Administration of diazepam during status epilepticus reduces development and severity of epilepsy in rat

A new derivative of valproic acid amide possesses a broad-spectrum antiseizure profile and unique activity against status epilepticus and organophosphate neuronal damage

PURPOSE

sec-Butyl-propylacetamide (SPD) is a one-carbon homolog of valnoctamide (VCD), a central nervous system (CNS)-active amide derivative of valproic acid (VPA) currently in phase II clinical trials. The study reported herein evaluated the anticonvulsant activity of SPD in a battery of rodent seizure and epilepsy models and assessed its efficacy in rat and guinea pig models of status epilepticus (SE) and neuroprotection in an organotypic hippocampal slice model of excitotoxic cell death.

METHODS

The anticonvulsant activity of SPD was evaluated in several rodent seizure and epilepsy models, including maximal electroshock (MES), 6-Hz psychomotor; subcutaneous (s.c.) metrazol-, s.c. picrotoxin, s.c. bicuculline, and audiogenic, corneal, and hippocampal kindled seizures following intraperitoneal administration. Results obtained with SPD are discussed in relationship to those obtained with VPA and VCD. SPD was also evaluated for its ability to block benzodiazepine-resistant SE induced by pilocarpine (rats) and soman (rats and guinea pigs) following intraperitoneal administration. SPD was tested for its ability to block excitotoxic cell death induced by the glutamate agonists N-methyl-D-aspartate (NMDA) and kainic acid (KA) using organotypic hippocampal slices and SE-induced hippocampal cell death using FluoroJade B staining. The cognitive function of SPD-treated rats that were protected against pilocarpine-induced convulsive SE was examined 10-14 days post-SE using the Morris water maze (MWM). The relationship between the pharmacokinetic profile of SPD and its efficacy against soman-induced SE was evaluated in two parallel studies following SPD (60 mg/kg, i.p.) administration in the soman SE rat model.

KEY FINDINGS

SPD was highly effective and displayed a wide protective index (PI = median neurotoxic dose/median effective dose [TD(50)/ED(50)]) in the standardized seizure and epilepsy models employed. The wide PI values of SPD demonstrate that it is effective at doses well below those that produce behavioral impairment. Unlike VCD, SPD also displayed anticonvulsant activity in the rat pilocarpine model of SE. Thirty minutes after the induction of SE, the calculated rat ED(50) for SPD against convulsive SE in this model was 84 mg/kg. SPD was not neuroprotective in the organotypic hippocampal slice preparation; however, it did display hippocampal neuroprotection in both SE models and cognitive sparing in the MWM, which was associated with its antiseizure effect against pilocarpine-induced SE. When administered 20 and 40 min after SE onset, SPD (100-174 mg/kg) produced long-lasting efficacy (e.g., 4-8 h) against soman-induced convulsive and electrographic SE in both rats and guinea pigs. SPD ED(50) values in guinea pigs were 67 and 92 mg/kg when administered at SE onset or 40 min after SE onset, respectively. Assuming linear pharmacokinetics (PK), the PK-PD (pharmacodynamic) results (rats) suggests that effective SPD plasma levels ranged between 8 and 40 mg/L (20 min after the onset of soman-induced seizures) and 12-50 mg/L (40 min after the onset of soman-induced seizures). The time to peak (t(max)) pharmacodynamic effect (PD-t(max)) occurred after the PK-t(max), suggesting that SPD undergoes slow distribution to extraplasmatic sites, which is likely responsible for antiseizure activity of SPD.

SIGNIFICANCE

The results demonstrate that SPD is a broad-spectrum antiseizure compound that blocks SE induced by pilocarpine and soman and affords in vivo neuroprotection that is associated with cognitive sparing. Its activity against SE is superior to that of diazepam in terms of rapid onset, potency, and its effect on animal mortality and functional improvement.

A systems level, functional genomics analysis of chronic epilepsy

Neither the molecular basis of the pathologic tendency of neuronal circuits to generate spontaneous seizures (epileptogenicity) nor anti-epileptogenic mechanisms that maintain a seizure-free state are well understood. Here, we performed transcriptomic analysis in the intrahippocampal kainate model of temporal lobe epilepsy in rats using both Agilent and Codelink microarray platforms to characterize the epileptic processes. The experimental design allowed subtraction of the confounding effects of the lesion, identification of expression changes associated with epileptogenicity, and genes upregulated by seizures with potential homeostatic anti-epileptogenic effects. Using differential expression analysis, we identified several hundred expression changes in chronic epilepsy, including candidate genes associated with epileptogenicity such as Bdnf and Kcnj13. To analyze these data from a systems perspective, we applied weighted gene co-expression network analysis (WGCNA) to identify groups of co-expressed genes (modules) and their central (hub) genes. One such module contained genes upregulated in the epileptogenic region, including multiple epileptogenicity candidate genes, and was found to be involved the protection of glial cells against oxidative stress, implicating glial oxidative stress in epileptogenicity. Another distinct module corresponded to the effects of chronic seizures and represented changes in neuronal synaptic vesicle trafficking. We found that the network structure and connectivity of one hub gene, Sv2a, showed significant changes between normal and epileptogenic tissue, becoming more highly connected in epileptic brain. Since Sv2a is a target of the antiepileptic levetiracetam, this module may be important in controlling seizure activity. Bioinformatic analysis of this module also revealed a potential mechanism for the observed transcriptional changes via generation of longer alternatively polyadenlyated transcripts through the upregulation of the RNA binding protein HuD. In summary, combining conventional statistical methods and network analysis allowed us to interpret the differentially regulated genes from a systems perspective, yielding new insight into several biological pathways underlying homeostatic anti-epileptogenic effects and epileptogenicity.

Modeling epileptogenesis and temporal lobe epilepsy in a non-human primate

Here we describe a new non-human primate model of temporal lobe epilepsy (TLE) to better investigate the cause/effect relationships of human TLE. Status epilepticus (SE) was induced in adult marmosets by pilocarpine injection (250mg/kg; i.p.). The animals were divided in 2 groups: acute (8h post-SE) and chronic (3 and 5 months post-SE). To manage the severity of SE, animals received diazepam 5min after the SE onset (acute group: 2.5 or 1.25mg/kg; i.p.; chronic group/; 1.25mg/kg; i.p). All animals were monitored by video and electrocorticography to assess SE and subsequent spontaneous recurrent seizures (SRS). To evaluate brain injury produced by SE or SRS we used argyrophil III, Nissl and neo-Timm staining techniques. Magnetic resonance image was also performed in the chronic group. We observed that pilocarpine was able to induce SE followed by SRS after a variable period of time. Prolonged SE episodes were associated with brain damage, mostly confined to the hippocampus and limbic structures. Similar to human TLE, anatomical disruption of dentate gyrus was observed after SRS. Our data suggest that pilocarpine marmoset model of epilepsy has great resemblance to human TLE, and could provide new tools to further evaluate the subtle changes associated with human epilepsy.

