Preictal Discharges Research Articles

AsHC 360 Exposure Influence on Epileptiform Discharges in Hippocampus of Infantile Male Rats In Vitro

Arsenic-containing hydrocarbons (AsHCs) are typical arsenolipids found in various marine organisms. They can penetrate the blood–brain barrier, specifically affecting synaptic plasticity and the learning and memory ability of hippocampal neurons. Temporal lobe epilepsy often occurs in the hippocampus. Thus, the possible influence of AsHCs exposure to temporal lobe epilepsy garnered attention. The present study investigated the effects of epileptiform discharges (EDs) signals introduced by low-magnesium ACSF in the hippocampus of infantile male rats in vitro, using electrophysiological techniques with multi-electrode arrays under AsHC 360 exposure. In our study of the effects of AsHC 360 on EDs signals, we found that inter-ictal discharges (IIDs) were not significantly impacted. When AsHC 360 was removed, any minor effects observed were reversed. However, when we examined the impact of AsHC 360 on ictal discharges (IDs), distinct patterns emerged based on the concentration levels. For low-concentration groups (5, 20, 60 μg As L−1), both the frequency and duration effects on IDs returned to normal post-elimination of AsHC 360. However, this recovery was not evident for concentrations of 100 μg As L−1 or higher. IDs were only observed in EDs signals during exposures to AsHC 360 concentrations up to 60 μg As L−1. In these conditions, ID frequencies significantly enhanced with the increased of AsHC 360 concentration. At high concentrations of AsHC 360 (≥100 μg As L−1), the transition from IIDs or pre-ictal discharges (PIDs) to IDs was notably inhibited. Additional study on co-exposure of AsHC 360 (100 μg As L−1) and agonist (10 nM (S)-(-)-Bay-K-8644) indicated that the regulation of EDs signals under AsHC 360 exposure could be due to directly interference with the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptor (AMPAR) expression which influences the binding of excitatory glutamate neurotransmitter to AMPAR. The results suggest that EDs activities in the hippocampus of infantile Sprague Dawley rats are concentration-dependent on AsHC 360 exposure. Thus, it provides a basis for the seafood intake with AsHCs for epileptic patients and those with potential seizures.

PV-specific loss of the transcriptional coactivator PGC-1α slows down the evolution of epileptic activity in an acute ictogenic model.

The transcriptional coactivator, PGC-1α (peroxisome proliferator-activated receptor γ coactivator 1α), plays a key role in coordinating energy requirement within cells. Its importance is reflected in the growing number of psychiatric and neurological conditions that have been associated with reduced PGC-1α levels. In cortical networks, PGC-1α is required for the induction of parvalbumin (PV) expression in interneurons, and PGC-1α deficiency affects synchronous GABAergic release. It is unknown, however, how this affects cortical excitability. We show here that knocking down PGC-1α specifically in the PV-expressing cells (PGC-1αPV-/-) blocks the activity-dependent regulation of the synaptic proteins, SYT2 and CPLX1. More surprisingly, this cell class-specific knockout of PGC-1α appears to have a novel antiepileptic effect, as assayed in brain slices bathed in 0 Mg2+ media. The rate of occurrence of preictal discharges developed approximately equivalently in wild-type and PGC-1αPV-/- brain slices, but the intensity of these discharges was lower in PGC-1αPV-/- slices, as evident from the reduced power in the γ range and reduced firing rates in both PV interneurons and pyramidal cells during these discharges. Reflecting this reduced intensity in the preictal discharges, the PGC-1αPV-/- brain slices experienced many more discharges before transitioning into a seizure-like event. Consequently, there was a large increase in the latency to the first seizure-like event in brain slices lacking PGC-1α in PV interneurons. We conclude that knocking down PGC-1α limits the range of PV interneuron firing and this slows the pathophysiological escalation during ictogenesis.NEW & NOTEWORTHY Parvalbumin expressing interneurons are considered to play an important role in regulating cortical activity. We were surprised, therefore, to find that knocking down the transcriptional coactivator, PGC-1α, specifically in this class of interneurons appears to slow ictogenesis. This anti-ictogenic effect is associated with reduced activity in preictal discharges, but with a far longer period of these discharges before the first seizure-like events finally start. Thus, PGC-1α knockdown may promote schizophrenia while reducing epileptic tendencies.

