotor response to amphetamine. Muskelin deficiency impairs social novelty detection while promoting the retention of spatial reference memory and fear extinction recall. This is strongly mirrored in either weaker or stronger resting-state functional connectivity between critical circuits mediating locomotor exploration and cognition. We show that Mkln1 deletion alters dendrite branching and spine structure, coinciding with enhanced AMPAR-mediated synaptic transmission but selective impairment in synaptic potentiation maintenance. We identify muskelin at excitatory synapses and highlight its role in regulating dendritic spine actin stability. Our findings point to aberrant spine actin modulation and changes in glutamatergic synaptic function as critical mechanisms that contribute to the neurobehavioral phenotype arising from Mkln1 ablation.

A murine muskelin knockout induces increased exploratory drive and alters cognition and functional connectivity. These effects correlate with actin-dependent changes in dendritic branching, spine structure, and AMPAR-mediated synaptic transmission.

What's wrong with my experiment?: The impact of hidden variables on neuropsychopharmacology research

The field of neuropsychopharmacology relies on behavioral assays to quantify behavioral processes related to mental illness and substance use disorders. Although these assays have been highly informative, sometimes laboratories have unpublished datasets from experiments that "didn't work". Often this is because expected outcomes were not observed in positive or negative control groups. While this can be due to experimenter error, an important alternative is that under-appreciated environmental factors can have a major impact on results. "Hidden variables" such as circadian cycles, husbandry, and social environments are often omitted in methods sections, even though there is a strong body of literature documenting their impact on physiological and behavioral outcomes. Applying this knowledge in a more critical manner could provide behavioral neuroscientists with tools to develop better testing methods, improve the external validity of behavioral techniques, and make better comparisons of experimental data across institutions. Here we review the potential impact of "hidden variables" that are commonly overlooked such as light-dark cycles, transport stress, cage ventilation, and social housing structure. While some of these conditions may not be under direct control of investigators, it does not diminish the potential impact of these variables on experimental results. We provide recommendations to investigators on which variables to report in publications and how to address "hidden variables" that impact their experimental results.

Simultaneous Alteration of the Circadian Variation of Memory, Hippocampal Synaptic Plasticity, and Metabolism in a Triple Transgenic Mouse Model of Alzheimer’s Disease

Alzheimer’s disease (AD) is characterized by progressive memory deficits accompanied by synaptic and metabolic deficits, namely of mitochondrial function. AD patients also display a disrupted circadian pattern. Thus, we now compared memory performance, synaptic plasticity, and mitochondria function in 24-week-old non-transgenic (non-Tg) and triple transgenic male mice modeling AD (3xTg-AD) at Zeitgeber 04 (ZT-4, inactive phase) and ZT-16 (active phase). Using the Morris water maze test to minimize the influence of circadian-associated locomotor activity, we observed a circadian variation in hippocampus-dependent learning performance in non-Tg mice, which was impaired in 3xTg-AD mice. 3xTg-AD mice also displayed a lack of circadian variation of their performance in the reversal spatial learning task. Additionally, the amplitude of hippocampal long-term potentiation also exhibited a circadian profile in non-Tg mice, which was not observed in 3xTg-AD mice. Moreover, cerebral cortical synaptosomes of non-Tg mice also displayed a circadian variation of FCCP-stimulated oxygen consumption as well as in mitochondrial calcium retention that were blunted in 3xTg-AD mice. In sum, this multidimensional study shows that the ability to maintain a circadian oscillation in brain behavior, synaptic plasticity, and synaptic mitochondria function are simultaneously impaired in 3xTg-AD mice, highlighting the effects of circadian misalignment in AD.

Behavioral Testing Design for Evaluation of Cognitive Disabilities

Intellectual disabilities (ID) constitute a class of human neurodevelopmental diseases and are a major medical and socioeconomic problem owing to their high incidence and enormous burden to the families of those affected. In the past three decades, mutant mouse technologies have provided powerful tools for elucidating the pathophysiological mechanisms underlying behavioral and developmental alterations related to IDs and for addressing new therapeutic strategies, and major progress has been made revealing previously unidentified genes involved in ID. However, the pathological hallmarks of IDs are very heterogeneous in regard to both the functional deficits observed and the severity of the phenotype, even within the same mutation types. For this reason, an appropriate experimental design is required to reduce the risk of false negatives and positives in animal functional genomic studies. This experimental design should address functions important to evaluate, tests, and the appropriate workflow. Here, we propose an extensive behavioral screen with detailed protocols, which was successfully used in a systematic mouse functional genomic approach to gain pathway-based insights into mechanisms leading to cognitive dysfunction in humans. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Assessment of circadian activity and ingestive behavior Basic Protocol 2: Assessment of neurological reflexes and motor abilities using the grip and rotarod tests Basic Protocol 3: Evaluation of anxiety-related behavior using the elevated plus maze Basic Protocol 4: Evaluation of recognition memory using the object recognition task Basic Protocol 5: Evaluation of social behavior using the social recognition test Basic Protocol 6: Evaluation of working memory using the Y-maze spontaneous alternation test Basic Protocol 7: Evaluation of emotional learning and memory using the fear conditioning test.

Phenotyping spontaneous locomotor activity in inbred and outbred mouse strains by using Digital Ventilated Cages

Mouse strains differ markedly in all behaviors, independently of their genetic background. We undertook this study to disentangle the diurnal activity and feature key aspects of three non-genetically altered mouse strains widely used in research, C57BL/6NCrl (inbred), BALB/cAnNCrl (inbred) and CRL:CD1(ICR) (outbred). With this aim, we conducted a longitudinal analysis of the spontaneous locomotor activity of the mice during a 24-h period for 2 months, in two different periods of the year to reduce the seasonality effect. Mice (males and females) were group-housed in Digital Ventilated Cages (Tecniplast), mimicking standard housing conditions in research settings and avoiding the potential bias provided in terms of locomotor activity by single housing. The recorded locomotor activity was analyzed by relying on different and commonly used circadian metrics (i.e., day and night activity, diurnal activity, responses to lights-on and lights-off phases, acrophase and activity onset and regularity disruption index) to capture key behavioral responses for each strain. Our results clearly demonstrate significant differences in the circadian activity of the three selected strains, when comparing inbred versus outbred as well as inbred strains (C57BL/6NCrl versus BALB/cAnNCrl). Conversely, males and females of the same strain displayed similar motor phenotypes; significant differences were recorded only for C57BL/6NCrl and CRL:CD1(ICR) females, which displayed higher average locomotor activity from prepuberty to adulthood. All strain-specific differences were further confirmed by an unsupervised machine learning approach. Altogether, our data corroborate the concept that each strain behaves under characteristic patterns, which needs to be taken into consideration in the study design to ensure experimental reproducibility and comply with essential animal welfare principles.

