Model Of Mesial Temporal Lobe Epilepsy Research Articles

Environmental enrichment delays limbic epileptogenesis and restricts pathologic synaptic plasticity.

Environmental exposures impart powerful effects on vulnerability to many brain diseases, including epilepsy. Mesial temporal lobe epilepsy (MTLE) is a common form of epilepsy, and it is often accompanied by neuropsychiatric comorbidities. This study tests the hypothesis that environmental enrichment (EE) confers antiepileptogenic, psychoprotective, and neuroprotective effects in the amygdala kindling model of MTLE, and explores potential neurobiologic mechanisms. At weaning, male Wistar rats were allocated into either EE (large cages containing running wheels and toys; n = 43) or standard housing (SH; standard laboratory cages; n = 39) conditions. At P56, a bipolar electrode was implanted into the left amygdala, and rats underwent rapid amygdala kindling until experiencing five class V seizures (Racine scale, fully kindled). The elevated plus maze was used to assess anxiety. Postmortem histologic and molecular analyses investigated potential biologic mediators of effects. EE significantly delayed kindling epileptogenesis, with EE rats requiring a significantly greater number of kindling stimulations to reach a fully kindled state compared to SH rats (p < 0.05). EE and kindling both reduced anxiety (p < 0.05). Timm's staining revealed significant reductions in aberrant mossy fiber sprouting in EE rats (p < 0.05), and these effects of EE were accompanied by reduced expression of TrkB and CRH genes. We identify beneficial effects of EE on vulnerability to limbic epileptogenesis and anxiety, and identify reduced pathologic neuroplasticity and plasticity-related gene expression as potential underlying mechanisms. Enhanced environmental stimulation represents a potential antiepileptogenic strategy that might also mitigate the common psychiatric comorbidities of MTLE.

Does angiogenesis play a role in the establishment of mesial temporal lobe epilepsy?

Mesial temporal lobe epilepsy (MTLE) is a focal epileptic disorder that is frequently associated with hippocampal sclerosis. This study investigated whether blocking angiogenesis prevents the development of seizures and hippocampal atrophy in the pilocarpine rat model of MTLE. To block angiogenesis, a subset of animals were given sunitinib orally. Continuous video recordings were performed to identify seizures. Brains were then extracted and sectioned, and hippocampal surfaces and angiogenesis were assessed. After a latent period of 6.6±2.6 days, the sham-treated pilocarpine rats presented convulsive seizures, while the pilocarpine rats treated with sunitinib did not develop seizures. Sham-treated pilocarpine rats but not sunitinib-treated pilocarpine rats had significantly smaller hippocampi. Endothelial cell counts in sham-treated pilocarpine rats were significantly greater than in controls and sunitinib-treated pilocarpine rats. Blocking angiogenesis immediately following the initial insult in this animal model prevented thus angiogenesis and hippocampal atrophy and averted the development of clinical seizures.

Lacosamide modulates interictal spiking and high-frequency oscillations in a model of mesial temporal lobe epilepsy

