Subchronic (36 h) exposure of rats to corticosterone (CS) (100 mg/pellet, subcutaneously), blocked the pyrogenic response to recombinant human interleukin 1b (rhIL-1b, 5 mg/kg, ip.). CS treatment reduced the basal mRNA levels of IL-1a and IL-1b, but elevated the mRNA levels of IL-6 in the hypothalamus and hippocampus as shown by RT-PCR. The CS treatment clamped the cytokine mRNA levels, and injection of rhIL-1b to CS treated rats did not significantly affect these altered mRNA levels. IL-6 bioactivity in serum was not significantly changed by CS treatment, but increased 50 times upon injection of rhIL-1b. rhIL-1b caused a significantly lower induction of serum IL-6 levels in CS pretreated rats (9-fold). The pyrogenic response to injection of rhIL-1b has returned 5 days after the removal of the corticosterone pellet, and the hypothalamic cytokine mRNA levels (IL-1a, IL-1b and IL-6) have returned to basal. These results suggest that altered and clamped hypothalamic IL-1a, IL-1b and IL-6 mRNA levels may be involved in the antipyretic effects of a pretreatment with high doses of CS and that these CS effects are rapidly reversible.

IL-β is an endogenous pyrogen that is inducedduring systemic lipopolysaccharide (LPS)- or IL-1-induced fever. We have examined the fever and cytokineresponses following i.p. injection of IL-1 agonists, IL-1a andIL-β, and compared these with response to LPS (i.p.) in wild-type and IL-β-deficient mice. The IL-β deficient mice appear to have elevated body temperature but exhibit a normal circadian temperature cycle. Exogenously injected IL-β, IL-1a, or LPS induced hyperresponsive fevers in the IL-βdeficient mice. We also observed phenotypic differences between wild-type and IL-β-deficient mice in hypothalamic basal mRNA levels for IL-1a and IL-6, but not for IL-βconverting enzyme or IL-1 receptor type I or type II. The IL-1a mRNA levels were down-regulated, whereas the IL-6 mRNA levels were up-regulated in the hypothalamus of IL-βdeficient mice as compared with wild-type mice. The IL-βdeficient mice also responded to LPS challenge with significantly higher serum corticosterone and with lower serum tumor necrosis factor type a levels than the wild-type mice. The data suggest that, in the redundant cascade of proinflammatory cytokines, IL-β plays an important but not obligatory role in fever induction by LPS or IL-1a, as well as in the induction of serum tumor necrosis factor type a and corticosterone responses either by LPS or by IL-1a or IL-β.

Aim: To determine the Ca2+ source and cellular mechanisms of spontaneous Ca2+ oscillations in hippocampal astrocytes. Methods: The cultured cells were loaded with Fluo-4 AM, the indicator of intracellular Ca2+, and the dynamic Ca2+ transients were visualized with confocal laser-scanning microscopy. Results: The spontaneous Ca2+ oscillations in astocytes were observed first in co-cultured hippocampal neurons and astrocytes. These oscillations were not affected by tetrodotoxin (TTX) treatment and kept up in purity cultured astrocytes. The spontaneous Ca2+ oscillations were not impacted after blocking the voltage-gated Ca2+ channels or ethylenediamine tetraacetic acid (EDTA) bathing, indicating that intracellular Ca2+ elevation was not the result of extracellular Ca2+ influx. Furthermore, the correlation between the spontaneous Ca2+ oscillations and the Ca2+ store in endoplasmic reticulum (ER) were investigated with pharmacological experiments. The oscillations were: 1) enhanced when cells were exposed to both low Na+ (70mmol/L) and high Ca2+ (5mmol/L) solution, and eliminated completely by 2 μmol/L thapsigargin, a blocker of sarcoplasmic reticulum Ca2+-ATPase; and 2) still robust after the application with either 50 μmol/L ryanodine or 400 μmol/L tetracaine, two specific antagonists of ryanodine receptors, but depressed in a dose-dependent manner by 2-APB, an InsP3 receptors (InsP3R) blocker. Conclusion: InsP3R-induced ER Ca2+ release is an important cellular mechanism for the initiation of spontaneous Ca2+ oscillation in hippocampal astrocytes.

Interleukin (IL)-β, IL-β, and tumor necrosis factor 0r (TNF-ot) are considered to act as endogenous pyrogens. Because of the complex pattern of cross-inductions between these cytokines, the relative role of the central and peripheral production of these cytokines in eliciting the fever response has not yet been clarified. The purpose of this study was to determine the role of IL-Β in the fever response by making use of mice carrying a null mutation in the IL-β gene. The intraperitoneal injections oflipopolysaccharide (LPS) (50bLg/kg) and recombinant murine (rm) IL-β (10 bg/kg), respectively, failed to evoke fever response in IL-β-deficient mice, whereas the same doses of LPS and rmIL-βcaused fever response in wild-type mice. The fever response could be induced in the IL-β-deficient mice by intracerebroventricular injection of recombinant human (rh) IL-β (500 ng/mouse), whereas intracerebroventricular injection of rmlL-β (100 ng/mouse) failed to produce fever response in the IL-β-deficient mice. These results suggest that central IL-Β is a necessary component of the fever response to both endogenous (IL-β) and exogenous (LPS) pyrogens in mice and that IL-β acts downstream from both peripheral and central IL-β.

The multiple actions of corticotropin-releasing factor (CRF) on neuroendocrine and behavioural functions can now be examined using new, high affinity, non peptidic antagonists which exhibit central activity upon systemic application. We have shown that compound CP 154,526 (butyl-ethyl-[2.5-dimethyl-7-(2、4、6-trimethyphenyl)-7H-pyrrtly [2.3d]pyrimidin-4-yl]amine) displaces [125][Tyo]CRF from rat hippocampal CRF receptors (ICso= 0.5 nM) and from pituitary CRF receptors (ICso=0.04 nM). The same compound inhibits in a concentration-dependent manner the ovine CRF (0.1 ixM)-stimulated adenylate cyclase activity in membranes of a mouse pituitary adenoma cell line, AtT20, with an ICso value of 50 nM. Systemic application of the CRF receptor antagonist (0.16mg/kgi.p.) blocked recombinant human interleukin-ll3 (5p.g/kgi.p.) induced fever in rats. The CRF receptor antagonist CP 154,526 (lmg/kgi.p.) also exhibited signs of anxiolytic-like activity in the elevated plus-maze test in rats.