Behavioral and pharmacological evaluation of a selectively bred mouse model of home cage hyperactivity

Functional kinome profiling reveals brain protein kinase signaling pathways and gene networks altered by acute voluntary exercise in rats

Regular exercise confers numerous physical and mental health benefits, yet individual variability in exercise participation and outcomes is still poorly understood. Uncovering the neurobiological mechanisms governing exercise behavior is essential for promoting physical activity and developing targeted interventions for related disorders. While genetic studies have provided insights, they often cannot account for protein-level alterations, such as changes in kinase activity. Here, we employ protein kinase activity profiling to delineate brain protein kinase activity and signaling networks modulated by acute voluntary exercise in rats. Focusing on the dorsal striatum, which governs voluntary exercise, as well as the hippocampus, which is susceptible to modulation by physical activity, we aim to understand the molecular basis of exercise behavior. Utilizing high throughput kinome array profiling and advanced pathway analyses, we identified protein kinase signaling pathways implicated in regulating voluntary exercise. Pathway analysis using Gene Ontology (GO) revealed significant alterations in 155 GO terms in the dorsal striatum and 206 GO terms in the hippocampus. Changes in kinase activity were observed in the striatum and hippocampus between the exercise (voluntary wheel running, VWR) and sedentary control rats. In both regions, global serine-threonine kinase (STK) activity was decreased, while global phospho-tyrosine kinase (PTK) activity was increased in VWR rats compared to control rats. We also identified specific kinases altered in VWR rats, including the IKappaB Kinase (IKK) and protein kinase delta (PKD) families. C-terminal src Kinase (CSK), epidermal growth factor (EGFR), and vascular endothelial growth factor receptor (VEGFR) tyrosine kinase were also enriched. These findings suggest regional heterogeneity of kinase activity following voluntary exercise, emphasizing potential molecular mechanisms underlying exercise behavior. This exploratory study lays the groundwork for future investigations into the causality of variations in exercise outcomes among individuals and different sexes, as well as the development of targeted interventions to promote physical activity and combat associated chronic diseases.

Social-defeat stress exposure during pregnancy induces abnormalities in spontaneous activity, sociality, and resilience to stress in offspring of mice

BACKGROUND

Environmental stress during prenatal periods can lead to neurodevelopmental disorders. Psychosocial stress can be studied using the social-defeat stress (SDS) animal model. However, the effects of prenatal exposure to SDS on the behavior of mature offspring mice have not been clarified. The present study assessed the spontaneous activity and social interaction of pups born to mothers exposed to SDS during gestation, as well as their post-maturity responses to environmental stimuli, focusing on changes in anxiety-like behavior following restraint stress exposure.

METHODS

Pregnant C57BL/6 J mice were subjected to SDS for 4 days, from E12.5-E15.5, using aggressive male ICR mice. We assessed the mature offspring (after 10 weeks of age) born to these mothers for spontaneous activity, anxiety-like behavior, and social interactions, and evaluated their activity levels post-maturity following restraint stress exposure.

RESULTS

The open field test (OF) indicated reduced travel distance and duration in the SDS group versus controls, whereas home-cage monitoring showed increased area traveled. In a novel environment, the SDS group showed a decrease in interest in stranger mice. In a multiple-animal rearing environment, the SDS group showed an increase in the frequency and number of contact with other individuals. Movement duration in the OF following restraint stress reduced significantly from 30 min to 4 h in the control versus SDS group.

CONCLUSIONS

Prenatal exposure to SDS can result in behavior resembling developmental disorders, impacting spontaneous activity and social interactions. Altered responses to stress suggest potential brain function abnormalities in offspring after maturation due to maternal SDS exposure.

Proteomic alteration in catalpol treatment of Alzheimer's disease by regulating HSPA5/ GPX4

Alzheimer's disease (AD), a chronic and progressive neurodegenerative disease, is characterized by the deposition of extracellular amyloid plaques and intracellular neurofibrillary tangles. Conventional anti-AD drugs exhibit high toxicity and adversely impact patients' quality of life. Therefore, novel treatments for AD are urgently required. In recent years, targeting ferroptosis through the modulation of lipid oxidation has emerged as a new approach in the treatment of neurodegenerative diseases. Catalpol, an iridoid glycoside isolated from the roots of Rehmannia glutinosa, has exhibited anti-inflammatory, antioxidant, and neuroprotective properties. Therefore, in this study, we investigated the protective effects and associated underlying mechanisms of catalpol in an APP/PS1 AD mouse model. Catalpol treatment significantly improved the cognitive capabilities and decreased Aβ1-40 and Aβ1-42 levels in mice. Morphological testing revealed that catalpol prevented neuronal loss and reduced mitochondrial swelling in the hippocampal CA1 region. Proteomic studies identified 2495 hippocampus proteins whose expression was associated with the mechanism of catalpol treatment, including 44 ferroptosis-related proteins. Bioinformatic analysis revealed that catalpol significantly increased the protein levels of HSPA5 and GPX4 in the hippocampus. Additionally, catalpol modulated biological pathways related to apoptosis, cytokine-mediated signaling, and ferroptosis. The considerable upregulation of HSPA5 and GPX4 with catalpol was further confirmed through western blotting. Catalpol exhibited neuroprotective effects through a variety of mechanisms. Among these, HSPA5 and GPX4, associated with ferroptosis, may play key roles in AD pathogenesis, and present promising therapeutic targets.

