Tryptophan(TRP)and its neurometabolite have been proposed to play a key role in central fatigue. Here, we established a new animal model of central fatigue induced by chronic sleep disorder(CFSD) through extended disturbance in the sleep-wake cycle, and investigated the relationship between brain- TRP levels and social interaction. The model was generated in 7-week-old rats by depriving them of sleep for 20 hours/day for 5 days. Fatigue level and social-interaction were measured with a treadmill test and a social-interaction test, respectively. Fatigue was classified into three levels : acute, subacute, and chronic. Further, TRP and 5-hydroxytryptamine(5-HT)concentrations were measured in the brain. Compared to control rats, CFSD rats suffering from sub-acute to chronic stage performed significantly worse on the treadmill test(sub-acute : p < 0. 05, chronic : p < 0. 001), and those suffering any stage spent considerably less time interacting socially(acute : p < 0. 01, sub-acute : p < 0. 001, chronic : p < 0. 01). CFSD-generated fatigue observed with treadmill-and socialinteraction tests is located centrally, and our procedure therefore specifically modeled central fatigue. TRP(but not 5-HT)concentration in the hypothalamus and hippocampus was 2. 5-fold higher in the CFSD group compared to the control group. CFSD results from increased TRP uptake, and might be related to social-interaction failure induced by central fatigue.
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