Brain Temperature in Spontaneously Hypertensive Rats during Physical Exercise in Temperate and Warm Environments

Determinants of body core temperatures at fatigue in rats subjected to incremental-speed exercise: The prominent roles of ambient temperature, distance traveled, initial core temperature, and measurement site

Understanding the factors that underlie the physical exercise-induced increase in body core temperature (T_CORE) is essential to developing strategies to counteract hyperthermic fatigue and reduce the risk of exertional heatstroke. This study analyzed the contribution of six factors to T_CORE attained at fatigue in Wistar rats (n = 218) subjected to incremental-speed treadmill running: ambient temperature (T_AMB), distance traveled, initial T_CORE, body mass, measurement site, and heat loss index (HLI). First, we ran hierarchical multiple linear regression analyses with data from different studies conducted in our laboratory (n = 353 recordings). We observed that T_AMB, distance traveled, initial T_CORE, and measurement site were the variables with predictive power. Next, regression analyses were conducted with data for each of the following T_CORE indices: abdominal (T_ABD), brain cortex (T_BRAIN), or colonic (T_COL) temperature. Our findings indicated that T_AMB, distance traveled (i.e., an exercise performance-related variable), initial T_CORE, and HLI predicted the three T_CORE indices at fatigue. Most intriguingly, HLI was inversely related to T_ABD and T_BRAIN but positively associated with T_COL. Lastly, we compared the temperature values at fatigue among these T_CORE indices, and the following descendent order was noticed - T_COL, T_ABD, and T_BRAIN - irrespective of T_AMB where experiments were conducted. In conclusion, T_CORE in rats exercised to fatigue depends primarily on environmental conditions, performance, pre-exercise T_CORE, and measurement site. Moreover, the influence of cutaneous heat loss on T_COL is qualitatively different from the influence on T_ABD and T_BRAIN, and the temperature values at fatigue are not homogenous within the body core.

Core body temperatures of rats subjected to treadmill exercise to fatigue or exhaustion: The journal Temperature toolbox

This study systematically reviewed the literature reporting the changes in rats' core body temperature (TCORE) induced by either incremental- or constant-speed running to fatigue or exhaustion. In addition, multiple linear regression analyses were used to determine the factors contributing to the TCORE values attained when exercise was interrupted. Four databases (EMBASE, PubMed, SPORTDiscus, and Web of Science) were searched in October 2021, and this search was updated in August 2022. Seventy-two studies (n = 1,538 rats) were included in the systematic review. These studies described heterogeneous experimental conditions; for example, the ambient temperature ranged from 5 to 40°C. The rats quit exercising with TCORE values varying more than 8°C among studies, with the lowest and highest values corresponding to 34.9°C and 43.4°C, respectively. Multiple linear regression analyses indicated that the ambient temperature (p < 0.001), initial TCORE (p < 0.001), distance traveled (p < 0.001; only incremental exercises), and running speed and duration (p < 0.001; only constant exercises) contributed significantly to explaining the variance in the TCORE at the end of the exercise. In conclusion, rats subjected to treadmill running exhibit heterogeneous TCORE when fatigued or exhausted. Moreover, it is not possible to determine a narrow range of TCORE associated with exercise cessation in hyperthermic rats. Ambient temperature, initial TCORE, and physical performance-related variables are the best predictors of TCORE at fatigue or exhaustion. From a broader perspective, this systematic review provides relevant information for selecting appropriate methods in future studies designed to investigate exercise thermoregulation in rats.

Physical exercise-induced thermoregulatory responses in trained rats: Effects of manipulating the duration and intensity of aerobic training sessions

