Self-sustaining Status Epilepticus Research Articles

Noradrenaline and Seizures: A Perspective on the Role of Adrenergic Receptors in Limbic Seizures.

Noradrenergic fibers originating from the locus coeruleus densely innervate limbic structures, including the piriform cortex, which is the limbic structure with the lowest seizure threshold. Noradrenaline (NA) modulates limbic seizures while stimulating autophagy through β2- adrenergic receptors (AR). Since autophagy is related to seizure threshold, this perspective questions whether modulating β2-AR focally within the anterior piriform cortex affects limbic seizures. In this perspective, we analyzed a potential role for β2-AR as an anticonvulsant target within the anterior piriform cortex, area tempestas (AT). We developed this perspective based on current literature on the role of NA in limbic seizures and autophagy. The perspective is also grounded on preliminary data obtained by microinfusing within AT either a β2-AR agonist (salbutamol) or a β2-AR antagonist (butoxamine) 5 minutes before bicuculline. β2-AR stimulation fully prevents limbic seizures induced by bicuculline micro-infusion in AT. Conversely, antagonism at β2-AR worsens bicuculline-induced seizure severity and prolongs seizure duration, leading to self-sustaining status epilepticus. These data indicate a specific role for β2-AR as an anticonvulsant in AT. NA counteracts limbic seizures. This relies on various receptors in different brain areas. The anterior piriform cortex plays a key role in patients affected by limbic epilepsy. The anticonvulsant effects of NA through β2-AR may be related to the stimulation of the autophagy pathway. Recent literature and present data draw a perspective where β2-AR stimulation while stimulating autophagy mitigates limbic seizures, focally within AT. The mechanism linking β2-AR to autophagy and seizure modulation should be extensively investigated.

Perspective on mTOR-dependent Protection in Status Epilepticus.

The piriform cortex, known as area tempestas, has a high propensity to trigger limbic epileptic seizures. Recent studies on human patients indicate that a resection containing the piriform cortex produces a marked improvement in patients suffering from intractable limbic seizures. This calls for looking back at the pharmacological and anatomical data on area tempestas. Within the piriform cortex, status epilepticus can be induced by impairing the desensitization of AMPA receptors. The mechanistic target of rapamycin complex1 (mTORC1) is a promising candidate. The present perspective aims to link the novel role of the piriform cortex with recent evidence on the modulation of AMPA receptors under the influence of mTORC1. This is based on recent evidence and preliminary data, leading to the formulation of interaction between mTORC1 and AMPA receptors to mitigate the onset of long-lasting, self-sustaining, neurotoxic status epilepticus. The perspective grounds its method on recent literature along with the actual experimental procedure to elicit status epilepticus from the piriform cortex and the method to administer the mTORC1 inhibitor rapamycin to mitigate seizure expression and brain damage. The available and present perspectives converge to show that rapamycin may disrupt the seizure circuitry initiated in the piriform cortex to mitigate seizure duration, severity, and brain damage. The perspective provides a novel scenario to understand refractory epilepsy and selfsustaining status epilepticus. It is expected to provide a beneficial outcome in patients suffering from temporal lobe epilepsy.

Methylene Blue Exerts Anticonvulsant and Neuroprotective Effects on Self-Sustaining Status Epilepticus (SSSE) Induced by Prolonged Basolateral Amygdala Stimulation in Wistar Rats.

BackgroundThis study was designed to investigate the potential anticonvulsant and neuroprotective effects of methylene blue (MB) on self-sustaining status epilepticus (SSSE) induced by prolonged basolateral amygdala stimulation (BLA) in Wistar rats.Material/MethodsThe rats were randomly divided into 4 groups: (1) the Control group (rats without any treatment); (2) the Sham group (rats received electrode implantation but without electrical stimulation); (3) the SSSE group (rats received electrode implantation and additional electrical stimulation); and (4) the SSSE+MB group (rats received 1 mg/kg MB intraperitoneal injection 5 min after SSSE). SSSE models were established by prolonged BLA stimulation. The severities of SSSE were assessed by the number of separate seizures and the accumulated time of seizures. The variations of malondialdehyde/glutathione (MDA/GSH) were assessed 24 h after the establishment of SSSE. Nissl staining was performed to detect the surviving neurons in hippocampal CA1 and CA3 regions, and Western blotting assays were used to detect Caspase-3 (CASP3), B cell lymphoma 2 (BCL2), and BCL2-associated X protein (BAX).ResultsCompared with the SSSE group, treatment with MB (1) markedly reduced the number and accumulated time of seizure activities; (2) significantly attenuated the increase of MDA and the decrease of GSH hippocampal levels; (3) markedly improved the cell morphology and alleviated the neuronal loss in hippocampal CA1 and CA3 regions; (4) significantly attenuated the increase of CASP3 and BAX and the decrease of BCL2 hippocampal levels.ConclusionsMB has a protective effect in the SSSE model and may be useful as an adjuvant for preventing or treating epilepsy in humans.

