Lacosamide modulates interictal spiking and high-frequency oscillations in a model of mesial temporal lobe epilepsy

Protective Activity of Novel Hydrophilic Synthetic Neurosteroids on Organophosphate Status Epilepticus-induced Chronic Epileptic Seizures, Non-Convulsive Discharges, High-Frequency Oscillations, and Electrographic Ictal Biomarkers

Nerve agents and organophosphates (OP) are neurotoxic chemicals that induce acute seizures, status epilepticus (SE), and mortality. Long-term neurologic and neurodegenerative effects manifest months to years after OP exposure. Current benzodiazepine anticonvulsants are ineffective in preventing such long-term neurobehavioral and neuropathological changes. New and effective anticonvulsants are needed for OP intoxication, especially for mitigating the long-term sequelae after acute exposure. We developed neurosteroids as novel anticonvulsants and neuroprotectants in OP exposure models. In this study, we evaluated the long-term efficacy of novel synthetic neurosteroids in preventing the development of chronic epilepsy and hyperexcitable ictal events in a rat OP model of SE. Rats were exposed to the OP nerve agent surrogate diisopropylfluorophosphate (DFP), and the experimental groups were treated with the synthetic neurosteroid valaxanolone (VX) or lysaxanolone (LX) 40 minutes post-exposure in conjunction with midazolam. Video-electroencephalography was monitored for two months to assess spontaneous recurrent seizures (SRS), epileptiform discharges, interictal spikes, and high-frequency oscillations (HFOs). Within 60 days of DFP exposure, rats developed chronic epilepsy characterized by frequent SRS, epileptiform discharges, and HFOs. LX treatment was associated with a dose-dependent reduction of epilepsy occurrence and overall seizure burden with a significant decrease in SRS and epileptiform discharges. It also significantly reduced the occurrence of epileptic biomarkers of HFOs and interictal spikes, indicating potential disease-modifying activity. Similarly, the neurosteroid analog VX also significantly attenuated SRS, discharges, HFOs, and ictal events. These results demonstrate the long-term protective effects of synthetic neurosteroids in the OP-exposed post-SE model, indicating their disease-modifying potential to prevent epilepsy and ictal abnormalities. SIGNIFICANCE STATEMENT: The effects of nerve agents and organophosphate (OP) exposure are persistent, and survivors suffer from a number of devastating, chronic neurological dysfunctions. Currently, there is no specific therapy for preventing this disastrous impact of OP exposure. We propose synthetic neurosteroids that activate tonic inhibition provide viable options for preventing the long-term neurological effects of OP intoxication. The results from this study reveal the disease-modifying potential of two novel synthetic neurosteroids in preventing epileptogenesis and chronic epileptic seizures after OP-induced SE.

Neurophysiology, Neuropsychology, and Epilepsy, in 2022: Hills We Have Climbed and Hills Ahead. Neurophysiology in epilepsy

Since the discovery of the human electroencephalogram (EEG), neurophysiology techniques have become indispensable tools in our armamentarium to localize epileptic seizures. New signal analysis techniques and the prospects of artificial intelligence and big data will offer unprecedented opportunities to further advance the field in the near future, ultimately resulting in improved quality of life for many patients with drug-resistant epilepsy. This article summarizes selected presentations from Day 1 of the two-day symposium "Neurophysiology, Neuropsychology, Epilepsy, 2022: Hills We Have Climbed and the Hills Ahead". Day 1 was dedicated to highlighting and honoring the work of Dr. Jean Gotman, a pioneer in EEG, intracranial EEG, simultaneous EEG/ functional magnetic resonance imaging, and signal analysis of epilepsy. The program focused on two main research directions of Dr. Gotman, and was dedicated to "High-frequency oscillations, a new biomarker of epilepsy" and "Probing the epileptic focus from inside and outside". All talks were presented by colleagues and former trainees of Dr. Gotman. The extended summaries provide an overview of historical and current work in the neurophysiology of epilepsy with emphasis on novel EEG biomarkers of epilepsy and source imaging and concluded with an outlook on the future of epilepsy research, and what is needed to bring the field to the next level.

Evolution of interictal activity in models of mesial temporal lobe epilepsy

Interictal activity and seizures are the hallmarks of focal epileptic disorders (which include mesial temporal lobe epilepsy, MTLE) in humans and in animal models. Interictal activity, which is recorded with cortical and intracerebral EEG recordings, comprises spikes, sharp waves and high-frequency oscillations, and has been used in clinical practice to identify the epileptic zone. However, its relation with seizures remains debated. Moreover, it is unclear whether specific EEG changes in interictal activity occur during the time preceding the appearance of spontaneous seizures. This period, which is termed "latent", has been studied in rodent models of MTLE in which spontaneous seizures start to occur following an initial insult (most often a status epilepticus induced by convulsive drugs such as kainic acid or pilocarpine) and may mirror epileptogenesis, i.e., the process leading the brain to develop an enduring predisposition to seizure generation. Here, we will address this topic by reviewing experimental studies performed in MTLE models. Specifically, we will review data highlighting the dynamic changes in interictal spiking activity and high-frequency oscillations occurring during the latent period, and how optogenetic stimulation of specific cell populations can modulate them in the pilocarpine model. These findings indicate that interictal activity: (i) is heterogeneous in its EEG patterns and thus, presumably, in its underlying neuronal mechanisms; and (ii) can pinpoint to the epileptogenic processes occurring in focal epileptic disorders in animal models and, perhaps, in epileptic patients.

