CSF levels of prostaglandins, especially the level of prostaglandin D2, are correlated with increasing propensity towards sleep in rats

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.

Rhythms in barriers and fluids: Circadian clock regulation in the aging neurovascular unit

The neurovascular unit is where two very distinct physiological systems meet: The central nervous system (CNS) and the blood. The permeability of the barriers separating these systems is regulated by time, including both the 24 h circadian clock and the longer processes of aging. An endogenous circadian rhythm regulates the transport of molecules across the blood-brain barrier and the circulation of the cerebrospinal fluid and the glymphatic system. These fluid dynamics change with time of day, and with age, and especially in the context of neurodegeneration. Factors may differ depending on brain region, as can be highlighted by consideration of circadian regulation of the neurovascular niche in white matter. As an example of a potential target for clinical applications, we highlight chaperone-mediated autophagy as one mechanism at the intersection of circadian dysregulation, aging and neurodegenerative disease. In this review we emphasize key areas for future research.

Causal association of sleep disturbances and low back pain: A bidirectional two-sample Mendelian randomization study

BACKGROUND

Previous observational studies have shown that low back pain (LBP) often coexists with sleep disturbances, however, the causal relationship remains unclear. In the present study, the causal relationship between sleep disturbances and LBP was investigated and the importance of sleep improvement in the comprehensive management of LBP was emphasized.

METHODS

Genetic variants were extracted as instrumental variables (IVs) from the genome-wide association study (GWAS) of insomnia, sleep duration, short sleep duration, long sleep duration, and daytime sleepiness. Information regarding genetic variants in LBP was selected from a GWAS dataset and included 13,178 cases and 164,682 controls. MR-Egger, weighted median, inverse-variance weighted (IVW), penalized weighted median, and maximum likelihood (ML) were applied to assess the causal effects. Cochran's Q test and MR-Egger intercept were performed to estimate the heterogeneity and horizontal pleiotropy, respectively. Outliers were identified and eliminated based on MR-PRESSO analysis to reduce the effect of horizontal pleiotropy on the results. Removing each genetic variant using the leave-one-out analysis can help evaluate the stability of results. Finally, the reverse causal inference involving five sleep traits was implemented.

RESULTS

A causal relationship was observed between insomnia-LBP (OR = 1.954, 95% CI: 1.119-3.411), LBP-daytime sleepiness (OR = 1.011, 95% CI: 1.004-1.017), and LBP-insomnia (OR = 1.015, 95% CI: 1.004-1.026), however, the results of bidirectional MR analysis between other sleep traits and LBP were negative. The results of most heterogeneity tests were stable and specific evidence was not found to support the disturbance of horizontal multiplicity. Only one outlier was identified based on MR-PRESSO analysis.

CONCLUSION

The main results of our research showed a potential bidirectional causal association of genetically predicted insomnia with LBP. Sleep improvement may be important in comprehensive management of LBP.

The Sleep-Promoting Ventrolateral Preoptic Nucleus: What Have We Learned over the Past 25 Years?

For over a century, the role of the preoptic hypothalamus and adjacent basal forebrain in sleep-wake regulation has been recognized. However, for years, the identity and location of sleep- and wake-promoting neurons in this region remained largely unresolved. Twenty-five years ago, Saper and colleagues uncovered a small collection of sleep-active neurons in the ventrolateral preoptic nucleus (VLPO) of the preoptic hypothalamus, and since this seminal discovery the VLPO has been intensively investigated by labs around the world, including our own. Herein, we first review the history of the preoptic area, with an emphasis on the VLPO in sleep-wake control. We then attempt to synthesize our current understanding of the circuit, cellular and synaptic bases by which the VLPO both regulates and is itself regulated, in order to exert a powerful control over behavioral state, as well as examining data suggesting an involvement of the VLPO in other physiological processes.

Sleep and homeostatic control of plasticity

Sleep homeostasis is a complex neurobiologic phenomenon involving a number of molecular pathways, neurotransmitter release, synaptic activity, and factors modulating neural networks. Sleep plasticity allows for homeostatic optimization of neural networks and the replay-based consolidation of specific circuits, especially important for cognition, behavior, and information processing. Furthermore, research is currently moving from an essentially brain-focused to a more comprehensive view involving other systems, such as the immune system, hormonal status, and metabolic pathways. When dysfunctional, these systems contribute to sleep loss and fragmentation as well as to sleep need. In this chapter, the implications of neural plasticity and sleep homeostasis for the diagnosis and treatment of some major sleep disorders, such as insomnia and sleep deprivation, obstructive sleep apnea syndrome, restless legs syndrome, REM sleep behavior disorder, and narcolepsy are discussed in detail with their therapeutical implications. This chapter highlights that sleep is necessary for the maintenance of an optimal brain function and is sensitive to both genetic background and environmental enrichment. Even in pathologic conditions, sleep acts as a resilient plastic state that consolidates prior information and prioritizes network activity for efficient brain functioning.

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

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

Brain Mechanisms of COVID-19-Sleep Disorders

2020 and 2021 have been unprecedented years due to the rapid spread of the modified severe acute respiratory syndrome coronavirus around the world. The coronavirus disease 2019 (COVID-19) causes atypical infiltrated pneumonia with many neurological symptoms, and major sleep changes. The exposure of people to stress, such as social confinement and changes in daily routines, is accompanied by various sleep disturbances, known as 'coronasomnia' phenomenon. Sleep disorders induce neuroinflammation, which promotes the blood-brain barrier (BBB) disruption and entry of antigens and inflammatory factors into the brain. Here, we review findings and trends in sleep research in 2020-2021, demonstrating how COVID-19 and sleep disorders can induce BBB leakage via neuroinflammation, which might contribute to the 'coronasomnia' phenomenon. The new studies suggest that the control of sleep hygiene and quality should be incorporated into the rehabilitation of COVID-19 patients. We also discuss perspective strategies for the prevention of COVID-19-related BBB disorders. We demonstrate that sleep might be a novel biomarker of BBB leakage, and the analysis of sleep EEG patterns can be a breakthrough non-invasive technology for diagnosis of the COVID-19-caused BBB disruption.