Can a Hybrid Line Break a Selection Limit on Behavioral Evolution in Mice?

Artificial selection yielded four replicate high runner (HR) lines of mice that reached apparent selection limits (~ threefold increase in wheel revolutions per day vs. four control lines), despite maintenance of additive genetic variance. After 68 generations, we used animal models to test for changes in additive-genetic variances and covariance of the two measured components (average speed and duration) of running distance. We also attempted to break the selection limit by crossing two HR lines, then continuing directional selection on this hybrid line and on the two parental lines for nine generations. The genetic correlation between speed and duration was positive in the base population, but evolved to be negative in the two parental HR lines. Although heritability for both speed and duration (but not distance) increased in the hybrid line, their genetic correlation remained negative. Hybrid F1 mice from generation 68 parents showed heterosis for running distance, which was lost in subsequent generations, and the hybrid line did not exceed the limit. Both male and female hybrids ran faster than parental lines for most generations, but running duration was intermediate or reduced, reflecting their negative genetic correlation. The evolved genetic trade-off between speed and duration may explain the inability for the hybrid line to break the selection limit for distance run, despite renewed additive genetic variance for at least one of its component traits.

An Shen Ding Zhi Ling Alleviates Symptoms of Attention Deficit Hyperactivity Disorder via Anti-Inflammatory Effects in Spontaneous Hypertensive Rats

Attention deficit hyperactivity disorder (ADHD) is a childhood-onset chronic neurobehavioral disorder, with multiple genetic and environmental risk factors. Chronic inflammation may be critical for the progression of ADHD. An Shen Ding Zhi Ling (ASDZL) decoction, a traditional Chinese medicine prescription, is clinically used in ADHD treatment. In this study, we investigated the effects and underlying anti-inflammatory mechanisms of ASDZL in young spontaneously hypertensive rats (SHRs), a widely used model of ADHD. SHRs were divided into the SHR model group (vehicle), atomoxetine group (4.56 mg/kg/day) and ASDZL group (21.25 g/kg/day), and orally administered for four weeks. Wistar Kyoto rats were used as controls (vehicle). We found that ASDZL significantly controlled hyperactivity and impulsivity, and improved spatial memory of SHRs in the open field test and Morris water maze test. ASDZL reduced the pro-inflammatory factors interleukin (IL)-1β, IL-4, IL-6, tumor necrosis factor (TNF)-α and monocyte chemoattractant protein (MCP)-1 and increased anti-inflammatory factor IL-10 in SHRs, and decreased the activation of microglia, astrocytes and mast cells in the prefrontal cortex (PFC) and hippocampus. Furthermore, the results indicated that ASDZL inhibited the neuroinflammatory response by protecting the integrity of the blood-brain barrier and suppressing the mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-κB signaling pathways of SHRs. In conclusion, these findings revealed that ASDZL attenuated ADHD symptoms in SHRs by reducing neuroinflammation.

Post-exposure environment modulates long-term developmental ethanol effects on behavior, neuroanatomy, and cortical oscillations

Developmental exposure to ethanol has a wide range of anatomical, cellular, physiological and behavioral impacts that can last throughout life. In humans, this cluster of effects is termed fetal alcohol spectrum disorder and is highly prevalent in western cultures. The ultimate expression of the effects of developmental ethanol exposure however can be influenced by post-exposure experience. Here we examined the effects of developmental binge exposure to ethanol (postnatal day 7) in C57BL/6By mice on a specific cohort of inter-related long-term outcomes including contextual memory, hippocampal parvalbumin-expressing neuron density, frontal cortex oscillations related to sleep-wake cycling including delta oscillation amplitude and sleep spindle density, and home-cage behavioral activity. When assessed in adults that were raised in standard housing, all of these factors were altered by early ethanol exposure compared to saline controls except home-cage activity. However, exposure to an enriched environment and exercise from weaning to postnatal day 90 reversed most of these ethanol-induced impairments including memory, CA1 but not dentate gyrus PV+ cell density, delta oscillations and sleep spindles, and enhanced home-cage behavioral activity in Saline- but not EtOH-treated mice. The results are discussed in terms of the inter-dependence of diverse developmental ethanol outcomes and potential mechanisms of post-exposure experiences to regulate those outcomes.

