De novo missense variants in the KCNQ2 gene encoding the Kv7.2 subunit of voltage‐gated potassium Kv7/M channels are the main cause of developmental and epileptic encephalopathy with neonatal onset. ...Although seizures usually resolve during development, cognitive/motor deficits persist. To gain a better understanding of the cellular mechanisms underlying network dysfunction and their progression over time, we investigated in vivo, using local field potential recordings of freely moving animals, and ex vivo in layers II/III and V of motor cortical slices, using patch‐clamp recordings, the electrophysiological properties of pyramidal cells from a heterozygous knock‐in mouse model carrying the Kv7.2 p.T274M pathogenic variant during neonatal, postweaning and juvenile developmental stages. We found that knock‐in mice displayed spontaneous seizures preferentially at postweaning rather than at juvenile stages. At the cellular level, the variant led to a reduction in M current density/conductance and to neuronal hyperexcitability. These alterations were observed during the neonatal period in pyramidal cells of layers II/III and during the postweaning stage in pyramidal cells of layer V. Moreover, there was an increase in the frequency of spontaneous network‐driven events mediated by GABA receptors, suggesting that the excitability of interneurons was also increased. However, all these alterations were no longer observed in layers II/III and V of juvenile mice. Thus, our data indicate that the action of the variant is regulated developmentally. This raises the possibility that the age‐related seizure remission observed in KCNQ2‐related developmental and epileptic encephalopathy patients results from a time‐limited alteration of Kv7 channel activity and neuronal excitability.
Key points
The electrophysiological impact of the pathogenic c.821C>T mutation of the KCNQ2 gene (p.T274M variant in Kv7.2 subunit) related to developmental and epileptic encephalopathy has been analysed both in vivo and ex vivo in layers II/III and V of motor cortical slices from a knock‐in mouse model during development at neonatal, postweaning and juvenile stages.
M current density and conductance are decreased and the excitability of layer II/III pyramidal cells is increased in slices from neonatal and postweaning knock‐in mice but not from juvenile knock‐in mice.
M current and excitability of layer V pyramidal cells are impacted in knock‐in mice only at the postweaning stage.
Spontaneous GABAergic network‐driven events can be recorded until the postweaning stage, and their frequency is increased in layers II/III of the knock‐in mice.
Knock‐in mice display spontaneous seizures preferentially at postweaning rather than at juvenile stages.
figure legend Knock‐in mice harbouring the heterozygous pathogenic p.T274M variant in the Kv7.2 subunit (c.821C>T mutation of the KCNQ2 gene) related to developmental and epileptic encephalopathy displayed epileptic seizures preferentially at postweaning rather than at juvenile developmental stages. At the cellular level, in motor cortical slices the variant led to a reduction in M current density, to a hyperexcitability of pyramidal cells and to an increase in the frequency of spontaneous network‐driven events mediated by GABA receptors. All these alterations were time limited and were observed in pyramidal cells of neonatal mice until postweaning, but not of juvenile mice, in which the pyramidal cells had electrophysiological properties similar to those of wild‐type mice.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Objective
Early onset epileptic encephalopathy with suppression‐burst is one of the most severe epilepsy phenotypes in human patients. A significant proportion of cases have a genetic origin, and the ...most frequently mutated gene is KCNQ2, encoding Kv7.2, a voltage‐dependent potassium channel subunit, leading to so‐called KCNQ2‐related epileptic encephalopathy (KCNQ2‐REE). To study the pathophysiology of KCNQ2‐REE in detail and to provide a relevant preclinical model, we generated and described a knock‐in mouse model carrying the recurrent p.(Thr274Met) variant.
Methods
We introduced the p.(Thr274Met) variant by homologous recombination in embryonic stem cells, injected into C57Bl/6N blastocysts and implanted in pseudopregnant mice. Mice were then bred with 129Sv Cre‐deleter to generate heterozygous mice carrying the p.(Thr274Met), and animals were maintained on the 129Sv genetic background. We studied the development of this new model and performed in vivo electroencephalographic (EEG) recordings, neuroanatomical studies at different time points, and multiple behavioral tests.
Results
The Kcnq2Thr274Met/+ mice are viable and display generalized spontaneous seizures first observed between postnatal day 20 (P20) and P30. In vivo EEG recordings show that the paroxysmal events observed macroscopically are epileptic seizures. The brain of the Kcnq2Thr274Met/+ animals does not display major structural defects, similar to humans, and their body weight is normal. Kcnq2Thr274Met/+ mice have a reduced life span, with a peak of unexpected death occurring for 25% of the animals by 3 months of age. Epileptic seizures were generally not observed when animals grew older. Behavioral characterization reveals important deficits in spatial learning and memory in adults but no gross abnormality during early neurosensory development.
