Inflammatory response and glia activation in developing rat hippocampus after status epilepticus

The Isotropic Fractionator as a Tool for Quantitative Analysis in Central Nervous System Diseases

One major aim in quantitative and translational neuroscience is to achieve a precise and fast neuronal counting method to work on high throughput scale to obtain reliable results. Here, we tested the isotropic fractionator (IF) method for evaluating neuronal and non-neuronal cell loss in different models of central nervous system (CNS) pathologies. Sprague-Dawley rats underwent: (i) ischemic brain damage; (ii) intraperitoneal injection with kainic acid (KA) to induce epileptic seizures; and (iii) monolateral striatal injection with quinolinic acid (QA) mimicking human Huntington's disease. All specimens were processed for IF method and cell loss assessed. Hippocampus from KA-treated rats and striatum from QA-treated rats were carefully dissected using a dissection microscope and a rat brain matrix. Ischemic rat brains slices were first processed for TTC staining and then for IF. In the ischemic group the cell loss corresponded to the neuronal loss suggesting that hypoxia primarily affects neurons. Combining IF with TTC staining we could correlate the volume of lesion to the neuronal loss; by IF, we could assess that neuronal loss also occurs contralaterally to the ischemic side. In the epileptic group we observed a reduction of neuronal cells in treated rats, but also evaluated the changes in the number of non-neuronal cells in response to the hippocampal damage. In the QA model, there was a robust reduction of neuronal cells on ipsilateral striatum. This neuronal cell loss was not related to a drastic change in the total number of cells, being overcome by the increase in non-neuronal cells, thus suggesting that excitotoxic damage in the striatum strongly activates inflammation and glial proliferation. We concluded that the IF method could represent a simple and reliable quantitative technique to evaluate the effects of experimental lesions mimicking human diseases, and to consider the neuroprotective/anti-inflammatory effects of different treatments in the whole brain and also in discrete regions of interest, with the potential to investigate non-neuronal alterations. Moreover, IF could be used in addition or in substitution to classical stereological techniques or TTC staining used so far, since it is fast, precise and easily combined with complex molecular analysis.

Time-course changes of hippocalcin expression in the mouse hippocampus following pilocarpine-induced status epilepticus

Hippocalcin participates in the maintenance of neuronal calcium homeostasis. In the present study, we examined the time-course changes of neuronal degeneration and hippocalcin protein level in the mouse hippocampus following pilocarpine-induced status epilepticus (SE). Marked neuronal degeneration was observed in the hippocampus after SE in a time-dependent manner, although neuronal degeneration differed according to the hippocampal subregions. Almost no hippocalcin immunoreactivity was detected in the pyramidal neurons of the cornu ammonis 1 (CA1) region from 6 h after SE. However, many pyramidal neurons in the CA2 region showed hippocalcin immunoreactivity until 24 h after SE. In the CA3 region, only a few hippocalcin immunoreactive cells were observed at 12 h after SE, and almost no hippocalcin immunoreactivity was observed in the pyramidal neurons from 24 h after SE. Hippocalcin immunoreactivity in the polymorphic cells of the dentate gyrus was markedly decreased from 6 h after SE. In addition, hippocalcin protein level in the hippocampus began to decrease from 6 h after SE, and was significantly decreased at 24 h and 48 h after pilocarpine-induced SE. These results indicate that marked reduction of hippocalcin level may be closely related to neuronal degeneration in the hippocampus following pilocarpine-induced SE.

Interleukin-1β increases neuronal death in the hippocampal dentate gyrus associated with status epilepticus in the developing rat

BACKGROUND

Interleukin-1β (IL-1β) increases necrotic neuronal cell death in the CA1 area after induced status epilepticus (SE) in developing rats. However, it remains uncertain whether IL-1β has a similar effect on the hippocampal dentate gyrus (DG). In this study, we analysed the effects of IL-1β on 14-day-old Wistar rats experiencing DG neuronal death induced by SE.

METHODS

SE was induced with lithium-pilocarpine. Six hours after SE onset, a group of pups was injected with IL-1β (at 0, 0.3, 3, 30, or 300ng/μL) in the right ventricle; another group was injected with IL-1β receptor (IL-1R1) antagonist (IL-1Ra, at 30ng/μL) of IL-1RI antagonist (IL-1Ra) alone, and additional group with 30ng/μL of IL-1Ra plus 3ng/μL of IL-1β. Twenty-four hours after SE onset, neuronal cell death in the dentate gyrus of the dorsal hippocampus was assessed using haematoxylin-eosin staining. Dead cells showed eosinophilic cytoplasm and condensed and fragmented nuclei.

RESULTS

We observed an increased number of eosinophilic cells in the hippocampal DG ipsilateral to the site of injection of 3ng/μL and 300ng/μL of IL-1β in comparison with the vehicle group. A similar effect was observed in the hippocampal DG contralateral to the site of injection of 3ng/μL of IL-1β. Administration of both of IL-1β and IL-1Ra failed to prevent an increase in the number of eosinophilic cells.

CONCLUSION

Our data suggest that IL-1β increases apoptotic neuronal cell death caused by SE in the hippocampal GD, which is a mechanism independent of IL-1RI activation.

1400W, a highly selective inducible nitric oxide synthase inhibitor is a potential disease modifier in the rat kainate model of temporal lobe epilepsy

Status epilepticus (SE) initiates epileptogenesis to transform normal brain to epileptic state which is characterized by spontaneous recurrent seizures (SRS). Prior to SRS, progressive changes occur in the brain soon after SE, for example, loss of blood-brain barrier (BBB) integrity, neuronal hyper-excitability (epileptiform spiking), neuroinflammation [reactive gliosis, high levels of reactive oxygen/nitrogen species (ROS/RNS)], neurodegeneration and synaptic re-organization. Our hypothesis was that modification of early epileptogenic events will alter the course of disease development and its progression. We tested the hypothesis in the rat kainate model of chronic epilepsy using a novel disease modifying drug, 1400W, a highly selective inhibitor of inducible nitric oxide synthase (iNOS/NOS-II). In an in vitro mouse brain slice model, using a multi-electrode array system, co-application of 1400W with kainate significantly suppressed kainate-induced epileptiform spiking. In the rats, in vivo, 4h after the induction of SE with kainate, 1400W (20mg/kg, i.p.) was administered twice daily for three days to target early events of epileptogenesis. The rats were subjected to continuous (24/7) video-EEG monitoring, remotely, for six months from epidurally implanted cortical electrodes. The 1400W treatment significantly reduced the epileptiform spike rate during the first 12-74h post-SE, which resulted in >90% reduction in SRS in long-term during the six month period when compared to the vehicle-treated control group (257±113 versus 19±10 episodes). Immunohistochemistry (IHC) of brain sections at seven days and six months revealed a significant reduction in; reactive astrogliosis and microgliosis (M1 type), extravascular serum albumin (a marker for BBB leakage) and neurodegeneration in the hippocampus, amygdala and entorhinal cortex in the 1400W-treated rats when compared to the vehicle control. In the seven day group, hippocampal Western blots revealed downregulation of inwardly-rectifying potassium (Kir 4.1) channels and glutamate transporter-1 (GLT-1) levels in the vehicle group, and 1400W treatment partially reversed Kir 4.1 levels, however, GLT-1 levels were unaffected. In the six month group, a significant reduction in mossy fiber staining intensity in the inner molecular layer of the dentate gyrus was observed in the 1400W-treated group. Overall these findings demonstrate that 1400W, by reducing the epileptiform spike rate during the first three days of post-insult, potentially modifies epileptogenesis and the severity of chronic epilepsy in the rat kainate model of TLE.