Carisbamate has powerful disease-modifying effects in the lithium-pilocarpine model of temporal lobe epilepsy

Lithium-pilocarpine, a relevant model of temporal lobe epilepsy was used to test the neuroprotective and antiepileptogenic effects of carisbamate. Status epilepticus (SE) was induced in adult rats by lithium and pilocarpine. Carisbamate (30, 60, 90, and 120 mg/kg) was injected at 1 and 9 h after SE onset and continued twice daily for 6 additional days. The reference groups received diazepam instead of carisbamate. Neuroprotection was assessed during the first 24 h of SE with Fluoro-Jade B and after 14 days with thionine staining. SE severity and epileptic outcome were assessed by video, and surface and depth electroencephalographic recordings. At the two highest doses, carisbamate treatment reduced SE severity; produced strong neuroprotection of hippocampus, ventral cortices, thalamus, and amygdala; prevented mossy fiber sprouting in the dentate gyrus of the hippocampus; and delayed or suppressed the occurrence of spontaneous motor seizures. Rats with no spontaneous motor seizures displayed spike-and-wave discharges that share all the characteristics of absence seizures. In conclusion, carisbamate is able to induce strong neuroprotection and affect the nature of epileptogenic events occurring during and after lithium-pilocarpine status epilepticus, reflecting marked insult- and disease-modifying effects.

Rapamycin suppresses mossy fiber sprouting but not seizure frequency in a mouse model of temporal lobe epilepsy

Temporal lobe epilepsy is prevalent and can be difficult to treat effectively. Granule cell axon (mossy fiber) sprouting is a common neuropathological finding in patients with mesial temporal lobe epilepsy, but its role in epileptogenesis is unclear and controversial. Focally infused or systemic rapamycin inhibits the mammalian target of rapamycin (mTOR) signaling pathway and suppresses mossy fiber sprouting in rats. We tested whether long-term systemic treatment with rapamycin, beginning 1 d after pilocarpine-induced status epilepticus in mice, would suppress mossy fiber sprouting and affect the development of spontaneous seizures. Mice that had experienced status epilepticus and were treated for 2 months with rapamycin displayed significantly less mossy fiber sprouting (42% of vehicle-treated animals), and the effect was dose dependent. However, behavioral and video/EEG monitoring revealed that rapamycin- and vehicle-treated mice displayed spontaneous seizures at similar frequencies. These findings suggest mossy fiber sprouting is neither pro- nor anti-convulsant; however, there are caveats. Rapamycin treatment also reduced epilepsy-related hypertrophy of the dentate gyrus but did not significantly affect granule cell proliferation, hilar neuron loss, or generation of ectopic granule cells. These findings are consistent with the hypotheses that hilar neuron loss and ectopic granule cells might contribute to temporal lobe epileptogenesis.

Prevention or modification of epileptogenesis after brain insults: experimental approaches and translational research

Diverse brain insults, including traumatic brain injury, stroke, infections, tumors, neurodegenerative diseases, and prolonged acute symptomatic seizures, such as complex febrile seizures or status epilepticus (SE), can induce "epileptogenesis," a process by which normal brain tissue is transformed into tissue capable of generating spontaneous recurrent seizures. Furthermore, epileptogenesis operates in cryptogenic causes of epilepsy. In view of the accumulating information about cellular and molecular mechanisms of epileptogenesis, it should be possible to intervene in this process before the onset of seizures and thereby either prevent the development of epilepsy in patients at risk or increase the potential for better long-term outcome, which constitutes a major clinical need. For identifying pharmacological interventions that prevent, interrupt or reverse the epileptogenic process in people at risk, two groups of animal models, kindling and SE-induced recurrent seizures, have been recommended as potentially useful tools. Furthermore, genetic rodent models of epileptogenesis are increasingly used in assessing antiepileptogenic treatments. Two approaches have been used in these different model categories: screening of clinically established antiepileptic drugs (AEDs) for antiepileptogenic or disease-modifying potential, and targeting the key causal mechanisms that underlie epileptogenesis. The first approach indicated that among various AEDs, topiramate, levetiracetam, carisbamate, and valproate may be the most promising. On the basis of these experimental findings, two ongoing clinical trials will address the antiepileptogenic potential of topiramate and levetiracetam in patients with traumatic brain injury, hopefully translating laboratory discoveries into successful therapies. The second approach has highlighted neurodegeneration, inflammation and up-regulation of immune responses, and neuronal hyperexcitability as potential targets for antiepileptogenesis or disease modification. This article reviews these areas of progress and discusses the challenges associated with discovery of antiepileptogenic therapies.

Mechanisms of epileptogenesis and potential treatment targets

Prevention of epileptogenesis after brain trauma is an unmet medical challenge. Recent molecular profiling studies have provided an insight into molecular changes that contribute to formation of ictogenic neuronal networks, including genes regulating synaptic or neuronal plasticity, cell death, proliferation, and inflammatory or immune responses. These mechanisms have been targeted to prevent epileptogenesis in animal models. Favourable effects have been obtained using immunosuppressants, antibodies blocking adhesion of leucocytes to endothelial cells, gene therapy driving expression of neurotrophic factors, pharmacological neurostimulation, or even with conventional antiepileptic drugs by administering them before the appearance of genetic epilepsy. Further studies are needed to clarify the optimum time window and aetiological specificity of treatments. Questions related to adverse events also need further consideration. Encouragingly, the recent experimental studies emphasise that the complicated process of epileptogenesis can be favourably modified, and that antiepileptogenesis as a treatment indication might not be an impossible mission.

Anticonvulsant activity of BmK AS, a sodium channel site 4-specific modulator

The anticonvulsant activity of BmK AS, a sodium channel site 4-selective modulator purified from scorpion venom (Buthus martensi Karsch), was investigated in unanesthetized rats with acute pentylenetetrazole (PTZ)- and pilocarpine-induced seizures. Rats were microinjected in the CA1 region with either saline or BmK AS, followed by epileptogenic doses of PTZ or pilocarpine 30 minutes later. The anticonvulsant efficacy of BmK AS in PTZ- or pilocarpine-evoked seizure-like behavior and cortical epileptiform EEG activity was assessed. Intrahippocampal injections of BmK AS (0.05-1 μg in 1 μL) produced dose-dependent anticonvulsant activity in the PTZ model, suppressing seizure-associated behavior and reducing both the number and duration of high-amplitude, high-frequency discharges (HAFDs) on the EEG. In contrast, BmK AS did not affect the epileptiform EEG in the pilocarpine model over the same dose range, although it did increase the latency to status epilepticus onset and slightly, but significantly, reduced the seizure score. In summary, our results demonstrate that the sodium channel site 4-selective modulator BmK AS is an effective inhibitor of PTZ- but not pilocarpine-induced acute seizures. These results indicate that BmK AS may serve as a novel probe in exploring the role of different sodium channel subtypes in an epileptogenic setting and as a potential lead in developing antiepileptic drugs specifically for the therapy of sodium channel site 4-related epilepsy.

