Action site of circulating interleukin-1 on the rabbit brain

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

Neural circuits mediating circulating interleukin-1β-evoked fever in the absence of prostaglandin E2 production

Infectious diseases and inflammatory conditions recruit the immune system to mount an appropriate acute response that includes the production of cytokines. Cytokines evoke neurally-mediated responses to fight pathogens, such as the recruitment of thermoeffectors, thereby increasing body temperature and leading to fever. Studies suggest that the cytokine interleukin-1β (IL-1β) depends upon cyclooxygenase (COX)-mediated prostaglandin E₂ production for the induction of neural mechanisms to elicit fever. However, COX inhibitors do not eliminate IL-1β-induced fever, thus suggesting that COX-dependent and COX-independent mechanisms are recruited for increasing body temperature after peripheral administration of IL-1β. In the present study, we aimed to build a foundation for the neural circuit(s) controlling COX-independent, inflammatory fever by determining the involvement of brain areas that are critical for controlling the sympathetic outflow to brown adipose tissue (BAT) and the cutaneous vasculature. In anesthetized rats, pretreatment with indomethacin, a non-selective COX inhibitor, did not prevent BAT thermogenesis or cutaneous vasoconstriction (CVC) induced by intravenous IL-1β (2 µg/kg). BAT and cutaneous vasculature sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) are required for IL-1β-evoked BAT thermogenesis and CVC, with or without pretreatment with indomethacin. Additionally, activation of glutamate receptors in the dorsomedial hypothalamus (DMH) is required for COX-independent, IL-1β-induced BAT thermogenesis. Therefore, our data suggests that COX-independent mechanisms elicit activation of neurons within the DMH and rRPa, which is sufficient to trigger and mount inflammatory fever. These data provide a foundation for elucidating the brain circuits responsible for COX-independent, IL-1β-elicited fevers.

Microorganisms in the Placenta: Links to Early-Life Inflammation and Neurodevelopment in Children

Prenatal exposure to various stressors can influence both early and later life childhood health. Microbial infection of the intrauterine environment, specifically within the placenta, has been associated with deleterious birth outcomes, such as preterm birth, as well as adverse neurological outcomes later in life. The relationships among microorganisms in the placenta, placental function, and fetal development are not well understood. Microorganisms have been associated with perinatal inflammatory responses that have the potential for disrupting fetal brain development. Microbial presence has also been associated with epigenetic modifications in the placenta, as well other tissues. Here we review research detailing the presence of microorganisms in the placenta and associations among such microorganisms, placental DNA methylation, perinatal inflammation, and neurodevelopmental outcomes.

The pathogenesis of tuberculous meningitis

Tuberculosis (TB) remains a leading cause of death globally. Dissemination of TB to the brain results in the most severe form of extrapulmonary TB, tuberculous meningitis (TBM), which represents a medical emergency associated with high rates of mortality and disability. Via various mechanisms the Mycobacterium tuberculosis (M.tb) bacillus disseminates from the primary site of infection and overcomes protective barriers to enter the CNS. There it induces an inflammatory response involving both the peripheral and resident immune cells, which initiates a cascade of pathologic mechanisms that may either contain the disease or result in significant brain injury. Here we review the steps from primary infection to cerebral disease, factors that contribute to the virulence of the organism and the vulnerability of the host and discuss the immune response and the clinical manifestations arising. Priorities for future research directions are suggested.

Neuroinflammation in hepatic encephalopathy: mechanistic aspects

Hepatic encephalopathy (HE) is a major neurological complication of severe liver disease that presents in acute and chronic forms. While elevated brain ammonia level is known to be a major etiological factor in this disorder, recent studies have shown a significant role of neuroinflammation in the pathogenesis of both acute and chronic HE. This review summarizes the involvement of ammonia in the activation of microglia, as well as the means by which ammonia triggers inflammatory responses in these cells. Additionally, the role of ammonia in stimulating inflammatory events in brain endothelial cells (ECs), likely through the activation of the toll-like receptor-4 and the associated production of cytokines, as well as the stimulation of various inflammatory factors in ECs and in astrocytes, are discussed. This review also summarizes the inflammatory mechanisms by which activation of ECs and microglia impact on astrocytes leading to their dysfunction, ultimately contributing to astrocyte swelling/brain edema in acute HE. The role of microglial activation and its contribution to the progression of neurobehavioral abnormalities in chronic HE are also briefly presented. We posit that a better understanding of the inflammatory events associated with acute and chronic HE will uncover novel therapeutic targets useful in the treatment of patients afflicted with HE.

Single episode of mild murine malaria induces neuroinflammation, alters microglial profile, impairs adult neurogenesis, and causes deficits in social and anxiety-like behavior

Cerebral malaria is associated with cerebrovascular damage and neurological sequelae. However, the neurological consequences of uncomplicated malaria, the most prevalent form of the disease, remain uninvestigated. Here, using a mild malaria model, we show that a single Plasmodium chabaudi adami infection in adult mice induces neuroinflammation, neurogenic, and behavioral changes in the absence of a blood-brain barrier breach. Using cytokine arrays we show that the infection induces differential serum and brain cytokine profiles, both at peak parasitemia and 15days post-parasite clearance. At the peak of infection, along with the serum, the brain also exhibited a definitive pro-inflammatory cytokine profile, and gene expression analysis revealed that pro-inflammatory cytokines were also produced locally in the hippocampus, an adult neurogenic niche. Hippocampal microglia numbers were enhanced, and we noted a shift to an activated profile at this time point, accompanied by a striking redistribution of the microglia to the subgranular zone adjacent to hippocampal neuronal progenitors. In the hippocampus, a distinct decline in progenitor turnover and survival was observed at peak parasitemia, accompanied by a shift from neuronal to glial fate specification. Studies in transgenic Nestin-GFP reporter mice demonstrated a decline in the Nestin-GFP(+)/GFAP(+) quiescent neural stem cell pool at peak parasitemia. Although these cellular changes reverted to normal 15days post-parasite clearance, specific brain cytokines continued to exhibit dysregulation. Behavioral analysis revealed selective deficits in social and anxiety-like behaviors, with no change observed in locomotor, cognitive, and depression-like behaviors, with a return to baseline at recovery. Collectively, these findings indicate that even a single episode of mild malaria results in alterations of the brain cytokine profile, causes specific behavioral dysfunction, is accompanied by hippocampal microglial activation and redistribution, and a definitive, but transient, suppression of adult hippocampal neurogenesis.