Systematic Review and Methodological Considerations for the Use of Single Prolonged Stress and Fear Extinction Retention in Rodents

Posttraumatic stress disorder (PTSD) is a mental health condition triggered by experiencing or witnessing a terrifying event that can lead to lifelong burden that increases mortality and adverse health outcomes. Yet, no new treatments have reached the market in two decades. Thus, screening potential interventions for PTSD is of high priority. Animal models often serve as a critical translational tool to bring new therapeutics from bench to bedside. However, the lack of concordance of some human clinical trial outcomes with preclinical animal efficacy findings has led to a questioning of the methods of how animal studies are conducted and translational validity established. Thus, we conducted a systematic review to determine methodological variability in studies that applied a prominent animal model of trauma-like stress, single prolonged stress (SPS). The SPS model has been utilized to evaluate a myriad of PTSD-relevant outcomes including extinction retention. Rodents exposed to SPS express an extinction retention deficit, a phenotype identified in humans with PTSD, in which fear memory is aberrantly retained after fear memory extinction. The current systematic review examines methodological variation across all phases of the SPS paradigm, as well as strategies for behavioral coding, data processing, statistical approach, and the depiction of data. Solutions for key challenges and sources of variation within these domains are discussed. In response to methodological variation in SPS studies, an expert panel was convened to generate methodological considerations to guide researchers in the application of SPS and the evaluation of extinction retention as a test for a PTSD-like phenotype. Many of these guidelines are applicable to all rodent paradigms developed to model trauma effects or learned fear processes relevant to PTSD, and not limited to SPS. Efforts toward optimizing preclinical model application are essential for enhancing the reproducibility and translational validity of preclinical findings, and should be conducted for all preclinical psychiatric research models.

Behavioral responses of three freshwater planaria species to light, visual and olfactory stimuli: Setting the stage for further ecotoxicological studies

Planarians are freshwater flatworms commonly used as environmental bioindicator due to their sensitivity of response and their ease of culturing in lab. Nevertheless, to date, very few studies describing their behavior have been led. This work aims to fill the literature gap by providing preliminary results through six behavioral challenges (locomotion, exploration, light stress, planarian light/dark test, shoaling and foraging) conducted with three different species Dugesia tigrina, Schmidtea mediterranea and Schmidtea polychroa. The behavioral responses of every species in each of these six assays were recorded and differences between species were highlighted, depending on the assays and conditions. Schmidtea polychroa is less active than the two others and had the highest light aversion. Reactions observed in response to diverse and realistic stimuli helped us to select the most suitable tests and choose the species that seem the most appropriate for future ecotoxicological and neurophysiological tests. Four tests - out of the six tested- seem reliable in order to standardize planarian behavioral tests.

Method to Obtain Pattern of Breathing in Senescent Mice through Unrestrained Barometric Plethysmography

Unrestrained barometric plethysmography (UBP) is a method for quantifying the pattern of breathing in mice, where breathing frequency, tidal volume, and minute ventilation are routinely reported. Moreover, information can be collected regarding the neural output of breathing, including the existence of central apneas and augmented breaths. An important consideration for UBP is obtaining a breathing segment with a minimal impact of anxious or active behaviors, to elucidate the response to breathing challenges. Here, we present a protocol that allows for short, quiet baselines to be obtained in aged mice, comparable to waiting for longer bouts of quiet breathing. The use of shorter time segments is valuable, as some strains of mice may be increasingly excitable or anxious, and longer periods of quiet breathing may not be achieved within a reasonable timeframe. We placed 22 month-old mice in a UBP chamber and compared four 15 s quiet breathing segments between minutes 60-120 to a longer 10 min quiet breathing period that took 2-3 h to acquire. We also obtained counts of central apneas and augmented breaths prior to the quiet breathing segments, following a 30 min familiarization period. We show that 10 min of quiet breathing is comparable to using a much shorter 15 s duration. Additionally, the time leading up to these 15 s quiet breathing segments can be used to gather data regarding apneas of central origin. This protocol allows investigators to collect pattern-of-breathing data in a set amount of time and makes quiet baseline measures feasible for mice that may exhibit increased amounts of excitable behavior. The UBP methodology itself provides a useful and noninvasive way to collect pattern-of-breathing data and allows for mice to be tested over several time points.

High-intensity interval training and calorie restriction promote remodeling of glucose and lipid metabolism in diet-induced obesity

Calorie restriction (CR) decreases adiposity, but the magnitude and defense of weight loss is less than predicted due to reductions in total daily energy expenditure (TEE). The purpose of the current investigation was to determine whether high-intensity interval training (HIIT) would increase markers of sympathetic activation in white adipose tissue (WAT) and rescue CR-mediated reductions in EE to a greater extent than moderate-intensity aerobic exercise training (MIT). Thirty-two 5-wk-old male C57BL/6J mice were placed on ad libitum HFD for 11 wk, followed by randomization to one of four groups (n = 8/group) for an additional 15 wk: 1) CON (remain on HFD), 2) CR (25% lower energy intake), 3) CR + HIIT (25% energy deficit created by 12.5% CR and 12.5% EE through HIIT), and 4) CR + MIT (25% energy deficit created by 12.5% CR and 12.5% EE through MIT). Markers of adipose thermogenesis (Ucp1, Prdm16, Dio2, and Fgf21) were unchanged in either exercise group in inguinal or epididymal WAT, whereas CR + HIIT decreased Ucp1 expression in retroperitoneal WAT and brown adipose tissue. HIIT rescued CR-mediated reductions in lean body mass (LBM) and resting energy expenditure (REE), and both were associated with improvements in glucose/insulin tolerance. Improvements in glucose metabolism in the CR + HIIT group appear to be linked to a molecular signature that enhances glucose and lipid storage in skeletal muscle. Exercise performed at either moderate or high intensity does not increase markers of adipose thermogenesis when performed in the presence of CR but remodels skeletal muscle metabolic and thermogenic capacity.

Dietary heat-killed Lactobacillus brevis SBC8803 promotes voluntary wheel-running and affects sleep rhythms in mice

AIMS

We previously reported that heat-killed Lactobacillus brevis SBC8803 enhances appetite via changes in autonomic neurotransmission. Here we assessed whether a diet supplemented with heat-killed SBC8803 affects circadian locomotor rhythmicity and sleep architecture.

