Cytokine- and microbially induced sleep responses of interleukin-10 deficient mice

Cyclooxygenase-2 (COX-2)-dependent mechanisms mediate sleep responses to microbial and thermal stimuli

Prostaglandins (PGs) play a crucial role in sleep regulation, yet the broader physiological context that leads to the activation of the prostaglandin-mediated sleep-promoting system remains elusive. In this study, we explored sleep-inducing mechanisms potentially involving PGs, including microbial, immune and thermal stimuli as well as homeostatic sleep responses induced by short-term sleep deprivation using cyclooxygenase-2 knockout (COX-2 KO) mice and their wild-type littermates (WT). Systemic administration of 0.4 µg lipopolysaccharide (LPS) induced increased non-rapid-eye movement sleep (NREMS) and fever in WT animals, these effects were completely absent in COX-2 KO mice. This finding underscores the essential role of COX-2-dependent prostaglandins in mediating sleep and febrile responses to LPS. In contrast, the sleep and fever responses induced by tumor necrosis factor α, a proinflammatory cytokine which activates COX-2, were preserved in COX-2 KO animals, indicating that these effects are independent of COX-2-related signaling. Additionally, we examined the impact of ambient temperature on sleep. The sleep-promoting effects of moderate warm ambient temperature were suppressed in COX-2 KO animals, resulting in significantly reduced NREMS at ambient temperatures of 30 °C and 35 °C compared to WT mice. However, rapid-eye-movement sleep responses to moderately cold or warm temperatures did not differ between the two genotypes. Furthermore, 6 h of sleep deprivation induced rebound increases in sleep with no significant differences observed between COX-2 KO and WT mice. This suggests that while COX-2-derived prostaglandins are crucial for the somnogenic effects of increased ambient temperature, the homeostatic responses to sleep loss are COX-2-independent. Overall, the results highlight the critical role of COX-2-derived prostaglandins as mediators of the sleep-wake and thermoregulatory responses to various physiological challenges, including microbial, immune, and thermal stimuli. These findings emphasize the interconnected regulation of body temperature and sleep, with peripheral mechanisms emerging as key players in these integrative processes.

Gut microbiota and sleep: Interaction mechanisms and therapeutic prospects

Sleep is crucial for wellness, and emerging research reveals a profound connection to gut microbiota. This review explores the bidirectional relationship between gut microbiota and sleep, exploring the mechanisms involved and the therapeutic opportunities it presents. The gut-brain axis serves as a conduit for the crosstalk between gut microbiota and the central nervous system, with dysbiosis in the microbiota impairing sleep quality and vice versa. Diet, circadian rhythms, and immune modulation all play a part. Specific gut bacteria, like Lactobacillus and Bifidobacterium, enhance sleep through serotonin and gamma-aminobutyric acid production, exemplifying direct microbiome influence. Conversely, sleep deprivation reduces beneficial bacteria, exacerbating dysbiosis. Probiotics, prebiotics, postbiotics, and fecal transplants show therapeutic potential, backed by animal and human research, yet require further study on safety and long-term effects. Unraveling this intricate link paves the way for tailored sleep therapies, utilizing microbiome manipulation to improve sleep and health. Accelerated research is essential to fully tap into this promising field for sleep disorder management.

Microglia Are Necessary to Regulate Sleep after an Immune Challenge

Microglia play a critical role in the neuroimmune response, but little is known about the role of microglia in sleep following an inflammatory trigger. Nevertheless, decades of research have been predicated on the assumption that an inflammatory trigger increases sleep through microglial activation. We hypothesized that mice (n = 30) with depleted microglia using PLX5622 (PLX) would sleep less following the administration of lipopolysaccharide (LPS) to induce inflammation. Brains were collected and microglial morphology was assessed using quantitative skeletal analyses and physiological parameters were recorded using non-invasive piezoelectric cages. Mice fed PLX diet had a transient increase in sleep that dissipated by week 2. Subsequently, following a first LPS injection (0.4 mg/kg), mice with depleted microglia slept more than mice on the control diet. All mice were returned to normal rodent chow to repopulate microglia in the PLX group (10 days). Nominal differences in sleep existed during the microglia repopulation period. However, following a second LPS injection, mice with repopulated microglia slept similarly to control mice during the dark period but with longer bouts during the light period. Comparing sleep after the first LPS injection to sleep after the second LPS injection, controls exhibited temporal changes in sleep patterns but no change in cumulative minutes slept, whereas cumulative sleep in mice with repopulated microglia decreased during the dark period across all days. Repopulated microglia had a reactive morphology. We conclude that microglia are necessary to regulate sleep after an immune challenge.

Pannexin 1 Transgenic Mice: Human Diseases and Sleep-Wake Function Revision

In humans and other vertebrates pannexin protein family was discovered by homology to invertebrate gap junction proteins. Several biological functions were attributed to three vertebrate pannexins members. Six clinically significant independent variants of the PANX1 gene lead to human infertility and oocyte development defects, and the Arg217His variant was associated with pronounced symptoms of primary ovarian failure, severe intellectual disability, sensorineural hearing loss, and kyphosis. At the same time, only mild phenotypes were observed in Panx1 knockout mice. In addition, a passenger mutation was identified in a popular line of Panx1 knockout mice, questioning even those effects. Using CRISPR/Cas9, we created a new line of Panx1 knockout mice and a new line of mice with the clinically significant Panx1 substitution (Arg217His). In both cases, we observed no significant changes in mouse size, weight, or fertility. In addition, we attempted to reproduce a previous study on sleep/wake and locomotor activity functions in Panx1 knockout mice and found that previously reported effects were probably not caused by the Panx1 knockout itself. We consider that the pathological role of Arg217His substitution in Panx1, and some Panx1 functions in general calls for a re-evaluation.

Lipoteichoic acid, a cell wall component of Gram-positive bacteria, induces sleep and fever and suppresses feeding

Fragments of the bacterial cell wall are bioactive microbial molecules that have profound effects on the function of the brain. Some of the cell wall constituents are common to both Gram-positive and Gram-negative bacteria, e.g., peptidoglycans, while other cell wall components are specific to either Gram-positive or Gram-negative microbes. Lipopolysaccharide (LPS), also called endotoxin, is found exclusively in Gram-negative bacteria, while lipoteichoic acid (LTA) is specific to Gram-positive bacteria. The effects of peptidoglycans, their fragments, and LPS are well characterized, they induce sleep, fever and anorexia. In the present study, we investigated the sleep, body temperature and food intake modulating effects of LTA. We found that intraperitoneal injection of 100 and 250 μg LTA from B. subtilis and S. aureus increases non-rapid-eye movement sleep (NREMS) in mice. The effects were dose-dependent, and the changes were accompanied by decreased motor activity and feeding as well as febrile responses. Intraperitoneal injection of 10 μg LTA induced monophasic increases in body temperature, while 100 and 250 μg LTA from B. subtilis induced initial hypothermia followed by fever. Treatment with 250 μg LTA from S. aureus elicited monophasic hypothermia. Administration of 300 μg/kg LTA from S. aureus directly into the portal vein elicited similar sleep responses in rats but did not affect body temperature. The sleep-modulating effects of LTA were similar to that of LPS in mice, although LTA appears to be less potent. These findings suggest that the role of LTA in signaling by Gram-positive bacteria in the host body is analogous to the role of LPS/endotoxin in signaling by Gram-negative microbes. LTA may play a role in the development of sickness response in clinically manifest Gram-positive bacterial infections and may contribute to sleep signaling by the commensal intestinal microbiota.

