Effect of intracerebroventricular administration of vasopressin on stress-induced hyperthermia in rats

Vasopressin has been reported to be an endogenous antipyretic peptide. The present study assessed whether this peptide has similar effects on stress-induced hyperthermia. Infusion of 3 ng of vasopressin into the lateral ventricle prior to a 40-min restraint stress reduced significantly the hyperthermic response of rats to this stress, compared to saline-injected controls. Half of the vasopressin-injected animals showed an immediate hypothermic response, with a significant reduction in body temperature of 0.34 degree C or more within 10 min; however, the effect of vasopressin on stress-induced hyperthermia remained significant after exclusion of these animals from the analysis. Administration of a V1 receptor antagonist prior to the stress did not affect the hyperthermic response, which may suggest that the hyperthermic response had reached maximal (ceiling) levels. Administration of vasopressin, or of the V1 receptor antagonist immediately after the stress, did not affect defervescence, suggesting that vasopressinergic systems are not implicated in the defervescence process. Thus, the results show that ICV administration of vasopressin reduces stress-induced hyperthermia. The mechanisms underlying the effects remain to be elucidated.

Vagotomy attenuates behavioural effects of interleukin-1 injected peripherally but not centrally

Peripheral and central injections of recombinant rat interleukin-1 beta (IL-1 beta) have been shown to decrease social exploration in rats. To test the involvement of vagal afferents in the communication between the immune system and the brain, sham-operated and vagotomized rats were injected peripherally or centrally with physiological saline or IL-1 beta 4 weeks after surgery. Vagotomy attenuated the depression in social exploration induced by i.p. administration of IL-1 beta (15 micrograms) but did not alter the behaviour-depressing effects of an intracerebroventricular (i.c.v.) injection of IL-1 beta (45 ng). These results confirm the role of vagal afferent nerves in the transmission of an immune message from the periphery to the brain, and show that vagotomy does not impair the direct sensitivity of the brain itself to immune signals.

An endogenous 55 kDa TNF receptor mediates cell death in a neural cell line

Tumor necrosis factor-alpha (TNF) is associated with developmental and injury-related events in the central nervous system (CNS). In the present study, we have examined the role of TNF on neurons using the clonal murine neuroblastoma line, N1E-115 (N1E). N1E cells represent a well-defined model for studying neuronal development since they can be maintained as either undifferentiated, mitotically active neuroblasts or as differentiated, mature neurons. Northern and reverse transcription-polymerase chain reaction (RT-PCR) analyses revealed that both undifferentiated and differentiated N1Es express transcripts for the 55 kDa TNF receptor (TNFR), but not the 75 kDa TNFR. The biological activity of the expressed TNF receptor was demonstrated by a dose dependent cytotoxicity to either recombinant murine or human TNF when the cells were incubated with the transcriptional inhibitor actinomycin D. The lack of the 75 kDa receptor mRNA expression and the dose dependent response to rHuTNF, an agonist specific for the murine 55 kDa receptor, suggest that the TNF induced cytotoxicity is mediated through the 55 kDa receptor in both the undifferentiated and differentiated N1Es. Light microscopic observations, flow cytometric analysis of hypodiploid DNA, and electrophoretic analysis of nucleosomal DNA fragmentation of N1Es treated with actinomycin D and TNF revealed features characteristic of both necrotic and apoptotic cell death. These findings demonstrate that blast and mature N1E cells express the 55 kDa TNF receptor which is responsible for inducing both necrotic and apoptotic death in these cells. The observation that actinomycin D renders N1E cells susceptible to the cytotoxic effects of TNF indicates that a sensitization step, such as removal of an endogenous protective factor or viral-mediated inhibition of transcription, may be necessary for TNF cytotoxicity in neurons.