MAIN METHODS AND KEY FINDINGS

Daily total activity gradually increased in mice over 4 weeks and supplementation with heat-killed SBC8803 significantly intensified the increase, which reached saturation at 25 days. Electroencephalography revealed that SBC8803 supplementation significantly reduced the total amount of time spent in non-rapid eye movement (NREM) sleep and increased the amount of time spent being awake during the latter half of the nighttime, but tended to increase the total amount of time spent in NREM sleep during the daytime. Dietary supplementation with SBC8803 can extend the duration of activity during the nighttime and of sleep during the daytime. Daily voluntary wheel-running and sleep rhythmicity become intensified when heat-killed SBC8803 is added to the diet.

SIGNIFICANCE

Dietary heat-killed SBC8803 can modulate circadian locomotion and sleep rhythms, which might benefit individuals with circadian rhythms that have been disrupted by stress or ageing.

TNF-α and its receptors modulate complex behaviours and neurotrophins in transgenic mice

Tumour necrosis factor-α (TNF-α) plays an important role not only in immunity but also in the normal functioning of the central nervous system (CNS). At physiological levels, studies have shown TNF-α is essential to maintain synaptic scaling and thus influence learning and memory formation while also playing a role in modulating pathological states of anxiety and depression. TNF-α signals mainly through its two receptors, TNF-R1 and TNF-R2, however the exact role that these receptors play in TNF-α mediated behavioural phenotypes is yet to be determined.

METHODS

We have assessed TNF(-/-), TNF-R1(-/-) and TNF-R2(-/-) mice against C57BL/6 wild-type (WT) mice from 12 weeks of age in order to evaluate measures of spatial memory and learning in the Barnes maze (BM) and Y-maze, as well as other behaviours such as exploration, social interaction, anxiety and depression-like behaviour in a battery of tests. We have also measured hippocampal and prefrontal cortex levels of the neurotrophins nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) as well as used immunohistochemical analyses to measure number of proliferating cells (Ki67) and immature neurons (DCX) within the dentate gyrus.

RESULTS

We have shown that young adult TNF(-/-) and TNF-R1(-/-) mice displayed impairments in learning and memory in the BM and Y-maze, while TNF-R2(-/-) mice showed good memory but slow learning in these tests. TNF(-/-)and TNF-R2(-/-) mice also demonstrated a decrease in anxiety like behaviour compared to WT mice. ELISA analyses showed TNF(-/-) and TNF-R2(-/-) mice had lower levels of NGF compared to WT mice.

CONCLUSION

These results indicate that while lack of TNF-α can decrease anxiety-like behaviour in mice, certain basal levels of TNF-α are required for the development of normal cognition. Furthermore our results suggest that both TNF-R1 and TNF-R2 signalling play a role in normal CNS function, with knockout of either receptor impairing cognition on the Barnes maze.

Neuronal nitric oxide synthase and NADPH oxidase interact to affect cognitive, affective, and social behaviors in mice

Both nitric oxide (NO) and reactive oxygen species (ROS) generated by nNOS and NADPH oxidase (NOX), respectively, in the brain have been implicated in an array of behaviors ranging from learning and memory to social interactions. Although recent work has elucidated how these separate redox pathways regulate neural function and behavior, the interaction of these two pathways in the regulation of neural function and behavior remains unspecified. Toward this end, the p47phox subunit of NOX, and nNOS were deleted to generate double knockout mice that were used to characterize the behavioral outcomes of concurrent impairment of the NO and ROS pathways in the brain. Mice were tested in a battery of behavioral tasks to evaluate learning and memory, as well as social, affective, and cognitive behaviors. p47phox deletion did not affect depressive-like behavior, whereas nNOS deletion abolished it. Both p47phox and nNOS deletion singly reduced anxiety-like behavior, increased general locomotor activity, impaired spatial learning and memory, and impaired preference for social novelty. Deletion of both genes concurrently had synergistic effects to elevate locomotor activity, impair spatial learning and memory, and disrupt prepulse inhibition of acoustic startle. Although preference for social novelty was impaired in single knockouts, double knockout mice displayed elevated levels of preference for social novelty above that of wild type littermates. These data demonstrate that, depending upon modality, deletion of p47phox and nNOS genes have dissimilar, similar, or additive effects. The current findings provide evidence that the NOX and nNOS redox signaling cascades interact in the brain to affect both cognitive function and social behavior.

Chronic electromyographic analysis of circadian locomotor activity in crayfish

Animals generally exhibit circadian rhythms of locomotor activity. They initiate locomotor behavior not only reflexively in response to external stimuli but also spontaneously in the absence of any specific stimulus. The neuronal mechanisms underlying circadian locomotor activity can, therefore, be based on the rhythmic changes in either reflexive efficacy or endogenous activity. In crayfish Procambarus clarkii, it can be determined by analyzing electromyographic (EMG) patterns of walking legs whether the walking behavior is initiated reflexively or spontaneously. In this study, we examined quantitatively the leg muscle activity that underlies the locomotor behavior showing circadian rhythms in crayfish. We newly developed a chronic EMG recording system that allowed the animal to freely behave under a tethered condition for more than 10 days. In the LD condition in which the animals exhibited LD entrainment, the rhythmic burst activity of leg muscles for stepping behavior was preceded by non-rhythmic tonic activation that lasted for 1323±488ms when the animal initiated walking. In DD and LL free-running conditions, the pre-burst activation lasted for 1779±31 and 1517±39ms respectively. In the mechanical stimulus-evoked walking, the pre-burst activation ended within 79±6ms. These data suggest that periodic changes in the crayfish locomotor activity under the condition of LD entrainment or free-running are based on activity changes in the spontaneous initiation mechanism of walking behavior rather than those in the sensori-motor pathway connecting mechanoreceptors with leg movements.

