Antioxidant gene expression in active and sedentary house mice (Mus domesticus) selected for high voluntary wheel-running behavior

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.

Mitochondrial haplotypes are not associated with mice selectively bred for high voluntary wheel running

Mitochondrial haplotypes have been associated with human and rodent phenotypes, including nonshivering thermogenesis capacity, learning capability, and disease risk. Although the mammalian mitochondrial D-loop is highly polymorphic, D-loops in laboratory mice are identical, and variation occurs elsewhere mainly between nucleotides 9820 and 9830. Part of this region codes for the tRNA^Arg gene and is associated with mitochondrial densities and number of mtDNA copies. We hypothesized that the capacity for high levels of voluntary wheel-running behavior would be associated with mitochondrial haplotype. Here, we analyzed the mtDNA polymorphic region in mice from each of four replicate lines selectively bred for 54 generations for high voluntary wheel running (HR) and from four control lines (Control) randomly bred for 54 generations. Sequencing the polymorphic region revealed a variable number of adenine repeats. Single nucleotide polymorphisms (SNPs) varied from 2 to 3 adenine insertions, resulting in three haplotypes. We found significant genetic differentiations between the HR and Control groups (F_st = 0.779, p ≤ 0.0001), as well as among the replicate lines of mice within groups (F_sc = 0.757, p ≤ 0.0001). Haplotypes, however, were not strongly associated with voluntary wheel running (revolutions run per day), nor with either body mass or litter size. This system provides a useful experimental model to dissect the physiological processes linking mitochondrial, genomic SNPs, epigenetics, or nuclear-mitochondrial cross-talk to exercise activity.

The effect of regular exercise on antioxidant enzyme activities and lipid peroxidation levels in both hippocampi after occluding one carotid in rat

Regular exercise has beneficial effects on cerebrovascular diseases; however, its biochemical mechanisms are not fully known. The purpose of this study was to determine antioxidant enzyme activities and lipid peroxidation of both hippocampi after applying exercise followed by occluding one common carotid. Wistar rats were divided into four groups of control, exercise, hypoperfusion and exercise-hypoperfusion (exe-hypo). In the exercise and exe-hypo groups, the rats were forced to run on a treadmill for 1 h a day for 2 months. The right common carotid of the animals in the (exe-hypo) group was occluded after the cessation of exercise. Surgery without occlusion of the carotid was applied on the control (without exercise) and exercise groups. All animals were sacrificed 1 and 24 h after surgery. The levels of malondialdehyde (MDA) and antioxidant enzyme activities in the hippocampi were measured. A significant interaction was observed between the exercise and hypoperfusion in both hippocampi (p<0.05). In comparison with the control group, there was significant elevation of catalase activity in the right and left hippocampus of the hypo group at 24 h (p<0.0001). Regarding the differences between the hemispheres, there was a significant increase in MDA and decrease in catalase activity in the left hippocampus in hypoperfusion group, but the exercise in the exe-hypo group succeeded in abolishing these alterations which were caused by hypoperfusion, This study shows that exercise pre-conditioning prevents some alterations in brain oxidant-antioxidant status which are induced by cerebral hypoperfusion. Further studies are needed in order to clarify the mechanism of exercise.

Modulation of endogenous antioxidant activity by resveratrol and exercise in mouse liver is age dependent

Aging is a multifactorial process in which oxidative damage plays an important role. Resveratrol (RSV) and exercise delay some of the damages occurring during aging and increase life span and health span. We treated mice at different ages with RSV during 6 months and trained them during the last 6 weeks to determine if RSV and exercise induce changes in endogenous antioxidant activities in liver and if their effects depend on the age of the animal at the beginning of the intervention. Aging was accompanied by the increase in oxidative damage in liver especially affecting the glutathione-dependent system. Both RSV and exercise reversed the effect of aging and maintained high activities of glutathione, glutathione peroxidase, and glutathione transferase activities in old animals.

NAD(P)H

quinone acceptor oxidoreductase activity was also increased. Modulation of antioxidant activities was not completely accompanied by changes at the protein level. Whereas glutathione peroxidase 1 protein increased in parallel to the higher activity in old animals,

NAD(P)H

quinone acceptor oxidoreductase protein decreased by RSV although the activity was enhanced. Our results indicate that RSV and exercise revert the effect of aging in liver of old animals maintaining higher antioxidant activities and decreasing oxidative damage. Short-term interventions are enough to produce beneficial effects of RSV or exercise at later ages.

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

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.

