Widespread patterns of neuronal damage following systemic or intracerebral injections of kainic acid: a histological study

Sequel of spontaneous seizures after kainic acid-induced status epilepticus and associated neuropathological changes in the subiculum and entorhinal cortex

Injection of the seaweed toxin kainic acid (KA) in rats induces a severe status epilepticus initiating complex neuropathological changes in limbic brain areas and subsequently spontaneous recurrent seizures. Although neuropathological changes have been intensively investigated in the hippocampus proper and the dentate gyrus in various seizure models, much less is known about changes in parahippocampal areas. We now established telemetric EEG recordings combined with continuous video monitoring to characterize the development of spontaneous seizures after KA-induced status epilepticus, and investigated associated neurodegenerative changes, astrocyte and microglia proliferation in the subiculum and other parahippocampal brain areas. The onset of spontaneous seizures was heterogeneous, with an average latency of 15 ± 1.4 days (range 3–36 days) to the initial status epilepticus. The frequency of late spontaneous seizures was higher in rats in which the initial status epilepticus was recurrent after its interruption with diazepam compared to rats in which this treatment was more efficient. Seizure-induced neuropathological changes were assessed in the subiculum by losses in NeuN-positive neurons and by Fluoro-Jade C staining of degenerating neurons. Neuronal loss was already prominent 24 h after KA injection and only modestly progressed at the later intervals. It was most severe in the proximal subiculum and in layer III of the medial entorhinal cortex and distinct Fluoro-Jade C labeling was observed there in 75% of rats even after 3 months. Glutamatergic neurons, labeled by in situ hybridization for the vesicular glutamate transporter 1 followed a similar pattern of cell losses, except for the medial entorhinal cortex and the proximal subiculum that appeared more vulnerable. Glutamate decarboxylase65 (GAD65) mRNA expressing neurons were generally less vulnerable than glutamate neurons. Reactive astrocytes and microglia were present after 24 h, however, became prominent only after 8 days and remained high after 30 days. In the proximal subiculum, parasubiculum and entorhinal cortex the number of microglia cells was highest after 30 days. Although numbers of reactive astrocytes and microglia were reduced again after 3 months, they were still present in most rats. The time course of astrocyte and microglia proliferation parallels that of epileptogenesis.

A neuronal population in hypothalamus that dramatically resists acute ischemic injury compared to neocortex

Pyramidal neurons (PyNs) of the cortex are highly susceptible to acute stroke damage, yet "lower" brain regions like hypothalamus and brain stem better survive global ischemia. Here we show for the first time that a "lower" neuron population intrinsically resists acute strokelike injury. In rat brain slices deprived of oxygen and glucose (OGD), we imaged anoxic depolarization (AD) as it propagated through neocortex or hypothalamus. AD, the initial electrophysiological event of stroke, is a front of depolarization that drains residual energy in compromised gray matter. The extent of AD reliably determines ensuing cortical damage, but do all CNS neurons generate a robust AD? During 10 min of OGD, PyNs depolarize without functional recovery. In contrast, magnocellular neuroendocrine cells (MNCs) in hypothalamus under identical stress generate a weak and delayed AD, resist complete depolarization, and rapidly repolarize when oxygen and glucose are restored. They recover their membrane potential, input resistance, and spike amplitude and can survive multiple OGD exposures. Two-photon microscopy in slices derived from a fluorescent mouse line confirms this protection, revealing PyN swelling and dendritic beading after OGD, whereas MNCs are not injured. Exposure to the Na(+)-K(+)-ATPase inhibitor ouabain (100 μM) induces AD similar to OGD in both cell types. Moreover, elevated extracellular K(+) concentration ([K(+)](o)) evokes spreading depression (SD), a milder version of AD, in PyNs but not MNCs. Therefore overriding the pump by OGD, ouabain, or elevated [K(+)](o) evokes a propagating depolarization in higher gray matter but not in MNCs. We suggest that variation in Na(+)-K(+)-ATPase pump efficiency during ischemia injury determines whether a neuronal type succumbs to or resists stroke.

Uncaria rhynchophylla Upregulates the Expression of MIF and Cyclophilin A in Kainic Acid-Induced Epilepsy Rats: A Proteomic Analysis

Uncaria rhynchophylla (Miq) Jack (UR) is a traditional Chinese herb and is used for the treatment of convulsive disorders, including epilepsy. Our previous study has shown that UR, as well as its major component rhynchophylline (RH), has an anticonvulsive effect and this effect is closely related to its scavenging activities of oxygen free radicals. The purpose of the present study was to investigate the effect of (UR) on the expression of proteins using a proteomics analysis in Sprague-Dawley (SD) rats with kainic acid (KA)-induced epileptic seizures. We profiled the differentially expressed proteins on two-dimensional electrophoresis (2-DE) maps derived from the frontal cortex and hippocampus of rat brain tissue 24 hours after KA-induced epileptic seizures. The results indicated that macrophage migration inhibitory factor (MIF) and cyclophilin A were under expressed in frontal cortex by an average of 0.19- and 0.23-fold, respectively. In the frontal cortex, MIF and cyclophilin A were significantly decreased in the KA group and these decreases were confirmed by the Western blots. However, in the hippocampus, only cyclophilin A was significantly decreased in the KA group. In addition, in real-time quantitative PCR (Q-PCR), MIF and cyclophilin A gene expressions were also significantly under expressed in the frontal cortex, and only the cyclophilin A gene was also significantly under expressed in the hippocampus in the KA group. These under expressions of MIF and cyclophilin A could be overcome by the treatment of UR and RH. In conclusion, the under expressions of MIF and cyclophilin A in the frontal cortex and hippocampus in KA-treated rats, which were overcome by both UR and UH treatment, suggesting that both MIF and cyclophilin A at least partly participate in the anticonvulsive effect of UR.

Histamine 1 receptor knock out mice show age-dependent susceptibility to status epilepticus and consequent neuronal damage

The central histaminergic neuron system is an important regulator of activity stages such as arousal and sleep. In several epilepsy models, histamine has been shown to modulate epileptic activity and histamine 1 (H1) receptors seem to play a key role in this process. However, little is known about the H1 receptor-mediated seizure regulation during the early postnatal development, and therefore we examined differences in severity of kainic acid (KA)-induced status epilepticus (SE) and consequent neuronal damage in H1 receptor knock out (KO) and wild type (WT) mice at postnatal days 14, 21, and 60 (P14, P21, and P60). Our results show that in P14 H1 receptor KO mice, SE severity and neuronal damage were comparable to those of WT mice, whereas P21 KO mice had significantly decreased survival, more severe seizures, and enhanced neuronal damage in various brain regions, which were observed only in males. In P60 mice, SE severity did not differ between the genotypes, but in KO group, neuronal damage was significantly increased. Our results suggest that H1 receptors could contribute to regulation of seizures and neuronal damage age-dependently thus making the histaminergic system as a challenging target for novel drug design in epilepsy.

Defining "epileptogenesis" and identifying "antiepileptogenic targets" in animal models of acquired temporal lobe epilepsy is not as simple as it might seem

The "latent period" between brain injury and clinical epilepsy is widely regarded to be a seizure-free, pre-epileptic state during which a time-consuming cascade of molecular events and structural changes gradually mediates the process of "epileptogenesis." The concept of the "latent period" as the duration of "epileptogenesis" implies that epilepsy is not an immediate result of brain injury, and that anti-epileptogenic strategies need to target delayed secondary mechanisms that develop sometime after an initial injury. However, depth recordings made directly from the dentate granule cell layers in awake rats after convulsive status epilepticus-induced injury have now shown that whenever perforant pathway stimulation-induced status epilepticus produces extensive hilar neuron loss and entorhinal cortical injury, hyperexcitable granule cells immediately generate spontaneous epileptiform discharges and focal or generalized behavioral seizures. This indicates that hippocampal injury caused by convulsive status epilepticus is immediately epileptogenic and that hippocampal epileptogenesis requires no delayed secondary mechanism. When latent periods do exist after injury, we hypothesize that less extensive cell loss causes an extended period during which initially subclinical focal seizures gradually increase in duration to produce the first clinical seizure. Thus, the "latent period" is suggested to be a state of "epileptic maturation," rather than a prolonged period of "epileptogenesis," and therefore the antiepileptogenic therapeutic window may only remain open during the first week after injury, when some delayed cell death may still be preventable. Following the perhaps unavoidable development of the first focal seizures ("epileptogenesis"), the most fruitful therapeutic strategy may be to interrupt the process of "epileptic maturation," thereby keeping focal seizures focal. This article is part of the Special Issue entitled 'New Targets and Approaches to the Treatment of Epilepsy'.