Early Life Trauma Has Lifelong Consequences for Sleep And Behavior

Sleep quality varies widely across individuals, especially during normal aging, with impaired sleep contributing to deficits in cognition and emotional regulation. Sleep can also be impacted by a variety of adverse events, including childhood adversity. Here we examined how early life adverse events impacted later life sleep structure and physiology using an animal model to test the relationship between early life adversity and sleep quality across the life span. Rat pups were exposed to an Adversity-Scarcity model from postnatal day 8–12, where insufficient bedding for nest building induces maternal maltreatment of pups. Polysomnography and sleep physiology were assessed in weaning, early adult and older adults. Early life adversity induced age-dependent disruptions in sleep and behavior, including lifelong spindle decreases and later life NREM sleep fragmentation. Given the importance of sleep in cognitive and emotional functions, these results highlight an important factor driving variation in sleep, cognition and emotion throughout the lifespan that suggest age-appropriate and trauma informed treatment of sleep problems.

Heterozygous loss of epilepsy gene KCNQ2 alters social, repetitive and exploratory behaviors

KCNQ/K_v7 channels conduct voltage‐dependent outward potassium currents that potently decrease neuronal excitability. Heterozygous inherited mutations in their principle subunits K_v7.2/KCNQ2 and K_v7.3/KCNQ3 cause benign familial neonatal epilepsy whereas patients with de novo heterozygous K_v7.2 mutations are associated with early‐onset epileptic encephalopathy and neurodevelopmental disorders characterized by intellectual disability, developmental delay and autism. However, the role of K_v7.2‐containing K_v7 channels in behaviors especially autism‐associated behaviors has not been described. Because pathogenic K_v7.2 mutations in patients are typically heterozygous loss‐of‐function mutations, we investigated the contributions of K_v7.2 to exploratory, social, repetitive and compulsive‐like behaviors by behavioral phenotyping of both male and female KCNQ2^+/− mice that were heterozygous null for the KCNQ2 gene. Compared with their wild‐type littermates, male and female KCNQ2^+/− mice displayed increased locomotor activity in their home cage during the light phase but not the dark phase and showed no difference in motor coordination, suggesting hyperactivity during the inactive light phase. In the dark phase, KCNQ2^+/− group showed enhanced exploratory behaviors, and repetitive grooming but decreased sociability with sex differences in the degree of these behaviors. While male KCNQ2^+/− mice displayed enhanced compulsive‐like behavior and social dominance, female KCNQ2^+/− mice did not. In addition to elevated seizure susceptibility, our findings together indicate that heterozygous loss of K_v7.2 induces behavioral abnormalities including autism‐associated behaviors such as reduced sociability and enhanced repetitive behaviors. Therefore, our study is the first to provide a tangible link between loss‐of‐function K_v7.2 mutations and the behavioral comorbidities of K_v7.2‐associated epilepsy.

Baicalin regulates the dopamine system to control the core symptoms of ADHD

We aimed to test the therapeutic effects of baicalin on attention deficit hyperactivity disorder (ADHD) in an animal model and to explain the potential mechanism. We investigated the therapeutic effects and mechanisms of baicalin in a spontaneously hypertensive rat (SHR) model of ADHD depending on the dopamine (DA) deficit theory. In this study, fifty SHRs were randomly divided into five groups: methylphenidate (MPH), baicalin (50 mg/kg, 100 mg/kg, or 150 mg/kg), and saline-treated. Ten Wistar Kyoto (WKY) rats were used as controls. All rats were orally administered the treatment for four weeks. Motor activity, spatial learning and memory ability were assessed with the open-field and Morris water-maze tests. The mRNA and protein levels of tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), synaptosomal-associated protein of molecular mass 25kD (SNAP25) and synataxin 1a in synaptosomes were detected with real-time polymerase chain reaction (PCR) and Western blot. In addition, DA levels were measured in the prefrontal cortex and striatum. The results indicated that both MPH and baicalin at doses of 150 mg/kg and 100 mg/kg significantly decreased the hyperactivity and improved the spatial learning memory deficit in the SHRs and increased the synaptosomal mRNA and protein levels of TH, SNAP25, VMAT2 and synataxin 1a compared with saline treatment. MPH significantly increased DA levels in both the prefrontal cortex (PFC) and striatum, while baicalin significantly increased DA levels only in the striatum. The results of the present study showed that baicalin treatment was effective for controlling the core symptoms of ADHD. Baicalin increased DA levels only in the striatum, which suggested that baicalin may target the striatum. The increased DA levels may partially be attributed to the increased mRNA and protein expression of TH, SNAP25, VMAT2, and syntaxin 1a. Therefore, these results suggested that the pharmacological effects of baicalin were associated with the synthesis, vesicular localization, and release of DA and might be effective in treating ADHD. However, further studies are required to better understand the molecular mechanisms underlying these findings.

