The role of cytokines in physiological sleep regulation

Obstructive sleep apnea syndrome is a systemic disease. Current evidence

Obstructive sleep apnea syndrome (OSAS) is a highly prevalent sleep disorder, characterized by repeated disruptions of breathing during sleep. This disease has many potential consequences including excessive daytime sleepiness, neurocognitive deterioration, endocrinologic and metabolic effects, and decreased quality of life. Metabolic syndrome is another highly prevalence emerging public health problem that represents a constellation of cardiovascular risk factors. Each single component of the cluster increases the cardiovascular risk, but the combination of factors is much more significant. It has been suggested that the presence of OSAS may increase the risk of developing some metabolic syndrome features. Moreover, OSAS patients are at an increased risk for vascular events, which represent the greatest morbidity and mortality of all associated complications. Although the etiology of OSAS is uncertain, intense local and systemic inflammation is present. A variety of phenomena are implicated in this disease such as modifications in the autonomic nervous system, hypoxemia-reoxygenation cycles, inflammation, and coagulation-fibrinolysis imbalance. OSAS patients also present increased levels of certain biomarkers linked to endocrine-metabolic and cardiovascular alterations among other systemic consequences. All of this indicates that, more than a local abnormality, OSAS should be considered a systemic disease.

Opiate modulation of IL-1alpha, IL-2, and TNF-alpha transport across the blood-brain barrier

Interleukin-1alpha (IL-1alpha), interleukin-2 (IL-2), and tumor necrosis factor alpha (TNF-alpha) are proinflammatory cytokines with potent neuromodulatory effects and are implicated in the etiology and pathogenesis of various psychological and neurological disorders. The findings that chronic morphine treatment alters both blood-brain barrier (BBB) function and cytokine production raises the possibility that morphine can also modulate cytokine transport across the BBB. Here, we found that acute morphine treatment (12 mg/kg i.p.) did not alter blood-to-brain transport of IL-1alpha, IL-2 or TNF-alpha. Whereas chronic morphine treatment (48 h after implantation of 75 mg morphine pellets) and withdrawal from morphine (10-15 min after an i.p. injection of 1mg/kg of naltroxone 48 h after implantation of 75 mg morphine pellets) did not alter blood-to-brain transport of IL-1alpha or TNF-alpha, both the chronic morphine treatment and withdrawal from morphine groups had increased blood-to-brain transport of IL-2. Typically, the permeability of the BBB to IL-2 is dominated by brain-to-blood efflux, with only limited blood-to-brain transport. Here, we found that chronic morphine and withdrawal from morphine did not alter brain-to-blood efflux, but induced a novel saturable blood-to-brain transport system. Whereas IL-1alpha, IL-2, and TNF-alpha are all proinflammatory cytokines, morphine exposure has individualized effects on their blood-to-brain transport.

Novel analysis of sleep patterns in rats separates periods of vigilance cycling from long-duration wake events

Rats are polyphasic sleepers. However, a formal definition of when one sleep episode ends and another begins has not been put forth. In the present study we examine the distribution of wake episode durations and based on this distribution conclude there are multiple components of wake. If the wake episode exceeds 300 s the wake episode is assigned to long-duration wake (LDW), if the episode is less than 300 s it is assigned to brief wake (BW). Further support for this separation was found in close analysis of the EEG power spectrum in BW versus LDW. We then used LDW episodes to separate one sleep episode from another. We term the sleep episodes vigilance cycling (VC) because the rat is cycling between the vigilance states of BW, slow-wave sleep (SWS), and rapid-eye movement sleep (REMS). We find that the characteristics of VC are different in the light period versus the dark period. We further find that as VC episodes progress, SWS pressure lessens, but the amount of time spent in REMS increases. These findings suggest that VC episodes are regulated and meaningful to the sleep behavior of rats. The use of the concepts of LDW and VC provides additional insights into the description of sleep patterns in rats that may be important in the development of a complete description of sleep behavior in this animal.

Sleep-wake behavior and responses to sleep deprivation of mice lacking both interleukin-1 beta receptor 1 and tumor necrosis factor-alpha receptor 1

Data indicate that interleukin (IL)-1 beta and tumor necrosis factor-alpha (TNFalpha) are involved in the regulation of non-rapid eye movement sleep (NREMS). Previous studies demonstrate that mice lacking the IL-1 beta type 1 receptor spend less time in NREMS during the light period, whereas mice lacking the p55 (type 1) receptor for TNFalpha spend less time in NREMS during the dark period. To further investigate roles for IL-1 beta and TNFalpha in sleep regulation we phenotyped sleep and responses to sleep deprivation of mice lacking both the IL-1 beta receptor 1 and TNFalpha receptor 1 (IL-1R1/TNFR1 KO). Male adult mice (IL-1R1/TNFR1 KO, n=14; B6129SF2/J, n=14) were surgically instrumented with EEG electrodes and with a thermistor to measure brain temperature. After recovery and adaptation to the recording apparatus, 48 h of undisturbed baseline recordings were obtained. Mice were then subjected to 6h sleep deprivation at light onset by gentle handling. IL-1R1/TNFR1 KO mice spent less time in NREMS during the last 6h of the dark period and less time in rapid eye movement sleep (REMS) during the light period. There were no differences between strains in the diurnal timing of delta power during NREMS. However, there were strain differences in the relative power spectra of the NREMS EEG during both the light period and the dark period. In addition, during the light period relative power in the theta frequency band of the REMS EEG differed between strains. After sleep deprivation, control mice exhibited prolonged increases in NREMS and REMS, whereas the duration of the NREMS increase was shorter and there was no increase in REMS of IL-1R1/TNFR1 KO mice. Delta power during NREMS increased in both strains after sleep deprivation, but the increase in delta power during NREMS of IL-1R1/TNFR1 KO mice was of greater magnitude and of longer duration than that observed in control mice. These results provide additional evidence that the IL-1 beta and TNFalpha cytokine systems play a role in sleep regulation and in the alterations in sleep that follow prolonged wakefulness.

Interleukin-1beta: a bridge between inflammation and excitotoxicity?

Interleukin-1 (IL-1) is a proinflammatory cytokine released by many cell types that acts in both an autocrine and/or paracrine fashion. While IL-1 is best described as an important mediator of the peripheral immune response during infection and inflammation, increasing evidence implicates IL-1 signaling in the pathogenesis of several neurological disorders. The biochemical pathway(s) by which this cytokine contributes to brain injury remain(s) largely unidentified. Herein, we review the evidence that demonstrates the contribution of IL-1beta to the pathogenesis of both acute and chronic neurological disorders. Further, we highlight data that leads us to propose IL-1beta as the missing mechanistic link between a potential beneficial inflammatory response and detrimental glutamate excitotoxicity.

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.

Gene expression in the rat brain during prostaglandin D2 and adenosinergically-induced sleep

Previous studies have supported the hypothesis that macromolecular synthesis occurs in the brain during sleep as a response to prior waking activities and that prostaglandin D2 (PGD2) is an endogenous sleep substance whose effects are dependent on adenosine A2a receptor-mediated signaling. We compared gene expression in the cerebral cortex, basal forebrain, and hypothalamus during PGD2-induced and adenosinergically-induced sleep to results from our previously published study of recovery sleep (RS) after sleep deprivation (SD). Immediate early gene expression in the cortex during sleep induced by PGD2- or by the selective adenosine A2a agonist CGS21680 showed limited similarity to that observed during RS while, in the basal forebrain and hypothalamus, widespread activation of immediate early genes not seen during RS occurred. In all three brain regions, PGD2 and CGS21680 reduced the expression of arc, a transcript whose expression is elevated during SD. Using GeneChips, the majority of genes induced by either PGD2 or CGS21680 were induced by both, suggesting activation of the same pathways. However, gene expression induced in the brain after PGD2 or CGS21680 treatment was distinct from that described during RS after SD and apparently involves glial cell gene activation and signaling pathways in neural-immune interactions.