Cerebellar inactivation impairs memory of learned prism gaze-reach calibrations

Three monkeys performed a visually guided reach-touch task with and without laterally displacing prisms. The prisms offset the normally aligned gaze/reach and subsequent touch. Naive monkeys showed adaptation, such that on repeated prism trials the gaze-reach angle widened and touches hit nearer the target. On the first subsequent no-prism trial the monkeys exhibited an aftereffect, such that the widened gaze-reach angle persisted and touches missed the target in the direction opposite that of initial prism-induced error. After 20-30 days of training, monkeys showed long-term learning and storage of the prism gaze-reach calibration: they switched between prism and no-prism and touched the target on the first trials without adaptation or aftereffect. Injections of lidocaine into posterolateral cerebellar cortex or muscimol or lidocaine into dentate nucleus temporarily inactivated these structures. Immediately after injections into cortex or dentate, reaches were displaced in the direction of prism-displaced gaze, but no-prism reaches were relatively unimpaired. There was little or no adaptation on the day of injection. On days after injection, there was no adaptation and both prism and no-prism reaches were horizontally, and often vertically, displaced. A single permanent lesion (kainic acid) in the lateral dentate nucleus of one monkey immediately impaired only the learned prism gaze-reach calibration and in subsequent days disrupted both learning and performance. This effect persisted for the 18 days of observation, with little or no adaptation.

Galanin receptor 1 deletion exacerbates hippocampal neuronal loss after systemic kainate administration in mice

Background

Galanin is a neuropeptide with a wide distribution in the central and peripheral nervous systems and whose physiological effects are mediated through three G protein-coupled receptor subtypes, GalR1, GalR2, and GalR3. Several lines of evidence indicate that galanin, as well as activation of the GalR1 receptor, is a potent and effective modulator of neuronal excitability in the hippocampus.

Methodology/Principal Findings

In order to test more formally the potential influence of GalR1 on seizure-induced excitotoxic cell death, we conducted functional complementation tests in which transgenic mice that exhibit decreased expression of the GalR1 candidate mRNA underwent kainate-induced status epilepticus to determine if the quantitative trait of susceptibility to seizure-induced cell death is determined by the activity of GalR1. In the present study, we report that reduction of GalR1 mRNA via null mutation or injection of the GalR1 antagonist, galantide, prior to kainate-induced status epilepticus induces hippocampal damage in a mouse strain known to be highly resistant to kainate-induced neuronal injury. Wild-type and GalR1 knockout mice were subjected to systemic kainate administration. Seven days later, Nissl and NeuN immune- staining demonstrated that hippocampal cell death was significantly increased in GalR1 knockout strains and in animals injected with the GalR1 antagonist. Compared to GalR1-expressing mice, GalR1-deficient mice had significantly larger hippocampal lesions after status epilepticus.

Conclusions/Significance

Our results suggest that a reduction of GalR1 expression in the C57BL/6J mouse strain renders them susceptible to excitotoxic injury following systemic kainate administration. From these results, GalR1 protein emerges as a new molecular target that may have a potential therapeutic value in modulating seizure-induced cell death.

The hippocampus of Ames dwarf mice exhibits enhanced antioxidative defenses following kainic acid-induced oxidative stress

INTRODUCTION

The vulnerability of the hippocampus to the effects of aging has been found to be associated with a decline in growth hormone/insulin like growth factor-1 (GH/IGF-1), and an increase in oxidative stress. We have evidence that long-living GH-deficient Ames dwarf mice have enhanced antioxidant protection in the periphery but the protection in the central nervous system is less clear.

MATERIAL AND METHODS

In the present study, we evaluated the antioxidative defense enzyme status in the hippocampus of Ames dwarf and wild type mice at 3, 12 and 24 months of age and examined the ability of each genotype to resist kainic acid-induced (KA) oxidative stress. An equiseizure concentration of KA was administered such that both genotypes responded with similar seizure scores and lipid peroxidation.

RESULTS

We found that GH-sufficient wild type mice showed an increase in oxidative stress as indicated by the reduced ratio of glutathione: glutathione disulfide following KA injection while this ratio was maintained in GH-deficient Ames dwarf mice. In addition, glutathione peroxidase activity (GPx) as well as GPx1 mRNA expression was enhanced in KA-injected Ames dwarf mice but decreased in wild type mice. There was no induction of Nrf-2 (an oxidative stress-induced transcription factor) gene expression in Ames dwarf mice following KA further suggesting maintenance of antioxidant defense in GH-deficiency under oxidative stress conditions.

DISCUSSION

Therefore, based on equiseizure administration of KA, Ames dwarf mice have an enhanced antioxidant defense capacity in the hippocampus similar to that observed in the periphery. This improved defense capability in the brain is likely due to increased GPx availability in Ames mice and may contribute to their enhanced longevity.

Classic hippocampal sclerosis and hippocampal-onset epilepsy produced by a single "cryptic" episode of focal hippocampal excitation in awake rats

In refractory temporal lobe epilepsy, seizures often arise from a shrunken hippocampus exhibiting a pattern of selective neuron loss called "classic hippocampal sclerosis." No single experimental injury has reproduced this specific pathology, suggesting that hippocampal atrophy might be a progressive "endstage" pathology resulting from years of spontaneous seizures. We posed the alternative hypothesis that classic hippocampal sclerosis results from a single excitatory event that has never been successfully modeled experimentally because convulsive status epilepticus, the insult most commonly used to produce epileptogenic brain injury, is too severe and necessarily terminated before the hippocampus receives the needed duration of excitation. We tested this hypothesis by producing prolonged hippocampal excitation in awake rats without causing convulsive status epilepticus. Two daily 30-minute episodes of perforant pathway stimulation in Sprague-Dawley rats increased granule cell paired-pulse inhibition, decreased epileptiform afterdischarge durations during 8 hours of subsequent stimulation, and prevented convulsive status epilepticus. Similarly, one 8-hour episode of reduced-intensity stimulation in Long-Evans rats, which are relatively resistant to developing status epilepticus, produced hippocampal discharges without causing status epilepticus. Both paradigms immediately produced the extensive neuronal injury that defines classic hippocampal sclerosis, without giving any clinical indication during the insult that an injury was being inflicted. Spontaneous hippocampal-onset seizures began 16-25 days postinjury, before hippocampal atrophy developed, as demonstrated by sequential magnetic resonance imaging. These results indicate that classic hippocampal sclerosis is uniquely produced by a single episode of clinically "cryptic" excitation. Epileptogenic insults may often involve prolonged excitation that goes undetected at the time of injury.

Inflammation enhances epileptogenesis in the developing rat brain

In many experimental systems, proinflammatory stimuli exhibit proconvulsant properties. There are also accumulating data suggesting that inflammation may contribute to epileptogenesis in experimental models as well as in humans. Using two different models (Lithium-pilocarpine induced-status epilepticus (SE) and rapid kindling), we address this issue in the developing brain. Using P14 Wistar rat pups, we showed that inflammation induced by LPS results, after SE, into a more severe disease in adulthood. The main histological feature was an active gliosis that was observed only when inflammation and SE was combined. The use of a kindling model at P14, a model where seizure progress without any neurodegeneration, permits to show that systemic inflammation is responsible of an enhancement of epileptogenesis. The role of inflammation should be further explored in immature brain to identify therapeutic targets that may be relevant to clinical practice where the association of inflammation and epileptic events is common.

