Treadmill running produces both positive and negative physiological adaptations in Sprague-Dawley rats

Forced treadmill exercise training exacerbates inflammation and causes mortality while voluntary wheel training is protective in a mouse model of colitis

The purpose of this study was to examine whether exercise training reduced inflammation and symptomology in a mouse model of colitis. We hypothesized that moderate forced treadmill running (FTR) or voluntary wheel running (VWR) would reduce colitis symptoms and colon inflammation in response to dextran sodium sulfate (DSS). Male C57Bl/6J mice were randomized to sedentary, moderate intensity FTR (8-12 m/min, 40 min, 6 weeks, 5x/week), or VWR (30 days access to wheels). DSS was given at 2% (w/v) in drinking water over 5 days. Mice discontinued exercise 24 h prior to and during DSS treatment. Colons were harvested on Days 6, 8 and 12 in FTR and Day 8 post-DSS in VWR experiments. Contrary to our hypothesis, we found that moderate FTR exacerbated colitis symptomology and inflammation as measured by significant (p<0.05) increases in diarrhea and IL-6, IL-1β, IL-17 colon gene expression. We also observed higher mortality (3/10 died vs. 0/10, p=0.07) in the FTR/DSS group. In contrast, VWR alleviated colitis symptoms and reduced inflammatory gene expression in the colons of DSS-treated mice (p<0.05). While DSS treatment reduced food/fluid intake and body weight, there was a tendency for FTR to exacerbate, and for VWR to attenuate, this effect. FTR (in the absence of DSS) increased gene expression of the chemokine and antibacterial protein CCL6 suggesting that FTR altered gut homeostasis that may be related to the exaggerated response to DSS. In conclusion, we found that FTR exacerbated, whereas VWR attenuated, symptoms and inflammation in response to DSS.

Effects of running wheel training on adult obese rats programmed by maternal prolactin inhibition

The inhibition of maternal prolactin production in late lactation leads to metabolic syndrome and hypothyroidism in adult offspring. Physical training is a therapeutic strategy that could prevent or reverse this condition. We evaluated the effects of a short-duration low-intensity running wheel training program on the metabolic and hormonal alterations in rats. Lactating Wistar rats were treated with bromocriptine (Bro, 1 mg twice a day) or saline on days 19, 20, and 21 of lactation, and the training of offspring began at 35 days of age. Offspring were divided into sedentary and trained controls (C-Sed and C-Ex) and sedentary and trained Bro-treated rats (Bro-Sed and Bro-Ex). Chronic exercise delayed the onset of weight gain in Bro-Ex offspring, and the food intake did not change during the experimental period. At 180 days, visceral fat mass was higher (+46%) in the Bro-Sed offspring than in C-Sed and Bro-Ex rats. As expected, running capacity was higher in trained animals. Most parameters observed in the Bro-Sed offspring were consistent with hypothyroidism and metabolic syndrome and were reversed in the Bro-Ex group. Chronic exercise did not influence the muscle glycogen in the C-Ex group; however, liver glycogen was higher (+30%) in C-Ex group and was unchanged in both Bro offspring groups. Bro-Ex animals had higher plasma lactate dehydrogenase levels, indicating skeletal muscle damage and intolerance of the training program. Low-intensity chronic training is able to normalize many clinical aspects in Bro animals; however, these animals might have had a lower threshold for exercise adaptation than the control rats.

Sexual activity counteracts the suppressive effects of chronic stress on adult hippocampal neurogenesis and recognition memory

Adult neurogenesis can be influenced by a variety of factors. Stress is one of the most potent inhibitors of hippocampal neurogenesis. Stress effects on adult hippocampal neurogenesis are affected differently by environmental factors, including social interaction. Sexual behavior between males and females in a social context has been suggested to influence neurogenesis and enhance hippocampal cell proliferation. However, the mechanisms of action of sexual interaction, the possible changes relative to stress state, and its effects on learning and memory remain uncertain. The current study examined the influence of sexual interaction on neurological responses in adult male mice and the function of sexual interaction relative to recognition memory in stress states. Changes in the expression of neurotrophic and transcription factors were assessed in reference to stress and/or sexual behaviors. The survival of newly generated cells and their rate of differentiation into neurons were determined in the hippocampus of chronically stressed and/or sexually experienced mice. Finally, to evaluate whether sexual experience alters adult hippocampal function, we tested learning and memory in a recognition memory task. The results demonstrated that sexual activity increased the expression of brain-derived neurotrophic factor, tyrosine kinase B, and cAMP response element-binding factor. Furthermore, the results supported the view that sexual interaction could be helpful for buffering adult hippocampal neurogenesis and recognition memory function against the suppressive actions of chronic stress.

Treadmill exercise does not change gene expression of adrenal catecholamine biosynthetic enzymes in chronically stressed rats

ABSTRACT Chronic isolation of adult animals represents a form of psychological stress that produces sympatho-adrenomedullar activation. Exercise training acts as an important modulator of sympatho-adrenomedullary system. This study aimed to investigate physical exercise-related changes in gene expression of catecholamine biosynthetic enzymes (tyrosine hydroxylase, dopamine-ß-hydroxylase and phenylethanolamine N-methyltransferase) and cyclic adenosine monophosphate response element-binding (CREB) in the adrenal medulla, concentrations of catecholamines and corticosterone (CORT) in the plasma and the weight of adrenal glands of chronically psychosocially stressed adult rats exposed daily to 20 min treadmill running for 12 weeks. Also, we examined how additional acute immobilization stress changes the mentioned parameters. Treadmill running did not result in modulation of gene expression of catecholamine synthesizing enzymes and it decreased the level of CREB mRNA in the adrenal medulla of chronically psychosocially stressed adult rats. The potentially negative physiological adaptations after treadmill running were recorded as increased concentrations of catecholamines and decreased morning CORT concentration in the plasma, as well as the adrenal gland hypertrophy of chronically psychosocially stressed rats. The additional acute immobilization stress increases gene expression of catecholamine biosynthetic enzymes in the adrenal medulla, as well as catecholamines and CORT levels in the plasma. Treadmill exercise does not change the activity of sympatho-adrenomedullary system of chronically psychosocially stressed rats.

Noninvasive strategies to promote functional recovery after stroke

Stroke is a common and disabling global health-care problem, which is the third most common cause of death and one of the main causes of acquired adult disability in many countries. Rehabilitation interventions are a major component of patient care. In the last few years, brain stimulation, mirror therapy, action observation, or mental practice with motor imagery has emerged as interesting options as add-on interventions to standard physical therapies. The neural bases for poststroke recovery rely on the concept of plasticity, namely, the ability of central nervous system cells to modify their structure and function in response to external stimuli. In this review, we will discuss recent noninvasive strategies employed to enhance functional recovery in stroke patients and we will provide an overview of neural plastic events associated with rehabilitation in preclinical models of stroke.

On aerobic exercise and behavioral and neural plasticity

Aerobic exercise promotes rapid and profound alterations in the brain. Depending upon the pattern and duration of exercise, these changes in the brain may extend beyond traditional motor areas to regions and structures normally linked to learning, cognition, and emotion. Exercise-induced alterations may include changes in blood flow, hormone and growth factor release, receptor expression, angiogenesis, apoptosis, neurogenesis, and synaptogenesis. Together, we believe that these changes underlie elevations of mood and prompt the heightened behavioral plasticity commonly observed following adoption of a chronic exercise regimen. In the following paper, we will explore both the psychological and psychobiological literatures relating to exercise effects on brain in both human and non-human animals and will attempt to link plastic changes in these neural structures to modifications in learned behavior and emotional expression. In addition, we will explore the therapeutic potential of exercise given recent reports that aerobic exercise may serve as a neuroprotectant and can also slow cognitive decline during normal and pathological aging.

