Evidence that interleukin-1beta and reactive oxygen species production play a pivotal role in stress-induced impairment of LTP in the rat dentate gyrus

Differential Effect of Repeated Lipopolysaccharide Treatment and Aging on Hippocampal Function and Biomarkers of Hippocampal Senescence

Markers of brain aging and cognitive decline are thought to be influenced by peripheral inflammation. This study compared the effects of repeated lipopolysaccharide (LPS) treatment in young rats to age-related changes in hippocampal-dependent cognition and transcription. Young Fischer 344 X Brown Norway hybrid rats were given intraperitoneal injections once a week for 7 weeks with either LPS or vehicle. Older rats received a similar injection schedule of vehicle. Old vehicle and young LPS rats exhibited a delay-dependent impairment in spatial memory. Further, LPS treatment reduced the hippocampal CA3-CA1 synaptic response. RNA sequencing, performed on CA1, indicated an increase in genes linked to neuroinflammation in old vehicle and young LPS animals. In contrast to an age-related decrease in transcription of synaptic genes, young LPS animals exhibited increased expression of genes that support the growth and maintenance of synapses. We suggest that the increased expression of genes for growth and maintenance of synapses in young animals represents neuronal resilience/recovery in response to acute systemic inflammation. Thus, the results indicate that repeated LPS treatment does not completely recapitulate the aging phenotype for synaptic function, possibly due to the chronic nature of systemic inflammation in aging and resilience of young animals to acute treatments.

Post-Operative Cognitive Dysfunction: An exploration of the inflammatory hypothesis and novel therapies

Post-Operative Cognitive Dysfunction (POCD) is a highly prevalent condition with significant clinical, social and financial impacts for patients and their communities. The underlying pathophysiology is becoming increasingly understood, with the role of neuroinflammation and oxidative stress secondary to surgery and anaesthesia strongly implicated. This review aims to describe the putative mechanisms by which surgery-induced inflammation produces cognitive sequelae, with a focus on identifying potential novel therapies based upon their ability to modify these pathways.

Nuclear deterrents: Intrinsic regulators of IL-1β-induced effects on hippocampal neurogenesis

Hippocampal neurogenesis, the process by which new neurons are born and develop into the host circuitry, begins during embryonic development and persists throughout adulthood. Over the last decade considerable insights have been made into the role of hippocampal neurogenesis in cognitive function and the cellular mechanisms behind this process. Additionally, an increasing amount of evidence exists on the impact of environmental factors, such as stress and neuroinflammation on hippocampal neurogenesis and subsequent impairments in cognition. Elevated expression of the pro-inflammatory cytokine interleukin-1β (IL-1β) in the hippocampus is established as a significant contributor to the neuronal demise evident in many neurological and psychiatric disorders and is now known to negatively regulate hippocampal neurogenesis. In order to prevent the deleterious effects of IL-1β on neurogenesis it is necessary to identify signalling pathways and regulators of neurogenesis within neural progenitor cells that can interact with IL-1β. Nuclear receptors are ligand regulated transcription factors that are involved in modulating a large number of cellular processes including neurogenesis. In this review we focus on the signalling mechanisms of specific nuclear receptors involved in regulating neurogenesis (glucocorticoid receptors, peroxisome proliferator activated receptors, estrogen receptors, and nuclear receptor subfamily 2 group E member 1 (NR2E1 or TLX)). We propose that these nuclear receptors could be targeted to inhibit neuroinflammatory signalling pathways associated with IL-1β. We discuss their potential to be therapeutic targets for neuroinflammatory disorders affecting hippocampal neurogenesis and associated cognitive function.

Systemic TNF-α produces acute cognitive dysfunction and exaggerated sickness behavior when superimposed upon progressive neurodegeneration

Inflammation influences chronic neurodegeneration but its precise roles are not yet clear. Systemic inflammation caused by infection, trauma or co-morbidity can alter the brain's inflammatory status, produce acute cognitive impairments, such as delirium, and drive new pathology and accelerated decline. Consistent with this, elevated systemic TNF-α is associated with more rapid cognitive decline over 6months in Alzheimer's disease patients. In the current study we challenged normal animals and those with existing progressive neurodegeneration (ME7 prion disease) with TNF-α (i.p.) to test the hypothesis that this cytokine has differential effects on cognitive function, sickness behavior and features of underlying pathology contingent on the animals' baseline condition. TNF-α (50μg/kg) had no impact on performance of normal animals (normal brain homogenate; NBH) on working memory (T-maze) but produced acute impairments in ME7 animals similarly challenged. Plasma TNF-α and CCL2 levels were equivalent in NBH and ME7 TNF-challenged animals but hippocampal and hypothalamic transcription of IL-1β, TNF-α and CCL2 and translation of IL-1β were higher in ME7+TNF-α than NBH+TNF-α animals. TNF-α produced an exaggerated sickness behavior response (hypothermia, weight loss, inactivity) in ME7 animals compared to that in NBH animals. However a single challenge with this dose was not sufficient to produce de novo neuronal death, synaptic loss or tau hyperphosphorylation that was distinguishable from that arising from ME7 alone. The data indicate that acutely elevated TNF-α has robust acute effects on brain function, selectively in the degenerating brain, but more sustained levels may be required to significantly impact on underlying neurodegeneration.

