WONOEP appraisal: Modeling early onset epilepsies.

Epilepsy has a peak incidence during the neonatal to early childhood period. These early onset epilepsies may be severe conditions frequently associated with comorbidities such as developmental deficits and intellectual disability and, in a significant percentage of patients, may be medication-resistant. The use of adult rodent models in the exploration of mechanisms and treatments for early life epilepsies is challenging, as it ignores significant age-specific developmental differences. More recently, models developed in immature animals, such as rodent pups, or in three-dimensional organoids may more closely model aspects of the immature brain and could result in more translatable findings. Although models are not perfect, they may offer a more controlled screening platform in studies of mechanisms and treatments, which cannot be done in pediatric patient cohorts. On the other hand, more simplified models with higher throughput capacities are required to deal with the large number of epilepsy candidate genes and the need for new treatment options. Therefore, a combination of different modeling approaches will be beneficial in addressing the unmet needs of pediatric epilepsy patients. In this review, we summarize the discussions on this topic that occurred during the XVI Workshop on Neurobiology of Epilepsy, organized in 2022 by the Neurobiology Commission of the International League Against Epilepsy. We provide an overview of selected models of early onset epilepsies, discussing their advantages and disadvantages. Heterologous expression models provide initial functional insights, and zebrafish, rodent models, and brain organoids present increasingly complex platforms for modeling and validating epilepsy-related phenomena. Together, these models offer valuable insights into early onset epilepsies and accelerate hypothesis generation and therapy discovery.

Neuronal deletion of Wwox, associated with WOREE syndrome, causes epilepsy and myelin defects.

WWOX-related epileptic encephalopathy (WOREE) syndrome caused by human germline bi-allelic mutations in WWOX is a neurodevelopmental disorder characterized by intractable epilepsy, severe developmental delay, ataxia and premature death at the age of 2-4 years. The underlying mechanisms of WWOX actions are poorly understood. In the current study, we show that specific neuronal deletion of murine Wwox produces phenotypes typical of the Wwox-null mutation leading to brain hyperexcitability, intractable epilepsy, ataxia and postnatal lethality. A significant decrease in transcript levels of genes involved in myelination was observed in mouse cortex and hippocampus. Wwox-mutant mice exhibited reduced maturation of oligodendrocytes, reduced myelinated axons and impaired axonal conductivity. Brain hyperexcitability and hypomyelination were also revealed in human brain organoids with a WWOX deletion. These findings provide cellular and molecular evidence for myelination defects and hyperexcitability in the WOREE syndrome linked to neuronal function of WWOX.

Local Field Potential-Based Programming: A Proof-of-Concept Pilot Study.

OBJECTIVES: Programming deep brain stimulation (DBS) is still based on a trial-and-error approach, often becoming a time-consuming process for both treating physicians and patients. Several strategies have been proposed to streamline DBS programming, most of which are preliminary and mainly address Parkinson's disease, a condition readily responsive to DBS adjustments. In the present proof-of-principle pilot study, we successfully demonstrate that local field potential (LFP)-based programming can be an effective approach when used for DBS indications that have a delayed temporal onset of benefit. MATERIALS AND METHODS: A recently commercialized implantable pulse generator (IPG) with the capability to non-invasively and chronically stream live and/or record LFPs from a DBS electrode after implantation was used to program one pediatric patient with generalized dystonia and an adult with seizures refractory to multiple medications and vagal nerve stimulation. RESULTS: The IPG survey function detected a peak in the delta range (1.95 Hz) in the left globus pallidus of the first patient. This LFP was detected when recording in the brain area adjacent to contacts 9 and 10 and absent when recording from other areas. The chronic recording of the 1.95 Hz LFP with two sets of stimulation showed a greater power increase with the settings associated with a worsening of dystonia. Broadband LFP home recording of "absence seizure" and "focal/partial seizure" was used in the second patient and reviewer with the IPG "timeline" and "event" functions. The chronic recording of the 2.93 Hz and 8.79 Hz (spit sensing) showed a reduced power with the stimulation setting associated with seizure control. CONCLUSIONS: The approach presented in this pilot proof-of-concept study may inform and streamline the DBS programming for conditions requiring clinicians and patients to wait weeks before appreciating any clinical benefit. Prospective studies on larger samples of patients are warranted.

