Sleep homeostasis

Sleep Deprivation Induces Gut Damage via Ferroptosis

Sleep deprivation (SD) has been associated with a plethora of severe pathophysiological syndromes, including gut damage, which recently has been elucidated as an outcome of the accumulation of reactive oxygen species (ROS). However, the spatiotemporal analysis conducted in this study has intriguingly shown that specific events cause harmful damage to the gut, particularly to goblet cells, before the accumulation of lethal ROS. Transcriptomic and metabolomic analyses have identified significant enrichment of metabolites related to ferroptosis in mice suffering from SD. Further analysis revealed that melatonin could rescue the ferroptotic damage in mice by suppressing lipid peroxidation associated with ALOX15 signaling. ALOX15 knockout protected the mice from the serious damage caused by SD-associated ferroptosis. These findings suggest that melatonin and ferroptosis could be targets to prevent devastating gut damage in animals exposed to SD. To sum up, this study is the first report that proposes a noncanonical modulation in SD-induced gut damage via ferroptosis with a clearly elucidated mechanism and highlights the active role of melatonin as a potential target to maximally sustain the state during SD.

Microglial TNFα controls daily changes in synaptic GABAARs and sleep slow waves

Microglia sense the changes in their environment. How microglia actively translate these changes into suitable cues to adapt brain physiology is unknown. We reveal an activity-dependent regulation of cortical inhibitory synapses by microglia, driven by purinergic signaling acting on P2RX7 and mediated by microglia-derived TNFα. We demonstrate that sleep induces microglia-dependent synaptic enrichment of GABAARs in a manner dependent on microglial TNFα and P2RX7. We further show that microglia-specific depletion of TNFα alters slow waves during NREM sleep and blunt memory consolidation in sleep-dependent learning tasks. Together, our results reveal that microglia orchestrate sleep-intrinsic plasticity of synaptic GABAARs, sculpt sleep slow waves, and support memory consolidation.

Thermoneutral temperature exposure enhances slow-wave sleep with a correlated improvement in amyloid pathology in a triple-transgenic mouse model of Alzheimer's disease

Accumulation of amyloid-β (Aβ) plays an important role in Alzheimer's disease (AD) pathology. There is growing evidence that disordered sleep may accelerate AD pathology by impeding the physiological clearance of Aβ from the brain that occurs in normal sleep. Therapeutic strategies for improving sleep quality may therefore help slow disease progression. It is well documented that the composition and dynamics of sleep are sensitive to ambient temperature. We therefore compared Aβ pathology and sleep metrics derived from polysomnography in 12-month-old female 3xTg-AD mice (n = 8) exposed to thermoneutral temperatures during the light period over 4 weeks to those of age- and sex-matched controls (n = 8) that remained at normal housing temperature (22°C) during the same period. The treated group experienced greater proportions of slow wave sleep (SWS)-i.e. epochs of elevated 0.5-2 Hz EEG slow wave activity during non-rapid eye movement (NREM) sleep-compared to controls. Assays performed on mouse brain tissue harvested at the end of the experiment showed that exposure to thermoneutral temperatures significantly reduced levels of DEA-soluble (but not RIPA- or formic acid-soluble) Aβ40 and Aβ42 in the hippocampus, though not in the cortex. With both groups pooled together and without regard to treatment condition, NREM sleep continuity and any measure of SWS within NREM at the end of the treatment period were inversely correlated with DEA-soluble Aβ40 and Aβ42 levels, again in the hippocampus but not in the cortex. These findings suggest that experimental manipulation of SWS could offer useful clues into the mechanisms and treatment of AD.

Sleep spindles in adolescents with major depressive disorder

Sleep spindle differences in adolescents with major depressive disorder (MDD) compared to healthy adolescents is an ongoing debate. Results mostly indicate decreased sleep spindle activity in adolescents with MDD. Given that sleep spindles predominate NREM and that acutely delaying the sleep period via a "sleep delay challenge" (SDC) increases non-rapid eye movement (NREM) sleep duration, it may be possible to increase spindle density in adolescents with MDD, which may provide a therapeutic benefit to depression symptoms. Here, we examined the impact of a SDC on spindle density and depression symptomology in adolescents with MDD (n = 66) and healthy controls (n = 62) tested across three nights: adaptation, normal sleep, and a SDC night which delayed bedtime by three hours. The results showed that; (1) there was no difference in spindle density between groups on the normal sleep night, (2) following the SDC, both males and females with MDD had a decrease in the frequency of slow spindles, while only females with MDD had an increase in the frequency of fast spindles, (3) acute SDC reduced depression symptoms in both groups, and (4) light sleep on the normal sleep night and slow spindle frequency at SDC predicted an 8 % improvement in depression symptoms, regardless of sex or MDD diagnosis. Taken together, these results suggest that; (a) spindles may be a useful biological marker of depression symptomatology regardless of clinical MDD diagnosis, and (b) that acute SDC may help alleviate depression symptoms in adolescents with MDD.

Improving sleep quality is essential for enhancing soluble Klotho levels in hemodialysis patients

PURPOSE

Sleep and Klotho seem to share common physiological pathways in aging. However, studies investigating this relationship are very few and none of them was done with a specific patient group. The aim of this study was to investigate the association of sleep quality and soluble Klotho levels in hemodialysis patients.

METHODS

100 hemodialysis patients were included in this study. Soluble Klotho levels were obtained from each patient and Pittsburgh Sleep Quality Index was performed by all patients. Association of soluble Klotho with sleep quality was calculated.

RESULTS

Soluble Klotho levels were significantly inversely correlated with total sleep quality score (p < 0.001, r = - 0.444). Among the subscales, soluble Klotho levels were negatively correlated with subjective sleep quality (p < 0.001, r = - 0.365), sleep latency (p = 0.002, r = - 0.312), sleep disturbance (p = 0.002, r = - 0.303) and daytime dysfunction (p = 0.027, r = - 0.221). Patients who had good sleep quality scores were found to have higher soluble Klotho levels [4.15 (0.05-22.68) vs. 1.14 (0.32-17.63), p < 0.001]. In regression analysis, total sleep quality score, subjective sleep quality and age were found to be independent negative factors for soluble Klotho levels.

CONCLUSION

In this study, a significant association between sleep quality and soluble Klotho levels was revealed in hemodialysis patients. Improving sleep quality will lead to increased soluble Klotho levels, which may further slow down the aging process in hemodialysis patients.

Adherence to a healthy sleep pattern and new-onset acute kidney injury

OBJECTIVES

To investigate the prospective association of individual sleep characteristics and a healthy sleep pattern with new-onset acute kidney injury in general population.

METHODS

The UK Biobank enrolled over 500,000 participants, aged 37-73years, across the UK from 2006 to 2010. Of these, 375,216 participants were included in the current study. A healthy sleep score, ranging from 0 to 5 points, was created by combining five major sleep characteristics, including sleep duration, chronotype, insomnia, snoring, and daytime sleepiness. New-onset acute kidney injury was defined by ICD-10 code N17, ascertained by primary care data, hospital inpatient data, death register records, or self-reported medical conditions.

RESULTS

During a median follow-up period of 12.0years, 14,492 (3.9%) participants developed acute kidney injury. Overall, the healthy sleep score was significantly inversely associated with the risk of new-onset acute kidney injury (per 1-point increment; hazards ratio, 0.95; 95%CI, 0.93-0.97), especially in nondiabetes (hazards ratio, 0.94; 95%CI, 0.92-0.96; vs. diabetes, hazards ratio, 1.01; 95%CI, 0.96-1.05; P-interaction=.008). The genetic predisposition of estimated glomerular filtration rate and acute kidney injury did not significantly modify the association between the healthy sleep score and acute kidney injury (both P-interactions >.05). Sleep 7-8 hours per day (vs. <7 hours or ≥9 hours; hazards ratio, 0.92; 95%CI, 0.88-0.96), early chronotype (vs. evening chronotype; hazards ratio, 0.93; 95%CI, 0.89-0.97), never or rarely insomnia (vs. sometimes/usually insomnia; hazards ratio, 0.93; 95%CI, 0.88-0.97) and no frequent daytime sleepiness (vs. often/always daytime sleepiness; hazards ratio, 0.90; 95%CI, 0.81-0.99) were significantly associated with a lower risk of new-onset acute kidney injury.

