Pathophysiological Characteristics Associated With Epileptogenesis in Human Hippocampal Sclerosis

Potassium and calcium channels in different nerve cells act as therapeutic targets in neurological disorders

The central nervous system, information integration center of the body, is mainly composed of neurons and glial cells. The neuron is one of the most basic and important structural and functional units of the central nervous system, with sensory stimulation and excitation conduction functions. Astrocytes and microglia belong to the glial cell family, which is the main source of cytokines and represents the main defense system of the central nervous system. Nerve cells undergo neurotransmission or gliotransmission, which regulates neuronal activity via the ion channels, receptors, or transporters expressed on nerve cell membranes. Ion channels, composed of large transmembrane proteins, play crucial roles in maintaining nerve cell homeostasis. These channels are also important for control of the membrane potential and in the secretion of neurotransmitters. A variety of cellular functions and life activities, including functional regulation of the central nervous system, the generation and conduction of nerve excitation, the occurrence of receptor potential, heart pulsation, smooth muscle peristalsis, skeletal muscle contraction, and hormone secretion, are closely related to ion channels associated with passive transmembrane transport. Two types of ion channels in the central nervous system, potassium channels and calcium channels, are closely related to various neurological disorders, including Alzheimer's disease, Parkinson's disease, and epilepsy. Accordingly, various drugs that can affect these ion channels have been explored deeply to provide new directions for the treatment of these neurological disorders. In this review, we focus on the functions of potassium and calcium ion channels in different nerve cells and their involvement in neurological disorders such as Parkinson's disease, Alzheimer's disease, depression, epilepsy, autism, and rare disorders. We also describe several clinical drugs that target potassium or calcium channels in nerve cells and could be used to treat these disorders. We concluded that there are few clinical drugs that can improve the pathology these diseases by acting on potassium or calcium ions. Although a few novel ion-channel-specific modulators have been discovered, meaningful therapies have largely not yet been realized. The lack of target-specific drugs, their requirement to cross the blood-brain barrier, and their exact underlying mechanisms all need further attention. This review aims to explain the urgent problems that need research progress and provide comprehensive information aiming to arouse the research community's interest in the development of ion channel-targeting drugs and the identification of new therapeutic targets for that can increase the cure rate of nervous system diseases and reduce the occurrence of adverse reactions in other systems.

Radiologic Classification of Hippocampal Sclerosis in Epilepsy

Temporal lobe epilepsy is a common form of epilepsy that is often associated with hippocampal sclerosis (HS). Although HS is commonly considered a binary assessment in radiologic evaluation, it is known that histopathologic changes occur in distinct clusters. Some subtypes of HS only affect certain subfields, resulting in minimal changes to the overall volume of the hippocampus. This is likely a major reason why whole hippocampal volumetrics have underperformed versus expert readers in the diagnosis of HS. With recent advancements in MRI technology, it is now possible to characterize the substructure of the hippocampus more accurately. However, this is not consistently addressed in radiographic evaluations. The histologic subtype of HS is critical for prognosis and treatment decision-making, necessitating improved radiologic classification of HS. The International League Against Epilepsy (ILAE) has issued a consensus classification scheme for subtyping HS histopathologic changes. This review aims to explore how the ILAE subtypes of HS correlate with radiographic findings, introduce a grading system that integrates radiologic and pathologic reporting in HS, and outline an approach to detecting HS subtypes by using MRI. This framework will not only benefit current clinical evaluations, but also enhance future studies involving high-resolution MRI in temporal lobe epilepsy.

Pharmacological evaluation of E2730, a novel selective uncompetitive GAT1 inhibitor, on epileptiform activities in resected brain tissues from human focal cortical dysplasia ex vivo

Focal cortical dysplasia (FCD) is an important etiology of focal epilepsy in children and adults. However, only a few preclinical models sufficiently reproduce the characteristic histopathologic features of FCD. To improve the success rate of clinical trials for antiseizure medications (ASMs) in patients with FCD, more human-relevant preclinical models are needed, and epileptic foci resected from patients are a powerful tool for this purpose. Here, we conducted ex vivo studies using epileptic foci resected from patients with FCD type II to evaluate the pharmacologic effects of the ASM candidate E2730, a selective uncompetitive inhibitor of γ-aminobutyric acid transporter 1. We used the same ex vivo assay system to assess carbamazepine (CBZ), an ASM often prescribed for focal epilepsy, as a reference. At the higher dose tested (200 µM), both E2730 and CBZ suppressed spontaneous epileptiform activities almost completely. At the lower dose (100 µM), CBZ reduced the area of brain tissue showing epileptiform activity, whereas E2730 significantly decreased the number of epileptiforms. These findings suggest that E2730-both as a single agent and in combination with CBZ-merits evaluation in clinical trials involving patients with FCD.

Statistical learning in epilepsy: Behavioral and anatomical mechanisms in the human brain

OBJECTIVE

Statistical learning, the fundamental cognitive ability of humans to extract regularities across experiences over time, engages the medial temporal lobe (MTL) in the healthy brain. This leads to the hypothesis that statistical learning (SL) may be impaired in patients with epilepsy (PWE) involving the temporal lobe, and that this impairment could contribute to their varied memory deficits. In turn, studies done in collaboration with PWE, that evaluate the necessity of MTL circuitry through disease and causal perturbations, provide an opportunity to advance basic understanding of SL.

METHODS

We implemented behavioral testing, volumetric analysis of the MTL substructures, and direct electrical brain stimulation to examine SL across a cohort of 61 PWE and 28 healthy controls.

