Occurrence Of Spontaneous Recurrent Seizures Research Articles

The effect of cardarine on the behavior of rats in a lithium-pylocarpine model of temporal lobe epilepsy

Epilepsy is a serious neuropsychiatric disorder characterized by the occurrence of spontaneous recurrent seizures and linked cognitive, psychoemotional, and social impairments. Objective research showed that up to 30% of epilepsy patients do not respond to current therapeutic interventions, necessitating the development of novel treatment options. In recent years, researchers actively studied the neuroprotective properties of peroxisome proliferator-activated receptor agonists (PPAR α, β/δ, γ). As nuclear transcription factors involved in inflammatory signaling pathways, PPARs play a role in the pathogenesis of neuropsychiatric disorders, such as epilepsy. Various nervous pathology models were used for the investigations. The neuroprotective properties of PPAR γ agonists were reported in epilepsy models, whereas sufficient investigation into PPAR β/δ agonists’ effects is lacking. The aim of this study was to evaluate the effectiveness of the PPAR β/δ receptor agonist cardarine in alleviating behavioral disruptions observed in rats exhibiting temporal lobe epilepsy in response to the lithium-pilocarpine model. The lithium-pilocarpine model is considered one of the most effective experimental models for studying temporal lobe epilepsy in humans. Administration of pilocarpine in animals results in acute seizures, followed by a latent period devoid of seizures. Subsequently, spontaneous recurrent seizures appear, marking the chronic phase of the model. Epilepsy was induced in male Wistar rats that were 7 weeks old, through the administration of pilocarpine, 24 hours after being injected with LiCl (127 mg/kg). The peripheral effects of pilocarpine were negated through the use of methyl bromide-scopolamine (1 mg/kg, administered intraperitoneally 1 hour before pilocarpine). Pilocarpine was administered in fractional doses of 10 mg/kg, every half hour, until the seizures reached at least stage 4 on the Racine scale, with a dose range of 20–40 mg/kg. Following pilocarpine administration, Cardarine was administered intraperitoneally at a dose of 2.5 mg/kg daily for a period of 7 days, with the initial injection taking place 24 hours post-administration. Behavioral tests were conducted during the chronic phase of the model, 2-2.5 months after pilocarpine injection, using several tests, including the Open Field (to measure exploratory behavior, motor activity, and anxiety levels), the Intruder-Resident test (to measure communicative behavior), the Y-maze test (to measure working memory), and the Morris Water Maze (to measure spatial memory in the short and long term). Untreated experimental animals with temporal lobe epilepsy exhibited heightened vertical and horizontal motor activity, increased anxiety in the Open Field test, reduced communicative activity in the Intruder-Resident test, and impaired memory in the Y-maze test and the Morris Water Maze. Cardarine reduced alterations in vertical movement (time of climbing) and anxiety levels (number of grooming behaviors) in the Open Field, hindered short-term memory in the Y-maze, and restrained communicative conduct in the Intruder-Resident test. However, the medication did not impact the rats’ survival rate, body weight changes, overall activity (distance traveled in the Open Field), and damage to learning and long-term memory in the Morris Water Maze. Thus, administration of cardarine partially neutralized behavioral disorders developing in rats in the lithium-pylocarpine model of temporal lobe epilepsy.