Cytokines, neurophysiology, neuropsychology, and psychiatric symptoms

Recent research has overcome the old paradigms of the brain as an immunologically privileged organ, and of the exclusive role of neurotransmitters and neuropeptides as signal transducers in the central nervous system. Growing evidence suggests that the signal proteins of the immune system - the cytokines - are also involved in modulation of behavior and induction of psychiatric symptoms. This article gives an overview on the nature of cytokines and the proposed mechanisms of immune-to-brain interaction. The role of cytokines in psychiatric symptoms, syndromes, and disorders like sickness behavior, major depression, and schizophrenia are discussed together with recent immunogenetic findings.

Role of cerebral endothelial cells in the astrocyte swelling and brain edema associated with acute hepatic encephalopathy

Brain edema is an important complication of acute hepatic encephalopathy (AHE), and astrocyte swelling is largely responsible for its development. Elevated blood and brain ammonia levels have been considered as major etiological factors in this edema. In addition to ammonia, recent studies have suggested that systemic infection, inflammation (and associated cytokines (CKs)), as well as endotoxin (lipopolysaccharide (LPS)) are also involved in AHE-associated brain edema. As endothelial cells (ECs) are the first resident brain cells exposed to blood-borne "noxious agents" (i.e., ammonia, CKs, LPS) that are present in AHE, these cells may be in a critical position to react to these agents and trigger a process resulting in astrocyte swelling/brain edema. We therefore examined the effect of conditioned media (CM) from ammonia, LPS and cytokine-treated cultured brain ECs on cell swelling in cultured astrocytes. CM from ammonia-treated ECs when added to astrocytes caused significant cell swelling, and such swelling was potentiated when astrocytes were exposed to CM from ECs treated with a combination of ammonia, LPS and CKs. We also found an additive effect when astrocytes were exposed to ammonia along with CM from ammonia-treated ECs. Additionally, ECs treated with ammonia showed a significant increase in the production of oxy-radicals, nitric oxide (NO), as well as evidence of oxidative/nitrative stress and activation of the transcription factor nuclear factor kappa B (NF-κB). CM derived from ECs treated with ammonia, along with antioxidants (AOs) or the NF-κB inhibitor BAY 11-7082, when added to astrocytes resulted in a significant reduction in cell swelling, as compared to the effect of CM from ECs-treated only with ammonia. We also identified increased nuclear NF-κB expression in rat brain cortical ECs in the thioacetamide (TAA) model of AHE. These studies suggest that ECs significantly contribute to the astrocyte swelling/brain edema in AHE, likely as a consequence of oxidative/nitrative stress and activation of NF-κB.

Effective induction of protective systemic immunity with nasally administered vaccines adjuvanted with IL-1

IL-1α and IL-1β were evaluated for their ability to provide adjuvant activity for the induction of serum antibody responses when nasally administered with protein antigens in mice and rabbits. In mice, intranasal (i.n.) immunization with pneumococcal surface protein A (PspA) or tetanus toxoid (TT) combined with IL-1β induced protective immunity that was equivalent to that induced by parenteral immunization. Nasal immunization of awake (i.e., not anesthetized) rabbits with IL-1-adjuvanted vaccines induced highly variable serum antibody responses and was not as effective as parenteral immunization for the induction of antigen-specific serum IgG. However, i.n. immunization of deeply anesthetized rabbits with rPA+IL-1α consistently induced rPA-specific serum IgG ELISA titers that were not significantly different than those induced by intramuscular (IM) immunization with rPA+alum although lethal toxin-neutralizing titers induced by nasal immunization were lower than those induced by IM immunization. Gamma scintigraphy demonstrated that the enhanced immunogenicity of nasal immunization in anesthetized rabbits correlated with an increased nasal retention of i.n. delivered non-permeable radio-labeled colloidal particles. Our results demonstrate that, in mice, IL-1 is an effective adjuvant for nasally administered vaccines for the induction of protective systemic immunity and that in non-rodent species, effective induction of systemic immunity with nasally administered vaccines may require formulations that ensure adequate retention of the vaccine within the nasal cavity.

Fetal inflammatory response and brain injury in the preterm newborn

Preterm birth can be caused by intrauterine infection and maternal/fetal inflammatory responses. Maternal inflammation (chorioamnionitis) is often followed by a systemic fetal inflammatory response characterized by elevated levels of proinflammatory cytokines in the fetal circulation. The inflammation signal is likely transmitted across the blood-brain barrier and initiates a neuroinflammatory response. Microglial activation has a central role in this process and triggers excitotoxic, inflammatory, and oxidative damage in the developing brain. Neuroinflammation can persist over a period of time and sensitize the brain to subinjurious insults in early and chronic phases but may offer relative tolerance in the intermediate period through activation of endogenous anti-inflammatory, protective, and repair mechanisms. Neuroinflammatory injury not only destroys what exists but also changes what develops.

Psychoneuroimmunology of stroke

Stroke is the major cause of disability in the Western world and is the third greatest cause of death, but there are no widely effective treatments to prevent the devastating effects of stroke. Extensive and growing evidence implicates inflammatory and immune processes in the occurrence of stroke and particularly in the subsequent injury. Several inflammatory mediators have been identified in the pathogenesis of stroke including specific cytokines, adhesion molecules, matrix metalloproteinases, and eicosanoids. An early clinical trial suggests that inhibiting interleukin-1 may be of benefit in the treatment of acute stroke.

The interaction of nuclear factor-kappa B and cytokines is associated with schizophrenia

BACKGROUND

Many reports suggest that schizophrenia is associated with the inflammatory response mediated by cytokines, and nuclear factor-kappa B (NF-kappaB) regulates the expression of cytokines. However, it remains unclear whether the interaction between NF-kappaB and cytokines is implicated in schizophrenia and whether the effect of neuroleptics treatment for 4 weeks is associated with the alteration of cytokines.

METHODS

Sixty-five healthy subjects and 83 first-episode schizophrenic patients who met DSM-IV criteria and who were never treated with neuroleptics previously were included. Serum levels of cytokines such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) were examined by using sandwich enzyme immunoassay (EIA). Peripheral blood mononuclear cell (PBMC) mRNA expressions of cytokines (IL-1beta, TNF-alpha) and NF-kappaB were detected by using semiquantitative reverse transcription polymerase chain reaction (RT-PCR). NF-kappaB activation was examined by using transcription factor assay kits.