RESULTS

We found that behavioral performance in an SL task was negatively associated with seizure frequency irrespective of seizure origin. The volume of hippocampal subfields CA1 and CA2/3 correlated with SL performance, suggesting a more specific role of the hippocampus. Transient direct electrical stimulation of the hippocampus disrupted SL. Furthermore, the relationship between SL and seizure frequency was selective, as behavioral performance in an episodic memory task was not impacted by seizure frequency.

SIGNIFICANCE

Overall, these results suggest that SL may be hippocampally dependent and that the SL task could serve as a clinically useful behavioral assay of seizure frequency that may complement existing approaches such as seizure diaries. Simple and short SL tasks may thus provide patient-centered endpoints for evaluating the efficacy of novel treatments in epilepsy.

The NLRP3 Inflammasome in Neurodegenerative Disorders: Insights from Epileptic Models

Neuroinflammation represents a dynamic process of defense and protection against the harmful action of infectious agents or other detrimental stimuli in the central nervous system (CNS). However, the uncontrolled regulation of this physiological process is strongly associated with serious dysfunctional neuronal issues linked to the progression of CNS disorders. Moreover, it has been widely demonstrated that neuroinflammation is linked to epilepsy, one of the most prevalent and serious brain disorders worldwide. Indeed, NLRP3, one of the most well-studied inflammasomes, is involved in the generation of epileptic seizures, events that characterize this pathological condition. In this context, several pieces of evidence have shown that the NLRP3 inflammasome plays a central role in the pathophysiology of mesial temporal lobe epilepsy (mTLE). Based on an extensive review of the literature on the role of NLRP3-dependent inflammation in epilepsy, in this review we discuss our current understanding of the connection between NLRP3 inflammasome activation and progressive neurodegeneration in epilepsy. The goal of the review is to cover as many of the various known epilepsy models as possible, providing a broad overview of the current literature. Lastly, we also propose some of the present therapeutic strategies targeting NLRP3, aiming to provide potential insights for future studies.

Astrocytes as a target for therapeutic strategies in epilepsy: current insights

Astrocytes are specialized non-neuronal glial cells of the central nervous system, contributing to neuronal excitability and synaptic transmission (gliotransmission). Astrocytes play a key roles in epileptogenesis and seizure generation. Epilepsy, as a chronic disorder characterized by neuronal hyperexcitation and hypersynchronization, is accompanied by substantial disturbances of glial cells and impairment of astrocytic functions and neuronal signaling. Anti-seizure drugs that provide symptomatic control of seizures primarily target neural activity. In epileptic patients with inadequate control of seizures with available anti-seizure drugs, novel therapeutic candidates are needed. These candidates should treat epilepsy with anti-epileptogenic and disease-modifying effects. Evidence from human and animal studies shows that astrocytes have value for developing new anti-seizure and anti-epileptogenic drugs. In this review, we present the key functions of astrocytes contributing to neuronal hyperexcitability and synaptic activity following an etiology-based approach. We analyze the role of astrocytes in both development (epileptogenesis) and generation of seizures (ictogenesis). Several promising new strategies that attempted to modify astroglial functions for treating epilepsy are being developed: (1) selective targeting of glia-related molecular mechanisms of glutamate transport; (2) modulation of tonic GABA release from astrocytes; (3) gliotransmission; (4) targeting the astrocytic Kir4.1-BDNF system; (5) astrocytic Na+/K+/ATPase activity; (6) targeting DNA hypo- or hypermethylation of candidate genes in astrocytes; (7) targeting astrocytic gap junction regulators; (8) targeting astrocytic adenosine kinase (the major adenosine-metabolizing enzyme); and (9) targeting microglia-astrocyte communication and inflammatory pathways. Novel disease-modifying therapeutic strategies have now been developed, such as astroglia-targeted gene therapy with a broad spectrum of genetic constructs to target astroglial cells.

Brain but not serum BDNF levels are associated with structural alterations in the hippocampal regions in patients with drug-resistant mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy is the most common type of focal epilepsy, imposing a significant burden on the health care system worldwide. Approximately one-third of patients with this disease who do not adequately respond to pharmacotherapy are considered drug-resistant subjects. Despite having some clues of how such epileptic activity and resistance to therapy emerge, coming mainly from preclinical models, we still witness a scarcity of human data. To narrow this gap, in this study, we aimed to estimate the relationship between hippocampal and serum levels of brain-derived neurotrophic factor (BDNF), one of the main and most widely studied neurotrophins, and hippocampal subfield volumes in patients with drug-resistant mesial temporal epilepsy undergoing neurosurgical treatment. We found that hippocampal (but not serum) BDNF levels were negatively correlated with the contralateral volumes of the CA1 and CA4 subfields, presubiculum, subiculum, dentate gyrus, and molecular layer of the hippocampus. Taken together, these findings are generally in accordance with existing data, arguing for a proepileptic nature of BDNF effects in the hippocampus and related brain structures.

