The inhibitory effect of interleukin-1beta on long-term potentiation is coupled with increased activity of stress-activated protein kinases

Time course of hippocampal IL-1 beta and memory consolidation impairments in aging rats following peripheral infection

We previously reported that aging F344XBN rats are more vulnerable to disruptions of memory consolidation processes following an injection of Escherichia coli than are young rats. Furthermore, this disruption was specific to hippocampal-dependent memory. In the present study we examined the time course of the proinflammatory cytokine IL-1 beta in young and old rats following a peripheral injection of E. coli. Compared to young rats, aging rats treated with E. coli showed an exaggerated and prolonged up-regulation of IL-1 beta protein in the hippocampus, but not in hypothalamus, parietal cortex, prefrontal cortex, serum or spleen. Aging rats showed greater hippocampal IL-1 beta protein levels than their young counterparts 4h after E. coli, and these levels remained significantly elevated for 8 but not 14 days after E. coli. In a second experiment, aging rats exhibited anterograde memory consolidation impairments 4 and 8 days after an E. coli injection, but not after 14 days. A third experiment revealed that following an E. coli injection, bacterial clearance from the spleen and peritoneum was not impaired in aged rats, suggesting that elevations in hippocampal IL-1 beta were not mediated by impaired clearance in the periphery in aging rats. These data suggest that the exaggerated and prolonged elevation of IL-1 beta, specifically in the hippocampus, may be responsible for hippocampal-dependent memory impairments observed in aging rats following a bacterial infection.

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.

Neuroprotective effect of sodium ferulate and signal transduction mechanisms in the aged rat hippocampus

AIM

To investigate whether the age-related increase in interleukin-1beta (IL-1beta) and c-Jun N-terminal kinases (JNK) pathway was coupled with a decrease in cell survival signaling pathways and whether sodium ferulate (SF) treatment was effective in preventing these age-associated changes.

METHODS

Groups of young and aged rats were fed for 4 weeks on a diet enriched in SF (100 mg/kg and 200 mg/kg per day). At the end of the period of dietary manipulation, Western blotting analysis was used to determine the expressions of IL-1beta, phosphorylated mitogen-activated protein kinase kinase (MKK)4, phospho-JNK, phospho-c-Jun, phosphorylated extracellular signal-regulated kinase (ERK1/2), phospho-MEK, phospho-Akt, phosphorylated ribosomal protein S6 protein kinase (p70S6K), and activated caspase-3 and caspase-7. Nissl staining was used to observe the morphological change in hippocampal CA1 regions. Immunohistochemical techniques for glial fibrillary acidic protein (GFAP) and integrin alphaM (OX-42) were used to determine the astrocyte and microglia activation.

RESULTS

IL-1beta protein levels, and phospho-MKK4, phospho-JNK1/2, and phospho-c-Jun were significantly enhanced in hippocampus prepared from age-matched control rats. Increased IL-1beta production and JNK1/2 activation was accompanied by downregulation of MEK/ERK1/2 pathway and Akt/p70S6K pathway, leading to cell apoptosis assessed by activation of caspase-3. Significantly, treatment of aged rats with SF (100 mg/kg and 200 mg/kg per day) for 4 weeks prevented the agerelated increase in IL-1beta and IL-1beta-induced JNK signaling pathway and also the age-related changes in ERK and Akt kinase.

CONCLUSION

SF plays neuroprotective roles through suppression of IL-1beta and IL-1beta-induced JNK signaling and upregulation of MEK/ERK1/2 and Akt/p70S6K survival 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.

From inflammation to sickness and depression: when the immune system subjugates the brain

In response to a peripheral infection, innate immune cells produce pro-inflammatory cytokines that act on the brain to cause sickness behaviour. When activation of the peripheral immune system continues unabated, such as during systemic infections, cancer or autoimmune diseases, the ensuing immune signalling to the brain can lead to an exacerbation of sickness and the development of symptoms of depression in vulnerable individuals. These phenomena might account for the increased prevalence of clinical depression in physically ill people. Inflammation is therefore an important biological event that might increase the risk of major depressive episodes, much like the more traditional psychosocial factors.

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.

ERK1/2 and CaMKII-mediated events in memory formation: is 5HT regulation involved?

Activity-dependent changes in neuronal efficacy underlie the formation and storage of new memories. Several studies indicate that modification of the phosphorylation/activation state of different protein kinases localized in the synapses or the nucleus plays a critical role in the induction and maintenance of plastic mechanisms and in the consolidation of long-lasting memories. Here we review some of the more recent findings concerning the regulation of two of the main protein kinase groups involved in memory processes and in neuronal plasticity: Ca2+/calmodulin-dependent protein kinase II (CaMKII), and the mitogen-activated protein kinase (MAPK) family. Since this issue of the journal is dedicated to serotonin (5HT) regulation of behavior, we will comment on the so far scanty, but significant, evidence for a role of 5HT in the regulation of CaMKII and MAPK.

A pivotal role for interleukin-4 in atorvastatin-associated neuroprotection in rat brain

Inflammatory changes, characterized by an increase in pro-inflammatory cytokine production and up-regulation of the corresponding signaling pathways, have been described in the brains of aged rats and rats treated with the potent immune modulatory molecule lipopolysaccharide (LPS). These changes have been coupled with a deficit in long-term potentiation (LTP) in hippocampus. The evidence suggests that anti-inflammatory agents, which attenuate the LPS-induced and age-associated increase in hippocampal interleukin-1beta (IL-1beta) concentration, lead to restoration of LTP. Here we report that atorvastatin, a member of the family of agents that act as inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, exerts powerful anti-inflammatory effects in brain and that these effects are mediated by IL-4 and independent of its cholesterol-lowering actions. Treatment of rats with atorvastatin increased IL-4 concentration in hippocampal tissue prepared from LPS-treated and aged rats and abrogated the age-related and LPS-induced increases in pro-inflammatory cytokines, interferon-gamma (IFNgamma) and IL-1beta, and the accompanying deficit in LTP. The effect of atorvastatin on the LPS-induced increases in IFNgamma and IL-1beta was absent in tissue prepared from IL-4(-/-) mice. The increase in IL-1beta in LPS-treated and aged rats is associated with increased microglial activation, assessed by analysis of major histocompatibility complex II expression, and the evidence suggests that IFNgamma may trigger this activation. We propose that the primary effect of atorvastatin is to increase IL-4, which antagonizes the effects of IFNgamma, the associated increase in microglial activation, and the subsequent cascade of events.

