Period-amplitude analysis reveals wake-dependent changes in the electroencephalogram during sleep deprivation

Scheduled feeding improves sleep in a mouse model of Huntington's disease

Sleep disturbances are common features of neurodegenerative disorders including Huntington's disease (HD). Sleep and circadian disruptions are recapitulated in animal models, providing the opportunity to evaluate the effectiveness of circadian interventions as countermeasures for neurodegenerative disease. For instance, time restricted feeding (TRF) successfully improved activity rhythms, sleep behavior and motor performance in mouse models of HD. Seeking to determine if these benefits extend to physiological measures of sleep, electroencephalography (EEG) was used to measure sleep/wake states and polysomnographic patterns in male and female wild-type (WT) and bacterial artificial chromosome transgenic (BACHD) adult mice, under TRF and ad lib feeding (ALF). Our findings show that male, but not female, BACHD mice exhibited significant changes in the temporal patterning of wake and non-rapid eye movement (NREM) sleep. The TRF intervention reduced the inappropriate early morning activity by increasing NREM sleep in the male BACHD mice. In addition, the scheduled feeding reduced sleep fragmentation (# bouts) in the male BACHD mice. The phase of the rhythm in rapid-eye movement (REM) sleep was significantly altered by the scheduled feeding in a sex-dependent manner. The treatment did impact the power spectral curves during the day in male but not female mice regardless of the genotype. Sleep homeostasis, as measured by the response to six hours of gentle handling, was not altered by the diet. Thus, TRF improves the temporal patterning and fragmentation of NREM sleep without impacting sleep homeostasis. This work adds critical support to the view that sleep is a modifiable risk factor in neurodegenerative diseases.

Hydrogen-rich water improves sleep consolidation and enhances forebrain neuronal activation in mice

Study Objectives

Sleep loss contributes to various health issues and impairs neurological function. Molecular hydrogen has recently gained popularity as a nontoxic ergogenic and health promoter. The effect of molecular hydrogen on sleep and sleep-related neural systems remains unexplored. This study investigates the impact of hydrogen-rich water (HRW) on sleep behavior and neuronal activation in sleep-deprived mice.

Methods

Adult C57BL/6J mice were implanted with electroencephalography (EEG) and electromyography (EMG) recording electrodes and given HRW (0.7-1.4 mM) or regular water for 7 days ad libitum. Sleep-wake cycles were recorded under baseline conditions and after acute sleep loss. Neuronal activation in sleep- and wake-related regions was assessed using cFos immunostaining.

Results

HRW increased sleep consolidation in undisturbed mice and increased non-rapid-eye movement and rapid-eye-movement sleep amount in sleep-deprived mice. HRW also decreased the average amount of time for mice to fall asleep after light onset. Neuronal activation in the lateral septum, medial septum, ventrolateral preoptic area, and median preoptic area was significantly altered in all mice treated with HRW.

Conclusions

HRW improves sleep consolidation and increases neuronal activation in sleep-related brain regions. It may serve as a simple, effective treatment to improve recovery after sleep loss.

Non-rapid eye movement sleep determines resilience to social stress

Resilience, the ability to overcome stressful conditions, is found in most mammals and varies significantly among individuals. A lack of resilience can lead to the development of neuropsychiatric and sleep disorders, often within the same individual. Despite extensive research into the brain mechanisms causing maladaptive behavioral-responses to stress, it is not clear why some individuals exhibit resilience. To examine if sleep has a determinative role in maladaptive behavioral-response to social stress, we investigated individual variations in resilience using a social-defeat model for male mice. Our results reveal a direct, causal relationship between sleep amount and resilience-demonstrating that sleep increases after social-defeat stress only occur in resilient mice. Further, we found that within the prefrontal cortex, a regulator of maladaptive responses to stress, pre-existing differences in sleep regulation predict resilience. Overall, these results demonstrate that increased NREM sleep, mediated cortically, is an active response to social-defeat stress that plays a determinative role in promoting resilience. They also show that differences in resilience are strongly correlated with inter-individual variability in sleep regulation.

Nonlinear relationship between sleep duration and non-suicidal self-injurious behaviour among Chinese adolescents

BACKGROUND

Previous studies have shown a positive association between sleep deprivation and non-suicidal self-injury (NSSI) among adolescents, but few studies have described the effects of oversleeping and weekend catch-up sleep on NSSI. The present study aimed to explore the nonlinear relationship between sleep duration and NSSI among Chinese adolescents.