Nearly one third of patients presenting with mesial temporal lobe epilepsy (MTLE), the most prevalent lesion-related epileptic disorder in adulthood, do not respond to currently available antiepileptic medications. Thus, there is a need to identify and characterize new antiepileptic drugs. In this study, we used the pilocarpine model of MTLE to establish the effects of a third generation drug, lacosamide (LCM), on seizures, interictal spikes and high-frequency oscillations (HFOs, ripples: 80-200 Hz, fast ripples: 250-500 Hz). Sprague-Dawley rats (250-300 g) were injected with pilocarpine to induce a status epilepticus (SE) that was pharmacologically terminated after 1h. Eight pilocarpine-treated rats were then injected with LCM (30 mg/kg, i.p.) 4h after SE and daily for 14 days. Eight pilocarpine-treated rats were used as controls and treated with saline. Three days after SE, all rats were implanted with bipolar electrodes in the hippocampal CA3 region, entorhinal cortex (EC), dentate gyrus (DG) and subiculum and EEG-video monitored from day 4 to day 14 after SE. LCM-treated animals showed lower rates of seizures (0.21 (± 0.11) seizures/day) than controls (2.6 (±0.57), p<0.05), and a longer latent period (LCM: 11 (± 1) days, controls: 6.25 (± 1), p<0.05). Rates of interictal spikes in LCM-treated rats were significantly lower than in controls in CA3 and subiculum (p<0.05). Rates of ripples and fast ripples associated with interictal spikes in CA3 and subiculum as well as rates of fast ripples occurring outside of interictal spikes in CA3 were also significantly lower in LCM-treated animals. In controls, interictal spikes and associated HFOs correlated to seizure clustering, while this was not the case for isolated HFOs. Our findings show that early treatment with LCM has powerful anti-ictogenic properties in the pilocarpine model of MTLE. These effects are accompanied by decreased rates of interictal spikes and associated HFOs. Isolated HFOs were also modulated by LCM, in a manner that appeared to be unrelated to its antiictogenic effects. These results thus suggest that distinct mechanisms may underlie interictal-associated and isolated HFOs in the pilocarpine model of MTLE.

Effects of site-specific infusions of methionine sulfoximine on the temporal progression of seizures in a rat model of mesial temporal lobe epilepsy

Glutamine synthetase (GS) in astrocytes is critical for metabolism of glutamate and ammonia in the brain, and perturbations in the anatomical distribution and activity of the enzyme are likely to adversely affect synaptic transmission. GS is deficient in discrete regions of the hippocampal formation in patients with mesial temporal lobe epilepsy (MTLE), a disorder characterized by brain glutamate excess and recurrent seizures. To investigate the role of site-specific inhibition of GS in MTLE, we chronically infused the GS inhibitor methionine sulfoximine (MSO) into one of the following areas of adult laboratory rats: (1) the angular bundle, n=6; (2) the deep entorhinal cortex (EC), n=7; (3) the stratum lacunosum-moleculare of CA1, n=7; (4) the molecular layer of the subiculum, n=10; (5) the hilus of the dentate gyrus, n=6; and (6) the lateral ventricle, n=6. Twelve animals were infused with phosphate buffered saline (PBS) into the same areas to serve as controls. All infusions were unilateral, and animals were monitored by continuous video-intracranial EEG recordings for 3 weeks to capture seizure activity. All animals infused with MSO into the entorhinal-hippocampal area exhibited recurrent seizures that were particularly frequent during the first 3 days of infusion and that continued to recur for the entire 3 week recording period. Only a fraction of animals infused with MSO into the lateral ventricle had recurrent seizures, which occurred at a lower frequency compared with the other MSO infused group. Infusion of MSO into the hilus of the dentate gyrus resulted in the highest total number of seizures over the 3-week recording period. Infusion of MSO into all brain regions studied, with the exception of the lateral ventricle, led to a change in the composition of seizure severity over time. Low-grade (stages 1-3) seizures were more prevalent early during infusion, while severe (stages 4-5) seizures were more prevalent later. Thus, the site of GS inhibition within the brain determines the pattern and temporal evolution of recurrent seizures in the MSO model of MTLE.

Reorganization of supramammillary-hippocampal pathways in the rat pilocarpine model of temporal lobe epilepsy: evidence for axon terminal sprouting.