CONCLUSIONS

A healthy sleep pattern was significantly associated with a lower risk of new-onset acute kidney injury, regardless of the genetic risks.

Forward genetic screen of Caenorhabditis elegans mutants with impaired sleep reveals a crucial role of neuronal diacylglycerol kinase DGK-1 in regulating sleep

The sleep state is widely observed in animals. The molecular mechanisms underlying sleep regulation, however, remain largely unclear. In the nematode Caenorhabditis elegans, developmentally timed sleep (DTS) and stress-induced sleep (SIS) are 2 types of quiescent behaviors that fulfill the definition of sleep and share conserved sleep-regulating molecules with mammals. To identify novel sleep-regulating molecules, we conducted an unbiased forward genetic screen based on DTS phenotypes. We isolated 2 mutants, rem8 and rem10, that exhibited significantly disrupted DTS and SIS. The causal gene of the abnormal sleep phenotypes in both mutants was mapped to dgk-1, which encodes diacylglycerol kinase. Perhaps due to the diminished SIS, dgk-1 mutant worms exhibited decreased survival following exposure to a noxious stimulus. Pan-neuronal and/or cholinergic expression of dgk-1 partly rescued the dgk-1 mutant defects in DTS, SIS, and post-stress survival. Moreover, we revealed that pkc-1/nPKC participates in sleep regulation and counteracts the effect of dgk-1; the reduced DTS, SIS, and post-stress survival rate were partly suppressed in the pkc-1; dgk-1 double mutant compared with the dgk-1 single mutant. Excessive sleep observed in the pkc-1 mutant was also suppressed in the pkc-1; dgk-1 double mutant, implying that dgk-1 has a complicated mode of action. Our findings indicate that neuronal DGK-1 is essential for normal sleep and that the counterbalance between DGK-1 and PKC-1 is crucial for regulating sleep and mitigating post-stress damage.

Portable and integrated microfluidic flow control system using off-the-shelf components towards organs-on-chip applications

Organ-on-a-chip (OoC) devices require the precise control of various media. This is mostly done using several fluid control components, which are much larger than the typical OoC device and connected through fluidic tubing, i.e., the fluidic system is not integrated, which inhibits the system's portability. Here, we explore the limits of fluidic system integration using off-the-shelf fluidic control components. A flow control configuration is proposed that uses a vacuum to generate a fluctuation-free flow and minimizes the number of components used in the system. 3D printing is used to fabricate a custom-designed platform box for mounting the chosen smallest footprint components. It provides flexibility in arranging the various components to create experiment-specific systems. A demonstrator system is realized for lung-on-a-chip experiments. The 3D-printed platform box is 290 mm long, 240 mm wide and 37 mm tall. After integrating all the components, it weighs 4.8 kg. The system comprises of a switch valve, flow and pressure controllers, and a vacuum pump to control the diverse media flows. The system generates liquid flow rates ranging from 1.5 [Formula: see text]Lmin[Formula: see text] to 68 [Formula: see text]Lmin[Formula: see text] in the cell chambers, and a cyclic vacuum of 280 mbar below atmospheric pressure with 0.5 Hz frequency in the side channels to induce mechanical strain on the cells-substrate. The components are modular for easy exchange. The battery operated platform box can be mounted on either upright or inverted microscopes and fits in a standard incubator. Overall, it is shown that a compact integrated and portable fluidic system for OoC experiments can be constructed using off-the-shelf components. For further down-scaling, the fluidic control components, like the pump, switch valves, and flow controllers, require significant miniaturization while having a wide flow rate range with high resolution.

ER proteostasis regulators cell-non-autonomously control sleep

Sleep is regulated by peripheral tissues under fatigue. The molecular pathways in peripheral cells that trigger systemic sleep-related signals, however, are unclear. Here, a forward genetic screen in C. elegans identifies 3 genes that strongly affect sleep amount: sel-1, sel-11, and mars-1. sel-1 and sel-11 encode endoplasmic reticulum (ER)-associated degradation components, whereas mars-1 encodes methionyl-tRNA synthetase. We find that these machineries function in non-neuronal tissues and that the ER unfolded protein response components inositol-requiring enzyme 1 (IRE1)/XBP1 and protein kinase R-like ER kinase (PERK)/eukaryotic initiation factor-2α (eIF2α)/activating transcription factor-4 (ATF4) participate in non-neuronal sleep regulation, partly by reducing global translation. Neuronal epidermal growth factor receptor (EGFR) signaling is also required. Mouse studies suggest that this mechanism is conserved in mammals. Considering that prolonged wakefulness increases ER proteostasis stress in peripheral tissues, our results suggest that peripheral ER proteostasis factors control sleep homeostasis. Moreover, based on our results, peripheral tissues likely cope with ER stress not only by the well-established cell-autonomous mechanisms but also by promoting the individual's sleep.

Safety and efficacy outcomes after intranasal administration of neural stem cells in cerebral palsy: a randomized phase 1/2 controlled trial

BACKGROUND

Neural stem cells (NSCs) are believed to have the most therapeutic potential for neurological disorders because they can differentiate into various neurons and glial cells. This research evaluated the safety and efficacy of intranasal administration of NSCs in children with cerebral palsy (CP). The functional brain network (FBN) analysis based on electroencephalogram (EEG) and voxel-based morphometry (VBM) analysis based on T1-weighted images were performed to evaluate functional and structural changes in the brain.

METHODS

A total of 25 CP patients aged 3-12 years were randomly assigned to the treatment group (n = 15), which received an intranasal infusion of NSCs loaded with nasal patches and rehabilitation therapy, or the control group (n = 10) received rehabilitation therapy only. The primary endpoints were the safety (assessed by the incidence of adverse events (AEs), laboratory and imaging examinations) and the changes in the Gross Motor Function Measure-88 (GMFM-88), the Activities of Daily Living (ADL) scale, the Sleep Disturbance Scale for Children (SDSC), and some adapted scales. The secondary endpoints were the FBN and VBM analysis.

RESULTS

There were only four AEs happened during the 24-month follow-up period. There was no significant difference in the laboratory examinations before and after treatment, and the magnetic resonance imaging showed no abnormal nasal and intracranial masses. Compared to the control group, patients in the treatment group showed apparent improvements in GMFM-88 and ADL 24 months after treatment. Compared with the baseline, the scale scores of the Fine Motor Function, Sociability, Life Adaptability, Expressive Ability, GMFM-88, and ADL increased significantly in the treatment group 24 months after treatment, while the SDSC score decreased considerably. Compared with baseline, the FBN analysis showed a substantial decrease in brain network energy, and the VBM analysis showed a significant increase in gray matter volume in the treatment group after NSCs treatment.

CONCLUSIONS

Our results showed that intranasal administration of NSCs was well-tolerated and potentially beneficial in children with CP.

TRIAL REGISTRATION

The study was registered in ClinicalTrials.gov (NCT03005249, registered 29 December 2016, https://www.

CLINICALTRIALS

gov/ct2/show/NCT03005249 ) and the Medical Research Registration Information System (CMR-20161129-1003).

Microglial TNFα orchestrates protein phosphorylation in the cortex during the sleep period and controls homeostatic sleep

Sleep intensity is adjusted by the length of previous awake time, and under tight homeostatic control by protein phosphorylation. Here, we establish microglia as a new cellular component of the sleep homeostasis circuit. Using quantitative phosphoproteomics of the mouse frontal cortex, we demonstrate that microglia-specific deletion of TNFα perturbs thousands of phosphorylation sites during the sleep period. Substrates of microglial TNFα comprise sleep-related kinases such as MAPKs and MARKs, and numerous synaptic proteins, including a subset whose phosphorylation status encodes sleep need and determines sleep duration. As a result, microglial TNFα loss attenuates the build-up of sleep need, as measured by electroencephalogram slow-wave activity and prevents immediate compensation for loss of sleep. Our data suggest that microglia control sleep homeostasis by releasing TNFα which acts on neuronal circuitry through dynamic control of phosphorylation.

