Stimulation by voluntary exercise of adrenal glucocorticoid secretion in mature female hamsters

Running wheel access fails to resolve impaired sustainable health in mice feeding a high fat sucrose diet

Diet and physical activity are thought to affect sustainable metabolic health and survival. To improve understanding, we studied survival of mice feeding a low-fat (LF) or high-saturated fat/high sugar (HFS) diet, each with or without free running wheel (RW) access. Additionally several endocrine and metabolic health indices were assessed at 6, 12, 18 and 24 months of age. As expected, HFS feeding left-shifted survival curve of mice compared to LF feeding, and this was associated with increased energy intake and increased (visceral/total) adiposity, liver triglycerides, and increased plasma cholesterol, corticosterone, HOMA-IR, and lowered adiponectin levels. Several of these health parameters improved (transiently) by RW access in HFS and LF fed mice (i.e., HOMA-IR, plasma corticosterone), others however deteriorated (transiently) by RW access only in HFS-fed mice (i.e., body adiposity, plasma resistin, and free cholesterol levels). Apart from these multiple and sometimes diverging health effects of RW access, RW access did not affect survival curves. Important to note, voluntary RW activity declined with age, but this effect was most pronounced in the HFS fed mice. These results thus challenge the hypothesis that voluntary wheel running can counteract HFS-induced deterioration of survival and metabolic health.

Spontaneous appetence for wheel-running: a model of dependency on physical activity in rat

According to human observations of a syndrome of physical activity dependence and its consequences, we tried to examine if running activity in a free activity paradigm, where rats had a free access to activity wheel, may present a valuable animal model for physical activity dependence and most generally to behavioral dependence. The pertinence of reactivity to novelty, a well-known pharmacological dependence predictor was also tested. Given the close linkage observed in human between physical activity and drugs use and abuse, the influence of free activity in activity wheels on reactivity to amphetamine injection and reactivity to novelty were also assessed. It appeared that (1) free access to wheel may be used as a valuable model for physical activity addiction, (2) two populations differing in activity amount also differed in dependence to wheel-running. (3) Reactivity to novelty did not appeared as a predictive factor for physical activity dependence (4) activity modified novelty reactivity and (5) subjects who exhibited a high appetence to wheel-running, presented a strong reactivity to amphetamine. These results propose a model of dependency on physical activity without any pharmacological intervention, and demonstrate the existence of individual differences in the development of this addiction. In addition, these data highlight the development of a likely vulnerability to pharmacological addiction after intense and sustained physical activity, as also described in man. This model could therefore prove pertinent for studying behavioral dependencies and the underlying neurobiological mechanisms. These results may influence the way psychiatrists view behavioral dependencies and phenomena such as doping in sport or addiction to sport itself.

Immediate Effects of a Single Exercise on Behavior and Memory in the Early Period of Traumatic Brain Injury in Rats

Objective

To evaluate the immediate effect of single exercise on physical performance and memory in the early stage of traumatic brain injury (TBI) in rats.

Methods

Ninety TBI rats were randomly assigned to T0 (sedentary), T10 (treadmill 10 m/min for 30 minutes), or T20 (treadmill 20 m/min for 30 minutes) groups, on day 3 (D3), D7, and D14 after TBI, respectively. Rotarod (RR), Barnes maze (BM), brain magnetic resonance imaging (MRI) and MR spectroscopy were performed immediately before and 6 hours after exercise. Rats were sacrificed for immunohistochemistry with heat shock protein 70 (Hsp70) and glial fibrillary acidic protein (GFAP).

Results

On D3, the T10 and T20 groups demonstrated significant improvement in RR (p<0.05). On D7, only the T20 group showed significantly enhanced RR (p<0.05). In BM on D3, the T20 group showed significant deterioration compared with the other groups (p<0.05). Lesion volume did not significantly differ among the groups. MR spectroscopy on D3 showed that only the T20 group had significantly increased choline/creatine and 0.9/creatine (p<0.05). In the perilesional area on D3, only T20 had a significantly higher Hsp70 and GFAP than the T0 group. On D7, Hsp70 was significantly higher in the T20 group than in the T0 group (p<0.05). In the ipsilesional hippocampus on D3, the T20 group showed a significantly higher Hsp70 and GFAP than the T0 group (p<0.05).

