Search

Status epilepticus (SE) is a life-threatening development of self-sustaining seizures that becomes resistant to benzodiazepines when treatment is delayed. Benzodiazepine pharmacoresistance is thought in part to result from internalization of synaptic GABAA receptors, which are the main target of the drug. The naturally occurring neurosteroid allopregnanolone is a therapy of interest against SE for its ability to modulate all isoforms of GABAA receptors. Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, has been partially effective in combination with benzodiazepines in mitigating SE-associated neurotoxicity. In this study, allopregnanolone as an adjunct to midazolam or midazolam-ketamine combination therapy was evaluated for efficacy against cholinergic-induced SE. Adult male rats implanted with electroencephalographic (EEG) telemetry devices were exposed to the organophosphorus chemical (OP) soman (GD) and treated with an admix of atropine sulfate and HI-6 at 1 minute after exposure followed by midazolam, midazolam-allopregnanolone, or midazolam-ketamine-allopregnanolone 40 minutes after seizure onset. Neurodegeneration, neuronal loss, and neuroinflammation were assessed 2 weeks after GD exposure. Seizure activity, EEG power integral, and epileptogenesis were also compared among groups. Overall, midazolam-ketamine-allopregnanolone combination therapy was effective in reducing cholinergic-induced toxic signs and neuropathology, particularly in the thalamus and hippocampus. Higher dosage of allopregnanolone administered in combination with midazolam and ketamine was also effective in reducing EEG power integral and epileptogenesis. The current study reports that there is a promising potential of neurosteroids in combination with benzodiazepine and ketamine treatments in a GD model of SE. SIGNIFICANCE STATEMENT: Allopregnanolone, a naturally occurring neurosteroid, reduced pathologies associated with soman (GD) exposure such as epileptogenesis, neurodegeneration, and neuroinflammation, and suppressed GD-induced toxic signs when used as an adjunct to midazolam and ketamine in a delayed treatment model of soman-induced status epilepticus (SE) in rats. However, protection was incomplete, suggesting that further studies are needed to identify optimal combinations of antiseizure medications and routes of administration for maximal efficacy against cholinergic-induced SE.

OBJECTIVE: In spite of anecdotal reports describing an association between chronic epilepsy and interictal aggressiveness, and of a few studies suggesting that such an association is common in temporal lobe epilepsy, this concept has not been generally accepted by epileptologists. In the course of studies of the long-term consequences of limbic status epilepticus (SE) in juvenile rats, we noticed that experimental animals, unlike littermate controls, could not be housed together because of severe fighting. We now report a study of interictal aggression in those rats. METHODS: Long-term behavioral consequences of lithium/pilocarpine SE were studied 3 months after SE had been induced with lithium and pilocarpine in male Wistar rats at age 28 days. Chronic spontaneous seizures developed in 100% of animals. We tested rats for territorial aggression under the resident-intruder paradigm. We measured the number of episodes of dominance (mounting and pinning), and agonistic behavior (attacks, boxing, and biting). RESULTS: Untreated lithium/pilocarpine SE induced a large increase in aggressive behavior, which involved all aspects of aggression in the resident-intruder paradigm when tested 3 months after SE. The experimental rats were dominant toward the controls, as residents or as intruders, and showed episodes of biting and boxing rarely displayed by controls. They also displayed increased aggressiveness compared with controls when tested against each other. SIGNIFICANCE: This robust model offers an opportunity to better understand the complex relationship between seizures, epilepsy, and aggression, and the role of age, SE vs. recurrent spontaneous seizures, and focal neuronal injury in the long-term behavioral effects of SE.