Adrenalectomy enhances pro-inflammatory cytokines gene expression, in the spleen, pituitary and brain of mice in response to lipopolysaccharide

To assess the possible influence of endogenous glucocorticoids on cytokine expression in the brain, adrenalectomized mice and sham operated mice were injected with saline or lipopolysaccharide (LPS, 10 micrograms/mouse, subcutaneously) and the levels of transcripts for IL-1 alpha, IL-1 beta, IL-1ra, IL-6 and tumor necrosis factor-alpha (TNF alpha) were determined 2 h after treatment in the spleen, pituitary, hypothalamus, hippocampus and striatum, using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). Levels of IL-1 beta were measured by ELISA in plasma and tissues of mice sacrificed after the administration of LPS or saline. LPS induced the expression of pro-inflammatory cytokines at the mRNA level in all tissues under investigation, except for TNF alpha in the hippocampus. This effect was potentiated by adrenalectomy in the spleen for IL-1 alpha and IL-1ra, the pituitary for cytokines other than IL-1ra, the hypothalamus for all cytokines, the hippocampus for cytokines other than TNF alpha, and the striatum for IL-1 alpha and IL-6. In saline-treated mice, adrenalectomy increased IL-1 alpha and IL-1 beta gene expression in the hypothalamus and IL-1 alpha gene expression in the hippocampus and striatum. LPS increased plasma and tissue levels of IL-1 beta, as determined by ELISA, and this effect was potentiated by adrenalectomy in plasma and tissues other than the spleen. These results can be interpreted to suggest that endogenous glucocorticoids regulate the neural components of the host response to infection and inflammation by inhibiting cytokine expression in peripheral organs and the brain.

Macrophages synthesize and secrete a 25-kilodalton protein that binds insulin-like growth factor-I

Primary (thymus) and secondary (spleen) murine lymphoid tissues express a 25-kDa protein that binds IGF-I. To determine the cellular source of this insulin-like growth factor binding protein (IGFBP), 11 murine or human cell lines representing T, B, and myeloid cells at various stages of differentiation were characterized by IGF-I affinity cross-linkage and Western ligand blotting. Mature myeloid cells, but not T or B cells, secrete a 25-kDa protein that is capable of binding IGF-I. CSF-1-derived bone marrow macrophages also synthesize this 25-kDa IGFBP. Thymic macrophages, which were estimated to secrete 2 ng of binding protein/10(6) cells-h, were used in conjunction with [125I] IGF-I affinity cross-linking to develop a protein binding immunomobility-shift assay to identify which IGFBP is produced by these cells. An anti-IGFBP-4Ab, but not an anti-IGFBP-2 Ab or normal rabbit serum, shifted the [125I] IGF-IGFBP complex to a higher m.w. position, indicating that the single 25-kDa IGFBP is IGFBP-4. Northern blotting confirmed that transcripts for IGFBP-4 as well as IGF-I are expressed in thymic macrophages. A putative 278-bp IGFBP-4 cDNA fragment (residues 341-618) of rat) that contains two unique cysteine residues found only in IGFBP-4 was cloned and sequenced from thymic macrophages. These clones differed from the rat sequence at only six residues (97% homology), and the deduced amino acid sequence from the murine cDNA was identical with that of the rat sequence. Subsequent studies revealed that IGF-I stimulates DNA synthesis in thymic macrophages. However, two different IGF-I analogues differing in the amino-terminus that bind equally well to the IGF-I receptor but poorly to IGFBPs are as effective as IGF-I at 100-fold lower concentrations. These data demonstrate that murine macrophages are a source of a single 25-kDa secreted protein that binds IGF-, that the molecular identity of this protein is IGFBP-4, and that this binding protein may antagonize the extracellular effects of IGF-I.

