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

Cytokines and brain excitability

Cytokines are molecules secreted by peripheral immune cells, microglia, astrocytes and neurons in the central nervous system. Peripheral or central inflammation is characterized by an upregulation of cytokines and their receptors in the brain. Emerging evidence indicates that pro-inflammatory cytokines modulate brain excitability. Findings from both the clinical literature and from in vivo and in vitro laboratory studies suggest that cytokines can increase seizure susceptibility and may be involved in epileptogenesis. Cellular mechanisms that underlie these effects include upregulation of excitatory glutamatergic transmission and downregulation of inhibitory GABAergic transmission.

Chronic neuropathic pain-like behavior correlates with IL-1β expression and disrupts cytokine interactions in the hippocampus

We have proposed that neuropathic pain engages emotional learning, suggesting the involvement of the hippocampus. Because cytokines in the periphery contribute to induction and maintenance of neuropathic pain but might also participate centrally, we used 2 neuropathic pain models, chronic constriction injury (CCI) and spared nerve injury (SNI), to investigate the temporal profile of hippocampal cytokine gene expression in 2 rat strains that show different postinjury behavioral threshold sensitivities. SNI induced long-lasting allodynia in both strains, while CCI induced allodynia with time-dependent recovery in Sprague Dawley (SD) and no allodynia in Wistar Kyoto (WK) rats. In WK rats, only SNI induced sustained upregulation of hippocampal interleukin (IL)-1β, while IL-6 expression was transiently increased and no significant changes in IL-1ra expression were detected. Conversely, in SD rats, SNI resulted in sustained and robust increased hippocampal IL-1β expression, which was only transient in rats with CCI. In this strain, IL-6 expression was not affected in any of the 2 injury models and IL-1ra expression was significantly increased in rats with SNI or CCI at late phases. We found that the degree and development of neuropathic pain depend on the specific nerve injury model and rat strain; that hippocampal IL-1β mRNA levels correlate with neuropathic pain behavior; that, in contrast to sham-operated animals, there are no correlations between hippocampal IL-1β and IL-1ra or IL-6 in neuropathic rats; and that alterations in cytokine expression are restricted to the hippocampus contralateral to the injury side, again implying that the observed changes reflect nociception.

Early molecular and synaptic dysfunctions in the prodromal stages of Alzheimer’s disease: focus on TNF-α and IL-1β

Alterations in cytokine expression as well as deficits in synaptic activity are two features observed in early, prodromal stages of Alzheimer’s disease (AD). The cytokines TNF-α and IL-1β are not only mediators of immune responses, but are also involved in regulating synaptic activity through their effects on neuronal excitability and Hebbian plasticity. We propose that early changes occurring in the AD brain, such as increases in soluble amyloid-β oligomers, may increase the expression of certain cytokines and subsequently cause alterations in cytokine-mediated synaptic activity. A shift of focus towards the prodromal stages of AD, which incorporate the earliest detectable molecular, electrophysiological and behavioral alterations, may provide novel therapeutic targets and potential biomarkers for this currently incurable neurodegenerative disease.

It takes guts to grow a brain: Increasing evidence of the important role of the intestinal microflora in neuro- and immune-modulatory functions during development and adulthood

A new study entitled "Normal gut microbiota modulates brain development and behavior", published in the Proceedings of the National Academy of Sciences, requires that we reconsider the notion that the brain is an immune-privileged site. The authors demonstrate that intestinal microbiota must be present within a set time-frame for normal synaptogenesis to occur in the brain. In the absence of intestinal microbiota, histopathological and behavioral abnormalities arise. These observations necessitate a new look at the many interconnections of the immune system and the brain, suggesting new frontiers for research and new therapeutic strategies for neurodevelopmental diseases.

Neutralization of interleukin-1β reduces cerebral edema and tissue loss and improves late cognitive outcome following traumatic brain injury in mice

Increasing evidence suggests that interleukin-1β (IL-1β) is a key mediator of the inflammatory response following traumatic brain injury (TBI). Recently, we showed that intracerebroventricular administration of an IL-1β-neutralizing antibody was neuroprotective following TBI in mice. In the present study, an anti-IL-1β antibody or control antibody was administered intraperitoneally following controlled cortical injury (CCI) TBI or sham injury in 105 mice and we extended our histological, immunological and behavioral analysis. First, we demonstrated that the treatment antibody reached target brain regions of brain-injured animals in high concentrations (> 11 nm) remaining up to 8 days post-TBI. At 48 h post-injury, the anti-IL-1β treatment attenuated the TBI-induced hemispheric edema (P < 0.05) but not the memory deficits evaluated using the Morris water maze (MWM). Neutralization of IL-1β did not influence the TBI-induced increases (P < 0.05) in the gene expression of the Ccl3 and Ccr2 chemokines, IL-6 or Gfap. Up to 20 days post-injury, neutralization of IL-1β was associated with improved visuospatial learning in the MWM, reduced loss of hemispheric tissue and attenuation of the microglial activation caused by TBI (P < 0.05). Motor function using the rotarod and cylinder tests was not affected by the anti-IL-1β treatment. Our results suggest an important negative role for IL-1β in TBI. The improved histological and behavioral outcome following anti-IL-1β treatment also implies that further exploration of IL-1β-neutralizing compounds as a treatment option for TBI patients is warranted.

Synaptic plasticity in the pathophysiology and treatment of bipolar disorder

Emerging evidence suggests that synaptic plasticity is intimately involved in the pathophysiology and treatment of bipolar disorder (BPD). Under certain conditions, over-strengthened and/or weakened synapses at different circuits in the brain could disturb brain functions in parallel, causing manic-like or depressive-like behaviors in animal models. In this chapter, we summarize the regulation of synaptic plasticity by medications, psychological conditions, hormones, and neurotrophic factors, and their correlation with mood-associated animal behaviors. We conclude that increased serotonin, norepinephrine, dopamine, brain-derived neurotrophic factor (BDNF), acute corticosterone, and antidepressant treatments lead to enhanced synaptic strength in the hippocampus and also correlate with antidepressant-like behaviors. In contrast, inhibiting monoaminergic signaling, long-term stress, and pathophysiological concentrations of cytokines weakens glutamatergic synaptic strength in the hippocampus and is associated with depressive-like symptoms.

Interleukin-1β with learning and memory

Interleukin-1β (IL-1β) is one of the first cytokines ever described. It has long been recognized to play an important role in mediating inflammation and orchestrating the physiological and behavioral adjustments that occur during sickness. Recently, accumulating evidence has indicated that IL-1β also adversely affects cognitive function. Nevertheless, there are also some reports showing no effects or even beneficial effects of IL-1β on learning and memory. The relationship between IL-1β and cognitive impairment has not been clearly elucidated. Here we reviewed the evidence of both negative and positive effects of IL-1β on learning and memory, and the key factors that may affect the effects of IL-1β on learning and memory were discussed.

