Prostaglandin D2 and sleep--a molecular genetic approach

Functions and mechanisms of adenosine and its receptors in sleep regulation

Sleep is a natural and recurring state of life. Long-term insomnia can lead to physical and mental fatigue, inattention, memory loss, anxiety, depression and other symptoms, imposing immense public health and economic burden worldwide. The sleep and awakening regulation system is composed of many nerve nuclei and neurotransmitters in the brain, and it forms a neural network that interacts and restricts each other to regulate the occurrence and maintenance of sleep-wake. Adenosine (AD) is a neurotransmitter in the central nervous system and a driver of sleep. Meanwhile, the functions and mechanisms underlying sleep-promoting effects of adenosine and its receptors are still not entirely clear. However, in recent years, the increasing evidence indicated that adenosine can promote sleep through inhibiting arousal system and activating sleep-promoting system. At the same time, astrocyte-derived adenosine in modulating sleep homeostasis and sleep loss-induced related cognitive and memory deficits plays an important role. This review, therefore, summarizes the current research on the functions and possible mechanisms of adenosine and its receptors in the regulation of sleep and homeostatic control of sleep. Understanding these aspects will provide us better ideas on clinical problems such as insomnia, hypersomnia and other sleep disorders.

A role for prostaglandins in rapid cycling suggested by episode-specific gene expression shifts in peripheral blood mononuclear cells: a preliminary report

OBJECTIVES

Over 12% of patients with bipolar disorder exhibit rapid cycling. The underlying biological mechanisms of this extreme form of bipolar disease are still unknown. This study aimed at replicating and extending findings of our previously published case report, where an involvement of prostaglandin synthesis-related genes in rapid cycling was first proposed.

METHODS

Psychopathological follow-up of the reported case was performed under cessation of celecoxib treatment. In a prospective observational study, patients with bipolar disorder (n = 47; of these, four had rapid cycling) or with monopolar depression (n = 97) were recruited over a period of three years. Repeated psychopathology measurements were conducted using standard instruments. Peripheral blood mononuclear cells (PBMC) were obtained during as many consecutive episodes as possible and processed for mRNA isolation and quantitative real-time reverse transcriptase polymerase chain reaction for prostaglandin D2 synthase (PTGDS), aldo-ketoreductase family 1, member C3 (AKR1C3), cyclooxygenase-2 (PAN means all splice variants) (COX2PAN ), prostaglandin-endoperoxide synthase 2 (PTGS2), and purinergic receptor P2X, ligand-gated ion channel 7 (P2RX7).

RESULTS

The follow-up of our original case of a patient with rapid cycling who had shown impressive psychopathological improvement under celecoxib revealed complete loss of this effect upon discontinuation of the COX2 inhibitor. Episode-specific gene expression measurements in PBMC of four newly recruited rapid cycling patients confirmed the higher expression of PTGDS in depressive compared to manic phases. Additionally, higher relative expression of PTGS2/COX2PAN was found. No comparable alterations were observable in samples available from the remaining 43 patients with bipolar disorder and the 97 monopolar depressed patients, emphasizing the advantages of the rapid cycling condition with its rapid and frequent shifts for identification of gene expression changes.

CONCLUSIONS

This study supports a role for prostaglandins in rapid cycling and advocates the cyclooxygenase cascade as a treatment target in this condition.

Dietary nutrients associated with short and long sleep duration. Data from a nationally representative sample

