Efficacy of current antiepileptics to prevent neurodegeneration in epilepsy models

Pentylenetetrazole-Induced Seizures in Wistar Male Albino Rats with Reference to Glutamate Metabolism

Background and Purpose

Epilepsy is a common and heterogenous neurological disorder characterized by recurrent spontaneous seizures. Animal models like rats play a crucial role in finding of mechanism of epilepsy in different brain regions. i.e., cerebral cortex, cerebellum, hippocampus, and pons medulla. Glutamate is an important excitatory neurotransmitter in the central nervous system and also glutamate plays a vital role in neuronal development and memory. The process of neuronal death evolved by glutamate receptor activation, has been hypothesized in both acute and chronic degenerative disorders including epilepsy. Considering the multifactorial neurochemical and neurophysiological malfunctions consequent to epileptic seizures, a few antiepileptic drugs are designed, to mitigate the debilitating aspects of epilepsy.

Methods

Rat model, pentylenetetrazole (PTZ), an anticonvulsant drug, was selected for the present study. Induction of epilepsy/convulsions was induced by an intraperitoneal injection of PTZ (60 mg/kg body weight) in saline. Biochemical assays performed through spectrophotometer.

Results

Glutamine and Glutamine synthetase levels were decreased in the epileptic rats brain regions i.e., hippocampus, cerebellum, cerebral cortex, and pons medulla; glutamate dehydrogenase and glutaminase levels were increased in all the regions of epilepsy induced rats. Highest values are recorded in hippocampus when compared to other brain regions.

Conclusion

PTZ suppresses the function of Glutamine and Glutamine synthetase activities in selected brain regions of rat and enhances the activities of the glutaminase and glutamate dehydrogenase when compared to control rats.

Robotic assessment of sensorimotor and cognitive deficits in patients with temporal lobe epilepsy

OBJECTIVE

Individuals with temporal lobe epilepsy (TLE) frequently demonstrate impairments in executive function, working memory, and/or declarative memory. It is recommended that screening for cognitive impairment is undertaken in all people newly diagnosed with epilepsy. However, standard neuropsychological assessments are a limited resource and thus not available to all. Our study investigated the use of robotic technology (the Kinarm robot) for cognitive screening.

METHODS

27 participants with TLE (17 left) underwent both a brief neuropsychological screening and a robotic (Kinarm) assessment. The degree of impairments and correlations between standardized scores from both approaches to assessments were analysed across different neurocognitive domains. Performance was compared between people with left and right TLE to look for laterality effects. Finally, the association between the duration of epilepsy and performance was assessed.

RESULTS

Across the 6 neurocognitive domains (attention, executive function, language, memory, motor and visuospatial) assessed by our neuropsychological screening, all showed scores that significantly correlated with Kinarm tasks assessing the same cognitive domains except language and memory that were not adequately assessed with Kinarm. Participants with right TLE performed worse on most tasks than those with left TLE, including both visuospatial (typically considered right hemisphere), and verbal memory and language tasks (typically considered left hemisphere). No correlations were found between the duration of epilepsy and either the neuropsychological screening or Kinarm assessment.

SIGNIFICANCE

Our findings suggest that Kinarm may be a useful tool in screening for neurocognitive impairment in people with TLE. Further development may facilitate an easier and more rapid screening of cognition in people with epilepsy and distinguishing patterns of cognitive impairment.

Neuroprotective Properties of Antiepileptics: What are the Implications for Psychiatric Disorders?

Since the discovery of the first antiepileptic compound, increasing attention has been paid to antiepileptic drugs (AEDs), and recently, with the understanding of the molecular mechanism underlying cells death, a new interest has revolved around a potential neuroprotective effect of AEDs. While many neurobiological studies in this field have focused on the protection of neurons, growing data are reporting how exposure to AEDs can also affect glial cells and the plastic response underlying recovery; however, demonstrating the neuroprotective abilities of AEDs remains a changeling task. The present work aims to summarize and review the literature available on the neuroprotective properties of the most commonly used AEDs. Results highlighted how further studies should investigate the link between AEDs and neuroprotective properties; while many studies are available on valproate, results for other AEDs are very limited and the majority of the research has been carried out on animal models. Moreover, a better understanding of the biological basis underlying neuro-regenerative defects may pave the way for the investigation of further therapeutic targets and eventually lead to an improvement in the actual treatment strategies.

SGK1.1 limits brain damage after status epilepticus through M current-dependent and independent mechanisms

Epilepsy is a neurological condition associated to significant brain damage produced by status epilepticus (SE) including neurodegeneration, gliosis and ectopic neurogenesis. Reduction of these processes constitutes a useful strategy to improve recovery and ameliorate negative outcomes after an initial insult. SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), has been shown to increase M-current density in neurons, leading to reduced excitability and protection against seizures. For this study, we used 4-5 months old male transgenic C57BL/6 J and FVB/NJ mice expressing near physiological levels of a constitutively active form of the kinase controlled by its endogenous promoter. Here we show that SGK1.1 activation potently reduces levels of neuronal death (assessed using Fluoro-Jade C staining) and reactive glial activation (reported by GFAP and Iba-1 markers) in limbic regions and cortex, 72 h after SE induced by kainate, even in the context of high seizure activity. This neuroprotective effect is not exclusively through M-current activation but is also directly linked to decreased apoptosis levels assessed by TUNEL assays and quantification of Bim and Bcl-x_L by western blot of hippocampal protein extracts. Our results demonstrate that this newly described antiapoptotic role of SGK1.1 activation acts synergistically with the regulation of cellular excitability, resulting in a significant reduction of SE-induced brain damage in areas relevant to epileptogenesis.

The Utility of the Repeatable Battery of Neuropsychological Status in Patients with Temporal and Non-temporal Lobe Epilepsy

OBJECTIVE

The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) is a brief neuropsychological battery that has been validated in the assessment of dementia and other clinical populations. The current study examines the utility of the RBANS in patients with epilepsy.

METHODS

Ninety-eight patients with epilepsy completed the RBANS as part of a more comprehensive neuropsychological evaluation. Performance on the RBANS was evaluated for patients with a diagnosis of temporal lobe epilepsy (TLE; n = 51) and other epilepsy patients (non-TLE, n = 47) in comparison to published norms. Multivariate analysis of variance compared group performances on RBANS indices. Rates of impairment were also compared across groups using cutoff scores of ≤1.0 and ≤1.5 standard deviations below the normative mean. Exploratory hierarchical regressions were used to examine the relations between epilepsy severity factors (i.e., age of onset, disease duration, and number of antiepileptic drugs [AEDs]) and RBANS performance.

RESULTS

TLE and non-TLE patients performed below the normative sample across all RBANS indices. Those with TLE performed worse than non-TLE patients on the Immediate and Delayed Memory indices and exhibited higher rates of general cognitive impairment. Number of AEDs was the only epilepsy severity factor that significantly predicted RBANS total performance, accounting for 14% of the variance.

CONCLUSIONS

These findings suggest that the RBANS has utility in evaluating cognition in patients with epilepsy and can differentiate TLE and non-TLE patients. Additionally, number of AEDs appears to be associated with global cognitive performance in adults with epilepsy.