RESULTS

Schizophrenic patients showed significantly higher serum levels and PBMC mRNA expressions of IL-1beta and TNF-alpha compared with healthy subjects. However, treatment with the neuroleptic risperidone for 4 weeks significantly decreased serum levels and PBMC mRNA expressions of IL-1beta in schizophrenic patients. NF-kappaB activation and PBMC mRNA expression in patients were significantly higher than those in healthy subjects. Furthermore, PBMC mRNA expressions of IL-1beta and TNF-alpha were positively correlated to NF-kappaB activation in both schizophrenic patients and healthy control subjects.

CONCLUSIONS

Schizophrenic patients showed activation of the cytokine system and immune disturbance. NF-kappaB activation may play a pivotal role in schizophrenia through interaction with cytokines.

Transport of interleukin-1 across cerebromicrovascular endothelial cells

BACKGROUND AND PURPOSE

The inflammatory cytokine interleukin-1 (IL-1) has profound actions in the brain, causing neuronal cell death and exacerbating brain damage. While circulating levels are normally low, IL-1 can be produced on the vascular side of the brain endothelium, and within the brain. The naturally occurring IL-1 receptor antagonist has been administered peripherally in a Phase II trial in acute stroke patients; understanding how IL-1 and IL-1 receptor antagonist penetrate the brain is, therefore, of considerable importance.

EXPERIMENTAL APPROACH

An in vitro blood-brain barrier model was generated by co-culture of porcine brain microvascular endothelial cells with astrocytes. The mechanisms of transcellular transport of IL-1beta and IL-1 receptor antagonist were characterized in this model, using endocytosis inhibitors and IL-1 receptor-blocking antibodies.

KEY RESULTS

Transcellular IL-1beta and IL-1 receptor antagonist transport was temperature-dependent and IL-1beta was transported with higher affinity than IL-1 receptor antagonist. IL-1beta inhibited IL-1 receptor antagonist transport more potently than IL-1 receptor antagonist inhibited IL-1beta transport. Transport of IL-1beta and IL-1 receptor antagonist was not via adsorptive-mediated endocytosis, although inhibition of microtubule assembly significantly attenuated transport of both cytokines. An antibody directed to the type II IL-1 receptor significantly reduced IL-1beta transport.

CONCLUSIONS AND IMPLICATIONS

These results are consistent with IL-1 and IL-1 receptor antagonist being transported across cultured cerebromicrovascular endothelial cells and suggest that IL-1beta transport may occur via a type II IL-1 receptor-dependent mechanism. Understanding IL-1 transport into the brain may have benefits, particularly in enhancing penetration of IL-1 receptor antagonist into the brain.

Delivery of peptide and protein drugs over the blood-brain barrier

Peptide and protein (P/P) drugs have been identified as showing great promises for the treatment of various neurodegenerative diseases. A major challenge in this regard, however, is the delivery of P/P drugs over the blood-brain barrier (BBB). Intense research over the last 25 years has enabled a better understanding of the cellular and molecular transport mechanisms at the BBB, and several strategies for enhanced P/P drug delivery over the BBB have been developed and tested in preclinical and clinical-experimental research. Among them, technology-based approaches (comprising functionalized nanocarriers and liposomes) and pharmacological strategies (such as the use of carrier systems and chimeric peptide technology) appear to be the most promising ones. This review combines a comprehensive overview on the current understanding of the transport mechanisms at the BBB with promising selected strategies published so far that can be applied to facilitate enhanced P/P drug delivery over the BBB.

Psychoneuroimmunology of stroke

There is now considerable evidence from both experimental and clinical studies that immune and inflammatory processes can contribute to the onset of stroke and the neurologic and psychologic outcomes. Several specific therapeutic targets have been identified that may significantly improve the devastating impact of stroke.

Highly purified lipoteichoic acid from gram-positive bacteria induces in vitro blood–brain barrier disruption through glia activation: Role of pro-inflammatory cytokines and nitric oxide

The co-culture of bovine brain capillary endothelial cells and rat primary glial cells was established as an in vitro blood-brain barrier model to investigate the mechanisms by which the Gram-positive bacterial cell wall components lipoteichoic acid and muramyl dipeptide induced injury of blood-brain barrier structure and function. We found that highly purified lipoteichoic acid disrupted blood-brain barrier integrity in a concentration- and time-dependent manner indirectly, through glia activation. Low trans-endothelial electrical resistance and high permeability to fluorescein isothiocyanate-inulin observed in the presence of lipoteichoic acid-activated glial cells were potentiated by muramyl dipeptide and could be reversed only when glial cells were activated by lipoteichoic acid at 10 microg/ml but not with a higher lipoteichoic acid concentration (30 microg/ml). Immunocytochemistry analysis revealed no evident changes in the distribution of the cytoskeleton protein F-actin and tight junction proteins occludin and claudin after lipoteichoic acid treatment. However, the tight junction associated protein AHNAK clearly revealed the morphological alteration of the endothelial cells induced by lipoteichoic acid. Lipoteichoic acid-activated glial cells produced nitric oxide and pro-inflammatory cytokines (tumor necrosis factor-alpha and interleukin-1beta) that contributed to lipoteichoic acid-induced blood-brain barrier disruption, since the direct treatment of the endothelial monolayer with tumor necrosis factor-alpha or interleukin-1beta increased blood-brain barrier permeability, whereas the pre-treatment of lipoteichoic acid-activated glial cells with antibodies against these two cytokines blocked lipoteichoic acid effects. Additionally, nitric oxide was also involved in blood-brain barrier damage, since the nitric oxide donor itself (diethylenetriamine-nitric oxide adduct) increased blood-brain barrier permeability and inducible nitric oxide synthase inhibitor (1400W) partially reversed lipoteichoic acid-induced trans-endothelial electrical resistance decrease.

Infection and the progression of hepatic encephalopathy in acute liver failure

BACKGROUND & AIMS

Progression of hepatic encephalopathy (HE) is a major determinant of outcome in acute liver failure (ALF). Our aim was to identify predictive factors of worsening HE, including the relation of encephalopathy with the systemic inflammatory response (SIRS) and infection.

METHODS

We included 227 consecutive patients with stage I-II HE prospectively enrolled in the U.S. Acute Liver Failure Study. Univariate and multivariate analysis of 27 variables at admission were performed separately for acetaminophen (n = 96) and nonacetaminophen (n = 131) etiologies.