This study investigated the effects of increasing the intensity and/or duration of aerobic training sessions on thermoregulatory responses in rats subjected to exercises in temperate and warm environments. Thirty-two adult male Wistar rats were divided into four groups: a control (CON) group and three groups that were subjected to an 8-week aerobic training, during which the physical overload was achieved by predominantly increasing the exercise intensity (INT), duration (DUR) or by increasing both in an alternate manner (ID). During the last week of training, the rats received an abdominal sensor implant to measure their core body temperature (TCORE) by telemetry. After the training protocol, the 32 rats were subjected to incremental speed-exercises in temperate (23 °C) and warm (32 °C) environments. The rats had their TCORE recorded while running on a treadmill, and the ratio between the increase in TCORE and distance traveled was calculated to estimate thermoregulatory efficiency. All training protocols increased the rats' thermoregulatory efficiency during the incremental-speed exercise at 23 °C; i.e., trained rats attained faster running speeds but unchanged TCORE at fatigue compared to CON rats. However, none of the load components of training sessions - intensity or duration - was more effective than the other in improving this efficiency. At 32 °C, the aerobic training protocols did not influence the exercise-induced thermoregulatory responses. Our data indicate that different progressions in aerobic training performed at temperate conditions improved thermoregulatory efficiency during incremental exercise in the same environment; this training-induced adaptation was not clearly observed when running in warmer conditions.

Core temperature circadian rhythm across aging in Spontaneously Hypertensive Rats

The purpose of this study was to evaluate the circadian rhythm of core temperature (Tcore) across aging in Spontaneously Hypertensive Rats (SHR) with comparison to the two rat strains often used as their normotensive control animals, namely, Wistar (WIS) and Wistar Kyoto (WKY).

METHODS

WIS, WKY and SHR rats were subdivided into three different groups according their age: WIS16, WIS48, WIS72, WKY16, WKY48, WKY72, SHR16, SHR48 and SHR72 weeks-old. Body mass and blood pressure were periodically measured along the experiments. All animal group had their circadian rhythm of Tcore evaluated over three consecutive days (72 h) by telemetry using an implanted temperature sensor. The Tcore circadian rhythm was averaged in 1-h blocks and analyzed using the cosinor method.

RESULTS

Sixteen-week-old SHR (SHR16) presented higher Tcore than WIS16 (from 06am to 06pm) and WKY16 (from 07am to 06pm). Both normotensive groups exhibited increases in Tcore during circadian rhythm with aging. The cosinor analysis showed no differences between strains and ages for the acrophase. An age effect on the SHR strain (SHR16 < SHR72) was observed regarding the amplitude. SHR16 had higher values regarding MESOR compared to WIS16 and WKY16. In addition, WIS72 and WKY72 showed higher values than WIS16 and WKY16, respectively. Finally, no differences were observed in the strength rhythm analysis.

CONCLUSIONS

SHR presented impaired thermoregulatory control at only 16 weeks of age when showing a higher body temperature during the activity phase, while other circadian rhythm parameters showed no differences across aging. Therefore, in taking our results as a whole we can conclude that WIS and WKY are appropriate Wistar strains to be used as normotensive controls for SHR.

Ramelteon modulates gamma oscillations in the rat primary motor cortex during non-REM sleep

Sleep disorders adversely affect daily activities and cause physiological and psychiatric problems. The shortcomings of benzodiazepine hypnotics have led to the development of ramelteon, a melatonin MT1 and MT2 agonist. Although the sleep-promoting effects of ramelteon have been documented, few studies have precisely investigated the structure of sleep and neural oscillatory activities. In this study, we recorded electrocorticograms in the primary motor cortex, the primary somatosensory cortex and the olfactory bulb as well as electromyograms in unrestrained rats treated with either ramelteon or vehicle. A neural-oscillation-based algorithm was used to classify the behavior of the rats into three vigilance states (e.g., awake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep). Moreover, we investigated the region-, frequency- and state-specific modulation of extracellular oscillations in the ramelteon-treated rats. We demonstrated that in contrast to benzodiazepine treatment, ramelteon treatment promoted NREM sleep and enhanced fast gamma power in the primary motor cortex during NREM sleep, while REM sleep was unaffected. Gamma oscillations locally coordinate neuronal firing, and thus, ramelteon modulates neural oscillations in sleep states in a unique manner and may contribute to off-line information processing during sleep.