The initiation and maintenance phases of cholinergic status epilepticus (SE) are associated with maladaptive trafficking of synaptic GABAA and glutamate receptors. The resulting pharmacoresistance reflects a decrease in synaptic GABAA receptors and increase in NMDA and AMPA receptors, which tilt the balance between inhibition and excitation in favor of the latter. If these changes are important to the pathophysiology of SE, both should be treated, and blocking their consequences should have therapeutic potential. We used a model of benzodiazepine-refractory SE (RSE) (Tetz et al., 2006) and a model of soman-induced SE to test this hypothesis. Treatment of RSE with combinations of the GABAAR agonists midazolam or diazepam and the NMDAR antagonists MK-801 or ketamine terminated RSE unresponsive to high-dose monotherapy with benzodiazepines, ketamine or other antiepileptic drugs (AEDs). It also reduced RSE-associated neuronal injury, spatial memory deficits and the occurrence of spontaneous recurrent seizures (SRS), tested several weeks after SE. Treatment of sc soman-induced SE similarly showed much greater reduction of EEG power by a combination of midazolam with ketamine, compared to midazolam monotherapy. When treating late (40 min after seizure onset), there may not be enough synaptic GABAAR left to be able to restore inhibition with maximal GABAAR stimulation, and further benefit is derived from the addition of an AED which increases inhibition or reduces excitation by a non-GABAergic mechanism. The midazolam-ketamine-valproate combination is effective in terminating RSE. 3-D isobolograms demonstrate positive cooperativity between midazolam, ketamine and valproate, without any interaction between the toxicity of these drugs, so that the therapeutic index is increased by combination therapy between GABAAR agonist, NMDAR antagonist and selective AEDs. We compared this drug combination based on the receptor trafficking hypothesis to treatments based on clinical practice. The midazolam-ketamine-valproate combination is far more effective in stopping RSE than the midazolam-fosphenytoin-valproate combination inspired from clinical guidelines. Furthermore, sequential administration of midazolam, ketamine and valproate is far less effective than simultaneous treatment with the same drugs at the same dose. These data suggest that we should re-evaluate our traditional treatment of RSE, and that treatment should be based on pathophysiology. The search for a better drug has to deal with the fact that most monotherapy leaves half the problem untreated. The search for a better benzodiazepine should acknowledge the main cause of pharmacoresistance, which is loss of synaptic GABAAR. Future clinical trials should consider treating both the failure of inhibition and the runaway excitation which characterize RSE, and should include an early polytherapy arm.

The transition from single seizures to status epilepticus (SE) is associated with malaptive trafficking of synaptic gamma-aminobutyric acid (GABAA) and glutamate receptors. The receptor trafficking hypothesis proposes that these changes are key events in the development of pharmacoresistance to antiepileptic drugs (AEDs) during SE, and that blocking their expression will help control drug-refractory SE (RSE). We tested this hypothesis in a model of SE induced by very high-dose lithium and pilocarpine (RSE), and in a model of SE induced by sc soman. Both models are refractory to benzodiazepines when treated 40 min after seizure onset. Our treatments aimed to correct the loss of inhibition because of SE-associated internalization of synaptic GABAA receptors (GABAAR), using an allosteric GABAAR modulator, sometimes supplemented by an AED acting at a nonbenzodiazepine site. At the same time, we reduced excitation because of increased synaptic localization of NMDA and AMPA (?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate) receptors (NMDAR, AMPAR (?-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor, N-methyl-D-aspartate receptors)) with an NMDAR channel blocker, since AMPAR changes are NMDAR-dependent. Treatment of RSE with combinations of the GABAAR allosteric modulators midazolam or diazepam and the NMDAR antagonists dizocilpine or ketamine terminated RSE unresponsive to high-dose monotherapy. It also reduced RSE-associated neuronal injury, spatial memory deficits, and the occurrence of spontaneous recurrent seizures (SRS), tested several weeks after SE. Treatment of soman-induced SE also reduced seizures, behavioral deficits, and epileptogenesis. Addition of an AED further improved seizure outcome in both models. Three-dimensional isobolograms demonstrated positive cooperativity between midazolam, ketamine, and valproate, without any interaction between the toxicity of these drugs, so that the therapeutic index was increased by combination therapy. The midazolam-ketamine-valproate combination based on the receptor trafficking hypothesis was far more effective in stopping RSE than the midazolam-fosphenytoin-valproate combination inspired from clinical guidelines for the treatment of SE. Furthermore, sequential administration of midazolam, ketamine, and valproate was far less effective than simultaneous treatment with the same drugs at the same dose. These data suggest that treatment of RSE should be based at least in part on its pathophysiology. The search for a better treatment should focus on the cause of pharmacoresistance, which is loss of synaptic GABAAR and gain of synaptic glutamate receptors. Both need to be treated. Monotherapy addresses only half the problem. Improved pharmacokinetics will not help pharmacoresistance because of loss of receptors. Waiting for one drug to fail before giving the second drugs gives pharmacoresistance time to develop. Future clinical trials should consider treating both the failure of inhibition and the runaway excitation which characterize RSE, and should include an early polytherapy arm. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures".