Neuroprotective effects of leptin following kainic acid-induced status epilepticus

We investigated the potential neuroprotective effects of leptin (LEP) against cellular damage, long-term recurrent spontaneous seizures, and behavioral changes associated with kainate (KA)-induced status epilepticus (SE). Adult Sprague-Dawley rats were sacrificed 24 hours after KA injections, and hippocampi were subjected to histological analysis. In the acute condition, one group received 12 mg/kg KA intraperitoneally (KAac group), and another group received 12 mg/kg KA intraperitoneally, followed by two intraperitoneal LEP injections of 4 mg/kg each, 1 and 13 hours after KA (KALEPac group). For long-term outcomes, one group received KA (KA group), and the other group received three intraperitoneal LEP injections (4 mg/kg at 1 hour, and 2mg/kg at 13 and 24 hours) after KA (KALEP group). Controls were sham manipulated. Behavioral tests started 6 weeks after SE. All rats that received KA underwent behavioral seizures of comparable severity. Compared with the KAac group, the KALEPac group had significantly larger pyramidal cell surface areas and fewer black-stained degenerating neurons with silver stain. The KALEP and KA groups were comparable with respect to recurrent spontaneous seizures, aggression, hyperactivity, and impaired memory. We show that leptin reduces cellular injury associated with KA-induced SE, but does not prevent long-term recurrent spontaneous seizures and behavioral deficits.

Loss of p53 results in protracted electrographic seizures and development of an aggravated epileptic phenotype following status epilepticus

The p53 tumor suppressor is a multifunctional protein, which regulates cell cycle, differentiation, DNA repair and apoptosis. Experimental seizures up-regulate p53 in the brain, and acute seizure-induced neuronal death can be reduced by genetic deletion or pharmacologic inhibition of p53. However, few long-term functional consequences of p53 deficiency have been explored. Here, we investigated the development of epilepsy triggered by status epilepticus in wild-type and p53-deficient mice. Analysis of electroencephalogram (EEG) recordings during status epilepticus induced by intra-amygdala kainic acid (KA) showed that seizures lasted significantly longer in p53-deficient mice compared with wild-type animals. Nevertheless, neuronal death in the hippocampal CA3 subfield and the neocortex was significantly reduced at 72 h in p53-deficient mice. Long-term continuous EEG telemetry recordings after status epilepticus determined that the sum duration of spontaneous seizures was significantly longer in p53-deficient compared with wild-type mice. Hippocampal damage and neuropeptide Y distribution at the end of chronic recordings was found to be similar between p53-deficient and wild-type mice. The present study identifies protracted KA-induced electrographic status as a novel outcome of p53 deficiency and shows that the absence of p53 leads to an exacerbated epileptic phenotype. Accordingly, targeting p53 to protect against status epilepticus or related neurologic insults may be offset by deleterious consequences of reduced p53 function during epileptogenesis or in chronic epilepsy.

Convulsive status epilepticus duration as determinant for epileptogenesis and interictal discharge generation in the rat limbic system

We analyzed with EEG-video monitoring the epileptic activity recorded during the latent and chronic periods in rats undergoing 30 or 120 min pilocarpine-induced convulsive status epilepticus (SE). Interictal discharges frequency in the entorhinal cortex (EC) of animals exposed to 120 min SE was significantly higher in the chronic than in the latent period. Following seizure appearance, interictal spikes diminished in duration in the CA3 of the 120 min SE group, and occurred at higher rates in the amygdala in all animals. Rats exposed to 120 min SE generated shorter seizures but presented twice as many non-convulsive seizures per day as the 30 min group. Finally, seizures most frequently initiated in CA3 in the 120 min SE group but had similar onset in CA3 and EC in the 30 min group. These findings indicate that convulsive SE duration influences the development of interictal and ictal activity, and that interictal discharges undergo structure-specific changes after seizure appearance.

Therapeutic approaches to epileptogenesis--hope on the horizon

Prevention of epileptogenesis is an unmet need in medicine. During the last 3 years, however, several preclinical studies have demonstrated remarkable favorable effects of novel treatments on genetic and acquired epileptogenesis. These include the use of immunosuppressants and treatments that modify cellular adhesion, proliferation, and/or plasticity. In addition, the use of antiepileptic drugs in rats with genetic epilepsy or proconvulsants in acquired epilepsy models has provided somewhat unexpected favorable effects. This review summarizes these studies, and introduces some caveats when interpreting the data. In particular, the effect of genetic background, the severity of epileptogenic insult, the method and duration of seizure monitoring, and size of animal population are discussed. Furthermore, a novel scheme for defining epileptogenesis-related terms is presented.

Leukocyte-endothelial adhesion mechanisms in epilepsy: cheers and jeers

A Role for Leukocyte-Endothelial Adhesion Mechanisms in Epilepsy. Fabene PF, Navarro MG, Martinello M, Rossi B, Merigo F, Ottoboni L, Bach S, Angiari S, Benati D, Chakir A, Zanetti L, Schio F, Osculati A, Marzola P, Nicolato E, Homeister JW, Xia L, Lowe JB, McEver RP, Osculati F, Sbarbati A, Butcher EC, Constantin G. Nat Med 2008;14(12):1377–1383. The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately one percent of the world population, are not well understood1,2,3. Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1, encoded by Selplg) and leukocyte integrins41 and L2. Inhibition of leukocyte-vascular interactions, either with blocking antibodies or by genetically interfering with PSGL-1 function in mice, markedly reduced seizures. Treatment with blocking antibodies after acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with the potential leukocyte involvement in epilepsy in humans, leukocytes were more abundant in brains of individuals with epilepsy than in controls. Our results suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy.