Effects of serotonergic activation by 5-hydroxytryptophan on sleep and body temperature of C57BL/6J and interleukin-6-deficient mice are dose and time related

STUDY OBJECTIVES

Extensive data implicate serotonin (5-hydroxytryptamine [5-HT]) in the regulation of sleep. Jouvet has hypothesized that 5-HT promotes wakefulness, yet is necessary for subsequent non-rapid eye movement (NREM) sleep, actions he proposes to be mediated by sleep factors. Studies in rat support this dual role for 5-HT. The objectives of this study were to (1) determine effects of serotonergic activation on sleep of mice and (2) elucidate a potential role for the cytokine interleukin-6 as a sleep factor mediating serotonergic effects on sleep.

DESIGN

C57BL/6J and B6.129S6-II6(tm1Kopf)(interleukin-6 knockout [IL-6 KO]) mice were purchased from the Jackson Laboratory and instrumented for recording the electroencephalogram and body temperature. After recovery, separate groups of mice were injected intraperitoneally at either light or dark onset with vehicle or with the 5-HT precursor 5-hydroxytryptophan (5-HTP). Sleep-wake behavior was determined and body temperature recorded for 24 hours after injections.

RESULTS

5-HTP induced hypothermia in both mouse strains. When injected at dark onset, the highest dose of 5-HTP (200 mg/kg) increased NREM sleep. Light onset administration initially increased wakefulness, with increases in NREM sleep apparent only during the subsequent dark period. For most parameters, there were no differences in responses between strains. However IL-6 KO mice at some doses exhibited a greater increase in NREM sleep.

CONCLUSIONS

5-HTP alters sleep-wake behavior and body temperature of mice in a manner similar to that of rats. Increases in NREM sleep after 5-HTP are apparent only during the dark period, which may represent a fundamental property of the serotonergic system. These results suggest that 5-HT should not be considered either wake promoting or NREM sleep promoting. Rather, the role of 5-HT in the regulation of sleep-wake behavior must be considered within the context of the degree to which the system is activated and the time at which the activation occurs.

Cytokine changes after surgical treatment of obstructive sleep apnoea syndrome

Obstructive sleep apnoea syndrome (OSAS) is associated with inflammatory processes and elevated plasma cytokines. This study assesses the effect of surgery in cytokine levels of OSAS patients. A total of 24 male patients with mild to moderate OSAS, confirmed with polysomnography underwent septoplasty and uvulo-palato-pharyngoplasty in a period of a year. Control group consisted of 12 overweighted subjects and 15 obese subjects. Peripheral venous blood was collected from each patient 1 week before surgical treatment and 6 months postoperatively. Spontaneous production of tumour necrosis factor (TNF-a) by monocytes and serum levels of IL-1beta and IL-6 were investigated. Control subjects were also examined for the same pro-inflammatory cytokines. Production of TNF-a and IL-6 were significantly elevated in OSAS patients and obese controls compared with overweighted control subjects (p < 0.05). Serum levels of IL-1beta did not differ among the study groups. Preoperative cytokine values were significantly correlated with the preoperative body mass index (BMI) and the apnoea/hypopnoea index (AHI) in OSAS patients. Surgery resulted a significant reduction in the TNF-a and IL-6 values of the study group. Decrease in cytokine level was strongly correlated with the AHI decrease. The postoperative relative percentage change of IL-6 values was significantly higher than this of TNF-a (p < 0.001). Surgical management of mild to moderate OSAS leads to a significant reduction in TNF-a and IL-6 values. Our data indicate that AHI is an independent risk factor of systemic inflammation; however it affects cytokines to a lesser degree compared with the BMI.

Systemic inflammation in non-obese children with obstructive sleep apnea

BACKGROUND

Obstructive sleep apnea (OSA) has been associated with increased systemic inflammatory responses that may contribute to an increased risk for end-organ morbidity. The changes in levels of pro-inflammatory cytokine IL-6 , and the anti-inflammatory cytokine IL-10, both of which play a major role in atherogenesis, a major consequence of OSA, have not specifically been assessed in pediatric patients.

METHODS

Consecutive non-obese children (aged 4-9years) who were polysomnographically diagnosed with OSA, and age-, gender-, ethnicity-, and BMI-matched control children underwent a blood draw the next morning after a sleep study and plasma samples were assayed for interleukins 6 (IL-6) and 10 (IL-10). These tests were repeated 4-6months after tonsillectomy and adenoidectomy (T&A) in children with OSA.

RESULTS

IL-6 levels were higher and IL-10 plasma levels were lower in children with OSA and returned to control levels after T&A.

CONCLUSIONS

Systemic inflammation is a constitutive component and consequence of OSA in many children, even in the absence of obesity, and is reversible upon treatment in most patients.

Sleep and inflammation

Among adults in the United States, sleep durations appear to have decreased in recent years. Inadequate sleep and sleep deprivation cause numerous neurobehavioral and physiological changes. A number of recent studies have reported associations between disrupted sleep/sleep deprivation and inflammatory responses, although the physiological mechanisms underlying these relationships remain unclear. Alterations in sleep due to lifestyle factors, the aging process, and disease states have all been associated with increases in a range of inflammatory markers. Several of these inflammatory processes have been associated with reduced health status (e.g., C-reactive protein and cardiovascular disease). Thus, maintaining adequate sleep duration and quality through good sleep habits and treatment of sleep disorders may reduce inflammatory processes associated with aging and increase the wellness phenotype.

Obesity and obstructive sleep apnea: pathogenic mechanisms and therapeutic approaches

Obstructive sleep apnea is a common disorder whose prevalence is linked to an epidemic of obesity in Western society. Sleep apnea is due to recurrent episodes of upper airway obstruction during sleep that are caused by elevations in upper airway collapsibility during sleep. Collapsibility can be increased by underlying anatomic alterations and/or disturbances in upper airway neuromuscular control, both of which play key roles in the pathogenesis of obstructive sleep apnea. Obesity and particularly central adiposity are potent risk factors for sleep apnea. They can increase pharyngeal collapsibility through mechanical effects on pharyngeal soft tissues and lung volume, and through central nervous system-acting signaling proteins (adipokines) that may affect airway neuromuscular control. Specific molecular signaling pathways encode differences in the distribution and metabolic activity of adipose tissue. These differences can produce alterations in the mechanical and neural control of upper airway collapsibility, which determine sleep apnea susceptibility. Although weight loss reduces upper airway collapsibility during sleep, it is not known whether its effects are mediated primarily by improvement in upper airway mechanical properties or neuromuscular control. A variety of behavioral, pharmacologic, and surgical approaches to weight loss may be of benefit to patients with sleep apnea, through distinct effects on the mass and activity of regional adipose stores. Examining responses to specific weight loss strategies will provide critical insight into mechanisms linking obesity and sleep apnea, and will help to elucidate the humoral and molecular predictors of weight loss responses.