High-Frequency Oscillations and Epileptogenic Network

Epilepsy is a network disease caused by aberrant neocortical large-scale connectivity spanning regions on the scale of several centimeters. High-frequency oscillations, characterized by the 80-600 Hz signals in electroencephalography, have been proven to be a promising biomarker of epilepsy that can be used in assessing the severity and susceptibility of epilepsy as well as the location of the epileptogenic zone. However, the presence of a high-frequency oscillation network remains a topic of debate as high-frequency oscillations have been previously thought to be incapable of propagation, and the relationship between high-frequency oscillations and the epileptogenic network has rarely been discussed. Some recent studies reported that high-frequency oscillations may behave like networks that are closely relevant to the epileptogenic network. Pathological highfrequency oscillations are network-driven phenomena and elucidate epileptogenic network development; high-frequency oscillations show different characteristics coincident with the epileptogenic network dynamics, and cross-frequency coupling between high-frequency oscillations and other signals may mediate the generation and propagation of abnormal discharges across the network.

Bilateral optogenetic activation of inhibitory cells favors ictogenesis

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal refractory epilepsy and is characterized by recurring seizures that are often refractory to medication. Since parvalbumin-positive (PV) interneurons were recently shown to play significant roles in ictogenesis, we established here how bilateral optogenetic stimulation of these interneurons in the hippocampus CA3 regions modulates seizures, interictal spikes and high-frequency oscillations (HFOs; ripples: 80-200 Hz, fast ripples: 250-500 Hz) in the pilocarpine model of MTLE. Bilateral optogenetic stimulation of CA3 PV-positive interneurons at 8 Hz (lasting 30 s, every 2 min) was implemented in PV-ChR2 mice for 8 consecutive days starting on day 7 (n = 8) or on day 13 (n = 6) after pilocarpine-induced status epilepticus (SE). Seizure occurrence was higher in both day 7 and day 13 groups of PV-ChR2 mice during periods of optogenetic stimulation ("ON"), compared to when stimulation was not performed ("OFF") (day 7 group = p < 0.01, day 13 group = p < 0.01). In the PV-ChR2 day 13 group, rates of seizures (p < 0.05), of interictal spikes associated with fast ripples (p < 0.01), and of isolated fast ripples (p < 0.01) during optogenetic stimulations were significantly higher than in the PV-ChR2 day 7 group. Our findings reveal that bilateral activation of PV-interneurons in the hippocampus (leading to a presumptive increase in GABA signaling) favors ictogenesis. These effects may also mirror the neuropathological changes that occur over time after SE in this animal model.

Melissa officinalis L. ameliorates oxidative stress and inflammation and upregulates Nrf2/HO-1 signaling in the hippocampus of pilocarpine-induced rats

Epilepsy is characterized by recurrent epileptic seizures, and its effective management continues to be a therapeutic challenge. Oxidative stress and local inflammatory response accompany the status epilepticus (SE). This study evaluated the effect of Melissa officinalis extract (MOE) on oxidative stress, inflammation, and neurotransmitters in the hippocampus of pilocarpine (PILO)-administered rats, pointing to the involvement of Nrf2/HO-1 signaling. Rats received PILO via intraperitoneal administration and were treated with MOE for 2 weeks. MOE prevented neuronal loss; decreased lipid peroxidation, Cox-2, PGE2, and BDNF; and downregulated glial fibrillary acidic protein in the hippocampus of PILO-treated rats. In addition, MOE enhanced GSH and antioxidant enzymes, upregulated Nrf2 and HO-1 mRNA abundance, and increased the nuclear translocation of Nrf2 in the hippocampus of epileptic rats. Na+/K+-ATPase activity and GABA were increased, and glutamate and acetylcholine were decreased in the hippocampus of epileptic rats treated with MOE. In conclusion, MOE attenuated neuronal loss, oxidative stress, and inflammation; activated Nrf2/HO-1 signaling; and modulated neurotransmitters, GFAP, and Na+/K+-ATPase in the hippocampus of epileptic rats. These findings suggest that M. officinalis can mitigate epileptogenesis, pending further studies to explore the exact underlying mechanisms.

Contusion brain damage in mice for modelling of post-traumatic epilepsy with contralateral hippocampus sclerosis: Comprehensive and longitudinal characterization of spontaneous seizures, neuropathology, and neuropsychiatric comorbidities

Traumatic brain injury (TBI) is a leading cause of acquired epilepsy referred to as post-traumatic epilepsy (PTE), characterized by spontaneous recurrent seizures (SRS) that start in the months or years following TBI. There is a critical need to develop small animal models for advancing the neurotherapeutics of PTE, which accounts for 20% of all acquired epilepsy cases. Despite many previous attempts, there are few PTE models with demonstrated consistency or longitudinal incidence of SRS, a critical feature for creating models for investigation of novel therapeutics for preventing PTE. Over the past few years, we have made in-depth updates and several advances to our mouse model of TBI in which SRS consistently occurs upon 24/7 monitoring for 4 months. Here, we show that an advanced cortical contusion damage in mice elicits a chronic state of PTE with SRS and robust epileptiform activity, along with cognitive comorbidities. We observed SRS in 33% and 87% of moderate and severe injury cohorts, respectively. Though incidence was higher in the severe cohort, moderate injury elicited a robust epileptogenesis. Progressive neuronal damage, neurodegeneration, and inflammation signals were evident in many brain regions; comorbid behavior and cognitive deficits were observed for up to 4-months. SRS onset was correlated with the inception of interneuron loss after TBI. Contralateral hippocampal sclerosis was unique and well correlated with SRS, confirming a potential network basis for epileptogenesis. Collectively, this mouse model exhibits a number of hallmark TBI sequelae reminiscent of human PTE. This model provides a vital tool for probing molecular pathological mechanisms and therapeutic interventions for post-traumatic epileptogenesis. SIGNIFICANCE STATEMENT: TBI is a leading cause of post-traumatic epilepsy (PTE). Despite many attempts to create PTE in animals, success has been limited due to a lack of consistent spontaneous "epileptic" seizures after TBI. We present a comprehensive phenotype of PTE after contusion brain injury in mice, which exhibits robust spontaneous seizures along with neuronal loss, inflammation, and cognitive dysfunction. Our broad profiling of a TBI mouse reveals features of progressive, long-lasting epileptic activity, unique contralateral hippocampal sclerosis, and comorbid mood and memory deficits. The PTE mouse shows a striking consistency in recapitulating major pathological sequelae of human PTE. This mouse model will be helpful in assessing mechanisms and interventions for TBI-induced epilepsy and mood dysfunction.