Interleukin-1β overproduction is a common cause for neuropathic pain, memory deficit, and depression following peripheral nerve injury in rodents

BACKGROUND

Chronic pain is often accompanied by short-term memory deficit and depression. Currently, it is believed that short-term memory deficit and depression are consequences of chronic pain. Here, we test the hypothesis that the symptoms might be caused by overproduction of interleukin-1beta (IL-1β) in the injured nerve independent of neuropathic pain following spared nerve injury in rats and mice.

RESULTS

Mechanical allodynia, a behavioral sign of neuropathic pain, was not correlated with short-term memory deficit and depressive behavior in spared nerve injury rats. Spared nerve injury upregulated IL-1β in the injured sciatic nerve, plasma, and the regions in central nervous system closely associated with pain, memory and emotion, including spinal dorsal horn, hippocampus, prefrontal cortex, nucleus accumbens, and amygdala. Importantly, the spared nerve injury-induced memory deficits, depressive, and pain behaviors were substantially prevented by peri-sciatic administration of IL-1β neutralizing antibody in rats or deletion of IL-1 receptor type 1 in mice. Furthermore, the behavioral abnormalities induced by spared nerve injury were mimicked in naïve rats by repetitive intravenous injection of re combinant rat IL-1β (rrIL-1β) at a pathological concentration as determined from spared nerve injury rats. In addition, microglia were activated by both spared nerve injury and intravenous injection of rrIL-1β and the effect of spared nerve injury was substantially reversed by peri-sciatic administration of anti-IL-1β.

CONCLUSIONS

Neuropathic pain was not necessary for the development of cognitive and emotional disorders, while the overproduction of IL-1β in the injured sciatic nerve following peripheral nerve injury may be a common mechanism underlying the generation of neuropathic pain, memory deficit, and depression.

Isolation rearing impaired sensorimotor gating but increased pro-inflammatory cytokines and disrupted metabolic parameters in both sexes of rats

Social isolation rearing (SIR) is an early stress paradigm of deprivation of the social contact since weaning. SIR has been used to investigate the mechanisms behind certain mental illnesses with neurodevelopmental origins, including schizophrenia. In schizophrenia, metabolic dysfunction has become a critical issue with increasing evidence for a possible connection between metabolism and immune systems in which metabolic changes are associated with pro-inflammatory cytokine (pro-CK) levels. The present study employed a rat model of SIR with both sexes to examine behaviors [locomotor activity and prepulse inhibition (PPI)], inflammatory markers [C-reactive protein, interleukin (IL)-1 beta, IL-6, IL-10, tumor necrosis factor (TNF)-alpha and interferon-gamma], and metabolism-related variables (body weight, blood pressure, and the profiles of glycemia and lipid). Our results revealed that around puberty, SIR rats of both sexes exhibited behaviorally a higher locomotor activity and a lower PPI performance. Biochemically, SIR rats had an elevated level of pro-CKs (IL-1 beta, IL-6, TNF-alpha, and interferon-gamma), and metabolic abnormalities (increased insulin resistance, decreased insulin sensitivity, and high blood pressure) in a time-dependent manner. The relationships between pro-CKs and metabolism were sex specific as IL-1 beta and interferon-gamma were correlated to glycemia metabolic indexes in males. The present study demonstrated SIR-induced longitudinal concomitant changes of pro-CKs and metabolic abnormalities, implying a more direct role of these two things in mental dysfunctions with a developmental origin.

Neuroinflammatory changes negatively impact on LTP: A focus on IL-1β

In recent years it has become clear that neuroinflammatory changes develop in the brain with age and that similar, though more profound changes, occur in neurodegenerative conditions and in animal models of neurodegeneration. These changes are linked with deterioration in plasticity and the evidence suggests that a key causative factor is microglial activation and the associated increase in production and release of inflammatory cytokines. Several groups have reported that interleukin (IL)-1β negatively impacts on hippocampal-dependent learning and has an inhibitory effect on LTP although this is concentration-dependent. Similarly other inflammatory cytokines, which are also produced by microglia similarly decrease LTP. The evidence supporting these findings will be reviewed here and will be discussed in the context of considering mechanisms by which the negative impact of neuroinflammation can be ameliorated. This article is part of a Special Issue entitled SI: Brain and Memory.