A CRISPR-Cas9-engineered mouse model for GPI-anchor deficiency mirrors human phenotypes and exhibits hippocampal synaptic dysfunctions

Inherited GPI-anchor biosynthesis deficiencies (IGDs) explain many cases of syndromic intellectual disability. Although diagnostic methods are improving, the pathophysiology underlying the disease remains unclear. Furthermore, we lack rodent models suitable for characterizing cognitive and social disabilities. To address this issue, we generated a viable mouse model for an IGD that mirrors the condition in human patients with a behavioral phenotype and susceptibility to epilepsy. Using this model, we obtained neurological insights such as deficits in synaptic transmission that will facilitate understanding of the pathophysiology of IGDs.

Pathogenic germline mutations in PIGV lead to glycosylphosphatidylinositol biosynthesis deficiency (GPIBD). Individuals with pathogenic biallelic mutations in genes of the glycosylphosphatidylinositol (GPI)-anchor pathway exhibit cognitive impairments, motor delay, and often epilepsy. Thus far, the pathophysiology underlying the disease remains unclear, and suitable rodent models that mirror all symptoms observed in human patients have not been available. Therefore, we used CRISPR-Cas9 to introduce the most prevalent hypomorphic missense mutation in European patients, Pigv:c.1022C > A (p.A341E), at a site that is conserved in mice. Mirroring the human pathology, mutant Pigv^341E mice exhibited deficits in motor coordination, cognitive impairments, and alterations in sociability and sleep patterns, as well as increased seizure susceptibility. Furthermore, immunohistochemistry revealed reduced synaptophysin immunoreactivity in Pigv^341E mice, and electrophysiology recordings showed decreased hippocampal synaptic transmission that could underlie impaired memory formation. In single-cell RNA sequencing, Pigv^341E-hippocampal cells exhibited changes in gene expression, most prominently in a subtype of microglia and subicular neurons. A significant reduction in Abl1 transcript levels in several cell clusters suggested a link to the signaling pathway of GPI-anchored ephrins. We also observed elevated levels of Hdc transcripts, which might affect histamine metabolism with consequences for circadian rhythm. This mouse model will not only open the doors to further investigation into the pathophysiology of GPIBD, but will also deepen our understanding of the role of GPI-anchor–related pathways in brain development.

Preoptic Area Modulation of Arousal in Natural and Drug Induced Unconscious States

The role of the hypothalamic preoptic area (POA) in arousal state regulation has been studied since Constantin von Economo first recognized its importance in the early twentieth century. Over the intervening decades, the POA has been shown to modulate arousal in both natural (sleep and wake) as well as drug-induced (anesthetic-induced unconsciousness) states. While the POA is well known for its role in sleep promotion, populations of wake-promoting neurons within the region have also been identified. However, the complexity and molecular heterogeneity of the POA has made distinguishing these two populations difficult. Though multiple lines of evidence demonstrate that general anesthetics modulate the activity of the POA, the region's heterogeneity has also made it challenging to determine whether the same neurons involved in sleep/wake regulation also modulate arousal in response to general anesthetics. While a number of studies show that sleep-promoting POA neurons are activated by various anesthetics, recent work suggests this is not universal to all arousal-regulating POA neurons. Technical innovations are making it increasingly possible to classify and distinguish the molecular identities of neurons involved in sleep/wake regulation as well as anesthetic-induced unconsciousness. Here, we review the current understanding of the POA's role in arousal state regulation of both natural and drug-induced forms of unconsciousness, including its molecular organization and connectivity to other known sleep and wake promoting regions. Further insights into the molecular identities and connectivity of arousal-regulating POA neurons will be critical in fully understanding how this complex region regulates arousal states.

Sleep deficiency and chronic pain: potential underlying mechanisms and clinical implications

Pain can be both a cause and a consequence of sleep deficiency. This bidirectional relationship between sleep and pain has important implications for clinical management of patients, but also for chronic pain prevention and public health more broadly. The review that follows will provide an overview of the neurobiological evidence of mechanisms thought to be involved in the modulation of pain by sleep deficiency, including the opioid, monoaminergic, orexinergic, immune, melatonin, and endocannabinoid systems; the hypothalamus-pituitary-adrenal axis; and adenosine and nitric oxide signaling. In addition, it will provide a broad overview of pharmacological and non-pharmacological approaches for the management of chronic pain comorbid with sleep disturbances and for the management of postoperative pain, as well as discuss the effects of sleep-disturbing medications on pain amplification.

The Sleep-Immune Crosstalk in Health and Disease

Sleep and immunity are bidirectionally linked. Immune system activation alters sleep, and sleep in turn affects the innate and adaptive arm of our body's defense system. Stimulation of the immune system by microbial challenges triggers an inflammatory response, which, depending on its magnitude and time course, can induce an increase in sleep duration and intensity, but also a disruption of sleep. Enhancement of sleep during an infection is assumed to feedback to the immune system to promote host defense. Indeed, sleep affects various immune parameters, is associated with a reduced infection risk, and can improve infection outcome and vaccination responses. The induction of a hormonal constellation that supports immune functions is one likely mechanism underlying the immune-supporting effects of sleep. In the absence of an infectious challenge, sleep appears to promote inflammatory homeostasis through effects on several inflammatory mediators, such as cytokines. This notion is supported by findings that prolonged sleep deficiency (e.g., short sleep duration, sleep disturbance) can lead to chronic, systemic low-grade inflammation and is associated with various diseases that have an inflammatory component, like diabetes, atherosclerosis, and neurodegeneration. Here, we review available data on this regulatory sleep-immune crosstalk, point out methodological challenges, and suggest questions open for future research.

