GABA(A) receptors in normal development and seizures: friends or foes?

Alterations in GABAA receptor-mediated inhibition triggered by status epilepticus and their role in epileptogenesis and increased anxiety

The triggers of status epilepticus (SE) in non-epileptic patients can vary widely, from idiopathic causes to exposure to chemoconvulsants. Regardless of its etiology, prolonged SE can cause significant brain damage, commonly resulting in the development of epilepsy, which is often accompanied by increased anxiety. GABAA receptor (GABAAR)-mediated inhibition has a central role among the mechanisms underlying brain damage and the ensuing epilepsy and anxiety. During SE, calcium influx primarily via ionotropic glutamate receptors activates signaling cascades which trigger a rapid internalization of synaptic GABAARs; this weakens inhibition, exacerbating seizures and excitotoxicity. GABAergic interneurons are more susceptible to excitotoxic death than principal neurons. During the latent period of epileptogenesis, the aberrant reorganization in synaptic interactions that follow interneuronal loss in injured brain regions, leads to the formation of hyperexcitable, seizurogenic neuronal circuits, along with disturbances in brain oscillatory rhythms. Reduction in the spontaneous, rhythmic "bursts" of IPSCs in basolateral amygdala neurons is likely to play a central role in anxiogenesis. Protecting interneurons during SE is key to preventing both epilepsy and anxiety. Antiglutamatergic treatments, including antagonism of calcium-permeable AMPA receptors, can be expected to control seizures and reduce excitotoxicity not only by directly suppressing hyperexcitation, but also by counteracting the internalization of synaptic GABAARs. Benzodiazepines, as delayed treatment of SE, have low efficacy due to the reduction and dispersion of their targets (the synaptic GABAARs), but also because themselves contribute to further reduction of available GABAARs at the synapse; furthermore, benzodiazepines may be completely ineffective in the immature brain.

Dual effects of ARX poly-alanine mutations in human cortical and interneuron development

Infantile spasms, with an incidence of 1.6 to 4.5 per 10,000 live births, are a relentless and devastating childhood epilepsy marked by severe seizures but also leads to lifelong intellectual disability. Alarmingly, up to 5% of males with this condition carry a mutation in the Aristaless-related homeobox ( ARX ) gene. Our current lack of human-specific models for developmental epilepsy, coupled with discrepancies between animal studies and human data, underscores the gap in knowledge and urgent need for innovative human models, organoids being one of the best available. Here, we used human neural organoid models, cortical organoids (CO) and ganglionic eminences organoids (GEO) which mimic cortical and interneuron development respectively, to study the consequences of PAE mutations, one of the most prevalent mutation in ARX . ARX PAE produces a decrease expression of ARX in GEOs, and an enhancement in interneuron migration. That accelerated migration is cell autonomously driven, and it can be rescued by inhibiting CXCR4. We also found that PAE mutations result in an early increase in radial glia cells and intermediate progenitor cells, followed by a subsequent loss of cortical neurons at later timepoints. Moreover, ARX expression is upregulated in COs derived from patients at 30 DIV and is associated with alterations in the expression of CDKN1C . Furthermore, ARX PAE assembloids had hyperactivity which were evident at early stages of development. With effective treatments for infantile spasms and developmental epilepsies still elusive, delving into the role of ARX PAE mutations in human brain organoids represents a pivotal step toward uncovering groundbreaking therapeutic strategies.

Investigative analysis of blood-brain barrier penetrating potential of electronic nicotine delivery systems (e-cigarettes) chemicals using predictive computational models

INTRODUCTION

Seizures are known potential side effects of nicotine toxicity and have been reported in electronic nicotine delivery systems (ENDS, e-cigarettes) users, with the majority involving youth or young adults.

AREAS COVERED

Using chemoinformatic computational models, chemicals (including flavors) documented to be present in ENDS were compared to known neuroactive compounds to predict the blood-brain barrier (BBB) penetration potential, central nervous system (CNS) activity, and their structural similarities. The literature search used PubMed/Google Scholar, through September 2023, to identify individual chemicals in ENDS and neuroactive compounds.The results show that ENDS chemicals in this study contain >60% structural similarity to neuroactive compounds based on chemical fingerprint similarity analyses. The majority of ENDS chemicals we studied were predicted to cross the BBB, with approximately 60% confidence, and were also predicted to have CNS activity; those not predicted to passively diffuse through the BBB may be actively transported through the BBB to elicit CNS impacts, although it is currently unknown.

EXPERT OPINION

In lieu of in vitro and in vivo testing, this study screens ENDS chemicals for potential CNS activity and predicts BBB penetration potential using computer-based models, allowing for prioritization for further study and potential early identification of CNS toxicity.

Seizures exacerbate excitatory: inhibitory imbalance in Alzheimer's disease and 5XFAD mice

Approximately 22% of Alzheimer's disease (AD) patients suffer from seizures, and the co-occurrence of seizures and epileptiform activity exacerbates AD pathology and related cognitive deficits, suggesting that seizures may be a targetable component of AD progression. Given that alterations in neuronal excitatory:inhibitory (E:I) balance occur in epilepsy, we hypothesized that decreased markers of inhibition relative to those of excitation would be present in AD patients. We similarly hypothesized that in 5XFAD mice, the E:I imbalance would progress from an early stage (prodromal) to later symptomatic stages and be further exacerbated by pentylenetetrazol (PTZ) kindling. Post-mortem AD temporal cortical tissues from patients with or without seizure history were examined for changes in several markers of E:I balance, including levels of the inhibitory GABAA receptor, the sodium potassium chloride cotransporter 1 (NKCC1) and potassium chloride cotransporter 2 (KCC2) and the excitatory NMDA and AMPA type glutamate receptors. We performed patch-clamp electrophysiological recordings from CA1 neurons in hippocampal slices and examined the same markers of E:I balance in prodromal 5XFAD mice. We next examined 5XFAD mice at chronic stages, after PTZ or control protocols, and in response to chronic mTORC1 inhibitor rapamycin, administered following kindled seizures, for markers of E:I balance. We found that AD patients with comorbid seizures had worsened cognitive and functional scores and decreased GABAA receptor subunit expression, as well as increased NKCC1/KCC2 ratios, indicative of depolarizing GABA responses. Patch clamp recordings of prodromal 5XFAD CA1 neurons showed increased intrinsic excitability, along with decreased GABAergic inhibitory transmission and altered glutamatergic neurotransmission, indicating that E:I imbalance may occur in early disease stages. Furthermore, seizure induction in prodromal 5XFAD mice led to later dysregulation of NKCC1/KCC2 and a reduction in GluA2 AMPA glutamate receptor subunit expression, indicative of depolarizing GABA receptors and calcium permeable AMPA receptors. Finally, we found that chronic treatment with the mTORC1 inhibitor, rapamycin, at doses we have previously shown to attenuate seizure-induced amyloid-β pathology and cognitive deficits, could also reverse elevations of the NKCC1/KCC2 ratio in these mice. Our data demonstrate novel mechanisms of interaction between AD and epilepsy and indicate that targeting E:I balance, potentially with US Food and Drug Administration-approved mTOR inhibitors, hold therapeutic promise for AD patients with a seizure history.

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Impaired GABAergic regulation and developmental immaturity in interneurons derived from the medial ganglionic eminence in the tuberous sclerosis complex

GABAergic interneurons play a critical role in maintaining neural circuit balance, excitation-inhibition regulation, and cognitive function modulation. In tuberous sclerosis complex (TSC), GABAergic neuron dysfunction contributes to disrupted network activity and associated neurological symptoms, assumingly in a cell type-specific manner. This GABAergic centric study focuses on identifying specific interneuron subpopulations within TSC, emphasizing the unique characteristics of medial ganglionic eminence (MGE)- and caudal ganglionic eminence (CGE)-derived interneurons. Using single-nuclei RNA sequencing in TSC patient material, we identify somatostatin-expressing (SST+) interneurons as a unique and immature subpopulation in TSC. The disrupted maturation of SST+ interneurons may undergo an incomplete switch from excitatory to inhibitory GABAergic signaling during development, resulting in reduced inhibitory properties. Notably, this study reveals markers of immaturity specifically in SST+ interneurons, including an abnormal NKCC1/KCC2 ratio, indicating an imbalance in chloride homeostasis crucial for the postsynaptic consequences of GABAergic signaling as well as the downregulation of GABAA receptor subunits, GABRA1, and upregulation of GABRA2. Further exploration of SST+ interneurons revealed altered localization patterns of SST+ interneurons in TSC brain tissue, concentrated in deeper cortical layers, possibly linked to cortical dyslamination. In the epilepsy context, our research underscores the diverse cell type-specific roles of GABAergic interneurons in shaping seizures, advocating for precise therapeutic considerations. Moreover, this study illuminates the potential contribution of SST+ interneurons to TSC pathophysiology, offering insights for targeted therapeutic interventions.

