Type 1 interleukin-1 receptor in the rat brain: distribution, regulation, and relationship to sites of IL-1-induced cellular activation

Interactions of interleukin-1 with neurotrophic factors in the central nervous system: beneficial or detrimental?

Interleukin (IL)-1 is a multifunctional cytokine that plays a key role in mediating inflammation in the brain. Many different cell types in the brain express the IL-1 receptor and respond to this cytokine by activating cell-type-specific signaling pathways leading to distinct functional responses, which collectively comprise the inflammatory response in the brain. One key effect of IL-1 in the brain is the induction of trophic factor production by glial cells, which has traditionally been considered a neuroprotective response to injury or disease. However, recent studies have shown that nerve growth factor, which is regulated by IL-1, can induce neuronal survival or apoptosis via different receptors. This article examines the interaction of IL-1 with different trophic factors in the brain.

The induced prostaglandin E2 pathway is a key regulator of the respiratory response to infection and hypoxia in neonates

Infection during the neonatal period commonly induces apnea episodes, and the proinflammatory cytokine IL-1beta may serve as a critical mediator between these events. To determine the mechanism by which IL-1beta depresses respiration, we examined a prostaglandin E(2) (PGE(2))-dependent pathway in newborn mice and human neonates. IL-1beta and transient anoxia rapidly induced brainstem-specific microsomal prostaglandin E synthase-1 (mPGES-1) activity in neonatal mice. Furthermore, IL-1beta reduced respiratory frequency during hyperoxia and depressed hypoxic gasping and autoresuscitation in mPGES-1 wild-type mice, but not in mPGES-1 knockout mice. In wild-type mice, PGE(2) induced apnea and irregular breathing patterns in vivo and inhibited brainstem respiratory rhythm generation in vitro. Mice lacking the EP3 receptor (EP3R) for PGE(2) exhibited fewer apneas and sustained brainstem respiratory activity, demonstrating that PGE(2) exerts its respiratory effects via EP3R. In human neonates, the infectious marker C-reactive protein was correlated with elevated PGE(2) in the cerebrospinal fluid, and elevated central PGE(2) was associated with an increased apnea frequency. We conclude that IL-1beta adversely affects breathing and its control by mPGES-1 activation and PGE(2) binding to brainstem EP3 receptors, resulting in increased apnea frequency and hypoxia-induced mortality.

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.

Proinflammatory cytokine synthesis in the injured mouse spinal cord: multiphasic expression pattern and identification of the cell types involved

We have studied the spatial and temporal distribution of six proinflammatory cytokines and identified their cellular source in a clinically relevant model of spinal cord injury (SCI). Our findings show that interleukin-1beta (IL-1beta) and tumor necrosis factor (TNF) are rapidly (<5 and 15 minutes, respectively) and transiently expressed in mice following contusion. At 30-45 minutes post SCI, IL-1beta and TNF-positive cells could already be seen over the entire spinal cord segment analyzed. Multilabeling analyses revealed that microglia and astrocytes were the two major sources of IL-1beta and TNF at these times, suggesting a role for these cytokines in gliosis. Results obtained from SCI mice previously transplanted with green fluorescent protein (GFP)-expressing hematopoietic stem cells confirmed that neural cells were responsible for the production of IL-1beta and TNF for time points preceding 3 hours. From 3 hours up to 24 hours, IL-1beta, TNF, IL-6, and leukemia inhibitory factor (LIF) were strongly upregulated within and immediately around the contused area. Colocalization studies revealed that all populations of central nervous system resident cells, including neurons, synthesized cytokines between 3 and 24 hours post SCI. However, work done with SCI-GFP chimeric mice revealed that at least some infiltrating leukocytes were responsible for cytokine production from 12 hours on. By 2 days post-SCI, mRNA signal for all the above cytokines had nearly disappeared. Notably, we also observed another wave of expression for IL-1beta and TNF at 14 days. Overall, these results indicate that following SCI, all classes of neural cells initially contribute to the organization of inflammation, whereas recruited immune cells mostly contribute to its maintenance at later time points.

Regulation of food intake by inflammatory cytokines in the brain

A number of inflammatory cytokines are synthesized and released after activation of the immune system. In addition to other biological effects, these cytokines can potently inhibit food intake. Cytokine-mediated inhibition of food intake is of particular importance because excessive production of peripheral inflammatory cytokines is often associated with the cachexia-anorexia syndrome seen in some chronic diseases. The weight loss in cachexia is associated with an increase in morbidity and mortality. Understanding how cytokines regulate food intake may be crucial in enhancing quality of life and facilitating recovery in patients exhibiting cachexia. This review describes the main inflammatory cytokines that influence food intake and explores how peripheral cytokines communicate with hypothalamic nuclei to influence feeding.

Leptin induces cyclooxygenase-2 via an interaction with interleukin-1beta in the rat brain

In addition to its central effects on appetite regulation, leptin has been implicated in immune function and inflammation. Previous data suggested that leptin acts as an inflammatory signal within the brain, as exogenously administered leptin induced fever, a typical brain-regulated inflammatory response. The present study aimed to delineate the inflammatory actions and cellular targets of leptin in the brain by examining its effects on the expression of interleukin (IL)-1beta and cyclooxygenase (COX)-2, two important inflammatory components of the fever response. Intracerebroventricular injection of leptin (5 microg/rat) induced IL-1beta and COX-2 mRNA and protein in the hypothalamus between 1 and 3 h after treatment as determined by reverse transcription-polymerase chain reaction and immunohistochemistry. Coinjection of IL-1 receptor antagonist (100 microg/rat, intracerebroventricular) attenuated leptin-induced COX-2, whereas IL-1 receptor antagonist had no effect on endogenous IL-1beta levels, suggesting that leptin induces COX-2 via, at least partly, IL-1beta action. IL-1beta protein expression was induced in macrophages in the meningis and perivascular space after leptin treatment, whereas COX-2 induction was observed in endothelial cells, indicating the roles for these non-neuronal cells in mediating inflammatory actions of leptin. In addition, neutralization of endogenous circulating leptin with anti-leptin antiserum attenuated intraperitoneal lipopolysaccharide (100 microg/kg)-induced brain IL-1beta and COX-2 upregulation, suggesting that leptin indeed acts as an inflammatory signal to the brain during systemic inflammation. These findings are in contrast to the effects of leptin on appetite regulation where it is believed to act primarily on neurons, thus presenting a distinct anatomical basis for the inflammatory and appetite regulatory actions of leptin in the brain.

Interleukin-1 beta-induced anorexia is reversed by ghrelin

Interleukins, in particular interleukin-1beta (IL-1beta), reduce food intake after peripheral and central administration, which suggests that they contribute to anorexia during various infectious, neoplastic, and autoimmune diseases. On the other hand, ghrelin stimulates food intake by acting on the central nervous system (CNS) and is considered an important regulator of food intake in both rodents and humans. In the present study, we investigated if ghrelin could reverse IL-1beta-induced anorexia. Intracerebroventricular (i.c.v.) injection of 15, 30 or 45 ng/microl of IL-1beta caused significant suppression of food intake in 20 h fasting animals. This effect lasted for a 24h period. Ghrelin (0.15 nmol or 1.5 nmol/microl) produced a significant increase in cumulative food intake in normally fed animals. However, it did not alter food intake in 20 h fasting animals. Central administration of ghrelin reduced the anorexic effect of IL-1beta (15 ng/microl). The effect was observed 30 min after injection and lasted for the next 24h. This study provides evidence that ghrelin is an orexigenic peptide capable of antagonizing IL-1beta-induced anorexia.

(Peri)vascular production and action of pro-inflammatory cytokines in brain pathology

In response to tissue injury or infection, the peripheral tissue macrophage induces an inflammatory response through the release of IL-1β (interleukin-1β) and TNFα (tumour necrosis factor α). These cytokines stimulate macrophages and endothelial cells to express chemokines and adhesion molecules that attract leucocytes into the peripheral site of injury or infection. The aims of the present review are to (i) discuss the relevance of brain (peri)vascular cells and compartments to bacterial meningitis, HIV-1-associated dementia, multiple sclerosis, ischaemic and traumatic brain injury, and Alzheimer's disease, and (ii) to provide an overview of the production and action of pro-inflammatory cytokines by (peri)vascular cells in these pathologies of the CNS (central nervous system). The brain (peri)vascular compartments are highly relevant to pathologies affecting the CNS, as infections are almost exclusively blood-borne. Insults disrupt blood and energy flow to neurons, and active brain-to-blood transport mechanisms, which are the bottleneck in the clearance of unwanted molecules from the brain. Perivascular macrophages are the most reactive cell type and produce IL-1β and TNFα after infection or injury to the CNS. The main cellular target for IL-1β and TNFα produced in the brain (peri)vascular compartment is the endothelium, where these cytokines induce the expression of adhesion molecules and promote leucocyte infiltration. Whether this and other effects of IL-1 and TNF in the brain (peri)vascular compartments are detrimental or beneficial in neuropathology remains to be shown and requires a clear understanding of the role of these cytokines in both damaging and repair processes in the CNS.

