STUDY OBJECTIVES:

Besides their well-established role in circadian rhythms, our findings that the forebrain expression of the clock-genes and increases and decreases, respectively, in relation to time spent awake suggest they also play a role in the homeostatic aspect of sleep regulation. Here, we determined whether time of day modulates the effects of elevated sleep pressure on clock-gene expression. Time of day effects were assessed also for recognized electrophysiological (EEG delta power) and molecular () markers of sleep homeostasis.

DESIGN:

EEG and qPCR data were obtained for baseline and recovery from 6-h sleep deprivation starting at ZT0, -6, -12, or -18.

SETTING:

Mouse sleep laboratory.

PARTICIPANTS:

Male mice.

INTERVENTIONS:

Sleep deprivation.

RESULTS:

The sleep-deprivation induced changes in and expression importantly varied with time of day, such that could even during sleep deprivations occurring at the decreasing phase in baseline. showed similar, albeit opposite dynamics. These unexpected results could be reliably predicted assuming that these transcripts behave according to a driven damped harmonic oscillator. As expected, the sleep-wake distribution accounted for a large degree of the changes in EEG delta power and . Nevertheless, the sleep deprivation-induced increase in delta power varied also with time of day with higher than expected levels when recovery sleep started at dark onset.

CONCLUSIONS:

and delta power are widely used as exclusive state variables of the circadian and homeostatic process, respectively. Our findings demonstrate a considerable cross-talk between these two processes. As in the brain responds to both sleep loss and time of day, this molecule is well positioned to keep track of to anticipate homeostatic sleep need. CITATION: Curie T; Mongrain V; Dorsaz S; Mang GM; Emmenegger Y; Franken P. Homeostatic and circadian contribution to EEG and molecular state variables of sleep regulation. 2013;36(3):311-323.