High-frequency oscillations detected by electroencephalography as biomarkers to evaluate treatment outcome, mirror pathological severity and predict susceptibility to epilepsy

High-frequency oscillations (HFOs) in the electroencephalography (EEG) have been extensively investigated as a potential biomarker of epileptogenic zones. The understanding of the role of HFOs in epilepsy has been advanced considerably over the past decade, and the use of scalp EEG facilitates recordings of HFOs. HFOs were initially applied in large scale in epilepsy surgery and are now being utilized in other applications. In this review, we summarize applications of HFOs in 3 subtopics: (1) HFOs as biomarkers to evaluate epilepsy treatment outcome; (2) HFOs as biomarkers to measure seizure propensity; (3) HFOs as biomarkers to reflect the pathological severity of epilepsy. Nevertheless, knowledge regarding the above clinical applications of HFOs remains limited at present. Further validation through prospective studies is required for its reliable application in the clinical management of individual epileptic patients.

The pilocarpine model of mesial temporal lobe epilepsy: Over one decade later, with more rodent species and new investigative approaches

Fundamental work on the mechanisms leading to focal epileptic discharges in mesial temporal lobe epilepsy (MTLE) often rests on the use of rodent models in which an initial status epilepticus (SE) is induced by kainic acid or pilocarpine. In 2008 we reviewed how, following systemic injection of pilocarpine, the main subsequent events are the initial SE, the latent period, and the chronic epileptic state. Up to a decade ago, rats were most often employed and they were frequently analysed only behaviorally. However, the use of transgenic mice has revealed novel information regarding this animal model. Here, we review recent findings showing the existence of specific neuronal events during both latent and chronic states, and how optogenetic activation of specific cell populations modulate spontaneous seizures. We also address neuronal damage induced by pilocarpine treatment, the role of neuroinflammation, and the influence of circadian and estrous cycles. Updating these findings leads us to propose that the rodent pilocarpine model continues to represent a valuable tool for identifying the basic pathophysiology of MTLE.

Effect of Lacosamide and Ethosuximide Chronic Treatment on Neural Precursor Cells and Cognitive Functions after Pilocarpine Induced Status Epilepticus in Mice

Seizures in about 40% of patients with epilepsy fail to respond to anti-seizure medication (ASM) and may lead to uncontrolled and prolonged seizures often inducing status epilepticus (SE). The aim of the study was to evaluate the impact of a long-term treatment with two different generation ASMs: ethosuximide (ETS, a classic ASM) and lacosamide (LCM, a 3rd generation ASM) on neural stem cells’ (NSCs’) proliferation and learning and memory functions after pilocarpine (PILO)-induced SE in mice. The following drugs were used: LCM (10 mg/kg), ETS (20 mg/kg), and PILO (300 mg/kg). Cell counting was done using confocal microscope and ImageJ software. Cognitive functions were evaluated with the Morris water maze (MWM) test. The level of several selected neurometabolites was measured with magnetic resonance spectroscopy (MRS). Obtained results indicated no significant impact of ETS treatment on the neurogenesis process in PILO mice. Interestingly, LCM significantly decreased the total amount of newborn neurons. The MWM test indicated no significant changes in the time and distance traveled by the ETS and LCM groups compared to PILO control mice, although all measured parameters were more favorable for the PILO mice treated with ASM. Conclusions: The presented results show that long term treatment with LCM and ETS seems to be safe for the cognitive functions and the proper course of neurogenesis in the mouse PILO-induced SE model, although one should remember that LCM administered chronically may act to reduce new neurons’ formation.

The Effect of Anti-seizure Medications on the Propagation of Epileptic Activity: A Review

The propagation of epileptiform events is a highly interesting phenomenon from the pathophysiological point of view, as it involves several mechanisms of recruitment of neural networks. Extensive in vivo and in vitro research has been performed, suggesting that multiple networks as well as cellular candidate mechanisms govern this process, including the co-existence of wave propagation, coupled oscillator dynamics, and more. The clinical importance of seizure propagation stems mainly from the fact that the epileptic manifestations cannot be attributed solely to the activity in the seizure focus itself, but rather to the propagation of epileptic activity to other brain structures. Propagation, especially when causing secondary generalizations, poses a risk to patients due to recurrent falls, traumatic injuries, and poor neurological outcome. Anti-seizure medications (ASMs) affect propagation in diverse ways and with different potencies. Importantly, for drug-resistant patients, targeting seizure propagation may improve the quality of life even without a major reduction in simple focal events. Motivated by the extensive impact of this phenomenon, we sought to review the literature regarding the propagation of epileptic activity and specifically the effect of commonly used ASMs on it. Based on this body of knowledge, we propose a novel classification of ASMs into three main categories: major, minor, and intermediate efficacy in reducing the propagation of epileptiform activity.

Anticonvulsant Effects of Topiramate and Lacosamide on Pilocarpine-Induced Status Epilepticus in Rats: A Role of Reactive Oxygen Species and Inflammation

BACKGROUND

Status epilepticus (SE) is a neurological disorder characterized by a prolonged epileptic activity followed by subsequent epileptogenic processes. The aim of the present study was to evaluate the early effects of topiramate (TPM) and lacosamide (LCM) treatment on oxidative stress and inflammatory damage in a model of pilocarpine-induced SE.