The ketogenic diet suppresses the cathepsin E expression induced by kainic acid in the rat brain

PURPOSE

The ketogenic diet has long been used to treat epilepsy, but its mechanism is not yet clearly understood. To explore the potential mechanism, we analyzed the changes in gene expression induced by the ketogenic diet in the rat kainic acid (KA) epilepsy model.

MATERIALS AND METHODS

KA-administered rats were fed the ketogenic diet or a normal diet for 4 weeks, and microarray analysis was performed with their brain tissues. The effects of the ketogenic diet on cathepsin E messenger ribonucleic acid (mRNA) expression were analyzed in KA-administered and normal saline-administered groups with semi-quantitative and real-time reverse transcription polymerase chain reaction (RT-PCR). Brain tissues were dissected into 8 regions to compare differential effects of the ketogenic diet on cathepsin E mRNA expression. Immunohistochemistry with an anti-cathepsin E antibody was performed on slides of hippocampus obtained from whole brain paraffin blocks.

RESULTS

The microarray data and subsequent RT-PCR experiments showed that KA increased the mRNA expression of cathepsin E, known to be related to neuronal cell death, in most brain areas except the brain stem, and these increases of cathepsin E mRNA expression were suppressed by the ketogenic diet. The expression of cathepsin E mRNA in the control group, however, was not significantly affected by the ketogenic diet. The change in cathepsin E mRNA expression was greatest in the hippocampus. The protein level of cathepsin E in the hippocampus of KA-administered rat was elevated in immunohistochemistry and the ketogenic diet suppressed this increase.

CONCLUSION

Our results showed that KA administration increased cathepsin E expression in the rat brain and its increase was suppressed by the ketogenic diet.

A review of current applications of mass spectrometry for neuroproteomics in epilepsy

The brain is unquestionably the most fascinating organ, and the hippocampus is crucial in memory storage and retrieval and plays an important role in stress response. In temporal lobe epilepsy (TLE), the seizure origin typically involves the hippocampal formation. Despite tremendous progress, current knowledge falls short of being able to explain its function. An emerging approach toward an improved understanding of the complex molecular mechanisms that underlie functions of the brain and hippocampus is neuroproteomics. Mass spectrometry has been widely used to analyze biological samples, and has evolved into an indispensable tool for proteomics research. In this review, we present a general overview of the application of mass spectrometry in proteomics, summarize neuroproteomics and systems biology-based discovery of protein biomarkers for epilepsy, discuss the methodology needed to explore the epileptic hippocampus proteome, and also focus on applications of ingenuity pathway analysis (IPA) in disease research. This neuroproteomics survey presents a framework for large-scale protein research in epilepsy that can be applied for immediate epileptic biomarker discovery and the far-reaching systems biology understanding of the protein regulatory networks. Ultimately, knowledge attained through neuroproteomics could lead to clinical diagnostics and therapeutics to lessen the burden of epilepsy on society.

The pontine respiratory group, particularly the Kölliker-Fuse nucleus, mediates phases of the hypoxic ventilatory response in unanesthetized goats

The objective of the present study was to test the hypothesis that, in the in vivo awake goat model, perturbation/lesion in the pontine respiratory group (PRG) would decrease the sensitivity to hypercapnia and hypoxia. The study reported herein was part of two larger studies in which cholinergic modulation in the PRG was attenuated by microdialysis of atropine and subsequently ibotenic acid injections neurotoxically lesioned the PRG. In 14 goats, cannula were bilaterally implanted into either the lateral (n=4) or medial (n=4) parabrachial nuclei or the Kölliker-Fuse nucleus (KFN, n=6). Before and after cannula implantation, microdialysis of atropine, and injection of ibotenic acid, hypercapnic and hypoxic ventilatory sensitivities were assessed. Hypercapnic sensitivity was assessed by three 5-min periods at 3, 5, and 7% inspired CO2. In all groups of goats, CO2 sensitivity was unaffected (P>0.05) by any PRG perturbations/lesions. Hypoxic sensitivity was assessed with a 30-min period at 10.8% inspired O2. The response to hypoxia was typically triphasic, with a phase 1 increase in pulmonary ventilation, a phase 2 roll-off, and a phase 3 prolonged increase associated with shivering and increased metabolic rate and body temperature. In all groups of goats, the phase 1 of the hypoxic ventilatory responses was unaffected by any PRG perturbations/lesions, and there were no consistent effects on the phase 2 responses. However, in the KFN group of goats, the phase 3 ventilatory, shivering, metabolic rate, and temperature responses were markedly attenuated after the atropine dialysis studies, and the attenuation persisted after the ibotenic acid studies. These findings support an integrative or modulatory role for the KFN in the phase 3 responses to hypoxia.

Water maze experience and prenatal choline supplementation differentially promote long-term hippocampal recovery from seizures in adulthood

Status epilepticus (SE) in adulthood dramatically alters the hippocampus and produces spatial learning and memory deficits. Some factors, like environmental enrichment and exercise, may promote functional recovery from SE. Prenatal choline supplementation (SUP) also protects against spatial memory deficits observed shortly after SE in adulthood, and we have previously reported that SUP attenuates the neuropathological response to SE in the adult hippocampus just 16 days after SE. It is unknown whether SUP can ameliorate longer-term cognitive and neuropathological consequences of SE, whether repeatedly engaging the injured hippocampus in a cognitive task might facilitate recovery from SE, and whether our prophylactic prenatal dietary treatment would enable the injured hippocampus to more effectively benefit from cognitive rehabilitation. To address these issues, adult offspring from rat dams that received either a control (CON) or SUP diet on embryonic days 12-17 first received training on a place learning water maze task (WM) and were then administered saline or kainic acid (KA) to induce SE. Rats then either remained in their home cage, or received three additional WM sessions at 3, 6.5, and 10 weeks after SE to test spatial learning and memory retention. Eleven weeks after SE, the brains were analyzed for several hippocampal markers known to be altered by SE. SUP attenuated SE-induced spatial learning deficits and completely rescued spatial memory retention by 10 weeks post-SE. Repeated WM experience prevented SE-induced declines in glutamic acid decarboxylase (GAD) and dentate gyrus neurogenesis, and attenuated increased glial fibrilary acidic protein (GFAP) levels. Remarkably, SUP alone was similarly protective to an even greater extent, and SUP rats that were water maze trained after SE showed reduced hilar migration of newborn neurons. These findings suggest that prophylactic SUP is protective against the long-term cognitive and neuropathological effects of KA-induced SE, and that rehabilitative cognitive enrichment may be partially beneficial.

Diazepam administration after prolonged status epilepticus reduces neurodegeneration in the amygdala but not in the hippocampus during epileptogenesis

An episode of status epilepticus (SE), if left untreated, can lead to death, or brain damage with long-term neurological consequences, including the development of epilepsy. The most common first-line treatment of SE is administration of benzodiazepines (BZs). However, the efficacy of BZs in terminating seizures is reduced with time after the onset of SE; this is accompanied by a reduced efficacy in protecting the hippocampus against neuronal damage, and is associated with impaired function and internalization of hippocampal GABA(A) receptors. In the present study, using Fluoro-Jade C staining, we found that administration of diazepam to rats at 3 h after the onset of kainic acid-induced SE, at a dose sufficient to terminate SE, had no protective effect on the hippocampus, but produced a significant reduction in neuronal degeneration in the amygdala, piriform cortex, and endopiriform nucleus, examined on days 7-9 after SE. Thus, in contrast to the hippocampus, the amygdala and other limbic structures are responsive to neuroprotection by BZs after prolonged SE, suggesting that GABA(A) receptors are not significantly altered in these structures during SE.