Exploring the Inhibitory Effect of Low-frequency Magnetic Fields on Epileptiform Discharges in Juvenile Rat Hippocampus

Stimulation with a low frequency electromagnetic field (LF-EMF) has proven to represent a powerful method for the suppression of seizures, as demonstrated in select clinical and laboratory studies. However, the mechanism by which LF-EMF suppresses seizures remains unclear. The purpose of the present study was to explore the modulatory effect of LF-EMF on epileptiform discharges (EDs) using rat hippocampal slices and investigate the underlying mechanisms that mediate these effects. EDs in hippocampal slices was induced by magnesium-free (zero-Mg2+) artificial cerebrospinal fluid (ACSF) and recorded using an in vitro micro-electrode array (MEA). A small sub-decimeter coil was designed and incorporated in a flexible magnetic stimulation device that allowed electromagnetic fields with different parameters to be delivered to slices. After a stable ED event was recorded, magnetic fields of 0.5 Hz (30 min) with a magnetic intensity of 0.13 mT (5 Vpp voltage input) and 0.25 mT (20 Vpp voltage input) were applied. The results indicated that a high-amplitude 0.5 Hz magnetic field could lead to persistent suppression of ictal discharges (IDs), while low-amplitude magnetic fields did not influence IDs. The persistent suppression of complex ED was prevented if the magnetic fields were applied in the presence of 10 μmol/L bicuculline (BIC), a γ-aminobutyric acid type A (GABAA) receptor antagonist, while the application of BIC subsequent to a magnetic field application led to the reappearance of ID. The addition of BIC resulted in EDs that had previously been inhibited by magnetic fields, reappearing. Low-frequency magnetic stimulation was able to inhibit the conversion from interictal discharges (IIDs) or preictal discharges (PIDs) to IDs. This suppression was attributed to the modulation of GABAA receptor activity.

The intrinsic cell type-specific excitatory connectivity of the developing mouse subiculum is sufficient to generate synchronous epileptiform activity.

The activity of local excitatory circuits of the subiculum has been suggested to be involved in the initiation of pathological activity in epileptic patients and experimental animal models of temporal lobe epilepsy. We have taken advantage of multimodal techniques to classify subicular cells in distinct subclasses and have investigated their morphofunctional properties and connectivity in vitro. Our results indicate that local subicular excitatory circuits are connected in a cell type-specific fashion and that synapses are preferentially established on basal vs. apical dendrites. We show that local excitatory circuits, isolated from extrasubicular inputs and pharmacologically disinhibited, are sufficient to initiate synchronous epileptiform activity in vitro. In conclusion, this work provides a high-resolution description of local excitatory circuits of the subiculum and highlights their mechanistic involvement in the generation of pathological activity. The subiculum has been suggested to be involved in the initiation of pathological discharges in human patients and animal models of temporal lobe epilepsy. Although converging evidence has revealed the existence of functional diversity within its principal neurons, much less attention has been devoted to its intrinsic connectivity and whether its local excitatory circuits are sufficient to generate epileptiform activity. Here, we have directly addressed these two key points in mouse subicular slices. First, using multivariate techniques, we have distinguished two groups of principal cells, which we have termed type1 and type2. These subgroups roughly overlap with what were classically indicated as regular and bursting cells, and showed differences in the extension and complexity of their apical dendrites. Functional connectivity was found both between similar (homotypic) and different (heterotypic) types of cells, with a marked asymmetry within heterotypic pairs. Unitary excitatory postsynaptic potentials (uEPSPs) revealed a high degree of variability both in amplitude, failure rate, rise time and half-width. Post hoc analysis of functionally connected pairs suggested that the observed uEPSPs were mediated by few contact sites, predominantly located on the basal dendrites. When surgically isolated from extrasubicular excitatory afferents, pharmacologically disinhibited subicular slices generated hyper-synchronous discharges. Thus, we conclude that local subicular excitatory circuits, connected according to cell type-specific rules, are sufficient to promote epileptiform activity. This conclusion fits well with a previous suggestion that local subicular events, purely mediated by excitatory connections, may underlie the pre-ictal discharges that govern interictal-ictal transitions.