Treating acute seizures with benzodiazepines: does seizure duration matter?

Several clinical trials have shown improved seizure control and outcome by early initiation of treatment with benzodiazepines, before arrival in the emergency department and before intravenous access can be established. Here, evidence is provided and reviewed for rapid treatment of acute seizures in order to avoid the development of benzodiazepine pharmacoresistance and the emergence of self-sustaining status epilepticus. Alterations in the physiology, pharmacology, and postsynaptic level of GABA-A receptors can develop within minutes to an hour and hinder the ability of synaptic inhibition to stop seizures while also impairing the efficacy of GABAergic agents, such as benzodiazepines, to boost impaired inhibition. In addition, heightened excitatory transmission further exacerbates the inhibitory/excitatory balance and makes seizure control even more resistant to treatment. The acute increase in the surface expression of NMDA receptors during prolonged seizures also may cause excitotoxic injury, cell death, and other pathological expressions and re-arrangements of receptor subunits that all contribute to long-term sequelae such as cognitive impairment and chronic epilepsy. In conclusion, a short window of opportunity exists when seizures are maximally controlled by first-line benzodiazepine treatment. After that, multiple pathological mechanisms quickly become engaged that make seizures increasingly more difficult to control with high risk for long-term harm.

Hypothermia did not prevent epilepsy following experimental status epilepticus

In epilepsy research, one of the major challenges is to prevent or at least mitigate development of epilepsy following acquired brain insult by early therapeutic interventions. So far, all pharmacological antiepileptogenic treatment approaches were largely unsuccessful in clinical trials and in experimental animal studies. In a well-established rat model of chronic epilepsy following self-sustaining status epilepticus (SSSE), we assessed the antiepileptogenic properties of 3-h-cooling induced directly after the end of SSSE. Occurrence of spontaneous seizures and seizure severity up to 8 weeks after SSSE were compared with normothermic SSSE controls. Furthermore, electrophysiological parameters assessing inhibition and excitation in the dentate gyrus were assessed at multiple time points. Post SSSE hypothermia did not prevent the occurrence of seizures in any animal. Eight weeks after SSSE, Racine motor seizures trended to be less severe following cooling (4.0±0.6) compared with normothermic controls (4.8±0.2) but the difference was not significant when testing for multiple comparisons. Early loss of inhibition that is typically seen following SSSE was somewhat attenuated in cooled animals 3h after SSSE as expressed by smaller paired-pulse ratios (PPR; 0.16±0.21) compared with normothermic controls (0.54±0.21) but difference was not significant either. Latency between stimulus artefact and excitatory post-synaptic potential 3h after SSSE, reciprocally reflecting neuronal excitation, was higher in animals that underwent hypothermia (8.29±2.45ms) compared with controls (4.82±0.66ms), difference was not significant after correction for multiple comparisons. In summary, the current experiments were not able to demonstrate prevention or mitigation of epileptogenesis with immediate short-term cooling following SSSE.

Prolonged depth electrode implantation in the limbic system increases the severity of status epilepticus in rats

Chronically implanted intracranial depth electrodes are widely used for studying electroencephalographic activities in deep cerebral locations and for electrical stimulation of such locations. We have previously reported that prolonged implantation of an electrode in the basolateral amygdala (BLA) of rats facilitates subsequent kindling from this site, indicating a pro-kindling or pro-epileptogenic effect. To further characterize this phenomenon, we analyzed data from experiments in which we induced a self-sustaining status epilepticus (SSSE) by BLA stimulation following different periods of post-surgical delay. In a total of 183 Sprague-Dawley rats, three groups with different periods of postsurgical delay to onset of electrical stimulation were compared: group 1 (16 days on average), group 2 (28 days) and group 3 (48 days). Three types of SSSE were observed after BLA stimulation: type 1 (nonconvulsive), type 2 (nonconvulsive occasionally interrupted by generalized convulsive activity), and type 3 (generalized convulsive). While groups 1 and 2 did not differ in the frequency of these SSSE types, the group with the longest interval between electrode implantation and stimulation (group 3) showed significantly more severe SSSE than the two other groups. The data indicate that intracranial electrode implantation may increase the sensitivity of the implanted area to seizure induction, extending previous findings in the kindling model. Potential mechanisms of these findings include the functional consequences of local microhemorrhages and blood-brain barrier destruction.

