Heat and exercise acclimation increases intracellular levels of Hsp72 and inhibits exercise-induced increase in intracellular and plasma Hsp72 in humans

In order to verify the effects of heat and exercise acclimation (HA) on resting and exercise-induced expression of plasma and leukocyte heat shock protein 72 (Hsp72) in humans, nine healthy young male volunteers (25.0 +/- 0.7 years; 80.5 +/- 2.0 kg; 180 +/- 2 cm, mean +/- SE) exercised for 60 min in a hot, dry environment (40 +/- 0A degrees C and 45 A +/- 0% relative humidity) for 11 days. The protocol consisted of running on a treadmill using a controlled hyperthermia technique in which the work rate was adjusted to elevate the rectal temperature by 1A degrees C in 30 min and maintain it elevated for another 30 min. Before and after the HA, the volunteers performed a heat stress test (HST) at 50% of their individual maximal power output for 90 min in the same environment. Blood was drawn before (REST), immediately after (POST) and 1 h after (1 h POST) HST, and plasma and leukocytes were separated and stored. Subjects showed expected adaptations to HA: reduced exercise rectal and mean skin temperatures and heart rate, and augmented sweat rate and exercise tolerance. In HST1, plasma Hsp72 increased from REST to POST and then returned to resting values 1 h POST (REST: 1.11 A +/- 0.07, POST: 1.48 A +/- 0.10, 1 h POST: 1.22 A +/- 0.11 ng mL(-1); p < 0.05). In HST2, there was no change in plasma Hsp72 (REST: 0.94 A +/- 0.08, POST: 1.20 A +/- 0.15, 1 h POST: 1.17 A +/- 0.16 ng mL(-1); p > 0.05). HA increased resting levels of intracellular Hsp72 (HST1: 1 A +/- 0.02 and HST2: 4.2 A +/- 1.2 density units, p < 0.05). Exercise-induced increased intracellular Hsp72 expression was observed on HST1 (HST1: REST, 1 A +/- 0.02 vs. POST, 2.9 A +/- 0.9 density units, mean +/- SE, p < 0.05) but was inhibited on HST2 (HST2: REST, 4.2 +/- 1.2 vs. POST, 4.4 +/- 1.1 density units, p > 0.05). Regression analysis showed that the lower the pre-exercise expression of intracellular Hsp72, the higher the exercise-induced increase (R = -0.85, p < 0.05). In conclusion, HA increased resting leukocyte Hsp72 levels and inhibited exercise-induced expression. This intracellular adaptation probably induces thermotolerance. In addition, the non-increase in plasma Hsp72 after HA may be related to lower stress at the cellular level in the acclimated individuals.

Aerobic exercise training improves skeletal muscle function and Ca(2+) handling-related protein expression in sympathetic hyperactivity-induced heart failure

Bueno CR Jr, Ferreira JC, Pereira MG, Bacurau AV, Brum PC. Aerobic exercise training improves skeletal muscle function and Ca(2+) handling-related protein expression in sympathetic hyperactivity-induced heart failure. J Appl Physiol 109: 702-709, 2010. First published July 1, 2010; doi: 10.1152/japplphysiol.00281.2010.-The cellular mechanisms of positive effects associated with aerobic exercise training on overall intrinsic skeletal muscle changes in heart failure (HF) remain unclear. We investigated potential Ca(2+) abnormalities in skeletal muscles comprising different fiber compositions and investigated whether aerobic exercise training would improve muscle function in a genetic model of sympathetic hyperactivity-induced HF. A cohort of male 5-mo-old wild-type (WT) and congenic alpha(2A)/alpha(2C) adrenoceptor knockout (ARKO) mice in a C57BL/6J genetic background were randomly assigned into untrained and trained groups. Exercise training consisted of a 8-wk running session of 60 min, 5 days/wk (from 5 to 7 mo of age). After completion of the exercise training protocol, exercise tolerance was determined by graded treadmill exercise test, muscle function test by Rotarod, ambulation and resistance to inclination tests, cardiac function by echocardiography, and Ca(2+) handling-related protein expression by Western blot. alpha(2A)/alpha(2C)ARKO mice displayed decreased ventricular function, exercise intolerance, and muscle weakness paralleled by decreased expression of sarcoplasmic Ca(2+) release-related proteins [alpha(1)-, alpha(2)-, and beta(1)-subunits of dihydropyridine receptor (DHPR) and ryanodine receptor (RyR)] and Ca(2+) reuptake-related proteins [sarco(endo) plasmic reticulum Ca(2+)-ATPase (SERCA) 1/2 and Na(+)/Ca(2+) exchanger (NCX)] in soleus and plantaris. Aerobic exercise training significantly improved exercise tolerance and muscle function and reestablished the expression of proteins involved in sarcoplasmic Ca(2+) handling toward WT levels. We provide evidence that Ca(2+) handling-related protein expression is decreased in this HF model and that exercise training improves skeletal muscle function associated with changes in the net balance of skeletal muscle Ca(2+) handling proteins.