Regulation of the Blood-Brain Barrier by Circadian Rhythms and Sleep

The blood-brain barrier (BBB) is an evolutionarily conserved, structural, and functional separation between circulating blood and the central nervous system (CNS). By controlling permeability into and out of the nervous system, the BBB has a critical role in the precise regulation of neural processes. Here, we review recent studies demonstrating that permeability at the BBB is dynamically controlled by circadian rhythms and sleep. An endogenous circadian rhythm in the BBB controls transporter function, regulating permeability across the BBB. In addition, sleep promotes the clearance of metabolites along the BBB, as well as endocytosis across the BBB. Finally, we highlight the implications of this regulation for diseases, including epilepsy.

Role of the L-PGDS-PGD2-DP1 receptor axis in sleep regulation and neurologic outcomes

To meet the new challenges of modern lifestyles, we often compromise a good night's sleep. In preclinical models as well as in humans, a chronic lack of sleep is reported to be among the leading causes of various physiologic, psychologic, and neurocognitive deficits. Thus far, various endogenous mediators have been implicated in inter-regulatory networks that collectively influence the sleep-wake cycle. One such mediator is the lipocalin-type prostaglandin D2 synthase (L-PGDS)-Prostaglandin D2 (PGD2)-DP1 receptor (L-PGDS-PGD2-DP1R) axis. Findings in preclinical models confirm that DP1R are predominantly expressed in the sleep-regulating centers. This finding led to the discovery that the L-PGDS-PGD2-DP1R axis is involved in sleep regulation. Furthermore, we showed that the L-PGDS-PGD2-DP1R axis is beneficial in protecting the brain from ischemic stroke. Protein sequence homology was also performed, and it was found that L-PGDS and DP1R share a high degree of homology between humans and rodents. Based on the preclinical and clinical data thus far pertaining to the role of the L-PGDS-PGD2-DP1R axis in sleep regulation and neurologic conditions, there is optimism that this axis may have a high translational potential in human therapeutics. Therefore, here the focus is to review the regulation of the homeostatic component of the sleep process with a special focus on the L-PGDS-PGD2-DP1R axis and the consequences of sleep deprivation on health outcomes. Furthermore, we discuss whether the pharmacological regulation of this axis could represent a tool to prevent sleep disturbances and potentially improve outcomes, especially in patients with acute brain injuries.

The Mutual Interaction Between Sleep and Epilepsy on the Neurobiological Basis and Therapy

BACKGROUND

Sleep and epilepsy are mutually related in a complex, bidirectional manner. However, our understanding of this relationship remains unclear.

RESULTS

The literatures of the neurobiological basis of the interactions between sleep and epilepsy indicate that non rapid eye movement sleep and idiopathic generalized epilepsy share the same thalamocortical networks. Most of neurotransmitters and neuromodulators such as adenosine, melatonin, prostaglandin D2, serotonin, and histamine are found to regulate the sleep-wake behavior and also considered to have antiepilepsy effects; antiepileptic drugs, in turn, also have effects on sleep. Furthermore, many drugs that regulate the sleep-wake cycle can also serve as potential antiseizure agents. The nonpharmacological management of epilepsy including ketogenic diet, epilepsy surgery, neurostimulation can also influence sleep.

CONCLUSION

In this paper, we address the issues involved in these phenomena and also discuss the various therapies used to modify them.

Opposing roles of PGD2 in GBM

BACKGROUND

The World Health Organization classifies glioblastoma (GBM) as a grade IV astrocytoma. Despite the advances in chemotherapy, surgery, and radiation treatments that improve a patient's length of survival, the overall trajectory of the disease remains unchanged. GBM cells produce significant levels of various types of bioactive lipids. Prostaglandin D₂ (PGD₂) influences both pro- and anti-tumorigenic activities in the cell; however, its role in GBM is unclear. Therefore, this study aimed to identify the impact of PGD₂ on GBM cell activities in vitro.

METHODS

First we looked to identify the presence of the PGD₂ synthesis pathway through RT-PCR, immunohistochemistry, and HPLC-MS/MS in three GBM cell lines. Then, to observe PGD₂'s effects on cell count and apoptosis/mitosis (Hoechst 33342 stain), and migration (Transwell Assay), the cells were treated in vitro with physiological (<1μM) and/or supraphysiological (>1μM) concentrations of PGD₂ over 72h. HPLC-MS/MS was used to identify the lipid composition of patients with either Grade II/III gliomas or GBM.

RESULTS

We identified the presence of endogenous PGD₂ with its corresponding enzymes and receptors. Exogenous PGD₂ both increased cell count (<1μM) and decreased cell count (10μM) in a concentration-dependent manner. There were no significant effects on apoptosis. A significant decrease in mitotic activity was seen only in U251MG, and a significant increase was seen in migration with 5μM PGD₂ treatments. A very significant increase of PGD₂ was seen from Grade II/III gliomas to GBM.

CONCLUSIONS

Our study demonstrates that prostaglandin D₂ possesses a dynamic, concentration-dependent effect in GBM cell activities. The increase of PGD₂ production in GBM patients suggests a pro-tumorigenic role of PGD₂ in glioma growth and invasion. Therefore, prostaglandin signaling in GBM requires further investigation to identify new targets for more effective therapies.

Cranial dural permeability of inflammatory nociceptive mediators: Potential implications for animal models of migraine

Background Application of inflammatory mediators to the cranial dura has been used as a method to activate and sensitize neurons in the meningeal sensory pathway in preclinical behavioral studies of headache mechanisms. However, the relatively high concentrations and volumes used in these studies raise the question of whether the applied agents might pass through the dura to act directly on central neurons, thus bypassing the dural afferent pathway. Methods We used a radiolabeling approach to quantify the meningeal permeability of two of the inflammatory mediators, 5-HT and PGE2, when applied to the cranial dura as part of an inflammatory mixture used in preclinical headache models. Results Both agents could be detected in samples taken four hours after dural application in the cerebrospinal fluid (CSF) and, in measurements made only for PGE2, in the central nervous system (CNS) as well. Based on our measurements, we made estimates of the CSF and CNS levels that would be attained with the higher concentrations and volumes of 5HT and PGE2 that were exogenously applied in previous pre-clinical headache studies. These estimated levels were comparable to or larger than normal endogenous levels, potentially large enough to have physiological effects. Conclusions The finding that the cranial meninges are permeable to the two tested inflammatory mediators PGE2 and 5-HT raises some uncertainty about whether the behavioral changes observed in prior pre-clinical headache studies with these as well as other agents can be attributed entirely to the activation of dural nociceptors, particularly when the agents are applied at concentrations several orders of magnitude above physiological levels.