Understanding Sleep Regulation in Normal and Pathological Conditions, and Why It Matters

Sleep occupies a peculiar place in our lives and in science, being both eminently familiar and profoundly enigmatic. Historically, philosophers, scientists and artists questioned the meaning and purpose of sleep. If Shakespeare's verses from MacBeth depicting "Sleep that soothes away all our worries" and "relieves the weary laborer and heals hurt minds" perfectly epitomize the alleviating benefits of sleep, it is only during the last two decades that the growing understanding of the sophisticated sleep regulatory mechanisms allows us to glimpse putative biological functions of sleep. Sleep control brings into play various brain-wide processes occurring at the molecular, cellular, circuit, and system levels, some of them overlapping with a number of disease-signaling pathways. Pathogenic processes, including mood disorders (e.g., major depression) and neurodegenerative illnesses such Huntington's or Alzheimer's diseases, can therefore affect sleep-modulating networks which disrupt the sleep-wake architecture, whereas sleep disturbances may also trigger various brain disorders. In this review, we describe the mechanisms underlying sleep regulation and the main hypotheses drawn about its functions. Comprehending sleep physiological orchestration and functions could ultimately help deliver better treatments for people living with neurodegenerative diseases.

Ischemic Stroke Disrupts Sleep Homeostasis in Middle-Aged Mice

Sleep disturbances, including insomnia and excessive daytime sleepiness, are highly prevalent in patients with ischemic stroke (IS), which severely impacts recovery and rehabilitation efforts. However, how IS induces sleep disturbances is unclear. Three experiments were performed on middle-aged C57BL/6J mice, instrumented with sleep recording electrodes and/or subjected to 1 h of middle cerebral artery (MCAO; Stroke group) or sham (Sham group) occlusion to induce IS. After 48 h of reperfusion (a) experiment 1 verified sensorimotor deficit (using Garcia scale) and infarction (using TTC staining) in this mouse model; (b) experiment 2 examined the effects of IS on the quality (sleep latency and NREM delta power) and quantity (duration) of sleep; and (c) experiment 3 determined the effects of IS on sleep homeostasis using sleep deprivation (SD) and recovery sleep (RS) paradigm. Stroke mice display (a) a significant correlation between sensorimotor deficit and cerebral infarction; (b) insomnia-like symptoms (increased sleep latency, reduced NREM duration and delta power) during the light (inactive) period and daytime sleepiness-like symptoms during the dark (active) period mimicking sleep in IS patients; and (c) impairments in the markers of sleep pressure (during SD) and sleep dissipation (during RS). Our results suggest that IS disrupts sleep homeostasis to cause sleep disturbances.

Sleep loss and addiction

Reducing sleep hours is a risk factor for developing cardiovascular, metabolic, and psychiatric disorders. Furthermore, previous studies have shown that reduction in sleep time is a factor that favors relapse in addicted patients. Additionally, animal models have demonstrated that both sleep restriction and sleep deprivation increase the preference for alcohol, methylphenidate, and the self-administration of cocaine. Therefore, the present review discusses current knowledge about the influence of sleep hours reduction on addictivebehaviors; likewise, we discuss the neuronal basis underlying the sleep reduction-addiction relationship, like the role of the orexin and dopaminergic system and neuronal plasticity (i.e., delta FosB expression). Potentially, chronic sleep restriction could increase brain vulnerability and promote addictive behavior.

Calculating genetic risk for dysfunction in pleiotropic biological processes using whole exome sequencing data

BACKGROUND

Numerous genes are implicated in autism spectrum disorder (ASD). ASD encompasses a wide-range and severity of symptoms and co-occurring conditions; however, the details of how genetic variation contributes to phenotypic differences are unclear. This creates a challenge for translating genetic evidence into clinically useful knowledge. Sleep disturbances are particularly prevalent co-occurring conditions in ASD, and genetics may inform treatment. Identifying convergent mechanisms with evidence for dysfunction that connect ASD and sleep biology could help identify better treatments for sleep disturbances in these individuals.

METHODS

To identify mechanisms that influence risk for ASD and co-occurring sleep disturbances, we analyzed whole exome sequence data from individuals in the Simons Simplex Collection (n = 2380). We predicted protein damaging variants (PDVs) in genes currently implicated in either ASD or sleep duration in typically developing children. We predicted a network of ASD-related proteins with direct evidence for interaction with sleep duration-related proteins encoded by genes with PDVs. Overrepresentation analyses of Gene Ontology-defined biological processes were conducted on the resulting gene set. We calculated the likelihood of dysfunction in the top overrepresented biological process. We then tested if scores reflecting genetic dysfunction in the process were associated with parent-reported sleep duration.

RESULTS

There were 29 genes with PDVs in the ASD dataset where variation was reported in the literature to be associated with both ASD and sleep duration. A network of 108 proteins encoded by ASD and sleep duration candidate genes with PDVs was identified. The mechanism overrepresented in PDV-containing genes that encode proteins in the interaction network with the most evidence for dysfunction was cerebral cortex development (GO:0,021,987). Scores reflecting dysfunction in this process were associated with sleep durations; the largest effects were observed in adolescents (p = 4.65 × 10^-3).

CONCLUSIONS

Our bioinformatic-driven approach detected a biological process enriched for genes encoding a protein-protein interaction network linking ASD gene products with sleep duration gene products where accumulation of potentially damaging variants in individuals with ASD was associated with sleep duration as reported by the parents. Specifically, genetic dysfunction impacting development of the cerebral cortex may affect sleep by disrupting sleep homeostasis which is evidenced to be regulated by this brain region. Future functional assessments and objective measurements of sleep in adolescents with ASD could provide the basis for more informed treatment of sleep problems in these individuals.

The Common Effects of Sleep Deprivation on Human Long-Term Memory and Cognitive Control Processes

Sleep deprivation is known to have adverse effects on various cognitive abilities. In particular, a lack of sleep has been reported to disrupt memory consolidation and cognitive control functions. Here, focusing on long-term memory and cognitive control processes, we review the consistency and reliability of the results of previous studies of sleep deprivation effects on behavioral performance with variations in the types of stimuli and tasks. Moreover, we examine neural response changes related to these behavioral changes induced by sleep deprivation based on human fMRI studies to determine the brain regions in which neural responses increase or decrease as a consequence of sleep deprivation. Additionally, we discuss about the possibility that light as an environmentally influential factor affects our sleep cycles and related cognitive processes.

Sleep, sleep homeostasis and arousal disturbances in alcoholism

The effects of alcohol on human sleep were first described almost 70 years ago. Since then, accumulating evidences suggest that alcohol intake at bed time immediately induces sleep [reduces the time to fall asleep (sleep onset latency), and consolidates and enhances the quality (delta power) and the quantity of sleep]. Such potent sleep promoting activity makes alcohol as one of the most commonly used "over the counter" sleep aid. However, the somnogenic effects, after alcohol intake, slowly wane off and often followed by sleep disruptions during the rest of the night. Repeated use of alcohol leads to the development of rapid tolerance resulting into an alcohol abuse. Moreover, chronic and excessive alcohol intake leads to the development of alcohol use disorder (AUD). Alcoholics, both during drinking periods and during abstinences, suffer from a multitude of sleep disruptions manifested by profound insomnia, excessive daytime sleepiness, and altered sleep architecture. Furthermore, subjective and objective indicators of sleep disturbances are predictors of relapse. Finally, within the USA, it is estimated that societal costs of alcohol-related sleep disorders exceed $18 billion. Thus, although alcohol associated sleep problems have significant economic and clinical consequences, very little is known about how and where alcohol acts to affect sleep. In this review, a conceptual framework and clinical research focused on understanding the relationship between alcohol and sleep is first described. In the next section, our new and exciting preclinical studies, to understand the cellular and molecular mechanism of how acute and chronic alcohol affects sleep, are described. In the end, based on observations from our recent findings and related literature, opportunities for the development of innovative strategies to prevent and treat AUD are proposed.