METHODS

Male Wistar rats were randomly divided into six groups and the two antiepileptic drugs (AEDs), TPM (40 and 80 mg/kg, i.p.) and LCM (10 and 30 mg/kg, i.p.), were injected three times repeatedly after pilocarpine administration. Rats were sacrificed 24 h post-SE and several parameters of oxidative stress and inflammatory response have been explored in the hippocampus.

RESULTS

The two drugs TPM and LCM, in both doses used, succeeded in attenuating the number of motor seizures compared to the SE-veh group 30 min after administration. Pilocarpine-induced SE decreased the superoxide dismutase (SOD) activity and reduced glutathione (GSH) levels while increasing the catalase (CAT) activity, malondialdehyde (MDA), and IL-1β levels compared to the control group. Groups with SE did not affect the TNF-α levels. The treatment with a higher dose of 30 mg/kg LCM restored to control level the SOD activity in the SE group. The two AEDs, in both doses applied, also normalized the CAT activity and MDA levels to control values. In conclusion, we suggest that the antioxidant effect of TPM and LCM might contribute to their anticonvulsant effect against pilocarpine-induced SE, whereas their weak anti-inflammatory effect in the hippocampus is a consequence of reduced SE severity.

Spatiotemporal Patterns of High-Frequency Activity (80-170 Hz) in Long-Term Intracranial EEG

OBJECTIVE

To determine the utility of high-frequency activity (HFA) and epileptiform spikes as biomarkers for epilepsy, we examined the variability in their rates and locations using long-term ambulatory intracranial EEG (iEEG) recordings.

METHODS

This study used continuous iEEG recordings obtained over an average of 1.4 years from 15 patients with drug-resistant focal epilepsy. HFA was defined as 80- to 170-Hz events with amplitudes clearly larger than the background, which was automatically detected with a custom algorithm. The automatically detected HFA was compared with visually annotated high-frequency oscillations (HFOs). The variations of HFA rates were compared with spikes and seizures on patient-specific and electrode-specific bases.

RESULTS

HFA included manually annotated HFOs and high-amplitude events occurring in the 80- to 170-Hz range without observable oscillatory behavior. HFA and spike rates had high amounts of intrapatient and interpatient variability. Rates of HFA and spikes had large variability after electrode implantation in most of the patients. Locations of HFA and spikes varied up to weeks in more than one-third of the patients. Both HFA and spike rates showed strong circadian rhythms in all patients, and some also showed multiday cycles. Furthermore, the circadian patterns of HFA and spike rates had patient-specific correlations with seizures, which tended to vary across electrodes.

CONCLUSION

Analysis of HFA and epileptiform spikes should consider postimplantation variability. HFA and epileptiform spikes, like seizures, show circadian rhythms. However, the circadian profiles can vary spatially within patients, and their correlations to seizures are patient-specific.

Neurosteroids and Focal Epileptic Disorders

Neurosteroids are a family of compounds that are synthesized in principal excitatory neurons and glial cells, and derive from the transformation of cholesterol into pregnenolone. The most studied neurosteroids—allopregnanolone and allotetrahydrodeoxycorticosterone (THDOC)—are known to modulate GABA_A receptor-mediated transmission, thus playing a role in controlling neuronal network excitability. Given the role of GABA_A signaling in epileptic disorders, neurosteroids have profound effects on seizure generation and play a role in the development of chronic epileptic conditions (i.e., epileptogenesis). We review here studies showing the effects induced by neurosteroids on epileptiform synchronization in in vitro brain slices, on epileptic activity in in vivo models, i.e., in animals that were made epileptic with chemoconvulsant treatment, and in epileptic patients. These studies reveal that neurosteroids can modulate ictogenesis and the occurrence of pathological network activity such as interictal spikes and high-frequency oscillations (80–500 Hz). Moreover, they can delay the onset of spontaneous seizures in animal models of mesial temporal lobe epilepsy. Overall, this evidence suggests that neurosteroids represent a new target for the treatment of focal epileptic disorders.

The subiculum and its role in focal epileptic disorders

The subicular complex (hereafter referred as subiculum), which is reciprocally connected with the hippocampus and rhinal cortices, exerts a major control on hippocampal outputs. Over the last three decades, several studies have revealed that the subiculum plays a pivotal role in learning and memory but also in pathological conditions such as mesial temporal lobe epilepsy (MTLE). Indeed, subicular networks actively contribute to seizure generation and this structure is relatively spared from the cell loss encountered in this focal epileptic disorder. In this review, we will address: (i) the functional properties of subicular principal cells under normal and pathological conditions; (ii) the subiculum role in sustaining seizures in in vivo models of MTLE and in in vitro models of epileptiform synchronization; (iii) its presumptive role in human MTLE; and (iv) evidence underscoring the relationship between subiculum and antiepileptic drug effects. The studies reviewed here reinforce the view that the subiculum represents a limbic area with relevant, as yet unexplored, roles in focal epilepsy.

HFO to Measure Seizure Propensity and Improve Prognostication in Patients With Epilepsy

The study of high frequency oscillations (HFO) in the electroencephalogram (EEG) as biomarkers of epileptic activity has merely focused on their spatial location and relationship to the epileptogenic zone. It has been suggested in several ways that the amount of HFO at a certain point in time may reflect the disease activity or severity. This could be clinically useful in several ways, especially as noninvasive recording of HFO appears feasible. We grouped the potential hypotheses into 4 categories: (1) HFO as biomarkers to predict the development of epilepsy; (2) HFO as biomarkers to predict the occurrence of seizures; (3) HFO as biomarkers linked to the severity of epilepsy, and (4) HFO as biomarkers to evaluate outcome of treatment. We will review the literature that addresses these 4 hypotheses and see to what extent HFO can be used to measure seizure propensity and help determine prognosis of this unpredictable disease.

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.