Sleep and body temperature in TNFα knockout mice: The effects of sleep deprivation, β3-AR stimulation and exogenous TNFα

Increased production of pro-inflammatory cytokines is assumed to mediate increased sleep under inflammatory conditions, such as systemic infections or recovery from sleep loss. The role of cytokines in sleep regulation under normal conditions is less clear. In the present study, we investigated the role of endogenous tumor necrosis factor alpha (TNFα) in sleep regulation using TNFα knockout (KO) mice. Under control conditions at thermoneutral ambient temperature, total sleep time did not differ between TNFα KO and wild-type (WT) mice, but TNFα KO mice had increased rapid-eye-movement sleep (REMS), accompanied by decreased motor activity and body temperature. Exposure to 17 °C induced decreases in total sleep time similarly in both genotypes. Sleep deprivation by gentle handling elicited robust rebound increases in non-rapid-eye movement sleep (NREMS), REMS and electroencephalographic (EEG) slow-wave activity (SWA), accompanied by suppressed motor activity and decreased body temperature; there was no significant difference between the responses of WT and KO mice. Systemic injection of the beta3-adrenergic receptor (β3-AR) agonist CL-316,243 induced increases in NREMS and body temperature. The temperature response, but not the sleep effect, was attenuated in the KO animals. Systemic injection of TNFα induced increased NREMS, reduced REMS and biphasic temperature responses in both genotypes. In the KO mice, the NREMS-promoting effects of exogenously administered TNFα was decreased, while REMS suppression was enhanced, and the first, hypothermic, phase of temperature response was attenuated. Overall, TNFα KO mice did not show any deficiency in sleep regulation which suggests that the role of endogenous TNFα in sleep regulation is less pronounced than previously suggested.

Regulation of breathing pattern by IL-10

Proinflammatory cytokines like interleukin-1β (IL-1β) affect the control of breathing. Our aim is to determine the effect of the anti-inflammatory cytokine IL-10 οn the control of breathing. IL-10 knockout mice (IL-10^-/-, n = 10) and wild-type mice (IL-10^+/+, n = 10) were exposed to the following test gases: hyperoxic hypercapnia 7% CO₂-93% O₂, normoxic hypercapnia 7% CO₂-21% O₂, hypoxic hypercapnia 7% CO₂-10% O₂, and hypoxic normocapnia 3% CO₂-10% O₂. The ventilatory function was assessed using whole body plethysmography. Recombinant mouse IL-10 (rIL-10; 10 μg/kg) was administered intraperitoneally to wild-type mice (n = 10) 30 min before the onset of gas challenge. IL-10 was administered in neonatal medullary slices (10-30 ng/ml, n = 8). We found that IL-10^-/- mice exhibited consistently increased frequency and reduced tidal volume compared with IL-10^+/+ mice during room air breathing and in all test gases (by 23.62 to 33.2%, P < 0.05 and -36.23 to -41.69%, P < 0.05, respectively). In all inspired gases, the minute ventilation of IL-10^-/- mice was lower than IL-10^+/+ (by -15.67 to -22.74%, P < 0.05). The rapid shallow breathing index was higher in IL-10^-/- mice compared with IL-10^+/+ mice in all inspired gases (by 50.25 to 57.5%, P < 0.05). The intraperitoneal injection of rIL-10 caused reduction of the respiratory rate and augmentation of the tidal volume in room air and also in all inspired gases (by -12.22 to -29.53 and 32.18 to 45.11%, P < 0.05, respectively). IL-10 administration in neonatal rat (n = 8) in vitro rhythmically active medullary slice preparations did not affect either rhythmicity or peak amplitude of hypoglossal nerve discharge. In conclusion, IL-10 may induce a slower and deeper pattern of breathing.

Possible Molecular Mediators Involved and Mechanistic Insight into Fibromyalgia and Associated Co-morbidities

Fibromyalgia is a chronic complex syndrome of non-articulate origin characterized by musculoskeletal pain, painful tender points, sleep problems and co-morbidities including depression, migraine. The etiopathogenesis of fibromyalgia is complex, variable and remains inconclusive. The etiological factors that have been defined include stress, genetic predisposition and environmental components. As per the reports of the American College of Rheumatology (ACR) the prevalence of fibromyalgia varies from 2 to 22% among the general population with poor diagnostic features primarily pain. Fibromyalgia encompasses a spectrum of co-morbid conditions with multifarious pathogenesis. The highly prevalent manifestations of fibromyalgia include heterogeneous pain and aches. Biochemical and neurobiological elements of fibromyalgia include neurotransmitters, hypothalamic pituitary adrenal axis (HPA axis), inflammatory cytokines, monoaminergic pathway, opioid peptides, sex hormones, nerve growth factor (NGF) and local free radical insult. An imbalance in the serotonergic system is the major underlying etiological factor that has been explored most widely. Owing to complex interplay of diverse pathophysiological pathways, overlapping co-morbidities such as depression have been clinically observed. Therapeutic management of fibromyalgia involves both non pharmacological and pharmacological measures. The current review presents various dysregulations and their association with symptoms of fibromyalgia along with their underlying neurobiological aspects.

Brown adipose tissue plays a central role in systemic inflammation-induced sleep responses

We previously identified brown adipose tissue (BAT) as a source of sleep-inducing signals. Pharmacological activation of BAT enhances sleep while sleep loss leads to increased BAT thermogenesis. Recovery sleep after sleep loss is diminished in mice that lack uncoupling protein 1 (UCP-1), and also in wild-type (WT) mice after sensory denervation of the BAT. Systemic inflammation greatly affects metabolism and the function of adipose tissue, and also induces characteristic sleep responses. We hypothesized that sleep responses to acute inflammation are mediated by BAT-derived signals. To test this, we determined the effects of systemic inflammation on sleep and body temperature in UCP-1 knockout (KO) and WT mice. Intraperitoneal injections of lipopolysaccharide, tumor necrosis factor-α, interleukin-1 beta and clodronate containing liposomes were used to induce systemic inflammation. In WT animals, non-rapid-eye movement sleep (NREMS) was elevated in all four inflammatory models. All NREMS responses were completely abolished in UCP-1 KO animals. Systemic inflammation elicited an initial hypothermia followed by fever in WT mice. The hypothermic phase, but not the fever, was abolished in UCP-1 KO mice. The only recognized function of UCP-1 is to promote thermogenesis in brown adipocytes. Present results indicate that the presence of UCP-1 is necessary for increased NREMS but does not contribute to the development of fever in systemic inflammation.

