Sleep-wake driven changes in non-rapid-eye-movement sleep (NREM) sleep (NREMS) EEG delta (δ-)power are widely used as proxy for a sleep homeostatic process. Here, we noted frequency increases in δ-waves in sleep-deprived mice, prompting us to re-evaluate how slow-wave characteristics relate to prior sleep-wake history. We identified two classes of δ-waves; one responding to sleep deprivation with high initial power and fast, discontinuous decay during recovery sleep (δ2) and another unrelated to time-spent-awake with slow, linear decay (δ1). Reanalysis of previously published datasets demonstrates that δ-band heterogeneity after sleep deprivation is also present in human subjects. Similar to sleep deprivation, silencing of centromedial thalamus neurons boosted subsequent δ2-waves, specifically. δ2-dynamics paralleled that of temperature, muscle tone, heart rate, and neuronal ON-/OFF-state lengths, all reverting to characteristic NREMS levels within the first recovery hour. Thus, prolonged waking seems to necessitate a physiological recalibration before typical NREMS can be reinstated.

16Sleep depriving mice affects clock gene expression, suggesting that these genes partake in sleep 17 homeostasis. The mechanisms linking wakefulness to clock gene expression are, however, not well 18 understood. We propose CIRBP because its rhythmic expression is i) sleep-wake driven and ii) necessary for 19 high-amplitude clock gene expression in vitro. We therefore expect Cirbp knock-out (KO) mice to exhibit 20 attenuated sleep-deprivation (SD) induced changes in clock gene expression, and consequently to differ in 21 their sleep homeostatic regulation. Lack of CIRBP indeed blunted the SD-incurred changes in cortical 22 expression of the clock gene Rev-erbα whereas it amplified the changes in Per2 and Clock. Concerning sleep 23 homeostasis, KO mice accrued only half the extra REM sleep wild-type (WT) littermates obtained during 24 recovery. Unexpectedly, KO mice were more active during lights-off which was accompanied by an 25 acceleration of theta oscillations. Thus, CIRBP adjusts cortical clock gene expression after SD and expedites 26 REM sleep recovery. 27 28 29 rhythms 30 31 32altered sleep homeostatic response to sleep deprivation (SD) [e.g. (Mang et al., 2016, Shaw et al., 49 2002, Viola et al., 2007, Wisor et al., 2002]. Furthermore, SD affects the expression of clock genes 50 such as Rev-erbα, Per1-3 and Dbp (Mongrain et al., 2010), but the mechanisms through which this 51 occurs are unclear. 52In this study, we examined one such mechanism and hypothesized that some of the SD-induced 53 changes in clock gene expression occur through Cold-Inducible RNA Binding Protein (CIRBP). 54Decreasing temperature in vitro increases CIRBP levels (Nishiyama et al., 1997) and the daily 55 changes in body temperature of the mouse are sufficient to drive robust cyclic levels of Cirbp and 56 CIRBP (Morf et al., 2012) in anti-phase with temperature. Although the daily changes in cortical 57temperature (Tcx) appear circadian, more than 80% of its variance is explained by the sleep-wake 58 distribution in the rat (Franken et al., 1992). Hence, the daily rhythms of cortical Cirbp become 59 strongly attenuated when controlling for these sleep-wake driven changes in Tcx by SDs (see Figure 60 1, based on Gene Expression Omnibus number GSE9442 from Maret et al., 2007). Furthermore, 61Cirbp is the top down-regulated gene after SD (Mongrain et al., 2010, Wang et al., 2010) 62 underscoring again its sleep-wake dependent expression. But how does CIRBP relate to clock gene 63 expression? 64 65Two independent studies showed that the temperature-driven changes in CIRBP are required 66 for high amplitude clock gene expression in temperature synchronized cells (Morf et al., 2012, Liu 67 et al., 2013. Therefore, we and others (Archer et al., 2014) hypothesized that changes in clock gene 68 expression during SD are a consequence of the sleep-wake driven changes in CIRBP. We used mice 69 4 lacking CIRBP (Cirbp KO) (Masuda et al., 2012) to test this hypothesis. We first assessed whether 70 also in the mouse the daily changes in Tcx ...

Sleep depriving mice affects clock-gene expression, suggesting that these genes contribute to sleep homeostasis. The mechanisms linking extended wakefulness to clock-gene expression are, however, not well understood. We propose CIRBP to play a role because its rhythmic expression is i) sleep-wake driven and ii) necessary for high-amplitude clock-gene expression in vitro. We therefore expect Cirbp knock-out (KO) mice to exhibit attenuated sleep-deprivation-induced changes in clock-gene expression, and consequently to differ in their sleep homeostatic regulation. Lack of CIRBP indeed blunted the sleep-deprivation incurred changes in cortical expression of Nr1d1, whereas it amplified the changes in Per2 and Clock. Concerning sleep homeostasis, KO mice accrued only half the extra REM sleep wild-type (WT) littermates obtained during recovery. Unexpectedly, KO mice were more active during lights-off which was accompanied with faster theta oscillations compared to WT mice. Thus, CIRBP adjusts cortical clock-gene expression after sleep deprivation and expedites REM-sleep recovery.