Glucagon-like peptide-1 protects synaptic and learning functions from neuroinflammation in rodents

Glucagon-like peptide-1 (GLP-1) is derived from the processing of proglucagon in intestinal L-cells and releases insulin from pancreatic β-cells as an incretin. The GLP-1 receptor has been proposed as a possible therapeutic target for the treatment of Alzheimer's disease, in which neuroinflammation is critical in the pathogenesis. The present study investigates whether GLP-1 (7-36) amide, an active fragment of GLP-1, protected against synaptic impairments induced by inflammation-related injurious agents (lipopolysaccharide [LPS], interleukin-1β [IL-1β], and H2 O2). In the Y-maze test, LPS (10 μg/mouse, i.c.v) significantly decreased the percentage alternation. Pretreatment with GLP-1 (7-36) amide (0.09-0.9 nmol/mouse, i.c.v.) prevented an impairment in spontaneous alternation performance. Pretreatment with LPS (10 μg/ml, 2 hr) impaired LTP induction but not paired-pulse facilitation in the CA1 region of rat hippocampal slices. This impairment was prevented by cotreatment with GLP-1 (7-36) amide (50 nM). IL-1β (0.57 nM) or H2 O2 (50 μM) also impaired LTP induction. This impairment was prevented by GLP-1 (7-36) amide (50 nM). These results suggest that GLP-1 (7-36) amide improves the synaptic impairments induced by inflammation-related injurious agents in the CA1 region of the hippocampus.

Modulation of NMDAR subunit expression by TRPM2 channels regulates neuronal vulnerability to ischemic cell death

Neuronal vulnerability to ischemia is dependent on the balance between prosurvival and prodeath cellular signaling. In the latter, it is increasingly appreciated that toxic Ca(2+) influx can occur not only via postsynaptic glutamate receptors, but also through other cation conductances. One such conductance, the Transient receptor potential melastatin type-2 (TRPM2) channel, is a nonspecific cation channel having homology to TRPM7, a conductance reported to play a key role in anoxic neuronal death. The role of TRPM2 conductances in ischemic Ca(2+) influx has been difficult to study because of the lack of specific modulators. Here we used TRPM2-null mice (TRPM2(-/-)) to study how TRPM2 may modulate neuronal vulnerability to ischemia. TRPM2(-/-) mice subjected to transient middle cerebral artery occlusion exhibited smaller infarcts when compared with wild-type animals, suggesting that the absence of TRPM2 is neuroprotective. Surprisingly, field potentials (fEPSPs) recorded during redox modulation in brain slices taken from TRPM2(-/-) mice revealed increased excitability, a phenomenon normally associated with ischemic vulnerability, whereas wild-type fEPSPs were unaffected. The upregulation in fEPSP in TRPM2(-/-) neurons was blocked selectively by a GluN2A antagonist. This increase in excitability of TRPM2(-/-) fEPSPs during redox modulation depended on the upregulation and downregulation of GluN2A- and GluN2B-containing NMDARs, respectively, and on augmented prosurvival signaling via Akt and ERK pathways culminating in the inhibition of the proapoptotic factor GSK3β. Our results suggest that TRPM2 plays a role in downregulating prosurvival signals in central neurons and that TRPM2 channels may comprise a therapeutic target for preventing ischemic damage.

Acetylcholinesterase inhibitors reduce neuroinflammation and -degeneration in the cortex and hippocampus of a surgery stress rat model

Exogenous stress like tissue damage and pathogen invasion during surgical trauma could lead to a peripheral inflammatory response and induce neuroinflammation, which can result in postoperative cognitive dysfunction (POCD). The cholinergic anti-inflammatory pathway is a neurohumoral mechanism that plays a prominent role by suppressing the inflammatory response. Treatments with acetylcholinesterase inhibitors enhance cholinergic transmission and may therefore act as a potential approach to prevent neuroinflammation. In the presence or absence of acetylcholinesterase inhibitors, adult Wistar rats underwent surgery alone or were additionally treated with lipopolysaccharide (LPS). Physostigmine, which can overcome the blood-brain barrier or neostigmine acting only peripheral, served as acetylcholinesterase inhibitors. The expression of pro- and anti-inflammatory cytokines in the cortex, hippocampus, spleen and plasma was measured after 1 h, 24 h, 3 d and 7 d using Real-Time PCR, western blot analysis or cytometric bead array (CBA). Fluoro-Jade B staining of brain slices was employed to elucidate neurodegeneration. The activity of acetylcholinesterase was estimated using a spectrofluorometric method. Surgery accompanied by LPS-treatment led to increased IL-1beta gene and protein upregulation in the cortex and hippocampus but was significantly reduced by physostigmine and neostigmine. Furthermore, surgery in combination with LPS-treatment caused increased protein expression of IL-1, TNF-alpha and IL-10 in the spleen and plasma. Physostigmine and neostigmine significantly decreased the protein expression of IL-1 and TNF-alpha. Neuronal degeneration and the activity of acetylcholinesterase were elevated after surgery with LPS-treatment and reduced by physostigmine and neostigmine. Along with LPS-treatment, acetylcholinesterase inhibitors reduce the pro-inflammatory response as well as neurodegeneration after surgery in the cortex and hippocampus. This combination may represent a tool to break the pathogenesis of POCD.