Mass Spectrometry as a Quantitative Proteomic Analysis Tool for the Search for Temporal Lobe Epilepsy Biomarkers: A Systematic Review

Temporal lobe epilepsy (TLE) is the most common form of epilepsy in adults. Tissue reorganization at the site of the epileptogenic focus is accompanied by changes in the expression patterns of protein molecules. The study of mRNA and its corresponding proteins is crucial for understanding the pathogenesis of the disease. Protein expression profiles do not always directly correlate with the levels of their transcripts; therefore, it is protein profiling that is no less important for understanding the molecular mechanisms and biological processes of TLE. The study and annotation of proteins that are statistically significantly different in patients with TLE is an approach to search for biomarkers of this disease, various stages of its development, as well as a method for searching for specific targets for the development of a further therapeutic strategy. When writing a systematic review, the following aggregators of scientific journals were used: MDPI, PubMed, ScienceDirect, Springer, and Web of Science. Scientific articles were searched using the following keywords: "proteomic", "mass-spectrometry", "protein expression", "temporal lobe epilepsy", and "biomarkers". Publications from 2003 to the present have been analyzed. Studies of brain tissues, experimental models of epilepsy, as well as biological fluids, were analyzed. For each of the groups, aberrantly expressed proteins found in various studies were isolated. Most of the studies omitted important characteristics of the studied patients, such as: duration of illness, type and response to therapy, gender, etc. Proteins that overlap across different tissue types and different studies have been highlighted: DPYSL, SYT1, STMN1, APOE, NME1, and others. The most common biological processes for them were the positive regulation of neurofibrillary tangle assembly, the regulation of amyloid fibril formation, lipoprotein catabolic process, the positive regulation of vesicle fusion, the positive regulation of oxidative stress-induced intrinsic apoptotic signaling pathway, removal of superoxide radicals, axon extension, and the regulation of actin filament depolymerization. MS-based proteomic profiling for a relevant study must accept a number of limitations, the most important of which is the need to compare different types of neurological and, in particular, epileptic disorders. Such a criterion could increase the specificity of the search work and, in the future, lead to the discovery of biomarkers for a particular disease.

Astrocytic pathology in Alpers' syndrome

Refractory epilepsy is the main neurological manifestation of Alpers' syndrome, a severe childhood-onset mitochondrial disease caused by bi-allelic pathogenic variants in the mitochondrial DNA (mtDNA) polymerase gamma gene (POLG). The pathophysiological mechanisms underpinning neuronal hyperexcitabilty leading to seizures in Alpers' syndrome remain unknown. However, pathological changes to reactive astrocytes are hypothesised to exacerbate neural dysfunction and seizure-associated cortical activity in POLG-related disease. Therefore, we sought to phenotypically characterise astrocytic pathology in Alpers' syndrome. We performed a detailed quantitative investigation of reactive astrocytes in post-mortem neocortical tissues from thirteen patients with Alpers' syndrome, eight neurologically normal controls and five sudden unexpected death in epilepsy (SUDEP) patients, to control for generalised epilepsy-associated astrocytic pathology. Immunohistochemistry to identify glial fibrillary acidic protein (GFAP)-reactive astrocytes revealed striking reactive astrogliosis localised to the primary visual cortex of Alpers' syndrome tissues, characterised by abnormal-appearing hypertrophic astrocytes. Phenotypic characterisation of individual GFAP-reactive astrocytes demonstrated decreased abundance of mitochondrial oxidative phosphorylation (OXPHOS) proteins and altered expression of key astrocytic proteins including Kir4.1 (subunit of the inwardly rectifying K⁺ ion channel), AQP4 (astrocytic water channel) and glutamine synthetase (enzyme that metabolises glutamate). These phenotypic astrocytic changes were typically different from the pathology observed in SUDEP tissues, suggesting alternative mechanisms of astrocytic dysfunction between these epilepsies. Crucially, our findings provide further evidence of occipital lobe involvement in Alpers' syndrome and support the involvement of reactive astrocytes in the pathogenesis of POLG-related disease.

Statistical learning in epilepsy: Behavioral, anatomical, and causal mechanisms in the human brain

Statistical learning, the fundamental cognitive ability of humans to extract regularities across experiences over time, engages the medial temporal lobe in the healthy brain. This leads to the hypothesis that statistical learning may be impaired in epilepsy patients, and that this impairment could contribute to their varied memory deficits. In turn, epilepsy patients provide a platform to advance basic understanding of statistical learning by helping to evaluate the necessity of medial temporal lobe circuitry through disease and causal perturbations. We implemented behavioral testing, volumetric analysis of the medial temporal lobe substructures, and direct electrical brain stimulation to examine statistical learning across a cohort of 61 epilepsy patients and 28 healthy controls. Behavioral performance in a statistical learning task was negatively associated with seizure frequency, irrespective of where seizures originated in the brain. The volume of hippocampal subfields CA1 and CA2/3 correlated with statistical learning performance, suggesting a more specific role of the hippocampus. Indeed, transient direct electrical stimulation of the hippocampus disrupted statistical learning. Furthermore, the relationship between statistical learning and seizure frequency was selective: behavioral performance in an episodic memory task was impacted by structural lesions in the medial temporal lobe and by antiseizure medications, but not by seizure frequency. Overall, these results suggest that statistical learning may be hippocampally dependent and that this task could serve as a clinically useful behavioral assay of seizure frequency distinct from existing neuropsychological tests. Simple and short statistical learning tasks may thus provide patient-centered endpoints for evaluating the efficacy of novel treatments in epilepsy.

Overview Article Astrocytes as Initiators of Epilepsy

Astrocytes play a dual role in the brain. On the one hand, they are active signaling partners of neurons and can for instance control synaptic transmission and its plasticity. On the other hand, they fulfill various homeostatic functions such as clearance of glutamate and K⁺ released from neurons. The latter is for instance important for limiting neuronal excitability. Therefore, an impairment or failure of glutamate and K⁺ clearance will lead to increased neuronal excitability, which could trigger or aggravate brain diseases such as epilepsy, in which neuronal hyperexcitability plays a role. Experimental data indicate that astrocytes could have such a causal role in epilepsy, but the role of astrocytes as initiators of epilepsy and the relevant mechanisms are under debate. In this overview, we will discuss the potential mechanisms with focus on K⁺ clearance, glutamate uptake and homoeostasis and related mechanisms, and the evidence for their causative role in epilepsy.