Ketamine Efficacy for Management of Status Epilepticus: Considerations for Prehospital Clinicians

Current first-line therapies for seizure management recommend benzodiazepines, which target gamma-aminobutyric acid type A channels to stop the seizure activity. However, seizures may be refractory to traditional first-line therapies, transitioning into status epilepticus and becoming resistant to gamma-aminobutyric acid type A augmenting drugs. Although there are other antiseizure medications available for clinicians to use in the intensive care unit, these options can be less readily available outside of the intensive care unit and entirely absent in the prehospital setting. Instead, patients frequently receive multiple doses of first-line agents with increased risk of hemodynamic or airway collapse. Ketamine is readily available in the prehospital setting and emergency department, has well-established antiseizure effects with a favorable safety profile, and is a drug often used for several other indications. This article aimed to explore the utilization of ketamine for seizure management in the prehospital setting, reviewing seizure pathophysiology, established treatment mechanisms of action and pharmacokinetics, and potential benefits of early ketamine use in status epilepticus.

Sex-specific behavioural deficits in adulthood following acute activation of the GABAA receptor in the neonatal mouse

INTRODUCTION

Sex differences exist in the prevalence of neurodevelopmental disorders (NDDs). Part of the aetiology of NDDs has been proposed to be alterations in the balance between excitatory and inhibitory neurotransmission, leading to the question of whether males and females respond differently to altered neurotransmitter balance. We investigated whether pharmacological alteration of GABAA signalling in early development results in sex-dependent changes in adult behaviours associated with NDDs.

METHODS

Male and female C57BL/6J mice received intraperitoneal injections of 0.5mg/kg muscimol or saline on postnatal days (P) 3-5 and were subjected to behavioural testing, specifically open field, light dark box, marble burying, sucralose preference, social interaction and olfactory habituation/dishabituation tests between P60-90.

RESULTS

Early postnatal administration of muscimol resulted in reduced anxiety in the light dark box test in both male and female adult mice. Muscimol reduced sucralose preference in males, but not females, whereas female mice showed reduced social behaviours. Regional alterations in cortical thickness were observed in the weeks following GABAA receptor activation, pointing to an evolving structural difference in the brain underlying adult behaviour.

CONCLUSIONS

We conclude that activation of the GABAA receptor in the first week of life resulted in long-lasting changes in a range of behaviours in adulthood following altered neurodevelopment. Sex of the individual affected the nature and severity of these abnormalities, explaining part of the varied pathophysiology and neurodevelopmental diagnosis that derive from excitatory/inhibitory imbalance.

Clinical Correlation of Altered Molecular Signatures in Epileptic Human Hippocampus and Amygdala

Widespread alterations in the expression of various genes could contribute to the pathogenesis of epilepsy. The expression levels of various genes, including major inhibitory and excitatory receptors, ion channels, cell type-specific markers, and excitatory amino acid transporters, were assessed and compared between the human epileptic hippocampus and amygdala, and findings from autopsy controls. Moreover, the potential correlation between molecular alterations in epileptic brain tissues and the clinical characteristics of patients undergoing epilepsy surgery was evaluated. Our findings revealed significant and complex changes in the expression of several key regulatory genes in both the hippocampus and amygdala of patients with intractable epilepsy. The expression changes in various genes differed considerably between the epileptic hippocampus and amygdala. Different correlation patterns were observed between changes in gene expression and clinical characteristics, depending on whether the patients were considered as a whole or were subdivided. Altered molecular signatures in different groups of epileptic patients, defined within a given category, could be viewed as diagnostic biomarkers. Distinct patterns of molecular changes that distinguish these groups from each other appear to be associated with epilepsy-specific functional consequences.

Socrates: A Novel N-Ethyl-N-nitrosourea-Induced Mouse Mutant with Audiogenic Epilepsy

Epilepsy is one of the common neurological diseases that affects not only adults but also infants and children. Because epilepsy has been studied for a long time, there are several pharmacologically effective anticonvulsants, which, however, are not suitable as therapy for all patients. The genesis of epilepsy has been extensively investigated in terms of its occurrence after injury and as a concomitant disease with various brain diseases, such as tumors, ischemic events, etc. However, in the last decades, there are multiple reports that both genetic and epigenetic factors play an important role in epileptogenesis. Therefore, there is a need for further identification of genes and loci that can be associated with higher susceptibility to epileptic seizures. Use of mouse knockout models of epileptogenesis is very informative, but it has its limitations. One of them is due to the fact that complete deletion of a gene is not, in many cases, similar to human epilepsy-associated syndromes. Another approach to generating mouse models of epilepsy is N-Ethyl-N-nitrosourea (ENU)-directed mutagenesis. Recently, using this approach, we generated a novel mouse strain, soc (socrates, formerly s8-3), with epileptiform activity. Using molecular biology methods, calcium neuroimaging, and immunocytochemistry, we were able to characterize the strain. Neurons isolated from soc mutant brains retain the ability to differentiate in vitro and form a network. However, soc mutant neurons are characterized by increased spontaneous excitation activity. They also demonstrate a high degree of Ca2+ activity compared to WT neurons. Additionally, they show increased expression of NMDA receptors, decreased expression of the Ca2+-conducting GluA2 subunit of AMPA receptors, suppressed expression of phosphoinositol 3-kinase, and BK channels of the cytoplasmic membrane involved in protection against epileptogenesis. During embryonic and postnatal development, the expression of several genes encoding ion channels is downregulated in vivo, as well. Our data indicate that soc mutation causes a disruption of the excitation-inhibition balance in the brain, and it can serve as a mouse model of epilepsy.

Increased Excitability of Layer 2 Cortical Pyramidal Neurons in the Supplementary Motor Cortex Underlies High Cocaine-Seeking Behaviors

BACKGROUND

Most efforts in addiction research have focused on the involvement of the medial prefrontal cortex, including the infralimbic, prelimbic, and anterior cingulate cortical areas, in cocaine-seeking behaviors. However, no effective prevention or treatment for drug relapse is available.

METHODS

We focused instead on the motor cortex, including both the primary and supplementary motor areas (M1 and M2, respectively). Addiction risk was evaluated by testing cocaine seeking after intravenous self-administration (IVSA) of cocaine in Sprague Dawley rats. The causal relationship between the excitability of cortical pyramidal neurons (CPNs) in M1/M2 and addiction risk was explored by ex vivo whole-cell patch clamp recordings and in vivo pharmacological or chemogenetic manipulation.

RESULTS

Our recordings showed that on withdrawal day 45 (WD45) after IVSA, cocaine, but not saline, increased the excitability of CPNs in the cortical superficial layers (primarily layer 2, denoted L2) but not in layer 5 (L5) in M2. Bilateral microinjection of the GABAA (gamma-aminobutyric acid A) receptor agonist muscimol to the M2 area attenuated cocaine seeking on WD45. More specifically, chemogenetic inhibition of CPN excitability in L2 of M2 (denoted M2-L2) by the DREADD (designer receptor exclusively activated by designer drugs) agonist compound 21 prevented drug seeking on WD45 after cocaine IVSA. This chemogenetic inhibition of M2-L2 CPNs had no effects on sucrose seeking. In addition, neither pharmacological nor chemogenetic inhibition manipulations altered general locomotor activity.

CONCLUSIONS

Our results indicate that cocaine IVSA induces hyperexcitability in the motor cortex on WD45. Importantly, the increased excitability in M2, particularly in L2, could be a novel target for preventing drug relapse during withdrawal.