Influence of neuropathology on convection-enhanced delivery in the rat hippocampus.

Local drug delivery techniques, such as convention-enhanced delivery (CED), are promising novel strategies for delivering therapeutic agents otherwise limited by systemic toxicity and blood-brain-barrier restrictions. CED uses positive pressure to deliver infusate homogeneously into interstitial space, but its distribution is dependent upon appropriate tissue targeting and underlying neuroarchitecture. To investigate effects of local tissue pathology and associated edema on infusate distribution, CED was applied to the hippocampi of rats that underwent electrically-induced, self-sustaining status epilepticus (SE), a prolonged seizure. Infusion occurred 24 hours post-SE, using a macromolecular tracer, the magnetic resonance (MR) contrast agent gadolinium chelated with diethylene triamine penta-acetic acid and covalently attached to albumin (Gd-albumin). High-resolution T1- and T2-relaxation-weighted MR images were acquired at 11.1 Tesla in vivo prior to infusion to generate baseline contrast enhancement images and visualize morphological changes, respectively. T1-weighted imaging was repeated post-infusion to visualize final contrast-agent distribution profiles. Histological analysis was performed following imaging to characterize injury. Infusions of Gd-albumin into injured hippocampi resulted in larger distribution volumes that correlated with increased injury severity, as measured by hyperintense regions seen in T2-weighted images and corresponding histological assessments of neuronal degeneration, myelin degradation, astrocytosis, and microglial activation. Edematous regions included the CA3 hippocampal subfield, ventral subiculum, piriform and entorhinal cortex, amygdalar nuclei, middle and laterodorsal/lateroposterior thalamic nuclei. This study demonstrates MR-visualized injury processes are reflective of cellular alterations that influence local distribution volume, and provides a quantitative basis for the planning of local therapeutic delivery strategies in pathological brain regions.

Anticonvulsant effect of dexmedetomidine in a rat model of self-sustaining status epilepticus with prolonged amygdala stimulation

Status epilepticus (SE), leading to 27 percent mortality in adult patients, becomes refractory to firstline intravenous diazepam, with prolonged seizure duration. The mechanism could be attributed to the declined inhibitory action of GABA; therefore, alternative medications acting on other targets are necessary. The aim of the present study was to examine whether DEX, a highly specific central α2-adrenoreceptor agonist, could show the anticonvulsant effect on self-sustaining SE (SSSE), and to explore the involved mechanisms. Five minutes after SSSE, which was induced in adult Wistar rats by constant amygdala stimulation for 25min, DEX was injected intraperitoneally at two dosages (50/100μg/kg). The number and cumulative time of repeated seizures were recorded; the levels of Glu/GABA and glutathione/malondialdehyde (GSH/MDA) in hippocampus tissue were detected. The results showed that DEX effectively decreased the number and cumulative time of repeated seizures, alleviated the levels of Glu and GSH/MDA in hippocampus tissue, but no effect was detected on the level of GABA, suggesting that DEX could be a potential agent for the treatment of SSSE, the possible mechanisms were antioxidation and inhibition of the Glu release.

Ketamine combinations for the field treatment of soman-induced self-sustaining status epilepticus. Review of current data and perspectives