Cannabinoid regulation of neurons in the dentate gyrus during epileptogenesis: Role of CB1R-associated proteins and downstream pathways

The hippocampal formation plays a central role in the development of temporal lobe epilepsy (TLE), a disease characterized by recurrent, unprovoked epileptic discharges. TLE is a neurologic disorder characterized by acute long-lasting seizures (i.e., abnormal electrical activity in the brain) or seizures that occur in close proximity without recovery, typically after a brain injury or status epilepticus. After status epilepticus, epileptogenic hyperexcitability develops gradually over the following months to years, resulting in the emergence of chronic, recurrent seizures. Acting as a filter or gate, the hippocampal dentate gyrus (DG) normally prevents excessive excitation from propagating through the hippocampus, and is considered a critical region in the progression of epileptogenesis in pathological conditions. Importantly, lipid-derived endogenous cannabinoids (endocannabinoids), which are produced on demand as retrograde messengers, are central regulators of neuronal activity in the DG circuit. In this review, we summarize recent findings concerning the role of the DG in controlling hyperexcitability and propose how DG regulation by cannabinoids (CBs) could provide avenues for therapeutic interventions. We also highlight possible pathways and manipulations that could be relevant for the control of hyperexcitation. The use of CB compounds to treat epilepsies is controversial, as anecdotal evidence is not always validated by clinical trials. Recent publications shed light on the importance of the DG as a region regulating incoming hippocampal excitability during epileptogenesis. We review recent findings concerning the modulation of the hippocampal DG circuitry by CBs and discuss putative underlying pathways. A better understanding of the mechanisms by which CBs exert their action during seizures may be useful to improve therapies.

Perspectives on the basis of seizure-induced respiratory dysfunction

Epilepsy is an umbrella term used to define a wide variety of seizure disorders and sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in epilepsy. Although some SUDEP risk factors have been identified, it remains largely unpredictable, and underlying mechanisms remain poorly understood. Most seizures start in the cortex, but the high mortality rate associated with certain types of epilepsy indicates brainstem involvement. Therefore, to help understand SUDEP we discuss mechanisms by which seizure activity propagates to the brainstem. Specifically, we highlight clinical and pre-clinical evidence suggesting how seizure activation of: (i) descending inhibitory drive or (ii) spreading depolarization might contribute to brainstem dysfunction. Furthermore, since epilepsy is a highly heterogenous disorder, we also considered factors expected to favor or oppose mechanisms of seizure propagation. We also consider whether epilepsy-associated genetic variants directly impact brainstem function. Because respiratory failure is a leading cause of SUDEP, our discussion of brainstem dysfunction focuses on respiratory control.

Visualization of cortical activation in human brain by flavoprotein fluorescence imaging

OBJECTIVE

To develop an innovative brain mapping and neuromonitoring method during neurosurgery, the authors set out to establish intraoperative flavoprotein fluorescence imaging (iFFI) to directly visualize cortical activations in human brain. The significance of iFFI was analyzed by comparison with intraoperative perfusion-dependent imaging (iPDI), which is considered the conventional optical imaging, and by performing animal experiments.

METHODS

Seven patients with intracerebral tumors were examined by iFFI and iPDI following craniotomy, using a single operative microscope equipped with a laser light source for iFFI and xenon lamp for iPDI. Images were captured by the same charge-coupled device camera. Responses to bipolar stimulation at selected points on the cortical surface were analyzed off-line, and relative signal changes were visualized by overlaying pseudocolor intensity maps onto cortical photographs. Signal changes exceeding 3 SDs from baseline were defined as significant. The authors also performed FFI and PDI on 10 mice using similar settings, and then compared signal patterns to intraoperative studies.

RESULTS

Signals acquired by iFFI exhibited biphasic spatiotemporal changes consisting of an early positive signal peak (F1) and a delayed negative signal peak (F2). In contrast, iPDI signals exhibited only 1 negative peak (P1) that was significantly delayed compared to F1 (p < 0.02) and roughly in phase with F2. Compared to F2 and P1, F1 was of significantly lower amplitude (p < 0.02) and located closer to the bipolar stimulus center (p < 0.03), whereas F2 and P1 were more widespread, irregular, and partially overlapping. In mice, the spatiotemporal characteristics of FFI and PDI resembled those of iFFI and iPDI, but the early positive signal was more robust than F1.

CONCLUSIONS

This is the first report in humans of successful intraoperative visualization of cortical activations by using iFFI, which showed rapid evoked cortical activity prior to perfusion-dependent signal changes. Further technical improvements can lead to establishment of iFFI as a real-time intraoperative tool.

Behavioral and Molecular Responses to Exogenous Cannabinoids During Pentylenetetrazol-Induced Convulsions in Male and Female Rats