Hypothalamic-Pituitary-Adrenal Axis Function in Sjogren's Syndrome: Mechanisms of Neuroendocrine and Immune System Homeostasis

To date, evidence suggests that rheumatic diseases are associated with hypofunctioning of the hypothalamic-pituitary-adrenal (HPA) axis. Sjögren's syndrome (SS), the second most common autoimmune disorder, is characterized by diminished lacrimal and salivary gland secretion. To examine HPA axis activity in SS patients, the adrenocorticotropin (ACTH) response to ovine corticotropin-releasing factor (oCRH) was used as a direct measure of corticotrophic function, and the plasma cortisol response to the ACTH released during oCRH stimulation as an indirect measure of adrenal function. Significantly lower basal ACTH and cortisol levels were found in patients with SS and were associated with a blunted pituitary and adrenal response to oCRH compared to normal controls. Fibromyalgia (FM) patients demonstrated elevated evening basal ACTH and cortisol levels and a somewhat exaggerated peak, delta, and net integrated ACTH response to oCRH. A subgroup of SS patients also met the diagnostic criteria for FM and demonstrated a pituitary-adrenal response that was intermediate to SS and FM. These findings suggest not only adrenal axis hypoactivity in SS and FM patients, but also that varying patterns of adrenal and thyroid axes dysfunction may exist in patients with different rheumatic diseases.

Interleukin-1beta mediates GDNF up-regulation upon dopaminergic injury in ventral midbrain cell cultures

We recently proposed the involvement of diffusible modulators in signalling astrocytes to increase glial cell line-derived neurotrophic factor (GDNF) expression after selective dopaminergic injury by H2O2 or L-DOPA. Here we report that interleukin-1beta (IL-1beta) is involved in this crosstalk between injured neurons and astrocytes. IL-1beta was detected only in the media from challenged neuron-glia cultures. Exogenous IL-1beta did not change GDNF protein levels in astrocyte cultures, and diminished GDNF levels in neuron-glia cultures. This decrease was not due to cell loss, as assessed by the MTT assay and immunocytochemistry. Neither H2O2 nor L-DOPA induced microglia proliferation or appeared to change its activation state. The IL-1 receptor antagonist (IL-1ra) prevented GDNF up-regulation in challenged cultures, showing that IL-1beta is involved in the signalling between injured neurons and astrocytes. Since IL-1ra decreased the number of dopaminergic neurons in H2O2-treated cultures, we propose that IL-1 has a neuroprotective role in this system involving GDNF up-regulation.

Neural-endocrine-immune complex in the central modulation of tumorigenesis: facts, assumptions, and hypotheses

For the precise coordination of systemic functions, the nervous system uses a variety of peripherally and centrally localized receptors, which transmit information from internal and external environments to the central nervous system. Tight interconnections between the immune, nervous, and endocrine systems provide a base for monitoring and consequent modulation of immune system functions by the brain and vice versa. The immune system plays an important role in tumorigenesis. On the basis of rich interconnections between the immune, nervous and endocrine systems, the possibility that the brain may be informed about tumorigenesis is discussed in this review article. Moreover, the eventual modulation of tumorigenesis by central nervous system is also considered. Prospective consequences of the interactions between tumor and brain for diagnosis and therapy of cancer are emphasized.

Molecular Aspects of Fever and Hyperthermia

A rise in core temperature during fever usually results from change in the thermocontroller characteristics, resulting in an elevation of the set point of body temperature. Time course and extent of natural fevers are variable, but an upper limit (41 degrees C in humans), at which core temperature is maintained for some time and reduced when the set point of body temperature returns to its normal level, rarely is exceeded. Although any rise in body temperature may result from fever, those rises that are not accompanied by supportive changes in thermoeffector activities are termed hyperthermia.

Cytokine, sickness behavior, and depression

Sufficient evidence is now available to accept the concept that the brain recognizes cytokines as molecular signals of sickness. Clarifying the way the brain processes information generated by the innate immune system is accompanied by a progressive elucidation of the cellular and molecular components of the intricate system that mediates cytokine-induced sickness behavior. We are still far, however, from understanding the whole. Among the hundreds of genes that proinflammatory cytokines can induce in their cellular targets, only a handful has been examined functionally. In addition, a dynamic view of the cellular interactions that occur at the brain sites of cytokine production and action is missing, together with a clarification of the mechanisms that favor the transition toward pathology.

Mifepristone (RU38486) influences the core temperature response of term pregnant rats to intraperitoneal lipopolysaccharide

Pregnancy alters the cytokine, prostanoid and core temperature responses of rats to infectious stimuli at a time when blood levels of the endogenous glucocorticoid corticosterone are elevated. Given that glucocorticoids attenuate bacterial pyrogen-induced fever in rats, the present experiments were carried out to test the hypothesis that administration of RU38486, a glucocorticoid type II receptor antagonist, would restore the febrile response to E. coli lipopolysaccharide (LPS) in pregnant rats on day 21 of gestation. Pregnant rats were randomly allocated to one of four experimental groups depending upon whether they received RU38486 (20 mg kg(-1) intragastric) or vehicle followed by E. coli LPS (160 microg kg(-1)i.p.; a minimal dose that elicits maximal febrile response in non-pregnant rats) or vehicle. Basal core temperature was not altered by intragastric administration of RU38486 or vehicle. Following intragastric administration of vehicle, intraperitoneal administration of E. coli LPS produced a significant hypothermia with latency, duration and magnitude of 0.5 h, 2 h and -1.3 degrees C, respectively. Following intragastric administration of RU38486, however, intraperitoneal administration of E. coli LPS elicited only a minimal decrease in core temperature which was not significantly different from control values. Thus, our data provide evidence that endogenous glucocorticoids play a role in modulating the early core temperature response to a relatively large dose of bacterial pyrogen in rats at term of pregnancy.

Interleukin-1beta induces hyperpolarization and modulates synaptic inhibition in preoptic and anterior hypothalamic neurons

Most of the inflammatory effects of the cytokine interleukin 1beta (IL-1beta) are mediated by induction of cyclooxygenase (COX)2 and the subsequent synthesis and release of prostaglandin E2. This transcription-dependent process takes 45-60 min, but IL-1beta, a well-characterized endogenous pyrogen also exerts faster neuronal actions in the preoptic area/anterior hypothalamus. Here, we have studied the fast (1-3 min) signaling by IL-1beta using whole-cell patch clamp recordings in preoptic area/anterior hypothalamus neurons. Exposure to IL-1beta (0.1-1 nM) hyperpolarized a subset ( approximately 20%) of preoptic area/anterior hypothalamus neurons, decreased their input resistance and reduced their firing rate. These effects were associated with an increased frequency of bicuculline-sensitive spontaneous inhibitory postsynaptic currents and putative miniature inhibitory postsynaptic currents, strongly suggesting a presynaptic mechanism of action. These effects require the type 1 interleukin 1 receptor (IL-1R1), and the adapter protein myeloid differentiation primary response protein (MyD88), since they were not observed in cultures obtained from IL-1R1 (-/-) or from MyD88 (-/-) mice. Ceramide, a second messenger of the IL-1R1-dependent fast signaling cascade, is produced by IL-1R1-MyD88-mediated activation of the neutral sphingomyelinase. C2-ceramide, its cell penetrating analog, also increased the frequency of miniature inhibitory postsynaptic currents in a subset of cells. Both IL-1beta and ceramide reduced the delayed rectifier and the A-type K(+) currents in preoptic area/anterior hypothalamus neurons. The latter effect may account in part for the increased spontaneous inhibitory postsynaptic current frequency as suggested by experiments with the A-type K(+) channel blockers 4-aminopyridine. Taken together our data suggest that IL-1beta inhibits the activity of preoptic area/anterior hypothalamus neurons by increasing the presynaptic release of GABA.

