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Time-frequency analysis of focal seizure electroencephalographic signals performed with depth electrodes in human temporal lobe structures has revealed the occurrence at onset of oscillations at approximately 30-100 Hz that feature a monotonic rapid decay in frequency content. This seizure onset pattern, referred to as chirp, has been identified as a highly specific and sensitive marker of focal seizures that are characterized by low-voltage fast activity. We report that this chirp pattern is also observed in animal models of temporal lobe epilepsy in both in vivo and in vitro preparations. We propose here that chirps mirror the involvement of synchronous interneuron firing that is known to represent a specific cellular mechanism leading to the initiation of focal seizures, in particular those characterized by low-voltage fast activity., (© 2024 The Author(s). Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

The identification of the epileptogenic zone (EZ) boundaries is crucial for effective focal epilepsy surgery. We verify the value of a neurophysiological biomarker of focal ictogenesis, characterized by a low-voltage fast-activity ictal pattern (chirp) recorded with intracerebral electrodes during invasive presurgical monitoring (stereoelectroencephalography [SEEG]). The frequency content of SEEG signals was retrospectively analyzed with semiautomatic software in 176 consecutive patients with focal epilepsies that either were cryptogenic or presented with discordant anatomoelectroclinical findings. Fast activity seizure patterns with the spectrographic features of chirps were confirmed by computer-assisted analysis in 95.4% of patients who presented with heterogeneous etiologies and diverse lobar location of the EZ. Statistical analysis demonstrated (1) correlation between seizure outcome and concordance of sublobar regions included in the EZ defined by visual analysis and chirp-generating regions, (2) high concordance in contact-by contact analysis of 68 patients with Engel class Ia outcome, and (3) that discordance between chirp location and the visually outlined EZ correlated with worse seizure outcome. Seizure outcome analysis confirms the fast activity chirp pattern is a reproducible biomarker of the EZ in a heterogeneous group of patients undergoing SEEG., (© 2024 International League Against Epilepsy.)

Musicogenic epilepsy (ME) is characterized by seizures triggered by music. The epileptogenic focus in this rare reflex epilepsy is often in the temporal lobe, although the precise localization is still unclear. A correlation between ME and the presence of GAD65 antibodies indicates a potential immunological pathogenic mechanism. We evaluated a 32-year-old woman with drug-resistant temporal lobe epilepsy as a candidate for epilepsy surgery. In the absence of clear clinical lateralizing signs, video-EEG monitoring with intracranial electrodes inserted through the foramen ovale was performed to record from the amygdalo-hippocampal regions. The foramen ovale electrodes revealed bilateral, asynchronous, and independent seizure onsets in the mesial temporal regions triggered by music. Testing for GAD65 antibodies confirmed high-titer positivity. The efficacy of epilepsy surgery in antiGAD65-positive ME patients remains limited. We highlight the use of semi-invasive recording with foramen ovale electrodes in ME, as it can reveal bilateral seizures of mesial origin that contraindicate surgery and support the consideration of immunotherapy options. PLAIN LANGUAGE SUMMARY: Musicogenic epilepsy is a type of epilepsy in which music triggers seizures. Our understanding of its origin and cause is still limited. We assessed a patient with music-induced seizures to see if surgery was an option. Since noninvasive tests before surgery were not clear, we used a minimally invasive method with electrodes inserted through a small opening in the skull called the foramen ovale to record the seizures. Thus, we found that the seizures started independently from both temporal lobes, contraindicating epilepsy surgery. We also found high levels of GAD65 antibodies indicating an immunological pathogenic mechanism., (© 2025 The Author(s). Epilepsia Open published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Background: Temporal lobe epilepsy with isolated amygdala enlargement (TLE-AE) still lacks a definite characterization and controversies exist., Methods: We conducted a retrospective study identifying brain MRI scans with isolated AE between 2015 and 2021. We collected clinical and paraclinical data of patients with TLE-AE and evaluated the outcome., Results: Forty-one subjects were included (20 males; AE: right 13; left 24; bilateral 4). A strong correlation was found between AE and MRI T2-hyperintensity (right: p < 0.005; left: p < 0.003). There was no history of febrile seizures; 85,4% had focal seizures with impaired awareness, 78,1% reported auras (epigastric sensation, déjà-vu, anxiety), 37% had psychiatric disturbances, 48,6% presented with cognitive impairment. We report that AE correlates with FDG-PET temporomesial hypometabolism (right: p = 0.022; left: p = 0.053), temporal interictal activity on EEG (n = 41), and temporal ictal findings during long-term video-EEG monitoring (n = 23). Epilepsy surgery (n = 17) revealed gliosis (n = 4), inflammatory infiltrates (n = 4), or low-grade epilepsy-associated neuroepithelial tumors (n = 5) in the amygdala. Other treatments were immunotherapy (n = 6) and only antiseizure medications (n = 17), with good prognosis (58,1% seizure-free and 17,1% only with auras at last follow-up). There was no correlation between longitudinal changes in seizure frequency and amygdala size (p = 0.848) and T2-hyperintensity (p = 0.909)., Conclusions: AE should be searched in TLE patients with typical aura, psychiatric and/or neurocognitive disturbances. The strong correlations found between AE lateralization and neurophysiological, FDG-PET, and MRI data support involvement of AE in the epileptogenic network. Drug resistance should prompt presurgical study. Inflammation in amygdala specimens and response after immunotherapy suggest an immune-mediated etiology in some TLE-AE cases., Competing Interests: Declarations. Conflicts of interest: The authors declare that they have no conflict of interest. Ethical approval: This study was done in accordance with the ethical standards of the institutional and/or national research committee and with the Helsinki declaration. Informed consent: Patients signed an informed consent, accepting the anonymous collection of their clinical data., (© 2024. Springer-Verlag GmbH Germany, part of Springer Nature.)