GABAA receptor-mediated seizure liabilities: a mixed-methods screening approach

GABAA receptors, members of the pentameric ligand-gated ion channel superfamily, are widely expressed in the central nervous system and mediate a broad range of pharmaco-toxicological effects including bidirectional changes to seizure threshold. Thus, detection of GABAA receptor-mediated seizure liabilities is a big, partly unmet need in early preclinical drug development. This is in part due to the plethora of allosteric binding sites that are present on different subtypes of GABAA receptors and the critical lack of screening methods that detect interactions with any of these sites. To improve in silico screening methods, we assembled an inventory of allosteric binding sites based on structural data. Pharmacophore models representing several of the binding sites were constructed. These models from the NeuroDeRisk IL Profiler were used for in silico screening of a compiled collection of drugs with known GABAA receptor interactions to generate testable hypotheses. Amoxapine was one of the hits identified and subjected to an array of in vitro assays to examine molecular and cellular effects on neuronal excitability and in vivo locomotor pattern changes in zebrafish larvae. An additional level of analysis for our compound collection is provided by pharmacovigilance alerts using FAERS data. Inspired by the Adverse Outcome Pathway framework, we postulate several candidate pathways leading from specific binding sites to acute seizure induction. The whole workflow can be utilized for any compound collection and should inform about GABAA receptor-mediated seizure risks more comprehensively compared to standard displacement screens, as it rests chiefly on functional data.

Revisiting the concept of drug-resistant epilepsy: A TASK1 report of the ILAE/AES Joint Translational Task Force

Despite progress in the development of anti-seizure medications (ASMs), one third of people with epilepsy have drug-resistant epilepsy (DRE). The working definition of DRE, proposed by the International League Against Epilepsy (ILAE) in 2010, helped identify individuals who might benefit from presurgical evaluation early on. As the incidence of DRE remains high, the TASK1 workgroup on DRE of the ILAE/American Epilepsy Society (AES) Joint Translational Task Force discussed the heterogeneity and complexity of its presentation and mechanisms, the confounders in drawing mechanistic insights when testing treatment responses, and barriers in modeling DRE across the lifespan and translating across species. We propose that it is necessary to revisit the current definition of DRE, in order to transform the preclinical and clinical research of mechanisms and biomarkers, to identify novel, effective, precise, pharmacologic treatments, allowing for earlier recognition of drug resistance and individualized therapies.

E2730, an uncompetitive γ-aminobutyric acid transporter-1 inhibitor, suppresses epileptic seizures in a rat model of chronic mesial temporal lobe epilepsy

OBJECTIVE

More than one third of mesial temporal lobe epilepsy (MTLE) patients are resistant to current antiseizure medications (ASMs), and half experience mild-to-moderate adverse effects of ASMs. There is therefore a strong need to develop and test novel ASMs. The objective of this work is to evaluate the pharmacokinetics and neurological toxicity of E2730, a novel uncompetitive inhibitor of γ-aminobutyric acid transporter-1, and to test its seizure suppression effects in a rat model of chronic MTLE.

METHODS

We first examined plasma levels and adverse neurological effects of E2730 in healthy Wistar rats. Adult male rats were implanted with osmotic pumps delivering either 10, 20, or 100 mg/kg/day of E2730 subcutaneously for 1 week. Blood sampling and behavioral assessments were performed at several timepoints. We next examined whether E2730 suppressed seizures in rats with chronic MTLE. These rats were exposed to kainic acid-induced status epilepticus, and 9 weeks later, when chronic epilepsy was established, were assigned to receive one of the three doses of E2730 or vehicle for 1 week in a randomized crossover design. Continuous video-electroencephalographic monitoring was acquired during the treatment period to evaluate epileptic seizures.

RESULTS

Plasma levels following continuous infusion of E2730 showed a clear dose-related increase in concentration. The drug was well tolerated at all doses, and any sedation or neuromotor impairment was mild and transient, resolving within 48 h of treatment initiation. Remarkably, E2730 treatment in chronically epileptic rats led to seizure suppression in a dose-dependent manner, with 65% of rats becoming seizure-free at the highest dose tested. Mean seizure class did not differ between the treatment groups.

SIGNIFICANCE

This study shows that continuous subcutaneous infusion of E2730 over 7 days results in a marked, dose-dependent suppression of spontaneous recurrent seizures, with minimal adverse neurological effects, in a rat model of chronic MTLE. E2730 shows strong promise as an effective new ASM to be translated into clinical trials.

Sigma-1 receptor and seizures

Over the last decade, sigma-1 receptor (Sig1R) has been recognized as a valid target for the treatment of seizure disorders and seizure-related comorbidities. Clinical trials with Sig1R ligands are underway testing therapies for the treatment of drug-resistant seizures, developmental and epileptic encephalopathies, and photosensitive epilepsy. However, the direct molecular mechanism by which Sig1R modulates seizures and the balance between excitatory and inhibitory pathways has not been fully elucidated. This review article aims to summarize existing knowledge of Sig1R and its involvement in seizures by focusing on the evidence obtained from Sig1R knockout animals and the anti-seizure effects of Sig1R ligands. In addition, this review article includes a discussion of the advantages and disadvantages of the use of existing compounds and describes the challenges and future perspectives on the use of Sig1R as a target for the treatment of seizure disorders.

Gamma-Aminobutyric Acid Type A Receptor Variants are Associated with Autism Spectrum Disorders

Despite several efforts to identify the causes of autism spectrum disorders (ASD), its etiology remains still unclear. Among other aspects, genes that encode neurotransmitter receptors are strong candidates for autism. Here, we wanted to study some genetic variants of gamma-aminobutyric acid (GABA) receptor subunit genes GABRB3, GABRG3, and GABRA5, located on chromosome 15q11-q13 that might contribute to the etiology of ASD in the affected children of West Bengal. rs7180158, rs2081648 (GABRB3); rs12910555 (GABRG3); rs35399885, rs35832850 (GABRA5) were analyzed in 316 children with ASD and 227 healthy controls. Phenotypic associations were evaluated by Childhood Autism Rating Scale (CARS). Gene expression levels were measured by quantitative real-time PCR. ASD probands showed a higher frequency of "A" allele for rs7180158, "G" allele for rs12901555, and "T" allele for rs35399885. The GA + AA genotypes (rs7180158) and CT + TT genotypes (rs35399885) were found to confer significant risk towards ASD. rs2081648 was found to have transmission bias in the family. Additionally, these variants were found to be associated with one or more of ASD-associated phenotypic traits. Multifactor dimensionality reduction (MDR) analyses showed mostly independent contributory effects of some of the variants. Again, the gene expression levels of GABRB3, GABRG3, and GABRA5 were downregulated in the cases than the controls. ForGABRA5 rs35399885, the CC genotypes corresponded to higher expression levels compared to the other groups. This study reveals that genetic variants of GABA_A receptor subunit genes are significantly associated with ASD. No data for the mentioned variants are found in the population of West Bengal, India.

Molecular Dynamics Refinement of Open State Serotonin 5-HT3A Receptor Structures

Pentameric ligand-gated ion channels play an important role in mediating fast neurotransmissions. As a member of this receptor family, cation-selective 5-HT₃ receptors are a clinical target for treating nausea and vomiting associated with chemotherapy and radiation therapy (Thompson and Lummis, 2006). Multiple cryo-electron microscopy (cryo-EM) structures of 5-HT₃ receptors have been determined in distinct functional states (e.g., open, closed, etc.) (Basak et al., 2018; Basak et al., 2018; Polovinkin et al., 2018; Zhang et al., 2015). However, recent work has shown that the transmembrane pores of the open 5-HT₃ receptor structures rapidly collapse and become artificially asymmetric in molecular dynamics (MD) simulations. To avoid this hydrophobic collapse, Dämgen and Biggin developed an equilibration protocol that led to a stable open state structure of the glycine receptor in MD simulations (Dämgen and Biggin, 2020). However, the protocol failed to yield open-like structures of the 5-HT₃ receptor in our simulations. Here, we present a refined equilibration protocol that involves the rearrangement of the transmembrane helices to achieve stable open state structures of the 5-HT₃ receptor that allow both water and ion permeation through the channel. Notably, channel gating is mediated through collective movement of the transmembrane helices, involving not only pore lining M2 helices but also their cross-talk with the adjacent M1 and M3 helices. Thus, the successful application of our refined equilibration protocol underscores the importance of the conformational coupling between the transmembrane helices in stabilizing open-like structures of the 5-HT₃ receptor.

