Status epilepticus-induced pathologic plasticity in a rat model of focal cortical dysplasia

Pathophysiological mechanisms underlying the development of focal cortical dysplasia and their association with epilepsy: Experimental models as a research approach

Focal cortical dysplasia (FCD) is a structural lesion that is the most common anatomical lesion identified in children, and the second most common in adults with drug-resistant focal-onset epilepsy. These lesions vary in size, location, and histopathological manifestations. FCDs are classified into three subtypes associated with loss-of-function mutations in PI3K/AKT, TSC1/TSC2, RHEB, and DEPDC/NPRL2/NPRL3. During the decades of research into FCD, experimental models have played an irreplaceable role in the research design of studies investigating disease pathogenesis, pathophysiology, and treatment. Further, the establishment of FCD experimental models has moved the field forward by (1) revealing the cellular processes and signaling pathways underlying FCD pathogenesis and (2) varying the methods and materials to study the function of FCD proteins. Currently, FCD experimental models are predominantly murine, with each model providing unique insights into FCD lesions. This review briefly summarizes the pathology and molecular functions of FCD, further comparing the available modeling methods and indexes, as well as the utilization of models, followed by an analysis of the similarities, advantages, and disadvantages between these models and human FCD.

Early developmental changes in a rat model of malformations of cortical development: Abnormal neuronal migration and altered response to NMDA-induced excitotoxic injury

Malformations of cortical development (MCDs) are caused by abnormal neuronal migration processes during the fetal period and are a major cause of intractable epilepsy in infancy. However, the timing of hyperexcitability or epileptogenesis in MCDs remains unclear. To identify the early developmental changes in the brain of the MCD rat model, which exhibits increased seizure susceptibility during infancy (P12-15), we analyzed the pathological changes in the brains of MCD model rats during the neonatal period and tested NMDA-induced seizure susceptibility. Pregnant rats were injected with two doses of methylazoxymethanol acetate (MAM, 15 mg/kg, i.p.) to induce MCD, while controls were administered normal saline. The cortical development of the offspring was measured by performing magnetic resonance imaging (MRI) on postnatal days (P) 1, 5, and 8. At P8, some rats were sacrificed for immunofluorescence, Golgi staining, and Western analysis. In another set of rats, the number and latency to onset of spasms were monitored for 90 min after the NMDA (5 mg/kg i.p.) injection at P8. In MCD rats, in vivo MR imaging showed smaller brain volume and thinner cortex from day 1 after birth (p < 0.001). Golgi staining and immunofluorescence revealed abnormal neuronal migration, with a reduced number of neuronal cell populations and less dendritic arborization at P8. Furthermore, MCD rats exhibited a significant reduction in the expression of NMDA receptors and AMPAR4, along with an increase in AMPAR3 expression (p < 0.05). Although there was no difference in the latency to seizure onset between MCD rats and controls, the MCD rats survived significantly longer than the controls. These results provide insights into the early developmental changes in the cortex of a MCD rat model and suggest that delayed and abnormal neuronal development in the immature brain is associated with a blunted response to NMDA-induced excitotoxic injury. These developmental changes may be involved in the sudden onset of epilepsy in patients with MCD or prenatal brain injury.

Altered functional connectivity and network excitability in a model of cortical dysplasia

Focal cortical dysplasias (FCDs) are malformations of cortical development that often result in medically refractory epilepsy, with a greater incidence in the pediatric population. The relationship between the disturbed cortical morphology and epileptogenic activity of FCDs remains unclear. We used the BCNU (carmustine 1-3-bis-chloroethyl-nitrosourea) animal model of cortical dysplasia to evaluate neuronal and laminar alterations and how these result in altered activity of intracortical networks in early life. We corroborated the previously reported morphological anomalies characteristic of the BCNU model, comprising slightly larger and rounder neurons and abnormal cortical lamination. Next, the neuronal activity of live cortical slices was evaluated through large field-of-view calcium imaging as well as the neuronal response to a stimulus that leads to cortical hyperexcitability (pilocarpine). Examination of the joint activity of neuronal calcium time series allowed us to identify intracortical communication patterns and their response to pilocarpine. The baseline power density distribution of neurons in the cortex of BCNU-treated animals was different from that of control animals, with the former showing no modulation after stimulus. Moreover, the intracortical communication pattern differed between the two groups, with cortexes from BCNU-treated animals displaying decreased inter-layer connectivity as compared to control animals. Our results indicate that the altered anatomical organization of the cortex of BCNU-treated rats translates into altered functional networks that respond abnormally to a hyperexcitable stimulus and highlight the role of network dysfunction in the pathophysiology of cortical dysplasia.

Neuroimmunology of status epilepticus

Status epilepticus (SE) is a very heterogeneous clinical condition often refractory to available treatment options. Evidence in animal models shows that neuroinflammation arises in the brain during SE due to the activation of innate immune mechanisms in brain parenchyma cells. Intervention studies in animal models support the involvement of neuroinflammation in SE onset, duration, and severity, refractoriness to treatments, and long-term neurological consequences. Clinical evidence shows that neuroinflammation occurs in patients with SE of diverse etiologies likely representing a common phenomenon, thus broadening the involvement of the immune system beyond the infective and autoimmune etiologies. There is urgent need for novel therapies for refractory SE that rely upon a better understanding of the basic mechanisms underlying this clinical condition. Preclinical and clinical evidence encourage consideration of specific anti-inflammatory treatments for controlling SE and its consequences in patients.

Insulin-Like Growth Factor-1 Promotes Synaptogenesis Signaling, a Major Dysregulated Pathway in Malformation of Cortical Development, in a Rat Model

Malformation of cortical development (MCD) is one of the main causes of intractable epilepsy in childhood. We explored a treatment based on molecular changes using an infant rat model of methylazoxymethanol (MAM)-induced MCD established by injecting MAM at gestational day 15. The offspring were sacrificed on postnatal day (P) 15 for proteomic analysis, which revealed significant downregulation in the synaptogenesis signaling pathway in the cortex of MCD rats. Recombinant human insulin-growth factor-1 (rhIGF-1) was injected from P12 to P14 twice daily and the effect of IGF1 on N-methyl-D-aspartate (NMDA)-induced spasms (15 mg/kg of NMDA, i.p.) was tested; the onset of P15 single spasm was significantly delayed (p = 0.002) and the number of spasms decreased (p < 0.001) in rhIGF1-pretreated rats (n = 17) compared to those in VEH-treated rats (n = 18). Electroencephalographic monitoring during spasms showed significantly reduced spectral entropy and event-related spectral dynamics of fast oscillation in rhIGF-1 treated rats. Magnetic resonance spectroscopy of the retrosplenial cortex showed decreased glutathione (GSH) (p = 0.039) and significant developmental changes in GSH, phosphocreatine (PCr), and total creatine (tCr) (p = 0.023, 0.042, 0.015, respectively) after rhIGF1 pretreatment. rhIGF1 pretreatment significantly upregulated expression of cortical synaptic proteins such as PSD95, AMPAR1, AMPAR4, NMDAR1, and NMDAR2A (p < 0.05). Thus, early rhIGF-1 treatment could promote synaptic protein expression, which was significantly downregulated by prenatal MAM exposure, and effectively suppress NMDA-induced spasms. Early IGF1 treatment should be further investigated as a therapeutic strategy in infants with MCD-related epilepsy.