Lipopolysaccharide modulation of thyrotropin-releasing hormone (TRH) and TRH-like peptide levels in rat brain and endocrine organs

Lipopolysaccharide (LPS) is a proinflammatory and depressogenic agent whereas thyrotropin-releasing hormone (TRH; pGlu-His-Pro-NH2) is an endogenous antidepressant and neuroprotective peptide. LPS and TRH also have opposing effects on K+ channel conductivity. We hypothesized that LPS can modulate the expression and release of not only TRH but also TRH-like peptides with the general structure pGlu-X-Pro-NH2, where "X" can be any amino acid residue. The response might be "homeostatic," that is, LPS might increase TRH and TRH-like peptide release, thereby moderating the cell damaging effects of this bacterial cell wall constituent. On the other hand, LPS might impair the synthesis and release of these neuropeptides, thus facilitating the induction of early response genes, cytokines, and other downstream biochemical changes that contribute to the "sickness syndrome." Sprague-Dawley rats (300 g) received a single intraperitoneal injection of 100 microg/kg LPS. Animals were then decapitated 0, 2, 4, 8, and 24 h later. Serum cytokines and corticosterone peaked 2 h after intraperitoneal LPS along with a transient decrease in serum T3. TRH and TRH-like peptides were measured by a combination of high-performance liquid chromatography and radioimmunoassay. TRH declined in the nucleus accumbens and amygdala in a manner consistent with LPS-accelerated release and degradation. Various TRH-like peptide levels increased at 2 h in the anterior cingulate, hippocampus, striatum, entorhinal cortex, posterior cingulate, and cerebellum, indicating decreased release and clearance of these peptides. These brain regions are part of a neuroimmunomodulatory system that coordinates the behavioral, endocrine, and immune responses to the stresses of sickness, injury, and danger. A sustained rise in TRH levels in pancreatic beta-cells accompanied LPS-impaired insulin secretion. TRH and Leu-TRH in prostate and TRH in epididymis remained elevated 2-24 h after intraperitoneal LPS. We conclude that these endogenous neuroprotective and antidepressant-like peptides both mediate and moderate some of the behavioral and toxic effects of LPS.

Marital quality and the marital bed: examining the covariation between relationship quality and sleep

The majority of adults sleep with a partner, and for a significant proportion of couples, sleep problems and relationship problems co-occur, yet there has been little systematic study of the association between close relationships and sleep. The association between sleep and relationships is likely to be bi-directional and reciprocal-the quality of close relationships influences sleep and sleep disturbances or sleep disorders influence close relationship quality. Therefore, the purpose of the present review is to summarize the extant research on (1) the impact of co-sleeping on bed partner's sleep, (2) the impact of sleep disturbance or sleep disorders on relationship functioning, and (3) the impact of close relationship quality on sleep. In addition, we provide a conceptual model of biopsychosocial pathways to account for the covariation between relationship functioning and sleep. Recognizing the dyadic nature of sleep and incorporating such knowledge into both clinical practice and research in sleep medicine may elucidate key mechanisms in the etiology and maintenance of both sleep disorders and relationship problems and may ultimately inform novel treatments.

Increased voluntary exercise in mice deficient for tumour necrosis factor-alpha and lymphotoxin-alpha

BACKGROUND

The endogenous mediators playing a role in the sensing of fatigue and cessation of exercise are yet to be characterized. We hypothesized that proinflammatory cytokines, in particular tumour necrosis factor-alpha (TNFalpha) and lymphotoxin-alpha (LT) transmit signals leading to fatigue.

MATERIALS AND METHODS

Mice were placed in a cage with a freely rotating exercise wheel and allowed to adapt for 24 h. The running distance was measured for two additional periods of 24 h. The effects of the administration of intravenous anti-TNF antibodies, intracerebral recombinant TNF, or intravenous lipopolysaccharide (LPS) were also determined.

RESULTS

Compared to normal littermates, the voluntary daily running distance was 1.8-fold greater in mice with a disruption of the gene for TNFalpha, and 3-fold greater in mice with a gene disruption for both TNFalpha and LT. Intravenous administration of a monoclonal antibody against murine TNFalpha did not affect the running distance of wild-type mice, whereas administration of TNF intracerebrally reduced by 4-fold the voluntary running distance of the animals. This demonstrates that fatigue is mediated by TNFalpha expressed in the central nervous system (CNS) and not by increased peripheral TNFalpha concentrations. TNFalpha and LT are strong inducers of prostaglandins, but mice with disrupted prostaglandin or prostacyclin receptors exhibited running distances not significantly different from their wild-type littermates. Thus, signalling molecules other than prostaglandins mediate the effect of TNFalpha and LT on exercise capacity.

CONCLUSIONS

Our finding that exercise capacity is controlled by TNFalpha is the first to define the endogenous mediators of fatigue, and may have important implications for diseases with impaired exercise tolerance.

Exercise, sleep and cytokines: is there a relation?

Physical exercise is a modality of non-pharmacological treatment for sleep disorders. Contradicting results are still found in studies of the effect of exercise on sleep. Among the substances that have been described as sleep modulators, cytokines produced during the recovery period after an acute exercise session are very important. Various studies have verified that physical exercise may alter the plasma concentration of the many pro-inflammatory cytokines that may in turn modulate sleep. A number of factors seem to mediate this effect of exercise, including duration, intensity, and form of exercise, in addition to temperature and metabolic alterations. The mechanisms through which exercise promotes alterations in sleep architecture remain to be clarified. Researchers speculate that many hormones and substances produced by metabolism may affect sleep. Therefore, the object of this review is to discuss the effects of exercise and cytokines on sleep, and the relation between these two sleep-regulating components, raising the hypothesis that the alterations in sleep promoted by exercise are mediated by cytokines, which, by increasing the nREM sleep phase, would stimulate the regenerating characteristics of sleep.

Neuroendocrine-immune correlates of circadian physiology: studies in experimental models of arthritis, ethanol feeding, aging, social isolation, and calorie restriction

Virtually all neuroendocrine and immunological variables investigated in animals and humans display biological periodicity. Circadian rhythmicity is revealed for every hormone in circulation as well as for circulating immune cells, lymphocyte metabolism and transformability, cytokines, receptors, and adhesion molecules. Clock genes, notably the three Period (Per1/Per2/Per3) genes and two Cryptochrome (Cry1/Cry2) genes, are present in immune and endocrine cells and are expressed in a circadian manner in human cells. This review discusses the circadian disruption of hormone release and immune-related mechanisms in several animal models in which circulating cytokines are modified including rat adjuvant arthritis, social isolation in rats and rabbits and alcoholism, the aging process and calorie restriction in rats. In every case the experimental manipulation used perturbed the temporal organization by affecting the shape and amplitude of a rhythm or by modifying the intrinsic oscillatory mechanism itself.

Possible links between behavioral and physiological indices of tiredness, fatigue, and exhaustion in advanced cancer

GOALS

In this theoretical paper, we present the Edmonton Fatigue Framework (EFF), a new framework for the study of tiredness, fatigue, and exhaustion in advanced cancer.

MATERIALS AND METHODS

The Fatigue Adaptation Model (FAM), the starting point for the EFF, was drawn from a literature review pertaining to fatigue in depression, chronic fatigue syndrome, cancer, shift workers, and athletes published in the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Medical Literature Analysis and Retrieval System Online (MEDLINE), PubMed, PsychINFO, SPORTdiscus, and CancerLit between 1995 and 2004, and from seven qualitative studies conducted by our group. The EFF, an elaboration of the FAM, was constructed after an expansion of our literature review to 2006 and team discussion. The EFF provides new insights into possible links between behavioral and physiological indices of tiredness, fatigue, and exhaustion as they occur in both ill and non-ill states. In this paper, however, we consider only possible links in advanced cancer.

CONCLUSIONS

We propose that stressors associated with advanced cancer and its supportive treatment trigger declines in four systems -- cognitive function, sleep quality, nutrition, and muscle endurance -- and that these declines reduce one's ability to adapt. While these systems each likely has its own effect on adaptation, we propose that the most important and serious effects arise from interactions among declines in cognitive function, sleep quality, nutrition, and muscle endurance.

CONCLUSIONS

Interventions for fatigue have been limited by a lack of understanding about its etiology. Hypotheses arising from the EFF; suggest a new direction for further study that focuses on interactions among cognitive function, sleep quality, nutrition, and muscle endurance.