Inhibitory synapse dysfunction and epileptic susceptibility associated with KIF2A deletion in cortical interneurons

Malformation of cortical development (MCD) is a family of neurodevelopmental disorders, which usually manifest with intellectual disability and early-life epileptic seizures. Mutations in genes encoding microtubules (MT) and MT-associated proteins are one of the most frequent causes of MCD in humans. KIF2A is an atypical kinesin that depolymerizes MT in ATP-dependent manner and regulates MT dynamics. In humans, single de novo mutations in KIF2A are associated with MCD with epileptic seizures, posterior pachygyria, microcephaly, and partial agenesis of corpus callosum. In this study, we conditionally ablated KIF2A in forebrain inhibitory neurons and assessed its role in development and function of inhibitory cortical circuits. We report that adult mice with specific deletion of KIF2A in GABAergic interneurons display abnormal behavior and increased susceptibility to epilepsy. KIF2A is essential for tangential migration of cortical interneurons, their positioning in the cerebral cortex, and for formation of inhibitory synapses in vivo. Our results shed light on how KIF2A deregulation triggers functional alterations in neuronal circuitries and contributes to epilepsy.

Developmental Inhibitory Changes in the Primary Somatosensory Cortex of the Stargazer Mouse Model of Absence Epilepsy

Childhood absence epilepsy seizures arise in the cortico-thalamocortical network due to multiple cellular and molecular mechanisms, which are still under investigation. Understanding the precise mechanisms is imperative given that treatment fails in ~30% of patients while adverse neurological sequelae remain common. Impaired GABAergic neurotransmission is commonly reported in research models investigating these mechanisms. Recently, we reported a region-specific reduction in the whole-tissue and synaptic GABA_A receptor (GABA_AR) α1 subunit and an increase in whole-tissue GAD65 in the primary somatosensory cortex (SoCx) of the adult epileptic stargazer mouse compared with its non-epileptic (NE) littermate. The current study investigated whether these changes occurred prior to the onset of seizures on postnatal days (PN) 17-18, suggesting a causative role. Synaptic and cytosolic fractions were biochemically isolated from primary SoCx lysates followed by semiquantitative Western blot analyses for GABA_AR α1 and GAD65. We found no significant changes in synaptic GABA_AR α1 and cytosolic GAD65 in the primary SoCx of the stargazer mice at the critical developmental stages of PN 7-9, 13-15, and 17-18. This indicates that altered levels of GABA_AR α1 and GAD65 in adult mice do not directly contribute to the initial onset of absence seizures but are a later consequence of seizure activity.

Novel variants in GABAA receptor subunits: A possible association with benzodiazepine resistance in patients with drug-resistant epilepsy

Benzodiazepines (BDZ) such as diazepam and lorazepam are popular as first-line treatment for acute seizures due to their rapid action and high efficacy. However, long-term usage of BDZ leads to benzodiazepine resistance, a phenomenon whose underlying mechanisms are still being investigated. One of the hypothesised mechanisms contributing to BDZ resistance is the presence of mutations in benzodiazepine-sensitive receptors. While a few genetic variants have been reported previously, knowledge of relevant pathogenic variants is still scarce. We used Sanger Sequencing to detect variants in the ligand-binding domain of BDZ-sensitive GABA_A receptor subunits α1-3 and 5 expressed in resected brain tissues of drug-resistant epilepsy (DRE) patients with a history of BDZ resistance and found two previously unreported predicted pathogenic frameshifting variants - NM_000807.4(GABRA2):c.367_368insG and NM_000810.4(GABRA5):c.410del - significantly enriched in these patients. The findings were further explored in resected DRE brain tissues through cellular electrophysiological experiments.

Loss of ARHGAP15 affects the directional control of migrating interneurons in the embryonic cortex and increases susceptibility to epilepsy

GTPases of the Rho family are components of signaling pathways linking extracellular signals to the control of cytoskeleton dynamics. Among these, RAC1 plays key roles during brain development, ranging from neuronal migration to neuritogenesis, synaptogenesis, and plasticity. RAC1 activity is positively and negatively controlled by guanine nucleotide exchange factors (GEFs), guanosine nucleotide dissociation inhibitors (GDIs), and GTPase-activating proteins (GAPs), but the specific role of each regulator in vivo is poorly known. ARHGAP15 is a RAC1-specific GAP expressed during development in a fraction of migrating cortical interneurons (CINs) and in the majority of adult CINs. During development, loss of ARHGAP15 causes altered directionality of the leading process of tangentially migrating CINs, along with altered morphology in vitro. Likewise, time-lapse imaging of embryonic CINs revealed a poorly coordinated directional control during radial migration, possibly due to a hyper-exploratory behavior. In the adult cortex, the observed defects lead to subtle alteration in the distribution of CALB2-, SST-, and VIP-positive interneurons. Adult Arhgap15-knock-out mice also show reduced CINs intrinsic excitability, spontaneous subclinical seizures, and increased susceptibility to the pro-epileptic drug pilocarpine. These results indicate that ARHGAP15 imposes a fine negative regulation on RAC1 that is required for morphological maturation and directional control during CIN migration, with consequences on their laminar distribution and inhibitory function.

Fruits for Seizures? A Systematic Review on the Potential Anti-Convulsant Effects of Fruits and their Phytochemicals

Epilepsy is a devastating neurological disorder. Current anti-convulsant drugs are only effective in about 70% of patients, while the rest remain drug-resistant. Thus, alternative methods have been explored to control seizures in these drug-resistant patients. One such method may be through the utilization of fruit phytochemicals. These phytochemicals have been reported to have beneficial properties such as anti-convulsant, anti-oxidant, and anti-inflammatory activities. However, some fruits may also elicit harmful effects. This review aims to summarize and elucidate the anti- or pro-convulsant effects of fruits used in relation to seizures in hopes of providing a good therapeutic reference to epileptic patients and their carers. Three databases, SCOPUS, ScienceDirect, and PubMed, were utilized for the literature search. Based on the PRISMA guidelines, a total of 40 articles were selected for critical appraisal in this review. Overall, the extracts and phytochemicals of fruits managed to effectively reduce seizure activities in various preclinical seizure models, acting mainly through the activation of the inhibitory neurotransmission and blocking the excitatory neurotransmission. Only star fruit has been identified as a pro-convulsant fruit due to its caramboxin and oxalate compounds. Future studies should focus more on utilizing these fruits as possible treatment strategies for epilepsy.

Distinct Functional Alterations and Therapeutic Options of Two Pathological De Novo Variants of the T292 Residue of GABRA1 Identified in Children with Epileptic Encephalopathy and Neurodevelopmental Disorders

Mutations of GABA_AR have reportedly led to epileptic encephalopathy and neurodevelopmental disorders. We have identified a novel de novo T292S missense variant of GABRA1 from a pediatric patient with grievous global developmental delay but without obvious epileptic activity. This mutation coincidentally occurs at the same residue as that of a previously reported GABRA1 variant T292I identified from a pediatric patient with severe epilepsy. The distinct phenotypes of these two patients prompted us to compare the impacts of the two mutants on the receptor function and to search for suitable therapeutics. In this study, we used biochemical techniques and patch-clamp recordings in HEK293 cells overexpressing either wild-type or mutated rat recombinant GABA_ARs. We found that the α1T292S variant significantly increased GABA-evoked whole-cell currents, shifting the dose-response curve to the left without altering the maximal response. In contrast, the α1T292I variant significantly reduced GABA-evoked currents, shifting the dose-response curve to the right with a severely diminished maximum response. Single-channel recordings further revealed that the α1T292S variant increased, while the α1T292I variant decreased the GABA_AR single-channel open time and open probability. Importantly, we found that the T292S mutation-induced increase in GABA_AR function could be fully normalized by the negative GABA_AR modulator thiocolchicoside, whereas the T292I mutation-induced impairment of GABA_AR function was largely rescued with a combination of the GABA_AR positive modulators diazepam and verapamil. Our study demonstrated that α1T292 is a critical residue for controlling GABA_AR channel gating, and mutations at this residue may produce opposite impacts on the function of the receptors. Thus, the present work highlights the importance of functionally characterizing each individual GABA_AR mutation for ensuring precision medicine.