Independent effects of rapid eye movement sleep deprivation and exposure to environmental heat stress on aerobic performance and thermoregulatory responses in exercising rats

Evidence indicates that aerobic performance is degraded either by environmental heat stress or sleep deprivation. However, whether these conditions interact to produce more significant performance impairment deserves further investigation. Therefore, this study investigated the effects of experimental sleep deprivation (24 h or 96 h) on aerobic performance and thermoregulatory responses in rats exercised on a treadmill at different environmental conditions. Adult male Wistar rats were subjected to rapid eye movement sleep deprivation (RSD) using the modified multiple platform method and were then subjected to an incremental-speed exercise until they were fatigued. Treadmill running was performed in a temperate (24°C) or warm (31°C) environment, and the colonic temperature (an index of core body temperature; T_CORE) and the tail-skin temperature (T_SKIN; an index of cutaneous heat loss) were recorded. 24-h and 96-h RSD produced small magnitude reductions in aerobic performance (Cohen's d = 0.47-0.58) and minor changes in thermoregulation. Relative to control rats, sleep-deprived rats showed a higher T_CORE at the exercise initiation and a higher threshold for activating cutaneous heat loss, but unchanged T_CORE and T_SKIN at fatigue. Exercise at 31°C induced large reductions in performance (d = 0.82-1.29) and marked changes in thermoregulation, as evidenced by higher T_CORE and T_SKIN at fatigue, compared to exercise at 24°C. Interestingly, none of the effects induced by RSD were exacerbated by environmental heat stress and vice-versa, indicating that both conditions did not interact. We conclude that RSD and heat stress modulate aerobic performance and thermoregulatory responses by acting independently.

Impaired thermoregulation in spontaneously hypertensive rats during physical exercise is related to reduced hypothalamic neuronal activation

This study aimed to evaluate the physical exercise-induced neuronal activation in brain nuclei controlling thermoregulatory responses in hypertensive and normotensive rats. Sixteen-week-old male normotensive Wistar rats (NWRs) and spontaneously hypertensive rats (SHRs) were implanted with an abdominal temperature sensor. After recovery, the animals were subjected to a constant-speed treadmill running (at 60% of the maximum aerobic speed) for 30 min at 25 °C. Core (T_core) and tail-skin (T_skin) temperatures were measured every minute during exercise. Ninety minutes after the exercise, the rats were euthanized, and their brains were collected to determine the c-Fos protein expression in the following areas that modulate thermoregulatory responses: medial preoptic area (mPOA), paraventricular hypothalamic nucleus (PVN), and supraoptic nucleus (SON). During treadmill running, the SHR group exhibited a greater increase in T_core and an augmented threshold for cutaneous heat loss relative to the NWR group. In addition, the SHRs showed reduced neuronal activation in the mPOA (< 49.7%) and PVN (< 44.2%), but not in the SON. The lower exercise-induced activation in the mPOA and PVN in hypertensive rats was strongly related to the delayed onset of cutaneous heat loss. We conclude that the enhanced exercise-induced hyperthermia in hypertensive rats can be partially explained by a delayed cutaneous heat loss, which is, in turn, associated with reduced activation of brain areas modulating thermoregulatory responses.

The magnitude of physical exercise-induced hyperthermia is associated with changes in the intestinal permeability and expression of tight junction genes in rats

We investigated whether the magnitude of exercise-induced hyperthermia influences intestinal permeability and tight junction gene expression. Twenty-nine male Wistar rats were divided into four groups: rest at 24 °C and exercise at 13 °C, 24 °C or 31 °C. The exercise consisted of a 90-min treadmill run at 15 m/min, and different ambient temperatures were used to produce distinct levels of exercise-induced hyperthermia. Before the experimental trials, the rats were treated by gavage with diethylenetriaminepentaacetic acid labeled with technetium-99 metastable as a radioactive probe. The rats' core body temperature (T_CORE) was measured by telemetry. Immediately after the trials, the rats were euthanized, and the intestinal permeability was assessed by measuring the radioactivity of blood samples. The mRNA levels of occludin and zonula occludens-1 (ZO-1) genes were determined in duodenum samples. Exercise at 24 °C increased T_CORE to values close to 39 °C, without changing permeability compared with the resting trial at the same environment. Meanwhile, rats' T_CORE exceeded 40 °C during exercise at 31 °C, leading to greater permeability relative to those observed after exercise in the other ambient temperatures (e.g., 0.0037%/g at 31 °C vs. 0.0005%/g at 13 °C; data expressed as medians; p < 0.05). Likewise, the rats exercised at 31 °C exhibited higher mRNA levels of ZO-1 and occludin genes than the rats exercised at 24 °C or 13 °C. The changes in permeability and gene expression were positively and significantly associated with the magnitude of hyperthermia. We conclude that marked hyperthermia caused by exercise in the warmer environment increases intestinal permeability and mRNA levels of tight junction genes.

