Seizure probability in animal models of acquired epilepsy: a perspective on the concept of the preictal state

Adenosine Kinase Isoforms in the Developing Rat Hippocampus after LiCl/Pilocarpine Status Epilepticus

LiCl/pilocarpine status epilepticus (SE) induced in immature rats leads, after a latent period, to hippocampal hyperexcitability. The excitability may be influenced by adenosine, which exhibits anticonvulsant activity. The concentration of adenosine is regulated by adenosine kinase (ADK) present in two isoforms—ADK-L and ADK-S. The main goal of the study is to elucidate the changes in ADK isoform expression after LiCl/pilocarpine SE and whether potential changes, as well as inhibition of ADK by 5-iodotubercidin (5-ITU), may contribute to changes in hippocampal excitability during brain development. LiCl/pilocarpine SE was elicited in 12-day-old rats. Hippocampal excitability in immature rats was studied by the model of hippocampal afterdischarges (ADs), in which we demonstrated the potential inhibitory effect of 5-ITU. ADs demonstrated significantly decreased hippocampal excitability 3 days after SE induction, whereas significant hyperexcitability after 20 days compared to controls was shown. 5-ITU administration showed its inhibitory effect on the ADs in 32-day-old SE rats compared to SE rats without 5-ITU. Moreover, both ADK isoforms were examined in the immature rat hippocampus. The ADK-L isoform demonstrated significantly decreased expression in 12-day-old SE rats compared to the appropriate naïve rats, whereas increased ADK-S isoform expression was revealed. A decreasing ADK-L/-S ratio showed the declining dominance of ADK-L isoform during early brain development. LiCl/pilocarpine SE increased the excitability of the hippocampus 20 days after SE induction. The ADK inhibitor 5-ITU exhibited anticonvulsant activity at the same age. Age-related differences in hippocampal excitability after SE might correspond to the development of ADK isoform levels in the hippocampus.

The role of interictal discharges in ictogenesis - A dynamical perspective

Interictal epileptiform discharge (IED) is a traditional hallmark of epileptic tissue that is generated by the synchronous activity of a population of neurons. Interictal epileptiform discharges represent a heterogeneous group of pathological activities that differ in shape, duration, spatiotemporal distribution, underlying cellular and network mechanisms, and their relationship to seizure genesis. The exact role of IEDs in epilepsy is still not well understood, and there remains a persistent dichotomy about the impact on IEDs on seizures. Proseizure, antiseizure, and no impact on ictogenesis have all been described in previous studies. In this article, we review the existing knowledge on the role of interictal discharges in seizure genesis, and we discuss how dynamical approaches to ictogenesis can explain the existing dichotomy about the multifaceted role of IEDs in ictogenesis. This article is part of the Special Issue "NEWroscience 2018".

Neuronal Circuit Activity during Neonatal Hypoxic-Ischemic Seizures in Mice

OBJECTIVE

To identify circuits active during neonatal hypoxic-ischemic (HI) seizures and seizure propagation using electroencephalography (EEG), behavior, and whole-brain neuronal activity mapping.

METHODS

Mice were exposed to HI on postnatal day 10 using unilateral carotid ligation and global hypoxia. EEG and video were recorded for the duration of the experiment. Using immediate early gene reporter mice, active cells expressing cfos were permanently tagged with reporter protein tdTomato during a 90-minute window. After 1 week, allowing maximal expression of the reporter protein, whole brains were processed, lipid cleared, and imaged with confocal microscopy. Whole-brain reconstruction and analysis of active neurons (colocalized tdTomato/NeuN) were performed.

RESULTS

HI resulted in seizure behaviors that were bilateral or unilateral tonic-clonic and nonconvulsive in this model. Mice exhibited characteristic EEG background patterns such as burst suppression and suppression. Neuronal activity mapping revealed bilateral motor cortex and unilateral, ischemic somatosensory cortex, lateral thalamus, and hippocampal circuit activation. Immunohistochemical analysis revealed regional differences in myelination, which coincide with these activity patterns. Astrocytes and blood vessel endothelial cells also expressed cfos during HI.

INTERPRETATION

Using a combination of EEG, seizure semiology analysis, and whole-brain neuronal activity mapping, we suggest that this rodent model of neonatal HI results in EEG patterns similar to those observed in human neonates. Activation patterns revealed in this study help explain complex seizure behaviors and EEG patterns observed in neonatal HI injury. This pattern may be, in part, secondary to regional differences in development in the neonatal brain. ANN NEUROL 2019;86:927-938.