The interaction between basic science epilepsy researchers and clinical epileptologists is a longstanding issue. Efforts to provide opportunities for a dialogue between preclinical and clinical epilepsy professionals are crucial to reduce the knowledge gap between them and improve the translational success of neurobiology-based research. The International League Against Epilepsy (ILAE) Research and Innovation Task Force circulated a survey to investigate the need for an update on new clinical epilepsy concepts within the basic science community. The 336 respondents included basic scientists (BS), preclinical scientists (PCSs), and/or clinical scientists (CSs). The majority of the 237 BSs/PCSs were engaged in preclinical studies in translational epilepsy research and declared translational research as a priority research interest. Fewer respondents from low-middle-income countries than from upper-middle or high-income countries (40.7% vs 65%) considered translational research a critical aspect of their research. A broad understanding of both clinical and neurobiological aspects of epilepsy was declared by 48% of BSs/PCSs; 96% of CSs declared a superficial knowledge of neurobiology of epilepsy. Most BSs/PCSs were aware that epilepsy is a complex condition that should be investigated with the help of clinical epileptologists, even though concerns were expressed on the relationship with clinicians. A focused training program on emerging clinical epileptological aspects tailored for BSs/PCSs was recommended by 81% of the participants; the majority of respondents preferred either 1- or 2-week in-presence tutoring or continuous online training coordinated by ILAE at the regional/national level. The survey also underscored the value of educational programs on neurobiology of epilepsy targeting CSs and low-middle-income countries (LMIC) investigators., (© 2024 The Author(s). Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

