Rat brain vascular distribution of interleukin-1 type-1 receptor immunoreactivity: relationship to patterns of inducible cyclooxygenase expression by peripheral inflammatory stimuli

Cytokine effects on the basal ganglia and dopamine function: the subcortical source of inflammatory malaise

Data suggest that cytokines released during the inflammatory response target subcortical structures including the basal ganglia as well as dopamine function to acutely induce behavioral changes that support fighting infection and wound healing. However, chronic inflammation and exposure to inflammatory cytokines appears to lead to persisting alterations in the basal ganglia and dopamine function reflected by anhedonia, fatigue, and psychomotor slowing. Moreover, reduced neural responses to hedonic reward, decreased dopamine metabolites in the cerebrospinal fluid and increased presynaptic dopamine uptake and decreased turnover have been described. This multiplicity of changes in the basal ganglia and dopamine function suggest fundamental effects of inflammatory cytokines on dopamine synthesis, packaging, release and/or reuptake, which may sabotage and circumvent the efficacy of current treatment approaches. Thus, examination of the mechanisms by which cytokines alter the basal ganglia and dopamine function will yield novel insights into the treatment of cytokine-induced behavioral changes and inflammatory malaise.

Lipopolysaccharide inhibits ghrelin-excited neurons of the arcuate nucleus and reduces food intake via central nitric oxide signaling

Lipopolysaccharide (LPS) induces anorexia and expression of inducible nitric oxide synthase (iNOS) in the hypothalamic arcuate nucleus (Arc). Peripheral administration of the iNOS inhibitor 1400 W counteracts the anorectic effects of LPS. Here we investigated the role of central NO signaling in LPS anorexia. In electrophysiological studies we tested whether 1400 W counteracts the iNOS-dependent inhibition of Arc neurons triggered by in vivo or in vitro stimulation with LPS. We used the hormone ghrelin as a functional reference stimulus because ghrelin is known to activate orexigenic Arc neurons. Further, we investigated whether in vitro LPS stimulation induces an iNOS-mediated formation of the second messenger cGMP. Since the STAT1 pathway contributes to the regulation of iNOS expression we investigated whether LPS treatment induces STAT1 phosphorylation in the Arc. Finally we tested the effect of intracerebroventricular injection of 1400 W on LPS-induced anorexia. Superfusion with 1400 W (10(-4) M) increased neuronal activity in 37% of neurons in Arc slices from LPS treated (100 μg/kg ip) but not from saline treated rats. Similarly, 1400 W excited 45% of Arc neurons after in vitro stimulation with LPS (100 ng/ml). In both approaches, a considerable percentage of 1400 W sensitive neurons were excited by ghrelin (10(-8)M; 50% and 75%, respectively). In vitro stimulation with LPS induced cGMP formation in the Arc, which was blocked by co-incubation with 1400 W. LPS treatment elicited a pSTAT1 response in the Arc of mice. Central 1400 W injection (4 μg/rat) attenuated LPS-induced anorexia and counteracted the LPS-dependent decrease in respiratory quotient and energy expenditure. In conclusion, the current findings substantiate a role of central iNOS dependent NO formation in LPS-induced effects on eating and energy homeostasis. A pharmacological blockade of NO formation might be a therapeutic approach to ameliorate disease-related anorexia.

Peripheral nerve injury alters blood-spinal cord barrier functional and molecular integrity through a selective inflammatory pathway

Peripheral nerve lesion triggers alterations in the spinal microenvironment that contribute to the pathogenesis of neuropathic pain. While neurons and glia have been implicated in these functional changes, it remains largely underexplored whether the blood-spinal cord barrier (BSCB) is also involved. The BSCB is an important component in the CNS homeostasis, and compromised BSCB has been associated with different pathologies affecting the spinal cord. Here, we demonstrated that a remote injury on the peripheral nerve in rats triggered a leakage of the BSCB, which was independent of spinal microglial activation. The increase of BSCB permeability to different size tracers, such as Evans Blue and sodium fluorescein, was restricted to the lumbar spinal cord and prominent for at least 4 weeks after injury. The spinal inflammatory reaction triggered by nerve injury was a key player in modulating BSCB permeability. We identified MCP-1 as an endogenous trigger for the BSCB leakage. BSCB permeability can also be impaired by circulating IL-1β. In contrast, antiinflammatory cytokines TGF-β1 and IL-10 were able to shut down the openings of the BSCB following nerve injury. Peripheral nerve injury caused a decrease in tight junction and caveolae-associated proteins. Interestingly, ZO-1 and occludin, but not caveolin-1, were rescued by TGF-β1. Furthermore, our data provide direct evidence that disrupted BSCB following nerve injury contributed to the influx of inflammatory mediators and the recruitment of spinal blood borne monocytes/macrophages, which played a major role in the development of neuropathic pain. These findings highlight the importance of inflammation in BSCB integrity and in spinal cord homeostasis.

Immunity, aging, and geriatric depression

Inflammatory processes are likely to play a causal role in geriatric depression. Geriatric depression occurs in the context of illnesses in which inflammatory processes are part of the pathogenesis. Both aging and depression are associated with immune responses, and the connectivity among mood-regulating structures may be modulated by inflammatory responses. Geriatric depression exacerbates the symptoms of comorbid disorders. Geriatric depression often occurs in persons exposed to chronic stress, a state precipitating geriatric depression and triggering proinflammatory responses. The successful treatment of comorbid conditions that increase central nervous system inflammatory responses has general health benefits and should be part of clinical practice.

Spatiotemporal nuclear factor interleukin-6 expression in the rat brain during lipopolysaccharide-induced fever is linked to sustained hypothalamic inflammatory target gene induction

Rats injected with lipopolysaccharide (LPS) show brain-controlled sickness symptoms, including fever. In these animals, early genomic activation of brain cells was previously monitored by immunohistochemical detection of transcription factors such as nuclear factor (NF)-κB or signal transducer and activator of transcription (STAT)3 and was linked to the initiation or maintenance of the febrile response. To investigate whether NF-IL6 might be another important transcription factor implicated in this kind of immune-to-brain signaling, rats were injected with LPS (100 μg/kg, intraperitoneally) or phosphate-buffered saline, and brains were analyzed by immunohistochemistry, real-time PCR, or Western blot 4, 6, 8, and 10 hours later. Moderate to strong LPS-induced nuclear NF-IL6 immunoreactivity (IR) occurred in a time-dependent manner within circumventricular organs, namely, the vascular organ of the lamina terminalis, the subfornical organ, the area postrema, and the median eminence, brain structures with a leaky blood-brain barrier. Furthermore, nuclear NF-IL6-IR was observed in the pituitary gland, the choroid plexus, and the meninges as well as blood vessels throughout the entire brain. Endothelial, microglial, and ependymal cells, astrocytes, perivascular macrophages, and neurons exhibited LPS-induced nuclear NF-IL6-IR; mRNA levels of NF-IL6, responsive inflammatory genes, and NF-IL6 protein levels were significantly elevated. As opposed to observations on STAT3 or NFκB, the percentage of NF-IL6-reactive cells increased in parallel to late phases of the febrile response. In conclusion, these results suggest a potential role for NF-IL6 in the maintenance or possibly the termination of LPS-induced fever. Moreover, we propose NF-IL6 to be a delayed brain cell activation marker.