Narcolepsy susceptibility gene CCR3 modulates sleep-wake patterns in mice

Narcolepsy is caused by the loss of hypocretin (Hcrt) neurons and is associated with multiple genetic and environmental factors. Although abnormalities in immunity are suggested to be involved in the etiology of narcolepsy, no decisive mechanism has been established. We previously reported chemokine (C-C motif) receptor 3 (CCR3) as a novel susceptibility gene for narcolepsy. To understand the role of CCR3 in the development of narcolepsy, we investigated sleep-wake patterns of Ccr3 knockout (KO) mice. Ccr3 KO mice exhibited fragmented sleep patterns in the light phase, whereas the overall sleep structure in the dark phase did not differ between Ccr3 KO mice and wild-type (WT) littermates. Intraperitoneal injection of lipopolysaccharide (LPS) promoted wakefulness and suppressed both REM and NREM sleep in the light phase in both Ccr3 KO and WT mice. Conversely, LPS suppressed wakefulness and promoted NREM sleep in the dark phase in both genotypes. After LPS administration, the proportion of time spent in wakefulness was higher, and the proportion of time spent in NREM sleep was lower in Ccr3 KO compared to WT mice only in the light phase. LPS-induced changes in sleep patterns were larger in Ccr3 KO compared to WT mice. Furthermore, we quantified the number of Hcrt neurons and found that Ccr3 KO mice had fewer Hcrt neurons in the lateral hypothalamus compared to WT mice. We found abnormalities in sleep patterns in the resting phase and in the number of Hcrt neurons in Ccr3 KO mice. These observations suggest a role for CCR3 in sleep-wake regulation in narcolepsy patients.

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.

Sleep dysfunction and its association to chronic rhinosinusitis: Updated review

Background

Poor sleep has significant effects on health contributing to increased morbidity and mortality. The direct and indirect costs of sleep dysfunction total well in to the billions of dollars annually in the United States. Chronic rhinosinusitis (CRS) affects up to 16% of the US population and has been linked to poor sleep quality with up to three quarters of patients with CRS reporting poor sleep quality. There is a growing body of literature evaluating the relationship between sleep and CRS. In this review, we organize and present the current knowledge on the associations between sleep and CRS as well as identify areas for further investigation.

Data sources

A structured literature search from 1946 to 2016 was conducted in the English language using OVID MEDLINE database, PubMed, and EMBASE.

Review methods

Abstracts were reviewed for relevance and appropriate studies were included in the narrative review.

Results

Studies were analyzed and discussed as they pertained to the following categories of CRS and sleep: (1) subjective measures of sleep dysfunction, (2) objective measures of sleep dysfunction, and (3) outcomes on sleep quality following treatment of CRS. Articles on the pathophysiology of sleep dysfunction in CRS were separately reviewed.

Conclusions

An evolving body of research demonstrates that quality of sleep is compromised in the majority of patients with CRS. Following treatment of CRS, there is significant improvement in subjective sleep quality, but additional research investigating objective measures following treatment is still needed. Additionally, further investigation is required to better elucidate the underlying pathophysiology of the relationship between sleep dysfunction and CRS.

Level of Evidence

N/A.

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.

Role of interleukin-10 (IL-10) in regulation of GABAergic transmission and acute response to ethanol

Mounting evidence indicates that ethanol (EtOH) exposure activates neuroimmune signaling. Alterations in pro-inflammatory cytokines after acute and chronic EtOH exposure have been heavily investigated. In contrast, little is known about the regulation of neurotransmission and/or modulation by anti-inflammatory cytokines in the brain after an acute EtOH exposure. Recent evidence suggests that interleukin-10 (IL-10), an anti-inflammatory cytokine, is upregulated during withdrawal from chronic EtOH exposure. In the present study, we show that IL-10 is increased early (1 h) after a single intoxicating dose of EtOH (5 g/kg, intragastric) in Sprague Dawley rats. We also show that IL-10 rapidly regulates GABAergic transmission in dentate gyrus neurons. In brain slice recordings, IL-10 application dose-dependently decreases miniature inhibitory postsynaptic current (mIPSC) area and frequency, and decreases the magnitude of the picrotoxin sensitive tonic current (Itonic), indicating both pre- and postsynaptic mechanisms. A PI3K inhibitor LY294002 (but not the negative control LY303511) ablated the inhibitory effects of IL-10 on mIPSC area and Itonic, but not on mIPSC frequency, indicating the involvement of PI3K in postsynaptic effects of IL-10 on GABAergic transmission. Lastly, we also identify a novel neurobehavioral regulation of EtOH sensitivity by IL-10, whereby IL-10 attenuates acute EtOH-induced hypnosis. These results suggest that EtOH causes an early release of IL-10 in the brain, which may contribute to neuronal hyperexcitability as well as disturbed sleep seen after binge exposure to EtOH. These results also identify IL-10 signaling as a potential therapeutic target in alcohol-use disorders and other CNS disorders where GABAergic transmission is altered.

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.

Neutralization of colony-stimulating factor 1 receptor prevents sickness behavior syndrome by reprogramming inflammatory monocytes to produce IL-10

Sickness behavior syndrome (SBS) as characterized by fatigue and depression impairs quality of life in patients with inflammatory diseases caused by infections and autoimmunity. Systemic engagement of CD40 in mice leads to an inflammatory syndrome with acute hepatitis, lymphadenopathy and development of SBS as evidenced by induction of sleep and weight loss. In the study presented here we show that the elimination of resident tissue macrophages in mice by antibody-mediated neutralization of colony-stimulating factor-1 receptor (CSF1R) did not prevent CD40 induced hepatitis, but conferred resistance to the development of SBS. The protective effect of CSF1R mAb on weight loss and behavior changes induced by CD40 activation coincided with the transformation of pro-inflammatory monocytes to IL-10 producing myeloid cells. In IL-10 knockout mice CSF1R neutralization failed to exert protection from the occurrence of SBS. This study establishes the unexpected key role of CSF1R in the polarization of inflammatory monocytes and thereby SBS in inflammatory liver diseases.