Epilepsy is a disabling, chronic brain disease,affecting ~1% of the World’s population, characterized by recurrent seizures (sudden, uncontrolled brain activity), which may manifest with motor symptoms (e.g., convulsions) or non-motor symptoms. Temporal lobe epilepsies (TLE) compromising the hippocampus are the most common form of focal epilepsies. Resistance in ~1/3 of epileptic patients to the first line of treatment, i.e., antiepileptic drugs (AEDs), has been an important motivation to seek alternative treatments. Among these, the plant Cannabis sativa (commonly known as marihuana) or compounds extracted from it (cannabinoids) have gained widespread popularity. Moreover, sex differences have been proposed in epilepsy syndromes and in cannabinoid action. In the hippocampus, cannabinoids interact with the CB1R receptor whose membrane levels are regulated by β-Arrestin2, a protein that promotes its endocytosis and causes its downregulation. In this article, we evaluate the modulatory role of WIN 55,212-2 (WIN), a synthetic exogenous cannabinoid on behavioral convulsions and on the levels of CB1R and β-Arrestin2 in female and male adolescent rats after a single injection of the proconvulsant pentylenetetrazol (PTZ). As epilepsies can have a considerable impact on synaptic proteins that regulate neuronal toxicity, plasticity, and cognition, we also measured the levels of key proteins markers of excitatory synapses, in order to examine whether exogenous cannabinoids may prevent such pathologic changes after acute seizures. We found that the exogenous administration of WIN prevented convulsions of medium severity in females and males and increased the levels of phosphorylated CaMKII in the hippocampus. Furthermore, we observed a higher degree of colocalization between CB1R and β-Arrestin2 in the granule cell layer.

Inhibiting SRC activity attenuates kainic-acid induced mouse epilepsy via reducing NR2B phosphorylation and full-length NR2B expression

OBJECTIVE

To explore the effect of SRC activation on spontaneously recurrent seizures and to investigate the underlying mechanisms of NR2B phosphorylation.

METHODS

C57BL/6 mice were injected intrahippocampally with kainic acid (KA, 0.4 μg/25 g) to induce status epilepticus (SE). Saracatinib(STB) was used as an SRC inhibitor. Spontaneously recurrent seizures were monitored from day 7 to day 14 after the KA injection. Nissl's stain and NeuN were used to detect neuron loss and Timm stain was used to evaluate mossy fibre sprouting 14 days after KA injection. We also investigated the effect of SRC on full-length expression of NR2B. MDL28170 was used to inhibit calpain activity. Western blotting and qPCR were performed to verify phosphorylation levels and expression of SRC and NR2B 24 h after KA injection.

RESULTS

The duration of status epileptics in the SRC inhibitor group decreased significantly compared to the KA group 24 h after the injection of KA (P < 0.05). The application of the SRC inhibitor significantly reduced the degree of contralateral mossy fibre sprouting (P < 0.05) and improved the degree of neuron loss (P < 0.01) compared to the epilepsy group. Full-length NR2B levels in the ipsilateral hippocampus decreased in the epilepsy group (P < 0.01) compared to the sham group, and it further decreased in the STB inhibitor group (P < 0.01). The effect of the STB inhibitor was counteracted by simultaneous inhibition of SRC activity and calpain activation, while the level of full-length NR2B increased compared to the KA+STB group(P < 0.01). Reduction of NR2B cleavage by MDL28170 significantly increased the duration of epileptic status compared to the KA group (P < 0.05).

SIGNIFICANCE

Our data indicated that the early application of SRC inhibitors exerted protective effects on seizure severity, loss of neurons, and sprouting of mossy fibres in KA-induced mouse epilepsy. Seizure severity attenuation due to SRC inhibition was associated with the decrease of NR2B in both the phosphorylation and full-length forms.

Arc and Homer1 are involved in comorbid epilepsy and depression: A microarray data analysis

BACKGROUND

Depression is one of the most common comorbid psychiatric condition associated with epilepsy. It has a negative impact on the patient's quality of life. However, the underlying molecular mechanisms leading to depression are currently unclear. The aim of this study was to determine the hub genes associated with epilepsy and depression.

METHODS

Gene expression profiles (GSE47752 and GSE20388) were downloaded from the gene expression omnibus (GEO) database. Differentially expressed genes (DEGs) for epilepsy and depression groups were separately searched. Subsequently, network analyses methods were employed to establish protein-protein interaction (PPI) networks, and to perform Gene Ontology (GO) terms and pathway enrichment analyses for co-expressed DEGs.

RESULTS

A total of 772 genes were upregulated in patients with epilepsy whereas 91 genes were up-regulated in patients with depression. In addition, 1304 genes were down-regulated in epilepsy whereas 141 genes were down-regulated in patients with depression. Among co-expressed DEGs, 5 DEGs were up-regulated and 19 were down-regulated. Further analysis revealed that the co-expressed DEGs were involved in regulation of vasculature development, regulation of angiogenesis, glutamate receptor signaling pathway, cellular response to interleukin-1 and positive regulation of protein kinase B signaling. The Arc and Homer1 genes were identified as the common candidate genes involved in the pathogenesis of epilepsy and depression.

CONCLUSIONS

Arc and Homer1 may contribute to the comorbidity of epilepsy and depression.

Envisioning the role of inwardly rectifying potassium (Kir) channel in epilepsy

Epilepsy is a devastating neurological disorder characterized by recurrent seizures attributed to the disruption of the dynamic excitatory and inhibitory balance in the brain. Epilepsy has emerged as a global health concern affecting about 70 million people worldwide. Despite recent advances in pre-clinical and clinical research, its etiopathogenesis remains obscure, and there are still no treatment strategies modifying disease progression. Although the precise molecular mechanisms underlying epileptogenesis have not been clarified yet, the role of ion channels as regulators of cellular excitability has increasingly gained attention. In this regard, emerging evidence highlights the potential implication of inwardly rectifying potassium (Kir) channels in epileptogenesis. Kir channels consist of seven different subfamilies (Kir1-Kir7), and they are highly expressed in both neuronal and glial cells in the central nervous system. These channels control the cell volume and excitability. In this review, we discuss preclinical and clinical evidence on the role of the several subfamilies of Kir channels in epileptogenesis, aiming to shed more light on the pathogenesis of this disorder and pave the way for future novel therapeutic approaches.