In mesial temporal lobe epilepsy (MTLE), spontaneous seizures likely originate from a multi-structural epileptogenic zone, including several regions of the limbic system connected to the hippocampal formation. In this study, we investigate the structural connectivity between the supramammillary nucleus (SuM) and the dentate gyrus (DG) in the model of MTLE induced by pilocarpine in the rat. This hypothalamic nucleus, which provides major extracortical projections to the hippocampal formation, plays a key role in the regulation of several hippocampus-dependent activities, including theta rhythms, memory function and emotional behavior, such as stress and anxiety, functions that are known to be altered in MTLE. Our findings demonstrate a marked reorganization of DG afferents originating from the SuM in pilocarpine-treated rats. This reorganization, which starts during the latent period, is massive when animals become epileptic and continue to evolve during epilepsy. It is characterized by an aberrant distribution and an increased number of axon terminals from neurons of both lateral and medial regions of the SuM, invading the entire inner molecular layer of the DG. This reorganization, which reflects an axon terminal sprouting from SuM neurons, could contribute to trigger spontaneous seizures within an altered hippocampal intrinsic circuitry.

Dynamics of interictal spikes and high-frequency oscillations during epileptogenesis in temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is characterized in humans and in animal models by a seizure-free latent phase that follows an initial brain insult; this period is presumably associated to plastic changes in temporal lobe excitability and connectivity. Here, we analyzed the occurrence of interictal spikes and high frequency oscillations (HFOs; ripples: 80–200Hz and fast ripples: 250–500Hz) from 48h before to 96h after the first seizure in the rat pilocarpine model of MTLE. Interictal spikes recorded with depth EEG electrodes from the hippocampus CA3 area and entorhinal cortex (EC) were classified as type 1 (characterized by a spike followed by a wave) or type 2 (characterized by a spike with no wave). We found that: (i) there was a switch in the distribution of both types of interictal spikes before and after the occurrence of the first seizure; during the latent phase both types of interictal spikes predominated in the EC whereas during the chronic phase both types of spikes predominated in CA3; (ii) type 2 spike duration decreased in both regions from the latent to the chronic phase; (iii) type 2 spikes associated to fast ripples occurred at higher rates in EC compared to CA3 during the latent phase while they occurred at similar rates in both regions in the chronic phase; and (iv) rates of fast ripples outside of spikes were higher in EC compared to CA3 during the latent phase. Our findings demonstrate that the transition from the latent to the chronic phase is paralleled by dynamic changes in interictal spike and HFO expression in EC and CA3. We propose that these changes may represent biomarkers of epileptogenicity in MTLE.

5-Aminovaleric acid suppresses the development of severe seizures in the methionine sulfoximine model of mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is one of the most common forms of drug-resistant, localization-related epilepsies in humans. One potential therapeutic target is the brain glutamine–glutamate–GABA metabolic pathway, which is perturbed in patients with MTLE. Loss of glutamine synthetase (GS) in astrocytes may be critically involved in this perturbation, which can be modeled by infusing the GS inhibitor methionine sulfoximine (MSO) into the entorhinal–hippocampal area in rats. Because 5-aminovaleric acid (5-AV) has been implicated in modulation of the glutamine–glutamate–GABA metabolic pathway, we hypothesized that 5-AV would alter the expression of seizures in the MSO model of MTLE.Male Sprague Dawley rats (300–330g) were implanted with an Alzet pump placed subcutaneously in the abdominal region to release either 5-AV (0.05mg/mL, n=6) or phosphate buffered saline (PBS, n=6) at a rate of 2.5μl/h over 28days. Five to 7days after surgery, all rats were implanted with an intracranial pump infusing MSO (2.5mg/mL; 0.25μl/h) unilaterally into the hippocampal formation. Following the second surgery, intracranial EEG was measured from the left and right hemispheres above the dorsal hippocampal formations for a continuous period of 21days. The EEG was correlated with simultaneous video recordings to determine the stage of seizures according to a modified Racine scale.Five-AV-treated rats experienced a 3.5 fold reduction in the number of seizures (6.7±1.4seizures/day) than PBS-treated rats (23.2±6.3seizures/day) during the first 2days following MSO pump placement (p<0.005). Both groups showed similar seizure frequency over days 3–21 (~1seizure/day). However, the fraction of the most severe type of seizures (Racine stages 4 and 5) increased over time in the PBS treated group, but not in the 5-AV treated group. Notably, 5-AV treated rats experienced a 2.3 and 2.6 fold lower fraction of stage 4 and 5 seizures than PBS-treated rats during the 2nd and 3rd weeks of MSO treatment respectively (p<0 .05 and p<0.001 respective to week).Five-AV markedly reduces the number of seizures initially and suppresses the development of the most severe type of seizures in the MSO model of MTLE. These results may have implications for the therapeutic use of 5-AV in treating mesial temporal lobe seizures and for our understanding of the chemical pathology of epileptogenesis and MTLE.

