Wheel-running activity and energy metabolism in relation to ambient temperature in mice selected for high wheel-running activity

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381

434

Summary Mammals expend energy in many ways, including basic cellular maintenance and repair, digestion, thermoregulation, locomotion, growth and reproduction. These processes can vary tremendously among species and individuals, potentially leading to large variation in daily energy expenditure (DEE). Locomotor energy costs can be substantial for large-bodied species and those with high-activity lifestyles. For humans in industrialized societies, locomotion necessary for daily activities is often relatively low, so it has been presumed that activity energy expenditure and DEE are lower than in our ancestors. Whether this is true and has contributed to a rise in obesity is controversial. In humans, much attention has centered on spontaneous physical activity (SPA) or non-exercise activity thermogenesis (NEAT), the latter sometimes defined so broadly as to include all energy expended due to activity, exclusive of volitional exercise. Given that most people in Western societies engage in little voluntary exercise, increasing NEAT may be an effective way to maintain DEE and combat overweight and obesity. One way to promote NEAT is to decrease the amount of time spent on sedentary behaviours (e.g. watching television). The effects of voluntary exercise on other components of physical activity are highly variable in humans, partly as a function of age, and have rarely been studied in rodents. However, most rodent studies indicate that food consumption increases in the presence of wheels; therefore, other aspects of physical activity are not reduced enough to compensate for the energetic cost of wheel running. Most rodent studies also show negative effects of wheel access on body fat, especially in males. Sedentary behaviours per se have not been studied in rodents in relation to obesity. Several lines of evidence demonstrate the important role of dopamine, in addition to other neural signaling networks (e.g. the endocannabinoid system), in the control of voluntary exercise. A largely separate literature points to a key role for orexins in SPA and NEAT. Brain reward centers are involved in both types of physical activities and eating behaviours, likely leading to complex interactions. Moreover, voluntary exercise and, possibly, eating can be addictive. A growing body of research considers the relationships between personality traits and physical activity, appetite, obesity and other aspects of physical and mental health. Future studies should explore the neurobiology, endocrinology and genetics of physical activity and sedentary behaviour by examining key brain areas, neurotransmitters and hormones involved in motivation, reward and/or the regulation of energy balance.

Section: Dee and Its Componentsmentioning

confidence: 94%

Section: Summary Of Experimental Studies With Humansmentioning

confidence: 98%

Section: Dee and Its Componentsmentioning

confidence: 99%

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The biological control of voluntary exercise, spontaneous physical activity and daily energy expenditure in relation to obesity: human and rodent perspectives

Garland

Schutz

Chappell

et al. 2011

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381

434

“…Our mice were working at 3.7ϫBMR [assuming an estimated BMR of 0.61·kJ·g -1 ·d -1 in the Workload mice; based on the RMR measured at 22°C and earlier measurements in this strain of mice at thermoneutrality, 30°C (Vaanholt et al, 2007)], and thus close to their maximal sustainable rate. Studies investigating maximal sustainable rates imposed by other factors than exercise, such as cold exposure and lactation, have shown that mice are capable of even higher rates of energy expenditure.…”

Section: Body Temperature and Plasma Corticosteronementioning

confidence: 99%

Behavioural and physiological responses to increased foraging effort in male mice

Vaanholt

Jong

Garland

et al. 2007

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SUMMARY Free-living animals must forage for food and hence may face energetic constraints imposed by their natural environmental conditions (e.g. ambient temperature, food availability). Simulating the variation in such constraints,we have experimentally manipulated the rate of work (wheel running) mice must do to obtain their food, and studied the ensuing behavioural and physiological responses. This was done with a line of mice selectively bred for high spontaneous wheel running and a randomly bred control line that vary in the amount of baseline wheel-running activity. We first determined the maximum workload for each individual. The maximum workload animals could engage in was around 23 km d–1 in both control and activity-selected mice,and was not associated with baseline wheel-running activity. We then kept mice at 90% of their individual maximum and measured several physiological and behavioural traits. At this high workload, mice increased wheel-running activity from an average of 10 to 20 km d–1, and decreased food intake and body mass by approximately 20%. Mass-specific resting metabolic rate strongly decreased from 1.43 to 0.98 kJ g–1d–1, whereas daily energy expenditure slightly increased from 2.09 to 2.25 kJ g–1 d–1. Costs of running decreased from 2.3 to 1.6 kJ km–1 between baseline and workload conditions. At high workloads, animals were in a negative energy balance, resulting in a sharp reduction in fat mass as well as a slight decrease in dry lean mass. In addition, corticosterone levels increased, and body temperature was extremely low in some animals at high workloads. When challenged to work for food, mice thus show significant physiological and behavioural adjustments.

“…One possible explanation for the lack of major alterations to the digestive track is that previous results Vaanholt et al, 2006;Swallow et al, 2001;Rezende et al, 2009) have demonstrated that the incremental cost of wheel running represents only a small portion of the total energy budgets of the mice. Koteja et al (1999) conclude: 'If wheel running in the selected lines continues to increase mainly by increases in velocity, then constraints related to energy acquisition are unlikely to be an important factor limiting further selective gain.'…”

Section: Controlmentioning

confidence: 99%

Effects of activity, genetic selection, and their interaction on muscle metabolic capacities and organ masses in mice

Kelly

Gomes

Kolb

et al. 2017

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Chronic voluntary exercise elevates total daily energy expenditure and food consumption, potentially resulting in organ compensation supporting nutrient extraction/utilization. Additionally, species with naturally higher daily energy expenditure often have larger processing organs, which may represent genetic differences and/or phenotypic plasticity. We tested for possible adaptive changes in organ masses of four replicate lines of house mice selected (37 generations) for high running (HR) compared with four non-selected control (C) lines. Females were housed with or without wheel access for 13-14 weeks beginning at 53-60 days of age. In addition to organ compensation, chronic activity may also require an elevated aerobic capacity. Therefore, we also measured hematocrit and both citrate synthase activity and myoglobin concentration in heart and gastrocnemius. Both selection (HR versus C) and activity (wheels versus no wheels) significantly affected morphological and biochemical traits. For example, with body mass as a covariate, mice from HR lines had significantly higher hematocrit and larger ventricles, with more myoglobin. Wheel access lengthened the small intestine, increased relative ventricle and kidney size, and increased skeletal muscle citrate synthase activity and myoglobin concentration. As compared with C lines, HR mice had greater training effects for ventricle mass, hematocrit, large intestine length and gastrocnemius citrate synthase activity. For ventricle and gastrocnemius citrate synthase activity, the greater training was quantitatively explainable as a result of greater wheel running (i.e. 'more pain, more gain'). For hematocrit and large intestine length, differences were not related to amount of wheel running and instead indicate inherently greater adaptive plasticity in HR lines.