Neocortical in vivo focal and spreading potassium responses and the influence of astrocytic gap junctional coupling.

Raised extracellular potassium ion (K+) concentration is associated with several disorders including migraine, stroke, neurotrauma and epilepsy. K+ spatial buffering is a well-known mechanism for extracellular K+ regulation/distribution. Astrocytic gap junction-mediated buffering is a controversial candidate for K+ spatial buffering. To further investigate the existence of a K+ spatial buffering and to assess the involvement of astrocytic gap junctional coupling in K+ redistribution, we hypothesized that neocortical K+ and concomitant spreading depolarization (SD)-like responses are controlled by powerful local K+ buffering mechanisms and that K+ buffering/redistribution occurs partially through gap junctional coupling. Herein, we show, in vivo, that a threshold amount of focally applied KCl is required to trigger local and/or distal K+ responses, accompanied by a SD-like response. This observation indicates the presence of powerful local K+ buffering which mediates a rapid return of extracellular K+ to the baseline. Application of gap junctional blockers, carbenoxolone and Gap27, partially modulated the amplitude and shape of the K+ response and noticeably decreased the velocity of the spreading K+ and SD-like responses. Opening of gap junctions by trimethylamine, slightly decreased the amplitude of the K+ response and markedly increased the velocity of redistribution of K+ and SD-like events. We conclude that spreading K+ responses reflect powerful local K+ buffering mechanisms which are partially modulated by gap junctional communication. Gap junctional coupling mainly affected the velocity of the K+ and SD-like responses.

Altered neocortical oscillations and cellular excitability in an in vitro Wwox knockout mouse model of epileptic encephalopathy.

Loss of function mutations of the WW domain-containing oxidoreductase (WWOX) gene are associated with severe and fatal drug-resistant pediatric epileptic encephalopathy. Epileptic seizures are typically characterized by neuronal hyperexcitability; however, the specific contribution of WWOX to that hyperexcitability has yet to be investigated. Using a mouse model of neuronal Wwox-deletion that exhibit spontaneous seizures, in vitro whole-cell and field potential electrophysiological characterization identified spontaneous bursting activity in the neocortex, a marker of the underlying network hyperexcitability. Spectral analysis of the neocortical bursting events highlighted increased phase-amplitude coupling, and a propagation from layer II/III to layer V. These bursts were NMDAR and gap junction dependent. In layer II/III pyramidal neurons, Wwox knockout mice demonstrated elevated amplitude of excitatory post-synaptic currents, whereas the frequency and amplitude of inhibitory post-synaptic currents were reduced, as compared to heterozygote and wild-type littermate controls. Furthermore, these neurons were depolarized and demonstrated increased action potential frequency, sag current, and post-inhibitory rebound. These findings suggest WWOX plays an essential role in balancing neocortical excitability and provide insight towards developing therapeutics for those suffering from WWOX disorders.

In Vivo Neocortical [K]o Modulation by Targeted Stimulation of Astrocytes.

A normally functioning nervous system requires normal extracellular potassium ion concentration ([K]o). Throughout the nervous system, several processes, including those of an astrocytic nature, are involved in [K]o regulation. In this study we investigated the effect of astrocytic photostimulation on [K]o. We hypothesized that in vivo photostimulation of eNpHR-expressing astrocytes leads to a decreased [K]o. Using optogenetic and electrophysiological techniques we showed that stimulation of eNpHR-expressing astrocytes resulted in a significantly decreased resting [K]o and evoked K responses. The amplitude of the concomitant spreading depolarization-like events also decreased. Our results imply that astrocytic membrane potential modification could be a potential tool for adjusting the [K]o.

Deep Brain Stimulation Rescues Memory and Synaptic Activity in a Rat Model of Global Ischemia.