Neurologic manifestations in children with COVID-19 from a tertiary center in Turkey and literature review

BACKGROUND

Since December 2019, coronavirus disease 2019 (COVID-19) has become a global pandemic caused by highly transmissible severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although respiratory disease and multisystem inflammatory syndrome in children (MIS-C) are main clinical presentations in children, numerous neurological manifestations are being described increasingly. We aimed to investigate new onset neurological symptoms associated with SARS-CoV-2 in pediatric patients in order to establish a possible relationship as well as to understand the underlying pathophysiological mechanisms between SARS-CoV-2 infection and neurological findings.

METHODS

We analyzed retrospectively children who had neurologic manifestations temporally associated with SARS-CoV-2 infection at Hacettepe University İhsan Doğramaci Children's Hospital. We performed a literature search between March 20, 2020 and March 30, 2021. Articles that report children with COVID-19 related neurological manifestations were included.

RESULTS

We have observed 15 consecutive cases with new onset neurological manifestations along with confirmed SARS-CoV-2 infection. Age at hospitalization ranged from three months to 17 years. Ten patients had central nervous system involvement, and most common manifestation was encephalopathy (5/10), which is also one of the most common manifestations of the patients mentioned in the relevant 39 articles we reviewed.

CONCLUSION

Children with COVID-19 can present with neurologic findings such as encephalopathy, seizures, cerebrovascular events as well as abnormal eye movements. Clinical suspicion and awareness are required to show the association between neurologic manifestations and COVID-19.

Parvalbumin Role in Epilepsy and Psychiatric Comorbidities: From Mechanism to Intervention

Parvalbumin is a calcium-binding protein present in inhibitory interneurons that play an essential role in regulating many physiological processes, such as intracellular signaling and synaptic transmission. Changes in parvalbumin expression are deeply related to epilepsy, which is considered one of the most disabling neuropathologies. Epilepsy is a complex multi-factor group of disorders characterized by periods of hypersynchronous activity and hyperexcitability within brain networks. In this scenario, inhibitory neurotransmission dysfunction in modulating excitatory transmission related to the loss of subsets of parvalbumin-expressing inhibitory interneuron may have a prominent role in disrupted excitability. Some studies also reported that parvalbumin-positive interneurons altered function might contribute to psychiatric comorbidities associated with epilepsy, such as depression, anxiety, and psychosis. Understanding the epileptogenic process and comorbidities associated with epilepsy have significantly advanced through preclinical and clinical investigation. In this review, evidence from parvalbumin altered function in epilepsy and associated psychiatric comorbidities were explored with a translational perspective. Some advances in potential therapeutic interventions are highlighted, from current antiepileptic and neuroprotective drugs to cutting edge modulation of parvalbumin subpopulations using optogenetics, designer receptors exclusively activated by designer drugs (DREADD) techniques, transcranial magnetic stimulation, genome engineering, and cell grafting. Creating new perspectives on mechanisms and therapeutic strategies is valuable for understanding the pathophysiology of epilepsy and its psychiatric comorbidities and improving efficiency in clinical intervention.

Interweaving epilepsy and neurodegeneration: Vitamin E as a treatment approach

Epilepsy is the most common neurological disorder, affecting nearly 50 million people worldwide. The condition can be manifested either due to genetic predisposition or acquired from acute insult which leads to alteration of cellular and molecular mechanisms. Evaluating the latest and the current knowledge in regard to the mechanisms underlying molecular and cellular alteration, hyperexcitability is a consequence of an imbalanced state wherein enhance excitatory glutamatergic and reduced inhibitory GABAergic signaling is considered to be accountable for seizures associated damage. However, neurodegeneration contributing to epileptogenesis has become increasingly appreciated. The components at the helm of neurodegenerative alterations during epileptogenesis include GABAergic neuronal and receptor changes, neuroinflammation, alteration in axonal transport, oxidative stress, excitotoxicity, and other cellular as well as functional changes. Targeting neurodegeneration with vitamin E as an antioxidant, anti-inflammatory and neuroprotective may prove to be one of the therapeutic approaches useful in managing epilepsy. In this review, we discuss and converse about the seizure-induced episodes as a link for the development of neurodegenerative and pathological consequences of epilepsy. We also put forth a summary of the potential intervention with vitamin E therapy in the management of epilepsy.

Exercise Improved the Anti-Epileptic Effect of Carbamazepine through GABA Enhancement in Epileptic Rats

Carbamazepine (CBZ) is an anticonvulsant drug that usually is used for the treatment of seizures. The anti-epileptic and the anti-epileptogenic effect of exercise has been reported, as well. This study was aimed to evaluate the synergic effect of combined therapy of exercise and CBZ in epileptic rats, as well as the alternation of the GABA pathway as a possible involved mechanism. The seizure was induced by pentylenetetrazol (PTZ) injection. Animals were divided into sham, seizure, exercise (EX), CBZ (25, 50 and 75), EX + CBZ (25, 50 and 75). Treadmill forced running for 30 min has been considered as the exercise 5 days per week for four weeks. CBZ was injected in doses of 25, 50 and 75 mg/kg, half an hour before seizure induction and 5 h after doing exercise in the animals forced to exercise. Seizure severity reduced and latency increased in the EX + CBZ (25) and EX + CBZ (50) groups compared to the seizure group. The distribution of GAD65 in both hippocampal CA1 and CA3 areas increased in the EX + CBZ (75) group. GABAA receptor α1 was up-regulated in the CA3 area of the EX + CBZ (75) group. The distribution of GAD65 in the cortical area increased in EX, EX + CBZ (50), CBZ (75) and EX + CBZ (75) groups. GABAA receptor α1 was up-regulated in the neocortex of EX + CBZ (50), CBZ (75) and EX + CBZ (75) groups. Our findings suggested that exercise has improved the efficacy of CBZ and reduced the anti-epileptic dose. The enhancement of GABA signaling might be involved in the synergistic effect of exercise and CBZ.

Cymbopogon citratus (DC.) Stapf, citral and geraniol exhibit anticonvulsant and neuroprotective effects in pentylenetetrazole-induced seizures in zebrafish

ETHNOPHARMACOLOGICAL RELEVANCE

Cymbopogon citratus (DC.) Stapf (C. citratus) is consumed as an infusion in folk medicine due to its pharmacological properties and action in the central nervous system. Epilepsy is a neurological disorder that affects millions of people. Since the currently available antiepileptic drugs often cause undesirable side effects, new alternative therapeutic strategies based on medicinal plants have been proposed.

AIM OF THE STUDY

This study aimed to investigate the anticonvulsant and neuroprotective effects of C. citratus essential oil (EO) and hydroalcoholic extract (E1) from its leaves, as well as of its related compounds citral (CIT) and geraniol (GER) against the effects of pentylenetetrazole (PTZ) induced seizures in zebrafish (Danio rerio).

MATERIALS AND METHODS

To evaluate the anticonvulsant properties of the samples, adult animals were pre-treated (by immersion) and subsequently exposed to PTZ solution. The involvement of GABA_A receptors in the antiepileptic effects was investigated by the coadministration of flumazenil (FMZ), a known GABA_A receptor antagonist. Oxidative stress markers malondialdehyde (MDA), glutathione (GSH), catalase (CAT) and nitric oxide (NO) were assessed in zebrafish brain homogenates after PTZ exposure.

RESULTS

All samples increased the latency time for the first seizure, which was reduced when animals were pretreated with FMZ, suggesting the involvement of GABA_A receptors in the observed properties. The association between CIT and GER at the lowest concentration studied showed a synergistic effect on the anticonvulsant activity. Decreases in MDA and NO levels and increases in GSH and CAT levels in the brain of treated animals suggested the neuroprotective effect of the compounds investigated.

CONCLUSIONS

Our results proved that C. citratus EO, E1, CIT and GER have anticonvulsant effects in zebrafish and could be used as a promising adjuvant therapeutic strategy for epilepsy treatment. Furthermore, zebrafish demonstrated to be an alternative animal model of epilepsy to evaluate the anticonvulsant and neuroprotective effects of C. citratus.