RESULTS

On multivariate analysis, acquisition of infection during stage I-II HE (P < 0.01), increased leukocyte levels at admission (P < 0.01), and decreased platelet count (P < 0.05) were predictive factors of worsening HE in the acetaminophen group. By contrast, only increased pulse rate (P < 0.05) and AST levels (P < 0.05) at admission were predictors in nonacetaminophen patients. In patients who progressed to deep HE, the first confirmed infection preceded progression in 15 of 19 acetaminophen patients compared with 12 of 23 nonacetaminophen patients. In patients who did not demonstrate positive microbiologic cultures, a higher number of components of SIRS at admission was associated with more frequent worsening of HE (25% vs. 35% vs. 50% for 0, 1, and >or=2 components of SIRS, P < 0.05). CONCLUSIONA: This prospective evaluation points to infection and/or the resulting systemic inflammatory response as important factors contributing to worsening HE in ALF, mainly in patients with acetaminophen- induced ALF. The use of prophylactic antibiotics in these patients and the mechanisms by which infection triggers hepatic encephalopathy require further investigation.

Differential induction of interleukin-1beta and tumour necrosis factor-alpha may account for specific patterns of leukocyte recruitment in the brain

In peripheral tissue, IL-1beta has been shown to induce TNFalpha expression and vice versa, resulting in mixed neutrophil and mononuclear cell recruitment to the site of injury. This has led to the concept of crosstalk in peripheral cytokine signalling pathways. In the brain parenchyma, however, restricted patterns of leukocyte recruitment following the focal injection of pro-inflammatory agents into the brain are observed. This study investigates the expression of the principal pro-inflammatory cytokines--IL-1beta and TNFalpha--in the brain after IL-1beta, TNFalpha, NMDA or endotoxin injection into the brain parenchyma of rats. Each of these agents gives rise to a distinct pattern of acute leukocyte recruitment at 24 h. We found that IL-1beta induces de novo synthesis of additional IL-1beta but not TNFalpha, as determined by RT-PCR and ELISA, and TNFalpha does not induce either itself or IL-1beta. Injection of NMDA results in IL-1beta, but not TNFalpha up-regulation. Injection of IL-1beta or NMDA is associated with neutrophil recruitment whereas injection of TNFalpha is associated with mononuclear cell recruitment. Following injection of endotoxin, both TNFalpha and IL-1beta levels are elevated and neutrophils and mononuclear cells are recruited to the brain. These data suggest that the signalling pathways that are present in the periphery are modified in the brain and that differential induction of TNFalpha and IL-1beta may have a role in the atypical pattern of leukocyte recruitment observed in the brain.

Neuroleptics normalize increased release of interleukin- 1 beta and tumor necrosis factor-alpha from monocytes in schizophrenia

Some recent reports show that schizophrenia is accompanied by changes in lymphocyte activity. This study investigated the activity of monocytes by determining their release of interleukin- 1 beta (IL- 1 beta) and tumor necrosis factor-alpha (TNF-alpha). Monocytes were immunomagnetically isolated from the peripheral blood of schizophrenic patients before and after neuroleptic medication and stimulated by lipopolisaccharide (LPS) in vitro. The monocytes of schizophrenic patients released significantly higher amounts of IL- 1 beta and TNF-alpha than those of healthy controls. Treatment with the typical neuroleptics haloperidol and perazine decreased the release of IL- 1 beta and TNF-alpha to the control levels. The study has shown that the activity of monocytes is increased in schizophrenia and that neuroleptic treatment normalizes this activity.

Cytokines and the central nervous system

Cytokines are involved both in the immune response and in controlling various events in the central nervous system, that is, they are equally immunoregulators and modulators of neural functions and neuronal survival. On the other hand, cytokine production is under the tonic control of the peripheral and the central nervous system and the cytokine balance can be modulated by the action of neurotransmitters released from nonsynaptic varicosities [131]. The neuroimmune interactions are therefore bidirectional-cytokines and other products of the immune cells can modulate the action, differentiation, and survival of neuronal cells, while the neurotransmitter and neuropeptide release play a pivotal role in influencing the immune response. Cytokines and their receptors are constitutively expressed by and act on neurons in the central nervous system, in both its normal and its pathological state, but cytokine overexpression in the brain is an important factor in the pathogenesis of neurotoxic and neurodegenerative disorders. Accordingly, it can be accepted that the peripheral and central cytokine compartments appear to be integrated, and their effects might synergize or inhibit each other; however, it should always be taken into account that they are spatiotemporally differentially regulated. New concepts are reviewed in the regulation of relations between cytokine balance and neurodegeneration, including intracellular receptor-receptor, cell-cell, and systemic neuroimmune interactions that promote the further elucidation of the complexities and cascade of the possible interactions between cytokines and the central nervous system.

Delivery of peptides and proteins through the blood-brain barrier

Peptide and protein therapeutics are generally excluded from transport from blood to brain, owing to the negligible permeability of these drugs to the brain capillary endothelial wall, which makes up the blood-brain barrier (BBB) in vivo. However, peptides or protein therapeutics may be delivered to the brain with the use of the chimeric peptide strategy for peptide drug delivery. Chimeric peptides are formed when a non-transportable peptide therapeutic is coupled to a BBB drug transport vector. Transport vectors are proteins such as cationized albumin, or the OX26 monoclonal antibody to the transferrin receptor; these proteins undergo absorptive-mediated and receptor-mediated transcytosis through the BBB, respectively. In addition to vector development, another important element of the chimeric peptide strategy is the design of strategies for coupling drugs to the vector that give high efficiency coupling and result in the liberation of biologically active peptides following cleavage of the bond linking the therapeutic and the transport vector. The avidin/biotin system has been recently shown to be advantageous in fulfilling these criteria for successful linker strategies. The use of the OX26 monoclonal antibody, the use of the avidin/biotin system as a linker strategy, and the design of a vasoactive intestinal peptide (VIP) analogue that is suitable for monobiotinylation and retention of biologic activity following cleavage, allowed for the recent demonstration of in vivo pharmacologic effects in brain following the systemic administration of relatively low doses (12 microg/kg) of neuropeptide.

Cytokine signals propagate through the brain

Interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) are proinflammatory cytokines that are constitutively expressed in healthy, adult brain where they mediate normal neural functions such as sleep. They are neuromodulators expressed by and acting on neurons and glia. IL-1 and TNFalpha expression is upregulated in several important diseases/disorders. Upregulation of IL-1 and/or TNFalpha expression, elicited centrally or systemically, propagates through brain parenchyma following specific spatio-temporal patterns. We propose that cytokine signals propagate along neuronal projections and extracellular diffusion pathways by molecular cascades that need to be further elucidated. This elucidation is a prerequisite for better understanding of reciprocal interactions between nervous, endocrine and immune systems.