Modelos experimentales en el estudio de la epileptogénesis

Epilepsy is a chronic neurological disease characterized by spontaneous recurrently occurring epileptic seizures as a consequence of abnormal, excessive and synchronous neuronal activity in the brain. Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy in adults, being characterized by hippocampal sclerosis, reactive gliosis, neurodegeneration, and synaptic reorganization. Animal models of TLE based on the administration of convulsive agents trigger a status epilepticus (SE) that progresses towards the occurrence of spontaneous recurrent seizures. Among these models are those induced by the systemic administration of pilocarpine or by intrahippocampal injection of kainic acid, both being characterized by 3 clearly defined phases: (i) acute SE seizures; (ii) latent period and (iii) occurrence of recurrent spontaneous seizures. These models not only reproduce most of the neuropathological TLE features but also allow for the identification of biomarkers of epileptogenesis and potential pharmacological targets. The use of neuroimaging techniques such as positron emission tomography (PET) with the radiotracer 18F-Fluorodeoxyglucose (18F-FDG) identifies brain hypometabolism in the latent period that not only localizes the epileptic focus but is also an biomarker of early diagnosis. Other neuroimaging techniques allow for detecting, among others, biomarkers of neuroinflammation, alterations in the permeability of the blood-brain barrier and astrocytic activation, all of them associated with epileptogenesis. Finally, the use of chemogenetics through DREADDs (Designer Receptors Exclusively Activated by Designer Drugs) technology in murine models leads to targeted modulation of astrocytic activity, being a novel tool that considers the contribution of the astrocytes role in brain metabolic alterations in epileptogenesis.

Perampanel Reduces Hyperthermia-Induced Seizures in Dravet Syndrome Mouse Model.

Treatment options for Dravet syndrome are limited. The aim of this study was to evaluate the antiepileptic effect of the AMPA receptor antagonist perampanel (PER) on a mouse model of Dravet syndrome (Scn1a E1099X/+). We report here that the PER (2 mg/kg) treatment inhibited the spontaneous recurrent seizures and attenuated epileptic activity in Scn1a E1099X/+ mice. In the hyperthermia-induced seizure experiment, PER clearly increased temperature tolerance and significantly ameliorated seizure frequency and discharge duration. PER also demonstrated antiepileptic effects in a cross-over study and a synergistic effect for attenuating heat-induced seizure when given in combination with stiripentol or valproic acid. The results showed that PER effectively decreased the occurrence of spontaneous recurrent seizures and showed significant therapeutic potential for hyperthermia-induced seizures with regard to both susceptibility and severity in a Dravet syndrome mouse model. Potential therapeutic effects of PER for treatment of Dravet syndrome were demonstrated.

Behavioral Deficits in Mice with Postnatal Disruption of Ndel1 in Forebrain Excitatory Neurons: Implications for Epilepsy and Neuropsychiatric Disorders.

Dysfunction of nuclear distribution element-like 1 (Ndel1) is associated with schizophrenia, a neuropsychiatric disorder characterized by cognitive impairment and with seizures as comorbidity. The levels of Ndel1 are also altered in human and models with epilepsy, a chronic condition whose hallmark feature is the occurrence of spontaneous recurrent seizures and is typically associated with comorbid conditions including learning and memory deficits, anxiety, and depression. In this study, we analyzed the behaviors of mice postnatally deficient for Ndel1 in forebrain excitatory neurons (Ndel1 CKO) that exhibit spatial learning and memory deficits, seizures, and shortened lifespan. Ndel1 CKO mice underperformed in species-specific tasks, that is, the nest building, open field, Y maze, forced swim, and dry cylinder tasks. We surveyed the expression and/or activity of a dozen molecules related to Ndel1 functions and found changes that may contribute to the abnormal behaviors. Finally, we tested the impact of Reelin glycoprotein that shows protective effects in the hippocampus of Ndel1 CKO, on the performance of the mutant animals in the nest building task. Our study highlights the importance of Ndel1 in the manifestation of species-specific animal behaviors that may be relevant to our understanding of the clinical conditions shared between neuropsychiatric disorders and epilepsy.

Neural Stem Cells and Cannabinoids in the Spotlight as Potential Therapy for Epilepsy.