Docosanoids and elovanoids from omega-3 fatty acids are pro-homeostatic modulators of inflammatory responses, cell damage and neuroprotection

The functional significance of the selective enrichment of the omega-3 essential fatty acid docosahexaenoic acid (DHA; 22C and 6 double bonds) in cellular membrane phospholipids of the nervous system is being clarified by defining its specific roles on membrane protein function and by the uncovering of the bioactive mediators, docosanoids and elovanoids (ELVs). Here, we describe the preferential uptake and DHA metabolism in photoreceptors and brain as well as the significance of the Adiponectin receptor 1 in DHA retention and photoreceptor cell (PRC) survival. We now know that this integral membrane protein is engaged in DHA retention as a necessary event for the function of PRCs and retinal pigment epithelial (RPE) cells. We present an overview of how a) NPD1 selectively mediates preconditioning rescue of RPE and PR cells; b) NPD1 restores aberrant neuronal networks in experimental epileptogenesis; c) the decreased ability to biosynthesize NPD1 in memory hippocampal areas of early stages of Alzheimer's disease takes place; d) NPD1 protection of dopaminergic circuits in an in vitro model using neurotoxins; and e) bioactivity elicited by DHA and NPD1 activate a neuroprotective gene-expression program that includes the expression of Bcl-2 family members affected by Aβ42, DHA, or NPD1. In addition, we highlight ELOVL4 (ELOngation of Very Long chain fatty acids-4), specifically the neurological and ophthalmological consequences of its mutations, and their role in providing precursors for the biosynthesis of ELVs. Then we outline evidence of ELVs ability to protect RPE cells, which sustain PRC integrity. In the last section, we present a summary of the protective bioactivity of docosanoids and ELVs in experimental ischemic stroke. The identification of early mechanisms of neural cell survival mediated by DHA-synthesized ELVs and docosanoids contributes to the understanding of cell function, pro-homeostatic cellular modulation, inflammatory responses, and innate immunity, opening avenues for prevention and therapeutic applications in neurotrauma, stroke and neurodegenerative diseases.

Crowdsourcing seizure detection: algorithm development and validation on human implanted device recordings

There exist significant clinical and basic research needs for accurate, automated seizure detection algorithms. These algorithms have translational potential in responsive neurostimulation devices and in automatic parsing of continuous intracranial electroencephalography data. An important barrier to developing accurate, validated algorithms for seizure detection is limited access to high-quality, expertly annotated seizure data from prolonged recordings. To overcome this, we hosted a kaggle.com competition to crowdsource the development of seizure detection algorithms using intracranial electroencephalography from canines and humans with epilepsy. The top three performing algorithms from the contest were then validated on out-of-sample patient data including standard clinical data and continuous ambulatory human data obtained over several years using the implantable NeuroVista seizure advisory system. Two hundred teams of data scientists from all over the world participated in the kaggle.com competition. The top performing teams submitted highly accurate algorithms with consistent performance in the out-of-sample validation study. The performance of these seizure detection algorithms, achieved using freely available code and data, sets a new reproducible benchmark for personalized seizure detection. We have also shared a 'plug and play' pipeline to allow other researchers to easily use these algorithms on their own datasets. The success of this competition demonstrates how sharing code and high quality data results in the creation of powerful translational tools with significant potential to impact patient care.

Targeted Interneuron Ablation in the Mouse Hippocampus Can Cause Spontaneous Recurrent Seizures

The death of GABAergic interneurons has long been hypothesized to contribute to acquired epilepsy. These experiments tested the hypothesis that focal interneuron lesions cause acute seizures [i.e., status epilepticus (SE)] and/or chronic epilepsy [i.e., persistent spontaneous recurrent seizures (SRSs)]. To selectively ablate interneurons, Gad2-ires-Cre mice were injected unilaterally in the CA1 area of the dorsal hippocampus with an adeno-associated virus containing the diphtheria toxin receptor (DTR). Simultaneously, an electrode, connected to a miniature telemetry device, was positioned at the injection site for chronic recordings of local field potentials (LFPs). Two weeks after virus transfection, intraperitoneal injection of DT consistently caused focal, specific, and extensive ablation of interneurons. Long-term, continuous monitoring revealed that all mice with DT-induced interneuron lesions had SRSs. Seizures lasted tens of seconds and interseizure intervals were several hours (or days); therefore, these interneuron lesions did not induce SE. The SRSs occurred 3-5 d after DT treatment, which is the estimated time required for DT-induced cell death; therefore, induction of SRSs occurred without the latent period typical of acquired epilepsy. In five of six DT-treated mice, SRSs stopped within days, suggesting that the DT-induced interneuron lesions did not usually cause epilepsy. In one mouse, however, SRSs occurred for ≥34 d after interneuron ablation, similar to epilepsy after experimental SE. Sham control mice had no detectable seizures, confirming that the SRSs were due to ablation of interneurons. These data show that selective interneuron ablation consistently caused SRSs but not SE; and, at least under the conditions used here, interneuron lesions rarely led to persistent SRSs (i.e., epilepsy).