Tumor necrosis factor alpha is a determinant of pathogenesis and disease progression in mycobacterial infection in the central nervous system

The pathogenesis of tuberculous meningitis, a devastating complication of tuberculosis in man, is poorly understood. We previously reported that rabbits with experimental tuberculous meningitis were protected from death by a combination of antibiotics and thalidomide therapy. Survival was associated with inhibition of tumor necrosis factor alpha (TNF-alpha) production by thalidomide. To test whether cerebrospinal fluid (CSF) levels of TNF-alpha correlated with pathogenesis, the response of rabbits infected in the central nervous system (CNS) with various mycobacterial strains was studied. CNS infection with Mycobacterium bovis Ravenel, M. bovis bacillus Calmette-Guérin (BCG) Pasteur, and M. bovis BCG Montreal were compared. M. bovis Ravenel induced the highest levels of TNF-alpha in the CSF in association with high leukocytosis, protein accumulation, and severe meningeal inflammation. BCG Pasteur had intermediate effects, and BCG Montreal was the least virulent. In addition, M. bovis Ravenel numbers were highest in the brain and CSF and the bacilli also disseminated more efficiently to distant organs, compared with BCG Pasteur and BCG Montreal. In subsequent experiments, rabbits were infected with either recombinant M. bovis BCG Montreal (vector), or BCG Montreal expressing the murine gene for TNF-alpha (BCG mTNF-alpha). BCG Montreal was rendered virulent by the expression of murine TNF-alpha, as demonstrated by high CSF leukocytosis, high protein accumulation, severe meningeal inflammation, persistent bacillary load, and progressive clinical deterioration. Taken together, these results demonstrate that the level of TNF-alpha produced during mycobacterial CNS infection determines, at least in part, the extent of pathogenesis.

Regulation of the hypothalamic-pituitary-adrenal axis by cytokines: actions and mechanisms of action

Glucocorticoids are hormone products of the adrenal gland, which have long been recognized to have a profound impact on immunologic processes. The communication between immune and neuroendocrine systems is, however, bidirectional. The endocrine and immune systems share a common "chemical language," with both systems possessing ligands and receptors of "classical" hormones and immunoregulatory mediators. Studies in the early to mid 1980s demonstrated that monocyte-derived or recombinant interleukin-1 (IL-1) causes secretion of hormones of the hypothalamic-pituitary-adrenal (HPA) axis, establishing that immunoregulators, known as cytokines, play a pivotal role in this bidirectional communication between the immune and neuroendocrine systems. The subsequent 10-15 years have witnessed demonstrations that numerous members of several cytokine families increase the secretory activity of the HPA axis. Because this neuroendocrine action of cytokines is mediated primarily at the level of the central nervous system, studies investigating the mechanisms of HPA activation produced by cytokines take on a more broad significance, with findings relevant to the more fundamental question of how cytokines signal the brain. This article reviews published findings that have documented which cytokines have been shown to influence hormone secretion from the HPA axis, determined under what physiological/pathophysiological circumstances endogenous cytokines regulate HPA axis activity, established the possible sites of cytokine action on HPA axis hormone secretion, and identified the potential neuroanatomic and pharmacological mechanisms by which cytokines signal the neuroendocrine hypothalamus.

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

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

Antipyretic activity of cinnamyl derivatives and related compounds in influenza virus-infected mice

Kakkon-to is composed of seven medicinal herbs and exhibited novel antipyretic activity by suppressing interleukin-1alpha production responsive to interferon in a murine intranasal influenza virus infection model. Using this model, antipyretic compounds with such novel biological activities were characterized from the herbs. The organic solvent-extractable fractions of Cinnamomum cassia among the herbs showed antipyretic activity. We selected six antipyretic compounds from 48 cinnamyl derivatives and related compounds that may be mainly involved in the fractions. Their antipyretic activity was significantly correlated with interleukin-1alpha regulatory activity. Four of them suppressed interleukin-1alpha production to a basal level and showed different mode of antipyretic action from that of aspirin in interleukin-1alpha-injected mice. Structure-bioactivity relationship of the four suggested that an ester bond played an important role for both antipyretic and interleukin-1alpha regulatory activities. These compounds may be useful in analyzing interleukin-1alpha-producing cells in fever production and the mechanism of defervescence by suppressing interferon-induced interleukin-1alpha production.

Studies on the mechanism of fever after intravenous administration of endotoxin

BACKGROUND

The sequential events in fever production after intravenous administration of lipopolysaccharide (LPS) remain unsettled and controversial. Vessels of the organum vasculosum laminae terminalis (OVLT) lack the tight junctions of the blood-brain barrier and allow substances of high molecular weight to enter the interstitium but not the neuropil. The present studies investigate the hypothesis that the OVLT is needed for fever production after intravenous administration of LPS in the rat.

METHODS

Electrolytic lesions were produced in the OVLT of rats. After recovery, left carotid and right atrial catheters were inserted, and 24 hours later calorimetry was performed. Blood was drawn for baseline assay for cytokines and LPS after which LPS was given intravenously, with studies continued for 5 hours, and additional blood samples were drawn at 90 and 300 minutes.

RESULTS

The maximal increment in rectal temperature for the sham lesion LPS group (1.25 +/- 0.44 degrees C) was significantly greater than for the sham-saline (-0.05 +/- 0.46 degrees C) and the lesion-LPS groups (0.35 +/- 0.45 degrees C) for minutes 120 to 300. Ninety minutes after LPS administration, serum levels of interleukin (IL)-6, tumor necrosis factor-alpha, and LPS were significantly elevated (p < 0.0001) above baseline for the sham-LPS and lesion-LPS groups. IL-1beta serum levels remained below detection levels.

CONCLUSION

Large lesions of the OVLT prevent and/or attenuate fever due to LPS even though tumor necrosis factor-alpha and IL-6 are greatly increased in serum. IL-1beta does not seem to be an endogenous humoral mediator in this model.

