Jeannine A. Majde

Humoral Links between Sleep and the Immune System

Abstract: In the last twenty years we have realized that the immune system synthesizes a class of peptides, termed cytokines, that play a central role in alerting the brain to ongoing inflammation in peripheral tissues. Among the brains responses to proinflammatory cytokines, or agents that induce these cytokines, are certain alterations in sleep profiles. Characteristically there is an increase in non‐rapid eye movement sleep (NREMS), and NREMS intensity is often accompanied by a decrease in rapid eye movement sleep (REMS). Cytokines appear to play a role in normal sleep regulation; during pathology, higher levels of cytokines amplify the physiological cytokine sleep mechanisms. In this review we summarize the extensive literature on the roles of interleukin‐1 (IL‐1) and tumor necrosis factor‐α (TNF‐α) in sleep regulation, and their interactions with the neuropeptides growth hormone‐releasing hormone (GHRH) and corticotropin‐releasing hormone (CRH). We reach the tentative conclusion that the sleep‐promoting actions of IL‐1 and GHRH are mediated via anterior hypothalamic neurons that are receptive to these substances. It also seems likely that TNF‐α and CRH also influence these neurons. In addition, we discuss an array of research issues raised by these studies that remain to be resolved.

Viral double-stranded RNA, cytokines, and the flu.

The symptoms of the flu, such as fever, drowsiness, and malaise, are the sole means by which this common clinical syndrome is defined. The syndrome is usually the first clinical manifestation of both acute bacterial and viral infections. In the case of acute bacterial infections, several proinflammatory cytokines induced by bacterial products have been implicated as the causative agents of the flu syndrome. Viruses induce similar cytokines to bacteria, plus substantial amounts of interferon-alpha (IFN-alpha), although the direct association of these cytokines with the viral flu syndrome is less clear. Furthermore, the viral inducer(s) of cytokines has not been defined. The best candidate cytokine inducer associated with a majority of viral infections is virus-associated double-stranded RNA (dsRNA). This review examines the essential physical properties of toxic dsRNA, the cytokines induced by it, its viral and cellular sources, evidence for its presence in infected cells, its quantities in normal and infected cells, its cytotoxic mechanisms, and its cell-penetration properties. Toxic effects of viruses and dsRNA are compared. Energetics and extraction artifact issues are also discussed. Whereas most research on dsRNA toxicity has employed synthetic dsRNA, studies with virus-associated dsRNA are featured when available. Finally, a model for how viral dsRNA might initiate systemic disease is presented.

Spontaneous sleep in mice with targeted disruptions of neuronal or inducible nitric oxide synthase genes

Nitric oxide (NO) affects almost every physiological process, including the regulation of sleep. There is strong evidence that NO plays an important role in rapid eye movement sleep (REMS) regulation. To further investigate the role of NO in sleep, we characterized spontaneous sleep in mice with targeted disruptions (knockout; KO) in the neuronal nitric oxide synthase (nNOS) or inducible (i)NOS genes. REMS in nNOS KO mice was substantially lower than that of their control mice. In contrast, the iNOS KO mice had significantly more REMS than their controls. Inducible NOS KO mice also had less non-REMS (NREMS) during the dark period. Results suggest that nNOS and iNOS play opposite roles in REMS regulation.

Influenza Viral Infections Enhance Sleep in Mice

Abstract Sleepiness is a common perception during viral infection. Nevertheless, very little is known about the effects of viral infection on sleep. The aim of the present study was to test whether sleep was altered by influenza viral infection in mice. After 2-3 days of baseline sleep recordings, Swiss-Webster mice were infected intranasally with a lethal (H1N1) or a nonlethal (H3N2) strain of influenza virus. Sleep was recorded again for an additional 3 days. Non–rapid eye movement sleep (NREMS) was dramatically increased after inoculation of the H1N1 virus with a latency about 16 hr. Rapid eye movement sleep (REMS) was significantly suppressed after a longer latency. Both changes lasted until the end of the recording and occurred in both young (35-day-old) and adult (90- to 100-day-old) animals. Control animals did not show changes in sleep after sham infection with allantoic fluid. The H1N1 virus also caused dramatic decreases in body temperature and locomotor activities with a latency about 4-5 hr after viral inoculation. The H3N2 virus induced very similar changes in sleep, although the effects were much smaller in magnitude than those induced by the H1N1 virus, even though a much higher dose (10-fold) of the H3N2 virus was used. The present study shows that influenza viral infection induces profound and long-lasting increase of NREMS and suppression of REMS. These viral-induced changes in sleep likely represent a host-defense response. [P.S.E.B.M. 1995, Vol 210]

Sleep in host defense

Sleep remains an important enigma in neurobiology; it has a robust adaptive value yet its function remains elusive. Changes in sleep are hallmarks of the acute phase response to infectious challenge. The molecular regulation of these responses involves a cytokine cascade within brain, including interleukin-1 and tumor necrosis factor, and several other substances such as growth hormone releasing hormone, prolactin, nitric oxide and nuclear factor kappaB. These substances are also involved in the regulation of normal spontaneous sleep. Fatigue and sleep disturbances are common in cancer patients and in those receiving cytokine therapy. Regardless, the role of sleep in cancer is relatively uninvestigated.

