A pericyte-glia scarring develops at the leaky capillaries in the hippocampus during seizure activity.

OBJECTIVE: Inflammatory cerebrovascular damage occurs in epilepsy. Here, we tested the hypothesis that a pericyte-glia scar forms around the outer wall of hippocampal capillaries in a model of temporal lobe epilepsy associated with hippocampal sclerosis. We studied the participation of stromal cells expressing platelet-derived growth factor receptor beta (PDGFRß) and extracellular matrix modifications to the perivascular scar during epileptogenesis. METHODS: We used NG2DsRed/C57BL6 mice and induced status epilepticus (SE) followed by epileptogenesis and spontaneous recurrent seizures (SRS) by means of unilateral intrahippocampal injection of kainic acid (KA). For pharmacological assessment, we used organotypic hippocampal cultures (OHCs) where ictal electrographic activity was elicited by KA or bicuculline. RESULTS: NG2DsRed pericytes, GFAP astroglia, and IBA1 microglia are reactive and converge to form a pericapillary multicellular scar in the CA hippocampal regions during epileptogenesis and at SRS. The capillaries are leaky as indicated by fluorescein entering the parenchyma from the peripheral blood. Concomitantly, PDGFRß transcript and protein levels were significantly increased. Within the regional scar, a fibrotic-like PDGFRß mesh developed around the capillaries, peaking at 1 week post-SE and regressing, but not resolving, at SRS. Abnormal distribution or accumulation of extracellular matrix collagens III/IV occurred in the CA regions during seizure progression. PDGFRß/DAPI cells were in direct contact with or adjacent to the damaged NG2DsRed pericytes at the capillary interface, consistent with the notion of stromal cell reactivity or fibroblast formation. Inducing electrographic activity in OHCs was sufficient to augment PDGFRß reactivity around the capillaries. The latter effect was pharmacologically mimicked by treating OHCs with the PDGFRß agonist PDGF-BB and it was diminished by the PDGFRß inhibitor imatinib. SIGNIFICANCE: The reported multicellular activation and scar are traits of perivascular inflammation and hippocampal sclerosis in experimental epilepsy, with an implication for neurovascular dysfunction. Modulation of PDGFRß could be exploited to target inflammation in this chronic disease setting.

Redistribution of PDGFRß cells and NG2DsRed pericytes at the cerebrovasculature after status epilepticus.

PURPOSE: The role of cerebrovascular dysfunction in seizure disorders is recognized. Blood-brain barrier (BBB) damage in epilepsy has been linked to endothelial and glial pathophysiological changes. Little is known about the involvement of pericytes, a cell type that contributes to BBB function. METHODS: NG2DsRed mice were used to visualize cerebrovascular pericytes. The pattern of vascular and parenchymal distributions of platelet-derived growth factor receptor beta (PDGFRß) cells was evaluated by immunohistochemistry. Status epilepticus was induced in NG2DsRed or C57BL/6J mice by intraperitoneal kainic acid (KA). Animals were perfused intracardially using FITC-Dextran or FITC-Albumin to visualize the cerebrovasculature. Colocalization was performed between NG2DsRed, PDGFRß and microglia IBA-1. Confocal 3D vessel reconstruction was used to visualize changes in cell morphology and position. PDGFRß expression was also evaluated in vitro using organotypic hippocampal cultures (OHC) treated with kainic acid to induce seizure-like activity. Co-localization of PDGFRß with the vascular marker RECA-1 and NG2 was performed. Finally, we assessed the expression of PDGFRß in brain specimens obtained from a cohort of patients affected by drug resistant epilepsy compared to available autoptic brain. RESULTS: In vivo, severe status epilepticus (SE) altered NG2DsRed vascular coverage. We found dishomogenous NG2DsRed perivascular ramifications after SE and compared to control. Concomitantly, PDGFRß(+) cells re-distributed towards the cerebrovasculature after severe SE. Cerebrovascular NG2DsRed partially colocalized with PDGFRß(+) while parenchymal PDGFRß(+) cells did not colocalize with IBA-1(+) microglia. Using in vitro OHC we found decreased NG2 vascular staining and increased PDGFRß(+) ramifications associated with RECA-1(+) microvessels after seizure-like activity. Cellular PDGFRß and NG2(+) colocalization was observed in the parenchyma. Finally, analysis of human TLE brains revealed perivascular and parenchymal PDGFRß(+) cell distributions resembling the murine in vivo and in vitro results. PDGFRß(+) cells at the cerebrovasculature were more frequent in TLE brain tissues as compared to the autoptic control. CONCLUSIONS: The rearrangement of PDGFRß(+) and vascular NG2DsRed cells after SE suggests a possible involvement of pericytes in the cerebrovascular modifications observed in epilepsy. The functional role of vascular-parenchymal PDGFRß(+) cell redistribution and the relevance of a pericyte response to SE remain to be fully elucidated.