A review of current applications of mass spectrometry for neuroproteomics in epilepsy

The brain is unquestionably the most fascinating organ, and the hippocampus is crucial in memory storage and retrieval and plays an important role in stress response. In temporal lobe epilepsy (TLE), the seizure origin typically involves the hippocampal formation. Despite tremendous progress, current knowledge falls short of being able to explain its function. An emerging approach toward an improved understanding of the complex molecular mechanisms that underlie functions of the brain and hippocampus is neuroproteomics. Mass spectrometry has been widely used to analyze biological samples, and has evolved into an indispensable tool for proteomics research. In this review, we present a general overview of the application of mass spectrometry in proteomics, summarize neuroproteomics and systems biology-based discovery of protein biomarkers for epilepsy, discuss the methodology needed to explore the epileptic hippocampus proteome, and also focus on applications of ingenuity pathway analysis (IPA) in disease research. This neuroproteomics survey presents a framework for large-scale protein research in epilepsy that can be applied for immediate epileptic biomarker discovery and the far-reaching systems biology understanding of the protein regulatory networks. Ultimately, knowledge attained through neuroproteomics could lead to clinical diagnostics and therapeutics to lessen the burden of epilepsy on society.

Diazepam administration after prolonged status epilepticus reduces neurodegeneration in the amygdala but not in the hippocampus during epileptogenesis

An episode of status epilepticus (SE), if left untreated, can lead to death, or brain damage with long-term neurological consequences, including the development of epilepsy. The most common first-line treatment of SE is administration of benzodiazepines (BZs). However, the efficacy of BZs in terminating seizures is reduced with time after the onset of SE; this is accompanied by a reduced efficacy in protecting the hippocampus against neuronal damage, and is associated with impaired function and internalization of hippocampal GABA(A) receptors. In the present study, using Fluoro-Jade C staining, we found that administration of diazepam to rats at 3 h after the onset of kainic acid-induced SE, at a dose sufficient to terminate SE, had no protective effect on the hippocampus, but produced a significant reduction in neuronal degeneration in the amygdala, piriform cortex, and endopiriform nucleus, examined on days 7-9 after SE. Thus, in contrast to the hippocampus, the amygdala and other limbic structures are responsive to neuroprotection by BZs after prolonged SE, suggesting that GABA(A) receptors are not significantly altered in these structures during SE.

Diazepam and pentobarbital protect against scorpion venom toxin-induced epilepsy

We have characterized earlier the long-term behavioural, electroencephalographic and histopatologic features after a single TsTx microinjection, consisting of a neuropeptide isolated from the Tityus serrulatus scorpion venom, into the hippocampus of rats. TsTx was able to induce status epilepticus (SE) and developed later epilepsy. The present study was designed to investigate the outcomes of diazepam plus pentobarbital administered at 30 min, 1, 2 or 6h after the beginning of TsTx-induced SE, on the development of spontaneous recurrent motor seizures (SRMSs), mossy fibre sprouting and hippocampal neurodegeneration in rats. The administration of diazepam (DZ)+pentobarbital (PB) 30 min after the beginning of the TsTx-induced SE was able to markedly reduce the frequency of the SRMSs and prevent the development of mossy fibres sprouting and hippocampal lesion. In the other groups the augment of the extent of hipocampal neurodegeneration, the frequency of SRMSs and degree of aberrant mossy fibre sprouting was directly proportional to the time that the animals were subjected to TsTx-induced SE. In conclusion, our results point out that the early blockade of the TsTx-induced SE with diazepam plus pentobarbital, was effective treatment against later epilepsy development. The effectiveness of this treatment depends on the time that the animals were subjected to the SE. Furthermore, the TsTx model could be a useful tool to study antiepileptogenic drugs in chronic epileptic animals, neuronal degeneration, as well as for the mechanisms underlying epilepsy.

Neuroprotective effects of diazepam, carbamazepine, phenytoin and ketamine after pilocarpine-induced status epilepticus

Cell damage and spatial localization deficits are often reported as long-term consequences of pilocarpine-induced status epilepticus. In this study, we investigated the neuroprotective effects of repeated drug administration after long-lasting status epilepticus. Groups of six to eight Wistar rats received microinjections of pilocarpine (2.4 mg/microl, 1 microl) in the right dorsal hippocampus to induce a status epilepticus, which was attenuated by thiopental injection (35 mg/kg, i.p.) 3 hrs after onset. Treatments consisted of i.p. administration of diazepam, ketamine, carbamazepine, or phenytoin at 4, 28, 52, and 76 hr after the onset of status epilepticus. Two days after the treatments, rats were tested in the Morris water maze and 1 week after the cognitive tests, their brains were submitted to histology to perform haematoxylin and eosin staining and glial fibrillary acidic protein (GFAP) immunofluorescence detection. Post-status epilepticus rats exhibited extensive gliosis and cell loss in the hippocampal CA1, CA3 (70% cell loss for both areas) and dentate gyrus (60%). Administration of all drugs reduced cell loss in the hippocampus, with best effects observed in brains slices of diazepam-treated animals, which showed less than 30% of loss in the three areas and decreased GFAP immunolabelling. Treatments improved spatial navigation during training trials and probe trial, with exception of ketamine. Interestingly, in the probe trial, only diazepam-treated animals showed preference for the goal quadrant. Our data point to significant neuroprotective effects of repeated administration of diazepam against status epilepticus-induced cell damage and cognitive disturbances.

Effects of SC58236, a selective COX-2 inhibitor, on epileptogenesis and spontaneous seizures in a rat model for temporal lobe epilepsy

Inflammation is an important biological process that is activated after status epilepticus and could be implicated in the development of epilepsy. Here we tested whether an anti-inflammatory treatment with a selective cox-2 inhibitor (SC58236) could prevent the development of epilepsy or modify seizure activity during the chronic epileptic phase. SC58236 was orally administered (10mg/kg) during the latent period for 7 days, starting 4h after electrically induced SE. Seizures were monitored using EEG/video monitoring until 35 days after SE. Cell death and inflammation were investigated using immunocytochemistry (NeuN and Ox-42). Sprouting was studied using Timm's staining after 1 week and after 4-5 months when rats were chronic epileptic. SC58236 was also administered during 5 days in chronic epileptic rats. Hippocampal EEG seizures were continuously monitored before, during and after treatment. SC58236 effectively reduced PGE(2) production but did not modify seizure development or the extent of cell death or microglia activation in the hippocampus. SC58236 treatment in chronic epileptic rats did not show any significant change in seizure duration or frequency of daily seizures. The fact that cox-2 inhibition, which effectively reduced prostaglandin levels, did not modify epileptogenesis or chronic seizure activity suggests that this type of treatment (starting after SE) will not provide an effective anti-epileptogenic or anti-epileptic therapy.

