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Am J Physiol Regul Integr Comp Physiol 282: R1762-R1772, 2002. First published February 7, 2002; doi:10.1152/ajpregu.00766.2001
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Vol. 282, Issue 6, R1762-R1772, June 2002

Site-specific modulation of LPS-induced fever and interleukin-1beta expression in rats by interleukin-10

Annemarie Ledeboer, Rob Binnekade, John J. P. Brevé, John G. J. M. Bol, Fred J. H. Tilders, and Anne-Marie Van Dam

Research Institute Neurosciences Free University, Department of Medical Pharmacology, VU University Medical Center, 1081 BT Amsterdam, The Netherlands


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Bacterial lipopolysaccharide (LPS) induces fever that is mediated by pyrogenic cytokines such as interleukin (IL)-1beta . We hypothesized that the anti-inflammatory cytokine IL-10 modulates the febrile response to LPS by suppressing the production of pyrogenic cytokines. In rats, intravenous but not intracerebroventricular infusion of IL-10 was found to attenuate fever induced by peripheral administration of LPS (10 µg/kg iv). IL-10 also suppressed LPS-induced IL-1beta production in peripheral tissues and in the brain stem. In contrast, central administration of IL-10 attenuated the febrile response to central LPS (60 ng/rat icv) and decreased IL-1beta production in the hypothalamus and brain stem but not in peripheral tissues and plasma. Furthermore, intravenous LPS upregulated expression of IL-10 receptor (IL-10R1) mRNA in the liver, whereas intracerebroventricular LPS enhanced IL-10R1 mRNA in the hypothalamus. We conclude that IL-10 modulates the febrile response by acting in the periphery or in the brain dependent on the primary site of inflammation and that its mechanism of action most likely involves inhibition of local IL-1beta production.

inflammation; brain; thermoregulation; endotoxin; cytokine


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

DURING SYSTEMIC INFLAMMATION, various brain-mediated responses occur as part of the acute phase reaction, including fever, sickness behavior, and activation of the hypothalamus-pituitary-adrenal (HPA) axis. Fever is a regulated rise in body temperature that is due to a change in the thermoregulatory setpoint (25). It is widely accepted that fever is controlled by thermosensitive neurons in the preoptic area of the anterior hypothalamus (POA). The febrile response to systemic inflammation involves the activation of blood monocytes and/or hepatic macrophages (Kupffer cells) by exogenous pyrogens, e.g., bacteria-derived lipopolysaccharide (LPS) or other endotoxins, which results in the production and release of cytokines such as interleukin-1beta (IL-1beta ), IL-6, and tumor necrosis factor-alpha (TNF-alpha ). These cytokines then act as endogenous pyrogens and signal, directly or indirectly, thermoregulatory neurons in the brain to initiate fever (reviewed in Ref. 25).

Cytokines produced outside the central nervous system (CNS) signal the brain by multiple routes, including humoral and neural pathways (53). Blood-borne cytokines may activate meningeal macrophages, cerebral endothelial cells, and perivascular microglial cells, thereby eliciting the local production of secondary mediators such as prostaglandin E2 and IL-6, which are implicated in fever (11, 17, 57). Circulating cytokines may also act on cells in circumventricular organs (CVOs) such as the organum vasculosum of the lamina terminalis and the area postrema (AP), which lack a functional blood-brain barrier (4, 48). The neurons located close to these CVOs innervate regions in the hypothalamus involved in thermoregulation. In addition, a role for the vagus nerve has been proposed in transmitting inflammatory signals from the periphery to the brain (21, 22, 42, 49, 61). Peripherally produced cytokines may activate vagal afferent nerves that innervate the nucleus of the solitary tract in the brain stem, from which catecholaminergic projections lead to the hypothalamus (5, 18, 50).

Because central administration of pyrogenic cytokines elicits fever in doses lower than those required after peripheral administration (12, 30, 31, 45), they are suggested to act within the brain. Indeed, irrespective of the exact signaling route, pyrogenic cytokines are produced in the brain following systemic LPS exposure. For instance, IL-1beta , TNF-alpha , and IL-6 mRNA and protein are expressed in microglial cells and/or neurons in the brain after peripheral administration of LPS (8, 9, 20, 28, 53, 54, 56). Furthermore, blocking the action of brain-derived IL-1beta or IL-6 by central administration of neutralizing antibodies to these cytokines (24, 46) or the IL-1 receptor antagonist (33) attenuates the febrile response to peripheral LPS, suggesting that these brain-derived cytokines play an instrumental role in the febrile response.

Production of pyrogenic cytokines by both peripheral macrophages and glial cells can be inhibited by IL-10 (29, 37, 58). Recent studies further show that IL-10 inhibits fever induced by systemic LPS administration in rats and mice (32, 36). Moreover, IL-10 knockout mice show exacerbated and prolonged febrile responses to LPS (32) and elevated TNF and IL-6 levels in the brain (1). These observations led us to hypothesize that IL-10, by acting on its receptor, may play a role in the control of fever by modulating cytokine production in peripheral organs and/or the brain.

The present study was designed to examine the role and site of action of IL-10 in the febrile response in rats. To elucidate target sites of IL-10, we compared the effects of central (intracerebroventricular) or peripheral (intravenous) administration of recombinant rat IL-10 (rrIL-10) on the febrile response to peripheral injection of LPS. In addition, we evaluated the effect of central administration of rrIL-10 on fever induced by central administration of LPS. To test the hypothesis that the effects of IL-10 on the febrile response involve modulation of the production of pyrogenic cytokines, we assessed the concentrations of IL-1beta , TNF-alpha , and IL-6 in plasma, peripheral tissues (liver, spleen, pituitary), and in the brain (hypothalamus and brain stem). To investigate site-specific expression and LPS-induced regulation of IL-10 receptors, we used quantitative RT-PCR to study mRNA expression of IL-10 receptor (IL-10R1; the ligand-binding chain) in the liver and hypothalamus. The present results show that IL-10 is a site-specific modulator of fever and can act either in the periphery and the brain by inhibiting local cytokine production.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Animals

Male Wistar rats (Harlan CPB, Horst, The Netherlands) were housed two per cage under controlled temperature (20-22°C) and light-dark conditions (lights on 7 AM, lights off 7 PM). Food and water were available ad libitum. At the time of the experiments, the animals had body weights of 250-300 g. To minimize stress-induced hyperthermia, rats were habituated to experimental procedures by noninvasive handling twice daily for 3 consecutive days before the experiments. The experimental protocol had been approved by the Institutional Committee for Animal Health and Care.

