Chronic interleukin-6 exposure alters electrophysiological properties and calcium signaling in developing cerebellar purkinje neurons in culture

The Neuroimmune System and the Cerebellum

The recognition that there is an innate immune system of the brain, referred to as the neuroimmune system, that preforms many functions comparable to that of the peripheral immune system is a relatively new concept and much is yet to be learned. The main cellular components of the neuroimmune system are the glial cells of the brain, primarily microglia and astrocytes. These cell types preform many functions through secretion of signaling factors initially known as immune factors but referred to as neuroimmune factors when produced by cells of the brain. The immune functions of glial cells play critical roles in the healthy brain to maintain homeostasis that is essential for normal brain function, to establish cytoarchitecture of the brain during development, and, in pathological conditions, to minimize the detrimental effects of disease and injury and promote repair of brain structure and function. However, dysregulation of this system can occur resulting in actions that exacerbate or perpetuate the detrimental effects of disease or injury. The neuroimmune system extends throughout all brain regions, but attention to the cerebellar system has lagged that of other brain regions and information is limited on this topic. This article is meant to provide a brief introduction to the cellular and molecular components of the brain immune system, its functions, and what is known about its role in the cerebellum. The majority of this information comes from studies of animal models and pathological conditions, where upregulation of the system facilitates investigation of its actions.

Interleukin-6 in Traumatic Brain Injury: A Janus-Faced Player in Damage and Repair

Traumatic brain injury (TBI) is a common and often devastating illness, with wide-ranging public health implications. In addition to the primary injury, victims of TBI are at risk for secondary neurological injury by numerous mechanisms. Current treatments are limited and do not target the profound immune response associated with injury. This immune response reflects a convergence of peripheral and central nervous system-resident immune cells whose interaction is mediated in part by a disruption in the blood-brain barrier (BBB). The diverse family of cytokines helps to govern this communication and among these, Interleukin (IL)-6 is a notable player in the immune response to acute neurological injury. It is also a well-established pharmacological target in a variety of other disease contexts. In TBI, elevated IL-6 levels are associated with worse outcomes, but the role of IL-6 in response to injury is double-edged. IL-6 promotes neurogenesis and wound healing in animal models of TBI, but it may also contribute to disruptions in the BBB and the progression of cerebral edema. Here, we review IL-6 biology in the context of TBI, with an eye to clarifying its controversial role and understanding its potential as a target for modulating the immune response in this disease.

Cytokines as emerging regulators of central nervous system synapses

Cytokines are key messengers by which immune cells communicate, and they drive many physiological processes, including immune and inflammatory responses. Early discoveries demonstrated that cytokines, such as the interleukin family members and TNF-α, regulate synaptic scaling and plasticity. Still, we continue to learn more about how these traditional immune system cytokines affect neuronal structure and function. Different cytokines shape synaptic function on multiple levels ranging from fine-tuning neurotransmission, to regulating synapse number, to impacting global neuronal networks and complex behavior. These recent findings have cultivated an exciting and growing field centered on the importance of immune system cytokines for regulating synapse and neural network structure and function. Here, we highlight the latest findings related to cytokines in the central nervous system and their regulation of synapse structure and function. Moreover, we explore how these mechanisms are becoming increasingly important to consider in diseases-especially those with a large neuroinflammatory component.

Immune-Triggered Forms of Plasticity Across Brain Regions

Immune cells play numerous roles in the host defense against the invasion of microorganisms and pathogens, which induces the release of inflammatory mediators (e.g., cytokines and chemokines). In the CNS, microglia is the major resident immune cell. Recent efforts have revealed the diversity of the cell types and the heterogeneity of their functions. The refinement of the synapse structure was a hallmark feature of the microglia, while they are also involved in the myelination and capillary dynamics. Another promising feature is the modulation of the synaptic transmission as synaptic plasticity and the intrinsic excitability of neurons as non-synaptic plasticity. Those modulations of physiological properties of neurons are considered induced by both transient and chronic exposures to inflammatory mediators, which cause behavioral disorders seen in mental illness. It is plausible for astrocytes and pericytes other than microglia and macrophage to induce the immune-triggered plasticity of neurons. However, current understanding has yet achieved to unveil what inflammatory mediators from what immune cells or glia induce a form of plasticity modulating pre-, post-synaptic functions and intrinsic excitability of neurons. It is still unclear what ion channels and intracellular signaling of what types of neurons in which brain regions of the CNS are involved. In this review, we introduce the ubiquitous modulation of the synaptic efficacy and the intrinsic excitability across the brain by immune cells and related inflammatory cytokines with the mechanism for induction. Specifically, we compare neuro-modulation mechanisms by microglia of the intrinsic excitability of cerebellar Purkinje neurons with cerebral pyramidal neurons, stressing the inverted directionality of the plasticity. We also discuss the suppression and augmentation of the extent of plasticity by inflammatory mediators, as the meta-plasticity by immunity. Lastly, we sum up forms of immune-triggered plasticity in the different brain regions with disease relevance. Together, brain immunity influences our cognition, sense, memory, and behavior via immune-triggered plasticity.

Alcohol alters IL-6 Signal Transduction in the CNS of Transgenic Mice with Increased Astrocyte Expression of IL-6

Neuroimmune factors, including the cytokine interleukin-6 (IL-6), are important chemical regulators of central nervous system (CNS) function under both physiological and pathological conditions. Elevated expression of IL-6 occurs in the CNS in a variety of disorders associated with altered CNS function, including excessive alcohol use. Alcohol-induced production of IL-6 has been reported for several CNS regions including the cerebellum. Cerebellar actions of alcohol occur through a variety of mechanisms, but alcohol-induced changes in signal transduction, transcription, and translation are known to play important roles. IL-6 is an activator of signal transduction that regulates gene expression. Thus, alcohol-induced IL-6 production could contribute to cerebellar effects of alcohol by altering gene expression, especially under conditions of chronic alcohol abuse, where IL-6 levels could be habitually elevated. To gain an understanding of the effects of alcohol on IL-6 signal transduction, we studied activation/expression of IL-6 signal transduction partners STAT3 (Signal Transducer and Activator of Transcription), CCAAT-enhancer binding protein (C/EBP) beta, and p42/p44 mitogen-activated protein kinase (MAPK) at the protein level. Cerebella of transgenic mice that express elevated levels of astrocyte produced IL-6 in the CNS were studied. Results show that the both IL-6 and chronic intermittent alcohol exposure/withdrawal affect IL-6 signal transduction partners and that the actions of IL-6 and alcohol interact to alter activation/expression of IL-6 signal transduction partners. The alcohol/IL-6 interactions may contribute to cerebellar actions of alcohol, whereas the effects of IL-6 alone may have relevance to cerebellar changes occurring in CNS disorders associated with elevated levels of IL-6.