Myoloid-Related Protein 8, an Endogenous Ligand of Toll-Like Receptor 4, Is Involved in Epileptogenesis of Mesial Temporal Lobe Epilepsy Via Activation of the Nuclear Factor-κB Pathway in Astrocytes

The role of Toll-like receptor 4 (TLR4) in the activation of innate immunity has been extensively studied in the past several years. Here, we are the first to report that myeloid-related protein 8 (MRP8), an endogenous TLR4 ligand, is involved in the epileptogenesis of mesial temporal lobe epilepsy (MTLE). We find that the expression of MRP8, TLR4, and interleukin 1-β (IL-1β) was upregulated in a MTLE model during both acute and chronic disease stages. We next investigated the possible roles played by astrocytes, which have been shown to be the major source of IL-1β during epilepsy. Stimulation via MRP8 led to the induction of IL-1β in astrocytes in vitro, accompanied by the activation of Nuclear Factor-κB, while knockdown of TLR4 or inhibition of NF-κB in astrocytes prevented this IL-1β induction. Thus, MRP8 may potentiate the perpetuation of MTLE by activating the NF-κB pathway in astrocytes, and could be a new target for anticonvulsant therapies.

Morphology and differentially expressed proteins in hippocampus of mesial temporal lobe epilepsy model of immature rats induced by pilocarpine

To examine the changes of morphology and differentially expressed proteins in hippocampus at the latent stage of chronic mesial temporal lobe epilepsy (MTLE) in immature rats, and to explore the global mechanism of chronic MTLE at a new point. MTLE models of immature rats were induced by lithium-pilocarpine. The rats were divided into 2 groups randomly: a control group (n=20) and an MTLE model group (n=20). At the latent stage, nissl and Timm staining were performed to evaluate the cell loss and mossy fiber sprouting. The differentially expressed proteins were separated by 2-dimensional polyacrylamide gel electrophoresis (2-DE) combined with matrix-assisted laser desorption/ ionization time of flight mass spectrometry (MALDI-TOF-MS) technology. Western blot was used to determine the differentially expression levels of partial proteins. Neuron loss and abnormal mossy fiber sprouting were obviously observed in the hippocampus in the MTLE model group; 2-DE patterns of hippocampus of the MTLE model group in latent stage and the control group were established. Thirty-one differential proteins were identified by MALDI-TOF-MS, which were categorized into several groups by biological functions: synaptic and neurotransmitter release related proteins, cytoskeletal proteins, cell junctions proteins, energy metabolism and mitochondrial proteins, biological enzymes, cellular structure related proteins, signal regulating molecular and others. The expression levels of partial proteins determined by Western blot were similar to the changes of proteomics. The differentially expressed proteins of synapse-related proteins such as dynamin-1, neurogranin and ubiquitin, which cause the synapse reorganization and mossy fiber terminal sprouting related to the formation of abnormal excitatory network, probably play critic roles in the mechanism of MTLE.

