Brain interleukin-1β and tumor necrosis factor-α are involved in lipopolysaccharide-induced delayed rectal allodynia in awake rats

Recently, we have developped a model of delayed (12 h) increase in sensitivity (allodynia) to rectal distension (RD) induced by intraperitoneal lipopolysaccharide (LPS) in awake rats. Thus, we examined whether central interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) are involved in LPS response. Abdominal contractions (criterion of visceral pain) were recorded in rats equipped with intramuscular electrodes. RDs were performed at various times after pharmacological treatments. RD induced abdominal contractions from a threshold volume of distension of 0.8 ml. At lowest volume (0.4 ml), this number was significantly increased 12 h after LPS. Intracerebroventricular (i.c.v.) injection of IL-1 receptor antagonist, IL-1β converting enzyme inhibitor or recombinant human TNF-α soluble receptor reduced LPS-induced increase of abdominal contractions at 0.4 ml volume of distension. When injected i.c.v., recombinant human IL-1β and recombinant bovine TNF-α reproduced LPS response at 9 and 12 h and at 6 and 9 h, respectively. These data suggest that IL-1β and TNF-α act centrally to induce delayed rectal hypersensitivity and that central release of these cytokines is responsible of LPS-induced delayed (12 h) rectal allodynia.     

The expression of proinflammatory cytokine mRNA in the sciatic–tibial nerve of ischemia–reperfusion injury

We evaluated the proinflammatory cytokines, TNF-α and IL-1β, mRNA expression in the rat sciatic and tibial nerves following ischemia–reperfusion (IR) injury, using competitive RT–PCR, to explore the role of cytokines in IR injury. The expressions of both TNF-α and IL-1β mRNA were related to severity of ischemia and occurred with reperfusion rather than ischemia alone. TNF-α gene expression peaked at 24 h of reperfusion, while that of IL-1β peaked at 12 h. These data support the notion that the proinflammatory cytokines TNF-α and IL-1β are involved in the inflammatory response of IR injury to the peripheral nervous system and may be involved in the pathophysiology of ischemic fiber degeneration.     

Mechanisms of tumor necrosis factor-α (TNF-α) hyperalgesia

Activation of immune cells by pathogens induces the release of a variety of proinflammatory cytokines, including IL-1β and TNF-α. Previous studies using IL-1β have demonstrated that this cytokine can alter brain function, resulting in a variety of ‘illness responses’ including increased sleep, decreased food intake, fever, etc. We have recently demonstrated that i.p. IL-1β also produces hyperalgesia and that this hyperalgesia (as well as most illness responses) is mediated via activation of subdiaphragmatic vagal afferents. The present series of studies were designed to provide an initial examination of the generality of proinflammatory cytokine-induced hyperalgesia by examining the effects of i.p. TNF-α on pain responsivity. These studies demonstrate that: (a) i.p. TNF-α produces dose-dependent hyperalgesia as measured by the tailflick test, (b) this hyperalgesia is mediated via the induced release of IL-1β, (c) hyperalgesia is mediated via activation of subdiaphragmatic vagal afferents, and (d) the effects of subdiaphragmatic vagotomy cannot be explained by a generalized depression of neural excitability.     

Blockade of angiotensin II AT1 receptors inhibits pressor action of centrally administered interleukin-1β in Sprague Dawley rats

The aim of the present study was to evaluate the influence of intraventricular administration of recombinant rat interleukin-1β (IL-1β) on regulation of resting blood pressure and heart rate and to test the hypothesis that the brain angiotensinergic system is involved in regulation of hemodynamic parameters by centrally applied IL-1β. The experiments were performed on Sprague Dawley rats, assigned to three series of experiments. In series 1 (control, n = 6), mean arterial pressure (MAP) and heart rate (HR) were recorded for 15 min under baseline conditions. This was followed by infusion of saline (0.9% sterile NaCl 5 μL/h) into the left cerebral ventricle (LCV). Measurements were continued during the next 60 min. In series 2 (n = 6) and 3 (n = 6) the experimental design was similar, except that in series 2 the animals were LCV infused with saline containing IL-1β (100 ng/h) and in series 3 with saline containing IL-1β (100 ng/h) and angiotensin type 1 (AT1) receptors antagonist (Losartan, 10 μg/h). LCV infusion of saline alone did not influence MAP and HR while administration of IL-1β elicited significant increase in MAP, but not in HR. The pressor effect was absent during combined infusion of IL-1β and Losartan. Results of the study provide evidence that centrally administered IL-1β exerts pressor effect, and reveal that this effect is mediated by stimulation of the brain angiotensin system and requires activation of AT1 receptors.     