Diffusion tensor imaging discriminates focal cortical dysplasia from normal brain parenchyma and differentiates between focal cortical dysplasia types

OBJECTIVES

Although diffusion tensor imaging (DTI) may facilitate the identification of cytoarchitectural changes associated with focal cortical dysplasia (FCD), the predominant aetiology of paediatric structural epilepsy, its potential has thus far remained unexplored in this population. Here, we investigated whether DTI indices can differentiate FCD from contralateral brain parenchyma (CBP) and whether clinical features affect these indices.

METHODS

In this single-centre, retrospective study, we considered children and adolescents with FCD-associated epilepsy who underwent brain magnetic resonance (MRI), including DTI. Fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity, and radial diffusivity, were calculated in both FCD and CBP. The DTI indices best discriminating between FCD and CBP were subsequently used to assess the link between DTI and selected clinical and lesion-related parameters.

RESULTS

We enrolled 32 patients (20 male; median age at MRI 4 years), including 15 with histologically confirmed FCD. FA values were lower (p = 0.03), whereas MD values were higher in FCD than in CBP (p = 0.04). The difference in FA values between FCD and CBP was more pronounced for a positive vs. negative history of status epilepticus (p = 0.004). Among histologically confirmed cases, the difference in FA values between FCD and CBP was more pronounced for type IIb versus type I FCD (p = 0.03).

CONCLUSIONS

FA and MD discriminate between FCD and CBP, while FA differentiates between FCD types. Status epilepticus increases differences in FA, potentially reflecting changes induced in the brain. Our findings support the potential of DTI to serve as a non-invasive biomarker to characterise FCD in the paediatric population.

Reorganization of Parvalbumin Immunopositive Perisomatic Innervation of Principal Cells in Focal Cortical Dysplasia Type IIB in Human Epileptic Patients

Focal cortical dysplasia (FCD) is one of the most common causes of drug-resistant epilepsy. As several studies have revealed, the abnormal functioning of the perisomatic inhibitory system may play a role in the onset of seizures. Therefore, we wanted to investigate whether changes of perisomatic inhibitory inputs are present in FCD. Thus, the input properties of abnormal giant- and control-like principal cells were examined in FCD type IIB patients. Surgical samples were compared to controls from the same cortical regions with short postmortem intervals. For the study, six subjects were selected/each group. The perisomatic inhibitory terminals were quantified in parvalbumin and neuronal nuclei double immunostained sections using a confocal fluorescent microscope. The perisomatic input of giant neurons was extremely abundant, whereas control-like cells of the same samples had sparse inputs. A comparison of pooled data shows that the number of parvalbumin-immunopositive perisomatic terminals contacting principal cells was significantly larger in epileptic cases. The analysis showed some heterogeneity among epileptic samples. However, five out of six cases had significantly increased perisomatic input. Parameters of the control cells were homogenous. The reorganization of the perisomatic inhibitory system may increase the probability of seizure activity and might be a general mechanism of abnormal network activity.

Glucocorticoid receptors participate in epilepsy in FCDII patients and MP model rats: A potential therapeutic target for epilepsy in patients with focal cortical dysplasia II (FCDII)

BACKGROUND

Glucocorticoid receptors (GRs) and mineralocorticoid receptors (MRs) are involved in neuronal excitability, neurogenesis, and neuroinflammation. However, the roles of GRs and MRs in epilepsy in focal cortical dysplasia II (FCDII) have not been reported.

RESEARCH DESIGN AND METHODS

We evaluated GRs and MRs expression and distribution in FCDII patients and methylazoxymethanol-pilocarpine-induced epilepsy model rats (MP rats), and the effects of a GR agonist on neurons in human FCDII and investigated the electrophysiological properties of cultured neurons and neurons of MP rats after lentivirus-mediated GR knockdown or overexpression and GR agonist or antagonist administration.

RESULTS

GR expression (not MR) was decreased in specimens from FCDII patients and model rats. GR agonist dexamethasone reduced neuronal excitatory transmission and increased neuronal inhibitory transmission in FCDII. GR knockdown increased the excitability of cultured neurons, and GR overexpression rescued the hyperexcitability of MP-treated neurons. Moreover, dexamethasone decreased neuronal excitability and excitatory transmission in MP rats, while GR antagonist exerted the opposite effects. Dexamethasone reduced the seizure number and duration by approximately 85% and 60% in MP rats within one to two hours.

CONCLUSIONS

These results suggested that GRs play an important role in epilepsy in FCDII and GR activation may have protective and antiepileptic effects in FCDII.

LncRNA Snhg5 Attenuates Status Epilepticus Induced Inflammation through Regulating NF-κΒ Signaling Pathway

Status epilepticus (SE) induced inflammation plays an important role in the pathogenesis of SE. Long non-coding RNA small nucleolar RNA host gene 5 (lncRNA Snhg5) has been reported in various inflammatory diseases. However, the mechanism of Snhg5 regulated inflammation in SE remains unclear. Therefore, this study aimed to clarify the role and mechanism of Snhg5 in SE-induced inflammation in vitro and vivo. In vitro, lipopolysaccharide (LPS)-induced inflammation in microglia was used to mimic the inflammation after SE. In vivo, SE model was induced by lithium chloride and pilocarpine. The level of Snhg5, p65, p-p65, p-inhibitor of kappaB (IκB)α, IκBα and inflammatory factors (tumor necrosis factor (TNF)-α, interleukin (IL)-1β) were measured via quantitative real-time PCR or Western blot. The Nissl stain and immunohistochemical stain were performed to observe hippocampal damage and microglia proliferation. The results showed Snhg5 was up-regulated in the rat and microglia. Knockdown of Snhg5 inhibited LPS-induced inflammation and relative expression of p-65/p65, p-IκBα/IκBα. Moreover, down-regulation of Snhg5 attenuated SE-induced inflammation and reduced the number of microglia in hippocampus. These findings indicated that Snhg5 modulates the inflammation via nuclear factor-kappaB (NF-κB) signaling pathway in SE rats.

Structural changes in the neocortex as correlates of variations in EEG spectra and seizure susceptibility in rat brains with different degrees of dysplasia

Disturbances of the early stages of neurogenesis lead to irreversible changes in the structure of the mature brain and its functional impairment, including increased excitability, which may be the basis for drug‐resistant epilepsy. The range of possible clinical symptoms is as wide as the different stages of disturbed neurogenesis may be. In this study, we used a quadruple model of brain dysplasia by comparing structural and functional disorders in animals whose neurogenesis was disturbed with a single dose of 1 Gy of gamma rays at one of the four stages of neurogenesis, that is, on days 13, 15, 17, or 19 of prenatal development.

