Picrotoxin-induced generalised convulsive seizure in rat: changes in regional distribution and frequency of the power of electroencephalogram rhythms

An integrated approach for early in vitro seizure prediction utilizing hiPSC neurons and human ion channel assays

Seizure liability remains a significant cause of attrition throughout drug development. Advances in stem cell biology coupled with an increased understanding of the role of ion channels in seizure offer an opportunity for a new paradigm in screening. We assessed the activity of 15 pro-seizurogenic compounds (7 CNS active therapies, 4 GABA receptor antagonists, and 4 other reported seizurogenic compounds) using automated electrophysiology against a panel of 14 ion channels (Nav1.1, Nav1.2, Nav1.6, Kv7.2/7.3, Kv7.3/7.5, Kv1.1, Kv4.2, KCa4.1, Kv2.1, Kv3.1, KCa1.1, GABA α1β2γ2, nicotinic α4β2, NMDA 1/2A). These were selected based on linkage to seizure in genetic/pharmacological studies. Fourteen compounds demonstrated at least one "hit" against the seizure panel and 11 compounds inhibited 2 or more ion channels. Next, we assessed the impact of the 15 compounds on electrical signaling using human-induced pluripotent stem cell neurons in microelectrode array (MEA). The CNS active therapies (amoxapine, bupropion, chlorpromazine, clozapine, diphenhydramine, paroxetine, quetiapine) all caused characteristic changes to electrical activity in key parameters indicative of seizure such as network burst frequency and duration. The GABA antagonist picrotoxin increased all parameters, but the antibiotics amoxicillin and enoxacin only showed minimal changes. Acetaminophen, included as a negative control, caused no changes in any of the parameters assessed. Overall, pro-seizurogenic compounds showed a distinct fingerprint in the ion channel/MEA panel. These studies highlight the potential utility of an integrated in vitro approach for early seizure prediction to provide mechanistic information and to support optimal drug design in early development, saving time and resources.

Electric Field Effects on Brain Activity: Implications for Epilepsy and Burst Suppression

Electric fields are now considered a major mechanism of epileptiform activity. However, it is not clear if another electrophysiological phenomenon, burst suppression, utilizes the same mechanism for its bursting phase. Thus, the purpose of this study was to compare the role of ephaptic coupling-the recruitment of neighboring cells via electric fields-in generating bursts in epilepsy and burst suppression. We used local injections of the GABA-antagonist picrotoxin to elicit epileptic activity and a general anesthetic, sevoflurane, to elicit burst suppression in rabbits. Then, we applied an established computational model of pyramidal cells to simulate neuronal activity in a 3-dimensional grid, with an additional parameter to trigger a suppression phase based on extra-cellular calcium dynamics. We discovered that coupling via electric fields was sufficient to produce bursting in scenarios where inhibitory control of excitatory neurons was sufficiently low. Under anesthesia conditions, bursting occurs with lower neuronal recruitment in comparison to seizures. Our model predicts that due to the effect of electric fields, the magnitude of bursts during seizures should be roughly 2-3 times the magnitude of bursts that occur during burst suppression, which is consistent with our in vivo experimental results. The resulting difference in magnitude between bursts during anesthesia and epileptiform bursts reflects the strength of the electric field effect, which suggests that burst suppression and epilepsy share the same ephaptic coupling mechanism.

Assessing seizure liability in vitro with voltage-sensitive dye imaging in mouse hippocampal slices

Non-clinical toxicology is a major cause of drug candidate attrition during development. In particular, drug-induced seizures are the most common finding in central nervous system (CNS) toxicity. Current safety pharmacology tests for assessing CNS functions are often inadequate in detecting seizure-inducing compounds early in drug development, leading to significant delays. This paper presents an in vitro seizure liability assay using voltage-sensitive dye (VSD) imaging techniques in hippocampal brain slices, offering a powerful alternative to traditional electrophysiological methods. Hippocampal slices were isolated from mice, and VSD optical responses evoked by stimulating the Schaffer collateral pathway were recorded and analyzed in the stratum radiatum (SR) and stratum pyramidale (SP). VSDs allow for the comprehensive visualization of neuronal action potentials and postsynaptic potentials on a millisecond timescale. By employing this approach, we investigated the in vitro drug-induced seizure liability of representative pro-convulsant compounds. Picrotoxin (PiTX; 1-100 μM), gabazine (GZ; 0.1-10 μM), and 4-aminopyridine (4AP; 10-100 μM) exhibited seizure-like responses in the hippocampus, but pilocarpine hydrochloride (Pilo; 10-100 μM) did not. Our findings demonstrate the potential of VSD-based assays in identifying seizurogenic compounds during early drug discovery, thereby reducing delays in drug development and providing insights into the mechanisms underlying seizure induction and the associated risks of pro-convulsant compounds.