Higher Levels of Pro-inflammatory Cytokines Are Associated With Higher Levels of Glutamate in the Anterior Cingulate Cortex in Depressed Adolescents

Animal models of stress and related conditions, including depression, have shown that elevated peripheral levels of inflammatory cytokines have downstream consequences on glutamate (Glu) in the brain. Although studies in human adults with depression have reported evidence of higher inflammation but lower Glu in the anterior cingulate cortex (ACC), the extent to which peripheral inflammation contributes to glutamatergic abnormalities in adolescents with depression is not well-understood. It is also unclear whether antioxidants, such as ascorbate (Asc), may buffer against the effects of inflammation on Glu metabolism. Fifty-five depressed adolescents were recruited in the present cross-sectional study and provided blood samples, from which we assayed pro-inflammatory cytokines, and underwent a short-TE proton magnetic spectroscopy scan at 3T, from which we estimated Glu and Asc in the dorsal ACC. In the 31 adolescents with usable cytokine and Glu data, we found that IL-6 was significantly positively associated with dorsal ACC Glu (β = 0.466 ± 0.199, p = 0.029). Of the 16 participants who had usable Asc data, we found that at higher levels of dorsal ACC Asc, there was a negative association between IL-6 and Glu (interaction effect: β = -0.906 ± 0.433, p = 0.034). Importantly, these results remained significant when controlling for age, gender, percentage of gray matter in the dorsal ACC voxel, BMI, and medication (antidepressant and anti-inflammatory) usage. While preliminary, our results underscore the importance of examining both immune and neural contributors to depression and highlight the potential role of anti-inflammatory compounds in mitigating the adverse effects of inflammation (e.g., glutamatergic neuroexcitotoxicity). Future studies that experimentally manipulate levels of inflammation, and of ascorbate, and that characterize these effects on cortical glutamate concentrations and subsequent behavior in animals and in humans are needed.

Comparative analysis of clinical, physiological, temperamental and personality characteristics of elderly subjects and young subjects with asthma

BACKGROUND

Asthma is a heterogeneous disease of a complex etiology in which genetic, environmental and personality variables are important factors determining the development of complicated strategies related to coping with stress and temperament traits. Our thesis is that coping styles in asthmatic patients are modified by the environment (chronic inflammation and stress) which affects individual temperament traits in the course of time. Thus, patient age is one of factors which determine the clinical image of asthma and its natural history.

AIM

The aim of the study was to evaluate the variables describing stress coping styles and temperament in young (18 to 35 years old) and elderly asthmatics (aged ≥60 years).

MATERIAL AND METHODS

A total of 200 patients, 104 elderly and 96 young asthmatics were enrolled in the study. Apart from medical examination, the following tests were performed in all subjects: the Formal Characteristics of Behavior- Temperament Inventory (FCB-TI), Coping Inventory for Stressful Situations (CISS), Beck Depression Inventory, State-Trait Anxiety Inventory, and Borg Rating of Perceived Exertion (RPE) Scale.

RESULTS

Elderly patients with asthma exhibited higher intensity of anxiety as a trait, a higher level of depression and experienced dyspnea, as well as higher levels of stress coping strategies such as Avoidance-Oriented Coping (AOC), Distraction Seeking (DS) and Social Diversion (SD) compared to young asthmatics. In elderly patients, Perseverance and Sensory Sensitivity traits have been observed to decline with the duration and development of asthma at later life stages as opposed to young asthmatics, in whom these temperament characteristics are elevated.

CONCLUSIONS

Asthma is a heterogeneous disease of a complex etiopathogenesis that has a complex interplay with mental health. The present study confirms a relationship between age and stress coping strategies as well as temperament traits.

Alcohol and IL-6 Alter Expression of Synaptic Proteins in Cerebellum of Transgenic Mice with Increased Astrocyte Expression of IL-6

Recent studies indicate that neuroimmune factors, including the cytokine interleukin-6 (IL-6), play a role in the CNS actions of alcohol. The cerebellum is a sensitive target of alcohol, but few studies have examined a potential role for neuroimmune factors in the actions of alcohol on this brain region. A number of studies have shown that synaptic transmission, and in particular inhibitory synaptic transmission, is an important cerebellar target of alcohol. IL-6 also alters synaptic transmission, although it is unknown if IL-6 targets are also targets of alcohol. This is an important issue because alcohol induces glial production of IL-6, which could then covertly influence the actions of alcohol. The persistent cerebellar effects of both IL-6 and alcohol typically involve chronic exposure and, presumably, altered gene and protein expression. Thus, in the current studies we tested the possibility that proteins involved in inhibitory and excitatory synaptic transmission in the cerebellum are common targets of alcohol and IL-6. We used transgenic mice that express elevated levels of astrocyte produced IL-6 to model persistently elevated expression of IL-6, as would occur in alcohol use disorders, and a chronic intermittent alcohol exposure/withdrawal paradigm (CIE/withdrawal) that is known to produce alcohol dependence. Multiple cerebellar synaptic proteins were assessed by Western blot. Results show that IL-6 and CIE/withdrawal have both unique and common actions that affect synaptic protein expression. These common targets could provide sites for IL-6/alcohol exposure/withdrawal interactions and play an important role in cerebellar symptoms of alcohol use such as ataxia.

Cancer Exacerbates Chemotherapy-Induced Sensory Neuropathy

For the constellation of neurologic disorders known as chemotherapy-induced peripheral neuropathy, mechanistic understanding and treatment remain deficient. Here, we present the first evidence that chronic sensory neuropathy depends on nonlinear interactions between cancer and chemotherapy. Global transcriptional profiling of dorsal root ganglia revealed differential expression, notably in regulators of neuronal excitability, metabolism, and inflammatory responses, all of which were unpredictable from effects observed with either chemotherapy or cancer alone. Systemic interactions between cancer and chemotherapy also determined the extent of deficits in sensory encoding and ion channel protein expression by single mechanosensory neurons, with the potassium ion channel Kv3.3 emerging as one potential contributor to sensory neuron dysfunction. Validated measures of sensorimotor behavior in awake, behaving animals revealed dysfunction after chronic chemotherapy treatment was exacerbated by cancer. Notably, errors in precise forelimb placement emerged as a novel behavioral deficit unpredicted by our previous study of chemotherapy alone. These original findings identify novel contributors to peripheral neuropathy and emphasize the fundamental dependence of neuropathy on the systemic interaction between chemotherapy and cancer. SIGNIFICANCE: These findings highlight the need to account for pathobiological interactions between cancer and chemotherapy as a major contributor to neuropathy and will have significant and immediate impact on future investigations in this field.

