Voluntary wheel running access produces opposite effects in male and female rats on both palatable diet consumption and associated ventral striatal opioid- and dopamine-related gene expression.

The relationship between physical activity levels and feeding behaviors has been a focus of preclinical research for decades, yet this interaction has only recently been explored for potential sex differences. The aim of the present study was to isolate sex-dependent effects of voluntary wheel running (RUN) vs. sedentary locked wheel (SED) home cage conditions on palatability-driven feeding behavior using a 2-diet choice task between standard chow and a high-fat diet. The sex-dependent effects of physical activity on feeding behavior were examined following a within-subject novel reversal design of physical activity conditions (i.e., RUN > SED > RUN), to assess temporal sensitivity of the interaction. Following the final 2 weeks of reestablished and sustained RUN vs. SED conditions in separate groups of both males and females, reward-related opioid and dopamine gene expression within the nucleus accumbens (Acb) brain region were analyzed. Results demonstrated that the initial RUN > SED transition led to sex-dependent effects of SED condition, as males increased, and females decreased their high fat consumption, compared to their respective high fat consumption during previous RUN condition phase. Following reintroduction to the RUN condition, males decreased, and females increased their high fat consumption, compared to their separate SED control group. Last, sex-dependent shifts in ventral striatal opioid- and dopamine-related gene expression were observed to parallel the behavioral effects. The major findings of the study reveal that SED and RUN home cage conditions shift palatability-driven feeding in the opposite direction for males and females, these effects are sensitive to reversal, and these sex-dependent feeding behaviors track sex-dependent changes to critical reward-related gene expression patterns in the Acb. Considering the present high rates of sedentary behavior and obesity, furthering our understanding of the interaction between physical activity (or lack thereof) and feeding behavior should be a priority, especially in the context of these divergent sex-dependent outcomes.

A meta-analysis of whole-body and heart mass effect sizes from a long-term artificial selection experiment for high voluntary exercise.

Selection experiments play an increasingly important role in comparative and evolutionary physiology. However, selection experiments can be limited by relatively low statistical power, in part because replicate line is the experimental unit for analyses of direct or correlated responses (rather than number of individuals measured). One way to increase the ability to detect correlated responses is through a meta-analysis of studies for a given trait across multiple generations. To demonstrate this, we applied meta-analytic techniques to two traits (body mass and heart ventricle mass, with body mass as a covariate) from a long-term artificial selection experiment for high voluntary wheel-running behavior. In this experiment, all 4 replicate High Runner (HR) lines reached apparent selection limits around generations 17-27, running approximately 2.5-3-fold more revolutions/day than the 4 non-selected Control (C) lines. Although both traits would also be expected to change in HR lines (relative heart size expected to increase, expected direction for body mass is less clear), the statistical significance has varied, despite repeated measurements. We compiled information from 33 unique studies and calculated a measure of effect size (Pearson's R). Our results indicate that, despite a lack of statistical significance in most generations, HR mice have evolved larger hearts and smaller bodies relative to Controls. Moreover, plateaus in effect sizes for both traits coincides with the generational range during which the selection limit for wheel-running behavior was reached. Finally, since the selection limit, absolute effect sizes for body mass and heart ventricle mass have gotten smaller (i.e., closer to 0).

Wheel-Running Exercise Alleviates Anxiety-Like Behavior via Down-Regulating S-Nitrosylation of Gephyrin in the Basolateral Amygdala of Male Rats.

Physical exercise has beneficial effect on anxiety disorders, but the underlying molecular mechanism remains largely unknown. Here, it is demonstrated that physical exercise can downregulate the S-nitrosylation of gephyrin (SNO-gephyrin) in the basolateral amygdala (BLA) to exert anxiolytic effects. It is found that the level of SNO-gephyrin is significantly increased in the BLA of high-anxiety rats and a downregulation of SNO-gephyrin at cysteines 212 and 284 produced anxiolytic effect. Mechanistically, inhibition of SNO-gephyrin by either Cys212 or Cys284 mutations increased the surface expression of GABAAR γ2 and the subsequent GABAergic neurotransmission, exerting anxiolytic effect in male rats. On the other side, overexpression of neuronal nitric oxide synthase in the BLA abolished the anxiolytic-like effects of physical exercise. This study reveals a key role of downregulating SNO-gephyrin in the anxiolytic effects of physical exercise, providing a new explanation for protein post-translational modifications in the brain after exercise.