Exercise training reduces cardiac angiotensin II levels and prevents cardiac dysfunction in a genetic model of sympathetic hyperactivity-induced heart failure in mice

The role of exercise training (ET) on cardiac renin-angiotensin system (RAS) was investigated in 3-5 month-old mice lacking alpha(2A-) and alpha(2C-)adrenoceptors (alpha(2A)/alpha(2C)ARKO) that present heart failure (HF) and wild type control (WT). ET consisted of 8-week running sessions of 60 min, 5 days/week. In addition, exercise tolerance, cardiac structural and function analysis were made. At 3 months, fractional shortening and exercise tolerance were similar between groups. At 5 months, alpha(2A)/alpha(2C)ARKO mice displayed ventricular dysfunction and fibrosis associated with increased cardiac angiotensin (Ang) II levels (2.9-fold) and increased local angiotensin-converting enzyme activity (ACE 18%). ET decreased alpha(2A)/alpha(2C)ARKO cardiac Ang II levels and ACE activity to age-matched untrained WT mice levels while increased ACE2 expression and prevented exercise intolerance and ventricular dysfunction with little impact on cardiac remodeling. Altogether, these data provide evidence that reduced cardiac RAS explains, at least in part, the beneficial effects of ET on cardiac function in a genetic model of HF.

Exercise training delays cardiac dysfunction and prevents calcium handling abnormalities in sympathetic hyperactivity-induced heart failure mice

Exercise training (ET) is a coadjuvant therapy in preventive cardiology. It delays cardiac dysfunction and exercise intolerance in heart failure (HF); however, the molecular mechanisms underlying its cardioprotection are poorly understood. We tested the hypothesis that ET would prevent Ca2+ handling abnormalities and ventricular dysfunction in sympathetic hyperactivity-induced HF mice. A cohort of male wildtype (WT) and congenic (alpha 2A/alpha 2C)-adrenoceptor knockout ((alpha 2A/alpha 2C)ARKO) mice with C57BL6/J genetic background (3-5 mo of age) were randomly assigned into untrained and exercise-trained groups. ET consisted of 8-wk swimming session, 60 min, 5 days/wk. Fractional shortening (FS) was assessed by two-dimensional guided M-mode echocardiography. The protein expression of ryanodine receptor (RyR), phospho-Ser(2809)-RyR, sarcoplasmic reticulum Ca2+ ATPase (SERCA2), Na+/Ca2+ exchanger (NCX), phospholamban (PLN), phospho-Ser(16)-PLN, and phospho-Thr(17)-PLN were analyzed by Western blotting. At 3 mo of age, no significant difference in FS and exercise tolerance was observed between WT and (alpha 2A/alpha 2C)ARKO mice. At 5 mo, when cardiac dysfunction is associated with lung edema and increased plasma norepinephrine levels, (alpha 2A/alpha 2C)ARKO mice presented reduced FS paralleled by decreased SERCA2 (26%) and NCX (34%). Conversely, (alpha 2A/alpha 2C)ARKO mice displayed increased phospho-Ser(16)-PLN (76%) and phospho-Ser(2809)-RyR (49%). ET in (alpha 2A/alpha 2C)ARKO mice prevented exercise intolerance, ventricular dysfunction, and decreased plasma norepinephrine. ET significantly increased the expression of SERCA2 (58%) and phospho-Ser(16)-PLN (30%) while it restored the expression of phospho-Ser(2809)-RyR to WT levels. Collectively, we provide evidence that improved net balance of Ca2+ handling proteins paralleled by a decreased sympathetic activity on ET are, at least in part, compensatory mechanisms against deteriorating ventricular function in HF.