C-Jun N-terminal kinase regulates adenosine A1 receptor-mediated synaptic depression in the rat hippocampus

Adenosine A1 receptors are ubiquitous mediators of presynaptic inhibition of neurotransmission in the central nervous system, yet the signalling pathway linking A1 receptor activation and decreased neurotransmitter release remains poorly resolved. We tested the contribution of c-Jun N-terminal kinase (JNK) to adenosine A1 receptor-mediated depression of field excitatory postsynaptic potentials (fEPSPs) in area CA1 of the rat hippocampus. We found that inhibition of JNK with SP600125 or JNK inhibitor V, but not an inactive analogue, attenuated the depression of fEPSPs induced by adenosine, hypoxia, and the A1 receptor agonist N(6)-cyclopentyladenosine (CPA). In contrast, the JNK inhibitor SP600125 did not inhibit GABA(B)-mediated synaptic depression. In support of our electrophysiological findings, Western blot analysis showed that A1 receptor stimulation resulted in a transient increase in JNK phosphorylation in the membrane fraction of hippocampal lysates. The total amount of JNK in the membrane fraction was unchanged by CPA treatment. The increase in phosphorylated JNK induced by A1 receptor stimulation was blocked by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), indicating that A1 receptors specifically activate JNK in the hippocampus. Together with functional data indicating that JNK inhibition decreased CPA-induced paired pulse facilitation, these results suggest that JNK activation is necessary for adenosine A1 receptor-mediated synaptic depression occurring at a presynaptic locus The adenosine A1 receptor-JNK signalling pathway may represent a novel mechanism underlying inhibition of neurotransmitter release in the CNS.

Exaggerated sickness behavior and brain proinflammatory cytokine expression in aged mice in response to intracerebroventricular lipopolysaccharide

Age-associated changes in glial reactivity may predispose individuals to exacerbated neuroinflammatory cytokine responses that are permissive to cognitive and behavioral complications. The purpose of this study was to determine if aging is associated with an exaggerated sickness response to central innate immune activation. Our results show that intracerebroventricular (i.c.v.) administration of lipopolysaccharide (LPS) caused a heightened proinflammatory cytokine response (IL-1beta, IL-6, and TNFalpha) in the cerebellum 2h post i.c.v. injection in aged mice compared to adults. This amplified inflammatory profile was consistent with a brain region-dependent increase in reactive glial markers (MHC class II, TLR2 and TLR4). Moreover, LPS caused a prolonged sickness behavior response in aged mice that was paralleled by a protracted expression of brain cytokines in the cerebellum and hippocampus. Finally, central LPS injection caused amplified and prolonged IL-6 levels at the periphery of aged mice. Collectively, these data establish that activation of the central innate immune system leads to exacerbated neuroinflammation and prolonged sickness behavior in aged as compared to adult mice.

JNK1 contributes to metabotropic glutamate receptor-dependent long-term depression and short-term synaptic plasticity in the mice area hippocampal CA1

Several recent reports implicate an important role played by c-Jun N-terminal kinases (JNKs) in long-term potentiation (LTP). However, little is known about how the isoforms of JNKs participate in synaptic plasticity. Here we showed that short-term synaptic plasticity was impaired in the hippocampal area CA1 of JNK1-deficient (JNK1-/-) mice; these mice showed normal LTP in response to a strong tetanus and no alteration of N-methyl-D-aspartate receptor-dependent long-term depression (LTD) in the hippocampus. However, LTD induced either by group I metabotropic glutamate receptors (mGluRs) agonist dihydroxyphenylglycine or by paired-pulse low-frequency stimulation was absent in both the JNK1-/- slices and in JNK inhibitor anthrax [1, 9-cd] pyrazol-6(2H)-1 (SP600125)-pretreated slices. Induction of mGluR-dependent LTD resulted in an increase in phosphorylation of JNK1 substrates, including p-c-Jun and p-ATF2 in wild-type (WT) mice, and these increases failed to occur in the JNK1-/- or SP600125-pretreated mice. These results demonstrated that JNK1 played a crucial role in the short-term synaptic plasticity and mGluR-dependent LTD, whereas hippocampus LTP was not affected by JNK1 deficiency.

The age-related attenuation in long-term potentiation is associated with microglial activation

It is well established that inflammatory changes contribute to brain ageing, and an increased concentration of proinflammatory cytokine, interleukin-1beta (IL-1beta), has been reported in the aged brain associated with a deficit in long-term potentiation (LTP) in rat hippocampus. The precise age at which changes are initiated is unclear. In this study, we investigate parallel changes in markers of inflammation and LTP in 3-, 9- and 15-month-old rats. We report evidence of increased hippocampal concentrations of the proinflammatory cytokines IL-1alpha, IL-18 and interferon-gamma (IFNgamma), which are accompanied by deficits in LTP in the older rats. We also show an increase in expression of markers of microglial activation, CD86, CD40 and intercellular adhesion molecules (ICAM). Associated with these changes, we observed a significant impairment of hippocampal LTP in the same rats. The importance of microglial activation in the attenuation of long-term potentiation (LTP) was demonstrated using an inhibitor of microglial activation, minocycline; partial restoration of LTP in 15-month-old rats was observed following administration of minocycline. We propose that signs of neuroinflammation are observed in middle age and that these changes, which are characterized by microglial activation, may be triggered by IL-18.

Centrally administered tumor necrosis factor-α facilitates the avoidance performance of Sprague–Dawley rats

In addition to their immunological functions, recent research has indicated that the pro-inflammatory cytokines can influence learning and memory processes. We have previously shown that a peripheral injection of TNFalpha facilitates the acquisition of a leverpress avoidance task 24 h post-injection. Because the improved acquisition is presumably mediated by central changes, the current experiment involved directly injecting TNFalpha into the third ventricle 24 h prior to training. The data indicate that low (20 ng) but not high (40 ng) doses of TNFalpha produced improved avoidance performance. Results are discussed in terms of possible monoaminergic sensitization induced by TNFalpha and the relationship of this to acquisition of the avoidance response.

Age and Neuroinflammation: A Lifetime of Psychoneuroimmune Consequences

This article reviews the literature indicating that the innate immune cells of the brain become more reactive with age. Although it is unclear how glia reactivity increases, emerging evidence suggests these alterations allow exacerbated neuroinflammation and sickness behavior following peripheral immune activation. This amplified or prolonged exposure to inflammatory cytokines in the brain may impair neuronal plasticity and underlie a heightened neuroinflammatory response in the aged that also may lead to other neurobehavioral impairments such as delirium, depression, and, potentially, the onset of neurologic disease. Therefore pharmacologic strategies to decrease neuroinflammation associated with infection may be important for improving recovery from sickness and reducing neurobehavioral deficits in the elderly.

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.

