Receptors for interleukin-1 (alpha and beta) in mouse brain: mapping and neuronal localization in hippocampus

Cytokines and their receptors in the central nervous system: physiology, pharmacology, and pathology

Numerous cytokines and their receptors have been identified in the brain, where they act as mediators of host defence responses and have direct effects on neuronal and glial function. Experimental tools for studying cytokine actions, their source and control of synthesis in the brain, actions and mechanisms of action will be reviewed here. In particular, the cytokines interleukin-1, interleukin-6, and tumour necrosis factor-alpha have been implicated in the central control of responses to systemic disease and injury and activation of fever, neuroendocrine, immune, and behavioural responses. The recent discovery of specific inhibitors of cytokine synthesis, release, or action may offer significant therapeutic benefit.

The kinetics of ACTH expression in rat leukocyte subpopulations

The pro-opiomelanocortin (POMC) gene encodes a family of peptides originally identified in the pituitary gland. An important POMC-derived peptide hormone, corticotropin (ACTH), is also produced by leukocytes and modulates in vitro immune functions. The present investigation was undertaken to determine the kinetics and cellular distribution of ACTH immunoreactivity (ACTH-ir) in vitro in rat splenic leukocyte subpopulations. Cells were cultured with Concanavalin A (ConA), lipopolysaccharide (LPS), or media alone. ACTH-ir was identified with a specific antiserum raised against ACTH 1-24. Double indirect-immunofluorescence was done at 0, 21, and 48 h for B, t-helper (Th), and T-cytotoxic (CTL) cells. Initial kinetic studies demonstrated peak ACTH-ir in all cell types at 18-21 h for both ConA and LPS treatments. A few leukocytes (1-2%) expressed ACTH-ir at 0 h and these were found to be macrophages (MO). Lymphocyte ACTH-ir is 0% at 0 h and rises to 90 +/- 5% and 75 +/- 6% at 21 h with ConA and LPS, respectively. This sharply contrasts with 9 +/- 4% of each cell type positive in media alone at 21 h. The percent immunoreactivity among the three lymphocyte subpopulations did not significantly differ at any single treatment at a single time point. However, there were significant differences in the intensity levels among the subpopulations. At 48 h of ConA or LPS treatment only 10 +/- 4% of B, Th and Tc were positive, while none were positive in media alone. Stimulated peritoneal MO also increase positivity for ACTH-ir (85 +/- 5%). These results indicate that rat splenic B, CTL, and Th lymphocytes can be immunologically stimulated to express the peptide hormone ACTH and that basal ACTH expression in macrophages is distinct from that in lymphocytes. Thus, lymphocyte-derived ACTH may be a paracrine or autocrine regulator of immune function.

Changes in the ratio of urinary alpha 1-microglobulin to ulinastatin levels in patients with Alzheimer-type dementia and vascular dementia

Relationships between urinary levels of alpha 1-microglobulin (alpha 1M) and ulinastatin (UT) in patients with dementia were investigated. There were no significant differences in alpha 1M and UT levels and alpha 1M: UT ratios among three groups: age-matched control subjects, patients with either Alzheimer-type senile dementia (ATD) or vascular dementia (VD). Although a positive correlation was established between alpha 1M and UT levels in these groups, the regression of the demented patients differed significantly from that of controls (P < 0.05). A tendency towards a negative correlation between alpha 1M: UT ratios and the levels of severity or duration of the disease was displayed in the ATD group, whereas a tendency toward a positive correlation between alpha 1M: UT ratios and the levels of severity was observed in the VD group. These results suggest that changes in the relationships between urinary levels of alpha 1M and UT may provide a useful biochemical index for diagnoses of ATD and VD.

Selective transport of blood-borne interleukin-1 alpha into the posterior division of the septum of the mouse brain

Film autoradiography was used to demonstrate the transport and sites of accumulation of blood-borne radioiodinated interleukin-1 alpha (II-1 alpha) and other cytokines into the brain after intravenous administration. [125 I]Il-1 alpha, [125I]Il-1 beta, [125I]interleukin-1 receptor antagonist (II-1ra), and [125I]tumor necrosis factor-alpha (TNF alpha) labeled the choroid plexus and the capillary network 30 min after injection into the blood, suggesting that these areas may serve as sites of blood-to-brain transport. [125I]Il-1alpha, but not [125I]Il-1beta, [125I]Il-1ra, [125I]TNF alpha, or [125I]interleukin-2 (Il-2), was also found localized to the caudal region of the septal nuclei. Only unlabeled II-1 alpha was able to inhibit this accumulation. These findings provide further evidence for the passage of select cytokines across the blood-brain barrier (BBB) and are the first to identify a target site within the central nervous system (CNS) for a transported cytokine.

Type 1 interleukin-1 receptor in the rat brain: distribution, regulation, and relationship to sites of IL-1-induced cellular activation

Systemic interleukin-1 (IL-1) activates the hypothalamo-pituitary-adrenal (HPA) axis, an effect exerted through increased synthesis and secretion of corticotropin-releasing factor (CRF) by parvicellular neurosecretory neurons. The site(s) and mechanism(s) through which circulating IL-1 may access central systems governing HPA axis output remain obscure. To identify potential cellular targets for blood-borne IL-1, we analyzed the distribution of mRNA encoding the rat type 1 IL-1 receptor (IL-1R1) in rat brain. Regional ribonuclease protection assays detected a single protected fragment corresponding to the membrane-bound form of the IL-1R1 mRNA in all areas analyzed. In situ hybridization revealed labeling predominantly over barrier-related cells, including the leptomeninges, non-tanycytic portions of the ependyma, the choroid plexus, and vascular endothelium. Low to moderate levels of the IL-1R1 mRNA were detected in just a few neuronal cell groups, including the basolateral nucleus of the amygdala, the arcuate nucleus of the hypothalamus, the trigeminal and hypoglossal motor nuclei, and the area postrema. No specific labeling for IL-1R1 mRNA was detected over neurons that respond to intravenous IL-1 beta by induction of transcription factor Fos, including hypophysiotropic CRF cells and brainstem catecholamine neurons. Injection of IL-1 beta did, however, provoke induction of mRNA encoding the immediate-early gene, NGFI-B, but not c-fos, in two major loci of IL-1R1 expression, vascular endothelial cells, and the area postrema. Intravenous injection of IL-1 beta acutely down-regulated IL-1R1 mRNA in perivascular cells, but not in neuronal cell groups. These results suggest the parenchymal sites of IL-1R1 expression in rat to be distinct from those reported previously in mouse. The common expression in both species of an IL-1R in non-neuronal elements highlights the possibility that IL-1-mediated activation of CRF neurons may result from cytokine-receptor interaction at vascular, and/or other barrier-related, sites to trigger release of secondary signalling molecules in a position to interact with components of HPA control circuitry.