Organophosphorus nerve agents (NA), potent irreversible cholinesterase inhibitors, could induce severe seizures, status epilepticus (SE), seizure-related brain damage (SRBD) and lethality. Despite the lack of data in the case of NA, clinical evidences suggest that SE survivors could suffer from neurological/cognitive deficits and impairments such as spontaneous recurrent seizures (epilepsy) after a latent period of epileptogenesis. It is beyond doubt that an effective and quick management of the initial seizures and prevention of SRBD are critical to prevent these long-term consequences, explaining why most experimental data are focusing on the 5–40min post-exposure time frame. However, in field conditions, treatment may be delayed and with the exception of NMDA receptor antagonists, currently no drug provides protection (against lethality, seizures, SRBD and neurological consequences) when seizures are left unabated for one hour or more. Ketamine (KET) is the only NMDA antagonist licensed as an injectable drug in different countries and remains an anesthetic of choice in some difficult field conditions. In this short review paper, after a presentation of some of the key points of the pathophysiology of NA-induced SE and a quick survey of the potential therapeutic avenues in the context of delayed treatment of NA-induced SE, we will review the recent data we obtained showing that KET, in combination with atropine sulfate (AS), with or without a benzodiazepine, considerably reduces soman-induced neuroinflammation, provides neuroprotection, histologically and functionally, and also positively modify soman-induced changes in brain metabolism. Finally, we will also mention some results from safety studies including those bringing evidence that, at difference with MK-801, KET does not impair thermoregulation and even seems to reduce AS-induced heat stress. All in all, KET, in combination, appears a good candidate for the out-of-hospital treatment of severe NA-induced SE.

Deep hypothermia terminates status epilepticus — an experimental study

In search for novel treatment approaches in status epilepticus, the anticonvulsant effect of moderate and deep hypothermia was assessed in a rodent model. Self-sustaining status epilepticus (SSSE) characterized by spontaneous high-amplitude discharges recorded from the dentate gyrus was induced in male adult rats by electrical stimulation of the perforant path. After the end of stimulation, rats underwent cooling to 30°C (n=7) and 20°C (n=10) for 120min and rewarming to 37°C for another 60min. Control SSSE animals (n=6) remained untreated for 180min. Frequency of epileptiform discharges was assessed every 10min. At the target temperature of 20°C, SSSE was completely suppressed in four rats, this effect was not observed in any animal of the other two groups (p=0.043). On rewarming, seizure activity did not reoccur. Discharge frequency was significantly lower in the 20°C group at most time points after 60min of cooling. Following deep hypothermia, eight animals were rewarmed, all survived and moved spontaneously at 37°C. These experimental data indicate the strong and enduring anticonvulsant and obviously safe properties of cooling down to 20°C. Patients with status epilepticus refractory to first- and second-line anticonvulsants may benefit from deep cooling as an effective non-pharmacological adjunct to anesthetic anticonvulsants.

Acute down‐regulation of adenosine A1 receptor activity in status epilepticus

Status epilepticus (SE) remains a potentially devastating condition that quickly becomes refractory to antiepileptic drug treatment and arises as a result of a failure of the brain's endogenous antiepileptic mechanisms. Understanding these mechanisms and how they are disrupted in SE is necessary in order to identify novel therapeutic approaches. Adenosine is considered an endogenous anticonvulsant. Extracellular concentrations increase coinciding with seizure termination; activation of A(1) receptors (A(1)Rs) reduces seizure-induced damage and epileptiform activity. The present study examines the effectiveness of focal drug delivery in a model of limbic SE that closely resembles the human condition and describes, for the first time, alterations in A(1)R signaling during prolonged seizures that may contribute to the progression from self-terminating seizures to self-sustaining SE (SSSE). We developed a rat perforant path stimulation model in which 50% of rats develop SSSE and tested whether modulation of A(1)Rs influenced SSSE development when drugs were infused to the dentate gyrus. We further determined the ability of A(1)Rs to modulate perforant path to granule cell transmission in hippocampal slices taken from sham-operated control and post-SE animals. Adenosine (3 μM) and the A(1)R-selective agonist 2-chloro-N(6)-cyclopentyladenosine (CCPA; 10 μM) reduced the severity of SSSE as measured by spike count, electroencephalography power and behavioral seizure score. In addition, CCPA suppressed the progression to SSSE. Surprisingly, the A(1)R-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 1 μm) had no effect on the severity of or progression to SSSE, suggesting a lack of intrinsic A(1)R activation. Immunohistochemistry revealed no alterations in total A(1)R expression. However, we observed a marked down-regulation of A(1)R modulation of neurotransmission in vitro, indicating acute A(1)R desensitization. These findings indicate that A(1)R activation can prevent the progression to SE and suggest that reduced A(1)R signaling promotes the transition of seizures to SSSE.