The roles of prostaglandin E2 and D2 in lipopolysaccharide-mediated changes in sleep

When living organisms become sick as a result of a bacterial infection, a suite of brain-mediated responses occur, including fever, anorexia and sleepiness. Systemic administration of lipopolysaccharide (LPS), a common constituent of bacterial cell walls, increases body temperature and non-rapid eye movement (NREM) sleep in animals and induces the production of pro-inflammatory prostaglandins (PGs). PGE2 is the principal mediator of fever, and both PGE2 and PGD2 regulate sleep-wake behavior. The extent to which PGE2 and PGD2 are involved in the effect of LPS on NREM sleep remains to be clarified. Therefore, we examined LPS-induced changes in body temperature and NREM sleep in mice with nervous system-specific knockouts (KO) for the PGE2 receptors type EP3 or EP4, in mice with total body KO of microsomal PGE synthase-1 or the PGD2 receptor type DP, and in mice treated with the cyclooxygenase (COX) inhibitor meloxicam. We observed that LPS-induced NREM sleep was slightly attenuated in mice lacking EP4 receptors in the nervous system, but was not affected in any of the other KO mice or in mice pretreated with the COX inhibitor. These results suggest that the effect of LPS on NREM sleep is partially dependent on PGs and is likely mediated mainly by other pro-inflammatory substances. In addition, our data show that the main effect of LPS on body temperature is hypothermia in the absence of nervous system EP3 receptors or in the presence of a COX inhibitor.

Sickness behaviour after lipopolysaccharide treatment in ghrelin deficient mice

Ghrelin is an orexigenic hormone produced mainly by the gastrointestinal system and the brain. Much evidence also indicates a role for ghrelin in sleep and thermoregulation. Further, ghrelin was recently implicated in immune system modulation. Administration of bacterial lipopolysaccharide (LPS) induces fever, anorexia, and increased non-rapid-eye movement sleep (NREMS) and these actions are mediated primarily by proinflammatory cytokines. Ghrelin reduces LPS-induced fever, suppresses circulating levels of proinflammatory cytokines and reduces the severity and mortality of various models of experimental endotoxemia. In the present study, we determined the role of intact ghrelin signaling in LPS-induced sleep, feeding, and thermoregulatory responses in mice. Sleep-wake activity was determined after intraperitoneal, dark onset administration of 0.4, 2 and 10 μg LPS in preproghrelin knockout (KO) and wild-type (WT) mice. In addition, body temperature, motor activity and changes in 24-h food intake and body weight were measured. LPS induced dose-dependent increases in NREMS, and suppressed rapid-eye movement sleep, electroencephalographic slow-wave activity, motor activity, food intake and body weight in both Ppg KO and WT mice. Body temperature changes showed a biphasic pattern with a decrease during the dark period followed by an increase in the light phase. The effects of the low and middle doses of LPS were indistinguishable between the two genotypes. Administration of 10 μg LPS, however, induced significantly larger changes in NREMS and wakefulness amounts, body temperature, food intake and body weight in the Ppg KO mice. These findings support a role for ghrelin as an endogenous modulator of inflammatory responses and a central component of arousal and feeding circuits.

Sleep and behavior during vesicular stomatitis virus induced encephalitis in BALB/cJ and C57BL/6J mice

Intranasal application of vesicular stomatitis virus (VSV) produces a well-characterized model of viral encephalitis in mice. Within one day post-infection (PI), VSV travels to the olfactory bulb and, over the course of 7 days, it infects regions and tracts extending into the brainstem followed by clearance and recovery in most mice by PI day 14 (PI 14). Infectious diseases are commonly accompanied by excessive sleepiness; thus, sleep is considered a component of the acute phase response to infection. In this project, we studied the relationship between sleep and VSV infection using C57BL/6 (B6) and BALB/c mice. Mice were implanted with transmitters for recording EEG, activity and temperature by telemetry. After uninterrupted baseline recordings were collected for 2 days, each animal was infected intranasally with a single low dose of VSV (5×10(4) PFU). Sleep was recorded for 15 consecutive days and analyzed on PI 0, 1, 3, 5, 7, 10, and 14. Compared to baseline, amounts of non-rapid eye movement sleep (NREM) were increased in B6 mice during the dark period of PI 1-5, whereas rapid eye movement sleep (REM) was significantly reduced during the light periods of PI 0-14. In contrast, BALB/c mice showed significantly fewer changes in NREM and REM. These data demonstrate sleep architecture is differentially altered in these mouse strains and suggests that, in B6 mice, VSV can alter sleep before virus progresses into brain regions that control sleep.

Antisomnogenic cytokines, quality of life, and chronic rhinosinusitis: a pilot study

OBJECTIVES/HYPOTHESIS

Sleep disturbance, reduced quality of life (QOL), and other components of "sickness behavior" in patients with chronic rhinosinusitis (CRS) are poorly understood. These complex changes in central behavior are due to the effects of immune mediators acting in the brain. We hypothesized that immune mediators that have been associated with CRS are also associated with sickness behavior, somnifacient complaints, and CRS disease-specific QOL.

STUDY DESIGN

Pilot study.

METHODS

Twenty patients with CRS were prospectively enrolled and completed the Pittsburgh Sleep Quality Index (PSQI), disease-specific QOL, and olfactory instruments. Ethmoid mucosa was obtained and reverse transcription-polymerase chain reaction was performed for the cytokines interleukin (IL)-4, -13, and transforming growth factor-β (TGF-β). Average change in crossover threshold was calculated, and differences in gene expression were correlated with sleep quality, CRS-specific QOL, and disease severity.

RESULTS

Patients with CRS reported overall poor sleep quality and poor CRS-specific QOL with significant correlations between them. Increased expression of TGF-β (r = -0.443; P = .050) and IL-4 (r = -0.548; P = .012) correlated with sleep dysfunction, whereas IL-13 expression was linearly associated with worse sleep quality (PSQI scores r = -0.417; P = .075). IL-4 and TGF-β expression was not associated with CRS disease severity or QOL, whereas significantly higher levels of IL-13 expression correlated with worse CRS disease severity and QOL.

CONCLUSIONS

Patients with CRS exhibited behavioral changes commonly referred to as sickness behavior, which include poor sleep quality and reduced QOL. The upregulation of IL-4 and TGF-β may contribute to inflammatory brain-mediated effects on sleep quality, whereas IL-13 may be a pleiotropic signaling molecule influencing sleep, QOL, and CRS disease severity.

LEVEL OF EVIDENCE

2b.

Chronic rhinosinusitis and sleep: a contemporary review

BACKGROUND

Patients with chronic rhinosinusitis (CRS) exhibit centrally mediated behavioral changes commonly referred to as "sickness behavior." Sleep alteration is a component of sickness behavior which is estimated to affect up to 70 million patients annually. Patients with CRS have poor sleep quality, and little is known about the underlying etiology and pathophysiology. This narrative review aims to further organize and present the current knowledge associating sleep and CRS.

METHODS

A literature search was conducted of the OVID MEDLINE database using key search words including: "chronic rhinosinusitis," "sleep," "sleep disorders," and "sleep dysfunction." Additional keywords "nasal obstruction," "nasal polyp," and "fatigue" were identified and used to further delineate relevant articles.

