Sleep-wake behavior and responses to sleep deprivation and immune challenge of protein kinase RNA-activated knockout mice.

Protein Kinase RNA-activated (PKR) is an enzyme that plays a role in many systemic processes, including modulation of inflammation, and is implicated in neurodegenerative diseases, such as Alzheimer's disease (AD). PKR phosphorylation results in the production of several cytokines involved in the regulation / modulation of sleep, including interleukin-1ß, tumor necrosis factor-α and interferon-γ. We hypothesized targeting PKR would alter spontaneous sleep of mice, attenuate responses to sleep deprivation, and inhibit responses to immune challenge. To test these hypotheses, we determined the sleep-wake phenotype of mice lacking PKR (knockout; PKR-/-) during undisturbed baseline conditions; in responses to six hours of sleep deprivation; and after immune challenge with lipopolysaccharide (LPS). Adult male mice (C57BL/6J, n = 7; PKR-/-, n = 7) were surgically instrumented with EEG recording electrodes and an intraperitoneal microchip to record core body temperature. During undisturbed baseline conditions, PKR -/- mice spent more time in non-rapid eye movement sleep (NREMS) and rapid-eye movement sleep (REMS), and less time awake at the beginning of the dark period of the light:dark cycle. Delta power during NREMS, a measure of sleep depth, was less in PKR-/- mice during the dark period, and core body temperatures were lower during the light period. Both mouse strains responded to sleep deprivation with increased NREMS and REMS, although these changes did not differ substantively between strains. The initial increase in delta power during NREMS after sleep deprivation was greater in PKR-/- mice, suggesting a faster buildup of sleep pressure with prolonged waking. Immune challenge with LPS increased NREMS and inhibited REMS to the same extent in both mouse strains, whereas the initial LPS-induced suppression of delta power during NREMS was greater in PKR-/- mice. Because sleep regulatory and immune responsive systems in brain are redundant and overlapping, other mediators and signaling pathways in addition to PKR are involved in the responses to acute sleep deprivation and LPS immune challenge.

The reciprocal link between sleep and immune responses.

Good sleep is necessary for both physical and mental health; sleep and immune responses are reciprocally and closely linked. Sleep loss impairs the immune response, while, on the other hand, the immune response, activated for instance by an infection, alters sleep. Sleep alterations induced by immune activation are mediated by cytokines such as interleukin-1. In the past, it was thought that cytokines were produced only by the immune system, and active only there as signaling molecules. Today it is clear that IL-1 and other cytokines are present and active in the healthy brain, where they physiologically interact with the brain circuits and the neurotransmitter systems (for instance the serotonergic, GABAergic, and cholinergic systems) that control sleep. These interactions are altered by immune response, and, as a result, non-rapid eye movement (NREM) sleep is increased and fragmented, whereas rapid eye movements (REM) sleep is inhibited.

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

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

Sleep and Microbes.

Sleep is profoundly altered during the course of infectious diseases. The typical response to infection includes an initial increase in nonrapid eye movement sleep (NREMS) followed by an inhibition in NREMS. REMS is inhibited during infections. Bacterial cell wall components, such as peptidoglycan and lipopolysaccharide, macrophage digests of these components, such as muramyl peptides, and viral products, such as viral double-stranded RNA, trigger sleep responses. They do so via pathogen-associated molecular pattern recognition receptors that, in turn, enhance cytokine production. Altered sleep and associated sleep-facilitated fever responses are likely adaptive responses to infection. Normal sleep in physiological conditions may also be influenced by gut microbes because the microbiota is affected by circadian rhythms, stressors, diet, and exercise. Furthermore, sleep loss enhances translocation of viable bacteria from the intestine, which provides another means by which sleep-microbe interactions impact neurobiology.

Corticotropin-releasing hormone (CRH) as a regulator of waking.