Neuroprotective effects of levetiracetam, both alone and combined with propylparaben, in the long-term consequences induced by lithium-pilocarpine status epilepticus

Status epilepticus (SE) is a neurological condition that frequently induces severe neuronal injury in the hippocampus, subsequent epileptogenesis and pharmacoresistant spontaneous recurrent seizures (SRS). The repeated administration of LEV (a broad-spectrum antiepileptic drug) during the post-SE period does not prevent the subsequent development of SRS. However, this treatment reduces SE-induced neurodegeneration in the hippocampus. Conversely, propylparaben (PPB) is a widely used antimicrobial that blocks voltage-dependent Na⁺ channels, induces neuroprotection and reduces epileptiform activity in vitro. The present study attempted to determine if the neuroprotective effects induced by LEV are augmented when combined with a sub-effective dose of PPB. Long-term SE-induced consequences (hyperexcitability, high glutamate release, neuronal injury and volume loss) were evaluated in the hippocampus of rats. LEV alone, as well as combined with PPB, did not prevent the occurrence of SRS. However, animals treated with LEV plus PPB showed high prevalence of low frequency oscillations (0.1-4 Hz and 8-90 bands, p < 0.001) and low prevalence of high frequency activity (90-250 bands, p < 0.001) during the interictal period. In addition, these animals presented lower extracellular levels of glutamate, decreased rate of neurodegeneration and a similar hippocampal volume compared to the control conditions. This study's results suggest that LEV associated with PPB could represent a new therapeutic strategy to reduce long-term consequences induced by SE that facilitate pharmacoresistant SRS.

Neuropharmacological and neuroprotective activities of some metabolites produced by cell suspension culture of Waltheria americana Linn

Waltheria americana is a plant used in Mexican traditional medicine to treat some nervous system disorders. The aims of the present study were to isolate and determine the neuropharmacological and neurprotective activities of metabolites produced by a cell suspension culture of Waltheria americana. Submerged cultivation of W. americana cells provided biomass. A methanol-soluble extract (WAsc) was obtained from biomass. WAsc was fractionated yielding the chromatographic fractions 4WAsc-H₂O and WAsc-CH₂Cl₂. For the determination of anticonvulsant activity in vivo, seizures were induced in mice by pentylenetetrazol (PTZ). Neuropharmacological activities (release of gamma amino butyric acid (GABA) and neuroprotection) of chromatographic fractions were determined by in vitro histological analysis of brain sections of mice post mortem. Fraction 4WAsc-H₂O (containing saccharides) did not produce neuronal damage, neurodegeneration, interstitial tissue edema, astrocytic activation, nor cell death. Pretreatment of animals with 4WAsc-H₂O and WAsc-CH₂Cl₂ from W. americana cell suspensions induced an increase in: GABA release, seizure latency, survival time, neuroprotection, and a decrease in the degree of severity of tonic/tonic-clonic convulsions, preventing PTZ-induced death of up to 100% of animals of study. Bioactive compounds produced in suspension cell culture of W. americana produce neuroprotective and neuropharmacological activities associated with the GABAergic neurotransmission system.

Neuroprotection as a Potential Therapeutic Perspective in Neurodegenerative Diseases: Focus on Antiepileptic Drugs

Neuroprotection is conceived as one of the potential tool to prevent or slow neuronal death and hence a therapeutic hope to treat neurodegenerative diseases, like Parkinson's and Alzheimer's diseases. Increase of oxidative stress, mitochondrial dysfunction, excitotoxicity, inflammatory changes, iron accumulation, and protein aggregation have been identified as main causes of neuronal death and adopted as targets to test experimentally the putative neuroprotective effects of various classes of drugs. Among these agents, antiepileptic drugs (AEDs), both the old and the newer generations, have shown to exert protective effects in different experimental models. Their mechanism of action is mediated mainly by modulating the activity of sodium, calcium and potassium channels as well as the glutamatergic and GABAergic (gamma-aminobutyric acid) synapses. Neurological pathologies in which a neuroprotective action of AEDs has been demonstrated in specific experimental models include: cerebral ischemia, Parkinson's disease, and Alzheimer's disease. Although the whole of experimental data indicating that neuroprotection can be achieved is remarkable and encouraging, no firm data have been produced in humans so far and, at the present time, neuroprotection still remains a challenge for the future.

Alteration of pentylenetetrazole-induced seizure threshold by chronic administration of ginger (Zingiber officinale) extract in male mice

CONTEXT

Zingiber officinale Roscoe (Zingiberaceae), or ginger, used in traditional Chinese medicine, has antioxidant activity and neuroprotective effects. The effects of this plant on clonic seizure have not yet been studied.

OBJECTIVE

The present study evaluated the anticonvulsant effect of ginger in a model of clonic seizures induced with pentylenetetrazole (PTZ) in male mice.

MATERIALS AND METHODS

The anticonvulsant effect of Z. officinale was investigated using i.v. PTZ-induced seizure models in mice. Different doses of the hydroethanolic extract of Z. officinale (25, 50, and 100 mg/kg) were administered intraperitonal (i.p.), daily for 1 week before induction of PTZ. Phenobarbital sodium (30 mg/kg), a reference standard, was also tested for comparison. The effect of ginger on to the appearance of three separate seizure endpoints, e.g., myoclonic, generalized clonic, and tonic extension phase, was recorded.

RESULTS

Hydroethanolic extract of Z. officinale significantly increased the onset time of myoclonic seizure at doses of 25-100 mg/kg (55.33 ± 1.91 versus 24.47 ± 1.33 mg/kg, p < 0.001) and significantly prevented generalized clonic (74.64 ± 3.52 versus 47.72 ± 2.31 mg/kg, p < 0.001) and increased the threshold for the forelimb tonic extension (102.6 ± 5.39 versus 71.82 ± 7.82 mg/kg, p < 0.01) seizure induced by PTZ compared with the control group.

DISCUSSION AND CONCLUSION

Based on the results, the hydroethanolic extract of ginger has anticonvulsant effects, possibly through an interaction with inhibitory and excitatory systems, antioxidant mechanisms, and oxidative stress inhibition.

Prospects of epileptogenesis prevention

Epilepsy is a common neurologic disease, affecting about 1-2% of the population. In around 30% of patients with epilepsy, their seizures are not satisfactorily controlled and drug-resistant epilepsy constitutes a real therapeutic challenge. Consequently, there are efforts aimed at the inhibition of epileptogenesis, a process of converting a normal into an epileptic brain. Data on this problem have been mainly obtained in post-status epilepticus rodent models in which spontaneous seizure activity and behavioral disturbances develop over time. Among antiepileptic drugs, diazepam at high dose of 20mg/kg given during status epilepticus, significantly inhibited the development of spontaneous seizures and also, a strong neuroprotective effect was evident. Also gabapentin and valproate (over a period of 40 days) proved effective in the inhibition of spontaneous seizure activity and reduction of behavioral deficit. However, there are also data that valproate (over 28 days) significantly improved the behavioral performance without affecting the occurrence of spontaneous seizures. A number of antiepileptic drugs, carbamazepine, lamotrigine, levetiracetam, phenobarbital, and topiramate were completely ineffective. Among non-antiepileptic drugs, some promise show rapamycin, losartan and combinations of anti-inflammatory drugs, targeting different inflammatory pathways. Inhibition of epileptogenesis may become a valuable therapeutic approach provided that there are reliable markers of this process. Actually, such markers begin to emerge.