Alterations in TRN-anterodorsal thalamocortical circuits affect sleep architecture and homeostatic processes in oxidative stress vulnerable Gclm-/- mice

Schizophrenia is associated with alterations of sensory integration, cognitive processing and both sleep architecture and sleep oscillations in mouse models and human subjects, possibly through changes in thalamocortical dynamics. Oxidative stress (OxS) damage, including inflammation and the impairment of fast-spiking gamma-aminobutyric acid neurons have been hypothesized as a potential mechanism responsible for the onset and development of schizophrenia. Yet, the link between OxS and perturbation of thalamocortical dynamics and sleep remains unclear. Here, we sought to investigate the effects of OxS on sleep regulation by characterizing the dynamics of thalamocortical networks across sleep-wake states in a mouse model with a genetic deletion of the modifier subunit of glutamate-cysteine ligase (Gclm knockout, KO) using high-density electrophysiology in freely-moving mice. We found that Gcml KO mice exhibited a fragmented sleep architecture and impaired sleep homeostasis responses as revealed by the increased NREM sleep latencies, decreased slow-wave activities and spindle rate after sleep deprivation. These changes were associated with altered bursting activity and firing dynamics of neurons from the thalamic reticularis nucleus, anterior cingulate and anterodorsal thalamus. Administration of N-acetylcysteine (NAC), a clinically relevant antioxidant, rescued the sleep fragmentation and spindle rate through a renormalization of local neuronal dynamics in Gclm KO mice. Collectively, these findings provide novel evidence for a link between OxS and the deficits of frontal TC network dynamics as a possible mechanism underlying sleep abnormalities and impaired homeostatic responses observed in schizophrenia.

Why It Is Important to Consider the Effects of Analgesics on Sleep: A Critical Review

We review the known physiological mechanisms underpinning all of pain processing, sleep regulation, and pharmacology of analgesics prescribed for chronic pain. In particular, we describe how commonly prescribed analgesics act in sleep-wake neural pathways, with potential unintended impact on sleep and/or wake function. Sleep disruption, whether pain- or drug-induced, negatively impacts quality of life, mental and physical health. In the context of chronic pain, poor sleep quality heightens pain sensitivity and may affect analgesic function, potentially resulting in further analgesic need. Clinicians already have to consider factors including efficacy, abuse potential, and likely side effects when making analgesic prescribing choices. We propose that analgesic-related sleep disruption should also be considered. The neurochemical mechanisms underlying the reciprocal relationship between pain and sleep are poorly understood, and studies investigating sleep in those with specific chronic pain conditions (including those with comorbidities) are lacking. We emphasize the importance of further work to clarify the effects (intended and unintended) of each analgesic class to inform personalized treatment decisions in patients with chronic pain. © 2021 American Physiological Society. Compr Physiol 11:1-31, 2021.

Dysfunction of ventral tegmental area GABA neurons causes mania-like behavior

The ventral tegmental area (VTA), an important source of dopamine, regulates goal- and reward-directed and social behaviors, wakefulness, and sleep. Hyperactivation of dopamine neurons generates behavioral pathologies. But any roles of non-dopamine VTA neurons in psychiatric illness have been little explored. Lesioning or chemogenetically inhibiting VTA GABAergic (VTAVgat) neurons generated persistent wakefulness with mania-like qualities: locomotor activity was increased; sensitivity to D-amphetamine was heightened; immobility times decreased on the tail suspension and forced swim tests; and sucrose preference increased. Furthermore, after sleep deprivation, mice with lesioned VTAVgat neurons did not catch up on lost sleep, even though they were starting from a sleep-deprived baseline, suggesting that sleep homeostasis was bypassed. The mania-like behaviors, including the sleep loss, were reversed by valproate, and re-emerged when treatment was stopped. Lithium salts and lamotrigine, however, had no effect. Low doses of diazepam partially reduced the hyperlocomotion and fully recovered the immobility time during tail suspension. The mania like-behaviors mostly depended on dopamine, because giving D1/D2/D3 receptor antagonists reduced these behaviors, but also partially on VTAVgat projections to the lateral hypothalamus (LH). Optically or chemogenetically inhibiting VTAVgat terminals in the LH elevated locomotion and decreased immobility time during the tail suspension and forced swimming tests. VTAVgat neurons help set an animal's (and perhaps human's) mental and physical activity levels. Inputs inhibiting VTAVgat neurons intensify wakefulness (increased activity, enhanced alertness and motivation), qualities useful for acute survival. In the extreme, however, decreased or failed inhibition from VTAVgat neurons produces mania-like qualities (hyperactivity, hedonia, decreased sleep).

Mitochondria: new players in homeostatic regulation of firing rate set points

Neural circuit functions are stabilized by homeostatic processes at long timescales in response to changes in behavioral states, experience, and learning. However, it remains unclear which specific physiological variables are being stabilized and which cellular or neural network components compose the homeostatic machinery. At this point, most evidence suggests that the distribution of firing rates among neurons in a neuronal circuit is the key variable that is maintained around a set-point value in a process called 'firing rate homeostasis.' Here, we review recent findings that implicate mitochondria as central players in mediating firing rate homeostasis. While mitochondria are known to regulate neuronal variables such as synaptic vesicle release or intracellular calcium concentration, the mitochondrial signaling pathways that are essential for firing rate homeostasis remain largely unknown. We used basic concepts of control theory to build a framework for classifying possible components of the homeostatic machinery that stabilizes firing rate, and we particularly emphasize the potential role of sleep and wakefulness in this homeostatic process. This framework may facilitate the identification of new homeostatic pathways whose malfunctions drive instability of neural circuits in distinct brain disorders.

The impact of daily caffeine intake on nighttime sleep in young adult men

Acute caffeine intake can delay sleep initiation and reduce sleep intensity, particularly when consumed in the evening. However, it is not clear whether these sleep disturbances disappear when caffeine is continuously consumed during daytime, which is common for most coffee drinkers. To address this question, we investigated the sleep of twenty male young habitual caffeine consumers during a double-blind, randomized, crossover study including three 10-day conditions: caffeine (3 × 150 mg caffeine daily), withdrawal (3 × 150 mg caffeine for 8 days, then switch to placebo), and placebo (3 × placebo daily). After 9 days of continuous treatment, electroencephalographically (EEG)-derived sleep structure and intensity were recorded during a scheduled 8-h nighttime sleep episode starting 8 (caffeine condition) and 15 h (withdrawal condition) after the last caffeine intake. Upon scheduled wake-up time, subjective sleep quality and caffeine withdrawal symptoms were assessed. Unexpectedly, neither polysomnography-derived total sleep time, sleep latency, sleep architecture nor subjective sleep quality differed among placebo, caffeine, and withdrawal conditions. Nevertheless, EEG power density in the sigma frequencies (12-16 Hz) during non-rapid eye movement sleep was reduced in both caffeine and withdrawal conditions when compared to placebo. These results indicate that daily caffeine intake in the morning and afternoon hours does not strongly impair nighttime sleep structure nor subjective sleep quality in healthy good sleepers who regularly consume caffeine. The reduced EEG power density in the sigma range might represent early signs of overnight withdrawal from the continuous presence of the stimulant during the day.

Challenging sleep homeostasis

In this commentary, I play the Devil’s advocate and assume the title of High Contrarian. I intend to be provocative to challenge long-standing ideas about sleep. I blame all on Professor Craig Heller, who taught me to think this way as a graduate student in his laboratory. Scientists should fearlessly jump into the foaming edge of what we know, but also consider how safe are their intellectual harbors. There are many ideas we accept as ‘known’: that sleep is ubiquitous in the animal kingdom, that it serves vital functions, that it plays an essential role in brain plasticity. All of this could be wrong. As one example, I reexamine the idea that sleep is regulated by a mysterious ‘homeostat’ that determines sleep need based on prior wake time.

Is insomnia disorder associated with time in bed extension?

Objective

There is a lack of evidence for extension of time in bed behaviors (i.e., getting to bed earlier, going out of bed later, staying in bed while awake and napping) as perpetuating factors of insomnia. The aim of this study is to assess if insomnia disorder is associated with extension of time in bed behaviors.