Ischemic stroke is responsible for a large number of neurological deficits including memory impairment. Deep brain stimulation (DBS), a well established therapeutic modality for the treatment of movement disorders, has recently shown potential beneficial effects on memory in animals and patients with Alzheimer's disease. Here, we test DBS for its ability to improve memory impairments by stimulating the entorhinal cortex (EC) in a rat model of global ischemia (GI). Two weeks after GI, adult male rats received high-frequency EC DBS for 1 h, and animals were assessed for changes in locomotor activity, learning, and memory 6 weeks later. GI produced spatial memory impairment that was ameliorated by DBS, with no difference between the group that received DBS for GI (GI-DBS ON group) and nonstroke control groups. Although GI led to a dramatic CA1 neuronal loss that could not be rescued with DBS, stimulation attenuated the reduction of CA1 synaptophysin expression after GI. Further, in vitro slice recordings showed a restoration of typical evoked synaptic dendritic fields in GI-DBS ON animals, indicating that the DBS-induced memory rescue is associated with increased synaptophysin expression and enhanced synaptic function. These results suggest that DBS may ameliorate the functional consequences of cerebral ischemia and point to be a potential new therapeutic approach.SIGNIFICANCE STATEMENT Deep brain stimulation (DBS) is remarkably effective in treating Parkinson's disease and is currently under investigation for the treatment of neuropsychiatric disorders including Alzheimer's disease. Until now, DBS has not been examined for its cognitive benefits in the context of hypoxic-ischemic injuries. Here, we investigated the effect of DBS in a rat model of global ischemia (GI) that mimics the neurological consequences occurring after a cardiac arrest. We show that DBS rescues memory deficits induced by GI and produces changes in synaptic activity in the hippocampus. Novel approaches to improve neurological outcomes after stroke are urgently needed; therefore, the present study highlights a possible role for DBS in the treatment of cognitive impairment associated with ischemia.

Cardiorespiratory depression from brainstem seizure activity in freely moving rats.

Cardiorespiratory dysfunction during or after seizures may contribute to sudden unexpected death in epilepsy. Disruption of lower brainstem cardiorespiratory systems by seizures is postulated to impair respiratory and cardiac function. Here, we explore the effects of brainstem seizures and stimulation on cardiorespiratory function using a rat model of intrahippocampal 4-aminopyridine (4-AP)-induced acute recurrent seizures. Cardiac and respiratory monitoring together with local field potential recordings from hippocampus, contralateral parietal cortex and caudal dorsomedial brainstem, were conducted in freely moving adult male Wistar rats. Seizures were induced by intrahippocampal injection of 4-AP. Increased respiratory rate but unchanged heart rate occurred during hippocampal and secondarily generalized cortical seizures. Status epilepticus without brainstem seizures increased respiratory and heart rates, whereas status epilepticus with intermittent brainstem seizures induced repeated episodes of cardiorespiratory depression leading to death. Respiratory arrest occurred prior to asystole which was the terminal event. Phenytoin (100 mg/kg, intraperitoneal injection), administered after 4-AP intrahippocampal injection, terminated brainstem seizures and the associated cardiorespiratory depression, preventing death in five of six rats. Focal electrical stimulation of the caudal dorsomedial brainstem also suppressed cardiorespiratory rates. We conclude that in our model, brainstem seizures were associated with respiratory depression followed by cardiac arrest, and then death. We hypothesize this model shares mechanisms in common with the classic sudden unexpected death in epilepsy (SUDEP) syndrome associated with spontaneous seizures.

Transitions between neocortical seizure and non-seizure-like states and their association with presynaptic glutamate release.

The transition between seizure and non-seizure states in neocortical epileptic networks is governed by distinct underlying dynamical processes. Based on the gamma distribution of seizure and inter-seizure durations, over time, seizures are highly likely to self-terminate; whereas, inter-seizure durations have a low chance of transitioning back into a seizure state. Yet, the chance of a state transition could be formed by multiple overlapping, unknown synaptic mechanisms. To identify the relationship between the underlying synaptic mechanisms and the chance of seizure-state transitions, we analyzed the skewed histograms of seizure durations in human intracranial EEG and seizure-like events (SLEs) in local field potential activity from mouse neocortical slices, using an objective method for seizure state classification. While seizures and SLE durations were demonstrated to have a unimodal distribution (gamma distribution shape parameter >1), suggesting a high likelihood of terminating, inter-SLE intervals were shown to have an asymptotic exponential distribution (gamma distribution shape parameter <1), suggesting lower probability of cessation. Then, to test cellular mechanisms for these distributions, we studied the modulation of synaptic neurotransmission during, and between, the in vitro SLEs. Using simultaneous local field potential and whole-cell voltage clamp recordings, we found a suppression of presynaptic glutamate release at SLE termination, as demonstrated by electrically- and optogenetically-evoked excitatory postsynaptic currents (EPSCs), and focal hypertonic sucrose application. Adenosine A1 receptor blockade interfered with the suppression of this release, changing the inter-SLE shape parameter from asymptotic exponential to unimodal, altering the chance of state transition occurrence with time. These findings reveal a critical role for presynaptic glutamate release in determining the chance of neocortical seizure state transitions.

