How (and why) the immune system makes us sleep

Roles of Microglial Phagocytosis and Inflammatory Mediators in the Pathophysiology of Sleep Disorders

Sleep serves crucial learning and memory functions in both nervous and immune systems. Microglia are brain immune cells that actively maintain health through their crucial physiological roles exerted across the lifespan, including phagocytosis of cellular debris and orchestration of neuroinflammation. The past decade has witnessed an explosive growth of microglial research. Considering the recent developments in the field of microglia and sleep, we examine their possible impact on various pathological conditions associated with a gain, disruption, or loss of sleep in this focused mini-review. While there are extensive studies of microglial implication in a variety of neuropsychiatric and neurodegenerative diseases, less is known regarding their roles in sleep disorders. It is timely to stimulate new research in this emergent and rapidly growing field of investigation.

A novel neurological function of rice bran: a standardized rice bran supplement promotes non-rapid eye movement sleep in mice through histamine H1 receptors

SCOPE

Although rice bran has been shown to be associated with a wide spectrum of health benefits, to date, there are no reports on its effects on sleep. We investigated the effect of rice bran on sleep and the mechanism underlying this effect.

METHODS AND RESULTS

Electroencephalography was used to evaluate the effects of standardized rice bran supplement (RBS) and doxepin hydrochloride (DH), a histamine H₁ receptor (H₁ R) antagonist used as a positive control, on sleep in mice. The mechanism of RBS action was investigated using knockout (KO) mice and ex vivo electrophysiological recordings. Oral administration of RBS and DH significantly decreased sleep latency and increased the amount of non-rapid eye movement sleep (NREMS) in mice. Similar to DH, RBS fully inhibited H₁ R agonist-induced increase in action potential frequency in tuberomammillary nucleus neurons. In H₁ R KO mice, neither RBS nor DH administration led to the increase in NREMS and decrease in sleep latency observed in WT mice. These results indicate that the sleep-promoting effect of RBS is completely dependent on H₁ R antagonism.

CONCLUSIONS

RBS decreases sleep latency and promotes NREMS through the inhibition of H₁ R, suggesting that it could be a promising therapeutic agent for insomnia.

Resveratrol in Hepatitis C Patients Treated with Pegylated-Interferon-α-2b and Ribavirin Reduces Sleep Disturbance

Background: Hepatitis C virus infection and interferon treatment have shown to be risk factors for sleep disorder health-related quality of life. Aim: To determine whether the effects of resveratrol on sleep disorders were associated with different tests in subjects with chronic hepatitis C treated with Peg-IFN-α and RBV. Patients and Methods: In this prospective, randomized, placebo controlled, double blind clinical trial, 30 subjects (Group A) with chronic hepatitis received Pegylated-Interferon-α2b (1.5 mg/kg per week), Ribavirin and placebo (N-acetylcysteine 600 mg and lactoferrin 23.6 g), while 30 subjects (Group B) received the same dosage of Pegylated-Interferon-α2b, Ribavirin and association of N-acetylcysteine 600 mg, lactoferrin 23.6 g and Resveratrol 19.8 mg for 12 months. All subjects underwent laboratory exams and questionnaires to evaluate mood and sleep disorders (General Health Questionnaire (GHQ), Profile of Mood States (POMS), Pittsburgh Sleep Quality Inventory (PSQI), Epworth Sleepiness Scale (ESS)). Results: The comparison between Group A and Group B showed significant differences after six months in C-reactive protein (p < 0.0001); after 12 months in aspartate aminotransferase (AST) (p < 0.0001) Viremia (p < 0.0001), HAI (p < 0.0012) and C-reactive protein (p < 0.0001); and at follow up in AST (p < 0.0001), Viremia (p < 0.0026) and C-reactive protein (p < 0.0001). Significant differences were observed after 12 month and follow-up in General Health Questionnaire, after 1, 6, 12 and follow-up in Profile of Mood States, after 6, 12, follow-up in Pittsburgh Sleep Quality Inventory and Epworth Sleepiness Scale. Conclusions: Supplementation with Resveratrol decreased General Health Questionnaire score and reduced sleep disorders in patients treated with Peg–IFN-α and RBV.

Mammary Tumors Induce Central Pro-inflammatory Cytokine Expression, but Not Behavioral Deficits in Balb/C Mice

Breast cancer survivors are more likely to develop mood disorders and cognitive deficits than women in the general population. Previous studies suggest that peripheral tumors elicit central pro-inflammatory cytokine production, in turn leading to depression and cognitive deficits. In the current study, two cohorts of female Balb/C mice received bilateral orthotopic injections of syngeneic 67NR, 4T07, or 4T1cells (1 × 105 cells per injection) to induce mammary tumors. Approximately three weeks later, learned fear (via fear conditioning) or depressive-like behavior (via tail suspension and forced swim test) was assessed. Proinflammatory cytokine levels were increased in the serum (IL-1β, TNFα, IFNγ) and livers (IL-1β, IL-6, TNFα) of mice with 4T07 or 4T1 tumors compared to 67NR tumors and the vehicle control. IL-1β was increased in both the hippocampus and cortex of mice injected with 4T07 or 4T1 cell lines relative to the other treatment groups. However, mammary tumors had no effect on hippocampal doublecortin + and did not alter depressive-like behavior or learned fear. These data demonstrate that similarly sized tumors can produce differential immune responses and that tumor-induced central pro-inflammatory cytokine production can exist in the absence of depressive-like behavior or cognitive deficits.

Depression and insomnia as mediators of the relationship between distress and quality of life in cancer patients

BACKGROUND

Distress in cancer patients leads to poorer quality of life (QOL) and negatively impacts survival. For efficient management of a patient's disease course, the interrelationships among distress, depression, insomnia, and QOL must be understood. This study aimed to investigate whether depression and insomnia mediate the relationship between distress and QOL in cancer patients.

METHODS

Cancer patients referred to a specialized psycho-oncology clinic (n=208) participated in this study. Distress, depression, insomnia, and QOL were measured with the following questionnaires: Distress Thermometer, Hospital Anxiety and Depression Scale, Insomnia Severity Index, and Functional Assessment of Cancer Therapy-General. Structural equation modeling and path analysis were performed to analyze the mediating effects of depression and insomnia on the relationship between distress and QOL.

RESULTS

Distress exerted nearly equal direct (ß=-0.291, p=0.002) and indirect (mediated by depression and insomnia) (ß=-0.299, p=0.003) negative effects on QOL. Depression exhibited the largest direct negative effect on QOL. The indirect effects of distress on QOL through depression alone, through insomnia alone, and through an insomnia to depression pathway were all significant (ß=-0.122, p=0.011; ß=-0.102, p=0.002; and ß=-0.075, p<0.001, respectively).

LIMITATIONS

The cross-sectional analyses limit the measurement of causal relationships between each variable.

CONCLUSIONS

Depression and insomnia, both individually and as part of an interrelated pathway, partially mediate the relationship between distress and QOL. Appropriate interventions to alleviate insomnia and depression may mitigate the negative impacts of distress on QOL in cancer patients.

Secular trends in Australian school children's sleep and perceived importance of sleep between 1985 and 2013

AIM

To examine secular trends in Australian children's actual sleep time as well as the perceived importance of sleep between 1985, 2004 and 2013.