Sleep loss changes microRNA levels in the brain: a possible mechanism for state-dependent translational regulation

MicroRNAs (miRNAs) are small ( approximately 22 nucleotides) non-coding RNA strands that base pair with mRNA to degrade it or inhibit its translation. Because sleep and sleep loss induce changes in many mRNA species, we hypothesized that sleep loss would also affect miRNA levels in the brain. Rats were sleep-deprived for 8h then decapitated; hippocampus, prefrontal and somatosensory cortices and hypothalamus tissues were harvested and frozen in liquid nitrogen. miRNA was extracted and then characterized using microarrays. Several let-7 miRNA microarray results using hippocampus and prefrontal cortex samples were verified by PCR. From the array data it was determined that about 50 miRNA species were affected by sleep loss. For example, in the hippocampus of sleep-deprived rats, miRNA expression increased compared to cage control samples. In contrast, the majority of miRNA species in the somatosensory and prefrontal cortices decreased, while in the hypothalamus miRNA species were both up- and down-regulated after sleep deprivation. The number of miRNA species affected by sleep loss, their differential expression in separate brain structures and their predicted targets suggest that they have a role in site-specific sleep mechanisms. Current results are, to our knowledge, the first demonstration of the homeostatic process, sleep, altering brain miRNA levels.

Inflammation and sleep in healthy individuals

STUDY OBJECTIVES

Inflammation is relatively common in individuals with a sleep disorder and is associated with quality of sleep. The purpose of this study was to examine whether inflammation is associated with quality of sleep in healthy individuals.

DESIGN & SETTING

Observational study in a General Clinical Research Center.

PARTICIPANTS

This study characterized inflammation and polysomno-graphically verified sleep in 124 African American and Caucasian American women and men without a sleep disorder.

MEASUREMENTS AND RESULTS

Circulating levels of 3 markers and/or mediators of inflammation known to be elevated in sleep disorders and in cardiovascular disease were determined (interleukin-6 [IL-6] endothelin-1 [ET-1], soluble intercellular adhesion molecule-1 [sICAM-1]). Sleep was characterized by polysomnography. Multiple linear regression analyses showed that increasing age, male sex, and African American ethnicity were independently associated with poorer sleep. After controlling for these variables, higher levels of ET-1 were independently associated with greater sleep latency (P < or = 0.01), greater rapid eye movement (REM) latency (P < or = 0.01), more slow wave sleep (P < or = 0.05), and less stage 1 sleep (P < or = 0.01). Higher IL-6 levels were independently associated with greater REM latency (P < or = 0.05).

CONCLUSIONS

The findings suggest that, in individuals without a known sleep disorder, ET-1, a potent vasoconstrictor and mediator of inflammation, is associated with more deep sleep, whereas both ET-1 and IL-6 are associated with increased latency of sleep and of REM. The findings underscore the complex relationships between peripheral markers of inflammation and sleep.

The hypothalamic peptidergic system, hypocretin/orexin and vigilance control

Using forward and reverse genetics, the genes (hypocretin/orexin ligand and its receptor) involved in the pathogenesis of the sleep disorder, narcolepsy, in animals, have been identified. Mutations in hypocretin related-genes are extremely rare in humans, but hypocretin-ligand deficiency is found in most narcolepsy-cataplexy cases. Hypocretin deficiency in humans can be clinically detected by CSF hypocretin-1 measures, and undetectably low CSF hypocretin-1 is now included in the revised international diagnostic criteria of narcolepsy. Since hypocretin-ligand deficiency is the major pathophysiology in human narcolepsy, hypocretin replacements (using hypocretin agonists or gene therapy) are promising future therapeutic options. New insights into the roles of hypocretin system on sleep physiology have also rapidly increased. Hypocretins are involved in various fundamental hypothalamic functions such as feeding, energy homeostasis and neuroendocrine regulation. Hypocretin neurons project to most ascending arousal systems (including monoaminergic and cholinergic systems), and generally exhibit excitatory inputs. Together with the recent finding of the sleep promoting system in the hypothalamus (especially in the GABA/galanin ventrolateral preoptic area which exhibits inhibitory inputs to these ascending systems), the hypothalamus is now recognized as the most important brain site for the sleep switch, and other peptidergic systems may also participate in this regulation. Meanwhile, narcolepsy now appears to be a more complex condition than previously thought. The pathophysiology of the disease is involved in the abnormalities of sleep and various hypothalamic functions due to hypocretin deficiency, such as the changes in energy homeostasis, stress reactions and rewarding. Narcolepsy is therefore, an important model to study the link between sleep regulation and other fundamental hypothalamic functions.

Reduced expression of TAC1, PENK and SOCS2 in Hcrtr-2 mutated narcoleptic dog brain

Background

Narcolepsy causes dramatic behavioral alterations in both humans and dogs, with excessive sleepiness and cataplexy triggered by emotional stimuli. Deficiencies in the hypocretin system are well established as the origin of the condition; both from studies in humans who lack the hypocretin ligand (HCRT) and in dogs with a mutation in hypocretin receptor 2 (HCRTR2). However, little is known about molecular alterations downstream of the hypocretin signals.

Results

By using microarray technology we have screened the expression of 29760 genes in the brains of Doberman dogs with a heritable form of narcolepsy (homozygous for the canarc-1 [HCRTR-2-2] mutation), and their unaffected heterozygous siblings. We identified two neuropeptide precursor molecules, Tachykinin precursor 1 (TAC1) and Proenkephalin (PENK), that together with Suppressor of cytokine signaling 2 (SOCS2), showed reduced expression in narcoleptic brains. The difference was particularly pronounced in the amygdala, where mRNA levels of PENK were 6.2 fold lower in narcoleptic dogs than in heterozygous siblings, and TAC1 and SOCS2 showed 4.4 fold and 2.8 fold decrease in expression, respectively. The results obtained from microarray experiments were confirmed by real-time RT-PCR. Interestingly, it was previously shown that a single dose of amphetamine-like stimulants able to increase wakefulness in the dogs, also produce an increase in the expression of both TAC1 and PENK in mice.

Conclusion

These results suggest that TAC1, PENK and SOCS2 might be intimately connected with the excessive daytime sleepiness not only in dogs, but also in other species, possibly including humans.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

Pro-inflammatory cytokine and acute phase protein responses to low-dose lipopolysaccharide (LPS) challenge in pigs

The objective of this study was to establish the pro-inflammatory cytokine and acute phase protein responses to low-dose lipopolysaccharide (LPS) challenge in pigs and to determine whether these immune parameters could also be measured in saliva. Possible gender differences in the acute phase reaction were also assessed. At 6 weeks of age, 24 male and 24 female pigs were injected intraperitoneally with a single dose of 0 or 5 μg/kg live weight (LW) of LPS fromEscherichia coli(treatment). Matched saliva and blood samples were taken at 0, 2, 4, 8, 12 or 24 h after treatment administration. Samples were analysed for concentrations of the pro-inflammatory cytokines tumor necrosis factor-alpha (TNF-α) and interleukin-1beta (IL-1β), the acute phase proteins C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (Hp), and cortisol. Low-dose LPS administration increased plasma levels of TNF-α (P<0·001), CRP (P<0·05) and SAA (P<0·05) but did not affect plasma concentrations of IL-1β or Hp (P>0·1). Treatment by time interactions showed that plasma levels of TNF-α and CRP in LPS-treated pigs peaked at 2 h (P<0·001) and 12 h (P<0·01), respectively. Low-dose LPS injection tended to increase plasma concentrations of cortisol (P=0·056) and the response to LPS differed between genders (P<0·05), with females showing higher cortisol responsiveness to the challenge (P<0·01). Males showed higher levels of both cytokines regardless of the treatment (P<0·05), probably due to the inhibition of cytokine synthesis by cortisol. Concentrations of both pro-inflammatory cytokines were consistently detectable in saliva and were present in higher concentrations than in plasma (P<0·001). Hence, plasma TNF-α, CRP and SAA are useful indicators of sub-acute inflammation/infection in pigs as simulated by a low-dose LPS challenge and gender differences exist in the pro-inflammatory cytokine response after a low dose of LPS.