This case report shows the importance of multimodal evaluation to formulate a proper diagnosis of negative motor seizures (NMSs). Only few reports in literature document NMSs with video-electroencephalographic (EEG) and electromyographic coregistration. A multimodal evaluation is crucial to exclude common mimics and propose correct therapy. We describe a case of a 62-year-old man with drug-resistant focal epilepsy and NMSs, evaluated with video-EEG recording with polygraphy, magnetoencephalography (MEG), and brain magnetic resonance imaging (MRI). Video-EEG monitoring showed 182 focal NMSs, with preserved awareness and comprehension. The patient reported complex paresthesia of the left hand followed by left facial grimace, left arm flaccid paralysis, and bradycardia. EEG showed ictal discharges in the right frontocentral region associated with sudden electromyographical silence in left limb muscles consistent with loss of tonic contraction from distal to proximal muscles of the arm. MEG localized the epileptic zone in the right opercular region, consistent with MRI evidence of type II cortical dysplasia in the right inferior frontal gyrus. Multimodal evaluation is essential to document the temporal relationship between ictal discharges, clinical onset of limb paresis, and electrophysiologic evidence of loss of tonic muscular contraction. It allows definition of the specific cortical area involved in NMSs, offering new insight into physiological brain functioning., (© 2024 The Author(s). Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Background and Objectives: Myelin is altered in several neurologic disorders. Published data demonstrate reduced white matter myelin content and lower oligodendrocyte cell number in postsurgical brain specimens obtained from patients with focal cortical dysplasia (FCD) and temporal lobe epilepsy; a pathogenic role of dysfunctional myelin in focal epilepsies has been proposed. Based on this evidence, our study aims to investigate the myelination status in the gray matter in postsurgical brain specimens from patients with FCDIIb., Methods: We collected specimens from patients with a histopathologic diagnosis of FCDIIb who underwent surgery between 1995 and 2022 in 2 epilepsy surgery centers in Milano; we used nonlesional samples and perilesional tissue within the same FCDIIb specimen as controls. Immunohistochemistry for myelin basic protein (MBP) and electron microscopy were used to quantify myelin alterations in the lesional core of FCDIIb specimens compared with nonlesional and perilesional control areas. Olig2 and breast carcinoma amplified sequence 1 immunohistochemistry, markers of oligodendrocytes, were also evaluated., Results: Sixteen patients with FCDIIb (24 ± 14 mean years at surgery, 44% female) and 4 controls (3 histopathology-negative epileptic patients and 1 patient with nonepileptic tumor; 32 ± 11 mean years at surgery, 50% female) were included. The cortical myeloarchitecture was disorganized in the FCD core lesion. MBP immunostained fiber density from 11 paired samples that included both the FCD lesional core and adjacent perilesional cortex in the same tissue section did not reveal a significant difference. Ultrastructural examination performed in the gray matter of 6 specimens from FCDIIb patients (both in the core and in the adjacent perilesional areas) and 2 controls revealed that exclusively in the FCDIIb core, myelinated fiber density was reduced and axons featured thin or no myelin coating and pathologic vacuoles. These changes were associated with a reduction of Olig2-immunostained cells in the FCDIIb cortex core., Discussion: Our findings demonstrate that the gray matter at the core of postsurgical FCDIIb specimens contains a high number of poorly myelinated axons and less oligodendrocytes; these findings suggest a potential contribution of altered myelination in the pathogenesis of FCDIIb.

Objective: Epilepsy surgery is a treatment option for patients with seizures that do not respond to pharmacotherapy. The histopathological characterization of the resected tissue has an important prognostic value to define postoperative seizure outcome in these patients. However, the diagnostic classification process based on microscopic assessment remains challenging, particularly in the case of focal cortical dysplasia (FCD). Imaging mass spectrometry is a spatial omics technique that could improve tissue phenotyping and patient stratification by investigating hundreds of biomolecules within a single tissue sample, without the need for target-specific reagents., Methods: An in situ proteomic technique called matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) is here investigated as a potential new tool to expand conventional diagnosis on standard paraffin brain tissue sections. Unsupervised and region of interest-based MALDI-MSI analyses of sections from 10 FCD type IIb (FCDIIb) cases were performed, and the results were validated by immunohistochemistry., Results: MALDI-MSI identified distinct histopathological features and the boundaries of the dysplastic lesion. The capability to visualize the spatial distribution of well-known diagnostic markers enabling multiplex measurements on single tissue sections was demonstrated. Finally, a fingerprint list of potential discriminant peptides that distinguish FCD core from peri-FCD tissue was generated., Significance: This is the first study that explores the potential application of MALDI-MSI in epilepsy postsurgery fixed tissue, by utilizing the well-characterized FCDIIb features as a model. Extending these preliminary analyses to a larger cohort of patients will generate spectral libraries of molecular signatures that discriminate tissue features and will contribute to patient phenotyping., (© 2024 The Author(s). Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

