Integrative studies on the mechanism of central and peripheral fatigue manifestation and the development of foods that have effects of anti-fatigue and fast restoration from fatigue

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By using spontaneous lever-pressing behavior for intracranial self stimulation in rats, behavioral motivation could quantitatively be determined. Physical loads which caused fatigue in rats has also been shown to cause decreases in motivation, in other words, increases in brain reward threshold. Additionally psychological loads to rats has caused increases in brain reward threshold and this suggested the manifestation of feeling of fatigue by psychological stress.κ-opioid, a kind of endogenous opioids, was elucidated to increase brain reward threshold and to decrease spontaneous motor activities in rats. On the other hand,κ-opioid antagonists depressed the decreases in spontaneous motor activities after low-intensity exercise load. These findings suggested the involvement of endogenousκ-opioid to manifestation of feeling of fatigue.The inhibition of energy production from fat in peripheral tissues was elucidated to cause activation of transforming growth factor-beta in the brain via vagus nerve and to lead to fatigue-like behavior in rats.