Cytokines in relapsing experimental autoimmune encephalomyelitis in DA rats: persistent mRNA expression of proinflammatory cytokines and absent expression of interleukin-10 and transforming growth factor-β

Experimental autoimmune encephalomyelitis (EAE) in rats is typically a brief and monophasic disease with sparse demyelination. However, inbred DA rats develop a demyelinating, prolonged and relapsing encephalomyelitis after immunization with rat spinal cord in incomplete Freund's adjuvant. This model enables studies of mechanisms related to chronicity and demyelination, two hallmarks of multiple sclerosis (MS). Here we have investigated, in situ, the dynamics of cytokine mRNA expression in the central nervous system (CNS) and peripheral lymphoid organs (lymph node cells and splenocytes) of diseased DA rats. We demonstrate that peripheral lymphoid cells stimulated in vitro with encephalitogenic peptides 69–87 and 87–101 of myelin basic protein responded with high mRNA expression for proinflammatory cytokines; Interferon-7, interleukin-12 (IL-12), tumour necrosis factors α and β, IL-1β and cytolysin. A high expression of mRNA for these proinflammatory cytokines was also observed in the CNS where it was accompanied by classical signs of inflammation such as expression of major histocompatibility complex class I and II, CD4, CDS and IL-2 receptor. The expression of mRNA for proinflammatory cytokines was remarkably long-lasting in DA rats as compared to LEW rats which display a brief and monophasic EAE. Furthermore, mRNAs for putative immunodownmodulatory cytokines i.e. transforming growth factor-β (TGF-/3), IL-10 and IL-4 were almost absent in DA rats, in both the CNS and in vitro stimulated peripheral lymphoid cells, while their levels were elevated in the CNS of LEW rats during the recovery phase. We conclude that the MS-like prolonged and relapsing EAE in DA rats is associated with a prolonged production of proinflammatory cytokines and/or low or absent production of immunodownmodulatory cytokines.     

The non-steroidal anti-inflammatory drug diclofenac sodium attenuates IFN-α induced alterations to monoamine turnover in prefrontal cortex and hippocampus

Interferon-α (IFN-α) administration induces major depression in a significant number of patients undergoing treatment for viral illnesses and other chronic diseases. Non-steroidal anti-inflammatory drugs (NSAIDs) are known to counteract a number of IFN-α-induced side effects, including pro-inflammatory cytokine activation and stress hormone release. To investigate this possibility further, we sought to determine the effect of the NSAID diclofenac sodium on monoamine turnover in brain induced by acute IFN-α exposure. Eleven male, Wistar rats (8 weeks old) were pretreated with diclofenac (20 mg/kg, s.c.) or saline, followed by intracerebroventricular (i.c.v.) infusion of IFN-α (1000 IU in 5 μl) or vehicle. The prefrontal cortex, striatum, and hippocampus were isolated and samples were assayed for monoamines and major metabolites by high-pressure liquid chromatography with electrochemical detection. The data show that acute IFN-α increased serotonin turnover in prefrontal cortex and increased dopamine turnover in hippocampus, while pre-treatment with diclofenac completely prevented these neurochemical responses. Importantly, these changes were recorded in two brain areas known to be important in depression and antidepressant action. These data offer support for a novel role of NSAIDs in modulating IFN-α-induced neurochemical alterations, and raise the possibility of the use of NSAIDs for the prevention of IFN-α-induced depression.     