Mislocalization of AQP4 precedes chronic seizures in the kainate model of temporal lobe epilepsy

It has been suggested that loss of the astrocytic water channel aquaporin-4 (AQP4) from perivascular endfeet in sclerotic hippocampi contributes to increased seizure propensity in human mesial temporal lobe epilepsy (MTLE). Whether this loss occurs prior to or as a consequence of epilepsy development remains to be resolved. In the present study, we investigated whether the expression and distribution of AQP4 was altered prior to (i.e., in the latent phase) or after the onset of chronic epileptic seizures (i.e., in the chronic phase) in the kainate (KA) model of MTLE. Immunogold electron microscopic analysis revealed that AQP4 density in adluminal endfoot membranes was reduced in KA treated rats already in the latent phase, while the AQP4 density in the abluminal endfoot membrane was stable or slightly increased. The decrease in adluminal AQP4 immunogold labeling was accompanied by a reduction in the density of AQP4's anchoring protein alpha-syntrophin. The latent and chronic phases were associated with an upregulation of the M1 isoform of AQP4, as judged by semi-quantitative Western blot analysis. Taken together, the findings in this model suggest that a mislocalization of AQP4--reflecting a loss of astrocyte polarization--is an integral part of the epileptogenic process.

Early-Life Stress Is Associated with Gender-Based Vulnerability to Epileptogenesis in Rat Pups

During development, the risk of developing mesial temporal lobe epilepsy (MTLE) increases when the developing brain is exposed to more than one insult in early life. Early life insults include abnormalities of cortical development, hypoxic-ischemic injury and prolonged febrile seizures. To study epileptogenesis, we have developed a two-hit model of MTLE characterized by two early-life insults: a freeze lesion-induced cortical malformation at post-natal day 1 (P1), and a prolonged hyperthermic seizure (HS) at P10. As early life stressors lead to sexual dimorphism in both acute response and long-term outcome, we hypothesized that our model could lead to gender-based differences in acute stress response and long-term risk of developing MTLE. Male and female pups underwent a freeze-lesion induced cortical microgyrus at P1 and were exposed to HS at P10. Animals were monitored by video-EEG from P90 to P120. Pre and post-procedure plasma corticosterone levels were used to measure stress response at P1 and P10. To confirm the role of sex steroids, androgenized female pups received daily testosterone injections to the mother pre-natally and post-natally for nine days while undergoing both insults. We demonstrated that after both insults females did not develop MTLE while all males did. This correlated with a rise in corticosterone levels at P1 following the lesion in males only. Interestingly, all androgenized females showed a similar rise in corticosterone at P1, and also developed MTLE. Moreover, we found that the cortical lesion significantly decreased the latency to generalized convulsion during hyperthermia at P10 in both genders. The cortical dysplasia volumes at adulthood were also similar between male and female individuals. Our data demonstrate sexual dimorphism in long-term vulnerability to develop epilepsy in the lesion + hyperthermia animal model of MTLE and suggest that the response to early-life stress at P1 contributes significantly to epileptogenesis in a gender-specific manner.

Interleukin‐1β and microRNA‐146a in an immature rat model and children with mesial temporal lobe epilepsy

Increasing evidence indicates that neuroinflammation plays a critical role in the pathogenesis of mesial temporal lobe epilepsy (MTLE). The aim of this study was to investigate the dynamic expression of interleukin (IL)-1β as a proinflammatory cytokine and microRNA (miR)-146a as a posttranscriptional inflammation-associated microRNA (miRNA) in the hippocampi of an immature rat model and children with MTLE. To study the expression of IL-1β and miR-146a, we performed a reverse transcription polymerase chain reaction, Western blot, and real-time quantitative PCR on the hippocampi of immature rats at 11 days of age. Expression was monitored in the acute, latent, and chronic stages of disease (2 h and 3 and 8 weeks after induction of lithium-pilocarpine status epilepticus, respectively), and in control hippocampal tissues corresponding to the same timeframes. Similar expression methods were applied to hippocampi obtained from children with MTLE and normal controls. The expression of IL-1β and miR-146a in both children and immature rats with MTLE differs according to the stage of MTLE development. Both IL-1β and miR-146a are significantly up-regulated, but in opposite ways: IL-1β expression is highest in the acute stage, when expression of miR-146a is at its lowest level; miR-146a expression is highest in the latent stage, when IL-1β expression is at its lowest level. Both IL-1β and miR-146a are up-regulated in the chronic stage, but not as much as in the other stages. Our study is the first to focus on the expression of miR-146a in the immature rat model of lithium-pilocarpine MTLE and in children with MTLE. We have detected that the expression of proinflammatory cytokine IL-1β and posttranscriptional inflammation-associated miR-146a is variable depending on the disease stage. Furthermore, both IL-1β and miR-146a are up-regulated in immature rats and children with MTLE. Our findings elucidate the role of inflammation in the pathogenesis of MTLE in the immature rat model and children. Therefore, modulation of the IL-1β-miR-146a axis may be a novel therapeutic target in the treatment of MTLE.