Conclusion

A single session of low-intensity exercise in the early period of TBI improves behavioral performance without inducing cognitive deficits. However, high-intensity exercise can exacerbate cognitive function in the early period after TBI. Therefore, the optimal timing of rehabilitation and exercise intensity are crucial in behavior and memory recovery after TBI.

Voluntary exercise protects against ulcerative colitis by up-regulating glucocorticoid-mediated PPAR-γ activity in the colon in mice

AIM

Voluntary exercise has been shown to protect against the development of ulcerative colitis, but the mechanism is not fully understood. We hypothesized that prior voluntary exercise would attenuate colonic inflammation and ameliorate clinical symptoms in dextran sulphate sodium (DSS)-induced ulcerative colitis by increasing glucocorticoid production and up-regulating PPAR-γ activity in the colon.

METHODS

Male C57Bl/6J mice were assigned to sedentary, exercise, exercise with PPAR-γ antagonist GW9662 or glucocorticoid synthesis inhibitor metyrapone. Following the completion of the 30 days' exercise training programme, they were treated with or without 2% DSS in drinking water for 5 days, followed by 5 days of regular water.

RESULTS

Compared with sedentary mice, exercise mice exhibited improved clinical symptoms (weight loss and diarrhoea) and less inflammation (expression of pro-inflammatory cytokines and histological injury) in response to DSS, whereas these beneficial effects were abolished by both GW9662 and metyrapone treatment. Molecular studies revealed that exercise significantly increased the expression of PPAR-γ, augmented the expression of steroidogenic enzymes (CYP11A1 and CYP11B1) and elevated corticosterone levels in the colon. GW9662 treatment reversed the expression of PPAR-γ without altering the expression of steroidogenic enzymes and corticosterone secretion in the colon, while metyrapone treatment blocked glucocorticoid secretion and abrogated the increase in PPAR-γ expression in the colon.

CONCLUSION

These findings suggest that prior voluntary exercise suppresses the expression of pro-inflammatory cytokines in the colon in response to inflammatory challenge by up-regulating glucocorticoid-mediated PPAR-γ activity, contributing to protection against the development of ulcerative colitis.

Effects of birth date and natal dispersal on faecal glucocorticoid concentrations in juvenile Common hamsters

In seasonally breeding animals, timing of reproduction in females can influence offspring development and survival. Temporal and energetic constraints are often more pronounced in juveniles born late in the season, and could activate the stress axis. Common hamsters (Cricetus cricetus) are hibernating rodents, and adult females produce up to three litters during the active season. Birth dates range from May to September, and shortly after natal emergence pups are weaned and start to disperse. In this study, we used faecal cortisol metabolites (FCM) as a non-invasive measure of recent glucocorticoid exposure. We compared FCM levels between early- (June/July) and late- (August/September) born juvenile Common hamsters during their first weeks after natal emergence. We further compared FCM levels in juveniles born in the study area and individuals that immigrated either early or late in the season. Additionally, we investigated potential effects of human disturbances on cortisol secretion patterns. FCM levels in late-born juveniles increased during the first weeks post-emergence and were significantly higher than those in early-born individuals during the post-weaning period. Late-immigrating juveniles had significantly higher FCM levels than early immigrants and residents during the same time period. Individuals that inhabited areas frequently used by humans had higher FCM levels than those in low-impact areas. These results indicate that the seasonal timing of birth and dispersal affect cortisol secretion patterns in juvenile Common hamsters. As all juveniles immerged into their hibernacula during early October, we assume that late-born and late-immigrated individuals have less time to prepare for hibernation. This could elevate energetic demands and increase exposure to predators and/or humans during food caching. These factors might lead to increased adrenal activity and thus, elevated FCM concentrations in these individuals. Potential consequences of these time constraints and associated physiological effects could be reflected in the lower overwinter survival rates of juveniles born late in the season.