Short sleep duration is associated with weight gain and obesity, diabetes, cardiovascular disease, psychiatric illness, and performance deficits. Likewise, long sleep duration is also associated with poor physical and mental health. The role of a healthy diet in habitual sleep duration represents a largely unexplored pathway linking sleep and health. This study evaluated associations between habitual sleep parameters and dietary/nutritional variables obtained via the National Health and Nutrition Examination Survey (NHANES), 2007-2008. We hypothesized that habitual very short (<5h) short (5-6h) and long (9+h) sleep durations are associated with intake of a number of dietary nutrient variables. Overall, energy intake varied across very short (2036kcal), short (2201kcal), and long (1926kcal) sleep duration, relative to normal (2151kcal) sleep duration (p=0.001). Normal sleep duration was associated with the greatest food variety (17.8), compared to very short (14.0), short (16.5) and long (16.3) sleep duration (p<0.001). Associations between sleep duration were found across nutrient categories, with significant associations between habitual sleep duration and proteins, carbohydrates, vitamins and minerals. In stepwise analyses, significant contributors of unique variance included theobromine (long sleep RR=0.910, p<0.05), vitamin C (short sleep RR=0.890, p<0.05), tap water (short sleep RR=0.952, p<0.001; very short (<5h) sleep RR=0.941, p<0.05), lutein+zeaxanthin (short sleep RR=1.123, p<0.05), dodecanoic acid (long sleep RR=0.812, p<0.05), choline (long sleep RR=0.450, p=0.001), lycopene (very short (<5h) sleep RR=0.950, p<0.05), total carbohydrate (very short (<5h) sleep RR=0.494, p<0.05; long sleep RR=0.509, p<0.05), selenium (short sleep RR=0.670, p<0.01) and alcohol (long sleep RR=1.172, p<0.01). Overall, many nutrient variables were associated with short and/or long sleep duration, which may be explained by differences in food variety. Future studies should assess whether these associations are due to appetite dysregulation, due to short/long sleep and/or whether these nutrients have physiologic effects on sleep regulation. In addition, these data may help us better understand the complex relationship between diet and sleep and the potential role of diet in the relationship between sleep and obesity and other cardiometabolic risks.

Adenosine receptor ligands and PET imaging of the CNS

Advances in radiotracer chemistry have resulted in the development of novel molecular imaging probes for adenosine receptors (ARs). With the availability of these molecules, the function of ARs in human pathophysiology as well as the safety and efficacy of approaches to the different AR targets can now be determined. Molecular imaging is a rapidly growing field of research that allows the identification of molecular targets and functional processes in vivo. It is therefore gaining increasing interest as a tool in drug development because it permits the process of evaluating promising therapeutic targets to be stratified. Further, molecular imaging has the potential to evolve into a useful diagnostic tool, particularly for neurological and psychiatric disorders. This chapter focuses on currently available AR ligands that are suitable for molecular neuroimaging and describes first applications in healthy subjects and patients using positron emission tomography (PET).

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.

Modelling facets of mania--new directions related to the notion of endophenotypes

The lack of appropriate animal models is a major limitation in research of bipolar disorder (BPD): at this time there are very few models for this devastating disease. Whereas limited attempts have been made to develop comprehensive models for BPD, the new notion of endophenotypes encourages us to explore the possibility of developing separate models for separate facets of the disorder. Since more models are available for depression, there is a dire need for models for mania that will be relatively easy and simple to induce and test and will therefore be practical for purposes of screening possible new drugs or mutant mice that are developed based on novel molecular theories. Such models may already be tentatively available as they were developed in the context of other disorders, but there is a need to validate them for mania. The present paper proposes such models for most of the facets of mania including: increased energy, activity or restlessness; extreme irritability; reduced sleep; provocative, intrusive or aggressive behaviour; increased sexual drive; abuse of drugs; distractibility, reduced ability to concentrate; and unrealistic beliefs in one's abilities and powers resulting in poor judgement. Validating these models may demand a major research effort but it may be worthy as validated models for the different facets of mania could then be used efficiently and may be utilized to construct a standard battery of tests that can serve to explore the various components of manic-like behaviour in rodents.

Establishment of a battery of simple models for facets of bipolar disorder: a practical approach to achieve increased validity, better screening and possible insights into endophenotypes of disease