Stress responses: the contribution of prostaglandin E(2) and its receptors

Stress is a state of physiological or psychological strain caused by adverse stimuli; responses to stress include activation of the sympathetic nervous system, glucocorticoid secretion and emotional behaviors. Prostaglandin E(2) (PGE(2)), acting through its four receptor subtypes (EP1, EP2, EP3 and EP4), is involved in these stress responses. Studies of EP-selective drugs and mice lacking specific EPs have identified the neuronal pathways regulated by PGE(2). In animals with febrile illnesses, PGE(2) acts on neurons expressing EP3 in the preoptic hypothalamus. In illness-induced activation of the hypothalamic-pituitary-adrenal axis, EP1 and EP3 regulate distinct neuronal pathways that converge at the paraventricular hypothalamus. During psychological stress, EP1 suppresses impulsive behaviors via the midbrain dopaminergic systems. PGE(2) promotes illness-induced memory impairment, yet also supports hippocampus-dependent memory formation and synaptic plasticity via EP2 in physiological conditions. In response to illness, PGE(2) is synthesized by enzymes induced in various cell types inside and outside the brain, whereas constitutively expressed enzymes in neurons and/or microglia synthesize PGE(2) in response to psychological stress. Dependent on the type of stress stimuli, PGE(2) released from different cell types activates distinct EP receptors, which mobilize multiple neuronal pathways, resulting in stress responses.

Transcriptome signature of the adult mouse choroid plexus

Background

Although the gene expression profile of several tissues in humans and in rodent animal models has been explored, analysis of the complete choroid plexus (CP) transcriptome is still lacking. A better characterization of the CP transcriptome can provide key insights into its functions as one of the barriers that separate the brain from the periphery and in the production of cerebrospinal fluid.

Methods

This work extends further what is known about the mouse CP transcriptome through a microarray analysis of CP tissue from normal mice under physiological conditions.

Results

We found that the genes most highly expressed are those implicated in energy metabolism (oxidative phosphorylation, glycolysis/gluconeogenesis) and in ribosomal function, which is in agreement with the secretory nature of the CP. On the other hand, genes encoding for immune mediators are among those with lower expression in basal conditions. In addition, we found genes known to be relevant during brain development, and not previously identified to be expressed in the CP, including those encoding for various axonal guidance and angiogenesis molecules and for growth factors. Some of these are known to influence the neural stem cell niche in the subventricular zone, highlighting the involvement of the CP as a likely modulator of neurogenesis. Interestingly, our observations confirm that the CP transcriptome is unique, displaying low homology with that of other tissues. Of note, we describe here that the closest similarity is with the transcriptome of the endothelial cells of the blood-brain barrier.

Conclusions

Based on the data presented here, it will now be possible to further explore the function of particular proteins of the CP secretome in health and in disease.

Interleukin-1 exerts distinct actions on different cell types of the brain in vitro

Interleukin-1 (IL-1) is a critical neuroinflammatory mediator in the central nervous system (CNS). In this study, we investigated the effect of IL-1 on inducing inflammation-related gene expression in three astrocyte, two microglial, and one brain endothelial cell line. Interleukin-1 beta (IL-1β) is found to be produced by the two microglial cell lines constitutively, but these cells do not respond to IL-1β stimulation. The three astrocyte cell lines responded to IL-1β stimulation by expressing MCP-1, CXCL-1, and VCAM-1, but different subtypes of astrocytes exhibited different expression profiles after IL-1β stimulation. The brain endothelial cells showed strongest response to IL-1β by producing MCP-1, CXCL-1, VCAM-1, ICAM-1, IL-6, and COX-2 mRNA. The induction of endothelial COX-2 mRNA is shown to be mediated by p38 MAPK pathway, whereas the induction of other genes is mediated by the NF-κB pathway. These results demonstrate that IL-1 exerts distinct cell type-specific action in CNS cells and suggest that IL-1-mediated neuroinflammation is the result of the summation of multiple responses from different cell types in the CNS to IL-1.

Joining the dots: neurobiological links in a functional analysis of depression

Depression is one of the major contributors to the Total Disease Burden and afflicts about one-sixth of Western populations. One of the most effective treatments for depression focuses upon analysis of causal chains in overt behaviour, but does not include brain-related phenomena as steps along these causal pathways. Recent research findings regarding the neurobiological concomitants of depressive behaviour suggest a sequence of structural and functional alterations to the brain which may also produce a beneficial outcome for the depressed individual--that of adaptive withdrawal from uncontrollable aversive stressors. Linking these brain-based explanations to models of observable contingencies for depressive behaviour can provide a comprehensive explanation of how depressive behaviour occurs and why it persists in many patients.

Urban air pollution targets the dorsal vagal complex and dark chocolate offers neuroprotection

Mexico City (MC) residents exposed to fine particulate matter and endotoxin exhibit inflammation of the olfactory bulb, substantia nigra, and vagus nerve. The goal of this study was to model these endpoints in mice and examine the neuroprotective effects of chocolate. Mice exposed to MC air received no treatment or oral dark chocolate and were compared to clean-air mice either untreated or treated intraperitoneally with endotoxin. Cyclooxygenase-2 (COX-2), interleukin 1 beta (IL-1β), and CD14 messenger RNA (mRNA) were quantified after 4, 8, and 16 months of exposure in target brain regions. After 16 months of exposure, the dorsal vagal complex (DVC) exhibited significant inflammation in endotoxin-treated and MC mice (COX-2 and IL-1β P<.001). Mexico City mice had olfactory bulb upregulation of CD14 (P=.002) and significant DVC imbalance in genes for antioxidant defenses, apoptosis, and neurodegeneration. These findings demonstrate sustained DVC inflammation in mice exposed to MC air, which is mitigated by chocolate administration.

Evolving refractory major depressive disorder diagnostic and treatment paradigms: toward closed-loop therapeutics

Current antidepressant therapies do not effectively control or cure depressive symptoms. Pharmaceutical therapies altogether fail to address an estimated 4 million Americans who suffer from a recurrent and severe treatment-resistant form of depression known as refractory major depressive disorder. Subjective diagnostic schemes, differing manifestations of the disorder, and antidepressant treatments with limited theoretical bases each contribute to the general lack of therapeutic efficacy and differing levels of treatment resistance in the refractory population. Stimulation-based therapies, such as vagus nerve stimulation, transcranial magnetic stimulation, and deep brain stimulation, are promising treatment alternatives for this treatment-resistant subset of patients, but are plagued with inconsistent reports of efficacy and variable side effects. Many of these problems stem from the unknown mechanisms of depressive disorder pathogenesis, which prevents the development of treatments that target the specific underlying causes of the disorder. Other problems likely arise due to the non-specific stimulation of various limbic and paralimbic structures in an open-loop configuration. This review critically assesses current literature on depressive disorder diagnostic methodologies, treatment schemes, and pathogenesis in order to emphasize the need for more stringent depressive disorder classifications, quantifiable biological markers that are suitable for objective diagnoses, and alternative closed-loop treatment options tailored to well-defined forms of the disorder. A closed-loop neurostimulation device design framework is proposed, utilizing symptom-linked biomarker abnormalities as control points for initiating and terminating a corrective electrical stimulus which is autonomously optimized for correcting the magnitude and direction of observed biomarker abnormality.