Spatiotemporal profile of Map2 and microglial changes in the hippocampal CA1 region following pilocarpine-induced status epilepticus

Status epilepticus (SE) triggers pathological changes to hippocampal dendrites that may promote epileptogenesis. The microtubule associated protein 2 (Map2) helps stabilize microtubules of the dendritic cytoskeleton. Recently, we reported a substantial decline in Map2 that coincided with robust microglia accumulation in the CA1 hippocampal region after an episode of SE. A spatial correlation between Map2 loss and reactive microglia was also reported in human cortex from refractory epilepsy. New evidence supports that microglia modulate dendritic structures. Thus, to identify a potential association between SE-induced Map2 and microglial changes, a spatiotemporal profile of these events is necessary. We used immunohistochemistry to determine the distribution of Map2 and the microglia marker IBA1 in the hippocampus after pilocarpine-induced SE from 4 hrs to 35 days. We found a decline in Map2 immunoreactivity in the CA1 area that reached minimal levels at 14 days post-SE and partially increased thereafter. In contrast, maximal microglia accumulation occurred in the CA1 area at 14 days post-SE. Our data indicate that SE-induced Map2 and microglial changes parallel each other’s spatiotemporal profiles. These findings may lay the foundation for future mechanistic studies to help identify potential roles for microglia in the dendritic pathology associated with SE and epilepsy.

Peripheral leukocyte profile in people with temporal lobe epilepsy reflects the associated proinflammatory state

INTRODUCTION

Markers of low-grade peripheral inflammation have been reported amongst people with epilepsy. The mechanisms underlying this phenomenon are unknown. We attempted to characterize peripheral immune cells and their activation status in people with temporal lobe epilepsy (TLE) and healthy controls.

METHODS AND RESULTS

Twenty people with TLE and 19 controls were recruited, and peripheral blood lymphocyte and monocyte subsets evaluated ex vivo by multi-color flow cytometry. People with TLE had higher expression of HLA-DR, CD69, CTLA-4, CD25, IL-23R, IFN-γ, TNF and IL-17 in CD4(+) lymphocytes than controls. Granzyme A, CTLA-4, IL-23R and IL-17 expression was also elevated in CD8(+) T cells from people with TLE. Frequency of HLA-DR in CD19(+) B cells and regulatory T cells CD4(+)CD25(+)Foxp3(+) producing IL-10 was higher in TLE when compared with controls. A negative correlation between CD4(+) expressing co-stimulatory molecules (CD69, CD25 and CTLA-4) with age at onset of seizures was found. The frequency of CD4(+)CD25(+)Foxp3(+) cells was also positively correlated with age at onset of seizures.

CONCLUSION

Immune cells of people with TLE show an activation profile, mainly in effector T cells, in line with the low-grade peripheral inflammation.

Kainic Acid-Induced Excitotoxicity Experimental Model: Protective Merits of Natural Products and Plant Extracts

Excitotoxicity is well recognized as a major pathological process of neuronal death in neurodegenerative diseases involving the central nervous system (CNS). In the animal models of neurodegeneration, excitotoxicity is commonly induced experimentally by chemical convulsants, particularly kainic acid (KA). KA-induced excitotoxicity in rodent models has been shown to result in seizures, behavioral changes, oxidative stress, glial activation, inflammatory mediator production, endoplasmic reticulum stress, mitochondrial dysfunction, and selective neurodegeneration in the brain upon KA administration. Recently, there is an emerging trend to search for natural sources to combat against excitotoxicity-associated neurodegenerative diseases. Natural products and plant extracts had attracted a considerable amount of attention because of their reported beneficial effects on the CNS, particularly their neuroprotective effect against excitotoxicity. They provide significant reduction and/or protection against the development and progression of acute and chronic neurodegeneration. This indicates that natural products and plants extracts may be useful in protecting against excitotoxicity-associated neurodegeneration. Thus, targeting of multiple pathways simultaneously may be the strategy to maximize the neuroprotection effect. This review summarizes the mechanisms involved in KA-induced excitotoxicity and attempts to collate the various researches related to the protective effect of natural products and plant extracts in the KA model of neurodegeneration.

A postnatal peak in microglial development in the mouse hippocampus is correlated with heightened sensitivity to seizure triggers

BACKGROUND

Explosive synaptogenesis and synaptic pruning occur in the hippocampus during the first two weeks of postnatal life, coincident with a heightened susceptibility to seizures in rodents. To determine the temporal correlation between microglial development and age-dependent susceptibility and response to seizures, we quantified developmental changes in basal microglia levels and seizure-induced microglial activation in the hippocampus of Cx3Cr1(GFP /+) transgenic mice.

METHODS

Basal levels of microglia were quantified in the hippocampi of Cx3Cr1(GFP /+) mice at P0, P5, P10, P15, P20, P25, P30, P40, and P60. Seizure susceptibility and seizure-induced microglial activation were assessed in response to febrile seizures (lipopolysaccharide followed by hyperthermia) and kainic acid-induced status epilepticus.

RESULTS

The density of microglia within the hippocampus increased rapidly after birth, reaching a peak during the second week of life - the age at which the animals became most vulnerable to seizure triggers. In addition, this peak of microglial development and seizure vulnerability during the second postnatal week represented the time of maximal seizure-induced microglia activation.

CONCLUSIONS

Overreactive innate immunity mediated by activated microglia may exacerbate acute injury to neuronal synapses and contribute to the long-term epileptogenic effects of early-life seizures. Anti-inflammatory therapy targeting excessive production of inflammatory mediators by activated microglia, therefore, may be an effective age-specific therapeutic strategy to minimize neuronal dysfunction and prevent increases in susceptibility to subsequent seizures in developing animals.

The anti-inflammatory activity of duloxetine, a serotonin/norepinephrine reuptake inhibitor, prevents kainic acid-induced hippocampal neuronal death in mice

Duloxetine (DXT), a potent serotonin/norepinephrine reuptake inhibitor, is widely used in the treatment of major depressive disorder. In the present study, we examined the effects of DXT treatment on seizure behavior and excitotoxic neuronal damage in the mouse hippocampal CA3 region following intraperitoneal kainic acid (KA) injection. DXT treatment showed no effect on KA-induced behavioral seizure activity. However, treatment with 10mg/kg DXT reduced KA-induced neuronal death in the hippocampal CA3 region at 72h after KA administration, and treatment with 20 and 40mg/kg DXT showed a noticeable neuroprotection in the hippocampal CA3 region after KA injection. In addition, KA-induced activations of microglia and astrocytes as well as KA-induced increases of TNF-α and IL-1β levels were also suppressed by DXT treatment. These results indicate that DXT displays the neuroprotective effect against KA-induced excitotoxic neuronal death through anti-inflammatory action.

Subventricular zone neural progenitors reverse TNF-alpha effects in cortical neurons

INTRODUCTION

Tumor necrosis factor alpha (TNFα) plays a physiological role in controlling synaptic transmission and plasticity in the healthy central nervous system by modulating glutamate receptor trafficking to the plasma membrane. TNFα expression is also rapidly induced in response to tissue injury and infection. By promoting the insertion of Ca(2+) permeable-AMPA receptors into the neuronal plasma membrane, this cytokine may cause excessive Ca(2+) influx into neurons, thus enhancing neuronal death.

METHODS

Primary cultures of cortical neurons were obtained from E18 foetal mice and incubated for 24 h with adult neural stem cells (aNPCs) either stimulated with lipopolysaccharide (LPS(+)aNPCs) or not (aNPCs). Cultures were treated with TNFα (100 ng/ml), and electrophysiological recordings were performed in different conditions to evaluate the effect of the cytokine on neuronal transmission.

RESULTS

In this study, we demonstrate that aNPCs from the subventricular zone reverse the effects induced by the cytokine. Moreover, we show that the effect of aNPCs on cortical neurons is mediated by cannabinoid CB1 receptor activation.