Exercise capacity in different stages of hypertension in spontaneously hypertensive rats

BACKGROUND

The aim of the present study was to investigate the exercise capacity of hypertensive rats at different stages of development of hypertension and to determine the most suitable index to evaluate the exercise capacity in different strains.

METHODS

Male spontaneously hypertensive rat (SHR) and normotensive Wistar rats (NWR) of 5, 8, 12 and 16 weeks were submitted to the exercise capacity test. The exercise running time was measured and the workload was calculated.

RESULTS

Normotensive and hypertensive rats when assess the exercise capacity by exercise running time exhibited a reduction in exercise performance over time. Moreover, hypertensive rats showed lower exercise capacity compared to normotensive control when analyzed by workload.

CONCLUSIONS

The present results indicate that hypertensive rats exhibit reduced exercise capacity compared to normotensive rats regardless of age assessed. Beside that, in experiments with strains with different body mass the most reliable index to assess exercise capacity is workload.

Comparative effects of two heat acclimation protocols consisting of high-intensity interval training in the heat on aerobic performance and thermoregulatory responses in exercising rats

Acclimation resulting from low- to moderate-intensity physical exertion in the heat induces several thermoregulatory adaptations, including slower exercise-induced increases in core body temperature. However, few studies have investigated the thermoregulatory adaptations induced by high-intensity interval training (HIIT) protocols. Thus, the present study aimed to compare the adaptations in rats’ thermoregulatory parameters and aerobic performance observed after two different heat acclimation regimens consisting of HIIT protocols performed in a hot environment. Twenty-three adult male Wistar rats were initially subjected to an incremental-speed exercise at 32°C until they were fatigued and then randomly assigned to one of the following three heat acclimation strategies: passive heat exposure without any exercise (untrained controls–UN; n = 7), HIIT performed at the maximal aerobic speed (HIIT_100%; n = 8) and HIIT performed at a high but submaximal speed (HIIT_85%; n = 8). Following the two weeks of interventions, the rats were again subjected to a fatiguing incremental exercise at 32°C, while their colonic temperature (T_COL) was recorded. The workload performed by the rats and their thermoregulatory efficiency were calculated. After the intervention period, rats subjected to both HIIT protocols attained greater workloads (HIIT_100%: 313.7 ± 21.9 J vs. HIIT_85%: 318.1 ± 32.6 J vs. UN: 250.8 ± 32.4 J; p < 0.01) and presented a lower ratio between the change in T_COL and the distance travelled (HIIT_100%: 4.95 ± 0.42°C/km vs. HIIT_85%: 4.33 ± 0.59°C/km vs. UN: 6.14 ± 1.03°C/km; p < 0.001) when compared to UN rats. The latter finding indicates better thermoregulatory efficiency in trained animals. No differences were observed between rats subjected to the two HIIT regimens. In conclusion, the two HIIT protocols induce greater thermoregulatory adaptations and performance improvements than passive heat exposure. These adaptations do not differ between the two training protocols investigated in the present study.

Thermoregulation in Hypertensive Rats during Exercise: Effects of Physical Training

Background

Spontaneously hypertensive rats (SHR) show deficit in thermal balance during physical exercise.

Objective

To assess the effects of low-intensity physical exercise training on thermal balance of hypertensive rats undergoing an acute exercise protocol.

Methods

Sixteen-week-old male Wistar rats and SHR were allocated into four groups: control Wistar rats (C-WIS), trained Wistar (T-WIS), control SHR (C-SHR) and trained SHR (T-SHR). Treadmill exercise training was performed for 12 weeks. Blood pressure, resting heart rate and total exercise time was measured before and after the physical exercise program. After the exercise program, a temperature sensor was implanted in the abdominal cavity, and the animals subjected to an acute exercise protocol, during which internal body temperature, tail skin temperature and oxygen consumption until fatigue were continuously recorded. Mechanical efficiency (ME), work, heat dissipation threshold and sensitivity were calculated. Statistical significance was set at 5%.