Expression of interleukin 1 alpha, interleukin 1 beta and interleukin 1 receptor antagonist mRNA in mouse brain: regulation by bacterial lipopolysaccharide (LPS) treatment

Lipopolysaccharide (LPS) stimulation is known to induce interleukin-1 (IL-1) mRNA expression in various immune cell types. Since IL-1 synthesis has been suggested to occur locally in brain tissue, we investigated the expression of IL-1 (alpha and beta) and IL-1 receptor antagonist (IL-1ra) mRNAs in various structures of the central nervous system, as well as in the spleen, following intraperitoneal injection of LPS (100 micrograms/mouse). After RNA extraction and amplification by the reverse transcription-polymerase chain reaction (RT-PCR), the PCR products were separated on an agarose gel, transferred and hybridized with digoxigenin-labeled probes synthetized by nested PCR. Glyceraldehyde phosphate deshydrogenase mRNA was used as an internal control. Under basal conditions the expression of IL-1 alpha, IL-1 beta and IL-1ra mRNAs in the brain was extremely low for the three cytokines; in the spleen these mRNAs were clearly detectable. Following LPS stimulation, mRNAs were strongly increased in all the tested tissues (cortex, hippocampus, hypothalamus, cerebellum, pituitary and spleen). The kinetics of mRNAs expressions in the brain were similar for all the tested regions, with a maximum at 6 h and a decrease up to 24 h after LPS administration. In the spleen the maximum was observed as soon as 1 h following stimulation. In conclusion, peripheral LPS stimulation induces a strong and transient expression of IL-1 alpha and IL-1 beta mRNAs in the brain. IL-1ra mRNA is also stimulated by LPS in various regions of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Endotoxin-induced appearance of immunoreactive interleukin-1 beta in ramified microglia in rat brain: a light and electron microscopic study

Interleukin-1 plays an important role as mediator of endotoxin-induced responses in the brain such as fever, sleep, anorexia, behavioural and neuroendocrine changes. In the present study, interleukin-1 beta immunocytochemistry has been performed at the light and electron microscopic level to study the cellular and subcellular localization of interleukin-1 beta in the brains of rats given endotoxin or saline. Light microscopic analysis of rats killed 4, 8 or 24h after endotoxin (2.5 mg/kg) given intraperitoneally or intravenously revealed a region-specific localization of immunoreactive interleukin-1 beta in macrophages and microglial cells. After saline treatment, no induction of interleukin-1 beta immunoreactivity occurred in the brain. After administration of endotoxin, many interleukin-1 beta-positive cells were found in the meninges, choroid plexus, circumventricular organs, cerebral cortex and hypothalamus. The number of interleukin-1 beta-positive microglial cells reached a maximum 8 h after administration of endotoxin, irrespective of the route of administration. In general, more interleukin-1 beta-positive microglial cells were found after intravenous than after intraperitoneal administration of endotoxin. Interleukin-1 beta-positive microglial cells were often grouped in patches in the vicinity of blood vessels. At the surface of the cerebral cortex, in the meninges, intermediate cell forms between interleukin-1 beta-positive macrophages and microglial cells were found. interleukin-1 beta-positive perivascular microglia were localized at the brain side of the basal lamina. Immunoreactive interleukin-1 beta was found at the luminal side of the endothelial cells lining the venules. Furthermore, microglial cells that extended their processes into the ependymal layer of the third ventricle were observed. Results of the electron microscopic studies revealed immunoreactive interleukin-1 beta in many cells with the cellular characteristics of microglial cells, but also, in some cells, identified as astrocytes. In microglial cells, immunoreactive interleukin-1 beta was found in the cytoplasm but not in the endoplasmatic reticulum or Golgi apparatus. These results show that after peripheral administration of endotoxin, immunoreactive interleukin-1 beta is induced in macrophages in the meninges and in the choroid plexus, as well as in microglial cells in parenchyma. Interleukin-1 beta produced by these cells may serve as a signal for adjacent or more distant targets (neurons, endothelial cells, microglial cells) to play a role in the induction of non-specific symptoms of sickness.

Role of interleukin-1 in stress responses. A putative neurotransmitter

Recently, the central roles of interleukin-1 (IL-1) in physical stress responses have been attracting attention. Stress responses have been characterized as central neurohormonal changes, as well as behavioral and physiological changes. Administration of IL-1 has been shown to induce effects comparable to stress-induced changes. IL-1 acts on the brain, especially the hypothalamus, to enhance release of monoamines, such as norepinephrine, dopamine, and serotonin, as well as secretion of corticotropin-releasing hormone (CRH). IL-1-induced activation of the hypothalamo-pituitary-adrenal (HPA) axis in vivo depends on secretion of CRH, an intact pituitary, and the ventral noradrenergic bundle that innervates the CRH-containing neurons in the paraventricular nucleus of the hypothalamus. Recent studies have shown that IL-1 is present within neurons in the brain, suggesting that IL-1 functions in neuronal transmission. We showed that IL-1 in the brain is involved in the stress response, and that stress-induced activation of monoamine release and the HPA axis were inhibited by IL-1 receptor antagonist (IL-1Ra) administration directly into the rat hypothalamus. IL-1Ra has been known to exert a blocking effect on IL-1 by competitively inhibiting the binding of IL-1 to IL-1 receptors. In the latter part of this review, we will attempt to describe the relationship between central nervous system diseases, including psychological disorders, and the functions of IL-1 as a putative neurotransmitter.

Differential dependence of ACTH secretion induced by various cytokines on the integrity of the paraventricular nucleus

Effect of different cytokines, human recombinant interleukin-1 alpha and beta (IL-1 alpha, IL-1 beta), interleukin-6 and tumor necrosis factor-alpha (TNF) on adrenocorticotropin (ACTH) secretion was compared in sham-operated rats and those with lesions of the hypothalamic paraventricular nucleus. IL-1 alpha was less active than IL-1 beta in stimulating ACTH in sham-operated rats. Intravenous injection of IL-1 beta in sham-operated animals resulted in a rapid elevation of ACTH secretion. Five days after surgical lesion of the paraventricular nucleus, the main hypothalamic source of hypophysiotropic corticotropin-releasing factor-41, the response to IL-1 beta was attenuated but not abolished. This suggests involvement of extra-paraventricular releasing factors in mediation of ACTH-releasing activity of IL-1 beta, altered responsiveness of pituitary to CRFs, and/or direct action of IL-1 beta on the corticotrope cells. TNF resulted in a biphasic stimulation of ACTH concentration, with peaks at 15 min and 90 min. In paraventricular-lesioned, TNF injected rats both of these ACTH peaks disappeared, suggesting that CRFs from the paraventricular origin mediates ACTH-inducing activity of TNF. IL-6 elevated ACTH secretion much later than the other intravenously injected cytokines, the peak was at 1 h in sham-lesioned rats. Paraventricular lesion completely prevented the increase of ACTH plasma levels after IL-6 injection. These data suggest that: (1) Effect of TNF and IL-6 on hypothalamo-pituitary-adrenal axis is mediated through the hypothalamic paraventricular nucleus and (2) IL-1 beta is able to release ACTH even in the absence of hypothalamic drive.