METHODS

Secular trends in children's sleep and their perception of the importance of sleep across three time points 1985 (N = 401), 2004 (N = 450) and 2013 (N = 395) were examined according to socio-economic status (SES), age and sex. The children self-reported their bedtime, wake-up time and their perceived importance of sleep, among other questions.

RESULTS

There were no significant differences in sleep duration between boys and girls in any of the survey years, nor were there differences in sleep duration between SES categories at any time point. Independent of survey year, age, sex and SES, there was a graded difference in sleep duration (minutes) across response categories for perceived importance of sleep. Overall, trends in the perceived importance of sleep appeared to match trends in actual sleep time, but not for all subgroups.

CONCLUSION

This study indicates that the sleep duration of high SES Australian school children is returning to, or near to, baseline sleep duration observed in 1985, while the sleep duration of low SES Australian children has remained at low levels.

Stress-Induced Sleep After Exposure to Ultraviolet Light Is Promoted by p53 in Caenorhabditis elegans

Stress-induced sleep (SIS) in Caenorhabditis elegans is important for restoration of cellular homeostasis and is a useful model to study the function and regulation of sleep. SIS is triggered when epidermal growth factor (EGF) activates the ALA neuron, which then releases neuropeptides to promote sleep. To further understand this behavior, we established a new model of SIS using irradiation by ultraviolet C (UVC) light. While UVC irradiation requires ALA signaling and leads to a sleep state similar to that induced by heat and other stressors, it does not induce the proteostatic stress seen with heat exposure. Based on the known genotoxic effects of UVC irradiation, we tested two genes, atl-1 and cep-1, which encode proteins that act in the DNA damage response pathway. Loss-of-function mutants of atl-1 had no defect in UVC-induced SIS but a partial loss-of-function mutant of cep-1, gk138, had decreased movement quiescence following UVC irradiation. Germline ablation experiments and tissue-specific RNA interference experiments showed that cep-1 is required somatically in neurons for its effect on SIS. The cep-1(gk138) mutant suppressed body movement quiescence controlled by EGF, indicating that CEP-1 acts downstream or in parallel to ALA activation to promote quiescence in response to ultraviolet light.

Neuroinflammation and Infection: Molecular Mechanisms Associated with Dysfunction of Neurovascular Unit

Neuroinflammation is a complex inflammatory process in the central nervous system, which is sought to play an important defensive role against various pathogens, toxins or factors that induce neurodegeneration. The onset of neurodegenerative diseases and various microbial infections are counted as stimuli that can challenge the host immune system and trigger the development of neuroinflammation. The homeostatic nature of neuroinflammation is essential to maintain the neuroplasticity. Neuroinflammation is regulated by the activity of neuronal, glial, and endothelial cells within the neurovascular unit, which serves as a “platform” for the coordinated action of pro- and anti-inflammatory mechanisms. Production of inflammatory mediators (cytokines, chemokines, reactive oxygen species) by brain resident cells or cells migrating from the peripheral blood, results in the impairment of blood-brain barrier integrity, thereby further affecting the course of local inflammation. In this review, we analyzed the most recent data on the central nervous system inflammation and focused on major mechanisms of neurovascular unit dysfunction caused by neuroinflammation and infections.

Burden of sleep disturbances and associated risk factors: A cross-sectional survey among HIV-infected persons on antiretroviral therapy across China

This study evaluated the prevalence and factors associated with sleep disturbance in a large cohort of HIV-infected patients across China. A cross-sectional study was conducted among HIV-infected patients on antiretroviral therapy at 20 AIDS clinics. The Pittsburgh Sleep Quality Index was self-administered by subjects. Socio-demographic characteristics, medical history and HIV-related clinical data were collected. 4103 patients had complete data for analysis. Sleep disturbances were observed in 43.1% of patients. Associated factors in multivariable analysis included psychological factors: anxiety (odds ratio [OR], 3.13; 95% confidence interval [CI], 2.44–4.00; P < 0.001), depression (OR, 2.09; 95% CI, 1.70–2.57; P < 0.001), and both anxiety and depression (OR, 5.90; 95% CI, 4.86–7.16; P < 0.001); sociodemographic factors: MSM (OR, 1.26; 95% CI, 1.04–1.52; P = 0.018), being single (OR, 1.45; 95%CI 1.21–1.74; P < 0.001), higher education (OR, 1.25; 95% CI, 1.03–1.53; P = 0.025); and clinical factors: suboptimal adherence (OR,1.51; 95% CI,1.23–1.85; P < 0.001), regimen-switching (OR, 1.94; 95% CI, 1.12–3.35; P = 0.018), and antidepressant use (OR, 1.98; 95% CI, 1.47–2.67; P = 0.044). Prevalence of sleep disturbance is high in this large Chinese cohort. Associated factors appear related to psychological and social-demographic factors. Health workers may consider routinely assessing sleep disturbances among HIV-infected patients, especially in the first three months after HIV diagnosis, and referring for mental health services, which may positively impact adherence to treatment.

Sleep-Promoting Effects and Possible Mechanisms of Action Associated with a Standardized Rice Bran Supplement

Natural sleep aids are becoming more popular due to the widespread occurrence of sleep disorders. The objective of this study was to assess the sleep-promoting effects of rice bran—a product that is considered as a functional ingredient. To evaluate the sleep-promoting effects of a standardized rice bran supplement (RBS), we employed a pentobarbital-induced sleep test and conducted analyses of sleep architecture. In addition, the effect of RBS on a caffeine-induced sleep disturbance was investigated. Oral administration of RBS (500 and 1000 mg/kg) produced a significant decrease in sleep latency and increase in sleep duration in pentobarbital-induced sleep in mice. Moreover, both RBS (1000 mg/kg) and doxepin hydrochloride (histamine H₁ receptor antagonist, 30 mg/kg) counteracted a caffeine-induced sleep disturbance in mice. In terms of sleep phases, RBS (500 mg/kg) promoted non-rapid eye movement sleep for the first 3 h following its administration. Lastly, we unveiled a possible mechanism for RBS action as the hypnotic effect of RBS was blocked by a histamine H₁ receptor agonist. The present study revealed sleep-promoting effects of RBS using various animal assays. Such effects seem to be mediated through the histaminergic system. Our findings suggest that RBS may be a promising natural aid for relieving sleep problems.

The NLRP3 inflammasome modulates sleep and NREM sleep delta power induced by spontaneous wakefulness, sleep deprivation and lipopolysaccharide

Both sleep loss and pathogens can enhance brain inflammation, sleep, and sleep intensity as indicated by electroencephalogram delta (δ) power. The pro-inflammatory cytokine interleukin-1 beta (IL-1β) is increased in the cortex after sleep deprivation (SD) and in response to the Gram-negative bacterial cell-wall component lipopolysaccharide (LPS), although the exact mechanisms governing these effects are unknown. The nucleotide-binding domain and leucine-rich repeat protein-3 (NLRP3) inflammasome protein complex forms in response to changes in the local environment and, in turn, activates caspase-1 to convert IL-1β into its active form. SD enhances the cortical expression of the somnogenic cytokine IL-1β, although the underlying mechanism is, as yet, unidentified. Using NLRP3-gene knockout (KO) mice, we provide evidence that NLRP3 inflammasome activation is a crucial mechanism for the downstream pathway leading to increased IL-1β-enhanced sleep. NLRP3 KO mice exhibited reduced non-rapid eye movement (NREM) sleep during the light period. We also found that sleep amount and intensity (δ activity) were drastically attenuated in NLRP3 KO mice following SD (homeostatic sleep response), as well as after LPS administration, although they were enhanced by central administration of IL-1β. NLRP3, ASC, and IL1β mRNA, IL-1β protein, and caspase-1 activity were greater in the somatosensory cortex at the end of the wake-active period when sleep propensity was high and after SD in wild-type but not NLRP3 KO mice. Thus, our novel and converging findings suggest that the activation of the NLRP3 inflammasome can modulate sleep induced by both increased wakefulness and a bacterial component in the brain.