Emerging Roles of Astrocyte Kir4.1 Channels in the Pathogenesis and Treatment of Brain Diseases

Inwardly rectifying Kir4.1 channels in astrocytes mediate spatial potassium (K⁺) buffering, a clearance mechanism for excessive extracellular K⁺, in tripartite synapses. In addition to K⁺ homeostasis, astrocytic Kir4.1 channels also play an essential role in regulating extracellular glutamate levels via coupling with glutamate transporters. Moreover, Kir4.1 channels act as novel modulators of the expression of brain-derived neurotrophic factor (BDNF) in astrocytes. Specifically, inhibition of astrocytic Kir4.1 channels elevates extracellular K⁺ and glutamate levels at synapses and facilitates BDNF expression in astrocytes. These changes elevate neural excitability, which may facilitate synaptic plasticity and connectivity. In this article, we summarize the functions and pharmacological features of Kir4.1 channels in astrocytes and highlight the importance of these channels in the treatment of brain diseases. Although further validation in animal models and human patients is required, astrocytic Kir4.1 channel could potentially serve as a novel therapeutic target for the treatment of depressive disorders and epilepsy.

Reactive astrocytes contribute to epileptogenesis in patients with cavernous angioma

OBJECTIVE

Patients with cavernous angioma (CA) often suffer from severe epilepsy, and surgical resection is often performed to attenuate these epileptic seizures. Several studies have suggested that surgical removal of the surrounding hemosiderin-pigmented tissues adjacent to CA achieves better seizure control than restricted lesionectomy. Pathological examination of the resected foci reveals not only hemosiderin pigmentation but also various degrees of inflammatory change, such as hemosiderin-laden macrophages, gliosis and fibrosis. However, there is some controversy regarding the epileptogenic potential of these regions due to the uncertain nature of the mechanisms contributing to these histopathological changes.

METHODS

To investigate the correlations between neuron hyperexcitability and evident pathological changes, we performed ex vivo flavoprotein fluorescence imaging using surgically resected epileptogenic foci surrounding CA. The mirror surfaces of the tissues used for the physiological experiment were also subjected to morphological examination.

RESULTS

Hemosiderin-laden macrophages and many gemistocytic astrocytes were observed in the area adjacent to CA, where horizontal spreading excitations were detected significantly more frequently. Outside these areas, we found fine granular iron deposits and only a few fibrillary astrocytes, and weakly propagating excitations were detected. Furthermore, areas of enhanced activation were more clearly correlated with the glial proliferation index than with iron deposition.

CONCLUSION

These results suggest that the epileptogenesis in patients with CA may be based on a biological process, such as alteration of glial function, rather than direct chemical reactions involving iron deposition.

Are HFOs in the Intra-operative ECoG Related to Hippocampal Sclerosis, Volume and IQ?

Temporal lobe epilepsy (TLE) is the most common form of refractory focal epilepsy and is often associated with hippocampal sclerosis (HS) and cognitive disturbances. Over the last decade, high frequency oscillations (HFOs) in the intraoperative electrocorticography (ioECoG) have been proposed to be biomarkers for the delineation of epileptic tissue but hippocampal ripples have also been associated with memory consolidation. Healthy hippocampi can show prolonged ripple activity in stereo- EEG. We aimed to identify how the HFO rates [ripples (80–250 Hz, fast ripples (250–500 Hz); prolonged ripples (80–250 Hz, 200–500 ms)] in the pre-resection ioECoG over subtemporal area (hippocampus) and lateral temporal neocortex relate to presence of hippocampal sclerosis, the hippocampal volume quantified on MRI and the severity of cognitive impairment in TLE patients. Volumetric measurement of hippocampal subregions was performed in 47 patients with TLE, who underwent ioECoG. Ripples, prolonged ripples, and fast ripples were visually marked and rates of HFOs were calculated. The intellectual quotient (IQ) before resection was determined. There was a trend toward higher rates of ripples and fast ripples in subtemporal electrodes vs. the lateral neocortex (ripples: 2.1 vs. 1.3/min; fast ripples: 0.9 vs. 0.2/min). Patients with HS showed higher rates of subtemporal fast ripples than other patients (Z = −2.51, p = 0.012). Prolonged ripples were only found in the lateral temporal neocortex. The normalized ratio (smallest/largest) of hippocampal volume was correlated to pre-resection IQ (r = 0.45, p = 0.015). There was no correlation between HFO rates and hippocampal volumes or HFO rates and IQ. To conclude, intra-operative fast ripples were a marker for HS, but ripples and fast ripples were not linearly correlated with either the amount of hippocampal atrophy, nor for pre-surgical IQ.

An Insight into Molecular Mechanisms and Novel Therapeutic Approaches in Epileptogenesis