Growth hormone, growth factors and hematopoiesis

Hypocellularity of primary lymphoid organs is a distinctive and reproducible characteristic of aged humans and animals. Similar changes have been reported in both hypophysectomized and dwarf rodents. In the bone marrow of these animals, there is an associated reduction in the number of erythroid, lymphoid and myeloid elements. Implantation of growth hormone (GH)-secreting GH3 pituitary cells or infusion of growth hormone into aged rodents dramatically improves cellularity of both the thymus gland and bone marrow. At present it is unknown whether these effects are due to direct effects of growth hormone on hematopoietic cells or if they are caused by the induction of insulin-like growth factor-1 (IGF-1) synthesis. We recently discovered that colony-stimulating factor-1 (CSF-1) and interleukin-3 (IL-3) induce expression and synthesis of the IGF-1 peptide in murine bone marrow cells. Transcripts for IGF-1 increase approximately 50-fold during differentiation over the negligible levels that are expressed in freshly isolated bone marrow cells. Two potential functions of macrophage-derived IGF-1 are to: (a) increase the proliferation of early or committed bone marrow progenitors and (b) reduce their rate of cell death. In support of the first possibility, IGF binding protein-3 significantly inhibits the proliferation of CSF-1-treated bone marrow cells and this inhibition can be reversed by addition of exogenous IGF-1. In support of the second possibility, we have induced apoptosis of both nonadherent bone marrow cells and a myeloid progenitor cell line by depriving these cells of CSFs. Preliminary results indicate that addition of IGF-1 to these cells reduces apoptotic cell death by 50%. These data establish that two different CSFs, CSF-1 and IL-3, induce abundant expression of IGF-1 as these cells differentiate into more mature hematopoietic cells. This model offers a novel approach for investigating the developmental expression of IGF-1 during defined differentiation pathways of hematopoietic cells. If IGF-1 is indeed proven to act as a survival factor for hematopoietic progenitors, these data would support the idea that the hypocellularity of primary lymphoid tissues in aged animals is related to the limited availability to these cells of either growth hormone or IGF-1.

Mechanisms of sickness-induced decreases in food-motivated behavior

Interleukin-1 beta (IL-1 beta) is a cytokine released by activated macrophages and monocytes, which mediates many of the local and systemic responses to inflammation. Interleukin-1 beta induces anorexia in rats when administered peripherally or centrally. An endogenous antagonist for the IL-1 type I receptor has been characterized and cloned (IL-1ra). We have used this protein to ascertain the site of action for the anorexic effects of IL-1 beta. Male rats were food restricted and trained on an operant schedule for food reinforcement. Administration of recombinant human IL-1 beta (4 micrograms i.p. or 40 ng i.c.v.) induced profound decreases in operant responding, with maximal effects 1-4 h post-injection. Interleukin-1ra pretreatment (2.4 mg i.p. or 24 micrograms i.c.v.) completely blocked these effects when administered by the same route. In contrast, i.c.v. Il-1ra only partially blocked the effects of i.p. IL-1 beta, and i.p. IL-1ra was unable to block the effects of i.c.v. IL-1 beta. Interleukin-1ra did not affect responding by itself. These results suggest that IL-1 beta acts as both peripheral and central IL-1 receptors to reduce food motivated behavior. To determine the central site of action of IL-1 beta, small quantities of IL-1 beta (5 and 30 ng) were infused into the ventromedial hypothalamus of male rats. Both doses produced profound decreases in responding; the magnitude and time course of these effects were nearly identical to those observed after i.c.v. administration. These results suggest that the VMH may serve as a central site of action for the depressive effects of IL-1 beta on food intake. There is much controversy over the pathways of communication from the immune system to the brain. To test the hypothesis that the peripheral immune stimulus is transmitted to the brain via a neutral communication pathway, mice were injected with lipopolysaccharide at a behaviorally active dose (10 micrograms i.p.). This treatment increased the concentrations of substance P, neurokinin A, and calcitonin gene-related peptide in mouse spinal cord in a prostaglandin-dependent manner. Maximal increases in neuropeptide content were observed 1 h post-injection. Finally, subdiaphragmatic vagotomy was found to attenuate the reduction in food-motivated behavior induced by both IL-1 beta and lipopolysaccharide in mice.