Peripheral infection and aging interact to impair hippocampal memory consolidation

We report that a peripheral injection of Escherichia coli produces both anterograde and retrograde amnesia in 24 month old, but not 3 month old rats for memories that depend on the hippocampus, that is, memory of context, contextual fear, and place learning. The anterograde effect was restricted to measures of long-term memory. Short-term memory was not affected, nor did E. coli produce amnesia for auditory-cue fear conditioning. There were no age related effects on memory in vehicle-treated rats. In addition to these age-related cognitive effects of E.coli, we report that it produced a marked increased in IL-1beta levels in the hippocampus, but not in parietal cortex or serum. These findings support the hypothesis that age is a vulnerability factor that increases the likelihood that an immune challenge will produce a cognitive impairment. It is possible that this cognitive vulnerability is mediated by age-related changes in the glial environment that results in an exaggerated brain pro-inflammatory response to infection.

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-1 mediates Alzheimer and Lewy body pathologies

Background

Clinical and neuropathological overlap between Alzheimer's (AD) and Parkinson's disease (PD) is now well recognized. Such cases of concurrent AD and Lewy body disease (AD/LBD) show neuropathological changes that include Lewy bodies (α-synuclein aggregates), neuritic amyloid plaques, and neurofibrillary tangles (hyperphosphorylated tau aggregates). The co-occurrence of these clinical and neuropathological changes suggests shared pathogenic mechanisms in these diseases, previously assumed to be distinct. Glial activation, with overexpression of interleukin-1 (IL-1) and other proinflammatory cytokines, has been increasingly implicated in the pathogenesis of both AD and PD.

Methods

Rat primary cultures of microglia and cortical neurons were cultured either separately or as mixed cultures. Microglia or cocultures were treated with a secreted fragment (sAPPα) of the β-amyloid precursor protein (βAPP). Neurons were treated with IL-1β or conditioned medium from sAPPα-activated microglia, with or without IL-1 receptor antagonist. Slow-release pellets containing either IL-1β or bovine serum albumin (control) were implanted in cortex of rats, and mRNA for various neuropathological markers was analyzed by RT-PCR. Many of the same markers were assessed in tissue sections from human cases of AD/LBD.

Results

Activation of microglia with sAPPα resulted in a dose-dependent increase in secreted IL-1β. Cortical neurons treated with IL-1β showed a dose-dependent increase in sAPPα release, an effect that was enhanced in the presence of microglia. IL-1β also elevated the levels of α-synuclein, activated MAPK-p38, and phosphorylated tau; a concomitant decrease in levels of synaptophysin occurred. Delivery of IL-1β by slow-release pellets elevated mRNAs encoding α-synuclein, βAPP, tau, and MAPK-p38 compared to controls. Finally, human cases of AD/LBD showed colocalization of IL-1-expressing microglia with neurons that simultaneously overexpressed βAPP and contained both Lewy bodies and neurofibrillary tangles.

Conclusion

Our findings suggest that IL-1 drives production of substrates necessary for formation of the major neuropathological changes characteristic of AD/LBD.

Electrophysiological properties and thermosensitivity of mouse preoptic and anterior hypothalamic neurons in culture

Responses of mouse preoptic and anterior hypothalamic neurons to variations of temperature are key elements in regulating the setpoint of homeotherms. The goal of the present work was to assess the relevance of culture preparations for investigating the cellular mechanisms underlying thermosensitivity in hypothalamic cells. Our working hypothesis was that some of the main properties of preoptic/anterior hypothalamic neurons in culture are similar to those reported by other authors in slice preparations. Indeed, cultured preoptic/anterior hypothalamic neurons share many of the physiological and morphological properties of neurons in hypothalamic slices. They display heterogenous dendritic arbors and somatic shapes. Most of them are GABAergic and their activity is synaptically driven by the activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptors. Active membrane properties include a depolarizing "sag" in response to hyperpolarization, and a low threshold spike, which is present in a majority of cells and is generated by T-type Ca2+ channels. In a fraction of the cells, the low threshold spike repeats rhythmically, either spontaneously, or in response to depolarization. The background synaptic noise in cultured neurons is characterized by the presence of numerous postsynaptic potentials which can be easily distinguished from the baseline, thus providing an opportunity for assessing their possible roles in thermosensitivity. An unexpected finding was that GABA-A receptors can generate both hyper- and depolarizing postsynaptic potentials in the same neuron. About 20% of the spontaneously firing preoptic/anterior hypothalamic neurons are warm-sensitive. Warming (32-41 degrees C) depolarizes some cells, a phenomenon which is Na+-dependent and tetrodotoxin-insensitive. The increased firing rate of warm-sensitive cells in response to warming can be prepotential and/or synaptically driven. Overall, our data suggest that a warm-sensitive phenotype is already developed in cultured cells. Therefore, and despite obvious differences in their networks, cultured and slice preparations of hypothalamic neurons can complement each other for further studies of warm-sensitivity at the cellular and molecular level.

c-Jun NH2-terminal kinase mediates interleukin-1beta-induced inhibition of lacrimal gland secretion

Sjögren's syndrome, an inflammatory disease affecting the lacrimal and salivary glands, is the leading cause of aqueous tear-deficient type of dry eye. We previously showed that interleukin-1beta (IL-1beta) protein is up regulated in the lacrimal gland of a murine model of Sjögren's syndrome and that exogenous addition of this cytokine inhibits neurotransmitter release and lacrimal gland protein secretion. In the present study we investigated the role of c-Jun NH2-terminal kinase (JNK) in IL-1beta-mediated inhibition of lacrimal gland secretion and tear production. In vitro, IL-1beta induced a time-dependent activation of JNK with a maximum 7.5-fold at 30 min. SP600125, a JNK inhibitor, inhibited, in a concentration-dependent manner, IL-1beta-induced activation of JNK with a maximum of 87% at 10(-4) m. In vivo, IL-1beta stimulated JNK and the expression of the inducible isoform of nitric oxide synthase (iNOS). IL-1beta inhibited high KCl and adrenergic agonist induced protein secretion by 85% and 66%, respectively. SP600125 alleviated the inhibitory effect of IL-1beta on KCl- and agonist-induced protein secretion by 79% and 47%, respectively, and completely blocked the expression of iNOS. Treatment for 7 days with SP600125 increased tear production in a murine model of Sjögren's syndrome dry eye. We conclude that JNK plays a pivotal role in IL-1beta-mediated inhibition of lacrimal gland secretion and subsequent dry eye.

The neurotrophin receptor p75NTR mediates early anti-inflammatory effects of estrogen in the forebrain of young adult rats

BACKGROUND

Estrogen suppresses microglial activation and extravasation of circulating monocytes in young animals, supporting an anti-inflammatory role for this hormone. However, the mechanisms underlying estrogen's anti-inflammatory effects, especially in vivo, are not well understood. The present study tests the hypothesis that anti-inflammatory effects of estrogen are mediated by the pan-neurotrophin receptor p75NTR. Previously, we reported that estrogen attenuated local increases of interleukin(IL)-1beta in the NMDA-lesioned olfactory bulb, while further increasing NGF expression.