When reached adulthood, the prenatally irradiated rats received EEG teletransmitter implantation. Thereafter, pilocarpine was administered and significant differences in susceptibility to seizure behavioral symptoms were detected depending on the degree of brain dysplasia. Before, during, and after the seizures significant correlations were found between the density of parvalbumin‐immunopositive neurons located in the cerebral cortex and the intensity of behavioral seizure symptoms or increases in the power of particular EEG bands. Neurons expressing calretinin or NPY showed also dysplasia‐related increases without, however, correlations with parameters of seizure intensity. The results point to significant roles of parvalbumin‐expressing interneurons, and also to expression of NPY—an endogenous anticonvulsant and neuroprotectant reducing susceptibility to seizures and supporting neuronal survival.

Striking MRI Changes of Focal Cortical Dysplasia Over Time: A Case Series and Literature Review

Purpose of Review

Brain MRI findings of focal cortical dysplasia (FCD) can undergo dramatic changes over time, which may be related to long-term epilepsy or a combination of histopathologic changes that necessitate further investigation.

Recent Findings

We describe 2 cases of FCD type IIb that initially displayed inconspicuous findings on MRI, however progressed to obvious signal changes on subsequent MRI 10-17 years later. Pathologic analysis indicates that the interval changes are likely attributed to reactive astrogliosis and diffuse parenchymal rarefaction. A few case reports and case series showing similar MRI changes have been described in the literature, the majority in pediatric patients. The adult cases we present add to the scientific evidence of these changes occurring in the adult population.

Summary

Our observations lead to several clinical suggestions, including closer interval follow-up imaging for nonlesional cases, the addition of postprocessing imaging methods, earlier surgical intervention, and meticulous surgical planning.

Abnormal Rat Cortical Development Induced by Ventricular Injection of rHMGB1 Mimics the Pathophysiology of Human Cortical Dysplasia

Cortical dysplasia (CD) is a common cause of drug-resistant epilepsy. Increasing studies have implicated innate immunity in CD with epilepsy. However, it is unclear whether innate immune factors induce epileptogenic CD. Here, we injected recombinant human high mobility group box 1 (rHMGB1) into embryonic rat ventricles to determine whether rHMGB1 can induce epileptogenic CD with pathophysiological characteristics similar to those of human CD. Compared with controls and 0.1 μg rHMGB1-treated rats, the cortical organization was severely disrupted in the 0.2 μg rHMGB1-treated rats, and microgyria and heterotopia also emerged; additionally, disoriented and deformed neurons were observed in the cortical lesions and heterotopias. Subcortical heterotopia appeared in the white matter and the gray–white junction of the 0.2 μg rHMGB1-treated rats. Moreover, there was decreased number of neurons in layer V–VI and an increased number of astrocytes in layer I and V of the cortical lesions. And the HMGB1 antagonist dexmedetomidine alleviated the changes induced by rHMGB1. Further, we found that TLR4 and NF-κB were increased after rHMGB1 administration. In addition, the excitatory receptors, N-methyl-D-aspartate receptor 1 (NR1), 2A (NR2A), and 2B (NR2B) immunoreactivity were increased, and immunoreactivity of excitatory amino acid transporter 1 (EAAT1) and 2 (EAAT2) were reduced in 0.2 μg rHMGB1-treated rats compared with controls. While there were no differences in the glutamic acid decarboxylase 65/67 (GAD65/67) immunoreactivity between the two groups. These results indicate that the excitation of cortical lesions was significantly increased. Furthermore, electroencephalogram (EEG) showed a shorter latency of seizure onset and a higher incidence of status epilepticus in the 0.2 μg rHMGB1-treated rats; the frequency and amplitude of EEG were higher in the treated rats than controls. Intriguingly, spontaneous electrographic seizure discharges were detected in the 0.2 μg rHMGB1-treated rats after 5 months of age, and spike-wave discharges of approximately 8 Hz were the most significantly increased synchronous propagated waves throughout the general brain cortex. Taken together, these findings indicate that rHMGB1 exposure during pregnancy could contribute to the development of epileptogenic CD, which mimicked some pathophysiological characteristics of human CD.

Case Report: Late-Onset Temporal Lobe Epilepsy Following Subarachnoid Hemorrhage: An Interplay Between Pre-existing Cortical Development Abnormality and Tissue Damage

Epileptogenicity following brain insult depends on various factors including severity of the resulting lesion and extent of brain damage. We report a 54-year-old female patient who developed medically refractory epilepsy resulting from the interplay of pre-existing and post-insult pathologies. She presented with subarachnoid hemorrhage (SAH) due to a ruptured aneurysm and underwent clipping surgery. Seizures started 3 months post-operatively. MRI revealed cerebral ischemia and hemosiderin deposits in the left temporal lobes, and left hippocampal atrophy was suspected. As anti-seizure medications and vagus nerve stimulation failed to control her seizures, she underwent left temporal lobe resection and placement of a ventriculoperitoneal shunt for the post-operative complication of hydrocephalus. She remains seizure-free to date. Neuropathology revealed a previously undiagnosed focal cortical dysplasia (FCD) type 1a. Brain insult likely had a second hit effect in the late onset of epilepsy in this patient with pre-existing mild MCD, in whom secondary epilepsy can be attributed to the interplay of multiple underlying pathologies.

Src/CK2/PTEN-Mediated GluN2B and CREB Dephosphorylations Regulate the Responsiveness to AMPA Receptor Antagonists in Chronic Epilepsy Rats

Both α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPAR) and N-methyl-D-aspartate receptor (NMDAR) have been reported as targets for treatment of epilepsy. To investigate the roles and interactions of AMPAR and NMDAR in ictogenesis of epileptic hippocampus, we analyzed AMPAR antagonists (perampanel and GYKI 52466)-mediated phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulation and glutamate ionotropic receptor NMDA type subunit 2B (GluN2B) tyrosine (Y) 1472 phosphorylation in epilepsy rats. Both perampanel and GYKI 52466 increased PTEN expression and its activity (reduced phosphorylation), concomitant with decreased activities (phosphorylations) of Src family-casein kinase 2 (CK2) signaling pathway. Compatible with these, they also restored the upregulated GluN2B Y1472 and Ca2+/cAMP response element-binding protein (CREB) serine (S) 133 phosphorylations and surface expression of glutamate ionotropic receptor AMPA type subunit 1 (GRIA1) to basal level in the epileptic hippocampus. These effects of perampanel and GYKI 52466 are observed in responders (whose seizure activities are responsive to AMPAR antagonists), but not non-responders (whose seizure activities were uncontrolled by AMPAR antagonists). Therefore, our findings suggest that Src/CK2/PTEN-mediated GluN2B Y1472 and CREB S133 regulations may be one of the responsible signaling pathways for the generation of refractory seizures in non-responders to AMPAR antagonists.

