Relative contributions of peripheral and central sources to levels of IL-1 alpha in the cerebral cortex of mice: assessment with species-specific enzyme immunoassays

Time and dose-dependent impairment of neonatal respiratory motor activity after systemic inflammation

Neonatal respiratory impairment during infection is common, yet its effects on respiratory neural circuitry are not fully understood. We hypothesized that the timing and severity of systemic inflammation is positively correlated with impairment in neonatal respiratory activity. To test this, we evaluated time- and dose-dependent impairment of in vitro fictive respiratory activity. Systemic inflammation (induced by lipopolysaccharide, LPS, 5 mg/kg, i.p.) impaired burst amplitude during the early (1 h) inflammatory response. The greatest impairment in respiratory activity (decreased amplitude, frequency, and increased rhythm disturbances) occurred during the peak (3 h) inflammatory response in brainstem-spinal cord preparations. Surprisingly, isolated medullary respiratory circuitry within rhythmic slices showed decreased baseline frequency and delayed onset of rhythm only after higher systemic inflammation (LPS 10 mg/kg) early in the inflammatory response (1 h), with no impairments at the peak inflammatory response (3 h). Thus, different components of neonatal respiratory circuitry have differential temporal and dose sensitivities to systemic inflammation, creating multiple windows of vulnerability for neonates after systemic inflammation.

Disparate Changes in Plasma and Brainstem Cytokine Levels in Adult and Ageing Rats Associated with Age-Related Changes in Facial Motor Neuron Number, Snout Muscle Morphology, and Exploratory Behavior

An overall increase in inflammatory cytokines with age in both the blood and the central nervous system (CNS) has been proposed to explain many aspects of ageing, including decreased motor function and neurodegeneration. This study tests the hypothesis that age-related increases in inflammatory cytokines in the blood and CNS lead to facial motor neuron degeneration. Groups of 3–5 female Sprague-Dawley rats aged 3, 12–18, and 24 months were used. Twelve cytokines interleukin (IL)-1α, IL-β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-12p70, IL-13, tumor necrosis factor-α (TNFα), interferon-γ, and granulocyte macrophage-colony stimulating factor were measured in blood plasma and compared with those in the brainstem after first flushing blood from its vessels. The open-field test was used to measure exploratory behavior, and the morphology of the peripheral target muscle of facial motor neurons quantified. Total numbers of facial motor neurons were determined stereologically in separate groups of 3- and 24-month-old rats. Ageing rats showed a significant 30–42% decrease in blood plasma (peripheral) concentrations of IL-12p70 and TNFα and a significant 43–49% increase in brainstem (central) concentrations of IL-1α, IL-2, IL-4, IL-10, and TNFα. They also showed significant reductions in motor neuron number in the right but not left facial nucleus, reduced exploratory behavior, and increase in peripheral target muscle size. Marginal age-related facial motoneuronal loss occurs in the ageing rat and is characterized by complex changes in the inflammatory signature, rather than a general increase in inflammatory cytokines.

Inflammation and schizophrenia: alterations in cytokine levels and perturbation in antioxidative defense systems

OBJECTIVE

Although several theories have been proposed including developmental/neurodegenerative processes, neurotransmitter abnormalities, viral infection, and immune dysfunction, the exact causative factor of schizophrenia is unclear. A relationship between inflammation and schizophrenia has been supported by abnormal cytokine production and altered antioxidant status. This study was aimed to examine the alterations in serum oxidative-antioxidative status and cytokine levels of schizophrenic patients.

METHODS

A total of 91 schizophrenic patients from Saudi Arabia and 50 age- and sex-matched healthy controls were enrolled in the present study. Fresh blood samples were collected to measure the levels of cytokines and markers of oxidative stress by spectrophotometric assays simultaneously.

RESULTS

We observed that there was a significant increase in the levels of tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 and a decrease in the levels of interferon-γ. Lipid peroxides are elevated in serum, while total-sulfhydryl levels were decreased. Also, the activities of superoxide dismutase and glutathione peroxidase were decreased, while the activities of catalase, glutathione reductase, and myeloperoxidase were found to be elevated in serum.

CONCLUSION

We conclude that inflammation resulting from dysregulation of cytokines and altered antioxidant systems may play a critical role in the etiology of schizophrenia.