RESULTS

The articles that specifically addressed sleep and CRS were dissected and presented as follows: (1) chronic rhinosinusitis and sleep; (2) chronic rhinosinusitis and fatigue; (3) chronic rhinosinusitis, nasal obstruction, and sleep; and (4) pathophysiology of sleep in chronic rhinosinusitis (cytokines in both sleep and chronic rhinosinusitis and their association to the neuroimmune biology of chronic rhinosinusitis).

CONCLUSION

Patients with CRS have sleep dysfunction that is associated with their disease severity and overall quality of life. The etiology of sleep dysfunction in CRS is most likely multifactorial. Increasing evidence suggests sleep dysfunction in patients with CRS is partly due to the inflammatory disease process, and sleep physiology in patients with CRS may be actively regulated by the inflammatory component of the disease.

A meta-analysis of differences in IL-6 and IL-10 between people with and without depression: exploring the causes of heterogeneity

Epidemiological evidence for the inflammatory hypothesis of depression is largely cross-sectional; people with depression have elevated levels of circulating pro-inflammatory markers compared to people without depression. The limitation of cross sectional research is the potential for extraneous factors to influence observed effects. The purpose of this meta-analysis of cross-sectional studies of interleukin(IL)-6 and IL-10 in people with and without depression is to provide a targeted analysis of potential moderator factors relating to the diagnosis of depression and to physical and psychiatric comorbidity. Electronic searches of Embase and Medline databases were conducted using subject headings "interleukin-6" or "interleukin-10" and those relating to depression. Studies were included if they measured circulating marker levels in serum or plasma in a group of people with and without depressive symptoms (99 studies for IL-6, 19 studies for IL-10). IL-6 was elevated in depressed compared to non-depressed groups (d = 0.46, 99% CI 0.34 to 0.58, I(2) = 85.9%). This effect was larger in subgroups where depressive disorders were diagnosed compared to those with only depressive symptoms via standardized inventory, and subgroups where participants were recruited from inpatient or outpatient settings compared to the general community. The effect was also larger in those who were not selected for a particular comorbidity compared to those selected for cardiovascular disease. IL-10 effect size was not significant (d = -0.31, 99% CI -0.95 to 0.32, I(2) = 94.1%) which was not accounted for in subgroup analyses or meta-regression, indicating there is not a global elevation in cytokines. These data highlight that comorbidity and behavioral aspects of depression need to be measured and controlled in future prospective and experimental research testing the inflammatory hypothesis of depression.

Endogenous interleukin-10 constrains Th17 cells in patients with inflammatory bowel disease

Background

Th17 cells play a role in inflammation. Interleukin (IL)-10 is a potent anti-inflammatory cytokine. However, it is poorly understood whether and how endogenous IL-10 impacts the development of Th17 cells in human pathologies.

Materials and methods

We examined the relationship between IL-10 and Th17 cells in patients with Crohn's disease and in IL-10-deficient (IL-10^-/-) mice. Th17 cells and dendritic cells (DCs) were defined by flow cytometry and evaluated by functional studies.

Results

We detected elevated levels of IL-17 and Th17 cells in the intestinal mucosa of patients with Crohn's disease. Intestinal DCs from Crohn's patients produced more IL-1β than controls and were superior to blood DCs in Th17 induction through an IL-1-dependent mechanism. Furthermore, IL-17 levels were negatively associated with those of IL-10 and were positively associated those of IL-1β in intestinal mucosa. These data point toward an in vivo cellular and molecular link among endogenous IL-10, IL-1, and Th17 cells in patients with Crohn's disease. We further investigated this relationship in IL-10^-/- mice. We observed a systemic increase in Th17 cells in IL-10^-/- mice when compared to wild-type mice. Similar to the intestinal DCs in patients with Crohn's disease, murine IL-10^-/- DCs produced more IL-1β than their wild-type counterparts and promoted Th17 cell development in an IL-1-dependent manner. Finally, in vivo blockade of IL-1 receptor signaling reduced Th17 cell accumulation and inflammation in a mouse model of chemically-induced colitis.

Conclusions

Endogenous IL-10 constrains Th17 cell development through the control of IL-1 production by DCs, and reaffirms the crucial anti-inflammatory role of IL-10 in patients with chronic inflammation.

Deficiency of corticotropin-releasing hormone type-2 receptor alters sleep responses to bacterial lipopolysaccharide in mice

In response to infectious stimuli, enhanced non-rapid eye movement sleep (NREMS) occurs, which is driven by pro-inflammatory cytokines. Those cytokines further elicit the release of corticotropin-releasing hormone (CRH), resulting in the activation of the hypothalamic-pituitary-adrenocortical axis. Signals of CRH are mediated by two receptor types, namely CRH-R1 and -R2. The role of CRH-R1 in wake-promoting effects of CRH has been rather clarified, whereas the involvement of CRH-R2 in sleep-wake regulation is poorly understood. To investigate whether CRH-R2 interferes with sleep responses to immune challenge, this study examined effects of bacterial lipopolysaccharide (LPS) on sleep in CRH-R2 deficient (KO) mice. CRH-R2 KO mice and control littermates (CL) were implanted with electrodes for recording electroencephalogram (EEG) and electromyogram. After recovery, LPS was applied by intraperitoneal injection at doses of 0.1, 1.0, or 10 μg at dark onset. In response to LPS injection NREMS of both genotypes was enhanced in a dose-dependent manner. However, CRH-R2 KO mice showed a larger increase, in particular after 10 μg of LPS compared to CL mice. During postinjection, reduced delta power for NREMS was detected in both genotypes after each dose, but the highest dose evoked a marked elevation of EEG activity in a limited frequency band (4 Hz). However, the EEG power of lower frequencies (1-2 Hz) increased more in CRH-R2 KO than in CL mice. The results indicated that CRH-R2 KO mice show greater NREMS responses to LPS, providing evidence that CRH-R2 participates in sleep-wake regulation via an interaction with the activated immune system.