Materials

LPS (Escherichia coli serotype 0128-B12; Sigma, St. Louis, MO) was dissolved in sterile water, divided in aliquots, and stored at -20°C. Before administration, appropiate dilutions were made in sterile, pyrogen-free saline (Braun, Melsungen, Germany). rrIL-10 (National Institute for Biological Standards and Control, Potters Bar, UK) (2) was diluted in a vehicle of sterile, pyrogen-free saline containing 0.1% (wt/vol) BSA (fatty acid-free, low endotoxin; Sigma).

Surgical Procedures

Rats were anesthesized with ketamine (50 mg/kg im; Kombivet, Etten-Leur, The Netherlands) and xylazine (Rompun, 5 mg/kg ip; Bayer, Leverkusen, Germany), and a permanent cannula was implanted into the right jugular vein according to Steffens (52) for continuous intravenous infusion and/or repeated blood sampling. In other groups of animals, a permanent 22-gauge guide cannula with an indwelling dummy cannula (Plastics One, Roanoke, VA) was implanted into the right lateral ventricle of the brain at stereotaxic coordinates: 1.5 mm lateral to the midline, 0.6 mm posterior to bregma, and 3.7 mm under the brain surface. Simultaneously, a battery-operated, temperature-sensitive radiotransmitter (Data Sciences, St. Paul, MN) was implanted into the peritoneal cavity of all rats. After surgery, rats were individually housed in macrolon cages (20 × 30 × 40 cm) and were allowed to recover for at least 6 days.

Experimental Procedures

In a pilot experiment in which serial blood samples were taken from a chronically implanted jugular vein cannula in rats that were given rrIL-10 intravenously, plasma levels of IL-10 showed a first-order decline with a half-life of plasma IL-10 concentrations of ~6 min. Therefore, we decided to deliver IL-10 by continuous infusion to reach steady-state IL-10 concentrations rather than by bolus injection.

All experiments started between 8 and 10 AM. In rats with a cannula in the lateral ventricle, the dummy cannnula was replaced by a 28-gauge stainless steel injector (Plastics One) just before the experiment. Because pilot experiments revealed no differences in temperature responses between vehicle/saline-treated rats and IL-10/saline-treated rats (data not shown), the latter were used as control groups in further experiments.

In experiment 1, groups of rats (total n = 8-9) were given vehicle or rrIL-10 (4 µg · h-1 per rat) via continuous intravenous infusion to freely moving rats at a flow rate of 5 µl/min using a microsyringe infusion pump (Harvard Apparatus, South Natick, MA). Thirty minutes after start of the infusion, LPS (10 µg/kg, 500 µl/rat) was administered to the rats by intravenous injection via a lateral tail vein. The control group (n = 3) was given the same dose of IL-10, followed by saline (500 µl/rat iv). Animals from each LPS-treated group (n = 5-6) and the entire control group were killed by decapitation 5 h after the administration of LPS to determine cytokine levels in plasma and tissues. Trunk blood was collected in cold heparin-coated tubes (Sarstedt, Etten-Leur, The Netherlands) and subsequently centrifuged (4,000 g, 15 min, 4°C). Aliquots of plasma were stored at -20°C until assayed. Parts of liver and spleen, the pituitary, the hypothalamus region (containing the POA), and the dorsal part of the brain stem (containing the AP) were dissected immediately, frozen in liquid nitrogen, and stored at -80°C until processing.

In experiment 2, groups of rats (n = 4) were given vehicle or rrIL-10 (100, 300, or 600 ng · h-1 per rat) via continuous infusion to the lateral ventricle (flow rate 5 µl/h) in freely moving rats. LPS (10 µg/kg) or saline (500 µl/rat) was injected intravenously in rats via a lateral tail vein 15 min after start of the intracerebroventricular infusion with IL-10 or vehicle.

In experiment 3, groups of rats (n = 10-11) were given LPS (60 ng/rat) or saline (5 µl/rat during 10 min) into the lateral ventricle in freely moving rats, followed by continuous intracerebroventricular infusion of vehicle or rrIL-10 (600 ng · h-1 per rat) at a rate of 5 µl/h. Animals from each LPS-treated group (n = 3-4) were killed by decapitation 3.5 or 6 h after the administration of LPS to determine cytokine levels in plasma and tissues. Trunk blood and tissues were collected as described (experiment 1).

In experiments 1-3, the body temperature was monitored by telemetry every 15 min for 6-8 h following LPS injection. The output signals from each of the intraperitoneally implanted transmitters (frequency in Hz) were monitored by a receiver (Data Sciences) placed under each animal's cage, channelled into a consolidation matrix (BCM 100) connected to a PC, and converted to degrees Celsius (°C) by the processor.

In experiment 4, the expression of endogenous IL-10R1 mRNA was studied. Groups of rats (n = 3-4) were untreated (control group) or injected with LPS (100 µg/kg iv) via a lateral tail vein and killed by decapitation after 3, 8, and 24 h. Other groups of animals (n = 5) were injected with LPS (600 ng/rat icv) or saline (5 µl/rat) and killed by decapitation after 3 and 6 h. Liver and hypothalamus were dissected immediately, frozen in liquid nitrogen, and stored at -80°C until processing.

Tissue Processing

For cytokine assays, dissected brain regions, pituitary gland, and fragments of liver and spleen were homogenized for 5 min in 200-500 µl of Tris-buffered saline (pH 7.5) containing a protease inhibitor cocktail (Sigma) using a rotor-stator homogenizer (Heidolph Instruments, Schwabach, Germany). Homogenates were centrifuged (16,000 g, 15 min, 4°C), and the supernatants were used for the determination of cytokine levels. Before assay, all homogenates were diluted to a protein concentration of ~1 mg/ml as determined by means of a Bradford assay (7).

For quantitative RT-PCR, tissue fragments were homogenized in 250 µl RNA lysis buffer containing 2% beta -mercaptoethanol (Promega, Madison, WI) and used for isolation of total RNA.

Cytokine Assays

IL-1beta , IL-6, and TNF-alpha concentrations were measured in plasma and tissue homogenates using ELISAs specific for rat IL-1beta (47), rat IL-6 (40), and rat TNF-alpha (41), respectively. Detection limits of the assays in plasma were 10, 16, and 40 pg/ml for IL-1beta , IL-6, and TNF-alpha , respectively. Cytokine levels in homogenates are expressed as picograms per milligram protein (detection limits: 1.5 pg/mg protein for IL-1beta and 16 pg/mg protein for IL-6 and TNF-alpha ).