Interleukin-6 Disrupts Synaptic Plasticity and Impairs Tissue Damage Compensation in Multiple Sclerosis

Background: Synaptic plasticity helps in reducing the clinical expression of brain damage and represents a useful mechanism to compensate the negative impact of new brain lesions in multiple sclerosis (MS). Inflammation, altering synaptic plasticity, could negatively influence the disease course in relapsing-remitting MS (RR-MS). Objective: In the present study, we explored whether interleukin (IL)-6, a major proinflammatory cytokine involved in MS pathogenesis, alters synaptic plasticity and affects the ability to compensate for ongoing brain damage. Methods: The effect of IL-6 incubation on long-term potentiation (LTP) induction was explored in vitro, in mice hippocampal slices. We also explored the correlation between the cerebrospinal fluid (CSF) levels of this cytokine and the LTP-like effect induced by the paired associative stimulation (PAS) in a group of RR-MS patients. Finally, we examined the correlation between the CSF levels of IL-6 at the time of diagnosis and the prospective disease activity in a cohort of 150 RR-MS patients. Results: In vitro LTP induction was abolished by IL-6. Consistently, in patients with MS, a negative correlation emerged between IL-6 CSF concentrations and the effect of PAS. In MS patients, longer disease duration before diagnosis was associated with higher IL-6 CSF concentrations. In addition, elevated CSF levels of IL-6 were associated with greater clinical expression of new inflammatory brain lesions, unlike in patients with low or absent IL-6 concentrations, who had a better disease course. Conclusions: IL-6 interfering with synaptic plasticity mechanisms may impair the ability to compensate the clinical manifestation of new brain lesions in RR-MS patients.

More than a drainage fluid: the role of CSF in signaling in the brain and other effects on brain tissue

Current progress in neuroscience demonstrates that the brain is not an isolated organ and is influenced by the systemic environment and extracerebral processes within the body. In view of this new concept, blood and cerebrospinal fluid (CSF) are important body fluids linking extracerebral and intracerebral processes. For decades, substantial evidence has been accumulated indicating that CSF modulates brain states and influences behavior as well as cognition. This chapter provides an overview of how CSF directly modulates the function of different types of brain cells, such as neurons, neural stem cells, and CSF-contacting cells. Alterations in CSF content occur in most pathologic central nervous system (CNS) conditions. In a classic view, the function of CSF is to drain waste products and detrimental factors derived from diseased brain parenchyma. This chapter presents examples for how intra- and extracerebral pathologic processes lead to alterations in the CSF content. Current knowledge about how pathologically altered CSF influences the functionality of brain cells will be presented. Thereby, it becomes evident that CSF has more than a drainage function and has a causal role for the etiology and pathogenesis of different CNS diseases.

Meta-analysis of Plasma Interleukine-6 Levels in Patients with Depressive Disorder

Growing body of evidence suggests that inflammatory processes play an important role in the pathophysiology and the clinical course of depressive disorder, as well as several others major psychiatric and somatic conditions. Interleukin (IL-6), one of the proinflammatory cytokines, has been extensively examined in a number of studies among depressed patients. To assess quantitatively the relationship between depression and IL-6, a systematic review of relevant literature published to October 2009 was performed and relevant data were meta-analysed using random-effects model. A positive association was found (standardized difference in means=1.055, p>0,001), although a significant heterogeneity among studies (Q(15)=141, p<0,001) points to relevance of further subgroup analyses.

Macrophage migration inhibitory factor modulates formalin induced behaviors in rats

Cytokine proteins are involved in different signaling pathways throughout the central nervous system. To study the efficacy of an inflammatory cytokine, the macrophage migration inhibitory factor (MIF), which acts via several receptor molecules including the receptor CXCR2, male rats’ behaviors were determined after intracerebroventricular (ICV) administration of MIF. There were three treatments: One group received only the cytokine, a second group received MIF and an CXCR2 antagonist (SB265610), and a third, control group received only the carrier medium saline. All rats were subjected to a subcutaneous injection of formalin in the hind paw after the ICV administration. Pain behaviors induced after formalin injection showed increased values in the MIF group of licking in the first phase and increased values of flexing, licking and paw-jerk in the second phase. On the contrary, spontaneous behaviors induced by formalin injection changed alternatively between the two groups compared with saline. These results suggest a possible effect of cytokine MIF on central nervous processes implicated in pain modulation mediated by the receptor CXCR2.

Identification and association of relationships between selected personal and environmental factors and formal components of temperament and strategies of coping with stress in asthmatic patients

Background: Personal and environmental factors might have an impact on strategies of coping with stress and temperamental traits according to the Regulative Theory of Temperament in asthmatic patients. They can modify the clinical picture, the course of a disease and effectiveness of treatment. Personal variables are key factors in determining formal characteristic of behavior and effective management method in asthmatic patients. Aim of study: The aim of the study was to identify selected personal and environmental factors, as well as factors inducing attacks and asthma exacerbations or maintaining them in a complex of personal traits of patients. Methods: Two hundred and eighty one participants were included in the study. Of this number 122 subjects were healthy volunteers and 159 were asthmatic patients. In all the subjects the authors applied the Formal Characteristic of Behaviour – FCZ-KT – Temperament Inventory, Coping Inventory for Stressful Situations (CISS), Beck Depression Inventory, State-Trait Anxiety Inventory and Borg Rating of Perceived Exertion (RPE) Scale. Genotyping of polymorphic forms of NR3C1 gene was conducted with PCR-RFLP and PCR-HRM methods. Expression of TGFβ1 gene was measured with the use of qRT-PCR. Results: The authors confirmed a significant influence of personal and environmental factors, such as: age, height, body weight, sex, asthma exacerbations, drugs administered by patients, allergy and psychopathological variables on strategies of coping with stress by asthmatic patients (Task-Oriented Coping, Emotion-Oriented Coping, Avoidance-Oriented Coping, distraction seeking, social diversion). Temperamental traits (Briskness, Perseverance, Sensory Sensitivity, Emotional Reactivity, Endurance, Activity) depend on age, sex, body weight, genetic predispositions and they are modified by asthma exacerbations, allergy, drugs administered by patients, depression and anxiety (state and trait). The authors confirmed a correlation between Tth111I polymorphic form of NR3C1 gene and perseverance (p= 0.0450). It was noted that an increase in the TGFβ1 expression level led to a decrease in the patients' emotional reactivity (p= 0.0212). Conclusions: Strategies of coping with stress and temperamental traits according to the Regulative Theory of Temperament in asthmatic patients are determined by personal and environmental factors.