Multiple Sex- and Circuit-Specific Mechanisms Underlie Exercise-Induced Stress Resistance.

Prior physical activity reduces the risk of future stress-related mental health disorders including depression, anxiety, and post-traumatic stress disorder. Rodents allowed to engage in voluntary wheel running are similarly protected from behavioral consequences of stress. The present review summarizes current knowledge on mechanisms underlying exercise-induced stress resistance. A conceptual framework involving the development (during exercise) and expression (during stress) of stress resistance from exercise is proposed. During the development of stress resistance, adaptations involving multiple exercise signals and molecular mediators occur within neural circuits orchestrating various components of the stress response, which then respond differently to stress during the expression of stress resistance. Recent data indicate that the development and expression of stress resistance from exercise involve multiple independent mechanisms that depend on sex, stressor severity, and behavioral outcome. Recent insight into the role of the prefrontal cortex in exercise-induced stress resistance illustrates these multiple mechanisms. This knowledge has important implications for the design of future experiments aimed at identifying the mechanisms underlying exercise-induced stress resistance.

The Estrous Cycle Coordinates the Circadian Rhythm of Eating Behavior in Mice.

The estrous cycle regulates rhythms of locomotor activity, body temperature, and circadian gene expression. In female mice, activity increases on the night of proestrus, when elevated estrogens cause ovulation. Exogenous estradiol regulates eating behavior rhythms in female mice fed a high-fat diet, but it is unknown whether endogenous estrogens regulate eating rhythms. In this study, we investigated whether diurnal and circadian eating behavior rhythms change systematically across the estrous cycle. We first studied diurnal eating behavior rhythms in female C57BL/6J mice in 12L:12D. Estrous cycle stages were determined by vaginal cytology while eating behavior and wheel revolutions were continuously measured. The mice had regular 4- to 5-day estrous cycles. Consistent with prior studies, the greatest number of wheel revolutions occurred on the night of proestrus into estrus when systemic levels of estrogens peak. The amplitude, or robustness, of the eating behavior rhythm also fluctuated with 4- to 5-day cycles and peaked primarily during proestrus or estrus. The phases of eating behavior rhythms fluctuated, but not at 4- or 5-day intervals, and phases did not correlate with estrous cycle stages. After ovariectomy, the eating behavior rhythm amplitude fluctuated at irregular intervals. In constant darkness, the amplitude of the circadian eating behavior rhythm peaked every 4 or 5 days and coincided with the circadian day that had the greatest number of wheel revolutions, a marker of proestrus. These data suggest that fluctuations of ovarian hormones across the estrous cycle temporally organize the robustness of circadian eating behavior rhythms so that it peaks during ovulation and sexual receptivity.

The improvement effect of exercise on rats with chronic stress-induced depression-like behavior: a discussion based on the kynurenine pathway.

OBJECTIVE: To observe the effects of 4 weeks of voluntary wheel running on depressive-like behavior in a rat chronic stress-induced depression model to explore the anti-depressive mechanism of exercise. METHODS: In this observational study, 36 Sprague-Dawley rats were randomly divided into control, stress model, and stress exercise groups (12 rats/group). The control group received no intervention, and the stress model and stress exercise group rats underwent chronic mild unpredictable stress and isolation. The stress exercise group rats also underwent 4 weeks of voluntary wheel running. Behavioral changes and hippocampal protein and mRNA expression levels were detected. RESULTS: Voluntary wheel running significantly increased horizontal and vertical movements, sucrose intake, and the sucrose preference percentage and reduced immobility time in the forced swimming test in depression model rats. The hippocampal tumor necrosis factor-α, interleukin (IL)-6, IL-1ß, and quinolinic acid levels were significantly decreased, while the IL-4, IL-10, and kynurenic acid levels were significantly increased. Kynurenine-3-monooxygenase and 3-hydroxyanthranilate-3, 4-dioxygenase mRNA levels were downregulated, and kynurenine aminotransferase mRNA was upregulated. CONCLUSION: Voluntary wheel running improved depressive-like behavior in depression model rats. The mechanism may be related to a kynurenine pathway metabolite level imbalance, which has neurotoxic and neuroprotective effects, caused by long-term voluntary wheel running.