Interleukin-1β inhibits the differentiation of hippocampal neural precursor cells into serotonergic neurons

Interleukin-1 beta (IL-1β) is one of pro-inflammatory cytokines. Recent studies have shown that IL-1β impairs hippocampal neurogenesis, mediates proliferation and differentiation of multipotent neural precursor cells (NPCs), and exerts effects of anti-proliferation, anti-neurogenesis, and pro-gliogenesis on embryonic hippocampal NPCs. The aim of this study was to examine the effect of IL-1β on the differentiation of hippocampal NPCs into functional serotonergic neurons, which play important roles in the pathophysiology and treatment of depression. Hippocampal NPCs were prepared from the hippocampus of neonatal rats (within 24h after birth). After three passages and phenotyping, hippocampal NPCs were cultured in a differentiating medium with various concentrations (5, 10, and 20 ng/mL) of IL-1β for 7 days. At the endpoint, the serotonergic differentiation of hippocampal NPCs in IL-1β-treated cultures decreased in a dose-dependent manner and this effect was blocked by IL-1ra, an IL-1 receptor antagonist capable of blocking the effects of IL-1 by binding to the same receptor (IL-1R1) without triggering signaling; serotonin in the lysate of the differentiated hippocampal NPCs decreased in IL-1β-treated cultures; and levels of Bcl-2 and phosphorylated extracellular-regulated kinase (pERK) were also lower in differentiated hippocampal NPCs with IL-1β treatment. These results support the hypothesis that IL-1β is an important factor in the stress-associated neuropathology and psychopathology and has relevance to the treatment of depressive symptoms in patients with depression.

Immunomodulation of microglia by docosahexaenoic acid and eicosapentaenoic acid

PURPOSE OF REVIEW

The omega-3 fatty acids (ω-3 FAs) docosahexaenoic acid and eicosapentaenoic acid are dietary components which have been ascribed many different health benefits. Inflammation is present in, and contributes to, pathological conditions in the central nervous system (CNS). Microglia are the primary cells with immune function in the CNS, and inflammation mediated by activated microglia is present in pathological conditions. In this review, we present and discuss findings on the modulation of microglial activities by ω-3 FAs in vivo as well as in vitro, and propose mechanisms for their effects.

RECENT FINDINGS

The majority of studies show that ω-3 FAs have anti-inflammatory effects on microglia. However, phagocytosis is an activity associated with inflammation and is increased by ω-3 FAs. This can be understood in the light of recent research on the resolution of inflammation. Resolution is induced by proresolving factors, which are metabolites of ω-3 FAs. Proresolving factors are anti-inflammatory and have been shown to increase phagocytosis. Other mechanisms of the anti-inflammatory actions of ω-3 FAs involve the peroxisome proliferator-activated receptor-γ, ω-3 FA incorporation into the cell membrane, and inhibition of ion currents.

SUMMARY

Immunomodulation by ω-3 FAs is mediated by several pathways that are interconnected and is a potential therapy for disorders in the CNS.

Contributions of central and systemic inflammation to the pathophysiology of Parkinson's disease

Idiopathic Parkinson's disease (PD) represents a complex interaction between the inherent vulnerability of the nigrostriatal dopaminergic system, a possible genetic predisposition, and exposure to environmental toxins including inflammatory triggers. Evidence now suggests that chronic neuroinflammation is consistently associated with the pathophysiology of PD. Activation of microglia and increased levels of pro-inflammatory mediators such as TNF-α, IL-1β and IL-6, reactive oxygen species and eicosanoids has been reported after post-mortem analysis of the substantia nigra from PD patients and in animal models of PD. It is hypothesised that chronically activated microglia secrete high levels of pro-inflammatory mediators which damage neurons and further activate microglia, resulting in a feed forward cycle promoting further inflammation and neurodegeneration. Moreover, nigrostriatal dopaminergic neurons are more vulnerable to pro-inflammatory and oxidative mediators than other cell types because of their low intracellular glutathione concentration. Systemic inflammation has also been suggested to contribute to neurodegeneration in PD, as lymphocyte infiltration has been observed in brains of PD patients and in animal models of PD, substantiating the current theory of a fundamental role of inflammation in neurodegeneration. We will examine the current evidence in the literature which offers insight into the premise that both central and systemic inflammation may contribute to neurodegeneration in PD. We will discuss the emerging possibility of the use of diagnostic tools such as imaging technologies for PD patients. Finally, we will present the immunomodulatory therapeutic strategies that are now under investigation and in clinical trials as potential neuroprotective drugs for PD.