In vivo evaluation of anticonvulsant and antioxidant effects of phenobarbital microemulsion for transdermal administration in pilocarpine seizure rat model

This study aimed to evaluate a microemulsion system (ME) containing phenobarbital in epilepsy model induced by pilocarpine in rats and to oxidative stress and histologic lesions in hippocampus. The microemulsion was applied to the shaved back of Wistar rats. The animals were divided into the following groups: control group (P400); ME50 40mg/kg, topically-t.p.; ME100, 40mg/kg, t.p.; EM50, 40mg/kg, t.p.; phenobarbital solution 40mg/kg (PS), oral. After 60min, behavioral changes were evaluated for 1h in the model of epileptical crisis induced by pilocarpine. Phenobarbital in microemulsion was able to increase the latency for status epilepticus (SE) (p<0.05), decrease the number of epileptical crisis (ME50: p<0.001; ME100: p<0.01) and decrease mortality rate by 80% compared to P400. In EM50 and PS groups, deaths were decreased by 53.3% and 100% respectively. The ME50 and ME100 groups were able to reduce oxidative stress in experimental animals when compared to the P400. The microemulsion was still capable of reducing neuronal damage in the hippocampal areas. The results of this study come in an innovative way, demonstrating the ability of transdermal ME50 and ME100 to reduce pilocarpine-induced epileptical crisis, oxidative stress, besides neuronal damages.

Effective termination of status epilepticus by rational polypharmacy in the lithium-pilocarpine model in rats: Window of opportunity to prevent epilepsy and prediction of epilepsy by biomarkers

The pilocarpine rat model, in which status epilepticus (SE) leads to epilepsy with spontaneous recurrent seizures (SRS), is widely used to study the mechanisms of epileptogenesis and develop strategies for epilepsy prevention. SE is commonly interrupted after 30-90min by high-dose diazepam or other anticonvulsants to reduce mortality. It is widely believed that SE duration of 30-60min is sufficient to induce hippocampal damage and epilepsy. However, resistance to diazepam develops during SE, so that an SE that is longer than 30min is difficult to terminate, and SE typically recurs several hours after diazepam, thus forming a bias for studies on epileptogenesis or antiepileptogenesis. We developed a drug cocktail, consisting of diazepam, phenobarbital, and scopolamine that allows complete and persistent SE termination in the lithium-pilocarpine model. A number of novel findings were obtained with this cocktail. (a) In contrast to previous reports with incomplete SE suppression, a SE of 60min duration did not induce epilepsy, whereas epilepsy with SRS developed after 90 or 120min SE; (b) by comparing groups of rats with 60 and 90min of SE, development of epilepsy could be predicted by behavioral hyperexcitability and decrease in seizure threshold, indicating that these read-outs are suited as biomarkers of epileptogenesis; (c) CA1 damage was prevented by the cocktail, but rats exhibited cell loss in the dentate hilus, which was related to development of epilepsy. These data demonstrate that the duration of SE needed for induction of epileptogenesis in this model is longer than previously thought.

A Spontaneous Recurrent Seizure Bioassay for Anti-Epileptogenic Molecules

Drug design in epilepsy is now tackling a new target - epileptogenesis. This is the process whereby a normal brain becomes susceptible to recurrent seizures. One of the stumbling blocks in the design and discovery of new chemical entities as antiepileptogenics is the implementation of an appropriate biological model. Current models, such as the maximal electroshock model, are models of seizures, not models of epileptogenesis. To develop such a model, we have extended and modified a chronic pilocarpine spontaneous recurrent seizure (SRS) model for the purposes of developing a bioassay with which to screen new compounds for putative antiepileptogenic bioactivity.

Acute administration of ginger (Zingiber officinale rhizomes) extract on timed intravenous pentylenetetrazol infusion seizure model in mice

PURPOSE

Zingiber officinale (Zingiberaceae) or ginger, which is used in traditional medicine has antioxidant activity and neuroprotective effects. The effects of this plant on clonic seizure have not yet been studied. The present study evaluated the anticonvulsant effect of ginger in a model of clonic seizures induced with pentylenetetrazole (PTZ) in male mice.

MATERIALS AND METHODS

The anticonvulsant effect of Z. officinale was investigated using i.v. PTZ-induced seizure models in mice. Different doses of the hydroethanolic extract of Z. officinale (25, 50, and 100mg/kg) were administered intraperitonal (i.p.), 2 and 24h before induction of PTZ. Phenobarbital sodium (30mg/kg), a reference standard, was also tested for comparison. The effect of ginger on to the appearance of three separate seizure endpoints (myoclonic, generalized clonus and forelimb tonic extension phase) was recorded.

RESULTS

The results showed that the ginger extract has anticonvulsant effects in all the experimental treatment groups of seizure tested as it significantly increased the seizure threshold. Hydroethanolic extract of Z. officinale significantly increased the onset time of myoclonic seizure at doses of 25-100mg/kg (p<0.001) and significantly prevented generalized clonic (p<0.001) and increased the threshold for the forelimb tonic extension (p<0.01) seizure 2 and 24h before induction of PTZ compared with control group.

CONCLUSION

Based on the results the hydroethanolic extract of ginger has anticonvulsant effects, possibly through an interaction with inhibitory and excitatory system, antioxidant mechanisms, oxidative stress and calcium channel inhibition.

Effect of topiramate on interleukin 6 expression in the hippocampus of amygdala-kindled epileptic rats

The objective of this study was to analyze the changes in expression and the possible functions of interleukin-6 (IL-6) in electrical kindling of the basolateral amygdala (BLA) in epileptic rats. Bipolar electrodes were implanted into the BLA of Sprague-Dawley rats, and the rats were then subjected to chronic electrical stimulation through the electrodes to induce kindling. The seizure characteristics and behavioral changes of the rats were observed, and electroencephalograms were recorded during and following kindling. The IL-6 mRNA expression in the hippocampi of the rats was analyzed using semi-quantitative reverse transcription-polymerase chain reaction, and control and topiramate (TPM)-treated groups were compared. The mean time-period required for kindling was 13.50±3.99 days, and the afterdischarge duration (ADD) measured between 21,450 and 119,720 msec. The expression of IL-6 mRNA was significantly upregulated in the kindled rats. TPM was able to depress the seizures and decrease the IL-6 level in the kindled rats. In conclusion, IL-6 mRNA was upregulated in the hippocampi of epileptic rats, and IL-6 may have participated in the process of kindling.

Pathophysiogenesis of mesial temporal lobe epilepsy: is prevention of damage antiepileptogenic?

Temporal lobe epilepsy (TLE) is frequently associated with hippocampal sclerosis, possibly caused by a primary brain injury that occurred a long time before the appearance of neurological symptoms. This type of epilepsy is characterized by refractoriness to drug treatment, so to require surgical resection of mesial temporal regions involved in seizure onset. Even this last therapeutic approach may fail in giving relief to patients. Although prevention of hippocampal damage and epileptogenesis after a primary event could be a key innovative approach to TLE, the lack of clear data on the pathophysiological mechanisms leading to TLE does not allow any rational therapy. Here we address the current knowledge on mechanisms supposed to be involved in epileptogenesis, as well as on the possible innovative treatments that may lead to a preventive approach. Besides loss of principal neurons and of specific interneurons, network rearrangement caused by axonal sprouting and neurogenesis are well known phenomena that are integrated by changes in receptor and channel functioning and modifications in other cellular components. In particular, a growing body of evidence from the study of animal models suggests that disruption of vascular and astrocytic components of the blood-brain barrier takes place in injured brain regions such as the hippocampus and piriform cortex. These events may be counteracted by drugs able to prevent damage to the vascular component, as in the case of the growth hormone secretagogue ghrelin and its analogues. A thoroughly investigation on these new pharmacological tools may lead to design effective preventive therapies.

