Endogenous Pyrogen Research Articles

Central substance P NK1 receptors are involved in fever induced by LPS but not by IL-1β and CCL3/MIP-1α in rats

Substance P (SP) is a neuropeptide that can modulate inflammatory mediator release through activation of NK1 receptors (NK1R). Some studies have also suggested the involvement of SP in lipopolysaccharide (LPS)-induced fever. However, the precise contribution of this neuropeptide to the pathways activated during fever is unknown. In this study we investigated the effect of a selective NK1R antagonist, SR140333B, on the febrile response induced by LPS and cytokines. Our results show that the systemic injection of SR140333B did not modify the fever induced by LPS at a dose that is able to reduce protein extravasation induced by SP in the skin. On the other hand, intracerebroventricular administration of SR140333B significantly reduced the fever induced by peripheral injection of LPS. These data emphasize an important role for SP in the central nervous system during the febrile response to LPS, and are reinforced by the fact that intracerebroventricular injection of SP also induced fever in a dose-dependent manner in captopril-treated rats. Considering that the febrile response can result from the generation of several endogenous pyrogens, among them interleukin (IL)-1β and macrophage inflammatory protein-1α (CCL3/MIP-1α), we also examined the effect of SR140333B on the fever induced by these cytokines which act through prostaglandin-dependent and -independent mechanisms, respectively. Surprisingly, SR140333B did not modify the febrile response to IL-1β or CCL3/MIP-1α. Altogether these data suggest that the central action of SP is essential for LPS-, but not for IL-1β- or CCL3/MIP-1α-induced fever.

Ccl22/MDC, is a prostaglandin dependent pyrogen, acting in the anterior hypothalamus to induce hyperthermia via activation of brown adipose tissue

CC Chemokine ligand 22 (Ccl22) is a selective, high affinity ligand at the CC chemokine receptor 4 (Ccr4). We have identified cDNAs encoding both ligand and receptor of the Ccl22–Ccr4 pair in cDNA libraries of the anterior hypothalamus/pre-optic area (AH/POA) by PCR. The AH/POA is the key brain region where endogenous pyrogens have been shown to act on warm sensitive neurons to affect thermogenesis in brown adipose tissue (BAT) and other thermogenically responsive tissues. We show that functional Ccr4 receptors are present in the AH/POA neurons as injection of Ccl22 into the POA but not to other hypothalamic nuclei induces an increase in core body temperature as measured by radiotelemetry. Indomethacin (5 mg/kg s.c) pre-treatment markedly reduced the hyperthermia evoked by POA injection of Ccl22 (10 ng/0.5 ul) and thus suggests that this hyperthermia is mediated through cyclooxygenase activation and thus likely through the formation and action of the pyrogen prostaglandin E2. The temperature elevation involves a decrease in the respiratory exchange ratio and increased activation of the brown adipose tissue as demonstrated by 18F-FDG–PET imaging. We describe a novel role to the ligand Ccl22 and its receptor Ccr4 in the anterior hypothalamus in temperature regulation that depends on the synthesis of the endogenous pyrogen, prostaglandin E2.

Cyclooxygenase-independent mechanism of ibuprofen-induced antipyresis: the role of central vasopressin V1 receptors

This study compared the antipyretic effects of ibuprofen and indomethacin regarding the efficacy in blocking fevers induced by lipopolysaccharide (LPS from E. coli) or pyrogenic mediators that act on prostaglandin (PG)-dependent and PG-independent pathways. The content of PGE₂ in the cerebrospinal fluid (CSF) and the dependence on central arginine vasopressin (AVP) release by both antipyretics were also compared during the reduction of LPS-induced fever. Finally, we investigated the effect of ibuprofen on hypothalamic cytokine content during LPS-induced fever. Ibuprofen (intraperitoneally, i.p.) dose-dependently inhibited the fever induced by LPS (intravenously, i.v.). Indomethacin (2 mg/kg) and ibuprofen (10 mg/kg) reduced the fever induced by i.c.v. injection of interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)-α, or arachidonic acid (AA). Ibuprofen, but not indomethacin, inhibited i.c.v. endothelin-1- and pre-formed pyrogenic factor (PFPF)-induced fever. Neither ibuprofen nor indomethacin affected fever by PGE₂ , PGF(2α) , or corticotrophin-releasing factor (CRF); however, both reduced the CSF PGE₂ content after LPS. Bilateral injection of the AVP V(1) receptor antagonist d(CH2)₅ Tyr(Me)AVP into the ventral septal area blocked both ibuprofen- and indomethacin-induced antipyresis. Ibuprofen did not modify the hypothalamic increase in either IL-1β or IL-6 induced by LPS. In conclusion, although the antipyretic effect of ibuprofen involves the blockage of central production of PGE₂ and the endogenous release of AVP, differently from low dose of indomethacin, ibuprofen not only reduced the fever induced by PGE₂ -dependent, but also, that induced by PGE₂ -independent endogenous pyrogens. Moreover, ibuprofen does not affect the hypothalamic synthesis/release of IL-1β and IL-6.