The role of interleukin-6 in the activation of the hypothalamo-pituitary-adrenocortical axis and brain indoleamines by endotoxin and interleukin-1β

Interleukin-6 (IL-6) is one of several cytokines that can stimulate the hypothalamo-pituitary-adrenocortical (HPA) axis. Because IL-6 is produced in response to the administration of endotoxin (LPS) and interleukin-1 (IL-1), it is possible that IL-6 contributes to the neuroendocrine and neurochemical changes induced by them. In this study, intraperitoneal (i.p.) injection of LPS elevated plasma concentrations of IL-6 while activating the HPA axis in a dose-dependent manner. Both responses reached a peak at around 2–3 h. Mouse IL-1β administration (100 ng, i.p.) induced large increases in plasma corticosterone and a substantial, but short-lived increase in plasma IL-6 with a peak at 2 h. Pretreatment of mice intraperitoneally with a monoclonal antibody to mouse IL-6 significantly attenuated the plasma ACTH and corticosterone responses to LPS at 3 h, but not at 1 h. Anti-IL-6 treatment also attenuated the LPS-induced increases of tryptophan and the serotonin catabolite, 5-hydroxyindoleacetic acid (5-HIAA), but not that of the norepinephrine catabolite, 3-methoxy,4-hydroxyphenylethyleneglycol (MHPG). Pretreatment of mice with anti-IL-6 significantly attenuated the IL-1-induced increases of plasma ACTH and corticosterone at 2 h, but not at 4 h. The IL-1-induced increases of MHPG, tryptophan and 5-HIAA in hypothalamus and brain stem were not significantly altered. These results suggest that IL-6 contributes to the later phases of the LPS- and IL-1-induced stimulations of the HPA axis and to the indoleaminergic responses to LPS, but not to IL-1.     

Brain IL-1beta increases neutrophil and decreases lymphocyte counts through stimulation of neuroimmune pathways.

Leukocytosis after cerebral injury is well described and may participate in the generation of cerebral damage. However, the mechanisms of brain-induced leukocytosis are still speculative. Since it is known that proinflammatory cytokines are involved in neuroimmunomodulation and since others and we have demonstrated high cytokine levels in the cerebrospinal fluid following injury, we supposed that brain cytokines may also influence leukocyte counts. In order to evaluate this hypothesis, we established an animal model using continuous intracerebroventricular (i.c.v.), intrahypothalamic (i.h.), or intravenous infusion of the proinflammatory cytokines tumor necrosis factor (TNF)-alpha and IL-1beta. Controls received vehicle solution. With this experimental paradigm we could show that i.c.v. and i.h. infusion of IL-1beta but not TNF-alpha dramatically increased neutrophil counts, whereas lymphocytes dropped. Blocking the hypothalamic-pituitary-adrenal (HPA) axis by hypophysectomy abolished the neutrophilia, whereas the lymphopenia remained unchanged. Furthermore, application of the beta2-adrenoreceptor antagonist propranolol prevented the decrease of lymphocytes and diminished the neutrophilia. All parameters normalized within 48 h after termination of infusion. So, our results demonstrate that brain IL-1beta can modify blood leukocyte counts through stimulation of both the sympathetic nervous system (SNS) and the HPA axis.     

Interleukin-1β-induced brain injury in the neonatal rat can be ameliorated by α-phenyl-n-tert-butyl-nitrone

To examine the possible role of inflammatory cytokines in mediating perinatal brain injury, we investigated effects of intracerebral injection of interleukin-1beta (IL-1β) on brain injury in the neonatal rat and the mechanisms involved. Intracerebral administration of IL-1β (1 μg/kg) resulted in acute brain injury, as indicated by enlargement of ventricles bilaterally, apoptotic death of oligodendrocytes (OLs) and loss of OL immunoreactivity in the neonatal rat brain. IL-1β also induced axonal and neuronal injury in the cerebral cortex as indicated by elevated expression of β-amyloid precursor protein, short beaded axons and dendrites, and loss of tyrosine hydroxylase-positive neurons in the substantia nigra and the ventral tegmental areas. Administration of α-phenyl-n-tert-butyl-nitrone (PBN, 100 mg/kg i.p.) immediately after the IL-1β injection protected the brain from IL-1β-induced injury. Protection of PBN was linked with the attenuated oxidative stress induced by IL-1β, as indicated by decreased elevation of 8-isoprostane content and by the reduced number of 4-hydroxynonenal or malondialdehyde or nitrotyrosine-positive cells following IL-1β exposure. PBN also attenuated IL-1β-stimulated inflammatory responses as indicated by the reduced activation of microglia. The finding that IL-1β induced perinatal brain injury was very similar to that induced by lipopolysaccharide (LPS), as we previously reported and that PBN was capable to attenuate the injury induced by either LPS or IL-1β suggests that IL-1β may play a critical role in mediating brain injury associated with perinatal infection/inflammation.     