RESULTS

The present studies show that this lesion enhances expression of the neurotrophin receptor p75NTR at the lesion site, and p75NTR expression is further enhanced by estrogen treatment to lesioned animals. Specifically, estrogen stimulates p75NTR expression in cells of microvessels adjacent to the lesion site. To determine the role of this receptor in mediating estrogen's anti-inflammatory effects, a p75NTR neutralizing antibody was administered at the same time the lesion was created (by stereotaxic injections of NMDA) and specific markers of the inflammatory cascade were measured. Olfactory bulb injections of NMDA+vehicle (preimmune serum) increased IL-1beta and activated the signaling molecule c-jun terminal kinase (JNK)-2 at 6 h. At 24 h, the lesion significantly increased matrix metalloproteinase (MMP)-9 and prostaglandin (PG)E2, a COX-2 mediated metabolite of arachadonic acid. All of these markers were significantly attenuated by estrogen in a time-dependent manner. However, estrogen's effects on all these markers were abolished in animals that received anti-p75NTR.

CONCLUSION

These data support the hypothesis that estrogen's anti-inflammatory effects may be, in part, mediated by this neurotrophin receptor. In view of the novel estrogen-dependent expression of p75NTR in cells associated with microvessels, these data also suggest that the blood brain barrier is a critical locus of estrogen's neuro-immune effects.

Spatial learning of mice lacking a neuron-specific epidermal growth factor family protein, NELL2

NELL2 is a neuron-specific thrombospondin-1-like extracellular protein containing six epidermal growth factor-like domains. We previously disrupted the NELL2 gene in mice by gene targeting and showed that long-term potentiation is enhanced in vivo in the dentate gyrus of NELL2-deficient mice. To further elucidate the physiological roles of NELL2, we performed a behavioral characterization of NELL2(-/-) and their heterozygous control mice. NELL2-deficient mice exhibited learning impairment in the Morris water maze task. However, we observed no difference in passive avoidance learning between NELL2(-/-) and NELL2(+/-) mice. These observations suggest that NELL2 plays an important role in hippocampus-dependent spatial learning and that emotional learning does not depend critically on NELL2.

Interleukin-1beta enhances NMDA receptor-mediated current but inhibits excitatory synaptic transmission

Interleukin (IL)-1beta is often characterized as the prototypic proinflammatory cytokine but is involved in various pathophysiological conditions in the central nervous system (CNS). A whole-cell recording technique was used to observe its effect on N-methyl-D-aspartate (NMDA)-evoked currents and spontaneous synaptic activity in cultured rat hippocampal neurons. The results showed that the frequencies but not the amplitudes of spontaneous excitatory postsynaptic currents (sEPSC) and miniature excitatory postsynaptic currents (mEPSC) were decreased by 10 or 100 ng/ml IL-1beta. IL-1beta at these concentrations also increased the NMDA receptor-mediated current. In addition, 10 ng/ml IL-1beta significantly increased the amplitude of the voltage-dependent Ca2+ current (I(Ca)). The increase in I(Ca) following treatment of cultures with IL-1beta resulted mainly from an increase in L-type current. These data suggest that IL-1beta modulates hippocampus-related functions via its effect on synaptic activity and Ca2+ signaling in neurons.

Impaired long-term potentiation in c-Jun N-terminal kinase 2-deficient mice

c-Jun N-terminal kinases (JNKs) are thought to be involved in regulating synaptic plasticity. We therefore investigated the specific role of JNK2 in modulating long-term potentiation (LTP) in hippocampus during development, using JNK2-deficient mice. The morphological structure and the numbers of both NeuN, a specific neuronal marker, and GABA-positive neurons in the hippocampal areas were similar in wild-type and Jnk2(-/-) mice. Western blot analysis revealed that JNK2 expression was higher and stable at 1 and 3 months of age, but JNK1 levels were lower at 1 month of age and almost undetectable in 3-month-old wild-type mice. In contrast to wild-type mice, there was a significant increase in JNK1 expression in JNK2 mutant mice, especially at 1 month of age. Electrophysiological studies demonstrated that LTP was impaired in both the CA1 and CA3 regions in 1-month-old, but not in adult, Jnk2(-/-) mice, probably owing to decreased presynaptic neurotransmitter release. Moreover, late-phase LTP, but not early-phase LTP, was impaired in the Jnk2(-/-) adult mice, suggesting that JNK2 plays a role in transforming early LTP to late LTP. Together, the data highlight the specific role of JNK2 in hippocampal synaptic plasticity during development.

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.

Activation of c-Jun-N-terminal kinase is critical in mediating lipopolysaccharide-induced changes in the rat hippocampus

Lipopolysaccharide (LPS) exerts a myriad of effects in rat hippocampus; it increases the concentration of the proinflammatory cytokine, interleukin-1beta (IL-1beta), and signalling via the IL-1 type I receptor (IL-1RI) resulting in phosphorylation of the stress-activated protein kinase, c-jun-N-terminal kinase (JNK) and impairment in long-term potentiation (LTP). This study was designed to establish whether activation of JNK is a pivotal event in mediating the effects of LPS in hippocampus and therefore LPS-treated rats were injected intracerebroventricularly with saline, the JNK inhibitor D-JNKI1, or with the anti-inflammatory cytokine IL-4, which antagonizes the effects of IL-1beta upstream of JNK activation. We report that IL-4 blocked the LPS-induced increase in IL-1RI expression and associated increases in phosphorylation of JNK and c-jun, whereas D-JNKI1 inhibited the LPS-induced phosphorylation of c-jun. Both IL-4 and D-JNKI1 inhibited the increase in caspase-3 staining which was associated with LPS treatment, and both abrogated the LPS-induced inhibition of LTP in perforant path-granule cell synapses. The data presented are consistent with the proposal that JNK activation, probably as a result of increased IL-1RI activation, is a critical step in mediating the detrimental effects of LPS in hippocampus.