RNA Isolation and cDNA Synthesis

Total RNA was isolated from tissue homogenates using the SV Total RNA Isolation System (Promega) as described by the manufacturer. Concentration and purity of the RNA were determined by measuring the absorbance at 260 and 280 nm in a microtiter plate reader (ICN Biomedicals, Zoetermeer, The Netherlands). One microgram of RNA was reverse transcribed into cDNA using the Reverse Transcription System (Promega) with oligo-dT primers and AMV enzyme, according to the manufacturer's instructions. The RT reaction was carried out at 42°C for 45 min, followed by deactivation of the enzyme for 5 min at 99°C and 5 min at 4°C.

Real-Time Quantitative PCR

For quantitative PCR, the SYBR Green PCR Core reagents kit (Applied Biosystems, Foster City, CA) was used. Amplification of cDNA was performed in MicroAmp Optical 96-well Reaction Plates (Applied Biosystems) on an ABI PRISM 7700 Sequence Detection System (Applied Biosystems). The reaction mixture (20 µl) was composed of 1× SYBR Green buffer, 3 mM MgCl2, 875 µM dNTP mixed with dUTP, 0.3 U AmpliTaq Gold, 0.12 U Amperase UNG, 15 pmol of each primer, 12.5 ng cDNA and nuclease-free H2O. The primers for rat IL-10R1 were 5'-CTGGTCACCCTGCCATTGAT-3' (forward) and 5'-AGGCATGGCTAAAATACAAAGAAAC-3' (reverse) (60) and for rat glyceraldehyde-3-phosphate dehydrogenase (GAPDH) 5'-GAACATCATCCCTGCATCCA-3' (forward) and 5'-CCAGTGAGCTTCCCG-TTCA-3' (reverse). The reaction conditions were an initial 2 min at 50°C, followed by 10 min at 95°C and 40 cycles of 15 s at 95°C and 1 min at 59°C. The levels of IL-10R1 mRNA expression were quantified relatively to the level of the housekeeping gene GAPDH using the following calculation: 2-(thresholdcycleoftargetmRNA-thresholdcycleofGAPDHmRNA) × 100.

Statistical Analysis

Body temperature data were analyzed by ANOVA for repeated measurements with treatment as the between-subject factor and time as the within-subject factor. Post hoc time-matched comparisons between groups were carried out by Fisher's least significant difference (LSD) multiple comparison test. ELISA and quantitative PCR data were analyzed by one- or two-way ANOVA, followed by Fisher's LSD test. If necessary, data were log-transformed before analysis. Parameters that could not be transformed to meet criteria of ANOVA were tested nonparametrically by the Mann-Whitney U-test. Correlations were analyzed using the Pearson correlation test. P values <0.05 were considered to indicate a significant difference. The statistical evaluation was carried out by using the NCSS 2000 statistical program.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Experiment 1

Effects of intravenous IL-10 on intravenous LPS-induced fever. Figure 1 shows the changes in body (core) temperature (Tc) in rats chronically infused with vehicle or rrIL-10 (4 µg · h-1 per rat iv) after intravenous injection with LPS or saline. Before LPS injection (-30 and -15 min), the body temperature was not different between the groups (basal value ~37.4°C). The transient increase in Tc observed 15-30 min after LPS injection represents stress-induced hyperthermia induced by the intravenous administration of LPS. Subsequently, Tc of IL-10/saline-injected rats returned to basal values and remained ~37°C. Tc from vehicle/LPS-injected rats tended to drop 60-90 min after LPS injection and subsequently shows a typical biphasic febrile response, a first phase peaking ~2.5-3 h after LPS injection (rise in Tc ~0.6°C compared with basal values) and a second phase peaking after 5-7 h (rise in Tc ~1.3°C). Chronic infusion with IL-10 significantly inhibited the second hyperthermic phase but not the first hyperthermic phase. In addition, IL-10 resulted in higher Tc 75-105 min after LPS, compared with the vehicle/LPS group.


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  		Fig. 1.   Peripheral administration of interleukin (IL)-10 attenuates the febrile response to peripheral lipopolysaccharide (LPS). Groups of rats were infused with vehicle or recombinant rat IL-10 (rrIL-10) (4 µg · h-1 per rat iv) throughout the experiment. Arrow indicates start of infusion. LPS (10 µg/kg) or saline was given as intravenous bolus at t = 0 h. At 5 h after LPS injection, some animals were killed for tissue collection (see MATERIALS AND METHODS). Data are means ± SE (LPS groups, n = 8-9). * P < 0.05 vehicle/LPS vs. IL-10/LPS.

Effects of intravenous IL-10 on intravenous LPS-induced cytokine levels in peripheral and brain tissues. At 5 h after injection of LPS, when Tc is rising, IL-1beta protein was detected in plasma and various tissue homogenates of rats (Fig. 2). In plasma and tissues of IL-10/saline-treated rats, IL-1beta was undetectable or detected at very low levels, except for liver and spleen. LPS markedly increased IL-1beta protein levels in plasma compared with IL-10/saline-treated rats (~63-fold). Chronic intravenous infusion with IL-10 significantly reduced plasma IL-1beta levels 5 h after LPS administration. In the liver, spleen, and pituitary gland, LPS elevated IL-1beta levels ~6-, 4-, and 12-fold, respectively, and infusion with IL-10 reduced IL-1beta levels in the liver and pituitary gland but not in the spleen.


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  		Fig. 2.   Effect of peripheral administration of IL-10 on tissue levels of IL-1beta following peripheral administration of LPS. IL-1beta concentrations were measured in plasma (A), liver (B), spleen (C), pituitary gland (D), hypothalamus (E), and brain stem (F). Rats were infused with vehicle or rrIL-10 (4 µg · h-1 per rat iv) throughout the experiment. LPS (10 µg/kg iv) or saline was given 30 min after start of the infusion, and rats were killed 5 h later. Data are means ± SE (n = 3-6). * P < 0.05, ** P < 0.01 vs. IL-10/saline group; #P < 0.05, ##P < 0.01 vs. vehicle/LPS group.

In the brain, IL-1beta levels were markedly increased by LPS in the brain stem (~26-fold) but not in the hypothalamus. IL-10 infusion blocked the rise in brain stem IL-1beta levels but had no effect on IL-1beta levels in the hypothalamus.

IL-6 plasma levels in rats of the vehicle/LPS group were 76 ± 29 pg/ml, whereas levels in rats of the IL-10/saline and IL-10/LPS groups were below detection limit of the assay (15 pg/ml). TNF-alpha was only detectable in plasma of four of six rats in the vehicle/LPS group (108 ± 29 pg/ml), and levels in rats of the other groups were below detection limit of the assay (40 pg/ml). Thus IL-10 reduced both IL-6 and TNF-alpha levels in plasma (Mann-Whitney U-test, P < 0.01 and P < 0.05, respectively). In all tissue homogenates, TNF-alpha and IL-6 levels were below detection limits (16 pg/mg protein).