Cardiac autonomic control and complexity during sleep are preserved after chronic sleep restriction in healthy subjects

Acute sleep deprivation (SD) alters cardiovascular autonomic control (CAC) and is associated with an increased risk of cardiovascular disorders. However, the effects of partial SD on CAC are unclear. Thus, we aimed to investigate the effects of partial SD on CAC during sleep. We randomized seventeen healthy subjects to a restriction group (RES, n = 8, subjects slept two-thirds of normal sleep time based on individual habitual sleep duration for 8 days and 8 nights) or a Control group (CON, n = 9, subjects were allowed to sleep their usual sleep time). Attended polysomnographic (PSG) studies were performed every night; a subset of them was selected for the analysis at baseline (day 3-D3), the first night after sleep restriction (day 5-D5), at the end of sleep restriction period (day 11-D11), and at the end of recovery phase (day 14-D14). We extracted electrocardiogram (ECG) and respiration from the PSG and divided into wakefulness (W), nonrapid eye movements (REM) sleep (N2 and N3) and REM sleep. CAC was evaluated by means of linear spectral analysis, nonlinear symbolic analysis and complexity indexes. In both RES and CON groups, sympathetic modulation decreased and parasympathetic modulation increased during N2 and N3 compared to W and REM at D3, D5, D11, D14. Complexity analysis revealed a reduction in complexity during REM compared to NREM sleep in both DEP and CON After 8 days of moderate SD, cardiac autonomic dynamics, characterized by decreased sympathetic, and increased parasympathetic modulation, and higher cardiac complexity during NREM sleep, compared to W and REM, are preserved.

Disciplined sleep for healthy living: Role of noradrenaline

Sleep is essential for maintaining normal physiological processes. It has been broadly divided into rapid eye movement sleep (REMS) and non-REMS (NREMS); one spends the least amount of time in REMS. Sleep (both NREMS and REMS) disturbance is associated with most altered states, disorders and pathological conditions. It is affected by factors within the body as well as the environment, which ultimately modulate lifestyle. Noradrenaline (NA) is one of the key molecules whose level increases upon sleep-loss, REMS-loss in particular and it induces several REMS-loss associated effects and symptoms. The locus coeruleus (LC)-NAergic neurons are primarily responsible for providing NA throughout the brain. As those neurons project to and receive inputs from across the brain, they are modulated by lifestyle changes, which include changes within the body as well as in the environment. We have reviewed the literature showing how various inputs from outside and within the body integrate at the LC neuronal level to modulate sleep (NREMS and REMS) and vice versa. We propose that these changes modulate NA levels in the brain, which in turn is responsible for acute as well as chronic psycho-somatic disorders and pathological conditions.

Early gene activation initiates neuroinflammation prior to VSV neuroinvasion: Impact on antiviral responses and sleep

Rapid eye movement (REM) sleep is rapidly and persistently suppressed during vesicular stomatitis virus (VSV) encephalitis in C57Bl/6J (B6) mice. REM sleep suppression was associated with a complex global brain chemokine/cytokine response with bimodal kinetics although regionally distinct cytokine profiles were readily identified. Cytokine mRNA was translated either immediately or suppressed until the pathogen was cleared from the CNS. Innate signaling pathway (TLRs, RIG-I) activation occurred rapidly and sequentially prior to VSV neuroinvasion suggesting that antiviral states are quickly established in the CNS in advance of viral pathogen penetration. Il1β suppressed REM sleep mimicking aspects of VSV-induced sleep alterations whereas some robustly induced chemokines may be protective of REM. Thus, multiple brain chemokines may mediate sleep across VSV encephalitis via differential somnogenic effects.

Signs of enhanced sleep and sleep-associated memory processing following the anti-inflammatory antibiotic minocycline in men

Pro-inflammatory cytokines can promote sleep and neuronal processes underlying memory formation. However, this has mainly been revealed in animal studies. In this double-blind, placebo-controlled within-subject designed study, we examined how changes in the balance between pro- and anti-inflammatory signalling affect sleep and sleep-associated memory consolidation in humans. After learning declarative memory tasks (word pairs, texts) and a procedural memory task (finger tapping) in the evening, 21 healthy young men orally received either 200 mg of the anti-inflammatory antibiotic minocycline or placebo shortly before nocturnal sleep. Sleep was allowed between 23:00 and 07:00 h and recorded polysomnographically. Retrieval of memories was tested two days later. Because of outliers or missing data, final sample size was reduced to n = 14-19. Our data suggest that rather than weakening sleep as expected based on animal studies, the anti-inflammatory agent promoted sleep and memory consolidation. Specifically, minocycline increased slow-wave activity (0.68-4.0 Hz) during non-rapid eye movement sleep stage 2 and selectively enhanced episodic aspects in memory (i.e. memory for the temporal order of events in the texts). In combination with previous results, our findings indicate that, in humans, reducing pro-inflammatory signalling can act towards deepening non-rapid eye movement sleep and enhancing its memory forming efficacy.

Reciprocal Relationship Between Sleep Macrostructure and Evening and Morning Cellular Inflammation in Rheumatoid Arthritis

OBJECTIVE

This study examined the reciprocal associations between sleep macrostructure and levels of cellular inflammation in rheumatoid arthritis (RA) patients and controls.

METHODS

RA patients (n = 24) and matched controls (n = 48) underwent all-night polysomnography, along with assessment of spontaneous- and Toll-like receptor-4-stimulated monocytic production of tumor necrosis factor α (TNF) and interleukin (IL)-6 at 11:00 PM and 8:00 AM.

RESULTS

As compared with controls, RA patients showed lower levels of sleep efficiency (mean [standard deviation], 88.1 [6.1] versus 83.8 [7.0]), a higher percentage stage 3 sleep (9.3 [6.4] versus 13.1 [6.9]), and higher levels of percentage of monocytes either spontaneously expressing TNF at 11:00 PM (log transformed, 1.07 [0.28] versus 1.22 [0.17]), and higher Toll-like receptor-4-stimulated production of IL6 at 8:00 AM (log transformed, 3.45 [0.80] versus 3.83 [0.39]). Higher levels of stimulated production of TNF at 11:00 PM were associated with higher sleep efficiency (0.74). In turn, sleep efficiency had a countervailing relationship on TNF production at 8:00 AM (-0.64). Higher levels of spontaneous and stimulated production of IL6 at 11:00 PM were associated with more stage 3 (0.39), stage 4 (0.43), and slow-wave sleep (0.49), with evidence that stage 4 had a countervailing relationship on IL6 production at 8:00 AM (-0.60).