Repeated stimulation of dopamine D1-like receptor and hyperactivation of mTOR signaling lead to generalized seizures, altered dentate gyrus plasticity, and memory deficits.

The acute activation of the dopamine D1-like receptors (D1R) is involved in a plethora of functions ranging from increased locomotor activity to the facilitation of consolidation, storage, and retrieval of memories. Although much less characterized, epileptiform activities, usually triggered by disruption of the glutamate and GABA balance, have also been reported to involve the dopaminergic transmission. Using a combination of biochemical, immunohistochemical, electrophysiological, and behavioral approaches we have investigated the consequences of repeated stimulation of D1R using the selective D1R-like agonist SKF81297. Here, we report that repeated systemic administration of SKF81297 induces kindled seizures in mice. These seizure episodes parallel the hyperactivation of the mTOR signaling in the hippocampus, leading to disrupted long-term potentiation (LTP) in the dentate gyrus (DG) and altered recognition memories. The mTOR inhibitor rapamycin delays the development of SKF81297-induced kindled seizures, and rescues LTP in the DG and object recognition. Our results show that repeated stimulation of D1R is sufficient to induce generalized seizures leading to the overactivation of mTOR signaling, disrupted hippocampal plasticity, and impaired long-term recognition memories. This work highlights the interest of mTOR inhibitors as therapeutic strategies to reverse plasticity and cognitive deficits.

Epileptiform activity induces vascular remodeling and zonula occludens 1 downregulation in organotypic hippocampal cultures: role of VEGF signaling pathways.

Recent studies suggest that blood-brain barrier (BBB) permeability contributes to epileptogenesis in symptomatic epilepsies. We have previously described angiogenesis, aberrant vascularization, and BBB alteration in drug-refractory temporal lobe epilepsy. Here, we investigated the role of vascular endothelial growth factor (VEGF) in an in vitro integrative model of vascular remodeling induced by epileptiform activity in rat organotypic hippocampal cultures. After kainate-induced seizure-like events (SLEs), we observed an overexpression of VEGF and VEGF receptor-2 (VEGFR-2) as well as receptor activation. Vascular density and branching were significantly increased, whereas zonula occludens 1 (ZO-1), a key protein of tight junctions (TJs), was downregulated. These effects were fully prevented by VEGF neutralization. Using selective inhibitors of VEGFR-2 signaling pathways, we found that phosphatidylinositol 3-kinase is involved in cell survival, protein kinase C (PKC) in vascularization, and Src in ZO-1 regulation. Recombinant VEGF reproduced the kainate-induced vascular changes. As in the kainate model, VEGFR-2 and Src were involved in ZO-1 downregulation. These results showed that VEGF/VEGFR-2 initiates the vascular remodeling induced by SLEs and pointed out the roles of PKC in vascularization and Src in TJ dysfunction, respectively. This suggests that Src pathway could be a therapeutic target for BBB protection in epilepsies.

Why and how to target angiogenesis in focal epilepsies.