Macrophages synthesize and secrete a 25-kilodalton protein that binds insulin-like growth factor-I

Primary (thymus) and secondary (spleen) murine lymphoid tissues express a 25-kDa protein that binds IGF-I. To determine the cellular source of this insulin-like growth factor binding protein (IGFBP), 11 murine or human cell lines representing T, B, and myeloid cells at various stages of differentiation were characterized by IGF-I affinity cross-linkage and Western ligand blotting. Mature myeloid cells, but not T or B cells, secrete a 25-kDa protein that is capable of binding IGF-I. CSF-1-derived bone marrow macrophages also synthesize this 25-kDa IGFBP. Thymic macrophages, which were estimated to secrete 2 ng of binding protein/10(6) cells-h, were used in conjunction with [125I] IGF-I affinity cross-linking to develop a protein binding immunomobility-shift assay to identify which IGFBP is produced by these cells. An anti-IGFBP-4Ab, but not an anti-IGFBP-2 Ab or normal rabbit serum, shifted the [125I] IGF-IGFBP complex to a higher m.w. position, indicating that the single 25-kDa IGFBP is IGFBP-4. Northern blotting confirmed that transcripts for IGFBP-4 as well as IGF-I are expressed in thymic macrophages. A putative 278-bp IGFBP-4 cDNA fragment (residues 341-618) of rat) that contains two unique cysteine residues found only in IGFBP-4 was cloned and sequenced from thymic macrophages. These clones differed from the rat sequence at only six residues (97% homology), and the deduced amino acid sequence from the murine cDNA was identical with that of the rat sequence. Subsequent studies revealed that IGF-I stimulates DNA synthesis in thymic macrophages. However, two different IGF-I analogues differing in the amino-terminus that bind equally well to the IGF-I receptor but poorly to IGFBPs are as effective as IGF-I at 100-fold lower concentrations. These data demonstrate that murine macrophages are a source of a single 25-kDa secreted protein that binds IGF-, that the molecular identity of this protein is IGFBP-4, and that this binding protein may antagonize the extracellular effects of IGF-I.

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.

Stress downregulates lipopolysaccharide-induced expression of proinflammatory cytokines in the spleen, pituitary, and brain of mice

Mice injected with LPS (10 mu g/mouse, sc) or saline were submitted to a 15-min restraint stress and sacrificed 1 or 2 h later to assess the effect of stress on the induction of interleukin-1beta (IL-1beta) and other proinflammatory cytokines (IL-1alpha, IL-1ra, IL-6, and tumor necrosis factor-alpha) in the spleen, pituitary, hypothalamus, hippocampus, and striatum. LPS-induced cytokine gene expression, as determined by comparative RT-PCR, was lower in stressed than in nonstressed mice. LPS increased plasma and tissue levels of IL-1beta, as determined by ELISA, but this effect was less marked in stressed than in nonstressed mice. These results are discussed in relation to the modulatory effects of glucocorticoids on cytokine production.

[Stress theories and the somatization process]

Stress theories aim at understanding pathophysiology of psychosomatic disorders. The first stress theories have been inspired by the principles of homeostasis. They view the response to stressors as a quasi reflex reaction which aims at normalizing disturbed homeostasis. More modern stress theories emphasize the intermediate role of cognitive and behavioural processes in the determinism of neuroendocrine and neurovegetative responses to stressors. Active attempts to control the situation are associated with activation of the sympathetic and adrenal medullary system whereas loss of control is associated with activation of the hypothalamic-pituitary-adrenal axis. Since the functional consequences of the activation of each of these physiological systems are not the same, the risk factors corresponding to each coping strategy are not the same. Whatever their details, physiological and psychobiological stress theories all emphasize the influence of psychic factors on bodily functions. However, mental states do not function independently of bodily functions. In the case of the influences of stress on immunity for instance, it has been shown that these influences represent the counterpart of feedback regulatory mechanisms in which the ability of the brain to regulate immune responses depends on the capacity of the immune system to influence brain functions. Activation of the immune system during infection or inflammation is accompanied by profound metabolic, neuroendocrine and behavioural changes which are mediated by the effects of immune products known as cytokines on brain cell targets. In view of the reciprocal relationships between peripheral organic systems and the brain, a purely psychosomatic view, from the psyche to the soma, is therefore no longer tenable. In addition, biological accounts of somatization processes run into the risk of minimizing the importance of perception and representation of somatic symptoms. Amplification of somatic symptoms is a common feature of neuroticism or negative affectivity and it bears no relationship with objective pathology. In order to understand somatization processes, there is therefore a need to study how the brain processes information it receives from the body and the way this information competes with information from the external environment.