Delayed Functional Networks Development and Altered Fast Oscillation Dynamics in a Rat Model of Cortical Malformation

Malformations of cortical development (MCD) is associated with a wide range of developmental delay and drug resistant epilepsy in children. By using resting-state functional magnetic resonance imaging (RS-fMRI) and event-related spectral perturbation (ERSP) of cortical electroencephalography (EEG) data, we tried to investigate the neural changes of spatiotemporal functional connectivity (FC) and fast oscillation (FO) dynamics in a rat model of methylazoxymethanol (MAM)-induced MCD. A total of 28 infant rats with prenatal exposure to MAM and those of age matched 28 controls with prenatal saline exposure were used. RS-fMRI were acquired at postnatal day 15 (P15) and 29 (P29), and correlation coefficient analysis of eleven region of interests (ROI) was done to find the differences of functional networks between four groups. Two hour-cortical EEGs were also recorded at P15 and P29 and the ERSP of gamma (30–80 Hz) and ripples (80–200 Hz) were analyzed. The rats with MCD showed significantly delayed development of superior colliculus-brainstem network compared to control rats at P15. In contrast to marked maturation of default mode network (DMN) in controls from P15 to P29, there was no clear development in MCD rats. The MCD rats showed significantly higher cortical gamma and ripples-ERSP at P15 and lower cortical ripples-ERSP at P29 than those of control rats. This study demonstrated delayed development of FC and altered cortical FO dynamics in rats with malformed brain. The results should be further investigated in terms of the epileptogenesis and cognitive dysfunction in patients with MCD.

In vivo MRI Successfully Reveals the Malformation of Cortical Development in Infant Rats

Objective: Malformations of cortical development (MCDs) are major causes of intractable epilepsies. To characterize the early neuroimaging findings of MCDs, we tried to identify the MRI features consistent with pathological findings in an infant rat MCD model, prenatally exposed to methylazoxymethanol (MAM), by using newly developed MRI techniques. Methods: At gestational day 15, two doses of MAM (15 mg/kg intraperitoneally) or normal saline were injected into pregnant rats. The offspring underwent in vivo MRI, including glutamate chemical exchange saturation transfer (GluCEST), ¹H-MR spectroscopy, and diffusion tensor imaging, at postnatal day (P) 15 using a 7T small-animal imaging system. Another set of prenatally MAM-exposed rats were sacrificed for histological staining. Results: At P15, the retrosplenial cortex (RSC) of rats with MCDs showed decreased neuronal nuclei, parvalbumin, and reelin expressions. Moreover, dendritic arborization of pyramidal cells in the RSC significantly decreased in infant rats with MCDs. In vivo MRI showed significantly decreased GluCEST (%) in the RSC of rats with MCDs (p = 0.000) and a significant correlation between GluCEST (%) and RSC thickness (r = 0.685, p = 0.003). The rats with MCDs showed reduced glutamate (p = 0.002), N-acetylaspartate (p = 0.002), and macromolecule and lipid levels (p = 0.027) and significantly reduced fractional anisotropy values in the RSC. Conclusion: In vivo MRI revealed reduced neuronal population and dendritic arborization in the RSC of infant rats with MCDs during the early postnatal period. These pathological changes of the cortex could serve as clinical imaging biomarkers of MCDs in infants.

Early Chronic Carbamazepine-in-Food Administration to MAM/Pilocarpine Rats Does Not Affect Convulsive Motor Seizures

Antiepileptic drug-resistance is a major health problem in patients with cortical dysplasia (CD). Whether drug-resistant epilepsy is associated with progressive brain damage is still debated. We previously generated a rat model of acquired CD, the methylazoxymethanol-pilocarpine (MP) rat, in which the occurrence of status epilepticus and subsequent spontaneous seizures induce progressive brain damage (Nobili et al., 2015). The present study tested the outcome of early-chronic carbamazepine (CBZ) administration on both seizure activity and brain damage in MP rats. We took advantage of the non-invasive CBZ-in-food administration protocol, established by Ali (2012), which proved effective in suppressing generalized convulsive seizures in kainic acid rat model of epilepsy. MP rats were treated immediately after the onset of the first spontaneous seizure with 300 mg/kg/day CBZ formulated in pellets for a two-months-trial. CBZ-treated rats were continuously video-monitored to detect seizure activity and were compared with untreated epileptic MP rats. Despite CBZ serum levels in treated rats were within the suggested therapeutic range for humans, CBZ affected spontaneous convulsive seizures in 2 out of 10 treated rats (responders), whereas the remaining animals (non-responders) did not show any difference when compared to untreated MP rats. Histological analysis revealed cortical thinning paralleled by robust staining of Fluoro-Jade⁺ (FJ⁺) degenerating neurons and diffuse tissue necrosis in CBZ-non-responder vs CBZ-responder rats. Data reported here suggest that MP rat model represents suitable experimental setting where to investigate mechanisms of CD-related drug-resistant epilepsy and to verify if modulation of seizures, with appropriate treatment, may reduce seizure-induced brain damage.

Inflammation and reactive oxygen species in status epilepticus: Biomarkers and implications for therapy

Preclinical studies in immature and adult rodents and clinical observations show that neuroinflammation and oxidative stress are rapid onset phenomena occurring in the brain during status epilepticus and persisting thereafter. Notably, both neuroinflammation and oxidative stress contribute to the acute and long-term sequelae of status epilepticus thus representing potential druggable targets. Antiinflammatory drugs that interfere with the IL-1β pathway, such as anakinra, can control benzodiazepine-refractory status epilepticus in animals, and there is recent proof-of-concept evidence for therapeutic effects in children with Febrile infection related epilepsy syndrome (FIRES). Inhibitors of monoacylglycerol lipase and P2X7 receptor antagonists are also promising antiinflammatory drug candidates for rapidly aborting de novo status epilepticus and provide neuroprotection. Antiinflammatory and antioxidant drugs administered to rodents during status epilepticus and transiently thereafter, prevent long-term sequelae such as cognitive deficits and seizure progression in animals developing epilepsy. Some drugs are already in medical use and are well-tolerated, therefore, they may be considered for treating status epilepticus and its neurological consequences. Finally, markers of neuroinflammation and oxidative stress are measureable in peripheral blood and by neuroimaging, which offers an opportunity for developing prognostic and predictive mechanistic biomarkers in people exposed to status epilepticus. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures.

Histological Characterization of the Irritative Zones in Focal Cortical Dysplasia Using a Preclinical Rat Model

Current clinical practice in focal epilepsy involves brain source imaging (BSI) to localize brain areas where from interictal epileptiform discharges (IEDs) emerge. These areas, named irritative zones, have been useful to define candidate seizures-onset zones during pre-surgical workup. Since human histological data are mostly available from final resected zones, systematic studies characterizing pathophysiological mechanisms and abnormal molecular/cellular substrates in irritative zones—independent of them being epileptogenic—are challenging. Combining BSI and histological analysis from all types of irritative zones is only possible through the use of preclinical animal models. Here, we recorded 32-channel spontaneous electroencephalographic data from rats that have focal cortical dysplasia (FCD) and chronic seizures. BSI for different IED subtypes was performed using the methodology presented in Bae et al. (2015). Post-mortem brain sections containing irritative zones were stained to quantify anatomical, functional, and inflammatory biomarkers specific for epileptogenesis, and the results were compared with those obtained using the contralateral healthy brain tissue. We found abnormal anatomical structures in all irritative zones (i.e., larger neuronal processes, glioreactivity, and vascular cuffing) and larger expressions for neurotransmission (i.e., NR2B) and inflammation (i.e., ILβ1, TNFα and HMGB1). We conclude that irritative zones in this rat preclinical model of FCD comprise abnormal tissues disregarding whether they are actually involved in icto-genesis or not. We hypothesize that seizure perpetuation happens gradually; hence, our results could support the use of IED-based BSI for the early diagnosis and preventive treatment of potential epileptic foci. Further verifications in humans are yet needed.