Neural-immune interface in the rat area postrema

The area postrema functions as one interface between the immune system and the brain. Immune cells within the area postrema express immunoreactivity for the pro-inflammatory cytokine, interleukin-1beta following challenge with immune stimulants, including lipopolysaccharide (from bacterial cell walls). As a circumventricular organ, the area postrema accesses circulating immune-derived mediators, but also receives direct primary viscerosensory signals via the vagus nerve. Neurons in the area postrema contribute to central autonomic network neurocircuitry implicated in brain-mediated host defense responses. These experiments were directed toward clarifying relationships between immune cells and neurons in the area postrema, with a view toward potential mechanisms by which they may communicate. We used antisera directed toward markers indicating microglia (CR3/CD11b; OX-42), resident macrophages (CD163; ED-2), or dendritic cell-like phenotypes (major histocompability complex class II; OX-6), in area postrema sections from lipopolysaccharide-treated rats processed for light, laser scanning confocal, and electron microscopy. Lipopolysaccharide treatment induced interleukin-1beta-like immunoreactivity in immune cells that either associated with the vasculature (perivascular cells, a subtype of macrophage) or associated with neuronal elements (dendritic-like, and unknown phenotype). Electron microscopic analysis revealed that some immune cells, including interleukin-1beta-positive cells, evinced membrane apposition with neuronal elements, including dendrites and terminals, that could derive from inputs to the area postrema such as vagal sensory fibers, or intrinsic area postrema neurons. This arrangement provides an anatomical substrate by which immune cells could directly and specifically influence individual neurons in the area postrema, that may support the induction and/or maintenance of brain responses to inflammation.

The bacterial endotoxin lipopolysaccharide has the ability to target the brain in upregulating its membrane CD14 receptor within specific cellular populations

Systemic injection of the bacterial endotoxin lipopolysaccharide (LPS) provides a very good mean for increasing the release of proinflammatory cytokines by circulating monocytes and tissue macrophages. There is now considerable evidence that LPS exerts its action on mononuclear phagocytes via the cell surface receptor CD14. The aim of the present study was to verify the hypothesis that the brain has also the ability to express the gene encoding the LPS receptor, which may allow a direct action of the endotoxin onto specific cellular populations during blood sepsis. Adult male Sprague-Dawley rats were sacrificed 1, 3, 6 and 24 h after systemic (i.v. or i.p.) injection of LPS or the vehicle solution. Brains were cut from the olfactory bulb to the medulla in 30-microm coronal sections and mRNA encoding rat CD14 was assayed by in situ hybridization histochemistry using a specific 35S-labeled riboprobe. The results show low levels of CD14 mRNA in the leptomeninges, choroid plexus and along blood vessels of the brain microvasculature under basal conditions. Systemic injection of the bacterial endotoxin caused a profound increase in the expression of the gene encoding CD14 within these same structures as well as in the circumventricular organs (CVOs) the organum vasculosum of the lamina terminalis, subfornical organ, median eminence and area postrema. In most of these structures, the signal for CD14 mRNA was first detected at 1 h, reached a peak at 3 h post-injection, declined at 6 h, and return to basal levels 24 h after LPS treatment. Quite interestingly, a migratory-like pattern of CD14 positive cells was observed from all sensorial CVOs to deeper parenchymal brain 3 and 6 h after LPS injection. At 6 h post-challenge, small positive cells were found throughout the entire parenchymal brain and dual-labeling procedure indicated that different cells of myeloid origin have the ability to express CD14 in response to systemic LPS. These included CVO microglia, choroid plexus and leptomeninge macrophages, parenchymal and perivascular-associated microglial cells, although specific nonmyeloid cells were also positive for the LPS receptor. These results provide the very first evidence of a direct role of LPS on specific cell populations of the central nervous system, which is likely to be responsible for the transcription of proinflammatory cytokines; first within accessible structures from the blood and thereafter through scattered parenchymal cells during severe sepsis.

CNS activational responses to staphylococcal enterotoxin B: T-lymphocyte-dependent immune challenge effects on stress-related circuitry

Staphylococcal enterotoxin B (SEB) is a bacterial superantigen that engages the immune system in a T-lymphocyte-dependent manner and induces a cytokine profile distinct from that elicited by the better-studied bacterial pathogen analog, lipopolysaccharide (LPS). Because of reports of SEB recruiting central nervous system (CNS) host defense mechanisms via pathways in common with LPS, we sought to further characterize central systems impacted by this agent. Rats were treated with SEB at doses of 50-5,000 mug/kg, and killed 0.5-6 hours thereafter. SEB injection produced a discrete pattern of Fos induction in brain that peaked at 2-3 hours postinjection and whose strength was dose-related. Induced Fos expression was predominantly subcortical and focused in a set of interconnected central autonomic structures, including aspects of the bed n. of the stria terminalis, central amygdala and lateral parabrachial nuclei; functionally related (and LPS-responsive) cell groups in the n. solitary tract, ventrolateral medulla, and paraventricular hypothalamic n. (PVH) were, by contrast, weakly responsive. SEB also activated cell groups in the limbic forebrain (lateral septal n, medial prefrontal cortex) and hypothalamic GABAergic neurons, which could account for its failure to elicit reliable increases in Fos-ir or corticotropin-releasing factor (CRF) mRNA in the PVH. SEB nevertheless did provoke reliable pituitary-adrenal secretory responses. The identification of subsets of central autonomic and limbic forebrain structures that are sensitive to SEB provides a basis for a systems-level understanding of the physiological and behavioral effects attributed to the superantigen. Core SEB-responsive cell groups exclude a medullary-PVH circuit implicated in pituitary-adrenal responses to LPS.

Peripheral injection of lipopolysaccharide prevents brain recruitment of leukocytes induced by central injection of interleukin-1

I.c.v. injection of interleukin-1beta induces infiltration of leukocytes into the brain. I.p. injection of bacterial endotoxin lipopolysaccharide induces the expression of interleukin-1 in the CNS without causing the entry of leukocytes into the brain. This suggests that during systemic inflammation trafficking of potentially damaging leukocytes into the CNS is inhibited. In this study, we investigated the effects of peripheral injection of lipopolysaccharide on brain leukocyte recruitment induced by i.c.v.-interleukin-1 in mice. I.c.v.-interleukin-1 induced widespread infiltration of leukocytes into the brain 16 h after the injection. Pretreatment with i.p.-lipopolysaccharide 2 h before the i.c.v. interleukin-1 injection completely blocked interleukin-1-induced leukocyte infiltration, whereas i.p.-LPS only attenuated the effect of interleukin-1 if it was given 12 h before i.c.v. interleukin-1 injection. I.p.-lipopolysaccharide given 24 h before i.c.v. interleukin-1 injection did not alter interleukin-1 induced leukocyte infiltration. I.c.v.-interleukin-1 induced expression of p- and e-selectins in brain vasculatures prior to the appearance of leukocytes in the brain parenchyma. Induction of p- and e-selectin was inhibited by the pretreatment of i.p.-lipopolysaccharide 2 h, but not 24 h, before i.c.v.-interleukin-1 injection. I.c.v.-interleukin-1-induced leukocyte infiltration was diminished in both e- and p- selectin knockout animals. These results suggest that systemic inflammation actively inhibits recruitment of leukocytes by CNS. Inhibition of the expression of p- and e-selectins is a mechanism by which peripheral inflammation regulate CNS leukocyte recruitment.

Interleukins, inflammation, and mechanisms of Alzheimer's disease

Alzheimer's disease (AD) is the most common progressive neurodegenerative form of dementia in the elderly and is characterized neuropathologically by neurofibrillary tangles (NFT), amyloid neuritic plaques (NP), and prominent synaptic and eventually neuronal loss. Although the molecular basis of AD is not clearly understood, a neuroinflammatory process, triggered by Abeta42, plays a central role in the neurodegenerative process. This inflammatory process is driven by activated microglia, astrocytes and the induction of proinflammatory molecules and related signaling pathways, leading to both synaptic and neuronal damage as well as further inflammatory cell activation. Epidemiologic data as well as clinical trial evidence suggest that nonsteroidal anti-inflammatory drug (NSAID) use may decrease the incidence of AD, further supporting a role for inflammation in AD pathogenesis. Although the precise molecular and cellular relationship between AD and inflammation remains unclear, interleukins and cytokines might induce activation of signaling pathways leading to futher inflammation and neuronal injury. This chapter will discuss the association between interleukins and neurodegeneration in AD and highlight the significance of genetic and clinical aspects of interleukins in disease expression and progression. As part of an emerging inflammatory signaling network underlying AD pathogenesis, beta-amyloid (Abeta) stimulates the glial and microglial production of interleukins and other cytokines, leading to an ongoing inflammatory cascade and contributing to synaptic dysfunction and loss, and later, neuronal death. Inflammatory pathways involving interleukin and cytokine signaling might suggest potential targets for intervention and influence the development of novel therapies to circumvent synaptic and neuronal dysfunction ultimately leading to AD neurodegeneration.