Significance
Taken together, our results indicate that we have generated a relevant model to study the pathophysiology of KCNQ2‐related epileptic encephalopathy and perform preclinical research for that devastating and currently intractable disease.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
OBJECTIVE:We investigated whether interictal epileptiform discharges (IED) in the human hippocampus are related to impairment of specific memory processes, and which characteristics of hippocampal ...IED are most associated with memory dysfunction.
METHODS:Ten patients had depth electrodes implanted into their hippocampi for preoperative seizure localization. EEG was recorded during 2,070 total trials of a short-term memory task, with memory processing categorized into encoding, maintenance, and retrieval. The influence of hippocampal IED on these processes was analyzed and adjusted to account for individual differences between patients.
RESULTS:Hippocampal IED occurring in the memory retrieval period decreased the likelihood of a correct response when they were contralateral to the seizure focus (p < 0.05) or bilateral (p < 0.001). Bilateral IED during the memory maintenance period had a similar effect (p < 0.01), particularly with spike-wave complexes of longer duration (p < 0.01). IED during encoding had no effect, and reaction time was also unaffected by IED.
CONCLUSIONS:Hippocampal IED in humans may disrupt memory maintenance and retrieval, but not encoding. The particular effects of bilateral IED and those contralateral to the seizure focus may relate to neural compensation in the more functional hemisphere. This study provides biological validity to animal models in the study of IED-related transient cognitive impairment. Moreover, it strengthens the argument that IED may contribute to cognitive impairment in epilepsy depending upon when and where they occur.
Objective
Glutamate‐gated N‐methyl‐d‐aspartate receptors (NMDARs) are instrumental to brain development and functioning. Defects in the GRIN2A gene, encoding the GluN2A subunit of NMDARs, cause ...slow‐wave sleep (SWS)‐related disorders of the epilepsy‐aphasia spectrum (EAS). The as‐yet poorly understood developmental sequence of early EAS‐related phenotypes, and the role of GluN2A‐containing NMDARs in the development of SWS and associated electroencephalographic (EEG) activity patterns, were investigated in Grin2a knockout (KO) mice.
Methods
Early social communication was investigated by ultrasonic vocalization (USV) recordings; the relationship of electrical activity of the cerebral cortex with SWS was studied using deep local field potential or chronic EEG recordings at various postnatal stages.
Results
Grin2a KO pups displayed altered USV and increased occurrence of high‐voltage spindles. The pattern of slow‐wave activity induced by low‐dose isoflurane was altered in Grin2a KO mice in the 3rd postnatal week and at 1 month of age. These alterations included strong suppression of the delta oscillation power and an increase in the occurrence of the spike‐wave bursts. The proportion of SWS and the sleep quality were transiently reduced in Grin2a KO mice aged 1 month but recovered by the age of 2 months. Grin2a KO mice also displayed spontaneous spike‐wave discharges, which occurred nearly exclusively during SWS, at 1 and 2 months of age.
Significance
The impaired vocal communication, the spike‐wave discharges occurring almost exclusively in SWS, and the age‐dependent alteration of SWS that were all seen in Grin2a KO mice matched the sleep‐related and age‐dependent manifestations seen in children with EAS, hence validating the Grin2a KO as a reliable model of EAS disorders. Our data also show that GluN2A‐containing NMDARs are involved in slow‐wave activity, and that the period of postnatal brain development (postnatal day 30) when several anomalies peaked might be critical for GluN2A‐dependent, sleep‐related physiological and pathological processes.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The epileptic encephalopathies are conditions in which neurological deterioration is attributable entirely or partly to epileptic activity and is due to very frequent or severe seizures or severely ...abnormal electroencephalograms (EEGs), or both. Evidence for the concept that seizures or the abnormal EEGs are responsible for the cognitive deterioration is the observation that patients can improve dramatically when therapy eliminates or reduces seizure frequency and improves or normalizes the EEG. For example, children with the syndrome of continuous spike–wave of sleep (CSWS) have electrical status epilepticus during sleep (ESES) and cognitive regression. Although seizures often occur in the disorder, there are indications that the EEG abnormalities are responsible for the cognitive regression. Interictal spikes, which correspond to a large intracellular depolarization with evoked action potentials, in many ways mimic a “miniseizure.” Interictal spikes can result in transitory cognitive impairment with the type of deficit dependent on where in the cortex the spike arises. We suggest that interictal spikes, particularly if frequent and widespread, can impair cognitive abilities, through interference with waking learning and memory, and memory consolidation during sleep.