Corticotropin-releasing hormone (CRH), expressed in widely distributed regions of the central nervous system (CNS), mediates the hypothalamic-pituitary-adrenal (HPA) axis and autonomic components of responses to stressors. Sleep, a fundamental CNS process, is altered in response to a variety of stressors. Although there is an extensive literature on the role of CRH in responses to stressors, there is relatively little information on the role of CRH in normal, spontaneous behavior. We hypothesize that CRH is involved in the regulation of waking in the absence of overt stressors. Some of the early evidence supporting this hypothesis was indirect. We summarize in this review studies from our laboratory and others that provide direct evidence that CRH is involved in the regulation of spontaneous waking. We also suggest on the basis of recent studies that some effects of CRH on waking and sleep may be mediated by actions within the CNS of the immunomodulatory cytokine interleukin (IL)-1. Collectively, these observations suggest that CRH contributes to the regulation of spontaneous waking in the absence of stressors, and also indicate a potential mechanism mediating complex alterations in sleep that occur in response to immune challenge.

Human immunodeficiency virus glycoproteins 160 and 41 alter sleep and brain temperature of rats.

Sleep is altered during all stages at which it has been recorded during chronic human immunodeficiency virus (HIV) infection, including the long latent phase before the development of AIDS; the mechanisms for such alterations are not known. The HIV envelope glycoprotein (gp) 120 alters sleep of rats in a manner somewhat similar to the alterations that occur in humans infected with HIV. To further determine which components of the virus may be responsible for altered behavior, we administered centrally into rats prior to dark onset recombinant HIV gp160 or gp41. Both glycoproteins increased non-rapid eye movements sleep, fragmented sleep, altered slow frequency components of the electroencephalogram, and induced modest febrile responses. These results complement and extend those previously obtained after gp120; HIV envelope glycoproteins are capable of altering sleep.

Beta (CC)-chemokines as modulators of sleep: implications for HIV-induced alterations in arousal state.

Sleep is altered early in the course of HIV infection, before the onset of AIDS, indicating effects of the virus on neural processes. Previous observations suggest HIV envelope glycoproteins are possible mediators of these responses. Because some beta (CC)-chemokine receptors serve as co-receptors for HIV and bind HIV envelope glycoproteins, we determined in this study whether selected CC chemokine ligands alter sleep and whether their mRNAs are detectable in brain regions important for sleep. CCL4/MIP-1beta, but not CCL5/RANTES, injected centrally into rats prior to dark onset increased non-rapid eye movements sleep, fragmented sleep, and induced fever. mRNA for the chemokine receptor CCR3 was detectable under basal conditions in multiple brain regions. These data suggest some CC chemokines may also be involved in processes by which HIV alters sleep.

Interleukin-10 (cytokine synthesis inhibitory factor) acts in the central nervous system of rats to reduce sleep.

Interleukin-10 (IL-10), originally designated a cytokine synthesis inhibitory factor, inhibits the synthesis of the pro-inflammatory cytokines IL-1 and tumor necrosis factor by stimulated human and mouse monocytes/macrophages; these cytokines are involved in the regulation of sleep. To determine if IL-10 reduces spontaneous sleep, we injected murine recombinant IL-10 intracerebroventricularly into rats prior to light onset. Non-rapid eye movements sleep was reduced. The behavioral responses to IL-10 were abolished by heat-inactivation of this cytokine. We believe these to be the first observations of central nervous system actions for this cytokine. These results further support the hypothesis that cytokines are involved in the regulation of sleep, and suggest an additional mechanism whereby sleep may be altered in response to an activated immune system.

IL-10 as a mediator in the HPA axis and brain.

Certain functional interactions between the nervous, endocrine, and immune systems are mediated by cytokines. The pro-inflammatory cytokines, interleukin-1 (IL-1) and tumor necrosis factor (TNF) were among the first to be recognized in this regard. A modulator of these cytokines, IL-10, has been shown to have a wide range of activities in the immune system; in this review, we describe its production and actions in the hypothalamic-pituitary-adrenal (HPA) axis. IL-10 is produced in pituitary, hypothalamic, and neural tissues in addition to lymphocytes. IL-10 enhances corticotropin releasing factor (CRF) and corticotropin (ACTH) production in hypothalamic and pituitary tissues, respectively. Further downstream in the HPA axis endogenous IL-10 has the potential to contribute to regulation of glucocorticosteroid production both tonically and following stressors. Our studies and those of others reviewed here indicate that IL-10 may be an important endogenous regulator in HPA axis activity and in CNS pathologies such as multiple sclerosis. Thus, in addition to its more widely recognized role in immunity, IL-10's neuroendocrine activities described here point to its role as an important regulator in communication between the immune and neuroendocrine systems.