Immunity and inflammation in status epilepticus and its sequelae: possibilities for therapeutic application

Status epilepticus (SE) is a life-threatening neurological emergency often refractory to available treatment options. It is a very heterogeneous condition in terms of clinical presentation and causes, which besides genetic, vascular and other structural causes also include CNS or severe systemic infections, sudden withdrawal from benzodiazepines or anticonvulsants and rare autoimmune etiologies. Treatment of SE is essentially based on expert opinions and antiepileptic drug treatment per se seems to have no major impact on prognosis. There is, therefore, urgent need of novel therapies that rely upon a better understanding of the basic mechanisms underlying this clinical condition. Accumulating evidence in animal models highlights that inflammation ensuing in the brain during SE may play a determinant role in ongoing seizures and their long-term detrimental consequences, independent of an infection or auto-immune cause; this evidence encourages reconsideration of the treatment flow in SE patients.

Axon Initial Segment Structural Plasticity is Involved in Seizure Susceptibility in a Rat Model of Cortical Dysplasia

Cortical dysplasia is the most common etiology of intractable epilepsy. Both excitability changes in cortical neurons and neural network reconstitution play a role in cortical dysplasia epileptogenesis. Recent research shows that the axon initial segment, a subcompartment of the neuron important to the shaping of action potentials, adjusts its position in response to changes in input, which contributes to neuronal excitability and local circuit balance. It is unknown whether axon initial segment plasticity occurs in neurons involved in seizure susceptibility in cortical dysplasia. Here, we developed a "Carmustine"- "pilocarpine" rat model of cortical dysplasia and show that it exhibits a lower seizure threshold, as indicated by behavior studies and electroencephalogram monitoring. Using immunofluorescence, we measured the axon initial segment positions of deep L5 somatosensory neurons and show that it is positioned closer to the soma after acute seizure, and that this displacement is sustained in the chronic phase. We then show that Nifedipine has a dose-dependent protective effect against axon initial segment displacement and increased seizure susceptibility. These findings further our understanding of the pathophysiology of seizures in cortical dysplasia and suggests Nifedipine as a potential therapeutic agent.

MK-801, but not naloxone, attenuates high-dose dextromethorphan-induced convulsive behavior: Possible involvement of the GluN2B receptor

Dextromethorphan (DM) is a dextrorotatory isomer of levorphanol, a typical morphine-like opioid. When administered at supra-antitussive doses, DM produces psychotoxic and neurotoxic effects in humans. Although DM abuse has been well-documented, few studies have examined the effects of high-dose DM. The present study aimed to explore the effects of a single high dose of DM on mortality and seizure occurrence. After intraperitoneal administration with a high dose of DM (80mg/kg), Sprague-Dawley rats showed increased seizure occurrence and intensity. Hippocampal expression levels of N-methyl-d-aspartate (NMDA) receptor subunits (GluN1<GluN2A<GluN2B), c-Fos and pro-apoptotic factors (Bax and cleaved caspase-3) were upregulated by DM treatment; while levels of anti-apoptotic factors (Bcl-2 and Bcl-xL) were downregulated. Consistently, DM also induced ultrastructural degeneration in the hippocampus. A non-competitive NMDA receptor antagonist, MK-801, attenuated these effects of high-dose DM, whereas an opioid antagonist, naloxone, did not affect DM-induced neurotoxicity. Moreover, pretreatment with a highly specific GluN2B subunit inhibitor, traxoprodil, was selectively effective in preventing DM-induced c-Fos expression and apoptotic changes. These results suggest that high-dose DM produces convulsive behaviors by activating GluN2B/NMDA signaling that leads to pro-apoptotic changes.

Alterations in Properties of Glutamatergic Transmission in the Temporal Cortex and Hippocampus Following Pilocarpine-Induced Acute Seizures in Wistar Rats

Temporal lobe epilepsy (TLE) is the most common type of focal epilepsy in humans, and is often developed after an initial precipitating brain injury. This form of epilepsy is frequently resistant to pharmacological treatment; therefore, the prevention of TLE is the prospective approach to TLE therapy. The lithium-pilocarpine model in rats replicates some of the main features of TLE in human, including the pathogenic mechanisms of cell damage and epileptogenesis after a primary brain injury. In the present study, we investigated changes in the properties of glutamatergic transmission during the first 3 days after pilocarpine-induced acute seizures in Wistar rats (PILO-rats). Using RT-PCR and electrophysiological techniques, we compared the changes in the temporal cortex (TC) and hippocampus, brain areas differentially affected by seizures. On the first day, we found a transient increase in a ratio of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl d-aspartate (NMDA) receptors in the excitatory synaptic response in pyramidal neurons of the CA1 area of the dorsal hippocampus, but not in the TC. This was accompanied by an increase in the slope of input-output (I/O) curves for fEPSPs recorded in CA1, suggesting an enhanced excitability in AMPARs in this brain area. There was no difference in the AMPA/NMDA ratio in control rats on the third day. We also revealed the alterations in NMDA receptor subunit composition in PILO-rats. The GluN2B/GluN2A mRNA expression ratio increased in the dorsal hippocampus but did not change in the ventral hippocampus or the TC. The kinetics of NMDA-mediated evoked EPSCs in hippocampal neurons was slower in PILO-rats compared with control animals. Ifenprodil, a selective antagonist of GluN2B-containing NMDARs, diminished the area and amplitude of evoked EPSCs in CA1 pyramidal cells more efficiently in PILO-rats compared with control animals. These results demonstrate that PILO-induced seizures lead to more severe alterations in excitatory synaptic transmission in the dorsal hippocampus than in the TC. Seizures affect the relative contribution of AMPA and NMDA receptor conductances in the synaptic response and increase the proportion of GluN2B-containing NMDARs in CA1 pyramidal neurons. These alterations disturb normal circuitry functions in the hippocampus, may cause neuron damage, and may be one of the important pathogenic mechanisms of TLE.

A New Rat Model of Epileptic Spasms Based on Methylazoxymethanol-Induced Malformations of Cortical Development

Malformations of cortical development (MCDs) can cause medically intractable epilepsies and cognitive disabilities in children. We developed a new model of MCD-associated epileptic spasms by treating rats prenatally with methylazoxymethanol acetate (MAM) to induce cortical malformations and postnatally with N-methyl-d-aspartate (NMDA) to induce spasms. To produce cortical malformations to infant rats, two dosages of MAM (15 mg/kg, intraperitoneally) were injected to pregnant rats at gestational day 15. In prenatally MAM-exposed rats and the controls, spasms were triggered by single (6 mg/kg on postnatal day 12 (P12) or 10 mg/kg on P13 or 15 mg/kg on P15) or multiple doses (P12, P13, and P15) of NMDA. In prenatally MAM-exposed rats with single NMDA-provoked spasms at P15, we obtain the intracranial electroencephalography and examine the pretreatment response to adrenocorticotropic hormone (ACTH) or vigabatrin. Rat pups prenatally exposed to MAM exhibited a significantly greater number of spasms in response to single and multiple postnatal NMDA doses than vehicle-exposed controls. Vigabatrin treatment prior to a single NMDA dose on P15 significantly suppressed spasms in MAM group rats (p < 0.05), while ACTH did not. The MAM group also showed significantly higher fast oscillation (25–100 Hz) power during NMDA-induced spasms than controls (p = 0.047). This new model of MCD-based epileptic spasms with corresponding features of human spasms will be valuable for future research of the developmental epilepsy.