Pannexin-1 Deficiency Decreases Epileptic Activity in Mice.

OBJECTIVE: Pannexin-1 (Panx1) is suspected of having a critical role in modulating neuronal excitability and acute neurological insults. Herein, we assess the changes in behavioral and electrophysiological markers of excitability associated with Panx1 via three distinct models of epilepsy. Methods Control and Panx1 knockout C57Bl/6 mice of both sexes were monitored for their behavioral and electrographic responses to seizure-generating stimuli in three epilepsy models-(1) systemic injection of pentylenetetrazol, (2) acute electrical kindling of the hippocampus and (3) neocortical slice exposure to 4-aminopyridine. Phase-amplitude cross-frequency coupling was used to assess changes in an epileptogenic state resulting from Panx1 deletion. RESULTS: Seizure activity was suppressed in Panx1 knockouts and by application of Panx1 channel blockers, Brilliant Blue-FCF and probenecid, across all epilepsy models. In response to pentylenetetrazol, WT mice spent a greater proportion of time experiencing severe (stage 6) seizures as compared to Panx1-deficient mice. Following electrical stimulation of the hippocampal CA3 region, Panx1 knockouts had significantly shorter evoked afterdischarges and were resistant to kindling. In response to 4-aminopyridine, neocortical field recordings in slices of Panx1 knockout mice showed reduced instances of electrographic seizure-like events. Cross-frequency coupling analysis of these field potentials highlighted a reduced coupling of excitatory delta-gamma and delta-HF rhythms in the Panx1 knockout. SIGNIFICANCE: These results suggest that Panx1 plays a pivotal role in maintaining neuronal hyperexcitability in epilepsy models and that genetic or pharmacological targeting of Panx1 has anti-convulsant effects.

Epilepsy as a manifestation of a multistate network of oscillatory systems.

The human brain, largely accepted as the most complex biological system known, is still far from being understood in its parts or as a whole. More specifically, biological mechanisms of epileptic states and state transitions are not well understood. Here, we explore the concept of the epilepsy as a manifestation of a multistate network composed of coupled oscillatory units. We also propose that functional coupling between neuroglial elements is a dynamic process, characterized by temporal changes both at short and long time scales. We review various experimental and modelling data suggesting that epilepsy is a pathological manifestation of such a multistate network - both when viewed as a coupled oscillatory network, and as a system of multistate stable state attractors. Based on a coupled oscillators model, we propose a significant role for glial cells in modulating hyperexcitability of the neuroglial networks of the brain. Also, using these concepts, we explain a number of observable phenomena such as propagation patterns of bursts within a seizure in the isolated intact hippocampus in vitro, postictal generalized suppression in human encephalographic seizure data, and changes in seizure susceptibility in epileptic patients. Based on our conceptual model we propose potential clinical applications to estimate brain closeness to ictal transition by means of active perturbations and passive measures during on-going activity.

Imaging the Effects of ß-Hydroxybutyrate on Peri-Infarct Neurovascular Function and Metabolism.