Results

Physical training and hypertension had no effect on thermal balance during physical exercise. Compared with C-WIS, the T-WIS group showed higher heat production, which was counterbalanced by higher heat dissipation. Hypertensive rats showed lower ME than normotensive rats, which was not reversed by the physical training.

Conclusion

Low-intensity physical training did not affect thermal balance in SHR subjected to acute exercise.

Rats with higher intrinsic exercise capacities exhibit greater preoptic dopamine levels and greater mechanical and thermoregulatory efficiencies while running

The present study investigated whether intrinsic exercise capacity affects the changes in thermoregulation, metabolism and central dopamine (DA) induced by treadmill running. Male Wistar rats were subjected to three incremental exercises and ranked as low-performance (LP), standard-performance (SP), and high-performance (HP) rats. In the first experiment, abdominal (TABD) and tail (TTAIL) temperatures were registered in these rats during submaximal exercise (SE) at 60% of maximal speed. Immediately after SE, rats were decapitated and concentrations of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were determined in the preoptic area (POA). In the second experiment, oxygen consumption was measured and mechanical efficiency (ME) was calculated in these rats during an incremental exercise. HP rats ran for longer periods and were fatigued with higher TABD values, with no difference in TTAIL. Nevertheless, thermoregulatory efficiency was higher in HP rats, compared with other groups. DA and DOPAC concentrations in the POA were increased by SE, with higher levels in HP compared with LP and SP rats. V̇o2 also differed between groups, with HP rats displaying a lower consumption throughout the incremental exercise but a higher V̇o2 at fatigue. ME, in turn, was consistently higher in HP than in LP and SP rats. Thus, our results show that HP rats have greater TABD values at fatigue, which seem to be related to a higher dopaminergic activity in the POA. Moreover, HP rats exhibited a greater thermoregulatory efficiency during exercise, which can be attributed to a lower V̇o2, but not to changes in tail heat loss mechanisms.

NEW & NOTEWORTHY Our findings reveal that rats with higher intrinsic exercise capacities have greater thermoregulatory efficiencies and increased dopaminergic activity in the preoptic area, a key brain area in thermoregulatory control, while exercising. Moreover, higher intrinsic exercise capacities are associated with decreased oxygen consumption for a given exercise intensity, which indicates greater mechanical efficiencies. Collectively, these findings help to advance our knowledge of why some rats of a given strain can exercise for longer periods than others.

Integrin ανβ5 in vitro inhibition limits pro-fibrotic response in cardiac fibroblasts of spontaneously hypertensive rats

Background

To date the TGF-β1 activation mediated by integrin ανβ5 during fibrosis is well-known. This process has been shown also in the heart, where cardiac fibroblasts (CF) differentiate into α-smooth muscle actin (α-SMA)-positive myofibroblasts (MyoFB). Here, we studied the effects on CF, isolated by spontaneously hypertensive rats (SHR), of integrin ανβ5 inhibition in MyoFB differentiation.

Methods

Staining and immunohistochemistry were performed on rat cardiac tissue. CF were isolated by enzymatic digestion from SHR (SHR-CF) and normotensive WKY (WKY-CF) rat hearts and then treated for in vitro evaluation.

Results

SHR heart tissues revealed a higher TGF-β1 expression vs. WKY samples. SHR-CF showed an enhanced SMAD2/3 activation and an up-regulated expression of α-SMA, a typical MyoFB marker, especially after TGF-β1 treatment. Immunostaining on cardiac tissues revealed a higher expression of integrin ανβ5 in SHR vs. WKY rat hearts. In vitro results confirmed the up-regulation of integrin ανβ5 expression in SHR-CF at basal condition and after TGF-β1 treatment, in comparison with WKY-CF. Inhibition of integrin ανβ5 by cilengitide treatment led a decreased expression of ανβ5, collagen I, and α-SMA in SHR-CF vs. WKY-CF, resulting in a diminished differentiation of CF into MyoFB. Taking together, results suggested that SHR-CF are more susceptible to TGF-β1, showing an up-regulated activation of SMAD2/3 signaling, and an increased ανβ5, α-SMA, and collagen I expression. Hypertension stimulus promoted an up-regulation of integrin ανβ5 on SHR cardiac tissue and its in vitro inhibition reverted pro-fibrotic events of SHR-CF.