Interleukin-1 beta induces histamine release in the rat hypothalamus in vivo

We have previously demonstrated the increase of histidine decarboxylase activity and histamine content in the murine hypothalamus after intracerebroventricular injection of lipopolysaccharide possibly due to inducible interleukin-1 beta (IL-1 beta). Therefore, we investigated the effects of IL-1 beta on brain histamine dynamics by directly injecting it into the tuberomammillary nucleus of the rat hypothalamus (TM) using an in vivo microdialysis method. Injection of artificial cerebrospinal fluid or recombinant murine IL-1 beta at 0.1 ng into the TM did not evoke a significant change in core temperature, however, a significant monophasic febrile response was observed following injection of IL-beta at more than 1 ng per animal. Histamine release in the anterior hypothalamic area in vivo was significantly augmented from 140 min to 360 min following injection of IL-1 beta at 10 ng dose. These results suggest the possibility that interrelationship between histamine and IL-1 beta may modulate the acute phase reaction in the central nervous system.

Interleukin-1 beta increases basic fibroblast growth factor mRNA expression in adult rat brain and organotypic hippocampal cultures

In situ hybridization was used to study the effect of IL-1 beta on acidic fibroblast growth factor (aFGF) and basic fibroblast growth factor (bFGF) mRNA expression in rat brain. Intraventricular injection of recombinant human IL-1 beta did not affect hybridization to aFGF mRNA but did induce significant and widespread increases in hybridization to bFGF mRNA. IL-1 beta induced increases in bFGF mRNA were bilaterally distributed and appeared to correspond with the distribution of non-neuronal cells. Thus, hybridization was increased in regions of both gray and white matter (e.g., corpus callosum), the ependymal lining of the third ventricle, and the pia matter. In hippocampus of IL-1 beta injected rats, hybridization was markedly increased in the molecular layers but not significantly increased in the neuronal cell layers. Elevations in bFGF mRNA were transient, peaking at 8 h postinjection in most areas. To determine if IL-1 beta effects were independent of activation of the hypothalamo-pituitary-adrenal axis, and to compare the cellular localization of increases in bFGF mRNA expression induced by IL-1 beta and bFGF, the regulation of bFGF expression was also studied in organotypic hippocampal slice cultures. Treatment of cultures with either IL-1 beta or bFGF stimulated the same general distribution of increases in bFGF mRNA as seen after IL-1 beta treatment in vivo with an additional effect on immature neurons within the hilar side of stratum granulosum; hybridization of bFGF mRNA was not increased in association with the more mature neurons of stratum pyramidale or stratum granulosum. Colocalization of bFGF cRNA hybridization with immunostaining for glial fibrillary acidic protein demonstrated that increases in bFGF mRNA induced both by IL-1 beta in vivo and in vitro and by bFGF in vitro were largely associated with astroglial cells. These findings suggest that IL-1 beta induction of bFGF contributes to the coactivation of these substances following various forms of insult to the CNS and initiates a cascade of trophic interactions that regulates processes of glial proliferation, neurotrophic factor expression, and neuroprotection.

Expression of type I and type II interleukin-1 receptors in mouse brain

Although binding sites for IL-1 have been identified in the mouse brain, it is still unknown whether these binding sites correspond to the type I or type II IL-1 receptor. Quantitative autoradiography was used to confirm the presence of specific binding sites for radiolabelled recombinant human IL-1 alpha (125I-HuIL-1 alpha) in the brain of DBA/2 mice. IL-1 binding was highest in the dentate gyrus, consisting of a single class of high affinity binding sites with a Kd of 0.1 nM and a Bmax of 57 fmol/mg protein. A similar Kd of 0.2 nM was obtained using isolated membranes from the whole hippocampus, although the number of binding sites was lower (2 fmol/mg protein). Affinity cross-linking of 125I-Hu-IL-1 alpha to hippocampal membranes revealed the existence of two types of IL-1 receptor proteins, consistent with the sizes of the type I (85 kD) and type II (60 kD) IL-1 receptor. Oligonucleotide probes were then synthesized and used in RT-PCR followed by Southern blotting to show that the whole brain expresses transcripts for both the type I and type II IL-1 receptors. The murine neuroblastoma cell line, C1300, expresses type I rather than type II IL-1 receptor mRNA. The type I receptor protein can be identified by flow cytometry on the membrane of the C1300 neuronal cell line using indirect immunofluorescence with a rat anti-mouse type I IL-1 receptor MoAb. These data show that mouse brain expresses both type I and type II IL-1 receptor mRNA and proteins and offer further support to the idea that type I IL-1 receptors are synthesized and expressed by neurons.

Immunology discovers physiology

Not so long ago, it was believed that the brain is totally devoid of immunologic reactions, that cytokines derived from activated leukocytes serve only as communication molecules between leukocytes and that the immune system is regulated solely by intrinsic mechanisms. One by one, these old-time, traditional views have fallen by the wayside as neuroscientists, endocrinologists and pharmacologists have begun to explore immunology. The old view was that the immune system is autonomous because it neither affects nor is it affected by other physiologic systems. The new view is that cells of the immune system are inextricably linked with other physiological systems, including the neuroendocrine, cardiovascular, reproductive and central nervous systems (CNS). Changes in one system evoke changes in the other, and it is likely that communication loops have evolved between cells of the immune system and those of other tissues to coordinate and regulate functional activities aimed at preserving homeostasis during inflammation. The integrated view of immunophysiologists that cells of the immune system interact with the entire body, rather than existing as a separate physiologic system that operates autonomously, should help to unravel a number of mysteries in immunoregulation, such as the well-recognized redundant and pleiotropic properties of cytokines. Unfortunately, very few of these ideas have been incorporated into studying immunity of domestic animals. A complete understanding of immunobiology will be achieved only after this new field of immunophysiology is integrated into current immunological thinking.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 receptor deficiency in brains from NZB and (NZB/NZW)F1 autoimmune mice

Interleukin-1 receptors (IL-1R) are expressed in the brain and the anterior pituitary of normal mice (C3H/He, Swiss), and appear to be involved in the neuroendocrine control of the immune response. Here we have studied the IL-1R density in the brain and the pituitary from several strains of autoimmune mice (NZB, (NZB/NZW)F1, MRL/MP-lpr), using quantitative autoradiography with recombinant human [125I]IL-1 alpha as a ligand. IL-1R was similar in the brain of C3H/He, Swiss and NZW (controls) and MRL/MP-lpr mice. In NZB mice a profound deficit (10% of control mice) in IL-1R was observed exclusively in the dentate gyrus. In (NZB/NZW)F1 the deficit was about 50%. These observations were independent of sex and age. Pituitary receptors were not affected in all the strains except NZW (30% increase). Competition experiments demonstrated that the affinity of IL-1R was not modified in dentate gyrus of (NZB/NZW)F1 and NZW mice. Thus, the number of IL-1R was the only parameter affected. This deficit was not reversed by corticosterone treatment (0.2 mg/20 g body weight, i.p.) and was poorly modified by lipopolysaccharide treatment (0.1 mg/20 g body weight, i.p.) compared to C3H/He mice. In conclusion, this central IL-1R deficit is unlikely to be the consequence of occupancy by abnormal synthesis of brain IL-1. This abnormality is tissue-specific with hereditary autosomal transmission. The role of central IL-1R in neuroimmunoendocrine interactions and in autoimmunity remains to be clarified.

