Extension of recovery time from fatigue by repeated rest with short‐term sleep during continuous fatigue load: Development of chronic fatigue model

Abstract

Homeostasis is known to be involved in maintaining the optimal internal environment, helping to achieve the best performance of biological functions. At the same time, a deviation from optimal conditions often attenuates the performance of biological functions, and such restricted performance could be considered as individual fatigue, including physical and mental fatigue. The present study seeks to develop an animal model of chronic or subacute fatigue in which the recovery time is extended through the gradual disruption of homeostasis. We show that repeated short-term rest periods with certain lengths of sleep during continuous fatigue loading extend recovery from spontaneous nighttime activity but not physical performance in comparison with a continuous fatigue-loading procedure. Furthermore, the immobility time in a forced swimming test was extended by repeated short-term rests. These results suggest that repeated short-term rest with certain lengths of sleep during continuous fatigue loading is able to extend the recovery from mental fatigue but not from physical fatigue and that this effect might occur via the disruption of a homeostatic mechanism that is involved in restoring the optimal internal environment.

Mapping the Alterations of Glutamate Using Glu-Weighted CEST MRI in a Rat Model of Fatigue

“…After 10 days of fatigue loading, the rats showed a significant decrease in nighttime spontaneous activity compared to the pre-fatigue level. This result confirms that our fatigue-loading procedure is sufficient to induce a fatigue state in rats and is consistent with previous reports using this fatigue loading procedure (rest and sleep deprivation) in spite of some modifications in the present study ( 25 , 30 ). Depressed spontaneous activity is a behavioral manifestation of fatigue, which may reflect an insufficient motivation of fatigued animals to move.…”

“…We established the fatigue model with rats based on the previous reports with some modifications ( 24 , 25 ). The procedure of fatigue loading was shown in Figure 1 .…”

“…In the present study, we investigated the glutamate levels with Glu-weighted CEST technology in an established animal model of prolonged fatigue ( 24 , 25 ). We measured the spontaneous activity of animals in their own homecages and glutamate levels in the whole brain and brain regions relevant to the pathophysiology of fatigue following 10-day chronic fatigue loading.…”

Sleep, Autonomic Nervous Function and Atherosclerosis

“…Although the underlying mechanisms of those findings are not clear at present, potential candidates include short sleep duration, low sleep quality, autonomic nervous dysfunction such as elevated sympathetic nervous function, and altered endocrine and immune functions. We reported that loading of psychological fatigue in rats was associated with disturbance of neuroendocrinological functions [86]. Furthermore, in the HSCAA cohort study, fatigue score was found to be closely associated with plasma leptin level in patients with cardiovascular risk factors [87].…”

Fatigue

“…Recently, animal models have been developed to include both and which, as the authors hope, ‘could be used to seek better preventive measures and to explore the neural and molecular mechanisms involved in severe, long‐lasting fatigue’ (Kanzaki et al . ).…”