Mark A. Chappell

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

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.

Circadian pattern of total and free corticosterone concentrations, corticosteroid-binding globulin, and physical activity in mice selectively bred for high voluntary wheel-running behavior

In vertebrates, baseline glucocorticoid concentrations vary predictably on a diel basis, usually peaking shortly before the onset of activity. Presumably, circadian patterns in glucocorticoid secretion have evolved to match predictable rises in energetic need. In mice from lines selectively bred for high voluntary wheel-running, previous studies have reported that baseline plasma corticosterone concentrations at two different times during the photophase are elevated twofold above those of non-selected control lines. Here, we tested the hypothesis that the elevated daytime corticosterone levels could be explained by a shift in the circadian pattern of corticosterone levels. We measured baseline total plasma corticosterone levels, corticosteroid-binding globulin (CBG) capacity, and calculated free corticosterone levels (corticosterone not bound to corticosteroid-binding globulin and potentially biologically active) at six points during the 24-hour cycle in males on a 12:12 photoperiod. We also examined the daily pattern of both wheel-running and home-cage activity. Based on combined analysis of all six points, the circadian pattern of total corticosterone, corticosteroid-binding globulin, and free corticosterone levels did not significantly differ between high-runner and control mice (linetype * time interaction P=0.56, 0.45, and 0.55, respectively); however, all varied with time (all P<0.0001) and mice from the selected lines had significantly elevated total (P=0.0125) and free (P=0.0140) corticosterone, with no difference in CBG binding capacity (P=0.77). All mice were active primarily during the dark phase, and the factorial increase in activity of selected relative to controls lines was 2.33 for total daily wheel revolutions and 2.76 for total daily home-cage activity. The onset of the active period for both measures of locomotor activity coincided with peak total and free corticosterone levels in both selected and control lines. These findings lend support to our hypothesis that elevated circulating corticosterone levels have evolved as an adaptation to support increased locomotor activity in the selected lines.

Standard Operative Temperatures and Thermal Energetics of the Antelope Ground Squirrel Ammospermophilus leucurus

We measured standard operative temperatures (Tes) for the diurnal ground squirrel Ammospermophilus leucurus in its Southern California desert habitat by using pelt-covered metal models of the animals. Values of Tes were used to predict duration of periods of activity, microhabitat use, and energy costs of thermoregulation at various times of the year. For A. leucurus, Tes (a direct measure of heat flow) specifies the thermal environment more realistically than any of the standard micrometeorological indices. In the hot season, Tes in unshaded areas can be 30 C above the upper critical temperature (Tuc) of A. leucurus and 20 C above air temperature for much of the day. Under such conditions maximum tolerable periods of surface activity for A. leucurus are 7-9 min. Even in the shade, Tes often exceeds Tuc, and the only available thermal refugia on hot days are in underground burrows. These findings strongly support the interpretation that the thermoregulatory strategy of A. leucurus involves cycles of transient hyperthermia followed by periods of passive heat dissipation underground. Rates of heat gain from the environment in summer are three to four times the rate of metabolic heat production, even for active individuals. In the cool season Tes in open areas is usually within the thermal neutral zone, and the thermoregulatory responses of A. leucurus follow the standard mammalian pattern.

Metabolism and thermoregulation in desert and montane grasshoppers

AbstractTemperature regulation and oxygen consumption were examined in two species of grasshoppers: Melanoplus sanguinipes from cold alpine tundra at elevation 3,800 m, and Trimerotropis pallidipennis from hot desert habitats at elevation 250 m. Both species utilized behavioral thermoregulation to keep body temperature (Tb) more constant than environmental temperatures (Te) during the day. The difference in average Tbin the two species was much less than the difference in Tes. Microclimate measurements indicate that temperature regulation is not difficult for M. sanguinipes, but T. pallidipennis must restrict activity for much of the day to avoid heat stress and can easily overheat if it moves into sunlit areas. Oxygen consumption (

Repeatability of aerobic performance in Red Junglefowl: Effects of ontogeny and nematode infection

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Repeatability of Maximal Aerobic Performance in Belding’s Ground Squirrels, Spermophilus beldingi

) at average Tband total daily energy expenditures are higher in M. sanguinipes than in T. pallidipennis, as is the Q10 for

Effects of size, sex, and voluntary running speeds on costs of locomotion in lines of laboratory mice selectively bred for high wheel-running activity.

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