Exercise training attenuates placental ischemia-induced hypertension and angiogenic imbalance in the rat

An imbalance between proangiogenic (vascular endothelial growth factor) and antiangiogenic (soluble fms-like tyrosine kinase 1) factors plays an important role in hypertension associated with reduced uteroplacental perfusion (RUPP). Exercise has been shown to stimulate proangiogenic factors, such as vascular endothelial growth factor, in both the pregnant and nonpregnant state; thus, we hypothesized that exercise training would attenuate both angiogenic imbalance and hypertension attributed to RUPP. Four groups of animals were studied, RUPP and normal pregnant controls and normal pregnant and RUPP+exercise training. Exercise training attenuated RUPP-induced hypertension (P<0.05), decreased soluble fms-like tyrosine kinase 1 (P<0.05), increased VEGF (P<0.05), and elevated the soluble fms-like tyrosine kinase 1:vascular endothelial growth factor ratio. The positive effects of exercise on angiogenic balance in the RUPP rats were confirmed by restoration (P<0.05) of the RUPP-induced decrease in endothelial tube formation in human umbilical vascular endothelial cells treated with serum from each of the experimental groups. Placental prolyl hydroxylase 1 was increased (P<0.05) in RUPP+exercise training rats. Decreased trolox equivalent antioxidant capacity in the placenta, amniotic fluid, and kidney of the RUPP rats was reversed by exercise. RUPP-induced increase in renal thiobarbituric acid reactive species was attenuated by exercise. The present data show that exercise training before and during pregnancy attenuates placental ischemia-induced hypertension, angiogenic imbalance, and oxidative stress in the RUPP rat and reveals that increased prolyl hydroxylase 1 is associated with decreased soluble fms-like tyrosine kinase 1, thus revealing several potential pathways for exercise training to mitigate the effects of placental ischemia-induced hypertension. Lastly, the present study demonstrates that exercise training may be a useful approach to attenuate the development of placental ischemia-induced hypertension during pregnancy.

Leukocyte, red blood cell and morphological adaptation to moderate physical training in rats undernourished in the neonatal period

Objective

To analyze the impact of moderate physical exercise on the total and differential leukocyte counts and red blood cell count of 36 sixty-day-old adult male Wistar rats subjected to early malnourishment.

Methods

The rats were divided in nourished (N - casein 17%) and malnourished groups (M - casein 8%) and thesegroups were then subdivided in trained (T) untrained (U) creating four groups NT, NU, MT and MU. The NT and MTgroups were submitted to moderate physical exercise using a treadmill (60 min/day, 5 days/week for 8 weeks). Onthe 1st day, before the training started T0 and 24 hours after the last training day of the week (T1 until T8), a 1 mLaliquot of blood was collected from the animals' tails for analysis. The total leukocyte count was evaluated in a cellcounter with an electronic microscope. The cyanmethemoglobin technique was used to measure the hemoglobin level. The hematocrit values were determined as a percentage using the micro-hematocrit technique with a microcapillaryreader and a cell counter was used to determine the red blood cell count. The t-test was used for statistical analysis and a p-value < 0.05 was considered significant. Data are expressed as means ± standard deviation.

Results

There was a significant difference in the total leukocyte count between the NT (9.1 ± 0.1) and MT groups (8.0 ± 0.1) from T1 and in neutrophils between the NT (22.1 ± 0.6) and MT groups (24.6 ± 1.8) from T7 (p < 0.05). There was no statistical significance in the hemoglobin, hematocrit and red blood cell count from T1.

Conclusions

According to the results of this study, moderate physical exercise seems to have induced physiologic adaptation in adult rats from T1.

Exercise offers anxiolytic potential: a role for stress and brain noradrenergic-galaninergic mechanisms

Although physical activity reduces anxiety in humans, the neural basis for this response is unclear. Rodent models are essential to understand the mechanisms that underlie the benefits of exercise. However, it is controversial whether exercise exerts anxiolytic-like potential in rodents. Evidence is reviewed to evaluate the effects of wheel running, an experimental mode of exercise in rodents, on behavior in tests of anxiety and on norepinephrine and galanin systems in neural circuits that regulate stress. Stress is proposed to account for mixed behavioral findings in this literature. Indeed, running promotes an adaptive response to stress and alters anxiety-like behaviors in a manner dependent on stress. Running amplifies galanin expression in noradrenergic locus coeruleus (LC) and suppresses stress-induced activity of the LC and norepinephrine output in LC-target regions. Thus, enhanced galanin-mediated suppression of brain norepinephrine in runners is supported by current literature as a mechanism that may contribute to the stress-protective effects of exercise. These data support the use of rodents to study the emotional and neurobiological consequences of exercise.

Placental and vascular adaptations to exercise training before and during pregnancy in the rat

Although exercise during pregnancy is generally recommended and thought to be beneficial to mother and fetus, the nature of the adaptations to exercise during pregnancy and how they may be beneficial remain poorly understood. Recent studies suggest that exercise may stimulate expression of several cytoprotective and pro-angiogenic molecules such as heat shock proteins (HSP) and vascular endothelial growth factors (VEGF). We hypothesized that exercise training during pregnancy improves angiogenic balance, increases HSP expression, and improves endothelial function. Female rats were given access to an exercise wheel for 6 wk before and during pregnancy. On day 19 of pregnancy tissues were collected and snap frozen for later analysis. Western blots were performed in skeletal muscle and placenta. HSP 27 (3.7 ± 0.36 vs. 2.2 ± 0.38; P < 0.05), HSP 60 (2.2 ± 0.73 vs. 0.49 ± 0.08; P < 0.05), and HSP 90 (0.33 ± 0.09 vs. 0.11 ± 0.02; P < 0.05) were increased in the placentas of exercise-trained rats compared with sedentary controls. In addition, exercise training increased (P < 0.05) plasma free VEGF and augmented (P < 0.05) endothelium-dependent vascular relaxation compared with nonexercise control rats. The present data indicates chronic exercise training stimulates HSP expression in the placenta and that regular exercise training increases circulating VEGF in pregnant but not in nonpregnant rats. Although the present findings suggest that exercise before and during pregnancy may promote the expression of molecules that could attenuate placental and vascular dysfunction in complicated pregnancies, further studies are needed to determine the safety and effectiveness of exercise training as a therapeutic modality in pregnancy.

Exercise does not protect against MPTP-induced neurotoxicity in BDNF haploinsufficient mice

Exercise has been demonstrated to potently protect substantia nigra pars compacta (SN) dopaminergic neurons from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurotoxicity. One mechanism proposed to account for this neuroprotection is the upregulation of neurotrophic factors. Several neurotrophic factors, including Brain Derived Neurotrophic Factor (BDNF), have been shown to upregulate in response to exercise. In order to determine if exercise-induced neuroprotection is dependent upon BDNF, we compared the neuroprotective effects of voluntary exercise in mice heterozygous for the BDNF gene (BDNF+/-) with strain-matched wild-type (WT) mice. Stereological estimates of SNpc DA neurons from WT mice allowed 90 days exercise via unrestricted running demonstrated complete protection against the MPTP-induced neurotoxicity. However, BDNF+/- mice allowed 90 days of unrestricted exercise were not protected from MPTP-induced SNpc DA neuron loss. Proteomic analysis comparing SN and striatum from 90 day exercised WT and BDNF+/- mice showed differential expression of proteins related to energy regulation, intracellular signaling and trafficking. These results suggest that a full genetic complement of BDNF is critical for the exercise-induced neuroprotection of SNpc DA neurons.