Central and peripheral cytokines mediate immune-brain connectivity

The immune system is a homeostatic system that contributes to maintain the constancy of the molecular and cellular components of the organism. Immune cells can detect the intrusion of foreign antigens or alteration of self-components and send information to the central nervous system (CNS) about this kind of perturbations, acting as a receptor sensorial organ. The brain can respond to such signals by emitting neuro/endocrine signals capable of affecting immune reactivity. Thus, the immune system, as other physiologic systems, is under brain control. Under disease conditions, when priorities for survival change, the immune system can, within defined limits, reset brain-integrated neuro-endocrine mechanisms in order to favour immune processes at the expenses of other physiologic systems. In addition, some cytokines initially conceived as immune products, such as IL-1 and IL-6, are also produced in the "healthy" brain by glial cells and even by some neurons. These and other cytokines have the capacity to affect synaptic plasticity acting as mediators of interactions between astrocytes and pre- and post-synaptic neurons that constitute what is actually defined as a tripartite synapse. Since the production of cytokines in the brain is affected by peripheral immune and central neural signals, it is conceivable that tripartite synapses can, in turn, serve as a relay system in immune-CNS communication.

A high cholesterol diet elevates hippocampal cytokine expression in an age and estrogen-dependent manner in female rats

BACKGROUND

While the effects of a proatherogenic diet have been widely studied in the context of systemic inflammation, much less is known about its effects on central or brain inflammation and its modulation with age. In this study, we examined the effect of a high cholesterol/choline diet in adult and older acyclic females to assess its impact on systemic and central inflammatory markers. Moreover, since the loss of ovarian hormones at menopause may predispose women to increased production of pro-inflammatory cytokines, we also tested the impact of estrogen replacement to adult and older females in diet-induced inflammation.

METHODS

Ovariectomized adult female rats and older (reproductive senescent) female rats were replaced with estrogen or a control pellet and maintained thereafter on a diet containing either 4% cholesterol/1% choline or control chow for 10 weeks. Interleukin 1beta (IL-1beta) expression in the liver was used as a marker of systemic inflammation, while a panel of cytokine/chemokines were used to examine the effects of diet on the hippocampus.

RESULTS

IL-1beta expression was elevated in the liver of adult and reproductive senescent females fed with the high cholesterol diet, although this was restricted to groups that were ovariectomized and not replaced with estrogen. Estrogen-treated animals of both ages did not have elevated IL-1beta levels when fed the high cholesterol diet. Diet-induced changes in cytokine/chemokine expression in the hippocampus however were critically age dependent and restricted to the reproductive senescent females. In this group, the high cholesterol diet led to an increase in interleukin (IL)-4, IL-6, IL-12p70, IL-13, RANTES (Regulated on Activation, Normal T Expressed and Secreted) and VEGF (vascular endothelial growth factor). Moreover, estrogen treatment to reproductive senescent females suppressed diet-induced expression of specific cytokines (RANTES, VEGF, IL-6) and attenuated the expression of others (IL-4, IL-12p70, and IL-13).

CONCLUSIONS

These data indicate that a proatherogenic diet presents a significant risk for central inflammation in older females that are deprived of estrogen treatment.

Synaptic correlates of increased cognitive vulnerability with aging: peripheral immune challenge and aging interact to disrupt theta-burst late-phase long-term potentiation in hippocampal area CA1

Variability in cognitive functioning increases markedly with age, as does cognitive vulnerability to physiological and psychological challenges. Exploring the basis of this vulnerability may provide important insights into the mechanisms underlying aging-associated cognitive decline. As we have previously reported, the cognitive abilities of aging (24-month-old) F344 x BN rats are generally good, but are more vulnerable to the consequences of a peripheral immune challenge (an intraperitoneal injection of live Escherichia coli) than those of their younger (3-month-old) counterparts. Four days after the injection, the aging, but not the young rats show profound memory deficits, specific to the consolidation of hippocampus-dependent memory processes. Here, we have extended these observations, using hippocampal slices to examine for the first time the combined effects of aging and a recent infection on several forms of synaptic plasticity. We have found that the specific deficit in long-lasting memory observed in the aged animals after infection is mirrored by a specific deficit in a form of long-lasting synaptic plasticity. The late-phase long-term potentiation induced in area CA1 using theta-burst stimulation is particularly compromised by the combined effects of aging and infection-a deficit that can be ameliorated by intra-cisterna magna administration of the naturally occurring antiinflammatory cytokine IL-1Ra (interleukin-1 receptor antagonist). These data support the idea that the combination of aging and a negative life event such as an infection might produce selective, early-stage failures of synaptic plasticity in the hippocampus, with corresponding selective deficits in memory.

Regulation of learning and memory by meningeal immunity: a key role for IL-4

Proinflammatory cytokines have been shown to impair cognition; consequently, immune activity in the central nervous system was considered detrimental to cognitive function. Unexpectedly, however, T cells were recently shown to support learning and memory, though the underlying mechanism was unclear. We show that one of the steps in the cascade of T cell-based support of learning and memory takes place in the meningeal spaces. Performance of cognitive tasks led to accumulation of IL-4-producing T cells in the meninges. Depletion of T cells from meningeal spaces skewed meningeal myeloid cells toward a proinflammatory phenotype. T cell-derived IL-4 was critical, as IL-4(-/-) mice exhibited a skewed proinflammatory meningeal myeloid cell phenotype and cognitive deficits. Transplantation of IL-4(-/-) bone marrow into irradiated wild-type recipients also resulted in cognitive impairment and proinflammatory skew. Moreover, adoptive transfer of T cells from wild-type into IL-4(-/-) mice reversed cognitive impairment and attenuated the proinflammatory character of meningeal myeloid cells. Our results point to a critical role for T cell-derived IL-4 in the regulation of cognitive function through meningeal myeloid cell phenotype and brain-derived neurotrophic factor expression. These findings might lead to the development of new immune-based therapies for cognitive impairment associated with immune decline.