In the mouse, Period-2 (Per2) expression in tissues peripheral to the suprachiasmatic nuclei (SCN) increases during sleep deprivation and at times of the day when animals are predominantly awake spontaneously, suggesting that the circadian sleep-wake distribution directly contributes to the daily rhythms in Per2. We found support for this hypothesis by recording sleep-wake state alongside PER2 bioluminescence in freely behaving mice, demonstrating that PER2 bioluminescence increases during spontaneous waking and decreases during sleep. The temporary reinstatement of PER2-bioluminescence rhythmicity in behaviorally arrhythmic SCN-lesioned mice submitted to daily recurring sleep deprivations substantiates our hypothesis. Mathematical modelling revealed that PER2 dynamics can be described by a damped harmonic oscillator driven by two forces: a sleep-wake-dependent force and a SCN-independent circadian force. Our work underscores the notion that in peripheral tissues the clock gene circuitry integrates sleep-wake information and could thereby contribute to behavioral adaptability to respond to homeostatic requirements.

Although brain temperature has neurobiological and clinical importance, it remains unclear which factors contribute to its daily dynamics and to what extent. Using a statistical approach, we previously demonstrated that hourly brain temperature values co-varied strongly with time spent awake (Hoekstra et al., 2019). Here we develop and make available a mathematical tool to simulate and predict cortical temperature in mice based on a 4-s sleep–wake sequence. Our model estimated cortical temperature with remarkable precision and accounted for 91% of the variance based on three factors: sleep–wake sequence, time-of-day (‘circadian’), and a novel ‘prior wake prevalence’ factor, contributing with 74%, 9%, and 43%, respectively (including shared variance). We applied these optimized parameters to an independent cohort of mice and predicted cortical temperature with similar accuracy. This model confirms the profound influence of sleep–wake state on brain temperature, and can be harnessed to differentiate between thermoregulatory and sleep–wake-driven effects in experiments affecting both.

In the mouse, Period-2 (Per2) expression in tissues peripheral to the suprachiasmatic nuclei (SCN) increases during sleep deprivation (SD) and when animals are predominantly awake spontaneously, suggesting that the circadian sleep-wake distribution directly contributes to the daily rhythms in Per2. We found support for this hypothesis by recording sleep-wake state alongside PER2 bioluminescence in freely behaving mice, demonstrating that PER2 increases during spontaneous waking and decreases during sleep. The temporary reinstatement of PER2 rhythmicity in behaviorally arrhythmic SCN-lesioned (SCNx) mice submitted to daily recurring SDs substantiates our hypothesis. Mathematical modelling revealed that PER2 dynamics can be described by a damped harmonic oscillator driven by two forces, a wake-driven and a SCN-independent circadian force. Our work underscores the notion that in peripheral tissues the clock gene circuitry integrates sleep-wake information and could thereby contribute to behavioral adaptability to respond to homeostatic requirements.

While brain temperature is of neurobiological and clinical importance, it is still unclear which factors contribute to its daily dynamics and to what degree. We recorded cortical temperature in mice alongside sleep-wake state during 4 days including a 6h sleep deprivation, and developed a mathematical tool to simulate temperature based on the sleep-wake sequence. The model estimated temperature with remarkable precision accounting for 91% of its variance based on three main factors with the sleep-wake sequence accounting for most of the variance (74%) and time-of-day (‘circadian’) the least (9%). As third factor, prior wake prevalence, was discovered to up-regulate temperature, explaining 43% of the variance. With similar accuracy the model predicted cortical temperature in a second, independent cohort using the parameters optimized for the first. Our model corroborates the profound influence of sleep-wake state on brain temperature, and can help differentiate thermoregulatory from sleep-wake driven effects in experiments affecting both.

Sleep-wake driven changes in NREM sleep (NREMS) EEG delta (δ: ~0.75-4.5Hz) power are widely used as proxy for a sleep homeostatic process. We noted frequency increases in δ-waves in sleep-deprived (SD) mice, prompting us to re-evaluate how slow-wave characteristics relate to prior sleep-wake history. We discovered two types of δ-waves; one responding to SD with high initial power and fast, discontinuous decay (δ2: ~2.5-3.5Hz) and another unrelated to time-spentawake with slow, linear decays (δ1: ~0.75-1.75Hz). Human experiments confirmed this δ-band heterogeneity. Similar to SD, silencing of centromedial thalamus neurons boosted δ2-waves, specifically. δ2-dynamics paralleled that of temperature, muscle tone, heart-rate, and neuronal UP/DOWN state lengths, all reverting to characteristic NREMS levels within the first recovery hour. Thus, prolonged waking seems to necessitate a physiological recalibration before typical NREMS can be reinstated. These short-lasting δ2-dynamics challenge accepted models of sleep regulation and function based on the merged δ-band as sleep-need proxy.