Brain cyclooxygenase-2 mediates interleukin-1-induced cellular activation in preoptic and arcuate hypothalamus, but not sickness symptoms

Interleukin-1beta acts on the CNS to induce fever, neuroendocrine activation, and behavioral changes, but cannot passively cross the blood-brain barrier. According to a widely accepted hypothesis interleukin-1beta induces the synthesis of cyclooxygenase-2 at the blood-brain interface, which produces prostaglandins that diffuse into brain parenchyma to activate neurons. We studied the role of brain cyclooxygenase-2 in interleukin-1beta-induced fever, neuroendocrine and behavioral responses and cellular activation by intracerebroventricular infusion of the cyclooxygenase-2 inhibitor NS-398. Central cyclooxygenase-2 inhibition attenuated extracellular signal-regulated kinase-1/2 phosphorylation and c-Fos induction in the median preoptic area and arcuate hypothalamus, but not in other hypothalamic or brainstem structures, after intraperitoneal interleukin-1beta administration. However, the same treatment did not affect interleukin-1beta-induced fever, rises in corticosterone or anorexia. These findings moderate the prevailing view and indicate that brain cyclooxygenase-2-dependent prostaglandin production is important to activation of the median preoptic and arcuate hypothalamus, but not necessarily involved in fever, rises in plasma corticosterone and anorexia after peripheral interleukin-1beta administration.

Leptin regulates leukocyte recruitment into the brain following systemic LPS-induced inflammation

The appetite suppressing hormone leptin has emerged as an important modulator of immune function and is now considered to be a critical link between energy balance and host defense responses to pathogens. These 'adaptive' responses can, in situations of severe and sustained systemic inflammation, lead to adverse effects including brain damage that is partly mediated by neutrophil recruitment into the brain. We examined the contribution of leptin to this process in leptin-deficient (ob/ob), -resistant (db/db) and wild-type (WT) mice injected intraperitoneally with a septic dose of lipopolysaccharide (LPS). This treatment induced a dramatic increase in the number of neutrophils entering the brain of WT mice, an effect that was almost totally abolished in the mutant mice and correlated with a significant reduction in the mRNA levels of interleukin-1beta, intracellular adhesion molecule-1 and neutrophil-specific chemokines. These effects were reversed with leptin replenishment in ob/ob mice leading to recovery of neutrophil recruitment into the brain. Moreover, 48 h food deprivation in WT mice, which decreased circulating leptin levels, attenuated the LPS-induced neutrophil recruitment as did a single injection of an anti-leptin antiserum 4 h before LPS treatment in WT mice. These results provide the first demonstration that leptin has a critical role in leukocyte recruitment to the brain following severe systemic inflammation with possible implications for individuals with altered leptin levels such as during obesity or starvation.

Rapid brain penetration of interleukin-1 receptor antagonist in rat cerebral ischaemia: pharmacokinetics, distribution, protection

BACKGROUND AND PURPOSE

Limited data on the brain penetration of potential stroke treatments have been cited as a major weakness contributing to numerous failed clinical trials. Thus, we tested whether interleukin-1 receptor antagonist (IL-1RA), established as a potent inhibitor of brain injury in animals and currently in clinical development, reaches the brain via a clinically relevant administration route, in experimental stroke.

EXPERIMENTAL APPROACH

Male, Sprague-Dawley rats [either naïve or exposed to middle cerebral artery occlusion (MCAo)] were given a single s.c. dose of IL-1RA (100 mg*kg(-1)). The pharmacokinetic profile of IL-1RA was assessed in plasma and CSF up to 24 h post-administration. Brain tissue distribution of administered IL-1RA was assessed using immunohistochemistry. In a separate experiment, the neuroprotective effect of the single s.c. dose of IL-1RA in MCAo was assessed versus a placebo control group.

KEY RESULTS

A single s.c. dose of IL-1RA reduced damage caused by MCAo by 33%. This dose resulted in sustained, high concentrations in plasma and CSF, penetrated brain tissue exclusively in areas of blood-brain barrier breakdown and co-localized with morphologically viable neurones. CSF concentrations did not reflect massive parenchymal infiltration of IL-1RA in MCAo animals compared to naïve.

CONCLUSIONS AND IMPLICATIONS

These data are the first to show that a potential treatment for stroke, IL-1RA, rapidly reaches salvageable brain tissue via an administration route that is clinically relevant. This allows confidence that IL-1RA, as a candidate for further clinical development, is able to confer its protective actions both peripherally and centrally.

High glucose and interleukin-1beta downregulate interleukin-1 type I receptor (IL-1RI) in retinal endothelial cells by enhancing its degradation by a lysosome-dependent mechanism

Diabetic retinopathy has been considered a low-grade chronic inflammatory disease. The production of interleukin-1beta (IL-1beta) in the retina is increased, and this finding has been correlated with an increase in blood-retinal barrier permeability, suggesting that IL-1beta might have an important role in the pathogenesis of diabetic retinopathy. However, in this context, no attention has been given to interleukin-1 type I receptor (IL-1RI), which is the receptor responsible for IL-1beta triggered effects. Therefore, we investigated the effect of high glucose and IL-1beta on the IL-1RI regulation in retinal endothelial cells. A time-dependent downregulation of IL-1RI protein levels was detected in retinal endothelial cells exposed (1-24h) to high glucose, mannitol or IL-1beta. Long-term exposure (7days) to high glucose or mannitol also decreased IL-1RI protein content. IL-1RI downregulation was due to its activation by IL-1beta, since it was inhibited by the presence of anti-IL-1RI or anti-IL-1beta antibodies. Moreover, IL-1RI downregulation was prevented by lysosome inhibitors, chloroquine and ammonium chloride, but not by proteasome inhibitors, MG132 and lactacystin. We also found that IL-1RI translocates to the nucleus after high glucose or IL-1beta treatment. In conclusion, our results indicate that high glucose, probably due to osmotic stress, and IL-1beta downregulate IL-1RI in retinal endothelial cells. The downregulation of IL-1RI is triggered by its activation and is due, at least partially, to lysosomal degradation. High glucose and IL-1beta also enhance the translocation of IL-1RI to the nucleus.

Neurobiology of inflammation-associated anorexia

Compelling data demonstrate that inflammation-associated anorexia directly results from the action of pro-inflammatory factors, primarily cytokines and prostaglandins E2, on the nervous system. For instance, the aforementioned pro-inflammatory factors can stimulate the activity of peripheral sensory neurons, and induce their own de novo synthesis and release into the brain parenchyma and cerebrospinal fluid. Ultimately, it results in the mobilization of a specific neural circuit that shuts down appetite. The present article describes the different cell groups and neurotransmitters involved in inflammation-associated anorexia and examines how they interact with neural systems regulating feeding such as the melanocortin system. A better understanding of the neurobiological mechanisms underlying inflammation-associated anorexia will help to develop appetite stimulants for cancer and AIDS patients.

