Circulating levels of endocannabinoids respond acutely to voluntary exercise, are altered in mice selectively bred for high voluntary wheel running, and differ between the sexes

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.

Does Behavior Evolve First? Correlated Responses to Selection for Voluntary Wheel-Running Behavior in House Mice

AbstractHow traits at multiple levels of biological organization evolve in a correlated fashion in response to directional selection is poorly understood, but two popular models are the very general "behavior evolves first" (BEF) hypothesis and the more specific "morphology-performance-behavior-fitness" (MPBF) paradigm. Both acknowledge that selection often acts relatively directly on behavior and that when behavior evolves, other traits will as well but most with some lag. However, this proposition is exceedingly difficult to test in nature. Therefore, we studied correlated responses in the high-runner (HR) mouse selection experiment, in which four replicate lines have been bred for voluntary wheel-running behavior and compared with four nonselected control (C) lines. We analyzed a wide range of traits measured at generations 20-24 (with a focus on new data from generation 22), coinciding with the point at which all HR lines were reaching selection limits (plateaus). Significance levels (226 P values) were compared across trait types by ANOVA, and we used the positive false discovery rate to control for multiple comparisons. This meta-analysis showed that, surprisingly, the measures of performance (including maximal oxygen consumption during forced exercise) showed no evidence of having diverged between the HR and C lines, nor did any of the life history traits (e.g., litter size), whereas body mass had responded (decreased) at least as strongly as wheel running. Overall, results suggest that the HR lines of mice had evolved primarily by changes in motivation rather than performance ability at the time they were reaching selection limits. In addition, neither the BEF model nor the MPBF model of hierarchical evolution provides a particularly good fit to the HR mouse selection experiment.

Maternal upbringing and selective breeding for voluntary exercise behavior modify patterns of DNA methylation and expression of genes in the mouse brain

Selective breeding has been utilized to study the genetic basis of exercise behavior, but research suggests that epigenetic mechanisms, such as DNA methylation, also contribute to this behavior. In a previous study, we demonstrated that the brains of mice from a genetically selected high runner (HR) line have sex-specific changes in DNA methylation patterns in genes known to be genomically imprinted compared to those from a non-selected control (C) line. Through cross-fostering, we also found that maternal upbringing can modify the DNA methylation patterns of additional genes. Here, we identify an additional set of genes in which DNA methylation patterns and gene expression may be altered by selection for increased wheel-running activity and maternal upbringing. We performed bisulfite sequencing and gene expression assays of 14 genes in the brain and found alterations in DNA methylation and gene expression for Bdnf, Pde4d and Grin2b. Decreases in Bdnf methylation correlated with significant increases in Bdnf gene expression in the hippocampus of HR compared to C mice. Cross-fostering also influenced the DNA methylation patterns for Pde4d in the cortex and Grin2b in the hippocampus, with associated changes in gene expression. We also found that the DNA methylation patterns for Atrx and Oxtr in the cortex and Atrx and Bdnf in the hippocampus were further modified by sex. Together with our previous study, these results suggest that DNA methylation and the resulting change in gene expression may interact with early-life influences to shape adult exercise behavior.

Locomotor play behavior evolves by random genetic drift but not as a correlated response to selective breeding for high voluntary wheel-running behavior

Locomotor play is vigorous and seemingly purposeless behavior, commonly observed in young mammals. It can be costly in terms of energy expenditure, increased injury risk, and predator exposure. The main hypothesized benefit of locomotor play is enhancement of neuromuscular development, with effects persisting into adulthood. We hypothesized that levels of locomotor play would have evolved as a correlated response to artificial selection for increased voluntary exercise behavior. We studied mice from 4 replicate lines bred for voluntary wheel running (High Runner or HR) at 6-8 weeks of age and four non-selected Control (C) lines. Mice were weaned at 21 days of age and play behavior was observed for generations 20 (22-24 days old), 68 (22-23 days old), and 93 (15 days old). We quantified locomotor play as (1) rapid, horizontally directed jerk-run sequences and (2) vertical "bouncing." We used focal sampling to continuously record behavior in cages containing 4-6 individuals during the first 2-3 h of the dark cycle. Observations were significantly repeatable between observers and days. A two-way, mixed-model simultaneously tested effects of linetype (HR vs. C), sex, and their interaction. Contrary to our hypothesis, HR and C lines did not differ in any generation, nor did we find sex differences. However, differences among the replicate HR lines and among the replicate C lines were detected, and may be attributed to the effects of random genetic drift (and possibly founder effects). Thus, play behavior did evolve in this selection experiment, but not as a correlated response to selection for voluntary exercise.

Hippocampal, Whole Midbrain, Red Nucleus, and Ventral Tegmental Area Volumes Are Increased by Selective Breeding for High Voluntary Wheel-Running Behavior

Uncovering relationships between neuroanatomy, behavior, and evolution are important for understanding the factors that control brain function. Voluntary exercise is one key behavior that both affects, and may be affected by, neuroanatomical variation. Moreover, recent studies suggest an important role for physical activity in brain evolution. We used a unique and ongoing artificial selection model in which mice are bred for high voluntary wheel-running behavior, yielding four replicate lines of high runner (HR) mice that run ∼3-fold more revolutions per day than four replicate nonselected control (C) lines. Previous studies reported that, with body mass as a covariate, HR mice had heavier whole brains, non-cerebellar brains, and larger midbrains than C mice. We sampled mice from generation 66 and used high-resolution microscopy to test the hypothesis that HR mice have greater volumes and/or cell densities in nine key regions from either the midbrain or limbic system. In addition, half of the mice were given 10 weeks of wheel access from weaning, and we predicted that chronic exercise would increase the volumes of the examined brain regions via phenotypic plasticity. We replicated findings that both selective breeding and wheel access increased total brain mass, with no significant interaction between the two factors. In HR compared to C mice, adjusting for body mass, both the red nucleus (RN) of the midbrain and the hippocampus (HPC) were significantly larger, and the whole midbrain tended to be larger, with no effect of wheel access nor any interactions. Linetype and wheel access had an interactive effect on the volume of the periaqueductal gray (PAG), such that wheel access increased PAG volume in C mice but decreased volume in HR mice. Neither linetype nor wheel access affected volumes of the substantia nigra, ventral tegmental area, nucleus accumbens, ventral pallidum (VP), or basolateral amygdala. We found no main effect of either linetype or wheel access on neuronal densities (numbers of cells per unit area) for any of the regions examined. Taken together, our results suggest that the increased exercise phenotype of HR mice is related to increased RN and hippocampal volumes, but that chronic exercise alone does not produce such phenotypes.