CONCLUSION

These data suggest that the role of aNPCs in preventing excitatory neurotransmission potentiation induced by TNFα on cortical neurons may have important implications for pathologies characterized by an inflammatory component affecting cortical neurons such as Alzheimer's disease.

Inflammation induced at different developmental stages affects differently the range of microglial reactivity and the course of seizures evoked in the adult rat

BACKGROUND

In the brain, inflammation occurs following a variety of types of brain damage, including epileptic seizures. Proinflammatory cytokines, like IL-1β or TNFα, can increase neuronal excitability and initiate spontaneous seizures or epileptogenesis. Recent studies indicate that the effects can be attenuated or even abolished in animals subjected to inflammation-inducing treatments at earlier developmental stages, termed "preconditioning". Immunocompetent microglial cells display particular sensitivity to subtle brain pathologies showing a morphological continuum from resting to reactive forms. Following inflammation, multiple ramified processes of resting microglia become gradually shorter, and the cells transform into macrophages. Parameters of the morphological variations were used here as indicators of the nervous tissue reactivity to seizures in adult rats experiencing inflammation at earlier stages of postnatal development.

METHODS

Systemic inflammation was induced with lipopolysaccharide (LPS) in 6-day-old or 30-day-old rats. In two-month-old survivors of the inflammatory status, seizures were evoked with pilocarpine injection. The seizure intensity was scored during a six-hour continuous observation period following the injection. Brain sections were immunostained for Iba1 to visualize microglia. Thereafter, morphology of microglial cells located in the hippocampal formation was analyzed using parameters such as solidity, circularity, ramification index, and area.

RESULTS

In naïve rats, seizure-induced transformations of microglial cells were reflected by strong changes in the parameters of their morphology. However, in the adult rats pretreated with LPS on their 6th or 30th postnatal days, the seizure-induced changes were significantly reduced, and microglial morphology remained significantly closer to normal. Significant amelioration of the acute phase of seizures was observed only when inflammation was induced in 30-day-old, but not in 6-day-old, rats.

CONCLUSIONS

The results confirm previous reports that moderate inflammation protects the nervous tissue from subsequent damage by reducing influences of proinflammatory factors on reactive glial cells. The young-age inflammation may have age-dependent effects on susceptibility to seizures induced in adulthood. This article is part of a Special Issue entitled "Status Epilepticus".

The role of leptin in the sporadic form of Alzheimer's disease. Interactions with the adipokines amylin, ghrelin and the pituitary hormone prolactin

Leptin (Lep) is emerging as a pivotal molecule involved in both the early events and the terminal phases of Alzheimer's disease (AD). In the canonical pathway, Lep acts as an anorexigenic factor via its effects on hypothalamic nucleus. However, additional functions of Lep in the hippocampus and cortex have been unravelled in recent years. Early events in the sporadic form of AD likely involve cellular level alterations which can have an effect on food intake and metabolism. Thus, AD can be conceivably interpreted as a multiorgan pathology that not only results in a dramatic neuronal loss in brain areas such as the hippocampus and the cortex (ultimately leading to a significant cognitive impairment) but as a disease which also affects body-weight homeostasis. According to this view, body-weight control disruptions are to be expected in both the early- and late-stage AD, concomitant with changes in serum Lep content, alterations in Lep transport across the blood-brain barrier (BBB) and Lep receptor-related signalling abnormalities. Lep is a member of the adipokine family of molecules, while the Lep receptor belongs to the class I cytokine receptors. Since cellular response to adipokine signalling can be either potentiated or diminished as a result of specific ligand-receptor interactions, Lep interactions with other members of the adipokine family including amylin, ghrelin and hormones such as prolactin require further investigation. In this review, we provide a general perspective on the functions of Lep in the brain, with a particular focus on the sporadic AD.

FTY720 attenuates excitotoxicity and neuroinflammation

Background

FTY720 (fingolimod, Gilenya™), a structural analog of sphingosine-1-phosphate (S1P), is the first oral drug approved for treatment the relapsing-remitting form of multiple sclerosis (MS), and its efficacy has been related to induced lymphopenia and consequent immunosuppression via modulation of S1P₁ receptors (S1P₁R). However, due to its lipophilic nature, FTY720 crosses the blood brain barrier (BBB) and could act directly on neural cells. In this study, we investigated the effectiveness of FTY720 as a neuroprotective agent using in vitro and in vivo models of excitotoxic neuronal death and examined if FTY720 exerts a direct action on neurons, or/and an indirect modulation of inflammation-mediated neurodegeneration as a possible mechanism of neuroprotection.

Methods

Primary neuronal and organotypic cortical cultures were treated with N-methyl-D-aspartic acid (NMDA) to induce excitotoxic cell death (measured by lactate dehydrogenase (LDH) assay or propidium iodide uptake, respectively). The effects of FTY720 treatment (10, 100 and 1,000 nM) on neuronal survival were examined. As an in vivo model of neuronal death and inflammation, we used intracerebroventricular (icv) administration of kainic acid (KA; 0.5 μg/2 μl) in Sprague–Dawley rats. FTY720 was applied icv (1 μg/2 μl), together with KA, plus intraperitoneally (ip; 1 mg/kg) 24 h before, and daily, until sacrifice 3 days after icv. Rats were evaluated for neurological score, neuronal loss in CA3 hippocampal region and activation of microglia at the lesion site. In addition, we tested FTY720 as a modulator of microglia responses using microglial cell cultures activated with lipopolysaccharide (LPS) and its effects in stress signalling pathways using western blotting for p38 and JNK1/2 mitogen-activated protein kinases (MAPKs).

Results

FTY720 was able to reduce excitotoxic neuronal death in vitro. Moreover, in vivo repeated FTY720 administration attenuated KA-induced neurodegeneration and microgliosis at the CA3 lesion site. Furthermore, FTY720 negatively modulates p38 MAPK in LPS-activated microglia, whereas it had no effect on JNK1/2 activation.

Conclusions

These data support a role for FTY720 as a neuroprotective agent against excitotoxin-induced neuronal death and as a negative modulator of neuroinflammation by targeting the p38 MAPK stress signalling pathway in microglia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-015-0308-6) contains supplementary material, which is available to authorized users.

Effect of pioglitazone on excitotoxic neuronal damage in the mouse hippocampus

Pioglitazone (PGZ), a synthetic peroxisome proliferator-activated receptor γ agonist, is known to regulate inflammatory process and to have neuroprotective effects against neurological disorders. In the present study, we examined the effects of 30 mg/kg PGZ on excitotoxic neuronal damage and glial activation in the mouse hippocampus following intracerebroventricular injection of kainic acid (KA). PGZ treatment significantly reduced seizure-like behavior. PGZ had the neuroprotective effect against KA-induced neuronal damage and attenuated the activations of astrocytes and microglia in the hippocampal CA3 region. In addition, MPO and NFκB immunoreactivities in the glial cells were also decreased in the PGZ-treated group. These results indicate that PGZ had anticonvulsant and neuroprotective effects against KA-induced excitotocix injury, and that neuroprotective effect of PGZ might be due to the attenuation of KA-induced activation in astrocytes and microglia as well as KA-induced increases in MPO and NFκB.