Interleukin-10/Ceftriaxone prevents E. coli-induced delays in sensorimotor task learning and spatial memory in neonatal and adult Sprague-Dawley rats

Intrauterine infection during pregnancy is associated with early activation of the fetal immune system and poor neurodevelopmental outcomes. Immune activation can lead to alterations in sensorimotor skills, changes in learning and memory and neural plasticity. Both interleukin-10 (IL-10) and Ceftriaxone have been shown to decrease immune system activation and increase memory capacity, respectively. Using a rodent model of intrauterine infection, we examined sensorimotor development in pups, learning and memory, via the Morris water maze, and long-term potentiation in adult rats. Pregnant rats at gestational day 17 were inoculated with 1 x 10(5) colony forming units of Escherichia coli (E. coli) or saline. Animals in the treatment group received IL-10/Ceftriaxone for 3 days following E. coli administration. Intrauterine infection delayed surface righting, negative geotaxis, startle response and eye opening. Treatment with IL-10/Ceftriaxone reduced the delay in these tests. Intrauterine infection impaired performance in the probe trial in the Morris water maze (saline 25.13+/-1.01; E. coli 20.75+/-1.01; E. coli+IL-10/Ceftriaxone 20.2+/-1.62) and reduced the induction of long-term potentiation (saline 141.5+/-4.3; E. coli 128.7+/-3.9; E. coli+IL-10/Ceftriaxone 140.0+/-10). In summary, the results of this study indicate that E. coli induced intrauterine infection delays sensorimotor and learning and memory, while IL-10/Ceftriaxone rescues some of these behaviors. These delays were also accompanied by an increase in interleukin-1beta levels, which indicates immune activation. IL-10/Ceftriaxone prevents these delays as well as decreases E. coli-induced interleukin-1beta activation and may offer a window of time in which suitable treatment could be administered.

Acute p38-mediated inhibition of NMDA-induced outward currents in hippocampal CA1 neurons by interleukin-1beta

Interleukin-1beta (IL-1beta) is a potent pro-inflammatory cytokine that is primarily produced by microglia in the brain. IL-1beta inhibits N-methyl-d-aspartate (NMDA)-induced outward currents (I(NMDA-OUT)) through IL-1 type I receptor (IL-1RI) in hippocampal CA1 neurons (Zhang, R., Yamada, J., Hayashi, Y., Wu, Z, Koyama, S., Nakanishi, H., 2008. Inhibition of NMDA-induced outward currents by interleukin-1beta in hippocampal neurons, Biochem. Biophys. Res. Commun. 372, 816-820). Although IL-1RI is associated with mitogen-activated protein kinases, their involvement in the effect of IL-1beta on I(NMDA-OUT) remains unclear. In the present study, we demonstrate that IL-1beta caused activation of p38 mitogen-activated protein kinase and that the p38 inhibitor SB203580 significantly blocked the effect of IL-1beta on I(NMDA-OUT) in hippocampal CA1 neurons. Furthermore, the intracellular perfusion of active recombinant p38alpha significantly decreased the mean amplitude of I(NMDA-OUT). In neurons prepared from inflamed hippocampus, the mean amplitude of I(NMDA-OUT) was significantly reduced. In the inflamed hippocampus, IL-1beta and IL-1RI were expressed mainly in microglia and neurons, respectively. These results suggest that IL-1beta increases the excitability of hippocampal CA1 neurons in the p38-dependent inhibition of I(NMDA-OUT).

Age-related neuroinflammatory changes negatively impact on neuronal function

Neuroinflammatory changes, characterized by an increase in microglial activation and often accompanied by upregulation of inflammatory cytokines like interleukin-1β (IL-1β), are common to many, if not all, neurodegenerative diseases. Similar, though less dramatic neuroinflammatory changes, are also known to occur with age. Among the consequences of these changes is an impairment in synaptic function and the evidence suggests that inflammatory cytokines may be the primary contributory factor responsible for the deficits in synaptic plasticity which have been identified in aged rodents. Specifically a decrease in the ability of aged rats to sustain long-term potentiation (LTP) in perforant path-granule cells of the hippocampus is associated with increased microglial activation. This review considers the evidence which suggests a causal relationship between these changes and the factors which contribute to the age-related microglial activation, and reflects on data which demonstrate that agents which inhibit microglial activation also improve ability of rats to sustain LTP.

Neutralization of interleukin-1beta modifies the inflammatory response and improves histological and cognitive outcome following traumatic brain injury in mice

Interleukin-1beta (IL-1beta) may play a central role in the inflammatory response following traumatic brain injury (TBI). We subjected 91 mice to controlled cortical impact (CCI) brain injury or sham injury. Beginning 5 min post-injury, the IL-1beta neutralizing antibody IgG2a/k (1.5 microg/mL) or control antibody was infused at a rate of 0.25 microL/h into the contralateral ventricle for up to 14 days using osmotic minipumps. Neutrophil and T-cell infiltration and microglial activation was evaluated at days 1-7 post-injury. Cognition was assessed using Morris water maze, and motor function using rotarod and cylinder tests. Lesion volume and hemispheric tissue loss were evaluated at 18 days post-injury. Using this treatment strategy, cortical and hippocampal tissue levels of IgG2a/k reached 50 ng/mL, sufficient to effectively inhibit IL-1betain vitro. IL-1beta neutralization attenuated the CCI-induced cortical and hippocampal microglial activation (P < 0.05 at post-injury days 3 and 7), and cortical infiltration of neutrophils (P < 0.05 at post-injury day 7). There was only a minimal cortical infiltration of activated T-cells, attenuated by IL-1beta neutralization (P < 0.05 at post-injury day 7). CCI induced a significant deficit in neurological motor and cognitive function, and caused a loss of hemispheric tissue (P < 0.05). In brain-injured animals, IL-1beta neutralizing treatment resulted in reduced lesion volume, hemispheric tissue loss and attenuated cognitive deficits (P < 0.05) without influencing neurological motor function. Our results indicate that IL-1beta is a central component in the post-injury inflammatory response that, in view of the observed positive neuroprotective and cognitive effects, may be a suitable pharmacological target for the treatment of TBI.

Unconjugated bilirubin exposure impairs hippocampal long-term synaptic plasticity

BACKGROUND

Jaundice is one of the most common problems encountered in newborn infants, due to immaturity of hepatic conjugation and transport processes for bilirubin. Although the majority of neonatal jaundice is benign, some neonates with severe hyperbilirubinemia develop bilirubin encephalopathy or kernicterus. Accumulation of unconjugated bilirubin (UCB) in selected brain regions may result in temporary or permanent impairments of auditory, motor, or cognitive function; however, the molecular mechanisms by which UCB elicits such neurotoxicity are still poorly understood. The present study is undertaken to investigate whether prolonged exposure of rat organotypic hippocampal slice cultures to UCB alters the induction of long-term synaptic plasticity.