Pattern Recognition and Gestalt Psychology: The Day Nüsslein‐Volhard Shouted “Toll!”

Pattern Recognition and Gestalt Psychology: The Day Nüsslein‐Volhard Shouted “Toll!”

Which Drugs for the Control of Fever in Critical Patients

It has been estimated that nosocomial fever occurs in approximately one-third of hospitalized patients. The incidence is even higher in critically-ill patients in whom both infectious and noninfectious etiologies of fever are common. Polypeptide cytokines (endogenous pyrogens) such as interleukin-1b (IL-1b), tumor necrosis factor (TNF) and interleukin-6 (IL-6) act directly on the hypothalamus to effect a fever response by promoting an increase in heat generation and a decrease in heat loss. There is widespread acceptance that in most if not all critically ill neurologic patients fever should be treated but still it is not clear if fever per se in nonneurologic critically ill patients should be treated too. We review physical and pharmacological methods presently utilized to treat fever in critically ill patients.

Febrile Seizures: Characterization of Double-Stranded RNA-Induced Gene Expression

An association has long been suspected between febrile seizures and interleukin-1beta, the most potent endogenous pyrogen. Interleukin-1beta production increases after double-stranded RNA stimulation in leukocytes of febrile seizure patients. To elucidate the genetics of the immune response, the gene expression pattern after double-stranded RNA stimulation was investigated using DNA microarray. Compared with the control group, expression of the genes ACCN4 (sodium channel), KCNC3 (potassium channel), GABRE (gamma-aminobutyric acid receptor epsilon subunit), RIPK2 (receptor interacting protein kinase-2), TLR4 (toll-like receptor-4), IL26 (interleukin-26), and TNF (tumor necrosis factor), and CASP1 (caspase-1) was increased in the febrile seizure group (P < 0.01). Because RIPK2 and CASP1 are associated with interleukin-1beta production, increased expression might cause increased interleukin-1beta production in the febrile seizure patients. The induced expression of several ion channel genes by double-stranded RNA may affect neuronal excitability which leads to seizure susceptibility during infection.

Endotoxin‐like reaction following once‐daily gentamicin

An endotoxin-like reaction is a host response to an agent that induces the release of endogenous pyrogens, including cytokines. The typical reaction that is associated with gentamicin is fever and chills, rigor, shivering, tachycardia with hypertension or hypotension, respiratory symptoms and muscle cramps. We report a case of a 92-year-old patient who developed an endotoxin-like reaction in the post-operative recovery unit following 200 mg of gentamicin. The reported side effect is not included in the drug sheet or in the British National Formulary. No similar incidents were reported in the UK. We discuss the clinical picture of this rare event, along with a review of the literature and recommendations.

Prostanoids in health and disease

The prostanoids are a family of lipid mediators generated by the action of cyclooxygenase on a 20-carbon unsaturated fatty acid, arachidonic acid. Prostanoids are generated widely in response to diverse stimuli and, acting in a paracrine or autocrine manner, play important roles in normal physiology and disease. This review summarizes the current knowledge on prostanoid generation and the roles of individual mediators, their biosynthetic pathways, and their receptors in health and disease.