Short-term voluntary exercise in the rat causes bone modeling without initiating a physiological stress response

Recent research has revealed a neuroendocrine connection between the skeleton and metabolism. Exercise alters both bone modeling and energy balance and may be useful in further developing our understanding of this complex interplay. However, research in this field requires an animal model of exercise that does not cause a physiological stress response in the exercised subjects. In this study, we develop a model of short-term voluntary exercise in the female rat that causes bone modeling without causing stress. Rats were randomly assigned to one of three age-matched groups: control, tower climbing, and squat exercise (rising to an erect bipedal stance). Exercise for 21 days resulted in bone modeling as assessed by peripheral quantitative computed tomography. Fecal corticosterone output was used to assess physiological stress at three time points during the study (preexercise, early exercise, and late in the exercise period). There were no differences in fecal corticosterone levels between groups or time points. This model of voluntary exercise in the rat will be useful for future studies of the influence of exercise on the relationship between skeletal and metabolic health and may be appropriate for investigation of the developmental origins of those effects.

Exercise increases BDNF levels in the striatum and decreases depressive-like behavior in chronically stressed rats

Early life stress in humans can affect the development of neurons and neurotransmitter systems and predispose an individual to the subsequent development of depression. Similarly, in rats, maternal separation causes anxiety and depressive-like behavior and decreased corticosterone levels. Patients receiving pharmacological treatment for depression often experience negative side-effects or do not respond optimally and therefore the use of exercise as alternative antidepressant treatment is investigated. The aim of the study was to see whether rats subjected to both early life stress and chronic stress later in life show differences in depressive-like behavior, neurotrophin levels, stress hormone levels and antioxidant capacity of serum after chronic voluntary exercise as treatment. Rat pups were maternally separated and one group were allowed access to running wheels for 6 weeks while control rats were also handled and put in cages without running wheels. All rats were subjected to chronic restraint stress during adulthood. A forced swim test was done to test for depressive-like behavior. Neurotrophins were measured in the ventral hippocampus and striatum; baseline stress hormones were measured in blood plasma as well as the anti-oxidative potential of serum. Compared to controls, rats that exercised had no difference in baseline stress hormones, but had decreased immobility times in the forced swim test, increased brain derived neurotrophic factor (BDNF) levels in the striatum and decreased anti-oxidative potential of their serum. The mechanism by which depressive-like behavior was improved may have been mediated through increased striatal BDNF levels, resulting in increased neuroplasticity and the prevention of neuronal death.

Mild to moderate early exercise promotes recovery from cerebral ischemia in rats

OBJECTIVE

We examined the effects of various exercise intensities on recovery from middle cerebral artery occlusion (MCAO) in rats.

METHODS

First, we administered a 120-minute left MCAO to male Sprague-Dawley rats and randomly assigned them to one of four groups: no exercise (Group 1), mild exercise (Group 2), moderate exercise (Group 3), and severe exercise (Group 4). Then, we trained the rats for 30 min per day for one week or two weeks. We used a five-point neurological evaluation scale to measure neurological deficits 1-day, 4-days, 7-days, 10-days and 14-days after MCAO and measured infarct volume by use of 2% 2,3,4-triphenyltetrazolium chloride in exercised brains. We also performed immunohistochemistry analysis of the brain to observe reactive astrocytosis at the peri-infarct region.

RESULTS

Neurological examination indicated that Group 2 and 3 recovered better than Group 1 after one week and two weeks (p < 0.05). Moreover, Group 2 and 3 had reduced brain infarct volume compared with Group 1 after one week (p < 0.05). There were no significant differences between Group 4 and Group 1. The thickness of the peri-infarct astrocytosis was significantly reduced in Group 4 relative to Group 1 after one week. There was a significant negative correlation between the extent of reactive astrocytosis and neurological recovery (r = -0.648, p < 0.01).

CONCLUSION

This study demonstrates that mild to moderate exercise that begins soon after induced cerebral ischemia promotes recovery and that astrocytes may have an important role in the recovery process.