Role of neurotransmitters in immune-mediated inflammatory disorders: a crosstalk between the nervous and immune systems

Immune-mediated inflammatory diseases (IMIDs) are a group of common heterogeneous disorders, characterized by an alteration of cellular homeostasis. Primarily, it has been shown that the release and diffusion of neurotransmitters from nervous tissue could result in signaling through lymphocyte cell-surface receptors and the modulation of immune function. This finding led to the idea that the neurotransmitters could serve as immunomodulators. It is now manifested that neurotransmitters can also be released from leukocytes and act as autocrine or paracrine modulators. Increasing data indicate that there is a crosstalk between inflammation and alterations in neurotransmission. The primary goal of this review is to demonstrate how these two pathways may converge at the level of the neuron and glia to involve in IMID. We review the role of neurotransmitters in IMID. The different effects that these compounds exert on a variety of immune cells are also reviewed. Current and future developments in understanding the cross-talk between the immune and nervous systems will undoubtedly identify new ways for treating immune-mediated diseases utilizing agonists or antagonists of neurotransmitter receptors.

Mice from lines selectively bred for voluntary exercise are not more resistant to muscle injury caused by either contusion or wheel running

Muscle injury can be caused by strenuous exercise, repetitive tasks or external forces. Populations that have experienced selection for high locomotor activity may have evolutionary adaptations that resist exercise-induced injury and/or enhance the ability to cope with injury. We tested this hypothesis with an experiment in which mice are bred for high voluntary wheel running. Mice from four high runner lines run ~three times more daily distance than those from four non-selected control lines. To test recovery from injury by external forces, mice experienced contusion via weight drop on the calf. After injury, running distance and speed were reduced in high runner but not control lines, suggesting that the ability of control mice to run exceeds their motivation. To test effects of injury from exercise, mice were housed with/without wheels for six days, then trunk blood was collected and muscles evaluated for injury and regeneration. Both high runner and control mice with wheels had increased histological indicators of injury in the soleus, and increased indicators of regeneration in the plantaris. High runner mice had relatively more central nuclei (regeneration indicator) than control in the soleus, regardless of wheel access. The subset of high runner mice with the mini-muscle phenotype (characterized by greatly reduced muscle mass and type IIb fibers) had lower plasma creatine kinase (indicator of muscle injury), more markers of injury in the deep gastrocnemius, and more markers of regeneration in the deep and superficial gastrocnemius than normal-muscled individuals. Contrary to our expectations, high runner mice were not more resistant to either type of injury.

A red nucleus-VTA glutamate pathway underlies exercise reward and the therapeutic effect of exercise on cocaine use

Physical exercise is rewarding and protective against drug abuse and addiction. However, the neural mechanisms underlying these actions remain unclear. Here, we report that long-term wheel-running produced a more robust increase in c-fos expression in the red nucleus (RN) than in other brain regions. Anatomic and functional assays demonstrated that most RN magnocellular portion (RNm) neurons are glutamatergic. Wheel-running activates a subset of RNm glutamate neurons that project to ventral tegmental area (VTA) dopamine neurons. Optogenetic stimulation of this pathway was rewarding, as assessed by intracranial self-stimulation and conditioned place preference, whereas optical inhibition blocked wheel-running behavior. Running wheel access decreased cocaine self-administration and cocaine seeking during extinction. Last, optogenetic stimulation of the RNm-to-VTA glutamate pathway inhibited responding to cocaine. Together, these findings indicate that physical exercise activates a specific RNm-to-VTA glutamatergic pathway, producing exercise reward and reducing cocaine intake.

Dietary PUFAs and Exercise Dynamic Actions on Endocannabinoids in Brain: Consequences for Neural Plasticity and Neuroinflammation

The brain and peripheral nervous system provide oversight to muscle physiology and metabolism. Muscle is the largest organ in the body and critical for glucose sensitivity, prevention of diabetes, and control of obesity. The central nervous system produces endocannabinoids (eCBs) that play a role in brain neurobiology, such as inflammation and pain. Interestingly, studies in humans and rodents show that a moderate duration of exercise increases eCBs in the brain and blood and influences cannabinoid receptors. Cannabinoid actions in the nervous system have advanced our understanding of pain, well-being, and disease. Nutrition is an important aspect of brain and eCB physiology because eCBs are biosynthesized from PUFAs. The primary eCB metabolites are derived from arachidonic acid, a 20:4n-6 (ω-6) PUFA, and the n-3 (ω-3) PUFAs, EPA and DHA. The eCBs bind to cannabinoid receptors CB1 and CB2 to exert a wide range of activities, such as stimulating appetite, influencing energy metabolism, supporting the immune system, and facilitating neuroplasticity. A diet containing different essential n-6 and n-3 PUFAs will dominate the formation of specific eCBs, and subsequently their actions as ligands for CB1 and CB2. The eCBs also function as substrates for cyclooxygenase enzymes, including potential substrates for the oxylipins (OxLs), which can be proinflammatory. Together, the eCBs and OxLs act as modulators of neuroinflammation. Thus, dietary PUFAs have implications for exercise responses via synthesis of eCBs and their effects on neuroinflammation. Neurotrophins also participate in interactions between diet and the eCBs, specifically brain-derived neurotrophic factor (BDNF). BDNF supports neuroplasticity in cooperation with the endocannabinoid system (ECS). This review will describe the role of PUFAs in eCB biosynthesis, discuss the ECS and OxLs in neuroinflammation, highlight the evidence for exercise effects on eCBs, and describe eCB and BDNF actions on neuroplasticity.