Intracerebral interleukin-1β impairs response to tumor invasion: involvement of adrenal catecholamines

Interleukin-1β (IL-1β) is released within the brain following stress, trauma, infection, and in specific brain disorders. This centrally acting IL-1β has recently been shown to impair peripheral immunity. Central administration of IL-1β suppresses natural killer (NK) cell activity impairs lung clearance of tumor cells and enhances tumor colonization. Using an in vivo model of tumor colonization (lung clearance of NK-sensitive MADB106 adenocarcinoma cells), this study examined the role of the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system (SNS) in mediating these effects. We demonstrate that adrenalectomy significantly attenuated the impaired lung clearance of MADB106 tumor cells induced by intracerebroventricular (i.c.v.) administration of IL-1β (20 ng). Supplementing adrenalectomized animals with corticosterone did not reinstate the effect. The effect of IL-1β on lung clearance was blocked by pretreatment with the β-adrenergic antagonist, nadolol (0.5 mg/kg), but not by the α-antagonist phentolamine (5 mg/kg). Peripheral noradrenergic pathways are not implicated given that systemic administration of the noradrenergic neurotoxin, 6-hydroxydopamine, did not block the effect of IL-1β. Taken together, these findings indicate that IL-1β impairs lung clearance of MADB106 tumor cells via the actions of adrenal catecholamines, most likely epinephrine, acting at β-adrenergic receptors in the periphery.     

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-1β (IL-1β) 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-1β (4 μg/rat) on social behaviour but not on body weight. Central administration of IL-1ra (60 μg/rat, i.c.v.) abrogated the effects of centrally administered IL-1β (30 ngn/rat, i.c.v.) on both social behaviour and body weight. Central injection of IL-1ra (4 μg/rat, i.c.v.) also attenuated the effects of i.p. administered IL-1β (4 μg/rat) on social behaviour but not on body weight. These results suggest that the effects of IL-1β on social behavior are mediated centrally and that its effect on the loss of body weight involves different receptor mechanisms.     

Intracerebral Mycobacterium bovis bacilli Calmette–Guerin infection-induced immune responses in the CNS

To study whether cerebral mycobacterial infection induces granuloma and protective immunity similar to systemic infection, we intracerebrally infected mice with Mycobacterium bovis bacilli Calmette–Guerin. Granuloma and IFN-γ⁺CD4⁺ T cell responses are induced in the central nervous system (CNS) similar to periphery, but the presence of IFN-γIL-17 double-positive CD4⁺ T cells is unique to the CNS. The major CNS source of TNF-α is microglia, with modest production by CD4⁺ T cells and macrophage. Protective immunity is accompanied by accumulation of Foxp3⁺CD4⁺ T cells and PD-L2⁺ dendritic cells, suggesting that both inflammatory and anti-inflammatory responses develop in the CNS following mycobacterial infection.     

Activation of caspase-8 by tumour necrosis factor receptor 1 is necessary for caspase-3 activation and apoptosis in oxygen–glucose deprived cultured cortical cells

TNF-α has been reported to be relevant in stroke-induced neuronal death. However the precise function of TNF-α in brain ischemia remains controversial since there are data supporting either a detrimental or a protective effect. Here we show that TNF-α is released after oxygen–glucose deprivation (OGD) of cortical cultures and is a major contributor to the apoptotic death observed without affecting the OGD-mediated necrotic cell death. In this paradigm, apoptosis depends on TNF-α-induced activation of caspase-8 and -3 without affecting the activation of caspase-9. By using knock-out mice for TNF-α receptor 1, we show that the activation of both caspase-3 and -8 by TNF-α is mediated by TNF-α receptor 1. The pro-apoptotic role of TNF-α in OGD is restricted to neurons and microglia, since astrocytes do not express either TNF-α or TNF-α receptor 1. Altogether, these results show that apoptosis of cortical neurons after OGD is mediated by TNF-α/TNF-α receptor 1.     