A role for interleukin-1β in determining the lineage fate of embryonic rat hippocampal neural precursor cells

Neurogenesis occurs in the hippocampus of the developing and adult brain due to the presence of multipotent stem cells and restricted precursor cells at different stages of differentiation. It has been proposed that they may be of potential benefit for use in cell transplantation approaches for neurodegenerative disorders and trauma. Prolonged release of interleukin-1β (IL-1β) from activated microglia has a deleterious effect on hippocampal neurons and is implicated in the impaired neurogenesis and cognitive dysfunction associated with aging, Alzheimer's disease and depression. This study assessed the effect of IL-1β on the proliferation and differentiation of embryonic rat hippocampal NPCs in vitro. We show that IL-1R1 is expressed on proliferating NPCs and that IL-1β treatment decreases cell proliferation and neurosphere growth. When NPCs were differentiated in the presence of IL-1β, a significant reduction in the percentages of newly-born neurons and post-mitotic neurons and a significant increase in the percentage of astrocytes was observed in these cultures. These effects were attenuated by IL-1 receptor antagonist. These data reveal that IL-1β exerts an anti-proliferative, anti-neurogenic and pro-gliogenic effect on embryonic hippocampal NPCs, which is mediated by IL-1R1. The present results emphasise the consequences of an inflammatory environment during NPC development, and indicate that strategies to inhibit IL-1β signalling may be necessary to facilitate effective cell transplantation approaches or in conditions where endogenous hippocampal neurogenesis is impaired.

The polyunsaturated fatty acids, EPA and DPA exert a protective effect in the hippocampus of the aged rat

Age is characterized by deficits in synaptic function identified by decreased performance of aged animals in spatial learning tasks and reduced ability of animals to sustain long term potentiation (LTP). Several cellular and molecular events are correlated with these deficits, many of which are indicative of age-related neuroinflammatory and oxidative cell stress. It is significant that agents which decrease microglial activation are commonly associated with restoration of function. We set out to examine whether the n-3 polyunsaturated fatty acid docosapentaenoic acid (DPA), which is a metabolite of eicosapentaenoic acid (EPA), could modulate the age-related increase in microglial activation and the associated increase in oxidative changes and therefore impact on synaptic function in aged rats. We demonstrate that docosapentaenoic acid possesses neurorestorative effects and is capable of downregulating microglial activation. The data show that it also decreases the coupled activation of sphingomyelinase and caspase 3, probably because of its ability to decrease age-related oxidative changes, and consequently attenuates the age-related decrease in spatial learning and long-term potentiation.

Long-term treadmill exposure protects against age-related neurodegenerative change in the rat hippocampus

The potential of exercise or environmental enrichment to prevent or reverse age-related cognitive decline in rats has been widely investigated. The data suggest that the efficacy of these interventions as neuroprotectants may depend upon the duration and nature of the protocols and age of onset. Investigations of the mechanisms underlying these neuroprotective strategies indicate a potential role for the neurotrophin family of proteins, including nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF). In this study, we have assessed the effects of 8 months of forced exercise, begun in middle-age, on the expression of long-term potentiation (LTP) and on spatial learning in the Morris water maze in aged Wistar rats. We also assessed these measures in a cage control group and in a group of rats exposed to the stationary treadmill for the same duration as the exercised rats. Our data confirm an age-related decline in expression of LTP and in spatial learning concomitant with decreased expression of NGF and BDNF mRNA in dentate gyrus (DG). The age-related impairments in both plasticity and growth factor expression were prevented in the long-term exercised group and, surprisingly, the treadmill control group. Given the extensive handling that the treadmill control group received and their regular exposure to an environment outside the home cage, this group can be considered to have experienced environmentally enriched conditions when compared with the cage control group. Significant correlations were observed between both learning and LTP and the expression of NGF and BDNF mRNA in the dentate gyrus. We conclude that decreased expression of NGF and BDNF in the dentate gyrus of aged rats is associated with impaired LTP and spatial learning. We suggest that the reversal of these age-related impairments by enrichment and exercise may be linked with prevention of the age-related decline in expression of these growth factors and, furthermore, that enrichment is as efficacious as exercise in preventing this age-related decline.

Age matters

The age of an experimental animal can be a critical variable, yet age matters are often overlooked within neuroscience. Many studies make use of young animals, without considering possible differences between immature and mature subjects. This is especially problematic when attempting to model traits or diseases that do not emerge until adulthood. In this commentary we discuss the reasons for this apparent bias in age of experimental animals, and illustrate the problem with a systematic review of published articles on long-term potentiation. Additionally, we review the developmental stages of a rat and discuss the difficulty of using the weight of an animal as a predictor of its age. Finally, we provide original data from our laboratory and review published data to emphasize that development is an ongoing process that does not end with puberty. Developmental changes can be quantitative in nature, involving gradual changes, rapid switches, or inverted U-shaped curves. Changes can also be qualitative. Thus, phenomena that appear to be unitary may be governed by different mechanisms at different ages. We conclude that selection of the age of the animals may be critically important in the design and interpretation of neurobiological studies.

