Importance of brain IL-1 type II receptors in fever and thermogenesis in the rat

Prior laparotomy or corticosterone potentiates lipopolysaccharide-induced fever and sickness behaviors

Stimulating sensitized immune cells with a subsequent immune challenge results in potentiated pro-inflammatory responses translating into exacerbated sickness responses (i.e. fever, pain and lethargy). Both corticosterone (CORT) and laparotomy cause sensitization, leading to enhanced sickness-induced neuroinflammation or pain (respectively). However, it is unknown whether this sensitization affects all sickness behaviors and immune cell responses equally. We show that prior CORT and prior laparotomy potentiated LPS-induced fever but not lethargy. Prior CORT, like prior laparotomy, was able to potentiate sickness-induced pain. Release of nitric oxide (NO) from peritoneal macrophages stimulated ex vivo demonstrates that laparotomy, but not CORT sensitizes these cells.

Prenatal opiate exposure attenuates LPS-induced fever in adult rats: role of interleukin-1beta

Much is known about the immunomodulatory effects of opiate exposure and withdrawal in adult rats. However, little research has delved into understanding the immunological consequences of prenatal opiate exposure and postnatal withdrawal. The purpose of the current study was to measure changes in responding to immune stimulation in adult rats following prenatal opiate exposure. Further, we sought to characterize the role of interleukin (IL)-1beta in these changes. Following prenatal exposure to the long-acting opiate l-alpha-acetylmethadol (LAAM), adult male and female rats were assessed for their fever response to lipopolysaccharide (LPS). Blood and tissue samples were collected to measure circulating IL-1beta and IL-1beta protein in the hypothalamus and spleen. Prenatal LAAM exposure resulted in a blunted fever response to LPS injection without any changes in basal body temperature or in response to saline injection. Circulating IL-1beta was not affected by prenatal LAAM exposure, nor was IL-1beta protein in the spleen. Interestingly, mature IL-1beta protein was elevated in the hypothalamus of prenatally LAAM-treated rats. These results indicate that prenatal opiate exposure blunts the fever response of adult offspring. Direct action of IL-1beta is likely not the cause of the dysfunction reported here. However, alterations in signaling mechanisms downstream from IL-1beta may play a role in the altered fever response in adult rats treated prenatally with opiates.

The expanding interleukin-1 family and its receptors: do alternative IL-1 receptor/signaling pathways exist in the brain?

Interleukin-1 (IL-1) has been implicated in neuroimmune responses and has pleiotropic actions in the brain. Compelling evidence has shown that IL-1 is a major mediator of inflammation and the progression of cell death in response to brain injury and cerebral ischemia. Its expression is strongly increased in these pathological conditions, and central administration of exogenous IL-1 significantly exacerbates ischemic brain damage. In contrast, inhibiting IL-1 actions (by intracerebroventricular [icv] injection of IL-1ra, neutralizing antibody to IL-1 or caspase-1 inhibitor) significantly reduces ischemic brain damage. IL-1 acts by binding to the IL-1 type-I receptor (IL-1RI), which is to date, the only known functional receptor for IL-1. However, our recent investigations suggest that IL-1 can act independently of IL-1RI, raising the possibility that additional, as yet undiscovered, receptor(s) for IL-1 exist in the brain. The recent characterization of putative, new IL-1 ligands and new IL-1 receptor-related molecules leads to the hypothesis that there might be alternative IL-1 signaling pathway(s) in the central nervous system (CNS).

Annual review prize lecture cytokines - killers in the brain?

Given at the Meeting of the Physiological Society held at the University of Southampton on 10 September 1998

Effect of IL-1alpha on the release of norepinephrine in rat hypothalamus

The increased release of norepinephrine (NE) in the brain as part of the 'acute phase response' has been postulated to result from a direct action of IL-1 on the hypothalamus. To test whether the effects of IL-1alpha were direct, we carried out in vivo experiments using microdialysis and measured NE release in the hypothalamus using high pressure liquid chromatography (HPLC). Two groups of male Sprague Dawley rats were either injected intraperitoneally with 1 ml of IL-1alpha (2 microg/ml) or had IL-1alpha 2 microl (100 ng/ml) infused directly into the medial hypothalamus. A significant increase in extracellular hypothalamic NE was observed in the animal group treated with IL-1alpha intraperitoneally and not in the controls or the group treated with IL-1alpha intracerebrally. One-way ANOVA showed a significant effect of drug and route of administration with the ip IL-1alpha treated group, differing from all other groups (vehicle ip, IL-1alpha ic, and vehicle ic). Therefore these findings suggest that some aspects of IL-1alpha actions on the HPA may be indirect requiring other intermediate steps or mediators outside the central nervous system.

Blockade of brain type II interleukin-1 receptors potentiates IL1beta-induced anorexia in mice

Interleukin-1beta (IL1beta) peripheral activities are mediated by type I IL1 receptors (IL1RI), whereas type II IL1 receptors (IL1RII) act as 'decoy' targets. To study the functionality of IL1RII in the brain, mice were treated with an intracerebroventricular injection of a neutralising MoAb directed against IL1RII (4E2, 1 microg) followed by recombinant rat IL1beta at a dose (2 ng) that produced a moderate but significant decrease of food intake 1 h 30 min after injection. The administration of 4E2 to IL-1beta treated mice significantly potentiated IL1beta-induced decrease in food intake without altering hypothermia. The effects of IL1beta were abrogated in the positive control group treated with IL1ra (2 microg, i.c.v). These results suggest that brain IL1RII down-regulate the effects of IL1beta on its cell targets in the brain.