We previously reported that blood-brain barrier (BBB) disruption was associated with a pathologic angiogenesis in patients with intractable temporal lobe epilepsy (TLE) and in vivo models. This was confirmed by the overexpression of vascular endothelial growth factor (VEGF) in neurons and astrocytes and of its receptor vascular endothelial growth factor-2 (VEGF-R2) (or flk1) in endothelial cells. Using an original in vitro model, we showed that seizures were sufficient to activate the VEGF/VEGF-R2 system, which promotes vascularization and tight junction disassembly. Such a BBB dysfunction was shown to contribute to epileptogenesis. Therefore, we postulate that drugs that target the specific VEGF-R2 pathways involved in permeability are able to repair the BBB, and, therefore, could reduce epileptogenicity.

Knock-in mice lacking the PDZ-ligand motif of mGluR7a show impaired PKC-dependent autoinhibition of glutamate release, spatial working memory deficits, and increased susceptibility to pentylenetetrazol.

The metabotropic glutamate receptor 7 (mGluR7) is widely expressed throughout the brain and primarily localized at presynaptic active zones, where it is thought to regulate neurotransmitter release. Protein interacting with C kinase 1 (PICK1), a postsynaptic density protein-95/disc-large tumor suppressor protein/zonula occludens-1 (PDZ)-domain protein, binds to the three C-terminal amino acids (-LVI) of the predominant mGluR7 splice variant, mGluR7a, and has been implicated in the synaptic clustering of this receptor. Here, we generated knock-in mice in which the C-terminal LVI coding sequence of exon 10 of the mGluR7 gene was replaced by three alanine codons (-AAA). Immunoprecipitation showed that the PICK1-mGluR7a interaction is disrupted in mGluR7a(AAA/AAA) mice. However, the synaptic localization of mGluR7a was not altered in cultured hippocampal neurons and brain sections prepared from the knock-in animals. In cerebellar granule cell cultures, the group III mGluR agonist l-AP-4 decreased the frequency of spontaneous excitatory currents in neurons derived from wild-type but not mGluR7a(AAA/AAA) mice, consistent with the interaction between mGluR7a and PICK1 being required for protein kinase C-mediated inhibition of glutamate release. At the behavioral level, the mGluR7a(AAA/AAA) mice showed no deficits in motor coordination, pain sensitivity, and anxiety but exhibited significant defects in hippocampus-dependent spatial working memory. In addition, they displayed a high susceptibility to the convulsant drug pentylenetetrazole. Together, these results indicate that PICK1 binding to the C-terminal region of mGluR7a is crucial for agonist-triggered presynaptic signaling in vivo.

Age-dependent vascular changes induced by status epilepticus in rat forebrain: implications for epileptogenesis.

Brain inflammation, angiogenesis and increased blood-brain barrier (BBB) permeability occur in adult rodent and human epileptogenic brain tissue. We addressed the role of these events in epileptogenesis using a developmental approach since the propensity to develop spontaneous seizures, therefore the induction of epileptogenesis, is age-dependent and increases with brain maturation. Inflammation, angiogenesis and BBB permeability were studied in postnatal day (PN)9 and PN21 rats, 1 week and 4 months after pilocarpine-induced status epilepticus. Brain inflammation was evaluated by interleukin(IL)-1beta immunohistochemistry; angiogenesis was quantified by measuring the density of microvessels identified by an anti-laminin antibody or by the intraluminal signal of FITC-albumin; BBB integrity was assessed by extravascular IgG immunostaining or detection of parenchymal extravasation of FITC-albumin. Neither inflammation nor angiogenesis or changes in BBB permeability were detected in PN9 rats after status epilepticus, and these rats did not develop spontaneous seizures in adulthood as assessed by video-EEG monitoring. Differently, status epilepticus in PN21 rats induced chronic inflammation, angiogenesis and BBB leakage in the hippocampus in 62% of rats, while in the remaining rats only transient inflammation in forebrain was observed. Epilepsy developed in about 62% of PN21 rats exposed to SE and these epileptic rats showed the three phenomena concomitantly in the hippocampus. PN21 rats that did not develop epilepsy 4 months after status epilepticus, as assessed by video-EEG monitoring, they did not show inflammation, angiogenesis or BBB damage in forebrain at this time. Our data show that age-dependent vascular changes and brain inflammation induced by status epilepticus are associated with epileptogenesis, suggesting that these phenomena are implicated in the mechanisms underlying the occurrence of spontaneous seizures.