A critical question regarding how focal seizures start is whether we can identify particular cell classes that drive the pathological process. This was the topic for debate at the recent International Conference for Technology and Analysis of Seizures (ICTALS) meeting (July 2022, Bern, CH) that we summarize here. The debate has been fueled in recent times by the introduction of powerful new ways to manipulate subpopulations of cells in relative isolation, mostly using optogenetics. The motivation for resolving the debate is to identify novel targets for therapeutic interventions through a deeper understanding of the etiology of seizures., (© 2023 The Authors. Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

The potassium released in the extracellular space during neuronal activity is rapidly removed by glia and neurons to maintain tissue homeostasis. Oligodendrocyte-derived myelin axonal coating contributes to potassium buffering and is therefore crucial to control brain excitability. We studied activity-dependent extracellular potassium ([K + ] o ) changes in the piriform cortex (PC), a region that features highly segregated bundles of myelinated and unmyelinated fibers. Four-aminopyridine (4AP; 50 μM) treatment or patterned high-frequency stimulations (hfST) were utilized to generate [K + ] o changes measured with potassium-sensitive electrodes in the myelinated lateral olfactory tract (LOT), in the unmyelinated PC layer I and in the myelinated deep PC layers in the ex vivo isolated guinea-pig brain. Seizure-like events induced by 4AP are initiated by the abrupt [K + ] o rise in the layer I formed by unmyelinated fibers (Uva et al., 2017). Larger [K + ] o shifts occurred in unmyelinated layers compared to the myelinated LOT. LOT hfST that mimicks pre-seizure discharges also generated higher [K + ] o changes in unmyelinated PC layer I than in LOT and deep PC layers. The treatment with the Kir4.1 potassium channel blocker BaCl 2 (100 μM) enhanced the [K + ] o changes generated by hfST in myelinated structures. Our data show that activity-dependent [K + ] o changes are intrinsically different in myelinated vs unmyelinated cortical regions. The larger [K + ] o shifts generated in unmyelinated structures may represent a vehicle for seizure generation., Competing Interests: Declaration of competing interest None., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Vadym Gnatkovsky,1 Alessandro Cattalini,1 Alessandro Antonini,2 Laura Spreafico,2 Matteo Saini,2 Francesco Noè,1 Camilla Alessi,1 Laura Librizzi,1 Laura Uva,1 Carlo Efisio Marras,3 Marco de Curtis,1 Sandro Ferrari2 1Unit of Epileptology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Milano, Italy; 2WISE Srl, Cologno Monzese, Milano, Italy; 3Neurosurgery Unit, Department of Neuroscience and Neurorehabilitation, IRCCS Bambino Gesù Children’s Hospital, Roma, ItalyCorrespondence: Vadym GnatkovskyUnit of Epileptology, Fondazione IRCCS Istituto Neurologico Carlo Besta, Via Amadeo, 42, Milano 20133, ItalyTel +39 0223944518Email Vadym.Gnatkovsky@istituto-besta.itBackground: Multielectrodes are implanted in central and peripheral nervous systems for rehabilitation and diagnostic purposes. The physical resistance of intracranial devices to mechanical stress is critical and fractures or electrode displacement may occur. We describe here a new recording device with stretchable properties based on Supersonic Cluster Beam Implantation (SCBI) technology with high mechanical adaptability to displacement and movement.Results: The capability of SCBI-based multichannel electrodes to record brain electrical activity was compared to glass/silicon microelectrodes in acute in vitro experiments on the isolated guinea pig brain preparation. Field potentials and power frequency analysis demonstrated equal recording features for SCBI and standard electrodes. Chronic in vivo epidural implantation of the SCBI electrodes confirmed excellent long-term recording properties in comparison to standard EEG metal electrodes. Tissue biocompatibility was demonstrated by neuropathological evaluation of the brain tissue 2 months after the implantation of the devices in the subarachnoid space.Conclusion: We confirm the biocompatibility of novel SCBI-based stretchable electrode devices and demonstrate their suitability for recording electrical brain activity in pre-clinical settings.Keywords: brain, field potentials, recording electrodes, supersonic cluster beam implantation