Exercise modulation of the host-tumor interaction in an orthotopic model of murine prostate cancer

The purpose of this study is to investigate the effects of exercise on cancer progression, metastasis, and underlying mechanisms in an orthotopic model of murine prostate cancer. C57BL/6 male mice (6-8 wk of age) were orthotopically injected with transgenic adenocarcinoma of mouse prostate C-1 cells (5 × 10(5)) and randomly assigned to exercise (n = 28) or a non-intervention control (n = 31) groups. The exercise group was given voluntary access to a wheel 24 h/day for the duration of the study. Four mice per group were serially killed on days 14, 31, and 36; the remaining 38 mice (exercise, n = 18; control, n = 20) were killed on day 53. Before death, MRI was performed to assess tumor blood perfusion. Primary tumor growth rate was comparable between groups, but expression of prometastatic genes was significantly modulated in exercising animals with a shift toward reduced metastasis. Exercise was associated with increased activity of protein kinases within the MEK/MAPK and PI3K/mTOR signaling cascades with subsequent increased intratumoral protein levels of HIF-1α and VEGF. This was associated with improved tumor vascularization. Multiplex ELISAs revealed distinct reductions in plasma concentrations of several angiogenic cytokines in the exercise group, which was associated with increased expression of angiogenic and metabolic genes in the skeletal muscle. Exercise-induced stabilization of HIF-1α and subsequent upregulation of VEGF was associated with "productive" tumor vascularization with a shift toward suppressed metastasis in an orthotopic model of prostate cancer.

Does physical activity reduce risk for Alzheimer's disease through interaction with the stress neuroendocrine system?

Lack of physical activity (PA) is a risk factor for Alzheimer's disease (AD), and PA interventions are believed to provide an effective non-pharmacological approach for attenuating the symptoms of this disease. However, the mechanism of action of these positive effects is currently unknown. It is possible that the benefits may be at least partially mediated by the effects on the neuroendocrine stress system. Chronic stress can lead to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, leading to aberrant basal and circadian patterns of cortisol secretion and a cascade of negative downstream events. These factors have been linked not only to reduced cognitive function but also increased levels of amyloid-β plaques and protein tau "tangles" (the neuropathological hallmarks of AD) in the non-demented mouse models of this disease. However, there is evidence that PA can have restorative effects on the stress neuroendocrine system and related risk factors relevant to AD. We explore the possibility that PA can positively impact upon AD by restoring normative HPA axis function, with consequent downstream effects upon underlying neuropathology and associated cognitive function. We conclude with suggestions for future research to test this hypothesis in patients with AD.

Voluntary running in mice beneficially modulates myocardial ischemic tolerance, signaling kinases, and gene expression patterns

Exercise triggers hormesis, conditioning hearts against damaging consequences of subsequent ischemia-reperfusion (I/R). We test whether “low-stress” voluntary activity modifies I/R tolerance and molecular determinants of cardiac survival. Male C57BL/6 mice were provided 7-day access to locked (7SED) or rotating (7EX) running-wheels before analysis of cardiac prosurvival (Akt, ERK 1/2) and prodeath (GSK3β) kinases, transcriptomic adaptations, and functional tolerance of isolated hearts to 25-min ischemia/45-min reperfusion. Over 7 days, 7EX mice increased running from 2.1 ± 0.2 to 5.3 ± 0.3 km/day (mean speed 38 ± 2 m/min), with activity improving myocardial I/R tolerance: 7SED hearts recovered 43 ± 3% of ventricular force with diastolic contracture of 33 ± 3 mmHg, whereas 7EX hearts recovered 63 ± 5% of force with diastolic dysfunction reduced to 23 ± 2 mmHg ( P < 0.05). Cytosolic expression (total protein) of Akt and GSK3β was unaltered, while ERK 1/2 increased 30% in 7EX vs. 7SED hearts. Phosphorylation of Akt and ERK 1/2 was unaltered, whereas GSK3β phosphorylation increased ∼90%. Microarray interrogation identified significant changes (≥1.3-fold expression change, ≤5% FDR) in 142 known genes, the majority (92%) repressed. Significantly modified paths/networks related to inflammatory/immune function (particularly interferon-dependent), together with cell movement, growth, and death. Of only 14 induced transcripts, 3 encoded interrelated sarcomeric proteins titin, α-actinin, and myomesin-2, while transcripts for protective actin-stabilizing ND1-L and activator of mitochondrial biogenesis ALAS1 were also induced. There was no transcriptional evidence of oxidative heat-shock or other canonical “stress” responses. These data demonstrate that relatively brief voluntary activity substantially improves cardiac ischemic tolerance, an effect independent of shifts in Akt, but associated with increased total ERK 1/2 and phospho-inhibition of GSK3β. Transcriptomic data implicate inflammatory/immune and sarcomeric modulation in activity-dependent protection.

Regular and moderate exercise before experimental sepsis reduces the risk of lung and distal organ injury

Physical activity modulates inflammation and immune response in both normal and pathologic conditions. We investigated whether regular and moderate exercise before the induction of experimental sepsis reduces the risk of lung and distal organ injury and survival. One hundred twenty-four BALB/c mice were randomly assigned to two groups: sedentary (S) and trained (T). Animals in T group ran on a motorized treadmill, at moderate intensity, 5% grade, 30 min/day, 3 times a week for 8 wk. Cardiac adaptation to exercise was evaluated using echocardiography. Systolic volume and left ventricular mass were increased in T compared with S group. Both T and S groups were further randomized either to sepsis induced by cecal ligation and puncture surgery (CLP) or sham operation (control). After 24 h, lung mechanics and histology, the degree of cell apoptosis in lung, heart, kidney, liver, and small intestine villi, and interleukin (IL)-6, KC (IL-8 murine functional homolog), IL-1β, IL-10, and number of cells in bronchoalveolar lavage (BALF) and peritoneal lavage (PLF) fluids as well as plasma were measured. In CLP, T compared with S groups showed: 1) improvement in survival; 2) reduced lung static elastance, alveolar collapse, collagen and elastic fiber content, number of neutrophils in BALF, PLF, and plasma, as well as lung and distal organ cell apoptosis; and 3) increased IL-10 in BALF and plasma, with reduced IL-6, KC, and IL-1β in PLF. In conclusion, regular and moderate exercise before the induction of sepsis reduced the risk of lung and distal organ damage, thus increasing survival.

In vivo cardiac anatomical and functional effects of wheel running in mice by magnetic resonance imaging

Physical activity is frequently used as a strategy to decrease pathogenesis and improve outcomes in chronic pathologies such as metabolic or cardiac diseases. In mice, it has been shown that voluntary wheel running (VWR) could induce an aerobic training effect and may provide a means of exploring the relationship between physical activity and the progression of pathology, or the effect of a drug on locomotor activity. To the best of our knowledge, in vivo magnetic resonance imaging (MRI) and other non-invasive methods had not been investigated for training evaluation in mice; therefore, it was proposed to test an MRI method coupled with a cardiorespiratory gating system on C57Bl/6 mice for in vivo heart anatomical and functional characterization in both trained and untrained animals. Twenty mice were either assigned to a 12-week VWR program or to a control group (CON - no wheel in the cage). At week 12, MRI scans showed an increase in the left ventricular (LV) wall mass in the VWR group compared with the CON group. The ex vivo measurements also found an increase in the heart and LV weight, as well as an increase in oxidative enzyme activities (i.e. cytochrome c oxidase [COx] in the soleus). In addition, correlations have been observed between ex vivo LV/body weight ratio, COx activity in the soleus and in vivo MRI LV wall mass/body weight. In conclusion, mouse cardiac MRI methods coupled with a cardio-respiratory gating system are sufficiently effective and feasible for non-invasive, training-induced heart hypertrophy characterization, and may be used for longitudinal training level follow-up in mouse models of cardiovascular and metabolic diseases.

