Hippocampal Transplants of Fetal GABAergic Progenitors Regulate Adult Neurogenesis in Mice with Temporal Lobe Epilepsy

GABAergic interneurons within the dentate gyrus of the hippocampus regulate adult neurogenesis, including proliferation, migration, and maturation of new granule cells born in the subgranular zone (SGZ) of the dentate gyrus (DG). In temporal lobe epilepsy (TLE), some adult-born granule cells migrate ectopically into the hilus, and these cells contribute to increased hyperexcitability and seizures. Yet, transplanting embryonic day 13.5 fetal mouse medial ganglionic eminence (MGE) GABAergic progenitors into the hippocampus of mice with TLE ameliorates spontaneous seizures, due in part, to increased postsynaptic inhibition of adult-born granule cells. Here, we asked whether MGE progenitor transplantation affects earlier stages of adult neurogenesis, by comparing patterns of neurogenesis in naive mice and epileptic (TLE) mice, with or without MGE transplants. In naive and TLE mice, transplanted MGE cells showed comparable migration and process outgrowth. However, in TLE mice with MGE transplants, fewer adult-born Type 3 progenitors migrated ectopically. Furthermore, more Type 3 progenitors survived and migrated into the granule cell layer (GCL), as determined by immunostaining for doublecortin or the thymidine analogue, bromodeoxyuridine (BrdU). To determine whether MGE transplants affected earlier stages of adult neurogenesis, we compared proliferation in the SGZ two-hours after pulse labeling with BrdU in naive vs. TLE mice and found no significant differences. Furthermore, MGE progenitor transplantation had no effect on cell proliferation in the SGZ. Moreover, when compared to naive mice, TLE mice showed increases in inverted Type 1 progenitors and Type 2 progenitors, concomitant with a decrease in the normally oriented radial Type 1 progenitors. Strikingly, these alterations were abrogated by MGE transplantation. Thus, MGE transplants appear to reverse seizure-induced abnormalities in adult neurogenesis by increasing differentiation and radial migration of adult-born granule cell progenitors, outcomes that may ameliorate seizures.

DL-3-n-butylphthalide promotes hippocampal neurogenesis and reduces mossy fiber sprouting in chronic temporal lobe epilepsy rats

Background A decrease in hippocampal neurogenesis is considered an important cause of cognitive impairment, while changes in mossy fiber sprouting are closely related to development of spontaneous recurrent seizures in chronic temporal lobe epilepsy (TLE). Racemic l-3-n-butylphthalide (DL-NBP) can alleviate cognitive impairment in ischemic stroke and Alzheimer’s disease by promoting neurogenesis. DL-NBP treatment can also improve cognitive function and reduce seizure incidence in chronic epileptic mice. However, the mechanisms of action of DL-NBP remain unclear. The aim of the present study was to examine the effects of DL-NBP on mossy fiber sprouting, hippocampal neurogenesis, spontaneous epileptic seizures, and cognitive functioning in the chronic phase of TLE. Methods Nissl staining was used to evaluate hippocampal injury, while immunofluorescent staining was used to analyze hippocampal neurogenesis. The duration of spontaneous seizures was measured by electroencephalography. The Morris water maze was used to evaluate cognitive function. Timm staining was used to assess mossy fiber sprouting. Results TLE animals showed reduced proliferation of newborn neurons, cognitive dysfunction, and spontaneous seizures. Treatment with DL-NBP after TLE increased the proliferation and survival of newborn neurons in the dentate gyrus, reversed the neural loss in the hippocampus, alleviated cognitive impairments, and decreased mossy fiber sprouting and long-term spontaneous seizure activity. Conclusions We provided pathophysiological and morphological evidence that DL-NBP might be a useful therapeutic for the treatment of TLE.