Effects of proportional assisted ventilation on exercise performance in idiopathic pulmonary fibrosis patients

Background: Patients with idiopathic pulmonary fibrosis (IPF) present an important ventilatory (imitation reducing their exercise capacity. Non-invasive ventilatory support has been shown to improve exercise capacity in patients with obstructive diseases; however, its effect on IPF patients remains unknown. Objective: The present study assessed the effect of ventilatory support using proportional, assist ventilation (PAV) on exercise capacity in patients with IPF. Methods: Ten patients (61.2 +/- 9.2 year-old) were submitted to a cardiopulmonary exercise testing, plethysmography and three submaximal. exercise tests (60% of maximum load): without ventilatory support, with continuous positive airway pressure (CPAP) and PAV. Submaximal tests were performed randomly and exercise capacity, cardiovascular and ventilatory response as well as breathlessness subjective perception were evaluated. Lactate plasmatic levels were obtained before and after submaximal. exercise. Results: Our data show that patients presented a limited exercise capacity (9.7 +/- 3.8 mL O(2)/kg/min). Submaximal. test was increased in patients with PAV compared with CPAP and without ventilatory support (respectively, 11.1 +/- 8.8 min, 5.6 +/- 4.7 and 4.5 +/- 3.8 min; p < 0.05). An improved arterial oxygenation and lower subjective perception to effort was also observed in patients with IPF when exercise was performed with PAV (p < 0.05). IPF patients performing submaximal exercise with PAV also presented a lower heart rate during exercise, although systolic and diastolic pressures were not different among submaximal tests. Our results suggest that PAV can increase exercise tolerance and decrease dyspnoea and cardiac effort in patients with idiopathic pulmonary fibrosis. (C) 2009 Elsevier Ltd. All rights reserved.

Obesity Decreases Time to Claudication and Delays Post-Exercise Hemodynamic Recovery in Elderly Peripheral Arterial Disease Patients

Background: Although obesity is usually observed in peripheral arterial disease (PAD) patients, the effects of the association between these diseases on walking capacity are not well documented. Objective: The main objectives of this study were to determine the effects of obesity on exercise tolerance and post-exercise hemodynamic recovery in elderly PAD patients. Methods: 46 patients with stable symptoms of intermittent claudication were classified according to their body mass index (BMI) into normal group (NOR) = BMI < 28.0 and obese or in risk of obesity group (OBE) = BMI >= 28.0. All patients performed a progressive graded treadmill test. During exercise, ventilatory responses were evaluated and pre- and post-exercise ankle and arm blood pressures were measured. Results: Exercise tolerance and oxygen consumption at total walking time were similar between OBE and NOR. However, OBE showed a lower claudication time (309 +/- 151 vs. 459 +/- 272 s, p = 0.02) with a similar oxygen consumption at this time. In addition, OBE presented a longer time for ankle brachial index recovery after exercise (7.8 +/- 2.8 vs. 6.3 +/- 2.6 min, p = 0.02). Conclusion: Obesity in elderly PAD patients decreased time to claudication, and delayed post-exercise hemodynamic recovery. These results suggest that muscle metabolic demand, and not total workload, is responsible for the start of the claudication and maximal exercise tolerance in PAD patients. Moreover, claudication duration might be responsible for the time needed to a complete hemodynamic recovery after exercise. Copyright (c) 2008 S. Karger AG, Basel

Sympathetic hyperactivity differentially affects skeletal muscle mass in developing heart failure: role of exercise training