Development of hyperthermia following intracerebroventricular administration of endotoxin in the rat: effect of kinin B1 and B2 receptor antagonists

1. E. coli lipopolysaccharide (LPS) produced a dose-dependent (dose range: 0.02-150 micrograms) increase in rat core temperature that was maximal 6 h after intracerebroventricular (i.c.v.) administration. LPS (200 ng) increased core temperature by 1.0 +/- 0.2 degrees C, 6 h following administration, as compared to vehicle-treated controls (-0.2 +/- 0.2 degrees C). 2. LPS-induced (200 ng) hyperthermia was prevented by co-administration of the bradykinin (BK) B2 receptor antagonist, Hoe 140 (10 and 30 pmol, i.c.v.) or by indomethacin (10 nmol, i.c.v.). 3. Systemic administration of Hoe 140 at doses up to 1 mumol kg-1, s.c., did not attenuate LPS-induced (200 ng, i.c.v.) hyperthermia. However, LPS hyperthermia was significantly reduced by systemic administration of indomethacin (1 mumol kg-1, i.v.). 4. Co-administration of the selective B1 receptor antagonists, [des-Arg9, Leu8]BK (0.1 - 1 nmol, i.c.v.) or [des-Arg10] Hoe 140 (0.1 - 1 nmol, i.c.v.), did not prevent LPS-induced hyperthermia. 5. It is concluded that the development of hyperthermia following central administration of endotoxin requires activation of central, but not peripheral bradykinin B2 receptors. The formation of kinins within the CNS may be an important initial component of CNS inflammation following infection.

Endogenous glucocorticoids down regulate central effects of interleukin-1 beta on body temperature and behaviour in mice

Adrenalectomy sensitizes laboratory animals to the pyrogenic and behavioural effects of proinflammatory cytokines. To determine whether these effects are mediated by central sites of action of glucocorticoids, interleukin-1 beta was injected intracerebroventricularly (i.c.v.) in adrenalectomized mice with or without corticosterone supplementation and in mice pretreated i.c.v. with the glucocorticoid type II receptor antagonist RU38486. Adrenalectomized mice were more sensitive to the depressing effects of i.c.v. IL-1 beta on body temperature and social exploration than sham-operated mice. Corticosterone supplementation reversed the increased sensitivity to the low (300 pg/mouse) but not to the high dose (900 pg/mouse) of IL-1 beta. Central administration of RU38486 (0.5-1 microgram/mouse) mimicked the effects of adrenalectomy on behaviour but not on body temperature. These results suggest that endogenous glucocorticoids released in response to IL-1 beta act in the brain to modulate the sensitivity of the cellular targets of this cytokine.

Differential effects of IL-1ra on sickness behavior and weight loss induced by IL-1 in rats

Peripheral and central injections of recombinant human interleukin-1 beta (IL-1 beta) have been shown to decrease social exploration and to induce body weight loss in rats. To characterize the receptor mechanisms of these effects, we used as a tool a specific antagonist of the receptors of IL-1, IL-1ra. Intraperitoneal (i.p.) administration of IL-1ra (8 mg/kg) blocked the effect of i.p. injection of IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 micrograms/rat, i.c.v.) abrogated the effects of centrally administered IL-1 beta (30 ng/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 micrograms/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1 beta (4 micrograms/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1 beta on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.

Central interleukin-1 beta stimulation of vasopressin release into the rat brain: activation of an antipyretic pathway

1. Arg8-vasopressin (AVP)-containing neurones of the bed nucleus of the stria terminalis (BST), which terminate in the ventral septal area (VSA) of the rat brain, provide a pathway which controls body temperature during fever. The present study was conducted to test the hypothesis that interleukin-1 beta (IL-1 beta) may trigger the antipyretic response by evoking AVP release from BST neurones projecting into the VSA. 2. The push-pull perfusion technique and radioimmunoassay were utilized to determine the AVP concentrations of retrieved VSA perfusion fluid in urethane-anaesthetized rats following BST infusion of vehicle or IL-1 beta (125 or 500 pg (2 microliters)-1). 3. Ventral septal AVP levels significantly increased from basal levels, in a dose-related manner, in response to IL-1 beta (0-500 pg). Electrical stimulation of the same areas of the BST also evoked AVP release into the VSA. 4. IL-1 beta infusions and electrical stimulation of the BST resulted in significant increases in rectal temperature. In IL-1 beta-treated animals (500 pg), the change in body temperature and VSA AVP release were negatively correlated (P < 0.001). However, external heating of the animals to approximately the same levels as electrically stimulated or IL-1 beta treated rats did not affect basal AVP release. 5. These data show that IL-1 beta is a potent stimulus for AVP release from BST neurones and supports BST involvement in neuro-immune interactions. We propose, that in addition to febrogenesis, IL-1 beta is also a key component in the process of endogenous antipyresis by activating vasopressinergic BST neurones to release AVP during fever.