Epilepsy is one of the most common brain diseases worldwide, having a huge burden in society. The main hallmark of epilepsy is the occurrence of spontaneous recurrent seizures, having a tremendous impact on the lives of the patients and of their relatives. Currently, the therapeutic strategies are mostly based on the use of antiepileptic drugs, and because several types of epilepsies are of unknown origin, a high percentage of patients are resistant to the available pharmacotherapy, continuing to experience seizures overtime. Therefore, the search for new drugs and therapeutic targets is highly important. One key aspect to be targeted is the aberrant adult hippocampal neurogenesis (AHN) derived from Neural Stem Cells (NSCs). Indeed, targeting seizure-induced AHN may reduce recurrent seizures and shed some light on the mechanisms of disease. The endocannabinoid system is a known modulator of AHN, and due to the known endogenous antiepileptic properties, it is an interesting candidate for the generation of new antiepileptic drugs. However, further studies and clinical trials are required to investigate the putative mechanisms by which cannabinoids can be used to treat epilepsy. In this manuscript, we will review how cannabinoid-induced modulation of NSCs may promote neural plasticity and whether these drugs can be used as putative antiepileptic treatment.

Kainic acid-induced status epilepticus decreases mGlu5 receptor and phase-specifically downregulates Homer1b/c expression

Globally, over 50 million people are affected by epilepsy, which is characterized by the occurrence of spontaneous recurrent seizures. Almost one-third of the patients show resistance to current anti-epileptic drugs, making the exploration of new molecular targets necessary. An interesting target may be Homer1, due to its diverse roles in epileptogenesis and synaptic plasticity. Indeed, Homer1 regulates group I metabotropic glutamate (mGlu) receptors (i.e. mGlu1 and mGlu5) scaffolding and signaling in neurons. In the present work, using the systemic kainic acid (KA)-induced status epilepticus (SE) model in adult rats, we investigated the mRNA and protein expression patterns of the mGlu5 receptor, Homer1a and Homer1b/c at 10, 80 and 120 days post-SE (i.e. T10, T80 and T120). Epileptogenesis was validated by electrophysiological recordings of seizures via electroencephalography (EEG) monitoring and through upregulation of glial fibrillary acidic protein. At the protein level, the mGlu5 receptor was downregulated in the late latent phase (T10) and the early- and late exponential growth phase (T80 and T120, respectively), which was best observed in the hippocampal CA1 region. At mRNA level, significant downregulation of the mGlu5 receptor was only detected in the late exponential growth phase. Homer1a expression did not change at any investigated time point. Interestingly, Homer1b/c was only downregulated in the late latent phase, a period where spontaneous seizures are extremely rare. Thus, this phase-specific downregulation may be indicative of an endogenous neuroprotective mechanism. In conclusion, these results suggest that Homer1b/c may be an interesting molecular target to prevent epileptogenesis and/or control seizures.

Early polytherapy for benzodiazepine-refractory status epilepticus

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

Upregulated SHP-2 expression in the epileptogenic zone of temporal lobe epilepsy and various effects of SHP099 treatment on a pilocarpine model.

Temporal lobe epilepsy (TLE) is defined as the sporadic occurrence of spontaneous recurrent seizures, and its pathogenesis is complex. SHP-2 (Src homology 2-containing protein tyrosine phosphatase 2) is a widely expressed cytosolic tyrosine phosphatase protein that participates in the regulation of inflammation, angiogenesis, gliosis, neurogenesis and apoptosis, suggesting a potential role of SHP-2 in TLE. Therefore, we investigated the expression patterns of SHP-2 in the epileptogenic brain tissue of intractable TLE patients and the various effects of treatment with the SHP-2-specific inhibitor SHP099 on a pilocarpine model. Western blotting and immunohistochemistry results confirmed that SHP-2 expression was upregulated in the temporal neocortex of patients with TLE. Double-labeling experiments revealed that SHP-2 was highly expressed in neurons, astrocytes, microglia and vascular endothelial cells in the epileptic foci of TLE patients. In the pilocarpine-induced C57BL/6 mouse model, SHP-2 upregulation in the hippocampus began one day after status epilepticus, reached a peak at 21days and then maintained a significantly high level until day 60. Similarly, we found a remarkable increase in SHP-2 expression at 1, 7, 21 and 60days post-SE in the temporal neocortex. In addition, we also showed that SHP099 increased reactive gliosis, the release of IL-1β, neuronal apoptosis and neuronal loss, while reduced neurogenesis and albumin leakage. Taken together, the increased expression of SHP-2 in the epileptic zone may be involved in the process of TLE.