The mTOR pathway is activated in glial cells in mesial temporal sclerosis

Mammalian target of rapamycin (mTOR) is a key protein kinase that regulates basic cellular processes, including development and growth. Mutations in mTOR cause tuberous sclerosis complex (TSC), a condition that is characterized by developmental brain malformations (cortical tubers) and epilepsy. Although considerable insight has been gained recently into the pathologic dysfunction of mTOR in tubers in TSC-related epilepsy, data on the mTOR cascade in mesial temporal lobe epilepsy (MTLE) are lacking. Immunohistochemical investigation with confocal microscopy was performed to evaluate mTOR cascade and to correlate its activity with cellular alterations observed in surgically resected samples of human neocortex and hippocampus in MTLE. We compared results in human tissue to findings in the rat pilocarpine model of sclerotic MTLE. In nonsclerotic and control hippocampus, many neurons in the CA1 subfield expressed high levels of phospho-S6 (p-S6), a reliable marker of mTOR activation. In nonsclerotic and control hippocampus, as well as in magnetic resonance imaging (MRI) normal human neocortex, protoplasmic astrocytes did not express p-S6. In contrast, in sclerotic hippocampus, prominent p-S6 immunostaining was observed mainly in astrocytes and microglia located in the areas of neuronal loss and astrogliosis, whereas neurons in preserved areas of CA1 expressed significantly lower levels of p-S6 immunopositivity than neurons in nonsclerotic or control CA1 subfields. In surgically resected neocortex with chronic astroglial scar tissue, only microglia revealed moderate p-S6 immunoreactivity. Different from human sclerotic epileptic hippocampus, astrogliosis in the chronic rat pilocarpine model of epilepsy was not characterized by glial cells with mTOR activation. The mTOR cascade is activated in astroglial cells in sclerotic MTLE, but not in astrocytes in chronic neocortical scarring or in the pilocarpine model of MTLE. These findings suggest that the astroglial "scar" in sclerotic MTLE has active, ongoing cellular changes. Targeting mTOR in MTLE may provide new pathways for the medical therapy of epilepsy.

A NOVEL ELECTRICAL STIMULATION PARADIGM FOR THE SUPPRESSION OF EPILEPTIFORM ACTIVITY IN ANIN VIVOMODEL OF MESIAL TEMPORAL LOBE STATUS EPILEPTICUS

In this study, we present a novel low-frequency electrical stimulation paradigm for mesial temporal lobe epilepsy (MTLE). The paradigm utilizes the hippocampal commissure as a unique stimulation target to simultaneously influence large portions of the bilateral hippocampal network. When applied to an acute rat model of MTLE, animals that received stimulation exhibited an 88% reduction in the signal power of the bilateral epileptiform activity relative to the control group. In addition, the stimulation entrained the hippocampal network's spontaneous epileptiform activity and disrupted its bilateral synchrony.