Sleep and fatigue in mice infected with murine gammaherpesvirus 68

Fatigue, a common symptom of many acute and chronic medical conditions, reduces both quality of life and workplace productivity and can be disabling. However, the pathophysiologic mechanisms that underlie fatigue can be difficult to study in human populations due to the patient heterogeneity, the variety of underlying causes and potential triggering events, and an inability to collect samples that may be essential to elucidation of mechanisms (e.g., brain). Although the etiology of chronic fatigue syndrome (CFS) remains elusive, some studies have implicated viral infections, including Epstein-Barr virus (EBV), a human gammaherpesvirus, as a potential factor in the pathogenesis of CFS. Murine gammaherpesvirus 68 (γHV68) is a mouse pathogen that shares many similarities with human γHVs, including EBV. In this study, we use γHV68-infected C57BL/6J mice as a model system for studying the impact of chronic viral infection on sleep-wake behavior, activity patterns, and body temperature profiles. Our data show that γHV68 alters sleep, activity, and temperature in a manner suggestive of fatigue. In mice infected with the highest dose used in this study (40,000plaque forming units), food intake, body weight, wheel running, body temperature, and sleep were normal until approximately 7days after infection. These parameters were significantly altered during days 7 through 11, returned to baseline levels at day 12 after infection, and remained within the normal range for the remainder of the 30-day period after inoculation. At that time, both infected and uninfected mice were injected with lipopolysaccharide (LPS), and their responses monitored. Uninfected mice given LPS developed a modest and transient febrile response during the initial light phase (hours 12 through 24) after injection. In contrast, infected mice developed changes in core body temperatures that persisted for at least 5days. Infected mice showed an initial hypothermia that lasted for approximately 12h, followed by a modest fever that persisted for several hours. For the remainder of the 5-day recording period, they showed mild hypothermia during the dark phase. Running wheel activity of infected mice was reduced for at least 5days after injection of LPS, but for only 12h in uninfected mice. Collectively, these observations indicate that (1) physiologic and behavioral processes in mice are altered and recover during an early phase of infection, and (2) mice with latent γHV68 infection have an exacerbated response to challenge with LPS. These findings indicate that laboratory mice with γHV68 infections may provide a useful model for the study of fatigue and other physiologic and behavioral perturbations that may occur during acute and chronic infection with gammaherpesviruses.

Metabolomic analysis identifies inflammatory and noninflammatory metabolic effects of genetic modification in a mouse model of Crohn's disease

Interleukin-10 is an immunosuppressive cytokine involved in the regulation of gastrointestinal mucosal immunity toward intestinal microbiota. Interleukin-10-deficient (IL10(-/-)) mice develop Crohn's disease-like colitis unless raised in germ-free conditions. Previous gas chromatography-mass spectrometry (GC-MS) metabolomic analysis revealed urinary metabolite differences between IL10(-/-) and wildtype C57BL/6 mice. To determine which of these differences were specifically associated with intestinal inflammation arising from IL10-deficiency, urine samples from IL10(-/-) and wildtype mice, housed in either conventional or specific pathogen-free conditions, were subjected to GC-MS metabolomic analysis. Fifteen metabolite differences, including fucose, xanthurenic acid, and 5-aminovaleric acid, were associated with intestinal inflammation. Elevated urinary levels of xanthurenic acid in IL10(-/-) mice were attributed to increased production of kynurenine metabolites that may induce T-cell tolerance toward intestinal microbiota. Liquid chromatography-mass spectrometry analysis confirmed that plasma levels of kynurenine and 3-hydroxykynurenine were elevated in IL10(-/-) mice. Eleven metabolite differences, including glutaric acid, 2-hydroxyglutaric acid, and 2-hydroxyadipic acid, were unaffected by the severity of inflammation. These metabolite differences may be associated with residual genes from the embryonic stem cells of the 129P2 mouse strain that were used to create the IL10(-/-) mouse, or may indicate novel functions of IL10 unrelated to inflammation.

Interleukin-10: a key cytokine in depression?

An increasing body of evidence implicates proinflammatory cytokines in psychiatric disorders, namely, in depression. Of notice, recent studies showed that anti-inflammatory cytokines, such as IL-10, also modulate depressive-like behavior. In this article, we propose that the anti-inflammatory cytokine IL-10 is a putative link between two of the most widely reported phenomenon observed in depressed patients: the disruption of the hypothalamic-pituitary-adrenal axis and the imbalanced production of cytokines. If so, IL-10 might represent a novel target for antidepressant therapy.

Modulation of sickness behavior by sleep: the role of neurochemical and neuroinflammatory pathways in mice

Activation of the immune system elicits several behavioral changes that are collectively called sickness behavior and consists in a strategy to overcome infection. Sleep deprivation can increase susceptibility to pathogens and to behavioral alterations. Thus, the present study aimed to determine how paradoxical sleep deprivation (PSD) affects the behavioral and neurochemical responses to lipopolysaccharide (LPS, potent activator of the immune response). Adult inbred mice were paradoxical sleep deprived (72 h), whereas the control group was kept in their home cages. Both groups received either an injection of saline or LPS (5, 10 or 20 microg/animal ip) before behavioral tasks and tissue collection. During the recovery sleep period, LPS provoked a strong inhibition of sleep rebound due to a suppression of paradoxical sleep. PSD increased the susceptibility of mice to LPS-induced immobility in the open field, which was capable of affecting the anxiety-like behavior also. These altered behavioral responses to LPS were accompanied by reduction in dopamine turnover within the striatum and increased expression of cyclooxygenase-2 in the cortex. The study provides some insights into how the sleep-wake cycle affects the expression of sickness behavior induced by LPS.

Cytokine mRNA induction by interleukin-1beta or tumor necrosis factor alpha in vitro and in vivo

Hypothalamic and cortical mRNA levels for cytokines such as interleukin-1beta (IL1beta), tumor necrosis factor alpha (TNFalpha), nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) are impacted by systemic treatments of IL1beta and TNFalpha. To investigate the time course of the effects of IL1beta and TNFalpha on hypothalamic and cortical cytokine gene expression, we measured mRNA levels for IL1beta, TNFalpha, interleukin-6 (IL-6), interleukin-10 (IL-10), IL1 receptor 1, BDNF, NGF, and glutamate decarboxylase-67 in vitro using hypothalamic and cortical primary cultures. IL1beta and TNFalpha mRNA levels increased significantly in a dose-dependent fashion after exposure to either IL1beta or TNFalpha. IL1beta increased IL1beta mRNA in both the hypothalamic and cortical cultures after 2-6 h while TNFalpha mRNA increased significantly within 30 min and continued to rise up to 2-6 h. Most of the other mRNAs showed significant changes independent of dose in vitro. In vivo, intracerebroventricular (icv) injection of IL1beta or TNFalpha also significantly increased IL1beta, TNFalpha and IL6 mRNA levels in the hypothalamus and cortex. IL1beta icv, but not TNFalpha, increased NGF mRNA levels in both these areas. Results support the hypothesis that centrally active doses of IL1beta and TNFalpha enhance their own mRNA levels as well as affect mRNA levels for other neuronal growth factors.