Lipopolysaccharide and interleukin-1 depress food-motivated behavior in mice by a vagal-mediated mechanism

In order to assess the role of vagal nerve afferents in the decrease in food-motivated behavior induced by proinflammatory cytokines, the effects of lipopolysaccharide (LPS, 400 micrograms/kg ip) and recombinant human interleukin-1 beta (IL-1, 750-1500 ng/mouse ip) were tested on nose poke for food in vagotomized and sham-operated mice. Subdiaphragmatic vagotomy attenuated the decrease in response rate induced by IL-1 and LPS. These results suggest that the peripheral immune message is transmitted to the brain via a neural rather than a humoral pathway.

Corticosterone regulates behavioral effects of lipopolysaccharide and interleukin-1 beta in mice

The modulatory role of endogenous corticoids in the behavioral effects of lipopolysaccharide (LPS) and recombinant human interleukin-1 beta (IL-1 beta) was studied in mice. Adrenalectomy enhanced the depression of social exploration induced by subcutaneous injection of 200 ng of IL-1 beta or 2 micrograms of LPS. This effect was mimicked by an acute injection of the progesterone antagonist RU-38486 (0.25-1 mg). Chronic replacement with a 15-mg corticosterone pellet abrogated the enhanced susceptibility of adrenalectomized animals to 200 ng of IL-1 beta but had only partial protective effects on their response to 400 ng of IL-1 beta and LPS. These results suggest that the pituitary-adrenal response to cytokines exerts an inhibitory feedback on the cell targets that mediate the behavioral effects of LPS and IL-1 beta.

Pyrogens specifically disrupt the acquisition of a task involving cognitive processing in the rat

In addition to changes in body temperature and other metabolic and physiological responses corresponding to immune activation, pyrogens can induce profound behavioral changes referred to collectively as sickness behavior. One feature of sickness behavior, sometimes reported in clinical settings, but rarely exposed to experimental analysis, is depressed cognitive functioning. The present series of five experiments sought to demonstrate the existence of specific cognitive deficits in rats, independently of any confounding performance effects of pyrogen injections. The behavioral task used, called autoshaping, consisted of presenting hungry Wistar rats with a stimulus (introduction of a retractable lever) that predicted food delivery. Control rats quickly learned to press the lever, although this response does not influence the probability of food delivery. When pyrogens (250 micrograms/kg lipopolysaccharide, 4 micrograms/rat interleukin-1 beta, or 300 mg/rat yeast) were injected to rats during acquisition of this task, they severely disrupted acquisition while the pyrogen was active. The same treatments were, however, without effect on performance when injected later, when performance had stabilized. It is argued that these results demonstrate specific, performance-independent effects of pyrogens on the cognitive processes needed for the acquisition of this task. The results are discussed in terms of the relationship between these effects and the cytokines induced in the brain by pyrogens, and in terms of the exact nature of the cognitive process likely to be affected.

Compared effects of cold ambient temperature and cytokines on macronutrient intake in rats

To compare the effects of cold and cytokines on spontaneous dietary self-selection, rats (n = 14) were given free access to carbohydrate, protein and fat diets for 4 hours a day. After a 10-day period of habituation to this regimen, they were injected with physiological saline, IL-1 beta (4 micrograms/rat ip) or LPS (83 micrograms/rat ip) or exposed to cold (5 degrees C), the order of treatments being randomized. LPS- and IL-1 beta-treated rats ate less, but ingested relatively more carbohydrate and less protein whereas relative fat intake remained unchanged. In contrast, cold exposed rats slightly increased their food intake but in a non significant manner. They also increased their relative intake of fat but did not change their relative intake of carbohydrate and protein. These results are discussed with respect to the pyrogenic and metabolic effects of cytokines.