Mild as well as severe insults produce necrotic, not apoptotic, cells: evidence from 60-min seizures

We tested the hypothesis that mild insults produce apoptotic, and severe insults necrotic, cells by subjecting adult Wistar rats to 60-min instead of 3-h generalized seizures. Rats' brains were evaluated 6 and 24h later for evidence of neuronal necrosis by light and electron microscopy, the presence of TUNEL staining and active caspase-3 immunoreactivity, and for evidence of DNA laddering 24h after seizures. Apoptotic neurons from the retrosplenial cortex of postnatal day 8 rat pups served as positive controls. Six and 24h after seizures, 16 and 15 brain regions respectively out of 24 showed significant numbers of acidophilic neurons by hematoxylin and eosin stain. Three brain regions had significant numbers of TUNEL-positive neurons 24h after seizures. No neurons showed active caspase-3 immunoreactivity. Acidophilic neurons were necrotic by electron-microscopic examination. Ultrastructurally, they were shrunken and electron-dense, with shrunken, pyknotic nuclei and swollen mitochondria with disrupted cristae. Nuclei did not contain the irregular chromatin clumps found after 3-h seizures. None of the six brain regions studied ultrastructurally that show DNA laddering 24h after 3-h seizures showed DNA laddering 24h after 60-min seizures, probably because there were too few damaged neurons, although the lack of chromatin clumping might have been a contributing factor. Following seizures, a mild as well as a severe insult produces caspase-3-negative necrotic neurons. These results do not support the hypothesis that mild insults produce apoptotic, and severe insults, necrotic, cells.

In vivo glutamate decline associated with kainic acid-induced status epilepticus

Neurophysiological, biochemical, and anatomical evidence implicates glutamatergic mechanisms in epileptic seizures. Until recently, however, longitudinal characterization of in vivo glutamate dynamics was not possible. Here, we present data using in vivo magnetic resonance spectroscopy (MRS) optimized for the detection of glutamate to identify changes that evolve following kainic acid (KA)-induced status epilepticus. Wild-type male Wistar rats underwent whole-brain MR imaging and single-voxel MRS on a clinical 3 T scanner equipped with a high-strength insert gradient coil. Scanning took place before and then 3 days, 28-32 days, and 42-50 days after induction of status epilepticus. Analyses compared 5 seizure (Sz), 5 no-seizure (NoSz; received KA but did not exhibit seizures), and 6 control (Con) animals. This longitudinal study demonstrated reduced glutamate levels in vivo in the dorsal hippocampus 3 days and 1 month following status epilepticus in Sz animals compared with Con animals. Additionally, previous results were replicated: in the Sz group, computed T2 was higher in the ventral hippocampus and limbic cortex 3 days after seizure activity compared with baseline but resolved in both regions at the 1 month scan, suggesting a transient edema. Three days following seizure activity, N-acetylaspartate (NAA) declined and lactate increased in the dorsal hippocampus of the Sz group compared with the Con and NoSz group; both metabolites approached baseline levels by the third scan. Taken together, these results support the conclusion that seizure activity following KA infusion causes loss of glutamatergic neurons.

Lack of kainic acid-induced gamma oscillations predicts subsequent CA1 excitotoxic cell death

Gamma oscillations are a prominent feature of hippocampal network activity, but their functional role remains debated, ranging from mere epiphenomena to being crucial for information processing. Similarly, persistent gamma oscillations sometimes appear prior to epileptic discharges in patients with mesial temporal sclerosis. However, the significance of this activity in hippocampal excitotoxicity is unclear. We assessed the relationship between kainic acid (KA)-induced gamma oscillations and excitotoxicity in genetically engineered mice in which N-methyl-D-aspartic acid receptor deletion was confined to CA3 pyramidal cells. Mutants showed reduced CA3 pyramidal cell firing and augmented sharp wave-ripple activity, resulting in higher susceptibility to KA-induced seizures, and leading to strikingly selective neurodegeneration in the CA1 subfield. Interestingly, the increase in KA-induced gamma-aminobutyric acid (GABA) levels, and the persistent 30-50-Hz gamma oscillations, both of which were observed in control mice prior to the first seizure discharge, were abolished in the mutants. Consequently, on subsequent days, mutants manifested prolonged epileptiform activity and massive neurodegeneration of CA1 cells, including local GABAergic neurons. Remarkably, pretreatment with the potassium channel blocker alpha-dendrotoxin increased GABA levels, restored gamma oscillations, and prevented CA1 degeneration in the mutants. These results demonstrate that the emergence of low-frequency gamma oscillations predicts increased resistance to KA-induced excitotoxicity, raising the possibility that gamma oscillations may have potential prognostic value in the treatment of epilepsy.

Protracted exposure to supraphysiological levels of corticosterone does not cause neuronal loss or damage and protects against kainic acid-induced neurotoxicity in the hippocampus of C57BL/6J mice

High levels of stress or stress hormones have been reported to exacerbate a variety of human disorders of the cardiovascular, gastrointestinal, immune, reproductive, and nervous systems. In rats, high glucocorticoid levels have been reported to cause neuronal death and injury as well as enhance susceptibility to neurotoxic agents and attenuate repair mechanisms; however, the impact of high dosages of CORT in mice has not been fully evaluated. We investigated the ability of supraphysiological levels of CORT to cause hippocampal neuronal death, and to modulate the neurotoxicity of kainic acid (KA) in male C57BL/6J mice. Timed-release CORT pellets (10, 35, 100 mg/21 d) were implanted subcutaneously in the back of mice, and the sustained release of glucocorticoid caused involution of the thymus and decreased the weight of the spleen. Kainic acid caused stage 1 seizures that were unaffected by CORT; however, steroid treatment decreased KA-associated mortality. Little neuronal damage was detected by the cupric-silver neurodegeneration stain. Neurotoxicity caused by an intraperitoneal injection of 25mg/kg KA was attenuated by seven days of CORT pre-treatment. The KA-induced increase in cupric-silver staining, reactive gliosis, microglial activation, and blood-brain barrier disruption was attenuated indicating neuroprotection. Our data indicate supraphysiological levels of CORT do not cause neuronal death or injury in hippocampus of C57BL/6J mice and provide neuroprotection against KA-induced neural damage.

Diffusion weighted magnetic resonance imaging of neuronal activity in the hippocampal slice model

Functional magnetic resonance imaging (fMRI) has become the leading modality for studying the working brain. Being based on measuring the haemodynamic changes after enhanced mass neuronal activity the spatiotemporal resolution of the method is somewhat limited. Alternative MR-based methods for detection of brain activity have been proposed and investigated and studies have reported functional imaging based on diffusion weighted (DW) MRI. The basis for such DW fMRI is believed to be the sensitivity of diffusion weighted MRI to changes in tissue micro-structure. However, it remains unclear whether signal changes observed with these methods reflect cell swelling related to neural activation, residual vascular effects, or a combination of both. Here we present evidence of a detectable, activity-related change in the diffusion weighted MR-signal from the cellular level in live hippocampal slices in the absence of vasculature. Slices are exposed to substances which evoke or inhibit neural activity and the effects are evaluated and compared. The results are also compared to earlier DW fMRI studies in humans.