Influence of diet on acute endocannabinoidome mediator levels post exercise in active women, a crossover randomized study

The extended endocannabinoid system, also termed endocannabinoidome, participates in multiple metabolic functions in health and disease. Physical activity can both have an acute and chronic impact on endocannabinoid mediators, as does diet. In this crossover randomized controlled study, we investigated the influence of diet on the peripheral response to acute maximal aerobic exercise in a sample of active adult women (n = 7) with no underlying metabolic conditions. We compared the impact of 7-day standardized Mediterranean diet (MedDiet) and control diet inspired by Canadian macronutrient intake (CanDiet) on endocannabinoidome and short-chain fatty acid metabolites post maximal aerobic exercise. Overall, plasmatic endocannabinoids, their congeners and some polyunsaturated fatty acids increased significantly post maximal aerobic exercise upon cessation of exercise and recovered their initial values within 1 h after exercise. Most N-acylethanolamines and polyunsaturated fatty acids increased directly after exercise when the participants had consumed the MedDiet, but not when they had consumed the CanDiet. This impact was different for monoacylglycerol endocannabinoid congeners, which in most cases reacted similarly to acute exercise while on the MedDiet or the CanDiet. Fecal microbiota was only minimally affected by the diet in this cohort. This study demonstrates that endocannabinoidome mediators respond to acute maximal aerobic exercise in a way that is dependent on the diet consumed in the week prior to exercise.

The Endocannabinoid System and Physical Activity—A Robust Duo in the Novel Therapeutic Approach against Metabolic Disorders

Rapidly increasing worldwide prevalence of obesity and related pathologies encompassing coronary heart disease, hypertension, metabolic syndrome, or type 2 diabetes constitute serious threats to global health and are associated with a significantly elevated risk of premature death. Considering the enormous burden of these pathologies, novel therapeutic and preventive patterns are indispensable. Dysregulation of one of the most complex biological systems in the human body namely, the endocannabinoid system (ECS) may result in metabolic imbalance and development of insulin resistance, type 2 diabetes, or non-alcoholic fatty liver disease. Furthermore, many studies showed that physical exercises, depending on their type, intensity, and frequency, exert various alterations within the ECS. Emerging evidence suggests that targeting the ECS via physical activity may produce robust beneficial effects on the course of metabolic pathologies. However, the data showing a direct correlation between the ECS and physical activity in the aspect of metabolic health are very scarce. Therefore, the aim of this review was to provide the most up-to-date state of knowledge about the interplay between the ECS activity and physical exercises in the novel therapeutic and preventive approach toward metabolic pathologies. We believe that this paper, at least in part, will fulfill the existing gap in knowledge and encourage researchers to further explore this very complex yet interesting link between the ECS, its action in physical activity, and subsequent positive outcomes for metabolic health.

Effects of Selective Breeding, Voluntary Exercise, and Sex on Endocannabinoid Levels in the Mouse Small-Intestinal Epithelium

The endocannabinoid (eCB) system in the gut communicates with the body and brain as part of the homeostatic mechanisms that affect energy balance. Although perhaps best known for its effects on energy intake, the eCB system also regulates voluntary locomotor behavior. Here, we examined gut eCB concentrations in relation to voluntary exercise, specifically in mice selectively bred for high voluntary wheel running behavior. We measured gut eCBs in four replicate non-selected Control (C) lines and four replicate lines of High Runner (HR) mice that had been selectively bred for 74 generations based on the average number of wheel revolutions on days 5 and 6 of a 6-day period of wheel access when young adults. On average, mice from HR lines run voluntarily on wheels ∼3-fold more than C mice on a daily basis. A recent study showed that circulating levels of primary endocannabinoids 2-arachidonoyl-sn-glycerol (2-AG) and anandamide (AEA) are altered by six days of wheel access, by acute wheel running, and differ between HR and C mice in sex-specific ways [1]. We hypothesized that eCBs in the upper small-intestinal epithelium (i.e., proximal jejunum), a region firmly implicated in eCB signaling, would differ between HR and C mice (linetype), between the sexes, between mice housed with vs. without wheels for six days, and would covary with amounts of acute running and/or home-cage activity (during the previous 30 minutes). We used the same 192 mice as in [1] , half males and half females, half HR and half C (all 8 lines), and half either given or not given access to wheels for six days. We assessed the eCBs, 2-AG and AEA, and their analogs docosahexaenoylglycerol (DHG), docosahexaenoylethanolamide (DHEA), and oleoylethanolamide (OEA). Both 2-AG and DHG showed a significant 3-way interaction of linetype, wheel access, and sex. In addition, HR mice had lower concentrations of 2-AG in the small-intestinal epithelium when compared to C mice, which may be functionally related to differences in locomotor activity or to differences in body composition and/or food consumption. Moreover, the amount of home-cage activity during the prior 30 min was a negative predictor of 2-AG and AEA concentrations in jejunum mucosa, particularly in the mice with no wheel access. Lastly, 2-AG, but not AEA, was significantly correlated with 2-AG in plasma in the same mice.

Trade-Offs (and Constraints) in Organismal Biology

AbstractTrade-offs and constraints are inherent to life, and studies of these phenomena play a central role in both organismal and evolutionary biology. Trade-offs can be defined, categorized, and studied in at least six, not mutually exclusive, ways. (1) Allocation constraints are caused by a limited resource (e.g., energy, time, space, essential nutrients), such that increasing allocation to one component necessarily requires a decrease in another (if only two components are involved, this is referred to as the Y-model, e.g., energy devoted to size versus number of offspring). (2) Functional conflicts occur when features that enhance performance of one task decrease performance of another (e.g., relative lengths of in-levers and out-levers, force-velocity trade-offs related to muscle fiber type composition). (3) Shared biochemical pathways, often involving integrator molecules (e.g., hormones, neurotransmitters, transcription factors), can simultaneously affect multiple traits, with some effects being beneficial for one or more components of Darwinian fitness (e.g., survival, age at first reproduction, fecundity) and others detrimental. (4) Antagonistic pleiotropy describes genetic variants that increase one component of fitness (or a lower-level trait) while simultaneously decreasing another. (5) Ecological circumstances (or selective regime) may impose trade-offs, such as when foraging behavior increases energy availability yet also decreases survival. (6) Sexual selection may lead to the elaboration of (usually male) secondary sexual characters that improve mating success but handicap survival and/or impose energetic costs that reduce other fitness components. Empirical studies of trade-offs often search for negative correlations between two traits that are the expected outcomes of the trade-offs, but this will generally be inadequate if more than two traits are involved and especially for complex physiological networks of interacting traits. Moreover, trade-offs often occur only in populations that are experiencing harsh environmental conditions or energetic challenges at the extremes of phenotypic distributions, such as among individuals or species that have exceptional athletic abilities. Trade-offs may be (partially) circumvented through various compensatory mechanisms, depending on the timescale involved, ranging from acute to evolutionary. Going forward, a pluralistic view of trade-offs and constraints, combined with integrative analyses that cross levels of biological organization and traditional boundaries among disciplines, will enhance the study of evolutionary organismal biology.