Diurnal sex differences in morphine withdrawal revealed by continuous assessment of voluntary home cage wheel running in the rat.

Animal studies modeling recreational opioid use show more severe withdrawal symptoms in male compared to female rats, whereas our study modeling opioid use for pain showed a greater withdrawal-induced decrease in wheel running in female rats. The objective of this experiment was to determine whether sex differences in spontaneous morphine withdrawal are caused by differences in assessment method (i.e., wheel running vs. somatic symptoms). Twice daily injections of morphine (5 - 20 mg/kg, s.c.) for 5 days produced a dose and time dependent decrease in wheel running that was greater in male compared to female rats. Termination of morphine administration resulted in an overall decrease in running and a decrease in the amount of running during the dark phase of the light cycle from 95 % to approximately 75 %. In male rats, this decrease in the percent of dark running was caused by a large decrease in dark phase running, whereas female rats had a slightly higher increase in light phase running. Withdrawal also reduced maximal running speed and caused a decrease in body weight that was larger in male than female rats. Withdrawal symptoms were greatest on the day following the last morphine injection, but persisted for all 3 days of assessment. Morphine withdrawal produced a greater decrease in dark phase wheel running and body weight in male rats and a greater increase in light phase running in female rats. Voluntary home cage wheel running provides a continuous measure of opioid withdrawal that is consistent with other measures of opioid withdrawal.

Wheel Running During Pregnancy Alleviates Anxiety-and Depression-Like Behaviors During the Postpartum Period in Mice: The Roles of NLRP3 Neuroinflammasome Activation, Prolactin, and the Prolactin Receptor in the Hippocampus.

Despite the increase in the prevalence of postpartum depression among maternal disorder, its treatment outcomes remain suboptimal. Studies have shown that exercise can reduce postpartum depressive episodes in the mother, but the effects of exercise during pregnancy on maternal behavior and the potential mechanisms involved remain poorly understood. From the second day of pregnancy to the day of birth, dams exercised for 1 h a day by running on a controlled wheel. The maternal behaviors of the dams were assessed on postpartum day 2 to postpartum day 8. Chronic restraint stress was applied from postpartum day 2 to day 12. Blood was collected on postpartum days 3 and 8, then subjected to ELISA to determine the serum concentration of prolactin. The weight of each dam and the food intake were recorded. Anxiety- and depression-like behavioral tests were conducted, and hippocampal neuroinflammation and prolactin receptor levels were measured. The dams exhibited elevated levels of anxiety and depression, decreased serum prolactin levels, decreased prolactin receptor expression, and activation of NLRP3-mediated neuroinflammation in the hippocampus following the induction of postpartum chronic restraint stress, which were reversed with controlled wheel running during pregnancy. Overall, the findings of this study revealed that the preventive effects of exercise during pregnancy on postpartum anxiety-and depression-like behaviors were accompanied by increased serum prolactin levels, hippocampal prolactin receptor expression and hippocampal NLRP3-mediated neuroinflammation.

Long-term voluntary running improves cognitive ability in developing mice by modulating the cholinergic system, antioxidant ability, and BDNF/PI3K/Akt/CREB pathway.