Neuroprotective effect of interleukin-6 regulation of voltage-gated Na(+) channels of cortical neurons is time- and dose-dependent

Interleukin-6 has been shown to be involved in nerve injury and nerve regeneration, but the effects of long-term administration of high concentrations of interleukin-6 on neurons in the central nervous system is poorly understood. This study investigated the effects of 24 hour exposure of interleukin-6 on cortical neurons at various concentrations (0.1, 1, 5 and 10 ng/mL) and the effects of 10 ng/mL interleukin-6 exposure to cortical neurons for various durations (2, 4, 8, 24 and 48 hours) by studying voltage-gated Na(+) channels using a patch-clamp technique. Voltage-clamp recording results demonstrated that interleukin-6 suppressed Na(+) currents through its receptor in a time- and dose-dependent manner, but did not alter voltage-dependent activation and inactivation. Current-clamp recording results were consistent with voltage-clamp recording results. Interleukin-6 reduced the action potential amplitude of cortical neurons, but did not change the action potential threshold. The regulation of voltage-gated Na(+) channels in rat cortical neurons by interleukin-6 is time- and dose-dependent.

IL-6 regulation of synaptic function in the CNS

A growing body of evidence supports a role for glial-produced neuroimmune factors, including the cytokine IL-6, in CNS physiology and pathology. CNS expression of IL-6 has been documented in the normal CNS at low levels and at elevated levels in several neurodegenerative or psychiatric disease states as well as in CNS infection and injury. The altered CNS function associated with these conditions raises the possibility that IL-6 has neuronal or synaptic actions. Studies in in vitro and in vivo models confirmed this possibility and showed that IL-6 can regulate a number of important neuronal and synaptic functions including synaptic transmission and synaptic plasticity, an important cellular mechanism of memory and learning. Behavioral studies in animal models provided further evidence of an important role for IL-6 as a regulator of CNS pathways that are critical to cognitive function. This review summarizes studies that have lead to our current state of knowledge. In spite of the progress that has been made, there is a need for a greater understanding of the physiological and pathophysiological actions of IL-6 in the CNS, the mechanisms underlying these actions, conditions that induce production of IL-6 in the CNS and therapeutic strategies that could ameliorate or promote IL-6 actions. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Increased astrocyte expression of IL-6 or CCL2 in transgenic mice alters levels of hippocampal and cerebellar proteins

Emerging research has identified that neuroimmune factors are produced by cells of the central nervous system (CNS) and play critical roles as regulators of CNS function, directors of neurodevelopment and responders to pathological processes. A wide range of neuroimmune factors are produced by CNS cells, primarily the glial cells, but the role of specific neuroimmune factors and their glial cell sources in CNS biology and pathology have yet to be fully elucidated. We have used transgenic mice that express elevated levels of a specific neuroimmune factor, the cytokine IL-6 or the chemokine CCL2, through genetic modification of astrocyte expression to identify targets of astrocyte produced IL-6 or CCL2 at the protein level. We found that in non-transgenic mice constitutive expression of IL-6 and CCL2 occurs in the two CNS regions studied, the hippocampus and cerebellum, as measured by ELISA. In the CCL2 transgenic mice elevated levels of CCL2 were evident in the hippocampus and cerebellum, whereas in the IL-6 transgenic mice, elevated levels of IL-6 were only evident in the cerebellum. Western blot analysis of the cellular and synaptic proteins in the hippocampus and cerebellum of the transgenic mice showed that the elevated levels of CCL2 or IL-6 resulted in alterations in the levels of specific proteins and that these actions differed for the two neuroimmune factors and for the two brain regions. These results are consistent with cell specific profiles of action for IL-6 and CCL2, actions that may be an important aspect of their respective roles in CNS physiology and pathophysiology.

Interleukin-1β and interleukin-6 affect electrophysiological properties of thalamic relay cells

By acknowledging the relation between brain and body in health and disease, inflammatory processes may play a key role in this reciprocal relation. Pro-inflammatory cytokines such as interleukin-1β (IL-1β) and interleukin-6 (IL-6) are some of the agents involved in those processes. What exactly is their role in the CNS however is not that clear so far. To address the question of how pro-inflammatory cytokines may affect information processing at the cellular and molecular levels, relay neurons in the thalamic dorsal lateral geniculate nucleus in mouse brain slices were exposed to those cytokines and studied with the patch-clamp technique. IL-1β promoted hyperpolarization of the resting membrane potential (Vrest), decrease of input resistance (Rin), decrease of Ih rectification, decrease in action potential (AP) threshold and decrease in the number of APs in low threshold calcium spike (LTS) bursts, while IL-6 promoted decrease of Rin and decrease in the number of APs in LTS bursts. Computer simulations provided candidates for ionic conductance affected by those cytokines. Collectively, these findings demonstrate that IL-1β and IL-6 have modulatory effects on electrophysiological properties of thalamic neurons, implying that the thalamic functions may be affected by systemic disorders that present with high levels of those cytokines.

Interleukin-6 inhibits voltage-gated sodium channel activity of cultured rat spinal cord neurons

OBJECTIVE

Interleukin-6 (IL-6) is a pleiotropic proinflammatory cytokine that plays a key role in the injuries and diseases of the central nervous system (CNS). A voltage-gated Na+ channel (VGSC) is essential for the excitability and electrical properties of the neurons. However, there is still limited information on the role of IL-6 in voltage-gated sodium channels. Our study aimed to investigate the effects of IL-6 on Na+ currents in cultured spinal-cord neurons.

METHODS

VGSC currents were activated and recorded using whole-cell patch-clamp technique in the cultured rat spinal cord neurons. The effects of IL-6 concentration and exposure duration were examined. To determine whether any change in the number of channels in the plasma membrane can inhibit IL-6 on VGSC currents, we examined the expression of α1A (SCN1α) subunit mRNA level and protein level in the neurons before and after IL-6 induction using real-time polymerase chain reaction.

RESULTS

We verified that IL-6, through a receptor-mediated mechanism, suppressed Na+ currents in a time- and dose-dependent manner, but did not alter the voltage-dependent activation and inactivation. Gp130 was involved in this inhibition. Furthermore, the spike amplitude was also inhibited by IL-6 in the doses that decreased the Na+ currents.

CONCLUSION

VGSC currents are significantly inhibited by IL-6. Our findings reveal that the potential neuroprotection of IL-6 may result from the inhibitory effects on VGSC currents.