METHODOLOGY/PRINCIPAL FINDINGS

Using electrophysiological recording techniques, we find that exposure of hippocampal slice cultures to clinically relevant concentrations of UCB for 24 or 48 h results in an impairment of CA1 long-term potentiation (LTP) and long-term depression (LTD) induction in a time- and concentration-dependent manner. Hippocampal slice cultures stimulated with UCB show no changes in the secretion profiles of the pro-inflammatory cytokines, interleukin-1beta and tumor necrosis factor-alpha, or the propidium ioide uptake. UCB treatment produced a significant decrease in the levels of NR1, NR2A and NR2B subunits of N-methyl-D-aspartate (NMDA) receptors through a calpain-mediated proteolytic cleavage mechanism. Pretreatment of the hippocampal slice cultures with NMDA receptor antagonist or calpain inhibitors effectively prevented the UCB-induced impairment of LTP and LTD.

CONCLUSION/SIGNIFICANCE

Our results indicate that the proteolytic cleavage of NMDA receptor subunits by calpain may play a critical role in mediating the UCB-induced impairment of long-term synaptic plasticity in the hippocampus. These observations provide new insights into the molecular mechanisms underlying UCB-induced impairment of hippocampal synaptic plasticity which, in turn, might provide opportunities for the development of novel therapeutic strategies that targets these pathways for treatment.

Inflammation, plasticity and real-time imaging after cerebral ischemia

With an incidence of approximately 350 in 100,000, stroke is the third leading cause of death and a major cause of disability in industrialized countries. At present, although progress has been made in understanding the molecular pathways that lead to ischemic cell death, the current clinical treatments remain poorly effective. There is mounting evidence that inflammation plays an important role in cerebral ischemia. Experimentally and clinically, brain response to ischemic injury is associated with an acute and prolonged inflammatory process characterized by the activation of resident glial cells, production of inflammatory cytokines as well as leukocyte and monocyte infiltration in the brain, events that may contribute to ischemic brain injury and affect brain recovery and plasticity. However, whether the post-ischemic inflammatory response is deleterious or beneficial to brain recovery is presently a matter of debate and controversies. Here, we summarize the current knowledge on the molecular mechanisms underlying post-ischemic neuronal plasticity and the potential role of inflammation in regenerative processes and functional recovery after stroke. Furthermore, because of the dynamic nature of the brain inflammatory response, we highlight the importance of the development of novel experimental approaches such as real-time imaging. Finally, we discuss the novel transgenic reporter mice models that have allowed us to visualize and to analyze the processes such as neuroinflammation and neuronal repair from the ischemic brains of live animals.

A potential role for pro-inflammatory cytokines in regulating synaptic plasticity in major depressive disorder

A growing body of data suggests that hyperactivation of the immune system has been implicated in the pathophysiology of major depressive disorder (MDD). Several pro-inflammatory cytokines, such as tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 (IL-1) have been found to be significantly increased in patients with MDD. This review focuses on these two cytokines based on multiple lines of evidence from genetic, animal behaviour, and clinical studies showing that altered levels of serum TNF-alpha and IL-1 are associated with increased risk of depression, cognitive impairments, and reduced responsiveness to treatment. In addition, recent findings have shown that centrally expressed TNF-alpha and IL-1 play a dual role in the regulation of synaptic plasticity. In this paper, we review and critically appraise the mechanisms by which cytokines regulate synaptic and neural plasticity, and their implications for the pathophysiology and treatment of MDD. Finally, we discuss the therapeutic potential of anti-inflammatory-based approaches for treating patients with severe mood disorders. This is a promising field for increasing our understanding of the mechanistic interaction between the immune system, synaptic plasticity, and antidepressants, and for the ultimate development of novel and improved therapeutics for severe mood disorders.

IL-6 release by LPS-stimulated peripheral blood mononuclear cells as a potential biomarker in Alzheimer's disease

BACKGROUND:

In Alzheimer's disease (AD), microglia are activated by amyloid-beta (Aβ) to release IL6 among other cytokines, which in turn may be neurotoxic. Prior studies suggest that the brain inflammatory response to various antigens can be modeled by measuring the release of IL6 from peripheral blood mononuclear cells stimulated by lipopolysaccharide (LPS). We sought to replicate these results and extend to an AD-specific stimulus (Aβ).

METHOD:

PBMCs were purified from 5 AD and 5 age-gender matched cognitively healthy controls and exposed to LPS at two concentrations (20 and 100 ng/ml) and Aβ_1-42(20 ug/ml). IL6 release was measured with standard ELISA kits, and the ratio of “IL6 release” with and without LPS stimulation was reported as the “IL6 release ratio.” Correlations were performed with Pearson's r².

RESULTS:

IL6 release ratios were increased in AD participants as compared to cognitively normal age-gender matched controls with LPS 100 ng/ml exposure at a trend level (p=.07). Aβ_1-42 increased the IL6 release ratio at a trend level (P=.07) with LPS 20 ng/ml exposure. IL6 release ratio was significantly correlated with worse performance on a verbal category fluency test (p=.03, r²=.49)and higher scores on the Neuropsychiatric Inventory (p=.01, r²=.63). There were trend level correlations of Il6 release with worse ratings on the CDR and MMSE.

CONCLUSIONS:

The IL6 release ratio derived from peripheral blood has potential as a biomarker of AD disease severity, both for cognitive outcomes and neuropsychiatric symptoms of AD.

Impaired long term memory consolidation in transgenic mice overexpressing the human soluble form of IL-1ra in the brain

Interleukin-1 (IL-1) is expressed following LTP induction and is required for long-term memory consolidation. We demonstrate that the long-term, but not short-term memory is impaired in a transgenic mouse strain overexpressing the human soluble interleukin-1 receptor antagonist (hsIL-1ra) in the brain. Overexpression of IL-1ra was found to reduce the basal as well as the novelty-induced upregulation of activity-regulated cytoskeleton-associated protein (Arc) in the dentate gyrus and in the retrosplenial cortex. Together with the finding that blocking IL-1 receptors interferes with the BDNF-ERK1/2 pathway, our data suggest an essential role played by physiological levels of IL-1 in long-term memory consolidation.

Interleukin-1 (IL-1): a central regulator of stress responses

Ample evidence demonstrates that the pro-inflammatory cytokine interleukin-1 (IL-1), produced following exposure to immunological and psychological challenges, plays an important role in the neuroendocrine and behavioral stress responses. Specifically, production of brain IL-1 is an important link in stress-induced activation of the hypothalamus-pituitary-adrenal axis and secretion of glucocorticoids, which mediate the effects of stress on memory functioning and neural plasticity, exerting beneficial effects at low levels and detrimental effects at high levels. Furthermore, IL-1 signaling and the resultant glucocorticoid secretion mediate the development of depressive symptoms associated with exposure to acute and chronic stressors, at least partly via suppression of hippocampal neurogenesis. These findings indicate that whereas under some physiological conditions low levels of IL-1 promote the adaptive stress responses necessary for efficient coping, under severe and chronic stress conditions blockade of IL-1 signaling can be used as a preventive and therapeutic procedure for alleviating stress-associated neuropathology and psychopathology.