The Neurobiology of Sleep and Wakefulness

Cortical electroencephalographic activity arises from corticothalamocortical interactions, modulated by wake-promoting monoaminergic and cholinergic input. These wake-promoting systems are regulated by hypothalamic hypocretin/orexins, while GABAergic sleep-promoting nuclei are found in the preoptic area, brainstem and lateral hypothalamus. Although pontine acetylcholine is critical for REM sleep, hypothalamic melanin-concentrating hormone/GABAergic cells may "gate" REM sleep. Daily sleep-wake rhythms arise from interactions between a hypothalamic circadian pacemaker and a sleep homeostat whose anatomical locus has yet to be conclusively defined. Control of sleep and wakefulness involves multiple systems, each of which presents vulnerability to sleep/wake dysfunction that may predispose to physical and/or neuropsychiatric disorders.

PGD2 stimulates osteoprotegerin synthesis via AMP-activated protein kinase in osteoblasts: Regulation of ERK and SAPK/JNK

AMP-activated protein kinase (AMPK), a key enzyme sensing cellular energy metabolism, is currently known to regulate multiple metabolic pathways. Osteoprotegerin plays a pivotal role in the regulation of bone metabolism by inhibiting osteoclast activation. We have previously reported that prostaglandin D2 (PGD2) stimulates the synthesis of osteoprotegerin through the activation of p38 mitogen-activated protein (MAP) kinase, p44/p42 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. On the basis of these findings, we herein investigated the implication of AMPK in PGD2-stimulated osteoprotegerin synthesis in these cells. PGD2 induced the phosphorylation of AMPKα (Thr-172) and AMPKβ (Ser-108), and the phosphorylation of acetyl-coenzyme A carboxylase, a direct AMPK substrate. Compound C, an AMPK inhibitor, which suppressed the phosphorylation of acetyl-coenzyme A carboxylase, significantly attenuated both the release and the mRNA levels of osteoprotegerin stimulated by PGD2. The PGD2-induced phosphorylation of p44/p42 MAP kinase and SAPK/JNK but not p38 MAP kinase were markedly inhibited by compound C. These results strongly suggest that AMPK regulates the PGD2-stimulated osteoprotegerin synthesis at a point upstream of p44/p42 MAP kinase and SAPK/JNK in osteoblasts.

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.

Roles of adenosine and its receptors in sleep-wake regulation

This chapter summarizes the current knowledge about the role of adenosine in the sleep-wake regulation with a focus on adenosine in the brain, regulation of adenosine levels, adenosine receptors, and manipulations of the adenosine system by the use of pharmacological and molecular biological tools. Adenosine is neither stored nor released as a classical neurotransmitter and is thought to be formed inside cells or on their surface, mostly by breakdown of adenine nucleotides. The extracellular level of adenosine increases in the cortex and basal forebrain (BF) during prolonged wakefulness and decreases during the sleep-recovery period. Therefore, adenosine is proposed to act as a homeostatic regulator of sleep. The endogenous somnogen prostaglandin (PG) D2 increases the extracellular level of adenosine under the subarachnoid space of the BF and promotes physiological sleep. There are four adenosine receptor subtypes: adenosine A1 receptor (R, A1R), A2AR, A2BR, and A3R. Both the A1R and the A2AR have been reported to be involved in sleep induction. The A2AR plays an important role in the somnogenic effects of PGD2. Activation of A2AR by its agonist infused into the brain potently increases sleep and the arousal effect of caffeine, an A1R and A2AR antagonist, was shown to be dependent on the A2AR. On the other hand, inhibition of wake-promoting neurons via the A1R also mediates the sleep-inducing effects of adenosine, whereas activation of A1R in the lateral preoptic area induces wakefulness. These findings indicate that A2AR plays a predominant role in sleep induction, whereas A1R regulates the sleep-wake cycle in a site-dependent manner.

Oxalic acid and diacylglycerol 36:3 are cross-species markers of sleep debt

Sleep is an essential biological process that is thought to have a critical role in metabolic regulation. In humans, reduced sleep duration has been associated with risk for metabolic disorders, including weight gain, diabetes, obesity, and cardiovascular disease. However, our understanding of the molecular mechanisms underlying effects of sleep loss is only in its nascent stages. In this study we used rat and human models to simulate modern-day conditions of restricted sleep and addressed cross-species consequences via comprehensive metabolite profiling. Serum from sleep-restricted rats was analyzed using polar and nonpolar methods in two independent datasets (n = 10 per study, 3,380 measured features, 407 identified). A total of 38 features were changed across independent experiments, with the majority classified as lipids (18 from 28 identified). In a parallel human study, 92 metabolites were identified as potentially significant, with the majority also classified as lipids (32 of 37 identified). Intriguingly, two metabolites, oxalic acid and diacylglycerol 36:3, were robustly and quantitatively reduced in both species following sleep restriction, and recovered to near baseline levels after sleep restriction (P < 0.05, false-discovery rate < 0.2). Elevated phospholipids were also noted after sleep restriction in both species, as well as metabolites associated with an oxidizing environment. In addition, polar metabolites reflective of neurotransmitters, vitamin B3, and gut metabolism were elevated in sleep-restricted humans. These results are consistent with induction of peroxisome proliferator-activated receptors and disruptions of the circadian clock. The findings provide a potential link between known pathologies of reduced sleep duration and metabolic dysfunction, and potential biomarkers for sleep loss.