Differential Electrographic Signatures Generated by Mechanistically-Diverse Seizurogenic Compounds in the Larval Zebrafish Brain

We assessed similarities and differences in the electrographic signatures of local field potentials (LFPs) evoked by different pharmacological agents in zebrafish larvae. We then compared and contrasted these characteristics with what is known from electrophysiological studies of seizures and epilepsy in mammals, including humans. Ultimately, our aim was to phenotype neurophysiological features of drug-induced seizures in larval zebrafish for expanding knowledge on the translational potential of this valuable alternative to mammalian models. LFPs were recorded from the midbrain of 4-d-old zebrafish larvae exposed to a pharmacologically diverse panel of seizurogenic compounds, and the outputs of these recordings were assessed using frequency domain analysis. This included analysis of changes occurring within various spectral frequency bands of relevance to mammalian CNS circuit pathophysiology. From these analyses, there were clear differences in the frequency spectra of drug-exposed LFPs, relative to controls, many of which shared notable similarities with the signatures exhibited by mammalian CNS circuits. These similarities included the presence of specific frequency components comparable to those observed in mammalian studies of seizures and epilepsy. Collectively, the data presented provide important information to support the value of larval zebrafish as an alternative model for the study of seizures and epilepsy. These data also provide further insight into the electrophysiological characteristics of seizures generated in nonmammalian species by the action of neuroactive drugs.

Novel test strategies for in vitro seizure liability assessment

INTRODUCTION

The increasing incidence of mental illnesses and neurodegenerative diseases results in a high demand for drugs targeting the central nervous system (CNS). These drugs easily reach the CNS, have a high affinity for CNS targets, and are prone to cause seizures as an adverse drug reaction. Current seizure liability assessment heavily depends on in vivo or ex vivo animal models and is therefore ethically debated, labor intensive, expensive, and not always predictive for human risk.

AREAS COVERED

The demand for CNS drugs urges the development of alternative safety assessment strategies. Yet, the complexity of the CNS hampers reliable detection of compound-induced seizures. This review provides an overview of the requirements of in vitro seizure liability assays and highlights recent advances, including micro-electrode array (MEA) recordings using rodent and human cell models.

EXPERT OPINION

Successful and cost-effective replacement of in vivo and ex vivo models for seizure liability screening can reduce animal use for drug development, while increasing the predictive value of the assays, particularly if human cell models are used. However, these novel test strategies require further validation and standardization as well as additional refinements to better mimic the human in vivo situation and increase their predictive value.

Electrophysiological and neurochemical evaluation of the adverse effects of REM sleep deprivation and epileptic seizures on rat's brain

AIM

The current study aims to investigate the impact of paradoxical (REM) sleep deprivation and/or epileptic seizures on rat's cortical brain tissues.

MAIN METHODS

Animals were divided into four groups; control, epileptic, REM sleep deprived and epileptic subjected to REM sleep deprivation. Electrocorticogram (ECoG) signals were recorded and quantitatively analyzed for each group. Concentrations of amino acid neurotransmitters; proinflammatory cytokines; and oxidative stress parameters; and acetylcholinesterase activity were determined in the cortex of the animals in different groups.

KEY FINDINGS

Results showed significant variations in the spectral distribution of ECoG waves in the epilepsy model, 24- and 48-hours of REM sleep deprivation and their combined effects indicating a state of cortical hyperexcitability. Significant increases in NO and taurine and significant decrement in glutamine, GABA and glycine were determined. In REM sleep deprived rats significant elevation in glutamate, aspartate, glycine and taurine and a significant lowering in GABA were obtained. This was accompanied by significant reduction in AchE and IL-β. In the cortical tissue of epileptic rats deprived from REM sleep significant increases in lipid peroxidation, TNF-α, IL-1β, IL-6 and aspartate and a significant reduction in AchE were observed.

SIGNIFICANCE

The present data indicate that REM sleep deprivation induces an increase in lipid peroxidation and storming in proinflammatory cytokines in the cortex of rat model of epilepsy during SRS. These changes are associated with a decreased seizure threshold as inferred from the increase in alpha and Beta waves and a decrease in Delta waves of ECoG.

Applicability of hiPSC-Derived Neuronal Cocultures and Rodent Primary Cortical Cultures for In Vitro Seizure Liability Assessment

Seizures are life-threatening adverse drug reactions which are investigated late in drug development using rodent models. Consequently, if seizures are detected, a lot of time, money and animals have been used. Thus, there is a need for in vitro screening models using human cells to circumvent interspecies translation. We assessed the suitability of cocultures of human-induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared with rodent primary cortical cultures for in vitro seizure liability assessment using microelectrode arrays. hiPSC-derived and rodent primary cortical neuronal cocultures were exposed to 9 known (non)seizurogenic compounds (pentylenetetrazole, amoxapine, enoxacin, amoxicillin, linopirdine, pilocarpine, chlorpromazine, phenytoin, and acetaminophen) to assess effects on neuronal network activity using microelectrode array recordings. All compounds affect activity in hiPSC-derived cocultures. In rodent primary cultures all compounds, except amoxicillin changed activity. Changes in activity patterns for both cell models differ for different classes of compounds. Both models had a comparable sensitivity for exposure to amoxapine (lowest observed effect concentration [LOEC] 0.03 µM), linopirdine (LOEC 1 µM), and pilocarpine (LOEC 0.3 µM). However, hiPSC-derived cultures were about 3 times more sensitive for exposure to pentylenetetrazole (LOEC 30 µM) than rodent primary cortical cultures (LOEC 100 µM). Sensitivity of hiPSC-derived cultures for chlorpromazine, phenytoin, and enoxacin was 10-30 times higher (LOECs 0.1, 0.3, and 0.1 µM, respectively) than in rodent cultures (LOECs 10, 3, and 3 µM, respectively). Our data indicate that hiPSC-derived neuronal cocultures may outperform rodent primary cortical cultures with respect to detecting seizures, thereby paving the way towards animal-free seizure assessment.

