| Keywords |
Heat stress ; Memory ; Cell proliferation ; Cental fatigue ; Hippocampus |
| Abstract |
Heat stress deteriorates memory function, and treadmill exercise increases neurogenesis and 5-hydroxytryptamine (serotonin, 5-HT) expression. The aim of this study is to examine the effects of treadmill exercise under heat stress conditions with central fatigue and memory function in relation to 5-HT expression and neurogenesis in the hippocampus. Male Sprague-Dawley rats weighing 250±10 g (7 weeks in age) were randomly divided into four groups (n=10 in each group): control in 22℃ group, exercise in 22℃ group, control in 35℃ group, and exercise in 35℃ group. The environmental temperature at 22℃ with relative humidity 40% set as the normal conditions and 35℃ with relative humidity 20% set as the heat stress conditions. All animals were injected intraperitoneally with 50 mg/kg 5-bromo-2'-deoxyuridine (BrdU) one hour before the starting of treadmill exercise once a day for 3 consecutive days. The animals were sacrificed immediately after finishing the last session of treadmill exercise on the 5 weeks of the experiment. Memory function was evaluated by determination of latency in the passive avoidance task. Central fatigue was determined by immunohistochemistry for the expressions of 5-HT and tryptphan hydroxylase (TPH), the limiting enzyme for 5-HT synthesis, in the dorsal raphe. New cells were detected by immunohistochemistry for BrdU in the hippocampal dentate gyrus. The present results explain that treadmill exercise under normal conditions increased by latency in passive avoidance task. In another words, memory function was enhanced by treadmill exercise. However, heat stress conditions will be shorten latency and treadmill exercise under heat stress conditions which was represent heat stress disturbed memory function. The expressions of 5-HT and TPH in the dorsal raphe were increased by both treadmill exercise and heat stress, which was represent that treadmill exercise and heat stress acted as the central fatigue-inducing factor. Neurogenesis in the dentate gyrus was increased by treadmill exercise under normal conditions, however, the increasing effect of treadmill exercise on neurogenesis was not appeared under heat stress conditions. The present study revealed that treadmill exercise enhanced memory function through increasing of neurogenesis. Heat stress, in contrast, exerted deteriorative effect on memory function through enhancing central fatigue and suppressing neurogenesis. As a result, treadmill exercise under heat stress conditions did not be effected to the memory enhancing. |