A behavioural study of neuroglobin-overexpressing mice under normoxic and hypoxic conditions

Neuroglobin (Ngb), a neuron-specific heme-binding protein that binds O2, CO and NO reversibly, and promotes in vivo and in vitro cell survival after hypoxic and ischaemic insult. Although the mechanisms of this neuroprotection remain unknown, Ngb might play an important role in counteracting the adverse effects of ischaemic stroke and cerebral hypoxia. Several Ngb overexpressing mouse models have confirmed this hypothesis; however, these models were not yet exposed to in-depth behavioural characterisations. To investigate the potential changes in behaviour due to Ngb overexpression, heterozygous mice and wild type (WT) littermates were subjected to a series of cognitive and behavioural tests (i.e., the SHIRPA primary screening, the hidden-platform Morris water maze, passive avoidance learning, 47h cage activity, open field exploration, a dark-light transition box, an accelerating rotarod, a stationary beam, a wire suspension task and a gait test) under normoxic and hypoxic conditions. No significant behavioural differences were found between WT and Ngb-overexpressing mice at three months old. However, one-year-old Ngb-overexpressing mice travelled more distance on the stationary beam compared with WT littermates. This result shows that the constitutive overexpression of Ngb might counteract the endogenous decrease of Ngb in crucial brain regions such as the cerebellum, thereby counteracting age-induced neuromotor dysfunction. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.

Automated video analysis system reveals distinct diurnal behaviors in C57BL/6 and C3H/HeN mice

Advances in rodent behavior dissection using automated video recording and analysis allows detailed phenotyping. This study compared and contrasted 15 diurnal behaviors recorded continuously using an automated behavioral analysis system for a period of 14 days under a 14/10 light/dark cycle in single housed C3H/HeN (C3H) or C57BL/6 (C57) male mice. Diurnal behaviors, recorded with minimal experimental interference and analyzed using phenotypic array and temporal distribution analysis showed bimodal and unimodal profiles in the C57 and C3H mice, respectively. Phenotypic array analysis revealed distinct behavioral rhythms in Activity-Like Behaviors (i.e. walk, hang, jump, come down) (ALB), Exploration-Like Behaviors (i.e. dig, groom, rear up, sniff, stretch) (ELB), Ingestion-Like Behaviors (i.e. drink, eat) (ILB) and Resting-Like Behaviors (i.e. awake, remain low, rest, twitch) (RLB) of C3H and C57 mice. Temporal distribution analysis demonstrated that strain and time of day affects the magnitude and distribution of the spontaneous homecage behaviors. Wheel running activity, water and food measurements correlated with timing of homecage behaviors. Subcutaneous (3 mg/kg, sc) or oral (0.02 mg/ml, oral) melatonin treatments in C57 mice did not modify either the total 24 h magnitude or temporal distribution of homecage behaviors when compared with vehicle treatments. We conclude that C3H and C57 mice show different spontaneous activity and behavioral rhythms specifically during the night period which are not modulated by melatonin.

Chronobiology of alcohol: studies in C57BL/6J and DBA/2J inbred mice

Human alcoholics display dramatic disruptions of circadian rhythms that may contribute to the maintenance of excessive drinking, thus creating a vicious cycle. While clinical studies cannot establish direct causal mechanisms, recent animal experiments have revealed bidirectional interactions between circadian rhythms and ethanol intake, suggesting that the chronobiological disruptions seen in human alcoholics are mediated in part by alterations in circadian pacemaker function. The present study was designed to further explore these interactions using C57BL/6J (B6) and DBA/2J (D2) inbred mice, two widely employed strains differing in both circadian and alcohol-related phenotypes. Mice were maintained in running-wheel cages with or without free-choice access to ethanol and exposed to a variety of lighting regimens, including standard light-dark cycles, constant darkness, constant light, and a "shift-lag" schedule consisting of repeated light-dark phase shifts. Relative to the standard light-dark cycle, B6 mice showed reduced ethanol intake in both constant darkness and constant light, while D2 mice showed reduced ethanol intake only in constant darkness. In contrast, shift-lag lighting failed to affect ethanol intake in either strain. Access to ethanol altered daily activity patterns in both B6 and D2 mice, and increased activity levels in D2 mice, but had no effects on other circadian parameters. Thus, the overall pattern of results was broadly similar in both strains, and consistent with previous observations that chronic ethanol intake alters circadian activity patterns while environmental perturbation of circadian rhythms modulates voluntary ethanol intake. These results suggest that circadian-based interventions may prove useful in the management of alcohol use disorders.

QTL analysis of measures of mouse home-cage activity using B6/MSM consomic strains

The activity of mice in their home cage is influenced greatly by the cycle of light and dark. In addition, home-cage activity shows remarkable time-dependent changes that result in a prominent temporal pattern. The wild-derived mouse strain MSM/Ms (MSM) exhibits higher total activity in the home cage than does C57BL/6 (B6), a commonly used laboratory strain. In addition, there is a clear strain difference in the temporal pattern of home-cage activity. This study aimed to clarify the genetic basis of strain differences in the temporal pattern of home-cage activity between MSM and B6. Through the comparison of temporal patterns of home-cage activity between B6 and MSM, the pattern can be classified into five temporal components: (1) resting phase, (2) anticipation phase, (3) 1st phase, (4) 2nd phase, and (5) 3rd phase. To identify quantitative trait loci (QTLs) involved in these temporal components, we used consomic strains established from crosses between B6 and MSM. Five consomic strains, for Chrs 2T (telomere), 3, 4, 13, and 14, showed significantly higher total activity than B6. In contrast, the consomic strains of Chrs 6C (centromere), 7T, 9, 11, and 15 were less active than B6. This indicates that multigenic factors regulate the total activity. Further analysis showed an impact of QTLs on the temporal components of home-cage activity. The present data showed that each temporal component was regulated by different combinations of multigenic factors, with some overlap. These temporal component-related QTLs are important to understand fully the genetic mechanisms that underlie home-cage activity.

Cognition in transmembrane domain neuregulin 1 mutant mice

Neuregulin 1 (NRG1), which has been implicated in the development of schizophrenia, is expressed widely throughout the brain and influences key neurodevelopmental processes such as myelination and neuronal migration. The heterozygous transmembrane domain Nrg1 mutant mouse (Nrg1 TM HET) exhibits a neurobehavioural phenotype relevant for schizophrenia research, characterized by the development of locomotor hyperactivity, social withdrawal, increased sensitivity to environmental manipulation, and changes to the serotonergic system. As only limited data are available on the learning and memory performance of Nrg1 TM HET mice, we conducted a comprehensive examination of these mice and their wild type-like littermates in a variety of paradigms, including fear conditioning (FC), radial arm maze (RAM), Y maze, object exploration and passive avoidance (PA). Male neuregulin 1 hypomorphic mice displayed impairments in the novel object recognition and FC tasks, including reduced interest in the novel object and reduced FC to a context, but not a discrete cue. These cognitive deficits were task-specific, as no differences were seen between mutant and control mice in spatial learning (i.e. RAM and Y maze) for both working and reference memory measures, or in the PA paradigm. These findings indicate that neuregulin 1 plays a moderate role in cognition and present further behavioural validation of this genetic mouse model for the schizophrenia candidate gene neuregulin 1.