Intercellular adhesion molecule-1 expression induced by interleukin (IL)-1 beta or an IL-1 beta fragment is blocked by an IL-1 receptor antagonist and a soluble IL-1 receptor.

The effects of a recombinant human interleukin-1 (IL-1) receptor antagonist (IL-1ra) and a recombinant human soluble IL-1 receptor (sIL-1R) on cytokine-induced intercellular adhesion molecule-1 (ICAM-1) expression in a human glioblastoma cell line and a neuroblastoma cell line were determined. Cells were incubated with IL-1 beta, tumor necrosis factor (TNF) alpha and interferon (IFN) gamma. Cells were also tested under identical conditions with an IL-1 beta synthetic peptide fragment (IL-1 beta 208-240) previously shown to possess biological activity. IL-1 beta, TNF alpha and IFN gamma potentiated ICAM-1 expression in both cell lines in a dose-related manner. The IL-1 beta 208-240 fragments, corresponding to the rabbit, rat and human sequences, enhanced ICAM-1 expression in glioblastoma cells at high doses. ICAM-1 expression induced by IL-1 beta, rabbit IL-1 beta 208-240 and human IL-1 beta 208-240 was blocked by the IL-1ra, while TNF alpha- and IFN gamma-induced ICAM-1 expression were not. ICAM-1 expression induced by IL-1 beta and human IL-1 beta 208-240 was also blocked by the sIL-1R. Our findings suggest that IL1 beta 208-240 acts as an IL-1 beta agonist in enhancing ICAM-1 expression in vitro and that this effect is receptor-mediated.

Blockade of 5-hydroxytryptamine (serotonin)-2 receptors alters interleukin-1-induced changes in rat sleep.

Recent data suggest that interleukin-1-induced enhancement of non-rapid eye movement sleep is mediated, in part, by the serotonergic system. To determine if sleep changes induced by interleukin-1 are mediated by a specific serotonergic receptor subtype, we evaluated interleukin-1 effects on sleep in rats pretreated with the 5-hydroxytryptamine (serotonin)-2 receptor antagonist ritanserin. Ritanserin (0.63 mg/kg, intraperitoneally) by itself did not alter sleep-wake behavior, although it did reduce cortical brain temperature. Interleukin-1 (5 ng, intracerebroventricularly) enhanced non-rapid eye movement sleep, suppressed rapid eye movement sleep, and induced a moderate febrile response. Pretreatment with ritanserin completely blocked the febrile response to interleukin-1 and abolished the interleukin-1-induced enhancement in non-rapid eye movement sleep that occurred during postinjection hours 3-4, without altering interleukin-1 effects on rapid eye movement sleep. The present data suggest that serotonin may partially mediate interleukin-1 effects on sleep by interacting with 5-hydroxytryptamine (serotonin)-2 receptors. These results also suggest that interactions between the serotonergic system and interleukin-1 may be important in regulating sleep-wake behavior.

5-Hydroxytryptophan, but not L-tryptophan, alters sleep and brain temperature in rats.