Reduced Astrocytic Contribution to the Turnover of Glutamate, Glutamine, and GABA Characterizes the Latent Phase in the Kainate Model of Temporal Lobe Epilepsy

The occurrence of spontaneous seizures in mesial temporal lobe epilepsy (MTLE) is preceded by a latent phase that provides a time window for identifying and treating patients at risk. However, a reliable biomarker of epileptogenesis has not been established and the underlying processes remain unclear. Growing evidence suggests that astrocytes contribute to an imbalance between excitation and inhibition in epilepsy. Here, astrocytic and neuronal neurotransmitter metabolism was analyzed in the latent phase of the kainate model of MTLE in an attempt to identify epileptogenic processes and potential biomarkers. Fourteen days after status epilepticus, [1-(13)C]glucose and [1,2-(13)C]acetate were injected and the hippocampal formation, entorhinal/piriform cortex, and neocortex were analyzed by (1)H and (13)C magnetic resonance spectroscopy. The (13)C enrichment in glutamate, glutamine, and γ-aminobutyric acid (GABA) from [1-(13)C]glucose was decreased in all areas. Decreased GABA content was specific for the hippocampal formation, together with a pronounced decrease in astrocyte-derived [1,2-(13)C]GABA and a decreased transfer of glutamine for the synthesis of GABA. Accumulation of branched-chain amino acids combined with decreased [4,5-(13)C]glutamate in hippocampal formation could signify decreased transamination via branched-chain aminotransferase in astrocytes. The results point to astrocytes as major players in the epileptogenic process, and (13)C enrichment of glutamate and GABA as potential biomarkers.

Involvement of the Thalamic Parafascicular Nucleus in Mesial Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (MTLE) is characterized by focal seizures, associated with hippocampal sclerosis, and often resistance to antiepileptic drugs. The parafascicular nucleus (PF) of the thalamus is involved in the generation of physiological oscillatory rhythms. It receives excitatory inputs from the cortex and inhibitory inputs from the basal ganglia, a system implicated in the control of epileptic seizures. The aim of this study was to examine the involvement of the PF in the occurrence of hippocampal paroxysmal discharges (HPDs) in a chronic animal model of MTLE in male mice. We recorded the local field potential (LFP) and the extracellular and intracellular activity of hippocampal and PF neurons during spontaneous HPDs in vivo. The end of the HPDs was concomitant with a slow repolarization in hippocampal neurons leading to an electrical silence. In contrast, it was associated in the PF with a transient increase in the power of the 10-20 Hz band in LFPs and a depolarization of PF neurons resulting in a sustained firing. We tested the role of the PF in the control of HPDs by single 130 Hz electrical stimulation of this nucleus and bilateral intra-PF injection of NMDA and GABA(A) antagonist and agonist. High-frequency PF stimulation interrupted ongoing HPDs at an intensity devoid of behavioral effects. NMDA antagonist and GABA(A) agonist suppressed hippocampal discharges in a dose-dependent way, whereas NMDA agonist and GABA(A) antagonist increased HPDs. Altogether, these data suggest that the PF nucleus plays a role in the modulation of MTLE seizures.

Kainic Acid-induced F-344 Rat model of Mesial Temporal Lobe Epilepsy: Gene Expression and Canonical Pathways

Mesial temporal lobe epilepsy (MTLE) is a severe neurological condition of unknown pathogenesis for which several animal models have been developed. To obtain a better understanding of the underlying molecular mechanisms and identify potential biomarkers of lesion progression, we used a rat kainic acid (KA) treatment model of MTLE coupled with global gene expression analysis to examine temporal (four hours, days 3, 14, or 28) gene regulation relative to hippocampal histopathological changes. The authors recommend reviewing the companion histopathology paper (Sharma et al. 2008) to get a better understanding of the work presented here. Analysis of filtered gene expression data using Ingenuity Pathways Analysis (Ingenuity Systems, http://www.ingenuity.com) revealed that a number of genes pertaining to neuronal plasticity (RhoA, Rac1, Cdc42, BDNF, and Trk), neurodegeneration (Caspase3, Calpain 1, Bax, a Cytochrome c, and Smac/Diablo), and inflammation/immune-response pathways (TNF-alpha, CCL2, Cox2) were modulated in a temporal fashion after KA treatment. Expression changes for selected genes known to have a role in neuronal plasticity were subsequently validated by quantitative polymerase chain reaction (qPCR). Notably, canonical pathway analysis revealed that a number of genes within the axon guidance signaling canonical pathway were up-regulated from Days 3 to 28, which correlated with aberrant mossy fiber (MF) sprouting observed histologically beginning at Day 6. Importantly, analysis of the gene expression data also identified potential biomarkers for monitoring neurodegeneration (Cox2) and neuronal/synaptic plasticity (Kalrn).