Epilepsy is the second most common neurological disease with abnormal neural activity involving the activation of various intracellular signalling transduction mechanisms. The molecular and system biology mechanisms responsible for epileptogenesis are not well defined or understood. Neuroinflammation, neurodegeneration and Epigenetic modification elicit epileptogenesis. The excessive neuronal activities in the brain are associated with neurochemical changes underlying the deleterious consequences of excitotoxicity. The prolonged repetitive excessive neuronal activities extended to brain tissue injury by the activation of microglia regulating abnormal neuroglia remodelling and monocyte infiltration in response to brain lesions inducing axonal sprouting contributing to neurodegeneration. The alteration of various downstream transduction pathways resulted in intracellular stress responses associating endoplasmic reticulum, mitochondrial and lysosomal dysfunction, activation of nucleases, proteases mediated neuronal death. The recently novel pharmacological agents modulate various receptors like mTOR, COX-2, TRK, JAK-STAT, epigenetic modulators and neurosteroids are used for attenuation of epileptogenesis. Whereas the various molecular changes like the mutation of the cell surface, nuclear receptor and ion channels focusing on repetitive episodic seizures have been explored by preclinical and clinical studies. Despite effective pharmacotherapy for epilepsy, the inadequate understanding of precise mechanisms, drug resistance and therapeutic failure are the current fundamental problems in epilepsy. Therefore, the novel pharmacological approaches evaluated for efficacy on experimental models of epilepsy need to be identified and validated. In addition, we need to understand the downstream signalling pathways of new targets for the treatment of epilepsy. This review emphasizes on the current state of novel molecular targets as therapeutic approaches and future directions for the management of epileptogenesis. Novel pharmacological approaches and clinical exploration are essential to make new frontiers in curing epilepsy.

Role of Astrocytic Inwardly Rectifying Potassium (Kir) 4.1 Channels in Epileptogenesis

Astrocytes regulate potassium and glutamate homeostasis via inwardly rectifying potassium (Kir) 4.1 channels in synapses, maintaining normal neural excitability. Numerous studies have shown that dysfunction of astrocytic Kir4.1 channels is involved in epileptogenesis in humans and animal models of epilepsy. Specifically, Kir4.1 channel inhibition by KCNJ10 gene mutation or expressional down-regulation increases the extracellular levels of potassium ions and glutamate in synapses and causes hyperexcitation of neurons. Moreover, recent investigations demonstrated that inhibition of Kir4.1 channels facilitates the expression of brain-derived neurotrophic factor (BDNF), an important modulator of epileptogenesis, in astrocytes. In this review, we summarize the current understanding on the role of astrocytic Kir4.1 channels in epileptogenesis, with a focus on functional and expressional changes in Kir4.1 channels and their regulation of BDNF secretion. We also discuss the potential of Kir4.1 channels as a therapeutic target for the prevention of epilepsy.

Proteomic profile differentiating between mesial temporal lobe epilepsy with and without hippocampal sclerosis

Hippocampal sclerosis (HS) is the most common neuropathological condition in adults with drug-resistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy (MTLE) syndrome. Although epileptogenic brain tissue is associated with glutamate excitotoxicity leading to oxidative stress, the proteins that are targets of oxidative damage remain to be determined. In the present study we designed comprehensive analyses of changes in protein expression level and protein oxidation status in the hippocampus or neocortex to highlight proteins associated with excitotoxicity by comparing MTLE patients with relatively mild excitotoxicity (MTLE patients without HS, MTLE-non-HS) and those with severe excitotoxicity (MTLE patients with HS, MTLE-HS). We performed 2-dimensional fluorescence difference gel electrophoresis, 2D-oxyblot analysis, and mass spectrometric amino acid sequencing. We identified 16 proteins at 18 spots in which the protein expression levels differed between sclerotic and non-sclerotic hippocampi. In the sclerotic hippocampus, the expression levels of several synaptic proteins were decreased, and those of some glia-associated proteins increased. We confirmed histologically that all MTLE-HS cases examined exhibited severe neuronal cell loss and remarkable astrocytic gliosis in the hippocampi. In all MTLE-non-HS cases examined, neurons were spared and gliosis was unremarkable. Therefore, we consider that decreased synaptic proteins are a manifestation of loss of neuronal cell bodies and dendrites, whereas increased glia-associated proteins are a manifestation of proliferation and hypertrophy of astrocytes. These are considered to be the result of hippocampal sclerosis. In contrast, the expression level of d-3-phosphoglycerate dehydrogenase (PHGDH), an l-serine synthetic enzyme expressed exclusively by astrocytes, was decreased, and that of stathmin 1, a neurite extension-related protein expressed by neurons, was increased in the sclerotic hippocampus. These findings cannot be explained solely as the result of hippocampal sclerosis. Rather, these changes can be involved in the continuation of seizure disorders in MTLE-HS. In addition, the protein carbonylation detection, an indicator of protein oxidation caused by excitotoxicity of multiple seizures and/or status epilepticus, revealed that the carbonyl level of collapsin response mediator protein 2 (CRMP2) increased significantly in the sclerotic hippocampus. In conclusion, protein identification following profiling of protein expression levels and detection of oxidative proteins indicated potential pathognomonic protein changes. The decreased expression of PHGDH, increased expression of stathmin 1, and carbonylation of CRMP2 differentiate between MTLE with and without HS. Therefore, further investigations of PHGDH, stathmin 1 and CRMP2 are promising to study more detailed effects of excitotoxicity on epileptogenic hippocampal tissue.

Subtemporal selective amygdalohippocampectomy in patients with mesial temporal lobe epilepsy: Systematic review of seizure and neuropsychological outcomes

In addition to standard anterior temporal lobectomy (ATL), subtemporal selective amygdalohippocampectomy (sSAH) is also a common technique for the treatment of medically intractable mesial temporal lobe epilepsy (MTLE). We conducted a systematic literature review to determine the seizure and neuropsychological outcomes in patients with MTLE who underwent sSAH. We searched PubMed and Embase using Medical Subject Headings and keywords related to sSAH, seizure outcome, and neuropsychological outcome. Titles, abstracts, and full-texts were screened in light of inclusion and exclusion criteria that were established a priori. Potential papers were reviewed by 3 reviewers, who reached a consensus on the final papers to be included. Literature review identified 208 abstracts from which a total of 29 full-text articles were reviewed. Six studies containing data from 4 countries (3 continents) met our inclusion criteria. The seizure-free rates at 12 months after sSAH ranged from 59.1% to 61.5% in 4 studies. Four studies showed that seizure-free rates ranged from 56% to 82.6% at 24 months after surgery. Six studies evaluated the neuropsychological changes of patients with MTLE after sSAH, including intelligence, verbal memory, nonverbal memory, language function, and so on. In terms of neuropsychological outcomes, there are some differences among the 6 studies. Taken together, sSAH can provide a considerable rate of seizure freedom. In addition, the neuropsychological outcomes of patients who underwent sSAH were slightly different among 6 studies. Therefore, large-scale case series or randomized controlled trials (RCTs) are needed to clarify the advantages and disadvantages of the sSAH.