Gabapentin is neuroprotective through glutamate receptor-independent mechanisms in staurosporine-induced apoptosis of cultured rat cerebellar neurons

The anticonvulsants that are currently available modulate the activity of neuronal receptors and ion channels, which are equally involved in apoptotic pathways. We investigated the hypothesis that gabapentin (GP), an anticonvulsant without effect on glutamate receptors acting as GABA analog, has neuroprotective properties. For comparison, we chose topiramate (TPM), which has been reported to be neuroprotective via AMPA receptors blockade. For this purpose, we used rat cerebellar granule neuron (CGN) cultures and we triggered apoptosis independent of glutamate receptors with staurosporine, a broad-spectrum protein kinase inhibitor. GP at therapeutic range concentration significantly increased cell viability in CGN cultures maintained in physiological KCl concentration and reversed apoptosis induced by staurosporine. Blockade of NMDA or AMPA receptors by MK801 or NBQX, respectively, did not alter GP neuroprotection, which was reversed instead by GABA. In contrast, protective effect of TPM on STS-treated CGN cultures was annihilated by NBQX, and not altered by MK801 or GABA. Treatments with neuroprotective concentrations of GP or TPM did not modify the expression of neuronal cell adhesion molecule or synaptophysin or the morphological aspect of neuronal endings. In summary, we report that GP is neuroprotective through glutamate-receptor independent mechanisms and without alteration of neuronal plasticity markers, which makes it a possible candidate for clinical neuroprotection trials.

Increased metallothionein I/II expression in patients with temporal lobe epilepsy

In the central nervous system, zinc is released along with glutamate during neurotransmission and, in excess, can promote neuronal death. Experimental studies have shown that metallothioneins I/II (MT-I/II), which chelate free zinc, can affect seizures and reduce neuronal death after status epilepticus. Our aim was to evaluate the expression of MT-I/II in the hippocampus of patients with temporal lobe epilepsy (TLE). Hippocampi from patients with pharmacoresistant mesial temporal lobe epilepsy (MTLE) and patients with TLE associated with tumor or dysplasia (TLE-TD) were evaluated for expression of MT-I/II, for the vesicular zinc levels, and for neuronal, astroglial, and microglial populations. Compared to control cases, MTLE group displayed widespread increase in MT-I/II expression, astrogliosis, microgliosis and reduced neuronal population. In TLE-TD, the same changes were observed, except that were mainly confined to fascia dentata. Increased vesicular zinc was observed only in the inner molecular layer of MTLE patients, when compared to control cases. Correlation and linear regression analyses indicated an association between increased MT-I/II and increased astrogliosis in TLE. MT-I/II levels did not correlate with any clinical variables, but MTLE patients with secondary generalized seizures (SGS) had less MT-I/II than MTLE patients without SGS. In conclusion, MT-I/II expression was increased in hippocampi from TLE patients and our data suggest that it is associated with astrogliosis and may be associated with different seizure spread patterns.

New approach to predicting proconvulsant activity with the use of Support Vector Regression

Antiepileptic drugs are commonly used for many therapeutic indications, including epilepsy, neuropathic pain, bipolar disorder and anxiety. Accumulating data suggests that many of them may lower the seizure threshold in men. In the present paper we deal with the possibility of using Support Vector Regression (SVR) to forecast the proconvulsant activity of compounds exerting anticonvulsant activity in the electroconvulsive threshold test in mice. A new approach to forecast this drug-related toxic effect by means of the support vector machine (SVM) in the regression mode is discussed below. The efficacy of this mathematical method is compared to the results obtained in vivo. Since SVR investigates the anticonvulsant activity of the compounds more thoroughly than it is possible using animal models, this method seems to be a very helpful tool for predicting additional dose ranges at which maximum anticonvulsant activity without toxic effects is observed. Good generalizing properties of SVR allow to assess the therapeutic dose range and toxicity threshold. Noteworthy, this method is very interesting for ethical reasons as this mathematical model enables to limit the use of living animals during the anticonvulsant screening process.

Hydroalcoholic extract of Zizyphus jujuba ameliorates seizures, oxidative stress, and cognitive impairment in experimental models of epilepsy in rats

The anticonvulsant effect of the hydroalcoholic extract of Zizyphus jujuba (HEZJ) fruit (100, 250, 500, and 1000 mg/kg, orally) was evaluated in experimental seizure models in rats. The effect of HEZJ on seizure-induced cognitive impairment, oxidative stress, and cholinesterase activity was also investigated. HEZJ (1000 mg/kg) exhibited maximum protection (100%) against generalized tonic-clonic seizures in the pentylenetetrazole (PTZ) seizure model and and 66.7% protection against tonic hindlimb extension in the maximal electroshock (MES) seizure model. Significant impairment in cognitive functions was observed in both PTZ- and MES-challenged rats. Pretreatment with HEZJ resulted in significant improvement in learning and memory. HEZJ also reversed the oxidative stress induced by both PTZ and MES. The significant decrease in cholinesterase activity observed in the PTZ and MES models was significantly reversed by pretreatment with HEZJ. Thus, the present study demonstrates the anticonvulsant effect of HEZJ as well as amelioration of cognitive impairment induced by seizures in rats.

Epileptic tolerance is associated with enduring neuroprotection and uncoupling of the relationship between CA3 damage, neuropeptide Y rearrangement and spontaneous seizures following intra-amygdala kainic acid-induced status epilepticus in mice

Brief, non-harmful seizures can activate endogenous protective programmes which render the brain resistant to damage caused by prolonged seizure episodes. Whether protection in epileptic tolerance is long-lasting or influences the subsequent development of epilepsy is uncertain. Presently, we investigated the relationship between hippocampal pathology, neuropeptide Y rearrangement and spontaneous seizures in sham- and seizure-preconditioned mice after status epilepticus induced by intra-amygdala kainate. Seizure-induced neuronal death at 24 h was significantly reduced in the ipsilateral hippocampal CA3 and hilus of tolerance mice compared to sham-preconditioned animals subject to status epilepticus. Damage to the CA3-hilus remained reduced in tolerance mice 21 days post-status. In sham-preconditioned mice subject to status epilepticus correlative statistics showed there was a strong inverse relationship between CA3, but not hilar, neuron counts and the number of spontaneous seizures. A strong positive association was also found between neuropeptide Y score and spontaneous seizure count in these mice. In contrast, there was no significant association between spontaneous seizure count and CA3 neuron loss or neuropeptide Y rearrangement in the tolerance mice. These data show that tolerance-conferred neuroprotection is long-lasting and that tolerance disrupts the normal association between CA3 damage, synaptic rearrangement and occurrence of spontaneous seizures in this model.

Pharmacological management of seizures and status epilepticus in critically ill patients

Seizures are serious complications seen in critically ill patients and can lead to significant morbidity and mortality if the cause is not identified and treated quickly. Uncontrolled seizures can lead to status epilepticus (SE), which is considered a medical emergency. The first-line treatment of seizures is an intravenous (IV) benzodiazepine followed by anticonvulsant therapy. Refractory SE can evolve into a nonconvulsive state requiring IV anesthetics or induction of pharmacological coma. To prevent seizures and further complications in critically ill patients with acute neurological disease or injury, short-term seizure prophylaxis should be considered in certain patients.