Dual mechanisms of rapid expression of anxiety-related behavior in pilocarpine-treated epileptic mice

A mouse model of epilepsy was generated by inducing status epilepticus (SE) for either 1.5 or 4.5h with pilocarpine to study anxiety-related behaviors, changes in the electroencephalogram of the cerebral cortex and hippocampus, and expression of hippocampal proteins. The viability and rate of success of SE induction were high in C57BL/6N mice but not in C57BL/6J mice. C57BL/6N mice were immotile during the first 2days after SE; however, by the third day, most mice were recovered and exhibited strong anxiety-related behaviors in response to the light/dark preference test and open field test. There was a striking difference in the temporal appearance of anxiety-related behavior between the two SE durations: 1.5h SE mice exhibited strong anxiety-related behavior 3days after SE that gradually attenuated over the next few weeks, whereas 4.5h SE mice exhibited strong anxiety-related behavior 3days after SE that persisted even at nearly 1year after SE. Mice receiving both SE durations exhibited generalized seizures (GS) after SE; however, there was a marked difference in the timing and duration of GS appearance. Mice in the 4.5h SE group exhibited spontaneous GS from 4days to at least 96days after SE. In contrast, mice in the 1.5h SE group exhibited GS only within the first several days after SE; however, epileptic spike clusters continuously appeared in the cerebral cortex and hippocampus for up to twelve days after SE. Among the hippocampal proteins tested, only brain derived-neurotrophic factor (BDNF) exhibited altered expression in parallel with anxiety-related behavior. These results showed the possibility that BDNF expression in the hippocampus might cause anxiety-related behavior in adulthood.

Forecasting Seizures Using Intracranial EEG Measures and SVM in Naturally Occurring Canine Epilepsy

Management of drug resistant focal epilepsy would be greatly assisted by a reliable warning system capable of alerting patients prior to seizures to allow the patient to adjust activities or medication. Such a system requires successful identification of a preictal, or seizure-prone state. Identification of preictal states in continuous long- duration intracranial electroencephalographic (iEEG) recordings of dogs with naturally occurring epilepsy was investigated using a support vector machine (SVM) algorithm. The dogs studied were implanted with a 16-channel ambulatory iEEG recording device with average channel reference for a mean (st. dev.) of 380.4 (+87.5) days producing 220.2 (+104.1) days of intracranial EEG recorded at 400 Hz for analysis. The iEEG records had 51.6 (+52.8) seizures identified, of which 35.8 (+30.4) seizures were preceded by more than 4 hours of seizure-free data. Recorded iEEG data were stratified into 11 contiguous, non-overlapping frequency bands and binned into one-minute synchrony features for analysis. Performance of the SVM classifier was assessed using a 5-fold cross validation approach, where preictal training data were taken from 90 minute windows with a 5 minute pre-seizure offset. Analysis of the optimal preictal training time was performed by repeating the cross validation over a range of preictal windows and comparing results. We show that the optimization of feature selection varies for each subject, i.e. algorithms are subject specific, but achieve prediction performance significantly better than a time-matched Poisson random predictor (p<0.05) in 5/5 dogs analyzed.

Hippocampal neuro-networks and dendritic spine perturbations in epileptogenesis are attenuated by neuroprotectin d1

Purpose

Limbic epileptogenesis triggers molecular and cellular events that foster the establishment of aberrant neuronal networks that, in turn, contribute to temporal lobe epilepsy (TLE). Here we have examined hippocampal neuronal network activities in the pilocarpine post-status epilepticus model of limbic epileptogenesis and asked whether or not the docosahexaenoic acid (DHA)-derived lipid mediator, neuroprotectin D1 (NPD1), modulates epileptogenesis.

Methods

Status epilepticus (SE) was induced by intraperitoneal administration of pilocarpine in adult male C57BL/6 mice. To evaluate simultaneous hippocampal neuronal networks, local field potentials were recorded from multi-microelectrode arrays (silicon probe) chronically implanted in the dorsal hippocampus. NPD1 (570 μg/kg) or vehicle was administered intraperitoneally daily for five consecutive days 24 hours after termination of SE. Seizures and epileptiform activity were analyzed in freely-moving control and treated mice during epileptogenesis and epileptic periods. Then hippocampal dendritic spines were evaluated using Golgi-staining.

Results

We found brief spontaneous microepileptiform activity with high amplitudes in the CA1 pyramidal and stratum radiatum in epileptogenesis. These aberrant activities were attenuated following systemic NPD1 administration, with concomitant hippocampal dendritic spine protection. Moreover, NPD1 treatment led to a reduction in spontaneous recurrent seizures.