Increased aggression in males in transgenic Tg2576 mouse model of Alzheimer's disease

Behavioural and psychological signs and symptoms of dementia encompass a wide range of neuropsychiatric disturbances which coincide with progressing cognitive decline in Alzheimer's disease (AD). Physical aggression and agitation, which occurs in 20-65% of AD patients, is physically and emotionally stressful, not only to patients but also to immediate family and caregivers. The exact mechanisms underlying the increased aggressive behaviour in AD has yet to be elucidated. We used a transgenic mouse model, denoted Tg2576, which over-expresses a mutated human amyloid precursor protein (APP) gene implicated in familial AD, to investigate aggressive behaviour of males at the stage of amyloid beta pathology preceding overt amyloid plaque deposition in the brain. The aggressive behaviour of transgenic and non-transgenic littermate males was evaluated in a standard resident-intruder test in which an isolated resident male responded aggressively toward an experimentally naïve intruder male of A/J strain. We showed that 7-month-old Tg2576 resident males demonstrated significantly higher and unchanged level of aggression towards intruder males during 3 consecutive encounters as compared to their non-transgenic littermate counterparts. These results validate further the Tg2576 mouse model of AD underscoring its usefulness in studying non-mnemonic changes in behaviour related to the disease.

Hyperactivity, startle reactivity and cell-proliferation deficits are resistant to chronic lithium treatment in adult Nr2e1(frc/frc) mice

The NR2E1 region on Chromosome 6q21-22 has been repeatedly linked to bipolar disorder (BP) and NR2E1 has been associated with BP, and more specifically bipolar I disorder (BPI). In addition, patient sequencing has shown an enrichment of rare candidate-regulatory variants. Interestingly, mice carrying either spontaneous (Nr2e1(frc) ) or targeted (Tlx(-) ) deletions of Nr2e1 (here collectively known as Nr2e1-null) show similar neurological and behavioral anomalies, including hypoplasia of the cerebrum, reduced neural stem cell proliferation, extreme aggression and deficits in fear conditioning; these are the traits that have been observed in some patients with BP. Thus, NR2E1 is a positional and functional candidate for a role in BP. However, no Nr2e1-null mice have been fully evaluated for behaviors used to model BP in rodents or pharmacological responses to drugs effective in treating BP symptoms. In this study we examine Nr2e1(frc/frc) mice, homozygous for the spontaneous deletion, for abnormalities in activity, learning and information processing, and cell proliferation; these are the phenotypes that are either affected in patients with BP or commonly assessed in rodent models of BP. The effect of lithium, a drug used to treat BP, was also evaluated for its ability to attenuate Nr2e1(frc/frc) behavioral and neural stem cell-proliferation phenotypes. We show for the first time that Nr2e1-null mice exhibit extreme hyperactivity in the open field as early as postnatal day 18 and in the home cage, deficits in open-field habituation and passive avoidance, and surprisingly, an absence of acoustic startle. We observed a reduction in neural stem/progenitor cell proliferation in Nr2e1(frc/frc) mice, similar to that seen in other Nr2e1-null strains. These behavioral and cell-proliferation phenotypes were resistant to chronic-adult-lithium treatment. Thus, Nr2e1(frc/frc) mice exhibit behavioral traits used to model BP in rodents, but our results do not support Nr2e1(frc/frc) mice as pharmacological models for BP.

Selecting exercise regimens and strains to modify obesity and diabetes in rodents: an overview

Exercise is part of a healthy lifestyle and frequently is an important component in combating chronic diseases, such as obesity and diabetes. Understanding the molecular events initiated by regular exercise is best studied in laboratory animals, with mice and rats being favoured for a number of reasons. However, the wide variety of rodent strains available for biomedical research often makes it challenging to select an animal strain suitable for studying specific disease outcomes. In the present review we focus on exercise as a management strategy for obesity and diabetes and we discuss: (i) exercise paradigms in humans shown to ameliorate signs and symptoms of obesity and diabetes; (ii) different rodent strains in terms of their advantages, disadvantages and limitations when using specific forms of exercise; (iii) the strengths and weaknesses of commonly used laboratory methods for rodent exercise; and (iv) the unintended consequences of exercise that are often manifested by increased hormonal and oxidative stress responses.

High-rate operant behavior in two mouse strains: a response-bout analysis

Operant behavior sometimes occurs in bouts characterized by an initiation rate, within-bout response rate, and bout length. The generality of this structure was tested using high-rate nose-poking in mice. Reinforcement of short interresponse times produced high response rates while a random-interval schedule held reinforcement rates constant. BALB/c mice produced bouts that were more frequent, longer, and contained a higher within-bout rate of responding (nine nose-pokes/s) than did the C57BL/6 mice (five nose-pokes/s). Adding a running wheel decreased total nose-pokes and bout length, and increased bout-initiation rate. Free-feeding reduced nose-poking by decreasing bout-initiation rate. Photoperiod reversal decreased bout-initiation rate but not total nose-poke rate. Despite strain differences in bout structure, both strains responded similarly to the interventions. The three bout measures were correlated with overall rate but not with each other. Log-survival analyses provided independent descriptors of the structure of high-rate responding in these two strains.

Chronic mild stress (CMS) in mice: of anhedonia, 'anomalous anxiolysis' and activity

Background

In a substantial proportion of depressed patients, stressful life events play a role in triggering the evolution of the illness. Exposure to stress has effects on different levels in laboratory animals as well and for the rat it has been shown that chronic mild stress (CMS) can cause antidepressant-reversible depressive-like effects. The adoption of the model to the mouse seems to be problematic, depending on the strain used and behavioural endpoint defined. Our aim was to evaluate the applicability of CMS to mice in order to induce behavioural alterations suggested to reflect depression-like symptoms.

Methodology/Principal Findings

A weekly CMS protocol was applied to male mice of different mouse strains (D2Ola, BL/6J and BL/6N) and its impact on stress-sensitive behavioural measures (anhedonia-, anxiety- and depression-related parameters) and body weight was assessed. Overnight illumination as commonly used stressor in CMS protocols was particularly investigated in terms of its effect on general activity and subsequently derived saccharin intake. CMS application yielded strain-dependent behavioural and physiological responses including ‘paradox’ anxiolytic-like effects. Overnight illumination was found to be sufficient to mimic anhedonic-like behaviour in BL/6J mice when being applied as sole stressor.