Gamma-aminobutyric acidergic transmission underlies interictal epileptogenicity in pediatric focal cortical dysplasia.

Dysregulation of γ-aminobutyric acidergic (GABAergic) transmission has been reported in lesional acquired epilepsies (gliomas, hippocampal sclerosis). We investigated its involvement in a developmental disorder, human focal cortical dysplasia (FCD), focusing on chloride regulation driving GABAergic signals. In vitro recordings of 47 human cortical acute slices from 11 pediatric patients who received operations for FCD were performed on multielectrode arrays. GABAergic receptors and chloride regulators were pharmacologically modulated. Immunostaining for chloride cotransporter KCC2 and interneurons were performed on recorded slices to correlate electrophysiology and expression patterns. FCD slices retain intrinsic epileptogenicity. Thirty-six of 47 slices displayed spontaneous interictal discharges, along with a pattern specific to the histological subtypes. Ictal discharges were induced in proepileptic conditions in 6 of 8 slices in the areas generating spontaneous interictal discharges, with a transition to seizure involving the emergence of preictal discharges. Interictal discharges were sustained by GABAergic signaling, as a GABAA receptor blocker stopped them in 2 of 3 slices. Blockade of NKCC1 Cl- cotransporters further controlled interictal discharges in 9 of 12 cases, revealing a Cl- dysregulation affecting actions of GABA. Immunohistochemistry highlighted decreased expression and changes in KCC2 subcellular localization and a decrease in the number of GAD67-positive interneurons in regions generating interictal discharges. Altered chloride cotransporter expression and changes in interneuron density in FCD may lead to paradoxical depolarization of pyramidal cells. Spontaneous interictal discharges are consequently mediated by GABAergic signals, and targeting chloride regulation in neurons may be considered for the development of new antiepileptic drugs. Ann Neurol 2019; 1-14 ANN NEUROL 2019;85:204-217.

Dynamic Preictal Discharges in Patients With Mesial Temporal Lobe Epilepsy.

It has been challenging to detect early changes preceding seizure onset in patients with epilepsy. This study investigated the preictal discharges (PIDs) by intracranial electroencephalogram of 11 seizures from 7 patients with mesial temporal lobe epilepsy. The EEG segments consisting of 30 seconds before ictal onset and 5 seconds after ictal onset were selected for analysis. After PID detection, the amplitude and interval were measured. According to the timing of PID onset, the 30-second period preceding seizure onset was divided into two stages: before PID stage and PID stage. The autocorrelation coefficients during the two stages were calculated and compared. Preictal discharge amplitude progressively increased, while PID interval gradually decreased toward seizure onset. The autocorrelation coefficients of PID channels were significantly higher during PID stage than before PID stage. There was an overlap between channels with PIDs and seizure onset channels (80.77%). Preictal discharges emerge prior to ictal event, with a dynamic change and a spatial correlation with seizure onset zone. These findings deepen our understanding of seizure generation and help early prediction and localization of seizure onset zone.

Different mechanisms of ripple‐like oscillations in the human epileptic subiculum