As illustrated in Fig. 6A, cytokine concentrations in plasma and hypothalamus of individual rats were plotted against their Tc at time of death. Within both the vehicle/LPS and IL-10/LPS groups, positive correlations were found between IL-1beta plasma levels and Tc 5 h after LPS injection (Pearson correlation coefficients 0.76 and 0.85, respectively). Pooled data from both groups showed a significant positive correlation (coefficient 0.86, P < 0.01). In addition, positive but not significant correlations were observed between Tc and plasma IL-6 and TNF-alpha levels in the vehicle/LPS group (coefficients 0.68 and 0.72, respectively). Thus, after peripheral administration of LPS, levels of IL-1beta and possibly other cytokines in plasma, but not in the hypothalamus, are determinants of the hyperthermic response.

Experiment 2

Effects of intracerebroventricular IL-10 on intravenous LPS-induced fever. The febrile response to peripheral (intravenous) administration of LPS showed similar kinetics as described for experiment 1. Central administration of IL-10 by continuous intracerebroventricular infusion at doses of 100, 300, and 600 ng/rat throughout the experiment did not affect the febrile response induced by intravenous LPS injection. Data of experiments with the IL-10 doses of 100 and 300 ng/rat are not shown. Data of the experiment with the dose of 600 ng/rat are illustrated in Fig. 3.


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  		Fig. 3.   Central administration of IL-10 does not affect the febrile response to peripheral LPS. Groups of rats were infused with vehicle or rrIL-10 (600 ng · h-1 per rat icv) throughout the experiment. Arrow indicates start of infusion. LPS (10 µg/kg) or saline was given as intravenous bolus at t = 0 h. Data are means ± SE (n = 4).

Experiment 3

Effects of intracerebroventricular IL-10 on intracerebroventricular LPS-induced fever. Figure 4 shows the changes in Tc in rats given vehicle or rrIL-10 (600 ng/rat) by intracerebroventricular infusion throughout the experiment, after intracerebroventricular injection with LPS or saline. The febrile response to intracerebroventricular LPS consisted of a typical single hyperthermic phase (rise in Tc ~1.5°C), with onset at ~60 min and peaking around 3-4 h after LPS injection, whereas IL-10/saline-infused animals did not show any hyperthermia. The febrile response was significantly attenuated in the IL-10/LPS-treated group compared with the vehicle/LPS-treated group.


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  		Fig. 4.   Central administration of IL-10 attenuates the febrile response to central LPS. Groups of rats were infused with vehicle or rrIL-10 (600 ng · h-1 per rat icv) throughout the experiment. Arrow indicates start of infusion. LPS (60 ng/rat) or saline was given intracerebroventricularly at t = 0 h. Data are means ± SE (n = 10-11). * P < 0.05 vehicle/LPS vs. IL-10/LPS.

Effects of intracerebroventricular IL-10 on intracerebroventricular LPS-induced cytokine levels in peripheral and brain tissues. IL-1beta levels were detected in various tissue homogenates of rats killed 3.5 and 6 h after administration of LPS, at the peak and at the end of the febrile response, respectively (Fig. 5). Plasma levels of IL-1beta remained below detection limit of the assay (10 pg/ml). In the liver, spleen, and pituitary gland, no marked differences in IL-1beta concentrations were observed between vehicle/LPS- and IL-10/LPS-infused rats. In the hypothalamus, IL-10 infusion significantly reduced IL-1beta levels at 3.5 and 6 h after LPS administration by more than twofold. In the brain stem, IL-1beta levels in IL-10/LPS-infused rats were markedly lower (~6-fold) than those in vehicle/LPS-infused rats at 6 h after LPS injection.


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  		Fig. 5.   Effect of central administration of IL-10 on tissue levels of IL-1beta following central administration of LPS. IL-1beta concentrations were measured in plasma (A), liver (B), spleen (C), pituitary gland (D), hypothalamus (E), and brain stem (F). Rats were infused with vehicle or rrIL-10 (600 ng · h-1 per rat icv) throughout the experiment. LPS (60 ng/rat icv) was given before start of infusion, and rats were killed 3.5 or 6 h later. Data are means ± SE (n = 3-4). #P < 0.05, ##P < 0.01 vs. vehicle/LPS group. dl, All values below detection limit.

No significant differences were observed in IL-6 and TNF-alpha levels in plasma and tissue homogenates of vehicle/LPS-treated rats compared with those in IL-10/LPS-treated rats (data not shown).

Figure 6B shows the correlations between IL-1beta concentrations in plasma and hypothalamus of individual rats with their body temperature at 3.5 h after central LPS administration. Within the vehicle/LPS and IL-10/LPS groups, positive correlations were found between IL-1beta levels in the hypothalamus and Tc (correlation coefficients 0.95 and 0.77, respectively). Pooled data from both groups showed a significant positive correlation (coefficient 0.91, P < 0.05), demonstrating that expression levels of IL-1beta in the hypothalamus, but not in plasma, are determinants of the hyperthermic response to central administration of LPS.


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  		Fig. 6.   Scatterplots of IL-1beta concentrations in plasma and hypothalamus vs. body temperatures at time of death of individual rats. A: 5 h after peripheral administration of LPS (data derived from experiment 1, see Figs. 1 and 2 legends for details). Body temperature correlates with plasma IL-1 concentrations (Pearson correlation coefficient = 0.86, P < 0.01) but not with hypothalamic IL-1. B: 3.5 h after central administration of LPS (data derived from experiment 3, see Figs. 4 and 5 legends for details). Body temperature correlates with hypothalamic IL-1 concentrations (Pearson correlation coefficient = 0.91, P < 0.05) but not with plasma IL-1.

Experiment 4

IL-10R1 mRNA expression in liver and hypothalamus. To investigate LPS-induced changes in expression levels of IL-10R1 mRNA, rats were given LPS (100 µg/kg iv) for 3, 8, and 24 h, and expression was studied in liver and hypothalamus by quantitative RT-PCR. As illustrated in Fig. 7A, IL-10R1 mRNA expression in the liver was upregulated 3 h after peripheral administration of LPS and still elevated after 24 h, compared with control rats. In contrast, IL-10R1 mRNA levels in the hypothalamus were not affected by LPS treatment at any of the time intervals studied.