Effect of a cage divider permitting social stimuli on stress and food intake in rats

The need to obtain data from individual laboratory animals has forced many researchers to singly-house small animals. This is costly to the researcher and isolation can adversely affect animal physiology and behavior which in turn may threaten the validity and generalization of experiment results to humans. We assessed the practical use of a housing device - dubbed "Buddy Barrier" (BB) - that allows social stimulation in a paired-housing situation while at the same time permitting the collection of individual measures that traditionally require individual-housing. To assess stress responses to the BB, adult male rats were single or pair-housed for several days with and without a BB in the cage. Fecal corticosterone metabolites (fCORT), food intake and body weight were monitored daily. Plasma CORT and adrenal catecholamine levels were assessed at the end of the housing manipulation. Stress hormone measures did not differ in paired vs. singly-housed rats and paired rats quickly habituated to introduction and removal of the BB. Barring a trend for paired rats to eat more in the first 4 h of the dark, there was no difference in 24 h intakes or body weight gain between singly and paired-housed rats. While the BB attenuated 24 h intakes in both groups, intakes normalized to non-BB conditions by the third BB reintroduction. A device such as the BB can enhance the welfare of animals by providing social enrichment without compromising the integrity of experimental protocols traditionally requiring single-housing. In times of lagging research funding it can also substantially reduce housing costs.

Infant temperament predicts life span in female rats that develop spontaneous tumors

In a recent study, we found that male rats that minimally explored a novel environment as infants died significantly faster than their more exploratory brothers. At death, these males had various complex pathologies, precluding identification of specific hormonal mechanisms underlying adult disease progression and mortality. To minimize the variance of disease processes at the end of life, we conducted a longitudinal study with female Sprague-Dawley rats prone to high rates of spontaneous mammary and pituitary tumors. For females that developed either mammary or pituitary tumors, those that had been neophobic (least exploratory) as infants died approximately 6 months earlier than their neophilic (most exploratory) sisters. In the case of mammary tumors, both benign and malignant, neophobic females developed palpable tumors earlier than neophilic females, whereas the interval between first palpation and death was the same for all females, indicating psychosocial regulation of early rather than later stages of the disease. Neophobic females' ovarian function aged more rapidly than their neophilic sisters. Concomitantly, they had lower corticosterone responses to restraint in late adulthood, ruling out high estrogen or corticosterone levels during senescence as causal factors in their accelerated mortality. During puberty, when mammary tissue is proliferating and differentiating, neophobic females experienced more irregular cycles with prolonged "luteal" phases, suggesting a role for prolactin, prolonged progesterone and fewer estrogen surges during this sensitive period for mammary tumor risk. Thus, we identified prolactin, estrogen, progesterone and possibly corticosterone dynamics as candidates for neuroendocrine mechanisms linking infant temperament with onset of adult neoplastic disease.

Effect of voluntary exercise on peripheral tissue glucocorticoid receptor content and the expression and activity of 11β-HSD1 in the Syrian hamster

Recent findings indicate that elevated levels of glucocorticoids (GC), governed by the expression of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) and GC receptors (GR), in visceral adipose tissue and skeletal muscle lead to increased insulin resistance and the metabolic syndrome. Paradoxically, evidence indicates that aerobic exercise attenuates the development of the metabolic syndrome even though it stimulates acute increases in circulating GC levels. To investigate the hypothesis that training alters peripheral GC action to maintain insulin sensitivity, young male hamsters were randomly divided into sedentary (S) and trained (T) groups ( n = 8 in each). The T group had 24-h access to running wheels over 4 wk of study. In muscle, T hamsters had lower 11β-HSD1 protein expression (19.2 ± 1.40 vs. 22.2 ± 0.96 optical density, P < 0.05), similar 11β-HSD1 enzyme activity (0.9 ± 0.27% vs. 1.1 ± 0.26), and lower GR protein expression (9.7 ± 1.86 vs. 15.1 ± 1.78 optical density, P < 0.01) than S hamsters. In liver, 11β-HSD1 protein expression tended to be lower in T compared with S (19.2 ± 0.56 vs. 21.4 ± 1.05, P = 0.07), whereas both enzyme activity and GR protein expression were similar. In contrast, visceral adipose tissue contained ∼2.7-fold higher 11β-HSD1 enzyme activity in T compared with S (12.9 ± 3.3 vs. 4.8 ± 1.5% conversion, P < 0.05) but was considerably smaller in mass (0.24 ± 0.02 vs. 0.71 ± 0.06 g). Thus the intracellular adaptation of GC regulators to exercise is tissue specific, resulting in decreases in GC action in skeletal muscle and increases in GC action in visceral fat. These adaptations may have important implications in explaining the protective effects of aerobic exercise on insulin resistance and other symptoms of the metabolic syndrome.