Rats with Malformations of Cortical Development Exhibit Decreased Length of AIS and Hypersensitivity to Pilocarpine-Induced Status Epilepticus

Malformations of cortical development (MCD) are critical brain development disorders associated with varied abnormalities in both anatomic structures and neural functioning. It is also a very common etiology to the epilepsy, in which the alteration on excitability of cortical neurons is hypothesized as one of important causes to the epileptic seizures. Due to the key role in regulating neuron firing properties, the plasticity of axon initial segment (AIS) was investigated in present study to further determine the relation between MCD and epilepsy. Our results showed a prolonged decrease in the length of AIS occurred in MCD animal models. Besides, the AIS was also found greatly shortened in MCD models during the acute, but not chronic phase of status epileptics compared with intact controls. Our findings of identification of AIS plasticity in MCD animal models and its hypersensitivity to status epilepsy are significant in furthering our understanding of the pathophysiological mechanisms involved in this disorder.

Upregulation of HMGB1, toll-like receptor and RAGE in human Rasmussen's encephalitis

Rasmussen encephalitis (RE) is a rare neurological disorder of childhood characterized by uni-hemispheric inflammation, progressive neurological deficits and intractable focal epilepsy. The pathogenesis of RE is still enigmatic. Activation of endogenous high-mobility group box-1 (HMGB1) and Toll-like receptor (TLR) has been proved to be with pro-inflammatory as well as pro-convulsant effects. We hypothesized that the epileptogenic mechanisms underlying RE are related to activation of HMGB1/TLR signaling. Immunnohistochemistry approach was used to examine the expression of HMGB1, TLR2, TLR4, receptor for advanced glycation end products (RAGE) in surgically resected human epileptic cortical specimens from RE (n=12), and compared that with control cortical issue (n=6). HMGB1 was ubiquitously detected in nuclei of astrocytes while its receptors were not detected in control cortex specimens. Marked expression of the receptors were observed in the lesions of RE. In particular, HMGB1 was in stead detected in cytoplasm of reactive astrocytes in RE cortex, predictive its release from glial cells. Significant greater HMGB1 and its receptors expression in RE vs. control was demonstrated by western blot. These results provide the novel evidence of intrinsic activation of these pro-inflammation pathways in RE, which suggest the specific targets in the treatment of epilepsy associated with RE.

Continuous neurodegeneration and death pathway activation in neurons and glia in an experimental model of severe chronic epilepsy

Whether seizures might determine the activation of cell death pathways and what could be the relevance of seizure-induced cell death in epilepsy are still highly debated issues. We recently developed an experimental model of acquired focal cortical dysplasia (the MAM-pilocarpine or MP rat) in which the occurrence of status epilepticus--SE--and subsequent seizures induced progressive cellular/molecular abnormalities and neocortical/hippocampal atrophy. Here, we exploited the same model to verify when, where, and how cell death occurred in neurons and glia during epilepsy course. We analyzed Fluoro Jade (FJ) staining and the activation of c-Jun- and caspase-3-dependent pathways during epilepsy, from few hours post-SE up to six months of spontaneous recurrent seizures. FJ staining revealed that cell injury in MP rats was not temporally restricted to SE, but extended throughout the different epileptic stages. The region-specific pattern of FJ staining changed during epilepsy, and FJ(+) neurons became more prominent in the dorsal and ventral hippocampal CA at chronic epilepsy stages. Phospho-c-Jun- and caspase-3-dependent pathways were selectively activated respectively in neurons and glia, at early but even more conspicuously at late chronic stages. Phospho-c-Jun activation was associated with increased cytochrome-c staining, particularly at chronic stages, and the staining pattern of cytochrome-c was suggestive of its release from the mitochondria. Taken together, these data support the content that at least in the MP rat model the recurrence of seizures can also sustain cell death mechanisms, thus continuously contributing to the pathologic process triggered by the occurrence of SE.

Distributions of Irritative Zones Are Related to Individual Alterations of Resting-State Networks in Focal Epilepsy

Alterations in the connectivity patterns of the fMRI-based resting-state networks (RSNs) have been reported in several types of epilepsies. Evidence pointed out these alterations might be associated with the genesis and propagation of interictal epileptiform discharges (IEDs). IEDs also evoke blood-oxygen-level dependent (BOLD) responses, which have been used to delineate irritative zones during preoperative work-up. Therefore, one may expect a relationship between the topology of the IED-evoked BOLD response network and the altered spatial patterns of the RSNs. In this study, we used EEG recordings and fMRI data obtained simultaneously from a chronic model of focal epilepsy in Wistar rats to verify our hypothesis. We found that IED-evoked BOLD response networks comprise both cortical and subcortical structures with a rat-dependent topology. In all rats, IEDs evoke both activation and deactivation types of BOLD responses. Using a Granger causality method, we found that in many cases areas with BOLD deactivation have directed influences on areas with activation (p<0.05). We were able to predict topological properties (i.e., focal/diffused, unilateral/bilateral) of the IED-evoked BOLD response network by performing hierarchical clustering analysis on major spatial features of the RSNs. All these results suggest that IEDs and disruptions in the RSNs found previously in humans may be different manifestations of the same transient events, probably reflecting altered consciousness. In our opinion, the shutdown of specific nodes of the default mode network may cause uncontrollable excitability in other functionally connected brain areas. We conclude that IED-evoked BOLD responses (i.e., activation and deactivation) and alterations of RSNs are intrinsically related, and speculate that an understanding of their interplay is necessary to discriminate focal epileptogenesis and network propagation phenomena across different brain modules via hub-based connectivity.

Brain Source Imaging in Preclinical Rat Models of Focal Epilepsy using High-Resolution EEG Recordings

Electroencephalogram (EEG) has been traditionally used to determine which brain regions are the most likely candidates for resection in patients with focal epilepsy. This methodology relies on the assumption that seizures originate from the same regions of the brain from which interictal epileptiform discharges (IEDs) emerge. Preclinical models are very useful to find correlates between IED locations and the actual regions underlying seizure initiation in focal epilepsy. Rats have been commonly used in preclinical studies of epilepsy; hence, there exist a large variety of models for focal epilepsy in this particular species. However, it is challenging to record multichannel EEG and to perform brain source imaging in such a small animal. To overcome this issue, we combine a patented-technology to obtain 32-channel EEG recordings from rodents and an MRI probabilistic atlas for brain anatomical structures in Wistar rats to perform brain source imaging. In this video, we introduce the procedures to acquire multichannel EEG from Wistar rats with focal cortical dysplasia, and describe the steps both to define the volume conductor model from the MRI atlas and to uniquely determine the IEDs. Finally, we validate the whole methodology by obtaining brain source images of IEDs and compare them with those obtained at different time frames during the seizure onset.