Central interleukin-10 attenuates lipopolysaccharide-induced changes in food intake, energy expenditure and hypothalamic Fos expression

Lipopolysaccharide (LPS) is often used to mimic acute infection and induces hypophagia, the selective partitioning of fat for energy, and fever. Interleukin-10 (IL-10) is an anti-inflammatory cytokine expressed in the brain which attenuates LPS-induced hypophagia; however the potential sites of interaction within the brain have not been investigated. Hypothalamic orexin (ORX) and melanin-concentrating hormone (MCH) regulate energy expenditure and food intake although the regulation of these neuropeptides through the interactions between central IL-10 and the inflammatory consequences of peripheral LPS have not been investigated. The present study in the rat investigated during the dark phase of the light-dark cycle the ability of central IL-10 (250 ng, i.c.v.) to attenuate the changes in food intake, energy substrate partitioning, and central Fos expression within the hypothalamus to peripheral LPS (100 microg/kg, i.p.); Fos expression changes specifically within ORX and MCH neurons were also investigated. Central IL-10 attenuated the peripheral LPS-induced hypophagia, reduction in motor activity, fever and reduction in respiratory exchange ratio. Central IL-10 also attenuated peripheral LPS-induced increases in Fos expression within ORX neurons and decreases in Fos expression within unidentified cells of the caudal arcuate nucleus. In contrast, both IL-10 and LPS injection independently decreased Fos expression within MCH neurons. The present study provides further insight into the interactions within the brain between the anti-inflammatory cytokine IL-10, the inflammatory consequences of LPS, and neuropeptides known to regulate energy expenditure and food intake.

Systemic endotoxin induces gene expression of inducible nitric oxide synthase in fetal rat brain

BACKGROUND

Few studies have examined the response of the fetus under stress, such as with maternal infection. Recent work has indicated that nitric oxide (NO) modulates corticotropin-releasing hormone (CRH) secretion by the hypothalamus, but details of the action of NO on the fetus remain unclear. Therefore, we investigated the expression of inducible nitric oxide synthase (iNOS) mRNA and the response pattern following lipopolysaccharide (LPS) loading using a rat model of fetal infection.

METHODS

Fetuses were delivered by cesarean section on day 20 of gestation and immediately placed in a chamber maintained at 37 degrees C and 100% relative humidity. The LPS group (n=12) was given 400 microg of LPS/100 g body weight, and the physiologic saline group (n=12) was given physiologic saline. Fetuses were then incubated for a further 3 hours. Fetuses were decapitated, the trunk blood was collected immediately after cesarean section or after 3 hours of incubation, and the fetal brains were fixed in formaldehyde and cryopreserved. Coronal cryosections of the brains were prepared, and a (35)S-uridine triphosphate-labeled antisense RNA probe for iNOS was then prepared. In situ hybridization was performed, and iNOS expression was evaluated semiquantitatively on the basis of optical density. In both groups, plasma corticosterone levels were determined with radioimmunoassay.

RESULTS

Expression of iNOS mRNA was not noted in the physiologic saline group (3 hours postpartum). In the LPS group, iNOS mRNA expression was observed in the subfornical organ, but not in the paraventricular nucleus. Plasma corticosterone levels were significantly elevated in the LPS group.

CONCLUSIONS

In 20-day-old rat fetuses, the hypothalamic-pituitary-adrenal axis was already mobilized in response to LPS-induced stress. These results suggest that iNOS is not involved in the acute response of the hypothalamic-pituitary-adrenal axis to LPS challenge in 20-day-old rat fetuses.

Peripheral osmotic stimulation inhibits the brain's innate immune response to microdialysis of acidic perfusion fluid adjacent to supraoptic nucleus

During the brain's innate immune response microglia, astroglia and ependymal cells resolve/repair damaged tissue and control infection. Released interleukin-1beta (IL-1beta) reaching cerebroventricles stimulates circumventricular organs (CVOs; subfornical organ, SFO; organum vasculosum lamina terminalis, OVLT), the median preoptic nucleus (MePO), and magnocellular and parvocellular neurons in the supraoptic (SON) and paraventricular (PVN) nuclei. Hypertonic saline (HS) also activates these osmosensory CVOs and neuroendocrine systems, but, in contrast to IL-1beta, inhibits the peripheral immune response. To examine whether the brain's innate immune response is attenuated by osmotic stimulation, sterile acidic perfusion fluid was microdialyzed (2 microl/min) in the SON area of conscious rats for 6 h with sterile HS (1.5 M NaCl) injected subcutaneously (15 ml/kg) at 5 h. Immunohistochemistry identified cytokine sources (IL-1beta(+); OX-42(+) microglia) and targets (IL-1R(+); inducible cyclooxygenase, COX-2(+); c-Fos(+)) near the probe, in CVOs, MePO, ependymal cells, periventricular hypothalamus, SON, and PVN. Inserting the probe stimulated magnocellular neurons (c-Fos(+); SON; PVN) via the MePO (c-Fos(+)), a response enhanced by HS. Microdialysis activated microglia (OX-42(+); amoeboid/hypertrophied; IL-1beta(+)) in the adjacent SON and bilaterally in perivascular areas of the PVN, periventricular hypothalamus and ependyma, coincident with c-Fos expression in ependymal cells and COX-2 in the vasculature. These microglial responses were attenuated by HS, coincident with activating parvocellular and magnocellular neuroendocrine systems and elevating circulating IL-1beta, oxytocin, and vasopressin. Acidosis-induced cellular injury from microdialysis activated the brain's innate immune response by a mechanism inhibited by peripheral osmotic stimulation.

Peripheral lipopolysaccharide administration induces cytokine mRNA expression in the viscera and brain of fever-refractory mice lacking microsomal prostaglandin E synthase-1

We examined the expression of interleukin (IL)-1beta, IL-6 and tumour necrosis factor (TNF) alpha in mice lacking microsomal prostaglandin E synthase-1 (mPGES-1), which neither produce prostaglandin E(2), nor mount a febrile response upon immune challenge. Intraperitoneal lipopolysaccharide (LPS) injection resulted in a strongly induced expression of all three cytokines in the brain and viscera, similar to wild-type animals. Several brain regions additionally showed modest induction of receptors for these cytokines in both genotypes. Telemetric recordings of body temperature showed that the mPGES-1 deficient mice remained afebrile upon LPS challenge, in contrast to the prominent fever displayed by the wild-type mice. These data demonstrate that LPS-induced cytokine expression occurs independently of prostaglandin E(2), and imply that endogenously expressed IL-1beta, IL-6, and TNFalpha are not pyrogenic per se, supporting the role of prostaglandin E(2) as the final and obligatory mediator of LPS-induced fever.