From the Obscure and Mysterious Acute Phase Response to Toll-Like Receptors and the Cytokine Network

The discovery of C-reactive protein (CRP) almost 80 years ago in the blood of patients with various infectious and inflammatory diseases initiated studies on the mysterious biological phenomenon called “the acute phase response” (APR). The complex metabolic alterations accompanying APR include changes in the plasma concentration of the majority of liver-produced proteins – acute phase proteins (APPs). The search for mediators released from the site of injury and able to stimulate hepatocytes led to the discovery of “Leukocytic Endogenous Mediator” (or ”Endogenous Pyrogen”), initially identified with interleukin-1. Only in 1987 was the main factor able to induce the majority of symptoms of APR discovered and named interleukin-6 (IL-6). The current paradigm assumes that APR is elicited by numerous proinflammatory cytokines, the principal role being played by the IL-6-family. The last decade has brought about significant progress in understanding the initiation of the acute phase response (recognition of pathogens by Toll-like receptors), interaction of cytokines and their receptors (origin and importance of soluble cytokine receptors, construction of hypercytokines by protein fusion), the mechanism of multi-step signal transduction from the plasma membrane to nuclear transcription factors (including the role of MAP kinases), as well as elucidation of the role of receptor cross-talk in cytokine networks in health and disease. Genomic techniques indicate that hundreds of genes participate in the development of APR. The data presented here emphasize the growing importance of APR for clinical medicine and confirm the close relationship between acute phase response and innate immunity. Keywords: Acute phase proteins, pro-inflammatory cytokines, cytokine pleiotropy and redundancy, soluble receptors and engineered hypercytokines, Toll-like receptors and pathogen recognition, cytokine networks and receptor cross-talk

Cytokine-induced neutrophil chemoattractant (CINC)-1 induces fever by a prostaglandin-dependent mechanism in rats

Cytokine-induced neutrophil chemoattractant-1 (CINC-1), a member of the ELR + CXC subfamily [ELR motif (glutamic acid-leucine-arginine) adjacent to the cysteine-X-cysteine (CXC) motif located at the N-terminus of the protein], is an acute-phase protein and its synthesis is induced by endogenous and exogenous pyrogens. However, there are no studies on the pyrogenic property of CINC-1. Therefore, the present study evaluates whether centrally administered CINC-1 promotes an integrated febrile response along with an increase in the prostaglandin (PG)E 2 content of the cerebrospinal fluid (CSF) of rats. The effects of antipyretic drugs on fever and on the PGE 2 content of the CSF as well as the effectiveness of a neutralizing anti-CINC-1 antibody on the fever induced by CINC-1 have also been investigated. Intracerebroventricular (i.c.v.) injection of CINC-1 induced a dose-dependent bell-shaped rise on body temperature and increased PGE 2 concentration in the CSF of conscious rats. Injected into the preoptic area of the anterior hypothalamus (AH/POA) (i.h.), CINC-1 also induced a dose-dependent bell-shaped increase in body temperature along with a decrease on tail skin temperature. Indomethacin (INDO, 2 mg kg − 1 , i.p.) and ibuprofen (IBU, 10 mg kg − 1 , i.p.) markedly reduced the fever evoked by i.c.v. injection of CINC-1 (25 ng/site). Orally given celecoxib (5 mg kg − 1 , 30 min. before) abolished the fever induced by CINC-1 i.c.v. or i.h. (50 pg) injection. The antipyretic drugs also blocked the PGE 2 increase after CINC-1 i.c.v. injection. Co-injected anti-CINC antibody (10 ng/site) strongly reduced the febrile response induced by CINC-1 (50 pg/site) injected intrahypothalamically. This is the first time that centrally injected CINC-1 has been reported to act directly on the pyrogen-sensitive neurons of AH/POA, promoting a thermoregulatory response that seems to depend on other endogenous pyrogens synthesis and, as seen here, on PGE 2.

The Central and Peripheral Production of Pro-inflammatory Cytokine, IL-1b after Immune and Stress Stimulation in Rats

Interleukin-1β (IL-1β), one of the pro-inflammatory cytokines, acts as an endogenous pyrogen and is an important mediator of behavioral and physiological responses to immune stimulation as well as exposure to stressors. The objective of the present study was to examine the pattern of central or peripheral IL-1 β response to lipopolysaccharide (LPS) or exposure to the foot shock stress (FS) in rats. After treatment of LPS (100 μg/kg) or exposure to the FS [ten times (0.8 mA) foot shocks for 5 sec each and 90 sec interval], body temperature and IL-1β levels in plasma, spleen and brain were measured. Both LPS and FS stimuli elicited increased body temperature but showed different patterns of peripheral IL-1 β levels. LPS produced a widespread increase in IL-1β levels in the plasma, spleen and brain, whereas FS produced a significant increase in IL-1β levels only in the brain regions but not in plasma and spleen. The present study suggests that IL-1β is, centrally or peripherally in different patterns, regulated by immune stimulation or exposure to stressors and IL-1β plays an important role in mediating responses of sickness-like behaviors induced by immune stimuli or stressors.