Cytokine receptors on glial cells

Given what evidence there is for the molecular and functional nature of cytokines and their cognate binding proteins in the immune system and the emerging similarities or even identities for these ligands and receptors in the nervous system, two general models may be relevant. The first emerging pattern is that receptors for related but distinct trophic factors in the CNS are in many instances multichain complexes with one or more shared components. The shared components of the receptor complex may be either signal- or nonsignal-transducing chains. A second emerging motif is that related ligands and related receptors fall into gene families. Undoubtedly, these models will facilitate the cloning of novel members of these families whose function is quite specific to the nervous system and in particular to glial cells. This article will review the function of the receptors for cytokines and families of differentiation/survival/growth factors as they operate on astrocytes, microglia, and oligodendrocytes in development, health, and disease.

"In situ" characterization of GnRH receptors: use of two radioimagers and comparison with quantitative autoradiography

New radioimagers, the HRRI (high resolution radioimager) and the Phosphorimager (phosphor screen : PS), apt to display more ample linear dose-response scale than radio-sensitive films, were tested in comparison with quantitative autoradiography (QA). GnRH receptor saturation experiments were achieved on tissue sections (rat pituitary, rat brain, human ovary) with a iodinate GnRH agonist (125I-[D-Ala6,Des-Gly10]-LH-RH Ethylamide) for determination of affinity constant (Kd). In rat pituitary, comparable results were obtained with the 3 methods (Kd: 0.4 to 0.6 nM). Discrepancies occurred in the hippocampus and in the granulosa cell layer of the preovulatory follicle, due to low resolutive (PS) or short linear dose-response (films) performances. In the hippocampus GnRH receptor affinity was under-estimated with PS (Kd: 2.3 vs 0.5 and 0.6 nM for QA and HRRI respectively). In the follicular granulosa cell layer it was over-estimated by QA (0.5 vs 50 nM for the HRRI), while PS did not allow resolution of this thin cell layer. In conclusion, the HRRI is a very powerful tool for the quantification of in situ radioligand binding (binding sites study and in situ hybridization) in very discrete areas.

Evidence for the production and action of interleukin-10 in pituitary cells

1. Interleukin-10 (IL-10) has a wide range of activities in the immune system such as modulation of interferon-gamma (IFN-gamma) and antibody production. The neuropeptide hormone corticotropin (ACTH) has similar activities, suggesting that a bidirectional communication mechanism operates between the immune and the neuroendocrine system involving these two substances. 2. Murine pituitary tumor cells (AtT-20) were found to produce up to 3 ng/ml of IL-10. 3. Pituitary cell corticotropin production was enhanced by IL-10 treatment. 4. IL-10 induced the production of ACTH in mouse splenocytes. 5. Authenticity of pituitary-derived IL-10 was shown by the demonstration of identical nucleic acid sequences of reverse-transcribed, polymerase chain reaction amplified fragments of cDNA obtained from murine splenocytes, a murine pituitary tumor cell line, and freshly isolated murine pituitaries.

Interleukin-1 receptor type I mRNA in mouse brain as affected by peripheral administration of bacterial lipopolysaccharide

Following administration of endotoxin in vivo, alterations of interleukin-1 (IL-1) receptor binding have been reported. In order to assess in vivo regulation of IL-1 receptor gene expression in brain, mRNA levels for IL-1 receptor type I were measured after peripheral administration of bacterial lipopolysaccharide in mice. When 25 micrograms of lipopolysaccharide were administered intraperitoneally, IL-1 receptor type I mRNA in the brain was increased after 3 h. After 20 h, the level was diminished. This result suggests that bacterial lipopolysaccharide affects regulation of IL-1 receptor type I mRNA expression in mouse brain.

Interleukin-1 beta inhibits Ca2+ channel currents in hippocampal neurons through protein kinase C

Interleukin-1 beta depresses the voltage-gated Ca2+ channel currents in acutely dissociated guinea-pig hippocampal CA1 neurons. This depression is observed with pathophysiological concentrations found in the cerebrospinal fluid (> or = 1.0 pg interluekin-1 beta/10 microliters). Interleukin-1 receptor antagonist (in concentrations 25-fold higher than interleukin-1 beta) completely blocked the interleukin-1 beta-induced depression of the Ca2+ channel current. This suggests that interleukin-1 beta action is through a specific interaction with an interleukin-1 membrane receptor site. The application of other cytokines and growth factors (interleukin-6, epidermal growth factor, and basic fibroblast growth factor), or bacterial lipopolysaccharide (endotoxin) had no effect, indicating specificity of action of interleukin-1 beta. The depression of the Ca2+ channel current by interleukin-1 beta was prevented by the extracellular application of pertussis toxin, and by the intracellular application of GDP[beta S], H-7, staurosporine or bisindolylmaleimide. Application of phorbol 12-myristate 13-acetate also depressed the Ca2+ channel current, but this phorbol ester-induced depression was not additive to that induced by interleukin-1 beta. These results suggest mediation of interleukin-1 beta action through a pertussis toxin-sensitive G-protein coupled interleukin-1 receptor associated with the activation of protein kinase C. The depression of the Ca2+ channel current by interleukin-1 beta may be involved in the regulation of neuronal excitability during pathological conditions and in the induction and/or progression of neurodegenerative processes.

Peripheral macrophage depletion prevents down regulation of central interleukin-1 receptors in mice after endotoxin administration

Interleukin-1 receptors (IL-1R) have been characterized in the brain and pituitary gland of mice. Previous studies have demonstrated that following lipopolysaccharide (LPS) injection, IL-1R density decreases in the dentate gyrus and in the choroid plexus. Receptors present in the anterior pituitary gland remain unchanged under the same experimental conditions. In this study, we investigated the role of peripheral macrophages in LPS-induced downregulation of IL-1 receptors. Mice were injected with liposomes encapsulated with dichloromethylene diphosphonate (Cl2MDP), which induced a profound depletion of peripheral macrophages. Immunocytochemistry was used to determine the efficiency of macrophage elimination. Depletion of macrophages did not affect the density of central and pituitary IL-1R in non-LPS-challenge mice. However, the liposome treatment prevented downregulation of IL-1R in the dentate gyrus observed following LPS administration. In addition, LPS induced a slight decrease in IL-1R density in the choroid plexus but not in the anterior pituitary gland of liposome treated mice. These results suggest that peripheral macrophages play an important role in the LPS-induced modulation of central IL-1R.