Interplay Between Amphetamine and Activity Level in Gene Networks of the Mouse Striatum

The psychostimulant amphetamine can be prescribed to ameliorate the symptoms of narcolepsy, attention-deficit hyperactivity disorder and to facilitate weight loss. This stimulant can also have negative effects including toxicity and addiction risk. The impact of amphetamine on gene networks is partially understood and this study addresses this gap in consideration of the physical activity. The striata of mice exposed to either amphetamine or saline treatment were compared in a mouse line selected for home cage physical overactivity, a phenotype that can be mitigated with amphetamine, and in a contemporary control line using RNA-seq. Genes presenting opposite expression patterns between treatments across lines included a pseudogene of coiled-coil-helix-coiled-coil-helix domain containing 2 gene (Chchd2), ribonuclease P RNA component H1 (Rpph1), short stature homeobox 2 (Shox2), transient receptor potential melastatin 6 (Trpm6), and tumor necrosis factor receptor superfamily, member 9 (Tnfrsf9). Genes presenting consistent treatment patterns across lines, albeit at different levels of significance included cholecystokinin (Cck), vasoactive intestinal polypeptide (Vip), arginine vasopressin (Avp), oxytocin/neurophysin (Oxt), thyrotropin releasing hormone (Trh), neurotensin (Nts), angiotensinogen (Agt), galanin (Gal), prolactin receptor (Prlr), and calcitonin receptor (Calcr). Potassium inwardly rectifying channel, subfamily J, member 6 (Kcnj6), and retinoic acid-related (RAR)-related orphan receptor alpha (Rora) were similarly differentially expressed between treatments across lines. Functional categories enriched among the genes presenting line-dependent amphetamine effect included genes coding for neuropeptides and associated with memory and neuroplasticity and synaptic signaling, energy, and redox processes. A line-dependent association between amphetamine exposure and the synaptic signaling genes neurogranin (Nrgn) and synaptic membrane exocytosis 1(Rims1) was highlighted in the gene networks. Our findings advance the understanding of molecular players and networks affected by amphetamine in support of the development of activity-targeted therapies that may capitalize on the benefits of this psychostimulant.

A new perspective of the hippocampus in the origin of exercise-brain interactions

Exercising regularly is a highly effective strategy for maintaining cognitive health throughout the lifespan. Over the last 20 years, many molecular, physiological and structural changes have been documented in response to aerobic exercise training in humans and animals, particularly in the hippocampus. However, how exercise produces such neurological changes remains elusive. A recent line of investigation has suggested that muscle-derived circulating factors cross into the brain and may be the key agents driving enhancement in synaptic plasticity and hippocampal neurogenesis from aerobic exercise. Alternatively, or concurrently, the signals might originate from within the brain itself. Physical activity also produces instantaneous and robust neuronal activation of the hippocampal formation and the generation of theta oscillations which are closely correlated with the force of movements. The repeated acute activation of the hippocampus during physical movement is likely critical for inducing the long-term neuroadaptations from exercise. Here we review the evidence which establishes the association between physical movement and hippocampal neuronal activation and discuss implications for long-term benefits of physical activity on brain function.

Divergent selection on home pen locomotor activity in a chicken model: Selection program, genetic parameters and direct response on activity and body weight

General locomotor activity (GLA) in poultry has attracted attention, as it negatively influences production costs (energy expenditure and feed consumption) and welfare parameters (bone strength, litter quality, feather pecking and cannibalism). Laying hen lines diverging in the average level of spontaneous locomotor activity in the home pen were developed by genetic selection using the founder New Hampshire line. Activity was recorded using RFID technology at around five weeks of age during four to five days in the home pen. After initial phenotyping, the least active birds were selected for the low activity line and the most active for the high activity line, with no gene transfer between lines. In each of six generations, approximately ten sires were mated to twenty dams producing 158 to 334 offspring per line per generation. The response to selection was rapid and of a considerable magnitude. In sixth generation, the level of GLA was approximately halved in the low and doubled in the high line compared to the control (7.2, 14.9 and 28.7 recordings/h). Estimated heritability of locomotor activity in the low and high line was 0.38 and 0.33, respectively. Males, in general, were more active than females. High line birds were significantly heavier than low line birds. In fourth, fifth, and sixth generation, low as well as high line birds were lighter than control line birds. This selection experiment demonstrates variation in heritability for GLA and, as a result, genetically diverged lines have been developed. These lines can be used as models for further studies of underlying physiological, neural and molecular genetic mechanisms of spontaneous locomotor activity.