Polymorphisms of interleukin-1β promoter in simple febrile seizures

Purpose : Febrile seizure (FS) is the most common type of seizure. The role of genetic factors in FSs has long been recognized. A positive family history can be elicited in 25-40% of patients with FSs; nonetheless, the genes responsible for FSs in the majority of the population remain unknown. Interleukin-1 β (IL-1 β) is a pro-inflammatory cytokine that acts as an endogenous pyrogen. Thus, IL-1 β could be involved in the pathophysiology of FSs. Methods : To determine whether or not single nucleotide polymorphisms of the IL-1 β gene are associated with susceptibility to simple FSs, IL-1 β promoter -31 and -511 genotyping was performed by means of polymerase chain reaction-restriction fragment (PCR-RF) length polymorphism in 40 FS patients (20 sporadic and 20 familial FS patients) and 33 controls. Results : There were no significant differences in the frequencies of -31 C/T and -511 C/T in the IL-1 β promoter gene, between simple FS patients and controls. Conclusion : The frequency of CT/CT increased relatively in familial FS patients. A study examining a larger number of FS patients is needed. (Korean J Pediatr 2008;51:1007-1011)

Endogenous opioids: role in prostaglandin-dependent and -independent fever

This study evaluated the participation of mu-opioid-receptor activation in body temperature (T(b)) during normal and febrile conditions (including activation of heat conservation mechanisms) and in different pathways of LPS-induced fever. The intracerebroventricular treatment of male Wistar rats with the selective opioid mu-receptor-antagonist cyclic d-Phe-Cys-Try-d-Trp-Arg-Thr-Pen-Thr-NH(2) (CTAP; 0.1-1.0 microg) reduced fever induced by LPS (5.0 microg/kg) but did not change T(b) at ambient temperatures of either 20 degrees C or 28 degrees C. The subcutaneous, intracerebroventricular, and intrahypothalamic injection of morphine (1.0-10.0 mg/kg, 3.0-30.0 microg, and 1-100 ng, respectively) produced a dose-dependent increase in T(b). Intracerebroventricular morphine also produced a peripheral vasoconstriction. Both effects were abolished by CTAP. CTAP (1.0 microg icv) reduced the fever induced by intracerebroventricular administration of TNF-alpha (250 ng), IL-6 (300 ng), CRF (2.5 microg), endothelin-1 (1.0 pmol), and macrophage inflammatory protein (500 pg) and the first phase of the fever induced by PGF(2alpha) (500.0 ng) but not the fever induced by IL-1beta (3.12 ng) or PGE(2) (125.0 ng) or the second phase of the fever induced by PGF(2alpha). Morphine-induced fever was not modified by the cyclooxygenase (COX) inhibitor indomethacin (2.0 mg/kg). In addition, morphine injection did not induce the expression of COX-2 in the hypothalamus, and CTAP did not modify PGE(2) levels in cerebrospinal fluid or COX-2 expression in the hypothalamus after LPS injection. In conclusion, our results suggest that LPS and endogenous pyrogens (except IL-1beta and prostaglandins) recruit the opioid system to cause a mu-receptor-mediated fever.

Methamphetamine-induced hyperthermia and lethal toxicity: Role of the dopamine and serotonin transporters

We examined the hyperthermic and lethal toxic effects of methamphetamine in dopamine transporter (DAT) and/or serotonin transporter (SERT) knockout (KO) mice. Methamphetamine (45 mg/kg) caused significant hyperthermia even in the mice with a single DAT gene copy and no SERT copies (DAT+/- SERT-/- mice). Mice with no DAT copies and a single SERT gene copy (DAT-/- SERT+/- mice) showed significant but reduced hyperthermia when compared to wild-type mice after methamphetamine. Surprisingly, DAT/SERT double KO mice exhibited a paradoxical hypothermia after methamphetamine. These results demonstrate that methamphetamine exerts a hyperthermic effect via DAT, or via SERT, in the absence of DAT. The selective norepinephrine transporter blocker (20 mg/kg nisoxetine) caused hyperthermia in DAT/SERT double KO mice, suggesting that the norepinephrine system is not responsible for methamphetamine-induced paradoxical hypothermia in the double KO mice. DAT gene deletion in mice strikingly increased LD50 of methamphetamine by 1.7-1.8 times that of wild-type mice, suggesting that the lethal toxic effect of methamphetamine is mainly dependent on DAT. Moreover, dissociation between hyperthermic and lethal toxic effects of methamphetamine in DAT single KO mice and DAT/SERT double KO mice suggest that hyperthermia is not a prerequisite for methamphetamine-induced lethality. Methamphetamine (45 mg/kg) significantly increased mRNA of interleukin-1beta, which is the major endogenous pyrogen, in the hypothalamus of wild-type mice but not in DAT/SERT double KO mice, which provides a partial mechanism of methamphetamine-induced paradoxical hypothermia. These results suggest that DAT and SERT are key molecules for hyperthermic and lethal toxic effects of methamphetamine.