Molecular aspects of fever and hyperthermia

After defining hyperthermia and fever, this article describes the complete chain of events leading to the genesis of fever, starting with the lipopolysaccharide-induced formation of endogenous pyrogens (cytokines), their interactions with relevant targets in the brain, the induction of enzymes responsible for the formation of prostaglandin E2, the activation of descending neuronal pathways via the EP3 receptor, and the stimulation of thermogenesis via this pathway to support the febrile shift of the thermoregulatory set point. This article also summarizes an alternative hypothesis to account for a rapid induction of the early phase of lipopolysaccharide-induced fever before the release of larger amounts of cytokines into the bloodstream. Other topics discussed include malignant hypothermia, drug-induced hypothermia, and the heat stroke syndrome.

IL-1R signaling within the central nervous system regulates CXCL12 expression at the blood-brain barrier and disease severity during experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the CNS characterized by disruption of the blood-brain barrier (BBB). This breach in CNS immune privilege allows undeterred trafficking of myelin-specific lymphocytes into the CNS where they induce demyelination. Although the mechanism of BBB compromise is not known, the chemokine CXCL12 has been implicated as a molecular component of the BBB whose pattern of expression is specifically altered during MS and which correlates with disease severity. The inflammatory cytokine IL-1beta has recently been shown to contribute not only to BBB permeability but also to the development of IL-17-driven autoimmune responses. Using experimental autoimmune encephalomyelitis, the rodent model of MS, we demonstrate that IL-1beta mediates pathologic relocation of CXCL12 during the induction phase of the disease, before the development of BBB disruption. We also show that CD4, CD8, and, surprisingly gammadelta T cells are all sources of IL-1beta. In addition, gammadelta T cells are also targets of this cytokine, contributing to IL-1beta-mediated production of IL-17. Finally, we show that the level of CNS IL-1R determines the clinical severity of experimental autoimmune encephalomyelitis. These data suggest that T cell-derived IL-1beta contributes to loss of immune privilege during CNS autoimmunity via pathologic alteration in the expression of CXCL12 at the BBB.

Interleukin-6 activates arginine vasopressin neurons in the supraoptic nucleus during immune challenge in rats

The increase of plasma arginin-vasopressin (AVP) release, which translates hypothalamic AVP neuron activation in response to immune challenge, appears to occur independently of plasma osmolality or blood pressure changes. Many studies have shown that major inflammatory mediators produced in response to peripheral inflammation, such as prostaglandin (PG)-E(2) and interleukin (IL)-1beta, excite AVP neurons. However, in vivo electrical activation of AVP neurons was still not assessed in relation to plasma AVP release, osmolality, or blood pressure or to the expression and role of inflammatory molecules like PG-E(2), IL-1beta, IL-6, and tumor necrosis factor-alpha (TNFalpha). This study aims at elucidating those factors that underlie the activation of AVP neurons in response to immune stimulation mimicked by an intraperitoneal injection of lipopolysaccharide (LPS) in male Wistar rats. LPS treatment concomittanlty decreased diuresis and increased plasma AVP as well as AVP neuron activity in vivo, and these effects occurred as early as 30 min. Activation was sustained for more than 6 h. Plasma osmolality did not change, whereas blood pressure only transiently increased during the first hour post-LPS. PG-E(2), IL-1beta, and TNFalpha mRNA expression were raised 3 h after LPS, whereas IL-6 mRNA level increased 30 min post-LPS. In vivo electrophysiological recordings showed that brain IL-6 injection increased AVP neuron activity similarly to peripheral LPS treatment. In contrast, brain injection of anti-IL-6 antibodies prevented the LPS induced-activation of AVP neurons. Taken together, these results suggest that the early activation of AVP neurons in response to LPS injection is induced by brain IL-6.

Cytokine, sickness behavior, and depression

The psychologic and behavioral components of sickness represent, together with fever response and associated neuroendocrine changes, a highly organized strategy of the organism to fight infection. This strategy, referred to as sickness behavior, is triggered by the proinflammatory cytokines produced by activated cells of the innate immune system in contact with specific pathogen-associated molecular patterns (PAMPs). Interleukin-1 and other cytokines act on the brain via (1) a neural route represented by the primary afferent neurons that innervate the body site where the infectious process takes place and (2) a humoral pathway that involves the production of proinflammatory cytokines. This article presents the current knowledge on the way this communication system is organized and regulated and the implications of these advances for understanding brain physiology and pathology.

The role of interleukin-6 in lipopolysaccharide-induced fever by mechanisms independent of prostaglandin E2

Fever has been shown to be elicited by prostaglandin E(2) (PGE(2)) binding to its receptors on thermoregulatory neurons in the anterior hypothalamus. The signals that trigger PGE(2) production are thought to include proinflammatory cytokines, such as IL-6. However, although the presence of IL-6 is critical for fever, IL-6 by itself is not or only weakly pyrogenic. Here we examined the relationship between IL-6 and PGE(2) in lipopolysaccharide (LPS)-induced fever. Immune-challenged IL-6 knockout mice did not produce fever, in contrast to wild-type mice, but the expression of the inducible PGE(2)-synthesizing enzymes, cyclooxygenase-2 and microsomal prostaglandin E synthase-1, was similarly up-regulated in the hypothalamus of both genotypes, which also displayed similarly elevated PGE(2) levels in the cerebrospinal fluid. Nevertheless, both wild-type and knockout mice displayed a febrile response to graded concentrations of PGE(2) injected into the lateral ventricle. There was no major genotype difference in the expression of IL-1beta and TNFalpha or their receptors, and pretreatment of IL-6 knockout mice with soluble TNFalpha receptor ip or intracerebroventricularly or a cyclooxygenase-2 inhibitor ip did not abolish the LPS unresponsiveness. Hence, although IL-6 knockout mice have both an intact PGE(2) synthesis and an intact fever-generating pathway downstream of PGE(2), endogenously produced PGE(2) is not sufficient to produce fever in the absence of IL-6. The findings suggest that IL-6 controls some factor(s) in the inflammatory cascade, which render(s) IL-6 knockout mice refractory to the pyrogenic action of PGE(2), or that it is involved in the mechanisms that govern release of synthesized PGE(2) onto its target neurons.

Prostaglandins and sickness behavior: old story, new insights

Previous evidence has shown that prostaglandins play a key role in the development of sickness behavior observed during inflammatory states. In particular, prostaglandin E2 (PGE2) is produced in the brain by a variety of inflammatory signals such as endotoxins or cytokines. Its injection has been also shown to induce symptoms of sickness behavior. The role of cyclooxygenase enzymes (COX), the rate-limiting enzymes converting arachidonic acid into prostaglandins, in sickness behavior has been extensively studied, and it has been demonstrated that strategies aiming at inhibiting these enzymes limit anorexia, body weight loss and fever in animals with inflammatory diseases. However, inhibiting COX activity may lead to negative gastric or cardiovascular effects, since COX enzymes play a role in the synthesis of others prostanoids with various and sometimes contrasting properties. Recently, prostaglandin E synthases (PGES), which specifically catalyze the final step of PGE2 biosynthesis, were characterized. Among these enzymes, the microsomal prostaglandin E synthase-1 (mPGES-1) was of a particular interest since it was shown to be up-regulated by inflammatory signals in a variety of cell types. Moreover, mPGES-1 was shown to be crucial for correct immune-to-brain communication and induction of fever and anorexia by pro-inflammatory agents. This review takes stock of previous knowledge and recent advances in understanding the role of prostaglandins and of their specific synthesizing enzymes in the molecular mechanisms underlying sickness behavior. The review concludes with a short summary of key questions that remain to be addressed and points out therapeutic developments in this research field.