Precision mapping of the epileptogenic network with low- and high-frequency stimulation of anterior nucleus of thalamus

OBJECTIVE

The goal of thalamic deep brain stimulation in epilepsy is to engage and modulate the epileptogenic network. We demonstrate how the anterior nucleus of thalamus (ANT) stimulation engages the epileptogenic network using electrophysiological measures (gamma response and post-stimulation excitability).

METHODS

Five patients with suspected temporal lobe epilepsy syndrome, undergoing stereo-electroencephalography (SEEG), were enrolled in the IRB approved study to undergo recording and stimulation of the ANT. We analyzed the extent of gamma-band response (activation or suppression) and post-stimulation change in excitability in various cortical regions during low (10 Hz) and high (50 Hz) frequency stimulations.

RESULTS

10 Hz stimulation increased cortical gamma, whereas 50 Hz stimulation suppressed the gamma responses. The maximum response to stimuli was in the hippocampus. High epileptogenicity regions were more susceptible to stimulation. Both 10-and 50 Hz stimulations decreased post-stimulation cortical excitability. The greater the gamma-band activation with 10 Hz stimulation, the greater was the decrease in post-stimulation excitability.

CONCLUSIONS

We define an EEG marker that delineates stimulation-specific nodal engagement. We proved that nodes that were engaged with the thalamus during stimulation were more likely to show a short term decrease in post-stimulation excitability.

SIGNIFICANCE

Patient-specific engagement patterns during stimulation can be mapped with SEEG that can be used to optimize stimulation parameters.

Postencephalitic epilepsy in dogs with meningoencephalitis of unknown origin: Clinical features, risk factors, and long-term outcome

Background

Although the presence of seizures in dogs with meningoencephalitis of unknown origin (MUO) has been associated with shorter survival times, data regarding the prevalence and risk factors for postencephalitic epilepsy (PEE) is lacking.

Objectives

To describe the clinical features, prevalence, risk factors, and long‐term outcome of PEE in dogs with MUO.

Animals

Sixty‐one dogs with presumptive diagnosis of MUO based on the clinicopathological and diagnostic imaging findings.

Methods

Retrospective study. Cases were identified by search of hospital medical records for dogs with suspected or confirmed MUO. Medical records of dogs meeting inclusion criteria were reviewed. Signalment, seizure history, clinicopathologic, and magnetic resonance imaging (MRI) findings were recorded.

Results

Among 61 dogs at risk of PEE, 14 (23%) dogs developed PEE. Three of 14 dogs with PEE (21%) developed drug‐resistant epilepsy. Dogs with PEE were younger (P = .03; OR_adjusted = 0.75; 95% confidence interval [CI], 0.58‐0.98) and had significantly shorter survival times (log‐rank test P = .04) when compared to dogs that did not develop epilepsy. The risk factors associated with the development of PEE were the presence of acute symptomatic seizures (ASS; P = .04; OR_adjusted = 4.76; 95% CI, 1.11‐20.4) and MRI lesions in the hippocampus (P = .04; OR_adjusted = 4.75; 95% CI, 1.07‐21.0).

Conclusions and Clinical Importance

Dogs with MUO and seizures at the early stage of the disease (ASS) seem to be at a higher risk of developing PEE.

Inwardly Rectifying Potassium Channel Kir4.1 as a Novel Modulator of BDNF Expression in Astrocytes

Brain-derived neurotrophic factor (BDNF) is a key molecule essential for neural plasticity and development, and is implicated in the pathophysiology of various central nervous system (CNS) disorders. It is now documented that BDNF is synthesized not only in neurons, but also in astrocytes which actively regulate neuronal activities by forming tripartite synapses. Inwardly rectifying potassium (Kir) channel subunit Kir4.1, which is specifically expressed in astrocytes, constructs Kir4.1 and Kir4.1/5.1 channels, and mediates the spatial potassium (K⁺) buffering action of astrocytes. Recent evidence illustrates that Kir4.1 channels play important roles in bringing about the actions of antidepressant drugs and modulating BDNF expression in astrocytes. Although the precise mechanisms remain to be clarified, it seems likely that inhibition (down-regulation or blockade) of astrocytic Kir4.1 channels attenuates K⁺ buffering, increases neuronal excitability by elevating extracellular K⁺ and glutamate, and facilitates BDNF expression. Conversely, activation (up-regulation or opening) of Kir4.1 channels reduces neuronal excitability by lowering extracellular K⁺ and glutamate, and attenuates BDNF expression. Particularly, the former pathophysiological alterations seem to be important in epileptogenesis and pain sensitization, and the latter in the pathogenesis of depressive disorders. In this article, we review the functions of Kir4.1 channels, with a focus on their regulation of spatial K⁺ buffering and BDNF expression in astrocytes, and discuss the role of the astrocytic Kir4.1-BDNF system in modulating CNS disorders.