Synthesis and Evaluation of Anticonvulsant Activity of Some Schiff Bases of 7-Amino-1,3-dihydro-2H-1,4-benzodiazepin-2-one

A variety of 1,3-dihydro-2H-1,4-benzodiazepin-2-one azomethines and 1,3-dihydro-2H-1,4-benzodiazepin-2-one benzamide were prepared, characterized and evaluated for the anticonvulsant activity in the rat using picrotoxin-induced seizure model. The prepared 1,3-dihydro-2H-1,4-benzodiazepin-2-one azomethine derivatives emerged potentially anticonvulsant molecular scaffolds exemplified by compounds, 7-{(E)-[(4-nitrophenyl)methylidene]amino}-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one, 7-[(E)-{[4-(dimethylamino)phenyl]methylidene}amino]-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one, 7-{(E)-[(4-bromo-2,6-difluorophenyl)methylidene]amino}-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one and 7-[(E)-{[3-(4-fluorophenyl)-1-phenyl-1H-pyrazol-4-yl]methylidene}amino]-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one. All these four compounds have shown substantial decrease in the wet dog shake numbers and grade of convulsions with respect to the standard drug diazepam. The most active compound, 7-[(E)-{[4-(dimethylamino)phenyl]methylidene}amino]-5-phenyl-1,3-dihydro-2H-1,4-benzodiazepin-2-one, exhibited 74 % protection against convulsion which was higher than the standard drug diazepam. Furthermore, to identify the binding mode of the interaction amongst the target analogs and binding site of the benzodiazepine receptor, molecular docking study and molecular dynamic simulation were carried out. Additionally, in silico pharmacokinetic and toxicity predictions of target compounds were carried out using AdmetSAR tool. Results of ADMET studies suggest that the pharmacokinetic parameters of all the target compounds were within the acceptable range to become a potential drug candidate as antiepileptic agents.

Lateralization of epilepsy using intra-hemispheric brain networks based on resting-state MEG data

Focal epilepsy originates within networks in one hemisphere. However, previous studies have investigated network topologies for the entire brain. In this study, magnetoencephalography (MEG) was used to investigate functional intra‐hemispheric networks of healthy controls (HCs) and patients with left‐ or right‐hemispheric temporal lobe or temporal plus extra‐temporal lobe epilepsy. 22 HCs, 25 left patients (LPs), and 16 right patients (RPs) were enrolled. The debiased weighted phase lag index was used to calculate functional connectivity between 246 brain regions in six frequency bands. Global efficiency, characteristic path length, and transitivity were computed for left and right intra‐hemispheric networks. The right global graph measures (GGMs) in the theta band were significantly different (p < .005) between RPs and both LPs and HCs. Right and left GGMs in higher frequency bands were significantly different (p < .05) between HCs and the patients. Right GGMs were used as input features of a Naïve‐Bayes classifier to classify LPs and RPs (78.0% accuracy) and all three groups (75.5% accuracy). The complete theta band brain networks were compared between LPs and RPs with network‐based statistics (NBS) and with the clustering coefficient (CC), nodal efficiency (NE), betweenness centrality (BC), and eigenvector centrality (EVC). NBS identified a subnetwork primarily composed of right intra‐hemispheric connections. Significantly different (p < .05) nodes were primarily in the right hemisphere for the CC and NE and primarily in the left hemisphere for the BC and EVC. These results indicate that intra‐hemispheric MEG networks may be incorporated in the diagnosis and lateralization of focal epilepsy.