Reelin deficiency causes granule cell dispersion in epilepsy

Cortical migration defects are often associated with epilepsy. In mesial temporal lobe epilepsy (MTLE), granule cell dispersion (GCD), a migration defect of dentate granule cells, is frequently observed. Little is known how GCD develops and to which extent it contributes to the development of seizure activity. Since the reelin-deficient reeler mouse mutant shows a similar migration defect of dentate cells, we performed a series of studies investigating whether reelin deficiency is involved in GCD development. We show that in MTLE patients and in a mouse model of MTLE, the development of GCD correlates with a loss of the extracellular matrix protein reelin. In addition, we present evidence that GCD occurs in the absence of neurogenesis, thus representing a displacement of mature neurons due to a reelin deficiency. Accordingly, antibody blockade of reelin function in naïve, adult mice induced GCD. Finally, we show that GCD formation can be prevented by infusion of exogenous reelin. In summary, these studies show that in epilepsy reelin dysfunction causes GCD development and that reelin is important for the maintenance of layered structures in the adult brain.

Intrahippocampal infusion of botulinum neurotoxin E (BoNT/E) reduces spontaneous recurrent seizures in a mouse model of mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (MTLE) is one of the most common forms of human epilepsy, and it is often resistant to conventional antiepileptic drug (AED) therapy. Here we tested whether a single intrahippocampal administration of the synaptic blocker botulinum neurotoxin E (BoNT/E) is effective in reducing spontaneous recurrent seizures (SRS) in a mouse model of MTLE. Unilateral intrahippocampal injection of kainic acid (KA) in mice was used as a model of MTLE. Electroencephalography (EEG) recordings of SRS were performed during the chronic phase of epilepsy, before and after administration of either BoNT/E or vehicle. Frequency of SRS was significantly decreased for at least 5 days following BoNT/E, but not vehicle, infusion. Our findings demonstrate that BoNT/E can effectively reduce seizure incidence in a mouse model of MTLE.

Granule cell dispersion develops without neurogenesis and does not fully depend on astroglial cell generation in a mouse model of temporal lobe epilepsy

Granule cell dispersion (GCD) appears as a characteristic morphological feature of the mesial temporal lobe epilepsy (MTLE). It has been suggested that this phenomenon could be due to an increased neurogenesis in the dentate gyrus. However, this hypothesis is still debated and recent clinical and experimental studies have shown that neurogenesis is rather decreased in MTLE. To further determine the role of neural and astroglial cell generation in GCD we examined the consequences of aging and irradiation, which are known to reduce progenitor cells, in a mouse model of MTLE induced by intrahippocampal kainate (KA) injection. We injected KA in hippocampus of three different types of mice; (1) young adult, (2) aged, and (3) irradiated mice. Newly generated cells were labeled by Bromodeoxyuridine (BrdU) and were characterized by immunohistochemistry. The extent of GCD was compared among the three animal groups. In young adult mice, BrdU-labeled neurons as well as doublecortin- and NeuroD-positive cells decreased progressively after KA injection whereas BrdU-labeled astrocytes and microglias increased. In aged and irradiated mice, where basal neurogenesis was already strongly reduced, GCD developed after KA injection to the same extent as in young adult mice. However, augmentation of the BrdU-labeled astrocytes after KA was less than 40% in irradiated mice in comparison to young and aged mice. Our data show that GCD occurs without neurogenesis. Furthermore GCD developed regardless of the degree of astroglial cell proliferation, suggesting that neural stem cell generation is not crucial for GCD.