Neuroimmune regulation of neurophysiology in the cerebellum

Recent studies have established the existence of an innate immune system in the central nervous system (CNS) and implicated a critical role for this system in both normal and pathological processes. Astrocytes and microglia, normal components of the CNS, are the primary cell types that comprise the innate immune system of the CNS. Basic to their role during normal and adverse conditions is the production of neuroimmune factors such as cytokines and chemokines, which are signaling molecules that initiate or coordinate downstream cellular actions. During adverse conditions, cytokines and chemokines function in defensive and repair. However, if expression of these factors becomes dysregulated, abnormal CNS function can result. Both neurons and glial cells of the CNS express receptors for cytokines and chemokines, but the biological consequence of receptor activation has yet to be fully resolved. Our studies show that neuroadaptive changes are produced in primary cultures of rat cerebellar cells chronically treated with the cytokine interleukin-6 (IL-6) and in the cerebellum of transgenic mice that chronically express elevated levels of IL-6 in the CNS. In the cerebellum in culture and in vivo, the neuroadaptive changes included alterations in the level of expression of proteins involved in gene expression, signal transduction, and synaptic transmission. Associated with these changes were alterations in neuronal function. A comparison of results from the cultured cerebellar cells and cerebellum of the transgenic mice indicated that the effects of IL-6 can vary across neuronal types. However, alterations in mechanisms involved in Ca(2+) homeostasis were observed in all cell types studied. These results indicate that modifications in cerebellar function are likely to occur in disorders associated with elevated levels of IL-6 in the cerebellum.

Calcium dysregulation and neuroinflammation: discrete and integrated mechanisms for age-related synaptic dysfunction

Some of the best biomarkers of age-related cognitive decline are closely linked to synaptic function and plasticity. This review highlights several age-related synaptic alterations as they relate to Ca(2+) dyshomeostasis, through elevation of intracellular Ca(2+), and neuroinflammation, through production of pro-inflammatory cytokines including interleukin-1 beta (IL-1β) and tumor necrosis factor-alpha (TNF-α). Though distinct in many ways, Ca(2+) and neuroinflammatory signaling mechanisms exhibit extensive cross-talk and bidirectional interactions. For instance, cytokine production in glial cells is strongly dependent on the Ca(2+) dependent protein phosphatase calcineurin, which shows elevated activity in animal models of aging and disease. In turn, pro-inflammatory cytokines, such as TNF, can augment the expression/activity of L-type voltage sensitive Ca(2+) channels in neurons, leading to Ca(2+) dysregulation, hyperactive calcineurin activity, and synaptic depression. Thus, in addition to discussing unique contributions of Ca(2+) dyshomeostasis and neuroinflammation, this review emphasizes how these processes interact to hasten age-related synaptic changes.

Neuroimmune regulation of homeostatic synaptic plasticity

Homeostatic synaptic plasticity refers to a set of negative-feedback mechanisms that are used by neurons to maintain activity within a functional range. While it is becoming increasingly clear that homeostatic regulation of synapse function is a key principle in the nervous system, the molecular details of this regulation are only beginning to be uncovered. Recent evidence implicates molecules classically associated with the peripheral immune system in the modulation of homeostatic synaptic plasticity. In particular, the pro-inflammatory cytokine TNFα, class I major histocompatibility complex, and neuronal pentraxin 2 are essential in the regulation of the compensatory synaptic response that occurs in response to prolonged neuronal inactivity. This review will present and discuss current evidence implicating neuroimmune molecules in the homeostatic regulation of synapse function. This article is part of the Special Issue entitled 'Homeostatic Synaptic Plasticity'.

Imipramine reverses alterations in cytokines and BDNF levels induced by maternal deprivation in adult rats

A growing body of evidence is pointing toward an association between immune molecules, as well brain-derived neurotrophic factor (BDNF) and the depression. The present study was aimed to evaluate the behavioral and molecular effects of the antidepressant imipramine in maternally deprived adult rats. To this aim, maternally deprived and non-deprived (control group) male rats were treated with imipramine (30mg/kg) once a day for 14 days during their adult phase. Their behavior was then assessed using the forced swimming test. In addition to this, IL-10, TNF-α and IL-1β cytokines were assessed in the serum and cerebrospinal fluid (CSF). In addition, BDNF protein levels were assessed in the prefrontal cortex, hippocampus and amygdala. In deprived rats treated with saline was observed an increase on immobility time, compared with non-deprived rats treated with imipramine (p<0.05). Deprived rats treated with saline presented a decrease on BDNF levels in the amygdala (p<0.05), compared with all other groups. The IL-10 levels were decreased in the serum (p<0.05). TNF-α and IL-1β levels were increased in the serum and CSF of deprived rats treated with saline (p<0.05). Interestingly, imipramine treatment reversed the effects of maternal deprivation on BDNF and cytokines levels (p<0.05). Finally, these findings further support a relationship between immune activation, neurotrophins and the depression, and considering the action of imipramine, it is suggested that classic antidepressants could exert their effects by modulating the immune system.

Interleukin-6 inhibits L-type calcium channel activity of cultured cerebellar granule neurons

Our previous work has shown that interleukin-6 (IL-6) implements its neuroprotective effect by inhibiting the intracellular Ca(2+) overload in neurons. Here, we examined whether regulation of L-type calcium channels (LCCs) activities is involved in the neuroprotective action of IL-6. In cultured cerebellar granule neurons (CGNs), patch-clamp recording showed that the whole-cell Ca(2+) current and LCC current were significantly reduced by IL-6 pretreatment (120 ng/ml, for 24 h). Calcium imaging data indicated that IL-6 significantly suppressed high K(+)-induced intracellular Ca(2+) overload and LCC Ca(2+) influx. Moreover, expression of the LCC subunit, Ca(v)1.2, was remarkably downregulated by IL-6 in cultured CGNs. These findings suggest that IL-6 exerts a neurotrophic effect by preventing Ca(2+) overload, at least partly through inhibition of LCC activity in cultured CGNs.

Elevated levels of serum IL-5 are associated with an increased likelihood of major depressive disorder

BACKGROUND

Inflammatory mediators in both the peripheral circulation and central nervous system (CNS) are dysregulated in major depressive disorder (MDD). Nevertheless, relatively little is known about the role of the T-helper (Th)-2 effector cytokines interleukin (IL)-5 and IL-13 in MDD.

METHODS

We examined the serum levels of these cytokines and a Th-1 comparison cytokine, interferon (IFN)-γ, in 116 individuals (MDD, n = 58; controls, n = 58).