Moderate physical exercise has positive effects on memory. The present study aimed to investigate the impact of long-term exercise on spatial memory in developing mice, as well as its association with the cholinergic system, antioxidant activities, apoptosis factor, and BDNF/PI3K/Akt/CREB pathway in the brain. In this study, Y maze and Novel object recognition (NOR) tests were employed to assess the impact of long-term voluntary exercise on memory. The cholinergic system, antioxidant activities, and apoptosis factors in the brain were quantified using Elisa. Additionally, western blot analysis was conducted to determine the expression of relevant proteins in the BDNF/PI3K/Akt/CREB pathway. The findings demonstrated that prolonged voluntary wheel running exercise enhanced memory in developing mice, concomitant with increased catalase (CAT) activity and decreased malondialdehyde (MDA) levels in the brain. Moreover, it could also increase the hippocampal acetylcholine (ACh) content and suppress the expression of neuronal apoptosis protein. Additionally, exercise also upregulated the expression of brain-derived neurotrophic factor (BDNF), tropomyosin receptor kinase B (TrkB), phosphoinositide 3 kinases (PI3K), Akt, cAMP response element-binding protein (CREB), and phosphorylated cAMP response element-binding protein (p-CREB) in the hippocampus. These findings suggest that long-term voluntary wheel running exercise improves the spatial memory of developing mice by modulating the cholinergic system, antioxidant activities, apoptosis factors, and activating the BDNF/PI3K/Akt/CREB pathway.

Biological Sex Influences Daily Locomotor Rhythms in Mice Held Under Different Housing Conditions.

Daily rhythms are programmed by a central circadian clock that is modulated by photoperiod. Here, we recorded locomotor activity rhythms in C57Bl/6 or mPer2Luc mice of both sexes held under different housing conditions. First, we confirm that the structure of locomotor activity rhythms differs between male and female mice in both genetic backgrounds. Male mice exhibit a nightly "siesta," whereas female mice fluctuate between nights with and without a nightly siesta, which corresponds with changes in locomotor activity levels, circadian period, and vaginal cytology. The nightly siesta is modulated by the presence of a running wheel in both sexes but is not required for the infradian patterning of locomotor rhythms in females. Finally, photoperiodic changes in locomotor rhythms differed by sex, and females displayed phase-jumping responses earlier than males under a parametric photoentrainment assay simulating increasing day length. Collectively, these results highlight that sex and sex hormones influence daily locomotor rhythms under a variety of different environmental conditions.

Effect of exercise duration on toluene-induced locomotor sensitization in mice: a focus on the Renin Angiotensin System.

RATIONALE: Exercise attenuates addictive behavior; however, little is known about the contribution of exercise duration to this positive effect. The Renin Angiotensin System (RAS) has been implicated both in addictive responses and in the beneficial effects of exercise; though, its role in the advantageous effects of exercise on toluene-induced addictive responses has not been explored. OBJECTIVES: To evaluate the impact of different exercise regimens in mitigating the expression of toluene-induced locomotor sensitization and to analyze changes in RAS elements' expression at the mesocorticolimbic system after repeated toluene exposure and following voluntary wheel running in toluene-sensitized animals. METHODS: Toluene-induced addictive-like response was evaluated with a locomotor sensitization model in mice. Toluene-sensitized animals had access to running wheels 1, 2, 4 or 24 h/day for 4 weeks; thereafter, locomotor sensitization expression was evaluated after a toluene challenge. RAS elements (ACE and ACE2 enzymes; AT1, AT2 and Mas receptors) expression was determined by Western blot in the VTA, NAc and PFCx of toluene-sensitized mice with and without exercise. RESULTS: Individual differences in toluene-induced locomotor sensitization development were observed. Access to wheel running 1 and 2 h/day reduced but 4 and 24 h/day completely blocked locomotor sensitization expression. Repeated toluene exposure changed RAS elements' expression in the VTA, NAc and PFCx, while exercise mainly modified ACE and AT1 in air-exposed and toluene-sensitized mice. CONCLUSIONS: Inhalant-exposed animals show different sensitization phenotypes. Exercise duration determined its efficacy to attenuate the addictive-like response. Toluene exposure and exercise each modified RAS, the latter also modifying toluene-induced changes.

The attenuation of activity-based anorexia by obese adipose tissue transplant is AgRP neuron-dependent.