Transport of interleukin-1 across cerebromicrovascular endothelial cells

BACKGROUND AND PURPOSE

The inflammatory cytokine interleukin-1 (IL-1) has profound actions in the brain, causing neuronal cell death and exacerbating brain damage. While circulating levels are normally low, IL-1 can be produced on the vascular side of the brain endothelium, and within the brain. The naturally occurring IL-1 receptor antagonist has been administered peripherally in a Phase II trial in acute stroke patients; understanding how IL-1 and IL-1 receptor antagonist penetrate the brain is, therefore, of considerable importance.

EXPERIMENTAL APPROACH

An in vitro blood-brain barrier model was generated by co-culture of porcine brain microvascular endothelial cells with astrocytes. The mechanisms of transcellular transport of IL-1beta and IL-1 receptor antagonist were characterized in this model, using endocytosis inhibitors and IL-1 receptor-blocking antibodies.

KEY RESULTS

Transcellular IL-1beta and IL-1 receptor antagonist transport was temperature-dependent and IL-1beta was transported with higher affinity than IL-1 receptor antagonist. IL-1beta inhibited IL-1 receptor antagonist transport more potently than IL-1 receptor antagonist inhibited IL-1beta transport. Transport of IL-1beta and IL-1 receptor antagonist was not via adsorptive-mediated endocytosis, although inhibition of microtubule assembly significantly attenuated transport of both cytokines. An antibody directed to the type II IL-1 receptor significantly reduced IL-1beta transport.

CONCLUSIONS AND IMPLICATIONS

These results are consistent with IL-1 and IL-1 receptor antagonist being transported across cultured cerebromicrovascular endothelial cells and suggest that IL-1beta transport may occur via a type II IL-1 receptor-dependent mechanism. Understanding IL-1 transport into the brain may have benefits, particularly in enhancing penetration of IL-1 receptor antagonist into the brain.

Central nervous action of interleukin-1 mediates activation of limbic structures and behavioural depression in response to peripheral administration of bacterial lipopolysaccharide

Although receptors for the pro-inflammatory cytokine interleukin-1 have long been known to be expressed in the brain, their role in fever and behavioural depression observed during the acute phase response (APR) to tissue infection remains unclear. This may in part be due to the fact that interleukin-1 in the brain is bioactive only several hours after peripheral administration of bacterial lipopolysaccharide (LPS). To study the role of cerebral interleukin-1 action in temperature and behavioural changes, and activation of brain structures during the APR, interleukin-1 receptor antagonist (IL-1ra; 100 microg) was infused into the lateral brain ventricle 4 h after intraperitoneal (i.p.) LPS injection (250 microg/kg) in rats. I.p. LPS administration induced interleukin-1beta (IL-1beta) production in systemic circulation as well as in brain circumventricular organs and the choroid plexus. Intracerebroventricular (i.c.v.) infusion of IL-1ra 4 h after i.p. LPS injection attenuated the reduction in social interaction, a cardinal sign of behavioural depression during sickness, and c-Fos expression in the amygdala and bed nucleus of the stria terminalis. However, LPS-induced fever, rises in plasma corticosterone, body weight loss and c-Fos expression in the hypothalamus and caudal brainstem were not altered by i.c.v. infusion of IL-1ra. These findings, together with our previous observations showing that i.c.v. infused IL-1ra diffuses throughout perivascular spaces, where macrophages express interleukin-1 receptors, can be interpreted to suggest that circulating or locally produced brain IL-1beta acts on these cells to bring about behavioural depression and activation of limbic structures during the APR after peripheral LPS administration.

Cytokines and their relationship to the symptoms and outcome of cancer

Tumours contain immune cells and a network of pro- and anti-inflammatory cytokines, which collaborate in the development and progression of cancer. Cytokine profiles might prove to be prognostic. The systemic effects of pro-inflammatory cytokines are associated with fatigue, depression and cognitive impairment, and can affect quality of life before, during and after treatment. In people with advanced cancer, pro-inflammatory cytokines are additionally associated with anorexia and cachexia, pain, toxicity of treatment and resistance to treatment. However, physical activity might modify cytokine levels and decrease fatigue in patients with cancer, and might also improve their prognosis.

Dual modulation of synaptic transmission in the nucleus tractus solitarius by prostaglandin E2 synthesized downstream of IL-1beta

The activation of the innate immune system induces the production of blood-borne proinflammatory cytokines like interleukin-1beta (IL-1beta), which in turn triggers brain-mediated adaptative responses referred to as sickness behaviour. These responses involve the modulation of neural networks in key regions of the brain. The nucleus tractus solitarius (NTS) of the brainstem is a key nucleus for immune-to-brain signalling. It is the main site of termination of vagal afferents and is adjacent to the area postrema, a circumventricular organ allowing blood-borne action of circulating IL-1beta. Although it is well described that IL-1beta activates cerebral endothelial and glial cells, it is still unknown if and how IL-1beta or downstream-synthesized molecules impact NTS synaptic function. In this study we report that IL-1beta did not modulate NTS synaptic transmission per se, whereas prostaglandin E(2) (PGE(2)), which is produced downstream of IL-1beta, produced opposite effects on spontaneous and evoked release. On the one hand, PGE(2) facilitated glutamatergic transmission between local NTS neurons by enhancing the frequency of spontaneous excitatory postsynaptic currents through a presynaptic receptor different from the classical EP1-4 subtypes. On the other hand, PGE(2) also depressed evoked excitatory input from vagal afferent terminals through presynaptic EP3 receptors coupled to G-proteins linked to adenylyl cyclase and protein kinase A activity. Our data show that IL-1beta-induced PGE(2) can modulate evoked and spontaneous release in the NTS differentially through different mechanisms. These data unravel some molecular mechanisms by which innate immune stimuli could signal to, and be integrated within, the brainstem to produce central adaptative responses.

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

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

Immune-to-brain signaling: how important are the blood-brain barrier-independent pathways?

A conceptual obstacle for understanding immune-to-brain signaling is the issue of the blood-brain barrier (BBB). In the last 30 years, several pathways have been investigated to address the question of how peripheral immune signals are transmitted into the brain. These pathways can be categorized into two types: BBB-dependent pathways and BBB-independent pathways. BBB-dependent pathways involve the BBB as a relay station or porous barrier, whereas BBB-independent pathways use neuronal routes that bypass the BBB. Recently, a complete BBB-dependent ascending pathway for immune-to-brain signaling has been described. Details of BBB-independent pathways are still under construction. In this review, I will summarize the current progress in unraveling immune-to-brain signaling pathways. In addition, I will provide a critical analysis of the literature to point to areas where our knowledge of the immunological afferent signaling to the central nervous system is still sorely lacking.

