O aumento da temperatura cerebral induzido pelo exercício físico é exacerbado na ausência crônica dos canais TRPV1 abdominais

Abstract

The first experimental design was aimed at evaluating the cortical brain temperature during different exercise intensities performed at thermoneutral conditions. Nine male Wistar rats were implanted with a cerebral guide cannula into the right frontal cortex and were subjected to running exercises until the voluntary interruption of effort (VIE) at three different speeds: 18 m/min (V18), 21 m/min (V21), and 24 m/min (V24). Brain temperature was measured by a thermistor inserted through the guide cannula. The highest exercise intensity was associated with a decreased total exercise time (V24: 62 ± 11 min versus V21: 149 ± 14 min versus V18: 207 ± 15 min; p < 0.001) and with higher rates of increase in brain temperature relative to the lower exercise intensities (V24: 0.058 ± 0.009°C/min versus V18: 0.017 ± 0.002°C/min and V21: 0.021 ± 0.002°C/min; p < 0.001). However, the exercise intensity did not affect brain temperature at the IVE (mean values between 40.1 and 40.4°C). Therefore, at thermoneutral conditions, exercise intensity influences the rate of increase in brain temperature, without affecting the absolute values measured when the effort was voluntary interrupted. The second set of experiments investigated if the lesions caused by the chronic implantation of a guide cannula or by the acute insertion of a thermistor into the brain affect exercise performance. Twelve rats were divided in two groups: a group that had a guide cannula implanted in the right frontal cortex, and another group that was not operated (control) The maximal treadmill velocity attained was not changed by the implant of the guide cannula or by the insertion of the thermistor when compared to the control group or to the first exercise performed before the surgery (First test: 28.6 ± 0.9 m/min versus Cannula: 28.6 ± 1.4 m/min versus Thermistor: 29.1 ± 1.4 m/min, p = 0.977). This results indicate that the experimental procedures used for measuring brain temperature do not affect the exercise performance. The third set of experiments was aimed at evaluating if the peripheral TRPV1 channels modulate the thermoregulation and physical performance during exercise performed at thermoneutral and warm environments. Twenty eight rats that were implanted with a cerebral guide cannula were subjected to two exercise protocols (progressive- or constant-speed) at two environmental conditions. During each protocol, the rats were treated with resiniferatoxin (RTX: 20 g/kg i.p.) to desensitized the peripheral TRPV1channels or were treated with vehicle. The treatment with RTX did not change the physical performance in either exercise protocol at both ambient temperatures. However, during the two exercises protocols, the desensitized rats presented a delay in the initial increase in tail skin temperature (progressivespeed exercise at thermoneutral conditions: minute 14: RTX: 26.85 ± 0.93°C versus Control: 30.28 ± 0.89°C; p < 0.05) and high values of brain temperature during exercise. This enhanced running hyperthermia persisted until the VIE during progressive-speed exercise (at thermoneutral conditions: RTX: 39.85 ± 0.23°C versus Control: 38.99 ± 0.20°C; p < 0.05). Therefore, the desensitization of peripheral TRPV1 channels modulates thermoregulation during exercise, without affecting physical performance.