IL-15 overexpression promotes endurance, oxidative energy metabolism, and muscle PPARδ, SIRT1, PGC-1α, and PGC-1β expression in male mice

Endurance exercise initiates a pattern of gene expression that promotes fat oxidation, which in turn improves endurance, body composition, and insulin sensitivity. The signals from exercise that initiate these pathways have not been completely characterized. IL-15 is a cytokine that is up-regulated in skeletal muscle after exercise and correlates with leanness and insulin sensitivity. To determine whether IL-15 can induce any of the metabolic adaptations associated with exercise, substrate metabolism, endurance, and molecular expression patterns were examined in male transgenic mice with constitutively elevated muscle and circulating IL-15 levels. IL-15 transgenic mice ran twice as long as littermate control mice in a run-to-exhaustion trial and preferentially used fat for energy metabolism. Fast muscles in IL-15 transgenic mice exhibited high expression of intracellular mediators of oxidative metabolism that are induced by exercise, including sirtuin 1, peroxisome proliferator-activated receptor (PPAR)-δ, PPAR-γ coactivator-1α, and PPAR-γ coactivator-1β. Muscle tissue in IL-15 transgenic mice exhibited myosin heavy chain and troponin I mRNA isoform expression patterns indicative of a more oxidative phenotype than controls. These findings support a role for IL-15 in induction of exercise endurance, oxidative metabolism, and skeletal muscle molecular adaptations induced by physical training.

Psychoneuroimmune implications of type 2 diabetes: redux

A sizable body of knowledge has arisen demonstrating that type 2 diabetes (T2D) is associated with alterations in the innate immune system. The resulting proinflammatory-leaning imbalance is implicated in the development of secondary disease complications and comorbidities, such as delayed wound healing, accelerated progress of atherosclerosis, and retinopathy, in people who have T2D. New experimental data and the results of recently published health-related quality-of-life surveys indicate that individuals who have T2D experience diminished feelings of happiness, well being, and satisfaction with life. These emotional and psychological consequences of T2D point to altered neuroimmunity as a previously unappreciated complication of T2D. This article discusses recent data detailing the impact of T2D on a person's PNI response.

Immune-to-brain signaling: how important are the blood-brain barrier-independent pathways?

A conceptual obstacle for understanding immune-to-brain signaling is the issue of the blood-brain barrier (BBB). In the last 30 years, several pathways have been investigated to address the question of how peripheral immune signals are transmitted into the brain. These pathways can be categorized into two types: BBB-dependent pathways and BBB-independent pathways. BBB-dependent pathways involve the BBB as a relay station or porous barrier, whereas BBB-independent pathways use neuronal routes that bypass the BBB. Recently, a complete BBB-dependent ascending pathway for immune-to-brain signaling has been described. Details of BBB-independent pathways are still under construction. In this review, I will summarize the current progress in unraveling immune-to-brain signaling pathways. In addition, I will provide a critical analysis of the literature to point to areas where our knowledge of the immunological afferent signaling to the central nervous system is still sorely lacking.

Brain cytokine flux in acute liver failure and its relationship with intracranial hypertension

BACKGROUND

In acute liver failure (ALF), it is unclear whether the systemic inflammatory response associated with intracranial hypertension is related to brain cytokine production.

AIM

To determine the relationship of brain cytokine production with severity of intracranial hypertension in ALF patients.

METHOD

We studied 16 patients with ALF. All patients were mechanically ventilated and cerebral blood flow measured using the Kety-Schmidt technique and intracranial pressure (ICP) measured with a Camino subdural catheter. We sampled blood from an artery and a reverse jugular catheter to measure proinflammatory cytokines (TNF-alpha, IL-6 and IL-1beta) and ammonia. Additionally, in 3 patients, serial samples were obtained over a 72 h period.

RESULTS

In ALF patients a good correlation between arterial pro-inflammatory cytokines and ICP (r (2) = 0.34, 0.50 and 0.52; for IL-6, IL-1beta and TNF-alpha respectively) was observed. There was a positive cerebral cytokine 'flux' (production), in ALF patients with uncontrolled ICP. Plasma ammonia between groups was not statistically significant. In the ALF patients studied longitudinally, brain proinflammatory cytokine production was associated with uncontrolled ICP.