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.

Long-chain polyunsaturated fatty acids modulate interleukin-1beta-induced changes in behavior, monoaminergic neurotransmitters, and brain inflammation in rats

Recent evidence has suggested that an imbalance between membrane (n-3) and (n-6) fatty acids may contribute to the etiology of autoimmune and neurodegenerative diseases. In this study, the mechanisms by which eicosapentaenoic acid (EPA), gamma-linolenic acid (GLA), and arachidonic acid (AA) modulate neurotransmitters, behavior, and brain inflammation were evaluated in rats that received central saline or interleukin-1beta (IL-1) administrations. In rats treated with saline, only the AA-enriched diet significantly increased anxiety-like behavior in the elevated plus maze, which was associated with increased corticosterone secretion. AA also increased the turnover of dopamine (DA), noradrenaline (NA), and serotonin (5-HT) in the amygdala and increased the prostaglandin (PG)E(2) level in the hippocampus. IL-1 administration slowed rat learning in the water maze and increased anxiety-like behavior, changes which were associated with increased homovanillic acid and 5-HT turnover, decreased NA in the hippocampus and amygdala, decreased DA in the frontal cortex, and decreased IL-10 in limbic brain regions. Increased corticosterone secretion following IL-1 administration was accompanied by increased NA turnover in the hippocampus (P < 0.05) and increased PGE(2) concentration (P < 0.01) in the limbic brain regions. Of the 3 diets tested, only EPA attenuated IL-1-induced behavioral changes (P < 0.05 or 0.01), which was associated with the modulation of EPA on the neuroendocrine and immune changes induced by IL-1. GLA reduced hippocampal PGE(2) concentration in rats given IL-1 (P < 0.01). AA did not counteract any of the changes induced by IL-1. These results suggest that EPA, GLA, and AA play different roles in the neuroendocrine-immune network.

Ebselen prevents chronic alcohol-induced rat hippocampal stress and functional impairment

BACKGROUND

Most of the previously published data suggest a role for oxidative or nitrosative stress in ethanol-induced nervous system damage. Moreover, ethanol is able to impair learning abilities in adult mammalian brain, a process suggested to be directly related to hippocampal neurogenesis. Ebselen, a synthetic compound with antioxidant properties, is able to prevent ethanol-induced impairment of neurogenesis in adult rats. The aim of the present work was to further demonstrate the ability of ebselen to prevent biochemical alterations, and preserve long-term potentiation (LTP) and learning abilities, in the hippocampus of chronic alcoholic adult rats.

METHODS

Biochemical markers of oxidative stress (glutathione and malondialdehyde) were assayed in hippocampi of control rats and animals fed a liquid alcoholic diet (Lieber-De Carli) supplemented or not with ebselen. Long-term potentiation and hippocampal-dependent tests were studied in all animal groups.

RESULTS

The hippocampal concentrations of glutathione and malondialdehyde were decreased and increased, respectively, in alcohol-treated animals, and did not differ from those of the control and the alcohol+ebselen groups. Long-term potentiation in hippocampal slices from ethanol-treated animals was prevented, when compared with controls, and occurred with a similar profile in control animals and in the alcohol+ebselen groups. Learning ability was tested with the Morris water maze test. Escape latencies were higher in ethanol-treated rats than in control animals or the ones treated with ethanol+ebselen.

CONCLUSIONS

The results herein strongly suggest that oxidative mechanisms may underlie the hippocampal effects of ethanol in adult rats, in view of the protective effect of ebselen.

Annurca apple-rich diet restores long-term potentiation and induces behavioral modifications in aged rats

The impairment of brain functions during aging could be prevented by an increase in antioxidative defenses. In fact, dietary manipulation with antioxidants or with antioxidant-rich extracts from vegetables and fruit can ameliorate age-associated behavioral alterations. Moreover, dietary supplements of antioxidants can reverse the age-dependent impairment to sustain long-term potentiation (LTP). There is evidence that fresh fruit could be more effective than antioxidant supplements or fruit and vegetable extracts but the effect of a diet enriched in fresh fruit on brain aging process has not been investigated until now. The aim of the present study was to verify whether dietary manipulation with fresh apples could influence age-induced changes in motor and emotional behavior and in LTP in rats. Groups of aged and young rats were fed with a standard diet or a diet supplemented with fresh apples of annurca variety for 10 weeks and assessed for behavioral performance in the open field and elevated plus maze tests and for the ability to sustain LTP. The brains were then removed, histochemically stained for superoxide dismutase (SOD) and SOD activity was measured by computer-assisted image analysis. The aged rats fed with the enriched diet showed a significant decrease in the anxiety level. Moreover, they improved in the ability to sustain LTP, reaching the level of the young rats. SOD activity was increased in the aged rats fed with the standard diet whereas SOD activity in the hippocampus of the aged rats treated with annurca apple was at the level of the young animals. These results suggest that a diet rich in annurca apple could have an important role in health-care during aging.