Models of cortical malformation--Chemical and physical

Pharmaco-resistant epilepsies, and also some neuropsychiatric disorders, are often associated with malformations in hippocampal and neocortical structures. The mechanisms leading to these cortical malformations causing an imbalance between the excitatory and inhibitory system are largely unknown. Animal models using chemical or physical manipulations reproduce different human pathologies by interfering with cell generation and neuronal migration. The model of in utero injection of methylazoxymethanol (MAM) acetate mimics periventricular nodular heterotopia. The freeze lesion model reproduces (poly)microgyria, focal heterotopia and schizencephaly. The in utero irradiation model causes microgyria and heterotopia. Intraperitoneal injections of carmustine 1-3-bis-chloroethyl-nitrosurea (BCNU) to pregnant rats produces laminar disorganization, heterotopias and cytomegalic neurons. The ibotenic acid model induces focal cortical malformations, which resemble human microgyria and ulegyria. Cortical dysplasia can be also observed following prenatal exposure to ethanol, cocaine or antiepileptic drugs. All these models of cortical malformations are characterized by a pronounced hyperexcitability, few of them also produce spontaneous epileptic seizures. This dysfunction results from an impairment in GABAergic inhibition and/or an increase in glutamatergic synaptic transmission. The cortical region initiating or contributing to this hyperexcitability may not necessarily correspond to the site of the focal malformation. In some models wide-spread molecular and functional changes can be observed in remote regions of the brain, where they cause pathophysiological activities. This paper gives an overview on different animal models of cortical malformations, which are mostly used in rodents and which mimic the pathology and to some extent the pathophysiology of neuronal migration disorders associated with epilepsy in humans.

Co-occurring malformations of cortical development and SCN1A gene mutations

OBJECTIVE

To report on six patients with SCN1A mutations and malformations of cortical development (MCDs) and describe their clinical course, genetic findings, and electrographic, imaging, and neuropathologic features.

METHODS

Through our database of epileptic encephalopathies, we identified 120 patients with SCN1A mutations, of which 4 had magnetic resonance imaging (MRI) evidence of MCDs. We collected two further similar observations through the European Task-force for Epilepsy Surgery in Children.

RESULTS

The study group consisted of five males and one female (mean age 7.4 ± 5.3 years). All patients exhibited electroclinical features consistent with the Dravet syndrome spectrum, cognitive impairment, and autistic features. Sequencing analysis of the SCN1A gene detected two missense, two truncating, and two splice-site mutations. Brain MRI revealed bilateral periventricular nodular heterotopia (PNH) in two patients and focal cortical dysplasia (FCD) in three, and disclosed no macroscopic abnormality in one. In the MRI-negative patient, neuropathologic study of the whole brain performed after sudden unexpected death in epilepsy (SUDEP), revealed multifocal micronodular dysplasia in the left temporal lobe. Two patients with FCD underwent epilepsy surgery. Neuropathology revealed FCD type IA and type IIA. Their seizure outcome was unfavorable. All four patients with FCD exhibited multiple seizure types, which always included complex partial seizures, the area of onset of which co-localized with the region of structural abnormality.

SIGNIFICANCE

MCDs and SCN1A gene mutations can co-occur. Although epidemiology does not support a causative role for SCN1A mutations, loss or impaired protein function combined with the effect of susceptibility factors and genetic modifiers of the phenotypic expression of SCN1A mutations might play a role. MCDs, particularly FCD, can influence the electroclinical phenotype in patients with SCN1A-related epilepsy. In patients with MCDs and a history of polymorphic seizures precipitated by fever, SCN1A gene testing should be performed before discussing any epilepsy surgery option, due to the possible implications for outcome.

Layer-specific gene expression in epileptogenic type II focal cortical dysplasia: normal-looking neurons reveal the presence of a hidden laminar organization

BACKGROUND

Type II focal cortical dysplasias (FCDs) are malformations of cortical development characterised by the disorganisation of the normal neocortical structure and the presence of dysmorphic neurons (DNs) and balloon cells (BCs). The pathogenesis of FCDs has not yet been clearly established, although a number of histopathological patterns and molecular findings suggest that they may be due to abnormal neuronal and glial proliferation and migration processes.In order to gain further insights into cortical layering disruption and investigate the origin of DNs and BCs, we used in situ RNA hybridisation of human surgical specimens with a neuropathologically definite diagnosis of Type IIa/b FCD and a panel of layer-specific genes (LSGs) whose expression covers all cortical layers. We also used anti-phospho-S6 ribosomal protein antibody to investigate mTOR pathway hyperactivation.

RESULTS

LSGs were expressed in both normal and abnormal cells (BCs and DNs) but their distribution was different. Normal-looking neurons, which were visibly reduced in the core of the lesion, were apparently located in the appropriate cortical laminae thus indicating a partial laminar organisation. On the contrary, DNs and BCs, labelled with anti-phospho-S6 ribosomal protein antibody, were spread throughout the cortex without any apparent rule and showed a highly variable LSG expression pattern. Moreover, LSGs did not reveal any differences between Type IIa and IIb FCD.

CONCLUSION

These findings suggest the existence of hidden cortical lamination involving normal-looking neurons, which retain their ability to migrate correctly in the cortex, unlike DNs which, in addition to their morphological abnormalities and mTOR hyperactivation, show an altered migratory pattern.Taken together these data suggest that an external or environmental hit affecting selected precursor cells during the very early stages of cortical development may disrupt normal cortical development.

Progressive brain damage, synaptic reorganization and NMDA activation in a model of epileptogenic cortical dysplasia

Whether severe epilepsy could be a progressive disorder remains as yet unresolved. We previously demonstrated in a rat model of acquired focal cortical dysplasia, the methylazoxymethanol/pilocarpine - MAM/pilocarpine - rats, that the occurrence of status epilepticus (SE) and subsequent seizures fostered a pathologic process capable of modifying the morphology of cortical pyramidal neurons and NMDA receptor expression/localization. We have here extended our analysis by evaluating neocortical and hippocampal changes in MAM/pilocarpine rats at different epilepsy stages, from few days after onset up to six months of chronic epilepsy. Our findings indicate that the process triggered by SE and subsequent seizures in the malformed brain i) is steadily progressive, deeply altering neocortical and hippocampal morphology, with atrophy of neocortex and CA regions and progressive increase of granule cell layer dispersion; ii) changes dramatically the fine morphology of neurons in neocortex and hippocampus, by increasing cell size and decreasing both dendrite arborization and spine density; iii) induces reorganization of glutamatergic and GABAergic networks in both neocortex and hippocampus, favoring excitatory vs inhibitory input; iv) activates NMDA regulatory subunits. Taken together, our data indicate that, at least in experimental models of brain malformations, severe seizure activity, i.e., SE plus recurrent seizures, may lead to a widespread, steadily progressive architectural, neuronal and synaptic reorganization in the brain. They also suggest the mechanistic relevance of glutamate/NMDA hyper-activation in the seizure-related brain pathologic plasticity.

