No latency to dentate granule cell epileptogenesis in experimental temporal lobe epilepsy with hippocampal sclerosis

Transient Seizure Clusters and Epileptiform Activity Following Widespread Bilateral Hippocampal Interneuron Ablation

Interneuron loss is a prominent feature of temporal lobe epilepsy in both animals and humans and is hypothesized to be critical for epileptogenesis. As loss occurs concurrently with numerous other potentially proepileptogenic changes, however, the impact of interneuron loss in isolation remains unclear. For the present study, we developed an intersectional genetic approach to induce bilateral diphtheria toxin-mediated deletion of Vgat-expressing interneurons from dorsal and ventral hippocampus. In a separate group of mice, the same population was targeted for transient neuronal silencing with DREADDs. Interneuron ablation produced dramatic seizure clusters and persistent epileptiform activity. Surprisingly, after 1 week seizure activity declined precipitously and persistent epileptiform activity disappeared. Occasional seizures (≈1/day) persisted to the end of the experiment at 4 weeks. In contrast to the dramatic impact of interneuron ablation, transient silencing produced large numbers of interictal spikes, a significant but modest increase in seizure occurrence and changes in EEG frequency band power. Taken together, findings suggest that the hippocampus regains relative homeostasis-with occasional breakthrough seizures-in the face of an extensive and abrupt loss of interneurons.

Emerging Molecular Targets for Anti-Epileptogenic and Epilepsy Modifying Drugs

The pharmacological treatment of epilepsy is purely symptomatic. Despite many decades of intensive research, causal treatment of this common neurologic disorder is still unavailable. Nevertheless, it is expected that advances in modern neuroscience and molecular biology tools, as well as improved animal models may accelerate designing antiepileptogenic and epilepsy-modifying drugs. Epileptogenesis triggers a vast array of genomic, epigenomic and transcriptomic changes, which ultimately lead to morphological and functional transformation of specific neuronal circuits resulting in the occurrence of spontaneous convulsive or nonconvulsive seizures. Recent decades unraveled molecular processes and biochemical signaling pathways involved in the proepileptic transformation of brain circuits including oxidative stress, apoptosis, neuroinflammatory and neurotrophic factors. The "omics" data derived from both human and animal epileptic tissues, as well as electrophysiological, imaging and neurochemical analysis identified a plethora of possible molecular targets for drugs, which could interfere with various stages of epileptogenetic cascade, including inflammatory processes and neuroplastic changes. In this narrative review, we briefly present contemporary views on the neurobiological background of epileptogenesis and discuss the advantages and disadvantages of some more promising molecular targets for antiepileptogenic pharmacotherapy.

Anti-Seizure and Neuronal Protective Effects of Irisin in Kainic Acid-Induced Chronic Epilepsy Model with Spontaneous Seizures

An increased level of reactive oxygen species is a key factor in neuronal apoptosis and epileptic seizures. Irisin reportedly attenuates the apoptosis and injury induced by oxidative stress. Therefore, we evaluated the effects of exogenous irisin in a kainic acid (KA)-induced chronic spontaneous epilepsy rat model. The results indicated that exogenous irisin significantly attenuated the KA-induced neuronal injury, learning and memory defects, and seizures. Irisin treatment also increased the levels of brain-derived neurotrophic factor (BDNF) and uncoupling protein 2 (UCP2), which were initially reduced following KA administration. Furthermore, the specific inhibitor of UCP2 (genipin) was administered to evaluate the possible protective mechanism of irisin. The reduced apoptosis, neurodegeneration, and spontaneous seizures in rats treated with irisin were significantly reversed by genipin administration. Our findings indicated that neuronal injury in KA-induced chronic epilepsy might be related to reduced levels of BDNF and UCP2. Moreover, our results confirmed the inhibition of neuronal injury and epileptic seizures by exogenous irisin. The protective effects of irisin may be mediated through the BDNF-mediated UCP2 level. Our results thus highlight irisin as a valuable therapeutic strategy against neuronal injury and epileptic seizures.

A mathematical model of neuroimmune interactions in epileptogenesis for discovering treatment strategies

The development of epilepsy (epileptogenesis) involves a complex interplay of neuronal and immune processes. Here, we present a first-of-its-kind mathematical model to better understand the relationships among these processes. Our model describes the interaction between neuroinflammation, blood-brain barrier disruption, neuronal loss, circuit remodeling, and seizures. Formulated as a system of nonlinear differential equations, the model reproduces the available data from three animal models. The model successfully describes characteristic features of epileptogenesis such as its paradoxically long timescales (up to decades) despite short and transient injuries or the existence of qualitatively different outcomes for varying injury intensity. In line with the concept of degeneracy, our simulations reveal multiple routes toward epilepsy with neuronal loss as a sufficient but non-necessary component. Finally, we show that our model allows for in silico predictions of therapeutic strategies, revealing injury-specific therapeutic targets and optimal time windows for intervention.