CONCLUSION

Our results provide novel data supporting brain production of cytokines in patients with uncontrolled intracranial hypertension indicating activation of the inflammatory cascade in the brain. Also, the appearance of these cytokines in the jugular bulb catheter may indicate a compromised blood brain barrier at this late stage.

Imbalance between pro-inflammatory and anti-inflammatory cytokines in bipolar disorder

BACKGROUND

The role of cytokines in bipolar disorder is still controversial. Although a few studies have found alterations of cytokines in bipolar disorder, their findings were inconsistent. The aim of this study was to determine whether the cytokines are involved in the pathophysiology of bipolar disorder.

METHODS

A total of 37 manic patients with bipolar disorder and 74 control subjects were recruited. The mitogen-induced production of tumor necrosis factor (TNF)-alpha, interleukin-6 (IL-6), IL-4, interferon (IFN)-gamma, and IL-2 was measured using quantitative sandwich ELISA at the time of admission and 6 weeks after mood stabilizer treatment.

RESULTS

IL-6 and TNF-alpha production of bipolar manic patients was significantly higher than those of normal controls, while IL-4 values of the patients were significantly lower than normal controls. IL-6/IL-4, TNF-alpha/IL-4, IL-2/IL-4, and IFN-gamma/IL-4 ratios were significantly higher in bipolar manic patients than in normal controls. After 6 weeks of treatment, the levels of IL-6 significantly decreased compared with baseline.

LIMITATIONS

The effect of various types of mood stabilizers on cytokine production should be considered.

CONCLUSIONS

These findings suggest that the increased activity of pro-inflammatory cytokines and an imbalance between pro-inflammatory and anti-inflammatory cytokines may play a role in the pathophysiology of bipolar disorder.

The catecholamine cytokine balance: interaction between the brain and the immune system

Cytokines are involved both in various immune reactions and in controlling certain events in the central nervous system (CNS). In our earlier studies, it was shown that monoamine neurotransmitters, released in stress situations, represent a tonic sympathetic control on cytokine production and on the balance of proinflammatory/anti-inflammatory cytokines. Basic and clinical studies have provided evidence that the biophase level of monoamines, determined by the balance of their release and uptake, is involved in the pathophysiology and treatment of depression, while inflammatory mediators might also have a role in its etiology. In this work, we studied the role of changes in norepinephrine (NE) level on the lipopolysaccharide (LPS) evoked tumor necrosis factor (TNF)-alpha and interleukin (IL)-10 response both in the plasma and in the hippocampus of mice. We demonstrated that the LPS induced TNF-alpha response is in direct correlation with the biophase level of NE, as it is significantly higher when the release of NE of vesicular origin was completely inhibited in an animal model of depression (reserpine treatment) and it is significantly lower in the case of increasing biophase levels of NE by genetic (NET-KO) or chemical (desipramine) disruption of NE reuptake. IL-10 was changed inversely to TNF-alpha levels only in the desipramine-treated animals. Our results showed that depression is related both to changes in peripheral and in hippocampal inflammatory cytokine production and to monoamine neurotransmitter levels. Since several anti-inflammatory drugs also have antidepressant effects, we hypothesized that antidepressants are also able to modulate the LPS-induced inflammatory response, which might contribute to their antidepressant effect.

Psychoneuroimmune Implications of Type 2 Diabetes

The idea that type 2 diabetes is associated with augmented innate immune function characterized by increased circulating levels of acute phase reactants and altered macrophage biology is fairly well established, even though the mechanisms involved in this complex interaction still are not entirely clear. To date, the majority of studies investigating innate immune function in type 2 diabetes are limited to the context of wound healing, atherosclerosis, stroke, and other commonly identified comorbidities. Several important recurring themes come out of these data. First, type 2 diabetes is associated with a state of chronic, subclinical inflammation. Second, in macrophages, type 2 diabetic conditions enhance proinflammatory reactions and impair anti-inflammatory responses. Third, after acute activation of the innate immune system in type 2 diabetes, recovery or resolution of inflammation is impaired. The consequences of type 2 diabetes-associated inflammatory alterations on PNI processes have been recognized only recently. Given the impact of diminished emotional well-being on the quality of life in patients who have type 2 diabetes, diabetes-induced exacerbation of PNI responses should be considered a serious complication of type 2 diabetes that warrants further clinical attention.