Role of Interleukin-4 in Regulation of Age-related Inflammatory Changes in the Hippocampus

It is well documented that long term potentiation (LTP) is impaired in the hippocampus of the aged animal. Among the changes that contribute to this impairment is an increase in hippocampal concentration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta), and increased IL-1beta-induced signaling. In this study we investigated the possibility that these changes were a consequence of decreased concentration of the anti-inflammatory cytokine, IL-4, and decreased IL-4-stimulated signaling. We report that functional IL-4 receptors are expressed on granule cells of the dentate gyrus and that receptor activation results in phosphorylation of JAK1 and STAT6. Hippocampal IL-4 concentration was decreased with age, and this was accompanied by a decrease in phosphorylation of JAK1 and STAT6. The evidence indicates that IL-4 modulates expression of IL-1beta mRNA and protein and that it attenuates IL-1beta-induced impairment of LTP and phosphorylation of JNK and c-Jun. We argued that, if a decrease in hippocampal IL-4 concentration significantly contributed to the age-related impairment in LTP, then restoration of IL-4 should restore LTP. To test this, we treated rats with VP015 (phospholipid microparticles-incorporating phosphatidylserine), which increases IL-4 concentration in hippocampus. The data indicate that the VP015-induced increase in IL-4 concentration in hippocampus of aged rats and lipopolysaccharide (LPS)-treated rats was accompanied by a reversal of the age-related and LPS-induced impairment in LTP in perforant path granule cell synapses. We propose that interplay between pro-inflammatory and anti-inflammatory responses impact significantly on synaptic function in the hippocampus of the aged rat.

Antiepileptogenic and anticonvulsant activity of interleukin-1β in amygdala-kindled rats

Ischaemic, excitotoxic and traumatic brain injuries have been associated with the occurrence of epileptic seizures. Microglia, the principal immune cells in the brain, produce a variety of proinflammatory and cytotoxic factors especially interleukin-1 (IL-1) early after an acute insult. We studied the effect of intracerebroventricularly administered IL-1beta on seizure acquisition and on fully kindled seizures in amygdala kindling model of epilepsy. IL-1beta (0.01 ng/rat) retarded acquisition of kindled behavioral seizures and growth of afterdischarges (AD). IL-1beta (0.01-10 ng/rat) also exhibited significant anticonvulsant effect on established kindled seizures and AD duration. This effect began 0.5 h after administration and was continued up to 72 h. Pretreatment of the kindled animals with nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methyl ester, or cyclooxygenase inhibitor, piroxicam, reversed the anticonvulsant effect of IL-1beta at early time points. Although most of the previous studies indicate a proconvulsant or convulsant property of IL-1, our results support a protective and antiepileptogenic role of IL-1beta.

Perinatal inflammatory cytokine challenge results in distinct neurobehavioral alterations in rats: implication in psychiatric disorders of developmental origin

Maternal stress, viral infection, and obstetric complications, which trigger cytokine signaling, are hypothesized to be involved in schizophrenia and its related disorders. The etiologic contribution of individual cytokines to such psychiatric disorders, however, remains to be evaluated. To estimate the impact of peripheral cytokine challenge on neurobehavioral development, we examined effects of four proinflammatory cytokines on rat neonates and their later behavioral performance. Sublethal doses of interleukin-1 alpha, interleukin-2, interleukin-6, or interferon-gamma were subcutaneously administered to rat pups for 9 days. These animals displayed alterations in physical development, including lower weight gain and/or accelerated eyelid opening. In addition, behavioral abnormalities related to fear/anxiety levels and sensorimotor gating emerged at different developmental stages, depending on the cytokine species administered. During juvenile stages, neonatal interleukin-2 treatment increased exploratory locomotor activity, whereas other cytokine treatments did not. At the post-puberty stage, however, the interleukin-2-induced abnormal motor activity became undetectable, whereas interleukin-1 alpha-treated rats developed abnormalities in startle response, prepulse inhibition (PPI), and social interaction. Subchronic treatment of an anti-psychotic drug, clozapine, ameliorated the impairment of prepulse inhibition without altering startle responses. These animal experiments illustrate that, during early postnatal development, inflammatory cytokine challenge in the periphery can induce future psycho-behavioral and/or cognitive impairments with various latencies, although the pathologic mechanisms underlying these abnormalities remain to be determined.

Reactive oxygen species and synaptic plasticity in the aging hippocampus

Aging is associated with a general decline in physiological functions including cognitive functions. Given that the hippocampus is known to be critical for certain forms of learning and memory, it is not surprising that a number of neuronal processes in this brain area appear to be particularly vulnerable to the aging process. Long-term potentiation (LTP), a form of synaptic plasticity that has been proposed as a biological substrate for learning and memory, has been used to examine age-related changes in hippocampal synaptic plasticity. A current hypothesis states that oxidative stress contributes to age-related impairment in learning and memory. This is supported by a correlation between age, memory impairment, and the accumulation of oxidative damage to cellular macromolecules. However, it also has been demonstrated that ROS are necessary components of signal transduction cascades during normal physiological processes. This review discusses the evidence supporting the dual role of reactive oxygen species (ROS) as cellular messenger molecules in normal LTP, as well their role as damaging toxic molecules in the age-related impairment of LTP. In addition, we will discuss parallel analyses of LTP and behavioral tests in mice that overexpress antioxidant enzymes and how the role of antioxidant enzymes and ROS in modulating these processes may vary over the lifespan of an animal.

Neuroprotective actions of eicosapentaenoic acid on lipopolysaccharide-induced dysfunction in rat hippocampus

Eicosapentaenoic acid (EPA) protects hippocampus from age-related and irradiation-induced changes that lead to impairment in synaptic function; the evidence suggests that this is due to its anti-inflammatory effects, specifically preventing changes induced by the proinflammatory cytokine, interleukin-1beta (IL-1beta). In this study, we have investigated the possibility that EPA may prevent the effects of lipopolysaccharide (LPS) administration, which have been shown to lead to deterioration of synaptic function in rat hippocampus. The data indicate that treatment of hippocampal neurones with EPA abrogated the LPS-induced increases in phosphorylation of the mitogen-activated protein kinase, c-Jun N-terminal kinase (JNK), the transcription factor, c-Jun and the mitochondrial protein, Bcl-2. In parallel, we report that intraperitoneal administration of LPS to adult rats increases phosphorylation of JNK, c-Jun and Bcl-2 in hippocampal tissue and that these changes are coupled with increased IL-1beta concentration. Treatment of rats with EPA abrogates these effects and also blocks the LPS-induced impairment in long-term potentiation in perforant path-granule cell synapses that accompanies these changes. We propose that the neuroprotective effect of EPA may be dependent on its ability to inhibit the downstream consequences of JNK activation.

BDNF mRNA expression in rat hippocampus following contextual learning is blocked by intrahippocampal IL-1β administration

The present study examined the modulating effects of an intrahippocampal injection of interleukin-1beta (IL-1beta) on brain-derived neurotrophic factor (BDNF) mRNA expression 0.5, 2, 4, and 6 h following contextual fear conditioning, a task known to increase BDNF mRNA, in rats. Contextual fear conditioning produced a time-dependent increase in BDNF mRNA that varied by region of hippocampus. IL-1beta blocked or reduced these increases in BDNF mRNA in the CA1, CA2, and dentate gyrus regions of the hippocampus, but had no effect in cortical regions. These data support the idea that IL-1beta-produced memory deficits may be mediated via BDNF mRNA reductions in hippocampus.