The lack of appropriate animal models for bipolar disorder (BPD) hinders the translation of novel molecular and genetic findings into the development of new more efficient treatments. Attempts to develop a comprehensive model for BPD did not result in a practical and valid model and at present most studies utilize a limited number of models for specific components of the disorder. Whereas there is a higher availability of models for the depression pole of BPD, only a few models represent the manic pole with the most frequently used being psychostimulant-induced hyperactivity. This last model had been important in studies of the disease and has some validity but it is clear that by itself cannot be considered to represent mania. Additional models for facets of BPD are needed to allow better screening of new drugs and new mutant mice. Such models may also support the exploration of endophenotypes of BPD and the mechanisms of the disease. An advantage of a battery approach is that each model can be only partially valid when used alone but the combination of a few models may result in strong validity. The present study suggests that such a battery can be based on existing models previously developed in the context of studying normal behavior or other disorders after an initial validation in the context of BPD. An example for this idea is described using the resident-intruder test for aggression. Present results show that 3 weeks oral treatment with 1.2-2.4% lithium (increasing doses), or 20 g/kg daily dose of valproate, significantly reduced aggressive behavior in resident mice without affecting non-aggressive social interactions. Accordingly, it is suggested that the simplified resident-intruder paradigm may model the aggression related to mania as part of a test battery for facets of BPD. It is further speculated that, pending further research, this paradigm can be combined with additional methods to explore changes in the LHPA axis that may be linked to an important endophenotype of BPD.

mRNA expression in mouse hypothalamus and basal forebrain during influenza infection: a novel model for sleep regulation

After influenza infection, C57BL/6J mice develop increased slow-wave sleep (SWS) during the dark phase of the day-night cycle, whereas BALB/cByJ mice develop decreased SWS during the light phase. A previous analysis of CXB recombinant inbred mice revealed a quantitative trait locus (QTL) designated Srilp (sleep response to influenza, light phase) that was related to expression of the BALB/cByJ sleep phenotype. Srilp was localized to the 10- to 12-cM region of mouse Chr 6 between D6Mit74 and D6Mit188. Temt (thioether S-methyltransferase), which is located at region B3 of Chr 6, is a potential candidate gene for Srilp. We evaluated the expression of Temt and other Srilp candidate genes in hypothalamus and basal forebrain of uninfected and influenza-infected C57BL/6J and BALB/cByJ mice. We report here that Temt expression varies significantly with respect to mouse strain, health status, brain region, and day-night phase. C57BL/6J mice show day-night variation in Temt expression in hypothalamus, but BALB/cByJ mice do not. Temt expression in basal forebrain is much higher in C57BL/6J mice than in BALB/cByJ mice. During influenza infection, both C57BL/6J and BALB/cByJ mice show reduced Temt mRNA in basal forebrain at 30 h postinoculation, but expression remains much lower in the BALB/cByJ strain. In contrast, prostaglandin-d-synthase ( Ptgds) and lipocalin 2 ( Lcn2) mRNA increase in basal forebrain of both strains after influenza infection. Administration of the TEMT inhibitor sinefungin reduces sleep in uninfected BALB/cByJ mice and attenuates influenza-induced sleep enhancement in C57BL/6J mice. These data suggest that strain- and infection-related alterations in sleep may be influenced by Temt expression and perhaps by subsequent effects on prostaglandin metabolism.

Enhanced Prospects for Drug Delivery and Brain Targeting by the Choroid Plexus–CSF Route

The choroid plexus (CP), i.e., the blood-cerebrospinal fluid barrier (BCSFB) interface, is an epithelial boundary exploitable for drug delivery to brain. Agents transported from blood to lateral ventricles are convected by CSF volume transmission (bulk flow) to many periventricular targets. These include the caudate, hippocampus, specialized circumventricular organs, hypothalamus, and the downstream pia-glia and arachnoid membranes. The CSF circulatory system normally provides micronutrients, neurotrophins, hormones, neuropeptides, and growth factors extensively to neuronal networks. Therefore, drugs directed to CSF can modulate a variety of endocrine, immunologic, and behavioral phenomema; and can help to restore brain interstitial and cellular homeostasis disrupted by disease and trauma. This review integrates information from animal models that demonstrates marked physiologic effects of substances introduced into the ventricular system. It also recapitulates how pharmacologic agents administered into the CSF system prevent disease or enhance the brain's ability to recover from chemical and physical insults. In regard to drug distribution in the CNS, the BCSFB interaction with the blood-brain barrier is discussed. With a view toward translational CSF pharmacotherapy, there are several promising innovations in progress: bone marrow cell infusions, CP encapsulation and transplants, neural stem cell augmentation, phage display of peptide ligands for CP epithelium, CSF gene transfer, regulation of leukocyte and cytokine trafficking at the BCSFB, and the purification of neurotoxic CSF in degenerative states. The progressively increasing pharmacological significance of the CP-CSF nexus is analyzed in light of treating AIDS, multiple sclerosis, stroke, hydrocephalus, and Alzheimer's disease.