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The dentate gyrus is considered to function as an inhibitory gate limiting excitatory input to the hippocampus. Following status epilepticus (SE), this gating function is reduced and granule cells ...become hyper-excitable. Dentate spikes (DS) are large amplitude potentials observed in the dentate gyrus (DG) of normal animals. DS are associated with membrane depolarization of granule cells, increased activity of hilar interneurons and suppression of CA3 and CA1 pyramidal cell firing. Therefore, DS could act as an anti-excitatory mechanism. Because of the altered gating function of the dentate gyrus following SE, we sought to investigate how DS are affected following pilocarpine-induced SE. Two weeks following lithium-pilocarpine SE induction, hippocampal EEG was recorded in male Sprague-Dawley rats with 16-channel silicon probes under urethane anesthesia. Probes were placed dorso-ventrally to encompass either CA1-CA3 or CA1-DG layers. Large amplitude spikes were detected from EEG recordings and subject to current source density analysis. Probe placement was verified histologically to evaluate the anatomical localization of current sinks and the origin of DS. In 9 of 11 pilocarpine-treated animals and two controls, DS were confirmed with large current sinks in the molecular layer of the dentate gyrus. DS frequency was significantly increased in pilocarpine-treated animals compared to controls. Additionally, in pilocarpine-treated animals, DS displayed current sinks in the outer, middle and/or inner molecular layers. However, there was no difference in the frequency of events when comparing between layers. This suggests that following SE, DS can be generated by input from medial and lateral entorhinal cortex, or within the dentate gyrus. DS were associated with an increase in multiunit activity in the granule cell layer, but no change in CA1. These results suggest that following SE there is an increase in DS activity, potentially arising from hyperexcitability along the hippocampal-entorhinal pathway or within the dentate gyrus itself.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Objective
Cognitive impairment is common in epilepsy, particularly in memory function. Interictal spikes (IISs) are thought to disrupt cognition, but it is difficult to delineate their contribution ...from general impairments in memory produced by etiology and seizures. We investigated the transient impact of focal IISs on the hippocampus, a structure crucial for learning and memory and yet highly prone to IISs in temporal lobe epilepsy (TLE).
Methods
Bilateral hippocampal depth electrodes were implanted into 14 Sprague‐Dawley rats, followed by intrahippocampal pilocarpine or saline infusion unilaterally. Rats that developed chronic spikes were trained in a hippocampal‐dependent operant behavior task, delayed‐match‐to‐sample. Depth‐electroencephalogram (EEG) was recorded during 5,562 trials among five rats, and within‐subject analyses evaluated the impact of hippocampal spikes on short‐term memory operations.
Results
Hippocampal spikes that occurred during memory retrieval strongly impaired performance (p < 0.001). However, spikes that occurred during memory encoding or memory maintenance did not affect performance in those trials. Hippocampal spikes also affected response latency, adding approximately 0.48 seconds to the time taken to respond (p < 0.001).
Interpretation
We found that focal IIS‐related interference in cognition extends to structures in the limbic system, which required intrahippocampal recordings. Hippocampal spikes seem most harmful if they occur when hippocampal function is critical, extending human studies showing that cortical spikes are most disruptive during active cortical functioning. The cumulative effects of spikes could therefore impact general cognitive functioning. These results strengthen the argument that suppression of IISs may improve memory and cognitive performance in patients with epilepsy. ANN NEUROL 2010;67:250–257
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Correlated activity in the entorhinal-hippocampal neuronal networks, supported by oscillatory and intermittent population activity patterns is critical for learning and memory. However, when ...and how correlated activity emerges in these networks during development remains largely unknown. Here, we found that during the first postnatal week in non-anaesthetized head-restrained rats, activity in the superficial layers of the medial entorhinal cortex (MEC) and hippocampus was highly correlated, with intermittent population bursts in the MEC followed by early sharp waves (eSPWs) in the hippocampus. Neurons in the superficial MEC layers fired before neurons in the dentate gyrus, CA3 and CA1. eSPW current-source density profiles indicated that perforant/temporoammonic entorhinal inputs and intrinsic hippocampal connections are co-activated during entorhinal-hippocampal activity bursts. Finally, a majority of the entorhinal-hippocampal bursts were triggered by spontaneous myoclonic body movements, characteristic of the neonatal period. Thus, during the neonatal period, activity in the entorhinal cortex (EC) and hippocampus is highly synchronous, with the EC leading hippocampal activation. We propose that such correlated activity is embedded into a large-scale bottom-up circuit that processes somatosensory feedback resulting from neonatal movements, and that it is likely to instruct the development of connections between neocortex and hippocampus.
In addition to affecting a person’s behaviour and risk of accidents, seizures are believed to result in various neuro-physiological changes that disrupt nervous system integrity. Although ...anti-epileptic treatments exist, they are not always effective and in some epilepsy syndromes, such as temporal lobe epilepsy, a large proportion of patients are pharmacologically resistant. In order to develop seizure-preventing treatments, researchers have been trying to identify the neurologicalprocesses leading to seizures. In this issue of Brain ,Neumannandco-workers use extracellular electro-physiological recordings to determine the temporal evolution of neuronal activity preceding and during spontaneous temporal lobe seizures in rats (Neumann et al., 2017). They provide evidence that ictal discharges preferentially recruit specific cell ensembles firing in stereotypical sequences. In contrast to the classic view that seizures result from excessive runaway excitation, they show that the predominant cell types activated during ictal discharges are fast-spiking, putative inhibitory interneurons.
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