Role for pro-inflammatory cytokines in regulating expression of GABA transporter type 1 and 3 in specific brain regions of kainic acid-induced status epilepticus

In general, pro-inflammatory cytokines (PICs) contribute to regulation of epilepsy-associated pathophysiological processes in the central nerve system. In this report, we examined the specific activation of PICs, namely IL-1β, IL-6 and TNF-α in rat brain after kainic acid (KA)-induced status epilepticus (SE). Also, we examined the role played by PICs in regulating expression of GABA transporter type 1 and 3 (GAT-1 and GAT-3, respectively), which are the two important subtypes of GATs responsible for the regulation of extracellular GABA levels in the brain. Our results show that IL-1β, IL-6 and TNF-α were significantly increased in the parietal cortex, hippocampus and amygdala of KA-rats as compared with sham control animals (P < 0.05, KA rats vs. control rats). KA-induced SE also significantly increased (P < 0.05 vs. controls) the protein expression of GAT-1 and GAT-3 in those brain regions. In addition, central administration of antagonists to IL-1β and TNF-α receptors significantly attenuated amplified GAT-1 and GAT-3 (P < 0.05 vs. vehicle control for each antagonist group). However, antagonist to IL-6 receptor failed to attenuate enhancement in expression of GAT-1 and GAT-3 induced by KA-induced SE. Overall, our data demonstrate that PIC pathways are activated in the specific brain regions during SE which thereby selectively leads to upregulation of GABA transporters. As a result, it is likely that de-inhibition of GABA system is increased in the brain. This support a role for PICs in engagement of the adaptive mechanisms associated with epileptic activity, and has pharmacological implications to target specific PICs for neuronal dysfunction and vulnerability related to epilepsy.

Inflammation and epilepsy in the developing brain: clinical and experimental evidence

There is an increasing evidence to support a role of inflammatory processes in epilepsy. However, most clinical and experimental studies have been conducted in adult patients or using adult rodents. The pediatric epilepsies constitute a varied group of diseases that are most frequently age specific. In this review, we will focus on the possible role of inflammation in pediatric epilepsy syndromes. We will first describe the clinical data available and provide an overview of our current understanding of the role of inflammation in these clinical situations. We will then review experimental data regarding the role of inflammation in epilepsy in the developing brain. To summarize, inflammation contributes to seizure precipitation, and reciprocally, prolonged seizures induce inflammation. There is also a relationship between inflammation and cell injury following status epilepticus, which differs according to the developmental stage. Finally, inflammation seems to contribute to epileptogenesis even in the developing brain. Based on the available data, we highlight the need for further studies dissecting the exact role of inflammation in epilepsy during development.

Neuroprotective and anti-inflammatory roles of the phosphatase and tensin homolog deleted on chromosome Ten (PTEN) Inhibition in a Mouse Model of Temporal Lobe Epilepsy

Excitotoxic damage represents the major mechanism leading to cell death in many human neurodegenerative diseases such as ischemia, trauma and epilepsy. Caused by an excess of glutamate that acts on metabotropic and ionotropic excitatory receptors, excitotoxicity activates several death signaling pathways leading to an extensive neuronal loss and a consequent strong activation of astrogliosis. Currently, the search for a neuroprotective strategy is aimed to identify the level in the signaling pathways to block excitotoxicity avoiding the loss of important physiological functions and side effects. To this aim, PTEN can be considered an ideal candidate: downstream the excitatory receptors activated in excitotoxicity (whose inhibition was shown to be not clinically viable), it is involved in neuronal damage and in the first stage of the reactive astrogliosis in vivo. In this study, we demonstrated the involvement of PTEN in excitotoxicity through its pharmacological inhibition by dipotassium bisperoxo (picolinato) oxovanadate [bpv(pic)] in a model of temporal lobe epilepsy, obtained by intraperitoneal injection of kainate in 2-month-old C57BL/6J male mice. We have demonstrated that inhibition of PTEN by bpv(pic) rescues neuronal death and decreases the reactive astrogliosis in the CA3 area of the hippocampus caused by systemic administration of kainate. Moreover, the neurotoxin administration increases significantly the scanty presence of mitochondrial PTEN that is significantly decreased by the administration of the inhibitor 6 hr after the injection of kainate, suggesting a role of PTEN in mitochondrial apoptosis. Taken together, our results confirm the key role played by PTEN in the excitotoxic damage and the strong anti-inflammatory and neuroprotective potential of its inhibition.

Tumor necrosis factor-α and interleukin-6 concentrations in cerebrospinal fluid of dogs after seizures

BACKGROUND

Idiopathic and acquired epilepsy are common in dogs. Up to 30% of these dogs are refractory to pharmacological treatment. Accumulating experimental evidence indicates that brain immune response and presence of inflammatory mediators decrease the threshold for individual seizures and contribute to epileptogenesis.

HYPOTHESIS

Dogs with seizures have higher cerebrospinal interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) concentrations compared to dogs with no seizures.

METHODS

A prospective double blinded study; cerebrospinal fluid (CSF) and serum IL-6, TNF-α and total protein (TP) concentrations were measured by a blinded investigator for the study group and CSF IL-6 and TNF-α levels and TP concentrations were measured in the control group (CG).

ANIMALS

Dogs presented with seizures that had enough CSF collected to allow analysis were included in the study group. Twelve apparently healthy, quarantined, stray dogs served as control (CG).

RESULTS

Cerebrospinal fluid TNF-α and IL-6 concentrations were significantly higher (P = .011, P = .039) in dogs with seizures (0 ± 70.66, 0.65 ± 10.93 pg/mL) compared to the CG (0 ± 19, 0.73 ± 0.55 pg/mL). When assessing cytokine concentrations of specifically the idiopathic epilepsy (IE) dogs compared to the CG, only TNF-α concentrations (8.66 ± 62, 0 ± 19 pg/mL) were significantly higher (P = .01). CSF TP concentrations were not significantly higher in the study dogs compared to the CG.

CONCLUSIONS AND CLINICAL IMPORTANCE

Higher TNF-α and IL-6 concentration in the CSF of dogs with naturally occurring seizures. The higher supports the hypothesis that inflammatory processes through certain mediators play a role in the pathogenesis of seizures in dogs.

IL-1β increases necrotic neuronal cell death in the developing rat hippocampus after status epilepticus by activating type I IL-1 receptor (IL-1RI)

Interleukin-1β (IL-1β) is associated with seizure-induced neuronal cell death in the adult brain. The contribution of IL-1β to neuronal injury induced by status epilepticus (SE) in the immature brain remains unclear. In the present study, we investigated the effects of IL-1β administration on hippocampal neuronal cell death associated with SE in the immature brain, and the role of the type I receptor of IL-1β (IL-1RI). SE was induced with lithium-pilocarpine in 14-days-old (P14) rat pups. Six hours after SE onset, pups were i.c.v. injected in the right ventricle with IL-1β (0, 0.3, 3, 30, or 300 ng), 30 ng of IL-1RI antagonist (IL-1Ra) alone, or 30 ng of IL-1Ra plus 3ng of IL-1β. As control groups, pups without seizures were injected with 3 ng of IL-1β or vehicle. Twenty-four hours after SE onset, neuronal cell death in the CA1 field of dorsal hippocampus was assessed by hematoxylin-eosin, Fluoro-Jade B and in vivo propidium iodide (PI) staining; expression of active caspase-3 (aCas-3) was also determined, using immunohistochemistry. The concentration-response curve of IL-1β showed a bell-shape. Only pups injected with 3 ng of IL-1β after SE showed a significant increase in the number of cells with eosinophilic cytoplasm and pyknotic nuclei, as well as F-JB positive cells with respect to the vehicle group. This effect was prevented when IL-1β was injected with IL-1Ra. Injection of 3 ng of IL-1β increased the number of PI-positive cells in CA1 area after SE. Injection of 3 ng of IL-1β did not produce hippocampal cell death in rats without seizures. Active caspase-3 expression was not observed after treatments in hippocampus. The activation of the IL-1β/IL-1RI system increases necrotic neuronal cell death caused by SE in rat pups.