Transient high-frequency oscillations (HFOs; 150-600Hz) in local field potentials generated by human hippocampal and parahippocampal areas have been related to both physiological and pathological processes. The cellular basis and effects of normal and abnormal forms of HFOs have been controversial. This lack of agreement is clinically significant, because HFOs may be good markers of epileptogenic areas. Better defining the neuronal correlate of specific HFO frequency bands could improve electroencephalographic analyses made before epilepsy surgery. Here, we recorded HFOs in slices of the subiculum prepared from human hippocampal tissue resected for treatment of pharmacoresistant epilepsy. With combined intra- or juxtacellular and extracellular recordings, we examined the cellular correlates of interictal and ictal HFO events. HFOs occurred spontaneously in extracellular field potentials during interictal discharges (IIDs) and also during pharmacologically induced preictal discharges (PIDs) preceding ictal-like events. Many of these events included frequencies >250Hz and so might be considered pathological, but a significant proportion were spectrally similar to physiological ripples (150-250Hz). We found that IID ripples were associated with rhythmic γ-aminobutyric acidergic and glutamatergic synaptic potentials with moderate neuronal firing. In contrast, PID ripples were associated with depolarizing synaptic inputs frequently reaching the threshold for bursting in most pyramidal cells. Our data suggest that IID and PID ripple-like oscillations (150-250Hz) in human epileptic hippocampus are associated with 2 distinct population activities that rely on different cellular and synaptic mechanisms. Thus, the ripple band could not help to disambiguate the underlying cellular processes.

Distinct Mechanisms Mediate Interictal and Pre-Ictal Discharges in Human Temporal Lobe Epilepsy

Distinct Mechanisms Mediate Interictal and Pre-Ictal Discharges in Human Temporal Lobe Epilepsy

Glutamatergic pre-ictal discharges emerge at the transition to seizure in human epilepsy

The mechanisms involved in the transition to an epileptic seizure remain unclear. To examine them, we used tissue slices from human subjects with mesial temporal lobe epilepsies. Ictal-like discharges were induced in the subiculum by increasing excitability along with alkalinization or low Mg(2+). During the transition, distinct pre-ictal discharges emerged concurrently with interictal events. Intracranial recordings from the mesial temporal cortex of subjects with epilepsy revealed that similar discharges before seizures were restricted to seizure onset sites. In vitro, pre-ictal events spread faster and had larger amplitudes than interictal discharges and had a distinct initiation site. These events depended on glutamatergic mechanisms and were preceded by pyramidal cell firing, whereas interneuron firing preceded interictal events that depended on both glutamatergic and depolarizing GABAergic transmission. Once established, recurrence of these pre-ictal discharges triggered seizures. Thus, the subiculum supports seizure generation, and the transition to seizure involves an emergent glutamatergic population activity.

Synchronization of GABAergic Inputs to CA3 Pyramidal Cells Precedes Seizure-Like Event Onset in Juvenile Rat Hippocampal Slices

Here we address how dynamics of glutamatergic and GABAergic synaptic input to CA3 pyramidal cells contribute to spontaneous emergence and evolution of recurrent seizure-like events (SLEs) in juvenile (P10-13) rat hippocampal slices bathed in low-[Mg(2+)] artificial cerebrospinal fluid. In field potential recordings from the CA3 pyramidal layer, a short epoch of high-frequency oscillation (HFO; 400-800 Hz) was observed during the first 10 ms of SLE onset. GABAergic synaptic input currents to CA3 pyramidal cells were synchronized and coincided with HFO, whereas the glutamatergic input lagged by approximately 10 ms. If the intracellular [Cl(-)] remained unperturbed (cell-attached recordings) or was set high with whole cell electrode solution, CA3 pyramidal cell firing peaked with HFO and GABAergic input. By contrast, with low intracellular [Cl(-)], spikes of CA3 pyramidal cells lagged behind HFO and GABAergic input. This temporal arrangement of HFO, synaptic input sequence, synchrony of GABAergic currents, and pyramidal cell firing emerged gradually with preictal discharges until the SLE onset. Blockade of GABA(A) receptor-mediated currents by picrotoxin reduced the inter-SLE interval and the number of preictal discharges and did not block recurrent SLEs. Our data suggest that dynamic changes of the functional properties of GABAergic input contribute to ictogenesis and GABAergic and glutamatergic inputs are both excitatory at the instant of SLE onset. At the SLE onset GABAergic input contributes to synchronization and recruitment of pyramidal cells. We conjecture that this network state is reached by an activity-dependent shift in GABA reversal potential during the preictal phase.