Methods

150 good sleepers and 173 insomniacs were recruited between December 2017 and June 2018. A cross-sectional survey was performed using the Wang Insomnia Integrated Questionnaire.

Results

Bedtime, rising time and time in bed were not different between good sleepers and insomniacs (Cohen’s d, <0.01, 0.07, 0.07, respectively; all p>0.05) and were not correlated with insomnia severity (all p>0.05). Staying in bed while awake during the night and in the morning where both different between good sleepers and insomniacs (Cohen’s d, 1.33 and 0.85, respectively; all p<0.001) and were positively correlated with insomnia severity (all p<0.001). Napping was more frequent (p<0.01) among good sleepers (63.3%) than insomniacs (48.6%) and a predictor of good sleep (p<0.01).

Conclusion

Going to bed earlier and getting out of bed later do not seem to be associated with insomnia. Staying in bed while awake during the night and in the morning are associated with insomnia but could be only signs of insomnia symptoms. Limiting time in bed to prevent insomnia might and suppressing insomniacs’ napping behavior to treat insomnia might not be effective.

Adaptation and survival: hypotheses about the neural mechanisms of unihemispheric sleep

Sleep and wakefulness are opposite brain and body conditions that accomplish different but complementary functions. However, these opposing conditions have been combined in some animals by the adoption of a sleep/wake strategy that allows them to survive, while maintaining both an interaction with the environment at the same time as enabling brain and body recovery. They sleep with half of the brain while keeping the other half awake: a state known as unihemispheric sleep (US). Sleep of cetaceans is exclusively in the form of US; therefore, they experience neither bihemispheric sleep (BS) nor REM sleep. US episodes have also been recorded in eared seals and some species of birds. In those animals, US episodes are intermingled with episodes of BS and REM sleep. Studies have reported both a lateralized release of some neurotransmitters and a drop of brain temperature during US. The aims of this article are to formulate hypotheses about the neural mechanisms of unihemispheric sleep(US) based on findings regarding the neural mechanisms of the sleep/wake cycle of mammals. The neural mechanisms of the sleep/wake cycle are largely preserved across species, allowing to hypothesize about those triggering and regulating US.

Astrocytes in the Ventrolateral Preoptic Area Promote Sleep

Although ventrolateral preoptic (VLPO) nucleus is regarded as a center for sleep promotion, the exact mechanisms underlying the sleep regulation are unknown. Here, we used optogenetic tools to identify the key roles of VLPO astrocytes in sleep promotion. Optogenetic stimulation of VLPO astrocytes increased sleep duration in the active phase in naturally sleep-waking adult male rats (n = 6); it also increased the extracellular ATP concentration (n = 3) and c-Fos expression (n = 3-4) in neurons within the VLPO. In vivo microdialysis analyses revealed an increase in the activity of VLPO astrocytes and ATP levels during sleep states (n = 4). Moreover, metabolic inhibition of VLPO astrocytes reduced ATP levels (n = 4) and diminished sleep duration (n = 4). We further show that tissue-nonspecific alkaline phosphatase (TNAP), an ATP-degrading enzyme, plays a key role in mediating the somnogenic effects of ATP released from astrocytes (n = 5). An appropriate sample size for all experiments was based on statistical power calculations. Our results, taken together, indicate that astrocyte-derived ATP may be hydrolyzed into adenosine by TNAP, which may in turn act on VLPO neurons to promote sleep.SIGNIFICANCE STATEMENT Glia have recently been at the forefront of neuroscience research. Emerging evidence illustrates that astrocytes, the most abundant glial cell type, are the functional determinants for fates of neurons and other glial cells in the central nervous system. In this study, we newly identified the pivotal role of hypothalamic ventrolateral preoptic (VLPO) astrocytes in the sleep regulation, and provide novel insights into the mechanisms underlying the astrocyte-mediated sleep regulation.

Is Sleep Associated with the S-Klotho Anti-Aging Protein in Sedentary Middle-Aged Adults? The FIT-AGEING Study

Sleep and Klotho have both been closely related to the ageing process, both playing a substantial role in the endocrine and immune systems and, thereby, in oxidative stress and chronic inflammation. However, there are no studies elucidating the relationship between sleep and Klotho. Therefore, this study investigated the association of sleep quantity and quality with the shed form of the α-Klotho gene (S-Klotho plasma levels) in sedentary middle-aged adults. A total of 74 volunteers (52.7% women; aged 53.7 ± 5.1) were recruited for the present study. Objective sleep quality parameters (total sleep time (TST), wake after sleep onset (WASO), and sleep efficiency (SE)) were determined using a wrist-worn accelerometer over seven consecutive days, and the subjective sleep quality was assessed by the Pittsburgh Sleep Quality Index (PSQI; higher scores indicate worse sleep quality). The S-Klotho plasma levels were measured in the ethylenediaminetetraacetic acid plasma using a solid-phase sandwich enzyme-linked immunosorbent assay. Objective sleep parameters were associated with the S-Klotho plasma levels only after including the age, fat mass percentage, and lean mass index as covariates. A direct relationship was observed between the subjective sleep quality (inverse of PSQI scores) and the S-Klotho plasma levels in sedentary middle-aged adults. Improving sleep quantity and quality could be considered an anti-aging therapeutic approach for the prevention, slowing, and even reversal of the physiological decline and degenerative pathologies that are certainly related to the aging process.

Pharmacological Modulation of Sleep Homeostasis in Rat: Novel Effects of an mGluR2/3 Antagonist

Increasing vigilance without incurring the negative consequences of extended wakefulness such as daytime sleepiness and cognitive impairment is a major challenge in treating many sleep disorders. The present work compares two closely related mGluR2/3 antagonists LY3020371 and LY341495 with two well-known wake-promoting compounds caffeine and d-amphetamine. Sleep homeostasis properties were explored in male Wistar rats by manipulating levels of wakefulness via (1) physiological sleep restriction (SR), (2) pharmacological action, or (3) a combination of these. A two-phase nonlinear mixed-effects model combining a quadratic and exponential function at an empirically estimated join point allowed the quantification of wake-promoting properties and any subsequent sleep rebound. A simple response latency task (SRLT) following SR assessed functional capacity of sleep-restricted animals treated with our test compounds. Caffeine and d-amphetamine increased wakefulness with a subsequent full recovery of non-rapid eye movement (NREM) and rapid eye movement (REM) sleep and were unable to fully reverse SR-induced impairments in SRLT. In contrast, LY3020371 increased wakefulness with no subsequent elevation of NREM sleep, delta power, delta energy, or sleep bout length and count, yet REM sleep recovered above baseline levels. Prior sleep pressure obtained using an SR protocol had no impact on the wake-promoting effect of LY3020371 and NREM sleep rebound remained blocked. Furthermore, LY341495 increased functional capacity across SRLT measures following SR. These results establish the critical role of glutamate in sleep homeostasis and support the existence of independent mechanisms for NREM and REM sleep homeostasis.

Caffeine-dependent changes of sleep-wake regulation: Evidence for adaptation after repeated intake

BACKGROUND

Circadian and sleep-homeostatic mechanisms regulate timing and quality of wakefulness. To enhance wakefulness, daily consumption of caffeine in the morning and afternoon is highly common. However, the effects of such a regular intake pattern on circadian sleep-wake regulation are unknown. Thus, we investigated if daily daytime caffeine intake and caffeine withdrawal affect circadian rhythms and wake-promotion in habitual consumers.

METHODS

Twenty male young volunteers participated in a randomised, double-blind, within-subject study with three conditions: i) caffeine (150 mg 3 x daily for 10 days), ii) placebo (3 x daily for 10 days) and iii) withdrawal (150 mg caffeine 3 x daily for eight days, followed by a switch to placebo for two days). Starting on day nine of treatment, salivary melatonin and cortisol, evening nap sleep as well as sleepiness and vigilance performance throughout day and night were quantified during 43 h in an in-laboratory, light and posture-controlled protocol.

RESULTS

Neither the time course of melatonin (i.e. onset, amplitude or area under the curve) nor the time course of cortisol was significantly affected by caffeine or withdrawal. During withdrawal, however, volunteers reported increased sleepiness, showed more attentional lapses as well as polysomnography-derived markers of elevated sleep propensity in the late evening compared to both the placebo and caffeine condition.