Endocannabinoid-Mediated Control of Neural Circuit Excitability and Epileptic Seizures

Research on endocannabinoid signaling has greatly advanced our understanding of how the excitability of neural circuits is controlled in health and disease. In general, endocannabinoid signaling at excitatory synapses suppresses excitability by inhibiting glutamate release, while that at inhibitory synapses promotes excitability by inhibiting GABA release, although there are some exceptions in genetically epileptic animal models. In the epileptic brain, the physiological distributions of endocannabinoid signaling molecules are disrupted during epileptogenesis, contributing to the occurrence of spontaneous seizures. However, it is still unknown how endocannabinoid signaling changes during seizures and how the redistribution of endocannabinoid signaling molecules proceeds during epileptogenesis. Recent development of cannabinoid sensors has enabled us to investigate endocannabinoid signaling in much greater spatial and temporal details than before. Application of cannabinoid sensors to epilepsy research has elucidated activity-dependent changes in endocannabinoid signaling during seizures. Furthermore, recent endocannabinoid research has paved the way for the clinical use of cannabidiol for the treatment of refractory epilepsy, such as Dravet syndrome, Lennox-Gastaut syndrome and tuberous sclerosis complex. Cannabidiol significantly reduces seizures and is considered to have comparable tolerability to conventional antiepileptic drugs. In this article, we introduce recent advances in research on the roles of endocannabinoid signaling in epileptic seizures and discuss future directions.

Excess interictal activity marks seizure prone cortical areas and mice in a genetic epilepsy model

Genetic epilepsies are often caused by variants in widely expressed genes, potentially impacting numerous brain regions and functions. For instance, gain-of-function (GOF) variants in the widely expressed Na+-activated K+ channel gene KCNT1 alter basic neurophysiological and synaptic properties of cortical neurons, leading to developmental epileptic encephalopathy. Yet, aside from causing seizures, little is known about how such variants reshape interictal brain activity, and how this relates to epileptic activity and other disease symptoms. To address this knowledge gap, we monitored neural activity across the dorsal cortex in a mouse model of human KCNT1-related epilepsy using in vivo, awake widefield Ca2+ imaging. We observed 52 spontaneous seizures and 1700 interictal epileptiform discharges (IEDs) in homozygous mutant (Kcnt1m/m) mice, allowing us to map their appearance and spread at high spatial resolution. Outside of seizures and IEDs, we detected ~46,000 events, representing interictal cortical activity, in both Kcnt1m/m and wild-type (WT) mice, and we classified them according to their spatial profiles. Spontaneous seizures and IEDs emerged within a consistent set of susceptible cortical areas, and seizures propagated both contiguously and non-contiguously within these areas in a manner influenced, but not fully determined, by underlying synaptic connectivity. Seizure emergence was predicted by a progressive concentration of total cortical activity within the impending seizure emergence zone. Outside of seizures and IEDs, similar events were detected in WT and Kcnt1m/m mice, suggesting that the spatial structure of interictal activity was largely preserved. Several features of these events, however, were altered in Kcnt1m/m mice. Most event types were briefer, and their intensity more variable, across Kcnt1m/m mice; mice showing more intense activity spent more time in seizure. Furthermore, the rate of events whose spatial profile overlapped with where seizures and IEDs emerged was increased in Kcnt1m/m mice. Taken together, these results demonstrate that an epilepsy-causing K+ channel variant broadly alters physiology. Yet, outside of seizures and IEDs, it acts not to produce novel types of cortical activity, but rather to modulate its amount. The areas where seizures and IEDs emerge show excessively frequent and intense interictal activity and the mean intensity of an individual's cortical activity predicts its seizure burden. These findings provide critical guidance for targeting future research and therapy development.

Pathogenic in-Frame Variants in SCN8A: Expanding the Genetic Landscape of SCN8A-Associated Disease

Numerous SCN8A mutations have been identified, of which, the majority are de novo missense variants. Most mutations result in epileptic encephalopathy; however, some are associated with less severe phenotypes. Mouse models generated by knock-in of human missense SCN8A mutations exhibit seizures and a range of behavioral abnormalities. To date, there are only a few Scn8a mouse models with in-frame deletions or insertions, and notably, none of these mouse lines exhibit increased seizure susceptibility. In the current study, we report the generation and characterization of two Scn8a mouse models (ΔIRL/+ and ΔVIR/+) carrying overlapping in-frame deletions within the voltage sensor of domain 4 (DIVS4). Both mouse lines show increased seizure susceptibility and infrequent spontaneous seizures. We also describe two unrelated patients with the same in-frame SCN8A deletion in the DIV S5-S6 pore region, highlighting the clinical relevance of this class of mutations.