This article investigated the efficacy of the combination of antiepileptic drug therapy in protecting against soman-induced seizure severity, epileptogenesis and performance deficits. Adult male rats with implanted telemetry transmitters for continuous recording of electroencephalographic (EEG) activity were exposed to soman and treated with atropine sulfate and the oxime HI-6 one minute after soman exposure and with midazolam, ketamine and/or valproic acid 40 min after seizure onset. Rats exposed to soman and treated with medical countermeasures were evaluated for survival, seizure severity, the development of spontaneous recurrent seizure and performance deficits; combination anti-epileptic drug therapy was compared with midazolam monotherapy. Telemetry transmitters were used to record EEG activity, and a customized MATLAB algorithm was used to analyze the telemetry data. Survival data, EEG power integral data, spontaneous recurrent seizure data and behavioral data are illustrated in figures and included as raw data. In addition, edf files of one month telemetry recordings from soman-exposed rats treated with delayed midazolam are provided as supplementary materials. Data presented in this article are related to research articles "Rational Polytherapy in the Treatment of Cholinergic Seizures" [1] and "Early polytherapy for benzodiazepine-refractory status epilepticus [4].

Treatment of status epilepticus (SE) in infants and children is challenging. There is a recognition that a broad set of developmental processes need to be considered to fully appreciate the physiologic complexity of severe seizures, and seizure outcomes, in infants and children. The development and use of basic models to elucidate important mechanisms will help further our understanding of these processes. Here we review some of the key experimental models and consider several areas relevant to treatment that could lead to productive translational research. Terminating seizures quickly is essential. Understanding pharmacoresistance of SE as it relates to receptor trafficking will be critical to seizure termination. Once a severe seizure is terminated, how will the developing brain respond? Basic studies suggest that there are important acute and long-term histopathologic, and pathophysiologic, consequences that, if left unaddressed, will produce long-lasting deficits on the form and function of the central nervous system. To fully utilize the evidence that basic models produce, age- and development- and model-specific frameworks have to be considered carefully. Studies have demonstrated that severe seizures can cause perturbations to developmental processes during critical periods of development that lead to life-long deficits. Unfortunately, some of the drugs that are commonly used to treat seizures may also produce negative outcomes by enhancing Cl--mediated depolarization, or by accelerating programmed cell death. More research is needed to understand these phenomena and their relevance to the human condition, and to develop rational drugs that protect the developing brain from severe seizures to the fullest extent possible.