Cell-specific and concentration-dependent actions of interleukin-1 in acute brain inflammation

Interleukin (IL)-1 is a pivotal pro-inflammatory cytokine and an important mediator of both acute and chronic central nervous system (CNS) injuries. Despite intense research in CNS IL-1 biology over the past two decades, its precise mechanism of action in inflammatory responses to acute brain disorders remains largely unknown. In particular, much effort has been focussed on using in vitro approaches to better understand the cellular and signalling mechanisms of actions of IL-1, yet some discrepancies in the literature regarding the effects produced by IL-1beta in in vitro paradigms of injury still exist, particularly as to whether IL-1 exerts neurotoxic or neuroprotective effects. Here we aim to review the cell-specific and concentration-dependent actions of IL-1 in brain cells, to depict the mechanism by which this cytokine induces neurotoxicity or neuroprotection in acute brain injury.

Interleukin-6 covaries inversely with hippocampal grey matter volume in middle-aged adults

BACKGROUND

Converging animal findings suggest that higher peripheral levels of inflammation are associated with activation of central inflammatory mechanisms that result in hippocampal neurodegeneration and related impairment of memory function. We have recently shown, consistent with animal findings, an inverse association between peripheral levels of interleukin-6 (IL-6), a relatively stable marker of systemic inflammation, and memory function in mid-life adults. In the current study, we extend this work to test whether systemic inflammation is associated with reduced grey matter volume of the hippocampus.

METHODS

For this purpose, we used a computational structural neuroimaging method (optimized voxel-based morphometry) to evaluate the relationship between plasma IL-6 levels and hippocampal grey matter volume in a sample of 76 relatively healthy community volunteers ages 30-54.

RESULTS

Peripheral levels of IL-6 covaried inversely with hippocampal grey matter volume, and this relationship persisted after accounting for several possible confounders, including age, gender, race, years of education, percent body fat, blood pressure, smoking, physical activity, hours of sleep, alcohol use, and total grey matter volume.

CONCLUSIONS

To our knowledge, this is the first report of a relationship between a peripheral marker of IL-6 and hippocampal grey matter volume, raising the possibility that low-grade systemic inflammation could plausibly presage subclinical cognitive decline in part via structural neural pathways.

Neuroinflammation and synaptic plasticity: theoretical basis for a novel, immune-centred, therapeutic approach to neurological disorders

The fascinating capacity that the central nervous system (CNS) has for encoding and retaining memories is thought to be based on activity-dependent forms of synaptic plasticity. The CNS and the immune systems are known to be engaged in an intense bidirectional crosstalk, and glial cells are now viewed as a crucial third element of the synapse. In this opinion article, we review the principal mechanisms by which the immune system, and in particular immune diffusible mediators, influences synaptic transmission and the induction of brain plastic phenomena. Thereafter, we consider the potential implications of inflammation-related overexpression of diffusible mediators in the disruption of synaptic plastic processes and neuronal networks functioning during human neurological diseases. Finally, we propose that a more accurate characterization of the mechanisms underlying the immune-mediated control of synaptic plasticity could represent, in the future, the basis for the development of a novel immune-centred therapeutic approach to neurological disorders.

Voltage-gated potassium channels in human immunodeficiency virus type-1 (HIV-1)-associated neurocognitive disorders

Human immunodeficiency virus type-1 (HIV-1)-associated dementia (HAD), a severe form of HIV-associated neurocognitive disorders (HAND), describes the cognitive impairments and behavioral disturbances which afflict many HIV-infected individuals. Although the precise mechanism leading to HAD is incompletely understood, it is commonly accepted its progression involves a critical mass of infected and activated mononuclear phagocytes (brain perivascular macrophages and microglia) releasing immune and viral products in the brain. These cellular and viral products induce neuronal dysfunction and injury via various signaling pathways. Emerging evidence indicates voltage-gated potassium (K(v)) channels, key regulators of cell excitability and animal behavior (learning and memory), are involved in the pathogenesis of HAD/HAND. Here we survey the literature and find that HAD-related alterations in cellular and viral products can increase neuronal K(v) channel activity, leading to neuronal dysfunction and cognitive deficits. Thus, neuronal K(v) channels may be a new target in the effort to develop therapies for HAD and perhaps other inflammatory neurodegenerative disorders.

Effect of cytokines on neuronal excitability

Numerous studies have shown that proinflammatory cytokines induce or facilitate pain and hyperalgesia in the presence of inflammation, injury to the nervous system or cancer. Besides acting as inflammatory mediators, increasing evidence indicates that cytokines may also specifically interact with receptor and ion channels regulating neuronal excitability, synaptic plasticity and injury under both physiological and pathological conditions. Here we summarize findings on two prototypical proinflammatory cytokines, tumor-necrosis factor-alpha and interleukin-1 beta, and their effects on neuronal excitability and ion channels with special regards to pain and hyperalgesia.

Neuroinflammation and disruption in working memory in aged mice after acute stimulation of the peripheral innate immune system

Acute cognitive disorders are common in elderly patients with peripheral infections but it is not clear why. Here, we injected old and young mice with Escherichia coli lipopolysaccharide (LPS) to mimic an acute peripheral infection and separated the hippocampal neuronal cell layers from the surrounding hippocampal tissue by laser capture microdissection and measured mRNA for several inflammatory cytokines (IL-1 beta, IL-6, and TNFalpha) that are known to disrupt cognition. The results showed that old mice had an increased inflammatory response in the hippocampus after LPS compared to younger cohorts. Immunohistochemistry further showed more microglial cells in the hippocampus of old mice compared to young adults, and that more IL-1 beta-positive cells were present in the dentate gyrus and in the CA1, CA2, and CA3 regions of LPS-treated old mice compared to young adults. In a test of cognition that required animals to effectively integrate new information with a preexisting schema to complete a spatial task, we found that hippocampal processing is more easily disrupted in old animals than in younger ones when the peripheral innate immune system is stimulated. Collectively, the results suggest that aging can facilitate neurobehavioral complications associated with peripheral infections probably by allowing the over expression of inflammatory cytokines in brain areas that mediate cognitive processing.