Neuropeptides as possible targets in sleep disorders

Insomnia and hypersomnia are frequent sleep disorders, and they are most often treated pharmacologically with hypnotics and wake-promoting compounds. These compounds act on classical neurotransmitter systems, such as benzodiazepines on GABA-A receptors, and amfetamine-like stimulants on monoaminergic terminals to modulate neurotransmission. In addition, acetylcholine, amino acids, lipids and proteins (cytokines) and peptides, are known to significantly modulate sleep and are, therefore, possibly involved in the pathophysiology of some sleep disorders. Due to the recent developments of molecular biological techniques, many neuropeptides have been newly identified, and some are found to significantly modulate sleep. It was also discovered that the impairment of the hypocretin/orexin neurotransmission (a recently isolated hypothalamic neuropeptide system) is the major pathophysiology of narcolepsy, and hypocretin replacement therapy is anticipated to treat the disease in humans. In this article, the authors briefly review the history of neuropeptide research, followed by the sleep modulatory effects of various neuropeptides. Finally, general strategies for the pharmacological therapeutics targeting the peptidergic systems for sleep disorders are discussed.

The importance of rhinitis on sleep, daytime somnolence, productivity and fatigue

PURPOSE OF REVIEW

The goal of treatment of allergic rhinitis should include improvement of daytime and nighttime symptoms, sleep, and quality of life. Congestion from allergic rhinitis is associated with decreased learning and productivity at work and school and a reduced quality of life. The release of inflammatory mediators and activation of inflammatory cells results in nasal congestion, causing disrupted sleep and subsequent daytime somnolence.

RECENT FINDINGS

This review presents evidence that allergic rhinitis causes sleep disruption, and discusses the pathophysiology of this process. The medications used to treat allergic rhinitis and their ability to improve sleep in patients with allergic rhinitis are reviewed.

SUMMARY

Some allergic rhinitis medications can be sedating; therefore, it is important to treat allergic rhinitis with medications that improve symptoms while producing few adverse effects. Medications such as the second-generation antihistamines and anticholinergic drugs are well tolerated, but have little effect on congestion. Intranasal corticosteroids reduce congestion, improve sleep and sleep problems, and reduce daytime sleepiness, fatigue, and inflammation. Recently, montelukast, a leukotriene receptor antagonist, has been added to the therapies approved for allergic rhinitis. Montelukast significantly improves both daytime and nighttime symptoms.

Cancer Chemotherapy-Related Symptoms: Evidence to Suggest a Role for Proinflammatory Cytokines

PURPOSE/OBJECTIVES

To provide an overview of the evidence that supports a role for the proinflammatory cytokines interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) in the etiology of cancer chemotherapy-related symptoms.

DATA SOURCES

Electronic nursing, psychology, and medicine databases; online meeting abstracts; and personal experimental observations.

DATA SYNTHESIS

Substantial evidence implicates the proinflammatory cytokines IL-1beta, TNF-alpha, and IL-6 in the etiology of chemotherapy-related anorexia, cachexia, anemia, pain, sleep disturbance, fatigue, and depression.

CONCLUSIONS

Further investigation into the role of these cytokines in the genesis of chemotherapy-related symptoms is warranted. The development of appropriate animal models likely will be key to understanding the relationship among cancer chemotherapy, proinflammatory cytokines, and symptoms.

IMPLICATIONS FOR NURSING

Nurses traditionally have been leaders in symptom management. The symptoms experienced by patients undergoing chemotherapy have a profound negative impact on quality of life and patients' ability to receive prescribed treatments. An understanding of potential mechanisms underlying the physiologic and behavioral consequences of chemotherapy administration will aid nurses in the development of interventions to effectively manage chemotherapy-related symptoms.

Daytime napping after a night of sleep loss decreases sleepiness, improves performance, and causes beneficial changes in cortisol and interleukin-6 secretion

Sleep loss has been associated with increased sleepiness, decreased performance, elevations in inflammatory cytokines, and insulin resistance. Daytime napping has been promoted as a countermeasure to sleep loss. To assess the effects of a 2-h midafternoon nap following a night of sleep loss on postnap sleepiness, performance, cortisol, and IL-6, 41 young healthy individuals (20 men, 21 women) participated in a 7-day sleep deprivation experiment (4 consecutive nights followed by a night of sleep loss and 2 recovery nights). One-half of the subjects were randomly assigned to take a midafternoon nap (1400-1600) the day following the night of total sleep loss. Serial 24-h blood sampling, multiple sleep latency test (MSLT), subjective levels of sleepiness, and psychomotor vigilance task (PVT) were completed on the fourth (predeprivation) and sixth days (postdeprivation). During the nap, subjects had a significant drop in cortisol and IL-6 levels (P < 0.05). After the nap they experienced significantly less sleepiness (MSLT and subjective, P < 0.05) and a smaller improvement on the PVT (P < 0.1). At that time, they had a significant transient increase in their cortisol levels (P < 0.05). In contrast, the levels of IL-6 tended to remain decreased for approximately 8 h (P = 0.1). We conclude that a 2-h midafternoon nap improves alertness, and to a lesser degree performance, and reverses the effects of one night of sleep loss on cortisol and IL-6. The redistribution of cortisol secretion and the prolonged suppression of IL-6 secretion are beneficial, as they improve alertness and performance.

Influenza virus-induced glucocorticoid and hypothalamic and lung cytokine mRNA responses in dwarf lit/lit mice

Influenza virus infection up-regulates cytokines such as interleukin-1beta (IL-1beta) and activates the somatotropic axis and the hypothalamic-pituitary axis. Mice with deficits in growth hormone releasing hormone (GHRH) signaling (lit/lit mice) respond to influenza virus challenge with a progressive decrease in sleep and lower survival rates. Current experiments characterize plasma glucocorticoid responses and hypothalamic and lung mRNA expression of sleep-related genes in lit/lit mice and their heterozygous controls after influenza virus challenge. lit/lit mice had higher basal and post-infection plasma corticosterone levels compared to controls. In contrast, the heterozygous mice increased hypothalamic GHRH-receptor, CRH-type 2 receptor, IL-1beta, and tumor necrosis factor-alpha (TNF-alpha) mRNAs after virus treatment while the lit/lit mice failed to up-regulate these substances. In contrast, lung levels of IL-1beta and TNF-alpha mRNAs were greater in the lit/lit mice. These data are consistent with the hypothesis that the sleep response to influenza infection is mediated, in part, by an up-regulation of hypothalamic sleep-related transcripts and they also show that a primary deficit in GHRH signaling is associated with enhanced corticosterone secretion and attenuated hypothalamic cytokine response to infection.

Sleep and Psychoneuroimmunology

Personal experience indicates we sleep differently when sick. Data reviewed demonstrate the extent to which sleep is altered during the course of infection of host organisms by several classes of pathogens. One important unanswered question is whether or not the alterations in sleep during infection are of functional relevance. That is, does the way we sleep when sick facilitate or impede recovery? One retrospective, preclinical study suggests that sleep changes during infection are of functional relevance. Toth and colleagues [102] analyzed sleep responses of rabbits to three different microbial infections. Those rabbits that exhibited robust increases in NREM sleep were more likely to survive than those that exhibited long periods of NREM sleep suppression. These tantalizing data suggest that the precise alterations in sleep through the course of infection are important determinants of morbidity and mortality. Data from healthy subjects demonstrate a role for at least two cytokines in the regulation of spontaneous, physiologic NREM sleep. A second critical yet unanswered question is whether or not cytokines mediate infection-induced alterations in sleep. The hypothesis that cytokines mediate infection-induced alterations in sleep is logical based on observations of the impact of infection on levels of cytokines in the peripheral immune system and in the brain. No attempts have been made to intervene with cytokine systems in brain during the course of infection to determine if there is an impact on infection-induced alterations in sleep. Although substantial progress has been made in elucidating the myriad mechanisms by which cytokines regulate and modulate sleep, much remains to be determined with respect to mechanistic and functional aspects of infection-induced alterations in sleep.