Early maladaptive internalization of synaptic GABAA receptors (GABAAR) and externalization of NMDA receptors (NMDAR) may explain the time-dependent loss of potency of standard anti-epileptic drugs (AED) in refractory status epilepticus (SE). We hypothesized that correcting the effects of changes in GABAAR and NMDAR would terminate SE, even when treatment is delayed 40 minutes. SE was induced in adult Sprague-Dawley rats with a high dose of lithium and pilocarpine. The GABAAR agonist midazolam, the NMDAR antagonist ketamine and the AED valproate were injected 40 min after SE onset in combination or as monotherapy. The midazolam-ketamine-valproate combination was more efficient than triple-dose midazolam, ketamine or valproate monotherapy or higher-dose dual therapy in reducing several parameters of SE severity. Triple therapy also reduced SE-induced acute neuronal injury and spatial memory deficits. In addition, simultaneous triple therapy was more efficient than sequential triple therapy: giving the three drugs simultaneously was more efficient at stopping seizures than the standard practice of giving them sequentially. Furthermore, midazolam-ketamine-valproate therapy suppressed seizures far better than the midazolam-fosphenytoin-valproate therapy, which follows evidence-based AES guidelines. These results show that a treatment aimed at correcting maladaptive GABAAR and NMDAR trafficking can reduce the severity of SE and its long-term consequences.

Status epilepticus is common in neonates and infants, and is associated with neuronal injury and adverse developmental outcomes. γ-Aminobutyric acidergic (GABAergic) drugs, the standard treatment for neonatal seizures, can have excitatory effects in the neonatal brain, which may worsen the seizures and their effects. Using a recently developed model of status epilepticus in postnatal day 7 rat pups that results in widespread neuronal injury, we found that the GABAA agonists phenobarbital and midazolam significantly increased status epilepticus-associated neuronal injury in various brain regions. Our results suggest that more research is needed into the possible deleterious effects of GABAergic drugs on neonatal seizures and on excitotoxic neuronal injury in the immature brain. Ann Neurol 2017;82:115-120.

ObjectiveTo evaluate acute and long-term effects of intravenous brivaracetam (BRV) and BRV + diazepam (DZP) combination treatment in a rat model of self-sustaining status epilepticus (SSSE).MethodsRats were treated with BRV (10 mg/kg) 10 min after initiation of perforant path stimulation (PPS) as early treatment; or BRV (10-300 mg/kg), DZP (1 mg/kg), or BRV (0.3-10 mg/kg) + DZP (1 mg/kg) 10 min after the end of PPS (established SSSE). Seizure activity was recorded electrographically for 24 h posttreatment (acute effects), and for 1 week at 6-8 weeks or 12 months' posttreatment (long-term effects). All treatments were compared with control rats using one-way analysis of variance (ANOVA) and Bonferroni's test, or Kruskal--Wallis and Dunn's multiple comparison tests, when appropriate.ResultsTreatment of established SSSE with BRV (10-300 mg/kg) resulted in dose-dependent reduction in SSSE duration and cumulative seizure time, achieving statistical significance at doses ≥100 mg/kg. Lower doses of BRV (0.3-10 mg/kg) + low-dose DZP (1 mg/kg) significantly reduced SSSE duration and number of seizures. All control rats developed spontaneous recurrent seizures (SRS) 6-8 weeks after SSSE, whereas seizure freedom was noted in 2/10, 5/10, and 6/10 rats treated with BRV 200 mg/kg, 300 mg/kg, and BRV 10 mg/kg + DZP, respectively. BRV (10-300 mg/kg) showed a dose-dependent trend toward reduction of SRS frequency, cumulative seizure time, and spike frequency, achieving statistical significance at 300 mg/kg. Combination of BRV (10 mg/kg) + DZP significantly reduced SRS frequency, cumulative seizure time, and spike frequency. In the 12-month follow-up study, BRV (0.3-10 mg/kg) + low-dose DZP markedly reduced SRS frequency, cumulative seizure time, and spike frequency, achieving statistical significance at some doses. Early treatment of SSSE with BRV 10 mg/kg significantly reduced long-term SRS frequency.SignificanceThese findings support clinical evaluation of BRV for treatment of status epilepticus or acute repetitive seizures.