In vitro preparations (defined here as cultured cells, brain slices, and isolated whole brains) offer a variety of approaches to modeling various aspects of seizures and epilepsy. Such models are particularly amenable to the application of anti-seizure compounds, and consequently are a valuable tool to screen the mechanisms of epileptiform activity, mode of action of known anti-seizure medications (ASMs), and the potential efficacy of putative new anti-seizure compounds. Despite these applications, all disease models are a simplification of reality and are therefore subject to limitations. In this review, we summarize the main types of in vitro models that can be used in epilepsy research, describing key methodologies as well as notable advantages and disadvantages of each. We argue that a well-designed battery of in vitro models can form an effective and potentially high-throughput screening platform to predict the clinical usefulness of ASMs, and that in vitro models are particularly useful for interrogating mechanisms of ASMs. To conclude, we offer several key recommendations that maximize the potential value of in vitro models in ASM screening. This includes the use of multiple in vitro tests that can complement each other, carefully combined with in vivo studies, the use of tissues from chronically epileptic (rather than naïve wild-type) animals, and the integration of human cell/tissue-derived preparations., (© 2023 The Authors. Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

Objective: Benchmarking has been proposed to reflect surgical quality and represents the highest standard reference values for desirable results. We sought to determine benchmark outcomes in patients after surgery for drug-resistant mesial temporal lobe epilepsy (MTLE)., Methods: This retrospective multicenter study included patients who underwent MTLE surgery at 19 expert centers on five continents. Benchmarks were defined for 15 endpoints covering surgery and epilepsy outcome at discharge, 1 year after surgery, and the last available follow-up. Patients were risk-stratified by applying outcome-relevant comorbidities, and benchmarks were calculated for low-risk ("benchmark") cases. Respective measures were derived from the median value at each center, and the 75th percentile was considered the benchmark cutoff., Results: A total of 1119 patients with a mean age (range) of 36.7 (1-74) years and a male-to-female ratio of 1:1.1 were included. Most patients (59.2%) underwent anterior temporal lobe resection with amygdalohippocampectomy. The overall rate of complications or neurological deficits was 14.4%, with no in-hospital death. After risk stratification, 377 (33.7%) benchmark cases of 1119 patients were identified, representing 13.6%-72.9% of cases per center and leaving 742 patients in the high-risk cohort. Benchmark cutoffs for any complication, clinically apparent stroke, and reoperation rate at discharge were ≤24.6%, ≤.5%, and ≤3.9%, respectively. A favorable seizure outcome (defined as International League Against Epilepsy class I and II) was reached in 83.6% at 1 year and 79.0% at the last follow-up in benchmark cases, leading to benchmark cutoffs of ≥75.2% (1-year follow-up) and ≥69.5% (mean follow-up of 39.0 months)., Significance: This study presents internationally applicable benchmark outcomes for the efficacy and safety of MTLE surgery. It may allow for comparison between centers, patient registries, and novel surgical and interventional techniques., (© 2024 The Authors. Epilepsia published by Wiley Periodicals LLC on behalf of International League Against Epilepsy.)

The development of seizures in epilepsy syndromes associated with malformations of cortical development (MCDs) has traditionally been attributed to intrinsic cortical alterations resulting from abnormal network excitability. However, recent analyses at single-cell resolution of human brain samples from MCD patients have indicated the possible involvement of adaptive immunity in the pathogenesis of these disorders. By exploiting the MethylAzoxyMethanol (MAM)/pilocarpine (MP) rat model of drug-resistant epilepsy associated with MCD, we show here that the occurrence of status epilepticus and subsequent spontaneous recurrent seizures in the malformed, but not in the normal brain, are associated with the outbreak of a destructive autoimmune response with encephalitis-like features, involving components of both cell-mediated and humoral immune responses. The MP brain is characterized by blood-brain barrier dysfunction, marked and persisting CD8+ T cell invasion of the brain parenchyma, meningeal B cell accumulation, and complement-dependent cytotoxicity mediated by antineuronal antibodies. Furthermore, the therapeutic treatment of MP rats with the immunomodulatory drug fingolimod promotes both antiepileptogenic and neuroprotective effects. Collectively, these data show that the MP rat could serve as a translational model of epileptogenic cortical malformations associated with a central nervous system autoimmune response. This work indicates that a preexisting brain maldevelopment predisposes to a secondary autoimmune response, which acts as a precipitating factor for epilepsy and suggests immune intervention as a therapeutic option to be further explored in epileptic syndromes associated with MCDs., Competing Interests: Competing interests statement:The authors declare no competing interest.