RESULTS

In our basic multivariate model controlling for the effects of potential confounders on the associations between MDD and the examined cytokines, each 1-unit increase in the serum IL-5 level increased the likelihood of belonging to the MDD group by 76% (OR 1.76, 95% CI 1.03-2.99, p = 0.04; model covariates: age, gender, marital status, daily smoking and alcohol use). The likelihood further increased in models additionally controlling for the effects of the use of antidepressants and NSAIDS, and a diagnosis of asthma. No such associations were detected with regard to IL-13 (OR 1.08, 95% CI 0.96-1.22, p = 0.22) or IFN-γ (OR 1.02, 95% CI 0.99-1.05, p = 0.23).

CONCLUSIONS

Elevated levels of IL-5, which uses the neural plasticity-related RAS GTPase-extracellular signal-regulated kinase (Ras-ERK) pathway to mediate its actions in the central nervous system (CNS), could be one of the factors underlying the depression-related changes in CNS plasticity.

Genetic evidence for an essential role of neuronally expressed IL-6 signal transducer gp130 in the induction and maintenance of experimentally induced mechanical hypersensitivity in vivo and in vitro

Tenderness and mechanical allodynia are key symptoms of malignant tumor, inflammation and neuropathy. The proinflammatory cytokine interleukin-6 (IL-6) is causally involved in all three pathologies. IL-6 not only regulates innate immunity and inflammation but also causes nociceptor sensitization and hyperalgesia. In general and in most cell types including immune cells and sensory neurons, IL-6 binds soluble μ receptor subunits which heteromerizes with membrane bound IL-6 signal transducer gp130. In the present study, we used a conditional knock-out strategy to investigate the importance of signal transducer gp130 expressed in C nociceptors for the generation and maintenance of mechanical hypersensitivity. Nociceptors were sensitized to mechanical stimuli by experimental tumor and this nociceptor sensitization was preserved at later stages of the pathology in control mice. However, in mice with a conditional deletion of gp130 in Nav1.8 expressing nociceptors mechanical hypersensitivity by experimental tumor, nerve injury or inflammation recovery was not preserved in the maintenance phase and nociceptors exhibited normal mechanical thresholds comparable to untreated mice. Together, the results argue for IL-6 signal transducer gp130 as an essential prerequisite in nociceptors for long-term mechanical hypersensitivity associated with cancer, inflammation and nerve injury.

Neuroadaptive changes in cerebellar neurons induced by chronic exposure to IL-6

IL-6 is an important signaling molecule in the CNS. CNS neurons express IL-6 receptors and their signal transduction molecules, consistent with a role for IL-6 in neuronal physiology. Research indicates that IL-6 levels are low in the normal brain but can be significantly elevated in CNS injury and disease. Relatively little is known about how the elevated levels of IL-6 affect neurons. In the current study we show that under conditions of chronic exposure, IL-6 induces alterations in the level of protein expression in developing CNS cells. Such changes may play a role in the altered CNS function observed in CNS conditions associated with elevated levels of IL-6 in the CNS.

Interleukin-6, a mental cytokine

Almost a quarter of a century ago, interleukin-6 (IL-6) was discovered as an inflammatory cytokine involved in B cell differentiation. Today, IL-6 is recognized to be a highly versatile cytokine, with pleiotropic actions not only in immune cells, but also in other cell types, such as cells of the central nervous system (CNS). The first evidence implicating IL-6 in brain-related processes originated from its dysregulated expression in several neurological disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. In addition, IL-6 was shown to be involved in multiple physiological CNS processes such as neuron homeostasis, astrogliogenesis and neuronal differentiation. The molecular mechanisms underlying IL-6 functions in the brain have only recently started to emerge. In this review, an overview of the latest discoveries concerning the actions of IL-6 in the nervous system is provided. The central position of IL-6 in the neuroinflammatory reaction pattern, and more specifically, the role of IL-6 in specific neurodegenerative processes, which accompany Alzheimer's disease, multiple sclerosis and excitotoxicity, are discussed. It is evident that IL-6 has a dichotomic action in the CNS, displaying neurotrophic properties on the one hand, and detrimental actions on the other. This is in agreement with its central role in neuroinflammation, which evolved as a beneficial process, aimed at maintaining tissue homeostasis, but which can become malignant when exaggerated. In this perspective, it is not surprising that 'well-meant' actions of IL-6 are often causing harm instead of leading to recovery.

Diverse roles of extracellular calcium-sensing receptor in the central nervous system

The G-protein-coupled calcium-sensing receptor (CaSR), upon activation by Ca(2+) or other physiologically relevant polycationic molecules, performs diverse functions in the brain. The CaSR is widely expressed in the central nervous system (CNS) and is characterized by a robust increase in its expression during postnatal brain development over adult levels throughout the CNS. Developmental increases in CaSR levels in brain correlate with myelinogenesis. Indeed, neural stem cells differentiating to the oligodendrocyte lineage exhibit the highest CaSR expression compared with those differentiating to astrocytic or neuronal lineages. In adult CNS, CaSR has broad relevance in maintaining local ionic homeostasis. CaSR shares an evolutionary relationship with the metabotropic glutamate receptor and forms heteromeric complexes with the type B-aminobutyric acid receptor subunits that affects its cell surface expression, activation, signaling, and functions. In normal physiology as well as in pathologic conditions, CaSR is activated by signals arising from mineral ions, amino acids, polyamines, glutathione, and amyloid-beta in conjunction with Ca(2+) and other divalent cationic ligands. CaSR activation regulates membrane excitability of neurons and glia and affects myelination, olfactory and gustatory signal integration, axonal and dendritic growth, and gonadotrophin-releasing hormonal-neuronal migration. Insofar as the CaSR is a clinically important therapeutic target for parathyroid disorders, development of its agonists or antagonists as therapeutics for CNS disorder could be a major breakthrough.

Exercise-induced release of cytokines in patients with major depressive disorder

BACKGROUND

Patients with major depressive disorder (MDD) may display elevated plasma levels of pro-inflammatory substances. Although the underlying mechanisms are unknown, inflammation has been proposed to play a direct role in the generation of depressive symptoms. Skeletal muscle is a potent producer of cytokines, and physical exercise has been suggested to alleviate symptoms of depression. In this study we therefore addressed the question of whether MDD patients display altered levels of pro-, anti-inflammatory and regulatory factors in the blood in response to acute exercise.

METHODS

Eighteen MDD patients and 18 healthy controls performed a maximal-workload exercise challenge. Blood samples were taken before the test, at sub-maximal and maximal workload, as well as 30 and 60 min after testing. The plasma levels of SAA, TNF-alpha, S-VCAM, S-ICAM, CRP, IFN-gamma, IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-8, IL-10, IL-12 and IL-13 were assayed using multiplex sandwich ELISA.