Increased levels of α4-containing GABAA receptors in focal cortical dysplasia: A possible cause of benzodiazepine resistance

Benzodiazepines are the first choice of anti-epileptic drugs used to treat seizures. However, it has been seen that their efficacy decreases with time leading to drug insensitivity, plausibly caused by an alteration in the expression of the benzodiazepine biding site on GABA_A receptors. This study was designed to investigate if the differential expression of GABA_A receptor subunits α1/α4/γ2/δ across the postsynaptic sites could contribute to benzodiazepine resistance in patients with focal cortical dysplasia (FCD), the most common cause of drug resistant epilepsy in pediatric population. Differential gene and cellular expression of GABA_A receptor subunits α1, α4, γ2 and δ were evaluated and validated using qPCR and immunohistochemistry. Whole cell patch clamp studies were performed on pyramidal neurons of resected cortical FCD samples to measure the spontaneous GABA_A receptor activity. Upregulation of α4-and γ2-subunits containing GABA_A receptors were observed at both mRNA and protein level. α1-and δ-subunits containing GABA_A receptors did not show any significant changes. Flumazenil treatment did not affect the kinetics of GABAergic events in FCD; however, it significantly reduced the frequency and amplitude of spontaneous GABAergic activity in non-seizure control samples. Our results demonstrate the enhanced expression of α4-containing GABA_A receptors and GABAergic activity in pyramidal neurons which in turn may contribute to benzodiazepine resistance in FCD patients.

Acute symptomatic seizures and COVID-19: Hospital-based study

Background and purpose

Post COVID-19 seizures are relatively rare. The aim of the present study was to estimate the frequency of acute symptomatic seizures among patients with COVID-19 and to discuss possible pathophysiological mechanisms.

Material and methods

Out of 439 cases with COVID-19 that were admitted to Assiut and Aswan University hospitals during the period from 1 June to 10 August 2020, 19 patients (4.3 %) presented with acute symptomatic seizures. Each patient underwent computed tomography (CT) or magnetic resonance imaging (MRI) of the brain and conventional electroencephalography (EEG). Laboratory investigations included: blood gases, complete blood picture, serum D-Dimer, Ferritin, C-reactive protein, renal and liver functions, and coagulation profile.

Results

Of the 19 patients, 3 had new onset seizures without underlying pathology (0.68 % out of the total 439 patients); 2 others (0.46 %) had previously diagnosed controlled epilepsy with breakthrough seizures. The majority of cases (14 patients, 3.19 %) had primary pathology that could explain the occurrence of seizures: 5 suffered a post COVID-19 stroke (3 ischemic and 2 hemorrhagic stroke); 6 patients had COVID-related encephalitis; 2 patients were old ischemic stroke patients; 1 patient had a brain tumor and developed seizures post COVID-19.

Conclusion

acute symptomatic seizure is not a rare complication of post COVID-19 infection. Both new onset seizures and seizures secondary to primary brain insult (post COVID encephalitis or recent stroke) were observed.

Gastrodin alleviates seizure severity and neuronal excitotoxicities in the rat lithium-pilocarpine model of temporal lobe epilepsy via enhancing GABAergic transmission

ETHNOPHARMACOLOGICAL RELEVANCE

Temporal lobe epilepsy remains one of the most drug-resistant focal epilepsy, leading to enormous healthcare burden. Among traditional herb medicine, some ingredients have the potential to treat seizure and alleviate the neuronal excitoxicity. The dried rhizome of Gastrodia elata Blume has been used to treat convulsive disorder, dizziness, dementia and migraine in eastern Asia.

AIM OF THE STUDY

To determine whether gastrodin, an active ingredient of Gastrodia elata Blume, can reduce lithium-pilocarpine induced seizure severity and neuronal excitotoxicity and explore the underlying mechanism.

MATERIALS AND METHODS

We divided the Sprague-Dawley rats into an experimental group (gastrodin group) and a control group (Dimethyl sulfoxide, vehicle group) and performed the behavioral analysis and electroencephalography to determine the effect of gastrodin on the seizure severity induced by lithium-pilocarpine injection. Nissl-stained histopathology elucidated the degree of rat hippocampal neuronal damage as markers of acute and subacute neuronal excitotoxicity. Besides, the Western blotting of dissected hippocampus was carried out to demonstrate the protein expression involving GABAergic transmission and metabolic pathway.

RESULTS

Gastrodin reduced the acute seizure severity in lithium-pilocarpine-induced seizure model. In electroencephalography recording, gastrodin exerted inhibitory action on epileptiform discharge. Compared with control group, gastrodin exhibited neuroprotective effect against seizure related hippocampal neuronal damage at acute and subacute stages. The Western blotting showed that gastrodin reversed the degradation of GABAA receptor after pilocarpine-induced seizures.

CONCLUSIONS

In the experimental seizure model, gastrodin showed anti-seizure and neuroprotective abilities. Enhancing the expression of GABAA receptor plays an important role in its antiepileptic mechanism. The results offer a new insight of developing new antiepileptic drugs from traditional Chinese medicine.

Experimental Therapeutic Strategies in Epilepsies Using Anti-Seizure Medications

Epilepsies are among the most common neurological problems. The disease burden in patients with epilepsy is significantly high, and epilepsy has a huge negative impact on patients' quality of life with epilepsy and their families. Anti-seizure medications are the mainstay treatment in patients with epilepsy, and around 70% of patients will ultimately control with a combination of at least two appropriately selected anti-seizure medications. However, in one-third of patients, seizures are resistant to drugs, and other measures will be needed. The primary goal in using experimental therapeutic medication strategies in patients with epilepsy is to prevent recurrent seizures and reduce the rate of traumatic events that may occur during seizures. So far, various treatments using medications have been offered for patients with epilepsies, which have been classified according to the type of epilepsy, the effectiveness of the medications, and the adverse effects. Medications such as Levetiracetam, valproic acid, and lamotrigine are at the forefront of these patients' treatment. Epilepsy surgery, neuro-stimulation, and the ketogenic diet are the main measures in patients with medication-resistant epilepsies. In this paper, we will review the therapeutic approach using anti-seizure medications in patients with epilepsy. However, it should be noted that some of these patients still do not respond to existing treatments; therefore, the limited ability of current therapies has fueled research efforts for the development of novel treatment strategies. Thus, it seems that in addition to surgical measures, we should look for more specific agents that have less adverse events and have a greater effect in stopping seizures.

Direct Structural Insights into GABAA Receptor Pharmacology

GABA_A receptors are pentameric ligand-gated ion channels that mediate most fast neuronal inhibition in the brain. In addition to their important physiological roles, they are noteworthy in their rich pharmacology; prominent drugs used for anxiety, insomnia, and general anesthesia act through positive modulation of GABA_A receptors. Direct structural information for how these drugs work was absent until recently. Efforts in structural biology over the past few years have revealed how important drug classes and natural products interact with the GABA_A receptor, providing a foundation for studies in dynamics and structure-guided drug design. Here, we review recent developments in GABA_A receptor structural pharmacology, focusing on subunit assemblies of the receptor found at synapses.

Evaluation of extraction methods for pharmacologically active compounds from anticonvulsant traditional Chinese medicines: Gou Teng, Tian Ma, Jiang Can using DART-TOF-MS

Chinese herbal medicines (CHMs) are classified as dietary supplements. Interactions with western medications, the presence of contaminants or adulterants, or a mis-labeled or mis-used CHM may lead to toxicological emergencies that can be undetected in death investigations. Laboratories must be able to efficiently analyze cases in which CHMs are suspected. Five extractions were evaluated for their ability to extract pharmacologically active compounds from herbal matrices: water, ethanol, microwave-assisted (MAE), ethanol : chloroform, and acid-wash. Anticonvulsive and other pharmacologically active compounds in Gou Teng, Tian Ma, and Jiang Can purchased from Beijing, China and New York were compared in the powder and the extracts using Direct Analysis in Real Time-Mass Spectrometry (DART-MS). Approximately 0.25 g of macerated herb was used per extraction. The water and ethanol extractions were simple liquid extractions. For the MAE, powdered herb was soaked in 65% ethanol, microwaved, and concentrated. The ethanol : chloroform extraction involved soaking in 1 : 1 ethanol : chloroform, sonication, and concentration. In the acid-wash extraction, powdered herb was soaked in acetic acid, followed by addition of sodium hydroxide, hexane extraction, and reconstitution in ethyl acetate. The powdered herbs and extracts were analyzed using a Jeol JMS T100LC AccuTOF DART-MS in positive and negative mode. Of the evaluated methods, no single extraction worked for all active compounds from the three CHMs. The MAE extract contained the most pharmacologically active compounds, while the acid-wash contained the least for the three products. Gou Teng purchased from different sources did exhibit a difference in pharmacologically active compounds, potentially from different species.