Conclusion

Inhibition of integrin ανβ5 exerted by cilengitide strongly diminished SHR-CF differentiation into detrimental MyoFB. So, integrin ανβ5 might be considered a novel therapeutic target and cilengitide an effective pharmacological tool to limit the progression of hypertension-induced cardiac fibrosis.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1730-1) contains supplementary material, which is available to authorized users.

Central cholinergic activation induces greater thermoregulatory and cardiovascular responses in spontaneously hypertensive than in normotensive rats

There is evidence that central cholinergic stimulation increases heat dissipation in normotensive rats besides causing changes on the cardiovascular system via modulation of baroreceptors activity. However, the contribution of the central cholinergic system on thermoregulatory responses and its relationship with cardiovascular adjustments in spontaneously hypertensive rats (SHRs), an animal model of reduced baroreceptor sensitivity and thermoregulatory deficit, has not been completely clarified. Therefore, the aim of this study was to verify the involvement of the central cholinergic system in cardiovascular and thermoregulatory adjustments in SHRs. Male Wistar rats (n = 17) and SHRs (n = 17) were implanted with an intracerebroventricular cannula for injections of 2 µL of physostigmine (phy) or saline solution. Tail temperature (T_tail), internal body temperature (T_int), systolic arterial pressure (SAP), heart rate (HR) and metabolic rate were registered during 60 min while the animals remained at rest after randomly receiving the injections. The variability of the SAP and the HR was estimated by the fast Fourier transform. Phy treatment began a succession of cardiovascular and thermoregulatory responses that resulted in increased SAP, reduced HR and increased T_tail in both Wistar and SHRs groups. The magnitude of these effects seems to be more intense in SHRs, since the improvement of heat dissipation reflected in T_int. Taken together, these results provide evidence that hypertensive rats present greater cardiovascular and thermoregulatory responses than normotensive rats after central cholinergic stimulation.

Automatic analysis of treadmill running to estimate times to fatigue and exhaustion in rodents

Introduction

The determination of fatigue and exhaustion in experimental animals is complicated by the subjective nature of the measurement. Typically, it requires an observer to watch exercising animals, e.g. rats running on the treadmill, and to identify the time of the event. In this study, we hypothesized that automatic analysis of the time-averaged position of a rat on a treadmill could be an objective way for estimating times to fatigue and exhaustion. To test this hypothesis, we compared these times measured by a human observer to the results of an automated video tracking system.

Methods

Rats, previously familiarized to running on the treadmill, ran at a fixed speed with zero incline, until exhaustion. The experiments were performed at either room temperature (24 °C) or in a hot environment (32 °C). Each experiment was video recorded. A trained observer estimated the times to fatigue and exhaustion. Then, video tracking software was used to determine the position of the animals on the treadmill belt. The times to fatigue and exhaustion were determined, based on the position on the treadmill using predefined criteria.

Results

Manual scores and the average position on the treadmill had significant correlation. Both the observer and the automated video tracking determined that exercise in a hot environment, compared with the exercise at room temperature, results in shorter times to exhaustion and fatigue. Also, estimates of times made by the observer and the automated video tracking were not statistically different from each other.

Discussion

A similarity between the estimates of times to fatigue and exhaustion made by the observer and the automated technique suggests that video tracking of rodents running on a treadmill can be used to determine both parameters in experimental studies. Video tracking technique allows for a more objective measure and would allow for an increased performance in experimentation. The Supplemental information to this manuscript contains an Excel file, which includes the code in Virtual Basic with freeware license, to process and visualize running data and automatically estimate the times to fatigue and exhaustion. Instructions for the software are also included.

Physical Exercise-Induced Cardiovascular and Thermoregulatory Adjustments Are Impaired in Rats Subjected to Cutaneous Artery Denervation