Post-exposure administration of diazepam combined with soluble epoxide hydrolase inhibition stops seizures and modulates neuroinflammation in a murine model of acute TETS intoxication

Tetramethylenedisulfotetramine (TETS) is a potent convulsant poison for which there is currently no approved antidote. The convulsant action of TETS is thought to be mediated by inhibition of type A gamma-aminobutyric acid receptor (GABAAR) function. We, therefore, investigated the effects of post-exposure administration of diazepam, a GABAAR positive allosteric modulator, on seizure activity, death and neuroinflammation in adult male Swiss mice injected with a lethal dose of TETS (0.15mg/kg, ip). Administration of a high dose of diazepam (5mg/kg, ip) immediately following the second clonic seizure (approximately 20min post-TETS injection) effectively prevented progression to tonic seizures and death. However, this treatment did not prevent persistent reactive astrogliosis and microglial activation, as determined by GFAP and Iba-1 immunoreactivity and microglial cell morphology. Inhibition of soluble epoxide hydrolase (sEH) has been shown to exert potent anti-inflammatory effects and to increase survival in mice intoxicated with other GABAAR antagonists. The sEH inhibitor TUPS (1mg/kg, ip) administered immediately after the second clonic seizure did not protect TETS-intoxicated animals from tonic seizures or death. Combined administration of diazepam (5mg/kg, ip) and TUPS (1mg/kg, ip, starting 1h after diazepam and repeated every 24h) prevented TETS-induced lethality and influenced signs of neuroinflammation in some brain regions. Significantly decreased microglial activation and enhanced reactive astrogliosis were observed in the hippocampus, with no changes in the cortex. Combining an agent that targets specific anti-inflammatory mechanisms with a traditional antiseizure drug may enhance treatment outcome in TETS intoxication.

3,4-Methylenedioxymethamphetamine enhances kainic acid convulsive susceptibility

Kainic acid (KA) causes seizures and neuronal loss in the hippocampus. The present study investigated whether a recreational schedule of 3,4-methylenedioxymethamphetamine (MDMA) favours the development of a seizure state in a model of KA-induced epilepsy and potentiates the toxicity profile of KA (20 or 30mg/kg). Adolescent male C57BL/6 mice received saline or MDMA t.i.d. (s.c. every 3h), on 1day a week, for 4 consecutive weeks. Twenty-four hours after the last MDMA exposure, the animals were injected with saline or KA (20 or 30mg/kg). After this injection, we evaluated seizures, hippocampal neuronal cell death, microgliosis, astrogliosis, and calcium binding proteins. MDMA pretreatment, by itself, did not induce neuronal damage but increased seizure susceptibility in all KA treatments and potentiated the presence of Fluoro-Jade-positive cells in CA1. Furthermore, MDMA, like KA, significantly decreased parvalbumin levels in CA1 and dentate gyrus, where it potentiated the effects of KA. The amphetamine derivative also promoted a transient decrease in calbindin and calretinin levels, indicative of an abnormal neuronal discharge. In addition, treatment of cortical neurons with MDMA (10-50μM) for 6 or 48h significantly increased basal Ca(2+), reduced basal Na(+) levels and potentiated kainate response. These results indicate that MDMA potentiates KA-induced neurodegeneration and also increases KA seizure susceptibility. The mechanism proposed includes changes in Calcium Binding Proteins expression, probably due to the disruption of intracellular ionic homeostasis, or/and an indirect effect through glutamate release.

Neuropeptide Y protects cerebral cortical neurons by regulating microglial immune function

Neuropeptide Y has been shown to inhibit the immunological activity of reactive microglia in the rat cerebral cortex, to reduce N-methyl-D-aspartate current (I_NMDA) in cortical neurons, and protect neurons. In this study, after primary cultured microglia from the cerebral cortex of rats were treated with lipopolysaccharide, interleukin-1β and tumor necrosis factor-α levels in the cell culture medium increased, and mRNA expression of these cytokines also increased. After primary cultured cortical neurons were incubated with the lipopolysaccharide-treated microglial conditioned medium, peak I_NMDA in neurons increased. These effects of lipopolysaccharide were suppressed by neuropeptide Y. After addition of the neuropeptide Y Y1 receptor antagonist BIBP3226, the effects of neuropeptide Y completely disappeared. These results suggest that neuropeptide Y prevents excessive production of interleukin-1β and tumor necrosis factor-α by inhibiting microglial reactivity. This reduces I_NMDA in rat cortical neurons, preventing excitotoxicity, thereby protecting neurons.

Widespread activation of microglial cells in the hippocampus of chronic epileptic rats correlates only partially with neurodegeneration

Activation of microglial cells (brain macrophages) soon after status epilepticus has been suggested to be critical for the pathogenesis of mesial temporal lobe epilepsy (MTLE). However, microglial activation in the chronic phase of experimental MTLE has been scarcely addressed. In this study, we questioned whether microglial activation persists in the hippocampus of pilocarpine-treated, epileptic Wistar rats and to which extent it is associated with segmental neurodegeneration. Microglial cells were immunostained for the universal microglial marker, ionized calcium-binding adapter molecule-1 and the activation marker, CD11b (also known as OX42, Mac-1). Using quantitative morphology, i.e., stereology and Neurolucida-based reconstructions, we investigated morphological correlates of microglial activation such as cell number, ramification, somatic size and shape. We find that microglial cells in epileptic rats feature widespread, activation-related morphological changes such as increase in cell number density, massive up-regulation of CD11b and de-ramification. The parameters show heterogeneity in different hippocampal subregions. For instance, de-ramification is most prominent in the outer molecular layer of the dentate gyrus, whereas CD11b expression dominates in hilus. Interestingly, microglial activation only partially correlates with segmental neurodegeneration. Major neuronal death in the hilus, CA3 and CA1 coincides with strong up-regulation of CD11b. However, microglial activation is also observed in subregions that do not feature neurodegeneration, such as the molecular and granular layer of the dentate gyrus. This in vivo study provides solid experimental evidence that microglial cells feature widespread heterogeneous activation that only partially correlates with hippocampal segmental neuronal loss in experimental MTLE.

Pyrrolidine dithiocarbamate (PDTC) inhibits the overexpression of MCP-1 and attenuates microglial activation in the hippocampus of a pilocarpine-induced status epilepticus rat model

The aim of this study was to investigate the effects of pyrrolidine dithiocarbamate (PDTC) on MCP-1 expression and microglial activation in the hippocampus of a rat model of pilocarpine (PILO)-induced status epilepticus (SE). Moreover, seizure susceptibility, frequency and severity as well as brain damage were analyzed and changes in behavior were recorded. Chemokine MCP-1 expression and microglial activation were detected by immunohistochemistry (IHC). Fluoro-Jade C (FJC) and NeuN staining were used for the evaluation of tissue damage. Our results showed that although SE resulted in the upregulation of MCP-1 and microglial activation in the rat hippocampus 24 h after seizure onset, pretreatment with PDTC significantly inhibited the MCP-1 overexpression and attenuated the microglial activation. These effects were accompanied by neurodegenerative amelioration. To the best of our knowledge, these findings indicated for the first time that the activation of the nuclear factor-κB (NF-κB) pathway may contribute to MCP-1 upregulation and microglial activation in the context of epilepsy. PDTC was also shown to exert anticonvulsant activity and to have a neuroprotective effect on the hippocampal CA1 and CA3 regions, potentially through attenuating microglial activation.

Maturation-dependent behavioral deficits and cell injury in developing animals during the subacute postictal period

Prolonged early-life seizures are associated with disruptions of affective and cognitive function. Postictal disturbances, temporary functional deficits that persist for hours to days after seizures, have not yet been thoroughly characterized. Here, we used kainic acid (KA) to induce status epilepticus (SE) in immature rats at three developmental stages (postnatal day (P) 15, 21, or 30) and subsequently assessed spatial learning and memory in a Barnes maze, exploratory behavior in an open field, and the spatiotemporal distribution of cell injury during the first 7-10 days of the postictal period. At 1 day post-SE, P15-SE rats showed no deficit in the Barnes maze but were hyperexploratory in an open field compared with their littermate controls. In contrast, P21- and P30-SE rats exhibited markedly impaired performance in the Barnes maze and exhibited significantly reduced open field exploration suggestive of anxiety-like behavior. These behavioral changes were transient in P15 rats but more persistent in P21 and enduring in P30 rats after KA-SE. The time course of behavioral deficits in P21 and P30 rats was temporally correlated with the presence of neuronal injury in the lateral septal nuclei, amygdala, and ventral subiculum/CA1, regions involved in modulation of the hypothalamic-pituitary-adrenal stress response.