Interleukin-1beta enhances GABAA receptor cell-surface expression by a phosphatidylinositol 3-kinase/Akt pathway: relevance to sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a frequent but poorly understood neurological complication in sepsis that negatively influences survival. Here we present clinical and experimental evidence that this brain dysfunction may be related to altered neurotransmission produced by inflammatory mediators. Compared with septic patients, SAE patients had higher interleukin-1beta (IL-1beta) plasma levels; interestingly, these levels decreased once the encephalopathy was resolved. A putative IL-1beta effect on type A gamma-aminobutyric acid receptors (GABA(A)Rs), which mediate fast synaptic transmission in most cerebral inhibitory synapses in mammals, was investigated in cultured hippocampal neurons and in Xenopus oocytes expressing native or foreign rat brain GABA(A)Rs, respectively. Confocal images in both cell types revealed that IL-1beta increases recruitment of GABA(A)Rs to the cell surface. Moreover, brief applications of IL-1beta to voltage-clamped oocytes yielded a delayed potentiation of the GABA-elicited chloride currents (I(GABA)); this effect was suppressed by IL-1ra, the natural IL-1 receptor (IL-1RI) antagonist. Western blot analysis combined with I(GABA) recording and confocal images of GABA(A) Rs in oocytes showed that IL-1beta stimulates the IL-1RI-dependent phosphatidylinositol 3-kinase activation and the consequent facilitation of phospho-Akt-mediated insertion of GABA(A)Rs into the cell surface. The interruption of this signaling pathway by specific phosphatidylinositol 3-kinase or Akt inhibitors suppresses the cytokine-mediated effects on GABA(A)R, whereas activation of the conditionally active form of Akt1 (myr-Akt1.ER*) with 4-hydroxytamoxifen reproduces the effects. These findings point to a previously unrecognized signaling pathway that connects IL-1beta with increased "GABAergic tone." We propose that through this mechanism IL-1beta might alter synaptic strength at central GABAergic synapses and so contribute to the cognitive dysfunction observed in SAE.

Systemic inflammatory response exacerbates the neuropsychological effects of induced hyperammonemia in cirrhosis

BACKGROUND/AIMS

Studies in acute liver failure show correlation between evidence of a systemic inflammatory response syndrome (SIRS) and progression of hepatic encephalopathy (HE). We tested the hypothesis that SIRS mediators, such as nitric oxide and proinflammatory cytokines, may exacerbate the neuropsychological effects of hyperammonemia in cirrhosis.

METHODS

Ten patients with cirrhosis were studied, 24-36 h after admission with clinical evidence of infection, and following its resolution. Hyperammonemia was induced by oral administration of an amino-acid (aa) solution mimicking hemoglobin composition. Inflammatory mediators, nitrate/nitrite, ammonia, aa profiles and a battery of neuropsychological tests were measured.

RESULTS

The hyperammonemia generated in response to the aa solution was similar prior to, and after resolution, of the inflammation (P=0.77). With treatment of the infection there were significant reductions in white blood cell count (WBC), C-reactive protein (CRP), nitrate/nitrite, interleukin-6, interleukin-1beta and tumour necrosis factor alpha. Induced hyperammonemia resulted in significant worsening of the neuropsychological scores when patients showed evidence of SIRS but not after its resolution.

CONCLUSIONS

The significant deterioration of neuropsychological test scores following induced hyperammonemia during the inflammatory state, but not after its resolution, suggests that the inflammation and its mediators may be important in modulating the cerebral effect of ammonia in liver disease.