Preoptic alpha 1- and alpha 2-noradrenergic agonists induce, respectively, PGE2-independent and PGE2-dependent hyperthermic responses in guinea pigs

We have shown previously that norepinephrine (NE) microdialyzed into the preoptic area (POA) of conscious guinea pigs stimulates local PGE(2) release. To identify the cyclooxygenase (COX) isozyme that catalyzes the production of this PGE(2) and the adrenoceptor (AR) subtype that mediates this effect, we microdialyzed for 6 h NE, cirazoline (alpha(1)-AR agonist), and clonidine (alpha(2)-AR agonist) into the POA of conscious guinea pigs pretreated intrapreoptically (intra-POA) with SC-560 (COX-1 inhibitor) or nimesulide or MK-0663 (COX-2 inhibitors) and measured the animals' core temperature (T(c)) and intra-POA PGE(2) responses. Cirazoline induced T(c) rises promptly after the onset of its dialysis without altering PGE(2) levels. NE and clonidine caused early falls followed by late rises of T(c); intra-POA PGE(2) levels were closely correlated with this thermal course. COX-1 inhibition attenuated the clonidine-induced T(c) and PGE(2) falls but not the NE-elicited hyperthermia, but COX-2 inhibition suppressed both the clonidine- and NE-induced T(c) and PGE(2) rises. Coinfused cirazoline and clonidine reproduced the late T(c) rise of clonidine but not its early fall and also not the early rise produced by cirazoline; on the other hand, the PGE(2) responses were similar to those to NE. Prazosin (alpha(1)-AR antagonist) and yohimbine (alpha(2)-AR antagonist) blocked the effects of their respective agonists. These results indicate that alpha(1)- and alpha(2)-AR agonists microdialyzed into the POA of conscious guinea pigs evoke distinct T(c) responses: alpha(1)-AR activation produces quick, PGE(2)-independent T(c) rises, and alpha(2)-AR stimulation causes an early T(c) fall and a late, COX-2/PGE(2)-dependent T(c) rise.

A cyclooxygenase-2 inhibitor attenuates spontaneous and TNF-alpha-induced non-rapid eye movement sleep in rabbits

Sleep is regulated in part by the brain cytokine network, including tumor necrosis factor-alpha (TNF-alpha). TNF-alpha activates the transcription factor nuclear factor-kappaB, which in turn promotes transcription of many genes, including cyclooxygenase-2 (COX-2). COX-2 is in the brain and is an enzyme responsible for production of prostaglandin D2. The hypothesis that central COX-2 plays a role in the regulation of spontaneous and TNF-alpha-induced sleep was investigated. Three doses (0.5, 5, and 50 microg) of NS-398, a highly selective COX-2 inhibitor, were injected intracerebroventricularly. The highest dose decreased non-rapid eye movement sleep. The intermediate and highest doses decreased electroencephalographic slow-wave activity; the greatest reduction occurred after 50 microg of NS-398 during the first 3-h postinjection period. Rapid eye movement sleep and brain temperature were not altered by any dose of NS-398. Pretreatment of rabbits with 5 or 50 microg of NS-398 blocked the TNF-alpha-induced increases in non-rapid eye movement sleep, electroencephalographic slow-wave activity, and brain temperature. These data suggest that COX-2 is involved in the regulation of spontaneous and TNF-alpha-induced sleep.