Global expression profiling of neurologic or psychiatric disorders has been confounded by variability among laboratories, animal models, tissues sampled, and experimental platforms, with the result being that few genes demonstrate consistent expression changes. We attempted to minimize these confounds by pooling dentate granule cell transcriptional profiles from 164 rats in seven laboratories, using three status epilepticus (SE) epilepsy models (pilocarpine, kainate, self-sustained SE), plus amygdala kindling. In each epilepsy model, RNA was harvested from laser-captured dentate granule cells from six rats at four time points early in the process of developing epilepsy, and data were collected from two independent laboratories in each rodent model except SSSE. Hierarchical clustering of differentially-expressed transcripts in the three SE models revealed complete separation between controls and SE rats isolated 1 day after SE. However, concordance of gene expression changes in the SE models was only 26-38% between laboratories, and 4.5% among models, validating the consortium approach. Transcripts with unusually highly variable control expression across laboratories provide a 'red herring' list for low-powered studies.

During status epilepticus (SE), synaptic γ-aminobutyric acid A receptors (GABAA Rs) become internalized and inactive, whereas spare N-methyl-d-aspartate receptors (NMDARs) assemble, move to the membrane, and become synaptically active. When treatment of SE is delayed, the number of synaptic GABAA Rs is drastically reduced, and a GABAA agonist cannot fully restore inhibition. We used a combination of low-dose diazepam (to stimulate the remaining GABAA Rs), ketamine (to mitigate the effect of the NMDAR increase), and valproate (to enhance inhibition at a nonbenzodiazepine site) to treat seizures in a model of severe cholinergic SE. High doses of diazepam failed to stop electrographic SE, showing that benzodiazepine pharmacoresistance had developed. The diazepam-ketamine-valproate combination was far more effective in stopping SE than triple-dose monotherapy using the same individual drugs. Isobolograms showed that this drug combination's therapeutic actions were synergistic, with positive cooperativity between drugs, whereas drug toxicity was simply additive, without positive or negative cooperativity. As a result, the therapeutic index was improved by this drug combination compared to monotherapy. These results suggest that synergistic drug combinations that target receptor changes can control benzodiazepine-refractory SE.

ObjectivePharmacoresistance remains an unsolved therapeutic challenge in status epilepticus (SE) and in cholinergic SE induced by nerve agent intoxication. SE triggers a rapid internalization of synaptic γ-aminobutyric acid A (GABAA ) receptors and externalization of N-methyl-d-aspartate (NMDA) receptors that may explain the loss of potency of standard antiepileptic drugs (AEDs). We hypothesized that a drug combination aimed at correcting the consequences of receptor trafficking would reduce SE severity and its long-term consequences.MethodsA severe model of SE was induced in adult Sprague-Dawley rats with a high dose of lithium and pilocarpine. The GABAA receptor agonist midazolam, the NMDA receptor antagonist ketamine, and/or the AED valproate were injected 40 min after SE onset in combination or as monotherapy. Measures of SE severity were the primary outcome. Secondary outcomes were acute neuronal injury, spontaneous recurrent seizures (SRS), and Morris water maze (MWM) deficits.ResultsMidazolam-ketamine dual therapy was more efficient than double-dose midazolam or ketamine monotherapy or than valproate-midazolam or valproate-ketamine dual therapy in reducing several parameters of SE severity, suggesting a synergistic mechanism. In addition, midazolam-ketamine dual therapy reduced SE-induced acute neuronal injury, epileptogenesis, and MWM deficits.SignificanceThis study showed that a treatment aimed at correcting maladaptive GABAA receptor and NMDA receptor trafficking can stop SE and reduce its long-term consequences. Early midazolam-ketamine dual therapy may be superior to monotherapy in the treatment of benzodiazepine-refractory SE.