Growth factors in Parkinson's disease

The etiology of Parkinson's disease, one of the most frequent neurodegenerative disorders in human, is unknown. New hopes concerning satisfactory therapies include transplants of autologous adrenal medullary chromaffin tissue, fetal mesencephalic dopaminergic neurons, and local application of growth factors with a neurotrophic capacity. A large body of evidence supports the notion that neurons require trophic support not only during a limited period of ontogenesis, but during their whole lifespan. Relevant molecules promote survival, transmitter synthesis and other differentiated properties, and become crucially important when a neuron is metabolically or toxically impaired. Several molecules, most of which occur in the striatum and the substantia nigra, have been identified that protect lesioned dopaminergic nigrostriatal neurons in culture or in animal models of Parkinson's disease. These include members of the neurotrophin, fibroblast growth factor, and insulin-like growth factor families as well as epidermal growth factor/transforming growth factor alpha, interleukins and ciliary neurotrophic factor. Whether their effects are merely pharmacological, or reflect a physiological role in the nigrostriatal system, is unclear as yet. This article reviews experiments that document the trophic effects of these factors on dopaminergic neurons and discusses their possible physiological and therapeutic relevance.

Cytokines as mediators in the central nervous system

Cytokines are soluble mediators involved in cell-cell regulations in the immunological and the hematopoietic system. We review various cytokine effects on the central nervous system, including growth-promoting activity, neuro-modulatory action, fever induction, sleep and decreased food intake. In addition, cytokines, neuropeptides, neurotransmitters and hormones all participate in an intricate inter-relationship to contribute to the development and maintenance of brain homeostasis. Cytokines are also involved in the wounding responses of injured brain after trauma, infection or neuro-degenerative processes. Pharmacological modulation of the expression and/or actions of cytokines in the brain may represent a new field of research of therapeutic benefit in the treatment of central disorders.

Activation of the hypothalamus-pituitary-adrenal axis by bacterial endotoxins: routes and intermediate signals

Peripheral administration of endotoxin induces brain-mediated responses, including activation of the hypothalamus-pituitary-adrenal (HPA) axis and changes in thermoregulation. This paper reviews the mechanisms by which endotoxin affects these responses. The effects on thermoregulation are complex and include macrophage-dependent hyperthermic and hypothermic responses. Low doses of endotoxin, given IP, activate peripheral macrophages to produce interleukin (IL)-1 beta, which enters the circulation and acts as a hormonal signal. IL-1 may pass fenestrated endothelium in the median eminence to stimulate corticotropin-releasing hormone (CRH) secretion from the CRH nerve-terminals. In addition, IL-1 may activate brain endothelial cells to produce IL-1, IL-6, prostaglandins, etc., and secrete these substances into the brain. By paracrine actions, these substances may affect neurons (e.g., CRH neurons) or act on microglial cells, which show IL-1-induced IL-1 production and therefore amplify and prolong the intracerebral IL-1 signal. In contrast, high doses of endotoxin given i.v. may directly stimulate endothelial cells to produce IL-1, IL-6, and prostaglandin-E2 (PGE2) and thereby activate the HPA axis in a macrophage-independent manner.

The role of brain-immune interactions in immunotoxicology

Certain xenobiotics (or the metabolites) can damage immunocompetence by directly interacting with one or more of the cells of the immune system and adversely affecting its function. It has also been proposed that xenobiotics may indirectly affect immune function by affecting other organ systems that will in turn affect immunocompetence. This review surveys evidence that supports the existence of a functional link between the brain and the immune system. In addition, we review data that support the concept that a xenobiotic-induced dysfunction in the neuroendocrine system may be associated with an immune dysfunction as well. Such chemicals do not necessarily interact directly with immunocompetent cells but would instead act to disrupt regulatory brain-immune interactions. This class of indirectly acting immunotoxic xenobiotics would not be detected in the typical in vitro screening assays.

Interleukin 1 beta inhibits synaptic strength and long-term potentiation in the rat CA1 hippocampus

Cytokines such as interleukin-1 beta (IL-1 beta) are released in the nervous system following inflammation or infection. Recently, IL-1 beta was shown to enhance synaptic inhibitory mechanisms. We therefore investigated the effect of IL-1 beta superfusion on long-term potentiation (LTP), the cellular model of memory and learning, evoked in the CA1 region by tetanic stimulation of the stratum radiatum in the rat hippocampal slice. IL-1 beta (150 pM-1.5 nM) superfused 10 min before tetanic stimulation significantly reduced LTP of the slope of the population excitatory postsynaptic potential (pEPSP) and the population spike (PS) amplitude in CA1 in a concentration-dependent manner. IL-1 beta (1.5 nM) applied for 10 min 1 h before tetanus significantly inhibited LTP of the PS amplitude and pEPSP slope and reduced pEPSP and PS values before tetanus as well, although the PS returned to control values before tetanus. Heat-inactivated IL-1 beta had no effect on pre-tetanus pEPSP or PS values or the induction of LTP. These data demonstrate that IL-1 beta modulates synaptic potentials and reduces LTP. These findings have important implications for the role of IL-1 beta in neuronal disorders following infection, perhaps best exemplified by HIV-1-associated dementia.

Intravenous administration of interleukin-1 beta induces Fos-like immunoreactivity in corticotropin-releasing hormone neurons in the paraventricular hypothalamic nucleus of the rat

It has been shown that acute administration of recombinant human interleukin 1 beta (IL-1) to rats elicits an activation of the pituitary-adrenal axis. In the present study we investigated immunohistochemically the expression of Fos-like immunoreactivity (Fos-LI) in the hypothalamus of rats following intravenous injection of IL-1. One, 2 and 4 h after IL-1 or physiological saline injections, rats were killed and perfused, and the brains processed for Fos-immunohistochemistry. Dense populations of neurons containing Fos-LI-positive nuclei were found in the paraventricular hypothalamic nuclei (PVH) of IL-1-treated rats. In particular, the dorsal medial parvocellular part, but also some of the other parvocellular subdivisions contained many Fos-LI neurons. Maximal induction of staining was found at a dose of 5 micrograms/rat after 1 or 2 h survival, while immunostaining had decreased to almost control levels after 4 h. No Fos-LI was found in the PVH of control animals. Double immunocytochemical staining for Fos and corticotropin-releasing hormone (CRH) revealed that Fos-LI was predominantly present in parvocellular CRH-containing neurons of the PVH. The finding that peripherally injected IL-1 induces Fos-LI in hypothalamic CRH neurons strengthens the hypothesis that these neurons are part of the circuitry mediating IL-1-induced activation of the pituitary-adrenal axis.