Angiogenesis is associated with blood-brain barrier permeability in temporal lobe epilepsy.

Previous studies from our group, focusing on neuro-glial remodelling in human temporal lobe epilepsy (TLE), have shown the presence of immature vascular cells in various areas of the hippocampus. Here, we investigated angiogenic processes in hippocampi surgically removed from adult patients suffering from chronic intractable TLE, with various aetiologies. We compared hippocampi from TLE patients to hippocampi obtained after surgery or autopsy from non-epileptic patients (NE). We quantified the vascular density, checked for the expression of angiogenic factors and their receptors and looked for any blood-brain barrier (BBB) leakage. We used a relevant model of rat limbic epilepsy, induced by lithium-pilocarpine treatment, to understand the sequence of events. In humans, the vessel density was significantly higher in TLE than in NE patients. This was neither dependent on the aetiology nor on the degree of neuronal loss, but was positively correlated with seizure frequency. In the whole hippocampus, we observed many complex, tortuous microvessels. In the dentate gyrus, when the granular layer was dispersed, long microvessels appeared radially orientated. Vascular endothelial factor (VEGF) and tyrosine kinase receptors were detected in different types of cells. An impairment of the BBB was demonstrated by the loss of tight junctions and by Immunoglobulines G (IgG) leakage and accumulation in neurons. In the rat model of TLE, VEGF over-expression and BBB impairment occurred early after status epilepticus, followed by a progressive increase in vascularization. In humans and rodents, angiogenic processes and BBB disruption were still obvious in the chronic focus, probably activated by recurrent seizures. We suggest that the persistent leakage of serum IgG in the interstitial space and their uptake by neurons may participate in hypoperfusion and in neuronal dysfunction occurring in TLE.

Blockade of T-type calcium channels prevents tonic-clonic seizures in a maximal electroshock seizure model.

T-type (Cav3) calcium channels play important roles in neuronal excitability, both in normal and pathological activities of the brain. In particular, they contribute to hyper-excitability disorders such as epilepsy. Here we have characterized the anticonvulsant properties of TTA-A2, a selective T-type channel blocker, in mouse. Using the maximal electroshock seizure (MES) as a model of tonic-clonic generalized seizures, we report that mice treated with TTA-A2 (0.3 mg/kg and higher doses) were significantly protected against tonic seizures. Although no major change in Local Field Potential (LFP) pattern was observed during the MES seizure, analysis of the late post-ictal period revealed a significant increase in the delta frequency power in animals treated with TTA-A2. Similar results were obtained for Cav3.1-/- mice, which were less prone to develop tonic seizures in the MES test, but not for Cav3.2-/- mice. Analysis of extracellular signal-regulated kinase 1/2 (ERK) phosphorylation and c-Fos expression revealed a rapid and elevated neuronal activation in the hippocampus following MES clonic seizures, which was unchanged in TTA-A2 treated animals. Overall, our data indicate that TTA-A2 is a potent anticonvulsant and that the Cav3.1 isoform plays a prominent role in mediating TTA-A2 tonic seizure protection.

Caffeic acid phenethyl ester (CAPE) prevents inflammatory stress in organotypic hippocampal slice cultures.