CONCLUSIONS

RA patients show evidence of sleep fragmentation, greater sleep depth, and higher levels of cellular inflammation. Sleep maintenance and sleep depth show countervailing relationships with evening and morning levels of monocytic production of TNF and IL-6, respectively, which support the hypothesis of a feedback loop between sleep maintenance, slow-wave sleep, and cellular inflammation that is cytokine specific.

The role of sleep in recovery following ischemic stroke: A review of human and animal data

Despite advancements in understanding the pathophysiology of stroke and the state of the art in acute management of afflicted patients as well as in subsequent neurorehabilitation training, stroke remains the most common neurological cause of long-term disability in adulthood. To enhance stroke patients' independence and well-being it is necessary, therefore, to consider and develop new therapeutic strategies and approaches. We postulate that sleep might play a pivotal role in neurorehabilitation following stroke. Over the last two decades compelling evidence for a major function of sleep in neuroplasticity and neural network reorganization underlying learning and memory has evolved. Training and learning of new motor skills and knowledge can modulate the characteristics of subsequent sleep, which additionally can improve memory performance. While healthy sleep appears to support neuroplasticity resulting in improved learning and memory, disturbed sleep following stroke in animals and humans can impair stroke outcome. In addition, sleep disorders such as sleep disordered breathing, insomnia, and restless legs syndrome are frequent in stroke patients and associated with worse recovery outcomes. Studies investigating the evolution of post-stroke sleep changes suggest that these changes might also reflect neural network reorganization underlying functional recovery. Experimental and clinical studies provide evidence that pharmacological sleep promotion in rodents and treatment of sleep disorders in humans improves functional outcome following stroke. Taken together, there is accumulating evidence that sleep represents a "plasticity state" in the process of recovery following ischemic stroke. However, to test the key role of sleep and sleep disorders for stroke recovery and to better understand the underlying molecular mechanisms, experimental research and large-scale prospective studies in humans are necessary. The effects of hospital conditions, such as adjusting light conditions according to the patients' sleep-wake rhythms, or sleep promoting drugs and non-invasive brain stimulation to promote neuronal plasticity and recovery following stroke requires further investigation.

The potential role of vagus-nerve stimulation in the treatment of HIV-associated depression: a review of literature

Depression is the most common comorbidity and neuropsychiatric complication in HIV. Estimates suggest that the prevalence rate for depression among HIV-infected individuals is three times that of the general population. The association between HIV and clinical depression is complex; however, chronic activation of inflammatory mechanisms, which disrupt central nervous system (CNS) function, may contribute to this association. Disruptions in CNS function can result in cognitive disorders, social withdrawal, fatigue, apathy, psychomotor impairment, and sleep disturbances, which are common manifestations in depression and HIV alike. Interestingly, the parasympathetic system-associated vagus nerve (VN) has primary homeostatic properties that restore CNS function following a stress or inflammatory response. Unfortunately, about 30% of adults with HIV are resistant to standard psychotherapeutic and psychopharmacological treatments for depression, thus suggesting the need for alternative treatment approaches. VN stimulation (VNS) and its benefits as a treatment for depression have been well documented, but remain unexplored in the HIV population. Historically, VNS has been delivered using a surgically implanted device; however, transcutanous VNS (tVNS) with nonsurgical auricular technology is now available. Although it currently lacks Food and Drug Administration approval in the US, evidence suggests several advantages of tVNS, including a reduced side-effect profile when compared to standard treatments and comparable results to implantable VNS in treating depression. Therefore, tVNS could offer an alternative for managing depression in HIV via regulating CNS function; moreover, tVNS may be useful for treatment of other symptoms common in HIV. From this, implications for nursing research and practice are provided.

Sleep Health: Reciprocal Regulation of Sleep and Innate Immunity

Sleep disturbances including insomnia independently contribute to risk of inflammatory disorders and major depressive disorder. This review and overview provides an integrated understanding of the reciprocal relationships between sleep and the innate immune system and considers the role of sleep in the nocturnal regulation of the inflammatory biology dynamics; the impact of insomnia complaints, extremes of sleep duration, and experimental sleep deprivation on genomic, cellular, and systemic markers of inflammation; and the influence of sleep complaints and insomnia on inflammaging and molecular processes of cellular aging. Clinical implications of this research include discussion of the contribution of sleep disturbance to depression and especially inflammation-related depressive symptoms. Reciprocal action of inflammatory mediators on the homeostatic regulation of sleep continuity and sleep macrostructure, and the potential of interventions that target insomnia to reverse inflammation, are also reviewed. Together, interactions between sleep and inflammatory biology mechanisms underscore the implications of sleep disturbance for inflammatory disease risk, and provide a map to guide the development of treatments that modulate inflammation, improve sleep, and promote sleep health.

Interleukin 37 expression in mice alters sleep responses to inflammatory agents and influenza virus infection

Multiple interactions between the immune system and sleep are known, including the effects of microbial challenge on sleep or the effects of sleep loss on facets of the immune response. Cytokines regulate, in part, sleep and immune responses. Here we examine the role of an anti-inflammatory cytokine, interleukin-37 (IL-37) on sleep in a mouse strain that expresses human IL-37b (IL37tg mice). Constitutive expression of the IL-37 gene in the brains of these mice under resting conditions is low; however, upon an inflammatory stimulus, expression increases dramatically. We measured sleep in three conditions; (a) under baseline conditions and after 6 h of sleep loss, (b) after bolus intraperitoneal administration of lipopolysaccharide (LPS) or IL-1β and (c) after intranasal influenza virus challenge. Under baseline conditions, the IL37tg mice had 7% more spontaneous non-rapid eye movement sleep (NREMS) during the light period than wild-type (WT) mice. After sleep deprivation both WT mice and IL37tg mice slept an extra 21% and 12%, respectively, during the first 6 h of recovery. NREMS responses after sleep deprivation did not significantly differ between WT mice and IL37tg mice. However, in response to either IL-1β or LPS, the increases in time spent in NREMS were about four-fold greater in the WT mice than in the IL37tg mice. In contrast, in response to a low dose of mouse-adapted H1N1 influenza virus, sleep responses developed slowly over the 6 day recording period. By day 6, NREMS increased by 10% and REMS increased by 18% in the IL37tg mice compared to the WT mice. Further, by day 4 IL37tg mice lost less weight, remained more active, and retained their body temperatures closer to baseline values than WT mice. We conclude that conditions that promote IL-37 expression attenuate morbidity to severe inflammatory challenge.

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Sleep responses to mild acute sleep deprivation are similar in mice transgenic for interleukin-37 (IL37tg) IL37tg and wild type (WT) mice.

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Sleep responses induced by either IL-β or LPS are greatly attenuated in IL37tg mice compared to WT mice.

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After influenza virus challenge, IL37tg mice have reduced morbidities and enhanced sleep responses.