[Effect of baicalin on behavioral characteristics of rats with attention deficit hyperactivity disorder]

OBJECTIVE

To investigate the effect of baicalin on the behavioral characteristics of rats with attention deficit hyperactivity disorder (ADHD), and to provide a basis for further research on baicalin in the treatment of ADHD.

METHODS

A total of 40 SHR rats were randomly divided into model group, methylphenidate hydrochloride (MPH) group, and low-, medium-, and high-dose baicalin groups, with 8 rats in each group. Eight WKY rats were selected as normal control group. The rats in the MPH group (0.07 mg/mL) and the low- (3.33 mg/mL), medium- (6.67 mg/mL), and high-dose (10 mg/mL) baicalin groups were given the corresponding drugs (1.5 mL/100 g) by gavage twice a day, and those in the normal control group and the model group were given an equal volume of normal saline by gavage twice a day. The course of treatment was 4 weeks for all groups. The open field test was performed to observe total moving distance and average moving speed on day 0 of experiment and at 7, 14, 21, and 28 days after gavage and to evaluate the control effects of drugs on hyperactivity and impulsive behavior. The Morris water maze test was used to observe the latency, time spent in the target quadrant, and number of platform crossings and to evaluate the effects of drugs on attention.

RESULTS

The open field test showed that the model group and the drug treatment groups had a significantly longer total moving distance and a significantly higher average moving speed than the normal control group on day 0 (P<0.05). On day 7, the MPH group had significant reductions in total moving distance and average moving speed compared with the model group (P<0.05). On day 14, the MPH group and the high-dose baicalin group had significant reductions in total moving distance and average moving speed compared with the model group (P<0.05). The data on days 21 and 28 showed that compared with the model group, the low-, medium-, and high-dose baicalin groups had gradual reductions in total moving distance and average moving speed (P<0.05). The water maze test showed that compared with the model group, the MPH group and the medium- and high-dose baicalin groups had a significantly longer time spent in the target quadrant (P<0.05), and the MPH group and the high-dose baicalin group had a significantly higher proportion of the moving distance in the target quadrant in total moving distance (P<0.05). The high-dose baicalin group had the highest number of platform crossings among all groups (P<0.05).

CONCLUSIONS

Both baicalin and MPH can regulate the motor ability and learning and memory abilities of SHR rats with ADHD and thus control the core symptoms of ADHD, i.e., hyperactivity, impulsive behavior, and inattention. Baicalin exerts its effect in a dose-dependent manner, and high-dose baicalin has the most significant effect, but compared with MPH, it needs a longer time to play its therapeutic effect.

Analysis of locomotor behavior in the German Mouse Clinic

BACKGROUND

Generation and phenotyping of mutant mouse models continues to increase along with the search for the most efficient phenotyping tests. Here we asked if a combination of different locomotor tests is necessary for comprehensive locomotor phenotyping, or if a large data set from an automated gait analysis with the CatWalk system would suffice.

NEW METHOD

First we endeavored to meaningfully reduce the large CatWalk data set by Principal Component Analysis (PCA) to decide on the most relevant parameters. We analyzed the influence of sex, body weight, genetic background and age. Then a combination of different locomotor tests was analyzed to investigate the possibility of redundancy between tests.

RESULT

The extracted 10 components describe 80% of the total variance in the CatWalk, characterizing different aspects of gait. With these, effects of CatWalk version, sex, body weight, age and genetic background were detected. In addition, the PCA on a combination of locomotor tests suggests that these are independent without significant redundancy in their locomotor measures.

COMPARISON WITH EXISTING METHODS

The PCA has permitted the refinement of the highly dimensional CatWalk (and other tests) data set for the extraction of individual component scores and subsequent analysis.

CONCLUSION

The outcome of the PCA suggests the possibility to focus on measures of the front and hind paws, and one measure of coordination in future experiments to detect phenotypic differences. Furthermore, although the CatWalk is sensitive for detecting locomotor phenotypes pertaining to gait, it is necessary to include other tests for comprehensive locomotor phenotyping.

Selection for high aerobic capacity has no protective effect against obesity in laboratory mice

Aerobic capacity (VO_2max measured during intensive physical exercise) both trained and intrinsic (i.e. genetically determined) has recently been deemed a good predictor of cardiometabolic risks. However, the underlying mechanisms linking VO_2max and health risk factors are not entirely clear, as it seems that not VO_2max per se, but rather some correlated traits, like spontaneous physical activity (SPA) are responsible for sustaining the lean phenotype. Here we investigated the link between genetically determined aerobic capacity, SPA and resistance to diet-induced health risks using replicated lines of mice selected for high aerobic capacity during swimming in mid-cold water (25°C) and Randomly Bred control mice. After four months of consumption of the western type HFat and HCarb diets and no forced nor voluntary training, we found no evidence of protective effects of intrinsic high VO_2max. The Selected mice displayed similar levels of blood glucose, cholesterol, triglycerides and body fat as the Random Bred control animals. Most notably we found no correlation between VO_2max and SPA levels. Our results therefore call into question the ubiquity of VO_2max as a predictor of metabolic health and leanness, at least in animal models.