Immunological perspectives of temporal lobe seizures

The temporal lobes are affected in many different neurological disorders, such as neurodegenerative diseases, viral and immunological encephalitides, and epilepsy. Both experimental and clinical evidence suggests a different inflammatory response to seizures in patients with temporal lobe epilepsy (TLE) in comparison to those with extra-TLE (XTLE). Proinflammatory cytokines and several autoantibodies have been shown to be associated with TLE compared to other epilepsy types suggesting the specific role and structure of the temporal lobe. Abundant experience suggests that activation of both innate and adaptive immunity is associated with epilepsy, particularly refractory focal epilepsy. Limbic encephalitis often triggers temporal lobe seizures, and a proportion of these disorders are immune-mediated. Histological evidence shows activation of specific inflammatory pathways in resected temporal lobes of epileptic patients, and certain epileptic disorders have shown increased incidence in patients with autoimmune diseases. Rapid activation of proinflammatory cytokines is observed after single seizures, but there is also evidence of chronic overproduction of cytokines and other inflammatory mediators in patients with TLE, suggesting a neuromodulatory role of inflammation in epilepsy. In this review we summarize current data on the presence and the role of immunological factors in temporal lobe seizures, and their possible involvement in epileptogenesis.

Expressions of tumor necrosis factor alpha and microRNA-155 in immature rat model of status epilepticus and children with mesial temporal lobe epilepsy

Recently, the role of inflammation has attracted great attention in the pathogenesis of mesial temporal lobe epilepsy (MTLE), and microRNAs start to emerge as promising new players in MTLE pathogenesis. In this study, we investigated the dynamic expression patterns of tumor necrosis factor alpha (TNF-α) and microRNA-155 (miR-155) in the hippocampi of an immature rat model of status epilepticus (SE) and children with MTLE. The expressions of TNF-α and miR-155 were significantly upregulated in the seizure-related acute and chronic stages of MTLE in the immature rat model and also in children with MTLE. Modulation of TNF-α expression, either by stimulation using myeloid-related protein (MRP8) or lipopolysaccharide or inhibition using lenalidomide on astrocytes, leads to similar dynamic changes in miR-155 expression. Our study is the first to focus on the dynamic expression pattern of miR-155 in the immature rat of SE lithium-pilocarpine model and children with MTLE and to detect their relationship at the astrocyte level. TNF-α and miR-155, having similar expression patterns in the three stages of MTLE development, and their relationship at the astrocyte level may suggest a direct interactive relationship during MTLE development. Therefore, modulation of the TNF-α/miR-155 axis may be a novel therapeutic target for the treatment of MTLE.

Excitotoxicity-induced immediate surge in hippocampal prostanoid production has latent effects that promote chronic progressive neuronal death

Excitotoxicity is involved in neurodegenerative conditions. We investigated the pathological significance of a surge in prostaglandin production immediately after kainic acid (KA) administration [initial phase], followed by a sustained moderate elevation in prostaglandin level [late phase] in the hippocampus of juvenile rats. Numerous pyknotic hippocampal neurons were observed 72 h after KA treatment; this number remained elevated on days 10 and 30. Gross hippocampal atrophy was observed on days 10 and 30. Pre-treatment with indomethacin ameliorated neuronal death on days 10 and 30, and prevented hippocampal atrophy on day 30. Microglial response was moderated by the indomethacin pre-treatment. Blockade of only late-phase prostaglandin production by post-treatment with indomethacin ameliorated neuronal death on day 30. These findings suggest a role for initial-phase prostaglandin production in chronic progressive neuronal death, which is exacerbated by late-phase prostaglandin production. Blockade of prostaglandin production has therapeutic implications in preventing long-term neurological sequelae following excitotoxic brain damage.

Early developmental outcomes in children following convulsive status epilepticus: a longitudinal study

PURPOSE

Convulsive status epilepticus (CSE) is the most common pediatric neurologic emergency and is often associated with unfavorable neurodevelopmental outcomes. The early developmental trajectory of children following CSE has not been previously investigated, leaving a gap in our understanding of how these adverse long-term outcomes emerge.

METHODS

We prospectively recruited children aged between 1 and 42 months from a predefined geographic region of North London who had at least one episode of CSE and classified them as prolonged febrile seizures (PFS) or nonfebrile CSE. Neuropsychological and imaging investigations were conducted within 6 weeks of CSE (baseline) and were repeated a year later (follow-up). Neurodevelopment was assessed using the Bayley Scales of Infant Development III and compared to normally developing children. Predictors of neurodevelopmental scores at baseline and follow-up were investigated using regression analyses.

KEY FINDINGS

Of the 54 children that underwent investigations a mean of 38 days following CSE, 27 had PFS (mean age 18.4 months) and 27 had nonfebrile CSE (mean age 15.5 months). In addition, 17 healthy controls were assessed (mean age 20.49 months). Children with nonfebrile CSE had a worse developmental outcome than children with PFS (p < 0.002), despite there being no differences in seizure characteristics. In contrast to expectations, the PFS group had a worse developmental outcome than controls (p = 0.002). There were no significant differences in performance from baseline to 1-year follow-up for the 70.4% of children who provided data. Seizure characteristics were not shown to be significant predictors of performance.

SIGNIFICANCE

CSE is associated with developmental impairments within 6 weeks of the acute event that continue to be present a year onward. This is also true of PFS cases that under-perform relative to controls despite mean scores within the clinically normal range. The absence of a change in performance from baseline to follow-up as well as the lack of a relationship between seizure characteristics and developmental outcomes supports the notion that premorbid abilities may be overshadowing any direct effects of CSE itself on outcome.

Epileptogenesis in the developing brain

The neonatal brain has poorly developed GABAergic circuits, and in many of them GABA is excitatory, favoring ictogenicity. Frequently repeated experimental seizures impair brain development in an age-dependent manner. At critical ages, they delay developmental milestones, permanently lower seizure thresholds, and can cause very specific cognitive and learning deficits, such as the permanent impairment of neuronal spatial maps. Some types of experimental status epilepticus cause neuronal necrosis and apoptosis, and are followed by chronic epilepsy with spontaneous recurrent seizures, others appear relatively benign, so that seizure-induced neuronal injury and epileptogenesis are highly age-, seizure model-, and species-dependent. Experimental febrile seizures can be epileptogenic, and hyperthermia aggravates both neuronal injury and epileptogenicity. Antiepileptic drugs, the mainstay of treatment, have major risks of their own, and can, at therapeutic or near-therapeutic doses, trigger neuronal apoptosis, which is also age-, drug-, cell type-, and species-dependent. The relevance of these experimental results to human disease is still uncertain, but while their brains are quite different, the basic biology of neurons in rodents and humans is strikingly similar. Further research is needed to elucidate the molecular mechanisms of epileptogenesis and of seizure- or drug-induced neuronal injury, in order to prevent their long-term consequences.