Background and Purpose- Recent evidence suggests great potential of metabolically targeted interventions for treating neurological disorders. We investigated the use of the endogenous ketone body ß-hydroxybutyrate (BHB) as an alternate metabolic substrate for the brain in the acute phase of ischemia because postischemic hyperglycemia and brain glucose metabolism elevation compromise functional recovery. Methods- We delivered BHB (or vehicle) 1 hour after ischemic insult induced by cortical microinjection of endothelin-1 in sensorimotor cortex of rats. Two days after ischemic insult, the rats underwent multimodal characterization of the BHB effects. We examined glucose uptake on 2-Deoxy-d-glucose chemical exchange saturation transfer magnetic resonance imaging, cerebral hemodynamics on continuous arterial spin labeling magnetic resonance imaging, resting-state field potentials by intracerebral multielectrode arrays, Neurological Deficit Score, reactive oxygen species production, and astrogliosis and neuronal death. Results- When compared with vehicle-administered animals, BHB-treated cohort showed decreased peri-infarct neuronal glucose uptake which was associated with reduced oxidative stress, diminished astrogliosis and neuronal death. Functional examination revealed ameliorated neuronal functioning, normalized perilesional resting perfusion, and ameliorated cerebrovascular reactivity to hypercapnia, suggesting improved functioning. Cellular and functional recovery of the neurogliovascular unit in the BHB-treated animals was associated with improved performance on the withdrawal test. Conclusions- We characterize the effects of the ketone body BHB administration at cellular and system levels after focal cortical stroke. The results demonstrate that BHB curbs the peri-infarct glucose-metabolism driven production of reactive oxygen species and astrogliosis, culminating in improved neurogliovascular and functional recovery.

Early-stage attenuation of phase-amplitude coupling in the hippocampus and medial prefrontal cortex in a transgenic rat model of Alzheimer's disease.

Alzheimer's disease (AD) is pathologically characterized by amyloid-ß peptide (Aß) accumulation, neurofibrillary tangle formation, and neurodegeneration. Preclinical studies on neuronal impairments associated with progressive amyloidosis have demonstrated some Aß-dependent neuronal dysfunction including modulation of gamma-aminobutyric acid-ergic signaling. The present work focuses on the early stage of disease progression and uses TgF344-AD rats that recapitulate a broad repertoire of AD-like pathologies to investigate the neuronal network functioning using simultaneous intracranial recordings from the hippocampus (HPC) and the medial prefrontal cortex (mPFC), followed by pathological analyses of gamma-aminobutyric acid (GABAA ) receptor subunits α1, α5, and δ, and glutamic acid decarboxylases (GAD65 and GAD67). Concomitant to amyloid deposition and tau hyperphosphorylation, low-gamma band power was strongly attenuated in the HPC and mPFC of TgF344-AD rats in comparison to those in non-transgenic littermates. In addition, the phase-amplitude coupling of the neuronal networks in both areas was impaired, evidenced by decreased modulation of theta band phase on gamma band amplitude in TgF344-AD animals. Finally, the gamma coherence between HPC and mPFC was attenuated as well. These results demonstrate significant neuronal network dysfunction at an early stage of AD-like pathology. This network dysfunction precedes the onset of cognitive deficits and is likely driven by Aß and tau pathologies. This article is part of the Special Issue "Vascular Dementia".

Brief activation of GABAergic interneurons initiates the transition to ictal events through post-inhibitory rebound excitation.

Activation of γ-aminobutyric acid (GABAA) receptors have been associated with the onset of epileptiform events. To investigate if a causal relationship exists between GABAA receptor activation and ictal event onset, we activated inhibitory GABAergic networks in the superficial layer (2/3) of the somatosensory cortex during hyperexcitable conditions using optogenetic techniques in mice expressing channelrhodopsin-2 in all GABAergic interneurons. We found that a brief 30ms light pulse reliably triggered either an interictal-like event (IIE) or ictal-like ("ictal") event in the in vitro cortical 4-Aminopyridine (4-AP) slice model. The link between light pulse and epileptiform event onset was lost following blockade of GABAA receptors with bicuculline methiodide. Additionally, recording the chronological sequence of events following a light pulse in a variety of configurations (whole-cell, gramicidin-perforated patch, and multi-electrode array) demonstrated an initial hyperpolarization followed by post-inhibitory rebound spiking and a subsequent slow depolarization at the transition to epileptiform activity. Furthermore, the light-triggered ictal events were independent of the duration or intensity of the initiating light pulse, suggesting an underlying regenerative mechanism. Moreover, we demonstrated that brief GABAA receptor activation can initiate ictal events in the in vivo 4-AP mouse model, in another common in vitro model of epileptiform activity, and in neocortical tissue resected from epilepsy patients. Our findings reveal that the synchronous activation of GABAergic interneurons is a robust trigger for ictal event onset in hyperexcitable cortical networks.