Conclusions/Significance

The CMS procedure induced some behavioural changes that are compatible with the common expectations, i.e. ‘anhedonic’ behaviour, but in parallel behavioural alterations were observed which would be described as ‘anomalous’ (e.g. decreased anxiety). The results suggest that a shift in the pattern of circadian activity has a particular high impact on the anhedonic profile. Changes in activity in response to novelty seem to drive the ‘anomalous’ behavioural alterations as well.

Light phase testing of social behaviors: not a problem

The rich repertoire of mouse social behaviors makes it possible to use mouse models to study neurodevelopmental disorders characterized by social deficits. The fact that mice are naturally nocturnal animals raises a critical question of whether behavioral experiments should be strictly conducted in the dark phase and whether light phase testing is a major methodologically mistake. Although mouse social tasks have been performed in both phases in different laboratories, there seems to be no general consensus on whether testing phase is a critical factor or not. A recent study from our group showed remarkably similar social scores obtained from inbred mice tested in the light and the dark phase, providing evidence that light phase testing could yield reliable results as robust as dark phase testing for the sociability test. Here we offer a comprehensive review on mouse social behaviors measured in light and dark phases and explain why it is reasonable to test laboratory mice in experimental social tasks in the light phase.

Social approach behaviors are similar on conventional versus reverse lighting cycles, and in replications across cohorts, in BTBR T+ tf/J, C57BL/6J, and vasopressin receptor 1B mutant mice

Mice are a nocturnal species, whose social behaviors occur primarily during the dark phase of the circadian cycle. However, laboratory rodents are frequently tested during their light phase, for practical reasons. We investigated the question of whether light phase testing presents a methodological pitfall for investigating mouse social approach behaviors. Three lines of mice were systematically compared. One cohort of each line was raised in a conventional lighting schedule and tested during the light phase, under white light illumination; another cohort was raised in a reverse lighting schedule and tested during their dark phase, under dim red light. Male C57BL/6J (B6) displayed high levels of sociability in our three-chambered automated social approach task when tested in either phase. BTBR T+ tf/J (BTBR) displayed low levels of sociability in either phase. Five cohorts of vasopressin receptor subtype 1b (Avpr1b) null mutants, heterozygotes, and wildtype littermate controls were tested in the same social approach paradigm: three in the dark phase and two in the light phase. All three genotypes displayed normal sociability in four out of the five replications. In the juvenile play test, testing phase had no effect on play soliciting behaviors in Avpr1b mice, but had modest effects on nose sniff and huddling. Taken together, these findings indicate that testing phase is not a crucial factor for studying some forms of social approach in juvenile and adult mice.

Quantitative trait loci for the circadian clock in Neurospora crassa

Neurospora crassa has been a model organism for the study of circadian clocks for the past four decades. Among natural accessions of Neurospora crassa, there is significant variation in clock phenotypes. In an attempt to investigate natural allelic variants contributing to quantitative variation, we used a quantitative trait loci mapping approach to analyze three independent mapping populations whose progenitors were collected from geographically isolated locations. Two circadian clock phenotypes, free-running period and entrained phase, were evaluated in the 188 F(1) progeny of each mapping population. To identify the clock QTL, we applied two QTL mapping analyses: composite interval mapping (CIM) and Bayesian multiple QTL analysis (BMQ). When controlling false positive rates < or =0.05, BMQ appears to be the more sensitive of the two approaches. BMQ confirmed most of the QTL from CIM (18 QTL) and identified 23 additional QTL. While 13 QTL colocalize with previously identified clock genes, we identified 30 QTL that were not linked with any previously characterized clock genes. These are candidate regions where clock genes may be located and are expected to lead to new insights in clock regulation.

Altered motor activity, exploration and anxiety in heterozygous neuregulin 1 mutant mice: implications for understanding schizophrenia

Human genetic studies have shown that neuregulin 1 (NRG1) is a potential susceptibility gene for schizophrenia. Nrg1 influences various neurodevelopmental processes, which are potentially related to schizophrenia. The neurodevelopmental theory of schizophrenia suggests that interactions between genetic and environmental factors are responsible for biochemical alterations leading to schizophrenia. To investigate these interactions and to match experimental design with the pathophysiology of schizophrenia, we applied a comprehensive behavioural phenotyping strategy for motor activity, exploration and anxiety in a heterozygous Nrg1 transmembrane domain mutant mouse model (Nrg1 HET) using different housing conditions and age groups. We observed a locomotion- and exploration-related hyperactive phenotype in Nrg1 HETs. Increased age had a locomotion- and exploration-inhibiting effect, which was significantly attenuated in mutant mice. Environmental enrichment (EE) had a stimulating influence on locomotion and exploration. The impact of EE was more pronounced in Nrg1 hypomorphs. Our study also showed a moderate task-specific anxiolytic-like phenotype for Nrg1 HETs, which was influenced by external factors. The behavioural phenotype detected in heterozygous Nrg1 mutant mice is not specific to schizophrenia per se, but the increased sensitivity of mutant mice to exogenous factors is consistent with the pathophysiology of schizophrenia and the neurodevelopmental theory. Our findings reinforce the importance of carefully controlling experimental designs for external factors and of comprehensive, integrative phenotyping strategies. Thus, Nrg1 HETs may, in combination with other genetic and drug models, help to clarify pathophysiological mechanisms behind schizophrenia.

Behavioral profiling of NPY in aggression and neuropsychiatric diseases

The abundantly expressed neuropeptide Y (NPY) has potent effects on feeding, body weight, and blood pressure, and exhibits important functions in various behavioral domains such as motor activity and anxiety. The potent neurotransmitter exerts its biological effects through at least five G-protein coupled receptors termed Y(1), Y(2), Y(4), Y(5), and y(6). The behavioral profile of NPY function has been extensively studied using traditional pharmacological and classic genetic animal models. Based on these studies, variations in the profile of NPY and its receptors have been found. To limit the variability and inconsistencies in the behavioral profile of NPY and to clarify its effects on certain domains in further detail, it is important to design a rational standardized strategy for behavioral testing, using a complement of different well-established and reproducible tests. This strategy can minimize the risk that false positive or false negative results lead to a contradictory and inconsistent behavioral characterization of NPY function. Ideally, such screening should be composed of an initial monitoring of general health, sensory functions, and motor abilities, before specific behavioral domains such as anxiety or aggression are investigated using a multi-tiered phenotyping approach. In this review, we will focus on a brief description of the latest insights into the behavioral profile of NPY in the selective lesser investigated domains such as aggression and depression-schizophrenia-related behaviors. We will combine this information with possible strategies to evaluate the different specific phenotypes in more detail.