Malformations of cortical development and neocortical focus

Developmental neocortical malformations resulting from abnormal neurogenesis, disturbances in programmed cell death, or neuronal migration disorders may cause a long-term hyperexcitability. Early generated Cajal-Retzius and subplate neurons play important roles in transient cortical circuits, and structural/functional disorders in early cortical development may induce persistent network disturbances and epileptic disorders. In particular, depolarizing GABAergic responses are important for the regulation of neurodevelopmental events, like neurogenesis or migration, while pathophysiological alterations in chloride homeostasis may cause epileptic activity. Although modern imaging techniques may provide an estimate of the structural lesion, the site and extent of the cortical malformation may not correlate with the epileptogenic zone. The neocortical focus may be surrounded by widespread molecular, structural, and functional disturbances, which are difficult to recognize with imaging technologies. However, modern imaging and electrophysiological techniques enable focused hypotheses of the neocortical epileptogenic zone, thus allowing more specific epilepsy surgery. Focal cortical malformation can be successfully removed with minimal rim, close to or even within eloquent cortex with a promising risk-benefit ratio.

Intrinsic epileptogenicity of dysplastic cortex: converging data from experimental models and human patients

Focal cortical dysplasia (FCD) is a brain malformation associated with particularly severe drug-resistant epilepsy that often requires surgery for seizure control. The molecular basis for such enhanced propensity to seizure generation in FCD is not as yet elucidated. To investigate cellular and molecular bases of epileptogenic mechanisms and possible effect of severe epilepsy on the malformed cortex we have here performed a parallel analysis of a rat model of acquired cortical dysplasia previously established in our laboratory, i.e., the methylazoxymethanol/pilocarpine (MAM-PILO) rats, and surgical samples from patients with type IIB FCD. Data from the MAM-PILO rat model and human FCD samples reveal in both conditions: (1) that status epilepticus (SE) and/or seizures can further modify the cellular and molecular settings of the malformed cortex; (2) excitation/inhibition imbalance, and dysregulation of the N-methyl-d-aspartate/ membrane-associated guanylate kinase (NMDA/MAGUK) expression; (3) activation of cell death in neurons and glia. The data therefore highlight the mechanistic relevance of glutamate/NMDA hyperactivation in FCD epileptogenesis and suggest that epilepsy is a pathologic process capable of affecting structure and function of both neurons and glia.

Long-duration epilepsy affects cell morphology and glutamatergic synapses in type IIB focal cortical dysplasia

To investigate hypothesized effects of severe epilepsy on malformed cortex, we analyzed surgical samples from eight patients with type IIB focal cortical dysplasia (FCD) in comparison with samples from nine non-dysplastic controls. We investigated, using stereological quantification methods, where appropriate, dysplastic neurons, neuronal density, balloon cells, glia, glutamatergic synaptic input, and the expression of N-methyl-D-aspartate (NMDA) receptor subunits and associated membrane-associated guanylate kinase (MAGUK). In all FCD patients, the dysplastic areas giving rise to epileptic discharges were characterized by larger dysmorphic neurons, reduced neuronal density, and increased glutamatergic inputs, compared to adjacent areas with normal cytology. The duration of epilepsy was found to correlate directly (a) with dysmorphic neuron size, (b) reduced neuronal cell density, and (c) extent of reactive gliosis in epileptogenic/dysplastic areas. Consistent with increased glutamatergic input, western blot revealed that NMDA regulatory subunits and related MAGUK proteins were up-regulated in epileptogenic/dysplastic areas of all FCD patients examined. Taken together, these results support the hypothesis that epilepsy itself alters morphology-and probably also function-in the malformed epileptic brain. They also suggest that glutamate/NMDA/MAGUK dysregulation might be the intracellular trigger that modifies brain morphology and induces cell death.

In vivo imaging of glia activation using 1H-magnetic resonance spectroscopy to detect putative biomarkers of tissue epileptogenicity

PURPOSE

  Long-lasting activation of glia occurs in brain during epileptogenesis, which develops after various central nervous system (CNS) injuries. Glia is the cell source of the biosynthesis and release of molecules that play a role in seizure recurrence and may contribute to epileptogenesis, thus representing a putative biomarker of epilepsy development and severity. In this study, we set up an in vivo longitudinal study using (1) H-magnetic resonance spectroscopy (MRS) to measure metabolite content in the rat hippocampus that could reflect the extent and the duration of glia activation. Our aim was to explore if glia activation during epileptogenesis, or in the chronic epileptic phase, can be used as a biomarker of tissue epileptogenicity (i.e., a measure of epilepsy severity).

METHODS

  (1) H-MRS measurements were done in the adult rat hippocampus every 24 h for 7 days after status epilepticus (SE) and in chronic epileptic rats, using a 7 T Bruker Biospec MRI (magnetic resonance imaging)/MRS scanner. We studied changes in metabolite levels that reflect astrocytes (myo-inositol, mIns; glutathione, GSH), microglia/macrophage activation and the associated neuronal cell injury/dysfunction (lactate, Lac; N-acetyl-aspartate, NAA). (1) H-MRS results were validated by post hoc immunohistochemistry using cell-specific markers. Data analysis was done to determine whether correlations exist between the metabolite changes and spontaneous seizure frequency or the extent of neuronal cell loss.

KEY FINDINGS

  The analysis of (1) H-MRS spectra showed a progressive increase in mIns and GSH levels after SE, which was maintained in epileptic rats. Lac signal transiently increased during epileptogenesis being undetectable in chronic epileptic tissue. NAA levels were chronically reduced from day 2 post-SE. Immunohistochemistry confirmed the activation of microglia and astrocytes and the progressive neuronal cell loss. GSH levels during epileptogenesis showed a negative correlation with the frequency of spontaneous seizures, whereas S100β levels in epileptic tissue were positively correlated with this outcome measure. A negative correlation was also found between GSH or mIns levels during epileptogenesis and the extent of neurodegeneration in hippocampus of epileptic rats.

SIGNIFICANCE

  (1) H-MRS is a valuable in vivo technique for determining the extent and temporal profile of glia activation after an epileptogenic injury. S100β levels measured in the epileptic tissue may represent a biomarker of seizure frequency, whereas GSH levels during epileptogenesis could serve as a predictive marker of seizure frequency. Both mIns and GSH levels measured before the onset of spontaneous seizures predict the extent of neuronal cell loss in epileptic tissue. These findings highlight the potential of serial (1) H-MRS analysis for searching epilepsy biomarkers for prognostic, diagnostic, or therapeutic purposes.

Atypical febrile seizures, mesial temporal lobe epilepsy, and dual pathology

Febrile seizures occurring in the neonatal period, especially when prolonged, are thought to be involved in the later development of mesial temporal lobe epilepsy (mTLE) in children. The presence of an often undetected, underlying cortical malformation has also been reported to be implicated in the epileptogenesis process following febrile seizures. This paper highlights some of the various animal models of febrile seizures and of cortical malformation and portrays a two-hit model that efficiently mimics these two insults and leads to spontaneous recurrent seizures in adult rats. Potential mechanisms are further proposed to explain how these two insults may each, or together, contribute to network hyperexcitability and epileptogenesis. Finally the clinical relevance of the two-hit model is briefly discussed in light of a therapeutic and preventive approach to mTLE.