Cross-fostering selectively bred High Runner mice affects adult body mass but not voluntary exercise

While nursing, mammals progress through critical developmental periods for the cardiovascular, musculoskeletal, and central nervous systems. The suckling period in mammals is therefore especially vulnerable to environmental factors that may affect the "developmental programming" of many complex traits. As a result, various aspects of maternal behavior and physiology can influence offspring in ways that have lasting effects into adulthood. Several recent studies of animal models have shown that maternal effects can partially program adult activity behaviors, which has important implications for health and locomotor performance. Here, we used cross-fostering to test for possible maternal effects on adult wheel-running behavior (voluntary exercise), maximal aerobic capacity during forced exercise (VO₂max), body mass and composition, and organ masses. Subjects were from a line of mice that has been selectively bred for ∼90 generations for high voluntary wheel-running behavior (High Runner; HR) and a non-selected Control (C) line. Adult HR mice run ∼3-fold the daily distances of C mice and have evolved other differences associated with exercise capacity, including elevated VO₂max, reduced body mass and fat mass, and larger hearts. At birth, we fostered offspring to create 4 experimental groups: C pups to other C dams (in-foster), HR pups to other HR dams (in-foster), C pups to HR dams (cross-foster), HR pups to C dams (cross-foster). Thus, all pups were fostered to a different mother. Mice were weaned 3 weeks later, and adult testing began at ∼6 weeks of age. At weaning, pups raised by HR dams were smaller than those raised by C dams for both sexes and as expected, HR pups raised by HR dams weighed less than C pups raised by C dams. As adults, mice raised by HR dams continued to have reduced body masses. As expected, adult HR mice ran approximately 3-fold more than their C counterparts and females ran more than males. However, cross-fostering did not statistically affect any aspect of wheel-running behavior (distance, duration, speed). Similarly, with body mass as a covariate, HR mice had higher VO₂max than C mice, and males had higher VO₂max than females, but cross-fostering had no effect. With body mass as a covariate, cross-fostering had variable effects on adult organ masses in a sex-specific manner. Overall, our results indicate that development of the adult High Runner phenotype does not require rearing by an HR dam, suggesting that high adult activity in humans may be independent of high maternal activity.

Effects of early-life exposure to Western diet and voluntary exercise on adult activity levels, exercise physiology, and associated traits in selectively bred High Runner mice

Exercise behavior is under partial genetic control, but it is also affected by numerous environmental factors, potentially including early-life experiences whose effects persist into adulthood. We studied genetic and early-life environmental effects on wheel-running behavior in a mouse model that includes four replicate high runner (HR) lines selectively bred for increased voluntary wheel running as young adults and four non-selected control (C) lines. In a full factorial design, mice from each line were granted wheel access or not and administered either standard or Western diet (WD) from weaning (3 weeks old) to 6 weeks of age (sexual maturity). In addition to acute effects, after a washout period of 8 weeks (∼6 human years) in which all mice had standard diet and no wheel access, we found both beneficial and detrimental effects of these early-life exposures. During the first week of treatments, WD increased distance run by 29% in C mice and 48% in HR mice (significant Diet × Linetype interaction), but diet effects disappeared by the third week. Across the three weeks of juvenile treatment, WD significantly increased fat mass (with lean mass as a covariate). Tested as adults, early-life exercise increased wheel running of C mice but not HR mice in the first week. Early-life exercise also reduced adult anxiety-like behavior and increased adult fasted blood glucose levels, triceps surae mass, subdermal fat pad mass, and brain mass, but decreased heart ventricle mass. Using fat mass as a covariate, early-life exercise treatment increased adult leptin concentration. In contrast, early-life WD increased adult wheel running of HR mice but not C mice. Early-life WD also increased adult lean mass and adult preference for Western diet in all groups. Surprisingly, early-life treatment had no significant effect on adult body fat or maximal aerobic capacity (VO2max). No previous study has tested for combined or interactive effects of early-life WD and exercise. Our results demonstrate that both factors can have long-lasting effects on adult voluntary exercise and related phenotypes, and that these effects are modulated by genetic background. Overall, the long-lasting effects of early-life exercise were more pervasive than those of WD, suggesting critical opportunities for health intervention in childhood habits, as well as possible threats from modern challenges. These results may be relevant for understanding potential effects of activity reductions and dietary changes associated with the obesity epidemic and COVID-19 pandemic.

Neurobiological Processes Induced by Aerobic Exercise through the Endocannabinoidome

Evidence suggesting the triangulation of the endocannabinoid system, exercise, and neurological health is emerging. In addition to the endocannabinoids N-arachidonoylethanolamine (anandamide; AEA) and 2-arachidonoylglycerol (2-AG), the expanded endocannabinoid system, known as the endocannabinoidome (eCBome), appears to be an important player in this relationship. The eCBome includes several endocannabinoid-like mediators such as N-acylethanolamines and 2-monoacylglycerols, the enzymes involved in their biosynthesis and degradation, and the receptors they affect. This review aims to relate the functional interactions between aerobic exercise, and the molecular and cellular pathways related to endocannabinoids, in the hypothalamus, hippocampus, and the periphery, with special attention given to associations with emotional state, cognition, and mental health. Given the well-documented roles of many eCBome members in regulating stress and neurological processes, we posit that the eCBome is an important effector of exercise-induced central and peripheral adaptive mechanisms that benefit mental health. Gut microbiota imbalance, affecting the gut-brain axis and metabolism, also influences certain eCBome-modulated inflammation pathways. The integrity of the gut microbiota could thus be crucial in the onset of neuroinflammation and mental conditions. Further studies on how the modulation by exercise of the peripheral eCBome affects brain functions could reveal to be key elements in the prevention and treatment of neuropsychological disorders.

