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.
Besides their well-established role in circadian rhythms, our findings that the forebrain expression of the clock-genes Per2 and Dbp 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 (Homer1a) markers of sleep homeostasis.
EEG and qPCR data were obtained for baseline and recovery from 6-h sleep deprivation starting at ZT0, -6, -12, or -18.
Mouse sleep laboratory.
Male mice.
Sleep deprivation.
The sleep-deprivation induced changes in Per2 and Dbp expression importantly varied with time of day, such that Per2 could even decrease during sleep deprivations occurring at the decreasing phase in baseline. Dbp 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 Homer1a. 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.
Per2 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 Per2 in the brain responds to both sleep loss and time of day, this molecule is well positioned to keep track of and to anticipate homeostatic sleep need.
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. SLEEP 2013;36(3):311-323.
Rhynchophylline (RHY) is an alkaloid component of Uncaria, which are plants extensively used in traditional Asian medicines. Uncaria treatments increase sleep time and quality in humans, and RHY ...induces sleep in rats. However, like many traditional natural treatments, the mechanisms of action of RHY and Uncaria remain evasive. Moreover, it is unknown whether RHY modifies key brain oscillations during sleep. We thus aimed at defining the effects of RHY on sleep architecture and oscillations throughout a 24-h cycle, as well as identifying the underlying molecular mechanisms. Mice received systemic RHY injections at two times of the day (beginning and end of the light period), and vigilance states were studied by electrocorticographic recordings.
RHY enhanced slow wave sleep (SWS) after both injections, suppressed paradoxical sleep (PS) in the light but enhanced PS in the dark period. Furthermore, RHY modified brain oscillations during both wakefulness and SWS (including delta activity dynamics) in a time-dependent manner. Interestingly, most effects were larger in females. A brain spatial transcriptomic analysis showed that RHY modifies the expression of genes linked to cell movement, apoptosis/necrosis, and transcription/translation in a brain region-independent manner, and changes those linked to sleep regulation (e.g., Hcrt, Pmch) in a brain region-specific manner (e.g., in the hypothalamus).
The findings provide support to the sleep-inducing effect of RHY, expose the relevance to shape wake/sleep oscillations, and highlight its effects on the transcriptome with a high spatial resolution. The exposed molecular mechanisms underlying the effect of a natural compound should benefit sleep- and brain-related medicine.
To evaluate the influence of chronotype on sleep stages and quantitative sleep EEG when sleep pressure is increased and sleep schedule remains constant.
A 5-day session comprising an adaptation ...night, a baseline night, two nights of sleep fragmentation, and a recovery night.
Chronobiology laboratory.
Twenty-four healthy subjects aged 19-34 years: 12 morning types and 12 evening types selected by questionnaire. Each group included 6 men and 6 women with a habitual sleep duration of 7 to 9 hours.
Two nights of behavioral sleep fragmentation induced by forced 5-min awakenings every half-hour.
Each night of polysomnography recording lasted 8 hours and was based on each subject's preferred sleep schedule. On both nights of sleep fragmentation, stage 1 sleep increased, while both total sleep time and minutes of slow wave sleep decreased. No difference was observed in sleep architecture between morning types and evening types during sleep fragmentation nights or during recovery night. Spectral analysis of all-night NREM sleep EEG showed that during the recovery night, morning types had a larger fronto-central increase in low frequency activities and a larger centro-parietal decrease in 14-15 Hz activity than evening types. The largest group difference was for slow wave activity in the fronto-central area during the first part of the sleep episode.
These results add further support to a postulated difference in homeostatic sleep regulation between morning types and evening types, with morning types showing indications of a higher homeostatic response to sleep disruption.
MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression that have been implicated in a plethora of neuronal processes. Nevertheless, their role in regulating brain activity in ...the context of sleep has so far received little attention. To test their involvement, we deleted mature miRNAs in post-mitotic neurons at two developmental ages, i.e., in early adulthood using conditional
knockout (cKO) mice and in adult mice using an inducible conditional
cKO (icKO) line. In both models, electroencephalographic (EEG) activity was affected and the response to sleep deprivation (SD) altered; while the rapid-eye-movement sleep (REMS) rebound was compromised in both, the increase in EEG delta (1 to 4 Hz) power during non-REMS (NREMS) was smaller in cKO mice and larger in icKO mice compared to controls. We subsequently investigated the effects of SD on the forebrain miRNA transcriptome and found that the expression of 48 miRNAs was affected, and in particular that of the activity-dependent
. In vivo inhibition of
in the brain increased EEG power during NREMS in the slow-delta (0.75 to 1.75 Hz) range, particularly after periods of prolonged wakefulness. Transcriptome analysis of primary cortical neurons in vitro revealed that
regulates genes involved in glutamatergic neurotransmission. A subset of these genes was also affected in the cortices of sleep-deprived,
-inhibited mice. Our data implicate miRNAs in the regulation of EEG activity and indicate that
links neuronal activity during wakefulness to brain synchrony during sleep through the regulation of glutamatergic signaling.
Circadian rhythms originate from molecular feedback loops. In mammals, the transcription factors CLOCK and BMAL1 act on regulatory elements (i.e. E-boxes) to shape biological functions in a rhythmic ...manner. The EPHA4 receptor and its ligands Ephrins (EFN) are cell adhesion molecules regulating neurotransmission and neuronal morphology. Previous studies showed the presence of E-boxes in the genes of
and specific Ephrins, and that
knockout mice have an altered circadian rhythm of locomotor activity. We thus hypothesized that the core clock machinery regulates the gene expression of
,
and
. CLOCK and BMAL1 (or NPAS2 and BMAL2) were found to have transcriptional activity on distal and proximal regions of
,
and
putative promoters. A constitutively active form of glycogen synthase kinase 3β (GSK3β; a negative regulator of CLOCK and BMAL1) blocked the transcriptional induction. Mutating the E-boxes of
distal promoter sequence reduced transcriptional induction. EPHA4 and EFNB2 protein levels did not show circadian variations in the mouse suprachiasmatic nucleus or prefrontal cortex. The findings uncover that core circadian transcription factors can regulate the gene expression of elements of the Eph/Ephrin system, which might contribute to circadian rhythmicity in biological processes in the brain or peripheral tissues.
•Hippocampal Aß pathology is linked to changes in wake/sleep duration.•Hippocampal Aß pathology also associates with changes in wake/sleep quality.•Sleep disturbances reciprocally impact Aß pathology ...in the hippocampus.•Future research should assess mechanisms and specificity of these relationships.
Alzheimer’s disease (AD) is a debilitating neurodegenerative disease characterized by progressive hippocampal-dependent explicit memory deficits that begin at the onset of the illness. An early hallmark of AD is the accumulation of amyloid-beta (Aß) proteins in brain structures involved in encoding and consolidation of memory, like the hippocampus and prefrontal cortex. Aß neurotoxicity is known to induce synaptic dysfunctions and neuronal death leading to cognitive decline. Another recurrent event observed in AD is sleep disturbances. Decreased sleep duration, sleep fragmentation, and circadian alterations are often observed in early AD. The origin of these disturbances, and especially the specific contribution of the hippocampal Aß pathology, remains to be determined. It is required to identify mechanisms impacting wakefulness and sleep architecture and microarchitecture given the role of sleep in memory encoding and consolidation. Sleep perturbations in AD are thus likely contributing to memory decline in the course of the disease. The central aim of this review is to address the bidirectional relationship between sleep and hippocampal Aß by discussing the literature featuring data on wakefulness and sleep variables (i.e., duration, electroencephalographic activity, daily distribution) in AD mouse models and on the effect of enforced sleep loss on Aß pathology in the hippocampus. The current state of knowledge on this topic emphasizes a clear need for more efforts to assess the precise impact of hippocampal Aß on wakefulness and sleep quality as well as the mechanisms mediating their reciprocal relationship.