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  		Fig. 7.   Kinetics of expression levels of IL-10 receptor (IL-10R1) mRNA in liver and hypothalamus of rats after peripheral (A) and central (B) administration of LPS. A: groups of rats (n = 3-4) were untreated (0 h) or killed 3, 8, and 24 h after LPS injection (100 µg/kg iv). B: groups of rats (n = 5) were injected with saline (0 h) or killed 3 and 6 h after LPS injection (600 ng/rat icv). Data are means ± SE. * P < 0.05, ** P < 0.01 vs. 0 h.

After central administration of LPS (600 ng/rat icv), IL-10R1 mRNA expression in the hypothalamus was significantly enhanced at 3 and 6 h after LPS, compared with control (saline injected) rats (Fig. 7B). IL-10R1 mRNA levels in the liver were not affected by central LPS administration.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

In the present study, we demonstrate that IL-10 can attenuate the febrile response to LPS both by acting in the CNS and in peripheral targets, depending on the site of the primary inflammatory response. Thus peripheral administration of IL-10 markedly attenuated the febrile response to peripheral LPS and inhibited LPS-induced production of the endogenous pyrogen IL-1beta in peripheral tissues and the brain stem but not in the hypothalamus. Conversely, central administration of IL-10 attenuated the hyperthermic response to central, but not to peripheral, LPS and inhibited IL-1beta production in the hypothalamus and brain stem but not in peripheral tissues.

Our findings that intravenous infusion of IL-10 inhibits the febrile response of rats to intravenously given LPS are consistent with previous data of mice given LPS by an intraperitoneal route (32). The present data show that IL-10 prevents the tendency of the body temperature to drop shortly after intravenous LPS administration, which may be reminiscent of the hypothermic phase reported after higher doses of LPS (13, 42). Because the LPS-induced hypothermia depends on macrophage-derived factors, including cytokines and prostaglandins (13, 59), we speculate that IL-10 may prevent the initial tendency to hypothermia by suppressing cytokine levels, as seen in mice (32). The data further show that the second phase of the hyperthermic response is selectively attenuated by circulating IL-10. This cryogenic effect of IL-10 is correlated with decreased levels of circulating IL-1beta , TNF-alpha , and IL-6 in plasma and supports the concept that suppression of circulating levels of IL-1beta and other pyrogenic cytokines attenuates the late phase of the febrile response (43, 44). In contrast, the first hyperthermic phase is not affected by IL-10 infusion and is therefore probably controlled by mechanisms different from those involved in the late phase.

Interestingly, the suppressing effect of IL-10 on fever is also associated with decreased concentrations of IL-1beta in the liver and the pituitary gland. Presumably, IL-1beta production by macrophages in these structures, in particular Kupffer cells in the liver (14), contributes to circulating IL-1beta levels. Thus the IL-10-mediated decrease in IL-1beta levels in plasma may reflect impaired production by blood monocytes and/or by tissue macrophages and may lead to reduced humoral signaling of IL-1beta to the brain. By suppressing IL-1beta concentrations in the liver, IL-10 may also affect fever by interfering with the neural route of signaling of IL-1beta . If hepatic IL-1beta is indeed involved in vagal afferent signaling, reduced production of intrahepatic IL-1beta may lead to a decreased activation of neurons in the lower brain stem and, consequently, to reduced actions of these neurons on thermoregulatory mechanisms in the hypothalamus (5, 50). In the pituitary gland, IL-1beta is produced by various endocrine and nonendocrine cells with activation by peripheral LPS (3, 55). Its local actions involve modulation of the secretion of a variety of hormones that are primarily under control of the hypothalamus (3). IL-10-induced downregulation of intrapituitary IL-1beta production may therefore have neuroendocrine implications, e.g., regulation of the HPA axis (51).

The present results further show that the brain stem represents a target for circulating IL-10. The effects of circulating IL-10 are most likely due to actions in the AP, a CVO that lacks a blood-brain barrier and is thereby easily accessible for endotoxins but also for cytokines in the bloodstream. Indeed, IL-1beta -immunoreactive cells have been found in the AP of rats 5 h after intravenous injection of this low dose of LPS (unpublished observations) that may represent microglial cells (55). Because IL-1 receptor type I mRNA is present in the AP (19), this brain structure not only produces IL-1beta but likely also expresses the receptors that are necessary to mediate its effects. Therefore, we postulate that the local inhibitory action of IL-10 on IL-1beta production in the AP may contribute to a diminished neural input to thermoregulatory centers in the hypothalamus and thereby inhibit the febrile response.

In the hypothalamus, IL-1beta concentrations were not affected by LPS, which is somewhat surprising as IL-1beta mRNA has been demonstrated in CVOs after administration of LPS (38). It probably relates to the low dose of LPS (10 µg/kg) used in the present study and/or the time interval studied. This may also explain the absence of detectable levels of TNF-alpha and IL-6 in tissue homogenates under these conditions.

Taken together, our findings suggest that peripherally administered IL-10 attenuates LPS-induced fever by inhibiting the production of pyrogenic cytokines in peripheral tissues and the brain stem and, consequently, interferes with humoral or neural signaling routes of these cytokines to the brain.

Strong IL-1beta production in the hypothalamus and brain stem was seen after central administration of LPS, i.e., when the primary inflammatory response is generated within the CNS. This is in accordance with the induction of IL-1beta mRNA and bioactivity in the CNS after intracerebroventricular LPS (15, 23, 39). Correlation analysis revealed that IL-1beta production in the hypothalamus is associated with a febrile response, which shows kinetics different from that observed after peripheral LPS (10, 35, present study). Interestingly, both the febrile response following central LPS and IL-1beta levels in the hypothalamus, but not in peripheral organs, were attenuated by central administration of IL-10, which is in agreement with findings in mice (16). In addition to the antipyretic effect, central administration of IL-10 also antagonized the effects of intracerebroventricular LPS on social exploratory behavior and body weight (6). Taken together, our data support the concept that brain-derived IL-1beta is involved in fever (33) and possibly other sickness symptoms induced by central administration of LPS.

From the preceding observations, we conclude that a local action of IL-10 may be required to have an effect on body temperature under the conditions used. It is thus conceivable that central administration of IL-10, at doses up to 600 ng/rat, does not affect the febrile response to peripherally injected LPS, as central IL-10 does not affect IL-1beta production in peripheral tissues, most likely because it does not reach such peripheral targets in sufficient concentrations.