Background: Neonatal and infant mortality rates are among the most significant indicators for assessing a country's healthcare and social development. This study examined the trends in neonatal, post-neonatal, and infant mortality in Italy from 2016 to 2020 and analysed differences between children of Italian and foreign parents based on areas of residence, as well as the leading causes of death. Special attention was given to the analysis of mortality in 2020, the first year of the Covid-19 pandemic, and its comparison with previous years., Methods: Data from 2016 to 2020 were collected by the Italian National Institute of Statistics and extracted from two national databases, the Causes of Death register and Live births registered in the population register. Neonatal, post-neonatal, and infant mortality rates were calculated using conventional definitions. The main analyses were conducted by comparing Italian citizens to foreigners and contrasting residents of the North with those of the South. Group comparisons were made using mortality rate ratios. The main causes of death were examined, and Poisson log-linear regression models were employed to investigate the relationships between mortality rate ratios for each cause of death and citizenship, place of residence and calendar year., Results: In Italy, in 2020, the neonatal mortality rate was 1.76 deaths per thousand live births and it was 55% higher in foreign children than in Italian children. Foreign children had a higher mortality rate than Italians for almost all significant causes of death. Children born in the South of Italy, both Italian and foreign, had an infant mortality rate about 70% higher than residents in the North. Regions with higher infant mortality were Calabria, Sicily, Campania, and Apulia. In the South, mortality from neonatal respiratory distress and prematurity was higher. In the first months of 2020, between March and June, the first Covid-19 wave, Italy experienced an increase in neonatal and infant mortality compared to the same period in 2016-2019, not directly related to SARS-CoV-19 infection. The primary cause was neonatal respiratory distress., Conclusions: The neonatal and infant mortality rates indicate the persistence of profound inequalities in Italy between the North and the South and between Italian and foreign children., (© 2024. The Author(s).)

Objective: Encephaloceles (ENCs) may cause clinical complications, including drug-resistant epilepsy that can be cured with epilepsy surgery., Methods: We describe clinical, diagnostic, and neuropathological findings of 12 patients with temporal ENC and epilepsy evaluated for surgery and compare them with a control group of 26 temporal lobe epilepsy (TLE) patients., Results: Six patients had unilateral and 6 bilateral temporal ENCs. Compared to TLEs, ENCs showed i) later epilepsy onset, ii) higher prevalence of psychiatric comorbidities, iii) no history of febrile convulsions, and iv) ictal semiology differences. Seven patients had MRI signs of gliosis, and 9 of intracranial hypertension. Interictal EEG analysis in ENCs demonstrated significant differences with controls: prominent activity in the beta/gamma frequency bands in frontal regions, interictal short sequences of low-voltage fast activity, and less frequent and more localized interictal epileptiform discharges. Ictal EEG patterns analyzed in 9 ENCs showed delayed and slower contralateral spread compared to TLEs. All ENCs that underwent surgery (7 lobectomies and 1 lesionectomy) are in Engel class I. Neuropathological examination revealed 4 patterns: herniated brain fragments, focal layer I distortion, white matter septa extending into the cortex, and altered gyral profile., Conclusions and Significance: The described peculiarities might help clinicians to suspect the presence of largely underdiagnosed ENCs., (© 2023. Fondazione Società Italiana di Neurologia.)