Hippocampal epileptogenesis in animal models of mesial temporal lobe epilepsy with hippocampal sclerosis: the importance of the "latent period" and other concepts

Prolonged chemoconvulsant-induced status epilepticus in rats has long been promoted as an animal model of mesial temporal lobe epilepsy with hippocampal sclerosis, under the assumption that these animals involve: (1) pathology similar to that of the human neurologic condition; (2) a seizure-free, "preepileptic" latent period of several weeks duration after injury, during which a secondary epileptogenic process gradually develops; and (3) a chronic epileptic state in which the hippocampus, in general, and the dentate gyrus, in particular, becomes a source of the spontaneous behavioral seizures that define these animals as "epileptic." Retrospective analysis suggests that all of these assumptions are in doubt. Neuropathologic studies have shown that prolonged status epilepticus causes greater extrahippocampal than hippocampal damage, and does not produce classic hippocampal sclerosis. In vivo electrophysiologic studies suggest that the hippocampus of these animals may not be "epileptic." Most importantly, studies using continuous video monitoring to detect spontaneous behavioral seizures indicate that these rats become epileptic soon after insult, before any delayed secondary processes have time to develop. High mortality, significant variability, and the lack of an extended "therapeutic window" after brain injury suggest the need to develop animal models that more closely resemble the human neurologic condition.

Minimal latency to hippocampal epileptogenesis and clinical epilepsy after perforant pathway stimulation-induced status epilepticus in awake rats

Hippocampal epileptogenesis is hypothesized to involve secondary mechanisms triggered by initial brain injury. Chemoconvulsant-induced status epilepticus has been used to identify secondary epileptogenic mechanisms under the assumption that a seizure-free, preepileptic "latent period" exists that is long enough to accommodate delayed mechanisms. The latent period is difficult to assess experimentally because early spontaneous seizures may be caused or influenced by residual chemoconvulsant that masks the true duration of the epileptogenic process. To avoid the use of chemoconvulsants and determine the latency to hippocampal epileptogenesis and clinical epilepsy, we developed an electrical stimulation-based method to evoke hippocampal discharges in awake rats and produce hippocampal injury and hippocampal-onset epilepsy reliably. Continuous video monitoring and granule cell layer recording determined whether hippocampal epileptogenesis develops immediately or long after injury. Bilateral perforant pathway stimulation for 3 hours evoked granule cell epileptiform discharges and convulsive status epilepticus with minimal lethality. Spontaneous stage 3-5 behavioral seizures reliably developed within 3 days poststimulation, and all 72 spontaneous behavioral seizures recorded in 10 animals were preceded by spontaneous granule cell epileptiform discharges. Histological analysis confirmed a reproducible pattern of limited hippocampal and extrahippocampal injury, including an extensive bilateral loss of hilar neurons throughout the hippocampal longitudinal axis. These results indicate that hippocampal epileptogenesis after convulsive status epilepticus is an immediate network defect coincident with neuron loss or other early changes. We hypothesize that the latent period is directly related and inversely proportional to the extent of neuron loss in brain regions involved in seizure initiation, spread, and clinical expression.

Temporal Profile of Clinical Signs and Histopathologic Changes in an F-344 Rat Model of Kainic Acid–induced Mesial Temporal Lobe Epilepsy

Since there is limited information in the literature, the purpose of this study was to investigate clinical signs, morphology, and temporal progression of lesions from Days 3 to 168 in a kainic acid (KA)-induced Fischer-344 (F-344) rat model of mesial temporal lobe epilepsy (MTLE). Following a single KA subcutaneous dose of 9 mg/kg to young adult male rats, 95% survived, 93% exhibited status epilepticus, and 80% eventually developed spontaneous motor seizures. Histopathology included hematoxylin and eosin (H&E), autofluorescence, Fluoro-Jade B, Timm’s, ED-1/CD68, GFAP, doublecortin, and Ki-67. Neuronal degeneration occurred on Day 3 in the hippocampal CA1, CA3, and dentate hilar regions; amyg-daloid and thalamic nuclei; and frontoparietotemporal, entorhinal and piriform cortices. Degeneration severity peaked on Day 6 and decreased progressively until Day 168. Aberrant mossy fiber (MF) sprouting was present in the inner molecular layer of dentate gyrus on Days 6–168. Microliosis and astrogliosis peaked on Day 28 and generally colocalized with the distribution of neuronal degeneration. Important correlates to human MTLE included induction of spontaneous seizures, more severe neuronal damage of CA1 than CA3 (in contrast to other animal models but similar to humans), hilar neuronal loss, activated microgliosis and astrogliosis, aberrant MF sprouting, and dentate granule cell neurogenesis. Aberrant MF sprouting prior to spontaneous motor seizures and reduced seizure frequency with a decrease in aberrant MF sprouting support the hypothesis that MF sprouts are necessary for spontaneous seizure generation and maintenance.

Pharmacologic suppression of oxidative damage and dendritic degeneration following kainic acid-induced excitotoxicity in mouse cerebrum

Intense seizure activity associated with status epilepticus and excitatory amino acid (EAA) imbalance initiates oxidative damage and neuronal injury in CA1 of the ventral hippocampus. We tested the hypothesis that dendritic degeneration of pyramidal neurons in the CA1 hippocampal area resulting from seizure-induced neurotoxicity is modulated by cerebral oxidative damage. Kainic acid (KA, 1 nmol/5 microl) was injected intracerebroventricularly to C57Bl/6 mice. F2-isoprostanes (F2-IsoPs) and F4-neuroprostanes (F4-NeuroPs) were used as surrogate measures of in vivo oxidative stress and biomarkers of lipid peroxidation. Nitric oxide synthase (NOS) activity was quantified by evaluating citrulline level and pyramidal neuron dendrites and spines were evaluated using rapid Golgi stains and a Neurolucida system. KA produced severe seizures in mice immediately after its administration and a significant (p<0.001) increase in F2-IsoPs, F4-NeuroPs and citrulline levels were seen 30 min following treatment. At the same time, hippocampal pyramidal neurons showed significant (p<0.001) reduction in dendritic length and spine density. In contrast, no significant change in neuronal dendrite and spine density or F2-IsoP, F4-NeuroPs and citrulline levels were found in mice pretreated with vitamin E (alpha-tocopherol, 100mg/kg, i.p.) for 3 days, or with N-tert-butyl-alpha-phenylnitrone (PBN, 200mg/kg, i.p.) or ibuprofen (inhibitors of cyclooxygenase, COX, 14 microg/ml of drinking water) for 2 weeks prior to KA treatment. These findings indicate novel interactions among free radical-induced generation of F2-IsoPs and F4-NeuroPs, nitric oxide and dendritic degeneration, closely associate oxidative damage to neuronal membranes with degeneration of the dendritic system, and point to possible interventions to limit severe damage in acute neurological disorders.

Effect of age on kainate-induced seizure severity and cell death

While the onset and extent of epilepsy increases in the aged population, the reasons for this increased incidence remain unexplored. The present study used two inbred strains of mice (C57BL/6J and FVB/NJ) to address the genetic control of age-dependent neurodegeneration by building upon previous experiments that have identified phenotypic differences in susceptibility to hippocampal seizure-induced cell death. We determined if seizure induction and seizure-induced cell death are affected differentially in young adult, mature, and aged male C57BL/6J and FVB/NJ mice administered the excitotoxin, kainic acid. Dose response testing was performed in three to four groups of male mice from each strain. Following kainate injections, mice were scored for seizure activity and brains from mice in each age group were processed for light microscopic histopathologic evaluation 7 days following kainate administration to evaluate the severity of seizure-induced brain damage. Irrespective of the dose of kainate administered or the age group examined, resistant strains of mice (C57BL/6J) continued to be resistant to seizure-induced cell death. In contrast, aged animals of the FVB/NJ strain were more vulnerable to the induction of behavioral seizures and associated neuropathology after systemic injection of kainic acid than young or middle-aged mice. Results from these studies suggest that the age-related increased susceptibility to the neurotoxic effects of seizure induction and seizure-induced injury is regulated in a strain-dependent manner, similar to previous observations in young adult mice.