Psychoneuroimmunology and the cytokine action in the CNS: implications for psychiatric disorders

1. Parallel to the current rapid development of new immunological methods, immune mechanisms are gaining more importance for our understanding of psychiatric disorders. The purpose of this article is to review basic and clinical investigations that elucidate the relationship between the CNS and the immune system. 2. The topical literature dealing with the interactions of immune system, neurotransmitters, psychological processes, and psychiatric disorders, especially in relation to cytokines, is reviewed. 3. An activation of the immune system in schizophrenia and depressive disorders has repeatedly been described. Cytokines, actively transported into the CNS, play a key role in this immune activation. It was recently observed that cytokines activate astrocytes and microglia cells, which in turn produce cytokines by a feedback mechanism. Moreover, they strongly influence the dopaminergic, noradrenergic, and serotonergic neurotransmission. 4. There are indications that the cascade of cytokines can be activated by neuronal processes. These findings close a theoretical gap between stress and its influence on immunity. Psychomotor, sickness behavior and sleep are related to IL-1; disturbances of memory and cognitive impairment are to IL-2, in part also to TNF-alpha. The hypersecretion of IL-2 is assumed to have a prominent influence on schizophrenia, and IL-6, on depressive disorders. 5. Although single cytokines most likely do not have a specificity for certain psychiatric disorders, a characteristic pattern of cytokine actions in the CNS, including influences of the cytokines on the blood-brain barrier, seems to play a role in psychiatric disorders. This may have therapeutic implications for the future.

Cascade of fever production in mice infected with influenza virus

The cascade of fever production in influenza was studied. To analyse fever production in a murine model, we selected DBA/2 mice that have the highest susceptibility in fibrile responses among seven mouse strains. Intranasal influenza infection- and interferon (IFN)-induced fever production was studied in this mouse model. Fever was induced prominently on day 2 after influenza infection and IFN activity was also increased in serum. Only the level of interleukin (IL)-1 alpha, an endogenous pyrogen, rose markedly in serum among cytokines (IL-1 alpha, IL-2, IFN-gamma, and tumor necrosis factor-alpha) examined. Fever was induced 14 hr after intraperitoneal IFN-alpha treatment and IL-1 alpha level rose significantly in the serum of the IFN-alpha-treated mice as compared with that of untreated mice. Fever production was significantly suppressed by treatment with anti-IFN-alpha/beta or anti-IL-1 alpha antibody in infected mice and the former significantly suppressed responsive IL-1 alpha production, indicating that elevated IFN activity induced IL-1 alpha production and subsequently fever production in infected mice. The activity of cyclooxygenase (COX) that produces prostaglandin (PG)E2 was significantly augmented in the brain of infected mice on day 2 after infection. Fever production was suppressed by the inhibition of COX activity with aspirin, although IL-1 alpha level was maintained at the elevated level. Therefore, influenza infection in mice turned on the following cascade for fever induction: IFN production, IL-1 alpha production, elevated COX activity, and PGE2 production. We elucidated the relationship among IFN activity, IL-1 alpha production and COX activity and demonstrated the cascade of fever production in influenza infection.

Comparison of saturable transport and extracellular pathways in the passage of interleukin-1 alpha across the blood-brain barrier

Blood-borne cytokines enter the brain by transport across the blood-brain barrier (BBB) or by leakage through extracellular pathways at sites, such as circumventricular organs (CVOs), without a BBB. We used radioactively labeled albumin (T-Alb) to differentiate the relative contribution of transport and extracellular pathways to the passage of interleukin-1 alpha ([125I]IL-1 alpha) across the BBB. The major mechanism of entry for [125I]IL-1 alpha after intravenous (i.v.) injection was a saturable transport system with extracellular pathways accounting for only a small fraction of entry into brain. CVOs concentrated blood-borne [125I]IL-1 alpha in a saturable manner to a much greater extent than did the cerebral cortex and cerebellum, but accounted for less that 5% of total brain uptake. After intracerebroventricular (i.c.v.) injection, [125I]IL-1 alpha and T-Alb were concentrated in the CVOs, especially the median eminence, although CVOs contained less that 1% of the substances injected. Distribution after i.c.v. injection was largely due to diffusion and leakage through extracellular pathways. We conclude that after i.c.v. injection, leakage across extracellular pathways accounts for the small but concentrated amount of [125I]IL-1 alpha found in CVOs. After i.v. injection, transport across the BBB accounts for the majority of [125I]IL-1 alpha in brain.

Hypothalamic prostaglandin E2 during lipopolysaccharide-induced fever in guinea pigs

Prostaglandin E2 (PGE2) is postulated to be a central mediator of fever. It is generally believed that it is produced in the preoptic area of the anterior hypothalamus (POA) because, among other evidence, its level increases both in the third ventricle and in the POA in response to pyrogens. However, lately, the question has arisen whether PGE2 might, in fact, be formed outside of the brain substance and then penetrate it, in particular through the organum vasculosum laminae terminalis. If produced outside the brain substance, the peripheral blockade of its synthesis should prevent lipopolysaccharides (LPS)-induced fever, whereas the intracarotid infusion of PGE2 should produce an increase in core temperature (T(C)) as well as in preoptic PGE2. To verify this hypothesis, continuous measurements of T(C) and preoptic PGE2 levels were made in conscious guinea pigs administered the PGE2 synthase inhibitor, indomethacin (10 or 50 mg/kg, im) 30 min before S. enteritidis LPS (2 mu g/kg, iv) or before PGE2 microdialyzed into the POA (1 mu g/mu l at 2 mu g/min for 2.5 h) and during PGE2 infused into a carotid artery (1 mu g and 10 mu g/mu l at 2 mu g/min for 1 h). LPS induced a biphasic 1.4 degrees C fever that was consistently associated with an increase in the level of PGE2 in the POA. Indomethacin at 10 mg/kg attenuated the course of the LPS-induced fever and prevented the associated increase in preoptic PGE2 for 90 min after fever onset; thereafter, PGE2 was significantly reduced by comparison with controls. Indomethacin at 50 mg/kg completely abolished both the fever and the increased levels of PGE2 in the POA; the fever induced by PGE2 microdialyzed into the POA was not affected by indomethacin pretreatment The intracarotid infusion of PGE2 produced T(C) falls and no increase in preoptic PGE2 levels. The indomethacin-induced blockade of fever and inhibition of the associated increase in preoptic PGE2 levels further substantiates the presumptive link between PGE2 in the POA and fever caused by LPS. The failure of exogenous PGE2 infusion to induce increases in T(C) and preoptic PGE2 levels excludes the possibility that PGE2 formed outside of the brain penetrates the POA and induces fever. Thus, in guinea pigs, the PGE2 associated with LPS-induced fever may be synthesized in the POA.