Caffeic acid phenethyl ester (CAPE) is an antioxidant component of propolis, a natural product secreted by honeybee. Recent literature shows that CAPE inhibits nuclear factor kappa B (NFkappaB) activation in cell lines. Since NFkappaB was shown to be a crucial factor in neuroinflammation and to be associated with some neuropathologies, CAPE might reduce these disorders in brain too and have therapeutic applications. To test this hypothesis we used a model of endotoxic insult (interferon-gamma, followed by lipopolysaccharide) on rat organotypic hippocampal cultures. Cerebral inflammatory responses were strongly inhibited by CAPE (100 microM): reductions of NFkappaB nuclear activity, tumor necrosis factor alpha and nitric oxide productions were observed. At the dose of maximal effects (100 microM), an increase of cAMP-responsive element binding protein (CREB) activity, which anti-inflammatory role is well known, was seen. We compared CAPE effects with those of other drugs: anti-inflammatory as acetyl-salicylate and dexamethasone (glucocorticoid), antioxidant as pyrrolidine dithiocarbamate, or selective permeant inhibitor of NFkappaB as SN 50 peptide. These studies lead us to conclude that CAPE presents an interesting and original neuropharmacological profile compared to these drugs and might be helpful in the prevention of neurotoxic events due to excessive inflammatory reaction in brain. CAPE interferes with several effectors of neuroinflammation that might have complementary and synergic effects and allows a rather durable control since an acute treatment at the time of endotoxin exposure allows to control inflammatory factors for over 48 h.

Inflammatory reactions in human medial temporal lobe epilepsy with hippocampal sclerosis.

Many experimental studies suggest that NFkappaB, a transcription factor involved in acute inflammation, and cytokines participate in neuronal excitability and/or glial scar formation in epilepsy. In this report, we looked for the expression of NFkappaB in hippocampi surgically removed in patients with medial temporal lobe epilepsy (MTLE) and hippocampal sclerosis (HS) who had an history of febrile convulsions. We analyzed 18 hippocampi from epileptic patients with MTLE and HS, and we used as control specimens three hippocampi from non-epileptic patients and four hippocampi from patients with cryptogenic MTLE without HS. We used antibodies raised against the NFkappaB-p65 subunit and we identified glial cells with specific antibodies. Hippocampi from patients with MTLE and HS displayed severe neuronal loss surrounded by gliosis in CA1 area and more or less in CA3/CA4 areas. Double immunolabeling showed that reactive astrocytes of lesioned areas over-expressed NFkappaB-p65 (significantly when compared to control specimens). Moreover, some surviving pyramidal neurons in these areas and numerous dentate granule cells were strongly positive for NFkappaB-p65 in cytoplasm and nucleus, whereas control hippocampi showed a faint basal cytoplasmic staining in neurons. These results suggest that in epileptic hippocampi with typical sclerosis, inflammatory processes are chronically active or transiently re-induced by recurrent seizures. Whether NFkappaB over-expression reflects protective or deleterious mechanisms in the epileptic focus remains to be elucidated.

Immature-like astrocytes are associated with dentate granule cell migration in human temporal lobe epilepsy.

In human temporal lobe epilepsy, a dispersion of dentate granule cells is frequently described in adults who had an early risk factor. To elucidate the role of glia in this phenomenon, we investigated neuronal dispersion, astrocyte organization and expression of intermediate filaments of mature and immature astrocytes (i.e. glial fibrillary acidic protein (GFAP) and vimentin, respectively) in seven subjects with early febrile seizures (F(+)) and five subjects with other etiologies than febrile seizures (F(-)). Compared to F(-) patients, a majority of F(+) subjects showed neuronal dispersion and vimentin expression in radial glia. However, in two patients with the maximal dispersion, radial processes expressed only GFAP. We suggest that granule cell migration that occurs in adult epileptic focus results from the transient occurrence of immature-like glia throughout the granular layer.

Cerebrovascular remodeling and epilepsy.

The role of the blood-brain barrier (BBB) in epilepsy has evolved from an obstacle for drug brain delivery to an etiological factor contributing to seizures. Recent evidence has shown cerebrovascular angiogenesis and increased BBB permeability in the epileptic foci of patients and in experimental models of seizure. The molecular players involved in cerebrovascular remodeling in the epileptic brain are similar to those reported for other brain disorders. The question arises whether pharmacological solutions restoring a proper BBB permeability and preventing dysregulated angiogenesis could be also beneficial in mitigating seizures. We now summarize the available data supporting the role of vascular remodeling and angiogenesis in the epileptic brain, taking into account that the BBB is a multi-cellular structure, reacting to physiological and pathological stimuli. Drugs targeting aberrant angiogenesis could be beneficial in reducing seizure burden when used in combination with available anti-epileptic drugs. We also offer an overview of novel cellular players, such as pericytes, which may participate in cerebrovascular remodeling in the epileptic brain. The possible role of angiogenesis in drug-resistant forms of epilepsy associated with neurovascular dysplasia is discussed. Finally, we speculate on whether the formation of leaky BBB vessels could have an impact on the cerebrovascular rheology and on the physiological mechanisms regulating brain homeostasis.