Endotoxin fever in granulocytopenic rats: evidence that brain cyclooxygenase-2 is more important than circulating prostaglandin E2

PGE(2) is a recognized mediator of many fevers, and cyclooxygenase (COX) is the major therapeutic target for antipyretic therapy. The source, as well as the site of action of PGE(2), as an endogenous pyrogen, is widely accepted as being central, but PGE(2) in the circulation, possibly from leukocytes, may also contribute to the development of fever. However, bacterial infections are important causes of high fever in patients receiving myelosuppressive chemotherapy, and such fevers persist despite the use of COX inhibitors. In the study reported here, the febrile response to bacterial LPS was measured in rats made leukopenic by cyclophosphamide. A striking increase in LPS fever occurred in these granulocytopenic rats when compared with febrile responses in normal animals. Unlike LPS fever in normal rats, fever in granulocytopenic rats was neither accompanied by an increase in blood PGE(2) nor inhibited by ibuprofen. Both leukopenic and normal rats showed LPS-induced COX-2-immunoreactivity in cells associated with brain blood vessels. Furthermore, LPS induced an increase of PGE(2) in cerebrospinal fluid. Induction of COX-2-expression and PGE(2) production was inhibited by ibuprofen in normal but not in leukopenic rats. Although the results presented are, in part, confirmatory, they add new information to this field and open a number of important questions as yet unresolved. Overall, the present results indicate that, in contrast to immunocompetent rats, leukocytes and/or other mechanisms other than PGE(2) are implicated in the mechanisms restricting and reducing the enhanced febrile response to endotoxin in immunosuppressed hosts.

Common and Divergent Immune Response Signaling Pathways Discovered in Peripheral Blood Mononuclear Cell Gene Expression Patterns in Presymptomatic and Clinically Apparent Malaria

Using genome-wide expression profiles from persons either experimentally challenged with malaria-infected mosquitoes or naturally infected with Plasmodium falciparum malaria, we present details of the transcriptional changes that occur with infection and that either are commonly shared between subjects with presymptomatic and clinically apparent malaria or distinguish these two groups. Toll-like receptor signaling through NF-kappaB pathways was significantly upregulated in both groups, as were downstream genes that function in phagocytosis and inflammation, including the cytokines tumor necrosis factor alpha, gamma interferon (IFN-gamma), and interleukin-1beta (IL-1beta). The molecular program derived from these signatures illuminates the closely orchestrated interactions that regulate gene expression by transcription factors such as IRF-1 in the IFN-gamma signal transduction pathway. Modulation of transcripts in heat shock and glycolytic enzyme genes paralleled the intensity of infection. Major histocompatibility complex class I molecules and genes involved in class II antigen presentation are significantly induced in 90% of malaria-infected persons regardless of group. Differences between early presymptomatic infection and natural infection involved genes that regulate the induction of apoptosis through mitogen-activated protein (MAP) kinases and signaling pathways through the endogenous pyrogen IL-1beta, a major inducer of fever. The induction of apoptosis in peripheral blood mononuclear cells from patients with naturally acquired infection impacted the mitochondrial control of apoptosis and the activation of MAP kinase pathways centered around MAPK14 (p38alpha and p38beta). Our findings confirm and extend findings regarding aspects of the earliest responses to malaria infection at the molecular level, which may be informative in elucidating how innate and adaptive immune responses may be modulated in different stages of infection.