Hypothalamic neuronal histamine modulates adaptive behavior and thermogenesis in response to endogenous pyrogen

Homeostatic involvement of hypothalamic neuronal histamine in adaptive behavior and thermogenesis was investigated when interleukin-1 beta (IL-1 beta), one of the endogenous pyrogens, was infused peripherally in rats. IL-1 beta decreased food and water intake and elevated body temperature. Depletion of neuronal histamine in the hypothalamus induced by alpha-fluoromethylhistidine, a suicide inhibitor of the histamine synthesizing enzyme histidine decarboxylase (HDC), attenuated the suppressive effect of IL-1 beta on food intake, facilitated the inhibitory effect on water intake, and enhanced its thermogenic effect. Simultaneously IL-1 beta increased activity of HDC and histamine-N-methyltransferase (HMT), a neuronal histamine catabolizing enzyme. Pretreatment with indomethacin completely blocked those increases in turnover of neuronal histamine induced by IL-1 beta. Hypothalamic prostaglandin E2 (PGE2) activated by peripheral IL-1 beta, but not peripheral PGE2, increased both activities of HDC and HMT. Ginsenoside Rg1, a major component of panax ginseng, modulated the suppressive effects of IL-1 beta on ingestive behavior, resulting in a lowering of body temperature. The findings suggest that the effects of IL-1 beta on ingestive behavior and thermogenesis may be modulated by dynamics of hypothalamic neuronal histamine through activation of hypothalamic PGE2 which is elevated by peripheral IL-1 beta.

Interleukin-2 as a neuroregulatory cytokine

Interleukin-2 (IL-2), the cytokine also known as T-cell growth factor, has multiple immunoregulatory functions and biological properties not only related to T-cells. In the past decade, substantial evidence accumulated to suggest that IL-2 is also a modulator of neural and neuroendocrine functions. First, extremely potent effects of IL-2 on neural cells were discovered, including activities related to cell growth and survival, transmitter and hormone release and the modulation of bioelectric activities. IL-2 may be involved in the regulation of sleep and arousal, memory function, locomotion and the modulation of the neuroendocrine axis. Second, the concept that IL-2 could act as a neuroregulatory cytokine has been supported by reports on the presence in rodent and human brain tissues of IL-2-like bioactivity, IL-2-like immunoreactivity, IL-2-like mRNA, IL-2 binding sites, IL-2 receptor (IL-2R alpha) and beta chain mRNA and IL-2R immunoreactivity. IL-2 and/or IL-2R molecules mainly localize to the frontal cortex, septum, striatum, hippocampal formation, hypothalamus, locus coeruleus, cerebellum, the pituitary and fiber tracts, such as the corpus callosum, where they are likely expressed by both neuronal and glial cells. Although the molecular biology of the brain IL-2/IL-2R system (including its relation to IL-15/IL-15R alpha) is not yet fully established by cloning and complete sequencing of all respective components, similarities (and to some extent differences) to peripheral counterparts are now apparent. The ability of IL-2 to readily penetrate the blood-brain barrier further suggests that this cytokine could regulate interactions between peripheral tissues and the central nervous system. Taken together, these data suggest that IL-2 of either immune and CNS origin can have access to functional IL-2R molecules on neurons and glia under normal conditions. Additionally, dysregulation of the IL-2/IL-2 receptor system could lead or contribute to functional and pathological alterations in the brain as in the immune system. Understanding the neurobiology of the IL-2/IL-2 receptor system should also help to explain neurologic, neuropsychiatric and neuroendocrine side effects occurring during IL-2 treatment of peripheral and brain tumors. Immunopharmacological manipulation either aiming at the activation or suppression of IL-2 signaling should consider functional interference with constitutive and inducible IL-2 receptors on brain cells in order to fulfil the high expectations associated with the use of this cytokine as a promising agent in immunotherapies, especially of brain tumors.

Bacterial lipopolysaccharide-induced changes in FOS protein expression in the rat brain: correlation with thermoregulatory changes and plasma corticosterone

In the present study the regions of the brain showing an increase in the number of FOS protein stained cells 180 min following intravenous saline or bacterial lipopolysaccharide (LPS) treatment were investigated and correlated with changes in body temperature and plasma corticosterone levels. Particular attention was given to the possible involvement of the circumventricular organs and regions of the brainstem containing central noradrenergic neurones. LPS at doses of 0.35, 3.5 and 50 micrograms caused highly significant increases in FOS protein expression in the organum vasculosum of lamina terminalis, the area postrema and the subfornical organ compared with saline controls. Marked increases in bacterial lipopolysaccharide-induced FOS protein expression were observed in the ventrolateral medulla, the nucleus of the solitary tract and the locus coeruleus which contain the A1, A2 and A6 noradrenergic neurones respectively. The changes in body temperature induced by LPS were found to be dependent upon the dose of LPS administered; the lowest dose employed (0.35 micrograms) induced an immediate and sustained fever, 3.5 micrograms LPS caused a biphasic response consisting of a hypothermic response followed by a febrile response, whereas 50 micrograms LPS induced a hypothermic response which then normalised by 160 min post-injection. Intravenous saline injection had no significant effect on body temperature. The occurance of LPS-induced hypothermia was coincident with increased FOS expression in the bed nucleus of stria terminalis, which houses vasopressinergic neurones involved in antipyresis, whereas in animals showing an LPS-induced febrile response there was no significant difference in the number of FOS stained cells in the bed nucleus of stria terminalis compared with saline treated animals. LPS also caused marked increases in FOS protein expression in the parvocellular regions of the paraventricular nucleus (pPVN) of the hypothalamus, the central nucleus of the amygdala and the ventral septal area. Plasma corticosterone was unaffected by the lowest dose of LPS (0.35 micrograms), however the higher doses employed (3.5 and 50 micrograms) caused significant increases in plasma corticosterone which correlated with the increases in the number of FOS stained cells in the pPVN. The results of the present study suggest that, in addition to the organum vasculosum of lamina terminalis, the area postrema and subfornical organ may be important in the responses to antigenic challenge that are mediated by the central nervous system. They also add support to the possible involvement of the bed nucleus of stria terminalis in LPS-induced hypothermia and of the involvement of the of the major noradrenergic cell groups (A1, A2 & A6) and a number of hypothalamic and extrahypothalamic forebrain regions in the interaction of immune and central nervous systems.