A simple quantitative method for analyzing electrographic status epilepticus in rats

Electrographic status epilepticus (ESE) is a medical emergency consisting of repetitive seizures and may result in death or severe brain damage. Epilepsy can develop following ESE. The properties of ESE (e.g., duration and intensity) are variable, as are the effects of putative therapeutic treatments. Therefore a straightforward method to quantify different components of ESE would be beneficial for both researchers and clinicians. A frequency range close to the gamma band was selected for extraction of seizure-related activity from the EEG. This filtering strategy reduced motion artifacts and other noise sources in the electrophysiological recordings, thus increasing the signal-to-noise ratio of the EEG spike activity. EEG spiking was quantified using an energy operator and modeled by an eighth-order polynomial. In a benzodiazepine-resistant rat model of pilocarpine-induced ESE, the efficacy of various pharmaceutical agents at suppressing ESE was analyzed with this and other methods on data collected for < or =24 h after ESE induction. This approach allows for the objective, quantitative, and rapid assessment of the effects of both short- and long-lasting pharmacological manipulations on ESE and other forms of prolonged repetitive electrical activity.

Hippocampal transcriptome after status epilepticus in mice rendered seizure damage-tolerant by epileptic preconditioning features suppressed calcium and neuronal excitability pathways

Preconditioning brain with a sub-lethal stressor can temporarily generate a damage-refractory state. Microarray analyses have defined the changes in hippocampal gene expression that follow brief preconditioning seizures, but not the transcriptome after a prolonged and otherwise injurious seizure in previously preconditioned brain. Presently, microarray analysis was performed 24 h after status epilepticus in mice that had received previously either seizure preconditioning (tolerance) or sham-preconditioning (injury). Transcriptional changes in the hippocampal CA3 subfield of >or=2 fold were detected for 1357 genes in the tolerance group compared to a non-seizure control group, with 54% up-regulated. Of these regulated genes, 792 were also regulated in the injury group. Among the remaining 565 genes regulated only in tolerance, 73% were down-regulated. Analysis of the genes differentially suppressed in tolerance identified calcium signaling, ion channels and excitatory neurotransmitter receptors, and the synapse as over-represented among pathways, functions and compartments. Finally, 12 days continuous EEG recordings determined mice with induced tolerance had fewer spontaneous electrographic seizures compared to the injury group. Our data suggest the transcriptional phenotype of neuroprotection in tolerance may be dictated by the biology of the preconditioning stressor, functions by transcriptional reduction of vulnerability to excitotoxicity, and has anti-epileptogenic effects.

Effective treatments of prolonged status epilepticus in developing rats

We determined the efficacy of diazepam (DZP) and pentobarbital (PTB) in controlling prolonged status epilepticus (SE) in developing rats. One-hour-long SE was induced with kainic acid (KA) or lithium pilocarpine (Li-Pilo) in Postnatal Day 9 (P9), 15 (P15) and 21 (P21) rats, which were then treated with varying doses of DZP (20-60 mg/kg) or PTB (20-60 mg/kg). At P9, neither drug stopped SE, and higher doses could not be used because of high mortality. At P15 and P21, DZP and PTB stopped both behavioral and electrographic SE in a dose-dependent fashion, with similar efficacy in the two seizure models. DZP stopped SE significantly faster than PTB. Administration of a low dose of PTB (20mg/kg) following an initially ineffective treatment with DZP 20mg/kg stopped SE in all rats. The data suggest that high doses of DZP and PTB are needed to stop prolonged SE in developing rats, but their effectiveness is age dependent.

Antiepileptogenic and antiictogenic effects of retigabine under conditions of rapid kindling: an ontogenic study

PURPOSE

To examine antiepileptogenic and antiictogenic potential of retigabine (RTG) under conditions of rapid kindling epileptogenesis during different stages of development.

METHODS

The experiments were performed in postnatal day 14 (P14), P21, and P35 male Wistar rats. After stereotaxic implantation of hippocampal stimulating and recording electrodes, the effects of RTG on baseline afterdischarge (AD) properties were studied. Next, the animals underwent rapid kindling (sixty 10 s trains, bipolar 20 Hz square wave pulses delivered every 5 min). The progression of seizures (kindling acquisition), and responses to test stimulations after kindling (retention) were compared between RTG and vehicle-treated rats. Additionally, the effects of RTG on the severity of seizures in previously kindled animals were examined.

RESULTS

When administered intraperitoneally in doses that induced only mild, or no motor deficits, RTG significantly dampened brain excitability, evident as the increase of AD threshold and shortening of AD duration. During kindling, RTG delayed the development of focal seizures in P14 rats, and prevented the occurrence of full limbic seizures at all three ages. At P14 and P21, but not at P35, pretreatment with RTG prevented the establishment of kindling-induced enhanced seizure susceptibility. Administration of RTG to kindled animals decreased the severity of seizures induced by test stimulation. The effect was most prominent at P14.

DISCUSSION

RTG exerted both antiepileptogenic and antiictogenic effects under conditions of rapid kindling model. These effects were apparent during postneonatal, early childhood, and adolescent stages of development.

Anticonvulsant effect of BmK IT2, a sodium channel-specific neurotoxin, in rat models of epilepsy

BACKGROUND AND PURPOSE

The sodium channel is a primary target for treating central nervous system disorders such as epilepsy. In this study the anticonvulsant effect of BmK IT2, a sodium channel-specific neurotoxin, was evaluated in different animal models of epilepsy.

EXPERIMENTAL APPROACH

Experiments were performed on freely moving rats made epileptic by administration of either pentylenetetrazole (PTZ) or pilocarpine. BmK IT2 (0.05-0.5 microg in 2 microl) was microinjected into the CA1 area and its effects on PTZ-induced widespread, seizure-like behaviour and cortex epileptiform EEG, as well as on pilocarpine-induced seizure-like behaviour and c-Fos expression were studied.

KEY RESULTS

Intrahippocampal application of BmK IT2 dose-dependently inhibited PTZ-induced seizure-like behaviour, and reduced the numbers and duration of the high amplitude and frequency discharges (HAFDs) of the epileptiform EEG component induced by PTZ. Similarly, in the pilocarpine-induced status epilepticus (SE) model, BmK IT2 significantly prolonged the latency to onset of the SE, reduced the severity of SE and suppressed hippocampal c-Fos expression during SE.

CONCLUSIONS AND IMPLICATIONS

BmK IT2 showed anticonvulsant activity as it inhibited the widespread seizures induced by PTZ and pilocarpine-induced SE in rats. This activity might be due to the modulation of sodium channels in the hippocampus. Hence, BmK IT2 could be used as a novel tool to explore the molecular and pathological mechanisms of epilepsy with regard to the involvement of sodium channels.