Reduced expression of α5GABAA receptors elicits autism-like alterations in EEG patterns and sleep-wake behavior

A reduction in the activity of GABA_A receptors, particularly α5 subunit-containing GABA_A receptors (α5GABA_ARs), has been implicated in the etiology of Autism Spectrum Disorders (ASD). Genetically modified mice that lack α5GABA_ARs (Gabra5^-/-) exhibit autism-like behaviors and both enhanced and impaired learning and memory, depending on the behavioral task. The aim of this study was to examine the electroencephalogram (EEG) activity and sleep-wake behaviors in Gabra5^-/- mice and wild-type mice. In addition, since some individuals with ASD can exhibit elevated innate immune response, mice were treated with lipopolysaccharide (LPS; 125mg/kg intraperitoneal injection) or vehicle and EEG and sleep-wake patterns were assessed. The results showed that Gabra5^-/- mice (n=3) exhibited elevated 0-2Hz EEG activity during all sleep-wake states (all p<0.04), decreased 8-12Hz EEG activity during REM sleep (p=0.04), and decreased sleep spindles under baseline conditions compared to wild-type controls (n=4) (all p≤0.03). Alterations in EEG activity and sleep-wake behavior were identified in Gabra5^-/- mice following treatment with LPS, however these changes were similar to those in wild-type mice. Our findings support the hypothesis that reduced α5GABA_AR activity contributes to an ASD phenotype. The results also suggest that Gabra5^-/- mice may serve as an animal model for ASD, as assessed through EEG activity and sleep-wake behaviors.

Estimating individual optimal sleep duration and potential sleep debt

In this study, we hypothesized that dynamics of sleep time obtained over consecutive days of extended sleep in a laboratory reflect an individual's optimal sleep duration (OSD) and that the difference between OSD and habitual sleep duration (HSD) at home represents potential sleep debt (PSD). We found that OSD varies among individuals and PSD showed stronger correlation with subjective/objective sleepiness than actual sleep time, interacting with individual's vulnerability of sleep loss. Furthermore, only 1 h of PSD takes four days to recover to their optimal level. Recovery from PSD was also associated with the improvement in glycometabolism, thyrotropic activity and hypothalamic-pituitary-adrenocortical axis. Additionally, the increase (rebound) in total sleep time from HSD at the first extended sleep would be a simple indicator of PSD. These findings confirmed self-evaluating the degree of sleep debt at home as a useful clinical marker. To establish appropriate sleep habits, it is necessary to evaluate OSD, vulnerability to sleep loss, and sleep homeostasis characteristics on an individual basis.

Elevated serum concentrations of lipopolysaccharide binding protein might prolong sleep stage one in middle-aged hypertensive males

PURPOSE

Sleep architecture can be affected by alteration in circulating lipopolysaccaride and cytokines. However, still unknown are the effects of lipopolysaccaride-binding protein (LBP) on sleep architecture. Therefore, potential relationship between alteration in serum LBP concentrations and sleep architecture was analyzed.

METHODS

This is a cross-sectional study. Consecutive 54 hypertensive males, aged 30-65 years. and with no obstructive sleep apnea via polysomnography, were recruited. Subjects were divided into two groups via the LBP median as hypertensives with higher and lower serum LBP (n = 27 and n = 27, respectively). Sleep architecture was assessed by polysomnography. Serum LBP, IL-1β, IL-6, and TNF-α were measured by commercial laboratories using sandwich-type enzyme immunoassay kit.

RESULTS

Hypertensive subjects with higher LBP showed significantly higher inflammatory status as assessed by IL-1β (18.85 ± 3.71 vs 16.15 ± 4.00 ng/L, P = 0.009), IL-6 (67.64 ± 11.22 vs 58.94 ± 11.32 ng/L, P = 0.004), and TNF-α (322.27 ± 59.17 vs 283.89 ± 61.87 pg/ml, P = 0.024) than did those with lower LBP. Hypertensives with higher serum LBP also exhibited prolonged N1 % (7.63 ± 3.55 vs 4.98 ± 2.90 %, P = 0.002), the transition from wakefulness to other sleep stages or follows arousal during sleep, than did those with lower LBP. A significant positive correlation was observed between serum LBP concentrations and N1 % (r = 0.378, P = 0.005) via Spearman's correlation and remained significant even after adjusting for age, apnea-hypopnea index, and body mass index.

CONCLUSION

Elevation in serum concentrations of LBP might prolong N1 % in this middle-aged hypertensive males, which needs to be confirmed further.

Hypocretin/orexin loss changes the hypothalamic immune response

Hypocretin, also known as orexin, maintains the vigilance state and regulates various physiological processes, such as arousal, sleep, food intake, energy expenditure, and reward. Previously, we found that when wild-type mice and hypocretin/ataxin-3 littermates (which are depleted of hypothalamic hypocretin-expressing neurons postnatally) were administered lipopolysaccharide (LPS), the two genotypes exhibited significant differences in their sleep/wake cycle, including differences in the degree of increase in sleep periods and in recovery from sickness behaviour. In the present study, we examined changes in the hypothalamic vigilance system and in the hypothalamic expression of inflammatory factors in response to LPS in hypocretin/ataxin-3 mice. Peripheral immune challenge with LPS affected the hypothalamic immune response and vigilance states. This response was altered by the loss of hypocretin. Hypocretin expression was inhibited after LPS injection in both hypocretin/ataxin-3 mice and their wild-type littermates, but expression was completely abolished only in hypocretin/ataxin-3 mice. Increases in the number of histidine decarboxylase (HDC)-positive cells and in Hdc mRNA expression were found in hypocretin/ataxin-3 mice, and this increase was suppressed by LPS. Hypocretin loss did not impact the change in expression of hypothalamic inflammatory factors in response to LPS, except for interferon gamma and colony stimulating factor 3. The number of c-Fos-positive/HDC-positive cells in hypocretin/ataxin-3 mice administered LPS injections was elevated, even during the rest period, in all areas, suggesting that there is an increase in the activity of histaminergic neurons in hypocretin/ataxin-3 mice following LPS injection. Taken together, our results suggest a novel role for hypocretin in the hypothalamic response to peripheral immune challenge. Our findings contribute to the understanding of the pathophysiology of narcolepsy.

Increased serum interleukin-6, not minimal hepatic encephalopathy, predicts poor sleep quality in nonalcoholic cirrhotic patients

BACKGROUND

Sleep-wake disturbances are common in patients with cirrhosis and have a considerable effect on health-related quality of life; however, the underlying mechanism behind the phenomenon is unclear. Cytokines are involved in the mediation of signalling pathways regulating fibrogenesis, leading to cirrhosis. In addition, increased cytokines could contribute to sleep disturbances.

AIM

To determine the relationship between pro-inflammatory cytokines and sleep disturbance in cirrhotic patients.

METHODS

Ninety-eight nonalcoholic cirrhotic patients without overt hepatic encephalopathy were enrolled in this cross-sectional study. The Pittsburgh Sleep Quality Index (PSQI) was used to assess sleep quality. The Psychometric Hepatic Encephalopathy Score (PHES) was used to examine cognitive performance and define minimal hepatic encephalopathy (MHE). The Hospital Anxiety and Depression Scale (HADS) was used to evaluate the mood status of the patients. Pro-inflammatory cytokines that include interleukin 6 (IL-6) and tumour necrosis factor-α, as well as HBV-DNA or HCV-RNA levels were determined in patients.

RESULTS

A total of 56 (57%) cirrhotic patients were identified as 'poor' sleepers (PSQI > 5). After multivariate analysis, IL-6 (P = 0.001) and HADS scores (P = 0.002) were found to be independent predictive factors of poor sleep quality. No significant relationships were observed between the sleep indices and the presence of MHE. HCV-RNA, but not HBV-DNA, viraemia was associated with sleep disturbance in cirrhotic patients.