Neurovascular unit remodelling in the subacute stage of stroke recovery.

Brain plasticity following focal cerebral ischaemia has been observed in both stroke survivors and in preclinical models of stroke. Endogenous neurovascular adaptation is at present incompletely understood yet its potentiation may improve long-term functional outcome. We employed longitudinal MRI, intracranial array electrophysiology, Montoya Staircase testing, and immunofluorescence to examine function of brain vessels, neurons, and glia in addition to forelimb skilled reaching during the subacute stage of ischemic injury progression. Focal ischemic stroke (~100mm3 or ~20% of the total brain volume) was induced in adult Sprague-Dawley rats via direct injection of endothelin-1 (ET-1) into the right sensori-motor cortex, producing sustained impairment in left forelimb reaching ability. Resting perfusion and vascular reactivity to hypercapnia in the peri-lesional cortex were elevated by approximately 60% and 80% respectively seven days following stroke. At the same time, the normal topological pattern of local field potential (LFP) responses to peripheral somatosensory stimulation was abolished and the average power of spontaneous LFP activity attenuated by approximately 50% relative to the contra-lesional cortex, suggesting initial response attenuation within the peri-infarct zone. By 21 days after stroke, perilesional blood flow resolved, but peri-lesional vascular reactivity remained elevated. Concomitantly, the LFP response amplitudes increased with distance from the site of ET-1 injection, suggesting functional remodelling from the core of the lesion to its periphery. This notion was further buttressed by the lateralization of spontaneous neuronal activity: by day 21, the average ipsi-lesional power of spontaneous LFP activity was almost twice that of the contra-lesional cortex. Over the observation period, the peri-lesional cortex exhibited increased vascular density, along with neuronal loss, astrocytic activation, and recruitment and activation of microglia and macrophages, with neuronal loss and inflammation extending beyond the peri-lesional cortex. These findings highlight the complex relationship between neurophysiological state and behaviour and provide evidence of highly dynamic functional changes in the peri-infarct zone weeks following the ischemic insult, suggesting an extended temporal window for therapeutic interventions.

Astrocytic gap junction blockade markedly increases extracellular potassium without causing seizures in the mouse neocortex.

Extracellular potassium concentration, [K+]o, is a major determinant of neuronal excitability. In the healthy brain, [K+]o levels are tightly controlled. During seizures, [K+]o increases up to 15mM and is thought to cause seizures due to its depolarizing effect. Although astrocytes have been suggested to play a key role in the redistribution (or spatial buffering) of excess K+ through Connexin-43 (Cx43)-based Gap Junctions (GJs), the relation between this dynamic regulatory process and seizure generation remains unknown. Here we contrasted the role of astrocytic GJs and hemichannels by studying the effect of GJ and hemichannel blockers on [K+]o regulation in vivo. [K+]o was measured by K+-sensitive microelectrodes. Neuronal excitability was estimated by local field potential (LFP) responses to forepaw stimulation and changes in the power of resting state activity. Starting at the baseline [K+]o level of 1.61±0.3mM, cortical microinjection of CBX, a broad spectrum connexin channel blocker, increased [K+]o to 11±3mM, Cx43 GJ/hemichannel blocker Gap27 increased it from 1.9±0.7 to 9±1mM. At these [K+]o levels, no seizures were observed. Cx43 hemichannel blockade with TAT-Gap19 increased [K+]o by only ~1mM. Microinjection of 4-aminopyridine, a known convulsant, increased [K+]o to ~10mM and induced spontaneously recurring seizures, whereas direct application of K+ did not trigger seizure activity. These findings are the first in vivo demonstration that astrocytic GJs are major determinants for the spatial buffering of [K+]o and that an increase in [K+]o alone does not trigger seizures in the neocortex.

Mortality with brainstem seizures from focal 4-aminopyridine-induced recurrent hippocampal seizures.