Development and pharmacological characterization of a model of sleep disruption-induced hypersensitivity in the rat

BACKGROUND

Sleep disturbance is a commonly reported co-morbidity in chronic pain patients, and conversely, disruption of sleep can cause acute and long-lasting hypersensitivity to painful stimuli. The underlying mechanisms of sleep disruption-induced pain hypersensitivity are poorly understood. Confounding factors of previous studies have been the sleep disruption protocols, such as the 'pedestal over water' or 'inverted flower pot' methods, that can cause large stress responses and therefore may significantly affect pain outcome measures.

METHODS

Sleep disruption was induced by placing rats for 8 h in a slowly rotating cylindrical cage causing arousal via the righting reflex. Mechanical (Von Frey filaments) and thermal (Hargreaves) nociceptive thresholds were assessed, and plasma corticosterone levels were measured (mass spectroscopy). Sleep disruption-induced hypersensitivity was pharmacologically characterized with drugs relevant for pain treatment, including gabapentin (30 mg/kg and 50 mg/kg), Ica-6p (Kv7.2/7.3 potassium channel opener; 10 mg/kg), ibuprofen (30 mg/kg and 100 mg/kg) and amitriptyline (10 mg/kg).

RESULTS

Eight hours of sleep disruption caused robust mechanical and heat hypersensitivity in the absence of a measurable change in plasma corticosterone levels. Gabapentin had no effect on reduced nociceptive thresholds. Ibuprofen attenuated mechanical thresholds, while Ica-6p and amitriptyline attenuated only reduced thermal nociceptive thresholds.

CONCLUSIONS

These results show that acute and low-stress sleep disruption causes mechanical and heat hypersensitivity in rats. Mechanical and heat hypersensitivity exhibited differential sensitivity to pharmacological agents, thus suggesting dissociable mechanisms for those two modalities. Ultimately, this model could help identify underlying mechanisms linking sleep disruption and hypersensitivity.

Suppression by resveratrol of prostaglandin D2-stimulated osteoprotegerin synthesis in osteoblasts

Resveratrol, a natural polyphenol with health-related properties mainly existing in grape skins and red wine, possesses beneficial effects on human being. We have previously reported that prostaglandin D2 (PGD2) stimulates heat shock protein 27 (HSP27) induction via activation of p44/p42 mitogen-activated protein (MAP) kinase, p38 MAP kinase and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) in osteoblast-like MC3T3-E1 cells. In the present study, we investigated the mechanism behind the effect of PGD2 on osteoprotegerin (OPG) synthesis and the effect of resveratrol on the OPG synthesis in MC3T3-E1 cells. PGD2 significantly stimulated both the OPG release and the expression levels of OPG mRNA. Resveratrol and SRT1720, an activator of SIRT1, markedly suppressed the PGD2-induced OPG release and the mRNA levels of OPG. PD98059, a specific MEK inhibitor, SB203580, a specific p38 MAP kinase inhibitor, and SP600125, a specific SAPK/JNK inhibitor suppressed the PGD2-stimulated OPG release. PGD2-induced phosphorylation of p38 MAP kinase and SAPK/JNK was attenuated by resveratrol or SRT1720. However, resveratrol or SRT1720 failed to affect the phosphorylation of myosin phosphatase-targeting subunit-1 (MYPT-1), a downstream substrate of Rho-kinase and p44/p42 MAP kinase. These results strongly suggest that resveratrol suppresses PGD2-stimulated OPG synthesis through inhibiting p38 MAP kinase and SAPK/JNK in osteoblasts, and that the suppressive effect is exerted at the point downstream of Rho-kinase but upstream of p38 MAP kinase or SAPK/JNK.

Headache, drugs and sleep

Background

Headache and sleep mechanisms share multiple levels of physiological interaction. Pharmacological treatment of headache syndromes may be associated with a broad range of sleep disturbances, either as a direct result of the pharmacology of the drug used, or by unmasking physiological alterations in sleep propensity seen as part of the headache symptom complex.

Purpose

This review summarises known sleep and circadian effects of various drugs commonly used in the management of headache disorders, with particular attention paid to abnormal sleep function emerging as a result of treatment.

Method

Literature searches were performed using MEDLINE, PubMed, and the Cochrane database using search terms and strings relating to generic drug names of commonly used compounds in the treatment of headache and their effect on sleep in humans with review of additional pre-clinical evidence where theoretically appropriate.

Conclusions

Medications used to treat headache disorders may have a considerable impact on sleep physiology. However, greater attention is needed to characterise the direction of the changes of these effects on sleep, particularly to avoid exacerbating detrimental sleep complaints, but also to potentially capitalise on homeostatically useful properties of sleep which may reduce the individual burden of headache disorders on patients.

Inhibitory G proteins and their receptors: emerging therapeutic targets for obesity and diabetes

The worldwide prevalence of obesity is steadily increasing, nearly doubling between 1980 and 2008. Obesity is often associated with insulin resistance, a major risk factor for type 2 diabetes mellitus (T2DM): a costly chronic disease and serious public health problem. The underlying cause of T2DM is a failure of the beta cells of the pancreas to continue to produce enough insulin to counteract insulin resistance. Most current T2DM therapeutics do not prevent continued loss of insulin secretion capacity, and those that do have the potential to preserve beta cell mass and function are not effective in all patients. Therefore, developing new methods for preventing and treating obesity and T2DM is very timely and of great significance. There is now considerable literature demonstrating a link between inhibitory guanine nucleotide-binding protein (G protein) and G protein-coupled receptor (GPCR) signaling in insulin-responsive tissues and the pathogenesis of obesity and T2DM. These studies are suggesting new and emerging therapeutic targets for these conditions. In this review, we will discuss inhibitory G proteins and GPCRs that have primary actions in the beta cell and other peripheral sites as therapeutic targets for obesity and T2DM, improving satiety, insulin resistance and/or beta cell biology.