Strain-dependent behavioral alterations induced by peripheral interleukin-1 challenge in neonatal mice

Interleukin-1 (IL-1) is implicated in the pathogenesis of various psychiatric diseases. Peripheral administration of IL-1alpha to neonatal rats induces cognitive and behavioral abnormalities and, therefore, the IL-1alpha-treated animals might serve as a schizophrenia model. The present study assessed genetic influences on IL-1alpha-triggered behavioral impairments, using four different strains of neonatal mice, C3H/He, DBA/2, C57BL/6, and ddY. Neonatal treatments with IL-1alpha differentially altered adult behavioral/cognitive traits in a strain-dependent manner. IL-1alpha treatment decreased prepulse inhibition in DBA/2 and C57BL/6 mice but not in C3H/He and ddY. The treatment increased locomotor activity and startle responses in DBA/2 mice and, conversely, decreased startle responses in C3H/He mice. Behavioral alterations were most remarkable in DBA/2 mice but undetectable in ddY mice. The magnitudes of IL-1alpha actions differed between the brain and periphery and were influenced by mouse genetic background. The IL-1-triggered acute signaling, Ikappa-B degradation, was significant in the frontal cortex of DBA/2 mice and in the hypothalamus of C3H/He mice. An increase in brain p38 MAP kinase phosphorylation was also most marked in the DBA/2 strain. In contrast, subchronic influences of IL-1alpha injections failed to illustrate the strain-dependent behavioral alterations. The peripheral effects of IL-1alpha did not match the strain-dependency of the behavioral alterations, either. Acceleration of tooth eruption and eyelid opening as well as attenuation of weight gain was most marked in C3H/He mice and the induction of serum amyloid protein was the largest in ddY mice. Thus, the peripheral effects of IL-1alpha in DBA/2 mice were relatively inferior to those in the other strains. The present animal study suggests that, in early postnatal development, circulating IL-1alpha trigger brain cytokine signaling and produce distinct influences on later neurobehavioral traits, both depending on genetic background.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Decreased fat mass in interleukin-1 receptor antagonist-deficient mice: impact on adipogenesis, food intake, and energy expenditure

Interleukin (IL)-1 is a regulator of inflammation but is also implicated in the control of energy homeostasis. Because the soluble IL-1 receptor antagonist (IL-1Ra) is markedly increased in the serum of obese patients and is overexpressed in white adipose tissue in obesity, we studied the metabolic consequences of genetic IL-1Ra ablation in mice. We have shown that IL-1Ra-/- mice have a lean phenotype due to decreased fat mass, related to a defect in adipogenesis and increased energy expenditure. The adipocytes were smaller in these animals, and the expression of genes involved in adipogenesis was reduced. Energy expenditure as measured by indirect calorimetry was elevated, and weight loss in response to a 24-h fast was increased in IL-1Ra-/- animals compared with wild-type mice. Lipid oxidation of IL-1Ra-/- mice was higher during the light period, reflecting their reduction in diurnal food intake. Interestingly, IL-1Ra-/- and IL-1Ra+/- mice presented an attenuation in high-fat diet-induced caloric hyperphagia, indicating a better adaptation to hypercaloric alimentation, which is in line with the role of IL-1Ra as a mediator of leptin resistance. Taken together, we show that IL-1Ra is an important regulator of adipogenesis, food intake, and energy expenditure.

Adipose tissue: a regulator of inflammation

Adipose tissue is a highly active organ. In addition to storing calories as triglycerides, it also secretes a large variety of proteins, including cytokines, chemokines and hormone-like factors, such as leptin, adiponectin and resistin. Intriguingly, many, if not most, of these adipose-derived proteins have dual actions; cytokines have both immunomodulatory functions and act as systemic or auto-/paracrine regulators of metabolism, while proteins such as leptin and adiponectin are regulators of both metabolism and inflammation. The production of pro-atherogenic chemokines by adipose tissue is of particular interest since their local secretion, e.g. by perivascular adipose depots, may provide a novel mechanistic link between obesity and the associated vascular complications.

Signaling pathways of interleukin-1 actions in the brain: anatomical distribution of phospho-ERK1/2 in the brain of rat treated systemically with interleukin-1beta

Interleukin-1beta is released at the periphery during infection and acts on the nervous system to induce fever, neuroendocrine activation, and behavioral changes. These effects are mediated by brain type I IL-1 receptors. In vitro studies have shown the ability of interleukin-1beta to activate mitogen-activated protein kinase signaling pathways including p38, c-Jun N-terminal kinase and extracellular signal-regulated protein kinase 1 and 2 (ERK1/2). In contrast to other mitogen-activated protein kinases, little is known about ERK1/2 activation in the rat brain in response to interleukin-1beta. The aim of the present study was therefore to investigate spatial and temporal activation of ERK1/2 in the rat brain after peripheral administration of interleukin-1beta using immunohistochemistry to detect the phosphorylated form of the kinase. In non-stimulated conditions, phosphorylated ERK1/2 immunoreactivity was observed in neurons throughout the brain. Administration of interleukin-1beta (60 microg/kg, i.p.) induced the phosphorylation of ERK1/2 in areas at the interface between brain and blood or cerebrospinal fluid: meninges, circumventricular organs, endothelial like cells of the blood vessels, and in brain nuclei involved in behavioral depression, fever and neuroendocrine activation: paraventricular nucleus of the hypothalamus, supraoptic nucleus, central amygdala and arcuate nucleus. Double labeling of phosphorylated ERK1/2 and cell markers revealed the expression of phosphorylated ERK1/2 in neurons, astrocytes and microglia. Since phosphorylated ERK1/2 was found in structures in which type I IL-1 receptor has already been identified as well as in structures lacking this receptor, activation of ERK1/2 is likely to occur in response to both direct and indirect action of interleukin-1beta on its target cells.

Homeostatic alterations induced by interleukin-1β microinjection into the orbitofrontal cortex in the rat

The present experiments were designed to elucidate the effect of direct orbitofrontal cortical administration of interleukin-1beta (IL-1beta) on the homeostatic regulation. Short- and long-term food intakes (FI), water intakes and body temperature (BT) were measured before and after a bilateral microinjection of IL-1beta (with or without paracetamol /P/ pretreatment) into the orbitofrontal cortex (OBF) of Wistar rats, and the effects were compared with those found in vehicle-treated and i.p. injected IL-1beta, IL-1beta+P or control animals. In addition, blood glucose levels (BGLs), along a glucose tolerance test, and plasma concentrations of insulin, leptin, cholesterol, triglycerides and urate were determined in cytokine treated and control rats. Short-term FI was suppressed after orbitofrontal cortical or peripheral application of IL-1beta. In the long-term FI, however, there was no significant difference among the groups. Cytokine microinjection into the OBF, similar to the i.p. administration, was also followed by a significant increase in BT. Pretreatment with P failed to influence the anorexigenic and hyperthermic effects of the centrally administered IL-1beta. The sugar load led to a diabetes-like prolonged elevation of BGL in the IL-1beta treated animals. Following cytokine administration, plasma levels of insulin and that of triglycerides were found decreased, whereas that of uric acid increased. The present findings confirm that the OBF is one of the neural routes through which IL-1beta exerts modulatory effect on the central homeostatic regulation.

Involvement of spinal cord nuclear factor κB activation in rat models of proinflammatory cytokine-mediated pain facilitation

Proinflammatory cytokines, such as interleukin-1beta and tumour necrosis factor-alpha, are released by activated glial cells in the spinal cord and play a major role in pain facilitation. These cytokines exert their actions, at least partially, through the activation of the transcription factor, nuclear factor kappaB (NF-kappaB). In turn, NF-kappaB regulates the transcription of many inflammatory mediators, including cytokines. We have previously shown that intrathecal injection of the human immunodeficiency virus-1 (HIV-1) envelope glycoprotein, gp120, induces mechanical allodynia via the release of proinflammatory cytokines. Here, we investigated whether NF-kappaB is involved in gp120-induced pain behaviour in Sprague-Dawley rats. Intrathecal administration of NF-kappaB inhibitors, pyrrolidinedithiocarbamate (PDTC) and SN50, prior to gp120 partially attenuated gp120-induced allodynia. In addition, PDTC delayed and reversed allodynia in a model of neuropathic pain induced by sciatic nerve inflammation. These observations suggest that intrathecal gp120 may lead to activation of NF-kappaB within the spinal cord. To reveal NF-kappaB activation, we assessed inhibitory factor kappaBalpha (IkappaBalpha) mRNA expression by in situ hybridization, as NF-kappaB activation up-regulates IkappaBalpha gene expression as part of an autoregulatory feedback loop. No or low levels of IkappaBalpha mRNA were detected in the lumbar spinal cord of vehicle-injected rats, whereas IkappaBalpha mRNA expression was markedly induced in the spinal cord following intrathecal gp120 in predominantly astrocytes and endothelial cells. Moreover, IkappaBalpha mRNA expression positively correlated with proinflammatory cytokine protein levels in lumbosacral cerebrospinal fluid. Together, these results demonstrate that spinal cord NF-kappaB activation is involved, at least in part, in exaggerated pain states.