The Immediate Effects of Vagus Nerve Stimulation in Intractable Epilepsy: An Intra-operative Electrocorticographic Analysis

The purpose of this study was to investigate whether and how vagus nerve stimulation (VNS) reduces the epileptogenic activity in the bilateral cerebral cortex in patients with intractable epilepsy. We analyzed the electrocorticograms (ECoGs) of five patients who underwent callosotomy due to intractable epilepsy even after VNS implantation. We recorded ECoGs and analyzed power spectrum in both VNS OFF and ON phases. We counted the number of spikes and electrodes with epileptic spikes, distinguishing unilaterally and bilaterally hemispherically spread spikes as synchronousness of the epileptic spikes in both VNS OFF and ON phases. There were 24.80 ± 35.55 and 7.20 ± 9.93 unilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.157), and 35.8 ± 29.21 and 10.6 ± 13.50 bilaterally spread spikes in the VNS OFF and ON phases, respectively (P = 0.027). The number of electrodes with unilaterally and bilaterally spread spikes in the VNS OFF and ON phases was 3.84 ± 2.13 and 3.59 ± 1.82 (P = 0.415), and 8.20 ± 3.56 and 6.89 ± 2.89 (P = 0.026), respectively. The ECoG background power spectra recordings in the VNS OFF and ON phases were also analyzed. The spectral power tended to be greater in the high-frequency band at VNS ON phase than OFF phase. This study showed the reduction of epileptogenic spikes and spread areas of the spikes by VNS as immediate effects, electrophysiologically.

Oscillotherapeutics - Time-targeted interventions in epilepsy and beyond

Oscillatory brain activities support many physiological functions from motor control to cognition. Disruptions of the normal oscillatory brain activities are commonly observed in neurological and psychiatric disorders including epilepsy, Parkinson's disease, Alzheimer's disease, schizophrenia, anxiety/trauma-related disorders, major depressive disorders, and drug addiction. Therefore, these disorders can be considered as common oscillation defects despite having distinct behavioral manifestations and genetic causes. Recent technical advances of neuronal activity recording and analysis have allowed us to study the pathological oscillations of each disorder as a possible biomarker of symptoms. Furthermore, recent advances in brain stimulation technologies enable time- and space-targeted interventions of the pathological oscillations of both neurological disorders and psychiatric disorders as possible targets for regulating their symptoms.

Perampanel, an antagonist of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors, for the treatment of epilepsy: studies in human epileptic brain and nonepileptic brain and in rodent models

Perampanel [Fycompa, 2-(2-oxo-1-phenyl-5-pyridin-2-yl-1,2-dihydropyridin-3-yl)benzonitrile hydrate 4:3; Eisai Inc., Woodcliff Lake, NJ] is an AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) receptor antagonist used as an adjunctive treatment of partial-onset seizures. We asked whether perampanel has AMPA receptor antagonist activity in both the cerebral cortex and hippocampus associated with antiepileptic efficacy and also in the cerebellum associated with motor side effects in rodent and human brains. We also asked whether epileptic or nonepileptic human cortex is similarly responsive to AMPA receptor antagonism by perampanel. In rodent models, perampanel decreased epileptic-like activity in multiple seizure models. However, doses of perampanel that had anticonvulsant effects were within the same range as those engendering motor side effects. Perampanel inhibited native rat and human AMPA receptors from the hippocampus as well as the cerebellum that were reconstituted into Xenopus oocytes. In addition, with the same technique, we found that perampanel inhibited AMPA receptors from hippocampal tissue that had been removed from a patient who underwent surgical resection for refractory epilepsy. Perampanel inhibited AMPA receptor-mediated ion currents from all the tissues investigated with similar potency (IC50 values ranging from 2.6 to 7.0 μM). Cortical slices from the left temporal lobe derived from the same patient were studied in a 60-microelectrode array. Large field potentials were evoked on at least 45 channels of the array, and 10 μM perampanel decreased their amplitude and firing rate. Perampanel also produced a 33% reduction in the branching parameter, demonstrating the effects of perampanel at the network level. These data suggest that perampanel blocks AMPA receptors globally across the brain to account for both its antiepileptic and side-effect profile in rodents and epileptic patients.

Long-term fish oil supplementation attenuates seizure activity in the amygdala induced by 3-mercaptopropionic acid in adult male rats

Several studies have provided evidence of significant effects of omega-3 fatty acids on brain functionality, including seizures and disorders such as epilepsy. Fish oil (FO) is a marine product rich in unsaturated omega-3 fatty acids. Considering that the amygdala is one of the brain structures most sensitive to seizure generation, we aimed to evaluate the effect of long-term chronic FO supplementation (from embryonic conception to adulthood) on the severity of seizures and amygdaloid electroencephalographic activity (EEG) in a 3-mercaptopropionic acid (3-MPA)-induced seizure model using adult rats. Female Wistar rats were fed a commercial diet supplemented daily with FO (300mg/kg) from puberty through mating, gestation, delivery, and weaning of the pups. Only the male pups were then fed daily with a commercial diet supplemented with the same treatment as the dam up to the age of 150days postpartum, when they were bilaterally implanted in the amygdala to record behavior and EEG activity before, during, and after seizures induced by administering 3-MPA. Results were compared with those obtained from rats supplemented with palm oil (PO) and rats treated with a vehicle (CTRL). The male rats treated with FO showed longer latency to seizure onset, fewer convulsive episodes, and attenuated severity compared those in the PO and CTRL groups according to the Racine scale. Moreover, long-term FO supplementation was associated with a reduction of the absolute power (AP) of the fast frequencies (12-25Hz) in the amygdala during the seizure periods. These findings support the idea that chronic supplementation with omega-3 of marine origin may have antiseizure properties as other studies have suggested.