Cellular localization of interleukin 6 mRNA and interleukin 6 receptor mRNA in rat brain

The distribution of interleukin 6 (IL-6) mRNA and IL-6 receptor (IL-6R) mRNA in the brain of adult male rats was studied at the light microscope level by in situ hybridization histochemistry using 35S-labelled oligonucleotides. The transcripts of both genes were localized in the pyramidal neurons and in the granular neurons of the hippocampus, in neurons of the habenular nucleus as well as in the dorsomedial and ventromedial hypothalamus, in the piriform cortex, in scattered neurons of the cortex and in granular cells of the cerebellum. The medial preoptic nucleus and the anterior tip of the lateral ventricle contained mRNA encoding IL-6 and its receptor. Moreover, white matter areas, such as the internal capsule, which consist of only fibres and glial cells, were found to have autoradiographic signals above background. The mRNAs for IL-6 and IL-6R in hippocampus and cerebellum are not different, as shown by Northern blot analyses of RNA isolated from these tissues. We postulate that the cytokine IL-6 is expressed constitutively in discrete regions of the CNS and that it is involved in the mechanisms coordinating metabolic, behavioural and neuroendocrine changes not only during illness but also under normal physiological conditions. Our results suggest that IL-6 mRNA and IL-6R mRNA are colocalized, thus supporting a role of the cytokine in autocrine and paracrine communication.

In situ hybridization study of interleukin-1 beta mRNA induced by kainic acid in the rat brain

The distribution patterns of interleukin-1 beta (IL-1 beta) mRNA in various brain regions of saline- and kainic acid-treated rats were examined using in situ hybridization technique. In normal rat brain, the signals of IL-1 beta mRNA were observed in the cerebellar Purkinje cells and in dispersed cells in the hypothalamus. In the case of the kainic acid treatment, IL-1 beta mRNA was intensely induced in the olfactory bulb, lateral septum, thalamus, hypothalamus, polymorphic layers of hippocampus, piriform cortex, amygdala, entorhinal cortex and cerebral cortex at 2 h after the injection of kainic acid. In the hypothalamic region, we observed the induction of IL-1 beta mRNA around the paraventricular hypothalamic nucleus, anterior hypothalamic area, dorsomedial and ventromedial hypothalamic nucleus, mammillary regions and arcuate nucleus. The signal of IL-1 beta mRNA was still expressed 4 h after treatment with kainic acid, less intensely than at 2 h, but above the control level. In these regions, IL-1 beta mRNA was expressed mainly in the glial cells, which were densely stained by Cresyl violet and did not contain glial fibrillary acidic protein. These results suggest that IL-1 beta is produced by a certain type of glial cells, maybe microglia, and might have regulatory functions in the central nervous system.

Species differences in [125I]interleukin-1 binding in brain, endocrine and immune tissues

There were dramatic species differences in the level of [125I]recombinant human interleukin-1 alpha ([125I]hIL-1 alpha) binding with high levels of binding present in mouse and rabbit tissues, while no specific binding was present in rat and guinea pig tissues. Utilizing [125I]hIL-1 alpha, moderate to high levels of specific binding were observed in EL-4 6.1 cells (representative of Type I IL-1 receptors) and in mouse hippocampus, spleen and testis; however, no specific [125I]hIL-1 alpha binding was present in Raji cells (representative of Type II IL-1 receptors) and in rat tissues. On the other hand, utilizing [125I]hIL-1 beta, high specific IL-1 binding was present in EL-4 6.1 and Raji cells and moderate binding was evident in mouse tissues, whereas specific [125I]hIL-1 beta binding to rat tissues was not detectable. Moreover, no IL-1 binding in rat tissues was observed using [125I]hIL-1 receptor antagonist, [125I]mouse IL-1 beta or the homologous radioligands [125I]rat IL-1 beta or [125I]rat IL-1 receptor antagonist. These data demonstrate that under optimal conditions for labeling Type I or Type II IL-1 receptors, no specific binding is observed in rat tissues suggesting the presence of novel IL-1 receptor(s) in rat tissues.

Cytokine stimulation increases intracellular calcium and alters the response to quisqualate in cultured cortical astrocytes

Cytokine levels are elevated in the central nervous system (CNS) in a variety of disorders and may contribute to abnormalities in CNS function associated with the disorders. To begin to understand the mechanisms through which elevated cytokines affect CNS cells, we have examined the effects of cytokines on astrocyte physiology within minutes of application as well as 24 h later. Both standard cultured cortical astrocytes and those induced to further differentiate by pre-treatment with forskolin were examined. Such treated astrocytes may more closely resemble those in brains exhibiting elevated cytokine levels. The cytokine focused upon was interleukin-1-beta (II-1 beta). Gamma-interferon (gamma-IFN) and tumor necrosis factor-alpha (TNF-alpha) were also examined in some studies. Changes in calcium levels produced by acute application of these cytokines were measured. The most pronounced effect was an immediate calcium elevation in response to II-1 beta in the forskolin pre-treated astrocytes. Longer term treatment with IL-1 beta in forskolin pre-treated astrocytes enhanced the calcium response to quisqualate stimulation, a glutamate neurotransmitter receptor agonist. These results suggest that situations that cause chronic changes in cytokine levels and involve astrocytic differentiation, such as chronic CNS infection or Alzheimer's disease, could change astrocytic responses to normal stimuli. Such changes may result in altered astrocytic support of neurons and therefore cause changes in CNS function.

Induction of microglial immunomolecules by anterogradely degenerating mossy fibres in the rat hippocampal formation

Degeneration of myelinated axonal connections is generally held to provide a strong stimulus for microglial expression of major histocompatibility complex (MHC) class II antigen. The present study demonstrates that strong microglial reactions also are induced by axonal and terminal degeneration of the unmyelinated hippocampal mossy fibres. After destruction of dentate granule cells by focal injections of colchicine (or transection of the mossy fibres) in adult rats, immunocytochemical analysis of the mossy fibre terminal fields in the dentate hilus and regio inferior of hippocampus proper (CA3) revealed profound changes in microglial cells with increased expression of the complement receptor type 3 and induction of MHC class I antigen, leukocyte common antigen, lymphocyte function-associated antigen-1 and MHC class II antigen. The microglial reaction, first detectable 4 days after the lesion, became maximal during the third postlesional week, and had almost vanished 6 weeks after the lesion. From recent studies we know that anterograde degeneration of myelinated Schaffer-collaterals from CA3 to regio superior of hippocampus proper and myelinated entorhinal perforant path fibres to fascia dentata is accompanied by microglial expression of MHC class I antigen, but not class II. Together with the present findings, this demonstrates that myelin debris is neither necessary nor sufficient to induce expression of microglial MHC class II antigen within the hippocampus.

Involvement of cytokines in acute neurodegeneration in the CNS

Cytokines, (particularly interleukins and growth factors) are synthesised in the brain, and induced by brain damage. Interleukin-I appears to directly mediate ischaemic and excitotoxic brain damage, whereas growth factors (e.g., bFGF, NGF), and the phospholipid binding protein lipocortin-1 exhibit neuroprotective actions. Central administration of recombinant interleukin-1 receptor antagonist markedly attenuates damage induced by focal cerebral ischaemia, or pharmacological activation of NMDA receptors in the rat brain. The mechanisms of action of these cytokines on neurodegeneration are unknown, but indirect evidence has implicated corticotropin releasing factor, arachidonic acid, and nitric oxide. In vitro effects of interleukin-1, growth factors, and lipocortin-1 have been reported on intracellular calcium homeostasis, which is critically important in neurodegeneration. Pharmacological modulation of the expression and/or actions of cytokines in the brain may be of considerable therapeutic benefit in the treatment of acute neurodegeneration.