Cholinergic status epilepticus (CSE) quickly becomes self-sustaining, independent of its initial trigger, and resistant to benzodiazepines and other antiepileptic drugs. We review a few of the many physiological changes associated with CSE, with an emphasis on receptor trafficking. Time-dependent internalization of synaptic γ-aminobutyric acid (GABA)A receptors explains, in part, the loss of inhibition and the loss of response to benzodiazepines in the early stages of CSE. The increase in N-methyl-d-aspartate receptors may contribute to the runaway excitation and excitotoxicity of CSE. These changes have therapeutic implications. The time-dependent increase in maladaptive changes points to the importance of early treatment. The involvement of both inhibitory and excitatory systems challenges current therapeutic guidelines, which recommend treating only one system, and questions the rationale for monotherapy. It suggests that polytherapy may be needed, especially when treatment is delayed, so that drugs can only reach a much reduced number of GABAA receptors. Finally, it raises the possibility that the current practice of waiting for one treatment to fail before starting the next drug may need to be reevaluated.

ObjectiveStatus Epilepticus (SE) is common in neonates and infants, and is associated with neuronal injury and adverse developmental outcomes. However, the role of SE in this injury is uncertain. Until now, we have lacked an animal model in which seizures result in neuronal injury in rodent models at ages below postnatal day 12 (P12) unless seizures are combined with inflammatory stressors.MethodsWe induced SE with high-dose lithium and pilocarpine in P7 rats, which are developmentally close to human neonates. Several EEG measures and O2 saturation were recorded during the 6h following initiation of SE. We assessed neuronal injury at 6 and 24h post-SE onset using Fluoro-Jade B staining (FJB) and caspase-3a immunoreactivity (IR).ResultsEEGs showed continuous polyspikes activity for 54.3 ± 6.7 min, while O2 saturation showed no significant hypoxemia. By 24h after SE onset, significant neuronal injury was observed in CA1/subiculum, CA3, dentate gyrus, thalamus, neocortex, amygdala, piriform cortex, lateral entorhinal cortex, hypothalamus, caudate putamen, globus pallidus, ventral pallidum, and nucleus accumbens. At 24h post-SE, caspase-3a IR was significantly increased in CA1/subiculum, thalamus, and neocortex compared to sham, and caspase-3a IR neurons had fragmented nuclei, suggesting that SE triggered an irreversible form of cell injury.SignificanceIn conclusion, we have developed a model of cholinergic SE in P7 rat pups, which combines high survival (69.9% survival at 24h) and widespread brain injury. These studies suggest that the immature brain is vulnerable to severe forms of SE.

ObjectivePharmacoresistance develops quickly during repetitive seizures, and refractory status epilepticus (RSE) remains a therapeutic challenge. The outcome of RSE is poor, with high mortality and morbidity. New treatments are needed. Deep hypothermia (20°C) is used clinically during reconstructive cardiac surgery and neurosurgery, and has proved safe and effective in those indications. We tested the hypothesis that deep hypothermia reduces RSE and its long-term consequences.MethodsWe used a model of SE induced by lithium and pilocarpine and refractory to midazolam. Several EEG measures were recorded in both hypothermic (n = 17) and normothermic (n = 20) animals. Neuronal injury (by Fluoro-Jade B), cell-mediated inflammation, and breakdown of the blood-brain barrier (BBB) (by immunohistochemistry) were studied 48 h following SE onset.ResultsNormothermic rats in RSE seized for 4.1 ± 1.1 h, and at 48 h they displayed extensive neuronal injury in many brain regions, including hippocampus, dentate gyrus, amygdala, entorhinal and pyriform cortices, thalamus, caudate/putamen, and the frontoparietal neocortex. Deep hypothermia (20°C) of 30 min duration terminated RSE within 12 min of initiation of hypothermia, reduced EEG power and seizure activity upon rewarming, and eliminated SE-induced neuronal injury in most animals. Normothermic rats showed widespread breakdown of the BBB, and extensive macrophage infiltration in areas of neuronal injury, which were completely absent in animals treated with hypothermia.InterpretationThese results suggest that deep hypothermia may open a new therapeutic avenue for the treatment of RSE and for the prevention of its long-term consequences.

In a rat model of status epilepticus (SE) induced by lithium and pilocarpine and refractory to midazolam, deep hypothermia (20 °C for 30 min) reduced EEG power over 50-fold, stopped SE within 12 min, and reduced EEG spikes by 87%. Hypothermia deserves further investigation as a treatment of last resort for refractory SE. This article is part of a Special Issue entitled "Status Epilepticus".