Kainic Acid-induced neurotoxicity: targeting glial responses and glia-derived cytokines

Glutamate excitotoxicity contributes to a variety of disorders in the central nervous system, which is triggered primarily by excessive Ca²⁺ influx arising from overstimulation of glutamate receptors, followed by disintegration of the endoplasmic reticulum (ER) membrane and ER stress, the generation and detoxification of reactive oxygen species as well as mitochondrial dysfunction, leading to neuronal apoptosis and necrosis. Kainic acid (KA), a potent agonist to the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate class of glutamate receptors, is 30-fold more potent in neuro-toxicity than glutamate. In rodents, KA injection resulted in recurrent seizures, behavioral changes and subsequent degeneration of selective populations of neurons in the brain, which has been widely used as a model to study the mechanisms of neurodegenerative pathways induced by excitatory neurotransmitter. Microglial activation and astrocytes proliferation are the other characteristics of KA-induced neurodegeneration. The cytokines and other inflammatory molecules secreted by activated glia cells can modify the outcome of disease progression. Thus, anti-oxidant and anti-inflammatory treatment could attenuate or prevent KA-induced neurodegeneration. In this review, we summarized updated experimental data with regard to the KA-induced neurotoxicity in the brain and emphasized glial responses and glia-oriented cytokines, tumor necrosis factor-α, interleukin (IL)-1, IL-12 and IL-18.

Kainic acid-induced changes in the opioid/nociceptin system and the stress/toxicity pathways in the rat hippocampus

Excitotoxicity is a contributing factor to the pathogenesis of acute or chronic neurodegenerative disease states. Kainic acid (KA) is an excitotoxic substance and the administration of it to rodents induces seizure activity (status epilepticus, SE) and leads to neurodegeneration. In this study the effect of KA-induced excitotoxicity on the G-protein activations and the gene expression levels of the opioid/nociceptin system receptors as MOPr, KOPr, DOPr, ORL-1, and PNOC (N/OFQ) were investigated, and the regulator effect of naloxone (Nal) on the gene expressions of the opioid system receptors against KA-induced seizures in the rat hippocampus was tested. In addition, the expression levels of stress-toxicity genes were assessed in the hippocampus following KA-induced excitotoxicity in order to determine the potential genetic targets which can be helpful for neuroprotective interventions. Our results indicate that the KA-induced excitotoxicity increased the mRNA levels of MOPr, DOPr, KOPr, PNOC, and ORL-1. However, G-protein activations of MOPr, DOPr, and KOPr remained relatively unchanged while both the potency and efficacy of N/OFQ were significantly increased. The PCR array data showed that KA-induced excitotoxicity altered the expression levels of genes in the cellular stress or toxicity pathways. Our data suggests that the induction of the opioid/nociceptin system may be involved in the cellular stress response following a neurodegenerative insult and that the genes modulated by the KA-treatment in the stress-toxicity pathways may be evaluated as targets of potential neuroprotective interventions.

Characterization of seizures induced by acute and repeated exposure to tetramethylenedisulfotetramine

Tetramethylenedisulfotetramine (tetramine; TETS) is a potent convulsant poison that is considered to be a chemical threat agent. To provide a basis for the investigation of antidotes for TETS-induced seizures, we characterized the convulsant activity of TETS in mice and rats when administered by the intraperitoneal, intravenous, oral, and intraventricular routes as a single acute dose and with repeated sublethal doses. In mice, parenteral and oral TETS caused immobility, myoclonic body jerks, clonic seizures of the forelimbs and/or hindlimbs, tonic seizures, and death. The CD₅₀ values for clonic and tonic seizures after oral administration were 0.11 and 0.22 mg/kg, respectively. Intraventricular administration of TETS (5-100 μg) in rats also caused clonic-tonic seizures and death. In mice, repeated sublethal doses of TETS at intervals of 2, 24, and 48 h failed to result in the development of persistent enhanced seizure responsivity ("kindling") as was observed with repeated pentylenetetrazol treatment. In mice, sublethal doses of TETS that produced clonic seizures did not cause observable structural brain damage as assessed with routine histology and Fluoro-Jade B staining 7 days after treatment. However, 1 to 3 days after a single convulsant dose of TETS the expression of glial fibrillary acidic protein, an astrocyte marker, and ionized calcium binding adaptor molecule 1, a microglia marker, were markedly increased in cortex and hippocampus. Although TETS doses that are compatible with survival are not associated with overt evidence of cellular injury or neurodegeneration, there is transient reactive astrocytosis and microglial activation, indicating that brain inflammatory responses are provoked.

Refractory epilepsy associated with microglial activation

BACKGROUND

Experimental and clinical studies support a pathogenic role of microglial activation and proliferation (MAP) in epileptogenesis.

METHODS

From a consecutive series of 319 surgically treated epilepsy cases, we retrospectively reviewed the histopathological sections of 92 cases to define the prevalence and severity of MAP after excluding the other 227 because of coexisting disorders that might contribute to MAP. Severity of MAP was compared with underlying abnormalities. We assessed the response to intravenous immunoglobulin and plasmapheresis in one patient with severe MAP who had failed multiple antiepileptic drugs and epilepsy surgery.

RESULTS

MAP was detected with routine (hematoxylin and eosin) stain in 46 of 92 cases (50%). MAP was mild in 32 cases (69.6%), moderate in 12 (26.1%), and severe in 2 (4.3%). The prevalence and severity of MAP were independent of underlying abnormalities. Immunomodulatory therapy was followed by a greater than 90% reduction in seizure activity in the treated patient.

CONCLUSION

MAP is prevalent in resected human epilepsy tissue. Failure to down-regulate MAP contributes to chronic neuronal hyperexcitability. We hypothesize that MAP initiates a cycle of inflammation-induced seizures and seizure-induced inflammation. Microglia-driven epilepsy may be a primary pathogenic process in a small number of cases, as suggested by the pathology and therapeutic response in our patient, but may contribute to epileptogenesis in many more.

Overexpression of apolipoprotein E4 increases kainic-acid-induced hippocampal neurodegeneration

Apolipoprotein E (apoE) has an intricate biological function in modulating immune responses and apoE isoforms exhibit diverse effects on neurodegenerative and neuroinflammatory disorders. In the present study, we investigated the individual roles of apoE isoforms in the kainic acid (KA)-induced hippocampal neurodegeneration with focus on immune response and microglia functions. ApoE2, 3 and 4 transgenic mice as well as wild-type (WT) mice were treated with KA by intranasal route. ApoE4 overexpressing mice revealed several peculiarities as compared with other transgenic mice and WT mice, i.e. (1) they had more severe KA-induced seizures than apoE2 and 3 mice, (2) they exhibited neuron loss in hippocampus that was higher than in apoE2, 3 and WT mice, (3) KA administration resulted in higher counts of their head drops in the cross-area of elevated plus-maze, (4) they showed lower KA-induced rearing activity than apoE2 mice in the open-field test, (5) their KA-induced microglial expression of MHC-II and CD86 was elevated compared to apoE3 mice, (6) the KA-induced increase of microglial iNOS was higher than that in the other groups of mice, and (7) the TNF-α and IL-6 expression was decreased 7 days after KA application compared to untreated mice and mice treated 1 day with KA. However, the signaling pathway of NFκB or Akt seemed not to be involved in apoE-isoform dependent susceptibility to KA-induced neurotoxicity. In conclusion, over-expression of apoE4 deteriorated KA-induced hippocampal neurodegeneration in C57BL/6 mice, which might result from a higher up-regulation of microglia activation compared to apoE2 and 3 transgenic mice and WT mice.