Objective: The influx of immune cells and serum proteins from the periphery into the brain due to a dysfunctional blood-brain barrier (BBB) has been proposed to contribute to the pathogenesis of seizures in various forms of epilepsy and encephalitis. We evaluated the pathophysiological impact of activated peripheral blood mononuclear cells (PBMCs) and serum albumin on neuronal excitability in an in vitro brain preparation., Methods: A condition of mild endothelial activation induced by arterial perfusion of lipopolysaccharide (LPS) was induced in the whole brain preparation of guinea pigs maintained in vitro by arterial perfusion. We analyzed the effects of co-perfusion of human recombinant serum albumin with human PBMCs activated with concanavalin A on neuronal excitability, BBB permeability (measured by FITC-albumin extravasation), and microglial activation., Results: Bioplex analysis in supernatants of concanavalin A-stimulated PBMCs revealed increased levels of several inflammatory mediators, in particular interleukin (IL)-1β, tumor necrosis factor (TNF)-α, interferon (INF)-γ, IL-6, IL-10, IL-17A, and MIP3α. LPS and human albumin arterially co-perfused with either concanavalin A-activated PBMCs or the cytokine-enriched supernatant of activated PBMCs (1) modulated calcium-calmodulin-dependent protein kinase II at excitatory synapses, (2) enhanced BBB permeability, (3) induced microglial activation, and (4) promoted seizure-like events. Separate perfusions of either nonactivated PBMCs or concanavalin A-activated PBMCs without LPS/human albumin (hALB) failed to induce inflammatory and excitability changes., Significance: Activated peripheral immune cells, such as PBMCs, and the extravasation of serum proteins in a condition of BBB impairment contribute to seizure generation., (© 2021 International League Against Epilepsy.)

Loss of myelin and altered oligodendrocyte distribution in the cerebral cortex are commonly observed both in postsurgical tissue derived from different focal epilepsies (such as focal cortical dysplasias and tuberous sclerosis) and in animal models of focal epilepsy. Moreover, seizures are a frequent symptom in demyelinating diseases, such as multiple sclerosis, and in animal models of demyelination and oligodendrocyte dysfunction. Finally, the excessive activity reported in demyelinated axons may promote hyperexcitability. We hypothesize that the extracellular potassium rise generated during epileptiform activity may be amplified by the presence of axons without appropriate myelin coating and by alterations in oligodendrocyte function. This process could facilitate the triggering of recurrent spontaneous seizures in areas of altered myelination and could result in further demyelination, thus promoting epileptogenesis., (© 2021 International League Against Epilepsy.)

We review here the neuronal mechanisms that cause seizures in focal epileptic disorders and, specifically, those involving limbic structures that are known to be implicated in human mesial temporal lobe epilepsy. In both epileptic patients and animal models, the initiation of focal seizures - which are most often characterized by a low-voltage fast onset EEG pattern - is presumably dependent on the synchronous firing of GABA-releasing interneurons that, by activating post-synaptic GABA A receptors, cause large increases in extracellular [K + ] through the activation of the co-transporter KCC2. A similar mechanism may contribute to seizure maintenance; accordingly, inhibiting KCC2 activity transforms seizure activity into a continuous pattern of short-lasting epileptiform discharges. It has also been found that interactions between different areas of the limbic system modulate seizure occurrence by controlling extracellular [K + ] homeostasis. In line with this view, low-frequency electrical or optogenetic activation of limbic networks restrain seizure generation, an effect that may also involve the activation of GABA B receptors and activity-dependent changes in epileptiform synchronization. Overall, these findings highlight the paradoxical role of GABA A signaling in both focal seizure generation and maintenance, emphasize the efficacy of low-frequency activation in abating seizures, and provide experimental evidence explaining the poor efficacy of antiepileptic drugs designed to augment GABAergic function in controlling seizures in focal epileptic disorders., Competing Interests: Declaration of Competing Interest The authors have no conflict of interest to disclose., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Dendritic spines are the postsynaptic sites for most excitatory glutamatergic synapses. We previously demonstrated a severe spine loss and synaptic reorganization in human neocortices presenting Type II focal cortical dysplasia (FCD), a developmental malformation and frequent cause of drug-resistant focal epilepsy. We extend the findings, investigating the potential role of complement components C1q and C3 in synaptic pruning imbalance. Data from Type II FCD were compared with those obtained in focal epilepsies with different etiologies. Neocortical tissues were collected from 20 subjects, mainly adults with a mean age at surgery of 31 years, admitted to epilepsy surgery with a neuropathological diagnosis of: cryptogenic, temporal lobe epilepsy with hippocampal sclerosis, and Type IIa/b FCD. Dendritic spine density quantitation, evaluated in a previous paper using Golgi impregnation, was available in a subgroup. Immunohistochemistry, in situ hybridization, electron microscopy, and organotypic cultures were utilized to study complement/microglial activation patterns. FCD Type II samples presenting dendritic spine loss were characterized by an activation of the classical complement pathway and microglial reactivity. In the same samples, a close relationship between microglial cells and dendritic segments/synapses was found. These features were consistently observed in Type IIb FCD and in 1 of 3 Type IIa cases. In other patient groups and in perilesional areas outside the dysplasia, not presenting spine loss, these features were not observed. In vitro treatment with complement proteins of organotypic slices of cortical tissue with no sign of FCD induced a reduction in dendritic spine density. These data suggest that dysregulation of the complement system plays a role in microglia-mediated spine loss. This mechanism, known to be involved in the removal of redundant synapses during development, is likely reactivated in Type II FCD, particularly in Type IIb; local treatment with anticomplement drugs could in principle modify the course of disease in these patients., (© 2022 The Authors. Brain Pathology published by John Wiley & Sons Ltd on behalf of International Society of Neuropathology.)