Novel orexigenic pathway prostaglandin D2-NPY system--involvement in orally active orexigenic δ opioid peptide

Prostaglandin (PG) D(2), the most abundant PG in the central nervous system (CNS), is a bioactive lipid having various central actions including sleep induction, hypothermia and modulation of the pain response. We found that centrally administered PGD(2) stimulates food intake via the DP(1) among the two receptor subtypes for PGD(2) in mice. Hypothalamic mRNA expression of lipocalin-type PGD synthase (L-PGDS), which catalyzes production of PGD(2) from arachidonic acid via PGH(2) in the CNS, was increased after fasting. Central administration of antagonist and antisense ODN for the DP(1) receptor remarkably decreased food intake, body weight and fat mass. The orexigenic activity of PGD(2) was also blocked by an antagonist of Y(1) receptor for NPY, the most potent orexigenic peptide in the hypothalamus. Thus, the central PGD(2)-NPY system may play a critical role in food intake regulation under normal physiological conditions. We also found that orally active orexigenic peptide derived from food protein activates the PGD(2)-NPY system, downstream of δ opioid receptor. We revealed that the δ agonist peptide, rubiscolin-6-induced orexigenic activity was mediated by L-PGDS in the leptomeninges but not parenchyma using conditional knockout mice. In this review, we discuss the PGD(2)-NPY system itself, and orexigenic signals to activate it.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Prostaglandin D2 and sleep/wake regulation

Prostaglandin (PG) D2 is the most potent endogenous sleep-promoting substance. PGD2 is produced by lipocalin-type PGD synthase localized in the leptomeninges, choroid plexus, and oligodendrocytes in the brain, and is secreted into the cerebrospinal fluid as a sleep hormone. PGD2 stimulates DP1 receptors localized in the leptomeninges under the basal forebrain and the hypothalamus. As a consequence, adenosine is released as a paracrine sleep-promoting molecule to activate adenosine A2A receptor-expressing sleep-promoting neurons and to inhibit adenosine A1 receptor-possessing arousal neurons. PGD2 activates a center of non-rapid eye movement (NREM) sleep regulation in the ventrolateral preoptic area, probably mediated by adenosine signaling, which activation inhibits the histaminergic arousal center in the tuberomammillary nucleus via descending GABAergic and galaninergic projections. The administration of a lipocalin-type PGD synthase inhibitor (SeCl4), DP1 antagonist (ONO-4127Na) or adenosine A2A receptor antagonist (caffeine) suppresses both NREM and rapid eye movement (REM) sleep, indicating that the PGD2-adenosine system is crucial for the maintenance of physiological sleep.

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.

Fatty-acid binding proteins modulate sleep and enhance long-term memory consolidation in Drosophila

Sleep is thought to be important for memory consolidation, since sleep deprivation has been shown to interfere with memory processing. However, the effects of augmenting sleep on memory formation are not well known, and testing the role of sleep in memory enhancement has been limited to pharmacological and behavioral approaches. Here we test the effect of overexpressing the brain-type fatty acid binding protein (Fabp7) on sleep and long-term memory (LTM) formation in Drosophila melanogaster. Transgenic flies carrying the murine Fabp7 or the Drosophila homologue dFabp had reduced baseline sleep but normal LTM, while Fabp induction produced increases in both net sleep and LTM. We also define a post-training consolidation “window” that is sufficient for the observed Fabp-mediated memory enhancement. Since Fabp overexpression increases consolidated daytime sleep bouts, these data support a role for longer naps in improving memory and provide a novel role for lipid-binding proteins in regulating memory consolidation concurrently with changes in behavioral state.

Methylxanthines and sleep

Caffeine is widely used to promote wakefulness and counteract fatigue induced by restriction of sleep, but also to counteract the effects of caffeine abstinence. Adenosine is a physiological molecule, which in the central nervous system acts predominantly as an inhibitory neuromodulator. Adenosine is also a sleep-promoting molecule. Caffeine binds to adenosine receptors, and the antagonism of the adenosinergic system is believed to be the mechanism through which caffeine counteracts sleep in humans as well as in other species. The sensitivity for caffeine varies markedly among individuals. Recently, genetic variations in genes related to adenosine metabolism have provided at least a partial explanation for this variability. The main effects of caffeine on sleep are decreased sleep latency, shortened total sleep time, decrease in power in the delta range, and sleep fragmentation. Caffeine may also decrease the accumulation of sleep propensity during waking, thus inducing long-term harmful effects on sleep quality.

An interaction between L-prostaglandin D synthase and arrestin increases PGD2 production

L-type prostaglandin synthase (L-PGDS) produces PGD(2), a lipid mediator involved in neuromodulation and inflammation. Here, we show that L-PGDS and arrestin-3 (Arr3) interact directly and can be co-immunoprecipitated endogenously from MG-63 osteoblasts. Perinuclear L-PGDS/Arr3 co-localization is observed in PGD(2)-producing MG-63 cells and is induced by the addition of the L-PGDS substrate or co-expression of COX-2 in HEK293 cells. Inhibition of L-PGDS activity in MG-63 cells triggers redistribution of Arr3 and L-PGDS to the cytoplasm. Perinuclear localization of L-PGDS is detected in wild-type mouse embryonic fibroblasts (MEFs) but is more diffused in MEFs-arr-2(-/-)-arr-3(-/-). Arrestin-3 promotes PGD(2) production by L-PGDS in vitro. IL-1β-induced PGD(2) production is significantly lower in MEFs-arr-2(-/-)-arr-3(-/-) than in wild-type MEFs but can be rescued by expressing Arr2 or Arr3. A peptide corresponding to amino acids 86-100 of arrestin-3 derived from its L-PGDS binding domain stimulates L-PGDS-mediated PGD(2) production in vitro and in MG-63 cells. We report the first characterization of an interactor/modulator of a PGD(2) synthase and the identification of a new function for arrestin, which may open new opportunities for improving therapies for the treatment of inflammatory diseases.