Many aspects of the immune system, including circulating cytokine levels as well as counts and function of various immune cell types, present circadian rhythms. Notably, the mortality rate of animals ...subjected to high doses of lipopolysaccharide is dependent on the time of treatment. In addition, the severity of symptoms of various inflammatory conditions follows a daily rhythmic pattern. The mechanisms behind the crosstalk between the circadian and immune systems remain elusive. Here we demonstrate that localized inflammation induced by turpentine oil (TURP) causes a time-dependent induction of interleukin (IL)-6 and has time-, gene- and tissue-specific effects on clock gene expression. More precisely, TURP blunts the peak of Per1 and Per2 expression in the liver while in other tissues, the expression nadir is elevated. In contrast, Rev-erbα expression remains relatively unaffected by TURP treatment. Co-treatment with the anti-inflammatory agent IL-1 receptor antagonist (IL-1Ra) did not alter the response of Per2 to TURP treatment in liver, despite the reduced induction of fever and IL-6 serum levels. This indicates that the TURP-mediated changes of Per2 in the liver might be due to factors other than systemic IL-6 and fever. Accordingly, IL-6 treatment had no effect on clock gene expression in HepG2 liver carcinoma cells. Altogether, we show that localized inflammation causes significant time-dependent changes in peripheral circadian clock gene expression, via a mechanism likely involving mediators independent from IL-6 and fever.
Traumatic injuries to the spinal cord or the brain have serious medical consequences and lead to long-term disability. The epidemiology, medical complications, and prognosis of isolated spinal cord ...injury (SCI) and traumatic brain injury (TBI) have been well described. However, there are limited data on patients suffering from concurrent SCI and TBI, even if a large proportion of SCI patients have concomitant TBI. The complications associated with this "dual-diagnosis" such as cognitive or behavioral dysfunction are well known in the rehabilitation setting, but evidence-based and standardized approaches for diagnosis and treatment are lacking. Our goal was to develop and characterize a pre-clinical animal model of concurrent SCI and TBI to help identifying "dual-diagnosis" tools. Female rats received a unilateral contusive SCI at the thoracic level alone (SCI group) or combined with a TBI centered on the contralateral sensorimotor cortex (SCI-TBI group). We first validated that the SCI extent was comparable between SCI-TBI and SCI groups, and that hindlimb function was impaired. We characterized various neurological outcomes, including locomotion, sleep architecture, brain activity during sleep, depressive- and anxiety-like behaviors, and working memory. We report that SCI-TBI and SCI groups show similar impairments in global locomotor function. While wake/sleep amount and distribution and anxiety- and depression-like symptoms were not affected in SCI-TBI and SCI groups in comparison to the control group (laminectomy and craniotomy only), working memory was impaired only in SCI-TBI rats. This pre-clinical model of concomitant SCI and TBI, including more severe variations of it, shows a translational value for the identification of biomarkers to refine the "dual-diagnosis" of neurotrauma in humans.
We have previously demonstrated that clock genes contribute to the homeostatic aspect of sleep regulation. Indeed, mutations in some clock genes modify the markers of sleep homeostasis and an ...increase in homeostatic sleep drive alters clock gene expression in the forebrain. Here, we investigate a possible mechanism by which sleep deprivation (SD) could alter clock gene expression by quantifying DNA-binding of the core-clock transcription factors CLOCK, NPAS2, and BMAL1 to the cis-regulatory sequences of target clock genes in mice. Using chromatin immunoprecipitation (ChIP), we first showed that, as reported for the liver, DNA-binding of CLOCK and BMAL1 to target clock genes changes in function of time-of-day in the cerebral cortex. Tissue extracts were collected at ZT0 (light onset), -6, -12, and -18, and DNA enrichment of E-box or E'-box containing sequences was measured by qPCR. CLOCK and BMAL1 binding to Cry1, Dbp, Per1, and Per2 depended on time-of-day, with maximum values reached at around ZT6. We then observed that SD, performed between ZT0 and -6, significantly decreased DNA-binding of CLOCK and BMAL1 to Dbp, consistent with the observed decrease in Dbp mRNA levels after SD. The DNA-binding of NPAS2 and BMAL1 to Per2 was also decreased by SD, although SD is known to increase Per2 expression in the cortex. DNA-binding to Per1 and Cry1 was not affected by SD. Our results show that the sleep-wake history can affect the clock molecular machinery directly at the level of chromatin binding thereby altering the cortical expression of Dbp and Per2 and likely other targets. Although the precise dynamics of the relationship between DNA-binding and mRNA expression, especially for Per2, remains elusive, the results also suggest that part of the reported circadian changes in DNA-binding of core clock components in tissues peripheral to the suprachiasmatic nuclei could, in fact, be sleep-wake driven.
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