Cytokine-to-brain communication: a review & analysis of alternative mechanisms

It is becoming well accepted that products of the immune system (cytokines) can signal the brain that infection has occurred. This cytokine-to-brain communication can result in marked alterations in brain function and behavior. This review examines alternative mechanisms that have been proposed to explain how such immune products can reach the brain via the blood to cause centrally-mediated "illness" responses. Finally, we describe a new view which argues that cytokines signal brain in quite a different manner, by stimulating afferent terminals of peripheral nerves at local sites of synthesis and release.

Recombinant interleukin-1 beta inhibits gastric acid secretion by activation of central sympatho-adrenomedullary outflow in rats

The inhibitory mechanism of gastric acid secretion induced by human recombinant interleukin-1 beta was investigated in bilaterally vagotomized, urethane-anesthetized rats. Intracerebroventricular administration of interleukin-1 beta (10, 50 and 100 ng/animal) dose dependently inhibited the gastric acid secretion induced by electrical stimulation of the vagus nerve at 3 Hz. Inhibition of gastric acid secretion induced by interleukin-1 beta (50 ng/animal) was abolished both by splanchnectomy and by phentolamine (5 mg/kg i.m.). Greater splanchnic nerves ramify into the adrenal branch and gastric sympathetic preganglionic branch. The interleukin-1 beta (50 ng/animal)-induced inhibition was also abolished by intracerebroventricular pretreatment with indomethacin (500 micrograms/animal), while pretreatment with the same dose of this reagent by the intraperitoneal route was without effect. These results suggest that centrally administered interleukin-1 beta induces a prostaglandin-mediated central excitation of the sympatho-adrenomedullary system, and the resultant activation of gastric alpha-adrenoceptors inhibits the vagally stimulated gastric acid secretion in rats.

Molecular mechanisms and neural pathways mediating the influence of interleukin-1 on the activity of neuroendocrine CRF motoneurons in the rat

The action of immune-system-derived cytokines to stimulate the release of corticotropin-releasing factor (CRF) from the hypothalamus and the consequent elaboration of ACTH and release of corticosteroids has provided an especially useful model to investigate the nature of the intercommunication of neuroendocrine and immunological pathways. Substantial evidence exists to support the production of cytokines, such as interleukin-1 (IL-1) alpha and beta, within the mammalian central nervous system. The mechanisms and neuronal circuitries involved in the effects of these cytokines of peripheral and central origin on the activity of neuroendocrine CRF motoneurons and the hypothalamic-pituitary-adrenal axis are described. Also included is a discussion of the influence of IL-1 on transduction signals controlling the release and the biosynthesis of CRF in the parvocellular division of the paraventricular nucleus of the hypothalamus and the relationship between these two distinct intracellular processes. The relevance of using immediate early genes as indices of neuronal activity in immune-challenged rats and the possible roles of c-fos and NGFI-B within neuroendocrine CRF motoneurons are outlined. Finally, the effects of acute immune response on neuroendocrine functions and brain neuronal activation are presented.

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.

Evidence for an immune response in major depression: a review and hypothesis

1. This paper reviews recent findings on cellular and humoral immunity and inflammatory markers in depression. 2. It is shown that major depression may be accompanied by systemic immune activation or an inflammatory response with involvement of phagocytic (monocytes, neutrophils) cells, T cell activation, B cell proliferation, an "acute" phase response with increased plasma levels of positive and decreased levels of negative acute phase proteins, higher autoantibody (antinuclear, antiphospholipid) titers, increased prostaglandin secretion, disorders in exopeptidase enzymes, such as dipeptidyl peptidase IV, and increased production of interleukin (IL)-1 beta and IL-6 by peripheral blood mononuclear cells. 3. It is hypothesized that increased monocytic production of interleukins (Il-1 beta and Il-6) in severe depression may constitute key phenomena underlying the various aspects of the immune and "acute" phase response, while contributing to hypothalamic-pituitary-adrenal-axis hyperactivity, disorders in serotonin metabolism, and to the vegetative symptoms (i.e. the sickness behavior) of severe depression.

What roles does the organum vasculosum laminae terminalis play in fever in rabbits?

Experiments were designed to clarify the role of the brain's organum vasculosum laminae terminalis (OVLT) in the development of fever in rabbits. Rectal and ear skin temperatures were recorded in conscious animals in which the OVLT had been electrolytically destroyed or in which the preoptic anterior hypothalamus (PO/AH) had been transected bilaterally. When the OVLT had been ablated the febrile responses to intravenous injection of interleukin-1 beta (IL-1 beta) or tumour necrosis factor alpha were significantly attenuated, while those to intracerebroventricular injection of IL-1 beta were not affected. Fever induced by intracerebroventricular injection of prostaglandin E2 (PGE2) was prolonged significantly. The febrile responses to intravenous injection of IL-1 beta and to intracerebroventricular injection of PGE2 were attenuated when the transection was located caudally to the anterior wall of the third ventricle and extended laterally more than about 3 mm in the ventricular wall. The results show that the OVLT region is a site through which signals to increase body temperature are transferred from the blood to the brain in rabbits.

Blood-borne interleukin-1 alpha is transported across the endothelial blood-spinal cord barrier of mice

1. Previous work has shown that one mechanism by which blood-borne interleukin-1 alpha (IL-1) may be able to affect the central nervous system (CNS) is by direct transport into the brain across the blood-brain barrier (BBB). The BBB of the brain consists of endothelial (between blood and interstitial fluid) and ependymal (between blood and cerebrospinal fluid) barriers. Which of these barriers IL-1 can cross has not previously been investigated. At the spinal cord, which could be the site of action for some of the effects of IL-1 such as analgesia, the BBB consists only of the endothelial barrier. 2. We show here that IL-1 labelled with 125I (I-IL) is transported across the BBB of the spinal cord by a saturable system similar to the one previously described for the brain. High performance liquid chromatography (HPLC) showed that most of the material entering the spinal cord represented intact I-IL. The BBB of the spinal cord was no more leaky to radioactively labelled albumin than the BBB of the brain and was not disrupted by 50 micrograms kg-1 of IL-1. 3. Capillary depletion showed that most of the I-IL entered the parenchymal-interstitial fluid space of the spinal cord with only a modest amount being sequestered by the endothelial cells of its BBB. 4. I-IL entered the cervical, thoracic and lumbar regions of the spinal cord equally well. I-IL entering at the brain and diffusing caudally was estimated only to account for about 1% of the total radioactivity found in the spinal cord after i.v. injection.(ABSTRACT TRUNCATED AT 250 WORDS)