The acute and chronic effects of the novel anticonvulsant lacosamide in an experimental model of status epilepticus

The effective management of status epilepticus (SE) continues to be a therapeutic challenge. The aim of this study was to investigate the efficacy of lacosamide treatment in an experimental model of self-sustaining SE. Rats were treated with lacosamide (3, 10, 30 or 50mg/kg) either 10 min (early treatment) or 40 min (late treatment) after the initiation of perforant path stimulation. Early lacosamide treatment significantly and dose-dependently reduced acute SE seizure activity; late treatment showed only a non-significant trend toward reduced seizure activity. Early lacosamide treatment also dose-dependently reduced the number of spontaneous recurrent seizures following a 6-week waiting period, with 70% reduction at the highest dose tested (50mg/kg); there was also a significant reduction in the number of spikes and the cumulative time spent in seizures. Late treatment with high-dose lacosamide (30-50mg/kg) reduced the number of animals that developed spontaneous recurrent seizures (33% vs 100% in controls, P<.05), but did not significantly reduce seizure severity or frequency in rats that developed spontaneous recurrent seizures. The results presented here suggest that lacosamide deserves investigation for the clinical treatment of SE. Potential for disease modification in this rat model of self-sustaining SE will require further studies.

Distinct Gene Expression Profiles Directed by the Isoforms of the Transcription Factor Neuron-Restrictive Silencer Factor in Human SK-N-AS Neuroblastoma Cells

Neuron-restrictive silencer factor (NRSF) and its isoforms are differentially regulated in rodent models of self-sustaining status epilepticus (SSSE). NRSF isoforms regulate genes associated with SSSE, including the proconvulsant tachykinins, brain-derived neurotrophic factor and multiple ion channels. NRSF isoforms may direct distinct gene expression patterns during SSSE, and the ratio of each isoform may be a causative factor in traumatic damage to the central nervous system. Here, we analysed global gene expression changes by microarray in human SK-N-AS neuroblastoma cells following the over-expression of NRSF and a truncated isoform, HZ4. We used bioinformatics software to analyse the microarray dataset and correlated these data with epilepsy candidate gene pathways. Findings were validated by reverse transcriptase-polymerase chain reaction. We demonstrated that NRSF and HZ4 direct overlapping as well as distinct gene expression patterns, and that they differentially modulated gene expression patterns associated with epilepsy. Finally, we revealed that NRSF gene expression may be modulated by the anticonvulsant, phenytoin. We have interpreted our data to reflect altered gene expression directed by NRSF that might be relevant for SSSE.

Early MR diffusion and relaxation changes in the parahippocampal gyrus precede the onset of spontaneous seizures in an animal model of chronic limbic epilepsy

Structural changes in limbic regions are often observed in individuals with temporal lobe epilepsy (TLE) and in animal models. However, the brain structural changes during the evolution into epilepsy remain largely unknown. Therefore, the purpose of this study was to define the temporal changes in limbic structures after experimental status epilepticus (SE) during the latency period of epileptogenesis in vivo, with quantitative diffusion tensor imaging (DTI) and T2 relaxometry in an animal model of chronic TLE. A pair of fifty micron electrodes was implanted into the ventral hippocampus in twelve male adult rats. Self-sustaining SE was induced with electrical stimulation in eleven rats. Three rats served as age-matched controls. In vivo diffusion tensor and T2 magnetic resonance imaging (MRI) was performed at 11.1 Tesla, pre- and post-implantation of electrodes and 3, 5, 7, 10, 20, 40 and 60 days post-SE to assess structural changes. Spontaneous seizures were identified with continuous time-locked video-monitoring. Following imaging in vivo, fixed, excised brains were MR imaged at 17.6 Tesla. Subsequently, histological analysis was correlated with MRI results. Following SE, 8/11 injured rats developed spontaneous seizures. Unique to these 8 rats, early T2, diffusivity and anisotropy changes were observed in vivo within the parahippocampal gyrus (contralateral) and fimbria (bilateral). In excised brains, bilateral increase in anisotropy was observed in the dentate gyrus, corresponding to mossy fiber sprouting as determined by Timm staining. Using T2 relaxometry and DTI, specific transient and long-term structural changes were observed only in rats that developed spontaneous limbic seizures.