Conclusions

Our results indicate that NPD1 displays neuroprotective bioactivity on the hippocampal neuronal network ensemble that mediates aberrant circuit activity during epileptogenesis. Insight into the molecular signaling mediated by neuroprotective bioactivity of NPD1 on neuronal network dysfunction may contribute to the development of anti-epileptogenic therapeutic strategies.

Forecasting seizures in dogs with naturally occurring epilepsy

Seizure forecasting has the potential to create new therapeutic strategies for epilepsy, such as providing patient warnings and delivering preemptive therapy. Progress on seizure forecasting, however, has been hindered by lack of sufficient data to rigorously evaluate the hypothesis that seizures are preceded by physiological changes, and are not simply random events. We investigated seizure forecasting in three dogs with naturally occurring focal epilepsy implanted with a device recording continuous intracranial EEG (iEEG). The iEEG spectral power in six frequency bands: delta (0.1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), low-gamma (30–70 Hz), and high-gamma (70–180 Hz), were used as features. Logistic regression classifiers were trained to discriminate labeled pre-ictal and inter-ictal data segments using combinations of the band spectral power features. Performance was assessed on separate test data sets via 10-fold cross-validation. A total of 125 spontaneous seizures were detected in continuous iEEG recordings spanning 6.5 to 15 months from 3 dogs. When considering all seizures, the seizure forecasting algorithm performed significantly better than a Poisson-model chance predictor constrained to have the same time in warning for all 3 dogs over a range of total warning times. Seizure clusters were observed in all 3 dogs, and when the effect of seizure clusters was decreased by considering the subset of seizures separated by at least 4 hours, the forecasting performance remained better than chance for a subset of algorithm parameters. These results demonstrate that seizures in canine epilepsy are not randomly occurring events, and highlight the feasibility of long-term seizure forecasting using iEEG monitoring.

Seizure predisposition after perinatal hypoxia: effects of subsequent age and of an epilepsy predisposing gene mutation

PURPOSE

There is a gap in our knowledge of the factors that modulate the predisposition to seizures following perinatal hypoxia. Herein, we investigate in a mouse model the effects of two distinct factors: developmental stage after the occurrence of the perinatal insult, and the presence of a seizure predisposing mutation.

METHODS

Effects of age: P6 (postnatal day 6) mouse pups were subjected to acute hypoxia down to 4% O2 over the course of 45 min. Seizure susceptibilities to flurothyl-induced seizures (single exposures) and to flurothyl kindling were determined at specific subsequent ages. Effects of mutation: Heterozygote mice, with deletion of one copy of the Kcn1a gene, subjected to P6 hypoxia were compared as adults to wild-type mice with respect to susceptibility to a single exposure to flurothyl and to the occurrence of spontaneous seizures as detected by hippocampal electroencephalography (EEG) and video recordings.

KEY FINDINGS

Effects of age: As compared to controls, wild-type mice exposed to P6 hypoxia had a shortened seizure latency in response to a single flurothyl exposure at P50, but not at P7 or P28 (p < 0.04). In addition, perinatal hypoxia at P6 enhanced the rate of development of flurothyl kindling performed at P28-38 (p < 0.03), but not at P7-17. Effects of mutation: Kcn1a heterozygous mice subjected to P6 hypoxia exhibited increased susceptibility to flurothyl-induced seizures at P50 as compared to Normoxia heterozygote littermates, and to wild-type Hypoxia and Normoxia mice. In addition, heterozygotes exposed to P6 hypoxia were the only group in which spontaneous seizures were detected during the period of long-term monitoring (p < 0.027 in all comparisons).

SIGNIFICANCE

Our data establish a mouse model of mild perinatal hypoxia in which we document the following: (1) the emergence, after a latent period, of increased susceptibility to flurothyl-induced seizures, and to flurothyl induced kindling; and (2) an additive effect of a gene mutation to the seizure predisposing consequences of perinatal hypoxia, thereby demonstrating that a modifier (or susceptibility) gene can exacerbate the long-term consequences of hypoxic injury.

Toward new paradigms of seizure detection

Great effort has been made toward defining and characterizing the pre-ictal state. Many studies have pursued the idea that there are recognizable electrographic (EEG-based) features which occur before overt clinical seizure activity. However, development of reliable EEG-based seizure detection and prediction algorithms has been difficult. In this review, we discuss the concepts of seizure detection vs. prediction and the pre-ictal "clinical milieu" and "EEG milieu". We proceed to discuss novel concepts of seizure detection based on the pre-ictal "physiological milieu"; in particular, we indicate some early evidence for the hypothesis that pre-ictal cell swelling/extracellular space constriction can be detected with novel optical methods. Development and validation of optical seizure detection technology could provide an entirely new translational approach for the many patients with intractable epilepsy.