Molecular identification of two types of interleukin-1 receptors in the murine pituitary gland

The present study was carried out to characterize interleukin-1 (IL-1) receptors on murine pituitary cells. Receptor autoradiography confirmed the existence of binding sites for IL-1 alpha in the murine adenohypophysis, but not in the neural or intermediate lobes. Specific binding of IL-1 to isolated pituitary membranes revealed a Kd of 0.9 nM with a Bmax of 37 fmol/mg protein. To examine the possibility that the adenohypophysis synthesizes a receptor for IL-1, immunocytochemistry experiments with a specific monoclonal antibody against the type I receptor revealed the existence of this protein in only the adenohypophysis. Identity of the type I IL-1 receptor was similar to that found on T cells as determined by: 1) amplification of the predicted 619 bp fragment spanning the cytoplasmic, transmembrane and extracellular domains from RNA of pituitary and T cell origin, as well as clonal AtT-20 pituitary cells, and 2) restriction fragment analysis and sequencing of the amplified cDNAs. The pituitary gland and AtT-20 cells also expressed transcripts for the newly identified type II receptor for IL-1 as assessed by amplification of a specific 325 bp fragment, restriction fragment analysis and nucleotide sequencing, and these transcripts were similar to those found on B lymphocytes. These data identify two different forms of the IL-1 receptor in both normal and transformed pituitary cells and establish that these receptors are similar at the molecular level to those first identified on T and B lymphocytes.

Interleukin 1 receptors in the brain and endocrine tissues

Immune activation is often accompanied by profound alterations in neurological and endocrine function, such as fever, increased somnolence, decreased appetite, activation of the hypothalamic-pituitary-adrenal axis, and suppression of the hypothalamic-pituitary-gonadal and hypothalamic-pituitary-thyroid axes. These well-recognized systemic responses to injury and infection have been attributed to circulating pro-inflammatory cytokines, the best characterized of which is interleukin 1 (IL-1). Here Emmett Cunningham and Errol De Souza discuss the mechanisms by which blood-borne IL-1 might affect such changes in the nervous and neuroendocrine systems.

An mRNA homologous to interleukin-1 receptor type I is expressed in cultured rat sympathetic ganglia

Interleukin-1 (IL-1) induces substance P (SP) gene expression in cultured rat superior cervical ganglion (SCG) explants. In order to study the molecular mechanism of this action of IL-1, the presence of an interleukin-1 receptor (IL-1R) activity and the identity of an mRNA homologous to known IL-1R sequence was determined in SCG. The SP increase is blocked by recombinant IL-1 receptor antagonist protein, so IL-1 must be interacting with a specific receptor. We have cloned cDNA homologous to IL-1R type I from rat SCG using a reverse transcription-polymerase chain reaction (RT-PCR). The resulting cDNA sequence is strongly homologous with mouse and human IL-1R cDNA of the T cell and fibroblast type (type I; encoding an 80-kDa protein). mRNA specific for IL-1R can be readily detected in intact SCG by quantitative RT-PCR and S1 hybridization. However, the level of IL-1R mRNA increases 3-6-fold by 2 days in culture. This increase is independent of the presence of dexamethasone, IL-1 beta or IL-1 receptor antagonist protein ligands. The increase of IL-1R following explantation, a model of nerve injury, may provide a mechanism linking inflammatory signalling to neuronal phenotypic changes.

Systemic interleukin-1 beta decreases brain-derived neurotrophic factor messenger RNA expression in the rat hippocampal formation

Brain-derived neurotrophic factor is selectively expressed at relatively high levels in the rat hippocampal formation (for review, see Ref. 12; see also Refs 8, 13, 19, 20, 27) where it is thought to be involved in mechanisms of neurodegeneration and/or neural protection related to the plasticity of hippocampal neurons. Functional responses to brain-derived neurotrophic factor appear to be mediated by a tyrosine receptor kinase B with the possible involvement of the p75 low-affinity nerve growth factor receptor protein. Among the many characteristics of Alzheimer's disease is an upregulation of immune mediators in and around senile plaques in Alzheimer's disease. Recently, interleukin-1 has been shown to be detrimental to the long-term survival of embryonic hippocampal neurons in culture. Thus, if the same occurs in vivo, it is possible that the accumulation of interleukin-1 in Alzheimer's disease hippocampus may be responsible for altered hippocampal neuron synaptic plasticity. This may occur either by a direct action of interleukin-1 on hippocampal neurons or possibly indirectly by stimulating beta-amyloid production. Other indirect mechanisms may involve growth or survival factors such as the neurotrophin brain-derived neurotrophic factor which is thought to play an important role in the plastic responses of hippocampal neurons. A recent study showed that brain-derived neurotrophic factor mRNA is selectively decreased in the dentate gyrus in Alzheimer's disease. The reason(s) for the decrease of brain-derived neurotrophic factor mRNA is not known, but one possibility may be associated with the enhanced expression of interleukin-1 in the hippocampus of Alzheimer's disease patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 binding sites on astrocytes

Interleukin-1 has been shown to have regulatory effects on glial cell functions. In this study, we examined the capacity of astroglial cells to specifically bind recombinant iodinated human interleukin-1 alpha. This was performed in mouse brain by both in situ and in vitro autoradiography, on areas of gliosis and on astrocytes and microglia primary and secondary cultures respectively. Specific binding was shown in the brain sections over areas of glial proliferation, and in addition, quantitative autoradiography was performed. Analysis of competition experiments by autoradiography led to EC50 values of 5 x 10(-11) M for human interleukin-1 alpha and approximately 10(-9) M for the interleukin-1 receptor antagonist. In cultures, iodinated human interleukin-1 alpha bound specifically to astrocytes but was unable to bind to microglial cells. Competition binding experiments in astrocyte cultures led to EC50 values of 8 x 10(-11) M and 1 x 10(-10) M for human interleukin-1 alpha and mouse interleukin-1 beta respectively, and an EC50 higher than 10(-9) M for the antagonist. The presence of interleukin-1 receptors on astroglial cells provides biochemical support for the various effects of interleukin-1 in the central nervous system, particularly those concerning the formation of scar tissue, possibly by astroglia proliferation after brain injury.

Localization of TNF alpha and IL-1 alpha immunoreactivities in striatal neurons after surgical injury to the hippocampus

Since the inflammatory process develops after transplantation to the brain, we sought to determine the presence of cytokines following a surgical trauma to the brain of an adult mouse. We report the early and marked presence of tumor necrosis factor-alpha and interleukin-1 alpha in neuronal somata of the striatum following a surgical injury to the hippocampus. The expression of cytokines later extends to neuronal cells of the hippocampus, thalamus, cerebral cortex, brain stem, and cerebellum and to glial cells of the corpus callosum. By contrast, these cytokines are not expressed by neuronal cells following injury to other regions, such as the striatum, cerebellum, and cortex. This study suggests a possible role for certain neurons in the brain's early reaction to a penetrating injury.