Microglia as a source and target of cytokines

Cytokines constitute a significant portion of the immuno- and neuromodulatory messengers that can be released by activated microglia. By virtue of potent effects on resident and invading cells, microglial cyto- and chemokines regulate innate defense mechanisms, help the initiation and influence the type of immune responses, participate in the recruitment of leukocytes to the CNS, and support attempts of tissue repair and recovery. Microglia can also receive cyto- and chemokine signals as part of auto- and paracrine communications with astrocytes, neurons, the endothelium, and leukocyte infiltrates. Strong responses and modulatory influences can be demonstrated, adding to the emerging view that microglial behavior is highly dependent on the (cytokine) environment and that reactions to a challenge may vary with the stimulation context. In principle, microglial activation aims at CNS protection. However, failed microglial engagement due to excessive or sustained activation could significantly contribute to acute and chronic neuropathologies. Dysregulation of microglial cytokine production could thereby promote harmful actions of the defense mechanisms, result in direct neurotoxicity, as well as disturb neural cell functions as they are sensitive to cytokine signaling.

Neuroendocrine-immune interactions in fish: a role for interleukin-1

Bi-directional communication between the hypothalamus-pituitary-adrenal (HPA)-axis and the sympathetic nervous system with the immune system is crucial to ensure homeostasis. Shared use of ligands and especially receptors forms a key component of this bi-directional interaction. Glucocorticoids (GC), the major end products of the HPA-axis differentially modulate immune function. Cytokines, especially interleukin-1 (IL-1), tumour necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), ensure immune signalling to the neuroendocrine system. In addition, hormones from leukocyte origin such as corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and beta-endorphin, as well as centrally synthesised and secreted cytokines, contribute to the communication network. In teleost fish cortisol is the major product of the hypothalamus-pituitary-interrenal (HPI)-axis which is the teleost equivalent of the HPA-axis. Moderate and substantial increases in cortisol during stressful circumstances negatively affect B-lymphocytes, whereas rescue of neutrophilic granulocytes may support innate immunity. Recent elucidation of lower vertebrate cytokine sequences has facilitated research into neuroendocrine-immune interactions in teleosts and the first evidence for a significant function of interleukin-1 in the bi-directional communication is discussed.

Astrogliosis in the adult and developing CNS: is there a role for proinflammatory cytokines?

Astrogliosis, characterized by the enhanced expression of GFAP, represents a remarkably homotypic response of astrocytes to all types of injuries of the CNS, including injuries of the developing CNS. As such, astrocytes serve as microsensors of the injured microenvironment regardless of their location in the CNS. The diversity of insults that engender astrogliosis and the brain-wide nature of the astrocytic response suggest that common injury factors serve as the trigger of this cellular reaction. One prominent theme that has emerged in recent years is that proinflammatory cytokines and chemokines serve as a stimulus for induction of astrogliosis. Here we present a brief critique of this hypothesis based on a review of literature and some of our own recentfindings. Studies of astrocytes, in vitro, clearly indicate that these cell types are responsive to a variety of growth factors, including cytokines and chemokines. A somewhat different picture, however, can be seen from data obtained in vivo. It is true that trauma and diseases of the nervous system, as well as some exposures to neurotoxic chemicals, can be associated with the expression in brain of large varieties of cytokines and chemokines. That these same conditions result in astrogliosis has fostered the circumstantial link between cytokine/chemokine expression and the induction of astrogliosis. Several lines of evidence argue against this view, including (a) suppression of cytokine expression does not suppress gliosis, (b) gliosis can occur in the absence of enhanced expression of cytokines, (c) elevations in brain cytokines can occur in the absence of gliosis and (d) the patterns of cytokine expression in the adult and developing CNS are more consistent with a trophic role for these chemical messengers rather than a role in the induction of inflammation. Enhanced expression of cytokines and chemokines after brain injury appear to be signal transduction events unrelated to the induction of astrogliosis.

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.

Induction of preprotachykinin-I and neurokinin-1 by adrenocorticotropin and prolactin. Implication for neuroendocrine-immune-hematopoietic axis

We studied the complex interactions within the neuroendocrine-immune-hematopoietic axis by determining a possible link among ACTH, PRL, PPT-I and the receptors for its peptides, NK-1 and NK-2. Indeed, ACTH and PRL induced the expression of PPT-I and NK-1 in human bone marrow stroma with no effect on NK-2. Consistent with a role for PPT-I in regulating the development of myeloid and erythroid progenitors, we found that ACTH and PRL, through NK-1 stimulated the proliferation of both types of progenitors. Induction of PPT-I was regulated at the transcriptional and post-transcriptional levels. The results showed that ACTH and PRL stimulated the proliferation of bone marrow progenitors, partly through PPT-I and NK-1 induction.

