運動時の温熱性疲労における脳内セロトニンの関与 <学位論文要旨>

The development of fatigue is more pronounced in the heat than thermoneutral environments. Fatigue during prolonged exercise is clearly influenced by a complex interaction between peripheral and central factors. However, the mechanism of central fatigue consistent with the higher core temperature during exercise is still unclear. The original central fatigue hypothesis suggested that an exercise-induced increase in extracellular serotonin (5-hydroxytryptamine; 5-HT) concentrations in several brain regions contributed to the development of fatigue during prolonged exercise. As serotonergic projection innervate the preoptic area and anterior hypothalamus (PO/AH), the thermoregulatory center, a change in the activity of these neurons may be expected to contribute to the control of body temperature. However, significant role of 5-HT in the fatigue process during exercise in the heat is not clearly indicated. Therefore, the present study aimed to assess the role of brain 5-HT on the thermoregulation and hyperthermia mediated central fatigue during exercise.

Appropriate experimental procedures were described in Chapter 2. In Chapter 3, experiment 1 showed the response of 5-HT in the PO/AH to thermoregulation during exercise in a warm environment. Exercise did not induce any changes in extracellular 5-HT release, although thermoregulatory responses and extracellular catecholamine release were more pronounced in a warm environment. In Chapter 4, experiment 2 indicated that increased extracellular 5-HT by pharmacological manipulation had no effect on the thermoregulatory response during exercise in a warm environment. These results suggested that enhanced release of only 5-HT in the PO/AH may not intervene thermoregulation during exercise in a warm environment. Chapter 5 focused on the relationship between the fatigue during exercise in the heat and 5-HT in the hippocampus. Experiment 3 suggested 5-HT release in the hippocampus might not involve in the hyperthermia mediated central fatigue.

The above results suggested that the acute increases in 5-HT release in the PO/AH and hippocampus are not essential factors of hyperthermia mediated central fatigue during exercise.