The improvement of exercise performance by physical training is related to increased hypothalamic neuronal activation

Abstract

The effects of physical training on hypothalamic activation after exercise and their relationship with heat dissipation were investigated. Following 8 weeks of physical training, trained (TR, n = 9) and untrained (UN, n = 8) Wistar rats were submitted to a regimen of incremental running until fatigue while body and tail temperatures were recorded. After exercise, hypothalamic c-Fos immunohistochemistry analysis was performed. The workload, body-heating rate, heat storage and body temperature threshold for cutaneous vasodilation were calculated. Physical training increased the number of c-Fos immunoreactive neurons in the paraventricular, medial preoptic and median preoptic nucleus by 112%, 90% and 65% (P < 0.01) after exercise, respectively. In these hypothalamic regions, increased neuronal activation was directly associated with the increased workload performed by TR animals (P < 0.01). Moreover, a reduction of 0.6°C in the body temperature threshold for cutaneous vasodilation was shown by TR animals (P < 0.01). This reduction was possibly responsible for the lower body-heating rate (0.019 ± 0.002°C/min, TR vs 0.030 ± 0.005°C/min, UN, P < 0.05) and the decreased ratio between heat storage and the workload performed by TR animals (18.18 ± 1.65 cal/kg, TR vs 31.38 ± 5.35 cal/kg, UN, P < 0.05). The data indicate that physical training enhances hypothalamic neuronal activation during exercise. This enhancement is the central adaptation relating to better physical performance, characterized by a lower ratio of heat stored to workload performed, due to improved heat dissipation.

Influence of Time-of-Day on Maximal Exercise Capacity Is Related to Daily Thermal Balance but Not to Induced Neuronal Activity in Rats

“…This is in agreement with previous observations that the highest level of c-fos protein in the SCN is found during the late night while little difference (if any) is observed between ZT2 and ZT16 (Edelstein et al, 2000 ). Furthermore, previous work (Soya et al, 2007 ; Lima et al, 2014a ; Santiago et al, 2016 ) showed that c-fos neuronal activation can detect strong changes in workload (~40–60%), however the present study showed a significant but less pronounced change (~20%). This might reflect a limitation of immunohistochemistry sensitivity that impairs the detection capacity for dynamic processes.…”

“…The resting protocol consisted of staying on the treadmill for 90 min. During the second experimental session 90 min after fatigue (Lima et al, 2014b ; Santiago et al, 2016 ; for a short review of c-fos protein expression, please refer to Kovàcs, 1998 ), animals were deeply anesthetized with ketamine and xylazine and were transcardially perfused with 40 mL of heparinized 0.01 M phosphate-buffered saline (PBS), followed by 400 mL of 4% paraformaldehyde (PFA) in 0.2 M phosphate-buffered saline (pH 7.4). The brains were removed for subsequent immunohistochemical analysis.…”

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

“…However, the same effect was observed in UN rats, suggesting that all three protocols, including passive heat exposure, have induced this adaptation, which was also reported in heat-acclimated humans [8][9][10]. Lower resting abdominal temperatures have also been observed in rats subjected to an 8-week aerobic training regime consisting of constant-speed sessions performed at 23˚C [36]. However, the existence of lower resting T COL in heat-acclimated rats should be analysed with caution, considering that rats were quickly manipulated to insert the colonic thermistor and attach the tail-skin thermocouple before placement on the treadmill.…”

“…In contrast, our findings disagree with the previous observations made by Santiago et al [36], who observed an increased tail heat loss during exercise following an 8-week aerobic training consisting of constant-speed sessions. In the latter study [36], all training and testing were performed in a temperate environment, and training was initiated when rats were very young (i.e., 4 weeks old); these differences in methods may explain the different results yielded by the two studies. Particularly, dry heat exchange through the tail is dependent on cutaneous vasodilation that favours convection, which is more relevant in temperate than in hot environments due to a greater thermal gradient between the skin and surroundings under the former conditions.…”

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

“…The training protocols consisted of running sessions on a treadmill across 8 weeks, with 5 weekly sessions always performed at the same time of day. The three protocols used in this study are described in detail in the Supporting Information section of the manuscript ( S1 – S3 Tables) and were adapted from a protocol proposed by Santiago et al [ 18 ]. At the last session of the aerobic training protocols, the increase in speed relative to the first session corresponded to 225% (INT), 125% (ID) and 38.5% (DUR; Fig 1A ), whereas the increase in duration corresponded to 38.5%, 100% and 225% in the INT, ID and DUR groups, respectively ( Fig 1B ).…”