Suppressive effects of levetiracetam on neuroinflammation and phagocytic microglia: A comparative study of levetiracetam, valproate and carbamazepine

We previously reported that treatment with levetiracetam (LEV) after status epilepticus (SE) termination by diazepam (DZP) prevents the development of spontaneous recurrent seizures. LEV suppresses increased expression levels of proinflammatory mediators during epileptogenesis after SE, but how LEV acts in neuroinflammatory processes is not yet known. In this study, we examined the effects of LEV on neuroinflammation and phagocytic microglia in vivo and in vitro and compared the effects of LEV with those of representative antiepileptic drugs valproate (VPA) and carbamazepine (CBZ). Repeated treatment with LEV for 30 days after the termination of pilocarpine-induced SE by DZP almost completely prevented the incidence of spontaneous recurrent seizures, while administration of VPA or CBZ showed no effect on the seizures. LEV clearly suppressed phagocytosis of mononuclear phagocytes, and cytokine expression was observed 2 days after SE. VPA attenuated neuroinflammation only, and CBZ showed no effect on changes after SE. Treatment with LEV significantly suppressed BV-2 microglial activation, which was defined by morphological changes, phagocytic activity and cytokine expression. By contrast, VPA and CBZ did not affect BV-2 microglial activity. In summary, LEV directly suppresses excess microglial phagocytosis during epileptogenesis, which might prevent the occurrence of spontaneous recurrent seizures after SE.

Targeting microRNA-134 for seizure control and disease modification in epilepsy.

MicroRNA-134 is a brain-enriched small noncoding RNA that has been implicated in diverse neuronal functions, including regulating network excitability. Increased expression of microRNA-134 has been reported in several experimental epilepsy models and in resected brain tissue from temporal lobe epilepsy patients. Rodent studies have demonstrated that reducing microRNA-134 expression in the brain using antisense oligonucleotides can increase seizure thresholds and attenuate status epilepticus. Critically, inhibition of microRNA-134 after status epilepticus can potently reduce the occurrence of spontaneous recurrent seizures. Altered plasma levels of microRNA-134 have been reported in epilepsy patients, suggesting microRNA-134 may have diagnostic value as a biomarker. This review summarises findings on the cellular functions of microRNA-134, as well as the preclinical evidence supporting anti-seizure and disease-modifying effects of targeting microRNA-134 in epilepsy. Finally, we draw attention to unanswered questions and some of the challenges and opportunities involved in preclinical development of a microRNA-based oligonucleotide treatment for epilepsy.

Baicalein improves cognitive deficits and hippocampus impairments in temporal lobe epilepsy rats

Temporal lobe epilepsy (TLE) is a chronic neurological disorder that is a refractory disease. Baicalein possesses various pharmacological activities, including neuroprotection in neurodegenerative disease. However, whether baicalein is protective in the treatment of TLE is not determined. Therefore, the present study investigated the role of baicalein in the treatment of TLE. Baicalein was injected intraperitoneally to TLE rats for two weeks after the onset of spontaneous recurrent seizures (SRS). Rats were observed for the occurrence of SRS, and cognitive and hippocampus injuries were evaluated. Oxidative stress and inflammatory cytokines were measured. Corticosterone and its receptor, actin-associated protein F-actin and cofilin-1 were investigated in the brains of epileptic rats. Baicalein significantly improved cognition and reduced hippocampus damage and mossy fibre sprouting in TLE rats without obvious SRS suppression. Baicalein produced excellent anti-oxidative and anti-inflammatory effects in TLE rats. Baicalein restored the disruption of the glucocorticoid signal pathway and actin-associated protein in TLE rats. These results suggest that the neuroprotective effects of baicalein on cognition and the hippocampus are associated with the suppression of oxidative stress and inflammation and the regulation of the glucocorticoid pathway and actin-associated protein in TLE rats. This evidence supports the use of baicalein as an adjuvant agent for epilepsy treatment.