Cytokines as mediators of depression: what can we learn from animal studies?

It has recently been postulated that cytokines may cause depressive illness in man. This hypothesis is based on the following observations: 1. Treatment of patients with cytokines can produce symptoms of depression; 2. Activation of the immune system is observed in many depressed patients; 3. Depression occurs more frequently in those with medical disorders associated with immune dysfunction; 4. Activation of the immune system, and administration of endotoxin (LPS) or interleukin-1 (IL-1) to animals induces sickness behavior, which resembles depression, and chronic treatment with antidepressants has been shown to inhibit sickness behavior induced by LPS; 5. Several cytokines can activate the hypothalamo-pituitary-adrenocortical axis (HPAA), which is commonly activated in depressed patients; 6. Some cytokines activates cerebral noradrenergic systems, also commonly observed in depressed patients; 7. Some cytokines activate brain serotonergic systems, which have been implicated in major depressive illness and its treatment. The evidence for each of these tenets is reviewed and evaluated along with the effects of cytokines in classical animal tests of depression. Although certain sickness behaviors resemble the symptoms of depression, they are not identical and each has distinct features. Thus the value of sickness behavior as an animal model of major depressive disorder is limited, so that care should be taken in extrapolating results from the model to the human disorder. Nevertheless, the model may provide insight into the etiology and the mechanisms underlying some symptoms of major depressive disorder. It is concluded that immune activation and cytokines may be involved in depressive symptoms in some patients. However, cytokines do not appear to be essential mediators of depressive illness.

A quantitative in situ hybridization and polymerase chain reaction study of microglial-macrophage expression of interleukin-1beta mRNA following permanent middle cerebral artery occlusion in mice

Interleukin-1beta (IL-1beta) is known to play a central role in ischemia-induced brain damage in rodents. In comparison to the rat, however, the available data on the cellular synthesis of IL-1beta mRNA and protein in the mouse are very limited. Here, we report on the time profile, the topography and the quantitative, cellular expression of IL-1beta mRNA in mice subjected to permanent occlusion of the distal middle cerebral artery (MCA). The in situ hybridization analysis showed that IL-1beta mRNA was expressed during the first post-surgical hour in a small number of high-expressing macrophage-like cells, located in cortical layers I and II of the future infarct. At 2 h, a significant number of faintly labeled IL-1beta mRNA-expressing cells had appeared in the developing peri-infarct, and the number remained constant at 4 h and 6 h, when the hybridization signal began to distribute to the cellular processes. Quantitative PCR performed on whole hemispheres showed a significant 20-fold increase in the relative level of IL-1beta mRNA at 12 h and a highly significant 42-fold increase at 24 h, at which time single IL-1beta mRNA-expressing cells were supplemented by aggregates and perivascular infiltrates of intensely labeled IL-1beta mRNA-expressing cells. Immunohistochemistry and double immunohistochemical stainings in addition to combined in situ hybridization, confirmed that the intensely labeled IL-1beta mRNA-expressing and IL-1beta protein synthesizing cells predominantly were glial fibrillary acidic protein-immunonegative, macrophage associated antigen-1-immunopositive microglia-macrophages. By day 5 there was a dramatic decline in the relative level of IL-1beta mRNA in the ischemic hemisphere. In summary, the data provide evidence that permanent occlusion of the distal MCA in mice results in expression of IL-1beta mRNA and IL-1beta synthesis in spatially and temporally segregated subpopulations of microglia and macrophages.

Inactivation of the cerebral NFkappaB pathway inhibits interleukin-1beta-induced sickness behavior and c-Fos expression in various brain nuclei

The behavioral effects of peripherally administered interleukin-1beta (IL-1beta) are mediated by the production of cytokines and other proinflammatory mediators at the level of the blood-brain interface and by activation of neural pathway. To assess whether this action is mediated by NFkappaB activation, rats were injected into the lateral ventricle of the brain with a specific inhibitor of NFkappaB activation, the NEMO Binding Domain (NBD) peptide that has been shown previously to abolish completely IL-1beta-induced NFkappaB activation and Cox-2 synthesis in the brain microvasculature. NFkappaB pathway inactivation significantly blocked the behavioral effects of intraperitoneally administered IL-1beta in the form of social withdrawal and decreased food intake, and dramatically reduced IL-1beta-induced c-Fos expression in various brain regions as paraventricular nucleus, supraoptic nucleus, and lateral part of the central amygdala. These findings strongly support the hypothesis that IL-1beta-induced NFkappaB activation at the blood-brain interface is a crucial step in the transmission of immune signals from the periphery to the brain that underlies further events responsible of sickness behavior.

Cytokine-induced sickness behaviour: a neuroimmune response to activation of innate immunity

Sickness refers to a coordinated set of subjective, behavioural and physiological changes that develop in sick individuals during the course of an infection. These changes are due to the effects of interleukin-1 (IL-1) and other proinflammatory cytokines on brain cellular targets. Sickness behaviour is mediated by proinflammatory cytokines that are temporarily expressed in the brain during infection. These centrally produced cytokines are the same as those expressed by innate immune cells and they act on brain receptors that are identical to those characterized on immune cells. Primary afferent nerves represent the main communication pathway between peripheral and central cytokines. Proinflammatory cytokines modulate learning and memory processes. The expression and action of proinflammatory cytokines in the brain in response to peripheral cytokines are regulated by various molecular intermediates including anti-inflammatory cytokines such as interleukin-10 (IL-10) and the IL-1 receptor antagonist (IL-1ra), growth factors such as insulin-like growth factor-1 (IGF-1), hormones such as glucocorticoids and neuropeptides such as vasopressin and alpha-melanotropin.

Differential regulation of type I and type II interleukin-1 receptors in focal brain inflammation

Most pathologies of the brain have an inflammatory component, associated with the release of cytokines such as interleukin-1beta (IL-1beta) from resident and infiltrating cells. The IL-1 type I receptor (IL-1RI) initiates a signalling cascade but the type II receptor (IL-1RII) acts as a decoy receptor. Here we have investigated the expression of IL-1beta, IL-1RI and IL-1RII in distinct inflammatory lesions in the rat brain. IL-1beta was injected into the brain to generate an inflammatory lesion in the absence of neuronal cell death whereas neuronal death was specifically induced by the microinjection of N-methyl-D-aspartate (NMDA). Using TaqMan RT-PCR and ELISA, we observed elevated de novo IL-1beta synthesis 2 h after the intracerebral microinjection of IL-1beta; this de novo IL-1beta remained elevated 24 h later. There was a concomitant increase in IL-1RI mRNA but a much greater increase in IL-1RII mRNA. Immunostaining revealed that IL-1RII was expressed on brain endothelial cells and on infiltrating neutrophils. In contrast, although IL-1beta and IL-1RI were elevated to similar levels in response to NMDA challenge, the response was delayed and IL-1RII mRNA expression was unchanged. The lesion-specific expression of IL-1 receptors suggests that the receptors are differentially regulated in a manner not directly related to the endogenous level of IL-1 in the CNS.