Kainate-induced mitochondrial oxidative stress contributes to hippocampal degeneration in senescence-accelerated mice

We have demonstrated that kainate (KA) induces a reduction in mitochondrial Mn-superoxide dismutase (Mn-SOD) expression in the rat hippocampus and that KA-induced oxidative damage is more prominent in senile-prone (SAM-P8) than senile-resistant (SAM-R1) mice. To extend this, we examined whether KA seizure sensitivity contributed to mitochondrial degeneration in these mouse strains. KA-induced seizure susceptibility in SAM-P8 mice paralleled prominent increases in lipid peroxidation and protein oxidation and was accompanied by significant impairment in glutathione homeostasis in the hippocampus. These findings were more pronounced in the mitochondrial fraction than in the hippocampal homogenate. Consistently, KA-induced decreases in Mn-SOD protein expression, mitochondrial transmembrane potential, and uncoupling protein (UCP)-2 expression were more prominent in SAM-P8 than SAM-R1 mice. Marked release of cytochrome c from mitochondria into the cytosol and a higher level of caspase-3 cleavage were observed in KA-treated SAM-P8 mice. Additionally, electron microscopic evaluation indicated that KA-induced increases in mitochondrial damage and lipofuscin-like substances were more pronounced in SAM-P8 than SAM-R1 animals. These results suggest that KA-mediated mitochondrial oxidative stress contributed to hippocampal degeneration in the senile-prone mouse.

Pilocarpine-induced status epilepticus in rats involves ischemic and excitotoxic mechanisms

The neuron loss characteristic of hippocampal sclerosis in temporal lobe epilepsy patients is thought to be the result of excitotoxic, rather than ischemic, injury. In this study, we assessed changes in vascular structure, gene expression, and the time course of neuronal degeneration in the cerebral cortex during the acute period after onset of pilocarpine-induced status epilepticus (SE). Immediately after 2 hr SE, the subgranular layers of somatosensory cortex exhibited a reduced vascular perfusion indicative of ischemia, whereas the immediately adjacent supragranular layers exhibited increased perfusion. Subgranular layers exhibited necrotic pathology, whereas the supergranular layers were characterized by a delayed (24 h after SE) degeneration apparently via programmed cell death. These results indicate that both excitotoxic and ischemic injuries occur during pilocarpine-induced SE. Both of these degenerative pathways, as well as the widespread and severe brain damage observed, should be considered when animal model-based data are compared to human pathology.

Pyruvate protects against kainate-induced epileptic brain damage in rats

Although the majority of epileptic seizures can be effectively controlled with antiepileptic drugs and/or surgery, a significant number progress to status epilepticus of sufficient duration to cause permanent brain damage. Combined treatment with antiepileptic drugs and neuroprotective agents, however, may help protect these individuals from permanent brain damage. Since toxicity induced by endogenous zinc contributes to epileptic brain injury, and since pyruvate is effective in reducing zinc-triggered neuronal death in cortical culture as well as ischemic neuronal death in vivo, we examined whether systemic pyruvate administration reduces seizure-induced brain damage. Na pyruvate (500 mg/kg) or osmolarity-matched saline (265 mg/kg NaCl, i.p.) were given to adult SD rats 30 or 150 min after 10 mg/kg kainite injection (i.p.), and there was no significant difference in the time course or severity of seizures between these groups. Zinc accumulation in neuronal cell bodies in the hippocampus, however, was much lower in the pyruvate than in the saline group. There was a close correlation between zinc accumulation and cell death, as assessed by acid-fuchsin and TUNEL staining. Pyruvate treatment markedly reduced neuronal death in the hippocampus, neocortex and thalamus. Pyruvate increased HSP-70 expression in hippocampal neurons. These results suggest that pyruvate, a natural glucose metabolite, may be useful as adjunct treatment in status epilepticus to reduce permanent brain damage.

In vivo mapping of temporospatial changes in manganese enhancement in rat brain during epileptogenesis

Mesial temporal lobe epilepsy is associated with structural and functional abnormalities, such as hippocampal sclerosis and axonal reorganization. The temporal evolution of these changes remains to be determined, and there is a need for in vivo imaging techniques that can uncover the epileptogenic processes at an early stage. Manganese-enhanced magnetic resonance imaging may be useful in this regard. The aim of this study was to analyze the temporospatial changes in manganese enhancement in rat brain during the development of epilepsy subsequent to systemic kainate application (10 mg/kg i.p.). MnCl(2) was given systemically on day 2 (early), day 15 (latent), and 11 weeks (chronic phase) after the initial status epilepticus. Twenty-four hours after MnCl(2) injection T1-weighted 3D MRI was performed followed by analysis of manganese enhancement. In the medial temporal lobes, there was a pronounced decrease in manganese enhancement in CA1, CA3, dentate gyrus, entorhinal cortex and lateral amygdala in the early phase. In the latent and chronic phases, recovery of the manganese enhancement was observed in all these structures except CA1. A significant increase in manganese enhancement was detected in the entorhinal cortex and the amygdala in the chronic phase. In the latter phase, the structurally intact cerebellum showed significantly decreased manganese enhancement. The highly differentiated changes in manganese enhancement are likely to represent the net outcome of a number of pathological and pathophysiological events, including cell loss and changes in neuronal activity. Our findings are not consistent with the idea that manganese enhancement primarily reflects changes in glial cells.

Induction of the Wnt inhibitor, Dickkopf-1, is associated with neurodegeneration related to temporal lobe epilepsy

Inhibition of the Wnt pathway by the secreted glycoprotein, Dickkopf-1 (Dkk-1) has been related to processes of excitotoxic and ischemic neuronal death. We now report that Dkk-1 is induced in neurons of the rat olfactory cortex and hippocampus degenerating in response to seizures produced by systemic injection of kainate (12 mg/kg, i.p.). There was a tight correlation between Dkk-1 expression and neuronal death in both regions, as shown by the different expression profiles in animals classified as "high" and "low" responders to kainate. For example, no induction of Dkk-1 was detected in the hippocampus of low responder rats, in which seizures did not cause neuronal loss. Induction of Dkk-1 always anticipated neuronal death and was associated with a reduction in nuclear levels of beta-catenin, which reflects an ongoing inhibition of the canonical Wnt pathway. Intracerebroventricular injections of Dkk-1 antisense oligonucleotides (12 nmol/2 microL) substantially reduced kainate-induced neuronal damage, as did a pretreatment with lithium ions (1 mEq/kg, i.p.), which rescue the Wnt pathway by acting downstream of the Dkk-1 blockade. Taken collectively, these data suggest that an early inhibition of the Wnt pathway by Dkk-1 contributes to neuronal damage associated with temporal lobe epilepsy. We also examined Dkk-1 expression in the hippocampus of epileptic patients and their controls. A strong Dkk-1 immunolabeling was found in six bioptic samples and in one autoptic sample from patients with mesial temporal lobe epilepsy associated with hippocampal sclerosis. Dkk-1 expression was undetectable or very low in autoptic samples from nonepileptic patients or in bioptic samples from patients with complex partial seizures without neuronal loss and/or reactive gliosis in the hippocampus. Our data raise the attractive possibility that drugs able to rescue the canonical Wnt pathway, such as Dkk-1 antagonists or inhibitors of glycogen synthase kinase-3beta, reduce the development of hippocampal sclerosis in patients with temporal lobe epilepsy.