A new mouse model of ADHD for medication development

ADHD is a major societal problem with increasing incidence and a stagnant track record for treatment advances. A lack of appropriate animal models has partly contributed to the incremental advance of this field. Hence, our goal was to generate a novel mouse model that could be useful for ADHD medication development. We reasoned that hyperactivity is a core feature of ADHD that could easily be bred into a population, but to what extent other hallmark features of ADHD would appear as correlated responses was unknown. Hence, starting from a heterogeneous population, we applied within-family selection over 16 generations to produce a High-Active line, while simultaneously maintaining an unselected line to serve as the Control. We discovered that the High-Active line demonstrated motor impulsivity in two different versions of the Go/No-go test, which was ameliorated with a low dose of amphetamine, and further displayed hypoactivation of the prefrontal cortex and dysregulated cerebellar vermal activation as indexed by c-Fos immunohistochemical staining. We conclude that the High-Active line represents a valid model for the Hyperactive-Impulsive subtype of ADHD and therefore may be used in future studies to advance our understanding of the etiology of ADHD and screen novel compounds for its treatment.

Cerebellum Transcriptome of Mice Bred for High Voluntary Activity Offers Insights into Locomotor Control and Reward-Dependent Behaviors

The role of the cerebellum in motivation and addictive behaviors is less understood than that in control and coordination of movements. High running can be a self-rewarding behavior exhibiting addictive properties. Changes in the cerebellum transcriptional networks of mice from a line selectively bred for High voluntary running (H) were profiled relative to an unselected Control (C) line. The environmental modulation of these changes was assessed both in activity environments corresponding to 7 days of Free (F) access to running wheel and to Blocked (B) access on day 7. Overall, 457 genes exhibited a significant (FDR-adjusted P-value < 0.05) genotype-by-environment interaction effect, indicating that activity genotype differences in gene expression depend on environmental access to running. Among these genes, network analysis highlighted 6 genes (Nrgn, Drd2, Rxrg, Gda, Adora2a, and Rab40b) connected by their products that displayed opposite expression patterns in the activity genotype contrast within the B and F environments. The comparison of network expression topologies suggests that selection for high voluntary running is linked to a predominant dysregulation of hub genes in the F environment that enables running whereas a dysregulation of ancillary genes is favored in the B environment that blocks running. Genes associated with locomotor regulation, signaling pathways, reward-processing, goal-focused, and reward-dependent behaviors exhibited significant genotype-by-environment interaction (e.g. Pak6, Adora2a, Drd2, and Arhgap8). Neuropeptide genes including Adcyap1, Cck, Sst, Vgf, Npy, Nts, Penk, and Tac2 and related receptor genes also exhibited significant genotype-by-environment interaction. The majority of the 183 differentially expressed genes between activity genotypes (e.g. Drd1) were under-expressed in C relative to H genotypes and were also under-expressed in B relative to F environments. Our findings indicate that the high voluntary running mouse line studied is a helpful model for understanding the molecular mechanisms in the cerebellum that influence locomotor control and reward-dependent behaviors.

Early-Life Effects on Adult Physical Activity: Concepts, Relevance, and Experimental Approaches

Locomotion is a defining characteristic of animal life and plays a crucial role in most behaviors. Locomotion involves physical activity, which can have far-reaching effects on physiology and neurobiology, both acutely and chronically. In human populations and in laboratory rodents, higher levels of physical activity are generally associated with positive health outcomes, although excessive exercise can have adverse consequences. Whether and how such relationships occur in wild animals is unknown. Behavioral variation among individuals arises from genetic and environmental factors and their interactions as well as from developmental programming (persistent effects of early-life environment). Although tremendous progress has been made in identifying genetic and environmental influences on individual differences in behavior, early-life effects are not well understood. Early-life effects can in some cases persist across multiple generations following a single exposure and, in principle, may constrain or facilitate the rate of evolution at multiple levels of biological organization. Understanding the mechanisms of such transgenerational effects (e.g., exposure to stress hormones in utero, inherited epigenetic alterations) may prove crucial to explaining unexpected and/or sex-specific responses to selection as well as limits to adaptation. One area receiving increased attention is early-life effects on adult physical activity. Correlational data from epidemiological studies suggest that early-life nutritional stress can (adversely) affect adult human activity levels and associated physiological traits (e.g., body composition, metabolic health). The few existing studies of laboratory rodents demonstrate that both maternal and early-life exercise can affect adult levels of physical activity and related phenotypes. Going forward, rodents offer many opportunities for experimental studies of (multigenerational) early-life effects, including studies that use maternal exposures and cross-fostering designs.