Increased IL-1beta in cortex of aged rats is accompanied by downregulation of ERK and PI-3 kinase

Ageing is accompanied by a myriad of changes, which lead to deficits in synaptic function and recent studies have identified an increase in concentration of the proinflammatory cytokine, interleukin-1beta (IL-1beta), as a factor which significantly contributes to deterioration of cell function. Here, we consider that increased IL-1beta concentration and upregulation of IL-1beta-induced cell signalling cascades may be accompanied by downregulation of survival signals, perhaps as a consequence of decreased neurotrophins-associated signalling. The data indicate that increased IL-1beta concentration was coupled with downregulation of ERK and phosphoinositide-3 kinase (PI-3 kinase) in cortical tissue prepared from aged rats. These changes could not be attributed to decreased concentration of NGF or BDNF but the evidence suggested that they may be a consequence of an age-related change in the anti-inflammatory cytokine, IL-4. Significantly, treatment of aged rats with eicosapentaenoic acid reversed the age-related increases in IL-1beta and IL-1beta-induced signalling and also the age-related changes in IL-4, ERK and PI-3 kinase.

Evidence of a protective effect of phosphatidylserine-containing liposomes on lipopolysaccharide-induced impairment of long-term potentiation in the rat hippocampus

Lipopolysaccharide (LPS) has a negative impact on long-term potentiation (LTP) in the rat hippocampus, which has been correlated with increased concentration of interleukin-1 beta (IL-1 beta) and activation of p38 and c-Jun N-terminal kinase (JNK). It has been documented that phosphatidylserine (PS)-containing liposomes induce anti-inflammatory signals and we report that pre-treatment of rats with PS liposomes prevented these LPS-induced effects while also inhibiting microglial activation. We also observed increased concentration of the anti-inflammatory cytokine interleukin-10 (IL-10), whose intracerebroventricular injection administration mimicked the effects of PS liposomes on LTP. This suggests that administration of PS liposomes protects against the deleterious effects of LPS possibly through generation of the anti-inflammatory cytokine IL-10.

Potent effect of interleukin-1 beta to evoke ATP and adenosine release from rat hippocampal slices

In this study the effect of IL-1 beta on [(3)H]purine release from rat hippocampal slices was explored. IL-1 beta (3 x 10(-18)-3 x 10(-14) M) concentration-dependently elevated the basal [(3)H]purine efflux, and this effect was reversed by the selective IL-1RI receptor antagonist IL-1ra (10(-12) M). HPLC analysis revealed that the amount of [(3)H]ATP and [(3)H]adenosine significantly increased in the effluent in response to IL-1 beta. The sodium channel inhibitor tetrodotoxin, the NMDA and non-NMDA receptor antagonists d(-)-2-amino-5-phosphonopentanoic acid (AP-5) plus 6-cyano-7-nitroquinoxaline-2,3-dione-disodium (CNQX) almost completely abolished IL-1 beta-evoked [(3)H]purine release. The effect of IL-1 beta on [(3)H]purine efflux was also prevented by the p38 MAP kinase inhibitor SB 203580, by the nucleoside transport inhibitor nitrobenzyl-thioinosine (NBTI) and by low temperature (4 degrees C). In summary IL-1 beta triggers a transporter mediated [(3)H]purine efflux in the hippocampus which is conveyed by glutamate receptor activation and the p38 MAP kinase pathway, and could serve as a mediator of IL-1 beta-induced synaptic depression.

Proinflammatory cytokines differentially affect leverpress avoidance acquisition in rats

Recent evidence indicates that the pro-inflammatory cytokines (PICs) can affect learning and memory processes. To examine the effect of the PICs on leverpress escape/avoidance conditioning, we injected male Sprague-Dawley rats with IL-1beta, IL-6 (both 3.0 microg/kg, i.p.), TNFalpha (6.0 microg/kg, i.p.) or vehicle, 24h before a single 4-h session of leverpress escape/avoidance conditioning. The TNFalpha-treated animals made more avoidance responses and fewer escape responses than controls during the last hour of the session. Further, both TNFalpha- and IL-1beta-treated animals had a higher percent avoidance than controls during the 4th hour of the session. None of the cytokines had an effect on the number of leverpresses during safety, a putative measure of anxiety. Results are discussed in terms of the differential central effects of the pro-inflammatory cytokines and the possible relationship to avoidance conditioning.

Enhanced long-term potentiation in vivo in dentate gyrus of NELL2-deficient mice

NELL2 is a neuron-specific thrombospondin-1-like extracellular protein containing six epidermal growth factor-like domains and is highly expressed in the hippocampus. We have previously shown that NELL2 promotes survival of neurons through mitogen-activated protein kinases. To clarify the function of NELL2 in vivo, we have generated a novel strain of mice with a targeted mutation in the NELL2 gene and assessed long-term potentiation (LTP) in vivo in the dentate gyrus of NELL2-deficient mice using extracellular recording techniques. Production of LTP at perforant path-granule cell synapses was significantly larger in NELL2-deficient mice than in wild-type controls. Thus, we propose that NELL2 plays an important role as a novel suppressor in LTP in vivo in the mouse dentate gyrus.

The role of c-Jun N-terminal kinase in the Aβ-mediated impairment of LTP and regulation of synaptic transmission in the hippocampus

The effects of the beta-amyloid peptide (Abeta) fragment 25-35 were investigated on hippocampal synaptic transmission and long-term potentiation (LTP) in vitro. Abeta([25-35]) was found to impair both post-tetanic potentiation (PTP) and LTP in the hippocampal CA1. The anthra[1,9-cd]pyrazol-6(2H)-one, SP600125, was used to inhibit c-Jun N-terminal kinase (JNK) activity, which is believed to mediate cell death. Prior application of SP600125 attenuated the Abeta([25-35])-mediated impairment of PTP and LTP, when measured from the pre-drug baseline. In the presence of SP600125 alone, we observed an increase in baseline synaptic transmission and reduction in paired-pulse facilitation, consistent with an increase in synaptic transmission. There was no alteration in the level of PTP and LTP obtained, when measured from the pre-drug baseline. In the presence of both SP600125 and Abeta, however, PTP was greatly enhanced compared with controls. We therefore suggest that the activation of the JNK signalling pathway mediates the effects of Abeta on synaptic plasticity. Our data also indicate that endogenous JNK activity may regulate neurotransmitter release in the hippocampal CA1 in vitro.

