Establishment and assessment of a rat model of fatigue.

To establish an animal model of fatigue, we kept rats in a cage filled with water to a height of 1.5 cm. We selected a weight-loaded forced swimming test for evaluation of the extent of fatigue. Animals kept in the wet cage for 5 days showed a reduction in 2-[18F]fluoro-2-deoxy-D-glucose uptake into their brain. The session for 1 day showed significantly increased 5-hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) and [3,4-dihydroxyphenyl-acetic acid (DOPAC)+homovanillic acid (HVA)]/dopamine (DA) ratios in all brain regions, but the session for 5 days showed the restoration of the 5-HIAA/5-HT ratio in the hippocampus and hypothalamus and in the (DOPAC+HVA)/DA ratio in the striatum and hypothalamus. Our data suggest that decreased glucose uptake and insufficient serotonin and dopamine turnover introduced by deprivation of rest were correlated with central fatigue.