Anorexia of infection: current prospects

The anorexia of infection is part of the host's acute phase response (APR). Despite being beneficial in the beginning, long lasting anorexia delays recovery and is ultimately deleterious. Microbial products such as bacterial cell wall compounds (e.g., lipopolysaccharides and peptidoglycans), microbial nucleic acids (e. g., bacterial DNA and viral double-stranded RNA), and viral glycoproteins trigger the APR and presumably also the anorexia during infections. Microbial products stimulate the production of proinflammatory cytokines (e.g., interleukins [ILs], tumor necrosis factor-alpha, interferons), which serve as endogenous mediators. Several microbial products and cytokines reduce food intake after parenteral administration, suggesting a role of these substances in the anorexia during infection. Microbial products are mainly released and cytokines are produced in the periphery during most infections; they might inhibit feeding through neural and humoral pathways activated by their peripheral actions. Activation of peripheral afferents by locally produced cytokines is involved in several cytokine effects, but is not crucial for the anorectic effect of microbial products and IL-1beta. Cytokines increase leptin expression in the adipose tissue, and leptin may contribute to, but is also not essential for, the anorectic effects of microbial products and cytokines. In addition, a direct action of cytokines and microbial products on the central nervous system (CNS) is presumably involved in the anorexia during infection. Cytokines can reach CNS receptors through circumventricular organs and through active or passive transport mechanisms or they can act through receptors on endothelial cells of the brain vasculature and stimulate the release of subsequent mediators such as eicosanoids. De novo CNS cytokine synthesis occurs in response to peripheral infections, but its role in the accompanying anorexia is still open to discussion. Central mediators of the anorexia during infection appear to be neurochemicals involved in the normal control of feeding, such as serotonin, dopamine, histamine, corticotropin releasing factor, neuropeptide Y, and alpha-melanocyte-stimulating hormone. Reciprocal, synergistic, and antagonistic interactions between various pleiotropic cytokines, and between cytokines and neurochemicals, form a complex network that mediates the anorexia during infection. Current knowledge on the mechanisms involved suggests some therapeutic options for treatment. Substances that block common key steps in cytokine synthesis or cytokine action, or inhibitors of eicosanoid synthesis, may hold more promise than attempts to antagonize specific cytokines. To target the neurochemical mediation of the anorexia during infection may be even more efficient. Future research should address these neurochemical mechanisms and the cytokine actions at the blood-brain barrier. Further unanswered questions concern the modulation of the anorexia during infection by gender and nutritional state.

Cytokine-cytokine interactions and the brain

Cytokine-cytokine interactions play a role in health and are crucial during immunological and inflammatory responses in disease. Cytokine interactions can result in additive, antagonist, or synergistic activities in maintaining physiological functions such as feeding, body temperature, and sleep, as well as in anorectic, pyrogenic, and somnogenic neurological manifestations of acute and chronic disease. These interactions involve signaling homology, convergence of signaling pathways, and/or positive or negative feedbacks within and among cytokine systems. The interplay of cytokines with neurotransmitters, peptides/neuropeptides, and hormones also influence cytokine action in the brain. Interactive chemical cascades involving cytokines are consistent with the homeostatic physiological mechanisms and with the multi-humoral, pleiotropic, and redundant processes that occur during acute and chronic disease.

Peptides crossing the blood-brain barrier: some unusual observations

An interactive blood-brain barrier (BBB) helps regulate the passage of peptides from the periphery to the CNS and from the CNS to the periphery. Many peptides cross the BBB by simple diffusion, mainly explained by their lipophilicity and other physicochemical properties. Other peptides cross by saturable transport systems. The systems that transport peptides into or out of the CNS can be highly specific, transporting MIF-1 but not Tyr-MIF-1, PACAP38 but not PACAP27, IL-1 but not IL-2, and leptin but not the smaller ingestive peptides NPY, orexin A, orexin B, CART (55-102[Met(O)(67)]), MCH, or AgRP(83-132). Although the peptides EGF and TGF-alpha bind to the same receptor, only EGF enters by a rapid saturable transport system, suggesting that receptors and transporters can represent different proteins. Even the polypeptide NGF enters faster than its much smaller subunit beta-NGF. The saturable transport of some compounds can be upregulated, like TNF-alpha in EAE (an animal model of multiple sclerosis) and after spinal cord injury, emphasizing the regulatory role of the BBB. As has been shown for CRH, saturable transport from brain to blood can exert effects in the periphery. Thus, the BBB plays a dynamic role in the communication of peptides between the periphery and the CNS.