Age-related changes in neutral sphingomyelin-specific phospholipase C activity in striatum, hippocampus, and frontal cortex: Implication for sensitivity to stress and inflammation

Previous studies show the enrichment of mammalian brain with neutral sphingomyelin-specific phospholipase C (ceramide-phosphocholine phosphodiesterase, EC 3.1.4.12; N-Sase), a key enzyme of sphingolipid metabolism and sphingolipid-induced signaling.

OBJECTIVE

The objective of this study was to evaluate the membrane-associated and cytosolic N-Sase activities in the brain regions associated with behavior (striatum, hippocampus, and frontal cortex).

RESULTS

Results showed higher membrane-associated N-Sase activity as compared to the N-Sase activity in the cytosolic fractions of all the evaluated brain regions. In the hippocampus, the N-Sase activity was significantly higher than in the striatum and cortex. In addition, age-related changes in the hippocampal N-Sase activities were profoundly higher than in the respective fractions isolated from the striatum and cortex. Age-related decreases in the hippocampal and striatal cytosolic N-Sase activities were accompanied by increases in the membrane N-Sase activities in those brain regions. There was a significant increase in the cortical membrane-associated N-Sase activity with age; however, to a much lesser extend than in other brain regions. The increase in the hippocampal membrane-associated N-Sase activity was accompanied by a higher expression of the inflammatory marker, interleukin-1 beta (IL-1 beta), with age. One of the important findings of the present study is the region-specific expression of heat shock protein 70 (hsp70). Frontal cortex showed lower hsp70 expression in both young and old age groups as compared to the striatal and hippocampal hsp70 levels which can contribute to the recently reported higher cortical sensitivity to oxidative stress.

CONCLUSION

In conclusion (a) our results, for the first time to our knowledge, demonstrated the association between the N-Sase activity and the stress/inflammatory markers expression in the brain regions controlling behavior; (b) these findings suggest the role of N-Sase as a contributor to the increased stress and inflammatory sensitivity among the brain regions with age.

Competitive interactions between endogenous LTD and LTP in the hippocampus underlie the storage of emotional memories and stress-induced amnesia

This speculative review serves two purposes. First, it as an extension of the ideas we developed in a previous review (Diamond et al., Hippocampus, 2004;14:281-291), and second, it is a rebuttal to Abraham's (Hippocampus, 2004;14:675-676) critique of that review. We had speculated on the functional significance of the finding that post-training LTP induction produces retrograde amnesia. We noted the similarities between the findings that strong tetanizing stimulation can produce LTP and retrograde amnesia, and that a strong emotional experience can produce a long-lasting memory and retrograde amnesia, as well. The commonalities between LTP induction and emotional learning provided the basis of our hypothesis that an emotional experience generates endogenous LTD/depotentiation, which reverses synaptic plasticity formed during previous learning experiences, and endogenous LTP, which underlies the storage of new information. Abraham raised several concerns with our review, including the criticism that our speculation "falters because there is no evidence that stress causes LTD or depotentiation," and that research on stress and hippocampus has "failed to report any LTP-like changes." Abraham's points are well-taken because stress, in isolation, does not appear to generate long-lasting changes in baseline measures of hippocampal excitability. Here, within the context of a reply to Abraham's critique, we have provided a review of the literature on the influence of stress, novelty, fear conditioning, and the retrieval of emotional memories on cognitive and physiological measures of hippocampal functioning. An emphasis of this review is our hypothesis that endogenous forms of depotentiation, LTD and LTP are generated only when arousing experiences occur in conjunction with memory-related activation of the hippocampus and amygdala. We conclude with speculation that interactions among the different forms of endogenous plasticity underlie a form of competition by synapses and memories for access to retrieval resources.

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.

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.

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.

Sleep protects excitatory cortical circuits against oxidative damage

Activity in excitatory cortical pathways increases the oxidative metabolism of the brain and the risk of oxidative damage. Oxyradicals formed during periods of activity are mopped up by neural pools of nuclear factor kappa-B resulting in their activation and translocation to cell nuclei. During waking hours, glucocorticoids inhibit transactivation by nuclear factor kappa-B, increase central norepinephrine release, and elevate expression of prostaglandin D2. The build-up of nuclear factor kappa-B and prostaglandin D2 produces sleep pressures leading to sleep onset, normally gated by circadian melatonin release. During slow wave sleep nuclear factor kappa-B induces transcription of synaptogenic and antioxidant products and synaptic remodeling follows. Synaptically remodeled neural circuits have modified conductivity patterns and timescales and need to be resynchronized with existing unmodified neural circuits. The resynchronization process, mediated by theta rhythm, occurs during rapid eye movement sleep and is orchestrated from pontine centers. Resynchronization of remodeled neural circuits produces dreams. The waking state results upon successful resynchronization. Rapid eye movement sleep deprivation results in a lack of resynchronization and leads to cognitive inefficiencies. The model presented here proposes that the primary purpose of sleep is to protect cortical circuits against oxidative damage by reducing cortical activity and by remodeling and resynchronizing cortical circuits during this period of reduced activity to sustain new patterns of activation more effectively.