Cannabis and exercise: Effects of Δ9-tetrahydrocannabinol on preference and motivation for wheel-running in mice

Recent surveys have revealed close links between cannabis and exercise. Specifically, cannabis usage before and/or after exercise is an increasingly common habit primarily aimed at boosting exercise pleasure, motivation, and performance whilst facilitating post-exercise recovery. However, whether these beliefs reflect the true impact of cannabis on these aspects of exercise is unknown. This study has thus examined the effects of cannabis' main psychoactive ingredient, namely Δ⁹-tetrahydrocannabinol (THC), on (i) mouse wheel-running preference and performance and (ii) running motivation and seeking behaviour. Wheel-running preference and performance were investigated using a T-maze with free and locked wheels located at the extremity of either arm. Running motivation and seeking were assessed by a cued-running operant task wherein wheel-running was conditioned by nose poking. Moreover, because THC targets cannabinoid type 1 (CB₁) receptors, i.e. receptors previously documented to control running motivation, this study also assessed the role of these receptors in running preference, performance, and craving-like behaviour. Whilst acute blockade or genetic deletion of CB₁ receptors decreased running preference and performance in the T-maze, THC proved ineffective on either variable. The failure of THC to affect running variables in the T-maze extended to running motivation, as assessed by cued-running under a progressive ratio (PR) reinforcement schedule. This ineffectiveness of THC was not related to the treatment protocol because it successfully increased motivation for palatable food. Although craving-like behaviour, as indexed by a cue-induced reinstatement of running seeking, was found to depend on CB₁ receptors, THC again proved ineffective. Neither running motivation nor running seeking were affected when CB₁ receptors were further stimulated by increasing the levels of the endocannabinoid 2-arachidonoylglycerol. These results, which suggest that the drive for running is insensitive to the acute stimulation of CB₁ receptors, raise the hypothesis that cannabis is devoid of effect on exercise motivation. Future investigation using chronic administration of THC, with and without other cannabis ingredients (e.g. cannabidiol), is however required before conclusions can be drawn.

Endocannabinoids and aging-Inflammation, neuroplasticity, mood and pain

Aging is associated with changes in hormones, slowing of metabolism, diminished physiological processes, chronic inflammation and high exposure to oxidative stress factors, generally described as the biological cost of living. Lifestyle interventions of diet and exercise can improve the quality of life during aging and lower diet-related chronic disease. The endocannabinoid system (ECS) has important effects on systemic metabolism and physiological systems, including the central and peripheral nervous systems. Exercise can reduce the loss of muscle mass and improve strength, and increase the levels of endocannabinoids (eCB) in brain and blood. Although the ECS exerts controls on multiple systems throughout life it affords benefits to natural aging. The eCB are synthesized from polyunsaturated fatty acids (PUFA) and the primary ones are produced from arachidonic acid (n-6 PUFA) and others from the n-3 PUFA, namely eicosapentaenoic and docosahexaenoic acids. The eCB ligands bind to their receptors, CB1 and CB2, with effects on appetite stimulation, metabolism, immune functions, and brain physiology and neuroplasticity. Dietary families of PUFA are a primary factor that can influence the types and levels of eCB and as a consequence, the downstream actions when the ligands bind to their receptors. Furthermore, the association of eCB with the synthesis of oxylipins (OxL) is a connection between the physiological actions of eCB and the lipid derived immunological OxL mediators of inflammation. OxL are ubiquitous and influence neuroinflammation and inflammatory processes. The emerging actions of eCB on neuroplasticity, well-being and pain are important to aging. Herein, we present information about the ECS and its components, how exercise and diet affects specific eCB, their role in neuroplasticity, neuroinflammation, pain, mood, and relationship to OxL. Poor nutrition status and low nutrient intakes observed with many elderly are reasons to examine the role of dietary PUFA actions on the ECS to improve health.

Turning strains into strengths for understanding psychiatric disorders

There is a paucity in the development of new mechanistic insights and therapeutic approaches for treating psychiatric disease. One of the major challenges is reflected in the growing consensus that risk for these diseases is not determined by a single gene, but rather is polygenic, arising from the action and interaction of multiple genes. Canonically, experimental models in mice have been designed to ascertain the relative contribution of a single gene to a disease by systematic manipulation (e.g., mutation or deletion) of a known candidate gene. Because these studies have been largely carried out using inbred isogenic mouse strains, in which there is no (or very little) genetic diversity among subjects, it is difficult to identify unique allelic variants, gene modifiers, and epigenetic factors that strongly affect the nature and severity of these diseases. Here, we review various methods that take advantage of existing genetic diversity or that increase genetic variance in mouse models to (1) strengthen conclusions of single-gene function; (2) model diversity among human populations; and (3) dissect complex phenotypes that arise from the actions of multiple genes.

Genetic Basis of Aerobically Supported Voluntary Exercise: Results from a Selection Experiment with House Mice

The biological basis of exercise behavior is increasingly relevant for maintaining healthy lifestyles. Various quantitative genetic studies and selection experiments have conclusively demonstrated substantial heritability for exercise behavior in both humans and laboratory rodents. In the "High Runner" selection experiment, four replicate lines of Mus domesticus were bred for high voluntary wheel running (HR), along with four nonselected control (C) lines. After 61 generations, the genomes of 79 mice (9-10 from each line) were fully sequenced and single nucleotide polymorphisms (SNPs) were identified. We used nested ANOVA with MIVQUE estimation and other approaches to compare allele frequencies between the HR and C lines for both SNPs and haplotypes. Approximately 61 genomic regions, across all somatic chromosomes, showed evidence of differentiation; 12 of these regions were differentiated by all methods of analysis. Gene function was inferred largely using Panther gene ontology terms and KO phenotypes associated with genes of interest. Some of the differentiated genes are known to be associated with behavior/motivational systems and/or athletic ability, including Sorl1, Dach1, and Cdh10 Sorl1 is a sorting protein associated with cholinergic neuron morphology, vascular wound healing, and metabolism. Dach1 is associated with limb bud development and neural differentiation. Cdh10 is a calcium ion binding protein associated with phrenic neurons. Overall, these results indicate that selective breeding for high voluntary exercise has resulted in changes in allele frequencies for multiple genes associated with both motivation and ability for endurance exercise, providing candidate genes that may explain phenotypic changes observed in previous studies.