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A dynamical systems model describes the development of epilepsy after different injuries

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Simulation results are in agreement with data from three animal models

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Model shows degeneracy: multiple distinct but linked mechanisms cause epileptogenesis

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Framework permits studying the effects of therapeutic interventions in silico

Proanthocyanidin from Vitis vinifera attenuates memory impairment due to convulsive status epilepticus

This study investigated the effects of proanthocyanidin-rich fraction (PRF) of Vitis vinifera seed extract on the markers of hippocampal-dependent memory in convulsive status epilepticus (CSE) rat model. One hundred juvenile Wistar rats were randomized into 6 groups. Group 1 (n = 10) received propylene glycol (PG 0.1 ml/100 g) intraperitoneally (i.p), while convulsion was induced in groups 2-6 (n = 18 each) using lithium (127 mg/kg i.p) and pilocarpine hydrochloride (40 mg/kg i.p). The established CSE rats in groups 2-6 received a daily treatment of PG (0.1 ml i.p), PRF (30 mg/kg i.p), PRF (20 mg/kg BW i.p), PRF (10 mg/kg BW i.p) or diazepam (5 mg/kg BW i.p) for seven days. Thereafter, they were kept untreated but with access to feed and water for 21 days. The control and CSE-treated rats were subjected to behavioral tests, while the biochemical and histomorphological evaluations of the hippocampus were done after the sacrifice. The results were presented as mean ± SEM in graphs or tables. The level of significance was considered when p < 0.05. There was significant decrease in the hippocampal-dependent memory, hippocampal weight and an increased malondialdehyde concentration following CSE. The activities of acetylcholinesterase decreased significantly in the PRF-treated CSE rats. The hippocampal glial cells and granule count increased significantly following CSE, with various neurodegenerative features in the CA1 of the hippocampus. These derangements were attenuated significantly following PRF treatment. Memory impairment following CSE may be attenuated with the administration of PRF from V. vinifera seed in rats.

Brain pathology in focal status epilepticus: evidence from experimental models

Status Epilepticus (SE) is often a neurological emergency characterized by abnormally sustained, longer than habitual seizures. The new ILAE classification reports that SE "…can have long-term consequences including neuronal death, neuronal injury…depending on the type and duration of seizures". While it is accepted that generalized convulsive SE exerts detrimental effects on the brain, it is not clear if other forms of SE, such as focal non-convulsive SE, leads to brain pathology and contributes to long-term deficits in patients. With the available clinical and experimental data, it is hard to discriminate the specific action of the underlying SE etiologies from that exerted by epileptiform activity. This information is highly relevant in the clinic for better treatment stratification, which may include both medical and surgical intervention for seizure control. Here we review experimental studies of focal SE, with an emphasis on focal non-convulsive SE. We present a repertoire of brain pathologies observed in the most commonly used animal models and attempt to establish a link between experimental findings and human condition(s). The extensive literature on focal SE animal models suggest that the current approaches have significant limitations in terms of translatability of the findings to the clinic. We highlight the need for a more stringent description of SE features and brain pathology in experimental studies in animal models, to improve the accuracy in predicting clinical translation.

How to Find Candidate Drug-targets for Antiepileptogenic Therapy?

Although over 25 antiepileptic drugs (AEDs) have become currently available for clinical use, the incidence of epilepsy worldwide and the proportions of drug-resistant epilepsy among them are not significantly reduced during the past decades. Traditional screens for AEDs have been mainly focused on their anti-ictogenic roles, and their efficacies primarily depend on suppressing neuronal excitability or enhancing inhibitory neuronal activity, almost without the influence on the epileptogenesis or with inconsistent results from different studies. Epileptogenesis refers to the pathological process of a brain from its normal status to the alterations with the continuous prone of unprovoked spontaneous seizures after brain insults, such as stroke, traumatic brain injury, CNS infectious, and autoimmune disorders, and even some specific inherited conditions. Recently growing experimental and clinical studies have discovered the underlying mechanisms for epileptogenesis, which are multi-aspect and multistep. These findings provide us a number of interesting sites for antiepileptogenic drugs (AEGDs). AEGDs have been evidenced as significantly roles of postponing or completely blocking the development of epilepsy in experimental models. The present review will introduce potential novel candidate drug-targets for AEGDs based on the published studies.