Neuroprotective Effects of Lacosamide and Memantine on Hyperoxic Brain Injury in Rats

In neonates supraphysiological oxygen therapy has been demonstrated to cause neuronal death in hippocampus, prefrontal cortex, parietal cortex, and retrosplenial cortex. There is a need for the detection of novel neuroprotective drugs. Neuroprotective effects of lacosamide or memantine have been demonstrated in adult patients with ischemia, trauma and status epilepticus. The effects in immature brains may be different. This study aimed to evaluate neuroprotective effects of lacosamide and memantine treatment in a hyperoxia-induced brain injury model in immature rats. This study was performed in the Animal Experiments Laboratory of Dokuz Eylul University Faculty of Medicine. Neonatal Wistar strain rat pups were exposed to hyperoxia (80% oxygen + 20% nitrogen) for five days postnatally. They were divided into five groups; hyperoxia + lacosamide, hyperoxia + memantine, hyperoxia + lacosamide and memantine, hyperoxia + saline, control groups. After termination of the experiment, brain tissues were examined. Neuron counting in examined regions were found to be higher in hyperoxia + memantine and hyperoxia + lacosamide and memantine groups than hyperoxia + saline group. The presence of apoptotic cells evaluated with TUNEL and active Caspase-3 in hyperoxia + memantine and hyperoxia + lacosamide and memantine groups were found to be lower compared to hyperoxia + saline group. This study demonstrates that neuron death and apoptosis in newborn rat brains after hyperoxia is reduced upon memantine treatment. This is the first study to show the effects of memantine and lacosamide on hyperoxia-induced damage in neonatal rat brains.

Evaluation of the impact of compound C11 a new anticonvulsant candidate on cognitive functions and hippocampal neurogenesis in mouse brain

Searching for the new and effective anticonvulsants in our previous study we developed a new hybrid compound C-11 derived from 2-(2,5-dioxopyrrolidin-1-yl) propanamide. C11 revealed high efficacy in acute animal seizure models such as the maximal electroshock model (MES), the pentylenetetrazole model (PTZ) and the 6 Hz (6 Hz, 32 mA) seizure model, as well as in the kindling model of epilepsy induced by repeated injection of PTZ in mice. In the aim of further in vivo C11 characterization, in the current studies we evaluated its influence on cognitive functions, neurodegeneration and neurogenesis process in mice after chronical treatment. All experiments were performed on 6 weeks old male C57/BL mice. The following drugs were used: C11, levetiracetam (LEV), ethosuximide (ETS) and lacosamide (LCM). We analyzed proliferation, migration and differentiation of newborn cells as well as neurodegenerative changes in a mouse brain after long-term treatment with aforementioned AEDs. Additionally, we evaluated changes in learning and memory functions in response to chronic C11, LEV, LCM and ETS treatment. C11 as well as LEV and ETS did not disturb the proliferation of newborn cells compared to the control mice, whereas LCM treatment significantly decreased it. Chronic AEDs therapy did not induce significant neurodegenerative changes. Behavioral studies with using Morris Water Maze test did not indicate any disturbances in the spatial learning and memory after C11 as well as LEV and ETS treatment in comparison to the control group except LCM mice where significant dysfunctions in time, distance and direct swim to the platform were observed. Interestingly, results obtained from in vivo MRI spectroscopy showed a statistically significant increase of one of the neurometabolites- N-acetyloaspartate (NAA) for LCM and LEV mice. A new hybrid compound C11 in contrast to LCM has no negative impact on the process of neurogenesis and neurodegeneration in the mouse hippocampus. Furthermore, chronic treatment with C11 turned out to have no negative impact on cognitive functions of treated mice, which, is certainly of great importance for further more advanced preclinical and especially clinical trials.

Paradoxical effects of optogenetic stimulation in mesial temporal lobe epilepsy

OBJECTIVE

To establish the effects induced by long-term, unilateral stimulation of parvalbumin (PV)-positive interneurons on seizures, interictal spikes, and high-frequency oscillations (80-500Hz) occurring after pilocarpine-induced status epilepticus (SE)-a proven model of mesial temporal lobe epilepsy (MTLE)-in transgenic mice expressing or not expressing ChR2.

METHODS

PV-ChR2 (n = 6) and PV-Cre (n = 6) mice were treated with pilocarpine to induce SE. Three hours after SE onset, unilateral optogenetic stimulation (450nm, 25mW, 20-millisecond pulses delivered at 8Hz for 30 seconds every 2 minutes) of CA3 PV-positive interneurons was implemented for 14 continuous days in both groups.

RESULTS

Rates of seizures (p < 0.01), interictal spikes (p < 0.001), and interictal spikes with fast ripples (250-500Hz) (p < 0.001) were lower in PV-ChR2 than in PV-Cre mice. Ripples (80-200Hz) occurring outside of interictal spikes had higher rates in the PV-ChR2 group (p < 0.01), whereas isolated fast ripples had lower rates (p < 0.01). However, seizure probability was higher during optogenetic stimulation in PV-ChR2 compared to PV-Cre animals (p < 0.05).

INTERPRETATION

Our findings show that the unilateral activation of CA3 PV-positive interneurons exerts anti-ictogenic effects associated with decreased rates of interictal spikes and fast ripples in this MTLE model. However, PV-positive interneuron stimulation can paradoxically trigger seizures in epileptic animals, supporting the notion that γ-aminobutyric acid type A signaling can also initiate ictogenesis. ANN NEUROL 2019;86:714-728.