The observed effects of exogenous IL-10 on fever implicate the presence of functional IL-10 receptors. Indeed, IL-10R1 mRNA is constitutively expressed both in peripheral organs (e.g., the liver) and in the hypothalamus. To test the hypothesis that IL-10 receptor expression is regulated at specific sites depending on the route of LPS administration, relatively high doses of LPS, but relevant for fever (33, 42), were administered peripherally or centrally. Interestingly, peripheral administration of LPS enhances IL-10R1 mRNA levels in the liver but not in the hypothalamus. Conversely, central LPS administration upregulated IL-10R1 mRNA expression in the hypothalamus but not in the liver. Although we cannot exclude the possibility that lower LPS doses as used in the fever studies regulate IL-10R1 expression to a lesser extent, the results indicate that LPS-induced IL-10 receptor modulation is site specific. This local (transient) upregulation of IL-10 receptors may further facilitate and/or amplify the inhibitory actions of IL-10. The presumed cellular sources of IL-10 receptors in the liver are Kupffer cells (27), in which IL-10 has been shown to inhibit IL-6 production and its own mRNA expression (26, 27). In the hypothalamus, IL-10 acts most likely on glial cells that are known to exhibit IL-10 receptors (34, unpublished observations), and IL-10 has been shown to be capable of inhibiting IL-1beta production in glial cells in vitro (29).

In conclusion, our data show that IL-10 can modulate brain-mediated fever in response to low doses of LPS. Whether it indeed does so seems dependent on IL-10 reaching its receptors in the compartment where the primary inflammatory response is initiated. The mechanisms mediating the site-specific, antipyretic effects of IL-10 relate to suppression of the production of pyrogenic cytokines, notably IL-1beta . Although our data show that IL-10 in the brain can attenuate the production of IL-1beta by brain cells, we propose that this mechanism plays a limited role in peripheral inflammation but may become crucial in conditions of infections or inflammation of the CNS, such as meningitis, encephalitis, or trauma.


    ACKNOWLEDGEMENTS

The authors thank Dr. A. B. Smit (Research Institute Neurosciences, Department of Molecular and Cellular Neurobiology, Faculty of Biology, Free University Amsterdam) for allowing the use of the ABI PRISM 7700 Sequence Detection System and Dr. A. A. Romanovsky (Trauma Research, St. Joseph's Hospital and Medical Center, Phoenix, AZ) for valuable comments. rrIL-10 and reagents for measurement of rat IL-1beta , TNF-alpha , and IL-6 were kindly provided by Dr. S. Poole and Dr. A. F. Bristow (National Institute for Biological Standards and Control, Division of Endocrinology, Potters Bar, UK).


    FOOTNOTES

This study was supported by the Janssen Research Foundation and the Biomed II program (PL-96-2492) (to A. Ledeboer) and Netherlands Organization for Scientific Research Grant 903-50-240 (to A-M. Van Dam).

Address for reprint requests and other correspondence: A-M. Van Dam, Research Institute Neurosciences Free Univ., Dept. of Medical Pharmacology, VU Medical Center, Van der Boechorststraat 7, 1081 BT, Amsterdam, The Netherlands (E-mail: amw.van_dam.pharm{at}med.vu.nl).

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

First published February 7, 2002;10.1152/ajpregu.00766.2001

Received 28 December 2001; accepted in final form 1 February 2002.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Agnello, D, Villa P, and Ghezzi P. Increased tumor necrosis factor and interleukin-6 production in the central nervous system of interleukin-10-deficient mice. Brain Res 869: 241-243, 2000[ISI][Medline].

2.   Ball, C, Vigues S, Gee CK, Poole S, and Bristow AF. Rat interleukin-10: production and characterisation of biologically active protein in a recombinant bacterial expression system. Eur Cytokine Netw 12: 187-193, 2001[ISI][Medline].

3.   Besedovsky, HO, and del Rey A. Immune-neuro-endocrine interactions: facts and hypotheses. Endocr Rev 17: 64-102, 1996[ISI][Medline].

4.   Blatteis, CM. Role of the OVLT in the febrile response to circulating pyrogens. Prog Brain Res 91: 409-412, 1992[ISI][Medline].

5.   Blatteis, CM, and Sehic E. Fever: how may circulating pyrogens signal the brain? News Physiol Sci 12: 1-9, 1997[Abstract/Free Full Text].

6.   Bluthé, R, Castanon N, Pousset F, Bristow A, Ball C, Lestage J, Michaud B, Kelley KW, and Dantzer R. Central injection of IL-10 antagonizes the behavioural effects of lipopolysaccharide in rats. Psychoneuroendocrinology 24: 301-311, 1999[ISI][Medline].

7.   Bradford, MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem 72: 248-254, 1976[ISI][Medline].

8.   Breder, CD, Hazuka C, Ghayur T, Klug C, Huginin M, Yasuda K, Teng M, and Saper CB. Regional induction of tumor necrosis factor alpha  expression in the mouse brain after systemic lipopolysaccharide administration. Proc Natl Acad Sci USA 91: 11393-11397, 1994[Abstract/Free Full Text].

9.   Buttini, M, and Boddeke H. Peripheral lipopolysaccharide stimulation induces interleukin-1beta messenger RNA in rat brain microglial cells. Neuroscience 65: 523-530, 1995[ISI][Medline].

10.   Cao, C, Matsumura K, Ozaki M, and Watanabe Y. Lipopolysaccharide injected into the cerebral ventricle evokes fever through induction of cyclooxygenase-2 in brain endothelial cells. J Neurosci 19: 716-725, 1999[Abstract/Free Full Text].

11.   Cao, C, Matsumura K, Yamagata K, and Watanabe Y. Induction by lipopolysaccharide of cyclooxygenase-2 mRNA in rat brain; its possible role in the febrile response. Brain Res 697: 187-196, 1995[ISI][Medline].

12.   Dascombe, MJ, Rothwell NJ, Sagay BO, and Stock MJ. Pyrogenic and thermogenic effects of interleukin-1beta in the rat. Am J Physiol Endocrinol Metab 256: E7-E11, 1989[Abstract/Free Full Text].

13.   Derijk, RH, Van Kampen M, Van Rooijen N, and Berkenbosch F. Hypothermia to endotoxin involves reduced thermogenesis, macrophage-dependent mechanisms, and prostaglandins. Am J Physiol Regulatory Integrative Comp Physiol 266: R1-R8, 1994[Abstract/Free Full Text].

14.   Derijk, R, Van Rooijen N, Tilders FJ, Besedovsky HO, Del Rey A, and Berkenbosch F. Selective depletion of macrophages prevents pituitary-adrenal activation in response to subpyrogenic, but not to pyrogenic, doses of bacterial endotoxin in rats. Endocrinology 129: 330-338, 1991[Abstract].

15.   De Simoni, MG, Del Bo R, De Luigi A, Simard S, and Forloni G. Central endotoxin induces different patterns of interleukin (IL)-1beta and IL-6 messenger ribonucleic acid expression and IL-6 secretion in the brain and periphery. Endocrinology 136: 897-902, 1995[Abstract].