Unilateral hippocampal CA3-predominant damage and short latency epileptogenesis after intra-amygdala microinjection of kainic acid in mice

Mesial temporal lobe epilepsy is the most common, intractable seizure disorder in adults. It is associated with an asymmetric pattern of hippocampal neuron loss within the endfolium (hilus and CA3) and CA1, with limited pathology in extra-hippocampal regions. We previously developed a model of focally-evoked seizure-induced neuronal death using intra-amygdala kainic acid (KA) microinjection and characterized the acute hippocampal pathology. Here, we sought to characterize the full extent of hippocampal and potential extra-hippocampal damage in this model, and the temporal onset of epileptic seizures. Seizure damage assessed at four stereotaxic levels by FluoroJade B staining was most prominent in ipsilateral hippocampal CA3 where it extended from septal to temporal pole. Minor but significant neuronal injury was present in ipsilateral CA1. Extra-hippocampal neuronal damage was generally limited in extent and restricted to the lateral septal nucleus, injected amygdala and select regions of neocortex ipsilateral to the seizure elicitation side. Continuous surface EEG recorded with implanted telemetry units in freely-moving mice detected spontaneous, epileptic seizures by five days post-KA in all mice. Epileptic seizure number averaged 1-4 per day. Hippocampi from epileptic mice 15 days post-KA displayed unilateral CA3 lesions, astrogliosis and increased neuropeptide Y immunoreactivity suggestive of mossy fiber rearrangement. These studies characterize a mouse model of unilateral hippocampal-dominant neuronal damage and short latency epileptogenesis that may be suitable for studying the cell and molecular pathogenesis of human mesial temporal lobe epilepsy.

What is animal experimentation telling us about new drug treatments of status epilepticus?

Basic research is mostly focused on the consequences of status epilepticus (SE) in terms of neuronal loss, behavior, epileptogenesis or disease-modifying effects such as preventing epilepsy or reducing seizure severity. Among the drugs tested, several were able to trigger neuroprotection but only a few had disease-modifying effects. At this point, many data are still missing, namely which drugs could efficiently stop SE or which mechanisms of action should be searched for to prevent the harmful consequences of SE.

Regulation of activity-dependent neuroprotective protein (ADNP) by the NO-cGMP pathway in the hippocampus during kainic acid-induced seizure

Activity-dependent neuroprotective protein (ADNP) is widely distributed in the cytoplasm of neurons and astrocytes of the hippocampus. Kainic acid (KA)-induced seizures increases neuronal nitric oxide synthase (nNOS) in neurons and inducible NOS (iNOS) in glia cells which coincides with a reduction in ADNP in the hippocampus. Inhibitors of NOS or soluble guanylyl cyclase (sGC) activity reduce ADNP under basal conditions in the absence of seizures. Treating animals with these inhibitors prior to KA-induced seizure, in particular, L-NAME (N(G)-nitro-l-arginine methyl ester), advances the onset of the first seizure but reverses the loss of ADNP by 3 days after the first seizure. This suggests that the NO-cGMP pathway has a role in regulating ADNP under both basal physiological conditions and in the pathophysiological changes produced during epileptogenesis.

Prenatal choline supplementation attenuates neuropathological response to status epilepticus in the adult rat hippocampus

Prenatal choline supplementation (SUP) protects adult rats against spatial memory deficits observed after excitotoxin-induced status epilepticus (SE). To examine the mechanism underlying this neuroprotection, we determined the effects of SUP on a variety of hippocampal markers known to change in response to SE and thought to underlie ensuing cognitive deficits. Adult offspring from rat dams that received either a control or SUP diet on embryonic days 12-17 were administered saline or kainic acid (i.p.) to induce SE and were euthanized 16 days later. SUP markedly attenuated seizure-induced hippocampal neurodegeneration, dentate cell proliferation, and hippocampal GFAP mRNA expression levels, prevented the loss of hippocampal GAD65 protein and mRNA expression, and altered growth factor expression patterns. SUP also enhanced pre-seizure hippocampal levels of BDNF, NGF, and IGF-1, which may confer a neuroprotective hippocampal microenvironment that dampens the neuropathological response to and/or helps facilitate recovery from SE to protect cognitive function.

Prophylactic treatment with levetiracetam after status epilepticus: lack of effect on epileptogenesis, neuronal damage, and behavioral alterations in rats

Levetiracetam (LEV) is a structurally novel antiepileptic drug (AED) which has demonstrated a broad spectrum of anticonvulsant activities both in experimental and clinical studies. Previous experiments in the kindling model suggested that LEV, in addition to its seizure-suppressing activity, may possess antiepileptogenic or disease-modifying activity. In the present study, we evaluated this possibility by using a rat model in which epilepsy with spontaneous recurrent seizures (SRS), behavioral alterations, and hippocampal damages develop after a status epilepticus (SE) induced by sustained electrical stimulation of the basal amygdala. Two experimental protocols were used. In the first protocol, LEV treatment was started 24h after onset of electrical amygdala stimulation without prior termination of the SE. In the second protocol, the SE was interrupted after 4h by diazepam, immediately followed by onset of treatment with LEV. Treatment with LEV was continued for 8 weeks (experiment #1) or 5 weeks (experiment #2) after SE, using continuous drug administration via osmotic minipumps. The occurrence of SRS was recorded during and after treatment. In addition, the rats were tested in a battery of behavioral tests, including the elevated-plus maze and the Morris water maze. Finally, the brains of the animals were analyzed for histological lesions in the hippocampal formation. With the experimental protocols chosen for these experiments, LEV did not exert antiepileptogenic or neuroprotective activity. Furthermore, the behavioral alterations, e.g., behavioral hyperexcitability and learning deficits, in epileptic rats were not affected by treatment with LEV after SE. These data do not support the idea that administration of LEV after SE prevents or reduces the long-term alterations developing after such brain insult in rats.

Effect of novel AMPA antagonist, NS1209, on status epilepticus

The current first line treatment of status epilepticus (SE) is based on the use of compounds that enhance GABAergic transmission or block sodium channels. These treatments discontinue SE in only two-thirds of patients, and therefore new therapeutic approaches are needed. We investigated whether a novel water-soluble AMPA antagonist, NS1209, discontinues SE in adult rats. SE was induced by electrical stimulation of the amygdala or subcutaneous administration of kainic acid. Animals were monitored continuously with video-electroencephalography during SE and drug treatment. We found that NS1209 could be safely administered to rats undergoing electrically induced SE at doses up to 50mg/kg followed by intravenous infusion of 5mg/kg for up to 24h. NS1209 administered as a bolus dose of 10-50mg/kg (i.p. or i.v.) followed by infusion of 4 or 5mg/kg h (i.v.) for 2-24h effectively discontinued electrically induced SE in all animals within 30-60 min, and there was no recurrence of SE after a 24-h infusion. Kainate-induced SE was similarly blocked by 10 or 30 mg/kg NS1209 (i.v.). To compare the efficacy and neuroprotective effects of NS1209 with those of diazepam (DZP), one group of rats received DZP (20mg/kg, i.p. and another dose of 10 mg/kg 6h later). By using the administration protocols described, the anticonvulsant effect of NS1209 was faster and more complete than that of DZP. NS1209 treatment (20 mg/kg bolus followed by 5mg/kg h infusion for 24 h) was neuroprotective against SE-induced hippocampal neurodegeneration, but to a lesser extent than DZP. These findings suggest that AMPA receptor blockade by NS1209 provides a novel and mechanistically complimentary addition to the armamentarium of drugs used to treat SE in humans.