Bacurau AV, Jardim MA, Ferreira JC, Bechara LR, Bueno CR Jr, Alba-Loureiro TC, Negrao CE, Casarini DE, Curi R, Ramires PR, Moriscot AS, Brum PC. Sympathetic hyperactivity differentially affects skeletal muscle mass in developing heart failure: role of exercise training. J Appl Physiol 106: 1631-1640, 2009. First published January 29, 2009; doi:10.1152/japplphysiol.91067.2008.-Sympathetic hyperactivity (SH) is a hallmark of heart failure (HF), and several lines of evidence suggest that SH contributes to HF-induced skeletal myopathy. However, little is known about the influence of SH on skeletal muscle morphology and metabolism in a setting of developing HF, taking into consideration muscles with different fiber compositions. The contribution of SH on exercise tolerance and skeletal muscle morphology and biochemistry was investigated in 3- and 7-mo-old mice lacking both alpha(2A)- and alpha(2C)-adrenergic receptor subtypes (alpha(2A)/alpha(2C)ARKO mice) that present SH with evidence of HF by 7 mo. To verify whether exercise training (ET) would prevent skeletal muscle myopathy in advanced-stage HF, alpha(2A)/alpha(2C)ARKO mice were exercised from 5 to 7 mo of age. At 3 mo, alpha(2A)/alpha(2C)ARKO mice showed no signs of HF and preserved exercise tolerance and muscular norepinephrine with no changes in soleus morphology. In contrast, plantaris muscle of alpha(2A)/alpha(2C)ARKO mice displayed hypertrophy and fiber type shift (IIA -> IIX) paralleled by capillary rarefaction, increased hexokinase activity, and oxidative stress. At 7 mo, alpha(2A)/alpha(2C)ARKO mice displayed exercise intolerance and increased muscular norepinephrine, muscular atrophy, capillary rarefaction, and increased oxidative stress. ET reestablished alpha(2A)/alpha(2C)ARKO mouse exercise tolerance to 7-mo-old wild-type levels and prevented muscular atrophy and capillary rarefaction associated with reduced oxidative stress. Collectively, these data provide direct evidence that SH is a major factor contributing to skeletal muscle morphological changes in a setting of developing HF. ET prevented skeletal muscle myopathy in alpha(2A)/alpha(2C)ARKO mice, which highlights its importance as a therapeutic tool for HF.

The role of local and systemic renin angiotensin system activation in a genetic model of sympathetic hyperactivity-induced heart failure in mice

Sympathetic hyperactivity (SH) and renin angiotensin system (RAS) activation are commonly associated with heart failure (HF), even though the relative contribution of these factors to the cardiac derangement is less understood. The role of SH on RAS components and its consequences for the HF were investigated in mice lacking alpha(2A) and alpha(2C) adrenoceptor knockout (alpha(2A)/alpha(2C) ARKO) that present SH with evidence of HF by 7 mo of age. Cardiac and systemic RAS components and plasma norepinephrine (PN) levels were evaluated in male adult mice at 3 and 7 mo of age. In addition, cardiac morphometric analysis, collagen content, exercise tolerance, and hemodynamic assessments were made. At 3 mo, alpha(2A)/alpha(2C)ARKO mice showed no signs of HF, while displaying elevated PN, activation of local and systemic RAS components, and increased cardiomyocyte width (16%) compared with wild-type mice (WT). In contrast, at 7 mo, alpha(2A)/alpha(2C)ARKO mice presented clear signs of HF accompanied only by cardiac activation of angiotensinogen and ANG II levels and increased collagen content (twofold). Consistent with this local activation of RAS, 8 wk of ANG II AT(1) receptor blocker treatment restored cardiac structure and function comparable to the WT. Collectively, these data provide direct evidence that cardiac RAS activation plays a major role underlying the structural and functional abnormalities associated with a genetic SH-induced HF in mice.

Pain threshold is achieved at intensity above anaerobic threshold in patients with intermittent claudication

PURPOSE: Walking training is considered as the first treatment option for patients with peripheral arterial disease and intermittent claudication (IC). Walking exercise has been prescribed for these patients by relative intensity of peak oxygen uptake (VO(2)peak), ranging from 40% to 70% VO(2)peak, or pain threshold (PT). However, the relationship between these methods and anaerobic threshold (AT), which is considered one of the best metabolic markers for establishing training intensity, has not been analyzed. Thus, the aim of this study was to compare, in IC patients, the physiological responses at exercise intensities usually prescribed for training (% VO(2) peak or % PT) with the ones observed at AT. METHODS: Thirty-three IC patients performed maximal graded cardiopulmonary treadmill test to assess exercise tolerance. During the test, heart rate (HR), VO(2), and systolic blood pressure were measured and responses were analyzed at the following: 40% of VO(2)peak; 70% of VO(2)peak; AT; and PT. RESULTS: Heart rate and VO(2) at 40% and 70% of VO(2)peak were lower than those at AT (HR: -13 +/- 9% and -3 +/- 8%, P < .01, respectively; VO(2): -52 +/- 12% and -13 +/- 15%, P < .01, respectively). Conversely, HR and VO(2) at PT were slightly higher than those at AT (HR: +3 +/- 8%, P < .01; VO(2): + 6 +/- 15%, P = .04). None of the patients achieved the respiratory compensation point. CONCLUSION: Prescribing exercise for IC patients between 40% and 70% of VO(2)peak will induce a lower stimulus than that at AT, whereas prescribing exercise at PT will result in a stimulus above AT. Thus, prescribing exercise training for IC patients on the basis of PT will probably produce a greater metabolic stimulus, promoting better cardiovascular benefits.

