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KMID : 1034320130040010028
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Sleep Medicine Research
2013 Volume.4 No. 1 p.28 ~ p.32
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Prolonged Sleep-Onset Latency during Chronic Sleep Restriction in Mice
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Kim Bo-Won
Hwang Eun-Jin
Kim Young-Soo
Choi Jee-Hyun
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Abstract
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Background and Objective: Even though we know that sleep is important for maintaining normal cognitive and behavioral functions, it is still unclear whether sustained sleep restriction, which is prevalent in modern society, is adaptive or whether it leads to a functionally and physiologically deteriorated state. On the assumption that sleep-onset latency (SOL) and sleep pressure are inversely correlated, we hypothesized that an adaptation to chronic sleep restriction (CSR) might pay off cumulative sleep pressure and thus we investigated the influence of CSR by measuring SOL as a function of sleep restriction day.
Methods: Mice (n = 9) were sleep deprived for 18 h a day using periodically rotating wheels. This was followed by a 6 h period of sleep opportunity (SO) that started at the beginning of each light period. This sleep restriction protocol was repeated for 5 consecutive days. SOL was defined as the duration of wake state from light-on time to first non-rapid eye movement epoch. Total wake time during SO was calculated following sleep restriction and during the same period on baseline and during the first recovery day.
Results: SOL gradually increased from the first day of sleep restriction onward (paired t-test; p < 0.01 for SR1 vs. SR5 and p < 0.05 for SR3 vs. SR5). The linear regression slope of SOL as the function of SR days in individual mice showed a significantly positive drift (average R-squared = 0.69, average slope = 8.1 min/day).
Conclusions: In the present study, sleep onset was delayed in sleep restriction day compared to the baseline sleep and SOL increased across chronic sleep restriction days in mice. This finding is different from our expectation that SOL will decrease compared to baseline sleep and then return to baseline level as CSR continues. Instead, SOL increased gradually as a function of sleep restriction days. This indicates that SOL may not simply reflect sleep pressure, rejecting our assumed inverse correlation between SOL and sleep pressure.
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KEYWORD
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Sleep, Chronic sleep restriction, SOL, Mice
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