Expression of amyloid precursor protein mRNAs in endothelial, neuronal and glial cells: modulation by interleukin-1

The origin of beta-amyloid deposited in senile plaques in Alzheimer's disease (AD) is not known. We compared the expression of protein precursor of beta-amyloid (APP) in the cell types involved in plaque formation. The levels of APP mRNA were determined in primary rat neurons and glial cells in culture, human endothelial cells and in a murine brain-derived endothelial cell line. Northern blot analysis was performed using an APP cDNA probe to detect the general APP sequence and an oligonucleotide (40 mer) complementary to the sequence of the Kunitz protease inhibitor (APP-KPI). The APP mRNA transcripts were abundant in all three cell types. The highest level of APP, normalized to beta-actin mRNA content, was expressed in neurons, followed by glial cells, where the APP expression was similar (94%) while in endothelial cells was lower (53%). The proportion between APP-KPI mRNA and total APP mRNA was high in endothelial, intermediate in glial and low in neuronal cells. We compared the effects of exposure to interleukin-1 (IL-1), a cytokine involved in several biological processes and elevated in AD, on APP mRNA expression in neuronal, glial and endothelial cells. In human endothelial and in brain-derived murine endothelial cells we observed a similar increase (50%) of total APP mRNA or APP-KPI mRNA after treatment with human recombinant IL-1 beta. In neuronal cells, IL-1 (200 ng/ml) substantially increased APP mRNA (175%), detected with both probes. In glial cells, the expression of APP mRNA did not appear to be altered by IL-1 (50-400 ng/ml). The results suggest a role of IL-1 in the neuronal mechanisms related to beta-amyloid protein deposition in AD.

Expression of interleukin (IL)-1 beta, IL-6 and their respective receptors in the normal rat brain and after injury

The expression of interleukin (IL)-1 beta, IL-6 and their respective receptors has been studied in the rat brain before and up to 24 h after injury. Messenger RNA transcripts of these four genes were detected by in situ hybridization (ISH) in different structures of the intact brain. The distribution was very similar for IL-1 beta, IL-6 and IL-6 receptor (IL-6R). The expression of IL-1R was more widespread. Within hours after injury, an increased expression of IL-1 beta, and thereafter of IL-6 was documented. The expression of IL-1R and IL-6R was also increased. This expression was bilateral and not restricted to the injured area. Within 24 h, all ISH patterns had returned to normal. The molecular data were confirmed by protein data. Indeed, the distribution of IL-6 (detected by immunocytochemistry) agreed with the ISH patterns for IL-6. Furthermore, extracellular fluid was collected by microdialysis at the site of the lesion during 12 h and successive fractions were assayed for the presence of bioactive IL-1 and IL-6. Increases in IL-1 and later in IL-6 levels were detected. The rapid and concomitant increased expression of IL-1 beta, IL-6 and their receptors after injury stresses their possible early role in inflammatory mechanisms also in the brain, before any recruitment of inflammatory cells from remote nervous and not nervous areas.

Type I interleukin-1 receptors in the mouse brain-endocrine-immune axis labelled with [125I]recombinant human interleukin-1 receptor antagonist

Iodine-125-labelled recombinant human interleukin-1 (IL-1) receptor antagonist ([125I]IL-1ra) was utilized to further determine the characteristics of IL-1 receptors in the brain-endocrine-immune axis. The binding of [125I]IL-1ra in homogenates of mouse hippocampus, spleen and testis was linear over a broad range of membrane protein concentrations, saturable, reversible, and of high affinity (KD, 20-30 pM). In competition studies, IL-1ra, recombinant human IL-1 alpha, IL-1 beta and a weak IL-1 beta analog inhibited [125I]IL-1ra binding to mouse tissues in parallel with their biological activities. In autoradiographic studies, [125I]IL-1ra and [125I]IL-1 alpha binding showed comparable distribution patterns with highest densities of binding sites present in the dentate gyrus of the hippocampus, choroid plexus, anterior pituitary, marginal zones and red pulp regions of the spleen, epididymis and interstitial area of the testis. The binding characteristics and distribution of [125I]IL-1ra are comparable to those of previously characterized Type I IL-1 receptors. These data provide further support for a role for IL-1 in coordinating brain-endocrine-immune responses to physiological and pharmacological stimuli.

Adrenalectomy does not change CRF secretion induced by interleukin-1 from rat perifused hypothalami

Interleukin-1 (IL-1) is a potent hypothalamic-pituitary-adrenal (H-P-A) axis activator. The hypothalamus is considered one of the main sites of action of IL-1 on the H-P-A axis, inducing CRF secretion, which is modulated by glucocorticoids. Glucocorticoids, which modulate CRF release by a negative feedback inhibition, have been postulated to exert a permissive action on the IL-1 effect on CRF secretion. Using a continuous perifusion system of rat hypothalami, the results of the present study indicate that at the same concentrations, IL-1 beta exerted a more potent effect than IL-1 alpha stimulating CRF secretion. The increase in hypothalamic CRF release induced by IL-1 was rapidly inhibited by both dexamethasone and corticosterone. However, adrenalectomy 2 or 8 days before did not modify CRF secretion induced by IL-1 from the in vitro perifused hypothalami. These data indicate that IL-1 does not seem to induce CRF secretion by interfering with an impeding action of glucocorticoids, although the cytokine effect is negatively modulated by corticosteroids.

Cytokines in neural regeneration

Growth factors with already established multiple effects on non-neural cells continue to be of considerable interest to researchers with regard to the nervous system, where regulation of cell maintenance and plasticity in relation to lesion and regeneration is part of their functional repertoire. Fibroblast growth factors, interleukins, and type beta transforming growth factors are prominent representatives of such proteins. Ciliary neurotrophic factor is another multifunctional neurokine. The proposed role of this molecule as a 'lesion factor', however, is still not firmly settled.

Interleukin-1 beta depresses calcium currents in CA1 hippocampal neurons at pathophysiological concentrations

Interleukin-1 is present in the central nervous system (CNS) during acute and chronic pathological processes. In the present study, we examined the interaction between recombinant human interleukin-1 beta (rhIL-1 beta) and the voltage-dependent calcium (Ca2+) current using the whole-cell patch clamp technique. RhIL-1 beta depressed the voltage-gated Ca2+ current in acutely dissociated guinea pig hippocampal CA1 neurons. This depression is rapid and is observed at pathophysiological concentrations (greater than or equal to 1.97 pg/10 microliters). Concomitant application of rhIL-1 beta and rhIL-1 receptor antagonist had no effect indicating neuroactive specificity of rhIL-1 beta. The depression of the inward Ca2+ current by IL-1 beta may play a role in: 1) the regulation of neuronal excitability; 2) the induction of neurological manifestations during disease; and 3) in the induction and/or progression of neurodegenerative processes.