Temporal and spatial patterns of c-fos mRNA induced by intravenous interleukin-1: a cascade of non-neuronal cellular activation at the blood-brain barrier

Brain cells responsive to a peripheral immune challenge, identified by in situ hybridization of c-fos mRNA following intravenous administration of the proinflammatory cytokine interleukin-1beta (IL-1) or sterile saline, were investigated at 0.5, 1, and 3 hours postinjection in rats. Doses of IL-1 ranged from 0.05 to 10 microg/kg; induction of c-fos mRNA occurred at > or = 0.5 pg/kg. The majority of IL-1-induced c-fos mRNA-positive cells were non-neuronal cells located in barrier regions of the brain. The cells became radiolabeled in two separate but related spatiotemporal patterns. The first pattern, occurring at 0.5 hour, was characterized by c-fos mRNA labeling of cells of the outer meninges (mainly arachnoid), blood vessels (arteries, veins, and capillaries), and choroid plexus. This activation pattern disappeared at 1 hour. At 3 hours, a second activation pattern appeared in cells located just inside the now quiescent barrier cells. In addition, the circumventricular organs each showed characteristic spatiotemporal labeling patterns resulting from successive activation of specific cell types, with a general spread of activation directed away from the circumventricular organs over time. At 3 hours post IL-1, c-fos and glial fibrillary acidic protein (GFAP) mRNAs showed colocalization in the arcuate nucleus/median eminence/glia limitans region. We propose that the first wave of activation is elicited by blood-borne immune signals, but the second wave is caused by molecules generated within the first set of activated cells. The transduced signal appears to propagate to neighboring receptive cells by extracellular diffusion. In this manner, blood-brain barrier cells can transduce peripheral IL-1 signals in widespread areas of the brain, although the circumventricular organs may be the most effective loci for signal transduction.

Pituitary corticotroph SOCS-3: novel intracellular regulation of leukemia-inhibitory factor-mediated proopiomelanocortin gene expression and adrenocorticotropin secretion

As pituitary leukemia-inhibitory factor (LIF) mediates neuroimmune signals to the hypothalamo-pituitary-adrenal axis, we tested the role of intracellular SOCS-3 in corticotroph function. SOCS-3, a cytokine-inducible protein of the suppressor of cytokine signaling (SOCS) family, is expressed in the murine pituitary in vivo. After i.p. injection of LIF (5.0 micrograms/mouse) or interleukin-1 beta (0.1 microgram/mouse) pituitary SOCS-3 mRNA was stimulated 9-fold and 6-fold, respectively. Also, in corticotroph AtT-20 cells LIF and interleukin-1 beta both potently stimulated SOCS-3 mRNA expression. In AtT-20 cells, stable overexpression of SOCS-3 inhibits basal and LIF-stimulated ACTH secretion in comparison to mock-transfected AtT-20 cells (basal: 4426 +/- 118 vs. 4973 +/- 138 pg/ml, P < 0.05; LIF-induced: 5511 +/- 172 vs. 9308 +/- 465 pg/ml, P < 0.001). Stable overexpression of SOCS-3 cDNA in AtT-20 cells also resulted in a significant 50% decrease of LIF-induced POMC mRNA levels (P < 0.05) and POMC promoter activity (P < 0.001), respectively. Western blot analysis revealed an inhibition of LIF-stimulated gp130 and STAT-3 phosphorylation in SOCS-3 overexpressing AtT-20 cells. Thus, SOCS-3 inhibits the Janus kinase (JAK) and signal transducers and activators of transcription (STAT) pathway, which is known to mediate LIF-stimulated ACTH secretion and POMC gene expression. In conclusion, SOCS-3 functions as an intracellular regulator of POMC gene expression and ACTH secretion, acting as a negative feedback mediator of the cytokine-mediated neuro-immuno-endocrine interface.