Voltage-gated sodium channels as therapeutic targets in epilepsy and other neurological disorders

Voltage-gated sodium channels (VGSCs) are key mediators of intrinsic neuronal and muscle excitability. Abnormal VGSC activity is central to the pathophysiology of epileptic seizures, and many of the most widely used antiepileptic drugs, including phenytoin, carbamazepine, and lamotrigine, are inhibitors of VGSC function. These antiepileptic drugs might also be efficacious in the treatment of other nervous system disorders, such as migraine, multiple sclerosis, neurodegenerative diseases, and neuropathic pain. In this Review, we summarise the structure and function of VGSCs and their involvement in the pathophysiology of several neurological disorders. We also describe the biophysical and molecular bases for the mechanisms of action of antiepileptic VGSC blockers and discuss the efficacy of these drugs in the treatment of epileptic and non-epileptic disorders. Overall, clinical and experimental data indicate that these drugs are efficacious for a range of diseases, and that the development of drugs with enhanced selectivity for specific VGSC isoforms might be an effective and novel approach for the treatment of several neurological diseases.

Neuroprotective effects of IGF-I following kainic acid-induced hippocampal degeneration in the rat

Insulin-like growth factor I (IGF-I) has been shown to act as a neuroprotectant both in in vitro studies and in in vivo animal models of ischemia, hypoxia, trauma in the brain or the spinal cord, multiple and amyotrophic lateral sclerosis, Alzheimer's and Parkinson's disease. In the present study, we investigated the neuroprotective potential of IGF-I in the "kainic acid-induced degeneration of the hippocampus" model of temporal lobe epilepsy. Increased cell death--as detected by FluoroJade B staining--and extensive cell loss--as determined by cresyl violet staining--were observed mainly in the CA3 and CA4 areas of the ipsilateral and contralateral hippocampus, 7 days following intrahippocampal administration of kainic acid. Kainic acid injection also resulted in intense astrogliosis--as assessed by the number of glial fibrillary acidic protein (GFAP) immunopositive cells--in both hemispheres, forming a clear astroglial scar ipsilaterally to the injection site. Heat-shock protein 70 (Hsp70) immunopositive cells were also observed in the ipsilateral dentate gyrus (DG) following kainic acid injection. When IGF-I was administered together with kainic acid, practically no signs of degeneration were detected in the contralateral hemisphere, while in the ipsilateral, there was a smaller degree of cell loss, reduced number of FluoroJade B-stained cells, decreased reactive gliosis and fewer Hsp70-positive cells. Our present results extend further the cases in which IGF-I is shown to exhibit neuroprotective properties in neurodegenerative processes in the CNS.

Evaluation of the anticonvulsant effect of Centella asiatica (gotu kola) in pentylenetetrazol-induced seizures with respect to cholinergic neurotransmission

The study described here was carried out to investigate the anticonvulsant effect of different extracts of Centella asiatica with respect to cholinergic activity on pentylenetetrazol (PTZ)-induced seizures. Rats were randomly divided into eight groups of six rats each: nonepileptic rats treated with saline; PTZ (60 mg/kg, IP)-induced seizure rats treated with saline; PTZ-induced seizure rats pretreated with n-hexane, chloroform, ethyl acetate, n-butanol, and water extracts of C. asiatica; and PTZ-induced seizure rats pretreated with diazepam (2mg/kg body wt). The seized rats pretreated with different extracts were administered a dose of 200mg/kg body wt orally for 1 week before induction of epilepsy. Increased acetylcholine content and decreased acetylcholinesterase activity were recorded in different brain regions during PTZ-induced seizures. Pretreatment with C. asiatica extracts caused recovery of the levels of acetylcholine and acetylcholinesterase. These findings suggest that C. asiatica causes perceptible changes in the cholinergic system as one of the facets of its anticonvulsant activity.

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.

Neuropathology in Drosophila mutants with increased seizure susceptibility

Genetic factors are known to contribute to seizure susceptibility, although the long-term effects of these predisposing factors on neuronal viability remain unclear. To examine the consequences of genetic factors conferring increased seizure susceptibility, we surveyed a class of Drosophila mutants that exhibit seizures and paralysis following mechanical stimulation. These bang-sensitive seizure mutants exhibit shortened life spans and age-dependent neurodegeneration. Because the increased seizure susceptibility in these mutants likely results from altered metabolism and since the Na(+)/K(+) ATPase consumes the majority of ATP in neurons, we examined the effect of ATPalpha mutations in combination with bang-sensitive mutations. We found that double mutants exhibit strikingly reduced life spans and age-dependent uncoordination and inactivity. These results emphasize the importance of proper cellular metabolism in maintaining both the activity and viability of neurons.

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.

Effects of the novel antiepileptic drug lacosamide on the development of amygdala kindling in rats

PURPOSE

The current treatment of epilepsy focuses exclusively on the prophylaxis or suppression of seizures and thus provides merely a symptomatic treatment, without clear influence on the course of the disease. There is a need for new drugs that act at different molecular targets than currently available antiepileptic drugs (AEDs) and for new therapies designed to block the process of epileptogenesis. In recent years, different research lines have examined the epileptogenic process in order to understand the different stages in this process, and with the hope that early recognition and intervention could prevent the development or progression of epilepsy. In animals, acquired epilepsy is studied most commonly with the kindling model and status epilepticus models. In the present study, we used the kindling model to evaluate whether the novel AED lacosamide affects kindling-induced epileptogenesis. This drug does not seem to act by any of the mechanisms of currently available AEDs, but the exact molecular mechanisms of action of lacosamide have not yet been clarified.

METHODS

Groups of 9-10 rats were treated with either vehicle or different doses of lacosamide (3, 10, or 30 mg/kg/day) over 22-23 days during amygdala kindling.

RESULTS

Daily administration of lacosamide during kindling acquisition produced a dose-dependent effect on kindling development. While the drug was inactive at 3 mg/kg/day, significant retardation of kindling was observed at 10 mg/kg/day, by which the average number of stimulations to reach kindling criterion was increased by >90%. A significant inhibitory effect on kindling acquisition was also observed with 30 mg/kg/day, but this dose of lacosamide was associated with adverse effects.

CONCLUSIONS

The present data demonstrate that lacosamide, in addition to exerting anticonvulsant activity, has the potential to retard kindling-induced epileptogenesis. Whether this indicates that lacosamide possesses antiepileptogenic or disease-modifying potential needs to be further evaluated, including studies in other models of acquired epilepsy.