Endogenous opioids and attenuated hypothalamic-pituitary-adrenal axis responses to immune challenge in pregnant rats

In late pregnant rats, the hypothalamic-pituitary-adrenal (HPA) axis is hyporesponsive to psychogenic stressors. Here, we investigated attenuated HPA responses to an immune challenge and a role for endogenous opioids. ACTH and corticosterone were assayed in blood samples from virgin and 21 d pregnant rats before and after endotoxin [lipopolysaccharide (LPS); 1 microg/kg, i.v.], interleukin-1beta (IL-1beta; 500 ng/kg, i.v.), or vehicle. In virgins, plasma ACTH concentrations increased 1 h after LPS and 15 min after IL-1beta, as did corticosterone, with no responses in pregnant rats. In situ hybridization revealed increased corticotrophin releasing hormone (CRH) mRNA expression in the dorsomedial parvocellular paraventricular nucleus (pPVN) and increased anterior pituitary pro-opiomelanocortin mRNA expression 4 h after IL-1beta in virgins; these responses were absent in pregnant rats. In contrast, immunocytochemistry showed that Fos expression was similarly increased in the nucleus tractus solitarius (NTS) A2 region in virgin and pregnant rats 90 min and 4 h after IL-1beta. Naloxone pretreatment (5 mg/kg, i.v.) restored ACTH and pPVN CRH mRNA responses after IL-1beta in pregnant rats but reduced the CRH mRNA response in virgins without affecting ACTH. Proenkephalin-A and mu-opioid receptor mRNA expression in the NTS was significantly increased in the pregnant rats, indicating upregulated brainstem opioid mechanisms. IL-1beta increased noradrenaline release in the PVN of virgin, but not pregnant, rats. However, naloxone infused directly into the PVN increased noradrenaline release after IL-1beta in pregnant rats. Thus, the HPA axis responses to immune signals are suppressed in pregnancy at the level of pPVN CRH neurons through an opioid mechanism, possibly acting by preterminal autoinhibition of NTS projections to the pPVN.

Dual effects of the lichen glucan PB-2, extracted from Flavoparmelia baltimorensis, on the induction of long-term potentiation in the dentate gyrus of the anesthetized rat: possible mediation via adrenaline beta- and interleukin-1 receptors

We have previously found that oral or intravenous (i.v.) administration of the polysaccharide fraction PB-2, extracted from the lichen Flavoparmelia baltimorensis, facilitated the induction of long-term potentiation (LTP) in the dentate gyrus (DG) in vivo. In this study, the mechanism underlying the effect of PB-2 on the induction of LTP was investigated in the DG of anesthetized rat focusing on the contribution of the interleukin-1 (IL-1) receptor and the adrenaline beta-receptor. An i.v. injection of IL-1ra (10(-9) g/kg), an antagonist of the IL-1 receptor, had no effect on the basal response in the DG; however, this treatment augmented the enhancement of LTP induced by a single i.v. injection of PB-2 (10(-3) g/kg). This potentiating effect was also observed following intracerebroventricular (i.c.v.) injection of IL-1ra (10(-15)-10(-11) g). An i.v. injection of IL-1beta (3.5 x 10(-15)-3.5 x 10(-9) g/kg) inhibited the induction of LTP, which was diminished by the previous application of IL-1ra. These results suggest that the activation of the IL-1 receptor induces the suppression of LTP in PB-2-treated rats, and that endogenous IL-1beta contributes to the IL-1 receptor activation. An i.c.v. infusion of metoprolol (7.5 x 10(-6) g), an antagonist of the adrenaline beta(1)-receptor, attenuated the enhancement of LTP induced by an i.v. injection of PB-2. These results suggest that PB-2 has two different effects on the LTP, an enhancing effect and an inhibiting one, and that it exhibited the significant enhancing effect on the LTP as a total balance of these effects.

Neuropeptide Y Y1 receptor mRNA in rodent brain: distribution and colocalization with melanocortin-4 receptor

The central neuropeptide Y (NPY) Y1 receptor (Y1-R) system has been implicated in feeding, endocrine, and autonomic regulation. In the present study, we systematically examined the brain distribution of Y1-R mRNA in rodents by using radioisotopic in situ hybridization histochemistry (ISHH) with a novel sensitive cRNA probe. Within the rat hypothalamus, Y1-R-specific hybridization was observed in the anteroventral periventricular, ventromedial preoptic, suprachiasmatic, paraventricular (PVH), dorsomedial, ventromedial, arcuate, and mamillary nuclei. In the rat, Y1-R mRNA expression was also seen in the subfornical organ, anterior hypothalamic area, dorsal hypothalamic area, and in the lateral hypothalamic area. In addition, Y1-R hybridization was evident in several extrahypothalamic forebrain and hindbrain sites involved in feeding and/or autonomic regulation in the rat. A similar distribution pattern of Y1-R mRNA was observed in the mouse brain. Moreover, by using a transgenic mouse line expressing green fluorescent protein under the control of the melanocortin-4 receptor (MC4-R) promoter, we observed Y1-R mRNA expression in MC4-R-positive cells in several brain sites such as the PVH and central nucleus of the amygdala. Additionally, dual-label ISHH demonstrated that hypophysiotropic PVH cells coexpress Y1-R and pro-thyrotropin-releasing hormone mRNAs in the rat. These observations are consistent with the proposed roles of the central NPY/Y1-R system in energy homeostasis.

Teneurin proteins possess a carboxy terminal sequence with neuromodulatory activity

We have previously shown that a bioactive neuropeptide-like sequence is present at the carboxy-terminus of the teneurin transmembrane proteins. We have subsequently called this peptide 'teneurin C-terminal associated peptide' (TCAP). The sequence encodes a peptide 40 or 41 amino acids long flanked by a cleavage motif on the amino terminus and an amidation motif on the carboxy terminus, characteristic of bioactive peptides. This sequence is highly conserved in all vertebrates. A TCAP-like sequence is encoded by each of the four teneurin genes. We have therefore examined the neurological role TCAP-1 may play in mice and rats. In situ hybridization studies showed that the teneurin-1 mRNA containing the TCAP-1 sequence is expressed in regions of the forebrain and limbic system regulating stress and anxiety. A synthetic version of amidated mouse/rat TCAP-1 was prepared by solid-phase synthesis and used to investigate the in vitro and in vivo activity. TCAP-1 induces a dose-dependent change in cAMP accumulation and MTT activity in immortalized mouse neurons. Administration of synthetic TCAP-1 into the basolateral amygdala significantly increases the acoustic startle response in low-anxiety rats and decreases the response in high-anxiety animals in a dose-dependent manner. When 30 pmol TCAP-1 is administered into the lateral ventricles each day for 5 days, the sensitization of the rats to the acoustic startle response is abolished. These data indicate that TCAP may possess functions that are independent of the teneurin proprotein and together, the teneurins and TCAP, may represent a novel system to regulate neuronal function and emotionality.

Cell type-specific interleukin-1beta signaling in the CNS

Interleukin-1beta (IL-1beta) is a potent and pleiotropic inflammatory cytokine that is highly produced in the CNS under conditions of damage, disease, or stress. This cytokine acts on CNS glia to effect inflammatory responses, mediated in part via activation of the nuclear factor-kappaB (NF-kappaB) transcription factor, and consequent induction of numerous cytokines. Neurons as well as astrocytes in the hippocampus also express the type 1 IL-1 receptor, indicating that this cytokine can influence neuronal function directly, yet IL-1beta does not induce production of cytokines in neurons as it does in glia. In contrast, IL-1beta regulates synaptic function of hippocampal neurons. Here we demonstrate that different signaling pathways mediate IL-1beta actions in neurons as compared with astrocytes. IL-1beta activates the p38 mitogen-activated protein kinase (MAPK) signaling pathway and induces the activation of CREB in hippocampal neurons, in contrast to the activation of NF-kappaB in hippocampal astrocytes, demonstrating cell type-specific signaling responses to IL-1 in the brain and yielding distinct functional responses.

IL-1 type I receptor plays a key role in mediating the recruitment of leukocytes into the central nervous system

This study investigates the role of type I IL-1 receptor (IL-1R1) in mediating the recruitment of leukocytes into the brain parenchyma in mice. Intracerebroventricular (icv) injection of interleukin IL-1beta induced infiltration of leukocytes between 8 and 72 h after the injection. Leukocytes were rarely found in the brain tissue of saline-injected animals. At 8h after IL-1beta injection, leukocytes were seen lining the blood vessels of the brain and sparsely scattered infiltration of leukocytes was found in the cortex. Peak infiltration of leukocytes, which distributed evenly throughout the brain, was seen at 16 h post-injection. The number of leukocytes in the brain declined thereafter and no leukocytes were found 72 h post-injection. This phenomenon was replicated in mice deficient in lymphotoxin-alpha (LT(alpha)), IL-6, interferon (IFN)-gamma receptor, or the tumor necrosis factor (TNF)-alpha receptor, but abrogated in animals deficient in IL-1R1. ICV injection of IFN-gamma or TNF-alpha, but not IL-6 or IL-12, also induced leukocyte infiltration into the brain. Injection of IL-1beta, IFN-gamma, TNF-alpha, IL-6, and IL-12 induced IL-1beta expression in the brain, with IL-6 and IL-12 being the least effective. Leukocyte infiltration induced by icv IFN-gamma and TNF-alpha was also abrogated in IL-1R1-knockout animals. The induced infiltrating leukocytes were identified as neutrophils. Chronic infection with Trypanosoma brucei resulted in the recruitment of T cells, but no other cell types, into the brain. This did not occur in IL-1R1-knockout mice. Thus, IL-1R1 appears to be important for the recruitment of leukocytes across the blood-brain barrier.