Endogenous gamma interferon produced in central nervous system by systemic infection infection with Theiler's virus in mice

Theiler's virus GD VII strain causes acute encephalomyelitis by intracerebral inoculation. We established acute encephalomyelitis in mice by the intravenous (i.v.) inoculation of Theiler's virus GD VII strain. Replication of Theiler's virus injected i.v. could be observed in both the brain and spinal cord of mice, and interferon (IFN)-γ could be detected in the extracts of brain and spinal cord in parallel with viral replication. Furthermore, by the injection of anti-IFN-γ monoclonal antibody (mAb) on Day 1 post-infection (p.i.), mortality and virus titres in the spinal cord increased compared with the control mice treated with normal rat globulin. The histological exacerbation of inflammation was observed in spinal cord of anti-IFN-γ mAb-treated mice. These results indicate that endogenous IFN-γ, produced locally in the brain and spinal cord of mice through both antiviral action and anti-inflammatory action of IFN-γ in central nervous system, plays an important role in Theiler's virus infection.     

Changes in expressions of proinflammatory cytokines IL-1β, TNF-α and IL-6 in the brain of senescence accelerated mouse (SAM) P8

The senescence-accelerated mouse (SAM) is known to be a murine model for accelerated aging. The SAMP8 strain shows age-related deterioration of learning and memory at an earlier age than control mice (SAMR1). In the present study, we investigated the changes in expressions of interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the brain of SAMP8. In the hippocampus of 10 months old SAMP8, the expression of IL-1 mRNA was significantly elevated in comparison with that of SAMR1. In both strains of SAMs, increases in IL-1β protein in the brain were observed at 10 months of age compared with 2 and 5 months. The only differences found between the strain in protein levels were at 10 months and were elevations in IL-1β in the hippocampus and hypothalamus, and in TNF-α and IL-6 in the cerebral cortex and the hippocampus in SAMP8 as compared with SAMR1. However, lipopolysaccharide-induced increases in the expression of these cytokines in brain did not differ between SAMP8 and SAMR1. Increases in expression of proinflammatory cytokines in the brain may be involved in the age-related neural dysfunction and/or learning deficiency in SAMP8.     

Release of hypothalamic corticotropin-releasing hormone and arginine-vasopressin by interleukin 1β and αMSH: studies in rats with different susceptibility to inflammatory disease

The susceptibility of Lewis rats is related to blunted hypothalamic-pituitary-adrenal (HPA) axis responsiveness to a variety of inflammatory and neuroendocrine stimuli. In contrast resistance to inflammatory disease of histocompatible Fischer rats is associated with their intact HPA axis responses to the same stimuli. We have examined the contribution of IL-1β to in vitro corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) release from hypothalamic explants derived from LEW/N and F344/N rats. The same animal model has been used to investigate the regulatory effect of αMSH, an immunosuppressive neurohormone, on IL-1β stimulated CRH and AVP secretion. CRH basal release in both strains was similar. However, LEW/N hypothalamic AVP basal secretion was significantly elevated. CRH relative response of LEW/N hypothalamic explants to IL-1β stimulation was lower compared to Fischer, which is consistent with their hyporesponsiveness to inflammatory mediators. AVP secretion however, was significantly decreased in hypothalamic explants from both strains after 40 min exposure to IL-1β. αMSH suppressed basal CRH and AVP release in both LEW/N and F344/N rats and prevented IL-1β stimulated CRH secretion in these strains. AVP was further diminished in F344/N explants following incubation with αMSH+IL-1β, while LEW/N level was significantly elevated. However, AVP levels remained significantly below baseline in explants from both strains after final incubation with IL-1β. Although our findings indicate a modulatory action of αMSH in HPA axis regulation in vitro, the physiological importance of this phenomenon in Lewis and Fischer rats requires further investigation.