We used two models of status epilepticus (SE) to study trafficking of N-methyl-d-aspartate (NMDA) receptors. SE is associated with increased surface expression of NR1 subunits of NMDA receptors, and with an increase of NMDA synaptic and extrasynaptic currents suggesting an increase in number of functional NMDA receptors on dentate granule cells. The therapeutic implications of these results are discussed.

After 1h of lithium-pilocarpine status epilepticus (SE), immunocytochemical labeling of NMDA receptor NR1 subunits reveals relocation of subunits from the interior to the cell surface of dentate gyrus granule cells and CA3 pyramidal cells. Simultaneously, an increase in NMDA-miniature excitatory postsynaptic currents (mEPSC) as well as an increase in NMDA receptor-mediated tonic currents is observed in hippocampal slices after SE. Mean-variance analysis of NMDA-mEPSCs estimates that the number of functional postsynaptic NMDA receptors per synapse increases 38% during SE, and antagonism by ifenprodil suggests that an increase in the surface representation of NR2B-containing NMDA receptors is responsible for the augmentation of both the phasic and tonic excitatory currents with SE. These results provide a potential mechanism for an enhancement of glutamatergic excitation that maintains SE and may contribute to excitotoxic injury during SE. Therapies that directly antagonize NMDA receptors may be a useful therapeutic strategy during refractory SE.

During flurothyl seizures in 4-day-old rats, cortical concentration of ATP, phosphocreatine and glucose fell while lactate rose. Cortical energy use rate more than doubled, while glycolytic rate increased fivefold. Calculation of the cerebral metabolic balance during sustained seizures suggests that energy balance could be maintained in hyperglycemic animals, and would decline slowly in normoglycemia, but would be compromised by concurrent hypoglycemia, hyperthermia or hypoxia. These results suggest that the metabolic challenge imposed on the brain by this model of experimental neonatal seizures is milder than that seen at older ages, but can become critical when associated with other types of metabolic stress.

Purpose: To study the pharmacologic and synaptic basis for the early loss of paired-pulse inhibition that occurs in the perforant-path stimulation model of status epilepticus. Methods: Hippocampal slices were prepared from mate Wistar rats. Test paired pulses (20- to 50-ms interstimulus interval) of the perforant path were used before and after an abbreviated period of perforant-path stimulation (1-5 min; 2-Hz continuous with 20 Hz of 10 s/min pulses) while either recording field potentials from the dentate gyrus granule cell layer or directly measuring whole-cell patch-clamp currents from granule cells. Paired-pulse field recordings also were obtained during perfusion of the gamma-aminobutyric acid (GABA)A antagonist bicuculline. Results: Prolonged loss of paired-pulse inhibition occurs after brief (< 5 min) perforant-path stimulation in vitro (similar to results in vivo) with the paired-pulse population spike amplitude ratio (P2/P1) increasing from a baseline of 0.53 +/- 0.29 to 1.17 +/- 0.09 after perforant-path stimulation (p < 0.05). After perfusion with the GABA(A) antagonist, bicuculline, the P2/P1 ratio also increased from a baseline of 0.52 +/- 0.16 to 1.15 +/- 0.26 (p < 0.05). After 1-2 min of perforant-path stimulation, a 22 6% (p < 0.05) decrease occurred in the P2/P1 amplitude ratio of paired-pulse evoked inhibitory postsynaptic currents. Conclusions: Similar to in vivo, loss of paired-pulse inhibition occurs with brief perforant-path stimulation in vitro. GABA(A) antagonism causes a similar loss of paired-pulse inhibition, and the effects of perforant-path stimulation on Postsynaptic inhibitory currents also are consistent with the involvement of GABA(A) synaptic receptors. The findings suggest that loss of inhibition at GABA synapses may be an important early event in the initiation of status epilepticus.