Autonomic neural regulation of immunity

The 'cytokine theory of disease' states that an overproduction of cytokines can cause the clinical manifestations of disease. Much effort has been expended to determine how cytokines are regulated in normal health. Transcriptional, translational and other molecular control mechanisms protect the host from excessive cytokine production. A recent discovery revealed an unexpected pathway that inhibits macrophage cytokine production. The inflammatory reflex is a physiological pathway in which the autonomic nervous system detects the presence of inflammatory stimuli and modulates cytokine production. Afferent signals to the brain are transmitted via the vagus nerve, which activates a reflex response that culminates in efferent vagus nerve signalling. Termed the 'cholinergic anti-inflammatory pathway', efferent activity in the vagus nerve releases acetylcholine (ACh) in the vicinity of macrophages within the reticuloendothelial system. ACh can interact specifically with macrophage alpha7 subunits of nicotinic ACh receptors, leading to cellular deactivation and inhibition of cytokine release. This 'hard-wired' connection between the nervous and immune systems can be harnessed therapeutically in animal models of inflammatory disease, via direct electrical stimulation of the vagus nerve, or through the use of cholinergic agonists that specifically activate the macrophage alpha7 subunit of the ACh receptor. Autonomic dysfunction has been associated with human inflammatory diseases including rheumatoid arthritis, diabetes and sepsis; whether this dysfunction results from the inflammatory component of these diseases, or is actually an underlying cause, is now less clear. The description of the cholinergic anti-inflammatory now brings to the fore several new therapeutic strategies for inflammatory disease, and suggests that many of these diseases may actually be diseases of autonomic dysfunction.

Impaired febrile responses to immune challenge in mice deficient in microsomal prostaglandin E synthase-1

Fever is a common, centrally elicited sign of inflammatory and infectious processes and is known to be induced by the action of PGE2 on its specific receptors in the thermogenic region of the hypothalamus. In the present work, using genetically modified mice, we examined the role of the inducible terminal PGE2-synthesizing enzyme microsomal prostaglandin E synthase-1 (mPGES-1) for the generation of immune-elicited fever. Animals with a deletion of the Ptges gene, which encodes mPGES-1, or their wild-type littermates were given either a subcutaneous injection of turpentine--a model for aseptic cytokine-induced pyresis--or an intraperitoneal injection of interleukin-1beta. While both procedures resulted in typical febrile responses in wild-type animals, these responses were strongly impaired in the mPGES-1 mutant mice. In contrast, both genotypes showed psychogenic stress-induced hyperthermia and displayed normal diurnal temperature variations. Both wild-type and mPGES-1 mutant mice also showed strongly reduced motor activity following turpentine injection. Taken together with previous observations on mPGES-1 induction in the brain vasculature during various inflammatory conditions and its role in endotoxin-induced pyresis, the present findings indicate that central PGE2 synthesis by mPGES-1 is a general and critical mechanism for fever during infectious and inflammatory conditions that is distinct from the mechanism(s) underlying the circadian temperature regulation and stress-induced hyperthermia, as well as the inflammation-induced activity depression.

Interleukin (IL)-6, but not IL-1, induction in the brain downstream of cyclooxygenase-2 is essential for the induction of febrile response against peripheral IL-1alpha

IL-1 is an endogenous pyrogen produced upon inflammation or infection. Previously, we showed that, upon injection with turpentine, IL-1 is induced in the brain in association with the development of fever. The role of endogenous IL-1 in the brain and the signaling cascade to activate thermosensitive neurons, however, remain to be elucidated. In this report, febrile response was analyzed after peripheral injection of IL-1alpha. We found that a normal febrile response was induced even in IL-1alpha/beta-deficient mice, indicating that production of IL-1 in the brain is not necessarily required for the response. In contrast, IL-6-deficient mice did not exhibit a febrile response. Cyclooxygenase (Cox)-2 expression in the brain was strongly induced 1.5 h after injection of IL-1alpha, whereas IL-6 expression was observed 3 h after the injection. Cox-2 expression in the brain was not influenced by IL-6 deficiency, whereas indomethacin, an inhibitor of cyclooxygenases, completely inhibited induction of IL-6. These observations suggest a mechanism of IL-1-induced febrile response in which IL-1 in the blood activates Cox-2, with the resulting prostaglandin E(2) inducing IL-6 in the brain, leading to the development of fever.

A critical role for the parabrachial nucleus in generating central nervous system responses elicited by a systemic immune challenge

Using Fos immunolabelling as a marker of neuronal activation, we investigated the role of the parabrachial nucleus in generating central neuronal responses to the systemic administration of the proinflammatory cytokine interleukin-1beta (1 microg/kg, i.a.). Relative to intact animals, parabrachial nucleus lesions significantly reduced the number of Fos-positive cells observed in the central amygdala (CeA), the bed nucleus of the stria terminalis (BNST), and the ventrolateral medulla (VLM) after systemic interleukin-1beta. In a subsequent experiment in which animals received parabrachial-directed deposits of a retrograde tracer, it was found that many neurons located in the nucleus tractus solitarius (NTS) and the VLM neurons were both retrogradely labelled and Fos-positive after interleukin-1beta administration. These results suggest that the parabrachial nucleus plays a critical role in interleukin-1beta-induced Fos expression in CeA, BNST and VLM neurons and that neurons of the NTS and VLM may serve to trigger or at least influence changes in parabrachial nucleus activity that follows systemic interleukin-1beta administration.

Potent effect of interleukin-1 beta to evoke ATP and adenosine release from rat hippocampal slices

In this study the effect of IL-1 beta on [(3)H]purine release from rat hippocampal slices was explored. IL-1 beta (3 x 10(-18)-3 x 10(-14) M) concentration-dependently elevated the basal [(3)H]purine efflux, and this effect was reversed by the selective IL-1RI receptor antagonist IL-1ra (10(-12) M). HPLC analysis revealed that the amount of [(3)H]ATP and [(3)H]adenosine significantly increased in the effluent in response to IL-1 beta. The sodium channel inhibitor tetrodotoxin, the NMDA and non-NMDA receptor antagonists d(-)-2-amino-5-phosphonopentanoic acid (AP-5) plus 6-cyano-7-nitroquinoxaline-2,3-dione-disodium (CNQX) almost completely abolished IL-1 beta-evoked [(3)H]purine release. The effect of IL-1 beta on [(3)H]purine efflux was also prevented by the p38 MAP kinase inhibitor SB 203580, by the nucleoside transport inhibitor nitrobenzyl-thioinosine (NBTI) and by low temperature (4 degrees C). In summary IL-1 beta triggers a transporter mediated [(3)H]purine efflux in the hippocampus which is conveyed by glutamate receptor activation and the p38 MAP kinase pathway, and could serve as a mediator of IL-1 beta-induced synaptic depression.

Sensory circumventricular organs: central roles in integrated autonomic regulation

Circumventricular organs (CVO) play a critical role as transducers of information between the blood, neurons and the cerebral spinal fluid (CSF). They permit both the release and sensing of hormones without disrupting the blood-brain barrier (BBB) and as a consequence of such abilities the CVOs are now well established to have essential regulatory actions in diverse physiological functions. The sensory CVOs are essential signal transducers located at the blood-brain interface regulating autonomic function. They have a proven role in the control of cardiovascular function and body fluid regulation, and have significant involvement in central immune response, feeding behavior and reproduction, the extent of which is still to be determined. This review will attempt to summarize the research on these topics to date. The complexities associated with sensory CVO exploration are intense, but should continue to result in valuable contributions to our understanding of brain function.