Epilepsy in patients with a brain tumour: focal epilepsy requires focused treatment

Brain tumours frequently cause epileptic seizures. Medical antiepileptic treatment is often met with limited success. Pharmacoresistance, drug interactions and adverse events are common problems during treatment with antiepileptic drugs. The unpredictability of epileptic seizures and the treatment-related problems deeply affect the quality of life of patients with a brain tumour. In this review, we focus on both clinical and basic aspects of possible mechanisms in epileptogenesis in patients with a brain tumour. We provide an overview of the factors that are involved in epileptogenesis, starting focally at the tumour and the peritumoral tissue and eventually extending to alterations in functional connectivity throughout the brain. We correlate this knowledge to the known mechanisms of antiepileptic drugs. We conclude that the underlying mechanisms of epileptogenesis in patients with a brain tumour are poorly understood. The currently available antiepileptic drugs have little to no influence on the known epileptogenic mechanisms that could contribute to the poor efficacy. Better understanding of focal changes that are involved in epileptogenesis may provide new tools for optimal treatment of both the seizures and the underlying tumour. In our opinion, therapy for every patient with a brain tumour suffering from epilepsy should first and foremost aim at eliminating the tumour as well as the epileptic focus through resection combined with postoperative treatment, and only if this strategy does not result in adequate seizure control should medical antiepileptic treatment be intensified. If this strategy, however, results in sustained seizure freedom, tapering of antiepileptic drugs should be considered in the long term.

Epilepsy is related to theta band brain connectivity and network topology in brain tumor patients

Background

Both epilepsy patients and brain tumor patients show altered functional connectivity and less optimal brain network topology when compared to healthy controls, particularly in the theta band. Furthermore, the duration and characteristics of epilepsy may also influence functional interactions in brain networks. However, the specific features of connectivity and networks in tumor-related epilepsy have not been investigated yet. We hypothesize that epilepsy characteristics are related to (theta band) connectivity and network architecture in operated glioma patients suffering from epileptic seizures. Included patients participated in a clinical study investigating the effect of levetiracetam monotherapy on seizure frequency in glioma patients, and were assessed at two time points: directly after neurosurgery (t1), and six months later (t2). At these time points, magnetoencephalography (MEG) was recorded and information regarding clinical status and epilepsy history was collected. Functional connectivity was calculated in six frequency bands, as were a number of network measures such as normalized clustering coefficient and path length.

Results

At the two time points, MEG registrations were performed in respectively 17 and 12 patients. No changes in connectivity or network topology occurred over time. Increased theta band connectivity at t1 and t2 was related to a higher total number of seizures. Furthermore, higher number of seizures was related to a less optimal, more random brain network topology. Other factors were not significantly related to functional connectivity or network topology.

Conclusions

These results indicate that (pathologically) increased theta band connectivity is related to a higher number of epileptic seizures in brain tumor patients, suggesting that theta band connectivity changes are a hallmark of tumor-related epilepsy. Furthermore, a more random brain network topology is related to greater vulnerability to seizures. Thus, functional connectivity and brain network architecture may prove to be important parameters of tumor-related epilepsy.

GABA transporter-1 activity modulates hippocampal theta oscillation and theta burst stimulation-induced long-term potentiation

The network oscillation and synaptic plasticity are known to be regulated by GABAergic inhibition, but how they are affected by changes in the GABA transporter activity remains unclear. Here we show that in the CA1 region of mouse hippocampus, pharmacological blockade or genetic deletion of GABA transporter-1 (GAT1) specifically impaired long-term potentiation (LTP) induced by theta burst stimulation, but had no effect on LTP induced by high-frequency stimulation or long-term depression induced by low-frequency stimulation. The extent of LTP impairment depended on the precise burst frequency, with significant impairment at 3-7 Hz that correlated with the time course of elevated GABAergic inhibition caused by GAT1 disruption. Furthermore, in vivo electrophysiological recordings showed that GAT1 gene deletion reduced the frequency of hippocampal theta oscillation. Moreover, behavioral studies showed that GAT1 knock-out mice also exhibited impaired hippocampus-dependent learning and memory. Together, these results have highlighted the important link between GABAergic inhibition and hippocampal theta oscillation, both of which are critical for synaptic plasticity and learning behaviors.