The precise role of serotonin (5-hydroxytryptamine) in the regulation of sleep is not fully understood. To further clarify this role for 5-hydroxytryptamine, the 5-hydroxytryptamine precursors L-tryptophan (40 and 80 mg/kg) and L-5-hydroxytryptophan (25-, 50-, 75-, 100 mg/kg) were injected intraperitoneally into freely behaving rats 15 min prior to dark onset, and subsequent effects on sleep-wake activity and cortical brain temperature were determined. L-5-hydroxytryptophan, but not L-tryptophan, induced dose-dependent changes in sleep-wake activity. During the 12-h dark period, non-rapid eye movement sleep was inhibited in post-injection hours 1-2 by the two lowest L-5-hydroxytryptophan doses tested, while the two highest doses induced a delayed increase in non-rapid eye movement sleep in post-injection hours 3-12. These highest doses inhibited non-rapid eye movement sleep during the subsequent 12-h light period. The finding that L-5-hydroxytryptophan, but not L-tryptophan, induced a dose-dependent and long-lasting decrease in cortical brain temperature regardless of whether or not non-rapid eye movement sleep was suppressed or enhanced contributes to a growing list of conditions showing that sleep-wake activity and thermoregulation, although normally tightly coupled, may be dissociated. The initial non-rapid eye movement sleep inhibition observed following low doses of L-5-hydroxytryptophan may be attributable to increased serotonergic activity since 5-hydroxytryptamine may promote wakefulness per se, whereas the delayed non-rapid eye movement sleep enhancement after higher doses may be due to the induction by 5-hydroxytryptamine of sleep-inducing factor(s), as previously hypothesized. The period of non-rapid eye movement sleep inhibition beginning 12 h after administration of L-5-hydroxytryptophan doses that increase non-rapid eye movement sleep is characteristic of physiological manipulations in which non-rapid eye movement sleep is enhanced. The results of the present study suggest that the complex effects of 5-HT on sleep depend on the degree and time course of activation of the serotonergic system such that 5-HT may directly inhibit sleep, yet induce a cascade of physiological processes that enhance subsequent sleep.

Hypothalamic serotonergic activity correlates better with brain temperature than with sleep-wake cycle and muscle tone in rats.

The activity of the serotonergic system varies in phase with the sleep-wake cycle, which is associated with changes in several physiological functions, including electroencephalographic activity, brain temperature, and locomotion. The aim of the present study was to clarify which of these parameters correlates better with serotonergic activity in spontaneous conditions. Voltammetric recordings by telemetry of serotonergic metabolism in the medial preoptic area and polygraphic recordings of sleep-wake activity (by means of electroencephalographic delta band, brain cortical temperature and neck electromyographic activity recordings) were simultaneously performed in freely moving rats. Univariate analyses of variance revealed that each variable under investigation was statistically correlated with serotonergic metabolism. When the variables were entered into the model simultaneously, both partial correlation and step-wise multiple regression analyses indicated that the highest correlation exists between serotonergic metabolism and brain cortical temperature. The present data show that serotonergic activity in the medial preoptic area is closely linked to physiological changes in brain temperature.

Factors altering the sleep of burned children.

Although few studies have been conducted on burn patients, they indicate that sleep of burned children is altered. We suggest in this review, on the basis of the limited data available that factors contributing to sleep disruption in burned individuals may be broadly categorized as pathophysiological responses to the injury, the pain and discomfort experienced by the patient and medications used to treat these symptoms, and the physical environment in the Burns Intensive Care Unit. The responses to thermal injury include alterations in circulating neuropeptides, hormones, and immune-active substances, many of which are known to regulate/modulate sleep. Medications for the management of pain and for treating symptoms of various injury-induced stress and anxiety disorders may also alter sleep. Finally, frequent disruptions of the patient by medical staff is but one of the many environmental factors that may contribute to disrupted sleep. Severe burns induce a hypermetabolic response that may result in peripheral wasting, that depletes substrates necessary for tissue repair, and is associated with reduced growth hormone. Burn-induced growth hormone insufficiency is aggressively treated to counteract peripheral wasting and to aid in wound healing of skin graft donor sites. We speculate that improvement of sleep quality would result in a less severe reduction in growth hormone due to the well documented relationship between slow-wave sleep onset and growth hormone secretion. Such improvement in spontaneous growth hormone secretion patterns may aid in recovery by supporting tissue repair and by minimizing the hypermetabolic response to thermal injury. The experiments to test such hypotheses remain to be conducted, yet the results of such experiments may provide the basis for beginning to answer the question of whether or not sleep aids in recovery from injury.

Serotonergic activation stimulates the pituitary-adrenal axis and alters interleukin-1 mRNA expression in rat brain.