This study aimed to investigate the chronic effects of caudal artery denervation on morphometric parameters of the tail vascular smooth muscle and on physical exercise-induced thermoregulatory and cardiovascular adjustments in rats. Male Wistar rats were subjected to caudal artery denervation or the sham procedure. Approximately 26-28 days after these procedures, their thermoregulatory and cardiovascular parameters were evaluated at rest and during or following a fatiguing treadmill run. At the end of the experiments, the rats were euthanized, and samples of their tails were removed to evaluate morphometric parameters of the vascular smooth muscle surrounding the caudal artery. Denervated rats showed morphological adaptations, including increased arterial wall thickness and wall-to-lumen ratios. In resting rats and following the fatiguing exercise, caudal artery denervation barely affected the thermoregulatory and cardiovascular parameters evaluated. By contrast, caudal artery denervation attenuated the increase in tail skin temperature, decreased the spontaneous baroreflex sensitivity, and exacerbated the increases in mean arterial pressure in exercising rats. The increased wall-to-lumen ratio of denervated rats correlated negatively with the maximum tail skin temperature attained or cutaneous heat loss sensitivity but correlated positively with the maximum diastolic blood pressure attained during exercise. In conclusion, cutaneous denervation induces vascular remodeling characterized by morphological adaptations of the tail vascular smooth muscle. This vascular remodeling likely underlies the impaired tail heat loss and blood pressure adjustments in denervated rats subjected to physical exercise. Therefore, we have highlighted the importance of cutaneous vascular innervation integrity in thermal and cardiovascular control in stress-challenged rats. In this sense, our findings advance the understanding of thermoregulatory and cardiovascular system reactions after a sustained cutaneous vascular innervation injury, which is essential for the treatment of some diseases, such as Parkinson's disease and type 1 and type 2 diabetes mellitus.

Pre-exercise exposure to the treadmill setup changes the cardiovascular and thermoregulatory responses induced by subsequent treadmill running in rats

Different methodological approaches have been used to conduct experiments with rats subjected to treadmill running. Some experimenters have exposed rats to the treadmill setup before initiating exercise to minimize the influences of handling and being placed in an anxiety-inducing environment on the physiological responses to subsequent running. Other experimenters have subjected rats to exercise immediately after placing them on the treadmill. Thus, the present study aimed to evaluate the effects of pre-exercise exposure to the treadmill on physical performance and cardiovascular and thermoregulatory responses during subsequent exercise. Male Wistar rats were subjected to fatiguing incremental-speed exercise at 24°C immediately after being placed on the treadmill or after being exposed to the treadmill for 70 min following removal from their home cages. Core body temperature (T_CORE), tail-skin temperature (T_SKIN), heart rate (HR) and mean arterial pressure (MAP) were recorded throughout the experiments. Rats exposed to the treadmill started exercise with higher T_CORE, lower HR and MAP, and unaltered T_SKIN. This exposure did not influence performance, but it markedly affected the exercise-induced increases in the four physiological parameters evaluated; for example, the T_SKIN increased earlier and at a higher T_CORE. Moreover, previous treadmill exposure notably allowed expected exercise-induced changes in cardiovascular parameters to be observed. Collectively, these data indicate that pre-exercise exposure to the treadmill induces important effects on physiological responses during subsequent treadmill running. The present data are particularly relevant for researchers planning experiments involving physical exercise and the recording of physiological parameters in rats.

Effects of manipulating the duration and intensity of aerobic training sessions on the physical performance of rats

This study investigated the effects of manipulating the load components of aerobic training sessions on the physical performance of rats. To achieve this purpose, adult male Wistar rats were divided into four groups: an untrained control (CON) group and training groups with a predominant overload in intensity (INT) or duration (DUR) or alternating and similar overloads in intensity and duration (ID). Prior to, during, and after 8 weeks of the control or training protocols, the performance of the rats (evaluated by their workload) was determined during fatiguing, incremental-speed treadmill running. Two additional incremental running tests were performed prior to and at the end of the protocols to measure the peak rate of oxygen consumption (VO2peak). As expected, the rats in the trained groups exhibited increased performance, whereas the untrained rats showed stable performance throughout the 8 weeks. Notably, the performance gain exhibited by the DUR rats reached a plateau after the 4th week. This plateau was not present in the INT or ID rats, which exhibited increased performance at the end of training protocol compared with the DUR rats. None of the training protocols changed the VO2peak values; however, these values were attained at faster speeds, which indicated increased running economy. In conclusion, our findings demonstrate that the training protocols improved the physical performance of rats, likely resulting from enhanced running economy. Furthermore, compared with overload in duration, overload in the intensity of training sessions was more effective at inducing performance improvements across the 8 weeks of the study.