Acute running stimulates hippocampal dopaminergic neurotransmission in rats, but has no influence on brain-derived neurotrophic factor

Hippocampal brain-derived neurotrophic factor (BDNF) protein is increased with exercise in rats. Monoamines seem to play a role in the regulation of BDNF, and monoamine neurotransmission is known to increase with exercise. The purpose of this study was to examine the influence of acute exercise on monoaminergic neurotransmission and BDNF protein concentrations. Hippocampal microdialysis was performed in rats that were subjected to 60 min of treadmill running at 20 m/min or rest. Two hours postexercise, the rats were killed, and the hippocampus was dissected. In experiments without microdialysis, hippocampus and serum samples were collected immediately after exercise. Exercise induced a twofold increase in hippocampal dopamine release. Noradrenaline and serotonin release were not affected. Hippocampal BDNF levels were not influenced, whether they were measured immediately or 2 h after the exercise protocol. Serum BDNF levels did not change either, but serum BDNF was negatively correlated to peripheral corticosterone concentrations, indicating a possible inhibitory reaction to the stress of running. Sixty minutes of exercise enhances dopamine release in the hippocampus of the rat in vivo. However, this increase is not associated with changes in BDNF protein levels immediately nor 2 h after the acute exercise bout. An increased corticosterone level might be the contributing factor for the absence of changes in BDNF.

Voluntary running exercise prevents β-cell failure in susceptible islets of the Zucker diabetic fatty rat

Physical activity improves glycemic control in type 2 diabetes (T2D), but its contribution to preserving β-cell function is uncertain. We evaluated the role of physical activity on β-cell secretory function and glycerolipid/fatty acid (GL/FA) cycling in male Zucker diabetic fatty (ZDF) rats. Six-week-old ZDF rats engaged in voluntary running for 6 wk (ZDF-A). Inactive Zucker lean and ZDF (ZDF-I) rats served as controls. ZDF-I rats displayed progressive hyperglycemia with β-cell failure evidenced by falling insulinemia and reduced insulin secretion to oral glucose. Isolated ZDF-I rat islets showed reduced glucose-stimulated insulin secretion expressed per islet and per islet protein. They were also characterized by loss of the glucose regulation of fatty acid oxidation and GL/FA cycling, reduced mRNA expression of key β-cell genes, and severe reduction of insulin stores. Physical activity prevented diabetes in ZDF rats through sustaining β-cell compensation to insulin resistance shown in vivo and in vitro. Surprisingly, ZDF-A islets had persistent defects in fatty acid oxidation, GL/FA cycling, and β-cell gene expression. ZDF-A islets, however, had preserved islet insulin mRNA and insulin stores compared with ZDF-I rats. Physical activity did not prevent hyperphagia, dyslipidemia, or obesity in ZDF rats. In conclusion, islets of ZDF rats have a susceptibility to failure that is possibly due to altered β-cell fatty acid metabolism. Depletion of pancreatic islet insulin stores is a major contributor to islet failure in this T2D model, preventable by physical activity.

Exercise as a potential treatment for drug abuse: evidence from preclinical studies

Epidemiological studies reveal that individuals who engage in regular aerobic exercise are less likely to use and abuse illicit drugs. Until recently, very few studies had examined the causal influences that mediate this relationship, and it was not clear whether exercise was effective at reducing substance use and abuse. In the past few years, several preclinical studies have revealed that exercise reduces drug self-administration in laboratory animals. These studies have revealed that exercise produces protective effects in procedures designed to model different transitional phases that occur during the development of, and recover from, a substance use disorder (e.g., acquisition, maintenance, escalation, and relapse/reinstatement of drug use). Moreover, recent studies have revealed several behavioral and neurobiological consequences of exercise that may be responsible for its protective effects in these assays. Collectively, these studies have provided convincing evidence to support the development of exercise-based interventions to reduce compulsive patterns of drug intake in clinical and at-risk populations.

Treadmill running frequency on anxiety and hippocampal adenosine receptors density in adult and middle-aged rats

Physical exercise protocols have varied widely across studies raising the question of whether there is an optimal intensity, duration and frequency that would produce maximal benefits in attenuating symptoms related to anxiety disorders. Although physical exercise causes modifications in neurotransmission systems, the involvement of neuromodulators such as adenosine has not been investigated after chronic exercise training. Anxiety-related behavior was assessed in the elevated plus-maze in adult and middle-aged rats submitted to 8 weeks of treadmill running 1, 3 or 7 days/week. The speed of running was weekly adjusted to maintain moderate intensity. The hippocampal adenosine A1 and A2A receptors densities were also assessed. Treadmill running protocol was efficient in increasing physical exercise capacity in adult and middle-aged rats. All frequencies of treadmill running equally decreased the time spent in the open arms in adult animals. Middle-aged treadmill control rats presented lower time spent in the open arms than adult treadmill control rats. However, treadmill running one day/week reversed this age effect. Adenosine A1 receptor was not changed between groups, but treadmill running counteracted the age-related increase in adenosine A2A receptors. Although treadmill running, independent from frequency, triggered anxiety in adult rats and treadmill running one day/week reversed the age-related anxiety, no consistent relationship was found with hippocampal adenosine receptors densities. Thus, our data suggest that as a complementary therapy in the management of mental disturbances, the frequency and intensity of physical exercise should be taken into account according to age. Besides, this is the first study reporting the modulation of adenosine receptors after chronic physical exercise, which could be important to prevent neurological disorders associated to increase in adenosine A2A receptors.

Exercise can induce temporary mitochondrial and contractile dysfunction linked to impaired respiratory chain complex activity

Exercise is considered to elicit a physiological response of the heart. Previous studies investigated the influence of repetitive exercise only at the end of the training period. We assessed the impact of 2 exercise protocols, differing in their treadmill inclination, on cardiac and mitochondrial function at different times during the training period. Within 10 weeks, animals trained with 16% incline developed hypertrophy (left ventricular posterior wall thickness: 1.6 ± 0.1 vs 2.4 ± 0.1 mm; P < .05) with normal function (ejection fraction: 75.2% ± 2.5% vs 75.6% ± 2.1%). However, at 6 weeks, there was temporary impairment of contractile function (ejection fraction: 74.5% ± 1.67% vs 65.8% ± 2.3%; P < .05) associated with decreased mitochondrial respiratory capacity (state 3 respiration: 326 ± 71 vs 161 ± 22 natoms/[min mg protein]; P < .05) and a gene expression shift from the adult (α) to the fetal (β) myosin heavy chain isoform. Although peroxisome proliferator-activated receptor gamma coactivator-1α expression was normal, nuclear respiratory factors (NRFs)-1 and -2 were significantly reduced (NRF-1: 1.00 ± 0.16 vs 0.55 ± 0.09; NRF-2: 1.00 ± 0.11 vs 0.63 ± 0.07; P < .05) after 6 weeks. These findings were associated with a reduction of electron transport chain complexes I and IV activity (complex I: 1016 ± 67 vs 758 ± 71 nmol/[min mg protein]; complex IV: 18768 ± 1394 vs 14692 ± 960 nmol/[min mg protein]; P < .05). Messenger RNA expression of selected nuclear encoded subunits of the electron transport chain was unchanged at all investigated time points. In contrast, animals trained with 10% incline showed less hypertrophy and normal function in echocardiography, normal maximal respiratory capacity, and unchanged complex activities at all 3 time points. Repetitive exercise may cause contractile and mitochondrial dysfunction characterized by impaired respiratory chain complex activities. This activity reduction is temporary and intensity related.