Cannabinoids: A New Perspective on Epileptogenesis and Seizure Treatment in Early Life in Basic and Clinical Studies

Neural hyperexcitability in the event of damage during early life, such as hyperthermia, hypoxia, traumatic brain injury, status epilepticus, or a pre-existing neuroinflammatory condition, can promote the process of epileptogenesis, which is defined as the sequence of events that converts a normal circuit into a hyperexcitable circuit and represents the time that occurs between the damaging event and the development of spontaneous seizure activity or the establishment of epilepsy. Epilepsy is the most common neurological disease in the world, characterized by the presence of seizures recurring without apparent provocation. Cannabidiol (CBD), a phytocannabinoid derived from the subspecies Cannabis sativa (CS), is the most studied active ingredient and is currently studied as a therapeutic strategy: it is an anticonvulsant mainly used in children with catastrophic epileptic syndromes and has also been reported to have anti-inflammatory and antioxidant effects, supporting it as a therapeutic strategy with neuroprotective potential. However, the mechanisms by which CBD exerts these effects are not entirely known, and the few studies on acute and chronic models in immature animals have provided contradictory results. Thus, it is difficult to evaluate the therapeutic profile of CBD, as well as the involvement of the endocannabinoid system in epileptogenesis in the immature brain. Therefore, this review focuses on the collection of scientific data in animal models, as well as information from clinical studies on the effects of cannabinoids on epileptogenesis and their anticonvulsant and adverse effects in early life.

Αlpha 5 subunit-containing GABAA receptors in temporal lobe epilepsy with normal MRI

GABAA receptors containing the α5 subunit mediate tonic inhibition and are widely expressed in the limbic system. In animals, activation of α5-containing receptors impairs hippocampus-dependent memory. Temporal lobe epilepsy is associated with memory impairments related to neuron loss and other changes. The less selective PET ligand [11C]flumazenil has revealed reductions in GABAA receptors. The hypothesis that α5 subunit receptor alterations are present in temporal lobe epilepsy and could contribute to impaired memory is untested. We compared α5 subunit availability between individuals with temporal lobe epilepsy and normal structural MRI ('MRI-negative') and healthy controls, and interrogated the relationship between α5 subunit availability and episodic memory performance, in a cross-sectional study. Twenty-three healthy male controls (median ± interquartile age 49 ± 13 years) and 11 individuals with MRI-negative temporal lobe epilepsy (seven males; 40 ± 8) had a 90-min PET scan after bolus injection of [11C]Ro15-4513, with arterial blood sampling and metabolite correction. All those with epilepsy and six controls completed the Adult Memory and Information Processing Battery on the scanning day. 'Bandpass' exponential spectral analyses were used to calculate volumes of distribution separately for the fast component [V F; dominated by signal from α1 (α2, α3)-containing receptors] and the slow component (V S; dominated by signal from α5-containing receptors). We made voxel-by-voxel comparisons between: the epilepsy and control groups; each individual case versus the controls. We obtained parametric maps of V F and V S measures from a single bolus injection of [11C]Ro15-4513. The epilepsy group had higher V S in anterior medial and lateral aspects of the temporal lobes, the anterior cingulate gyri, the presumed area tempestas (piriform cortex) and the insulae, in addition to increases of ∼24% and ∼26% in the ipsilateral and contralateral hippocampal areas (P < 0.004). This was associated with reduced V F:V S ratios within the same areas (P < 0.009). Comparisons of V S for each individual with epilepsy versus controls did not consistently lateralize the epileptogenic lobe. Memory scores were significantly lower in the epilepsy group than in controls (mean ± standard deviation -0.4 ± 1.0 versus 0.7 ± 0.3; P = 0.02). In individuals with epilepsy, hippocampal V S did not correlate with memory performance on the Adult Memory and Information Processing Battery. They had reduced V F in the hippocampal area, which was significant ipsilaterally (P = 0.03), as expected from [11C]flumazenil studies. We found increased tonic inhibitory neurotransmission in our cohort of MRI-negative temporal lobe epilepsy who also had co-morbid memory impairments. Our findings are consistent with a subunit shift from α1/2/3 to α5 in MRI-negative temporal lobe epilepsy.

Effects of Mulberry on The Central Nervous System: A Literature Review

Background

Mulberry, including several species belonging to genus Morus, has been widely used as a traditional medicine for a long time. Extracts and active components of mulberry have many positive neurological and biological effects and can become potential candidates in the search for new drugs for neurological disorders.

Objectives

We aimed to systematically review the medical literature for evidence of mulberry effects on the central nervous system.

Methods

We conducted a systematic search in nine databases. We included all in vivo studies investigating the effect of mulberry on the central nervous system with no restrictions.

Results

We finally included 47 articles for quality synthesis. Our findings showed that mulberry and its components possessed an antioxidant effect, showed a reduction in the cerebral infarct volume after stroke. They also improved the cognitive function, learning process, and reduced memory impairment in many animal models. M. alba and its extracts ameliorated Parkinson's disease-like behaviors, limited the complications of diabetes mellitus on the central nervous system, possessed anti-convulsant, anti-depressive, and anxiolytic effects.

Conclusion

Mulberry species proved beneficial to many neurological functions in animal models. The active ingredients of each species, especially M. alba, should be deeper studied for screening potential candidates for future treatments.

How does the COVID-19 cause seizure and epilepsy in patients? The potential mechanisms

The new coronavirus has spread throughout the world in a very short time and now has become a pandemic. Most infected people have symptoms such as dry cough, dyspnea, tiredness, and fever. However, the Covid-19 infection disrupts various organs, including the liver, kidney, and nervous system. Common neurological symptoms of the Covid-19 infection include delirium, confusion, headache, and loss of sense of smell and taste. In rare cases it can cause stroke and epilepsy. The virus enters the nervous system either directly through nerve pathways or indirectly through the ACE2 receptor. The neurological symptoms of a Covid-19 infection in the brain are mainly due to either the entry of pro-inflammatory cytokines into the nervous system or the production of these cytokines by microglia and astrocytes. Pro-inflammatory cytokines can cause blood-brain barrier disruption, increase in glutamate and aspartate and reduce GABA levels, impairs the function of ion channels, and finally, high levels of cytokines can cause epilepsy. Understanding the potential mechanisms is necessary to gain better insight into COVID-19 induced seizure pathogenesis and to design the correct treatment strategies to achieve appropriate treatment for seizure and epilepsy.

Connexin Hemichannel Mimetic Peptide Attenuates Cortical Interneuron Loss and Perineuronal Net Disruption Following Cerebral Ischemia in Near-Term Fetal Sheep

Perinatal hypoxia-ischemia is associated with disruption of cortical gamma-aminobutyric acid (GABA)ergic interneurons and their surrounding perineuronal nets, which may contribute to persisting neurological deficits. Blockade of connexin43 hemichannels using a mimetic peptide can alleviate seizures and injury after hypoxia-ischemia. In this study, we tested the hypothesis that connexin43 hemichannel blockade improves the integrity of cortical interneurons and perineuronal nets. Term-equivalent fetal sheep received 30 min of bilateral carotid artery occlusion, recovery for 90 min, followed by a 25-h intracerebroventricular infusion of vehicle or a mimetic peptide that blocks connexin hemichannels or by a sham ischemia + vehicle infusion. Brain tissues were stained for interneuronal markers or perineuronal nets. Cerebral ischemia was associated with loss of cortical interneurons and perineuronal nets. The mimetic peptide infusion reduced loss of glutamic acid decarboxylase-, calretinin-, and parvalbumin-expressing interneurons and perineuronal nets. The interneuron and perineuronal net densities were negatively correlated with total seizure burden after ischemia. These data suggest that the opening of connexin43 hemichannels after perinatal hypoxia-ischemia causes loss of cortical interneurons and perineuronal nets and that this exacerbates seizures. Connexin43 hemichannel blockade may be an effective strategy to attenuate seizures and may improve long-term neurological outcomes after perinatal hypoxia-ischemia.