Gene expression in the rat cerebral cortex: comparison of recovery sleep and hypnotic-induced sleep

Most hypnotic medications currently on the market target some aspect of GABAergic neurotransmission. Although all such compounds increase sleep, these drugs differentially affect the activity of the cerebral cortex as measured by the electroencephalogram. Whereas benzodiazepine medications such as triazolam tend to suppress slow wave activity in the cortex, the GABA(B) ligand gamma-hydroxybutyrate greatly enhances slow wave activity and the non-benzodiazepine, zolpidem, which binds to the omega1 site on the GABA(A) receptor/Cl(-) ionophore complex, is intermediate in this regard. Our previous studies have demonstrated that a small number of genes exhibit increased expression in the cerebral cortex of the mouse and rat during recovery sleep after sleep deprivation: egr-3, fra-2, grp78, grp94, ngfi-b, and nr4a3. Using these genes as a panel of biomarkers associated with sleep, we asked whether hypnotic medications induce similar molecular changes in the rat cerebral cortex to those observed when both sleep continuity and slow wave activity are enhanced during recovery sleep. We find that, although each drug increases the expression of a subset of genes in the panel of biomarkers, no drug fully replicates the molecular changes in the cortex associated with recovery sleep. Furthermore, high levels of slow wave activity in the cortex are correlated with increased expression of fra-2 whereas the expression of grp94 is correlated with body temperature. These results demonstrate that sleep-related changes in gene expression may be affected by physiological covariates of sleep and wakefulness rather than by vigilance state per se.

Platelet activating factor and its metabolite promote sleep in rabbits

Platelet activating factor (PAF) is a key inflammatory mediator. PAF and its receptor are found in brain and PAF affects or is affected by the production of sleep promoting cytokines such as interleukin-1. PAF also interacts with several other sleep-regulatory substances such as nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, nitric oxide, prostaglandins, and prolactin. We thus hypothesized that PAF would increase sleep. In these experiments, each rabbit received an injection of 25 microl of 2% DMSO to obtain control values, and on a separate day received PAF or lyso-PAF, a metabolite of PAF. Ten, 100 and 500 nmol for each substance was injected intracerebroventricularly. Both PAF and lyso-PAF enhanced non-rapid eye movement (NREM) sleep but not REM sleep. Lyso-PAF, but not PAF, induced hyperthermia. Results are consistent with the hypothesis that the brain cytokine network is involved in physiological sleep regulation.

A role for cardiotrophin-like cytokine in the circadian control of mammalian locomotor activity

The suprachiasmatic nucleus (SCN) drives circadian rhythms of locomotor behavior by releasing factors that act on receptor sites near the third ventricle. Here we show that cardiotrophin-like cytokine (CLC) satisfies multiple criteria for a circadian regulator of locomotor activity. In the mouse, CLC is expressed in a subpopulation of SCN vasopressin neurons with a circadian rhythm that peaks during the daily period of locomotor quiescence. CLC receptors flank the third ventricle, and acute infusion of CLC into the third ventricle produced a transient blockade of locomotor activity without affecting the circadian clock. The hypothalamic infusion of neutralizing antibodies to the CLC receptor produced extra daily locomotor activity at the time when CLC is maximally expressed. These results suggest that CLC is probably an SCN output signal important for shaping daily rhythms of behavior; moreover, they indicate an unexpected role for a cytokine in adult brain function.

Cytokines and sleep

Personal experience and empirical data indicate sleep is altered during sickness. Important signaling molecules of the peripheral immune system called cytokines orchestrate responses to infection. Through a variety of mechanisms, the brain detects activation of the peripheral immune system. The brain responds to infection by altering physiological processes and complex behavior, including sleep. These changes in physiology and behavior collectively function to support the immune system, and under normal circumstances the health of the host is restored. Several of these cytokines, and their receptors, are present in normal healthy brain. Some cytokines regulate sleep under physiological conditions, in the absence of infection or immune challenge. For example, interleukin-1 directly alters discharge patterns of neurons in hypothalamic and brainstem circuits implicated in the regulation of sleep-wake behavior. Many other cytokines modulate sleep because they interact with neurotransmitter, peptide, and/or hormone systems to initiate a cascade of responses that subsequently alter sleep-wake behavior. Because cytokines regulate/modulate sleep-wake behavior in the absence of immune challenge, and cytokine concentrations and profiles are altered during infection, it is likely that cytokines mediate infection-induced alterations in sleep. Whether the changes in sleep that occur during infection are beneficial and aid in recovery remains to be determined.

Sleep disturbances as predictors of hospitalization for back disorders-a 28-year follow-up of industrial employees

STUDY DESIGN

A prospective cohort study.

OBJECTIVE

To study the relationship of sleep disturbances with severe back disorders leading to hospitalization.

SUMMARY OF BACKGROUND DATA

Sleep disturbances are associated with persistent pain syndromes, but little is known about their relationship with back disorders.

METHODS

The first hospital admission for back disorders from 1973 to 2000 was studied in a cohort of metal industry workers (n = 902). The occurrence of sleep disturbances at baseline was categorized as: none; 1 type (either difficulties in falling asleep/waking up at night or nightmares); or both types. Cox proportional hazards regression was used to estimate the time between the assessment of risk factors and first hospital admission for back disorders.

RESULTS

Those individuals who had 1 type of sleep disturbance had a 2.1-fold (95% confidence interval 1.1-3.8) risk of back-related hospitalization, and those with both types of disturbance a 2.4-fold (1.2-4.6) risk, compared with those with no sleep disturbances. The hazard ratios were 2.1; 1.0-4.6 and 2.9; 1.2-7.1, respectively, when patients with chronic back disease or recurrent back symptoms at baseline were excluded from the analyses.

CONCLUSION

These findings suggest that sleep disturbances are predictive of hospitalization for back disorders. The mechanism underlying this association warrants further study.

Bidirectional communication between the brain and the immune system: implications for physiological sleep and disorders with disrupted sleep

This review describes mechanisms of immune-to-brain and brain-to-immune signaling involved in mediating physiological sleep and altered sleep with disease. The central nervous system (CNS) modulates immune function by signaling target cells of the immune system through autonomic and neuroendocrine pathways. Neurotransmitters and hormones produced and released by these pathways interact with immune cells to alter immune functions, including cytokine production. Cytokines produced by cells of the immune and nervous systems regulate sleep. Cytokines released by immune cells, particularly interleukin-1beta and tumor necrosis factor-alpha, signal neuroendocrine, autonomic, limbic and cortical areas of the CNS to affect neural activity and modify behaviors (including sleep), hormone release and autonomic function. In this manner, immune cells function as a sense organ, informing the CNS of peripheral events related to infection and injury. Equally important, homeostatic mechanisms, involving all levels of the neuroaxis, are needed, not only to turn off the immune response after a pathogen is cleared or tissue repair is completed, but also to restore and regulate natural diurnal fluctuations in cytokine production and sleep. The immune system's ability to affect behavior has important implications for understanding normal and pathological sleep. Sleep disorders are commonly associated with chronic inflammatory diseases and chronic age- or stress-related disorders. The best studied are rheumatoid arthritis, fibromyalgia and chronic fatigue syndromes. This article reviews our current understanding of neuroimmune interactions in normal sleep and sleep deprivation, and the influence of these interactions on selected disorders characterized by pathological sleep.

Cytokines and normal sleep

PURPOSE OF REVIEW

Cytokines are mediators of immune system responses with multiple biologic actions on several target tissues. Over the past two decades, research has explored the interactions between cytokines and sleep mechanisms of the brain. This short review highlights selected findings that have advanced our understanding of the relation between cytokines and sleep.