Anorexia nervosa (AN) is an eating disorder observed primarily in girls and women, and is characterized by a low body mass index, hypophagia, and hyperactivity. The activity-based anorexia (ABA) paradigm models aspects of AN, and refers to the progressive weight loss, hypophagia, and hyperactivity developed by rodents exposed to time-restricted feeding and running wheel access. Recent studies identified white adipose tissue (WAT) as a primary location of the 'metabolic memory' of prior obesity, and implicated WAT-derived signals as drivers of recidivism to obesity following weight loss. Here, we tested whether an obese WAT transplant could attenuate ABA-induced weight loss in normal female mice. Recipient mice received a WAT transplant harvested from normal chow-fed, or HFD-fed obese mice; obese fat recipient (OFR) and control fat recipient (CFR) mice were then tested for ABA. During ABA, OFR mice survived longer than CFR mice, defined as maintaining 75% of their initial body weight. Next, we tested whether agouti-related peptide (AgRP) neurons, which regulate feeding behavior and metabolic sensing, mediate this effect of obese WAT transplant. CFR and OFR mice received either control or neonatal AgRP ablation, and were assessed for ABA. OFR intact mice maintained higher body weights longer than CFR intact mice, and this effect was abolished by neonatal AgRP ablation; further, ablation reduced survival in OFR, but not CFR mice. In summary, obese WAT transplant communicates with AgRP neurons to increase body weight maintenance during ABA. These findings encourage the examination of obese WAT-derived factors as potential treatments for AN.

Effects of food restriction on voluntary wheel-running behavior and body mass in selectively bred High Runner lines of mice.

Food restriction can have profound effects on various aspects of behavior, physiology, and morphology. Such effects might be amplified in animals that are highly active, given that physical activity can represent a substantial fraction of the total daily energy budget. More specifically, some effects of food restriction could be associated with intrinsic, genetically based differences in the propensity or ability to perform physical activity. To address this possibility, we studied the effects of food restriction in four replicate lines of High Runner (HR) mice that have been selectively bred for high levels of voluntary wheel running. We hypothesized that HR mice would respond differently than mice from four non-selected Control (C) lines. Healthy adult females from generation 65 were housed individually with wheels and provided access to food and water ad libitum for experimental days 1-19 (Phase 1), which allowed mice to attain a plateau in daily running distances. Ad libitum food intake of each mouse was measured on days 20-22 (Phase 2). After this, each mouse experienced a 20 % food restriction for 7 days (days 24-30; Phase 3), and then a 40 % food restriction for 7 additional days (days 31-37; Phase 4). Mice were weighed on experimental days 1, 8, 9, 15, 20, and 23-37 and wheel-running activity was recorded continuously, in 1-minute bins, during the entire experiment. Repeated-measures ANOVA of daily wheel-running distance during Phases 2-4 indicated that HR mice always ran much more than C, with values being 3.29-fold higher during the ad libitum feeding trial, 3.58-fold higher with -20 % food, and 3.06-fold higher with -40 % food. Seven days of food restriction at -20 % did not significantly reduce wheel-running distance of either HR (-5.8 %, P = 0.0773) or C mice (-13.3 %, P = 0.2122). With 40 % restriction, HR mice showed a further decrease in daily wheel-running distance (P = 0.0797 vs. values at 20 % restriction), whereas C mice did not (P = 0.4068 vs. values at 20 % restriction) and recovered to levels similar to those on ad libitum food (P = 0.3634). For HR mice, daily running distances averaged 11.4 % lower at -40 % food versus baseline values (P = 0.0086), whereas for C mice no statistical difference existed (-4.8 %, P = 0.7004). Repeated-measures ANOVA of body mass during Phases 2-4 indicated a highly significant effect of food restriction (P = 0.0001), but no significant effect of linetype (P = 0.1764) and no interaction (P = 0.8524). Both HR and C mice had a significant reduction in body mass only when food rations were reduced by 40 % relative to ad libitum feeding, and even then the reductions averaged only -0.60 g for HR mice (-2.6 %) and -0.49 g (-2.0 %) for C mice. Overall, our results indicate a surprising insensitivity of body mass to food restriction in both high-activity (HR) and ordinary (C) mice, and also insensitivity of wheel running in the C lines of mice, thus calling for studies of compensatory mechanisms that allow this insensitivity.

Dietary restriction plus exercise change gene expression of Cxcl12 abundant reticular cells in female mice.