Adjuncts to Physical Training of Patients With Severe COPD: Oxygen or Noninvasive Ventilation?

BACKGROUND: Previous studies have shown positive effects from noninvasive ventilation (NIV) or supplemental oxygen on exercise capacity in patients with COPD. However, the best adjunct for promoting physiologic adaptations to physical training in patients with severe COPD remains to be investigated. METHODS: Twenty-eight patients (mean +/- SD age 68 +/- 7 y) with stable COPD (FEV(1) 34 +/- 9% of predicted) undergoing an exercise training program were randomized to either NIV (n = 14) or supplemental oxygen (n = 14) during group training to maintain peripheral oxygen saturation (S(pO2)) >= 90%. Physical training consisted of treadmill walking (at 70% of maximal speed) 3 times a week, for 6 weeks. Patients were assessed at baseline and after 6 weeks. Assessments included physiological adaptations during incremental exercise testing (ratio of lactate concentration to walk speed, oxygen uptake [(V) over dot(O2)], and dyspnea), exercise tolerance during 6-min walk test, leg fatigue, maximum inspiratory pressure, and health-related quality of life. RESULTS: Two patients in each group dropped out due to COPD exacerbations and lack of exercise program adherence, and 24 completed the training program. Both groups improved 6-min walk distance, symptoms, and health-related quality of life. However, there were significant differences between the NIV and supplemental-oxygen groups in lactate/speed ratio (33% vs -4%), maximum inspiratory pressure (80% vs 23%), 6-min walk distance (122 m vs 47 m), and leg fatigue (25% vs 11%). In addition, changes in S(pO2)/speed, (V) over dot(O2), and dyspnea were greater with NIV than with supplemental-oxygen. CONCLUSIONS: NIV alone is better than supplemental oxygen alone in promoting beneficial physiologic adaptations to physical exercise in patients with severe COPD.

Creatine supplementation spares muscle glycogen during high intensity intermittent exercise in rats

Background: The effects of creatine (CR) supplementation on glycogen content are still debatable. Thus, due to the current lack of clarity, we investigated the effects of CR supplementation on muscle glycogen content after high intensity intermittent exercise in rats. Methods: First, the animals were submitted to a high intensity intermittent maximal swimming exercise protocol to ensure that CR-supplementation was able to delay fatigue ( experiment 1). Then, the CR-mediated glycogen sparing effect was examined using a high intensity intermittent sub-maximal exercise test ( fixed number of bouts; six bouts of 30-second duration interspersed by two-minute rest interval) ( experiment 2). For both experiments, male Wistar rats were given either CR supplementation or placebo (Pl) for 5 days. Results: As expected, CR-supplemented animals were able to exercise for a significant higher number of bouts than Pl. Experiment 2 revealed a higher gastrocnemius glycogen content for the CR vs. the Pl group (33.59%). Additionally, CR animals presented lower blood lactate concentrations throughout the intermittent exercise bouts compared to Pl. No difference was found between groups in soleus glycogen content. Conclusion: The major finding of this study is that CR supplementation was able to spare muscle glycogen during a high intensity intermittent exercise in rats.