Spontaneous and influenza virus-induced sleep are altered in TNF-α double-receptor deficient mice

Tumor necrosis factor-alpha (TNF-alpha) is associated with sleep regulation in health and disease. Previous studies assessed sleep in mice genetically deficient in the TNF-alpha 55-kDa receptor. In this study, spontaneous and influenza virus-induced sleep profiles were assessed in mice deficient in both the 55-kDa and 75-kDa TNF-alpha receptors [TNF-2R knockouts (KO)] and wild-type (WT) strain controls. Under baseline conditions the TNF-2R KO mice had less non-rapid eye movement sleep (NREMS) than WTs during the nighttime and more rapid eye movement sleep (REMS) than controls during the daytime. The differences between nighttime maximum and daytime minimum values of electroencephalogram (EEG) delta power during NREMS were greater in the TNF-2R KO mice than in WTs. Viral challenge (mouse-adapted influenza X-31) enhanced NREMS and decreased REMS in both strains roughly to the same extent. EEG delta power responses to viral challenge differed substantially between strains; the WT animals increased, whereas the TNF-2R KO mice decreased their EEG delta wave power during NREMS. There were no differences between strains in body temperatures or locomotor activity in uninfected mice or after viral challenge. Analyses of cortical mRNAs confirmed that the TNF-2R KO mice lacked both TNF-alpha receptors; these mice also had higher levels of orexin mRNA and reduced levels of the purine P2X7 receptor compared with WTs. Results reinforce the hypothesis that TNF-alpha is involved in physiological sleep regulation but plays a limited role in the acute-phase response induced by influenza virus.

Spontaneous release of stable viral double-stranded RNA into the extracellular medium by influenza virus-infected MDCK epithelial cells: implications for the viral acute phase response

SummaryThe viral factor responsible for triggering the acute phase response, or ‘flu’ syndrome, associated with many acute viral infections is not defined. One candidate viral factor is double-stranded RNA (dsRNA) generated during viral replication. In this report we demonstrate by reverse-transcriptase polymerase-chain reaction that nuclease-stable viral RNA was released from influenza-infected MDCK epithelial cells at the time of cell lysis. Removal of virion-associated RNA by ultracentrifugation left equal amounts of positive-and negative-strand viral RNA in the medium that resisted degradation by endogenous RNase in the medium and by exogenous RNase added prior to phenol extraction. These data are the first demonstration that viral RNA with characteristics of dsRNA is spontaneously released from dying influenza virus-infected cells, and thus is available to amplify cytokine induction and contribute to systemic disease.

Cytokines and Sleep

Infectious challenges induce sleep responses in the host characterized by an increase in non-rapid eye movement sleep (NREMS) followed by a period of decreased NREMS. Such sleep responses represent on

Microbial cell-wall contaminants in peptides: A potential source of physiological artifacts

Microbial cell-wall products (MCWP) such as endotoxins are easily introduced into peptides produced under standard laboratory conditions. Because these products stimulate the induction of cytokines and other mediators, which, in turn, trigger a broad range of physiological responses. MCWP in peptide preparations are potential sources of artifacts. This brief tutorial outlines the physical/chemical nature of MCWP, some of their sources, their physiological effects, and a simple method to control for them in some peptide preparations.

Cytokines in immune function and sleep regulation.

Publisher Summary This chapter presents a mechanistic explanation for sleep homeostasis and addresses the issues of the cellular mechanisms leading to sleep. The chapter discusses sleep-regulatory substances (SRS) that are linked to host defense and focuses on interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interferons (IFNs). The chapter also discusses how sleep is part of the acute-phase response (APR) induced by viral challenge. The accumulation of SRSs in cerebrospinal fluid during prolonged wakefulness (W) provides very strong support of the hypothesis that sleep is regulated, in part, by humoral agents. Detailed discussion of involvement of IL-1β, TNF-α and other cytokines in sleep regulation are presented. Injection of exogenous low doses of IL-1β or TNF-α enhances nonrapid eye movement sleep (NREMS). Conditions that enhance endogenous production of IL-1β or TNF-α, for example, excessive food intake or infectious disease, promote NREMS. Conversely, inhibition of endogenous IL-1β and TNF-α, using antibodies or endogenous inhibitors such as their soluble receptors, inhibits spontaneous sleep. These inhibitors of IL-1β and TNF-α also inhibit sleep rebound after sleep deprivation. Brain level of IL-1β mRNA and IL-1 and plasma level of IL-1β vary with the sleep–wake cycle with highest levels correlating with high sleep propensity.