16.   Di Santo, E, Sironi M, Pozzi P, Gnocchi P, Isetta AM, Delvaux A, Goldman M, Marchant A, and Ghezzi P. Interleukin-10 inhibits lipopolysaccharide-induced tumor necrosis factor and interleukin-1beta production in the brain without affecting the activation of the hypothalamus-pituitary-adrenal axis. Neuroimmunomodulation 2: 149-154, 1995[ISI][Medline].

17.   Elmquist, JK, Breder CD, Sherin JE, Scammell TE, Hickey WF, Dewitt D, and Saper CB. Intravenous lipopolysaccharide induces cyclooxygenase 2-like immunoreactivity in rat brain perivascular microglia and meningeal macrophages. J Comp Neurol 381: 119-129, 1997[ISI][Medline].

18.   Ericsson, A, Kovacs KJ, and Sawchenko PE. A functional anatomical analysis of central pathways subserving the effects of interleukin-1 on stress-related neuroendocrine neurons. J Neurosci 14: 897-913, 1994[Abstract].

19.   Ericsson, A, Liu C, Hart RP, and Sawchenko PE. Type 1 interleukin-1 receptor in the rat brain: distribution, regulation, and relationship to sites of IL-1-induced cellular activation. J Comp Neurol 361: 681-698, 1995[ISI][Medline].

20.   Gatti, S, and Bartfai T. Induction of tumor necrosis factor-alpha mRNA in the brain after peripheral endotoxin treatment: comparison with interleukin-1 family and interleukin-6. Brain Res 624: 291-294, 1993[ISI][Medline].

21.   Gaykema, RP, Dijkstra I, and Tilders FJ. Subdiaphragmatic vagotomy suppresses endotoxin-induced activation of hypothalamic corticotropin-releasing hormone neurons and ACTH secretion. Endocrinology 136: 4717-4720, 1995[Abstract].

22.   Goldbach, JM, Roth J, and Zeisberger E. Fever suppression by subdiaphragmatic vagotomy in guinea pigs depends on the route of pyrogen administration. Am J Physiol Regulatory Integrative Comp Physiol 272: R675-R681, 1997[Abstract/Free Full Text].

23.   Ilyin, SE, Gayle D, Flynn MC, and Plata-Salaman CR. Interleukin-1beta system (ligand, receptor type I, receptor accessory protein and receptor antagonist), TNF-alpha , TGF-beta 1 and neuropeptide Y mRNAs in specific brain regions during bacterial LPS-induced anorexia. Brain Res Bull 45: 507-515, 1998[ISI][Medline].

24.   Klir, JJ, McClellan JL, and Kluger MJ. Interleukin-1beta causes the increase in anterior hypothalamic interleukin-6 during LPS-induced fever in rats. Am J Physiol Regulatory Integrative Comp Physiol 266: R1845-R1848, 1994[Abstract/Free Full Text].

25.   Kluger, MJ. Fever: role of pyrogens and cryogens. Physiol Rev 71: 93-127, 1991[Abstract].

26.   Knolle, PA, Loser E, Protzer U, Duchmann R, Schmitt E, zum Buschenfelde KH, Rose-John S, and Gerken G. Regulation of endotoxin-induced IL-6 production in liver sinusoidal endothelial cells and Kupffer cells by IL-10. Clin Exp Immunol 107: 555-561, 1997[ISI][Medline].

27.   Knolle, PA, Uhrig A, Protzer U, Trippler M, Duchmann R, Meyer zum Buschenfelde KH, and Gerken G. Interleukin-10 expression is autoregulated at the transcriptional level in human and murine Kupffer cells. Hepatology 27: 93-99, 1998[ISI].

28.   Laye, S, Parnet P, Goujon E, and Dantzer R. Peripheral administration of lipopolysaccharide induces the expression of cytokine transcripts in the brain and pituitary of mice. Brain Res Mol Brain Res 27: 157-162, 1994[Medline].

29.   Ledeboer, A, Brevé JJP, Poole S, Tilders FJH, and Van Dam AM. Interleukin-10, interleukin-4 and transforming growth factor-beta differentially regulate lipopolysaccharide-induced production of proinflammatory cytokines and nitric oxide in co-cultures of rat astroglial and microglial cells. Glia 30: 134-142, 2000[ISI][Medline].

30.   LeMay, LG, Vander AJ, and Kluger MJ. Role of interleukin 6 in fever in rats. Am J Physiol Regulatory Integrative Comp Physiol 258: R798-R803, 1990[Abstract/Free Full Text].

31.   Lenczowski, MJ, Bluthe RM, Roth J, Rees GS, Rushforth DA, van Dam AM, Tilders FJ, Dantzer R, Rothwell NJ, and Luheshi GN. Central administration of rat IL-6 induces HPA activation and fever but not sickness behavior in rats. Am J Physiol Regulatory Integrative Comp Physiol 276: R652-R658, 1999[Abstract/Free Full Text].

32.   Leon, LR, Kozak W, Rudolph K, and Kluger MJ. An antipyretic role for interleukin-10 in LPS fever in mice. Am J Physiol Regulatory Integrative Comp Physiol 276: R81-R89, 1999[Abstract/Free Full Text].

33.   Luheshi, G, Miller AJ, Brouwer S, Dascombe MJ, Rothwell NJ, and Hopkins SJ. Interleukin-1 receptor antagonist inhibits endotoxin fever and systemic interleukin-6 induction in the rat. Am J Physiol Endocrinol Metab 270: E91-E95, 1996[Abstract/Free Full Text].

34.   Mizuno, T, Sawada M, Marunouchi T, and Suzumura A. Production of interleukin-10 by mouse glial cells in culture. Biochem Biophys Res Commun 205: 1907-1915, 1994[ISI][Medline].

35.   Morimoto, A, Murakami N, Nakamori T, and Watanabe T. Evidence for separate mechanisms of induction of biphasic fever inside and outside the blood-brain barrier in rabbits. J Physiol 383: 629-637, 1987[Abstract/Free Full Text].

36.   Nava, F, Calapai G, Facciolá G, Cuzzocrea S, Marciano MC, De Sarro A, and Caputi AP. Effects of interleukin-10 on water intake, locomotory activity, and rectal temperature in rat treated with endotoxin. Int J Immunopharmacol 19: 31-38, 1997[ISI][Medline].

37.   Pousset, F, Cremona S, Dantzer R, Kelley K, and Parnet P. Interleukin-4 and interleukin-10 regulate IL-1beta induced mouse primary astrocyte activation. Glia 26: 12-21, 1999[ISI][Medline].