CONCLUSIONS

The typical pattern of caffeine intake with consumption in both the morning and afternoon hours may not necessarily result in a circadian phase shift in the evening nor lead to clear-cut benefits in alertness. The time-of-day independent effects of caffeine withdrawal on evening nap sleep, sleepiness and performance suggest an adaptation to the substance, presumably in the homeostatic aspect of sleep-wake regulation.

Sleep Time in the European Starling Is Strongly Affected by Night Length and Moon Phase

Sleep is considered to be of crucial importance for performance and health, yet much of what we know about sleep is based on studies in a few mammalian model species under strictly controlled laboratory conditions. Data on sleep in different species under more natural conditions may yield new insights in the regulation and functions of sleep. We therefore performed a study with miniature electroencephalogram (EEG) data loggers in starlings under semi-natural conditions, group housed in a large outdoor enclosure with natural temperature and light. The birds showed a striking 5-h difference in the daily amount of non-rapid-eye-movement (NREM) sleep between winter and summer. This variation in the amount of NREM sleep was best explained by night length. Most sleep occurred during the night, but when summer nights became short, the animals displayed mid-day naps. The decay of NREM sleep spectral power in the slow-wave range (1.1-4.3 Hz) was steeper in the short nights than in the longer nights, which suggests that birds in summer have higher sleep pressure. Additionally, sleep was affected by moon phase, with 2 h of NREM sleep less during full moon. The starlings displayed very little rapid-eye-movement (REM) sleep, adding up to 1.3% of total sleep time. In conclusion, this study demonstrates a pronounced phenotypical flexibility in sleep in starlings under semi-natural conditions and shows that environmental factors have a major impact on the organization of sleep and wakefulness.

Tired and stressed: Examining the need for sleep

A key feature of circadian rhythms is the sleep/wake cycle. Sleep causes reduced responsiveness to the environment, which puts animals in a particularly vulnerable state; yet sleep has been conserved throughout evolution, indicating that it fulfils a vital purpose. A core function of sleep across species has not been identified, but substantial advances in sleep research have been made in recent years using the genetically tractable model organism, Drosophila melanogaster. This review describes the universality of sleep, the regulation of sleep, and current theories on the function of sleep, highlighting a historical and often overlooked theory called the Free Radical Flux Theory of Sleep. Additionally, we summarize our recent work with short-sleeping Drosophila mutants and other genetic and pharmacological tools for manipulating sleep which supports an antioxidant theory of sleep and demonstrates a bi-directional relationship between sleep and oxidative stress.

Region-specific adenosinergic modulation of the slow-cortical rhythm in urethane-anesthetized rats

Slow cortical rhythm (SCR) is a rhythmic alternation of UP and DOWN states during sleep and anesthesia. SCR-associated slow waves reflect homeostatic sleep functions. Adenosine accumulating during prolonged wakefulness and sleep deprivation (SD) may play a role in the delta power increment during recovery sleep. NREM sleep is a local, use-dependent process of the brain. In the present study, direct effect of adenosine on UP and DOWN states was tested by topical application to frontal, somatosensory and visual cortices, respectively, in urethane-anesthetized rats. Local field potentials (LFPs) were recorded using an electrode array inserted close to the location of adenosine application. Multiple unit activity (MUA) was measured from layer V-VI in close proximity of the recording array. In the frontal and somatosensory cortex, adenosine modulated SCR with slow kinetics on the LFP level while MUA remained mostly unaffected. In the visual cortex, adenosine modulated SCR with fast kinetics. In each region, delta power increment was based on the increased frequency of state transitions as well as increased height of UP-state associated slow waves. These results show that adenosine may directly modulate SCR in a complex and region-specific manner which may be related to the finding that restorative processes may take place with varying duration and intensity during recovery sleep in different cortical regions. Adenosine may play a direct role in the increment of the slow wave power observed during local sleep, furthermore it may shape the region-specific characteristics of the phenomenon.

Epidermal Growth Factor Signaling Promotes Sleep through a Combined Series and Parallel Neural Circuit

Sleep requires sleep-active neurons that depolarize to inhibit wake circuits. Sleep-active neurons are under the control of homeostatic mechanisms that determine sleep need. However, little is known about the molecular and circuit mechanisms that translate sleep need into the depolarization of sleep-active neurons. During many stages and conditions in C. elegans, sleep requires a sleep-active neuron called RIS. Here, we defined the transcriptome of RIS and discovered that genes of the epidermal growth factor receptor (EGFR) signaling pathway are expressed in RIS. Because of cellular stress, EGFR directly activates RIS. Activation of EGFR signaling in the ALA neuron has previously been suggested to promote sleep independently of RIS. Unexpectedly, we found that ALA activation promotes RIS depolarization. Our results suggest that ALA is a drowsiness neuron with two separable functions: (1) it inhibits specific behaviors, such as feeding, independently of RIS, (2) and it activates RIS. Whereas ALA plays a strong role in surviving cellular stress, surprisingly, RIS does not. In summary, EGFR signaling can depolarize RIS by an indirect mechanism through activation of the ALA neuron that acts upstream of the sleep-active RIS neuron and through a direct mechanism using EGFR signaling in RIS. ALA-dependent drowsiness, rather than RIS-dependent sleep bouts, appears to be important for increasing survival after cellular stress, suggesting that different types of behavioral inhibition play different roles in restoring health. VIDEO ABSTRACT.

Galanin Neurons Unite Sleep Homeostasis and α2-Adrenergic Sedation

Our urge to sleep increases with time spent awake, until sleep becomes inescapable. The sleep following sleep deprivation is longer and deeper, with an increased power of delta (0.5–4 Hz) oscillations, a phenomenon termed sleep homeostasis [1, 2, 3, 4]. Although widely expressed genes regulate sleep homeostasis [1, 4, 5, 6, 7, 8, 9, 10] and the process is tracked by somnogens and phosphorylation [1, 3, 7, 11, 12, 13, 14], at the circuit level sleep homeostasis has remained mysterious. Previously, we found that sedation induced with α2-adrenergic agonists (e.g., dexmedetomidine) and sleep homeostasis both depend on the preoptic (PO) hypothalamus [15, 16]. Dexmedetomidine, increasingly used for long-term sedation in intensive care units [17], induces a non-rapid-eye-movement (NREM)-like sleep but with undesirable hypothermia [18, 19]. Within the PO, various neuronal subtypes (e.g., GABA/galanin and glutamate/NOS1) induce NREM sleep [20, 21, 22] and concomitant body cooling [21, 22]. This could be because NREM sleep’s restorative effects depend on lower body temperature [23, 24]. Here, we show that mice with lesioned PO galanin neurons have reduced sleep homeostasis: in the recovery sleep following sleep deprivation there is a diminished increase in delta power, and the mice catch up little on lost sleep. Furthermore, dexmedetomidine cannot induce high-power delta oscillations or sustained hypothermia. Some hours after dexmedetomidine administration to wild-type mice there is a rebound in delta power when they enter normal NREM sleep, reminiscent of emergence from torpor. This delta rebound is reduced in mice lacking PO galanin neurons. Thus, sleep homeostasis and dexmedetomidine-induced sedation require PO galanin neurons and likely share common mechanisms.

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This is the first identification of a cell type underlying sleep homeostasis

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Preoptic galanin neurons are essential for sleep homeostasis

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Galanin neurons mediate the sedative and hypothermic actions of dexmedetomidine

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Dexmedetomidine causes an EEG delta power rebound dependent on galanin neurons

Impacts of Subchronic, High-Level Noise Exposure on Sleep and Metabolic Parameters: A Juvenile Rodent Model

BACKGROUND

Noise is an environmental factor that has been associated with metabolic and sleep disorders. Sleep is a vital function, since it underpins physiologic processes and cognitive recovery and development. However, the effects of chronic noise exposure on the developing organism are still subject to debate.

OBJECTIVE

The objective of the present study was to assess the effects of subchronic, high-level noise exposure on sleep, apnea, and homeostasis in juvenile rats.