Long-term swimming in an inescapable stressful environment attenuates the stimulatory effect of endurance swimming on duodenal calcium absorption in rats

Endurance swimming is known to increase duodenal calcium absorption in normal rats and bone strength in estrogen-deficient rats. Because the stress resulting from forced training often attenuates the stimulatory effect of exercise, swimming in an inescapable chamber should reveal both the positive effect of the exercise and the negative effect of stress. In the work reported herein, swimming rats showed no signs of stress during 2 weeks of training. However, stress response gradually developed thereafter and peaked at weeks 6 and 7. In rats swimming for 2 weeks, transcellular duodenal calcium transport was enhanced ~2-fold. In contrast, calcium absorption was reduced in rats swimming for 8 weeks, consistent with the absence of swimming-induced upregulation of calcium transporter genes in the 8-week group. In conclusion, prolonged stress hindered the stimulatory effect of swimming on duodenal calcium absorption, and thus endurance exercise should be performed without forced training or stress to retain its beneficial effect on calcium metabolism.

The neurobiology of the stress-resistant brain

The 2010 Neurobiology of Stress Workshop brought together scientists from all over the world to share and discuss their results from studies examining the consequences of acute, repeated, and chronic stressor exposure on health and disease. Session IV entitled "The neurobiology of the stress-resistant brain" explored how we can intervene to promote stress resistance and stress resilience. Four scientists, who explore this topic from unique and convergent perspectives, presented their experimental results derived from studies in rat (Fleshner and Maier), non-human primates (Lyons), and human (Raskind). Summaries of each presentation, supporting publications, and overall take-home messages from the session are presented.

Exercise-induced cardiac preconditioning: how exercise protects your achy-breaky heart

The ability of exercise to protect the heart against ischemia-reperfusion (I/R) injury is well known in both human epidemiological studies and experimental animal models. In this review article, we describe what is currently known about the ability of exercise to precondition the heart against infarction. Just 1 day of exercise can protect the heart against ischemia/reperfusion damage, and this protection is upheld with months of exercise, making exercise one of the few sustainable preconditioning stimuli. Exercise preconditioning depends on the model and intensity of exercise, and appears to involve heightened oxidant buffering capacity, upregulated subunits of sarcolemmal ATP-sensitive potassium channels, and adaptations to cardiac mitochondria. We review the putative mechanisms involved in exercise preconditioning and point out many areas where future research is necessary to advance our understanding of how this stimulus confers resistance against I/R damage.

More resistant tendons obtained from the association of Heteropterys aphrodisiaca and endurance training

BACKGROUND

Popular Brazilian medicine uses Heteropterys aphrodisiaca infusion as a tonic or stimulant, for the treatment of nervous debility and breakdown and for muscle and bone weakness. This study investigated the effects of Heteropterys aphrodisiaca infusion on the tendon properties and extracellular matrix of rats under endurance training.

METHODS

Wistar rats were grouped as follows: CS- control sedentary, HS- H. aphrodisiaca sedentary, CT-control trained, HT- H. aphrodisiaca trained. The training protocol consisted in running on a motorized treadmill, five times a week, with weekly increase in treadmill speed and duration. Control groups received water while the HS and HT groups received H. aphrodisiaca infusion, daily, by gavage for the 8 weeks of training. Achilles tendons were frozen for biochemical and biomechanical analysis or preserved in Karnovsky's fixative, then processed for histomorphological analysis with light microscopy.

RESULTS

Biomechanical analysis showed significant increase in maximum load, maximum stress, modulus of elasticity and stiffness of the HT animals' tendons. The metalloproteinase-2 activity was reduced in the HT group. The compression region of HT animals' tendons had a stronger and more intense metachromasy, which suggests an increase in glycosaminoglycan concentration in this region of the tendon. The most intense birefringence was observed in both compression and tension regions of HT animals' tendons, which may indicate a higher organizational level of collagen bundles. The hydroxyproline content increased in the HT group.

CONCLUSIONS

The association of endurance training with H. aphrodisiaca resulted in more organized collagen bundles and more resistant tendons to support higher loads from intense muscle contraction. Despite the clear anabolic effects of Heteropterys aphrodisiaca and the endurance exercise association, no side effects were observed, such as those found for synthetic anabolic androgenic steroids.

Habitual exercise increases resistance of lymphocytes to oxidant-induced DNA damage by upregulating expression of antioxidant and DNA repairing enzymes

The underlying mechanisms of adaptation from staying physically active are not completely revealed. This study examined the effects of 8 and 20 weeks of habitual voluntary exercise on the susceptibility of lymphocytes to oxidant-induced DNA damage, antioxidant enzyme activities in cardiac and skeletal muscles, and circulatory antioxidant profile. Forty young adult rats were randomly assigned to sedentary control and exercise groups for an experimental period of 8 or 20 weeks. Animals assigned to exercise groups were subjected to 24 h daily free access to an in-cage running wheel with circumference of 1.19 m. A magnetic digital counter was attached to the running wheel to record daily exercise distance run by the animals. Control rats were housed in cages without a running wheel, located next to the exercised animals. Body weight and food intake were recorded weekly. After the experimental periods of 8 and 20 weeks, blood, left ventricle, soleus and plantaris muscles were collected for analysis. No significant difference was found in plasma total antioxidant capacity between exercised and control animals in the 8 and 20 week groups according to our ferric reducing/antioxidant power (FRAP) analysis. However, modified FRAP for ascorbic acid (FRASC) analysis indicated that plasma ascorbic acid content was significantly increased by 46 and 34% in 8 and 20 week exercise groups, respectively, when compared with the corresponding control groups. Superoxide dismutase (SOD) activity was significantly elevated by 39% in erythrocytes of animals exercised for 8 weeks relative to control animals. In the 20 week exercise group, Glutathione peroxidase (GPx) activity in ventricle and plantaris was significantly upregulated by 477 and 290%, respectively, relative to control values. As demonstrated by comet assay, the oxidant-induced DNA damage was significantly reduced by 21 and 45% in lymphocytes of animals exercised for 8 and 20 weeks, respectively, when compared with the corresponding control lymphocytes. Our qRT-PCR analysis showed that the transcript expression of SOD2 was significantly elevated by 939% in lymphocytes of animals exercised for 8 weeks relative to control animals. Increased expressions of SOD2 (by 19%), catalase (25%), APEX nuclease (multifunctional DNA repair enzyme) 1 (APEX1; 46%), Protein kinase, DNA-activated, catalytic polypeptide (Prkdc; 9%) and O-6-methylguanine-DNA methyltransferase (Mgmt; 26%) were found in lymphocytes of animals exercised for 20 weeks relative to control rats. These results demonstrate that habitual exercise confers increased resistance of lymphocytes to oxidant-induced DNA damage, and this protective effect is possibly attributed to the regular exercise-induced elevated expression of antioxidant and DNA repairing enzymes.