Long-term potentiation and memory

One of the most significant challenges in neuroscience is to identify the cellular and molecular processes that underlie learning and memory formation. The past decade has seen remarkable progress in understanding changes that accompany certain forms of acquisition and recall, particularly those forms which require activation of afferent pathways in the hippocampus. This progress can be attributed to a number of factors including well-characterized animal models, well-defined probes for analysis of cell signaling events and changes in gene transcription, and technology which has allowed gene knockout and overexpression in cells and animals. Of the several animal models used in identifying the changes which accompany plasticity in synaptic connections, long-term potentiation (LTP) has received most attention, and although it is not yet clear whether the changes that underlie maintenance of LTP also underlie memory consolidation, significant advances have been made in understanding cell signaling events that contribute to this form of synaptic plasticity. In this review, emphasis is focused on analysis of changes that occur after learning, especially spatial learning, and LTP and the value of assessing these changes in parallel is discussed. The effect of different stressors on spatial learning/memory and LTP is emphasized, and the review concludes with a brief analysis of the contribution of studies, in which transgenic animals were used, to the literature on memory/learning and LTP.

Sulindac improves memory and increases NMDA receptor subunits in aged Fischer 344 rats

Inflammatory processes in the central nervous system are thought to contribute to Alzheimer's disease (AD). Chronic administration of nonsteroidal anti-inflammatory drugs (NSAIDs) decreases the incidence of Alzheimer's disease. There are very few studies, however, on the cognitive impact of chronic NSAID administration. The N-methyl-d-aspartate (NMDA) receptor is implicated in learning and memory, and age-related decreases in the NMDA NR2B subunit correlate with memory deficits. Sulindac, an NSAID that is a nonselective cyclooxygenase (COX) inhibitor was chronically administered to aged Fischer 344 rats for 2 months. Sulindac, but not its non-COX active metabolite, attenuated age-related deficits in learning and memory as assessed in the radial arm water maze and contextual fear conditioning tasks. Sulindac treatment also attenuated an age-related decrease in the NR1 and NR2B NMDA receptor subunits and prevented an age-related increase in the pro-inflammatory cytokine, interleukin 1beta (IL-1beta), in the hippocampus. These findings support the inflammation hypothesis of aging and have important implications for potential cognitive enhancing effects of NSAIDs in the elderly.

Lipopolysaccharide-induced increase in signalling in hippocampus is abrogated by IL-10--a role for IL-1 beta?

Parenterally administered lipopolysaccharide (LPS) increases the concentration of the pro-inflammatory cytokine interleukin-1beta (IL-1beta) in the rat hippocampus and evidence suggests that this effect plays a significant role in inhibiting long-term potentiation (LTP). The anti-inflammatory cytokine IL-10, antagonizes certain effects of IL-1beta, so if the effects of LPS are mediated through an increase in IL-1beta, it might be predicted that IL-10 would also abrogate the effect of LPS. Here, we report that IL-10 reversed the inhibitory effect of LPS on LTP and the data couple this with an inhibitory effect on the LPS-induced increase in IL-1beta. LPS treatment increased hippocampal expression of IL-1 receptor Type I protein. Consistent with the LPS-induced increases in IL-1beta concentration and receptor expression, were downstream changes which included enhanced phosphorylation of IRAK and the stress-activated kinases, JNK and p38; these LPS-induced changes were reversed by IL-10, which concurs with the idea that these events are triggered by increased activation of IL-1RI by IL-1beta. We provide evidence which indicates that LPS treatment leads to evidence of cell death and this was reversed in hippocampus prepared from LPS-treated rats which received IL-10. The evidence is therefore consistent with the idea that IL-10 acts to protect neuronal tissue from the detrimental effects induced by LPS.

Evidence that lipopolysaccharide-induced cell death is mediated by accumulation of reactive oxygen species and activation of p38 in rat cortex and hippocampus

Lipopolysaccharide (LPS) administration stimulates immune activation, inflammation and deterioration in cell function. Neuronal tissue in cortex and hippocampus are particularly susceptible. In this study, we report that LPS induces cell death as measured by caspase-3 activation and DNA fragmentation and that this is coupled with stimulation of the mitogen-activated protein kinase, p38. We provide evidence of co-localization of activated p38 and caspase-3 in cells prepared from cortical and hippocampal tissue after LPS treatment. Furthermore, administration of the p38 inhibitor, SB203580, abolished the LPS-induced increase in caspase-3 activation. We observed that LPS treatment provoked accumulation of reactive oxygen species (ROS) while in vitro incubation of cortical and hippocampal tissue with H(2)O(2) increased p38 activity. In addition, H(2)O(2)-induced activation of caspase-3 was abrogated by SB203580. We propose, based on the data presented, that the action of LPS to induce cell death in cortex and hippocampus may be mediated by ROS accumulation and activation of p38.

Effect of OFR and [Ca2+]i on the activation of p38 MAPK in isolated rabbit liver during cold preservation and reperfusion period

AIM

To study the effect of OFR (oxygen-derieved free radicals) and calcium on the activation of p38 MAPK in isolated rabbit liver during cold preservation and reperfusion period.

METHODS

Based on the cold preservation-reperfusion model of isolated rabbit liver, isolated livers were divided into 4 groups according to the concentration of allopurinol or verapamil in the preservation solution. Liver tissue samples were harvested at the time points of before cold preservation, at the end of cold preservation, and during reperfusion period (5 min, 10 min, 60 min, 120 min). The phosphorylation level of p38MAPK and its activity in liver tissue were detected by Western-Blotting and immunoprecipitation respectively. The content of OFR and concentration of intracellular calciumion ([Ca²⁺]_i) were also measured by the corresponding method.

RESULTS

The content of OFR was increased to its peak value at 5 min during reperfusion period, the difference among the four groups was significant (groups A, B, C, D: 2.32±0.22, 1.82±0.15, 1.63±0.11, 1.29±0.10, P<0.05, t = 2.57). At 10 min during reperfusion period, the phosphorylation level and its activity of p38MAPK reached its peak value, and there was significant difference among the four groups (Groups A, B, C, D: p38MAPK phosphorylation level (76.2±7.0, 61.4±5.9, 47.3±2.5, 37.7±3.0, P<0.05, t = 2.61.Groups A, B, C, D: p38MAPK activity) 82.7±6.8, 69.7±5.2, 54.5±5.5, 41.2±3.1, P<0.05, t = 2.61. Groups A, E, F, G: p38MAPK phosphorylation level (80.3±8.7, 63.3±4.2, 50.4±5.6, 39.2±5.7, P<0.05, t = 2.61. Groups A, E, F, G: p38MAPK activity (80.8±8.9, 66.7±4.2, 53.7±4.1, 39.4±5.5, P<0.05, t = 2.61). The peak value of OFR content and [Ca²⁺]_i was significantly and positively correlated with the peak value of p38MAPK phosphorylation level and activity (P<0.05, R_OFR = 0.976, R_Ca = 0.970).