METHODS

Twenty-four 3-wk-old male Wistar rats were exposed to noise [[Formula: see text], [Formula: see text]] for 5 wk and 2 d during the 12-h rest period. Data on sleep stages, food and water intake, apnea, and body and organ weight were recorded.

RESULTS

Five weeks of high-level noise exposure were associated with hyperphagia ([Formula: see text]), body weight gain ([Formula: see text]), a heavier thymus ([Formula: see text]), and heavier adrenal glands ([Formula: see text]). A sleep analysis highlighted microstructural differences in the active period: in particular, the mean daily amount of rapid eye movement (REM) sleep as a proportion of total sleep time (TST) was higher. The mean daily amount of non-REM (NREM) sleep was lower in the exposed group, meaning that the intergroup difference in the TST was not significant. During a 1-h, noise-free plethysmographic recording during the rest period, the mean total amount of active wakefulness (AW) was lower in the exposed group (by 9.1 min), whereas the mean duration of an episode of REM sleep was higher (by 1.8 min), and the TST was higher (by 10.7 min).

DISCUSSION

Subchronic exposure of juvenile rats to high-intensity noise during the rest period was associated with some small but significant sleep disturbances, greater food and water intakes, greater body weight gain, and greater thymus and adrenal gland weights. The main effects of noise exposure on sleep were also observed in the 1-h plethysmography session after 5 wk of exposure. https://doi.org/10.1289/EHP4045.

Genetic sleep deprivation: using sleep mutants to study sleep functions

Sleep is a fundamental conserved physiological state in animals and humans. It may serve multiple functions, ranging from energy conservation to higher brain operation. Understanding sleep functions and the underlying mechanisms requires the study of sleeplessness and its consequences. The traditional approach to remove sleep is sleep deprivation (SD) by sensory stimulation. However, stimulation-induced SD can be stressful and can cause non-specific side effects. An emerging alternative method is "genetic SD", which removes sleep using genetics or optogenetics. Sleep requires sleep-active neurons and their regulators. Thus, genetic impairment of sleep circuits might lead to more specific and comprehensive sleep loss. Here, I discuss the advantages and limits of genetic SD in key genetic sleep model animals: rodents, zebrafish, fruit flies and roundworms, and how the study of genetic SD alters our view of sleep functions. Genetic SD typically causes less severe phenotypes compared with stimulation-induced SD, suggesting that sensory stimulation-induced SD may have overestimated the role of sleep, calling for a re-investigation of sleep functions.

Sex differences in sleep and sleep loss-induced cognitive deficits: The influence of gonadal hormones

Males and females can respond differentially to the same environmental stimuli and experimental conditions. Chronic sleep loss is a frequent and growing problem in many modern societies and has a broad variety of negative outcomes for health and well-being. While much has been done to explore the deleterious effects of sleep deprivation (SD) on cognition in both human and animal studies over the last few decades, very little attention has been paid to the part played by sex differences and gonadal steroids in respect of changes in cognitive functions caused by sleep loss. The effects of gonadal hormones on sleep regulation and cognitive performances are well established. Reduced gonadal function in menopausal women and elderly men is associated with sleep disturbances and cognitive decline as well as dementia, which suggests that sex steroids play a key role in modulating these conditions. Finding out whether there are sex differences in respect of the effect of insufficient sleep on cognition, and how neuroendocrine mediators influence cognitive impairment induced by SD could provide valuable insights into the best therapies for each sex. In this review, we aim to highlight the involvement of sex differences and gonadal hormone status on the severity of cognitive deficits induced by sleep deficiency in both human and animal studies.

Adenosine has two faces: Regionally dichotomous adenosine tone in a model of epilepsy with comorbid sleep disorders

OBJECTIVE

Adenosine participates in maintaining the excitatory/inhibitory balance in neuronal circuits. Studies indicate that adenosine levels in the cortex and hippocampus increase and exert sleep pressure in sleep-deprived and control animals, whereas in epilepsy reduced adenosine tone promotes hyperexcitability. To date, the role of adenosine in pathological conditions that result in both seizures and sleep disorders is unknown. Here, we determined adenosine tone in sleep and seizure regulating brain regions of K_v1.1 knockout (KO) mice, a model of temporal epilepsy with comorbid sleep disorders.

METHODS

1) Reverse phase-high performance liquid chromatography (RP-HPLC) was performed on brain tissue to determine levels of adenosine and adenine nucleotides. 2) Multi-electrode array extracellular electrophysiology was used to determine adenosine tone in the hippocampal CA1 region and the lateral hypothalamus (LH).

RESULTS

RP-HPLC indicated a non-significant decrease in adenosine (~50%, p = 0.23) in whole brain homogenates of KO mice. Regional examination of relative levels of adenine nucleotides indicated decreased ATP and increased AMP in the cortex and hippocampus and increased adenosine in cortical tissue. Using electrophysiological and pharmacological techniques, estimated adenosine levels were ~35% lower in the KO hippocampal CA1 region, and 1-2 fold higher in the KO LH. Moreover, the increased adenosine in KO LH contributed to lower spontaneous firing rates of putative wake-promoting orexin/hypocretin neurons.

INTERPRETATION

This is the first study to demonstrate a direct correlation of regionally distinct dichotomous adenosine levels in a single model with both epilepsy and comorbid sleep disorders. The weaker inhibitory tone in the dorsal hippocampus is consistent with lower seizure threshold, whereas increased adenosine in the LH is consistent with chronic partial sleep deprivation. This work furthers our understanding of how adenosine may contribute to pathological conditions that underlie sleep disorders within the epileptic brain.

Light and Cognition: Roles for Circadian Rhythms, Sleep, and Arousal

Light exerts a wide range of effects on mammalian physiology and behavior. As well as synchronizing circadian rhythms to the external environment, light has been shown to modulate autonomic and neuroendocrine responses as well as regulating sleep and influencing cognitive processes such as attention, arousal, and performance. The last two decades have seen major advances in our understanding of the retinal photoreceptors that mediate these non-image forming responses to light, as well as the neural pathways and molecular mechanisms by which circadian rhythms are generated and entrained to the external light/dark (LD) cycle. By contrast, our understanding of the mechanisms by which lighting influences cognitive processes is more equivocal. The effects of light on different cognitive processes are complex. As well as the direct effects of light on alertness, indirect effects may also occur due to disrupted circadian entrainment. Despite the widespread use of disrupted LD cycles to study the role circadian rhythms on cognition, the different experimental protocols used have subtly different effects on circadian function which are not always comparable. Moreover, these protocols will also disrupt sleep and alter physiological arousal, both of which are known to modulate cognition. Studies have used different assays that are dependent on different cognitive and sensory processes, which may also contribute to their variable findings. Here, we propose that studies addressing the effects of different lighting conditions on cognitive processes must also account for their effects on circadian rhythms, sleep, and arousal if we are to fully understand the physiological basis of these responses.

Sleep and Sedative States Induced by Targeting the Histamine and Noradrenergic Systems

Sedatives target just a handful of receptors and ion channels. But we have no satisfying explanation for how activating these receptors produces sedation. In particular, do sedatives act at restricted brain locations and circuitries or more widely? Two prominent sedative drugs in clinical use are zolpidem, a GABA_A receptor positive allosteric modulator, and dexmedetomidine (DEX), a selective α2 adrenergic receptor agonist. By targeting hypothalamic neuromodulatory systems both drugs induce a sleep-like state, but in different ways: zolpidem primarily reduces the latency to NREM sleep, and is a controlled substance taken by many people to help them sleep; DEX produces prominent slow wave activity in the electroencephalogram (EEG) resembling stage 2 NREM sleep, but with complications of hypothermia and lowered blood pressure—it is used for long term sedation in hospital intensive care units—under DEX-induced sedation patients are arousable and responsive, and this drug reduces the risk of delirium. DEX, and another α2 adrenergic agonist xylazine, are also widely used in veterinary clinics to sedate animals. Here we review how these two different classes of sedatives, zolpidem and dexmedetomideine, can selectively interact with some nodal points of the circuitry that promote wakefulness allowing the transition to NREM sleep. Zolpidem enhances GABAergic transmission onto histamine neurons in the hypothalamic tuberomammillary nucleus (TMN) to hasten the transition to NREM sleep, and DEX interacts with neurons in the preoptic hypothalamic area that induce sleep and body cooling. This knowledge may aid the design of more precise acting sedatives, and at the same time, reveal more about the natural sleep-wake circuitry.