RESULTS

Exercise-induced significant changes in the plasma levels of inflammatory substances in both MDD patients and controls. IL-8, IL-6 and TNF-alpha increased, and IL-4 decreased during the challenge in both groups. In addition, IFN-gamma decreased in the controls. There was a significant difference in IL-6 reactivity between the groups at the sub-max timepoint.

LIMITATIONS

Group sizes are comparably limited.

CONCLUSION

Exercise induces changes in the blood levels of cytokines in unmedicated MDD patients. Whether these changes affect symptoms of depression should be evaluated in long-term studies of the anti-depressive effects of exercise.

IL-6 as a biomarker of ischemic cerebrovascular disease

The lack of a rapid and clinically accurate diagnostic tool remains a major obstacle to optimal care of patients with stroke. Cytokine changes in patients with acute stroke have been insufficiently studied. The purpose of this study is to delineate the relevance of IL-6 as a biochemical marker of stroke diagnosis, taking into account the genetic basis, and changes of the protein in serum and cerebrospinal fluid in relation to stroke development. Inflammation has an important role in ischemic cerebrovascular disease pathophysiology. Proinflammatory cytokines, such as IL-6, have been implicated in several mechanisms that might promote ischemic brain injury and an early neurological worsening. Cardiovascular diseases constitute one of the principal health problems in developing countries. Over the past few years, several studies have found evidence of the important role of inflammation in the ischemic cerebrovascular disease. The availability of a diagnostic biomarker panel for patients with stroke symptoms would be enormously valuable to complement clinical data and to precede radiological findings. IL-6 levels in cerebrospinal fluid and serum seem to reflect either the extent of tissue damage, or the accompanying clinical worsening. The -174 G/C functional polymorphism in the IL-6 gene might not be solely involved in disease susceptibility but also in linkage disequilibrium with other functional polymorphisms. Further studies are needed to solve this. Presently, the association between IL-6 genotype and stroke remains undetermined. Development of new neuroprotective therapies targeted to modulate cytokine-induced inflammation could be a promising way to prevent early deterioration in acute ischemic stroke.

Chronic interleukin-6 alters the level of synaptic proteins in hippocampus in culture and in vivo

There is now considerable evidence that the level of expression of the proinflammatory cytokine, interleukin-6 (IL-6), is increased in the central nervous system (CNS) during neuroinflammatory conditions such as occurs in neurological disorders and in disease and injury. However, our understanding of the consequences of increased expression of IL-6 on the CNS is still limited, especially with respect to the developing nervous system, which is known to be particularly vulnerable to environmental factors. To address this issue, we investigated the properties of cultured hippocampal neurons exposed chronically to IL-6 during the main period of morphological and physiological development, which occurs during the first 2 weeks of culture. IL-6 was tested at 500 U/mL, considered to reflect a pathophysiologic concentration. The morphological features of neuronal development in the control and IL-6-treated cultures appeared similar. However, Western blot analysis showed a significant reduction in the level of Group-II metabotropic receptors (mGluR2/3) and L-type Ca(2+) channels in the IL-6-treated cultures. A similar reduction in mGluR2/3 and L-type Ca(2+) channel protein was observed in transgenic mice that over-express IL-6 in the CNS through astrocyte production starting early in development. Analysis of Ca(2+) signals produced by spontaneous synaptic network activity in the hippocampal cultures and effects of a mGluR2/3 agonist and antagonist showed that the reduced levels of mGluR2/3 impact on the functional properties of hippocampal synaptic network activity. These results have important implications relative to the mechanisms responsible for altered CNS function during conditions associated with increased levels of IL-6 in the CNS.

Purkinje neuron physiology is altered by the inflammatory factor interleukin-6

The cytokine interleukin-6 (IL-6) is produced by cells of the central nervous system (CNS) during a variety of neuroinflammatory states, in which it is thought to play a role in neuroprotection and/or neuropathology associated with neurological disease. In addition, CNS expression of IL-6 during non-pathological conditions may also occur, although the conditions for such IL-6 production remain elusive. Expression of IL-6 and its receptor and signal transducing elements by neurons and glia within the cerebellum implicate a role of IL-6 in modulating cerebellar function under normal conditions and in contributing to pathology and pathophysiology within the cerebellum during CNS disease states. Evidence for such a role of IL-6 comes from studies using transgenic mice that chronically express IL-6 within the CNS. These mice exhibit profound cerebellar pathology and significant alterations of Purkinje neuron electrical and synaptic activity. Additional evidence comes from in vitro studies using primary cultures of cerebellar cortex that have been chronically exposed to exogenously applied IL-6. Consistent with the IL-6 transgenic mice, chronic IL-6 treated Purkinje neurons in culture exhibit alterations of endogenous electrophysiological properties as well as changes in intracellular Ca2+ homeostasis and signaling. Despite these changes in Purkinje neuron physiology, chronic IL-6 does not affect the survival or morphology of Purkinje neurons in culture. Thus, by itself, IL-6 is able to modulate key components of cerebellar circuitry during periods of chronic expression, such as during neuroinflammation, and may be an important player in the movement disorders associated with a number of CNS disease states.

Chronic LPS exposure produces changes in intrinsic membrane properties and a sustained IL-beta-dependent increase in GABAergic inhibition in hippocampal CA1 pyramidal neurons

Chronic inflammation has been reported to be a significant factor in the induction and progression of a number of chronic neurological disorders including Alzheimer's disease and Down syndrome. It is believed that inflammation may promote synaptic dysfunction, an effect that is mediated in part by pro-inflammatory cytokines such as interleukin-1beta (IL-1beta). However, the role of IL-1beta and other cytokines in synaptic transmission is still poorly understood. In this study, we have investigated how synaptic transmission and neuronal excitability in hippocampal pyramidal neurons are affected by chronic inflammation induced by exposing organotypic slices to the bacterial cell-wall product lipopolysaccharide (LPS). We report that CA1 pyramidal neurons recorded in whole cell from slices previously exposed to LPS for 7 days had resting membrane potential and action potential properties similar to those of the controls. However, they had significantly lower membrane resistance and a more elevated action potential threshold, and displayed a slower frequency of action potential discharge. Moreover, the amplitude of pharmacologically isolated postsynaptic gamma-aminobutyric acid (GABA)ergic potentials, but not excitatory glutamatergic postsynaptic potentials, was significantly larger following chronic LPS exposure. Interestingly, co-incubation of the IL-1 receptor antagonist (IL-1Ra) concurrently with LPS prevented the increase in GABAergic transmission, but not the reduction in intrinsic neuronal excitability. Finally, we confirmed that LPS dramatically increased IL-1beta, and IL-1beta-dependent IL-6 levels in the culture medium for 2 days before returning to baseline. We conclude that CA1 pyramidal neurons in slices chronically exposed to LPS show a persistent decrease in excitability due to a combined decrease in intrinsic membrane excitability and an enhancement in synaptic GABAergic input, the latter being dependent on IL-1beta. Therefore, chronic inflammation in hippocampus produces IL-1beta-dependent and -independent effects in neuronal and synaptic function that could contribute significantly to cognitive disturbances.