Gene expression associated with an enriched environment after transient focal ischemia

Recent studies have demonstrated that animals housed in an enriched environment after an experimental stroke obtained a better functional outcome than those housed in a standard cage; however, little is known about the gene expression associated with this functional recovery. The purpose of the present study was to elucidate the expression of genes in an enriched environment after experimental stroke in the ischemic and non-ischemic sides of the cortices. Transient focal brain ischemia was produced by the occlusion of the right middle cerebral artery (t-MCAO) in male Sprague-Dawley rats. The rats were divided into 3 groups: ischemic rats housed in the enriched environment, ischemic rats housed in standard cages, and non-ischemic rats in standard cages. Four weeks after t-MCAO, the rats were sacrificed and gene expression was examined. Motor function was improved in ischemic rats housed in the enriched environment compared with those in standard cages; however, there were no significant differences in the size of the infarct area between the ischemic rats in the enriched environment and those in standard cages. Decreases in the expression of Egr-1, -2, and BDNF mRNA in both sides of the cortices were detected in rats housed in the enriched environment, indicating that gene expression was altered throughout the brain at 4 weeks after transient focal ischemia.

Hypothalamic pituitary adrenal axis responses to low-intensity stressors are reduced after voluntary wheel running in rats

Regular physical exercise is beneficial for both physical and mental health. By contrast, stress is associated with deleterious effects on health and there is growing evidence that regular physical exercise counteracts some of the effects of stress. However, most previous studies have suggested that prior exercise does not alter the acute hypothalamic pituitary adrenal (HPA) axis responses to stress. The present series of studies provides evidence that in rats, 6 weeks (but not 1 or 3 weeks) of voluntary wheel running reduces the HPA axis responses to lower-intensity stressors such as an i.p. saline injection, exposure to a novel environment or exposure to moderate intensity noise, but not to more intense stressors such as predator odour exposure or restraint. Daily exercise does not appear to be necessary for the reduction in HPA axis responses, with intermittent access (24 h out of each 72-h period) to a running wheel for 6 weeks, resulting in similar decrements in adrenocorticotrophic hormone and corticosterone release in response to 85 dBA noise exposure. Data from in situ hybridisation for c-fos mRNA are consistent with the hypothesis that voluntary exercise results in a decrease in HPA axis responsiveness to a low-intensity stressor at a central level, with no changes in primary sensory processing. Together, these data suggest that 6 weeks of daily or intermittent exercise constrains the HPA axis response to mild, but not more intense stressors, and that this regulation may be mediated at a central level beyond the primary sensory input.

Running exercise effects on spatial and avoidance tasks in ovariectomized rats

Since previous studies have shown that ovariectomy impairs memory and cognition, we investigated whether physical exercise would affect ovariectomy-induced memory deficits in inhibitory avoidance and Morris water maze tasks. Female adult Wistar rats were assigned to one of the following groups: sham (submitted to surgery without removal of the ovaries), exercise, ovariectomy (Ovx) and Ovx plus exercise. Thirty days after ovariectomy or sham surgery, animals were submitted to 1 month of treadmill exercise training for 20 min, three times per week. Rats were than tested in inhibitory avoidance and Morris water maze tasks in order to verify ovariectomy effects on aversive and spatial memory performance. Results show that ovariectomized rats were impaired in aversive memory and spatial navigation, both in reference and working memory protocols. Confirming the working hypothesis, ovariectomized rats submitted to exercise had those impairments prevented. These findings support that physical exercise might constitute an important strategy to minimize cognitive deficits found in post-menopausal women.

Hippocampal mossy fiber sprouting induced by forced and voluntary physical exercise

Alterations in the function and organization of synapses have been proposed to induce learning and memory. Previous studies have demonstrated that mossy fiber induced by overtraining in a spatial learning task can be related with spatial long-term memory formation. In this work we analyzed whether physical exercise could induce mossy fiber sprouting by using a zinc-detecting histologic technique (Timm). Rats were submitted to 3 and 5days of forced or voluntary exercise. Rat brains were processed for Timm's staining to analyze mossy fiber projection at 7, 12 and 30days after the last physical exercise session. A significant increase of mossy fiber terminals in the CA3 stratum oriens region was observed after 5days of forced or voluntary exercise. Interestingly, the pattern of Timm's staining in CA3 mossy fibers was significantly altered when analyzed 12days after exercise but not at 7days post-exercise. In contrast, animals trained for only 3days did not show increments of mossy fiber terminals in the stratum oriens. Altogether, these results demonstrate that sustained or programmed exercise can alter mossy fiber sprouting. Further Investigations are necessary to determine whether mossy fiber sprouting induced by exercise is also involved in learning and memory processes.

The power of exercise: buffering the effect of chronic stress on telomere length

Background

Chronic psychological stress is associated with detrimental effects on physical health, and may operate in part through accelerated cell aging, as indexed by shorter telomeres at the ends of chromosomes. However, not all people under stress have distinctly short telomeres, and we examined whether exercise can serve a stress-buffering function. We predicted that chronic stress would be related to short telomere length (TL) in sedentary individuals, whereas in those who exercise, stress would not have measurable effects on telomere shortening.

Methodology and Principal Findings

63 healthy post-menopausal women underwent a fasting morning blood draw for whole blood TL analysis by a quantitative polymerase chain reaction method. Participants completed the Perceived Stress Scale (Cohen et al., 1983), and for three successive days reported daily minutes of vigorous activity. Participants were categorized into two groups-sedentary and active (those getting Centers for Disease Control-recommended daily amount of activity). The likelihood of having short versus long telomeres was calculated as a function of stress and exercise group, covarying age, BMI and education. Logistic regression analyses revealed a significant moderating effect of exercise. As predicted, among non-exercisers a one unit increase in the Perceived Stress Scale was related to a 15-fold increase in the odds of having short telomeres (p<.05), whereas in exercisers, perceived stress appears to be unrelated to TL (B = −.59, SE = .78, p = .45).

Discussion

Vigorous physical activity appears to protect those experiencing high stress by buffering its relationship with TL. We propose pathways through which physical activity acts to buffer stress effects.

Selecting exercise regimens and strains to modify obesity and diabetes in rodents: an overview

Exercise is part of a healthy lifestyle and frequently is an important component in combating chronic diseases, such as obesity and diabetes. Understanding the molecular events initiated by regular exercise is best studied in laboratory animals, with mice and rats being favoured for a number of reasons. However, the wide variety of rodent strains available for biomedical research often makes it challenging to select an animal strain suitable for studying specific disease outcomes. In the present review we focus on exercise as a management strategy for obesity and diabetes and we discuss: (i) exercise paradigms in humans shown to ameliorate signs and symptoms of obesity and diabetes; (ii) different rodent strains in terms of their advantages, disadvantages and limitations when using specific forms of exercise; (iii) the strengths and weaknesses of commonly used laboratory methods for rodent exercise; and (iv) the unintended consequences of exercise that are often manifested by increased hormonal and oxidative stress responses.