The effects of endogenous interleukin-1 bioactivity on locus coeruleus neurons in response to bacterial and viral substances

In a previous study, we found that microinjection of the cytokine interleukin-1 (IL-1) into the locus coeruleus (LC) increased the electrophysiological activity of LC neurons. To determine if endogenous IL-1 similarly affects the LC, brain IL-1 was induced with lipopolysaccharide (LPS), a substance derived from Gram-negative bacteria. LPS microinjected directly into the LC increased the activity of LC neurons in anesthetized rats, and this effect was blocked by microinfusion of the IL-1 receptor antagonist (IL-1RA) protein into the LC indicating the involvement of IL-1 receptors. Similarly, intraperitoneal (i.p.) LPS injection increased the activity of LC neurons in a dose- and time-related manner that was sensitive to IL-1RA. The change in the activity of LC neurons caused by a single i.p. injection of LPS was surprisingly long-lasting, and evolved over a period of at least 3 weeks. Other microbial substances-namely, peptidoglycan from Gram-positive bacteria and poly-inosine/poly-cytosine (poly(I)/(C)), which resembles RNA viruses-were used to determine the generality of the findings with LPS. Both i.p. peptidoglycan and poly(I)/(C) increased LC activity but with lesser efficacy than LPS. IL-1RA reversed the increase in the activity of LC neurons caused by i.p. peptidoglycan treatment; however, that caused by i.p. Poly(I)/(C) was not diminished by IL-1RA. Thus, the increased activity of LC neurons caused by LPS and peptidoglycan requires IL-1 receptor binding, suggesting the involvement of endogenously-produced IL-1. In contrast, poly(I)/(C) increased the activity of LC neurons but this did not critically involve IL-1 receptors in the LC.

Interleukin-1beta modulates state-dependent discharge activity of preoptic area and basal forebrain neurons: role in sleep regulation

Interleukin-1beta (IL-1) is a pro-inflammatory cytokine that has been implicated in the regulation of nonrapid eye movement (nonREM) sleep. IL-1, IL-1 receptors and the IL-1 receptor antagonist (ra) are present normally in discrete brain regions, including the preoptic area (POA) of the hypothalamus and the adjoining magnocellular basal forebrain (BF). The POA/BF have been implicated in the regulation of sleep-wakefulness. We hypothesized that IL-1 promotes nonREM sleep, in part by altering the state-dependent discharge activity of POA/BF neurons. We recorded the sleep-wake discharge profiles of 83 neurons in the lateral POA/BF and assessed the effects of IL-1, IL-1ra, and IL-ra + IL-1 delivered through a microdialysis probe on state-dependent neuronal discharge activity. IL-1 decreased the discharge rate of POA/BF neurons as a group (n = 55) but wake-related and sleep-related neurons responded differently. IL-1 significantly decreased the discharge rate of wake-related neurons. Of 24 wake-related neurons studied, 19 (79%) neurons exhibited a greater than 20% change in their discharge in the presence of IL-1 during waking. IL-1 suppressed the discharge activity of 18 of 19 responsive neurons. Of 13 sleep-related neurons studied, IL-1 increased the discharge activity of five and suppressed the discharge activity of four neurons. IL-1ra increased the discharge activity of four of nine neurons and significantly attenuated IL-1-induced effects on neuronal activity of POA/BF neurons (n = 19). These results suggest that the sleep-promoting effects of IL-1 may be mediated, in part, via the suppression of wake-related neurons and the activation of a subpopulation of sleep-related neurons in the POA/BF.

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

Interleukin-1 beta (IL-1 beta) is thought to act on the brain to induce fever, neuroendocrine activation, and behavioral changes during disease through induction of prostaglandins at the blood-brain barrier (BBB). However, despite the fact that IL-1 beta induces the prostaglandin-synthesizing enzyme cyclooxygenase-2 (COX-2) in brain vascular cells, no study has established the presence of IL-1 receptor type 1 (IL-1R1) protein in these cells. Furthermore, although COX inhibitors attenuate expression of the activation marker c-Fos in the preoptic and paraventricular hypothalamus after administration of IL-1 beta or bacterial lipopolysaccharide (LPS), they do not alter c-Fos induction in other structures known to express prostaglandin receptors. The present study thus sought to establish whether IL-1R1 protein is present and functional in the rat cerebral vasculature. In addition, the distribution of IL-1R1 protein was compared to IL-1 beta- and LPS-induced COX-2 expression. IL-1R1-immunoreactive perivascular cells were mostly found in choroid plexus and meninges. IL-1R1-immunoreactive vessels were seen throughout the brain, but concentrated in the preoptic area, subfornical organ, supraoptic hypothalamus, and to a lesser extent in the paraventricular hypothalamus, cortex, nucleus of the solitary tract, and ventrolateral medulla. Vascular IL-1R1-ir was associated with an endothelial cell marker, not found in arterioles, and corresponded to the induction patterns of phosphorylated c-Jun and inhibitory-factor kappa B mRNA upon IL-1 beta stimulation, and colocalized with peripheral IL-1 beta- or LPS-induced COX-2 expression. These observations indicate that functional IL-1R1s are expressed in endothelial cells of brain venules and suggest that vascular IL-1R1 distribution is an important factor determining BBB prostaglandin-dependent activation of brain structures during infection.

Nuclear factor κB nuclear translocation as a crucial marker of brain response to interleukin-1. A study in rat and interleukin-1 type I deficient mouse

The signalling pathways that mediate early central effects of interleukin-1 (IL-1) during the acute phase reaction have been poorly elucidated. Interaction of IL-1beta to its specific receptor interleukin-1 receptor type I (IL-1RI) leads to nuclear factor kappa B (NuFkappaB) nuclear translocation and a robust transcriptional activation of inhibitor of kappa B alpha (IkappaBalpha) within the rat brain. Indeed, we demonstrated that IL-1RI expressed in blood brain barrier (BBB) cells and in circumventricular organs (CVOs) is crucial for p65-NFkappaB translocation induced by peripheral injection of IL-1beta. Moreover, it has been previously shown that monitoring IkappaBalpha mRNA synthesis is an effective tool to investigate the activity of the transcription factor NFkappaB into the CNS. However in the present study we observed time-related and cell-type differences between IkappaBalpha mRNA synthesis and p65-NFkappaB translocation. This indicates that the expression of IkappaBalpha mRNA does not strictly parallel p65-NFkappaB nuclear translocation, suggesting that these markers are not interchangeable to investigate NFkappaB activity but must be studied together. Thus, we hypothesize that IL-1beta reached the brain across the CVOs that lack a BBB and endothelial cells all over the brain and interacted with its receptors to induce NFkappaB translocation. The study of the consequences of the impairment of NFkappaB pathway activation in in vivo experimentation should bring important clues about the precise role of this transcription factor.

Vagal afferent input from the acid-challenged rat stomach to the brainstem: Enhancement by interleukin-1β

Exposure of the gastric mucosa to back-diffusing concentrations of HCl (0.25 M, pH 0.51) stimulates vagal afferent input to the brainstem. Here we have examined whether pretreatment of rats with the proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha causes sensitization of vagal afferent pathways to HCl. Rats were pretreated i.p. with interleukin-1beta, tumor necrosis factor-alpha (10 microg/kg) or their vehicle (sterile saline) 24, 48 and 96 h before intragastric administration of HCl (0.25 M, 1 ml/100 g). Activation of neurons in the nucleus tractus solitarii was visualized by c-Fos immunohistochemistry 2 h after the HCl challenge. I.p. administration of interleukin-1beta and tumor necrosis factor-alpha alone induced c-Fos in the brainstem, an effect that was gone after 24 h. At this time, however, the effect of HCl to cause expression of c-Fos in the nucleus tractus solitarii was significantly enhanced by pretreatment with interleukin-1beta and tumor necrosis factor-alpha. The sensitizing effect of i.p.-administered interleukin-1beta was sustained for more than 48 h and prevented by the interleukin-1 receptor antagonist anakinra. Intracisternal administration of interleukin-1beta and tumor necrosis factor-alpha (100 ng) failed to amplify the HCl-evoked expression of c-Fos in the brainstem. These results show that peripheral administration of the proinflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha induces prolonged sensitization of vagal afferent pathways to gastric HCl challenge. This effect seems to arise from a peripheral action on vagal afferents and may be of relevance to gastric chemonociception.

Interleukin 1 beta enhances conditioned fear memory in rats: possible involvement of glucocorticoids

Central administration of 15 ng interleukin (IL)-1beta in the rat significantly enhanced conditioned fear memory assessed by a passive avoidance task, when retested at 24 and 48 h post-training. Pain threshold was unaffected by 15 ng IL-1beta administration. IL-1beta treatment also increased serum corticosterone. This increase in serum corticosterone was further enhanced in rats given both IL-1beta and footshock. Furthermore, the glucocorticoid receptor antagonist mifepristone blocked IL-1beta-induced elevation in corticosterone and also attenuated the enhanced conditioned fear memory. Central administration of IL-1beta significantly increased prostaglandin E2 and decreased the anti-inflammatory cytokine IL-10 release from whole blood cultures; therefore this treatment appears to be effective in inducing an inflammatory response in both the periphery and the brain. The present study confirms that IL-1beta can enhance conditioned fear memory, an effect which is correlated with changes in glucocorticoid function. This facilitation of defensive behaviour could reflect adaptive responses which may enhance survival during sickness.