CONCLUSION

Allopurinol can significantly inhibit the OFR content of isolated liver tissues while verapamil can significantly inhibit the overload of Ca²⁺ concentration of isolated liver cells. The OFR content and overload of intracellular calciumion concentration are closely related with p38MAPK activation during cold preservation and reperfusion period. So activation of p38MAPK signal pathway may be an important mechanism of OFR and Ca²⁺ , which play a critical role in the ischemia-reperfusion injury of donor liver.

Behavioral changes in rats after acute, chronic and repeated administration of interleukin-1beta: relevance for affective disorders

BACKGROUND

Acute, peripheral and central administration of recombinant rat interleukin-1beta (IL-1beta) has been shown to decrease social exploration and locomotor activity and to induce alterations in brain biogenic amines in rats. The aims of this study were to examine whether acute, repeated and chronic administration of IL-1beta to rats may interfere with shuttle box escape learning, a model for anxiety- and depression-like behavior.

METHODS

Sixty-four adult male viral-free Sprague-Dawley rats (200-300 g weight) housed in groups of four at 25 degrees C with a 12:12 light:dark cycle were used in the experiments. They were divided into 8 groups, i.e. 4 control and 4 experimental. The latter were divided into an acute group receiving a single intra-peritoneally (i.p.) challenge of IL-1beta (tested at the shuttle box 1 and 24 h later); a chronic group with daily i.p. injections of IL-1beta for 7 days (tested at the shuttle box 1 h later); and a group with repeated administration, i.e. one i.p. injection on the first day and a second challenge on the seventh day (tested at the shuttle box 1 h later). The control animals followed the same injecting and testing schedule but were treated i.p. with saline.

RESULTS

The acute group treated with one IL-1beta challenge and tested 1 (P=0.001) and 24 h (P=0.002) later showed significant time elongations in the escape trials. The animals treated chronically with IL-1beta for seven consecutive days showed a significant increase in the latency at the escape trials (P=0.0001). Repeated administration of IL-1beta on the first day and a second on the seventh day did not significantly alter the time elongation in the escape trial.

DISCUSSION

Acute and chronic administration of IL-1beta significantly increase the latency of escape to a foot shock, whereas repeated IL-1beta administration does not induce a sensitization of these behavioral responses.

Impaired interleukin-1 signaling is associated with deficits in hippocampal memory processes and neural plasticity

The cytokine interleukin-1 (IL-1) is produced by peripheral immune cells as well as glia and neurons within the brain; it plays a major role in immune to brain communication and in modulation of neural, neuroendocrine, and behavioral systems during illness. Although previous studies demonstrated that excess levels of IL-1 impaired memory processes and neural plasticity, it has been suggested that physiological levels of IL-1 are involved in hippocampal-dependent memory and long-term potentiation (LTP). To examine this hypothesis, we studied IL-1 receptor type I knockout (IL-1rKO) mice in several paradigms of memory function and hippocampal plasticity. In the spatial version of the water maze test, IL-1rKO mice displayed significantly longer latency to reach a hidden platform, compared with wild-type controls. Furthermore, IL-1rKO exhibited diminished contextual fear conditioning. In contrast, IL-1rKO mice were similar to control animals in hippocampal-independent memory tasks; i.e., their performance in the visually guided task of the water maze and the auditory-cued fear conditioning was normal. Electrophysiologically, anesthetized IL-1rKO mice exhibited enhanced paired-pulse inhibition in response to perforant path stimulation and no LTP in the dentate gyrus. In vitro, decreased paired-pulse responses, as well as a complete absence of LTP, were observed in the CA1 region of hippocampal slices taken from IL-1rKO mice compared with WT controls. These results suggest that IL-1 contributes to the regulation of memory processes as well as short- and long-term plasticity within the hippocampus. These findings have important implications to several conditions in humans, which are associated with long-term defects in IL-1 signaling, such as mutations in the IL-1 receptor accessory protein-like gene, which are involved in a frequent form of X-linked mental retardation.

Low doses of interleukin-1beta improve the leverpress avoidance performance of Sprague-Dawley rats

Recent research has indicated that the pro-inflammatory cytokines, particularly interleukin-1beta (IL-1beta), can affect learning and memory. We injected male Sprague-Dawley rats with IL-1beta (1.0, 3.0, or 6.0 microg/kg, i.p.) or saline vehicle, 24h before a single 4-h session of leverpress escape/avoidance conditioning. No effect of IL-1beta at any dose was observed in the number of escape responses across the 4-h session. However, subjects treated with the two lower doses (1.0 and 3.0 microg/kg) of IL-1beta performed more avoidance responses during the final hour of the 4-h session than the other two groups. Subjects treated with the highest dose of IL-1beta (6.0 microg/kg) did not differ from controls. Results are discussed in terms of the possible mechanisms behind the IL-1beta-induced enhancement of learning, as well as the observed dose-response relationship.

Activation of the c-Jun N-terminal kinase signaling cascade mediates the effect of amyloid-beta on long term potentiation and cell death in hippocampus: a role for interleukin-1beta?

Amyloid-beta (Abeta) is a major constituent of the neuritic plaque found in the brain of Alzheimer's disease patients, and a great deal of evidence suggests that the neuronal loss that is associated with the disease is a consequence of the actions of Abeta. In the past few years, it has become apparent that activation of c-Jun N-terminal kinase (JNK) mediates some of the effects of Abeta on cultured cells; in particular, the evidence suggests that Abeta-triggered JNK activation leads to cell death. In this study, we investigated the effect of intracerebroventricular injection of Abeta(1-40) on signaling events in the hippocampus and on long term potentiation in Schaffer collateral CA1 pyramidal cell synapses in vivo. We report that Abeta(1-40) induced activation of JNK in CA1 and that this was coupled with expression of the proapoptotic protein, Bax, cytosolic cytochrome c, poly-(ADP-ribose) polymerase cleavage, and Fas ligand expression in the hippocampus. These data indicate that Abeta(1-40) inhibited expression of long term potentiation, and this effect was abrogated by administration of the JNK inhibitor peptide, D-JNKI1. In parallel with these findings, we observed that Abeta-induced changes in caspase-3 activation and TdT-mediated dUTP nick-end labeling staining in neuronal cultured cells were inhibited by D-JNKI1. We present evidence suggesting that interleukin (IL)-1beta plays a significant role in mediating the effects of Abeta(1-40) because Abeta(1-40) increased hippocampal IL-1beta and because several effects of Abeta(1-40) were inhibited by the caspase-1 inhibitor Ac-YVAD-CMK. On the basis of our findings, we propose that Abeta-induced changes in hippocampal plasticity are likely to be dependent upon IL-1beta-triggered activation of JNK.