Novel approach to the behavioural characterization of inbred mice: automated home cage observations

Here we present a newly developed tool for continuous recordings and analysis of novelty-induced and baseline behaviour of mice in a home cage-like environment. Aim of this study was to demonstrate the strength of this method by characterizing four inbred strains of mice, C57BL/6, DBA/2, C3H and 129S2/Sv, on locomotor activity. Strains differed in circadian rhythmicity, novelty-induced activity and the time-course of specific behavioural elements. For instance, C57BL/6 and DBA/2 mice showed a much faster decrease in activity over time than C3H and 129S2/Sv mice. Principal component analysis revealed two major factors within locomotor activity, which were defined as 'level of activity' and 'velocity/stops'. These factors were able to distinguish strains. Interestingly, mice that displayed high levels of activity in the initial phase of the home cage test were also highly active during an open-field test. Velocity and the number of stops during movement correlated positively with anxiety-related behaviour in the elevated plus maze. The use of an automated home cage observation system yields temporal changes in elements of locomotor activity with an advanced level of spatial resolution. Moreover, it avoids the confounding influence of human intervention and saves time-consuming human observations.

Activity changes and marked stereotypic behavior precede Aβ pathology in TgCRND8 Alzheimer mice

Alzheimer's disease (AD) is not only characterized by cognitive decline and neuropathological changes, but also by non-cognitive behavioral symptoms like restlessness, sleep disturbance, and wandering. These symptoms are categorized in the "Behavioral and Psychological Symptoms of Dementia" (BPSD). We investigated transgenic and wildtype mice of an APP transgenic mouse model of AD (TgCRND8) with respect to 24 h activity and spontaneous home cage behavior at 30, 60, 90 and 120 days of age. At all test days, transgenic and wildtype animals differed significantly with respect to activity patterns. In addition, activity rhythms changed distinctly in transgenic mice with increasing age. Transgenic mice also clearly showed more stereotypic behavior, which correlated significantly at 90 and 120 days of age with elevated corticosterone metabolite concentrations in fecal samples. Activity patterns in TgCRND8 mice resemble altered rhythms of activity in AD patients. Stereotypic behaviors may be caused by the same mechanisms as non-cognitive behavioral symptoms of AD. Thus, it is likely that analogies to BPSD that precede Abeta pathology are found in APP-overexpressing TgCRND8 mice.

Low amplitude entrainment of mice and the impact of circadian phase on behavior tests

A tremendous increase in the use of genetically engineered mice as experimental animals has led to increased scrutiny of mouse models generally and mouse behavioral paradigms specifically. Although mice are nocturnal, for practical reasons, most experimental procedures, including behavioral studies, are conducted during their inactive, sleep phase. Accumulating evidence indicates that myriad behavioral, cellular and biochemical processes fluctuate with circadian rhythmicity; however, time of day at which experiments are conducted is rarely controlled. The impact of circadian phase on the reliability of experimental results has received little attention and the present data are conflicting. This study addressed two questions. First, will laboratory mice in a typical animal care facility entrain to a low amplitude light cycle using bright/dim rather than light/dark cycles? A positive answer will make reversing photocycle easy to implement in any facility as dim light suitable for animal husbandry and behavioral testing can substitute for darkness during work hours. By monitoring home cage wheel running, we examined the effectiveness of a dim/bright photocycle as a zeitgeiber. We found that mice subjected to dim/bright photocycles effectively entrained such that their subjective night and activity onset coincided with the beginning of the dim light period, suggesting a potential strategy for standardization and management of circadian phase in nocturnal animals. In a second experiment, we asked what effect circadian phase has on behavioral performance in commonly used mouse behavioral tests. We found no main effect of circadian phase on outcome in open field activity, elevated plus maze emotionality, water maze spatial memory, novel object exploration and hyperactivity in response to amphetamine; however, we observed occasional interactions between circadian phase and both strain and sex that were neither consistent nor systematic. These data suggest that the tests examined here are relatively impervious to circadian phase. In general, testing mice during their active phase is more suitable for behavioral studies; a reversed dim/bright photocycle potentially offers one practical strategy for managing rodents' circadian cycles.

Effect of Y1 receptor deficiency on motor activity, exploration, and anxiety

Neuropeptide Y (NPY) in the CNS plays an important regulatory role in anxiety-related responses as exogenous administration of NPY exerts an anxiolytic-like effect in rodents. This effect is believed to be mediated by the Y(1) receptor system as pharmacological modulation of this Y(1) receptor system results in an increase in anxiety. Here we present a comprehensive phenotyping strategy for characterizing Y(1) receptor knockout animals at different times of the circadian rhythm using several motor activity-, exploration-, and anxiety-related behavioural tasks including open field, elevated plus maze, light-dark, and hole board test. We show that Y(1) deficiency has an important effect on motor activity and explorative-like behaviours and that it results in marked alterations in anxiety-related behaviours. Importantly, the behavioural phenotype of the Y(1) receptor knockout mice is circadian rhythm-dependent and also influenced by stimuli such as restraint stress. In addition, we found evidence for increases in working memory. Taken together, these findings suggest an important role of Y(1) receptors in the regulation of motor activity, exploration, and anxiety-related behaviours. This role is also influenced by several factors such as circadian rhythm and stress exposure confirming the importance of a comprehensive strategy and of using genetic animal models in behavioural neuroscience.

Common genetic effects on variation in impulsivity and activity in mice

Impulsivity is a complex psychological construct that impacts on behavioral predispositions in the normal range and has been shown to have a genetic element through the examination of hereditary patterns of abnormal conditions such as attention deficit/hyperactivity disorder and obsessive compulsive disorder. In this study, we took advantage of the isogenic nature of inbred strains of mice to determine the contribution of genes to impulsive behaviors by examining the performance of four separate mouse strains in a novel murine delayed-reinforcement paradigm, during which the animals had to choose between rewards that were relatively small but available immediately and larger but progressively delayed rewards. To control for maternal effects, all the mice were cross-fostered to a common strain immediately after birth. Under these conditions, we found significant differences between the strains on behaviors indexing impulsive choice and on independent measures of locomotor activity, which subsequent heritability analysis showed could be related, in part, to genetic effects. Moreover, the two aspects of behavior were found to co-vary, with the more active animals also displaying more impulsive behavior. This was not attributable to mundane confounds related to individual task requirements but instead indicated the existence of common genetic factors influencing variation in both impulsivity and locomotor activity. The data are discussed in terms of the coexistence of impulsivity and hyperactivity, interactions between environmental and genetic effects, and possible candidate genes.