Histaminergic neurons protect the developing hippocampus from kainic acid-induced neuronal damage in an organotypic coculture system

The central histaminergic neuron system inhibits epileptic seizures, which is suggested to occur mainly through histamine 1 (H1) and histamine 3 (H3) receptors. However, the importance of histaminergic neurons in seizure-induced cell damage is poorly known. In this study, we used an organotypic coculture system and confocal microscopy to examine whether histaminergic neurons, which were verified by immunohistochemistry, have any protective effect on kainic acid (KA)-induced neuronal damage in the developing hippocampus. Fluoro-Jade B, a specific marker for degenerating neurons, indicated that, after the 12 h KA (5 microM) treatment, neuronal damage was significantly attenuated in the hippocampus cultured together with the posterior hypothalamic slice containing histaminergic neurons [HI plus HY (POST)] when compared with the hippocampus cultured alone (HI) or with the anterior hypothalamus devoid of histaminergic neurons. Moreover, alpha-fluoromethylhistidine, an inhibitor of histamine synthesis, eliminated the neuroprotective effect in KA-treated HI plus HY (POST), and extracellularly applied histamine (1 nM to 100 microM) significantly attenuated neuronal damage only at 1 nM concentration in HI. After the 6 h KA treatment, spontaneous electrical activity registered in the CA1 subregion contained significantly less burst activity in HI plus HY (POST) than in HI. Finally, in KA-treated slices, the H3 receptor antagonist thioperamide enhanced the neuroprotective effect of histaminergic neurons, whereas the H1 receptor antagonists triprolidine and mepyramine dose-dependently decreased the neuroprotection in HI plus HY (POST). Our results suggest that histaminergic neurons protect the developing hippocampus from KA-induced neuronal damage, with regulation of neuronal survival being at least partly mediated through H1 and H3 receptors.

Models of epileptogenesis in adult animals available for antiepileptogenesis drug screening

Epileptogenesis is the process by which parts of a normal brain are converted to a hyperexcitable brain, often after an injury. Researchers must understand this process before they know where and how to change it. Animal models are used to evaluate the process of epileptogenesis by studing status epelepticus, electrical kindling, or other methods that provoke injuries. All are associated with neuronal loss to more or less degree, synaptic reorganization, axon sprouting, neurogenesis, gliosis, and changes in gene expression in neurons and astrocytes. He describes several types of animal models and how they might be useful in developing effective strategies for preventing epilepsy.

Antiepileptic drugs and neuroprotection: current status and future roles

There has been a growing interest in the use of antiepileptic drugs (AEDs) for neuroprotection, and in the possible role of AEDs in disease modification (i.e., antiepileptogenesis). Increased understanding of the mechanisms underlying brain injury has led to advances in the study of neuroprotection. However, defining the clinical paradigm and selecting appropriate outcomes to detect neuroprotective effects present challenges to clinicians studying the neuroprotective properties of drugs. Established AEDs, such as phenytoin, phenobarbital, and carbamazepine, have shown neuroprotective activity in an ischemic/hypoxic model of neuronal injury. Animal model studies also have suggested that newer AEDs, such as levetiracetam, topiramate, and zonisamide, may have neuroprotective or antiepileptogenic properties. However, the prevention of epileptogenesis by an AED has yet to be demonstrated in clinical trials. The future of neuroprotection may involve established and newer AEDs, as well as other compounds, such as immunophilins, caspase inhibitors, endocannabinoids, and antioxidants.

Antiepileptic effects of botulinum neurotoxin E

Experimental studies suggest that the delivery of antiepileptic agents into the seizure focus might be of potential utility for the treatment of focal-onset epilepsies. Botulinum neurotoxin E (BoNT/E) causes a prolonged inhibition of neurotransmitter release after its specific cleavage of the synaptic protein synaptosomal-associated protein of 25 kDa (SNAP-25). Here, we show that BoNT/E injected into the rat hippocampus inhibits glutamate release and blocks spike activity of pyramidal neurons. BoNT/E effects persist for at least 3 weeks, as determined by immunodetection of cleaved SNAP-25 and loss of intact SNAP-25. The delivery of BoNT/E to the rat hippocampus dramatically reduces both focal and generalized kainic acid-induced seizures as documented by behavioral and electrographic analysis. BoNT/E treatment also prevents neuronal loss and long-term cognitive deficits associated with kainic acid seizures. Moreover, BoNT/E-injected rats require 50% more electrical stimulations to reach stage 5 of kindling, thus indicating a delayed epileptogenesis. We conclude that BoNT/E delivery to the hippocampus is both antiictal and antiepileptogenic in experimental models of epilepsy.

Primary prevention of epilepsy in patients with different epileptogenic conditions

Epileptic seizures are a common complication of several clinical conditions affecting the CNS. In these cases, the occurrence of seizures and epilepsy may increase the functional damage provoked by the underlying epileptogenic condition and affect the patient's quality of life to a significant extent. Therefore, the search of effective means for primary prevention of seizures and epilepsy is necessary in these cases. However, the use of antiepileptic drugs for the primary prevention of seizures and epilepsy can be considered only if the ratio between efficacy, safety and tolerability of treatment is favorable, in that the advantages, in terms of seizure prevention, outweigh the disadvantages in terms of adverse effects and overall costs of treatment. In this article, the efficacy, safety and tolerability of antiepileptic drugs for the primary prevention of seizures and epilepsy are reviewed. The areas covered include: the definition of early (provoked) and late (unprovoked) seizures; knowledge of the overall risk of seizures and epilepsy in CNS disorders for which primary prevention of seizures can be attempted; rationale for the use of antiepileptic drugs for the primary prevention of epilepsy; experimental data on the antiepileptogenic properties of antiepileptic drugs; available literature findings on the prevention of early and late seizures, with specific emphasis on randomized clinical trials; and the main problems with experimental trials for the primary prevention of epileptic seizures. On this basis, practice recommendations for the primary prevention of epilepsy will be offered where indicated. Suggestions for future research are also made as concluding remarks, by indicating the areas of investigation and the design of future studies.

Atipamezole, an alpha(2)-adrenoceptor antagonist, has disease modifying effects on epileptogenesis in rats

Stimulation of alpha(2)-adrenoceptors delays the development of kindling, a model of epileptogenesis in humans. Blocking alpha(2)-adrenoceptors is proconvulsant, but has beneficial effects on somatomotor recovery after experimental stroke. We investigated whether atipamezole, a selective alpha(2)-adrenoceptor antagonist, affects the recovery process from status epilepticus (SE)-induced brain damage, which affects the risk of epileptogenesis. Vehicle or atipamezole (100 microg/kg/h) treatment was started 1 week after the induction of SE and continued for 9 weeks using Alzet minipumps (n = 70). Development and severity of epilepsy, spatial and emotional learning, and histologic analysis were used as outcome measures. There were no differences in the percentage of animals with epilepsy in the different treatment groups. In the atipamezole group, however, daily seizure frequency was lower (P < 0.01), a higher percentage of epileptic animals had mild epilepsy (<1 seizure/day; P < 0.01), and seizure frequency did not increase over time compared with the vehicle group. The atipamezole group had milder hilar cell damage (P < 0.05) and less intense mossy fiber sprouting (P < 0.05). Behavioral impairments were similar between groups. Our data indicate that chronic treatment with atipamezole does not prevent epileptogenesis. There is, however, a disease-modifying effect; that is, the epilepsy that develops is milder and non-progressive. These data warrant further studies.