INTRODUCTION: Low energy availability due to excessive exercise lowers bone mass and impairs various physiological functions, including immunity and hematopoiesis. We focused on Cxcl12 abundant reticular (CAR) cells, which are bone marrow mesenchymal stem cells and are essential for the maintenance of hematopoietic and immune cells in bone marrow. We examine the functional changes in CAR cells resulting from dietary restriction combined with exercise. MATERIALS AND METHODS: Five-week-old wild-type female mice were divided into an ad libitum group (CON), a 60% dietary restriction group (DR), an ad libitum with exercise group (CON + ex), and a 60% dietary restriction with exercise group (DR + ex). Blood parameters, bone structure parameters, and bone marrow fat volume were evaluated after 5 weeks. In addition, bone marrow CAR cells were isolated by cell sorting and analyzed for gene expression by RT-qPCR. RESULTS: Bone mineral density (BMD) was significantly decreased in DR and DR + ex compared to CON and CON + ex. Especially, cortical bone mass and thickness were significantly decreased in DR and DR + ex groups, whereas trabecular bone mass was significantly increased. Bone marrow fat volume was significantly increased in DR and DR + ex groups compared to CON and CON + ex. The number of leukocytes in the blood was significantly decreased in the DR + ex group compared to the other three groups. RT-qPCR showed a significant decrease in gene expression of both Foxc1 and Runx2 in CAR cells of the DR + ex group compared to CON. CONCLUSION: Dietary restriction combined with exercise promotes CAR cell differentiation into bone marrow adipocyte and suppresses osteoblast differentiation.

Important role of NPY-Y4R signalling in the dual control of feeding and physical activity.

The control of feeding and physical activity is tightly linked and coordinated. However the underlying mechanisms are unclear. One of the major regulatory systems of feeding behaviour involves neuropeptide Y (NPY) signalling, with the signalling mediated through NPY Y4 receptor also known to influence activity. Here we show that mice globally lacking the Npy4r (Npy4r-/-) in the absence of access to a running wheel behaved WT-like with regards to food intake, energy expenditure, respiratory exchange ratio and locomotion regardless of being fed on a chow or high fat diet. Interestingly however, when given the access to a running wheel, Npy4r-/- mice while having a comparable locomotor activity, showed significantly higher wheel-running activity than WT, again regardless of dietary conditions. This higher wheel-running activity in Npy4r-/-mice arose from an increased dark-phase running time rather than changes in number of running bouts or the running speed. Consistently, energy expenditure was higher in Npy4r-/- than WT mice. Importantly, food intake was reduced in Npy4r-/-mice under wheel access condition which was due to decreased feeding bouts rather than changes in meal size. Together, these findings demonstrate an important role of Npy4r signalling in the dual control of feeding and physical activity, particularly in the form of wheel-running activity.

Atlas of exercise-induced brain activation in mice.

OBJECTIVES: There is significant interest in uncovering the mechanisms through which exercise enhances cognition, memory, and mood, and lowers the risk of neurodegenerative diseases. In this study, we utilize forced treadmill running and distance-matched voluntary wheel running, coupled with light sheet 3D brain imaging and c-Fos immunohistochemistry, to generate a comprehensive atlas of exercise-induced brain activation in mice. METHODS: To investigate the effects of exercise on brain activity, we compared whole-brain activation profiles of mice subjected to treadmill running with mice subjected to distance-matched wheel running. Male mice were assigned to one of four groups: a) an acute bout of voluntary wheel running, b) confinement to a cage with a locked running wheel, c) forced treadmill running, or d) placement on an inactive treadmill. Immediately following each exercise or control intervention, blood samples were collected for plasma analysis, and brains were collected for whole-brain c-Fos quantification. RESULTS: Our dataset reveals 255 brain regions activated by acute exercise in mice, the majority of which have not previously been linked to exercise. We find a broad response of 140 regulated brain regions that are shared between voluntary wheel running and treadmill running, while 32 brain regions are uniquely regulated by wheel running and 83 brain regions uniquely regulated by treadmill running. In contrast to voluntary wheel running, forced treadmill running triggers activity in brain regions associated with stress, fear, and pain. CONCLUSIONS: Our findings demonstrate a significant overlap in neuronal activation signatures between voluntary wheel running and distance-matched forced treadmill running. However, our analysis also reveals notable differences and subtle nuances between these two widely used paradigms. The comprehensive dataset is accessible online at www.neuropedia.dk, with the aim of enabling future research directed towards unraveling the neurobiological response to exercise.