Voluntary exercise training in mice increases the expression of antioxidant enzymes and decreases the expression of TNF-alpha in intestinal lymphocytes

Acute exercise in mice induces intestinal lymphocyte (IL) apoptosis. Freewheel running reduces apoptosis and forced exercise training increases splenocyte antioxidant levels. The purpose of this study was to examine the effect of freewheel running and acute exercise on mouse IL numbers and concentrations of apoptosis and antioxidant proteins and pro-inflammatory cytokines in IL. Female C57BL/6 mice had access to in-cage running wheels (RW) or cages without wheels (NRW) for 16 weeks and were randomized at the end of training to no exercise control (TC) or to treadmill exercise with sacrifice after 90 min of running (TREAD; 30 min, 22 m min(-1); 30 min, 25 m min(-1); 30 min, 28 m min(-1); 2 degrees slope). IL were analyzed for pro-(caspase 3 and 7) and anti-(Bcl-2) apoptotic proteins, endogenous antioxidants (glutathione peroxidase: GPx; catalase: CAT) and the pro-inflammatory cytokine, TNF-alpha. RW mice had higher cytochrome oxidase (p<0.001) and citrate synthase (p<0.01) activities in plantaris and soleus muscles and higher GPx and CAT expression in IL (p<0.05) (indicative of training) compared with NRW mice. TNF-alpha expression was lower (p<0.05) and IL numbers higher (p<0.05) in RW vs. NRW mice. No training effect was observed for apoptotic protein expression, although TREAD resulted in higher caspase and lower Bcl-2. These results suggest that freewheel running in mice for 16 weeks enhances antioxidant and reduces TNF-alpha expression in IL but does not reduce pro-apoptotic protein expression after acute exercise. Results are discussed in terms of implications for inflammatory bowel diseases where apoptotic proteins and TNF-alpha levels are elevated.

The evolution of gene expression in mouse hippocampus in response to selective breeding for increased locomotor activity

The evolution of behavior has been notoriously difficult to study at the molecular level, but mouse genetic technology offers new promise. We applied selective breeding to increase voluntary wheel running in four replicate lines of Mus domesticus (S mice) while maintaining four additional lines through random breeding to serve as controls (C mice). The goal of the study was to identify the gene expression profile of the hippocampus that may have evolved to facilitate the increased voluntary running. The hippocampus was of interest because it is known to display marked physiological responses in association with wheel running itself. We used high-density oligonucleotide arrays representing 11,904 genes. To control for the confounding influence of physical activity itself on gene expression, animals were housed individually without access to running wheels, and were sampled during the day when they are normally inactive. Two-month-old female mice in estrus were used (n = 16 total; two per line; 8 S and 8 C). After correcting for an acceptable false discovery rate (10%), 30 genes, primarily involved in transcription and translation, significantly increased expression whereas 23 genes, distributed among many categories including immune function and neuronal signaling, decreased expression in S versus C mice. These changes were relatively small in magnitude relative to the changes in gene expression that occur in the hippocampus in response to wheel running itself. A priori tests of dopamine receptor expression levels demonstrated an increase of approximately 20% in the expression of D2 and D4 receptors. These results suggest that relatively small changes in the expression patterns of hippocampal genes underlie large changes in phenotypic response to selection, and that the genetic architecture of running motivation likely involves the dopaminergic system as well as CNS signaling machinery.

Lifelong voluntary exercise in the mouse prevents age-related alterations in gene expression in the heart

We present the first quantitative gene expression analysis of cardiac aging under conditions of sedentary and active lifestyles using high-density oligonucleotide arrays representing 11,904 cDNAs and expressed sequence tags (ESTs). With these data, we test the hypothesis that exercise attenuates the gene expression changes that normally occur in the aging heart. Male mice (Mus domesticus) were sampled from the 16th generation of selective breeding for high voluntary exercise. For the selective breeding protocol, breeders were chosen based on the maximum number of wheel revolutions run on days 5 and 6 of a test at 8 wk of age. For the colony sampled herein, mice were housed individually over their entire lifetimes (from weaning) either with or without access to running wheels. The hearts of these two treatment groups (active and sedentary) were assayed at middle age (20 mo) and old age (33 mo). Genes significantly affected by age in the hearts of the sedentary population by at least a 50% expression change (n = 137) were distributed across several major categories, including inflammatory response, stress response, signal transduction, and energy metabolism. Genes significantly affected by age in the active population were fewer (n = 62). Of the 42 changes in gene expression that were common to both treatment groups, 32 (72%) displayed smaller fold changes as a result of exercise. Thus exercise offset many age-related gene expression changes observed in the hearts of the sedentary animals. These results suggest that adaptive physiological mechanisms that are induced by exercise can retard many effects of aging on heart muscle at the transcriptional level.