Activation of brain metabolism and fos during limbic seizures: The role of Locus Coeruleus

The noradrenergic nucleus Locus Coeruleus (LC) densely innervates limbic structures. In rats, the damage to LC by the neurotoxin DSP-4, converts episodic limbic seizures induced by bicuculline infusion in the anterior piriform cortex (APC) into self-sustaining status epilepticus (SE). SE induced by this approach is similar to SE induced by co-infusing cyclothiazide and bicuculline into APC in rats bearing an intact LC. As opposed to other commonly used rat SE models (e.g. systemic kainate or pilocarpine), this approach allows one to analyze the effects of SE on brain regions which are solely due to spreading of seizure activity, rather than to direct effect of systemic chemoconvulsant.We evaluated the expression of Fos protein (an immediate early gene product), and the local cerebral metabolic rates for [14C] 2-deoxyglucose (lCMRglc), in rats following SE induced either by cyclothiazide+bicuculline or by DSP-4+bicuculline.We demonstrated that regional Fos expression after SE does not parallel the increase in lCMRglc, in LC-lesioned rats. In DSP-4+bicuculline rats there is an overall lower expression of the protein as compared with the cyclothiazide+bicuculline or bicuculline alone groups; even more, such a difference co-exists with an higher lCMRglc in the DSP-4+bicuculline-treated rats in some regions, as compared with the other groups.These data show that LC neurons play an important role in determining immediate early genes expression even in conditions of strong pathological activation, such as limbic SE. This might have relevant effects in the plastic mechanisms related with epileptogenesis.

Advances in the pathophysiology of status epilepticus

Status epilepticus (SE) describes an enduring epileptic state during which seizures are unremitting and tend to be self-perpetuating. We describe the clinical phases of generalized convulsive SE, impending SE, established SE, and subtle SE. We discuss the physiological and biochemical cascades which characterize self-sustaining SE (SSSE) in animal models. At the transition from single seizures to SSSE, GABA(A) (gamma-aminobutyric acid) receptors move from the synaptic membrane to the cytoplasm, where they are functionally inactive. This reduces the number of GABA(A) receptors available for binding GABA or GABAergic drugs, and may in part explain the development of time-dependent pharmacoresistance to benzodiazepines and the tendency of seizures to become self-sustaining. At the same time, 'spare' subunits of AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA (N-methyl-D-aspartic acid) receptors move from subsynaptic sites to the synaptic membrane, causing further hyperexcitability and possibly explaining the preserved sensitivity to NMDA blockers late in the course of SE. Maladaptive changes in neuropeptide expression occur on a slower time course, with depletion of the inhibitory peptides dynorphin, galanin, somatostatin and neuropeptide Y, and with an increased expression of the proconvulsant tachykinins, substance P and neurokinin B. Finally, SE-induced neuronal injury and epileptogenesis are briefly discussed.

Selective loss of dentate hilar interneurons contributes to reduced synaptic inhibition of granule cells in an electrical stimulation‐based animal model of temporal lobe epilepsy

Neuropeptide-containing hippocampal interneurons and dentate granule cell inhibition were investigated at different periods following electrical stimulation-induced, self-sustaining status epilepticus (SE) in rats. Immunohistochemistry for somatostatin (SOM), neuropeptide Y (NPY), parvalbumin (PV), cholecystokinin (CCK), and Fluoro-Jade B was performed on sections from hippocampus contralateral to the stimulated side and studied by confocal laser scanning microscopy. Compared to paired age-matched control animals, there were fewer SOM and NPY-immunoreactive (IR) interneurons in the hilus of the dentate gyrus in animals with epilepsy (40-60 days after SE), and 1, 3, and 7 days following SE. In the hilus of animals that had recently undergone SE, some SOM-IR and NPY-IR interneurons also stained for Fluoro-Jade B. Furthermore, there was electron microscopic evidence of the degeneration of SOM-IR interneurons following SE. In contrast, the number of CCK and PV-IR basket cells in epileptic animals was similar to that in controls, although it was transiently diminished following SE; there was no evidence of degeneration of CCK or PV-IR interneurons. Patch-clamp recordings revealed a diminished frequency of inhibitory postsynaptic currents in dentate granule cells (DGCs) recorded from epileptic animals and animals that had recently undergone SE compared with controls. These results confirm the selective vulnerability of a particular subset of dentate hilar interneurons after prolonged SE. This loss may contribute to the reduced GABAergic synaptic inhibition of granule cells in epileptic animals.