METHODS

Data from China's National Adolescent Health Surveillance for the years 2014 to 2015 were collected from 15,713 students located across four provinces in China. A self-report questionnaire was used to assess sleep duration and 12-month NSSI. Binomial logistic regression models were used to examine the association between NSSI and sleep duration. The locally estimated scatter plot smoothing (LOESS) method was used to explore the associations of total NSSI number with sleep duration, and binomial regression analysis was used to test this relationship.

RESULTS

About 68.5% of adolescents reported sleeping less than 8 h on weeknights, while 37.8% of adolescents slept more than 10 h per night during weekends. The 12-month prevalence rate of NSSI was 29.4%. Compared to adolescents who reported weekend catch-up sleep of 0-1 h, those who slept < 0 h (adjusted odds ratio [aOR] = 1.38, 95% Confidence Interval [95% CI]: 1.16-1.64) had a higher risk of NSSI. Males who reported ≥3 h of weekend catch-up sleep had significantly increased odds of NSSI (aOR = 1.20, 95%CI: 1.01-1.42). Notably, a positive U-shaped association was observed between the sleep duration and the total NSSI number.

CONCLUSIONS

The findings reveal a nonlinear relationship between sleep duration and NSSI among Chinese adolescents. Therefore, it is necessary to be vigilant and screen for sleep duration among adolescents in NSSI treatment or prevention.

Sleep loss mediates the effect of stress on nitrergic signaling in female mice

Nitric oxide (NO) has been implicated as an important neurotransmitter in stress responses and sleep regulatory processes. However, the role of NO in the relationship between stress and sleep remains unclear. The medial septum (MS) and vertical diagonal band (VDB), regions of the basal forebrain involved in sleep regulation, contain nitric oxide synthase (NOS) producing neurons. Additionally, NOS neurons in the dorsal raphe nucleus (DRN) encode information about stress duration. The role of nitrergic neurons in these regions in subserving sex-specific responses to stress and sleep loss has yet to be elucidated. In this study, NADPH-d, an index of NOS activity, was used to examine the effects of acute restraint stress and sleep loss on NOS activity in the MS, VDB, and DRN. We show that NOS activity in response to restraint stress, total sleep deprivation (TSD), and partial sleep restriction (PSR) differs based on sex and region. Initial analysis showed no effect of restraint stress or TSD on NOS activity in the basal forebrain. However, investigation of each sex separately revealed that restraint stress and TSD significantly decrease NOS activity in the MS of females, but not males. Interestingly, the difference in NOS activity between restraint stress and TSD in females was not significant. Furthermore, PSR was not sufficient to affect NOS activity in males or females. These data suggest that restraint stress and sleep loss regulate NOS activation in a sex-dependent manner, and that the NOS stress response in females may be mediated by sleep loss.

Angelman syndrome and melatonin: What can they teach us about sleep regulation

In 1965, Dr Harry Angelman reported a neurodevelopmental disorder affecting three unrelated children who had similar symptoms: brachycephaly, mental retardation, ataxia, seizures, protruding tongues, and remarkable paroxysms of laughter. Over the past 50 years, the disorder became Angelman's namesake and symptomology was expanded to include hyper-activity, stereotypies, and severe sleep disturbances. The sleep disorders in many Angelman syndrome (AS) patients are broadly characterized by difficulty falling and staying asleep at night. Some of these patients sleep less than 4 hours a night and, in most cases, do not make up this lost sleep during the day-leading to the speculation that AS patients may "need" less sleep. Most AS patients also have severely reduced levels of melatonin, a hormone produced by the pineal gland exclusively at night. This nightly pattern of melatonin production is thought to help synchronize internal circadian rhythms and promote nighttime sleep in humans and other diurnal species. It has been proposed that reduced melatonin levels contribute to the sleep problems in AS patients. Indeed, emerging evidence suggests melatonin replacement therapy can improve sleep in many AS patients. However, AS mice show sleep problems that are arguably similar to those in humans despite being on genetic backgrounds that do not make melatonin. This suggests the hypothesis that the change in nighttime melatonin may be a secondary factor rather than the root cause of the sleeping disorder. The goals of this review article are to revisit the sleep and melatonin findings in both AS patients and animal models of AS and discuss what AS may tell us about the underlying mechanisms of, and interplay between, melatonin and sleep.