Allopregnanolone, the active metabolite of progesterone protects against neuronal damage in picrotoxin-induced seizure model in mice

Progesterone exerts anti-seizure effect against several chemoconvulsants. However, there is no published report on the interaction between progesterone and picrotoxin (PTX). The present study evaluated the effects of progesterone and its active metabolite, allopregnanolone against PTX-induced seizures, brain lipid peroxidation and DNA fragmentation in male mice. Finasteride, a 5alpha-reductase inhibitor and indomethacin, an inhibitor of 3infinity-hydroxysteroid dehydrogenase were assessed against progesterone's effects on PTX-induced seizures, brain lipid peroxidation and DNA fragmentation. PTX produced clonic-tonic seizures in mice with CD50 and CD97 of 2.4 and 4.0mg/kg, i.p. respectively. Progesterone significantly countered PTX-induced seizures, with ED50 of 78.30mg/kg and ED97 of 200mg/kg. Progesterone antagonized PTX-induced DNA fragmentation. Finasteride (200mg/kg) and indomethacin (1mg/kg) reversed the anti-seizure and anti-DNA fragmentation effects of progesterone. Allopregnanolone, also protected against PTX-induced seizures and DNA fragmentation. There was no significant change in the brain lipid peroxidation parameters in any of the treatment groups. It may be concluded that progesterone protects against PTX-induced seizures and DNA fragmentation through its active metabolites allopregnanolone and 5alpha-pregnan-3,20-dione. However, it appears from the present study that, the neuroprotection with progesterone is primarily on account of allopregnalone. The therapeutic potential of allopregnanolone deserves to be evaluated clinically.

Cell swelling precedes seizures induced by inhibition of astrocytic metabolism

It is currently unknown what processes take place at the interface between non-ictal and ictal activity during seizure initiation. In this study, using paralysed awake rats, we focally inhibited astrocytic metabolism with fluorocitrate (FC), causing seizures. We measured changes in electroencephalogram (EEG) (0-300 Hz), and extracellular ion-concentrations during ictal onsets defining possible relationships with impedance-determined cell swelling. In animals showing ictal activity (69%) there were spike-wave discharges, spike-wave discharges followed by spreading depression and spreading depression without any discharges. In a high proportion of spike-wave discharges (>95%), just prior to the first spike-wave discharge, there was a decrease in the volume of the extracellular space. Following the initiation of cell swelling and prior to discharges, there were increases in high-frequency (150-300 Hz) EEG activity, increases in extracellular potassium- and decreases in extracellular calcium-concentrations. We suggest that EEG and ionic changes are not causative of cell swelling. Cell swelling due to metabolic failure in astrocytes at the injected site may release excitatory amino acids. At the same time, our results suggest ion homeostasis is not maintained and increased neuronal excitability and synchronisation occur. These could be the drivers changing normal brain activity into ictal activity.

Loss of phase synchrony in an animal model of partial status epilepticus

Interrupting a focal, chronic infusion of GABA to the rat motor cortex initiates the progressive emergence of a sustained spiking electroencephalographic (EEG) activity, associated with myoclonic jerks of the corresponding body territory. This activity is maintained over several hours, has an average frequency of 1.5 Hz, is localized to the infusion site and never generalizes. The GABA withdrawal syndrome (GWS) has therefore features of partial status epilepticus. Changes in EEG signals associated with the GWS were studied in freely moving rats by measuring the phase synchrony between bilateral epidural records from the neocortex. Our results showed (i) epileptic activity was associated with a striking decrease in phase synchrony between all pairs of electrodes including the focus, predominantly in the 1-6 Hz frequency range. There was a mean decrease of 75.34+/-5.26% in phase synchrony levels between the period before GABA interruption and the period after epileptic activity appeared. (ii) This reduction in synchrony contrasted with an increase of power spectral density in the corresponding EEG channels over the same 1-6 Hz frequency range, (iii) neither changes in synchrony nor in nonlinear dynamics were detected before the first EEG spikes, (iv) systemic injection of ketamine, an antagonist of N-methyl-d-aspartic acid (NMDA) receptors, modified transiently both epileptic activity and the synchrony profile. (v) Spiking activity and synchrony changes were suppressed by reperfusion of GABA. Our data suggest that, during a partial status epilepticus, interactions between the epileptic focus and connected neocortical neuronal populations are dramatically decreased in low frequencies.

The role of 5-HT7 receptors in the control of seizures

Serotonin exerts its effects via at least 14 different receptor subtypes, but the role of only a few of them has been studied in relation to the control of seizures. A negative role of 5-HT(7) receptors has recently been proposed. To evaluate further in unstressed and stressed animals the possible role of this receptor subtype in the control of brain excitability, we treated mice with antagonists and agonists of these receptors prior to exposure to swim stress and the intravenous infusion of picrotoxin, a non-competitive GABA(A) receptor antagonist. In accordance with the previous studies, swim stress increased the doses of picrotoxin producing two convulsant signs (running/bouncing clonus, tonic hindlimb extension) and death, i.e., swim stress increased the seizure threshold for picrotoxin. SB-269970 (10-30 mg/kg ip), a selective antagonist of 5-HT(7) receptors, and ritanserin (1 mg/kg ip), a nonselective 5-HT (2/7) antagonist, failed to affect, while 5-carboxamidotryptamine (5-CT), a potent 5-HT (1/7) receptor agonist, increased in unstressed and swim-stressed mice the doses of picrotoxin producing convulsions and death. The anticonvulsant effect obtained with 5-CT 0.5 mg/kg was not greater than that obtained with 0.1 mg/kg. The 5-CT (0.1 mg/kg ip)-induced increase of the seizure threshold for picrotoxin in stressed mice was abolished with SB-269970 (10 mg/kg), but not with WAY-100635 (0.3 mg/kg), a selective antagonist of 5-HT(1A) receptors, suggesting that the anticonvulsant effect of 5-CT against convulsions produced by picrotoxin was achieved via 5-HT(7) receptors. The results suggest a positive role of 5-HT(7) receptors in the control of seizures.