Chronic stress enhances synaptic plasticity due to disinhibition in the anterior cingulate cortex and induces hyper-locomotion in mice

The anterior cingulate cortex (ACC) is involved in the pathophysiology of a variety of mental disorders, many of which are exacerbated by stress. There are few studies, however, of stress-induced modification of synaptic function in the ACC that is relevant to emotional behavior. We investigated the effects of chronic restraint stress (CRS) on behavior and synaptic function in layers II/III of the ACC in mice. The duration of field excitatory postsynaptic potentials (fEPSPs) was longer in CRS mice than in control mice. The frequency of miniature inhibitory postsynaptic currents (mIPSCs) recorded by whole-cell patch-clamping was reduced in CRS mice, while miniature excitatory postsynaptic currents (mEPSCs) remained unchanged. Paired-pulse ratios (PPRs) of the fEPSP and evoked EPSC were larger in CRS. There was no difference in NMDA component of evoked EPSCs between the groups. Both long-term potentiation (LTP) and long-term depression of fEPSP were larger in CRS mice than in control mice. The differences between the groups in fEPSP duration, PPRs and LTP level were not observed when the GABA(A) receptor was blocked by bicuculline. Compared to control mice, CRS mice exhibited hyper-locomotive activity in an open field test, while no difference was observed between the groups in anxiety-like behavior in a light/dark choice test. CRS mice displayed decreased freezing behavior in fear conditioning tests compared to control mice. These findings suggest that CRS facilitates synaptic plasticity in the ACC via increased excitability due to disinhibition of GABA(A) receptor signalling, which may underlie induction of behavioral hyper-locomotive activity after CRS.

Exercise neuroprotection in a rat model of binge alcohol consumption

BACKGROUND

Excessive alcohol intake produces structural and functional deficits in corticolimbic pathways that are thought to underlie cognitive deficits in the alcohol use disorders (AUDs). Animal models of binge alcohol administration support the direct link of high levels of alcohol consumption and neurotoxicity in the hippocampus and surrounding cortex. In contrast, voluntary wheel running enhances hippocampal neurogenesis and generally promotes the health of neurons.

METHODS

We investigated whether voluntary exercise prior to binge alcohol exposure could protect against alcohol-induced cell loss. Female Long-Evans rats exercised voluntarily for 14 days before undergoing 4 days of binge alcohol consumption. Brains were harvested immediately after the last dose of alcohol and examined for various histological markers of neurodegeneration, including both cell death (FluoroJade B) and cell birth (Ki67) markers.

RESULTS

Rats that exercised prior to binge exposure were significantly less behaviorally intoxicated, which was not a result of enhanced hepatic metabolism. Rats that exercised prior to binge alcohol consumption had reduced loss of dentate gyrus granule cells and fewer FluoroJade B positive cells in the dentate gyrus and associated entorhinal-perirhinal cortex compared to nonexercisers. However, exercise did not protect against cell death in the piriform cortex nor protect against alcohol-induced decreases in cell proliferation, evidenced by a similar alcohol-induced reduction in Ki67 labeled cells between exercise and sedentary rats.

CONCLUSIONS

We conclude that exercise can reduce behavioral sensitivity to ethanol intoxication and protect vulnerable brain areas from alcohol-induced cell death. Exercise neuroprotection of alcohol-induced brain damage has important implications in understanding the neurobiology of the AUDs as well as in developing novel treatment strategies.

The role of transient outward K+ current in electrical remodelling induced by voluntary exercise in female rat hearts

Regular exercise can lead to electrical remodelling of the heart. The cellular mechanisms associated with these changes are not well understood, and are difficult to study in human tissue but are important given that exercise is recommended to the general population. We have investigated the role played by the transient outward K+ current (I(to)) in the changes in electrical activity seen in response to voluntary exercise training in rats. Female rats undertook 6 weeks of voluntary wheel running exercise (TRN) or were sedentary controls (SED). Monophasic action potentials (MAPs) were recorded from the surface of whole hearts. Whole cell patch clamp recordings of I(to); mRNA and protein levels of selected targets in sub-epicardial (EPI) and sub-endocardial myocardium of SED and TRN hearts were compared. In TRN rats, heart weight:body weight was significantly increased and epicardial MAPs significantly prolonged. I(to) density was reduced in TRN EPI myocytes, such that the transmural gradient of I(to) was significantly reduced (P < 0.05). Computer modelling of these changes in I(to) predicted the observed changes in action potential profile. However, transmural gradients in mRNA and protein expression for Kv4.2 or mRNA levels of the Kv4.2 regulators; KChIP2 and Irx-5 were not significantly altered by voluntary exercise. We conclude that voluntary exercise electrical remodelling is caused, at least in part, by a decrease in EPI I(to), possibly because of fewer functional channels in the membrane, which results in a fall in the transmural action potential duration gradient.

Development and characterization of an overtraining animal model

PURPOSE

Development of an endurance training-overtraining protocol for Wistar rats that includes increased workload and is characterized by analyses of performance and biomarkers.

METHODS

The running protocol lasted 11 wk: 8 wk of daily exercise sessions followed by 3 wk of increasing training frequency (two, three, and four times), with decreasing recovery time between sessions (4, 3, and 2 h) to cause an imbalance between overload and recovery. The performance tests were made before training (T1) and after the 4th (T2), 8th (T3), 9th (T4), 10th (T5), and 11th (T6) training weeks. All rats showed significantly increased performance at T4, at which time eight rats, termed the trained group (Tr), were sacrificed for blood and muscle assays. After T6, two groups were distinguishable by differences in the slope (alpha) of a line fitted to the individual performances at T4, T5, and T6: nonfunctional overreaching (NFOR; alpha < -15.05 kg x m) and functional overreaching (FOR; alpha >or= -15.05 kg x m).

RESULTS

Data were presented as mean +/- SD. FOR maintained the performance at T6 similar to Tr at T4 (530.6 +/- 85.3 and 487.5 +/- 61.4 kg x m, respectively). The FOR and the Tr groups showed higher muscle citrate synthase activity (approximately 40%) and plasma glutamine/glutamate ratio (Gm/Ga; 4.5 +/- 1.7 and 4.5 +/- 0.9, respectively) than the sedentary control (CO) group (2.8 +/- 0.5). The NFOR group lost the performance acquired at T4 (407.3 +/- 88.2 kg x m) after T6 (280.5 +/- 93.1 kg x m) and exhibited sustained leukocytosis. NFOR's Gm/Ga (3.1 +/- 0.2) and muscle citrate synthase activity were similar to CO values.

CONCLUSIONS

The decline in performance in the NFOR group could be related to the decrease in muscle oxidative capacity. We observed a trend in the Gm/Ga and leukocytosis that is similar to what has been sometimes observed in overtrained humans. This controlled training-overtraining animal model may be useful for seeking causative mechanisms of performance decline.

Repeatability of exercise behaviors in mice

PURPOSE

Measurements of exercise behaviors in rodents such as maximal treadmill endurance and physical activity are often used in the literature; however, minimal data are available regarding the repeatability of measurements used for these exercise behaviors. This study assessed the repeatability of a commonly used maximal exercise endurance treadmill test as well as voluntary physical activity measured by wheel running in mice.

METHODS

Repeatability of treadmill tests were analyzed for both inbred and outbred mice in addition to a 10 week repeatability analysis using Balb/cJ mice (n=20). Voluntary daily physical activity was assessed by distance, duration, and speed of wheel running (WR). Physical activity measurements on days 5 and 6 of WR in a large cohort (n=739) of both inbred and outbred mice were compared.

RESULTS

No significant differences (p>0.05) in exercise endurance were found between different cohorts of Balb/cJ and DBA/2J mice indicating strains overall generally test the same; however, significant differences between tests were seen within BaD2F(2) animals (p<0.001). Bland-Altman analysis revealed a lack of agreement between weekly endurance tests within mouse, and correlation analysis showed lack of consistent correlations between weekly endurance tests within mouse. No significant differences were found for WR measurements within mouse between days (p=0.99). High correlations between days within mouse for WR were found (r=0.74-0.85).