Effects of i.c.v. administration of interleukin-1 on sleep and body temperature of interleukin-6-deficient mice

Cytokines in brain contribute to the regulation of physiological processes and complex behavior, including sleep. The cytokines that have been most extensively studied with respect to sleep are interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, and IL-6. Administration of these cytokines into laboratory animals, or in some cases into healthy human volunteers, increases the amount of time spent in non-rapid eye movement (NREM) sleep. Although antagonizing the IL-1 or TNF systems reduces the amount of time laboratory animals spend in NREM sleep, interactions among these three cytokine systems as they pertain to the regulation of physiological NREM sleep are not well understood. To further elucidate mechanisms in brain by which IL-1beta, TNFalpha, and/or IL-6 contribute to NREM sleep regulation, we injected recombinant murine interleukin-1beta (muIL-1beta) into C57BL/6J mice and into IL-6-deficient mice (IL-6 knockout, KO). IL-6 KO (B6.129S6-Il6(tm1Kopf); n=13) and C57BL/6J mice (n=14) were implanted with telemeters to record the electroencephalogram (EEG) and core body temperature, as well as with indwelling guide cannulae targeted to one of the lateral ventricles. After recovery and habituation, mice were injected intracerebroventricularly just prior to dark onset on different days with either 0.5 microl vehicle (pyrogen-free saline; PFS) or with 0.5 microl PFS containing one of four doses of muIL-1beta (2.5 ng, 5 ng, 10 ng, 50 ng). No mouse received more than two doses of muIL-1beta, and administration of muIL-1beta doses was counter-balanced to eliminate potential order effects. Sleep-wake behavior was determined for 24 h after injections. i.c.v. administration of muIL-1beta increased in NREM sleep of both mouse strains in a dose-related fashion, but the maximal increase was of greater magnitude in C57Bl/6J mice. muIL-1beta induced fever in C57Bl/6J mice but not in IL-6 KO mice. Collectively, these data demonstrate IL-6 is necessary for IL-1 to induce fever, but IL-6 is not necessary for IL-1 to alter NREM sleep.

Effect of environmental temperature on sleep, locomotor activity, core body temperature and immune responses of C57BL/6J mice

Ambient temperature exerts a prominent influence on sleep. In rats and humans, low ambient temperatures generally impair sleep, whereas higher temperatures tend to promote sleep. The purpose of the current study was to evaluate sleep patterns and core body temperatures of C57BL/6J mice at ambient temperatures of 22, 26 and 30 degrees C under baseline conditions, after sleep deprivation (SD), and after infection with influenza virus. C57BL/6J mice were surgically implanted with electrodes for recording electroencephalogram (EEG) and electromyogram (EMG) and with intraperitoneal transmitters for recording core body temperature (T(c)) and locomotor activity. The data indicate that higher ambient temperatures (26 and 30 degrees C) promote spontaneous slow wave sleep (SWS) in association with reduced delta wave amplitude during SWS in C57BL/6J mice. Furthermore, higher ambient temperatures also promote recuperative sleep after SD. Thus, in mice, higher ambient temperatures reduced sleep depth under normal conditions, but augmented the recuperative response to sleep loss. Mice infected with influenza virus while maintained at 22 or 26 degrees C developed more SWS, less rapid eye movement sleep, lower locomotor activity and greater hypothermia than did mice maintained at 30 degrees C during infection. In addition, despite equivalent viral titers, mice infected with influenza virus at 30 degrees C showed less leucopenia and lower cytokine induction as compared with 22 and 26 degrees C, respectively, suggesting that less inflammation develops at the higher ambient temperature.

Spontaneous, homeostatic, and inflammation-induced sleep in NF-kappaB p50 knockout mice

The dimeric transcription factor nuclear factor-kappaB (NF-kappaB) regulates several endogenous sleep-modulatory substances and thereby serves as a pivotal mediator of sleep-wake homeostasis. To further define the role of NF-kappaB in sleep regulation, we monitored sleep and temperature in mice that lack the p50 subunit of NF-kappaB [p50 knockout (KO) mice]. Compared with the control B6129PF2/J strain, p50 KO mice spend more time in slow-wave sleep (SWS) and rapid eye movement sleep (REMS) under normal conditions and show enhanced homeostatic recovery of sleep after sleep loss. p50 KO mice also show increased SWS and reduced REMS and temperature after the administration of lipopolysaccharide, yet they are behaviorally less responsive to challenge with influenza virus. These data support a role for NF-kappaB, and, in particular, for the p50 subunit, in the regulation of sleep in healthy mice and in mice experiencing immune challenge.

Facilitation of spike-wave discharge activity by lipopolysaccharides in Wistar Albino Glaxo/Rijswijk rats

In normal rats the proinflammatory cytokines like interleukin-1beta, interleukin-6, which are induced by bacterial lipopolysaccharides, are able to control thalamo-cortical excitability by exerting strong effects on physiological synchronization such as sleep and on pathological synchronization like that in epileptic discharges. To investigate whether proinflammatory cytokines or lipopolysaccharides could modulate absence seizures resulting from a very different generator mechanism than the already investigated bicuculline-, kindling- and kainate-induced seizures, we used a genetically epileptic Wistar Albino Glaxo/Rijswijk rat strain, which is spontaneously generating high voltage spike-wave discharges. Wistar Albino Glaxo/Rijswijk rats responded with an increase of the number of spike-wave discharges to lipopolysaccharide injection (from 10 microg/kg to 350 microg/kg). Repetitive administration of 350 microg/kg lipopolysaccharides daily for 5 days increased the number of spike-wave discharges on the first, second and third days but the number of spike-wave discharges returned to the control value on day 5, at the 5th injection of lipopolysaccharides, showing a tolerance to lipopolysaccharides. The lipopolysaccharide-induced increase in spike-wave discharges was not directly correlated with the elevation of the core body temperature, as it is in febrile seizures, although lipopolysaccharide induced prostaglandin and is clearly pyrogenic at the doses used. Indomethacin, the prostaglandin synthesis inhibitor, efficiently blocked lipopolysaccharide-induced enhancement of spike-wave discharge genesis suggesting that the spike-wave discharge facilitating effect of lipopolysaccharides involves induction of cyclooxygenase 2 and subsequent synthesis and actions of prostaglandin E2. Low dose (40 mg/kg, i.p.) of competitive N-methyl-d-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid, and low dose of lipopolysaccharide (20 microg/kg) showed a synergistic interaction to increase the number of spike-wave discharges, whereas at supramaximal doses of lipopolysaccharide and the N-methyl-D-aspartate antagonist no synergy was present. The data reveal a functional connection between absence epileptic activity and lipopolysaccharide induction of prostaglandin synthesis and prostaglandin action and suggest some common cellular targets in epilepsy and lipopolysaccharide-induced inflammation.