CONCLUSIONS

Sleep disturbance is found commonly in cirrhotic patients and a high serum IL-6 level is predictive of poor sleep quality. Minimal hepatic encephalopathy by itself may not contribute to sleep dysfunction in cirrhotic patients.

Enhanced sleep reverses memory deficits and underlying pathology in Drosophila models of Alzheimer's disease

To test the hypothesis that sleep can reverse cognitive impairment during Alzheimer's disease, we enhanced sleep in flies either co-expressing human amyloid precursor protein and Beta-secretase (APP:BACE), or in flies expressing human tau. The ubiquitous expression of APP:BACE or human tau disrupted sleep. The sleep deficits could be reversed and sleep could be enhanced when flies were administered the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Expressing APP:BACE disrupted both Short-term memory (STM) and Long-term memory (LTM) as assessed using Aversive Phototaxic Suppression (APS) and courtship conditioning. Flies expressing APP:BACE also showed reduced levels of the synaptic protein discs large (DLG). Enhancing sleep in memory-impaired APP:BACE flies fully restored both STM and LTM and restored DLG levels. Sleep also restored STM to flies expressing human tau. Using live-brain imaging of individual clock neurons expressing both tau and the cAMP sensor Epac1-camps, we found that tau disrupted cAMP signaling. Importantly, enhancing sleep in flies expressing human tau restored proper cAMP signaling. Thus, we demonstrate that sleep can be used as a therapeutic to reverse deficits that accrue during the expression of toxic peptides associated with Alzheimer's disease.

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THIP can be used to enhance sleep in two Drosophila models of Alzheimer's disease.

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Enhanced sleep reverses memory deficits in fly's expressing human APP:BACE and tau.

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Enhanced sleep restores cAMP levels in clock neurons expressing tau.

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Sleep can be used as a therapeutic to reverse Alzheimer's disease related deficits.

Sleep and Microbes

Sleep is profoundly altered during the course of infectious diseases. The typical response to infection includes an initial increase in nonrapid eye movement sleep (NREMS) followed by an inhibition in NREMS. REMS is inhibited during infections. Bacterial cell wall components, such as peptidoglycan and lipopolysaccharide, macrophage digests of these components, such as muramyl peptides, and viral products, such as viral double-stranded RNA, trigger sleep responses. They do so via pathogen-associated molecular pattern recognition receptors that, in turn, enhance cytokine production. Altered sleep and associated sleep-facilitated fever responses are likely adaptive responses to infection. Normal sleep in physiological conditions may also be influenced by gut microbes because the microbiota is affected by circadian rhythms, stressors, diet, and exercise. Furthermore, sleep loss enhances translocation of viable bacteria from the intestine, which provides another means by which sleep-microbe interactions impact neurobiology.

Sleep function: Toward elucidating an enigma

Sleep function remains controversial. Individual perspectives frame the issue of sleep function differently. We briefly illustrate how sleep measurement and the evolution, tissue organization levels, molecular mechanisms, and regulation of sleep could influence one's view of sleep function. Then we discuss six viable theories of sleep function. Sleep serves host-defense mechanisms and conserves caloric expenditures, but these functions likely are opportunistic functions evolving later in evolution. That sleep replenishes brain energy stores and that sleep serves a glymphatic function by removing toxic byproducts of waking activity are attractive ideas, but lack extensive supporting experimental evidence. That sleep restores performance is experimentally demonstrated and has obvious evolutionary value. However, this hypothesis lacks experimentally verified mechanisms although ideas relating to this issue are presented. Finally, the ideas surrounding the broad hypothesis that sleep serves a connectivity/plasticity function are many and attractive. There is experimental evidence that connectivity changes with sleep, sleep loss, and with changing afferent input, and that those changes are linked to sleep regulatory mechanisms. In our view, this is the leading contender for the primordial function of sleep. However, much refinement of ideas and innovative experimental approaches are needed to clarify the sleep-connectivity relationship.

Potential pleiotropic beneficial effects of adjuvant melatonergic treatment in posttraumatic stress disorder

Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune, and autonomic system, similar to chronic stress and may play a central role in the development of stress-related disorders. Recent articles have focused on the role of sleep and circadian disruption in the pathophysiology of posttraumatic stress disorder (PTSD), suggesting that chronodisruption plays a causal role in PTSD development. Direct and indirect human and animal PTSD research suggests circadian system-linked neuroendocrine, immune, metabolic and autonomic dysregulation, linking circadian misalignment to PTSD pathophysiology. Recent experimental findings also support a specific role of the fundamental synchronizing pineal hormone melatonin in mechanisms of sleep, cognition and memory, metabolism, pain, neuroimmunomodulation, stress endocrinology and physiology, circadian gene expression, oxidative stress and epigenetics, all processes affected in PTSD. In the current paper, we review available literature underpinning a potentially beneficiary role of an add-on melatonergic treatment in PTSD pathophysiology and PTSD-related symptoms. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. We conclude that adjuvant melatonergic treatment could provide a potentially promising treatment strategy in the management of PTSD and especially PTSD-related syndromes and comorbidities. Rigorous preclinical and clinical studies are needed to validate this hypothesis.

Fatigue with up- vs downregulated brain arousal should not be confused

Fatigue is considered to be an important and frequent factor in motivation problems. However, this term lacks clinical and pathophysiological validity. Semantic precision has to be improved. Lack of drive and tiredness with increased sleepiness as observed in fatigue in the context of inflammatory and immunological processes (hypoaroused fatigue) has to be separated from inhibition of drive and tiredness with prolonged sleep onset latency as observed in major depression (hyperaroused fatigue). Subjective experiences as reported by patients, as well as clinical, behavioral, and neurobiological findings support the validity and importance of this distinction. A practical clinical procedure for how to separate hypo- from hyperaroused fatigue will be proposed.

Disruption of the astrocytic TNFR1-GDNF axis accelerates motor neuron degeneration and disease progression in amyotrophic lateral sclerosis

Considerable evidence indicates that neurodegeneration in amyotrophic lateral sclerosis (ALS) can be conditioned by a deleterious interplay between motor neurons and astrocytes. Astrocytes are the major glial component in the central nervous system (CNS) and fulfill several activities that are essential to preserve CNS homeostasis. In physiological and pathological conditions, astrocytes secrete a wide range of factors by which they exert multimodal influences on their cellular neighbours. Among others, astrocytes can secrete glial cell line-derived neurotrophic factor (GDNF), one of the most potent protective agents for motor neurons. This suggests that the modulation of the endogenous mechanisms that control the production of astrocytic GDNF may have therapeutic implications in motor neuron diseases, particularly ALS. In this study, we identified TNF receptor 1 (TNFR1) signalling as a major promoter of GDNF synthesis/release from human and mouse spinal cord astrocytes in vitro and in vivo To determine whether endogenously produced TNFα can also trigger the synthesis of GDNF in the nervous system, we then focused on SOD1^G93A ALS transgenic mice, whose affected tissues spontaneously exhibit high levels of TNFα and its receptor 1 at the onset and symptomatic stage of the disease. In SOD1^G93A spinal cords, we verified a strict correlation in the expression of the TNFα, TNFR1 and GDNF triad at different stages of disease progression. Yet, ablation of TNFR1 completely abolished GDNF rises in both SOD1^G93A astrocytes and spinal cords, a condition that accelerated motor neuron degeneration and disease progression. Our data suggest that the astrocytic TNFR1-GDNF axis represents a novel target for therapeutic intervention in ALS.