The 4-Aminopyridine Model of Acute Seizures in vitro Elucidates Efficacy of New Antiepileptic Drugs

Up to date, preclinical screening for new antiepileptic substances is performed by a combination of different in vivo models of acute seizures, for which large numbers of animals are necessary. So far, little attention has been paid to in vitro models, which are also able to detect antiepileptic efficacy and in principle could likewise serve for exploratory preclinical screening. One of the established in vitro models of acute seizures is the 4-aminopyridine (4-AP) model. Previous studies have shown that the 4-AP model is capable to recapitulate the antiepileptic efficacy of standard antiepileptic drugs (AEDs) such as valproate or carbamazepine. Here, we employed a dual methodological approach using electrophysiology and optical imaging to systematically test the antiepileptic efficacy of three new-generation AEDs with distinct mechanisms of action (lacosamide, zonisamide, and levetiracetam). We found that frequency of 4-AP induced seizure like events (SLE) was the most sensitive parameter to detect dose-dependent antiepileptic effects in these compounds. Specifically, levetiracetam reduced SLE frequency while lacosamide and zonisamide at higher doses completely blocked SLE incidence. Analysis of the intrinsic optical signal additionally revealed a subiculum-specific reduction of the area involved in the propagation of ictal activity when lacosamide or zonisamide were administered. Taken together, our data adds some evidence that acute seizure models in vitro are in principle capable to detect antiepileptic effects across different mechanisms of action with efficacy similar to acute models in vivo. Further studies with negative controls, e.g., penicillin as a proconvulsant, and other clinically relevant AEDs are needed to determine if this acute in vitro model might be useful as exploratory screening tool. In view of the increasing sensitivity toward animal welfare, an affective in vitro model may help to reduce the number of laboratory animals deployed in burdening in vivo experiments and to preselect substances for subsequent testing in time- and cost-laborious models of chronic epilepsy.

Agomelatine alleviates neuronal loss through BDNF signaling in the post-status epilepticus model induced by kainic acid in rat

Recently, we have reported that while agomelatine (Ago) is unable to prevent development of epilepsy it exerts a strong neuroprotective and anti-inflammatory response in the KA post-status epilepticus (SE) rat model. In the present study, we aimed to explore whether the brain-derived neurotrophic factor (BDNF) in the hippocampus is involved in the neuroprotective effect of Ago against the KA-induced SE and epileptiform activity four months later in rats. Lacosamide (LCM) was used as a positive control. The EEG-recorded seizure activity was also evaluated in two treatment protocols. In Experiment#1, Ago given repeatedly at a dose of 40 mg/kg during the course of SE was unable neither to modify EEG-recorded epileptiform activity nor the video- and EEG-recorded spontaneous seizures four months later compared to LCM (50 mg/kg). However, both Ago and LCM inhibited the expression of BDNF in the mossy fibers and also prevented neuronal loss in the dorsal hippocampal and the piriform cortex after SE. In Experiment#2, acute injection of Ago and LCM on epileptic rats, characterized by high seizure rates, did not prevent EEG-recorded paroxysmal events while only LCM decreased either absolute or relative powers of gamma (28-60 Hz) and high (HI) (60-120 Hz) frequency bands to baseline in the frontal and parietal cortex, respectively. Our results suggest that the protection against neuronal loss in specific limbic regions and overexpressed BDNF in the mossy fibers resulting from the repeated treatment with Ago and LCM, respectively, during SE is not a prerequisite for alleviation of epileptogenesis and development of epilepsy. In addition, a reduction of gamma and HI bands in the frontal and parietal cortex is not associated with EEG-recorded paroxysmal events after acute injection of LCM.

High-frequency oscillations and focal seizures in epileptic rodents

High-pass filtering (> 80 Hz) of EEG signals has enabled neuroscientists to analyze high-frequency oscillations (HFOs; i.e., ripples: 80-200 Hz and fast ripples: 250-500 Hz) in epileptic patients presenting with focal seizures and in animal models mimicking this condition. Evidence obtained from these studies indicate that HFOs mirror pathological network activity that may initiate and sustain ictogenesis and epileptogenesis. HFOs are observed in temporal lobe regions of epileptic animals during interictal periods but they also occur before seizure onset and during the ictal period, suggesting that they can pinpoint to the mechanisms of seizure generation. Accordingly, ripples and fast ripples predominate during two specific seizure onset patterns termed low-voltage fast and hypersynchronous, respectively. In this review we will: (i) summarize these experimental studies; (ii) consider the evolution of HFOs over time during epileptogenesis; (iii) address data obtained with optogenetic stimulating procedures both in vitro and in vivo, and (iv) take into account the impact of anti-epileptic drugs on HFOs. We expect these findings to contribute to understanding the neuronal mechanisms leading to ictogenesis and epileptogenesis thus leading to the development of mechanistically targeted anti-epileptic strategies.

Inverted-U response of lacosamide on pilocarpine-induced status epilepticus and oxidative stress in C57BL/6 mice is independent of hippocampal collapsin response mediator protein-2

OBJECTIVE

Currently, lacosamide (LCM) is not approved for use in status epilepticus (SE) but several shreds of evidence are available to support its use. The present study was, therefore, undertaken to evaluate the effect of LCM on pilocarpine (PILO) induced SE and neurodegeneration in C57BL/6 mice and to ascertain the involvement of CRMP-2 in mediating above effect.

METHODS

Pilocarpine-induced SE model was developed to explore the effect of LCM 20, 40 and 80 mg/kg in mice. We assessed the seizure severity, seizure latency, spontaneous alternation behavior (SAB) and motor coordination by behavioral observation. Histopathological evaluation and measurement of the levels of CRMP-2, reduced glutathione (GSH) and malondialdehyde (MDA) were carried out in mice hippocampus.

RESULTS

LCM exhibited a biphasic effect i.e., protection against SE at 20 mg/kg and 40 mg/kg dose whilst aggravated seizure-like behavior and mortality at 80 mg/kg. Further, it increased percentage alternation (i.e., restored spatial memory) in SAB and elevated motor impairment with increasing dose. Histologically, LCM 20 mg/kg and 40 mg/kg (but not 80 mg/kg) reduced neurodegeneration. LCM 20 mg/kg and 40 mg/kg reversed the elevated MDA and GSH levels while 80 mg/kg showed a tendency to increase oxidative stress. In contrast, LCM (at all doses) reversed the pilocarpine-induced elevation of collapsin response mediator protein-2 (CRMP-2).