RU486 blocks the anti-inflammatory effects of exercise in a murine model of allergen-induced pulmonary inflammation

In an ovalbumin (OVA)-driven murine model of allergic pulmonary inflammation, we have shown previously that moderate-intensity aerobic exercise training attenuates inflammatory responses, disease progression, and NF-kappaB activation within the sensitized lung. Glucocorticoids (GCs), potent anti-inflammatory agents, have been shown to alter transcriptional events that are important in asthmatic pathogenesis, such as NF-kappaB activation. Notably, exercise training can alter the production and signaling capacity of endogenous GCs. Because GCs exert their anti-inflammatory effects through binding to intracellular glucocorticoid receptors (GRs), we examined the role of the GR in facilitating the anti-inflammatory effects of exercise. Results show that, in exercised OVA-sensitized mice, treatment with the GR antagonist RU486 blocked the exercise-induced reductions in cellular infiltration of the airways (p < .05), KC and soluble VCAM-1 protein levels in the bronchoalveloar lavage fluid (p < .05), and NF-kappaB translocation and DNA binding within the lung to levels similar to those observed in sedentary OVA-sensitized mice. Importantly, RU486 treatment also blocked exercise-induced increases in GR nuclear translocation to the levels seen in sensitized control mice. Together, these results suggest that GR nuclear translocation and NF-kappaB activation play roles in mediating the anti-inflammatory effects of exercise in allergen-mediated lung pathology.

Stress regulation of sulfotransferases in male rat liver

Sulfotransferase (SULT) catalyzed sulfation is responsible for hormone regulation and xenobiotic detoxification. Induction of SULTs by various hormones has been reported. Stress regulation of SULTs has not been reported, however. Here we report that rat liver SULTs can be regulated by physical stress (forced running, EX) and chemical stress (the organophosphorus pesticide parathion, PS). Both EX and PS increased rat liver phenol-sulfating SULT1A1 and hydroxysteroid-sulfating SULT2A1 activities. The increase in SULT1A1 activity did not correlate with protein (Western blot) or mRNA (RT-PCR) results but correlated well with increased non-protein soluble thiols. This suggests a possible Cys modification mechanism for stress regulation of SULT1A1. In vitro studies on GSH/GSSG effects on SULT1A1 activity support this conclusion. In contrast, SULT2A1 activity following physical or chemical stress treatments correlated well with protein and mRNA levels. This suggests a stress regulation mechanism of SULT2A1 at the gene transcription level, possibly occurring via hormones.

Fear of novelty in infant rats predicts adult corticosterone dynamics and an early death

Individuals who are fearful of novelty have a larger hypothalamic-pituitary-adrenal axis response than do nonfearful individuals. We hypothesized that a fearful behavioral style emerging early in life would be associated with life-long altered adrenal activity. Because there is ample physiological evidence both costs and benefits of adrenal activation, we determined whether such a stable emotional-neuroendocrine trait was associated with differential morbidity and mortality. To conduct such lifespan work, we studied a relatively short-lived mammal: the Norway rat. We first established that an animal's hesitation or willingness to explore a novel environment ("neophobia" and "neophilia," respectively) is an identifiable and stable behavioral trait in young-adult males and that neophobia, compared with neophilia, was associated with a greater glucocorticoid response to novelty. Second, we were able to detect behavioral differences among infant rats within a family, and this behavioral disposition at infancy predicted the magnitude of the glucocorticoid response in late middle age. Males identified as neophobic during infancy died sooner than their less fearful brothers. Although both types of males died with similar pathologies (tumors), neophobic males were 60% more likely to die at any point in time. This lifespan study identifies an emotional trait in infancy that predicts an early death and an associated neuroendocrine trait in adulthood that is a potential mechanism underlying the relationship between behavioral style and longevity.