Valproic acid down-regulates the conversion of arachidonic acid to eicosanoids via cyclooxygenase-1 and -2 in rat brain

Sodium valproate, a mood stabilizer, when chronically administered to rats (200 mg/kg i.p. daily for 30 days) significantly reduced the brain protein levels of cyclooxygenase (COX)-1 and COX-2, without altering the mRNA levels of these enzymes. COX activity was decreased, as were the brain concentrations of 11-dehydrothromboxane B2 and prostaglandin E2 (PGE2), metabolites of arachidonic acid (AA) produced via COX. In contrast, the brain protein level of 5-lipoxygenase and the concentration of its AA metabolite leukotriene B4 were unchanged. In view of published evidence that lithium chloride administered chronically to rats, like chronic valproate, reduces AA turnover within brain phospholipids, and that lithium post-transcriptionally down-regulates COX-2 but not COX-1 protein level and enzyme activity, these observations suggest that mood stabilizers generally modulate the release and recycling of AA within brain phospholipids, and the conversion of AA via COX-2 to PGE2 and related eicosanoids. If targeting this part of the 'AA cascade' accounts for their therapeutic action, non-steroidal anti-inflammatory drugs or selective COX-2 inhibitors might prove effective in bipolar disorder.

Chronic lithium downregulates cyclooxygenase-2 activity and prostaglandin E(2) concentration in rat brain

Rats treated with lithium chloride for 6 weeks have been reported to demonstrate reduced turnover of arachidonic acid (AA) in brain phospholipids, and decreases in mRNA and protein levels, and enzyme activity, of AA-selective cytosolic phospholipase A(2)(cPLA(2)). We now report that chronic lithium administration to rats significantly reduced the brain protein level and enzyme activity of cyclooxygenase-2 (COX-2), without affecting COX-2 mRNA. Lithium also reduced the brain concentration of prostaglandin E(2) (PGE(2)), a bioactive product of AA formed via the COX reaction. COX-1 and the Ca(2+)-independent iPLA(2) (type VI) were unaffected by lithium. These and prior results indicate that lithium targets a part of the AA cascade that involves cPLA(2) and COX-2. This effect may contribute to lithium's therapeutic action in bipolar disorder.

Molecular genetic studies on sleep-wake regulation, with special emphasis on the prostaglandin D(2) system

To elucidate the exact role of the PGD(2) system in sleep-wake regulation in vivo, the sleep behavior of knockout mice, generated in the author's and other laboratories, was examined for lipocalin-type PGD synthase (L-PGDS), PGD receptor, adenosine A(2A) receptor, and histamine H(1) receptor; transgenic mice overexpressing the human L-PGDS gene, generated in the author's laboratory, were also examined. The circadian profiles of sleep patterns of wild-type and the genetically manipulated mice were essentially identical, indicating the possibility that the deficiency of one system may be effectively compensated by some other systems during development. Available evidence indicated that the PGD(2) system is involved in the homeostatic regulation of non-rapid eye movement sleep and that the arousal effect of orexin A is mediated by the histamine H(1) receptor system.

Prostaglandin D2 in sleep-wake regulation: recent progress and perspectives

Prostaglandin (PG) D2 is one of the most active endogenous sleep-promoting substances, which induces physiological sleep in rodents, primates, and most probably in humans as well. In this update article, we review recent experimental results concerning the molecular mechanisms underlying sleep-wake regulation by PGD2, the link between the humoral regulation by the PGD2 system, and the neural network involved in the promotion of non-rapid eye movement (NREM) sleep and the abnormality of NREM sleep regulation found in gene-manipulated mice for PGD synthase.

Choroid plexus in the central nervous system: biology and physiopathology

Choroid plexuses (CPs) are localized in the ventricular system of the brain and form one of the interfaces between the blood and the central nervous system (CNS). They are composed of a tight epithelium responsible for cerebrospinal fluid secretion, which encloses a loose connective core containing permeable capillaries and cells of the lymphoid lineage. In accordance with its peculiar localization between 2 circulating fluid compartments, the CP epithelium is involved in numerous exchange processes that either supply the brain with nutrients and hormones, or clear deleterious compounds and metabolites from the brain. Choroid plexuses also participate in neurohumoral brain modulation and neuroimmune interactions, thereby contributing greatly in maintaining brain homeostasis. Besides these physiological functions, the implication of choroid plexuses in pathological processes is increasingly documented. In this review, we focus on some of the novel aspects of CP functions in relation to brain development, transfer of neuro-humoral information, brain/immune system interactions, brain aging, and cerebral pharmaco-toxicology.