Effects of long-term voluntary wheel running and selective breeding for wheel running on femoral nutrient canals.

The nutrient artery provides ~50%-70% of the total blood volume to long bones in mammals. Studying the functional characteristics of this artery in vivo can be difficult and expensive, so most researchers have measured the nutrient foramen, an opening on the outer surface of the bone that served as the entry point for the nutrient artery during development and bone ossification. Others have measured the nutrient canal (i.e., the passage which the nutrient artery once occupied), given that the external dimensions of the foramen do not necessarily remain uniform from the periosteal surface to the medullary cavity. The nutrient canal, as an indicator of blood flow to long bones, has been proposed to provide a link to studying organismal activity (e.g., locomotor behavior) from skeletal morphology. However, although external loading from movement and activity causes skeletal remodeling, it is unclear whether it affects the size or configuration of nutrient canals. To investigate whether nutrient canals can exhibit phenotypic plasticity in response to physical activity, we studied a mouse model in which four replicate high runner (HR) lines have been selectively bred for high voluntary wheel-running behavior. The selection criterion is the average number of wheel revolutions on days 5 and 6 of a 6-day period of wheel access as young adults (~6-8 weeks old). An additional four lines are bred without selection to serve as controls (C). For this study, 100 female mice (half HR, half C) from generation 57 were split into an active group housed with wheels and a sedentary group housed without wheels for 12 weeks starting at ~24 days of age. Femurs were collected, soft tissues were removed, and femora were micro-computed tomography scanned at a resolution of 12 µm. We then imported these scans into AMIRA and created 3D models of femoral nutrient canals. We tested for evolved differences in various nutrient canal traits between HR and C mice, plastic changes resulting from chronic exercise, and the selection history-by-exercise interaction. We found few differences between the nutrient canals of HR versus C mice, or between the active and sedentary groups. We did find an interaction between selection history and voluntary exercise for the total number of nutrient canals per femur, in which wheel access increased the number of canals in C mice but decreased it in HR mice. Our results do not match those from an earlier study, conducted at generation 11, which was prior to the HR lines reaching selection limits for wheel running. The previous study found that mice from the HR lines had significantly larger total canal cross-sectional areas compared to those from C lines. However, this discrepancy is consistent with studies of other skeletal traits, which have found differences between HR and C mice to be somewhat inconsistent across generations, including the loss of some apparent adaptations with continued selective breeding after reaching a selection limit for wheel-running behavior.

Effects of chronic alcohol intoxication on aerobic exercise-induced adaptations in female mice.

Chronic alcohol intoxication decreases muscle strength/function and causes mitochondrial dysfunction. Aerobic exercise training improves mitochondrial oxidative capacity and increases muscle mass and strength. Presently, the impact of chronic alcohol on aerobic exercise-induced adaptations was investigated. Female C57BL/6Hsd mice were randomly assigned to one of four groups: control sedentary (CON SED; n = 26), alcohol sedentary (ETOH SED; n = 27), control exercise (CON EX; n = 28), and alcohol exercise (ETOH EX; n = 25). Exercise mice had running wheel access for 2 h a day, 7 days a week. All mice were fed either control or an alcohol-containing liquid diet. Grip strength testing and EchoMRI were performed before and after the interventions. After 6 wk, hindlimb muscles were collected for molecular analyses. A subset of mice performed a treadmill run to fatigue (RTF), then abstained from alcohol for 2 wk and repeated the RTF. Alcohol decreased lean mass and forelimb grip strength compared with control-fed mice. Alcohol blunted the exercise-induced increase in muscle mass (plantaris and soleus), type IIa fiber percentage in the plantaris, and run time to fatigue. Mitochondrial markers (Citrate synthase activity and Complex I-IV, COXIV and Cytochrome C protein expression) were increased with exercise regardless of ETOH in the gastrocnemius but not tibialis anterior muscle. Two weeks of alcohol abstinence improved RTF time in ETOH EX but not in ETOH SED. These data suggest that alcohol impairs some exercise-induced adaptations in skeletal muscle, but not all were negatively affected, indicating that exercise may be a beneficial behavior even while consuming alcohol.NEW & NOTEWORTHY Alcohol consumption during an aerobic exercise training period prevented training-induced increases in run to fatigue time and grip strength. Cessation of alcohol allowed for recovery of endurance performance within 2 wk. The worsened exercise performance after alcohol was unrelated to impairments in markers of mitochondrial health. Therefore, some adaptations to exercise training are impaired with alcohol use (endurance performance, muscle growth, and strength), while others remain mostly unaffected (mitochondrial health).