Single-unit recordings performed in temporal lobe epilepsy patients and in models of temporal lobe seizures have shown that interneurons are active at focal seizure onset. We performed simultaneous patch-clamp and field potential recordings in entorhinal cortex slices of GAD65 and GAD67 C57BL/6J male mice that express green fluorescent protein in GABAergic neurons to analyze the activity of specific interneuron (IN) subpopulations during acute seizure-like events (SLEs) induced by 4-aminopyridine (4-AP; 100 μm). IN subtypes were identified as parvalbuminergic (IN PV , n = 17), cholecystokinergic (IN CCK ), n = 13], and somatostatinergic (IN SOM , n = 15), according to neurophysiological features and single-cell digital PCR. IN PV and IN CCK discharged at the start of 4-AP-induced SLEs characterized by either low-voltage fast or hyper-synchronous onset pattern. In both SLE onset types, IN SOM fired earliest before SLEs, followed by IN PV and IN CCK discharges. Pyramidal neurons became active with variable delays after SLE onset. Depolarizing block was observed in ∼50% of cells in each INs subgroup, and it was longer in IN (∼4 s) than in pyramidal neurons (<1 s). As SLE evolved, all IN subtypes generated action potential bursts synchronous with the field potential events leading to SLE termination. High-frequency firing throughout the SLE occurred in one-third of IN PV and IN SOM We conclude that entorhinal cortex INs are very active at the onset and during the progression of SLEs induced by 4-AP. These results support earlier in vivo and in vivo evidence and suggest that INs have a preferential role in focal seizure initiation and development. SIGNIFICANCE STATEMENT Focal seizures are believed to result from enhanced excitation. Nevertheless, we and others demonstrated that cortical GABAergic networks may initiate focal seizures. Here, we analyzed for the first time the role of different IN subtypes in seizures generated by 4-aminopyridine in the mouse entorhinal cortex slices. We found that in this in vitro focal seizure model, all IN types contribute to seizure initiation and that INs precede firing of principal cells. This evidence is in agreement with the active role of GABAergic networks in seizure generation., (Copyright © 2023 the authors.)

Epilepsies affecting the limbic regions are common and generate seizures often resistant to pharmacological treatment. Clinical evidence demonstrates that diverse regions of the mesial portion of the temporal lobe participate in limbic seizures; these include the hippocampus, the entorhinal, perirhinal and parahippocampal regions and the piriform cortex. The network mechanisms involved in the generation of olfactory-limbic epileptiform patterns will be here examined, with particular emphasis on acute interictal and ictal epileptiform discharges obtained by treatment with pro-convulsive drugs and by high-frequency stimulations on in vitro preparations, such as brain slices and the isolated guinea pig brain. The interactions within olfactory-limbic circuits can be summarized as follows: independent, region-specific seizure-like events (SLE) are generated in the olfactory and in the limbic cortex; SLEs generated in the hippocampal-parahippocampal regions tend to remain within these areas; the perirhinal region controls the neocortical propagation and the generalization of limbic seizures; interictal spiking in the olfactory regions prevents the invasion by SLEs generated in limbic regions. The potential relevance of these observations for human focal epilepsy is discussed., (Copyright © 2023. Published by Elsevier Inc.)