The encephalopathy in sepsis

Brain dysfunction is a severe complication of sepsis with an incidence ranging from 9% to 71% that is associated with increased morbidity and mortality. Its diagnosis relies mainly on neurologic examination with clinical manifestations ranging from confusion to coma. An electroencephalogram, somatosensory evoked potentials, and measurement of plasma S-100b protein and neuron-specific enolase can be useful for the detection of brain dysfunction. Brain MRI can identify brain lesions such as cerebral infarction, posterior reversible encephalopathy syndrome, and leukoencephalopathy. The mechanism of sepsis-associated encephalopathy involves inflammatory and non-inflammatory processes that affect endothelial cells, glial cells, and neurons and induce blood-brain barrier breakdown, derangements of intracellular metabolism, and cell death. Specific treatments for sepsis-associated encephalopathy need to be developed. Currently, treatment is mainly the management of sepsis.

Macrophage-activating lipopeptide-2 (MALP-2) induces a localized inflammatory response in rats resulting in activation of brain sites implicated in fever

Macrophage-activating lipopeptide-2 (MALP-2) has been identified as the pathogen-associated molecular pattern of Mycoplasma fermentans, which causes stimulation of the innate immune system through the activation of the heterodimeric Toll-like receptors (TLRs) 2 and 6. Based on the reported protective effects of MALP-2 on healing of skin wounds, the central goal of this study was to evaluate the capacity of MALP-2 to induce a localized inflammatory response in an established model of a subcutaneous air pouch. Injections of MALP-2 into the pouch caused fever and some components of sickness behavior in rats. At the subcutaneous site of localized inflammation, a massive formation of tumor necrosis factor-alpha (TNF), interleukin-6 (IL-6), and prostaglandin E2 (PGE2) could be demonstrated in response to injections of MALP-2. Moderate amounts of IL-6 and PGE2 seemed to enter the systemic circulation of MALP-2-treated rats. The IL-6, which appeared in the blood after injection of MALP-2 into the air pouch was sufficient to cause a direct activation of brain cells in areas which lack a complete blood-brain barrier, namely in the sensory circumventricular organs (sCVOs), the organum vasculosum laminae terminalis (OVLT), the subfornical organ (SFO), and the area postrema (AP). The stimulation of cells at these brain sites was revealed by demonstration of a nuclear translocation of the transcription factor STAT3 (signal transducer and activator of transcription 3). Corresponding to the circulating levels of IL-6, the nuclear STAT3 activation of cells within the sCVOs was much less pronounced after local subcutaneous when compared to systemic treatment with MALP-2. In conclusion, cells within the subcutaneous compartment are activated by the TLR2/6 agonist MALP-2. Fever and sickness behavior induced by injection of MALP-2 into subcutaneous tissue may, in part, be mediated by a spillover of IL-6 from the subcutaneous site of inflammation into the blood to cause activation of brain sites which are implicated in the manifestation of these illness responses.

From inflammation to sickness and depression: when the immune system subjugates the brain

In response to a peripheral infection, innate immune cells produce pro-inflammatory cytokines that act on the brain to cause sickness behaviour. When activation of the peripheral immune system continues unabated, such as during systemic infections, cancer or autoimmune diseases, the ensuing immune signalling to the brain can lead to an exacerbation of sickness and the development of symptoms of depression in vulnerable individuals. These phenomena might account for the increased prevalence of clinical depression in physically ill people. Inflammation is therefore an important biological event that might increase the risk of major depressive episodes, much like the more traditional psychosocial factors.

Vagus–brain communication in atherosclerosis-related inflammation: A neuroimmunomodulation perspective of CAD

The current understanding of the pathophysiology of atherosclerosis leading to coronary artery disease (CAD) emphasizes the role of inflammatory mediators. Given the bidirectional communication between the immune and central nervous systems, an important question is whether the brain can be "informed" about and modulate CAD-related inflammation. A candidate communicator and modulator is the vagus nerve. Until now, the vagus nerve has received attention in cardiology mainly due to its role in the parasympathetic cardiovascular response. However, the vagus nerve can also "inform" the brain about peripheral inflammation since its paraganglia have receptors for interleukin-1. Furthermore, its efferent branch has a local anti-inflammatory effect. These effects have not been considered in research on the vagus nerve in CAD or in vagus nerve stimulation trials in CAD. In addition, various behavioural interventions, including relaxation, may influence CAD prognosis by affecting vagal activity. Based on this converging evidence, we propose a neuroimmunomodulation approach to atherogenesis. In this model, the vagus nerve "informs" the brain about CAD-related cytokines; in turn, activation of the vagus (via vagus nerve stimulation, vagomimetic drugs or relaxation) induces an anti-inflammatory response that can slow down the chronic process of atherogenesis.

Effect of endotoxin treatment on the expression and localization of spinal cyclooxygenase, prostaglandin synthases, and PGD2 receptors

Systemic inflammation leads to increased expression of spinal cyclooxygenase (COX)-2 and to a subsequent increase of prostaglandin (PG) biosynthesis, which contribute to the development of hyperalgesia and allodynia. In this study, endotoxin caused a sequential induction of membrane bound prostaglandin E synthase-1 and lipocalin-type PGD synthase (L-PGDS) in the mouse spinal cord. L-PGDS expression was detected in the leptomeninges, oligodendrocytes, and interestingly, in discrete perivascular cells. Endotoxin-caused increase was most prominent in oligodendrocytes. Endotoxin-induced COX-2 and membrane bound prostaglandin E synthase-1 were restricted to the leptomeninges and perivascular cells. COX-1 was not influenced by endotoxin. We found COX-1 expressed in microglia, some of them in close proximity to L-PGDS-positive oligodendrocytes and co-localization of COX-1 with L-PGDS in perivascular and leptomeningeal cells under control conditions. It can be assumed, that PGD2 biosynthesis under control conditions is mediated via COX-1 and that during inflammation, increased PGD2 is dependent on COX-2. We found the PGD2 receptors DP1 and chemoattractant receptor homologous molecule expressed on T helper type 2 cells (CRTH2) localized in neurons of the dorsal, and motoneurons in the ventral horn. The localization of the PGD2 receptors DP1 and CRTH in spinal cord neurons, particularly in neurons of lamina I and II involved in the processing of nociceptive stimuli, supports a role of PGD2 under inflammatory conditions.

Identification of rat brainstem neuronal structures activated during cancer-induced anorexia

In cancer-related anorexia, body weight loss is paradoxically associated with reduced appetite, which is contrary to the situation during starvation, implying that the normal coupling of food intake to energy expenditure is disarranged. Here we examined brainstem mechanisms that may underlie suppression of food intake in a rat model of cancer anorexia. Cultured Morris 7777 hepatoma cells were injected subcutaneously in Buffalo rats, resulting in slowly growing tumor and reduced food intake and body weight loss after about 10 days. The brainstem was examined for induced expression of the transcription factors Fos and FosB as signs of neuronal activation. The results showed that anorexia and retarded body weight growth were associated with Fos protein expression in the area postrema, the general visceral region of the nucleus of the solitary tract, and the external lateral parabrachial nucleus, structures that also display Fos after peripheral administration of satiating or anorexigenic stimuli. The magnitude of the Fos expression was specifically related to the size of induced tumor, and not associated with weight loss per se, because it was not present in pair-fed or food-deprived rats. It also appeared to be independent of proinflammatory cytokines, as determined by the absence of increased cytokine levels in plasma and induced cytokine and cyclooxygenase expression in the brain. The findings thus provide evidence that cancer-associated anorexia and weight loss in this model is associated with activation of brainstem circuits involved in the suppression of food intake, and suggest that this occurs by inflammatory-independent mechanisms.