Hormones and the Evolution of Complex Traits: Insights from Artificial Selection on Behavior

Although behavior may often be a fairly direct target of natural or sexual selection, it cannot evolve without changes in subordinate traits that cause or permit its expression. In principle, changes in endocrine function could be a common mechanism underlying behavioral evolution because they are well positioned to mediate integrated responses to behavioral selection. More specifically, hormones can influence both motivational (e.g., brain) and performance (e.g., muscles) components of behavior simultaneously and in a coordinated fashion. If the endocrine system is often "used" as a general mechanism to effect responses to selection, then correlated responses in other aspects of behavior, life history, and organismal performance (e.g., locomotor abilities) should commonly occur because any cell with appropriate receptors could be affected. Ways in which behavior coadapts with other aspects of the phenotype can be studied directly through artificial selection and experimental evolution. Several studies have targeted rodent behavior for selective breeding and reported changes in other aspects of behavior, life history, and lower-level effectors of these organismal traits, including endocrine function. One example involves selection for high levels of voluntary wheel running, one aspect of physical activity, in four replicate High Runner (HR) lines of mice. Circulating levels of several hormones (including insulin, testosterone, thyroxine, triiodothyronine) have been characterized, three of which-corticosterone, leptin, and adiponectin-differ between HR and control lines, depending on sex, age, and generation. Potential changes in circulating levels of other behaviorally and metabolically relevant hormones, as well as in other components of the endocrine system (e.g., receptors), have yet to be examined. Overall, results to date identify promising avenues for further studies on the endocrine basis of activity levels.

Long-lasting impairments in adult neurogenesis, spatial learning and memory from a standard chemotherapy regimen used to treat breast cancer

The negative impact of chemotherapy on cognitive function in cancer patients has gained increasing attention in the last decade. Whilst the short-term acute effects on cognition are expected following chemotherapy, the persistence of such impairments in the long-term is still in question. This is despite clinical evidence indicating cognitive difficulties may persist well beyond treatment and affect quality of life. In the present study, we assessed the long-term (3 months) cognitive impact of chemotherapy in a mouse model intended to mimic the human female post-menopausal population receiving chemotherapy for breast cancer. Ovariectomized, female, C57BL/6J mice received two doses of Doxorubicin, Cyclophosphamide, and 5-Fluorouracil or saline vehicle (control), separated by one week. During this interval, mice received BrdU injections to label dividing cells. Results indicate a persistent impairment in learning and recall (1h, 24h and 48h) on the Morris water maze, reduced survival and differentiation of new neurons (BrdU+/NeuN+), and a persistent decline in proliferation of new cells (Ki67(+)) in the dentate gyrus. Locomotor activity, motor performance, and anxiety-like behavior were unaffected. We further evaluated the efficacy of a diet enriched in omega-3-fatty acids (DHA+EPA+DPA), in reversing long-term chemotherapy deficits but no rescue was observed. The model described produces long-term cognitive and cellular impairments from chemotherapy that mimic those observed in humans. It could be useful for identifying mechanisms of action and to test further the ability of lifestyle interventions (e.g., diet) for ameliorating chemotherapy-induced cognitive impairments.

The impact of maternal neglect on genetic hyperactivity

Early environmental conditions are increasingly appreciated as critical in shaping behavior and cognition. Evidence suggests that stressful rearing environments can have an enduring impact on behaviors in adulthood, but few studies have explored the possibility that rearing environment could exacerbate genetic hyperactivity disorders. Uncovering a strong environmental influence on the transmission of hyperactivity could provide novel avenues for translational research. Recently we developed a selectively bred High-Active line of mice to model ADHD, providing a unique resource to address the question of environmental transmission. The High-Active line demonstrates transgenerational hyperactivity, but the influence of the postnatal environment (i.e. maternal care provided by dams) on hyperactivity had not been systemically quantified. This study employed a cross-fostering method to simultaneously address 1) whether High-Active and Control pups are provided with similar levels of care in the early environment, and 2) whether any differences in rearing environment influence hyperactive behavior. High-Active dams demonstrated impairment in all measures of maternal competence relative to Controls, which reduced survival rates and significantly reduced the body mass of offspring in early life and at weaning. While the deteriorated postnatal environment provided by High-Active dams was ultimately sufficient to depress Control activity, the hyperactivity of High-Active offspring remained unaffected by fostering condition. These data not only confirm the power of genetics to influence hyperactivity across generations, but also provide evidence that early rearing environments may not have a significant impact on the extreme end of hyperactive phenotypes.