Corticotropin-releasing hormone heterogeneous nuclear RNA (hnRNA) and immunoreactivity are induced in extrahypothalamic brain sites by kainic-acid-induced seizures and are modulated by estrogen

Corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) are pivotal mediators of the hormonal response to stressors and are found within neurons of the paraventricular nucleus of the hypothalamus (PVN) and several extrahypothalamic sites where expression is activity-dependent. Previous work has shown increased CRH immunoreactivity in extrahypothalamic sites after kainic-acid (KA)-induced seizures in male rats. This study examined the induction of CRH heterogeneous nuclear RNA (hnRNA), AVP hnRNA and c-fos as a measure of gene transcription and cell activation following kainic-acid (KA)-induced seizures. KA or saline was administered to intact male rats, ovariectomized (OVX) females and OVX females treated with 17beta-estradiol (E2). Animals were sacrificed 0, 15, 60 or 120 min following KA treatment. In the PVN, CRH hnRNA levels were increased by KA treatment at 15, 60, and 120 min. AVP hnRNA and c-fos mRNA in the PVN were also significantly elevated above controls at all time points. Elevations in CRH hnRNA were also identified in hippocampus, the lateral bed nucleus of the stria terminalis (BNST) and globus pallidus at 60 and 120 min following KA and in the piriform cortex, and central nucleus of the amygdala at 120 min after KA. CRH hnRNA levels at 120 min in the PVN, amygdala, cingulate cortex, hippocampus (CA1), piriform cortex, and BNST were lower in OVX+E2 females compared to females without E2. To determine if the increases in CRH hnRNA translated to increased CRH peptide, immunocytochemistry was performed. CRH immunoreactivity was increased in the amygdala, BNST, cingulate cortex, PVN and globus pallidus within 3 h after KA treatment and in the piriform cortex and hippocampus by 6 h after KA. These results suggest a time-dependent activation of the CRH system following activation of kainate receptors, which may result in long-term changes in the expression of extrahypothalamic CRH.

Thalamic changes in mesial temporal sclerosis: a limbic system pathology. A case report

Hippocampal abnormalities correlated with mesial temporal sclerosis (MTS) are well documented. MTS may be associated with extrahippocampal anomalies involving limbic structures along a known neuroanatomic pathway (Papez circuit). We report a patient with MTS and thalamic changes. Seizure-related thalamic damage could have been caused by abnormal electric discharges from the mamillary body to the anterior thalamus through the mamillothalamic tract. This suggests that MTS is not limited to the temporal lobe but could represent a limbic system pathology.

Recurrent circuits in layer II of medial entorhinal cortex in a model of temporal lobe epilepsy

Patients and laboratory animal models of temporal lobe epilepsy display loss of layer III pyramidal neurons in medial entorhinal cortex and hyperexcitability and hypersynchrony of less vulnerable layer II stellate cells. We sought to test the hypothesis that loss of layer III pyramidal neurons triggers synaptic reorganization and formation of recurrent, excitatory synapses among layer II stellate cells in epileptic pilocarpine-treated rats. Laser-scanning photo-uncaging of glutamate focally activated neurons in layer II while excitatory synaptic responses were recorded in stellate cells. Photostimulation revealed previously unidentified, functional, recurrent, excitatory synapses between layer II stellate cells in control animals. Contrary to the hypothesis, however, control and epileptic rats displayed similar levels of recurrent excitation. Recently, hyperexcitability of layer II stellate cells has been attributed, at least in part, to loss of GABAergic interneurons and inhibitory synaptic input. To evaluate recurrent inhibitory circuits in layer II, we focally photostimulated interneurons while recording inhibitory synaptic responses in stellate cells. IPSCs were evoked more than five times more frequently in slices from control versus epileptic animals. These findings suggest that in this model of temporal lobe epilepsy, reduced recurrent inhibition contributes to layer II stellate cell hyperexcitability and hypersynchrony, but increased recurrent excitation does not.

Gastrodia elata modulated activator protein 1 via c-Jun N-terminal kinase signaling pathway in kainic acid-induced epilepsy in rats

Gastrodia elata (Orchidaceae) is a Chinese herb. Our previous study showed that Gastrodia elata is able to reduce epileptic seizures, oxygen free radicals, microglia activation, and apoptosis in kainic acid (KA)-treated rats. Activator protein 1 (AP-1) is involved in modulating the neuronal plasticity and apoptosis. Therefore, the aim of this study was to investigate the role of AP-1 in antiepileptic effect of Gastrodia elata. Gastrodia elata (0.5, 1.0g/kg) or valproic acid (VA, 250mg/kg) was administered orally in Sprague-Dawley rats for 1 week before and 2 weeks after intraperitoneal injection of KA. Protein levels of AP-1 were determined by measuring c-Jun and c-Fos proteins, and the mitogen-activated protein (MAP) kinases activations were determined by measuring the phosphorylations of extracellular signal-regulated kinases, p38, and c-Jun N-terminal kinases (JNKs) in the frontal cortex and the hippocampus of rat brain using Western blotting. These results indicated that pre-treatment with Gastrodia elata or VA activated JNK signal pathway and c-Jun expression, while post-treatment with Gastrodia elata or VA suppressed both the JNK signaling pathway and the c-Jun expression induced by KA. These findings suggested that Gastrodia elata regulated the AP-1 expression via the JNK signaling pathway in KA-induced epilepsy.

Kainic acid dose affects delayed cell death mechanism after status epilepticus

Kainic acid (KA)-induced status epilepticus (SE) produces hippocampal neuronal death, which varies from necrosis to apoptosis or programmed cell death (PCD). We examined whether the type of neuronal death was dependent on KA dose. Adult rats were induced SE by intraperitoneal injection of KA at 9 mg/kg (K9) or 12 mg/kg (K12). Hippocampal neuronal death was assessed by TUNEL staining, electron microscopy, and Western blotting of caspase-3 on days 1, 3 and 7 after SE induction. K12 rats showed higher a mortality rate and shorter latency to the onset of SE when compared with K9 rats. In both groups, acidophilic and pyknotic neurons were evident in CA1 at 24h after SE and neuronal loss developed from day 3. The degenerated neurons became TUNEL-positive on days 3 and 7 in K9 rats but not in K12 rats. Caspase-3 activation was detected on days 3 and 7 in K9 rats but was undetectable in K12 rats. Ultrastructural study revealed shrunken neurons exhibiting pyknotic nuclei containing small and dispersed chromatin clumps 24h after SE in CA1. No cells exhibited apoptosis. On days 3 and 7, the degenerated neurons were necrotic with high electron density and small chromatin clumps. There were no ultrastructural differences between the K9 and K12 groups. These results revealed that differences in KA dose affected the delayed cell death (3 and 7 days after SE); however, no effect was seen on the early cell death (24h after SE). Moderate-dose KA induced necrosis, while low-dose KA induced PCD.

Preferential neuron loss in the rat piriform cortex following pilocarpine-induced status epilepticus

Structures within the piriform cortex (PC) including the endopiriform nucleus (DEN) and pre-endopiriform nucleus (pEn) have been implicated to be involved in seizure genesis in models of temporal lobe epilepsy. We used stereological methods to examine the specificity and extent of neuron loss in the PC of pilocarpine-treated rats. Both 7 days and 2 months post-status epilepticus rats showed significant neuron loss in the pEn and DEN, layer III of the intermediate PC, and layers II and III of the caudal PC. Total losses in the PC were 40 and 46% in 7 days and 2 months post-status epilepticus rats, respectively (p<0.01). The numbers of parvalbumin (PV)- and cholecystokinin (CCK)-immunopositive neuron profiles significantly decreased, and somatostatin (SS)-immunopositive neuron profiles tended to decrease. A large decrease in the number of PV-immunopositive neuron profiles occurred in the pEn, adjoining parts of the DEN and deep layer III of the PC, portions of the DEN bordering the claustrum and agranular insular cortex, and layer III of the caudal PC. The regions with decreased numbers of PV-, CCK-, and SS-immunopositive neuron profiles overlapped with those where many Nissl-stained neurons were lost and many degenerating cell bodies were detected. These results suggest that the decreases in the numbers of PV/SS/CCK-immunopositive neurons are related to neuron loss rather than to a low rate of synthesis of their peptides or proteins.