Interactions between neurotransmitters and immunomodulators within the central nervous system may be functionally relevant for communication between the immune system and the brain. Previous studies indicate that cytokines such as interleukin-1 (IL-1) alter activity of the serotonergic system at multiple levels. This study tested the hypothesis that serotonergic activation modulates cytokine mRNA expression in brain. Serotonergic activation was induced by injecting rats intraperitoneally (i.p.) prior to dark onset with the serotonin precursor L-5-hydroxytryptophan (5-HTP; 100 mg/kg). Cytokine mRNA expression in discrete brain regions at selected time points was determined by means of ribonuclease protection assay. Plasma corticosterone concentrations were also measured to determine if the hypothalamic-pituitary-adrenal axis is activated in response to this treatment, which potentially could exert feedback regulating cytokine message expression in brain. Plasma corticosterone was elevated for 4 h after 5-HTP administration. At this time IL-1alpha mRNA expression was reduced in the hippocampus, hypothalamus, and brainstem, and IL-1beta mRNA was reduced in the hippocampus. Six hours after 5-HTP injection, IL-1beta mRNA increased in the hypothalamus. These results show that activation of the serotonergic system affects cytokine message expression in rat brain, possibly by actions of corticosterone.

Interleukin-1 is involved in responses to sleep deprivation in the rabbit.

Interleukin-1 (IL-1) is hypothesized to be involved in sleep regulation. Antibodies directed against interleukin-1 beta (anti-IL-1 beta) were injected intracerebroventricularly (ICV) into normal rabbits to determine the effects of the reduction of endogenous IL-1 beta on spontaneous sleep/wake behavior. A 100 micrograms dose of anti-IL-1 beta reduced non-rapid eye movements sleep (NREMS) by about 20-min during the first 4-h postinjection without affecting REMS, amplitudes of electroencephalographic (EEG) slow waves, or brain temperature. Plasma concentrations of IL-1 beta, as determined by radioimmunoassay, were detectable in 39 of 79 (49%) blood samples taken before and after 4-h total sleep deprivation (SD). Plasma concentrations of IL-1 beta were, on average, significantly elevated following SD. There was a rebound in NREMS duration and of amplitudes of EEG slow waves of about 2-h duration following SD. This rebound in both parameters was exaggerated if rabbits received vehicle or anti-IL-1 beta in conjunction with SD. However, ICV administration of anti-IL-1 beta at the beginning or end of the SD period attenuated, relative to values obtained after administration of vehicle, the NREMS rebound following SD. It is concluded that SD alters the responsiveness of rabbits to experimental manipulation and that responses to SD in the rabbit are mediated, in part, by IL-1.

Somnogenic and pyrogenic effects of interleukin-1beta and lipopolysaccharide in intact and vagotomized rats.

The vagus nerve appears to serve a role in mediating peripheral immunologic influences on CNS processes. Previous work demonstrates that subdiaphragmatic vagotomy prevents or attenuates many of the behavioral and physiological responses to exogenous interleukin-1 (IL-1) or lipopolysaccharide (LPS). We determined whether the somnogenic effects of IL-1 and LPS were altered in vagotomized rats, and whether the effects of vagotomy on IL-1- and LPS-induced alterations in sleep would vary as a function of circadian phase. The data indicate that vagotomy does not influence the normal circadian patterns of sleep and wakefulness in untreated rats, or modify the pyrogenic or somnogenic effects of intracerebroventricular administration of IL-1. However, in unchallenged animals vagotomy reduces basal brain temperatures, increases delta wave amplitudes during slow-wave sleep (SWS), and induces a reduced rate of weight gain, gastric distension, and adrenal hypoplasia. Vagotomy attenuates the febrile effects of IL-1 during both light and dark phases, attenuated IL-1-induced sleep enhancement during the dark phase, and attenuated IL-1-induced increases in delta wave amplitudes within SWS during the light period. In LPS-treated rats, vagotomy attenuates the febrile and SWS responses to LPS after administration at light onset, but not after administration at dark onset. These results indicate that subdiaphragmatic vagotomy attenuates several of the somnogenic and pyrogenic effects of IL-1beta and LPS, although the effectiveness of the vagal transection in modulating these responses is influenced by circadian factors.

Rat strain differences suggest a role for corticotropin-releasing hormone in modulating sleep.