Role of Lacosamide in Preventing Pentylenetetrazole Kindling-Induced Alterations in the Expression of the Gamma-2 Subunit of the GABAA Receptor in Rats

Background:

Epilepsy remains challenging to treat still no etiologic treatment has been identified, however, some antiepileptic drugs (AEDs) are able to modify the pathogenesis of the disease. Lacosamide (LCM) has been shown to possess complex anticonvulsant and neuroprotective actions, being an enhancer of the slow inactivation of voltage-gated sodium channels, and it has the potential to prevent epileptogenesis. Recent evidence has shown that LCM indirectly improves the function of GABAA receptors. Receptors at most GABAergic synapses involve the gamma-2 subunit, which contributes to both phasic and tonic inhibition, and its presence assures benzodiazepine sensitivity. Moreover, mutant gamma-2 subunits were associated with generalized epilepsy syndromes. In animal models, the expression of the gamma-2 subunit of the gamma-aminobutyric acid A receptor (GABAAg2) was shown to be increased in pentylenetetrazole (PTZ)-induced chemical kindling in Wistar rats.

Objective:

This study hypothesized that LCM might affect the kindling process by influencing the expression of GABAA receptors in the hippocampus.

Methods:

The gene and protein expression levels of the GABAAg2 were studied using RT-qPCR and immunofluorescent staining.

Results:

It was found that LCM treatment (10 mg/kg i.p. daily for 57 days) reduced the maximal intensity of the PTZ-induced seizures but did not prevent kindling. On the other hand, LCM treatment reverted the increase of mRNA expression of GABAAg2 in the hippocampus and prevented the decrease of GABAAg2 protein in the hippocampal CA1 region.

Conclusion:

LCM could exhibit modulatory effects on the GABAergic system of the hippocampus that may be independent of the anticonvulsant action.

Venom-derived modulators of epilepsy-related ion channels

Epilepsy is characterised by spontaneous recurrent seizures that are caused by an imbalance between neuronal excitability and inhibition. Since ion channels play fundamental roles in the generation and propagation of action potentials as well as neurotransmitter release at a subset of excitatory and inhibitory synapses, their dysfunction has been linked to a wide variety of epilepsies. Indeed, these unique proteins are the major biological targets for antiepileptic drugs. Selective targeting of a specific ion channel subtype remains challenging for small molecules, due to the high level of homology among members of the same channel family. As a consequence, there is a growing trend to target ion channels with biologics. Venoms are the best known natural source of ion channel modulators, and venom peptides are increasingly recognised as potential therapeutics due to their high selectivity and potency gained through millions of years of evolutionary selection pressure. Here we describe the major ion channel families involved in the pathogenesis of various types of epilepsy, including voltage-gated Na⁺, K⁺, Ca²⁺ channels, Cys-loop receptors, ionotropic glutamate receptors and P2X receptors, and currently available venom-derived peptides that target these channel proteins. Although only a small number of venom peptides have successfully progressed to the clinic, there is reason to be optimistic about their development as antiepileptic drugs, notwithstanding the challenges associated with development of any class of peptide drug.

Drug Development for Rare Paediatric Epilepsies: Current State and Future Directions

Rare diseases provide a challenge in the evaluation of new therapies. However, orphan drug development is of increasing interest because of the legislation enabling facilitated support by regulatory agencies through scientific advice, and the protection of the molecules with orphan designation. In the landscape of the rare epilepsies, very few syndromes, namely Dravet syndrome, Lennox-Gastaut syndrome and West syndrome, have been subject to orphan drug development. Despite orphan designations for rare epilepsies having dramatically increased in the past 10 years, the number of approved drugs remains limited and restricted to a handful of epilepsy syndromes. In this paper, we describe the current state of orphan drug development for rare epilepsies. We identified a large number of compounds currently under investigation, but mostly in the same rare epilepsy syndromes as in the past. A rationale for further development in rare epilepsies could be based on the match between the drug mechanisms of action and the knowledge of the causative gene mutation or by evidence from animal models. In case of the absence of strong pathophysiological hypotheses, exploratory/basket clinical studies could be helpful to identify a subpopulation that may benefit from the new drug. We provide some suggestions for future improvements in orphan drug development such as promoting paediatric drug investigations, better evaluation of the incidence and the prevalence, together with the natural history data, and the development of new primary outcomes.

Electroencephalographic analysis in soman-exposed 21-day-old rats and the effects of midazolam or LY293558 with caramiphen

Acute nerve agent exposure induces status epilepticus (SE), which can cause brain damage or death. Research aiming at developing effective therapies for controlling nerve agent-induced SE is commonly performed in adult rats. The characteristics of nerve agent-induced SE in young rats are less clear; relevant knowledge is necessary for developing effective pediatric therapies. Here, we have used electroencephalographic (EEG) recordings and analysis to study seizures in postnatal day 21 rats exposed to 1.2 × LD₅₀ of soman, and compared the antiseizure efficacy of midazolam (MDZ)-currently considered by the Food and Drug Administration to replace diazepam for treating SE in victims of nerve agent exposure-with that of LY293558, an AMPA/GluK1 receptor antagonist, administered in combination with caramiphen, an antimuscarinic with N-methyl-d-aspartate receptor antagonistic properties. Prolonged SE developed in 80% of the rats and was reflected in behavioral seizures/convulsions. Both MDZ and LY293558 + caramiphen stopped the SE induced by soman, but there was a significant recurrence of seizures within 24 h postexposure only in the MDZ-treated group, as revealed in the raw EEG data and their representation in the frequency domain using a fast Fourier transform and in spectral analysis over 24 hours. In contrast to the high efficacy of LY293558 + caramiphen, MDZ is not an effective treatment for SE induced by soman in young animals.

Human Hyperekplexic Mutations in Glycine Receptors Disinhibit the Brainstem by Hijacking GABAA Receptors

Hyperekplexia disease is usually caused by naturally occurring point mutations in glycine receptors (GlyRs). However, the γ-aminobutyric acid type A receptor (GABA_AR) seems to be also involved regarding the therapeutic basis for hyperekplexia using benzodiazepines, which target GABA_ARs but not GlyRs. Here, we show that the function of GABA_ARs was significantly impaired in the hypoglossal nucleus of hyperekplexic transgenic mice. Such impairment appeared to be mediated by interaction between GABA_AR and mutant GlyR. The GABA_AR dysfunction was caused only by mutant GlyR consisting of homomeric α₁ subunits, which locate primarily at pre- and extra-synaptic sites. In addition, the rescue effects of diazepam were attenuated by Xli-093, which specifically blocked diazepam-induced potentiation on α₅-containing GABA_AR, a major form of pre- and extra-synaptic GABA_AR in the brainstem. Thus, our results suggest that the pre- and extra-synaptic GABA_ARs could be a potential therapeutic target for hyperekplexia disease caused by GlyR mutations.

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Hyperekplexic mutant GlyRs interact with GABA_ARs and disrupt the GABA_AR function

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Pre- and extra-synaptic GABA_ARs are deficient in the hyperekplexia disease

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α₅-Containing GABA_AR is a potential therapeutic target for the hyperekplexia disease

Expression and Functional Properties of NMDA and GABAA Receptors during Differentiation of Human Induced Pluripotent Stem Cells into Ventral Mesencephalic Neurons

Ionotropic glutamate and GABA receptors regulate the differentiation and determine the functional properties of mature neurons. Both insufficient and excessive activity of these neurotransmission systems are associated with various nervous system diseases. Our knowledge regarding the expression profiles of these receptors and the mechanisms of their regulation during the differentiation of specialized human neuron subtypes is limited. Here the expression profiles of the NMDA and GABA_A receptor subunits were explored during in vitro differentiation of human induced pluripotent stem cells (iPSCs) into ventral mesencephalic neurons. The correlation between the neuronal maturation and the expression dynamics of these genes was investigated, and the functional activity of these receptors was assessed by calcium imaging. The role of NMDA and GABA_A receptors in neurite outgrowth and the development of spontaneous activity was analyzed using the viral transduction of neural progenitors with the reporter genes TagGFP and TagRFP. The data indicate that agonists of the investigated receptors can be employed for optimization of existing protocols for neural differentiation of iPSCs, in particular for acceleration of neuronal maturation.