38.   Quan, N, Stern EL, Whiteside MB, and Herkenham M. Induction of pro-inflammatory cytokine mRNAs in the brain after peripheral injection of subseptic doses of lipopolysaccharide in the rat. J Neuroimmunol 93: 72-80, 1999[ISI][Medline].

39.   Quan, N, Sundar SK, and Weiss JM. Induction of interleukin-1 in various brain regions after peripheral and central injections of lipopolysaccharide. J Neuroimmunol 49: 125-134, 1994[ISI][Medline].

40.   Rees, GS, Ball C, Ward HL, Gee CK, Tarrant G, Mistry Y, Poole S, and Bristow AF. Rat interleukin 6: expression in recombinant Escherichia coli, purification and development of a novel ELISA. Cytokine 11: 95-103, 1999[ISI][Medline].

41.   Rees, GS, Gee CK, Ward HL, Ball C, Tarrant GM, Poole S, and Bristow AF. Rat tumour necrosis factor-alpha : expression in recombinant Pichia pastoris, purification, characterization and development of a novel ELISA. Eur Cytokine Netw 10: 383-392, 1999[ISI][Medline].

42.   Romanovsky, AA, Simons CT, Szekely M, and Kulchitsky VA. The vagus nerve in the thermoregulatory response to systemic inflammation. Am J Physiol Regulatory Integrative Comp Physiol 273: R407-R413, 1997[Abstract/Free Full Text].

43.   Roth, J, and de Souza GEP Fever induction pathways: evidence from responses to systemic or local cytokine formation. Braz J Med Biol Res 34: 301-314, 2001[ISI][Medline].

44.   Roth, J, Martin D, Storr B, and Zeisberger E. Neutralization of pyrogen-induced tumour necrosis factor by its type 1 soluble receptor in guinea-pigs: effects on fever and interleukin-6 release. J Physiol 509: 267-275, 1998[Abstract/Free Full Text].

45.   Rothwell, NJ. Central effects of TNF alpha  on thermogenesis and fever in the rat. Biosci Rep 8: 345-352, 1988[ISI][Medline].

46.   Rothwell, NJ, Busbridge NJ, Lefeuvre RA, Hardwick AJ, Gauldie J, and Hopkins SJ. Interleukin-6 is a centrally acting endogenous pyrogen in the rat. Can J Physiol Pharmacol 69: 1465-1469, 1991[ISI][Medline].

47.   Safieh-Garabedian, B, Poole S, Allchorne A, Winter J, and Woolf CJ. Contribution of interleukin-1beta to the inflammation-induced increase in nerve growth factor levels and inflammatory hyperalgesia. Br J Pharmacol 115: 1265-1275, 1995[ISI][Medline].

48.   Saper, CB, and Breder CD. The neurologic basis of fever. N Engl J Med 330: 1880-1886, 1994[Free Full Text].

49.   Sehic, E, and Blatteis CM. Blockade of lipopolysaccharide-induced fever by subdiaphragmatic vagotomy in guinea pigs. Brain Res 726: 160-166, 1996[ISI][Medline].

50.   Simons, CT, Kulchitsky VA, Sugimoto N, Homer LD, Szekely M, and Romanovsky AA. Signaling the brain in systemic inflammation: which vagal branch is involved in fever genesis? Am J Physiol Regulatory Integrative Comp Physiol 275: R63-R68, 1998[Abstract/Free Full Text].

51.   Smith, EM, Cadet P, Stefano GB, Opp MR, and Hughes TK, Jr. IL-10 as a mediator in the HPA axis and brain. J Neuroimmunol 100: 140-148, 1999[ISI][Medline].

52.   Steffens, AB. A method for frequent sampling in blood continuous infusion of liquids of fluids in the rats without disturbing the animal. Physiol Behav 4: 833-839, 1969.

53.   Tilders, FJ, DeRijk RH, Van Dam AM, Vincent VA, Schotanus K, and Persoons JH. Activation of the hypothalamus-pituitary-adrenal axis by bacterial endotoxins: routes and intermediate signals. Psychoneuroendocrinology 19: 209-232, 1994[ISI][Medline].

54.   Vallieres, L, and Rivest S. Regulation of the genes encoding interleukin-6, its receptor, and gp130 in the rat brain in response to the immune activator lipopolysaccharide and the proinflammatory cytokine interleukin-1beta . J Neurochem 69: 1668-1683, 1997[ISI][Medline].

55.   Van Dam, AM, Bol JG, Gaykema RP, Goehler LE, Maier SF, Watkins LR, and Tilders FJ. Vagotomy does not inhibit high dose lipopolysaccharide-induced interleukin-1beta immunoreactivity in rat brain and pituitary gland. Neurosci Lett 285: 169-172, 2000[ISI][Medline].

56.   Van Dam, AM, Brouns M, Louisse S, and Berkenbosch F. Appearance of interleukin-1 in macrophages and in ramified microglia in the brain of endotoxin-treated rats: a pathway for the induction of non-specific symptoms of sickness? Brain Res 588: 291-296, 1992[ISI][Medline].

57.   Van Dam, AM, De Vries HE, Kuiper J, Zijlstra FJ, De Boer AG, Tilders FJ, and Berkenbosch F. Interleukin-1 receptors on rat brain endothelial cells: a role in neuroimmune interaction? FASEB J 10: 351-356, 1996[Abstract].

58.   De Waal Malefyt, R, Abrams J, Bennett B, Figdor CG, and de Vries JE. Interleukin 10 (IL-10) inhibits cytokine synthesis by human monocytes: an autoregulatory role of IL-10 produced by monocytes. J Exp Med 174: 1209-1220, 1991[Abstract/Free Full Text].

59.   Wang, J, Ando T, and Dunn AJ. Effect of homologous interleukin-1, interleukin-6 and tumor necrosis factor-alpha on the core body temperature of mice. Neuroimmunomodulation 4: 230-236, 1997[ISI][Medline].

60.   Ward, H, Vigues S, Poole S, and Bristow AF. The rat interleukin-10 receptor: cloning and sequencing of cDNA coding for the alpha -chain protein sequence, and demonstration by Western blotting of expression in the rat brain. Cytokine 15: 237-240, 2001[ISI][Medline].

61.   Watkins, LR, Goehler LE, Relton JK, Tartaglia N, Silbert L, Martin D, and Maier SF. Blockade of interleukin-1 induced hyperthermia by subdiaphragmatic vagotomy: evidence for vagal mediation of immune-brain communication. Neurosci Lett 183: 27-31, 1995[ISI][Medline].

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