CONCLUSION

LCM protected against pilocarpine-induced SE, associated neurodegeneration and improved pilocarpine-associated impairment of spatial memory. The study reveals that CRMP-2 may not be mediating the inverted-U-response of LCM at least in pilocarpine model. Therefore, the anti-oxidant effect of LCM (and not its ability to modulate CRMP-2) was anticipated as the mechanism underlying neuroprotection.

Phase-amplitude coupling and epileptogenesis in an animal model of mesial temporal lobe epilepsy

Polyrhythmic coupling of oscillatory components in electrophysiological signals results from the interactions between neuronal sub-populations within and between cell assemblies. Since the mechanisms underlying epileptic disorders should affect such interactions, abnormal level of cross-frequency coupling is expected to provide a signal marker of epileptogenesis. We measured phase-amplitude coupling (PAC), a form of cross-frequency coupling between neural oscillations, in a rodent model of mesial temporal lobe epilepsy. Sprague-Dawley rats (n = 4, 250-300 g) were injected with pilocarpine (380 mg/kg, i.p) to induce a status epilepticus (SE) that was stopped after 1 h with diazepam (5 mg/kg, s.c.) and ketamine (50 mg/kg, s.c.). Control animals (n = 6) did not receive any injection or treatment. Three days after SE, all animals were implanted with bipolar electrodes in the hippocampal CA3 subfield, entorhinal cortex, dentate gyrus and subiculum. Continuous video/EEG recordings were performed 24/7 at a sampling rate of 2 kHz, over 15 consecutive days. Pilocarpine-treated animals showed interictal spikes (5.25 (±2.5) per minute) and seizures (n = 32) that appeared 7 (±0.8) days after SE. We found that CA3 was the seizure onset zone in most epileptic animals, with stronger ongoing PAC coupling between seizures than in controls (Kruskal-Wallis test: chi2 (1,36) = 46.3, Bonferroni corrected, p < 0.001). Strong PAC in CA3 occurred between the phase of slow-wave oscillations (<1 Hz) and the amplitude of faster rhythms (50-180 Hz), with the strongest bouts of high-frequency activity occurring preferentially on the ascending phase of the slow wave. We also identified that cross-frequency coupling in CA3 (rho = 0.44, p < 0.001) and subiculum (rho = 0.41, p < 0.001) was positively correlated with the daily number of seizures. Overall, our study demonstrates that cross-frequency coupling may represent a signal marker in epilepsy and suggests that this methodology could be transferred to clinical scalp MEG and EEG recordings.

Inhibition of sympathetic sprouting in CCD rats by lacosamide

BACKGROUND

Early hyperexcitability activity of injured nerve/neuron is critical for developing sympathetic nerve sprouting within dorsal root ganglia (DRG) since lacosamide (LCM), an anticonvulsant, inhibits Na⁺ channel. The present study tried to test the potential effect of LCM on inhibiting sympathetic sprouting in vivo.

METHODS

Lacosamide (50 mg/kg) was daily injected intraperitoneally into rats subjected to chronic compression DRG (CCD), an animal model of neuropathic pain that exhibits sympathetic nerve sprouting, for the 1st 7 days after injury. Mechanical sensitivity was tested from day 3 to day 18 after injury, and then DRGs were removed off. Immunohistochemical staining for tyrosine hydroxylase (TH) was examined to observe sympathetic sprouting, and patch-clamp recording was performed to test the excitability and Na⁺ current of DRG neurons.

RESULTS

Early systemic LCM treatment significantly reduced TH immunoreactivity density in injured DRG, lowered the excitability level of injured DRG neurons and increased paw withdrawal threshold. These effects on reducing sympathetic sprouting, inhibiting excitability and suppressing pain behaviour were observed 10 days after the end of early LCM injection. In vitro 100 μmol/L LCM instantly reduced the excitability of CCD neurons via inhibiting Na⁺ current and reducing the amplitude of AP.

CONCLUSIONS

All the findings suggest, for the first time, that early administration of LCM inhibited sympathetic sprouting and then alleviated neuropathic pain.

SIGNIFICANCE

Early LCM administration inhibited sympathetic sprouting within DRG in CCD rats via reducing hyperexcitability of neurons. Early LCM administration suppressed neuropathic pain in CCD rats.

Lacosamide and Levetiracetam Have No Effect on Sharp-Wave Ripple Rate

Pathological high-frequency oscillations are a novel marker used to improve the delineation of epileptogenic tissue and, hence, the outcome of epilepsy surgery. Their practical clinical utilization is curtailed by the inability to discriminate them from physiological oscillations due to frequency overlap. Although it is well documented that pathological HFOs are suppressed by antiepileptic drugs (AEDs), the effect of AEDs on normal HFOs is not well known. In this experimental study, we have explored whether physiological HFOs (sharp-wave ripples) of hippocampal origin respond to AED treatment. The results show that application of a single dose of levetiracetam or lacosamide does not reduce the rate of sharp-wave ripples. In addition, it seems that these new generation drugs do not negatively affect the cellular and network mechanisms involved in sharp-wave ripple generation, which may provide a plausible explanation for the absence of significant negative effects on cognitive functions of these drugs, particularly on memory.