Sleep-deprived mice show altered cytokine production manifest by perturbations in serum IL-1ra, TNFa, and IL-6 levels

Serum cytokine and chemokine levels were examined in mice following 36 h of sleep deprivation, or after exposure to a known physical stressor (rotational stress). Significant changes in inflammatory cytokines/chemokines (IL-1beta, TNFalpha, IL-1ra, IL-6, and MIP-1beta, MCP-1) were observed following each manipulation, but qualitative and quantitative differences were seen. Interestingly, only physical stress was associated with measured increases in serum corticosterone levels, and with independent evidence (using in vitro immune allostimulation) for a generalized immunosuppression secondary to the experimental manipulation. Our data suggest that altered cytokine production following sleep perturbation occurs by a different mechanism from that (HPA axis) commonly attributed to stress per se.

Alterations in EEG activity and sleep after influenza viral infection in GHRH receptor-deficient mice

Viral infections induce excess non-rapid eye movement sleep (NREMS) in mice. Growth hormone-releasing hormone receptor (GHRH receptor) was previously identified as a candidate gene responsible for NREMS responses to influenza challenge in mice. The dwarf lit/lit mouse with a nonfunctional GHRH receptor was used to assess the role of the GHRH receptor in viral-induced NREMS. After influenza A virus infection the duration and intensity [electroencephalogram (EEG) delta power] of NREMS increased in heterozygous mice with the normal phenotype, whereas NREMS and EEG delta power decreased in homozygous lit/lit mice. Lit/lit mice developed a pathological state with EEG slow waves and enhanced muscle tone. Other influenza-induced responses (decreases in rapid eye movement sleep, changes in the EEG high-frequency bands during the various stages of vigilance, hypothermia, and decreased motor activity) did not differ between the heterozygous and lit/lit mice. GH replacement failed to normalize the NREMS responses in the lit/lit mice after influenza inoculation. Decreases in NREMS paralleled hypothermia in the lit/lit mice. Lung virus levels were similar in the two mouse strains. Lit/lit mice had a higher death rate after influenza challenge than the heterozygotes. In conclusion, GHRH signaling is involved in the NREMS response to influenza infection.

Brain-immune interactions in sleep

This chapter discusses various levels of interactions between the brain and the immune system in sleep. Sleep-wake behavior and the architecture of sleep are influenced by microbial products and cytokines. On the other hand, sleep processes, and perhaps also specific sleep states, appear to promote the production and/or release of certain cytokines. The effects of immune factors such as endotoxin and cytokines on sleep reveal species specificity and usually strong dependence on parameters such as substance concentration, time relative to administration or infection with microbial products, and phase relation to sleep and/or the light-dark cycle. For instance, endotoxin increased SWS and EEG SWA in humans only at very low concentrations, whereas higher concentrations increased sleep stage 2 only, but not SWS. In animals, increases in NREM sleep and SWA were more consistent over a wide range of endotoxin doses. Also, administration of pro-inflammatory cytokines such as IL-6 and IFN-alpha in humans acutely disturbed sleep while in rats such cytokines enhanced SWS and sleep. Overall, the findings in humans indicate that strong nonspecific immune responses are acutely linked to an arousing effect. Although subjects feel subjectively tired, their sleep flattens. However, some observations indicate a delayed enhancing effect on sleep which could be related to the induction of secondary, perhaps T-cell-related factors. This would also fit with results in animals in which the T-cell-derived cytokine IL-2 enhanced sleep while cytokines with immunosuppressive functions like IL-4 and L-10 suppressed sleep. The most straightforward similarity in the cascade of events inducing sleep in both animals and humans is the enhancing effect of GHRH on SWS, and possibly the involvement of the pro-inflammatory cytokine systems of IL-1 beta and TNF-alpha. The precise mechanisms through which administered cytokines influence the central nervous system sleep processes are still unclear, although extensive research has identified the involvement of various molecular intermediates, neuropeptides, and neurotransmitters (cp. Fig. 5, Section III.B). Cytokines are not only released and found in peripheral blood mononuclear cells, but also in peripheral nerves and the brain (e.g., Hansen and Krueger, 1997; März et al., 1998). Cytokines are thereby able to influence the central nervous system sleep processes through different routes. In addition, neuronal and glial sources have been reported for various cytokines as well as for their soluble receptors (e.g., Kubota et al., 2001a). Links between the immune and endocrine systems represent a further important route through which cytokines influence sleep and, vice versa, sleep-associated processes, including variations in neurotransmitter and neuronal activity may influence cytokine levels. The ability of sleep to enhance the release and/or production of certain cytokines was also discussed. Most consistent results were found for IL-2, which may indicate a sleep-associated increase in activity of the specific immune system. Furthermore, in humans the primary response to antigens following viral challenge is enhanced by sleep. In animals results are less consistent and have focused on the secondary response. The sleep-associated modulation in cytokine levels may be mediated by endocrine parameters. Patterns of endocrine activity during sleep are probably essential for the enhancement of IL-2 and T-cell diurnal functions seen in humans: Whereas prolactin and GH release stimulate Th1-derived cytokines such as IL-2, cortisol which is decreased during the beginning of nocturnal sleep inhibits Th1-derived cytokines. The immunological function of neurotrophins, in particular NGF and BDNF, has received great interest. Effects of sleep and sleep deprivation on this cytokine family are particularly relevant in view of the effects these endogenous neurotrophins can have not only on specific immune functions and the development of immunological memories, but also on synaptic reorganization and neuronal memory formation.

Role of corticotropin-releasing hormone in stressor-induced alterations of sleep in rat

Corticotropin-releasing hormone (CRH) mediates responses to a variety of stressors. We subjected rats to a 1-h period of an acute stressor, physical restraint, and determined the impact on subsequent sleep-wake behavior. Restraint at the beginning of the light period, but not the dark period, increased waking and reduced rapid eye movement sleep without dramatically altering slow-wave sleep (SWS). Electroencephalogram (EEG) slow-wave activity during SWS and brain temperature were increased by this manipulation. Central administration of the CRH receptor antagonist astressin blocked the increase in waking after physical restraint, but not during the period of restraint itself. Blockade of CRH receptors with astressin attenuated the restraint-induced elevation of brain temperature, but not the increase of EEG slow-wave activity during subsequent SWS. Although corticosterone increased after restraint in naive animals, it was not altered by this manipulation in rats well habituated to handling and injection procedures. These results suggest that under these conditions central CRH, but not the hypothalamic-pituitary-adrenal axis, is involved in the alterations in sleep-wake behavior and the modulation of brain temperature of rats exposed to physical restraint.

Invited review: genetic dissection of sleep

Recent advances in genomics open up new avenues in the analysis of complex behaviors such as sleep. In this analysis, the mouse is the model species of choice because it is amenable to high throughput phenotype and genotype analysis. With the use of the mouse model, unprecedented progress in our understanding of sleep physiology and the treatment of sleep disorders is awaited. This review is intended to provide an overview of available methods and techniques for genetic dissection of sleep in mice. Limits and advantages of different approaches are discussed to highlight the necessity for combining methods to avoid erroneous interpretations. The gap between understanding mechanisms of sleep and its functions may be bridged by finding its molecular bases.