Subdiaphragmatic vagotomy blocks induction of IL-1 beta mRNA in mice brain in response to peripheral LPS

To test the possibility that the vagus nerve is involved in the communication between the immune system and the brain, we injected sham-operated and vagotomized mice with physiological saline or lipopolysaccharide (LPS; 400 micrograms/kg ip). Vagotomy attenuated LPS-induced depression of general activity measured 2 h after treatment but did not alter the increase in plasma levels of IL-1 beta in response to LPS. In addition, vagotomy abrogated the LPS-induced increase in the levels of transcripts for IL-1 beta, as determined by semiquantitative polymerase chain reaction after reverse transcription, in the hypothalamus and hippocampus, but not in the pituitary of vagotomized mice. This relationship between the effects of vagotomy on the behavioral effects of LPS and the LPS-induced brain expression of IL-1 beta mRNA indicates that vagal afferent fibers play a prominent role in the pathways of communication between the immune system and the brain.

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.

Peripheral administration of lipopolysaccharide induces the expression of cytokine transcripts in the brain and pituitary of mice

The reverse transcription polymerase chain reaction (RT-PCR) was used to assess the induction of mRNA of the proinflammatory cytokines IL-1 beta, IL-6 and TNF alpha in the spleen, pituitary, hypothalamus and hippocampus of mice after an intraperitoneal injection of lipopolysaccharide (LPS, 10 micrograms/mouse). The kinetics of cytokine gene expression induced by peripheral LPS in the pituitary and brain structures were different from that observed in the spleen. For IL-1 beta the dose-response curve was also measured and also found to be different. These results support the idea that one pathway by which peripheral immune stimuli affect brain functions includes local synthesis of proinflammatory cytokines in certain brain structures.

Reduction in food and water intake induced by microinjection of interleukin-1 beta in the ventromedial hypothalamus of the rat

Interleukin-1 (IL-1) is a cytokine which is released during immune activation and mediates some of the host's responses to infection and inflammation. Increasing evidence suggests that it also has a role as an intrinsic neuromodulator in the central nervous system. We report here that microinjections of 5 and 30 ng (286 fmol and 1.71 pmol) of recombinant human IL-1 beta in the ventromedial nucleus of the hypothalamus (VMH) of adult male rats time- and dose-dependently induce anorexia and weight loss in two experimental paradigms: rats allowed free-access to food and water and food-restricted rats trained to press a lever for food on a fixed ratio 10 schedule. IL-1 beta (5 ng) diminished food and water consumption by 45 and 30%, respectively, and decreased body weight for at least 24 h postinjection in rats fed ad lib. These effects were more severe and lasted at least 48 h after infusion of the larger dose of 30 ng. The IL-1 beta-induced anorexia and weight loss were neither as large nor as long-lasting in food-restricted rats. Operant responding for food was decreased 2-4 h postinfusion of 5 ng IL-1 beta and 2-8 h after 30 ng IL-1 beta, but in both cases returned to baseline within 24 h. Body weight was decreased compared to saline injections from 4 to 24 h postinfusion. Nevertheless, when allowed to eat ad lib for the 24 h immediately following the behavioral testing, body weight returned to control (5 ng) or near control levels (30 ng).(ABSTRACT TRUNCATED AT 250 WORDS)

[Current studies on the neurobiology of chronic fatigue syndrome]

Cytokines are soluble mediators which are released by activated immune cells during infection and inflammation. The possibility that fatigue is mediated by the effects of cytokines on the central nervous system is supported by several converging lines of evidence: 1) infusions of cytokines to immunocompromised patients induce flu-like symptoms including fatigue and malaise; 2) peripheral and central injection of cytokines to laboratory rodents induce sickness behaviour; 3) symptoms of sickness behaviour occurring during experimental infections can be abrogated by administration of anti-cytokine treatments; 4) although many pitfalls in the detection of cytokines still exist, patients afflicted with the chronic fatigue syndrome have been found in some studies to display instances of excessive production of cytokines. Experimental studies have confirmed that cytokines are interpreted by the brain as internal signals for sickness. Furthermore, there is evidence that sickness is a motivation which reorganizes the organism's priorities in face of this particular threat which is represented by infectious pathogens. The elucidation of the mechanisms that are involved in these effects and in particular, the role of the cytokines which are produced in the brain in response to peripheral immune stimuli and to stressors, should give new insight on the way sickness and recovery processes are organized in the brain.

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)