Neuroinflammation: the devil is in the details

There is significant interest in understanding inflammatory responses within the brain and spinal cord. Inflammatory responses that are centralized within the brain and spinal cord are generally referred to as 'neuroinflammatory'. Aspects of neuroinflammation vary within the context of disease, injury, infection, or stress. The context, course, and duration of these inflammatory responses are all critical aspects in the understanding of these processes and their corresponding physiological, biochemical, and behavioral consequences. Microglia, innate immune cells of the CNS, play key roles in mediating these neuroinflammatory responses. Because the connotation of neuroinflammation is inherently negative and maladaptive, the majority of research focus is on the pathological aspects of neuroinflammation. There are, however, several degrees of neuroinflammatory responses, some of which are positive. In many circumstances including CNS injury, there is a balance of inflammatory and intrinsic repair processes that influences functional recovery. In addition, there are several other examples where communication between the brain and immune system involves neuroinflammatory processes that are beneficial and adaptive. The purpose of this review is to distinguish different variations of neuroinflammation in a context-specific manner and detail both positive and negative aspects of neuroinflammatory processes. In this review, we will use brain and spinal cord injury, stress, aging, and other inflammatory events to illustrate the potential harm and benefits inherent to neuroinflammation. Context, course, and duration of the inflammation are highly important to the interpretation of these events, and we aim to provide insight into this by detailing several commonly studied insults. This article is part of the 60th anniversary supplemental issue.

Functions and Mechanisms of Sleep

Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. Currently, all researchers agree there is no single physiological role sleep serves. Nevertheless, it is quite evident that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state. This review details the physiological processes involved in sleep regulation and the possible functions that sleep may serve. This description of the brain circuitry, cell types, and molecules involved in sleep regulation is intended to further the reader's understanding of the functions of sleep.

Changes in Neuronal Excitability by Activated Microglia: Differential Na(+) Current Upregulation in Pyramid-Shaped and Bipolar Neurons by TNF-α and IL-18

Microglia are activated during pathological events in the brain and are capable of releasing various types of inflammatory cytokines. Here, we demonstrate that the addition of 5% microglia activated by 1 μg/ml lipopolysaccharides (LPS) to hippocampal cultures upregulates Na⁺ current densities (I_NavD) of bipolar as well as pyramid-shaped neurons, thereby increasing their excitability. Deactivation of microglia by the addition of 10 ng/ml transforming growth factor-β (TGF-β) decreases I_NavD below control levels suggesting that the residual activated microglial cells influence neuronal excitability in control cultures. Preincubation of hippocampal cultures with 10 ng/ml tumor necrosis factor-α (TNF-α), a major cytokine released by activated microglia, upregulated I_NavD significantly by ~30% in bipolar cells, whereas in pyramid-shaped cells, the upregulation only reached an increase of ~14%. Incubation of the cultures with antibodies against either TNF-receptor 1 or 2 blocked the upregulation of I_NavD in bipolar cells, whereas in pyramid-shaped cells, increases in I_NavD were exclusively blocked by antibodies against TNF-receptor 2, suggesting that both cell types respond differently to TNF-α exposure. Since additional cytokines, such as interleukin-18 (IL-18), are released from activated microglia, we tested potential effects of IL-18 on I_NavD in both cell types. Exposure to 5–10 ng/ml IL-18 for 4 days increased I_NavD in both pyramid-shaped as well as bipolar neurons, albeit the dose–response curves were shifted to lower concentrations in bipolar cells. Our results suggest that by secretion of cytokines, microglial cells upregulate Na⁺ current densities in bipolar and pyramid-shaped neurons to some extent differentially. Depending on the exact cytokine composition and concentration released, this could change the balance between the activity of inhibitory bipolar and excitatory pyramid-shaped cells. Since bipolar cells show a larger upregulation of I_NavD in response to TNF-α as well as respond to smaller concentrations of IL-18, our results offer an explanation for the finding, that in certain conditions of brain inflammations periods of dizziness are followed by epileptic seizures.

The role of interleukin-6 signaling in nervous tissue

The cytokine interleukin-6 (IL-6) plays a critical role in the pathogenesis of inflammatory disorders and in the physiological homeostasis of neural tissue. Profound neuropathological changes, such as multiple sclerosis (MS), Parkinson's and Alzheimer's disease are associated with increased IL-6 expression in brain. Increased nocturnal concentrations of serum IL-6 are found in patients with impaired sleep whereas IL-6-deficient mice spend more time in rapid eye movement sleep associated with dreaming. IL-6 is crucial in the differentiation of oligodendrocytes, regeneration of peripheral nerves and acts as a neurotrophic factor. It exerts its cellular effects through two distinct pathways which include the anti-inflammatory pathway involving the membrane-bound IL-6 receptor (IL-6R) expressed on selective cells, including microglia, in a process known as classical signaling that is also critical for bacterial defense. In classical signaling binding of IL-6 to the membrane-bound IL-6R activates the β-receptor glycoprotein 130 (gp130) and subsequent down-stream signaling. The alternative, rather pro-inflammatory pathway, shown to mediate neurodegeneration in mice, termed trans-signaling, depends on a soluble form of the IL-6R that is capable of binding IL-6 to stimulate a response on distal cells that express gp130. A naturally occurring soluble form of gp130 (sgp130) has been identified that can specifically bind and neutralize the IL-6R/IL-6 complex. Thus, trans-signaling is blocked but classical signaling is completely unaffected. A modified, recombinant dimerized version of sgp130 (sgp130Fc) has successfully been used to block inflammatory processes in mice and may also be used in the clarification of IL-6 trans-signaling in neurological diseases.

Nocturnal Pruritus: The Battle for a Peaceful Night's Sleep

Chronic pruritus is a debilitating condition with numerous etiologies. Many patients suffer from nocturnal pruritus, which can decrease quality of life and affect mortality in hemodialysis patients. Nocturnal pruritus may occur in all sleep stages but is most prevalent in stages N1 and N2. Further research is needed to elucidate the pathophysiology of nocturnal itch, which will aid in the development of tailored management strategies.

Sleep and immunomodulatory responses to systemic lipopolysaccharide in mice selectively expressing interleukin-1 receptor 1 on neurons or astrocytes

Sleep-wake behavior is altered in response to immune challenge. Although the precise mechanisms that govern sickness-induced changes in sleep are not fully understood, interleukin-1β (IL-1) is one mediator of these responses. To better understand mechanisms underlying sleep and inflammatory responses to immune challenge, we used two transgenic mouse strains that express IL-1 receptor 1 (IL1R1) only in the central nervous system and selectively on neurons or astrocytes. Electroencephalographic recordings from transgenic and wild-type mice reveal that systemic challenge with lipopolysaccharide (LPS) fragments sleep, suppresses rapid eye movement sleep (REMS), increases non-REMS (NREMS), diminishes NREM delta power, and induces fever in all genotypes. However, the magnitude of REMS suppression is greater in mice expressing IL1R1 on astrocytes compared with mice in which IL1R1 is selectively expressed on neurons. Furthermore, there is a delayed increase in NREM delta power when IL1R1 is expressed on astrocytes. LPS-induced sleep fragmentation is reduced in mice expressing IL1R1 on neurons. Although LPS increases IL-1 and IL-6 in brain of all genotypes, this response is attenuated when IL1R1 is expressed selectively on neurons or on astrocytes. Collectively, these data suggest that in these transgenic mice under the conditions of this study it is neuronal IL1R1 that plays a greater role in LPS-induced suppression of REMS and NREM delta power, whereas astroglial IL1R1 is more important for sleep fragmentation after this immune challenge. Thus, aspects of central responses to LPS are modulated by IL1R1 in a cell type-specific manner.