Organotypic brain slices: a model to study the neurovascular unit micro-environment in epilepsies.

BACKGROUND: It is now recognized that the neuro-vascular unit (NVU) plays a key role in several neurological diseases including epilepsy, stroke, Alzheimer's disease, multiple sclerosis and the development of gliomas. Most of these disorders are associated with NVU dysfunction, due to overexpression of inflammatory factors such as vascular endothelial growth factor (VEGF). Various in vitro models have been developed previously to study the micro-environment of the blood-brain barrier (BBB). However none of these in vitro models contained a complete complement of NVU cells, nor maintained their interactions, thus minimizing the influence of the surrounding tissue on the BBB development and function. The organotypic hippocampal culture (OHC) is an integrative in vitro model that allows repeated manipulations over time to further understand the development of cell circuits or the mechanisms of brain diseases. METHODS/DESIGN: OHCs were cultured from hippocampi of 6-7 day-old Sprague Dawley rats. After 2 weeks in culture, seizures were induced by application of kainate or bicuculline into culture medium. The regulation of BBB integrity under physiological and pathological conditions was evaluated by immunostaining of the main tight junction (TJ) proteins and of the basal membrane of microvessels. To mimic or prevent BBB disassembly, we used diverse pro- or anti-angiogenic treatments. DISCUSSION: This study demonstrates that NVU regulation can be investigated using OHCs. We observed in this model system an increase in vascularization and a down-regulation of TJ proteins, similar to the vascular changes described in a chronic focus of epileptic patients, and in rodent models of epilepsy or inflammation. We observed that Zonula occludens-1 (ZO-1) protein disappeared after seizures associated with neuronal damage. In these conditions, the angiopoeitin-1 system was down-regulated, and the application of r-angiopoeitin-1 allowed TJ re-assembly. This article demonstrates that organotypic culture is a useful model to decipher the links between epileptic activity and vascular damage, and also to investigate NVU regulation in diverse neurological disorders.

Spatio-temporally restricted blood-brain barrier disruption after intra-amygdala kainic acid-induced status epilepticus in mice.

Mesial temporal lobe epilepsy (MTLE) is the most common, intractable seizure disorder in adults. Blood-brain barrier (BBB) disruption, including interruption of endothelial tight cell junctions and serum protein and immunoglobulin G (IgG) extravasation into brain parenchyma, has been reported in experimental and human MTLE and implicated in disease pathogenesis. Triggering status epilepticus in mice by intra-amygdala microinjection of kainic acid produces damage mainly within the CA3 subfield of the ipsilateral hippocampus, and recurrent spontaneous seizures emerge during the following week. To investigate whether BBB impairment is a feature of this model, we characterized endothelial tight cell junction proteins and IgG and albumin in the hippocampus up to three weeks after status epilepticus. Hippocampal microvessels displayed a reduction in continuous staining for zonula occludens 1 (ZO-1), the main tight junction protein, after status epilepticus and in epileptic mice, although western blotting found ZO-1 protein levels in the hippocampal subfields were not different from controls at any time. Increased IgG and albumin were detected in damaged and non-damaged ipsilateral hippocampal subfields, mainly 4-24h after status epilepticus, although increased serum protein extravasation was also found in the CA3 subfield in epileptic mice. Thus, BBB opening or damage occurs mainly in the period shortly after status epilepticus but may also persist within the CA3 subfield as a feature of the pathophysiology of chronic epilepsy in this model.

IgG leakage may contribute to neuronal dysfunction in drug-refractory epilepsies with blood-brain barrier disruption.