Administration of simvastatin after kainic acid-induced status epilepticus restrains chronic temporal lobe epilepsy

In this study, we examined the effect of chronic administration of simvastatin immediately after status epilepticus (SE) on rat brain with temporal lobe epilepsy (TLE). First, we evaluated cytokines expression at 3 days post KA-lesion in hippocampus and found that simvastatin-treatment suppressed lesion-induced expression of interleukin (IL)-1β and tumor necrosis factor-α (TNF-α). Further, we quantified reactive astrocytosis using glial fibrillary acidic protein (GFAP) staining and neuron loss using Nissl staining in hippocampus at 4-6 months after KA-lesion. We found that simvastatin suppressed reactive astrocytosis demonstrated by a significant decrease in GFAP-positive cells, and attenuated loss of pyramidal neurons in CA3 and interneurons in dentate hilar (DH). We next assessed aberrant mossy fiber sprouting (MFS) that is known to contribute to recurrence of spontaneous seizure in epileptic brain. In contrast to the robust MFS observed in saline-treated animals, the extent of MFS was restrained by simvastatin in epileptic rats. Attenuated MFS was related to decreased neuronal loss in CA3 and DH, which is possibly a mechanism underlying decreased hippocampal susceptibility in animal treated with simvastatin. Electronic encephalography (EEG) was recorded during 4 to 6 months after KA-lesion. The frequency of abnormal spikes in rats with simvastatin-treatment decreased significantly compared to the saline group. In summary, simvastatin treatment suppressed cytokines expression and reactive astrocytosis and decreased the frequency of discharges of epileptic brain, which might be due to the inhibition of MFS in DH. Our study suggests that simvastatin administration might be a possible intervention and promising strategy for preventing SE exacerbating to chronic epilepsy.

Dietary supplementation with α-tocopherol reduces neuroinflammation and neuronal degeneration in the rat brain after kainic acid-induced status epilepticus

Vitamin E (as α-tocopherol, α-T) is proposed to alleviate glia-mediated inflammation in neurological diseases, but such a role in epilepsy is still elusive. This study investigated the effect of α-T supplementation on glial activation, neuronal cell death and oxidative stress of rat brain exposed to kainate-induced seizures. Animals were fed for 2 weeks with a α-T-enriched diet (estimated intake of 750 mg/kg/day) before undergoing status epilepticus. Compliance to supplementation was demonstrated by the remarkable increase in brain α-T. Four days after seizure, brain α-T returned to baseline and lipid peroxidation markers decreased as compared to non-supplemented rats. Status epilepticus induced a lower up-regulation of astrocytic and microglial antigens (GFAP and MHC II, respectively) and production of pro-inflammatory cytokines (IL-1β and TNF-α) in supplemented than in non-supplemented animals. This anti-inflammatory effect was associated with a lower neuronal cell death. In conclusion, α-T dietary supplementation prevents oxidative stress, neuroglial over-activation and cell death occurring after kainate-induced seizures. This evidence paves the way to an anti-inflammatory and neuroprotective role of α-T interventions in epilepsy.

Expression and localization of the iron-siderophore binding protein lipocalin 2 in the normal rat brain and after kainate-induced excitotoxicity

Lipocalin 2 (LCN2) is produced by mammalian hosts to bind bacterial siderophore and sequester free iron as part of an innate immune response, and could also play a role in tissue iron homeostasis, but thus far, little is known about its expression in the CNS. The present study was carried out to study the expression of the lipocalin in the normal rat brain and after neuronal injury induced by kainate (KA). Low levels of LCN2 mRNA and protein expression were detected in most regions of the normal brain except the olfactory bulb, brainstem and cerebellum. KA lesions resulted in damage to the hippocampus, leading to an early increase at three days and a sustained elevation in LCN2 mRNA level of 16-fold, and protein expression at 80-fold in the lesioned tissue compared to controls at 2 weeks post-KA injection. The sustained elevation in mRNA expression was not detected among other lipocalins surveyed using real-time RT-PCR - apoD, PGDS, Rbp4 and LCN5. Single and double immunostaining confirmed that LCN2 is present in astrocytes in the olfactory bulb, brainstem and cerebellum of the normal brain, and reactive astrocytes in the KA-lesioned hippocampus. In conclusion, the present study showed LCN2 to be present in select brain regions, and is upregulated in astrocytes after neuronal injury induced by kainate. We postulate that, as in the periphery, LCN2 may have a role in iron transport or trafficking in the CNS.

Minozac treatment prevents increased seizure susceptibility in a mouse "two-hit" model of closed skull traumatic brain injury and electroconvulsive shock-induced seizures

The mechanisms linking traumatic brain injury (TBI) to post-traumatic epilepsy (PTE) are not known and no therapy for prevention of PTE is available. We used a mouse closed-skull midline impact model to test the hypotheses that TBI increases susceptibility to seizures in a "two-hit" injury model, and that suppression of cytokine upregulation after the first hit will attenuate the increased susceptibility to the second neurological insult. Adult male CD-1 mice underwent midline closed skull pneumatic impact. At 3 and 6 h after impact or sham procedure, the mice were injected IP with either Minozac (Mzc), a suppressor of proinflammatory cytokine upregulation, or vehicle (saline). On day 7 after sham operation or TBI, seizures were induced using electroconvulsive shock (ECS), and susceptibility to seizures was measured by the current required for seizure induction. Activation of glia, neuronal injury, and metallothionein-immunoreactive cells were quantified in the hippocampus by immunohistochemical methods. Neurobehavioral function over 14-day recovery was quantified using the Barnes maze. Following TBI there was a significant increase in susceptibility to seizures induced by ECS, and this susceptibility was prevented by suppression of cytokine upregulation with Mzc. Astrocyte activation, metallothionein expression, and neurobehavioral impairment were also increased in the two-hit group subjected to combined TBI and ECS. These enhanced responses in the two-hit group were also prevented by suppression of proinflammatory cytokine upregulation with Mzc. These data implicate glial activation in the mechanisms of epileptogenesis after TBI, and identify a potential therapeutic approach to attenuate the delayed neurological sequelae of TBI.

Antecedent ethanol attenuates cerebral ischemia/reperfusion-induced leukocyte-endothelial adhesive interactions and delayed neuronal death: role of large conductance, Ca2+-activated K+ channels

EtOH-PC reduces postischemic neuronal injury in response to cerebral (I/R). We examined the mechanism underlying this protective effect by determining (i) whether it was associated with a decrease in I/R-induced leukocyte-endothelial adhesive interactions in postcapillary venules, and (ii) whether the protective effects were mediated by activation of large conductance, calcium-activated potassium (BK(Ca)) channels. Mice were administered ethanol by gavage or treated with the BK(Ca) channel opener, NS1619, 24 hours prior to I/R with or without prior treatment with the BK(Ca) channel blocker, PX. Both CCA were occluded for 20 minutes followed by two and three hours of reperfusion, and rolling (LR) and adherent (LA) leukocytes were quantified in pial venules using intravital microscopy. The extent of DND, apoptosis and glial activation in hippocampus were assessed four days after I/R. Compared with sham, I/R elicited increases in LR and LA in pial venules and DND and apoptosis as well as glial activation in the hippocampus. These effects were attenuated by EtOH-PC or antecedent NS1619 administration, and this protection was reversed by prior treatment with PX. Our results support a role for BK(Ca) channel activation in the neuroprotective effects of EtOH-PC in cerebral I/R.

Kainic acid-induced neurodegenerative model: potentials and limitations

Excitotoxicity is considered to be an important mechanism involved in various neurodegenerative diseases in the central nervous system (CNS) such as Alzheimer's disease (AD). However, the mechanism by which excitotoxicity is implicated in neurodegenerative disorders remains unclear. Kainic acid (KA) is an epileptogenic and neuroexcitotoxic agent by acting on specific kainate receptors (KARs) in the CNS. KA has been extensively used as a specific agonist for ionotrophic glutamate receptors (iGluRs), for example, KARs, to mimic glutamate excitotoxicity in neurodegenerative models as well as to distinguish other iGluRs such as α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptors and N-methyl-D-aspartate receptors. Given the current knowledge of excitotoxicity in neurodegeneration, interventions targeted at modulating excitotoxicity are promising in terms of dealing with neurodegenerative disorders. This paper summarizes the up-to-date knowledge of neurodegenerative studies based on KA-induced animal model, with emphasis on its potentials and limitations.