Evaluation of the effects of chronic mild stressors on hedonic and physiological responses: sex and strain compared

The chronic mild stress (CMS) paradigm was developed in order to simulate in animals the symptom of anhedonia, a major feature of depression. Typically, changes in hedonic status are interpreted from a decrease in either intake or preference for a mild sucrose solution. Although the incidence of clinical depression is significantly higher in women than in men, the study of this disorder in most animal models of depression has been based on the responses of male rodents. The purpose of this study was to compare the effects of 6 weeks of CMS administration among male and female rats of two rat strains, Sprague-Dawley (SD) and Long Evans (LE), with respect to physiological (body, adrenal gland, and spleen weight) and biochemical (plasma corticosterone levels) indices of stress as well as evaluations of 1 and 24 h sucrose intake and preference. Estrous cycle was tracked throughout the study. Overall, our results indicate a slower rate of weight gain in animals, greater in males, exposed to the chronic stressor regime. Furthermore, CMS is shown to disrupt estrous cycling, predominantly in the Long Evans strain of rats. The main behavioral finding was a significant reduction in 24 h sucrose intake in female treated groups, which was not accompanied by alterations in preference. Corticosterone levels were elevated in CMS-treated animals relative to the singly housed control groups, but exposure to a subsequent stressor was not influenced by the stress history. Taken together, the effects of chronic stressor exposure are evident, based on physiological and biochemical indices, although none of the measures distinguished any striking gender specific reactions. The usefulness of sucrose intake or preference as behavioral indices of CMS-induced anhedonia in males and females is modest at best.

Influence of regular voluntary exercise on spontaneous and social stress-affected sleep in mice

To investigate the impact of regular physical exercise on sleep, we assessed sleep-wake behaviour in male C57BL/6N mice with and without long-term access (i.e. 4 weeks) to a running wheel. We studied sleep-wake behaviour during undisturbed conditions as well as after social stress. The exercising mice ran approximately 4 km/day, which affected their physical constitution, their spontaneous sleep-wake pattern and their endocrine and sleep responses to stress. When compared with the control mice, exercising animals had more muscle substance, less body fat and heavier adrenal glands. At baseline, exercising mice showed fewer, but longer-lasting, sleep episodes (indicating improved sleep consolidation) and less rapid-eye-movement sleep. In both control and exercising mice, mild social stress (elicited by a 15-min social conflict) evoked elevated plasma levels of adrenocorticotrophic hormone and corticosterone, an increase in non-rapid-eye-movement sleep, an enhancement of low-frequency activity in the electroencephalogram within non-rapid-eye-movement sleep (indicating increased sleep intensity) and a decrease in wakefulness. However, as compared with the control animals, exercising mice responded to social stress with higher corticosterone levels, but not adrenocorticotrophic hormone levels, suggesting an increased sensitivity of their adrenal glands to adrenocorticotrophic hormone. Moreover, in control mice, social stress increased rapid-eye-movement sleep in parallel to non-rapid-eye-movement sleep, whereas this stressor selectively decreased rapid-eye-movement sleep in exercising animals. Corticosterone is known to decrease rapid-eye-movement sleep. Therefore, changes in the regulation of the hypothalamic-pituitary-adrenocortical axis as a result of the long-term exercise may contribute to the observed differences in spontaneous and social stress-affected sleep. In conclusion, regular exercise appears to increase sleep quality and reverses the effects of mild social stress on rapid-eye-movement sleep.

Fasting-induced increases in food hoarding are dependent on the foraging-effort level

Two strategies that have evolved to help animals meet energy demands are increases in body fat and in hoarded food. Reliance on each varies, but both are characterized by energy stored in excess of current demands for future use. Fasted Siberian hamsters decrease their lipid stores and, upon refeeding, food hoarding rather than food intake increases. Here, we tested the effect of foraging-effort level on fasting-induced increases in food hoarding and whether decreases in total body fat or individual fat pad masses were associated with the hoarding increases. This was accomplished by housing female Siberian hamsters in a foraging/hoarding system where they earned food pellets upon completion of a programmed number of wheel revolutions (10, 75 or 200 per 75-mg pellet), or had no foraging requirement (free food and an active or blocked running wheel). After baseline, half the hamsters in each group were food deprived for 32 h and then refed (control hamsters were killed after the fast without refeeding). Fasted-refed hamsters increased foraging and food hoarding, especially at the lowest foraging effort, but not food intake, with few exceptions. These responses became progressively smaller as foraging effort increased. Fasting induced similar losses in carcass lipid across foraging efforts, but the lipid loss was not uniform across the fat pads and was not clearly related to hoard size. Collectively, the fasting-induced, increased food hoarding may be triggered by an overall change in energy metabolism rather than by a general or fat-pad-specific decrease in lipid stores.