Acute sleep deprivation elevates brain and body temperature in rats

Available sleep deprivation studies lack data on simultaneous changes in hypothalamic, cortical and body temperature during sleep deprivation and recovery. Ten adult male Wistar rats chronically implanted with electroencephalogram, electro-oculogram and electromyogram electrodes for recording sleep were used in this study. Hypothalamic and cortical temperatures were measured by pre-implanted thermocouples. A radio transmitter (TA10TAF-40, DSI USA) was implanted intraperitoneally to measure body temperature. All the temperatures were measured simultaneously at 15-s intervals during baseline conditions, sleep deprivation and recovery sleep. Sleep deprivation was carried out for 24 hr by the gentle handling method; however, sleep and temperature were only recorded during the first 12 hr of deprivation. During sleep deprivation the body, hypothalamic and cortical temperatures increased significantly as compared to baseline. During recovery sleep, body and cortical temperature recovered earlier than the hypothalamic temperature. Hypothalamic temperature remained higher than the baseline values throughout 12 hr of recovery sleep. In the recovery sleep, cortical temperature decreased immediately and reached near baseline by 4 hr. We observed a quicker return of cortical temperature towards control temperature during recovery sleep compared with hypothalamic and body temperature. The results of the present study show that acute sleep deprivation results in a rise in both cortical and hypothalamic temperature, along with body temperature. A rise in cortical temperature may be a contributing factor for cognitive dysfunction resulting from sleep deprivation.

Somatostatin+/nNOS+ neurons are involved in delta electroencephalogram activity and cortical-dependent recognition memory

Slow-wave activity (SWA) is an oscillatory neocortical activity occurring in the electroencephalogram delta (δ) frequency range (~0.5-4 Hz) during nonrapid eye movement sleep. SWA is a reliable indicator of sleep homeostasis after acute sleep loss and is involved in memory processes. Evidence suggests that cortical neuronal nitric oxide synthase (nNOS) expressing neurons that coexpress somatostatin (SST) play a key role in regulating SWA. However, previous studies lacked selectivity in targeting specific types of neurons that coexpress nNOS-cells which are activated in the cortex after sleep loss. We produced a mouse model that knocks out nNOS expression in neurons that coexpress SST throughout the cortex. Mice lacking nNOS expression in SST positive neurons exhibited significant impairments in both homeostatic low-δ frequency range SWA production and a recognition memory task that relies on cortical input. These results highlight that SST+/nNOS+ neurons are involved in the SWA homeostatic response and cortex-dependent recognition memory.

Bmal1 function in skeletal muscle regulates sleep

Sleep loss can severely impair the ability to perform, yet the ability to recover from sleep loss is not well understood. Sleep regulatory processes are assumed to lie exclusively within the brain mainly due to the strong behavioral manifestations of sleep. Whole-body knockout of the circadian clock gene Bmal1 in mice affects several aspects of sleep, however, the cells/tissues responsible are unknown. We found that restoring Bmal1 expression in the brains of Bmal1-knockout mice did not rescue Bmal1-dependent sleep phenotypes. Surprisingly, most sleep-amount, but not sleep-timing, phenotypes could be reproduced or rescued by knocking out or restoring BMAL1 exclusively in skeletal muscle, respectively. We also found that overexpression of skeletal-muscle Bmal1 reduced the recovery response to sleep loss. Together, these findings demonstrate that Bmal1 expression in skeletal muscle is both necessary and sufficient to regulate total sleep amount and reveal that critical components of normal sleep regulation occur in muscle.

Acute Sleep Deprivation Induces a Local Brain Transfer Information Increase in the Frontal Cortex in a Widespread Decrease Context

Sleep deprivation (SD) has adverse effects on mental and physical health, affecting the cognitive abilities and emotional states. Specifically, cognitive functions and alertness are known to decrease after SD. The aim of this work was to identify the directional information transfer after SD on scalp EEG signals using transfer entropy (TE). Using a robust methodology based on EEG recordings of 18 volunteers deprived from sleep for 36 h, TE and spectral analysis were performed to characterize EEG data acquired every 2 h. Correlation between connectivity measures and subjective somnolence was assessed. In general, TE showed medium- and long-range significant decreases originated at the occipital areas and directed towards different regions, which could be interpreted as the transfer of predictive information from parieto-occipital activity to the rest of the head. Simultaneously, short-range increases were obtained for the frontal areas, following a consistent and robust time course with significant maps after 20 h of sleep deprivation. Changes during sleep deprivation in brain network were measured effectively by TE, which showed increased local connectivity and diminished global integration. TE is an objective measure that could be used as a potential measure of sleep pressure and somnolence with the additional property of directed relationships.