CONCLUSIONS

High intra-mouse variability between repeated endurance tests suggests that treadmill testing in an enclosed chamber with shock grid for motivation to run in mice is not repeatable. Conversely, high correlation and agreement between days of wheel-running measurements suggest that voluntary activity (WR) is repeatable and stable within individual mice.

Adaptations to high-intensity intermittent exercise in rodents

In humans, exercise-induced plasma volume (PV) expansion is typically associated with an increase in plasma albumin content, due in part to an increase in hepatic albumin synthesis. We tested the ability of a 12-day high-intensity intermittent exercise protocol to induce an increase in PV in rodents. Since albumin synthesis is transcriptionally regulated, we tested the hypothesis that exercise training would induce an increase in hepatic albumin gene expression. Fifty adult male Sprague-Dawley rats weighing between 245 and 350 g were randomly assigned to one of five groups: cage control (CC), sham exercise (sham), continuous moderate-intensity exercise training (MI), high-intensity intermittent exercise training (HI), or a single day of HI training (1-HI). Twenty-four hours after the last training session, rats were anesthetized. PV was determined, and the liver was removed, flash frozen, and stored for later analysis. Citrate synthase (CS) activity of the red quadriceps muscle, a marker of aerobic adaptation, increased with training (MI and HI) and in response to 1-HI (P < 0.05). We did not see a significant exercise-induced PV expansion as PV averaged 23.6 +/- 2.7 ml/kg body wt in the CC group and 26.6 +/- 1.3 ml/kg body wt in the HI group (P > 0.05). However, hepatic albumin mRNA expression, as determined by real-time PCR, increased 2.9 +/- 0.4- and 4.1 +/- 0.4-fold after MI and HI, respectively, compared with CC. A single bout of HI (1-HI) did not alter hepatic albumin mRNA expression. These data demonstrate an increase in both CS activity and hepatic albumin gene expression with 12 days of aerobic exercise training in the rodent with a rapid (within 24 h) adaptation in the skeletal muscle to high-intensity intermittent exercise.

Impact of lifelong sedentary behavior on mitochondrial function of mice skeletal muscle

This study investigated the impact of lifelong sedentariness on skeletal muscle mass and mitochondrial function. Thirty C57BL/6 strain mice (2 months) were randomly divided into three groups (young-Y; old sedentary-OS; old active-OA). Young animals were sacrificed after 1 week of quarantine, and OS and OA groups were individually placed into standard cages and in cages with running wheels, respectively, until sacrifice (25 months). Body weights and hind-limb skeletal muscle wet weights were obtained from all groups. Mitochondrial respiratory functional measures (i.e., state 3 and 4 respiration, respiratory control ratio, and ratio of nanomoles of ADP phosphorylated by nanomoles of O2 consumed [ADP/O]) and biochemical markers of oxidative damage (aconitase activity, protein carbonyl derivatives, sulfhydryl groups) were measured in isolated mitochondrial suspensions. Our results reveal that lifelong sedentary behavior has a negative impact on the age-related loss of skeletal muscle mass and on the isolated mitochondrial function of mixed skeletal muscle of mice, which is associated with an increased oxidative damage to mitochondrial biomolecules.

Physical exercise can reverse the deficit in fear memory induced by maternal deprivation

Maternal deprivation during the first 10 days of life induces significant behavioral alterations in rodents which persist through adulthood. Physical exercise reduces the cognitive deficits associated with pharmacologic and pathological conditions. Here we investigated whether forced physical exercise alters memory deficits caused by postnatal maternal deprivation. Male rats were divided into four groups: (1) control, (2) deprived, (3) exercised, and (4) deprived+exercised. In groups 2 and 4, pups were deprived from their mothers for 3h/day during the first 10 days post-birth. In groups 3 and 4, from postnatal day 45 (PND-45) on, animals were submitted to forced treadmill exercise. At adulthood, animals were submitted to four different behavioral tasks: open field, Morris water maze (MWM), object recognition (OR) and inhibitory avoidance (IA). Maternal deprivation had no effect on open field behavior, but disrupted memory in the three other tasks. Physical exercise alone had no effect, except for a slight enhancement of MWM learning. Importantly, physical exercise reversed the deficit of IA and reduced the deficit of spatial memory but not that of OR seen in deprived animals. It is possible that physical exercise may counteract the influence of maternal deprivation on neurohumoral or hormonal memory modulatory systems related to stress. Indeed, the decreasing order of the effect of exercise on the memory disturbances induced by deprivation roughly follows the descending degree of stress associated with each task (IA>MWM>OR). Maternal deprivation is known to hinder hormonal mechanisms involved in coping with stress.

Voluntary wheel running initially increases adrenal sensitivity to adrenocorticotrophic hormone, which is attenuated with long-term training

Although exercise is a common and potent activator of the hypothalamic-pituitary adrenal (HPA) axis, the effects of exercise on the acute stress response are not well understood. Here, we investigated the effects of short- (2 wk) and long-term (8 wk) voluntary wheel running on adrenal sensitivity to ACTH stimulation and the acute stress response to restraint in male rats. Diurnal glucocorticoid patterns were measured on days 7 (all groups) and 35 (8-wk groups). Rats were subjected to 20 min of restraint stress on either week 1 or on week 7 of treatment to assess HPA activation. One week later, exogenous ACTH (75 ng/kg) was administered to assess adrenal sensitivity to ACTH. Following this, adrenals were collected and analyzed for key proteins involved in corticosterone (CORT) synthesis. By the end of week 1, exercising (E) animals had twofold higher peak diurnal CORT levels compared with sedentary (S) animals ( P < 0.01). CORT values were not different between groups at week 8. In response to restraint stress at week 2, CORT values in E were approximately threefold greater than in S ( P < 0.05). No difference was found between E and S rats in the response to, or recovery from, restraint at week 8. During the ACTH challenge at week 2, E demonstrated a ∼2.5-fold increase in adrenal sensitivity compared with S, while no difference was found between E and S at week 8. The expression of steroidogenic acute regulatory protein was found to be ∼50% higher in the adrenals in E compared with S at week 2 ( P < 0.05), but no difference existed between groups at week 8. These results show that volitional wheel running initially causes hyperactivation of the HPA axis, due to enhanced adrenal sensitivity to ACTH, but that these alterations in HPA activity are completely restored by 8 wk of training.

Chronic voluntary wheel running facilitates corticosterone response habituation to repeated audiogenic stress exposure in male rats

Voluntary exercise is associated with the prevention and treatment of numerous physical and psychological illnesses, yet the mechanisms by which it confers this protection remain unclear. In contrast, stress, particularly under conditions of prolonged or repeated exposure when glucocorticoid levels are consistently elevated, can have a devastating impact on health. It has been suggested that the benefits of physical exercise may lie in an ability to reduce some of the more deleterious health effects of stress and stress hormones. The present series of experiments provides evidence that voluntary exercise facilitates habituation of corticosterone but not adrenocorticotropin hormone responses to repeated stress presentations. After 6 weeks of running wheel access or sedentary housing conditions, rats were exposed to 11 consecutive daily 30 min presentations of 98 dB noise stress. Similar corticosterone responses in exercised rats and sedentary controls were observed following the first, acute stress presentation. While both groups demonstrated habituation of corticosterone secretory responses with repeated noise stress exposures, the rate of habituation was significantly facilitated in exercised animals. These results suggest that voluntary exercise may reduce the negative impact of prolonged or repeated stress on health by enhancing habituation of the corticosterone response ultimately reducing the amount of glucocorticoids the body and brain are exposed to.