Dependence of rat hippocampal c-Fos expression on intensity and duration of exercise

The expression of c-Fos, an immediately early gene, is a marker of neural activity. In the present study, the effect of treadmill exercise on c-Fos expression was investigated in various regions of the rat hippocampus via immunohistochemistry. The first part of the experiment was aimed at determining the dependence of c-Fos expression on the intensity of treadmill exercise. In most of the hippocampal regions studied, increasing c-Fos expression was observed with increasing exercise intensity. In the second part of the experiment, the dependence of c-Fos expression on the duration of treadmill exercise was investigated. The c-Fos expression induced by mild-intensity exercise increased until the 7th day of exercise and subsequently decreased. Results of the present study suggest that the effect of treadmill exercise on neuronal activity in the hippocampus is intensity-and duration-dependent.

Neuroplasticity in old age: sustained fivefold induction of hippocampal neurogenesis by long-term environmental enrichment

Neurons are continually born from endogenous stem cells and added to the dentate gyrus throughout life, but adult hippocampal neurogenesis declines precipitously with age. Short-term exposure to an enriched environment leads to a striking increase in new neurons, along with a substantial improvement in behavioral performance. Could this plastic response be relevant for explaining the beneficial effects of leading "an active life" on brain function and pathology? Adult hippocampal neurogenesis in mice living in an enriched environment from the age of 10 to 20 months was fivefold higher than in controls. Relatively, the increase in neuronal phenotypes was entirely at the expense of newly generated astrocytes. This cellular plasticity occurred in the context of significant improvements of learning parameters, exploratory behavior, and locomotor activity. Enriched living mice also had a reduced lipofuscin load in the dentate gyrus, indicating decreased nonspecific age-dependent degeneration. Therefore, in mice signs of neuronal aging can be diminished by a sustained active and challenging life, even if this stimulation started only at medium age. Activity exerts not only an acute but also a sustained effect on brain plasticity.

Plasma corticosterone response to acute and chronic voluntary exercise in female house mice

Plasma levels of corticosterone (B) respond acutely to exercise in all mammals that have been studied, but the literature contains conflicting reports regarding how chronic activity alters this response. We measured acute and chronic effects of voluntary activity on B in a novel animal model, mice selectively bred for high voluntary wheel running. Female mice were housed with or without wheels for 8 wk beginning at 26 days of age. Wheel-access selection mice had significantly higher B at night 8, day 15, and night 29, compared with wheel-access controls. Elevation of B was an acute effect of voluntary exercise. When adjusted for running in the previous 20 min, no difference between wheel-access selection and control animals remained. No training effect on B response was observed. These results are among the strongest evidence that, in some animals, the acute B response is unaffected by chronic voluntary exercise. In mice without wheels, selection mice had significantly higher B than controls at day 15, night 29, and night 50, suggesting that selection resulted in a modulation of the hypothalamic-pituitary-adrenal axis. Growth over the first 4 wk of treatment was significantly and inversely related to average night B levels within each of the four treatment groups.

Glucocorticoid response to forced exercise in laboratory house mice (Mus domesticus)

We examined the time course and sex differences of the glucocorticoid response to forced, moderate-intensity treadmill exercise in outbred laboratory house mice. Mice (n = 64 total) were divided into eight groups, each of four males and four females, which were run on a motorized treadmill at 1.0 km/h for either 0, 2, 5, 10, 15, 25, 40, or 60 min. Serum samples were taken immediately after exercise and corticosterone (CORT) concentration was determined by radioimmunoassay. Resting CORT levels ranged between 11.6 and 29.5 ng/mL for both sexes. CORT levels increased with length of exercise and then exhibited a plateau by 25 min in females and by 40 min in males. Females displayed a significantly more rapid increase in serum CORT levels and attained higher maximal CORT levels than males. Females also had significantly larger adrenal glands, both in absolute terms and relative to body mass.