Activation of the prostaglandin system in response to sleep loss in healthy humans: potential mediator of increased spontaneous pain

Insufficient duration of sleep is a highly prevalent behavioral pattern in society that has been shown to cause an increase in spontaneous pain and sensitivity to noxious stimuli. Prostaglandins (PGs), in particular PGE2, are key mediators of inflammation and pain, and we investigated whether PGE2 is a potential mediator in sleep-loss-induced changes in nociceptive processing. Twenty-four participants (7 females, age 35.1+/-7.1 years) stayed for 7 days in the Clinical Research Center. After two baseline days, participants were randomly assigned to either 3 days of 88 h of sleep deprivation (TSD, N=15) or 8h of sleep per night (N=9), followed by a night of recovery sleep. Participants rated the intensity of various pain-related symptoms every 2h across waking periods on computerized visual analog scales. PGE2 was measured in 24-h-urine collections during baseline and third sleep deprivation day. Spontaneous pain, including headache, muscle pain, stomach pain, generalized body pain, and physical discomfort significantly increased by 5-14 units on a 100-unit scale during TSD, compared to the sleep condition. Urinary PGE2 metabolite significantly increased by about 30% in TSD over sleep condition. TSD-induced increase in spontaneous pain, in particular headache and muscle pain, was significantly correlated with increase in PGE2 metabolite. Activation of the PGE2 system appears to be a potential mediator of increased spontaneous pain in response to insufficient sleep.

Prostaglandin D(2) sustains the pyrogenic effect of prostaglandin E(2)

Prostaglandin D(2) (PGD(2)) is involved in a variety of physiological and pathophysiological processes, but its role in fever is poorly understood. Here we investigated the effects of central PGD(2) administration on body temperature and prostaglandin levels in the cerebrospinal fluid (CSF) of rats. Administration of PGD(2) into the cisterna magna (i.c.m) evoked a delayed fever response that was paralleled by increased levels of prostaglandin E(2) (PGE(2)) in the CSF. The elevated PGE(2) levels were not caused by an increased expression of cyclooxygenase 2 or microsomal prostaglandin E synthase-1 in the hypothalamus. Interestingly, i.c.m. pretreatment of animals with PGD(2) considerably sustained the pyrogenic effects of i.c.m. administered PGE(2). These data indicate that PGD(2) might control the availability of PGE(2) in the CSF and suggest that centrally produced PGD(2) may play a role in the maintenance of fever.

Prostaglandin involvement in hyperthermia induced by sleep deprivation: a pharmacological and autoradiographic study

AIMS

Hyperthermia is a characteristic functional effect of sleep deprivation (SD). We hypothesize here that prostaglandin E2 (PGE2) could be involved in hyperthermia induced by sleep deprivation.

MAIN METHODS

To address this issue we examined the effects of a selective cyclo-oxygenase-2 inhibitor (COX-2) agent on hyperthermia induced by SD in rats. We also investigated binding to PGE2 receptors in hypothalamic brain areas of sleep-deprived rats using in vitro autoradiography. Male Wistar rats were deprived of sleep for 96 h using the platform technique. Sleep deprived and control groups received saline or Celecoxib (20, 30 and 40 mg/kg; p.o.) daily during the SD period. Colonic temperature was measured daily.

KEY FINDINGS

Results indicated that core temperature of sleep-deprived rats that receiving saline increased from the first to the fourth day of SD compared to baseline and to the respective control group. However, the hyperthermia induced by SD was not blocked by COX-2 inhibitor at any dose. [(3)H]PGE2 binding did not differ significantly among the groups in any of a number of hypothalamic areas examined.

SIGNIFICANCE

Although SD rats showed no response to the COX-2 inhibitor and no alterations in [(3)H]PGE2 binding, the possibility remains that other prostaglandin system and/or receptor subtypes may be altered by SD.

Episode-specific differential gene expression of peripheral blood mononuclear cells in rapid cycling supports novel treatment approaches

Molecular mechanisms underlying bipolar affective disorders are unknown. Difficulties arise from genetic and phenotypic heterogeneity of patients and the lack of animal models. Thus, we focused on only one patient (n = 1) with an extreme form of rapid cycling. Ribonucleic acid (RNA) from peripheral blood mononuclear cells (PBMC) was analyzed in a three-tiered approach under widely standardized conditions. Firstly, RNA was extracted from PBMC of eight blood samples, obtained on two consecutive days within one particular episode, including two different consecutive depressive and two different consecutive manic episodes, and submitted to (1) screening by microarray hybridizations, followed by (2) detailed bioinformatic analysis, and (3) confirmation of episode-specific regulation of genes by quantitative real-time polymerase chain reaction (qRT-PCR).Secondly, results were validated in additional blood samples obtained one to two years later. Among gene transcripts elevated in depressed episodes were prostaglandin D synthetase (PTGDS) and prostaglandin D2 11-ketoreductase (AKR1C3), both involved in hibernation. We hypothesized them to account for some of the rapid cycling symptoms. A subsequent treatment approach over 5 months applying the cyclooxygenase inhibitor celecoxib (2 x 200 mg daily) resulted in reduced severity rating of both depressed and manic episodes. This case suggests that rapid cycling is a systemic disease, resembling hibernation, with prostaglandins playing a mediator role.

Central prostaglandin D(2) exhibits anxiolytic-like activity via the DP(1) receptor in mice

We found that prostaglandin (PG) D(2), the most abundant PG produced in the central nervous system (CNS), exhibited anxiolytic-like activity at a dose of 10-100pmol/mouse after intracerebroventricular (i.c.v.) administration in the elevated plus-maze test in mice. A DP(1) receptor-selective agonist, BW245C, mimicked the anxiolytic-like activity of PGD(2), while a DP(2) receptor agonist 13,14-dihydro-15-keto-PGD(2) was inactive. The anxiolytic-like activity of PGD(2) was blocked by a DP(1) antagonist, BWA868C, suggesting that PGD(2)-induced anxiolytic-like activity was mediated by the DP(1) receptor. Adenosine A(2A) or GABA(A) receptor antagonists, SCH58261 or bicuculline, respectively, also blocked its anxiolytic-like activity. Taken together, centrally administered PGD(2) may induce anxiolytic-like activity via the A(2A) and GABA(A) receptors, downstream of the DP(1) receptor.