Zimelidine decreases seizure susceptibility in stressed mice

To further evaluate whether selective serotonin reuptake inhibitors (SSRIs) have pro- or anticonvulsant properties and whether these properties will be modified by stress, we studied the effect of zimelidine on the convulsions produced by picrotoxin, a GABA(A) receptor antagonist, in unstressed and swim stressed mice. Zimelidine potentiated the ability of swim stress to enhance the threshold doses of intravenously administered picrotoxin producing convulsant signs and death, without having an effect in unstressed mice. The anticonvulsant effect of zimelidine was counteracted with mianserin, the antagonist of 5-HT(2A/2C), and diminished with WAY-100635, a selective antagonist of 5-HT(1A) receptors. In stressed mice, WAY-100635 prevented the anticonvulsant effect of 8-OH-DPAT, a 5-HT(1A) receptor agonist. SB-269970 and ketanserin, the antagonists of 5-HT(7) and 5-HT(2A) receptors, respectively, failed to reduce the effect of zimelidine. The results suggest the involvement of 5-HT(2C) and 5-HT(1A) receptors in the anticonvulsant effects of zimelidine and possibly other SSRIs in stress.

Stimulation of 5-HT 1A receptors increases the seizure threshold for picrotoxin in mice

To evaluate the possible role of 5-HT 1A and 5-HT 2A receptors in the anticonvulsant effect of swim stress, mice were pre-treated with agonists and antagonists of these receptors prior to exposure to stress and the intravenous infusion of picrotoxin. 8-OH-DPAT ((+/-)-8-hydroxy-2-(di-n-propylamino) tetralin) and WAY-100635 (a selective agonist and antagonist of 5-HT 1A receptors), DOI (1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) and ketanserin (a 5-HT 2A/2C receptor agonist and antagonist) were used. Results demonstrated that 1 and 3 mg/kg of 8-OH-DPAT increased the doses of picrotoxin producing running/bouncing clonus, tonic hindlimb extension and death in stressed and unstressed mice, respectively. Pre-treatment with WAY (0.3 mg/kg) prevented the effect of 8-OH-DPAT (3 mg/kg). DOI (2.5 mg/kg) and ketanserin (1 mg/kg) failed to affect the seizure threshold for picrotoxin. The results show that stimulation of 5-HT 1A receptors exerts anticonvulsant actions in stressed and unstressed mice, while stimulation of 5-HT 2A/2C receptors does not interfere with the effect of stress on picrotoxin-induced convulsions.

Increase in 20–50Hz (gamma frequencies) power spectrum and synchronization after chronic vagal nerve stimulation

OBJECTIVE

Though vagus nerve stimulation (VNS) is an important option in pharmaco-resistant epilepsy, its mechanism of action remains unclear. The observation that VNS desynchronised the EEG activity in animals suggested that this mechanism could be involved in VNS antiepileptic effects in humans. Indeed VNS decreases spiking bursts, whereas its effects on the EEG background remain uncertain. The objective of the present study is to investigate how VNS affects local and inter regional syncronization in different frequencies in pharmaco-resistant partial epilepsy.

METHODS

Digital recordings acquired in 11 epileptic subjects 1 year and 1 week before VNS surgery were compared with that obtained 1 month and 1 year after VNS activation. Power spectrum and synchronization were then analyzed and compared with an epileptic group of 10 patients treated with AEDs only.

RESULTS

VNS decreases the synchronization of theta frequencies (P < 0.01), whereas it increases gamma power spectrum and synchronization (< 0.001 and 0.01, respectively).

CONCLUSIONS

The reduction of theta frequencies and the increase in power spectrum and synchronization of gamma bands can be related to VNS anticonvulsant mechanism. In addition, gamma modulation could also play a seizure-independent role in improving attentional performances.

SIGNIFICANCE

These results suggest that some antiepileptic mechanisms affected by VNS can be modulated by or be the reflection of EEG changes.