Maternal Ube3a Loss Disrupts Sleep Homeostasis But Leaves Circadian Rhythmicity Largely Intact

Individuals with Angelman syndrome (AS) suffer sleep disturbances that severely impair quality of life. Whether these disturbances arise from sleep or circadian clock dysfunction is currently unknown. Here, we explored the mechanistic basis for these sleep disorders in a mouse model of Angelman syndrome (Ube3a(m-/p+) mice). Genetic deletion of the maternal Ube3a allele practically eliminates UBE3A protein from the brain of Ube3a(m-/p+) mice, because the paternal allele is epigenetically silenced in most neurons. However, we found that UBE3A protein was present in many neurons of the suprachiasmatic nucleus--the site of the mammalian circadian clock--indicating that Ube3a can be expressed from both parental alleles in this brain region in adult mice. We found that while Ube3a(m-/p+) mice maintained relatively normal circadian rhythms of behavior and light-resetting, these mice exhibited consolidated locomotor activity and skipped the timed rest period (siesta) present in wild-type (Ube3a(m+/p+)) mice. Electroencephalographic analysis revealed that alterations in sleep regulation were responsible for these overt changes in activity. Specifically, Ube3a(m-/p+) mice have a markedly reduced capacity to accumulate sleep pressure, both during their active period and in response to forced sleep deprivation. Thus, our data indicate that the siesta is governed by sleep pressure, and that Ube3a is an important regulator of sleep homeostasis. These preclinical findings suggest that therapeutic interventions that target mechanisms of sleep homeostasis may improve sleep quality in individuals with AS.

SIGNIFICANCE STATEMENT

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by loss of expression of the maternal copy of the UBE3A gene. Individuals with AS have severe sleep dysfunction that affects their cognition and presents challenges to their caregivers. Unfortunately, current treatment strategies have limited efficacy due to a poor understanding of the mechanisms underlying sleep disruptions in AS. Here we demonstrate that abnormal sleep patterns arise from a deficit in accumulation of sleep drive, uncovering the Ube3a gene as a novel genetic regulator of sleep homeostasis. Our findings encourage a re-evaluation of current treatment strategies for sleep dysfunction in AS, and suggest that interventions that promote increased sleep drive may alleviate sleep disturbances in individuals with AS.

Effects of partial sleep deprivation on slow waves during non-rapid eye movement sleep: A high density EEG investigation

OBJECTIVE

Changes in slow waves during non-rapid eye movement (NREM) sleep in response to acute total sleep deprivation are well-established measures of sleep homeostasis. This investigation utilized high-density electroencephalography (hdEEG) to examine topographic changes in slow waves during repeated partial sleep deprivation.

METHODS

Twenty-four participants underwent a 6-day sleep restriction protocol. Spectral and period-amplitude analyses of sleep hdEEG data were used to examine changes in slow wave energy, count, amplitude, and slope relative to baseline.

RESULTS

Changes in slow wave energy were dependent on the quantity of NREM sleep utilized for analysis, with widespread increases during sleep restriction and recovery when comparing data from the first portion of the sleep period, but restricted to recovery sleep if the entire sleep episode was considered. Period-amplitude analysis was less dependent on the quantity of NREM sleep utilized, and demonstrated topographic changes in the count, amplitude, and distribution of slow waves, with frontal increases in slow wave amplitude, numbers of high-amplitude waves, and amplitude/slopes of low amplitude waves resulting from partial sleep deprivation.

CONCLUSIONS

Topographic changes in slow waves occur across the course of partial sleep restriction and recovery.

SIGNIFICANCE

These results demonstrate a homeostatic response to partial sleep loss in humans.

Shell neurons of the master circadian clock coordinate the phase of tissue clocks throughout the brain and body

Background

Daily rhythms in mammals are programmed by a master clock in the suprachiasmatic nucleus (SCN). The SCN contains two main compartments (shell and core), but the role of each region in system-level coordination remains ill defined. Herein, we use a functional assay to investigate how downstream tissues interpret region-specific outputs by using in vivo exposure to long day photoperiods to temporally dissociate the SCN. We then analyze resulting changes in the rhythms of clocks located throughout the brain and body to examine whether they maintain phase synchrony with the SCN shell or core.

Results

Nearly all of the 17 tissues examined in the brain and body maintain phase synchrony with the SCN shell, but not the SCN core, which indicates that downstream oscillators are set by cues controlled specifically by the SCN shell. Interestingly, we also found that SCN dissociation diminished the amplitude of rhythms in core clock gene and protein expression in brain tissues by 50–75 %, which suggests that light-driven changes in the functional organization of the SCN markedly influence the strength of rhythms in downstream tissues.

Conclusions

Overall, our results reveal that body clocks receive time-of-day cues specifically from the SCN shell, which may be an adaptive design principle that serves to maintain system-level phase relationships in a changing environment. Further, we demonstrate that lighting conditions alter the amplitude of the molecular clock in downstream tissues, which uncovers a new form of plasticity that may contribute to seasonal changes in physiology and behavior.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0157-x) contains supplementary material, which is available to authorized users.