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.

Central prostaglandin D(2) stimulates food intake via the neuropeptide Y system in mice

We found that prostaglandin (PG) D(2), the most abundant PG in the central nervous system, stimulates food intake after intracerebroventricular administration in mice. The orexigenic effect of PGD(2) was mimicked by a selective agonist for the DP(1) receptor among two receptor subtypes for PGD(2), and abolished by its antagonist. Central administration of an antagonist or antisense oligodeoxynucleotide for the DP(1) receptor remarkably decreased food intake, body weight and fat mass. Hypothalamic mRNA levels of lipocalin-type PGD synthase were up-regulated after fasting. The orexigenic activity of PGD(2) was also abolished by an antagonist for neuropeptide Y (NPY) Y(1) receptor. Taken together, PGD(2) may stimulate food intake through central DP(1) receptor coupled to the NPY system.

Elevated inflammatory markers in response to prolonged sleep restriction are associated with increased pain experience in healthy volunteers

CONTEXT

Sleep disturbances, pain, and inflammation co-occur in various medical conditions, but their interrelationships are poorly understood.

OBJECTIVE

We investigated the effects of reduced sleep duration (by approximately 50%) to 4 h/night across 10 days, on peripherally circulating inflammatory mediators. In addition, we tested the prediction that degree of inflammation is quantitatively related to the extent to which pain is increased in response to prolonged sleep restriction.

DESIGN

Randomized, 16 day controlled in-laboratory study conducted in GCRC.

METHODS

Eighteen volunteers were randomly assigned to either 12 days of sleeping 8 h/night or 4 h/night. Participants rated mood and pain symptoms throughout experimental days. Urine was collected and blood was drawn frequently on the baseline day and after the 10th experimental day for 25 hours.

OUTCOME MEASURES

Levels of plasma interleukin (IL)-6, serum C-reactive protein (CRP), plasma soluble tumor necrosis factor receptor p55 (sTNF-R p55), urinary levels of prostaglandin (PG) metabolites D2 and E2, subjective assessment of pain and tiredness-fatigue.

RESULTS

IL-6 levels were elevated in the 4-h sleep condition over the 8-h sleep condition (P <0.05). CRP levels showed the same trend as IL-6, but did not differ significantly between groups (P = 0.11). Levels of sTNF-R p55 were unchanged in both groups. PG E2 and 11beta-F2alpha metabolite increased in 4-h sleepers, but did not differ significantly from the 8-h sleepers. Elevated IL-6 levels were strongly associated with increased pain ratings in response to sleep restriction (r = 0.67, P <0.01), and this association could not be explained by elevations in tiredness-fatigue.

CONCLUSION

Insufficient sleep quantity may facilitate and/or exacerbate pain through elevations of IL-6. In disorders where sleep disturbances are common, insufficient sleep quantity itself may establish and maintain its co-occurrence with pain and increased inflammation.

Effects of COX-2 inhibitor in temporomandibular joint acute inflammation

Since it is recognized that cyclo-oxygenase-2 mediates nociception and the sleep-wake cycle as well, and that acute inflammation of the temporomandibular joint (TMJ) results in sleep disturbances, we hypothesized that cyclo-oxygenase-2 inhibitor would restore the sleep pattern in this inflammatory rat model. First, sleep was monitored after the injection of Freund's adjuvant (FA group) or saline (SHAM group) into the rats' temporomandibular joint. Second, etoricoxib was co-administered in these groups. The Freund's adjuvant group showed a reduction in sleep efficiency, in rapid eye movement (REM), and in non-REM sleep, and an increase in sleep and REM sleep latency when compared with the SHAM group, while etoricoxib substantially increased sleep quality in the Freund's adjuvant group. These parameters returned progressively to those found in the SHAM group. Etoricoxib improved the sleep parameters, suggesting the involvement of the cyclo-oxygenase-2 enzyme in acute inflammation of the TMJ, specifically in REM sleep.

Prostaglandin D2 protects neonatal mouse brain from hypoxic ischemic injury

Prostaglandin D2 (PGD) is synthesized by hematopoietic PGD synthase (HPGDS) or lipocalin-type PGDS (L-PGDS), depending on the organ in which it is produced, and binds specifically to either DP1 or DP2 receptors. We investigated the role of PGD2 in the pathogenesis of hypoxic-ischemic encephalopathy (HIE) in neonatal mice at postnatal day 7. In wild-type mice, hypoxia-ischemia increased PGD2 production in the brain up to 90-fold compared with the level in sham-operated brains at 10 min after cessation of hypoxia. Whereas the size of the infarct was not changed in L-PGDS or DP2 knock-out mouse brains compared with that in the wild-type HIE brains, it was significantly increased in HPGDS-L-PGDS double knock-out or DP1 knock-out mice. The PGD2 level in L-PGDS, HPGDS, and HPGDS-L-PGDS knock-out mice at 10 min of reoxygenation was 46, 7, and 1%, respectively, of that in the wild-type ones, indicating the infarct size to be in inverse relation to the amount of PGD2 production. DP1 receptors were exclusively expressed in endothelial cells after 1 h of reoxygenation, and cerebral blood flow decreased more rapidly after the onset of hypoxia and did not return to the baseline level after reoxygenation in HPGDS-L-PGDS knock-out mice. Endothelial cells were severely damaged in HPGDS-L-PGDS and DP1 knock-out mice after 1 h of reoxygenation. In the human neonatal HIE brain, HPGDS-positive microglia were increased in number. In conclusion, it is probable that PGD2 protected the neonatal brain from hypoxic-ischemic injury mainly via DP1 receptors by preventing endothelial cell degeneration.

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.