Conditioned place preference for cocaine and methylphenidate in female mice from lines selectively bred for high voluntary wheel-running behavior

Behavioral addictions can come in many forms, including overeating, gambling and overexercising. All addictions share a common mechanism involving activation of the natural reward circuit and reinforcement learning, but the extent to which motivation for natural and drug rewards share similar neurogenetic mechanisms remains unknown. A unique mouse genetic model in which four replicate lines of female mice were selectively bred (>76 generations) for high voluntary wheel running (High Runner or HR lines) alongside four non-selected control (C) lines were used to test the hypothesis that high motivation for exercise is associated with greater reward for cocaine (20 mg/kg) and methylphenidate (10 mg/kg) using the conditioned place preference (CPP) test. HR mice run ~three times as many revolutions/day as C mice, but the extent to which they have increased motivation for other rewards is unknown. Both HR and C mice displayed significant CPP for cocaine and methylphenidate, but with no statistical difference between linetypes for either drug. Taken together, results suggest that selective breeding for increased voluntary running has modified the reward circuit in the brain in a way that increases motivation for running without affecting cocaine or methylphenidate reward.

Can Physical Activity Support the Endocannabinoid System in the Preventive and Therapeutic Approach to Neurological Disorders?

The worldwide prevalence of neurological and neurodegenerative disorders, such as depression or Alzheimer's disease, has spread extensively throughout the last decades, becoming an enormous health issue. Numerous data indicate a distinct correlation between the altered endocannabinoid signaling and different aspects of brain physiology, such as memory or neurogenesis. Moreover, the endocannabinoid system is widely regarded as a crucial factor in the development of neuropathologies. Thus, targeting those disorders via synthetic cannabinoids, as well as phytocannabinoids, becomes a widespread research issue. Over the last decade, the endocannabinoid system has been extensively studied for its correlation with physical activity. Recent data showed that physical activity correlates with elevated endocannabinoid serum concentrations and increased cannabinoid receptor type 1 (CB1R) expression in the brain, which results in positive neurological effects including antidepressant effect, ameliorated memory, neuroplasticity development, and reduced neuroinflammation. However, none of the prior reviews presented a comprehensive correlation between physical activity, the endocannabinoid system, and neuropathologies. Thus, our review provides a current state of knowledge of the endocannabinoid system, its action in physical activity, as well as neuropathologies and a possible correlation between all those fields. We believe that this might contribute to finding a new preventive and therapeutic approach to both neurological and neurodegenerative disorders.

The therapeutic potential of exercise for neuropsychiatric diseases: A review

Exercise is known to have a myriad of health benefits. There is much to be learned from the effects of exercise and its potential for prevention, attenuation and treatment of multiple neuropsychiatric diseases and behavioral disorders. Furthermore, recent data and research on exercise benefits with respect to major health crises, such as, that of opioid and general substance use disorders, make it very important to better understand and review the mechanisms of exercise and how it could be utilized for effective treatments or adjunct treatments for these diseases. In addition, mechanisms, epigenetics and sex differences are examined and discussed in terms of future research implications.

Is Experimental Evolution of an Increased Aerobic Exercise Performance in Bank Voles Mediated by Endocannabinoid Signaling Pathway?

The level of physical activity achieved in a given situation depends on both physiological abilities and behavioral characteristics (motivation). We used a unique animal model to test a hypothesis that evolution of an increased aerobic exercise performance can be facilitated by evolution of motivation to undertake physical activity, mediated by brain endocannabinoid system. Bank voles (Myodes glareolus) from "aerobic" A lines selected for 22 generations for high swim-induced aerobic metabolism (VO2swim) achieved 65% higher "voluntary maximum" VO2swim than voles from unselected, "control" C lines. In C lines, VO2swim was 24% lower than the maximum forced-running aerobic metabolism (VO2run), while in A lines VO2swim and VO2run were practically the same. Thus, the selection changed both the aerobic capacity and motivation to exercise at the top performance level. We applied a pharmacological treatment manipulation to test a hypothesis that the endocannabinoid signaling pathway 1) affects the voles performance in the aerobic exercise trials, and 2) has been modified in the selection process. Administration of the CB1 receptor antagonist (Rimonabant) did not affect the level of metabolism, but administration of the endocannabinoid reuptake inhibitor (AM404) decreased VO2swim both in A and C lines (4%, p = 0.03) and tended to decrease VO2run (2%, p = 0.07). The significant effect of AM404 suggests the involvement of endocannabinoids in signaling pathways controlling the motivation to be active. However, the response to AM404 did not differ between A and C lines (interaction effect, p ≥ 0.29). Thus, the results did not provide a support to the hypothesis that modifications of endocannabinoid signaling have played a role in the evolution of increased aerobic exercise performance in our experimental evolution model system.

SUMMARY STATEMENT

The results corroborated involvement of endocannabinoids in the regulation of physical activity, but did not support the hypothesis that modification of endocannabinoid signaling played a role in the evolution of increased aerobic exercise performance in our experimental evolution model.

The Endocannabinoid System as a Potential Mechanism through which Exercise Influences Episodic Memory Function

Emerging research demonstrates that exercise, including both acute and chronic exercise, may influence episodic memory function. To date, mechanistic explanations of this effect are often attributed to alterations in long-term potentiation, neurotrophic production, angiogenesis, and neurogenesis. Herein, we discuss a complementary mechanistic model, suggesting that the endocannabinoid system may, in part, influence the effects of exercise on memory function. We discuss the role of the endocannabinoid system on memory function as well as the effects of exercise on endocannabinoid alterations. This is an exciting line of inquiry that should help delineate new insights into the mechanistic role of exercise on memory function.

