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Hypothalamic temperature of rats subjected to treadmill running in a cold environment.

Fonseca CG, Pires W, Lima MR, Guimarães JB, Lima NR, Wanner SP - PLoS ONE (2014)

Bottom Line: Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies.Interestingly, external cooling prevented this early increase in the temperature differential from the 2nd to the 8th min of running.Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

View Article: PubMed Central - PubMed

Affiliation: Exercise Physiology Laboratory, School of Physical Education, Physiotherapy and Occupational Therapy, Universidade Federal de Minas Gerais, Belo Horizonte (MG), Brazil.

ABSTRACT
Different strategies for cooling the body prior to or during physical exercise have been shown to improve prolonged performance. Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies. Therefore, our first aim sought to measure the hypothalamic temperature (Thyp) of rats subjected to treadmill running in a cold environment. Moreover, evidence suggests that Thyp and abdominal temperature (Tabd) are regulated by different physiological mechanisms. Thus, this study also investigated the dynamics of exercise-induced changes in Thyp and Tabd at two ambient temperatures: 25°C (temperate environment) and 12°C (cold). Adult male Wistar rats were used in these experiments. The rats were implanted with a guide cannula in the hypothalamus and a temperature sensor in the abdominal cavity. After recovery from this surgery, the rats were familiarized with running on a treadmill and were then subjected to the two experimental trials: constant-speed running (20 m/min) at 12°C and 25°C. Both Thyp and Tabd increased during exercise at 25°C. In contrast, Thyp and Tabd remained unchanged during fatiguing exercise at 12°C. The temperature differential (i.e., Thyp - Tabd) increased during the initial min of running at 25°C and thereafter decreased toward pre-exercise values. Interestingly, external cooling prevented this early increase in the temperature differential from the 2nd to the 8th min of running. In addition, the time until volitional fatigue was higher during the constant exercise at 12°C compared with 25°C. Together, our results indicate that Thyp and Tabd are regulated by different mechanisms in running rats and that external cooling affected the relationship between both temperature indexes observed during exercise without environmental thermal stress. Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

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Correlation between the rate of increase in the hypothalamic temperature (panel A) or the abdominal temperature (panel B) and the total exercise time during constant-speed running at ambient temperatures of 25°C and 12°C.
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pone-0111501-g006: Correlation between the rate of increase in the hypothalamic temperature (panel A) or the abdominal temperature (panel B) and the total exercise time during constant-speed running at ambient temperatures of 25°C and 12°C.

Mentions: Next, the association between the different indexes of Tcore and physical performance was addressed. At 25°C, we observed a significant negative correlation between the rate of increase in Thyp and the total exercise time (r = –0.72, P = 0.004). In contrast, no significant correlations were observed between the rate of increase in Tabd and physical performance during treadmill running at 25°C (r = –0.35, P = 0.22; Figure 6B). When the animals ran at 12°C, no significant correlations were observed between the running performance and the rate of increase in Thyp (r = −0.18; P = 0.56; Figure 6A) or Tabd (r = –0.48; P = 0.10; Figure 6B).


Hypothalamic temperature of rats subjected to treadmill running in a cold environment.

Fonseca CG, Pires W, Lima MR, Guimarães JB, Lima NR, Wanner SP - PLoS ONE (2014)

Correlation between the rate of increase in the hypothalamic temperature (panel A) or the abdominal temperature (panel B) and the total exercise time during constant-speed running at ambient temperatures of 25°C and 12°C.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4218756&req=5

pone-0111501-g006: Correlation between the rate of increase in the hypothalamic temperature (panel A) or the abdominal temperature (panel B) and the total exercise time during constant-speed running at ambient temperatures of 25°C and 12°C.
Mentions: Next, the association between the different indexes of Tcore and physical performance was addressed. At 25°C, we observed a significant negative correlation between the rate of increase in Thyp and the total exercise time (r = –0.72, P = 0.004). In contrast, no significant correlations were observed between the rate of increase in Tabd and physical performance during treadmill running at 25°C (r = –0.35, P = 0.22; Figure 6B). When the animals ran at 12°C, no significant correlations were observed between the running performance and the rate of increase in Thyp (r = −0.18; P = 0.56; Figure 6A) or Tabd (r = –0.48; P = 0.10; Figure 6B).

Bottom Line: Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies.Interestingly, external cooling prevented this early increase in the temperature differential from the 2nd to the 8th min of running.Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

View Article: PubMed Central - PubMed

Affiliation: Exercise Physiology Laboratory, School of Physical Education, Physiotherapy and Occupational Therapy, Universidade Federal de Minas Gerais, Belo Horizonte (MG), Brazil.

ABSTRACT
Different strategies for cooling the body prior to or during physical exercise have been shown to improve prolonged performance. Because of ethical and methodological issues, no studies conducted in humans have evaluated the changes in brain temperature promoted by cooling strategies. Therefore, our first aim sought to measure the hypothalamic temperature (Thyp) of rats subjected to treadmill running in a cold environment. Moreover, evidence suggests that Thyp and abdominal temperature (Tabd) are regulated by different physiological mechanisms. Thus, this study also investigated the dynamics of exercise-induced changes in Thyp and Tabd at two ambient temperatures: 25°C (temperate environment) and 12°C (cold). Adult male Wistar rats were used in these experiments. The rats were implanted with a guide cannula in the hypothalamus and a temperature sensor in the abdominal cavity. After recovery from this surgery, the rats were familiarized with running on a treadmill and were then subjected to the two experimental trials: constant-speed running (20 m/min) at 12°C and 25°C. Both Thyp and Tabd increased during exercise at 25°C. In contrast, Thyp and Tabd remained unchanged during fatiguing exercise at 12°C. The temperature differential (i.e., Thyp - Tabd) increased during the initial min of running at 25°C and thereafter decreased toward pre-exercise values. Interestingly, external cooling prevented this early increase in the temperature differential from the 2nd to the 8th min of running. In addition, the time until volitional fatigue was higher during the constant exercise at 12°C compared with 25°C. Together, our results indicate that Thyp and Tabd are regulated by different mechanisms in running rats and that external cooling affected the relationship between both temperature indexes observed during exercise without environmental thermal stress. Our data also suggest that attenuated hypothalamic hyperthermia may contribute to improved performance in cold environments.

Show MeSH
Related in: MedlinePlus