Cognitive Impairment and Mossy Fiber Sprouting in a Rat Model of Drug-Resistant Epilepsy Induced by Lithium–Pilocarpine

Background: The mossy fiber sprouting (MFS) in the dentate gyrus is a common pathological change of epilepsy. Previous studies suggested that it is associated with drug-resistant epilepsy, and mossy cells control spontaneous seizures and spatial memory. Methods: We investigated the correlations among cognitive impairment, MFS, seizure frequency and drug resistance in a rat model of epilepsy induced by lithium–pilocarpine. Phenytoin and phenobarbital were used to screen drug resistance. Cognitive function and MFS were detected through the novel object recognition (NOR) test, Morris water maze (MWM) test and Timm staining. Results: The results showed that object memory and spatial memory functions were both significantly impaired in rats with epilepsy, and only spatial memory impairment was more severe in rats with drug-resistant epilepsy. More frequent spontaneous seizures and more obvious MFS were observed in the drug-resistant rats. The seizure frequency was significantly associated with the MWM performance but not with the NOR performance in rats with epilepsy. The degree of MFS was significantly associated with seizure frequency and spatial memory function. Conclusion: Taken together, these correlations among drug resistance, seizure frequency, spatial memory impairment and MFS suggested the possibility of a common pathological mechanism. More studies are needed to clarify the underlying mechanism behind these correlations and the detailed role of MFS in epilepsy. The mechanism of mossy cell change may be an important target for the treatment of seizures, drug resistance and cognitive dysfunction in patients with epilepsy.

Food intake precipitates seizures in temporal lobe epilepsy

Various factors have been considered as potential seizure precipitants. We here assessed the temporal association of food intake and seizure occurrence, and characteristics of seizures and epilepsy syndromes involved. 596 seizures from 100 consecutive patients undergoing long-term video-EEG monitoring were analyzed. Preictal periods of 60 min were assessed as to the occurrence of food intake, and latencies between food intake and seizure onset were analyzed. Seizures of temporal origin were highly significantly more frequently preceded by food intake compared to those of extratemporal origin; and were associated with shorter food intake-seizure latency. Seizure precipitation by food intake showed male predominance. Shorter food intake-seizure latency was associated with less severe seizures and less frequent contralateral spread of epileptic discharges. We here show for the first time that not only in specific rare reflex epilepsies but in the most frequent form of focal epilepsy, temporal lobe epilepsy, seizures are significantly precipitated by food intake. Seizure occurrence was increased over a period of up to one hour following food intake, and remained more localized in terms of both ictal EEG spread and as reflected by seizure severity. This finding supports the emerging concepts of ictogenesis, implying a continuum between reflex and spontaneous seizures—instead a dichotomy between them.

Kv1.1 channels mediate network excitability and feed-forward inhibition in local amygdala circuits

Kv1.1 containing potassium channels play crucial roles towards dampening neuronal excitability. Mice lacking Kv1.1 subunits (Kcna1−/−) display recurrent spontaneous seizures and often exhibit sudden unexpected death. Seizures in Kcna1−/− mice resemble those in well-characterized models of temporal lobe epilepsy known to involve limbic brain regions and spontaneous seizures result in enhanced cFos expression and neuronal death in the amygdala. Yet, the functional alterations leading to amygdala hyperexcitability have not been identified. In this study, we used Kcna1−/− mice to examine the contributions of Kv1.1 subunits to excitability in neuronal subtypes from basolateral (BLA) and central lateral (CeL) amygdala known to exhibit distinct firing patterns. We also analyzed synaptic transmission properties in an amygdala local circuit predicted to be involved in epilepsy-related comorbidities. Our data implicate Kv1.1 subunits in controlling spontaneous excitatory synaptic activity in BLA pyramidal neurons. In the CeL, Kv1.1 loss enhances intrinsic excitability and impairs inhibitory synaptic transmission, notably resulting in dysfunction of feed-forward inhibition, a critical mechanism for controlling spike timing. Overall, we find inhibitory control of CeL interneurons is reduced in Kcna1−/− mice suggesting that basal inhibitory network functioning is less able to prevent recurrent hyperexcitation related to seizures.