Automated home cage observations as a tool to measure the effects of wheel running on cage floor locomotion

This paper introduces automated observations in a modular home cage system as a tool to measure the effects of wheel running on the time distribution and daily organization of cage floor locomotor activity in female C57BL/6 mice. Mice (n = 16) were placed in the home cage system for 6 consecutive days. Fifty percent of the subjects had free access to a running wheel that was integrated in the home cage. Overall activity levels in terms of duration of movement were increased by wheel running, while time spent inside a sheltering box was decreased. Wheel running affected the hourly pattern of movement during the animals' active period of the day. Mice without a running wheel, in contrast to mice with a running wheel, showed a clear differentiation between novelty-induced and baseline levels of locomotion as reflected by a decrease after the first day of introduction to the home cage. The results are discussed in the light of the use of running wheels as a tool to measure general activity and as an object for environmental enrichment. Furthermore, the possibilities of using automated home cage observations for e.g. behavioural phenotyping are discussed.

Altered circadian locomotor activity in APP23 mice: a model for BPSD disturbances

Over the past decade, clinical Alzheimer's disease research has been challenged with an increased interest in noncognitive symptomatology, commonly referred to as behavioural and psychological signs and symptoms of dementia (BPSD). In accordance, major attention is being paid to behavioural alterations in the phenotyping of transgenic mouse models. Besides an age-dependent decline of cognitive functions, the APP23 model was previously shown to exhibit cage activity disturbances, reminiscent of diurnal rhythm disturbances in Alzheimer patients. To further scrutinize these observations, circadian patterns of horizontal locomotor activity were assessed in 3-, 6- and 12-month-old APP23 mice and wild-type littermates in a test paradigm continuously recording cage activity over a period ranging from 1 to 3 days. At the age of 3 months, APP23 profiles resembled the wild-type pattern to a large extent, although minor differences were already noticeable. Six-month-old APP23 mice displayed an altered activity profile with a first indication of increased activity during the second half of the active phase, reminiscent of sundowning behaviour in Alzheimer patients. This bimodal overnight activity pattern became even more evident at the age of 12 months. The APP23 model was therefore shown to display an age-dependent development of cage activity disturbances and sundowning-like behaviour. A comparison is made with actigraphic recordings of human Alzheimer patients exhibiting sundowning behaviour. This first report of diurnal rhythm disturbances and sundowning-like phenomena in a transgenic mouse model greatly adds to the validity of the APP23 model.

The dark phase improves genetic discrimination for some high throughput mouse behavioral phenotyping

Dark-phase testing has previously been shown by others to improve the outcome of some 'classical' behavior test situations. However, the importance of such ethological correctness and the effect of the light/dark cycle on high throughput behavioral testing situations such as 'mutant vs. wild type' and 'screening', are less or unknown, respectively. These testing situations differ from the 'classical' in that they are designed primarily to discriminate between genetically different mice rather than provide a detailed assessment of ability or psychosocial state. Here we test the hypotheses that dark-phase testing affects the outcome of high throughput behavioral tests and that dark-phase testing improves discrimination between genetically distinct mice (C57BL/6J, 129S1/SvImJ and B6129F1) using high throughput behavioral tests. Our results demonstrate that, although all successful tests showed some effect of phase, only the SHIRPA primary screen, open-field test and motor learning on the rotarod showed improved strain discrimination in the dark phase. Surprisingly, the social interaction test did not show a clear benefit to either phase, and interestingly, the tail-flick test discriminated strains better in the light phase. However, since the preponderance of our data shows that dark-phase testing improves, or does not affect, strain discrimination, we conclude that for these strains and tests, dark-phase testing provided superior outcomes. If discrimination is not achieved in the dark phase, then light phase-testing would be undertaken.

Activity patterns as a correlate for sleep–wake behaviour in mice

Sleep-wake behaviour in mice is known to interact with various behavioural dimensions. Therefore, it is necessary to control for such dimensions when evaluating sleep in mice. The characterisation of sleep in rodents usually is based on EEG signals. Since this method demands the invasive implantation of electrodes, it cannot be integrated into general behavioural phenotyping procedures. Thus, non- or minimum-invasive methods are needed for the analysis of sleep-wake behaviour. Although physiological parameters, like for instance general locomotor activity, allow for the assessment of sleep-wake behaviour in mice, existing methods lack reliability especially in measuring stationary and three-dimensional activities. In this study, a small magnet was implanted subcutaneously near the neck muscles of mice and each movement of the magnet was registered via a sensor plate. For validation of the described method, the effects of sleep deprivation were evaluated by both the magnet and the EEG in parallel. Our results show that the data obtained via the subcutaneously implanted magnet represent a reliable and sensitive measurement of quantitative aspects of sleep-wake behaviour: spatial variation as well as stationary activities could be dissociated from sleep. Qualitative sleep characteristics were not detected. In summary, this minimum invasive method allows for the detection of quantitative alterations in sleep-wake behaviour in mice, thus, offering a useful, rapid pre-screen in animal sleep research.

Behavioral and physiological mouse assays for anxiety: a survey in nine mouse strains

In order to find better and new treatments for anxiety in humans, a variety of paradigms are used to study anxiety-related processes in rodents. We studied mice in two different anxiety-related assays: the physiological stress-induced hyperthermia (SIH) paradigm and the behavioral light-dark exploration (LD) test. Eight inbred strains (129S6/SvEvTac, 129S1/SvImJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, DBA/2J, and FVB/NJ) and one outbred strain (CD1-ICR) were tested in both assays repeatedly. This study describes the first strain survey for the SIH paradigm. All strains showed an SIH response, but the magnitude of the response varied between lines. The inbred strain distribution pattern for the behavioral responses in the LD assay was not correlated with the SIH response. The lack of a significant correlation suggests that there is no genetic relation between such responses. Mice could be tested repeatedly in both assays without affecting the results. A new paradigm, in which both assays were combined, elucidated that behavioral responses were not altered by segments of the SIH paradigm. In contrast, exposure to the light-dark box instead of the home-cage showed a strain-dependent effect on the physiological response. We conclude that a combination of behavioral and physiological responses might lead to a better understanding in anxiety-related processes.