[Neural and molecular mechanisms of fatigue and recovery from fatigue]

Fatigue is an indispensable biosignal for maintaining life. However, the neural/molecular mechanisms of fatigue are still unclear. Here, the recent progress in this field is introduced, mostly through our project research under the control of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japanese Government. The sensing mechanisms of fatigue in the brain might be related to the orbitofrontal-dorsoprefrontal-cingulate triangle circuits. We hypothesized the neural circuits for fatigue sensation through our PET study on chronic fatigue patients and healthy volunteers. The serotonergic system might be involved in the sensation in the prefrontal cortex, although the hyperserotonin hypothesis might be wrong. The fatigue sensation is somehow related to hypofunction of the glutamatergic system through reduced uptake of acetyl-carnitine in the discrete brain regions. For creation of new methods and drugs overcoming fatigue, different types of animal models of fatigue were developed. By using such animal models, the green leaf odor, ascorbic acid, acetyl-carnitine, and tetrahydrobiopterin have been found to be effective.