Epilepsy induced by extended amygdala-kindling in rats: lack of clear association between development of spontaneous seizures and neuronal damage

Most patients with temporal lobe epilepsy (TLE), the most common type of epilepsy, show pronounced loss of neurons in limbic brain regions, including the hippocampus, amygdala, and parahippocampal regions. Hippocampal damage in patients with TLE is characterized by extensive neuronal loss in the CA3 and CA1 sectors and the hilus of the dentate gyrus. There is a long and ongoing debate on whether this type of hippocampal damage, referred to as hippocampal sclerosis, is the cause or consequence of TLE. Furthermore, hippocampal damage may contribute to the progressive features of TLE. The present study was designed to determine whether development of spontaneous recurrent seizures (SRS) after extended kindling of the amygdala in rats is associated with neuronal damage. The kindling model of TLE was chosen because previous studies have shown that only part of the rats develop SRS after extended kindling, thus allowing to compare the brain pathology of rats that received the same number of amygdala stimulation but did or did not develop SRS. For extended kindling, rats were stimulated twice daily 3-5 days a week for up to about 280 stimulations. During long-term EEG/video monitoring, SRS were observed in 50% of the rats over the period of extended kindling. SRS often started with myoclonic jerks or focal seizures and subsequently progressed into secondarily generalized seizures, so that the development of SRS recapitulated the earlier kindling of elicited seizures. No obvious neurodegeneration was observed in the CA1 and CA3 sectors of the hippocampus, the amygdala, parahippocampal regions or thalamus. A significant bilateral reduction in neuronal density was determined in the dentate hilus after extended kindling, but this reduction in hilar cell density did not significantly differ between rats with and without observed SRS. Determination of the total number of hilar neurons and of hilar volume indicated that the reduced neuronal density in the dentate hilus was due to expansion of hilar area but not to neuronal damage. The data demonstrate that extended kindling does not cause any hippocampal damage resembling hippocampal sclerosis, but that SRS develop in the absence of such damage.

Striking Differences in Individual Anticonvulsant Response to Phenobarbital in Rats with Spontaneous Seizures after Status Epilepticus

PURPOSE

More than one third of patients with epilepsy have inadequate control of seizures with drug therapy, but mechanisms of intractability are largely unknown. Because of this large number of pharmacoresistant patients with epilepsy, the existing process of antiepileptic drug (AED) discovery and development must be reevaluated with a focus on preclinical models of therapy-resistant epilepsy syndromes such as mesial temporal lobe epilepsy (TLE). However, although various rodent models of TLE are available, the pharmacoresponsiveness of most models is not well known. In the present study, we used a post-status epilepticus model of TLE to examine whether rats with spontaneous recurrent seizures (SRSs) differ in their individual responses to phenobarbital (PB).

METHODS

Status epilepticus was induced in Sprague-Dawley rats by prolonged electrical stimulation of the basolateral amygdala. Once the rats had developed SRSs, seizure frequency and severity were determined by continuous EEG/video recording over a 6-week period (i.e., a predrug control period of 2 weeks, followed by PB treatment for 2 weeks, and a postdrug control period of 2 weeks). PB was administered twice daily at maximal tolerated doses.

RESULTS

Analysis of plasma drug concentrations showed that drug concentrations within the therapeutic range (10-40 microg/ml) were maintained in all rats throughout the period of treatment. In six (55%) of 11 rats, complete control of seizures was achieved, and another rat exhibited a >90% reduction of seizure frequency. These seven rats were considered responders. The remaining four (36%) rats showed either no response at all (n=3) or only moderate reduction in seizure frequency and were therefore considered nonresponders. Plasma drug concentrations did not differ between these two groups of rats.

CONCLUSIONS

These data demonstrate that, similar to patients with epilepsy, rats with SRSs markedly differ in their individual responses to AED treatment. Pharmacoresistant rats selected by prolonged drug treatment from groups of rats with SRSs may provide a unique model to study mechanisms of pharmacoresistance and to identify novel AEDs for treating seizures of patients currently not controlled with existing therapies.

Progression of Brain Damage after Status Epilepticus and Its Association with Epileptogenesis: A Quantitative MRI Study in a Rat Model of Temporal Lobe Epilepsy

PURPOSE

This study examined the hypothesis that neurodegeneration continues after status epilepticus (SE) ends and that the severity of damage at the early phase of the epileptogenic process predicts the outcome of epilepsy in a long-term follow-up.

METHODS

SE was induced in rats by electrical stimulation of the amygdala, and the progression of structural alterations was monitored with multiparametric magnetic resonance imaging (MRI). Absolute T2, T1rho, and diffusion (Dav) images were acquired from amygdala, piriform cortex, thalamus, and hippocampus for < or = 4.5 months after SE. Frequency and type of spontaneous seizures were monitored with video-electroencephalography recordings. Histologic damage was assessed from Nissl, Timm, and Fluoro-Jade B preparations at 8 months.

RESULTS

At the acute phase (2 days after SE induction), quantitative MRI revealed increased T2, T1rho, and Dav values in the primary focal area (amygdala), reflecting disturbed water homeostasis and possible early structural damage. Pathologic T2 and T1rho were observed in mono- or polysynaptically connected regions, including the piriform cortex, midline thalamus, and hippocampus. The majority of acute MRI abnormalities were reversed by 9 days after SE. In later time points (> 20 days after induction), both the T1rho and diffusion MRI revealed secondarily affected areas, most predominantly in the amygdala and hippocampus. At this time, animals began to have spontaneous seizures. The initial pathology revealed by MRI had a low predictive value for the subsequent severity of epilepsy and tissue damage.

CONCLUSIONS

The results demonstrate progressive neurodegeneration after SE in the amygdala and the hippocampus and stress the need for continued administration of neuroprotectants in the treatment of SE even after electrographic seizure activity has ceased.

The neurobiology of antiepileptic drugs for the treatment of nonepileptic conditions

Antiepileptic drugs (AEDs) are commonly prescribed for nonepileptic conditions, including migraine headache, chronic neuropathic pain, mood disorders, schizophrenia and various neuromuscular syndromes. In many of these conditions, as in epilepsy, the drugs act by modifying the excitability of nerve (or muscle) through effects on voltage-gated sodium and calcium channels or by promoting inhibition mediated by gamma-aminobutyric acid (GABA) A receptors. In neuropathic pain, chronic nerve injury is associated with the redistribution and altered subunit compositions of sodium and calcium channels that predispose neurons in sensory pathways to fire spontaneously or at inappropriately high frequencies, often from ectopic sites. AEDs may counteract this abnormal activity by selectively affecting pain-specific firing; for example, many AEDs suppress high-frequency action potentials by blocking voltage-activated sodium channels in a use-dependent fashion. Alternatively, AEDs may specifically target pathological channels; for example, gabapentin is a ligand of alpha2delta voltage-activated calcium channel subunits that are overexpressed in sensory neurons after nerve injury. Emerging evidence suggests that effects on signaling pathways that regulate neuronal plasticity and survival may be a factor in the delayed clinical efficacy of AEDs in some neuropsychiatric conditions, including bipolar affective disorder.

Should antiepileptic drugs be withdrawn in seizure-free patients?