Wogonin preventive impact on hippocampal neurodegeneration, inflammation and cognitive defects in temporal lobe epilepsy

Previous studies demonstrated that the pathophysiological changes after temporal lobe epilepsy (TLE) such as oxidative stress, inflammatory reaction contribute to cognitive defect and neuronal damage. The present study was conducted to evaluate the anticonvulsant effect of wogonin ameliorates kainate-induced TLE, and to investigate the mechanism underlying these effects. Rats were divided into control, wogonin, kainate, and wogonin-pretreated kainate groups. The rat model of TLE was induced by unilateral intrahippocampal injection of 0.4 ug/ul of kainate. The results showed that the cognitive function in TLE rats was significantly impaired, and wogonin treatment improved cognitive function in the Morris water maze (MWM). H & E staining and TUNEL staining showed obvious damage in the hippocampus of TLE rats, and wogonin alleviated the damage. To evaluate the oxidative stress, the expression of MDA and GSH in plasma were detected. Nrf-2 and HO-1 mRNA expression in the hippocampus were detected. The levels of MDA in plasma increased in TLE rats, and the levels of GSH in plasma and Nrf-2, HO-1 in the brain decreased. Treatment with wogonin alleviated these changes. We also detected the mRNA expression of inflammatory mediators like IL-1β, TNF-α, and NF kB in the brain. The inflammatory reaction was significantly activated in the brain of TLE rats, and wogonin alleviated neuroinflammation. We detected the mRNA expression of Bcl-2, Bax, caspase-3, in the hippocampus. The levels of Bcl-2 decreased in TLE rats, Bax and caspase-3 increased, while wogonin alleviated these changes. The present study indicated that wogonin exerted a noticeable neuroprotective effect in kainate-induced TLE rats.

Dynamic oxygen changes during status epilepticus and subsequent endogenous kindling

OBJECTIVE

Brain tissue oxygen (partial oxygen pressure [pO2 ]) levels are tightly regulated to stay within the normoxic zone, with deviations on either side resulting in impaired brain function. Whereas pathological events such as ischemic attacks and brief seizures have previously been shown to result in pO2 levels well below the normoxic zone, oxygen levels during prolonged status epilepticus (SE) and the subsequent endogenous kindling period are unknown.

METHODS

We utilized two models of acquired temporal lobe epilepsy in rats: intrahippocampal kainic acid infusion and prolonged perforant pathway stimulation. Local tissue oxygen was measured in the dorsal hippocampus using an optode during and for several weeks following SE.

RESULTS

We observed hyperoxia in the hippocampus during induced SE in both models. Following termination of SE, 88% of rats initiated focal self-generated spiking activity in the hippocampus within the first 7 days, which was associated with dynamic oxygen changes. Self-generated and recurring epileptiform activity subsequently organized into higher-frequency bursts that became progressively longer and were ultimately associated with behavioral seizures that became more severe with time and led to postictal hypoxia.

SIGNIFICANCE

Induced SE and self-generated recurrent epileptiform activity can have profound and opposing effects on brain tissue oxygenation that may serve as a biomarker for ongoing pathological activity in the brain.

Age and Ketogenic Diet Have Dissociable Effects on Synapse-Related Gene Expression Between Hippocampal Subregions

As the number of individuals living beyond the age of 65 is rapidly increasing, so is the need to develop strategies to combat the age-related cognitive decline that may threaten independent living. Although the link between altered neuronal signaling and age-related cognitive impairments is not completely understood, it is evident that declining cognitive abilities are at least partially due to synaptic dysfunction. Aging is accompanied by well-documented changes in both excitatory and inhibitory synaptic signaling across species. Age-related synaptic alterations are not uniform across the brain, however, with different regions showing unique patterns of vulnerability in advanced age. In the hippocampus, increased activity within the CA3 subregion has been observed across species, and this can be reversed with anti-epileptic medication. In contrast to CA3, the dentate gyrus shows reduced activity with age and declining metabolic activity. Ketogenic diets have been shown to decrease seizure incidence and severity in epilepsy, improve metabolic function in diabetes type II, and improve cognitive function in aged rats. This link between neuronal activity and metabolism suggests that metabolic interventions may be able to ameliorate synaptic signaling deficits accompanying advanced age. We therefore investigated the ability of a dietary regimen capable of inducing nutritional ketosis and improving cognition to alter synapse-related gene expression across the dentate gyrus, CA3 and CA1 subregions of the hippocampus. Following 12 weeks of a ketogenic or calorie-matched standard diet, RTq-PCR was used to quantify expression levels of excitatory and inhibitory synaptic signaling genes within CA1, CA3 and dentate gyrus. While there were no age or diet-related changes in CA1 gene expression, expression levels were significantly altered within CA3 by age and within the dentate gyrus by diet for several genes involved in presynaptic glutamate regulation and postsynaptic excitation and plasticity. These data demonstrate subregion-specific alterations in synaptic signaling with age and the potential for a ketogenic diet to alter these processes in dissociable ways across different brain structures that are uniquely vulnerable in older animals.