Neuroinflammation associated with aging sensitizes the brain to the effects of infection or stress

The aging brain is characterized by a shift from the homeostatic balance of inflammatory mediators to a proinflammatory state. This increase in neuroinflammation is marked by increased numbers of activated and primed microglia, increased steady-state levels of inflammatory cytokines and decreases in anti-inflammatory molecules. These conditions sensitize the aged brain to produce an exaggerated response to the presence of an immune stimulus in the periphery or following exposure to a stressor. In the brain, proinflammatory cytokines can have profound effects on behavioral and neural processes. As the aged brain is primed to respond to inflammatory stimuli, infection or stress may produce more severe detriments in cognitive function in the aged. Typically after an immune stimulus, aged animals display prolonged sickness behaviors, increased cytokine induction and greater cognitive impairments compared to adults. Additionally, aging can also augment the central response to stressors leading to exaggerated cytokine induction and increased decrements in learning and memory. This alteration in neuroinflammation and resultant sensitization to extrinsic and intrinsic stressors can have considerable effects upon the elderly's recovery and coping during disease and stress.

The type 1 interleukin 1 receptor is not required for the death of murine hippocampal dentate granule cells and microglia activation

Alterations in inflammatory process, neuronal death, and glia response have been observed under manipulation of interleukin-1 (IL-1) and subsequent signaling through the type 1 IL-1 receptor (IL-1R1). To investigate the influence of IL-1R1 activation in the pathophysiology of a chemical-induced injury to the murine hippocampus, we examined the level and pattern of neuronal death and neuroinflammation in male weanling mice exposed to trimethyltin hydroxide (2.0 mg TMT/kg, i.p.). Dentate granule cell death occurred at 6 h post-TMT as detected by active caspase 3 immunostaining and presence of lectin positive microglia. The severity of neuronal death and microglia response increased by 12-24 h with elevations in mRNA levels for TNFalpha and IL-1alpha. In IL-1R1 null (IL-1R1-/-) mice, the pattern and severity of neuronal death at 24 or 72 h post-TMT was similar as compared to wildtype (WT) mice. In both groups, mRNA levels for TNFalpha and MIP-1alpha were elevated, no significant change was seen in either IL-1alpha or IL-1beta, and the early activation of microglia, including their ability to progress to a phagocytic phenotype, was maintained. Compared to WT mice, IL-1R1-/- mice displayed a limited glial fibrillary acidic protein (GFAP) astrocytic response, as well as a preferential induction in mRNA levels of Fas signaling components. Cumulatively, these results indicate that IL-1R1 activation is not necessary for TMT-induced death of dentate granule neurons or local activation of microglia; however, IL-1R1 signaling is involved in mediating the structural response of astrocytes to injury and may regulate apoptotic mechanisms via Fas signaling components.

Effects of Lipopolysaccharide on56Fe-Particle Radiation-Induced Impairment of Synaptic Plasticity in the Mouse Hippocampus

Space radiation, including high-mass, high-Z, high-energy particles (HZE; e.g. (56)Fe), represents a significant health risk for astronauts, and the central nervous system (CNS) may be a vulnerable target. HZE-particle radiation may directly affect neuronal function, or during immunological challenge, it may alter immune system-to-CNS communication. To test these hypotheses, we exposed mice to accelerated iron particles ((56)Fe; 600 MeV/nucleon; 1, 2, 4 Gy; brain only) and 1 month later prepared hippocampal slices to measure the effects of radiation on neurotransmission and synaptic plasticity in CA1 neurons. In a model of immune system-to-CNS communication, these electrophysiological parameters were measured in irradiated mice additionally challenged with the peripheral immunological stressor lipopolysaccharide (LPS) injected intraperitoneally 4 h before the slice preparation. Exposure to (56)Fe particles alone increased dendritic excitability and inhibited plasticity. In control mice (0 Gy), LPS treatment also inhibited synaptic plasticity. Paradoxically, in mice exposed to 2 Gy, the LPS treatment restored synaptic plasticity to levels similar to those found in controls (0 Gy, no LPS). Our results indicate that HZE-particle radiation alters normal electrophysiological properties of the CNS and the hippocampal response to LPS.

Cytokines and neuronal ion channels in health and disease

The biophysical properties and the spatial distribution of ion channels define the signaling characteristics of individual neurons. Function, number localization, and ratio of receptor and ion channels are dynamically modulated in response to diverse stimuli and undergo dynamic changes in both physiological and pathological conditions. Increasing evidence indicates that cytokines may specifically interact with receptor and ion channels regulating neuronal excitability, synaptic plasticity, and injury. Interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha, two proinflammatory cytokines implicated in various pathophysiological conditions of the CNS, have been particularly studied. Literature data indicate that these cytokines (1) directly and promptly modulate ion channel activity, (2) exert different (and often opposite) effects on the same channels, and (3) act on ion channels both at physiological and pathological concentrations. Consequently, cytokines are now regarded as novel neuromodulators, opening important perspectives in the current view of brain behavior.

Interactions of interleukin-1 with neurotrophic factors in the central nervous system: beneficial or detrimental?

Interleukin (IL)-1 is a multifunctional cytokine that plays a key role in mediating inflammation in the brain. Many different cell types in the brain express the IL-1 receptor and respond to this cytokine by activating cell-type-specific signaling pathways leading to distinct functional responses, which collectively comprise the inflammatory response in the brain. One key effect of IL-1 in the brain is the induction of trophic factor production by glial cells, which has traditionally been considered a neuroprotective response to injury or disease. However, recent studies have shown that nerve growth factor, which is regulated by IL-1, can induce neuronal survival or apoptosis via different receptors. This article examines the interaction of IL-1 with different trophic factors in the brain.

Pro-inflammatory cytokines and their effects in the dentate gyrus

The older notion of a central nervous system existing in essential isolation from the immune system has changed dramatically in recent years as the body of evidence relating to the interactions between these two systems has grown. Here we address the role of a particular subset of immune modulatory molecules, the pro-inflammatory cytokines, in regulating neuronal function and viability in the dentate gyrus of the hippocampus. These inflammatory mediators are known to be elevated in many neuropathological conditions, such as Alzheimer's disease, Parkinson's disease and ischaemic injury that follows stroke. Pro-inflammatory cytokines, such as tumour necrosis factor-alpha (TNF-alpha), interleukin 1-beta (IL-1beta) and interleukin 18 (IL-18), have been shown to regulate neurotoxicity; although, due to the complexity of the cytokine action in neurons and glia, the effect may be either facilitatory or protective, depending on the circumstances. As well as their role in neurotoxicity and neuroprotection, the pro-inflammatory cytokines have also been shown to be potent regulators of synaptic function. In particular, TNF-alpha, IL-1beta and IL-18 have all been shown to inhibit long-term potentiation, a form of neuronal plasticity widely believed to underlie learning and memory, both in the early p38 mitogen activated protein kinase-dependant phase and the later protein synthesis-dependant phase. In this article we address the mechanisms underlying these cytokine effects in the dentate gyrus of the hippocampus.