Focal epilepsies are often associated with blood-brain barrier disruption. In 4 entorhinal cortex tissue samples and 13 hippocampal samples from patients with pharmacoresistent temporal lobe epilepsy, we observed immunoglobulin G (IgG) leakage in the parenchyma and IgG-positive neurons that had evidence of neurodegeneration, such as shrinkage and eosinophilia. These findings were not present in samples from 12 nonepileptic control subjects. To complement these findings, we used a rat in vivo model that mimics the development of limbic epilepsy with blood-brain barrier disruption. During epileptogenesis, IgG leakage and neuronal IgG uptake increased concomitantly with the occurrence of seizures. Immunoglobulin G accumulation in neurons was selective, particularly for interneurons and pyramidal neurons. Immunohistochemistry and electron microscopy showed that IgG uptake in the rat neurons was associated with eosinophilia, shrinkage, and ultrastructural degenerative changes. Moreover, IgG-positive neurons lost their NeuN immunohistochemical staining. Together, these observations suggest that IgG leakage is related to neuronal impairment and may be a pathogenic mechanism in epileptogenesis and chronic epilepsy.

[Inflammation, angiogenesis and epilepsy]. / Inflammation, angiogenèse et épilepsie.

It is well admitted now that gliosis participates in epileptogenesis, particularly in symptomatic focal epilepsies, like temporal lobe epilepsy. Indeed, astrocytic and microglial activation was shown to release numerous inflammatory factors that modify neuronal excitability or contribute to neuronal loss. These redundant processes maintain chronic epilepsy. However, other sources of inflammation exist. Several studies pointed out the epileptogenicity of blood-brain barrier disruption due to the leakage of leukocytes and serum proteins, triggering inflammatory and immune responses which disturb the neuronal environment. Recently, it was proposed that peripheral inflammation plays a key-role in epilepsy, mainly mediated by circulating cytokines which promote leukocyte extravasation.

PICK1 uncoupling from mGluR7a causes absence-like seizures.

Absence epilepsy is a neurological disorder that causes a recurrent loss of consciousness and generalized spike-and-wave discharges on an electroencephalogram (EEG). The role of metabotropic glutamate receptors (mGluRs) and associated scaffolding proteins in absence epilepsy has been unclear to date. We investigated a possible role for these proteins in absence epilepsy, focusing on the mGluR7a receptor and its PDZ-interacting protein, protein interacting with C kinase 1 (PICK1), in rats and mice. Injection of a cell-permeant dominant-negative peptide or targeted mutation of the mGluR7a C terminus, both of which disrupt the interaction between the receptor and PDZ proteins, caused behavioral symptoms and EEG discharges that are characteristic of absence epilepsy. Inactivation of the Pick1 gene also facilitated pharmacological induction of the absence epilepsy phenotype. The cortex and thalamus, which are known to participate in absence epilepsy, were involved, but the hippocampus was not. Our results indicate that disruption of the mGluR7a-PICK1 complex is sufficient to induce absence epilepsy-like seizures in rats and mice, thus providing, to the best of our knowledge, the first animal model of metabotropic glutamate receptor-PDZ protein interaction in absence epilepsy.

Increased number of neural progenitors in human temporal lobe epilepsy.

An increased neurogenesis is reported in animal models of mesial temporal lobe epilepsy (MTLE) but the fate of newborn cells is unknown. Here, we attempted to demonstrate neurogenesis in adult epileptic tissue obtained after hippocampectomy. MTLE hippocampi showed increased expression of division markers and of Musashi-1, a marker of neural progenitors, compared to control hippocampi. Large quantities of Musashi-1+ cells were obvious in the subgranular layer and the subventricular zone, both known neurogenic areas, and in the fissura hippocampi. Musashi-1 was expressed by small cells that were mainly vimentin+ or nestin+, rarely Dcx+ or PSA-NCAM+ and negative for markers of mature neurons or astrocytes. Some of them are present in the granular layer, the hilus, and CA1 area resembling the ectopic positions described in rodents. These findings demonstrate that neural progenitors proliferate in chronic epilepsy and suggest that the fissura hippocampi behaves like another neurogenic area.