Circadian regulation of sleep and the sleep EEG under constant sleep pressure in the rat.
OBJECTIVE
Sleep is regulated by homeostatic and circadian processes. Slow wave activity (SWA; 1-4 Hz) in the NREM sleep electroencephalogram (EEG) reflects sleep homeostasis. Activity of faster EEG frequencies (10-25 Hz) is thought to be under influence of circadian factors. The relative contribution of both processes to the distribution of sleep and wakefulness and EEG activity in rodents remains uncertain.


METHODS
Continuous EEG recording in rats in constant dark conditions (DD) were performed and a sleep deprivation protocol consisting of 2 h sleep deprivation followed by 2 h of rest (2h/2h) was applied for 48 h to obtain a constant sleep pressure.


METHODS
Basic sleep research laboratory.


METHODS
Adult male Wistar rats.


METHODS
Sleep deprivation.


RESULTS
Under the 2h/2h protocol, the circadian modulation of waking, NREM and REM sleep was markedly reduced compared to the baseline, affecting the frequency of vigilance state episodes and the duration of REM sleep and waking episodes. In contrast, NREM sleep episode duration still showed a daily modulation. Consecutive 2h values of SWA in NREM sleep were stabile during the 2h\2h protocol, while NREM sleep EEG activity within the higher frequencies (7-25 Hz) still demonstrated strong circadian modulation, which did not differ from baseline.


CONCLUSIONS
In rats, the daily modulation of REM sleep is less pronounced compared to NREM sleep and waking. In contrast to SWA, activity in higher frequencies (7-25 Hz) in the NREM sleep EEG have an endogenous circadian origin and are not influenced by sleep homeostatic mechanisms.
Yasenkov
Roman
R
Laboratory for Neurophysiology, Department of Molecular Cell Biology Leiden University Medical Center, Leiden, The Netherlands.
Deboer
Tom
T
D000704:Analysis of Variance; D000818:Animals; D001143:Arousal; D001522:Behavior, Animal; D002940:Circadian Rhythm / Q000502:physiology*; D004195:Disease Models, Animal; D004569:Electroencephalography / Q000379:methods* / Q000706:statistics & numerical data; D004576:Electromyography / Q000379:methods / Q000706:statistics & numerical data; D006706:Homeostasis; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D012890:Sleep / Q000502:physiology*; D012892:Sleep Deprivation / Q000175:diagnosis* / Q000503:physiopathology; D012895:Sleep, REM; D013312:Stress, Physiological; D013997:Time Factors; D014851:Wakefulness
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