Abnormalities in the Polysomnographic, Adenosine and Metabolic Response to Sleep Deprivation in an Animal Model of Hyperammonemia

Patients with liver cirrhosis can develop hyperammonemia and hepatic encephalopathy (HE), accompanied by pronounced daytime sleepiness. Previous studies with healthy volunteers show that experimental increase in blood ammonium levels increases sleepiness and slows the waking electroencephalogram. As ammonium increases adenosine levels in vitro, and adenosine is a known regulator of sleep/wake homeostasis, we hypothesized that the sleepiness-inducing effect of ammonium is mediated by adenosine. Eight adult male Wistar rats were fed with an ammonium-enriched diet for 4 weeks; eight rats on standard diet served as controls. Each animal was implanted with electroencephalography/electromyography (EEG/EMG) electrodes and a microdialysis probe. Sleep EEG recording and cerebral microdialysis were carried out at baseline and after 6 h of sleep deprivation. Adenosine and metabolite levels were measured by high-performance liquid chromatography (HPLC) and targeted LC/MS metabolomics, respectively. Baseline adenosine and metabolite levels (12 of 16 amino acids, taurine, t4-hydroxy-proline, and acetylcarnitine) were lower in hyperammonemic animals, while putrescine was higher. After sleep deprivation, hyperammonemic animals exhibited a larger increase in adenosine levels, and a number of metabolites showed a different time-course in the two groups. In both groups the recovery period was characterized by a significant decrease in wakefulness/increase in NREM and REM sleep. However, while control animals exhibited a gradual compensatory effect, hyperammonemic animals showed a significantly shorter recovery phase. In conclusion, the adenosine/metabolite/EEG response to sleep deprivation was modulated by hyperammonemia, suggesting that ammonia affects homeostatic sleep regulation and its metabolic correlates.

Regulation of inflammation by lipid mediators in oral diseases

Lipid mediators (LM) of inflammation are a class of compounds derived from ω-3 and ω-6 fatty acids that play a wide role in modulating inflammatory responses. Some LM possess pro-inflammatory properties, while others possess proresolving characteristics, and the class switch from pro-inflammatory to proresolving is crucial for tissue homeostasis. In this article, we review the major classes of LM, focusing on their biosynthesis and signaling pathways, and their role in systemic and, especially, oral health and disease. We discuss the detection of these LM in various body fluids, focusing on diagnostic and therapeutic applications. We also present data showing gender-related differences in salivary LM levels in healthy controls, leading to a hypothesis on the etiology of inflammatory diseases, particularly Sjögren's syndrome. We conclude by enumerating open areas of research where further investigation of LM is likely to result in therapeutic and diagnostic advances.

Neuronal substrates of sleep homeostasis; lessons from flies, rats and mice

Sleep homeostasis is a fundamental property of vigilance state regulation that is highly conserved across species. Neuronal systems and circuits that underlie sleep homeostasis are not well understood. In Drosophila, a neuronal circuit involving neurons in the ellipsoid body and in the dorsal Fan-shaped body is a candidate for both tracing sleep need during waking and translating it to increased sleep drive and expression. Sleep homeostasis in rats and mice involves multiple neuromodulators acting on multiple wake- and sleep-promoting neuronal systems. A functional central homeostat emerges from A₁ receptor mediated actions of adenosine on wake-promoting neurons in the basal forebrain and hypothalamus, and A_2A adenosine receptor-mediated actions on sleep-promoting neurons in the preoptic hypothalamus and nucleus accumbens.

Analysis of the NK2 homeobox gene ceh-24 reveals sublateral motor neuron control of left-right turning during sleep

Sleep is a behavior that is found in all animals that have a nervous system and that have been studied carefully. In Caenorhabditis elegans larvae, sleep is associated with a turning behavior, called flipping, in which animals rotate 180° about their longitudinal axis. However, the molecular and neural substrates of this enigmatic behavior are not known. Here, we identified the conserved NK-2 homeobox gene ceh-24 to be crucially required for flipping. ceh-24 is required for the formation of processes and for cholinergic function of sublateral motor neurons, which separately innervate the four body muscle quadrants. Knockdown of cholinergic function in a subset of these sublateral neurons, the SIAs, abolishes flipping. The SIAs depolarize during flipping and their optogenetic activation induces flipping in a fraction of events. Thus, we identified the sublateral SIA neurons to control the three-dimensional movements of flipping. These neurons may also control other types of motion.

DOI:http://dx.doi.org/10.7554/eLife.24846.001

Although sleeping individuals do not move voluntarily, they are not completely immobile. Both people and animals regularly change position in their sleep, but it is not known why these movements occur or what regulates them.

One of the simplest animals known to require sleep is the nematode worm Caenorhabditis elegans, which is often used by researchers to study the molecular basis of behavior. In common with more complex animals, worms go to sleep lying on either their left or right side and then switch periodically between the two. This “flipping” behavior is typically not seen outside of sleep.

By screening worms with mutations in different genes, Schwarz and Bringmann identified one mutant that does not flip during sleep. The mutant lacked a gene called ceh-24, which is normally active in a set of four neurons known as SIAs. These are a type of motor neuron; that is, neurons that control the contraction of muscles.

The body wall muscles of C. elegans run along the length of its body and are organized into “quadrants” that each cover a quarter of the worm. Schwarz and Bringmann show that unlike other C. elegans motor neurons, SIA neurons control each quadrant separately. By activating specific SIA neurons the worms can contract the muscles on each side of the body independently, and thereby flip from one side to the other.

Further investigation revealed that the SIA motor neurons can also control other types of complex movement. Additional experiments are now needed to determine how the neurons support these behaviors. Another challenge will be to work out the purpose of posture changes during sleep for C. elegans and other animals.

DOI:http://dx.doi.org/10.7554/eLife.24846.002

Circuit-based interrogation of sleep control

Sleep is a fundamental biological process observed widely in the animal kingdom, but the neural circuits generating sleep remain poorly understood. Understanding the brain mechanisms controlling sleep requires the identification of key neurons in the control circuits and mapping of their synaptic connections. Technical innovations over the past decade have greatly facilitated dissection of the sleep circuits. This has set the stage for understanding how a variety of environmental and physiological factors influence sleep. The ability to initiate and terminate sleep on command will also help us to elucidate its functions within and beyond the brain.

Prophylactic Role of Oral Melatonin Administration on Neurogenesis in Adult Balb/C Mice during REM Sleep Deprivation

Purpose. The aim of this study was to assess the effect of melatonin in the proliferation of neural progenitors, melatonin concentration, and antiapoptotic proteins in the hippocampus of adult mice exposed to 96 h REM sleep deprivation (REMSD) prophylactic administration of melatonin for 14 days. Material and Methods. Five groups of Balb/C mice were used: (1) control, (2) REMSD, (3) melatonin (10 mg/kg) plus REMSD, (4) melatonin and intraperitoneal luzindole (once a day at 5 mg/kg) plus REMSD, and (5) luzindole plus REMSD. To measure melatonin content in hippocampal tissue we used HPLC. Bcl-2 and Bcl-xL proteins were measured by Western Blot and neurogenesis was determined by injecting 5-bromo-2-deoxyuridine (BrdU) and BrdU/nestin expressing cells in the subgranular zone of the dentate gyrus were quantified by epifluorescence. Results. The melatonin-treated REMSD group showed an increased neural precursor in 44% with respect to the REMSD group and in 28% when contrasted with the control group (P < 0.021). The melatonin-treated REMSD group also showed the highest expression of Bcl-2 and Bcl-xL as compared to the rest of the groups. Conclusion. The exogenous administration of melatonin restores the tissue levels of sleep-deprived group and appears to be an efficient neuroprotective agent against the deleterious effects of REMSD.