Cyclicity of spontaneous recurrent seizures in pilocarpine model of temporal lobe epilepsy in rat

Pilocarpine administration to rats results in status epilepticus (SE) and after a latency period to the occurrence of spontaneous seizures. The model is commonly used to investigate mechanisms of epileptogenesis as well as the antiepileptic effects of novel compounds. Surprisingly, there have been no video-EEG studies determining the duration of latency period from SE to the appearance of the first spontaneous seizures or the type and frequency of spontaneous seizures at early phase of pilocarpine-induced epilepsy even though such information is critical for design of such studies. To address these questions, we induced SE with pilocarpine in 29 adult male Wistar rats with cortical electrodes. Rats were continuously video-EEG monitored during SE and up to 23 days thereafter. The first spontaneous seizures occurred 7.2+/-3.6 days after SE. During the follow-up, the mean daily seizure frequency was 2.6+/-1.9, the mean seizure duration 47+/-7 s, and the mean behavioral seizure score 3.2+/-0.9. Typically first seizures were partial (score 1-2). Interestingly, spontaneous seizures occurred in clusters with cyclicity, peaking every 5 to 8 days. These data show that in the pilocarpine model of temporal lobe epilepsy the latency period is short. Because many of the early seizures are partial and the seizures occur in clusters, the true phenotype of epilepsy triggered by pilocarpine-induced SE may be difficult to characterize without continuous long-term video-EEG monitoring. Finally, our data suggest that the model can be used for studies aiming at identifying the mechanisms of seizure clustering.

Administration of Levetiracetam after prolonged status epilepticus does not protect from mitochondrial dysfunction in a rodent model

Neuronal death and dysfunction occur after status epilepticus (SE), and is associated with mitochondrial enzyme damage. We previously showed, using the rat perforant pathway stimulation model, that levetiracetam administration (LEV; 1000 mg/kg intraperitoneal) during established SE reduces seizure severity and prevents mitochondrial dysfunction. We now show that administration of the same dose of LEV after 5h SE, does not protect from mitochondrial dysfunction.

New data suggest that discontinuation of status epilepticus is not necessary for antiepileptogenic effect in immature brain

Treatment of Experimental Status Epilepticus in Immature Rats: Dissociation between Anticonvulsant and Antiepileptogenic Effects

Suchomelova L, Baldwin RA, Kubova H, Thompson KW, Sankar R, Wasterlain CG

Pediatr Res 2006;59:237–243

We studied the effects of treating status epilepticus (SE) induced by lithium and pilocarpine at postnatal day 15 (P15) or 28 (P28), on the severity of acute SE and of SEinduced epileptogenesis. Rats received topiramate (10 or 50 mg/kg, IP) or diazepam (5 mg/kg, IP) 20, 40 or 70 min after pilocarpine, and three months after SE 24-h video/EEG recordings were obtained for one (P28) or two weeks (P15) continuously.

In P15 rats, topiramate did not modify the course of SE, yet treatment at 20 or 40 min completely prevented the development of spontaneous recurrent seizures (SRS) while later treatment (70 min) was partially effective in reducing the severity and frequency of SRS. Diazepam was effective against acute SE at all time points tested. Early (20 min) but not late treatment with diazepam had the effect of reducing the frequency and severity of SRS.

In P28 rats, both drugs reduced the cumulative seizure time. Early treatment (20 min) with either drug reduced the incidence of chronic epilepsy. Late treatment (40/70 min) did not alter the incidence of SRS, but decreased their frequency. This study demonstrates that, in the treatment of SE, anticonvulsant and antiepileptogenic effects can be dissociated in a development-specific manner: topiramate was antiepileptogenic without being an effective anticonvulsant in P15 animals at the doses tested. Diazepam, on the other hand, was a better anticonvulsant than an antiepileptogenic agent in the P15 animals at the dose tested. Such effects were not seen in the older animals.

Kainic acid dose affects delayed cell death mechanism after status epilepticus

Kainic acid (KA)-induced status epilepticus (SE) produces hippocampal neuronal death, which varies from necrosis to apoptosis or programmed cell death (PCD). We examined whether the type of neuronal death was dependent on KA dose. Adult rats were induced SE by intraperitoneal injection of KA at 9 mg/kg (K9) or 12 mg/kg (K12). Hippocampal neuronal death was assessed by TUNEL staining, electron microscopy, and Western blotting of caspase-3 on days 1, 3 and 7 after SE induction. K12 rats showed higher a mortality rate and shorter latency to the onset of SE when compared with K9 rats. In both groups, acidophilic and pyknotic neurons were evident in CA1 at 24h after SE and neuronal loss developed from day 3. The degenerated neurons became TUNEL-positive on days 3 and 7 in K9 rats but not in K12 rats. Caspase-3 activation was detected on days 3 and 7 in K9 rats but was undetectable in K12 rats. Ultrastructural study revealed shrunken neurons exhibiting pyknotic nuclei containing small and dispersed chromatin clumps 24h after SE in CA1. No cells exhibited apoptosis. On days 3 and 7, the degenerated neurons were necrotic with high electron density and small chromatin clumps. There were no ultrastructural differences between the K9 and K12 groups. These results revealed that differences in KA dose affected the delayed cell death (3 and 7 days after SE); however, no effect was seen on the early cell death (24h after SE). Moderate-dose KA induced necrosis, while low-dose KA induced PCD.