Anticonvulsant effects of acute and repeated fluoxetine treatment in unstressed and stressed mice

Comorbidity of epilepsy and depression is not rare. Stress can affect both depression and seizures. Therefore, it is important to know whether an antidepressant drug has pro- or anticonvulsant properties and whether these properties will be modified by stress. We tested the effects of the antidepressant drug fluoxetine on the seizure threshold for picrotoxin in unstressed and swim-stressed mice. The mice were, prior to exposure to swim stress and the intravenous infusion of picrotoxin (a non-competitive GABA(A) receptor antagonist), pretreated with fluoxetine (a selective serotonin reuptake inhibitor), either acutely or repeatedly (5 days), and the latency to the onset of two convulsant signs and death was registered. The convulsant signs were running/bouncing clonus and tonic hindlimb extension. As expected, swim stress enhanced the seizure threshold for picrotoxin. Fluoxetine (20 mg/kg ip) given acutely increased in unstressed and swim-stressed mice the dose of picrotoxin producing tonic hindlimb extension and in unstressed mice the dose of picrotoxin producing death. Neither 10 nor 20 mg/kg of fluoxetine affected doses of picrotoxin needed to produce running bouncing/clonus. Repeated treatment with fluoxetine (20 mg/kg ip) enhanced significantly in unstressed and swim-stressed mice doses of picrotoxin needed to produce tonic hindlimb extension and death, and in stressed mice also the dose of picrotoxin producing running/bouncing clonus. The results demonstrate that the antidepressant drug fluoxetine, given acutely or repeatedly, shows anticonvulsant properties against convulsions induced in unstressed and swim-stressed mice by antagonist of GABA(A) receptors, picrotoxin. Swim stress failed to modify the anticonvulsant properties of fluoxetine.

Gamma rhythms are not integral to EEG spindle phenomena

OBJECTIVE

Gamma rhythms (30-100 Hz) have been shown to be associated with spindling activity induced by picrotoxin. To determine if gamma power is unique to picrotoxin spindles or is an integral part of physiological and pathological spindling activity we analysed and compared the strength and brain distribution of gamma EEG power during 4 spindling activities in the rat.

METHODS

The electroencephalogram (EEG) was recorded from rats with chronically implanted electrodes during natural sleep, barbiturate anaesthesia, during naturally occurring absence epilepsy spike and wave discharges and following the systemic application of picrotoxin. Spectral analysis was applied off-line to compare the strength and brain distribution of gamma EEG power during the 4 spindling activities.

RESULTS

Each spindle type contained significantly different levels of gamma power. Gamma power was significantly increased over background levels during picrotoxin spindles, slightly increased during absence spindles, slightly decreased during sleep spindles and significantly suppressed during barbiturate spindles

CONCLUSIONS

Changes in the power of gamma frequencies during spindle types suggest that gamma frequencies are neither the cause of nor an integral part of a spindle. They appear to be correlated with levels of consciousness and may contribute to the process of epileptogenesis.

SIGNIFICANCE

The findings are consistent with high frequency EEG activity being related to seizure-tendency.

Physiological and pathological spindling phenomena have similar regional EEG power distributions

Sleep spindles in human and in rat are known to have a thalamocortical substrate. It has also been suggested that absence epilepsy spike and wave discharges may be generated by a similar mechanism. In addition, we have previously reported a possible thalamocortical origin of the EEG spindling rhythmic discharges associated with myoclonic jerks in the picrotoxin rat model of primary generalised epilepsy. To investigate whether pathological and physiological brain rhythms have common mechanisms of generation, we analysed four electroencephalographic (EEG) spindling activities in the rat. These were the non-convulsive spindle discharges induced by picrotoxin (picrotoxin spindles), naturally occurring absence epilepsy spike and wave discharges (absence spindles), spindle discharges during natural sleep (sleep spindles) and spindling activity that occurs under barbiturate anaesthesia (barbiturate spindles). We used power spectral analysis to define and compare the strength and brain distribution of EEG power during the spindling activities in 12 forebrain and 7 brainstem regions. There were brain-wide differences in power for each of the different spindle types with the pathological rhythms of the epilepsies containing more power than the physiological rhythms. There were also similar differences in the expression of spindles related to the region examined and no thalamic emphasis. These results provide evidence for a similar regional EEG power distribution for all four types of spindling activity and thus for the different spindles being expressions of a single phenomenon.

Epileptic fast intracerebral EEG activity: evidence for spatial decorrelation at seizure onset

Low-voltage rapid discharges (or fast EEG ictal activity) constitute a characteristic electrophysiological pattern in focal seizures of human epilepsy. They are characterized by a decrease of signal voltage with a marked increase of signal frequency (typically beyond 25 Hz). They have long been observed in stereoelectroencephalographic (SEEG) signals recorded with intra-cerebral electrodes, generally occurring at seizure onset and simultaneously involving distinct brain regions. Spectral properties of rapid ictal discharges as well as spatial correlations measured between SEEG signals generated from distant sites before, during and after these discharges were studied. Cross-correlation estimates within typical EEG sub-bands and statistical tests performed in 10 patients suffering from partial epilepsy (frontal, temporal or fronto-temporal) reveal that SEEG signals are significantly de-correlated during the discharge period compared with periods that precede and follow this discharge. These results can be interpreted as a functional decoupling of distant brain sites at seizure onset followed by an abnormally high re-coupling when the seizure develops. They lead to the concept of 'disruption' that is complementary of that of 'activation' (revealed by significantly high correlations between signals recorded during seizures), both giving insights into our understanding of pathophysiological processes involved in human partial epilepsies as well as in the interpretation of clinical semiology.