Endothelial-specific knockdown of interleukin-1 (IL-1) type 1 receptor differentially alters CNS responses to IL-1 depending on its route of administration

Interleukin-1 (IL-1) has been implicated as a critical mediator of neuroimmune communication. In the brain, the functional receptor for IL-1, type 1 IL-1 receptor (IL-1R1), is localized primarily to the endothelial cells. In this study, we created an endothelial-specific IL-1R1 knockdown model to test the role of endothelial IL-1R1 in mediating the effects of IL-1. Neuronal activation in the hypothalamus was measured by c-fos expression in the paraventricular nucleus and the ventromedial preoptic area. In addition, two specific sickness symptoms, febrile response and reduction of locomotor activity, were studied. Intracerebroventricular injection of IL-1 induced leukocyte infiltration into the CNS, activation of hypothalamic neurons, fever, and reduced locomotor activity in normal mice. Endothelial-specific knockdown of IL-1R1 abrogated all these responses. Intraperitoneal injection of IL-1 also induced neuronal activation in the hypothalamus, fever, and reduced locomotor activity, without inducing leukocyte infiltration into the brain. Endothelial-specific knockdown of IL-1R1 suppressed intraperitoneal IL-1-induced fever, but not the induction of c-fos in hypothalamus. When IL-1 was given intravenously, endothelial knockdown of IL-1R1 abolished intravenous IL-1-induced CNS activation and the two monitored sickness symptoms. In addition, endothelial-specific knockdown of IL-1R1 blocked the induction of cyclooxygenase-2 expression induced by all three routes of IL-1 administration. These results show that the effects of intravenous and intracerebroventricular IL-1 are mediated by endothelial IL-1R1, whereas the effects of intraperitoneal IL-1 are partially dependent on endothelial IL-1R1.

Expression and localization of p80 interleukin-1 receptor protein in the rat spinal cord

The biological effects of interleukin (IL)-1 are mediated by two distinct receptors, the p80 or type I (IL-1RI) and p68 or type II (IL-1RII) receptors. Because IL-1RII has a short, 29-amino acid cytoplasmic domain which may not be sufficient for signaling, there is considerable evidence indicating that IL-1 may signal exclusively through the IL-1RI receptor. Here, we report the expression, distribution, and cellular localization of the IL-1RI protein in the adult rat spinal cord in vivo and embryonic spinal cord in vitro. We found that IL-1RI was expressed in both the gray and white matter throughout the entire length of the spinal cord and was localized in neurons of the anterior horn, astrocytes, oligodendrocytes, and central canal ependymal cells. Interestingly, resting microglia were negative for IL-1RI. In primary cultures obtained from the embryonic day (E) 15 rats, IL-1RI was expressed in neurons, astrocytes, and oligodendrocytes as well as microglia. These data provide both in vivo and in vitro evidence that neurons and glial cells express the IL-1RI proteins. The differential expression of IL-1RI in the developing, but not mature, microglia may indicate the difference of these cells in response to IL-1 stimuli during maturation. The distribution and cellular localization of IL-1RI proteins in the spinal cord provide a molecular basis for understanding the reciprocal interaction between the immune and the central nervous systems.

STAT3 and COX-2 activation in the guinea-pig brain during fever induced by the Toll-like receptor-3 agonist polyinosinic:polycytidylic acid

Intra-arterial injections of synthetic double-stranded RNA (polyinosinic:polycytidylic acid, PIPC) at a dose of 500 microg/kg evoked pronounced fever in guinea-pigs. PIPC-induced fever could be antagonized by treatment with the non-selective cyclooxygenase (COX) inhibitor diclofenac and was, in part, attenuated by the administration of the selective COX-2-inhibitor nimesulide (dose: 5 mg/kg for both COX inhibitors). We further investigated whether direct activation of brain cells during PIPC-induced fever could be demonstrated. Using radioactive in situ hybridization, we demonstrated that treatment with PIPC resulted in an upregulation of COX-2 and interleukin-1 beta mRNA in the guinea-pig brain. Thus, COX-2-specific hybridization signals seemed to be mainly associated with brain blood vessels. Intra-arterial injections of PIPC further induced the pronounced nuclear translocation of the transcription factor STAT3 in the endothelium of various fore- and hindbrain areas and in the meninges. In brain structures that lacked a tight blood-brain barrier, i.e. the sensory circumventricular organs (area postrema, vascular organ of laminae terminalis, subfornical organ), the astrocytes and a population of still undetermined cellular phenotype also showed marked STAT3 activation in response to PIPC. The Toll-like receptor-3 agonist PIPC therefore caused a similar activation of brain cells as that reported for other experimental models of systemic inflammation.

Proinflammatory cytokine gene induction by human T-cell leukemia virus type 1 (HTLV-1) and HTLV-2 Tax in primary human glial cells

Infection with human T-cell leukemia virus type 1 (HTLV-1) can result in the development of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), a chronic inflammatory disease of the central nervous system (CNS). HTLV-2 is highly related to HTLV-1 at the genetic level and shares a high degree of sequence homology, but infection with HTLV-2 is relatively nonpathogenic compared to HTLV-1. Although the pathogenesis of HAM/TSP remains to be fully elucidated, previous evidence suggests that elevated levels of the proinflammatory cytokines in the CNS are associated with neuropathogenesis. We demonstrate that HTLV-1 infection in astrogliomas results in a robust induction of interleukin-1beta (IL-1beta), IL-1alpha, tumor necrosis factor alpha (TNF-alpha), TNF-beta, and IL-6 expression. HTLV encodes for a viral transcriptional transactivator protein named Tax that also induces the transcription of cellular genes. To investigate and compare the effects of Tax1 and Tax2 expression on the dysregulation of proinflammatory cytokines, lentivirus vectors were used to transduce primary human astrocytomas and oligodendrogliomas. The expression of Tax1 in primary human astrocytomas and oligodendrogliomas resulted in significantly higher levels of proinflammatory cytokine gene expression compared to Tax2. Notably, Tax1 expression uniquely sensitized primary human astrocytomas to apoptosis. A Tax2/Tax1 chimera encoding the C-terminal 53 amino acids of the Tax1 fused to the Tax2 gene (Tax(221)) demonstrated a phenotype that resembled Tax1, with respect to proinflammatory cytokine gene expression and sensitization to apoptosis. The patterns of differential cytokine induction and sensitization to apoptosis displayed by Tax1 and Tax2 may reflect differences relating to the heightened neuropathogenicity associated with HTLV-1 infection and the development of HAM/TSP.