Septal GABAergic neurons are selectively vulnerable to pilocarpine-induced status epilepticus and chronic spontaneous seizures

The septal region of the basal forebrain plays a critical role modulating hippocampal excitability and functional states. Septal circuits may also play a role in controlling abnormal hippocampal hyperexcitability in epilepsy. Both lateral and medial septal neurons are targets of hippocampal axons. Since the hippocampus is an important epileptogenic area in temporal lobe epilepsy, we hypothesize that excessive excitatory output will promote sustained neurodegeneration of septal region neurons. Pilocarpine-induced status epilepticus (SE) was chosen as a model to generate chronic epileptic animals. To determine whether septal neuronal populations are affected by hippocampal seizures, immunohistochemical assays were performed in brain sections obtained from age-matched control, latent period (7 days post-SE) and chronically epileptic (more than one month post-SE survival) rats. An anti-NeuN (neuronal nuclei) antibody was used to study total neuronal numbers. Anti-ChAT (choline acetyltransferase), anti-GAD (glutamic acid decarboxylase) isoenzymes (65 and 67), and anti-glutamate antibodies were used to reveal cholinergic, GABAergic and glutamatergic neurons, respectively. Our results revealed a significant atrophy of medial and lateral septal areas in all chronically epileptic rats. Overall neuronal density in the septum (medial and lateral septum), assessed by NeuN immunoreactivity, was significantly reduced by approximately 40% in chronically epileptic rats. The lessening of neuronal numbers in both regions was mainly due to the loss of GABAergic neurons (80-97% reduction in medial and lateral septum). In contrast, populations of cholinergic and glutamatergic neurons were spared. Overall, these data indicate that septal GABAergic neurons are selectively vulnerable to hippocampal hyperexcitability, and suggest that the processing of information in septohippocampal networks may be altered in chronic epilepsy.

Animal models of post-traumatic epilepsy

Epilepsy is a major unfavorable long-term consequence of traumatic brain injury (TBI). Moreover, TBI is one of the most important predisposing factors for the development of epilepsy, particularly in young adults. Understanding the molecular and cellular cascades that lead to the development of post-traumatic epilepsy (PTE) is key for preventing its development or modifying the disease process in such a way that epilepsy, if it develops, is milder and easier-to-treat. Tissue from TBI patients undergoing epileptogenesis is not available for such studies, which underscores the importance of developing clinically relevant animal models of PTE. The goal of this review is to (1) provide a description of PTE in humans, which is critical for the development of clinically relevant models of PTE, (2) review the characteristics of currently available PTE models, and (3) provide suggestions for the development of future models of PTE based on our current understanding of the mechanisms of TBI and epilepsy. The development of clinically relevant models of PTE is critical to advance our understanding of the mechanisms of post-traumatic epileptogenesis and epilepsy, as well as for producing breakthroughs in the development and testing of novel antiepileptogenic treatments.

Diverse mechanisms of antiepileptic drugs in the development pipeline

There is a remarkable array of new chemical entities in the current antiepileptic drug (AED) development pipeline. In some cases, the compounds were synthesized in an attempt improve upon the activity of marketed AEDs. In other cases, the discovery of antiepileptic potential was largely serendipitous. Entry into the pipeline begins with the demonstration of activity in one or more animal screening models. Results from testing in a panel of such models provide a basis to differentiate agents and may offer clues as to the mechanism. Target activity may then be defined through cell-based studies, often years after the initial identification of activity. Some pipeline compounds are believed to act through conventional targets, whereas others are structurally novel and may act by novel mechanisms. Follow-on agents include the levetiracetam analogs brivaracetam and seletracetam that act as SV2A-ligands; the valproate-like agents valrocemide, valnoctamide, propylisopropyl acetamide, and isovaleramide; the felbamate analog flurofelbamate, a dicarbamate, and the unrelated carbamate RWJ-333369; the oxcarbazepine analog licarbazepine, which probably acts as a use-dependent sodium channel blockers, and its prodrug acetate BIA 2-093; various selective partial benzodiazepine receptor agonists, including ELB139, which is a positive allosteric modulator of alpha3-containing GABA(A) receptors. A variety of AEDs that may act through novel targets are also in clinical development: lacosamide, a functionalized amino acid; talampanel, a 2,3-benzodiazepine selective noncompetitive AMPA receptor antagonist; NS1209, a competitive AMPA receptor antagonist; ganaxolone, a neuroactive steroid that acts as a positive modulator of GABA(A) receptors; retigabine, a KCNQ potassium channel opener with activity as a GABA(A) receptor positive modulator; the benzanilide KCNQ potassium channel opener ICA-27243 that is more selective than retigabine; and rufinamide, a triazole of unknown mechanism.

Treatment of experimental status epilepticus in immature rats: dissociation between anticonvulsant and antiepileptogenic effects

We studied the effects of treating status epilepticus (SE) induced by lithium and pilocarpine at postnatal day 15 (P15) or 28 (P28), on the severity of acute SE and of SE-induced epileptogenesis. Rats received topiramate (10 or 50 mg/kg, IP) or diazepam (5 mg/kg, IP) 20, 40 or 70 min after pilocarpine, and three months after SE 24-h video/EEG recordings were obtained for one (P28) or two weeks (P15) continuously. In P15 rats, topiramate did not modify the course of SE, yet treatment at 20 or 40 min completely prevented the development of spontaneous recurrent seizures (SRS) while later treatment (70 min) was partially effective in reducing the severity and frequency of SRS. Diazepam was effective against acute SE at all time points tested. Early (20 min) but not late treatment with diazepam had the effect of reducing the frequency and severity of SRS. In P28 rats, both drugs reduced the cumulative seizure time. Early treatment (20 min) with either drug reduced the incidence of chronic epilepsy. Late treatment (40/70 min) did not alter the incidence of SRS, but decreased their frequency. This study demonstrates that, in the treatment of SE, anticonvulsant and antiepileptogenic effects can be dissociated in a development-specific manner: topiramate was antiepileptogenic without being an effective anticonvulsant in P15 animals at the doses tested. Diazepam, on the other hand, was a better anticonvulsant than an antiepileptogenic agent in the P15 animals at the dose tested. Such effects were not seen in the older animals.

Regulation of the expression of GABAA receptor subunits by an antiepileptic drug QYS

It has been reported that the antiepileptic drug qingyangshenylycosides (QYS) modulated the function of GABAergic system. However, little is known about the effects of QYS on the gene expression of GABA receptors in the central nervous system (CNS). In the present study, we examined the effects of QYS on the expression of GABAA receptor subunits in different regions of the mouse brain. The results showed that treatment of QYS significantly increased the expressions of Gabra1, Gabra2 and Gabr4 and decreased the expression of Gabrg2 in inferior colliculus. Moreover, Gabrb2 expression was up-regulated and Gabra5 was down-regulated in hippocampus, while the expressions of Gabra1 and Gabrb2 were induced in cortex after QYS treatment. These data indicated that QYS had different effects on the expression of GABAA receptor subunits in different brain regions. These results may help to reveal the molecular mechanism of anticonvulsant action of QYS.