Estrogen-mediated individual differences in female rat voluntary running behavior.

Regular exercise has numerous health benefits, but the human population displays significant variability in exercise participation. Rodent models, such as voluntary wheel running (VWR) in rats, can provide insight into the underlying mechanisms of exercise behavior and its regulation. In this study, we focused on the role of estrogen on VWR in female rats. Female rats run more than males, and we aimed to determine to what extent running levels in females were regulated by estrogen signaling. The running behavior of rats (duration, speed, and total distance run) was measured under normal physiological conditions, ovariectomy (OVX), and estrogen replacement in an OVX background. Results show cyclic variations in running linked to the estrous cycle. Ovariectomy markedly reduced running and eliminated the cyclic pattern. Estrogen replacement through estradiol benzoate (EB) injections and osmotic minipumps reinstated running activity to pre-OVX levels and restored the cyclic pattern. Importantly, individual differences and ranking are preserved such that high versus low runners before OVX remain high and low runners after treatment. Further analysis revealed that individual variation in running distance was primarily caused by rats running different speeds, but rats also varied in running duration. However, it is noteworthy that this model also displays features distinct from estrogen-driven running behavior under physiological conditions, notably a delayed onset and a broader duration of running activity. Collectively, this estrogen causality VWR model presents a unique opportunity to investigate sex-specific mechanisms that control voluntary physical activity.NEW & NOTEWORTHY This study investigates estrogen's role in voluntary wheel running (VWR) behavior in female rats. Female rats exhibit greater running than males, with estrogen signaling regulating this activity. The estrous cycle influences running, whereas ovariectomy reduces it, and estrogen replacement restores it, maintaining individual differences under all conditions. Both running speed and duration contribute to VWR variations. These findings emphasize individual estrogen regulation in female exercise and provide an estrogen replacement animal model for investigating neurobiological underpinnings that drive voluntary exercise behavior.

Preexposure to running attenuates rats' running-based flavour avoidance: Testing associative blocking with a cover cues or context change.

Voluntary running in activity wheels by rats leads to a Pavlovian conditioned aversion to the flavour consumed immediately before the running, causing the rats to avoid that flavour. This learning process, known as running-based flavour avoidance learning (FAL), is weakened when the rats have had repeated exposure to the wheels before. According to the associative account, the association between the background context and running established during the preexposure phase blocks the conditioning of the target flavour because the running is highly predictable by the background context from the outset of the FAL phase. Experiments 1 and 2 examined this account by introducing another flavour as a cue signalling wheel access during the preexposure phase. In the framework of the associative account, the introduction of this cue should impede the formation of the context-running association during the preexposure phase, thereby hindering the contextual blocking of aversive conditioning for the target flavour in the FAL phase. This would result in unweakened FAL. Although the results of Experiment 1 align with this prediction, in Experiment 2, when highly distinct flavours were used as the target and second cues, the preexposure effect was not eliminated. This contradicts the predictions of the associative account, indicating that Experiment 1 may have been influenced by stimulus generalisation. In Experiment 3, changing background contexts between the preexposure and FAL phases had no impact on the preexposure effect, contrary to the predictions of the associative account. In general, the associative account was not supported.