Interaction of neurotransmitters and neurochemicals with lymphocytes

Neurotransmitters and neurochemicals can act on lymphocytes by binding to receptors expressed by lymphocytes. This review describes lymphocyte expression of receptors for a selection of neurotransmitters and neurochemicals, the anatomical locations where lymphocytes can interact with neurotransmitters, and the effects of the neurotransmitters on lymphocyte function. Implications for health and disease are also discussed.

Biological/Genetic Regulation of Physical Activity Level: Consensus from GenBioPAC

PURPOSE

Physical activity unquestionably maintains and improves health; however, physical activity levels globally are low and not rising despite all the resources devoted to this goal. Attention in both the research literature and the public policy domain has focused on social-behavioral factors; however, a growing body of literature suggests that biological determinants play a significant role in regulating physical activity levels. For instance, physical activity level, measured in various manners, has a genetic component in both humans and nonhuman animal models. This consensus article, developed as a result of an American College of Sports Medicine-sponsored round table, provides a brief review of the theoretical concepts and existing literature that supports a significant role of genetic and other biological factors in the regulation of physical activity.

CONCLUSIONS

Future research on physical activity regulation should incorporate genetics and other biological determinants of physical activity instead of a sole reliance on social and other environmental determinants.

Electrocardiograms of mice selectively bred for high levels of voluntary exercise: Effects of short-term exercise training and the mini-muscle phenotype

Changes in cardiac function that occur with exercise training have been studied in detail, but those accompanying evolved increases in the duration or intensity of physical activity are poorly understood. To address this gap, we studied electrocardiograms (ECGs) of mice from an artificial selection experiment in which four replicate lines are bred for high voluntary wheel running (HR) while four non-selected lines are maintained as controls (C). ECGs were recorded using an ECGenie (Mouse Specifics, Inc.) both before and after six days of wheel access (as used in the standard protocol to select breeders). We hypothesized that HR mice would show innate differences in ECG characteristics and that the response to training would be greater in HR mice relative to C mice because the former run more. After wheel access, in statistical analyses controlling for variation in body mass, all mice had lower heart rates, and mice from HR lines had longer PR intervals than C lines. Also after wheel access, male mice had increased heart rate variability, whereas females had decreased heart rate variability. With body mass as a covariate, six days of wheel access significantly increased ventricle mass in both HR and C males. Within the HR lines, a subset of mice known as mini-muscle individuals have a 50% reduction in hindlimb muscle mass and generally larger internal organs, including the heart ventricles. As compared with normal-muscled individuals, mini-muscle individuals had a longer QRS complex, both before and after wheel access. Some studies in other species of mammals have shown correlations between athletic performance and QRS duration. Correlations between wheel running and either heart rate or QRS duration (before wheel running) among the eight individual lines of the HR selection experiment or among 17 inbred mouse strains taken from the literature were not statistically significant. However, total revolutions and average speed were negatively correlated with PR duration among lines of the HR selection experiment for males, and duration of running was negatively correlated with PR duration among 17 inbred strains for females. We conclude that HR mice have enhanced trainability of cardiac function as compared with C mice (as indicated by their longer PR duration after wheel access), and that the mini-muscle phenotype causes cardiac changes that have been associated with increased athletic performance in previous studies of mammals.

Reduced non-bicarbonate skeletal muscle buffering capacity in mice with the mini-muscle phenotype

Muscle pH decreases during exercise, which may impair function. Endurance training typically reduces muscle buffering capacity as a result of changes in fiber-type composition, but existing comparisons of species that vary in activity level are ambiguous. We hypothesized that high-runner (HR) lines of mice from an experiment that breeds mice for voluntary wheel running would have altered muscle buffering capacity as compared with their non-selected control counterparts. We also expected that 6 days of wheel access, as used in the selection protocol, would reduce buffering capacity, especially for HR mice. Finally, we expected a subset of HR mice with the 'mini-muscle' phenotype to have relatively low buffering capacity as a result of fewer type IIb fibers. We tested non-bicarbonate buffering capacity of thigh muscles. Only HR mice expressing the mini-muscle phenotype had significantly reduced buffering capacity, females had lower buffering capacity than males, and wheel access had no significant effect.

Monoacylglycerol lipase inhibition alters social behavior in male and female rats after post-weaning social isolation

Post-weaning social isolation (PSI) has been shown to increase aggressive behavior and alter medial prefrontal cortex (mPFC) function in rats. The present study sought to determine whether this phenotype would be normalized by increasing levels of the endocannabinoid 2-arachidonoylglycerol (2-AG) using pharmacological inhibition of monoacylglycerol lipase (MAGL). Male and female Sprague-Dawley rats were exposed to either 4 weeks of PSI or social rearing (SR) starting on postnatal day 21, then underwent a 15 min trial of social interaction with a novel, same-sex juvenile rat. Rats were administered an acute injection of the MAGL inhibitor MJN110 or vehicle prior to the social interaction. Rats received either 0 mg/kg (vehicle), 1 mg/kg, or 5 mg/kg of MJN110. Both doses of MJN110 decreased aggressive grooming, a measure of agonistic behavior, in both males and females, largely driven by decreased aggressive grooming in PSI rats. There were no effects of MJN110 on overall social behavior or play behavior, while modest effects were observed on locomotor activity in SR rats only. While social interaction increased c-Fos expression in the mPFC of both males and females, MJN110 reduced c-Fos preferentially in females. These results suggest that 2-AG can modulate specific social behaviors during adolescence, and may affect mPFC function differentially in males and females.