Monitoring stress tolerance and occurrences of upper respiratory illness in basketball players by means of psychometric tools and salivary biomarkers

The aim of the study was to evaluate the possible relationships between stress tolerance, training load, banal infections and salivary parameters during 4 weeks of regular training in fifteen basketball players. The Daily Analysis of Life Demands for Athletes` questionnaire (sources and symptoms of stress) and the Wisconsin Upper Respiratory Symptom Survey were used on a weekly basis. Salivary cortisol and salivary immunoglobulin A (SIgA) were collected at the beginning (before) and after the study, and measured by enzyme-linked immunosorbent assay (ELISA). Ratings of perceived exertion (training load) were also obtained. The results from ANOVA with repeated measures showed greater training loads, number of upper respiratory tract infection episodes and negative sensation to both symptoms and sources of stress, at week 2 (p < 0.05). Significant increases in cortisol levels and decreases in SIgA secretion rate were noted (before to after). Negative sensations to symptoms of stress at week 4 were inversely and significantly correlated with SIgA secretion rate. A positive and significant relationship between sources and symptoms of stress at week 4 and cortisol levels were verified. In summary, an approach incorporating in conjunction psychometric tools and salivary biomarkers could be an efficient means of monitoring reaction to stress in sport. Copyright (C) 2010 John Wiley & Sons, Ltd.

Strength training increases walking tolerance in intermittent claudication patients: randomized trial

Objective: To analyse the effects of strength training (ST) in walking capacity in patients with intermittent claudication (IC) compared with walking training (WT) effects. Methods. Thirty patients with IC were randomized into ST and WT. Both groups trained twice a week for 12 weeks at the same rate of perceived exertion. ST consisted of three sets of 10 repetitions of whole body exercises. WT consisted of 15 bouts of 2-minute walking. Before and after the training program walking capacity, peak VO(2), VO(2) at the first stage of treadmill test, ankle brachial index, ischemic window, and knee extension strength were measured. Results: ST improved initial claudication distance (358 +/- 224 vs 504 +/- 276 meters; P < .01), total walking distance (618 +/- 282 to 775 +/- 334 meters; P < .01), VO(2), at the first stage of treadmill test (9.7 +/- 2.6 vs 8.1 +/- 1.7 mL . kg(-1) . minute; P < .01), ischemic window (0.81 +/- 1.16 vs 0.43 +/- 0.47 mm Hg minute meters(-1); P = .04), and knee extension strength (19 +/- 9 vs 21 +/- 8 kg and 21 +/- 9 vs 23 +/- 9; P < .01). Strength increases correlated with the increase in initial claudication distance (r = 0.64; P = .01.) and with the decrease ill VO(2) measured at the first stage of the treadmill test (r = -0.52; P = .04 and r = -0.55; P = .03). Adaptations following ST were similar to the ones observed after WT; however, patients reported lower pain during ST than WT (P < .01). Conclusion: ST improves functional limitation similarly to WT but it produces lower pain, suggesting that this type of exercise could be useful and should be considered in patients with IC. (J Vase Surg 2010;51:89-95.)

Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training

Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) (similar to 10g .day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects.

Activity of the medial prefrontal cortex and amygdala underlies one-trial tolerance of rats in the elevated plus-maze

The anxiolytic effects of benzodiazepines are reduced after a single exposure of rats to elevated plus-maze test (EPM). Midazolam showed an anxioselective profile in animals submitted to one session (T1) but did not change the usual exploratory behavior of rats exposed twice (T2) to the EPM. In this study we examined further the one-trial tolerance by performing a factor analysis of the exploratory behavior of rats injected with saline before both trials as well as an immunohistochemistry study for quantification of Fos expression in encephalic structures after these sessions. Factor analysis of all behavioral categories revealed that factor I consisted of anxiety-related categories in T1 whereas these same behavioral categories loaded on factor 2 in T2. Risk assessment was also dissociated as it loaded stronger on T2 (factor 3) than on T1 (factor 4). Locomotor activity in T1 loaded on factor 5. Immunohistochemistry analyses showed that Fos expression predominated in limbic structures in T1 group. The medial prefrontal cortex and amygdala were the main areas activated in T2 group. These data suggest that anxiety and risk assessment behaviors change their valence across the EPM sessions. T2 is characterized by the emergence of a fear factor, more powerful risk assessment and medial prefrontal cortex activation. The amygdala functions as a switch between the anxiety-like patterns of T1 to the cognitive control of fear prevalent in T2. The EPM retest session is proposed as a tool for assessing the cognitive activity of rodents in the control of fear. (c) 2007 Elsevier B.V. All rights reserved.