Hyperthermia is a surrogate marker of inflammation‐mediated cause of brain damage in acute ischaemic stroke

The influence of temperature on the outcome observed in experimental models of ischaemic stroke has not been definitively proved in patients with stroke. Interleukin-6 (IL-6) acts as important endogenous pyrogen, and it is an important regulator of spontaneous body temperature during cerebral ischaemia. The objective of this study was to determine, during the acute phase of cerebral ischaemia, the potential relationship between proinflammatory cytokines and hyperthermia as a cause of larger cerebral infarcts. We studied 229 patients with a first-ever acute hemispheric infarction admitted within the first 24 h from onset of symptoms. On admission, axillary temperature was recorded and blood chemistry studies and cranial computed tomography were performed. We classified body temperature into two groups: hyperthermia (>or=37.5 degrees C) and normothermia (<37.5 degrees C). We determined proinflammatory markers [IL-6, tumour necrosis factor-alpha (TNF-alpha), intercellular adhesion molecule (ICAM-1) and vascular cellular adhesion molecule] on admission. Two outcome variables were evaluated: (i) infarct volume; (ii) Canadian Stroke Scale (CSS) at 3 months (CSS <or= 7 was considered poor outcome and CSS > 7 good outcome). Patients with hyperthermia had higher infarct volume [46.5 (9.8-78.5) cm(3) vs. 19.1 (5.0-23.5) cm(3); P < 0.0001], as well as poor outcome at 3 months. Plasma levels of IL-6, TNF-alpha and ICAM-1 were significantly higher in the group of patients with hyperthermia than in the normothermic group. There was a significant correlation between body temperature on admission and infarct volume (r = 0.302; P < 0.0001), and between proinflammatory markers (IL-6 and TNF-alpha) and infarct volume. A significant association was also found between proinflammatory markers (IL-6, TNF-alpha, and ICAM-1) and poor outcome. However, after adjustment for potential confounders, hyperthermia was not independently associated with either larger infarct volume or with poor outcome at 3 months. Inflammatory mediators play a role in acute ischaemic brain damage independently of hyperthermia.

In vitro pyrogen test for toxic or immunomodulatory drugs

Pyrogenic contaminations of some classes of injectable drugs, e.g. toxic or immunomodulatory as well as false-positive drugs, represent a major risk which cannot yet be excluded due to the limitations of current tests. Here we describe a modification of the In vitro Pyrogen Test termed AWIPT (Adsorb, Wash, In vitro Pyrogen Test), which addresses this problem by introducing a pre-incubation step in which pyrogenic contaminations in the test sample are adsorbed to albumin-coated beads. After rinsing, the beads are incubated with human whole blood and the release of the endogenous pyrogen interleukin-1β is measured as a marker of pyrogenic activity. Intentional contaminations with lipopolysaccharide were retrieved from the chemotherapeutic agents paclitaxel, cisplatin and liposomal daunorubicin, the antibiotic gentamicin, the antifungal agent liposomal amphotericin B, and the corticosteroid prednisolone at lower dilutions than in the standard in vitro pyrogen test. This represents a promising new approach for the detection of pyrogenic contamination in drugs or in drugs containing interfering additives and should lead to improved safety levels.

Ceramide mediates the rapid phase of febrile response to IL-1β

IL-1beta was identified after a long search for the endogenous pyrogen. It acts by inducing synthesis of prostaglandin E2, which mediates the late phase of IL-1beta-induced fever. Here we show by radiotelemetry that the early phase of the fever response to IL-1beta is mediated by ceramide. Hypothalamic application of the cell-penetrating C2-ceramide mimics the rapid phase of the IL-1beta-induced fever. Inhibition of ceramide synthesis blocks the rapid phase of fever but does not affect the slower prostaglandin E2-dependent phase, which is blocked by indomethacin or by null mutation of the EP3 prostanoid receptor. Electrophysiological experiments on preoptic area/anterior hypothalamic neurons show that C2-ceramide, but not dihydroceramide, mimics the rapid hyperpolarizing effects of IL-1beta on the activity of warm-sensitive hypothalamic neurons. IL-1beta-mediated hyperpolarization is blocked by PP2, the selective inhibitor of the protein tyrosine kinase Src, which is known to be activated by ceramide. These in vivo and in vitro data suggest that ceramide fulfills the criteria for an endogenous pyrogen.

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

Most of the inflammatory effects of the cytokine interleukin 1β (IL-1β) 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-1β, 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-1β using whole-cell patch clamp recordings in preoptic area/anterior hypothalamus neurons. Exposure to IL-1β (0.1–1 nM) hyperpolarized a subset (∼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-1β 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-1β inhibits the activity of preoptic area/anterior hypothalamus neurons by increasing the presynaptic release of GABA.