The chemokine CCL2 modulates Ca2+dynamics and electrophysiological properties of cultured cerebellar Purkinje neurons

The chemokine CCL2 is produced at high levels in the central nervous system (CNS) during infection, injury, neuroinflammation and other pathological conditions. Cells of the CNS including neurons and glia express receptors for CCL2 and these receptors may contribute to a signaling system through which pathologic conditions in the CNS are communicated. However, our understanding of the consequences of activation of chemokine signaling in the CNS is limited, especially for neurons. In many cell types, chemokine signaling alters intracellular Ca(2+) dynamics. Therefore, we investigated the potential involvement of this mechanism in neuronal signaling activated by CCL2. In addition, we examined the effects of CCL2 on neuronal excitability. The studies focused on the rat cerebellar Purkinje neuron, an identified CNS neuronal type reported to express both CCL2 and its receptor, CCR2. Immunohistochemical studies of Purkinje neurons in situ confirmed that they express CCR2 and CCL2. The effect of exogenous application on Purkinje neurons was studied in a cerebellar culture preparation. CCL2 was tested by micropressure or bath application, at high concentrations (13-100 nm) to simulate conditions during a pathologic state. Results show that Purkinje neurons express receptors for CCL2 and that activation of these receptors alters several neuronal properties. CCL2 increased resting Ca(2+) levels, enhanced the Ca(2+) response evoked by activation of metabotropic glutamate receptor 1 and depressed action potential generation in the cultured Purkinje neurons. Passive membrane properties were unaltered. These modulatory effects of CCL2 on neuronal properties are likely to contribute to the altered CNS function associated with CNS disease and injury.

Chronic interleukin-6 exposure alters metabotropic glutamate receptor-activated calcium signalling in cerebellar Purkinje neurons

Chronic central nervous system expression of the cytokine interleukin-6 (IL-6) is thought to contribute to the histopathological, pathophysiological, and cognitive deficits associated with various neurological disorders. However, the effects of chronic IL-6 expression on neuronal function are largely unknown. Previous studies have shown that chronic IL-6 exposure alters intrinsic electrophysiological properties and intracellular Ca2+ signalling evoked by ionotropic glutamate receptor activation in cerebellar Purkinje neurons. In the current study, using primary cultures of rat cerebellum, we investigated the effects of chronic IL-6 exposure on metabotropic glutamate receptor (mGluR)-activated Ca2+ signalling and release from intracellular Ca2+ stores. Chronic exposure (6-10 days) of Purkinje neurons to 500 units/mL IL-6 resulted in elevated resting Ca2+ levels and increased intracellular Ca2+ signals evoked by the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) compared to untreated control neurons. Chronic IL-6 treatment also augmented Ca2+ signals evoked by brief 100 mm K+ depolarization, although to a lesser degree than responses evoked by DHPG. Depleting intracellular Ca2+ stores with sarcoplasmic-endoplasmic reticulum ATPase inhibitors (thapsigargin or cyclopiazonic acid) or blocking ryanodine receptor-dependent release from intracellular stores (using ryanodine) resulted in a greater reduction of DHPG- and K+-evoked Ca2+ signals in chronic IL-6-treated neurons than in control neurons. The present data show that chronic exposure to elevated levels of IL-6, such as occurs in various neurological diseases, alters Ca2+ signalling involving release from intracellular stores. The results support the hypothesis that chronic IL-6 exposure disrupts neuronal function and thereby may contribute to the pathophysiology associated with many neurological diseases.

Interleukin-6 protects cultured cerebellar granule neurons against glutamate-induced neurotoxicity

Cytokine interleukin-6 (IL-6) has been showed to be an important mediator of neuroimmune responses. However, effects of IL-6 in the central nervous system (CNS) are quite complex and diverse, and mechanisms through which IL-6 influences neuronal functions are primarily unknown. In the present study, we explored protective effect of IL-6 that was chronically applied to cerebellar granule neurons (CGNs) in culture against neurodamage induced by glutamate and mechanisms involved in the neuroprotective effect of IL-6. The chronic IL-6 exposure significantly prevented the CGNs from the glutamate-induced attenuation of neuronal vitality. This neuroprotective effect of IL-6 depended on its concentrations. IL-6 at 2.5 ng/ml did not markedly improve the neuronal vitality, but IL-6 at 5 and 10 ng/ml notably improved the neuronal vitality. The glutamate-evoked neuronal apoptosis also was strikingly inhibited by the chronic IL-6 pretreatment. Intracellular Ca2+ in the CGNs lacking IL-6 pretreatment acutely rose as soon as these neurons were stimulated by glutamate and were maintained at higher levels during the whole 18-min period of glutamate attack. Although intracellular Ca2+ in the IL-6-pretreated CGNs also produced an acute and transient elevation in response to the glutamate insult, they quickly dropped and recovered to basal levels before the glutamate application. Anti-gp130 monoclonal antibody (mAb) blocked the suppressive effect of IL-6 on the glutamate-induced intracellular Ca2+ overload. These results reveal that IL-6 can protect neurons against glutamate-induced neurotoxicity, and suggest that the neuroprotective effect of IL-6 may be via gp130 signal transducing pathway to suppress the glutamate-evoked intracellular Ca2+ overload.

Interleukin-6 produces neuronal loss in developing cerebellar granule neuron cultures

CNS levels of the cytokine interleukin-6 (IL-6) are elevated during CNS injury and disease, but it is unclear if IL-6 contributes to the pathologic process. Our studies show that in a well-characterized CNS developmental model system, primary cultures of rodent cerebellar granule neurons, chronic exposure to IL-6 during neuronal development can result in cell damage and death in a subpopulation of developing granule neurons. Chronic exposure to IL-6 also increased the susceptibility of the granule neurons to a toxic insult produced by excessive activation of NMDA receptors. These results are consistent with a role for IL-6 in the neuropathology observed in the developing CNS during injury and disease.