High-runner mice have reduced incentive salience for a sweet-taste reward when housed with wheel access

To explore reward substitution in the context of voluntary exercise, female mice from four replicate high-runner (HR) lines (bred for wheel running) and four non-selected control (C) lines were given simultaneous access to wheels and palatable solutions as competing rewards (two doses of saccharin [0.1, 0.2% w/v]; two doses of common artificial sweetener blends containing saccharin [Sweet 'N Low^®: 0.1, 0.2% w/v], aspartame [Equal^®: 0.04, 0.08% w/v], or sucralose [Splenda^®: 0.08, 0.16% w/v]; or two doses of sucrose [3.5, 10.5% w/v]). Wheel running and fluid consumption were measured daily, with each dose (including plain water) lasting two days and two "washout" days between solutions. In a separate set of mice, the experiment was repeated without wheel access. The artificial sweeteners had no statistical effect on wheel running. However, based on proportional responses, both doses of sucrose significantly elevated wheel running in C but not HR mice. In contrast, the high dose of sucrose suppressed home-cage activity for both linetypes. Both sucrose and the artificial blends generally increased fluid consumption in a dose-dependent manner. When they had access to wheels, HR had a significantly smaller increase in consumption of artificial sweetener blends when compared with C mice, but not when housed without wheels. Overall, these results provide further evidence that the reward system of HR mice has evolved, and specifically suggest that HR mice have a reduced incentive salience for some artificial sweetener blends, likely attributable to the stronger competing reward of wheel running that has evolved in these lines.

Maternal exposure to Western diet affects adult body composition and voluntary wheel running in a genotype-specific manner in mice

Some human diseases, including obesity, Type II diabetes, and numerous cancers, are thought to be influenced by environments experienced in early life, including in utero. Maternal diet during the perinatal period may be especially important for adult offspring energy balance, potentially affecting both body composition and physical activity. This effect may be mediated by the genetic background of individuals, including, for example, potential "protective" mechanisms for individuals with inherently high levels of physical activity or high basal metabolic rates. To examine some of the genetic and environmental factors that influence adult activity levels, we used an ongoing selection experiment with 4 replicate lines of mice bred for high voluntary wheel running (HR) and 4 replicate, non-selected control lines (C). Dams (half HR and half C) were fed a "Western" diet (WD, high in fat and sucrose) or a standard diet (SD) from 2weeks prior to mating until their pups could feed on solid food (14days of age). We analyzed dam and litter characteristics from birth to weaning, and offspring mass and physical activity into adulthood. One male offspring from each litter received additional metabolic and behavioral tests. Maternal WD caused pups to eat solid food significantly earlier for C litters, but not for HR litters (interaction of maternal environment and genotype). With dam mass as a covariate, mean pup mass was increased by maternal WD but litter size was unaffected. HR dams had larger litters and tended to have smaller pups than C dams. Home-cage activity of juvenile focal males was increased by maternal WD. Juvenile lean mass, fat mass, and fat percent were also increased by maternal WD, but food consumption (with body mass as a covariate) was unaffected (measured only for focal males). Behavior in an elevated plus maze, often used to indicate anxiety, was unaffected by maternal WD. Maximal aerobic capacity (VO₂max) was also unaffected by maternal WD, but HR had higher VO₂max than C mice. Adult lean, fat, and total body masses were significantly increased by maternal WD, with greater increase for fat than for lean mass. Overall, no aspect of adult wheel running (total distance, duration, average running speed, maximum speed) or home-cage activity was statistically affected by maternal WD. However, analysis of the 8 individual lines revealed that maternal WD significantly increased wheel running in one of the 4 HR lines. On average, all groups lost fat mass after 6days of voluntary wheel running, but the absolute amount lost was greater for mice with maternal WD resulting in no effect of maternal WD on absolute or % body fat after wheel access. All groups gained lean and total body mass during wheel access, regardless of maternal WD or linetype. Measured after wheel access, circulating leptin, adiponectin, and corticosterone concentrations were unaffected by maternal WD and did not differ between HR and C mice. With body mass as a covariate, heart ventricle mass was increased by maternal WD in both HR and C mice, but fat pads, liver, spleen, and brain masses were unaffected. As found previously, HR mice had larger brains than C mice. Body mass of grand-offspring was unaffected by grand-maternal WD, but grand-offspring wheel running was significantly increased for one HR line and decreased for another HR line by grand-maternal WD. In summary, maternal Western diet had long-lasting and general effects on offspring adult morphology, but effects on adult behavior were limited and contingent on sex and genetic background.

Caffeine stimulates voluntary wheel running in mice without increasing aerobic capacity

The "energy drink" Red Bull and the "sports drink" Gatorade are often marketed to athletes, with claims that they cause performance gains. However, both are high in sugars, and also consumed by non-athletes. Few studies have addressed the effects of these drinks or their biologically active components in rodent exercise models. We used three experiments to test effects on both voluntary exercise behavior and maximal aerobic capacity in lines of mice known to differ in "athletic" traits. Mice from four replicate High Runner (HR) lines have been selectively bred for voluntary running on wheels, and run approximately three times as many revolutions per day as do mice from four non-selected Control (C) lines. HR mice also have higher endurance and maximal oxygen consumption (VO₂max) during forced treadmill exercise. In Experiment 1, we tested the hypothesis that Gatorade or Red Bull might cause or allow mice to increase their voluntary wheel running. On days 5 and 6 of 6days of wheel access, as is used to select breeders, HR mice ran 3.3-fold more than C, and females ran 1.2-fold more than males, with no linetype by sex interaction. On day 7, mice were administered Gatorade, Red Bull or tap water. During the subsequent 19-hour period, Gatorade had no statistical effect on running, but Red Bull significantly increased distance run by both sexes and in both HR and C lines. The increase in distance run caused by Red Bull was attributable to time spent running, not an increase in mean (or maximum) speed. As previous studies have found that sucrose alone does not generally increase wheel running, we tested two other active ingredients in Red Bull, caffeine and taurine, in Experiment 2. With a similar testing protocol, caffeine alone and caffeine+taurine increased running by about half the magnitude of Red Bull. In Experiment 3, we tested the hypothesis that Red Bull or caffeine alone can increase physiological performance ability during aerobic exercise, measured as VO₂max. In a repeated-measures design spanning 6days, females were housed with water bottles containing Red Bull, caffeine or water in a randomized order, and tested for VO₂max twice while receiving each fluid (6 total trials). Neither Red Bull nor caffeine significantly affected either VO₂max or a measure of trial cooperativity (rated on a scale of 1-5), but both treatments significantly reduced tiredness (rated on a scale of 1-3) scored at the end of trials for both HR and C lines. Taken together, our results suggest that caffeine increases voluntary exercise levels of mice by delaying fatigue, rather than increasing aerobic capacity.