RECENT FINDINGS

A complex network of cytokines and their receptors exists in brain. Cytokines may either promote or inhibit sleep. Of cytokines studied thus far, evidence indicates that interleukin-1 and tumor necrosis factor play a role in the regulation of non-rapid eye movement sleep. Their sites of action for regulating such sleep likely include the hypothalamic preoptic area and the basal forebrain. Mechanisms of action include direct receptor-mediated effects on neurons and the synthesis and release of numerous transmitters, peptides, and hormones that lead to subsequent changes in sleep. Among others, the cascade of responses induced by cytokines that may lead to subsequent alterations in sleep includes alterations in nitric oxide synthesis and effects on neurohormonal systems such as growth hormone releasing hormone. The activation by cytokines of the hypothalamic-pituitary-adrenal axis also influences sleep. Studies suggest that there is a significant overlap between neurohormonal systems such as the somatotropic and hypothalamic-pituitary-adrenal axes and cytokines, particularly with regard to their effects on sleep-wake regulation.

SUMMARY

There is increasing evidence of a role for cytokines in regulating spontaneous non-rapid eye movement sleep. The somatotropic hormonal system and hypothalamic-pituitary-adrenal axis mediate, in part, the effects of cytokines on sleep.

Glutamate induces the expression and release of tumor necrosis factor-alpha in cultured hypothalamic cells

Tumor necrosis factor-alpha (TNFalpha) affects several CNS functions such as regulation of sleep, body temperature, and feeding during pathology. There is also evidence for TNFalpha involvement in physiological sleep regulation, e.g., TNFalpha induces sleep and brain levels of TNFalpha increase during prolonged wakefulness. The immediate cause of enhanced TNFalpha production in brain is unknown. We investigated whether glutamate could signal TNFalpha production because glutamate is a neurotransmitter associated with cell activation and wakefulness. We used primary cultures of fetal rat hypothalamic cells to examine the expression and release of TNFalpha. Immunostaining for neuron specific enolase revealed that the cultures were 50-60% neuronal and 40-50% non-neuronal cells. TNFalpha was detected in both the media and cells under basal conditions. Stimulation of the cells with 1 mM glutamate for 2 h produced an increase in media content of TNFalpha, whereas cell content was elevated at earlier time points. Using trypan blue exclusion and MTT assays, there was no evidence of cell toxicity with this stimulation protocol. Immunocytochemical staining revealed that TNFalpha was expressed by approximately 25% of the neurons and approximately 75% of the glial cell in the culture. Stimulation of the cultures with glutamate did not increase the percentage of cells expressing TNFalpha. We conclude that TNFalpha is constitutively expressed and released by healthy cultures of hypothalamic cells and that activation of the cells with a non-toxic challenge of glutamate increases TNFalpha production. These findings support the hypothesis that TNFalpha can participate in normal physiological regulation of sleep and feeding.

Clinical assessment of blood leukocytes, serum cytokines, and serum immunoglobulins as responses to sleep deprivation in laboratory rats

The specific systems and mechanisms affected by sleep deprivation that may perpetuate disease processes in humans still are speculative. In laboratory rats, prolonged sleep deprivation induces a state marked by abnormal control over indigenous bacteria that results in transient infections of internal tissues and eventual lethal septicemia. The present studies investigated changes in blood, serum, and bone marrow parameters that may provide diagnostic clues to immunopathology. Prolonged sleep deprivation was produced in rats by the disk-over-water method, a well-established and selective means that does not interfere with normal waking behaviors. Measurements included bone and blood differential white blood cell counts, multiple serum cytokines and chemokines, several major Ig classes and subclasses, and serum endotoxin concentrations. The results indicated mild, regenerative neutrophilia in sleep-deprived rats, initially accompanied by immature neutrophils and later by monocytosis. The corresponding serum cytokine profile revealed an evolving proinflammatory state, particularly by high incidence of interleukin-1β, implicating mononuclear phagocytes and resident tissue cells as main intermediary sources. In addition, multiple serum Ig classes were increased by sleep deprivation without experimental administration of an exogenous antigen. Despite this immune activation, there was failure to eradicate invading bacteria and toxins, suggesting competing anti-inflammatory processes or interference with immune effector functions during sleep deprivation. Nearly all of the immune-related events that emerged as responses to sleep deprivation have been implicated as etiological or provocative factors in other disease processes and may provide means by which sleep deprivation as a risk factor in disease may become understood.

Sleep disturbances in the rotenone animal model of Parkinson disease

Parkinson disease (PD) is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) and the presence of intracytoplasmatic inclusions known as Lewy bodies. Chronic administration of rotenone (RT) produces Parkinson's-like symptoms in rats. Because PD patients have disrupted sleep patterns, we determined if chronic RT administration produces similar changes in rat sleep. RT was administered for 28 days to rats. Basal and vehicle (VH) rats received saline or dimethyl sulfoxide and polyethylene glycol (1:1), respectively. VH infusion induced a progressive decrease in non-rapid eye movement sleep (NREMS) during the 4-week period of VH infusion and REMS was reduced in the third and fourth week of VH infusion. VH infusion did not induce dopaminergic cell degeneration. Rats receiving RT infusion also showed decreased NREMS during the treatment. REMS was dramatically reduced on day 7 although subsequently on days 13 and 20 REMS was similar to basal values. After 4 weeks of RT infusion, time in REMS was decreased again. In RT-treated rats, progressive dopaminergic cell degeneration occurred in the SNc. After 4 weeks of daily injections of L-dopa in RT-infused rats, NREMS values remained similar to those values obtained after RT alone. L-dopa therapy did, however, induce a recovery of REMS in weeks 3 and 4 of RT infusion. Dopaminergic cell damage persisted in the L-dopa-RT-infused rats. We conclude that the RT-PD rat model is associated with large long-term sleep disruption, however, the vehicle, DMSO/PEG had as large an effect as RT on sleep, thus changes in sleep cannot be ascribed to loss of dopaminergic cells. Such results question the validity of the RT-PD rat model.

Interleukin-1beta induces CREB-binding protein (CBP) mRNA in brain and the sequencing of rat CBP

Interleukin-1 beta (IL-1) and CREB have many CNS actions including sleep regulation and hippocampal-dependent learning. CREB acts in part via CREB-binding protein (CBP). We thus determined whether IL-1 could induce CBP gene expression. Initially, cultured hippocampal cells were treated with IL-1 and differential display reverse transcription was used to identify up- and down-regulated genes. We then sequenced rat CBP. Of the IL-1-upregulated genes, CBP and adenine nucleotide translocator-1 (ANT-1) were investigated in vivo. In these experiments, IL-1 was given to rats intraventricularly and sacrificed 2 h later; both CBP and ANT-1 transcripts were upregulated in the cerebral cortex and hypothalamus. We conclude that rat CBP shares many of the functional domains as human and murine CBP and that IL-1 upregulates genes previously associated with learning and sleep.