Effect of calorie restriction on spontaneous physical activity and body mass in mice divergently selected for basal metabolic rate (BMR)

Spontaneous physical activity (SPA) represents an important component of daily energy expenditures in animals and humans. Intra-specific variation in SPA may be related to the susceptibility to metabolic disease or obesity. In particular, reduced SPA under conditions of limited food availability may conserve energy and prevent loss of body and fat mass ('thrifty genotype hypothesis'). However, both SPA and its changes during food restriction show wide inter-individual variations. We studied the effect of 30% caloric restriction (CR) on SPA in laboratory mice divergently selected for high (H-BMR) and low (L-BMR) basal metabolic rate. Selection increased SPA in the H-BMR line but did not change it in the L-BMR mice. This effect reflected changes in SPA intensity but not SPA duration. CR increased SPA intensity more strongly in the L-BMR line than in the H-BMR line and significantly modified the temporal variation of SPA. However, the initial between-line differences in SPA were not affected by CR. Loss of body mass during CR did not differ between both lines. Our results show that the H-BMR mice can maintain their genetically determined high SPA under conditions of reduced food intake without sacrificing their body mass. We hypothesize that this pattern may reflect the higher flexibility in the energy budget in the H-BMR line, as we showed previously that mice from this line reduced their BMR during CR. These energy savings may allow for the maintenance of elevated SPA in spite of reduced food intake. We conclude that the effect of CR on SPA is in large part determined by the initial level of BMR, whose variation may account for the lack of universal pattern of behavioural responses to CR.

Genetic approaches in comparative and evolutionary physiology

Whole animal physiological performance is highly polygenic and highly plastic, and the same is generally true for the many subordinate traits that underlie performance capacities. Quantitative genetics, therefore, provides an appropriate framework for the analysis of physiological phenotypes and can be used to infer the microevolutionary processes that have shaped patterns of trait variation within and among species. In cases where specific genes are known to contribute to variation in physiological traits, analyses of intraspecific polymorphism and interspecific divergence can reveal molecular mechanisms of functional evolution and can provide insights into the possible adaptive significance of observed sequence changes. In this review, we explain how the tools and theory of quantitative genetics, population genetics, and molecular evolution can inform our understanding of mechanism and process in physiological evolution. For example, lab-based studies of polygenic inheritance can be integrated with field-based studies of trait variation and survivorship to measure selection in the wild, thereby providing direct insights into the adaptive significance of physiological variation. Analyses of quantitative genetic variation in selection experiments can be used to probe interrelationships among traits and the genetic basis of physiological trade-offs and constraints. We review approaches for characterizing the genetic architecture of physiological traits, including linkage mapping and association mapping, and systems approaches for dissecting intermediary steps in the chain of causation between genotype and phenotype. We also discuss the promise and limitations of population genomic approaches for inferring adaptation at specific loci. We end by highlighting the role of organismal physiology in the functional synthesis of evolutionary biology.

Effects of voluntary exercise on spontaneous physical activity and food consumption in mice: Results from an artificial selection experiment

We evaluated the effect of voluntary exercise on spontaneous physical activity (SPA) and food consumption in mice from 4 replicate lines bred for 57 generations for high voluntary wheel running (HR) and from 4 non-selected control (C) lines. Beginning at ~24 days of age, mice were housed in standard cages or in cages with attached wheels. Wheel activity and SPA were monitored in 1-min intervals. Data from the 8th week of the experiment were analyzed because mice were sexually mature and had plateaued in body mass, weekly wheel running distance, SPA, and food consumption. Body mass, length, and masses of the retroperitoneal fat pad, liver, and heart were recorded after the 13th week. SPA of both HR and C mice decreased with wheel access, due to reductions in both duration and average intensity of SPA. However, total activity duration (SPA+wheel running; min/day) was ~1/3 greater when mice were housed with wheels, and food consumption was significantly increased. Overall, food consumption in both HR and C mice was more strongly affected by wheel running than by SPA. Duration of wheel running had a stronger effect than average speed, but the opposite was true for SPA. With body mass as a covariate, chronic wheel access significantly reduced fat pad mass and increased heart mass in both HR and C mice. Given that both HR and C mice housed with wheels had increased food consumption, the energetic cost of wheel running was not fully compensated by concomitant reductions in SPA. The experiment demonstrates that both duration and intensity of both wheel running and SPA were significant predictors of food consumption. This sort of detailed analysis of the effects of different aspects of physical activity on food consumption has not previously been reported for a non-human animal, and it sets the stage for longitudinal examination of energy balance and its components in rodent models.