Temperature regulation is compromised in experimental limbic status epilepticus

Temperature dysregulation is well known in generalized convulsive status epilepticus but so far has not been reported in non-convulsive forms. In order to detect possible subtle alterations, we have analyzed the capability to compensate for external cooling in an animal model of limbic status epilepticus. Rats with electrically induced self-sustaining status epilepticus (SSSE) ( n = 6) as well as rats without electrical stimulation ( n = 6) were cooled for 3 h and then rewarmed for another hour. The time course of changes in epidural temperature in animals of both groups that underwent cooling and in control rats that were not cooled and not stimulated ( n = 6) was compared. In animals with limbic SSSE, temperature fell continuously and was significantly lower at all time points under cooling as compared with each of the two other groups. In animals that were not stimulated, temperature under cooling fell by 1 to 2 °C only and was not significantly different at any time point as compared with controls. The effect of cooling was reversible in both groups. The current data indicate that temperature homeostasis in limbic status epilepticus is markedly disturbed. This finding may suggest ictal involvement of primary thermoregulatory neurons in the anterior hypothalamus probably by spread of epileptic activity from temporo-mesial structures.

Anticonvulsant properties of hypothermia in experimental status epilepticus

Status epilepticus in patients often does not respond to first-line anticonvulsants, and subsequent treatment escalation with continuous intravenous anesthetics may be associated with significant side-effects. Therefore, alternative treatment regimens are urgently needed. Hypothermia has been shown to reduce excitatory transmission and may thus serve as an interesting adjunct in the management of status epilepticus. In the current experiments, three treatment groups were compared. Animals with self-sustaining status epilepticus were treated with external cooling for 3 h, with low-dose diazepam, or with a combination of both. The effect of these regimens on epileptic activity was compared with untreated controls. Animals that underwent cooling were rewarmed, and all animals were monitored for 5 h to assess occurrence and severity of motor seizures and frequency and amplitude of spontaneous epileptic discharges. Cooling alone significantly reduced number and severity of motor seizures but did not alter epileptic discharges. Cooling in addition to low-dose diazepam significantly diminished amplitudes and frequencies of epileptic discharges, while diazepam alone had only a minor reducing effect on discharge amplitudes. However, at later stages of status epilepticus, diazepam significantly reduced motor seizures. Following rewarming, the discharge frequency tended to increase again, suggesting partial reversibility. The current experiments show that in status epilepticus hypothermia exhibits anticonvulsant effects which are most pronounced if co-administered with low-dose diazepam. The results still require confirmation in other animal models and also clinical studies are urgently needed. However, our data indicate that cooling could well become a future adjunct in the treatment of status epilepticus in patients.

Treatment with valproate after status epilepticus: Effect on neuronal damage, epileptogenesis, and behavioral alterations in rats

Epileptogenesis, i.e. the process leading to epilepsy with spontaneous recurrent seizures, can be initiated by a number of brain damaging insults, including traumatic brain injury, status epilepticus (SE), and stroke. Such acquired epilepsy is often associated with memory impairment and behavioral problems. There has been a growing interest in the use of antiepileptic drugs (AEDs) for neuroprotection and prevention or modification of epileptogenesis induced by such brain insults. One promising candidate in this respect is valproic acid (VPA), a widely used AED that has been reported to exert neuroprotective activity in a number of in vitro and in vivo models. The present study investigated whether VPA reduces brain damage and improves functional outcome in a rat model of post-SE epilepsy. A self-sustaining SE was induced by prolonged electrical stimulation of the basal amygdala via a depth electrode. SE was terminated after 4 h by diazepam, immediately followed by onset of treatment with VPA. VPA was injected i.p. at a bolus dose of 400 mg/kg, followed by three times daily administration of 200 mg/kg for 4 weeks. A control group received vehicle instead of VPA after SE. Spontaneous seizures were recorded in all rats of both groups following termination of treatment, without significant inter-group difference in seizure frequency or severity. However, treatment with VPA after SE prevented the hyperexcitability and locomotor hyperactivity observed in vehicle-treated epileptic rats. Furthermore, VPA completely counteracted the neuronal damage in the hippocampal formation, including the dentate hilus. The data demonstrate that, although VPA does not prevent the occurrence of spontaneous seizures after SE, it exerts powerful neuroprotective effects and prevents part of the behavioral alterations, demonstrating that administration of VPA immediately after SE exerts a favorable effect on long-term functional outcome.