Risk factors for seizures in very low birthweight infants with periventricular leukomalacia

This population-based observational study aimed to determine the perinatal factors that were associated with the occurrence of seizures in very low birthweight infants with periventricular leukomalacia. The study sample consisted of 545 infants from the Israel National Very Low Birthweight Infant Database, gestational age 24 to 36 weeks, who survived beyond 28 days of age, in whom a late cranial ultrasonographic examination was performed and in whom periventricular leukomalacia was diagnosed. To evaluate the association between periventricular leukomalacia and confounding variables on the occurrence of seizures, the chi-square test, univariate analysis, and a logistic regression model were used. Of the 545 infants who developed periventricular leukomalacia, 102 (18.7%) had seizures. Significant independent predictors of seizures among these infants were decreasing gestational age, intraventricular hemorrhage, posthemorrhagic hydrocephalus, sepsis, and necrotizing enterocolitis. Infants with both sepsis and necrotizing enterocolitis had a 4.6-fold increased risk of seizures, further suggesting a possible role of infection in the pathogenesis of brain injury in preterm infants.

Interleukin-6 covaries inversely with cognitive performance among middle-aged community volunteers

OBJECTIVE

Recent evidence suggests that higher peripheral levels of interleukin 6 (IL-6) are associated with poorer cognitive function and predict future cognitive decline among the elderly. The current investigation extends the study of relationships between plasma IL-6 and cognitive performance to healthy middle-aged adults and to an examination of more specific cognitive domains.

METHODS

Five hundred relatively healthy community volunteers aged 30 to 54 had blood drawn for the determination of plasma IL-6 levels and completed a battery of neuropsychological tests evaluating memory and executive function.

RESULTS

After controlling for age, gender, race, and education, hierarchical regression analyses revealed an inverse relationship between circulating levels of IL-6 and performance on clusters of tests assessing auditory recognition memory, attention/working memory, and executive function. In contrast, there was no association between IL-6 and performance on tests of general memory. Secondary analyses demonstrated that relationships between IL-6 and auditory recognition and working memory and executive function were independent of a number of health factors, including body mass index, smoking, and hypertension.

CONCLUSIONS

These findings contribute to a growing body of evidence linking chronic inflammation to poorer cognitive functioning and extend these findings to a midlife community sample, raising the possibility that IL-6 may represent a biomarker for risk of future cognitive decline.

IL-1beta induces a MyD88-dependent and ceramide-mediated activation of Src in anterior hypothalamic neurons

The proinflammatory cytokine interleukin 1beta (IL-1beta), acting at IL-1R1 receptors, affects neuronal signaling under both physiological and pathophysiological conditions. The molecular mechanism of the rapid synaptic actions of IL-1beta in neurons is not known. We show here that within minutes of IL-1beta exposure, the firing rate of anterior hypothalamic (AH) neurons in culture was inhibited. This effect was prevented by pre-exposure of the cells to the Src family inhibitor, PP2, suggesting the involvement of Src in the hyperpolarizing effects of IL-1beta. The IL-1beta stimulation of neurons induced a rapid increase in the phosphorylation of the tyrosine kinase Src and kinase suppressor of Ras (ceramide activated protein kinase (CAPK)/KSR) in neurons grown on glia from IL-1RI(-/-) mice. These effects of IL-1beta were dependent on the association of the cytosolic adaptor protein, MyD88, to the IL-1 receptor, and on the activation of the neutral sphingomyelinase, leading to production of ceramide. A cell-permeable analog of ceramide mimicked the effects of IL-1beta on the cultured AH neurons. These results suggest that ceramide may be the second messenger of the fast IL-1beta actions in AH neurons, and that this IL-1beta/ceramide pathway may underlie the fast non-transcription-dependent, electrophysiological effects of IL-1beta observed in AH neurons in vivo.

Interleukin-1 beta modulates AMPA receptor expression and phosphorylation in hippocampal neurons

Interleukin (IL)-1beta is a pro-inflammatory cytokine involved in modulating inflammation and stress responses in the brain. Central administration of IL-1beta impairs both memory functions and long-term potentiation (LTP) induction. However, the molecular events responsible for the downstream effects of IL-1beta are not fully understood. Given the potential regulatory role of IL-1beta in LTP, we assessed whether IL-1beta influences surface expression and phosphorylation of glutamate receptors. We found that IL-1beta, but not IL-10 or tumour necrosis factor (TNF)-alpha, down-regulated the surface expression and Ser831 phosphorylation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor subunit GluR1. Agents that block IL-1beta receptor activity abolished these effects. In contrast, no change in the surface expression of the N-methyl-d-aspartate (NMDA) receptor subunit NR1 was observed. The inhibition of NMDA receptor activity or depletion of extracellular calcium blocked IL-1beta effects on GluR1 phosphorylation and surface expression. NMDA-mediated calcium influx was also regulated by IL-1beta. These findings suggest that IL-1beta selectively regulates AMPA receptor phosphorylation and surface expression through extracellular calcium and an unknown mechanism involving NMDA receptor activity.

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.

Mononuclear phagocytes in the pathogenesis of neurodegenerative diseases

Brain mononuclear phagocytes (MP, bone marrow monocyte-derived macrophages, perivascular macrophages, and microglia) function to protect the nervous system by acting as debris scavengers, killers of microbial pathogens, and regulators of immune responses. MP are activated by a variety of environmental cues and such inflammatory responses elicit cell injury and death in the nervous system. MP immunoregulatory responses include secretion of neurotoxic factors, mobilization of adaptive immunity, and cell chemotaxis. This incites tissue remodelling and blood-brain barrier dysfunction. As disease progresses, MP secretions engage neighboring cells in a vicious cycle of autocrine and paracrine amplification of inflammation leading to tissue injury and ultimately destruction. Such pathogenic processes tilt the balance between the relative production of neurotrophic and neurotoxic factors and to disease progression. The ultimate effects that brain MP play in disease revolves "principally" around their roles in neurodegeneration. Importantly, common functions of brain MP in neuroimmunity link highly divergent diseases (for example, human immunodeficiency virus type-one associated dementia, Alzheimer's disease and Parkinson's disease). Research into this process from our own laboratories and those of others seek to harness MP inflammatory processes with the intent of developing therapeutic interventions that block neurodegenerative processes and improve the quality of life in affected people.