Distribution of lacosamide in the rat brain assessed by in vitro slice technique

Lacosamide is a newer anticonvulsant and is the only one that enhances the slow inactivation of voltage gated sodium channels. It is also claimed to have disease-modifying potential, but its pharmacokinetic properties have been much less discussed in the literature. In rats, lacosamide shows restricted distribution to tissues, and the brain-to-plasma partition coefficient (K_p) is only 0.553. In this study, the brain disposition of lacosamide was evaluated in rat brains, and its neuropharmacokinetic parameters (i.e., protein binding and intracellular accumulation) were assessed using in vitro methods. Brain slice experiments and brain homogenate binding studies were performed for several drugs acting on the central nervous system, and drugs were assayed by using a liquid chromatography-mass spectrometry system. By applying a combined approach, it was found that (1) the unbound volume of distribution in the brain for lacosamide (V_u,brain = 1.37) was lower than that of other classical anticonvulsants; (2) the unbound fraction of lacosamide in the brain (0.899) was slightly lower than its unbound fraction in plasma (0.96); (3) the unbound intracellular-to-extracellular concentration ratio of lacosamide was 1.233, meaning that lacosamide was accumulated in the intracellular space because of its physicochemical properties and zwitterionic structure; and (4) the unbound brain-to-plasma concentration ratio of lacosamide was lower than the total brain-to-plasma concentration ratio (K_p,uu,brain = 0.42 vs. K_p = 0.553). In conclusion, the limited brain distribution of lacosamide is not related to its nonspecific protein-binding capacity; rather, an active transport mechanism across the blood-brain barrier may be involved, which reduces the anticonvulsant and/or antiepileptogenic actions of this drug.

Update on the mechanisms and roles of high-frequency oscillations in seizures and epileptic disorders

High-frequency oscillations (HFOs) are a type of brain activity that is recorded from brain regions capable of generating seizures. Because of the close association of HFOs with epileptogenic tissue and ictogenesis, understanding their cellular and network mechanisms could provide valuable information about the organization of epileptogenic networks and how seizures emerge from the abnormal activity of these networks. In this review, we summarize the most recent advances in the field of HFOs and provide a critical evaluation of new observations within the context of already established knowledge. Recent improvements in recording technology and the introduction of optogenetics into epilepsy research have intensified experimental work on HFOs. Using advanced computer models, new cellular substrates of epileptic HFOs were identified and the role of specific neuronal subtypes in HFO genesis was determined. Traditionally, the pathogenesis of HFOs was explored mainly in patients with temporal lobe epilepsy and in animal models mimicking this condition. HFOs have also been reported to occur in other epileptic disorders and models such as neocortical epilepsy, genetically determined epilepsies, and infantile spasms, which further support the significance of HFOs in the pathophysiology of epilepsy. It is increasingly recognized that HFOs are generated by multiple mechanisms at both the cellular and network levels. Future studies on HFOs combining novel high-resolution in vivo imaging techniques and precise control of neuronal behavior using optogenetics or chemogenetics will provide evidence about the causal role of HFOs in seizures and epileptogenesis. Detailed understanding of the pathophysiology of HFOs will propel better HFO classification and increase their information yield for clinical and diagnostic purposes.

High-frequency oscillations and mesial temporal lobe epilepsy

The interest of epileptologists has recently shifted from the macroscopic analysis of interictal spikes and seizures to the microscopic analysis of short events in the EEG that are not visible to the naked eye but are observed once the signal has been filtered in specific frequency bands. With the use of new technologies that allow multichannel recordings at high sampling rates and the development of computer algorithms that permit the automated analysis of extensive amounts of data, it is now possible to extract high-frequency oscillations (HFOs) between 80 and 500Hz from the EEG; HFOs have been further categorised as ripples (80-200Hz) and fast ripples (250-500Hz). Within the context of epileptic disorders, HFOs should reflect the pathological activity of neural networks that sustain seizure generation, and could serve as biomarkers of epileptogenesis and ictogenesis. We review here the presumptive cellular mechanisms of ripples and fast ripples in mesial temporal lobe epilepsy. We also focus on recent findings regarding the occurrence of HFOs during epileptiform activity observed in in vitro models of epileptiform synchronization, in in vivo models of mesial temporal lobe epilepsy and in epileptic patients. Finally, we address the effects of anti-epileptic drugs on HFOs and raise some questions and issues related to the definition of HFOs.

Anti-Epileptic Drug Combination Efficacy in an In Vitro Seizure Model - Phenytoin and Valproate, Lamotrigine and Valproate

In this study, we investigated the relative efficacy of different classes of commonly used anti-epileptic drugs (AEDs) with different mechanisms of action, individually and in combination, to suppress epileptiform discharges in an in vitro model. Extracellular field potential were recorded in 450 μm thick transverse hippocampal slices prepared from juvenile Wistar rats, in which “epileptiform discharges” (ED’s) were produced with a high-K⁺ (8.5 mM) bicarbonate-buffered saline solution. Single and dual recordings in stratum pyramidale of CA1 and CA3 regions were performed with 3–5 MΩ glass microelectrodes. All drugs—lamotrigine (LTG), phenytoin (PHT) and valproate (VPA)—were applied to the slice by superfusion at a rate of 2 ml/min at 32°C. Effects upon frequency of ED’s were assessed for LTG, PHT and VPA applied at different concentrations, in isolation and in combination. We demonstrated that high-K⁺ induced ED frequency was reversibly reduced by LTG, PHT and VPA, at concentrations corresponding to human therapeutic blood plasma concentrations. With a protocol using several applications of drugs to the same slice, PHT and VPA in combination displayed additivity of effect with 50μM PHT and 350μM VPA reducing SLD frequency by 44% and 24% individually (n = 19), and together reducing SLD frequency by 66% (n = 19). 20μM LTG reduced SLD frequency by 32% and 350μM VPA by 16% (n = 18). However, in combination there was a supra-linear suppression of ED’s of 64% (n = 18). In another independent set of experiments, similar results of drug combination responses were also found. In conclusion, a combination of conventional AEDs with different mechanisms of action, PHT and VPA, displayed linear additivity of effect on epileptiform activity. More intriguingly, a combination of LTG and VPA considered particularly efficacious clinically showed a supra-additive suppression of ED’s. This approach may be useful as an in vitro platform for assessing drug combination efficacy.