Corticotropin-releasing hormone (CRH) mediates many of the hormonal, behavioral, and autonomic responses to a variety of stressors. There is also evidence suggesting that CRH may be involved in the modulation of physiologic waking. Lewis (LEW) rats possess a hypothalamic gene defect that results in reduced synthesis and secretion of CRH relative to genetically related Fischer 344 (F344) and Sprague-Dawley (Sp-D) rat strains. We therefore hypothesized that LEW rats would spend less time awake, and more time asleep, than either F344 or Sp-D rats. Adult male LEW, F344, and Sp-D rats were surgically provided with electroencephalograph (EEG) recording electrodes, and a thermistor to measure cortical brain temperature [T(cort)]. Additional rats were also provided with a chronic guide cannula directed into a lateral cerebral ventricle. Spontaneous sleep-wake behavior was determined from 48-h recordings of the EEG, T(cort), and body movements from freely behaving, undisturbed rats. Analyses of 48-h recordings from undisturbed animals indicate that LEW rats spend less time awake and more time in slow-wave sleep, relative to the other strains tested. Rapid eye movement sleep did not differ consistently between rat strains. LEW and Sp-D rats exhibit the same degree of waking in response to intracerebroventricular administration of CRH, indicating central mechanisms mediating behavioral responses to exogenously administered CRH are intact in LEW rats. These data provide support for the hypothesis that CRH may be a modulator of waking and sleep.

Pituitary CRH receptor blockade reduces waking in the rat.

We have previously hypothesized that corticotropin-releasing hormone (CRH) is involved in the regulation of physiological waking. Central administration of CRH receptor antagonists reduces spontaneous waking in the rat. Some of the responses to central administration of CRH receptor antagonists may be mediated by mechanisms involving the hypothalamic-pituitary-adrenal axis, either by direct actions on the hypothalamus or by actions at the level of the pituitary due to leakage of the antagonists from the cerebrospinal fluid to blood. To further clarify the role of the hypothalamic-pituitary-adrenal axis as a mediator of responses to CRH receptor blockade, we administered intravenously into freely behaving rats in their home recording cages two specific CRH receptor antagonists, astressin or alpha-helical CRH, and determined subsequent changes in waking and sleep. Our results indicate that both antagonists reduce spontaneous waking, but with different time courses. Astressin, a potent antagonist of pituitary CRH receptors, reduces waking during postinjection hours 9-10, whereas high doses of alpha-helical CRH reduce waking only during the first postinjection hour. These results indicate that some effects of CRH on sleep-wake behavior may be meditated by pituitary CRH receptors.

Responsiveness of rats to interleukin-1: effects of monosodium glutamate treatment of neonates.

Monosodium glutamate (MSG) treatment of neonatal rats results in degenerative lesions of the medial basal hypothalamus, particularly the arcuate nucleus (AN). The AN is rich in corticotropin-releasing hormone (CRF) and adrenocorticotrophic hormone/alpha-melanocyte-stimulating hormone (alpha-MSH). These substances are part of a negative feedback mechanism for the regulation of interleukin-1 (IL1), a cytokine with diverse biologic actions including a role in sleep regulation. The purpose of these experiments was to determine the effects of exposure of neonatal rats to MSG on their responsiveness as adults to IL1. Adult rats, treated as neonates with MSG or the saline, were injected intracerebroventricularly during the light phase with three doses of IL1 (2.5, 10.0, 25.0 ng) and sleep-wake activity determined and brain temperature recorded for the next 6 hr. IL1 administration induced fever in both treatment groups at each dose of IL1 tested, and the febrile response of the MSG rats to the 25.0 ng dose of IL1 was greater than that of the saline control rats. In saline-treated rats, the 2.5 ng dose of IL1 enhanced non-rapid-eye-movement sleep (NREMS) without affecting rapid-eye-movement sleep (REMS) or wakefulness, whereas the 25.0 ng dose of IL1 inhibited both NREMS and REMS. In contrast, only the 10.0 ng dose of IL1 altered NREMS in MSG-treated rats. These results support the hypothesis that CRF- and alpha-MSH-containing perikarya are involved in regulation of IL1 actions.