Mode-Dependent Effect of Xenon Inhalation on Kainic Acid-Induced Status Epilepticus in Rats

Previous studies have reported the possible neuroprotective effects of xenon treatment. The purpose of this study was to define the range of effective xenon ratio, most effective xenon ratio, and time-window for intervention in the kainic acid (KA) – induced status epilepticus (SE) rat model. Different ratios of xenon (35% xenon, 21% oxygen, 44% nitrogen, 50% xenon, 21% oxygen, 29% nitrogen, 70% xenon, 21% oxygen, and 9% nitrogen) were used to treat the KA-induced SE. Our results confirmed the anti-seizure role of 50 and 70% xenon mixture, with a stronger effect from the latter. Further, 70% xenon mixture was dispensed at three time points (0 min, 15 min delayed, and 30 min delayed) after KA administration, and the results indicated the anti-seizure effect at all treated time points. The results also established that the neuronal injury in the hippocampus and entorhinal cortex (EC), assessed using Fluoro-Jade B (FJB) staining, were reversed by the xenon inhalation, and within 30 min after KA administration. Our study, therefore, indicates the appropriate effective xenon ratio and time-window for intervention that can depress seizures. The prevention of neuronal injury and further reversal of the loss of effective control of depress network in the hippocampus and EC may be the mechanisms underlying the anti-seizure effect of xenon.

Targeted hippocampal GABA neuron ablation by Stable Substance P-saporin causes hippocampal sclerosis and chronic epilepsy in rats

Cryptogenic temporal lobe epilepsy develops in the absence of identified brain injuries, infections, or structural malformations, and in these cases, an unidentified pre-existing abnormality may initiate febrile seizures, hippocampal sclerosis, and epilepsy. Although a role for GABAergic dysfunction in epilepsy is intuitively obvious, no causal relationship has been established. In this study, hippocampal GABA neurons were targeted for selective elimination to determine whether a focal hippocampal GABAergic defect in an otherwise normal brain can initiate cryptogenic temporal lobe epilepsy with hippocampal sclerosis. We used Stable Substance P-saporin conjugate (SSP-saporin) to target rat hippocampal GABA neurons, which selectively and constitutively express the neurokinin-1 receptors that internalize this neurotoxin. Bilateral and longitudinally extensive intrahippocampal microinjections of SSP-saporin caused no obvious behavioral effects for several days. However, starting ~4 days postinjection, rats exhibited episodes of immobilization, abnormal flurries of "wet-dog" shakes, and brief focal motor seizures characterized by facial automatisms and forepaw clonus. These clinically subtle behaviors stopped after ~4 days. Convulsive status epilepticus did not develop, and no deaths occurred. Months later, chronically implanted rats exhibited spontaneous focal motor seizures and extreme hippocampal sclerosis. These data suggest that hippocampal GABAergic dysfunction is epileptogenic and can produce the defining features of cryptogenic temporal lobe epilepsy.

Experience-Dependent Effects of Muscimol-Induced Hippocampal Excitation on Mnemonic Discrimination

Memory requires similar episodes with overlapping features to be represented distinctly, a process that is disrupted in many clinical conditions as well as normal aging. Data from humans have linked this ability to activity in hippocampal CA3 and dentate gyrus (DG). While animal models have shown the perirhinal cortex is critical for disambiguating similar stimuli, hippocampal activity has not been causally linked to discrimination abilities. The goal of the current study was to determine how disrupting CA3/DG activity would impact performance on a rodent mnemonic discrimination task. Rats were surgically implanted with bilateral guide cannulae targeting dorsal CA3/DG. In Experiment 1, the effect of intra-hippocampal muscimol on target-lure discrimination was assessed within subjects in randomized blocks. Muscimol initially impaired discrimination across all levels of target-lure similarity, but performance improved on subsequent test blocks irrespective of stimulus similarity and infusion condition. To clarify these results, Experiment 2 examined whether prior experience with objects influenced the effect of muscimol on target-lure discrimination. Rats that received vehicle infusions in a first test block, followed by muscimol in a second block, did not show discrimination impairments for target-lure pairs of any similarity. In contrast, rats that received muscimol infusions in the first test block were impaired across all levels of target-lure similarity. Following discrimination tests, rats from Experiment 2 were trained on a spatial alternation task. Muscimol infusions increased the number of spatial errors made, relative to vehicle infusions, confirming that muscimol remained effective in disrupting behavioral performance. At the conclusion of behavioral experiments, fluorescence in situ hybridization for the immediate-early genes Arc and Homer1a was used to determine the proportion of neurons active following muscimol infusion. Contrary to expectations, muscimol increased neural activity in DG. An additional experiment was carried out to quantify neural activity in naïve rats that received an intra-hippocampal infusion of vehicle or muscimol. Results confirmed that muscimol led to DG excitation, likely through its actions on interneuron populations in hilar and molecular layers of DG and consequent disinhibition of principal cells. Taken together, our results suggest disruption of coordinated neural activity across the hippocampus impairs mnemonic discrimination when lure stimuli are novel.