Discontinuation of antiepileptic drug (AED) treatment is a valuable option in patients with epilepsy who have been seizure free for 2 years or longer. However, the decision to withdraw AEDs must be based on a balanced view of the overall risk of seizure relapse, the factors most likely to affect that risk, and the medical, emotional and social implications of treatment continuation versus treatment withdrawal. In a critical review of 28 studies accounting for 4571 patients (2758 children, 1020 adults and a combined group of 793), most with at least 2 years of seizure remission, the proportion of patients with relapses during or after AED withdrawal ranged from 12 to 66%. Using life-table analysis, the cumulative probability of remaining seizure-free in children was 66-96% at 1 year and 61-91% at 2 years after withdrawal of AEDs. The corresponding values in adults were 39-74% and 35-57%, respectively. The relapse rate was highest in the first 12 months (especially in the first 6 months) after withdrawal and tended to decrease thereafter. Based on a previously published meta-analysis of data published up to 1992, the pooled relapse risk was 25% (95% CI 21, 30%) at 1 year and 29% (95% CI 24, 34%) at 2 years after AED withdrawal. The factors associated with a higher-than-average risk of seizure relapse included adolescent-onset epilepsy, partial seizures, the presence of an underlying neurological condition, and abnormal EEG findings at the time of AED withdrawal in children. Factors associated with a lower-than-average risk were childhood-onset epilepsy, idiopathic generalised epilepsy and - for children - a normal EEG. Selected epilepsy syndromes (e.g. benign epilepsy with centrotemporal spikes and juvenile myoclonic epilepsy) may be associated with significantly different outcomes after AED withdrawal. All these factors and their combinations may contribute to the development of guidelines for practising physicians to help them in making the best decision related to treatment discontinuation. The decision plan should also take into account social factors (driving license, job and leisure activities) as well as emotional and personal factors, and must be tailored to and discussed with the individual patient and his/her family.

Death mechanisms in status epilepticus-generated neurons and effects of additional seizures on their survival

Status epilepticus (SE) increases neurogenesis in the subgranular zone (SGZ) of the adult dentate gyrus, but many of the newborn cells die, partly through caspase-induced apoptosis. Here we provide immunohistochemical evidence indicating that the caspase-evoked death of the new neurons involves the mitochondrial but not the death-receptor-mediated pathway. Cytochrome c released from mitochondria was found in a subset of progenitor cell progeny, while Fas ligand and tumor necrosis factor 1 receptor-associated domain as well as the mitochondria-related, caspase-independent apoptosis-inducing factor were not detected. We also show that additional seizures, induced at different stages during neuronal differentiation of progenitor cell progeny following SE, neither potentiate cell death mechanisms in the SGZ nor compromise the survival of the new cells. Thus, we found similar expression of cytochrome c, active caspase-3, caspase-cleaved PARP, and TUNEL/Hoechst-positive DNA fragmentation, as well as numbers of new cells in the SGZ in rats exposed to additional seizures at days 6 and 7 or days 33 and 34 following SE as in control animals only subjected to SE. We propose that the degree of survival of newly generated neurons is determined primarily by the initial SE insult and the ensuing pathology in the tissue environment, whereas spontaneous seizures play a minor role.

Implementing a bioassay to screen molecules for antiepileptogenic activity: chronic pilocarpine versus subdudral haematoma models

BACKGROUND

There is a need to discover novel chemical compounds that will inhibit the pathological process of epileptogenesis (i.e. agents that will prevent the long-term formation of an active seizure focus following a brain insult). The goal of this paper is to identify a bioassay of value in drug design when screening new chemical entities as putative antiepileptogenic agents.

METHODS

We focused on two models: the pilocarpine chronic seizure model of spontaneous recurrent seizures (SRSs) and a chronic subdural haematoma model of SRSs. Both models were evaluated using more than 20 Sprague-Dawley rats for each model.

RESULTS

In the pilocarpine-induced model of SRSs, 80% of animals went on to develop SRSs when the dose of pilocarpine was 380 mg/kg i.p. In 50 animals that developed SRSs, the average number of seizures per 15 days of observation was 3.8 seizures with a range of 2-23 seizures per 15-day period. The chronic subdural model was inefficient in producing SRSs.

CONCLUSIONS

A pilocarpine-induced SRS model of epilepsy affords a reliable model of epileptogenesis suitable for evaluating new chemical entities as putative antiepileptogenics.

Expression and activation of caspase 3 following status epilepticus in the rat

It is in dispute whether caspase 3 contributes to status epilepticus (SE)-induced cell loss. We hypothesized that caspase 3-mediated cell death continues beyond the acute phase of SE. We induced SE with either kainic acid or electrical stimulation of the amygdala in Wistar and Sprague-Dawley rats. Caspase 3 immunohistochemistry, Western blot analysis and enzyme activity measurements were used to determine cellular localization and the time course of caspase 3 expression and activation. Immunohistochemistry indicated that caspase 3 protein expression increased following SE, peaking at 16-24 h. Cleavage of procaspase 3 to active fragments (p20-17) was detected 2-7 days after SE. Caspase 3 enzyme activity was elevated at 8 h and further increased up to 19.4-fold at 7 days following SE. Activation of caspase 3 after SE occurred in the hippocampus and the extrahippocampal temporal lobe but not in the thalamus. Caspase 3-immunoreactive cells represented only a minority of degenerating cells as assessed by Fluoro-Jade B and TUNEL staining. Analysis of double-labelled sections indicated that active caspase 3 was located in astrocytes rather than neurons or microglia. There was increased caspase 3 expression in both rat strains, and it was independent of the method used to induce SE. These data demonstrate that caspase 3 contributes to the cell death occurring within the first week after SE, but in only a small proportion of degenerating cells. These results suggest that, contrary to expectations, caspase 3 inhibitors would have only limited benefits in the treatment of SE.

N-methyl-D-aspartate receptor blockade after status epilepticus protects against limbic brain damage but not against epilepsy in the kainate model of temporal lobe epilepsy

Most patients with temporal lobe epilepsy (TLE), the most common type of epilepsy, show pronounced loss of neurons in limbic brain regions, including the hippocampus. The massive neurodegeneration in the hippocampus is known as hippocampal sclerosis, and is considered one of the hallmarks of this type of difficult-to-treat epilepsy. There is a long and ongoing debate on whether this sclerosis is the result of an initial pathological event, such as a status epilepticus (S.E.), stroke or head trauma, which often precedes the development of TLE, or is caused by the spontaneous recurrent seizures (SRS) once epilepsy has developed. At present, pharmacological prevention of limbic sclerosis is not available. In a clinical situation, such prevention would only be possible if delayed cell death developing after an initial pathological event is involved. Assuming that sclerotic brain lesions provoke epileptogenesis and that delayed cell death is involved in these lesions, it should be possible to prevent both the lesions and the epilepsy by a prophylactic treatment after an initial insult such as an S.E. In order to test this hypothesis, we used a rat model of TLE in which limbic brain lesions and epilepsy with SRS develop after a kainate-induced S.E. A single low dose of the N-methyl-D-aspartate (NMDA) receptor blocker dizocilpine (MK-801) significantly reduced the damage in limbic regions, including the hippocampus and piriform cortex, and completely protected several rats from such damage when given after an S.E. of 90 min induced by kainate, strongly suggesting that delayed cell death is involved in the damage. This was substantiated by the use of molecular and immunohistochemical markers of delayed active ("programmed") cell death. However, the neuroprotection by dizocilpine did not prevent the development of SRS after the S.E., suggesting that structures not protected by dizocilpine may play a role in the genesis of SRS or that epileptogenesis is not the consequence of structural lesions in the limbic system. The only brain regions that exhibited neuronal damage in all rats with SRS were the hilus of the dentate gyrus and the mediodorsal thalamus, although treatment with dizocilpine reduced the severity of damage in the latter region. The data indicate that NMDA receptor blockade immediately after a prolonged S.E. is an effective means to reduce the damage produced by a sustained S.E. in several brain regions, including the hippocampus, but show that this partial neuroprotection of the limbic system does not prevent the development of epilepsy.