Depression in Autoimmune Diseases

Up to 50% of patients with autoimmune diseases show an impairment of health-related quality of life and exhibit depression-like symptoms. The immune system not only leads to inflammation in affected organs, but also mediates behavior abnormalities including fatigue and depression-like symptoms. This review focuses on the different pathways involved in the communication of the immune system with the neuronal network and the body's timing system. The latter is built up by a hierarchically organized expression of clock genes. As discussed here, the activation of the immune system interferes with high amplitude expression of clock genes, an effect which may play a pivotal role in depression-like behavior in autoimmune diseases.

Call it Worm Sleep

The nematode Caenorhabditis elegans stops feeding and moving during a larval transition stage called lethargus and following exposure to cellular stressors. These behaviors have been termed 'sleep-like states'. We argue that these behaviors should instead be called sleep. Sleep during lethargus is similar to sleep regulated by circadian timers in insects and mammals, and sleep in response to cellular stress is similar to sleep induced by sickness in other animals. Sleep in mammals and Drosophila shows molecular and functional conservation with C. elegans sleep. The simple neuroanatomy and powerful genetic tools of C. elegans have yielded insights into sleep regulation and hold great promise for future research into sleep regulation and function.

Peripheral and central blockade of interleukin-6 trans-signaling differentially affects sleep architecture

The immune system is known to essentially contribute to the regulation of sleep. Whereas research in this regard focused on the pro-inflammatory cytokines interleukin-1 and tumor necrosis factor, the role of interleukin-6 (IL-6) in sleep regulation has been less intensely studied, probably due to the so far seemingly ambiguous results. Yet, this picture might simply reflect that the effects of IL-6 are conveyed via two different pathways (with possibly different actions), i.e., in addition to the 'classical' signaling pathway via the membrane bound IL-6 receptor (IL-6R), IL-6 stimulates cells through the alternative 'trans-signaling' pathway via the soluble IL-6R. Here, we concentrated on the contributions of the trans-signaling pathway to sleep regulation. To characterize this contribution, we compared the effect of blocking IL-6 trans-signaling (by the soluble gp130Fc fusion protein) in the brain versus body periphery. Thus, we compared sleep in transgenic mice expressing the soluble gp130Fc protein only in the brain (GFAP mice) or in the body periphery (PEPCK mice), and in wild type mice (WT) during a 24-h period of undisturbed conditions and during 18 h following a 6-h period of sleep deprivation. Compared with WT mice, PEPCK mice displayed less sleep, particularly during the late light phase, and this was accompanied by decreases in slow wave sleep (SWS) and rapid eye movement (REM) sleep. Following sleep deprivation PEPCK mice primarily recovered REM sleep rather than SWS. GFAP mice showed a slight decrease in REM sleep in combination with a profound and persistent increase in EEG theta activity. In conclusion, peripheral and central nervous IL-6 trans-signaling differentially influences brain activity. Peripheral IL-6 trans-signaling appears to more profoundly contribute to sleep regulation, mainly by supporting SWS.

Sleep fragmentation and sepsis differentially impact blood-brain barrier integrity and transport of tumor necrosis factor-α in aging

The factors by which aging predisposes to critical illness are varied, complex, and not well understood. Sepsis is considered a quintessential disease of old age because the incidence and mortality of severe sepsis increases in old and the oldest old individuals. Aging is associated with dramatic changes in sleep quality and quantity and sleep increasingly becomes fragmented with age. In healthy adults, sleep disruption induces inflammation. Multiple aspects of aging and of sleep dysregulation interact via neuroimmune mechanisms. Tumor necrosis factor-α (TNF), a cytokine involved in sleep regulation and neuroimmune processes, exerts some of its effects on the CNS by crossing the blood-brain barrier (BBB). In this study we examined the impact of sepsis, sleep fragmentation, and aging on BBB disruption and TNF transport into brain. We used the cecal ligation and puncture (CLP) model of sepsis in young and aged mice that were either undisturbed or had their sleep disrupted. There was a dichotomous effect of sepsis and sleep disruption with age: sepsis disrupted the BBB and increased TNF transport in young mice but not in aged mice, whereas sleep fragmentation disrupted the BBB and increased TNF transport in aged mice, but not in young mice. Combining sleep fragmentation and CLP did not produce a greater effect on either of these BBB parameters than did either of these manipulations alone. These results suggest that the mechanisms by which sleep fragmentation and sepsis alter BBB functions are fundamentally different from one another and that a major change in the organism's responses to those insults occurs with aging.

Optogenetic stimulation of astrocytes in the posterior hypothalamus increases sleep at night in C57BL/6J mice

A distributed network of neurons regulates wake, non‐rapid eye movement (NREM) sleep, and REM sleep. However, there are also glia in the brain, and there is growing evidence that neurons and astroglia communicate intimately to regulate behaviour. To identify the effect of optogenetic stimulation of astrocytes on sleep, the promoter for the astrocyte‐specific cytoskeletal protein, glial fibrillary acidic protein (GFAP) was used to direct the expression of channelrhodopsin‐2 (ChR2) and the linked reporter gene, enhanced yellow fluorescent protein (EYFP), in astrocytes. rAAV‐GFAP‐ChR2 (H134R)‐EYFP or rAAV‐GFAP‐EYFP was microinjected (750 nL) into the posterior hypothalamus (bilateral) of mice. Three weeks later baseline sleep was recorded (0 Hz) and 24 h later optogenetic stimulation applied during the first 6 h of the lights‐off period. Mice with ChR2 were given 5, 10 or 30 Hz stimulation for 6 h (10‐ms pulses; 1 mW; 1 min on 4 min off). At least 36 h elapsed between the stimulation periods (5, 10, 30 Hz) and although 0 Hz was always first, the order of the other three stimulation rates was randomised. In mice with ChR2 (n = 7), 10 Hz, but not 5 or 30 Hz stimulation increased both NREM and REM sleep during the 6‐h period of stimulation. Delta power did not increase. In control mice (no ChR2; n = 5), 10 Hz stimulation had no effect. This study demonstrates that direct stimulation of astrocytes powerfully induces sleep during the active phase of the sleep–wake cycle and underlines the inclusion of astrocytes in network models of sleep–wake regulation.

Chrono-immunology: progress and challenges in understanding links between the circadian and immune systems

Development of inflammatory diseases, such as metabolic syndrome and cancer, is prevalent in individuals that encounter continuous disruption of their internal clock. Further, daily oscillations in susceptibility to infection as well as a multitude of other immunological processes have been described. Much progress has been made and various mechanisms have been proposed to explain circadian variations in immunity; yet much is still unknown. Understanding the crosstalk between the circadian and the immune systems will allow us to manipulate clock outputs to prevent and treat inflammatory diseases in individuals at risk. This review briefly summarizes current knowledge about circadian rhythms and their role in the immune system and highlights progress and challenges in chrono-immunological research.