Bacterial endotoxin-induced behavioral alterations in two variations of the Morris water maze

Several studies report that lipopolysaccharide (LPS) or interleukin-1beta (IL-1beta) may affect behavior in a variety of learning tasks, including the Morris water maze (MWM), though the nature of these effects varies with testing parameters. The present study used C57BL/6J mice to evaluate the effect of a single intraperitoneal LPS injection 4 h prior to day 1 of testing, LPS before each day of testing, or saline prior to each test day, on performance in two variations of the MWM. In the first experiment, one that utilized a standard hidden platform, LPS clearly affected performance, as shown by increased latencies and greatly decreased swimming speeds. However, a modest effect on distance swam was only present during later test days. These data show a clear deficit in performance (driven by decreased swim speed), and some evidence for learning decrements on later test days. To explore to what degree the effects of LPS in the water maze were the result of alterations in performance factors such as motor behavior, a second experiment was conducted in which a highly visible jet-black platform was utilized. Despite eliminating the need for spatial learning, mice administered LPS still exhibited significantly increased latency scores and decreased swim speed. However, there was no difference between treatment groups in distance swam. These results reinforce the idea that, even when present, potential learning effects of LPS may sometimes be difficult to untangle from performance effects unrelated to learning, and underscore the need for utilizing behavioral tests that offer suitable control for LPS-induced performance effects.

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.

Inflammation in areas of remote changes following focal brain lesion

Focal brain lesions can lead to metabolic and structural changes in areas distant from but connected to the lesion site. After focal ischemic or excitotoxic lesions of the cortex and/or striatum, secondary changes have been observed in the thalamus, substantia nigra pars reticulata, hippocampus and spinal cord. In all these regions, inflammatory changes characterized by activation of microglia and astrocytes appear. In the thalamus, substantia nigra pars reticulata and hippocampus, an expression of proinflammatory cytokine like tumor necrosis factor-alpha and interleukin-1beta is induced. However, time course of expression and cellular localisation differ between these regions. Neuronal damage has consistently been observed in the thalamus, substantia nigra and spinal cord. It can be present in the hippocampus depending on the procedure of induction of focal cerebral ischemia. This secondary neuronal damage has been linked to antero- and retrograde degeneration. Anterograde degeneration is associated with somewhat later expression of cytokines, which is localised in neurons. In case of retrograde degeneration, the expression of cytokines is earlier and is localised in astrocytes. Pharmacological intervention aiming at reducing expression of tumor necrosis factor-alpha leads to reduction of secondary neuronal damage. These first results suggest that the inflammatory changes in remote areas might be involved in the pathogenesis of secondary neuronal damage.

Peripheral lipopolysaccharide administration impairs two-way active avoidance conditioning in C57BL/6J mice

Peripheral administration of lipopolysaccharide (LPS) or interleukin-1 (IL-1) may lead to alterations of CNS function and behavioral changes designated "sickness behavior." Further, some experiments show evidence of LPS- and cytokine-mediated alterations in learning and memory. The current series of experiments examined the effects of a single or repeated intraperitoneal LPS injections, at a number of doses and time points before or after test sessions, on behavior in a two-way active avoidance conditioning paradigm. Subjects were able to avoid the mild shock stimulus, escape it, or fail to respond to it. Subjects treated with LPS at many, but not all, of the time points sampled showed impaired learning, by exhibiting significantly fewer avoidance responses than controls. Furthermore, an LPS-induced increase in non-cued inter-trial interval crossings was observed during the later days of testing, suggesting that a greater percentage of their avoidance responses was not conditioned and their behavior was less efficient. Taken together, the results suggest that LPS-treated animals showed a diminished association between conditioned stimulus (CS) and unconditioned stimulus (US). These results support the theory that peripheral immune stimuli may induce deleterious effects on learning, and extend the work to a negatively reinforced operant procedure.

Dual effects of the lichen glucan PB-2, extracted from Flavoparmelia baltimorensis, on the induction of long-term potentiation in the dentate gyrus of the anesthetized rat: possible mediation via adrenaline beta- and interleukin-1 receptors

We have previously found that oral or intravenous (i.v.) administration of the polysaccharide fraction PB-2, extracted from the lichen Flavoparmelia baltimorensis, facilitated the induction of long-term potentiation (LTP) in the dentate gyrus (DG) in vivo. In this study, the mechanism underlying the effect of PB-2 on the induction of LTP was investigated in the DG of anesthetized rat focusing on the contribution of the interleukin-1 (IL-1) receptor and the adrenaline beta-receptor. An i.v. injection of IL-1ra (10(-9) g/kg), an antagonist of the IL-1 receptor, had no effect on the basal response in the DG; however, this treatment augmented the enhancement of LTP induced by a single i.v. injection of PB-2 (10(-3) g/kg). This potentiating effect was also observed following intracerebroventricular (i.c.v.) injection of IL-1ra (10(-15)-10(-11) g). An i.v. injection of IL-1beta (3.5 x 10(-15)-3.5 x 10(-9) g/kg) inhibited the induction of LTP, which was diminished by the previous application of IL-1ra. These results suggest that the activation of the IL-1 receptor induces the suppression of LTP in PB-2-treated rats, and that endogenous IL-1beta contributes to the IL-1 receptor activation. An i.c.v. infusion of metoprolol (7.5 x 10(-6) g), an antagonist of the adrenaline beta(1)-receptor, attenuated the enhancement of LTP induced by an i.v. injection of PB-2. These results suggest that PB-2 has two different effects on the LTP, an enhancing effect and an inhibiting one, and that it exhibited the significant enhancing effect on the LTP as a total balance of these effects.

Downregulation of IL-4-induced signalling in hippocampus contributes to deficits in LTP in the aged rat

Ageing is characterized by deficits in learning and memory and by a deficit in long-term potentiation (LTP) in hippocampus. Several age-related changes, including dysfunction of calcium homeostatic mechanisms and upregulation of inflammatory processes are likely to contribute to these deficits. Here we exploited the fact that aged rats fall into a subgroup which fail to sustain LTP in perforant path granule cell synapses as a result of tetanic stimulation, and a subgroup which sustains LTP in a manner indistinguishable from young rats, in an effort to identify differential changes in the two subgroups. The age-related increase in IL-1beta concentration and IL-1beta-induced signalling was more profound in aged rats which failed to sustain LTP. We demonstrate that functional IL-4 receptors are expressed in rat hippocampus and that age is associated with a decrease in IL-4 concentration accompanied by a decrease in phosphorylation of JAK-1 and STAT-6. We propose that the imbalance between pro-inflammatory and anti-inflammatory cytokines in the aged brain significantly contributes to age-related deficits in synaptic function.