OBJECTIVE: Sudden unexplained death in epilepsy is the leading cause of death in young adult epilepsy patients, typically occurring during the early postictal period, presumably resulting from brainstem and cardiorespiratory dysfunction. We hypothesized that ictal discharges in the brainstem disrupt the cardiorespiratory network, causing mortality. To study this hypothesis, we chose an animal model comprising focal unilateral hippocampal injection of 4-aminopyridine (4-AP), which produced focal recurrent hippocampal seizures with secondary generalization in awake, behaving rats. METHODS: We studied ictal and interictal intracranial electrographic activity (iEEG) in 23 rats implanted with a custom electrode array into the hippocampus, the contralateral cortex, and brainstem. The hippocampal electrodes contained a cannula to administer the potassium channel blocker and convulsant (4-AP). iEEG was recorded continuously before, during, and after seizures induced by 4-AP infusion into the hippocampus. RESULTS: The control group (n = 5) was monitored for 2-3 months, and the weekly baseline iEEG recordings showed long-term stability. The low-dose group (1 µL 4-AP, 40 mm, n = 5) exhibited local electrographic seizures without spread to the contralateral cerebral cortex or brainstem. The high-dose group (5 µL 4-AP, 40 mm, n = 3) had several hippocampal electrographic seizures, which spread contralaterally and triggered brainstem discharges within 40 min, and were associated with violent motor seizures followed by dyspnea and respiratory arrest, with cortical and hippocampal iEEG flattening. The group that received high-dose 4-AP without brainstem implantation (n = 5) had similar seizure-related respiratory difficulties. Finally, five rats that received high-dose 4-AP without EEG recording also developed violent motor seizures with postictal respiratory arrest. Following visualized respiratory arrest in groups III, IV, and V, manual respiratory resuscitation was successful in five of 13 animals. SIGNIFICANCE: These studies show that hippocampal seizure activity can spread or trigger brainstem epileptiform discharges that may cause mortality, possibly mediated by respiratory network dysfunction.

Hungry Neurons: Metabolic Insights on Seizure Dynamics.

Epilepsy afflicts up to 1.6% of the population and the mechanisms underlying the appearance of seizures are still not understood. In past years, many efforts have been spent trying to understand the mechanisms underlying the excessive and synchronous firing of neurons. Traditionally, attention was pointed towards synaptic (dys)function and extracellular ionic species (dys)regulation. Recently, novel clinical and preclinical studies explored the role of brain metabolism (i.e., glucose utilization) of seizures pathophysiology revealing (in most cases) reduced metabolism in the inter-ictal period and increased metabolism in the seconds preceding and during the appearance of seizures. In the present review, we summarize the clinical and preclinical observations showing metabolic dysregulation during epileptogenesis, seizure initiation, and termination, and in the inter-ictal period. Recent preclinical studies have shown that 2-Deoxyglucose (2-DG, a glycolysis blocker) is a novel therapeutic approach to reduce seizures. Furthermore, we present initial evidence for the effectiveness of 2-DG in arresting 4-Aminopyridine induced neocortical seizures in vivo in the mouse.

Differential expression of astrocytic connexins in a mouse model of prenatal alcohol exposure.

Maternal alcohol consumption during gestation can cause serious injury to the fetus, and may result in a range of physiological and behavioral impairments, including increased seizure susceptibility, that are collectively termed fetal alcohol spectrum disorder (FASD). The cellular mechanisms underlying increased seizure susceptibility in FASD are not well understood, but could involve altered excitatory coupling of neuronal populations mediated by gap junction proteins. We utilized a mouse model of the prenatal alcohol exposure (PAE) to study the expression pattern of connexin (Cx) major components of gap junctions, and pannexin proteins, which form membrane channels, in the brain of 2-3weeks old PAE and control postnatal offspring. PAE during the first trimester-equivalent period of pregnancy in mice resulted in significant up-regulation of Cx30 mRNA and Cx30 total protein in the hippocampus of PAE animals compared to age-matched controls. Surface level expression of both dimeric and monomeric Cx30 were also found to be significantly up-regulated in both hippocampus and cerebral cortex of PAE animals compared to age-matched controls. On the membrane surface, the fast migrating form of Cx43 was found to be up-regulated in the hippocampus of PAE mice. However, we did not see any up-regulation of the phosphorylated forms of Cx43 on the membrane surface. These results indicate that the expression and processing of astrocytic connexins (Cx30, Cx43) are up-regulated in the brain of PAE offspring, and these changes could play a role in the cerebral hyperexcitability observed in these animals.