Hippocampal neurodegeneration, spontaneous seizures, and mossy fiber sprouting in the F344 rat model of temporal lobe epilepsy

The links among the extent of hippocampal neurodegeneration, the frequency of spontaneous recurrent motor seizures (SRMS), and the degree of aberrant mossy fiber sprouting (MFS) in temporal lobe epilepsy (TLE) are a subject of contention because of variable findings in different animal models and human studies. To understand these issues further, we quantified these parameters at 3-5 months after graded injections of low doses of kainic acid (KA) in adult F344 rats. KA was administered every 1 hr for 4 hr, for a cumulative dose of 10.5 mg/kg bw, to induce continuous stages III-V motor seizures for >3 hr. At 4 days post-KA, the majority of rats (77%) exhibited moderate bilateral neurodegeneration in different regions of the hippocampus; however, 23% of rats exhibited massive neurodegeneration in all hippocampal regions. All KA-treated rats displayed robust SRMS at 3 months post-KA, and the severity of SRMS increased over time. Analyses of surviving neurons at 5 months post-KA revealed two subgroups of rats, one with moderate hippocampal injury (HI; 55% of rats) and another with widespread HI (45%). Rats with widespread HI exhibited greater loss of CA3 pyramidal neurons and robust aberrant MFS than rats with moderate HI. However, the frequency of SRMS (approximately 3/hr) was comparable between rats with moderate and widespread HI. Thus, in comparison with TLE model using Sprague-Dawley rats (Hellier et al. [1998] Epilepsy Res. 31:73-84), a much lower cumulative dose of KA leads to robust chronic epilepsy in F344 rats. Furthermore, the occurrence of SRMS in this model is always associated with considerable bilateral hippocampal neurodegeneration and aberrant MFS. However, more extensive hippocampal CA3 cell loss and aberrant MFS do not appear to increase the frequency of SRMS. Because most of the features are consistent with mesial TLE in humans, the F344 model appears ideal for testing the efficacy of potential treatment strategies for mesial TLE.

Fear conditioning is impaired in systemic kainic acid and amygdala-stimulation models of epilepsy

PURPOSE

The lateral nucleus of the amygdala is critical for fear conditioning, a paradigm of emotional learning, which requires recognition of an unconditioned stimulus as aversive and association of conditioned stimuli with an unconditioned stimulus. Some patients with temporal lobe epilepsy have amygdaloid damage associated with impaired emotional learning. Fear conditioning also is impaired at least in some animal models of epilepsy. We studied whether contextual or tone-cued fear conditioning is impaired in two status epilepticus models of epilepsy and whether impairment correlates with the extent of damage in the lateral nucleus of the amygdala.

METHODS

We induced epilepsy in rats by either systemic kainic acid administration or electrical amygdala stimulation. Behavioral reactions in all phases of fear conditioning were analyzed from videotapes. Damage to the lateral nucleus of the amygdala was analyzed from thionin-stained sections both histologically and by volumetry.

RESULTS

Immediate reflexive responses to unconditioned and conditioned stimuli were preserved, whereas the freezing response to an unconditioned stimulus was reduced. Contextual conditioning was severely impaired, whereas tone-cued conditioning was better preserved. The lateral nucleus pathology did not correlate with impaired fear conditioning.

CONCLUSIONS

These data suggest that processing of complex contextual stimuli is severely affected in experimental epilepsy, whereas conditioning to simple cues is better preserved.

Increased estrogen receptor beta expression correlates with decreased spine formation in the rat hippocampus

Estrogens play an important role in the brain function acting through two receptor types, ERalpha and ERbeta, both well-recognized as transcription factors. In this study, we investigated the ERbeta mRNA and protein levels in the rat hippocampus by using two in vivo models that are known to affect synapse formation. Natural estrous-proestrous cycle was used as a model in which a marked decrease in the density of hippocampal synapses was previously observed between proestrus and estrus. We have found that ERbeta mRNA and protein were displayed in high levels in the estrus and in low levels in the proestrous phase. By applying kainic acid (KA) to adult rats, we demonstrated that up-regulation of ERbeta mRNA and protein in hippocampal CA regions was vulnerable to KA-induced excitotoxicity. Furthermore, we note a concomitant decrease of ERbeta in the excitotoxicity-resistant denate gyrus that undergoes intense plastic changes, including synaptogenesis. These data suggested that decreases in ERbeta expression correlated with increase in synapse formation. This notion has been tested in vitro in hippocampal cultures, in which overexpression of ERbeta by means of gene transfection resulted in the lowering of the dendritic spine density that was elevated by estrogen. In summary, our results suggest that ERbeta inhibits synapse formation in hippocampal neurons.

Hyperexcitability, interneurons, and loss of GABAergic synapses in entorhinal cortex in a model of temporal lobe epilepsy

Temporal lobe epilepsy is the most common type of epilepsy in adults, and its pathophysiology remains unclear. Layer II stellate cells of the entorhinal cortex, which are hyperexcitable in animal models of temporal lobe epilepsy, provide the predominant synaptic input to the hippocampal dentate gyrus. Previous studies have ascribed the hyperexcitability of layer II stellate cells to GABAergic interneurons becoming "dormant" after disconnection from their excitatory synaptic inputs, which has been reported to occur during preferential loss of layer III pyramidal cells. We used whole-cell recording from slices of entorhinal cortex in pilocarpine-treated epileptic rats to test the dormant interneuron hypothesis. Hyperexcitability appeared as multiple action potentials and prolonged depolarizations evoked in layer II stellate cells of epileptic rats but not controls. However, blockade of glutamatergic synaptic transmission caused similar percentage reductions in the frequency of spontaneous IPSCs in layer II stellate cells of control and epileptic rats, suggesting similar levels of excitatory synaptic input to GABAergic interneurons. Direct recordings and biocytin labeling revealed two major types of interneurons in layer III whose excitatory synaptic drive in epileptic animals was undiminished. Interneurons in layer III did not appear to be dormant; therefore, we tested whether loss of GABAergic synapses might underlie hyperexcitability of layer II stellate cells. Stereological evidence of fewer GABAergic interneurons, fewer gephyrin-immunoreactive punctae, and reduced frequency of spontaneous IPSCs and miniature IPSCs (recorded in tetrodotoxin) confirmed that layer II stellate cell hyperexcitability is attributable, at least in part, to reduced inhibitory synaptic input.

Mutations in amyloid precursor protein and presenilin-1 genes increase the basal oxidative stress in murine neuronal cells and lead to increased sensitivity to oxidative stress mediated by amyloid beta-peptide (1-42), HO and kainic acid: implications for Alzheimer's disease

Oxidative stress is observed in Alzheimer's disease (AD) brain, including protein oxidation and lipid peroxidation. One of the major pathological hallmarks of AD is the brain deposition of amyloid beta-peptide (Abeta). This 42-mer peptide is derived from the beta-amyloid precursor protein (APP) and is associated with oxidative stress in vitro and in vivo. Mutations in the PS-1 and APP genes, which increase production of the highly amyloidogenic amyloid beta-peptide (Abeta42), are the major causes of early onset familial AD. Several lines of evidence suggest that enhanced oxidative stress, inflammation, and apoptosis play important roles in the pathogenesis of AD. In the present study, primary neuronal cultures from knock-in mice expressing mutant human PS-1 and APP were compared with those from wild-type mice, in the presence or absence of various oxidizing agents, viz, Abeta(1-42), H2O2 and kainic acid (KA). APP/PS-1 double mutant neurons displayed a significant basal increase in oxidative stress as measured by protein oxidation, lipid peroxidation, and 3-nitrotyrosine when compared with the wild-type neurons (p < 0.0005). Elevated levels of human APP, PS-1 and Abeta(1-42) were found in APP/PS-1 cultures compared with wild-type neurons. APP/PS-1 double mutant neuron cultures exhibited increased vulnerability to oxidative stress, mitochondrial dysfunction and apoptosis induced by Abeta(1-42), H2O2 and KA compared with wild-type neuronal cultures. The results are consonant with the hypothesis that Abeta(1-42)-associated oxidative stress and increased vulnerability to oxidative stress may contribute significantly to neuronal apoptosis and death in familial early onset AD.