Possible pathomechanisms of sudden infant death syndrome: key role of chronic hypoxia, infection/inflammation states, cytokine irregularities, and metabolic trauma in genetically predisposed infants

Chronic hypoxia, viral infections/bacterial toxins, inflammation states, biochemical disorders, and genetic abnormalities are the most likely trigger of sudden infant death syndrome (SIDS). Autopsy studies have shown increased pulmonary density of macrophages and markedly more eosinophils in the lungs accompanied by increased T and B lymphocytes. The elevated levels of immunoglobulins, about 20% more muscle in the pulmonary arteries, increased airway smooth muscle cells, and increased fetal hemoglobin and erythropoietin are evidence of chronic hypoxia before death. Other abnormal findings included mucosal immune stimulation of the tracheal wall, duodenal mucosa, and palatine tonsils, and circulating interferon. Low normal or higher blood levels of cortisol often with petechiae on intrathoracic organs, depleted maternal IgG antibodies to endotoxin core (EndoCAb) and early IgM EndoCAb triggered, partial deletions of the C4 gene, and frequent IL-10-592*A polymorphism in SIDS victims as well as possible hypoxia-induced decreased production of antiinflammatory, antiimmune, and antifibrotic cytokine IL-10, may be responsible for the excessive reactions to otherwise harmless infections. In SIDS infants, during chronic hypoxia and times of infection/inflammation, several proinflammatory cytokines are released in large quantities, sometimes also representing a potential source of tissue damage if their production is not sufficiently well controlled, eg, by pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP). These proinflammatory cytokines down-regulate gene expression of major cytochrome P-450 and/or other enzymes with the specific effects on mRNA levels, protein expression, and enzyme activity, thus affecting metabolism of several endogenous lipophilic substances, such as steroids, lipid-soluble vitamins, prostaglandins, leukotrienes, thromboxanes, and exogenous substances. In SIDS victims, chronic hypoxia, TNF-alpha and other inflammatory cytokines, and arachidonic acid (AA) as well as n-3 polyunsaturated fatty acids (FA), stimulated and/or augmented superoxide generation by polymorphonuclear leukocytes, which contributed to tissue damage. Chronic hypoxia, increased amounts of nonheme iron in the liver and adrenals of these infants, enhanced activity of CYP2C9 regarded as the functional source of reactive oxygen species (ROS) in some endothelial cells, and nicotine accumulation in tissues also intensified production of ROS. These increased quantities of proinflammatory cytokines, ROS, AA, and nitric oxide (NO) also resulted in suppression of many CYP450 and other enzymes, eg, phosphoenolpyruvate carboxykinase (PEPCK), an enzyme important in the metabolism of FA during gluconeogenesis and glyceroneogenesis. PEPCK deficit found in SIDS infants (caused also by vitamin A deficiency) and eventually enhanced by PACAP lipolysis of adipocyte triglycerides resulted in an increased FA level in blood because of their impaired reesterification to triacylglycerol in adipocytes. In turn, the overproduction and release of FA into the blood of SIDS victims could lead to the metabolic syndrome and an early phase of type 2 diabetes. This is probably the reason for the secondary overexpression of the hepatic CYP2C8/9 content and activity reported in SIDS infants, which intensified AA metabolism. Pulmonary edema and petechial hemorrhages often present in SIDS victims may be the result of the vascular leak syndrome caused by IL-2 and IFN-alpha. Chronic hypoxia with the release of proinflammatory mediators IL-1alpha, IL-1beta and IL-6, and overloading of the cardiovascular and respiratory systems due to the narrowing airways and small pulmonary arteries of these children could also contribute to the development of these abnormalities. Moreover, chronic hypoxia of SIDS infants induced also production of hypoxia-inducible factor 1alpha (HIF-1alpha), which stimulated synthesis and release of different growth factors by vascular endothelial cells and intensified subclinical inflammatory reactions in the central nervous system, perhaps potentiated also by PACAP and VIP gene mutations. These processes could lead to the development of brainstem gliosis and disorders in the release of neuromediators important for physiologic sleep regulation. All these changes as well as eventual PACAP abnormalities could result in disturbed homeostatic control of the cardiovascular and respiratory responses of SIDS victims, which, combined with the nicotine effects and metabolic trauma, finally lead to death in these often genetically predisposed children.

The association between interleukin-6, sleep, and demographic characteristics

We examined the relationship between the pro-inflammatory cytokine IL-6 and sleep architecture in 70 healthy men and women. Blood was drawn in the early morning for assessment of IL-6 followed by nocturnal sleep monitoring with polysomnography. Sleep records were scored for sleep stages using standard criteria. Morning IL-6 levels were positively correlated with REM latency after sleep onset [rho = .31, p = .01], percent (%) stage 1 sleep [rho = .23, p = .053], % wake after sleep onset (WASO) [rho = .29, p<.05]. IL-6 levels were negatively correlated with sleep efficiency [rho = -.36, p<.01] and slow wave sleep (SWS) [rho = -.26, p<.05]. After controlling for demographic variables including race, gender, age, and BMI, multiple hierarchical regression analyses revealed that morning IL-6 levels accounted for a significant portion of the variance of REM latency (p<.01), sleep efficiency (p<.01), and % WASO (p = .01). IL-6 was no longer associated with % stage 1 sleep, SWS, and total sleep time after controlling for the demographic characteristics. These findings suggest that the inflammatory marker IL-6 is associated with sleep quality and that certain individual characteristics such as race, gender, and age modify that relationship. Higher IL-6 levels were associated with lower quality of sleep among healthy asymptomatic men and women.

Circadian responses to endotoxin treatment in mice

We tested the ability of Escherichia coli lipopolysaccharide (LPS) to phase-shift the activity circadian rhythm in C57Bl/6J mice. Intraperitoneal administration of 25 microg/kg LPS induced photic-like phase delays (-43+/-10 min) during the early subjective night. These delays were non-additive to those induced by light at CT 15, and were reduced by the previous administration of sulfasalazine, a NF-kappaB activation inhibitor. At CT 15, LPS induced c-Fos expression in the dorsal area of the suprachiasmatic nuclei (SCN). Our results suggest that the activation of the immune system should be considered an entraining signal for the murine circadian clock.

Microarray analysis of postmortem temporal cortex from patients with schizophrenia

To examine molecular mechanisms associated with schizophrenia this study measured expression of approximately 12,000 genes in the middle temporal gyrus from 12 subjects with schizophrenia and 14 matched normal controls. Among the most consistent changes in genes with robust expression were significant decreases in the expression of myelination-related genes MAG, PLLP (TM4SF11), PLP1, ERBB3 in subjects with schizophrenia. There was also altered expression of genes regulating neurodevelopment (TRAF4, Neurod1, histone deacetylase 3), a circadian pacemaker (PER1), and several other genes involved in regulation of chromatin function and signaling mechanisms. These findings support the hypothesis that schizophrenia is associated with abnormalities in oligodendroglia and provide initial evidence suggesting a role for epigenetic mechanisms and altered circadian rhythms in this disorder.

Age impairments in sleep, metabolic and immune functions

Age-related sleep impairments are chronic and common, occurring even in the absence of diagnosable disorders. Additional loss of sleep occurs with clinical sleep disorders, many of which can be ameliorated. This literature, reviewed below, raises the question of the possible biological consequences of age-related, chronic sleep loss, an area that is poorly understood at present. Some of the more age-relevant theories about sleep loss will be explored in a review of current research on sleep deprivation arising from normal aging, experimental induction and pathology. The biological consequences of sleep deprivation in young adults include metabolic, systemic inflammatory and immune changes that are similar to those of aging and age-related disorders. The possibility that chronic sleep impairment contributes to age changes in metabolism, systemic inflammation and immunocompetence is explored.

Interleukin-6: a cytokine to forget

It is known that proinflammatory cytokines such as interleukin-6 (IL-6) are expressed in the central nervous system (CNS) during disease conditions and affect several brain functions including memory and learning. In contrast to these effects observed during pathological conditions, here we describe a physiological function of IL-6 in the "healthy" brain in synaptic plasticity and memory consolidation. During long-term potentiation (LTP) in vitro and in freely moving rats, IL-6 gene expression in the hippocampus was substantially increased. This increase was long lasting, specific to potentiation, and was prevented by inhibition of N-methyl-D-aspartate receptors with (+/-)-2-amino-5-phosphonopentanoic acid (AP-5). Blockade of endogenous IL-6 by application of a neutralizing anti-IL-6 antibody 90 min after tetanus caused a remarkable prolongation of LTP. Consistently, blockade of endogenous IL-6, 90 min after hippocampus-dependent spatial alternation learning resulted in a significant improvement of long-term memory. In view of the suggested role of LTP in memory formation, these data implicate IL-6 in the mechanisms controlling the kinetics and amount of information storage.