Analysis of Interleukin-1β-induced Cell Signaling Activation in Rat Hippocampus following Exposure to Gamma Irradiation

Among the many reported effects of irradiation in cells is activation of the stress-activated protein kinase, c-Jun N-terminal kinase (JNK), which has been shown to result in apoptotic cell death. The trigger that leads to JNK activation has not been identified, although, in rat hippocampus at least, irradiation-induced apoptosis has been coupled with increased accumulation of reactive oxygen species (ROS). Significantly, irradiation-induced changes in hippocampus are abrogated by treatment of rats with the polyunsaturated fatty acid, eicosapentaenoic acid (EPA). A close coupling between ROS accumulation and concentration of the pro-inflammatory cytokine, interleukin-1 beta (IL-1 beta) in hippocampus has been reported, and the evidence suggests that IL-1 beta may be responsible for the enhanced ROS production. Here we set out to assess the possibility that whole body gamma-irradiation increases IL-1 beta concentration in hippocampus and to investigate the consequences of such a change. We present evidence that reveals that the irradiation-induced increase in IL-1 beta concentration in hippocampus is accompanied by increased expression of IL-1 type I receptor and IL-1 accessory protein and increased activation of IL-1 receptor-activated kinase. These changes, which were coupled with increased activation of JNK and evidence of apoptotic cell death, were absent in hippocampus of rats that received EPA treatment. Significantly, EPA treatment enhanced hippocampal IL-10 concentration that was inversely correlated with IL-1 beta concentration. The data are consistent with the idea that EPA exerts anti-inflammatory and neuroprotective effects in the central nervous system.

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.

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.

The vitamin-E analog trolox and the NMDA antagonist MK-801 protect pyramidal neurons in hippocampal slice cultures from IL-1beta-induced neurodegeneration

The neurotoxic effect of the pro-inflammatory cytokine interleukin (IL)-1beta was studied in monolayer cultures, obtained using roller-drum incubation of hippocampal slices from neonatal Sprague Dawley rats. Following exposure to recombinant rat IL-1beta for four days, a concentration dependent loss was observed in the number of NMDAR1 receptor subunit immunoreactive pyramidal neurons in the cultures, reaching significance at 10 ng/ml rIL-1beta. Also incubation with recombinant mouse IL-1beta caused a loss of pyramidal neurons, with a significant effect at a concentration of 30 pg/ml. The vitamin E analog trolox (30 microM) was found to exert a protective effect against the rIL-1beta induced neuronal degeneration. A neuroprotective action against rIL-1beta was also found after co-incubation with the NMDA antagonist dizocilpine (MK-801; 30 microM), while no protection was found with the GABAA mimetic clomethiazole. Hence, the pro-inflammatory cytokine IL-1beta is neurotoxic to hippocampal pyramidal neurons when studied in an in vitro system with advanced phenotypic characteristics. The neuroprotective effects exerted by trolox and MK-801 suggest that free radicals and NMDA receptor-mediated processes are involved in IL-1beta -induced neurodegeneration.

Neuroprotective effect of eicosapentaenoic acid in hippocampus of rats exposed to gamma-irradiation

Exposure to irradiation leads to detrimental changes in several cell types. In this study we assessed the changes induced in hippocampus by exposure of rats to whole body irradiation; the findings reveal that irradiation leads to apoptotic cell death in hippocampus, and as a consequence, long term potentiation in perforant path-granule cell synapses is markedly impaired. The evidence is consistent with the view that irradiation induced an increase in reactive oxygen species and that this leads to stimulation of the stress-activated protein kinase, JNK, and activation of the transcription factor, c-Jun. Consequent upon activation of JNK, a cascade of cell signaling events was stimulated that ultimately resulted in apoptosis, as suggested by parallel increases in cytochrome c translocation, caspase-3 activation, poly(ADP-ribose) polymerase cleavage, and terminal dUTP nick-end labeling staining. Treatment of rats with eicosapentaenoic acid inhibited the irradiation-induced increase in reactive oxygen species production and the subsequent cellular signaling events, suggesting that oxidative stress triggered apoptotic cell death in the hippocampus of rats exposed to irradiation. Significantly, when the compromise in cell viability induced by irradiation was prevented by eicosapentaenoic acid, long term potentiation was sustained in a manner similar to that in the sham-treated control group.