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.

Enriched environment attenuates behavioral seizuresand depression in chronictemporal lobe epilepsy.

Temporal lobe epilepsy (TLE) is commonly associated with depression, anxiety, and cognitive impairment. Despite significant progress in our understanding of the pathophysiology of TLE, it remains the most common form of refractory epilepsy. Enriched environment (EE) has a beneficial effect in many neuropsychiatric disorders. However, the effect of EE on cognitive changes in chronic TLE has not been evaluated. Accordingly, the present study evaluated the effects of EE on chronic epilepsy-induced alterations in cognitive functions, electrophysiology, and cellular changes in the hippocampus. Status epilepticus (SE) was induced in 2-month-old male Wistar rats with lithium and pilocarpine. Six weeks' post SE, epileptic rats were either housed in their respective home cages or in an enrichment cage (6h/day) for 14days. Seizure behavior was video-monitored 2weeks before and during exposure to EE. Depression-like behavior, anxiety-like behavior, and spatial learning and memory were assessed using the sucrose preference test (SPT), elevated plus maze (EPM), and Morris water maze (MWM), respectively. Delta and theta power in the CA1 region of hippocampus was assessed from recordings of local field potentials (LFPs). Cellular changes in hippocampus were assessed by histochemistry followed by unbiased stereologic analysis. EE significantly reduced seizure episodes and seizure duration in epileptic rats. In addition, EE alleviated depression and hyperactivity, and restored delta and theta power of LFP in the hippocampal CA1 region. However, EE neither ameliorated epilepsy-induced spatial learning and memory deficits nor restored cell density in hippocampus. This is the first study that evaluates the role of EE in a chronic TLE model, where rats were exposed to EE after occurrence of spontaneous recurrent seizures (SRS). Given that 30% of TLE patients are refractory to drug treatment, therapeutic strategies that utilize components of EE could be designed to alleviate seizures and psychiatric comorbidities associated with TLE.

Antimuscarinic-induced convulsions in fasted mice after food intake: no evidence of spontaneous seizures, behavioral changes or neuronal damage

Prolonged or repeated seizures have been shown to cause spontaneous recurrent seizures, increased anxiety‑related behavior, locomotor hyperactivity, impaired functions of learning and memory, and neuronal damage in the hippocampus and other brain regions in animals. Mice and rats treated with antimuscarinic drugs after fasting for twodays or less develop convulsions after being allowed to eat ad libitum. To address whether such behavioral and neuroanatomic changes occur following these convulsions, mice treated i.p. with saline (control) or 2.4mg/kg atropine and given food after 24 h of fasting were grouped according to seizure scores for behavioral and histological analysis. Following convulsions, the occurrence of spontaneous recurrent seizures was observed for 30days. Motor activity and grooming behavior were assessed in the open field, and memory was assessed using the novel object recognition test 4 and 7days after onset of convulsions, respectively. Animals allocated for the histological analysis were decapitated 7days after onset of convulsions and hippocampal slices were evaluated for the percentage of degenerating neurons stained with Fluoro‑Jade C. Spontaneous recurrent seizures, locomotor alterations, anxiety‑related behavior, memory impairment, and neuronal loss in the granular layer of the dentate gyrus were not detected in the animals with seizure score 1-2 or 3-5. These results are in accordance with those related to the absence of behavioral changes, cognitive deficits, and hippocampal neuronal damage after single brief seizures in animals and patients with epilepsy.

Decreased neuron loss and memory dysfunction in pilocarpine-treated rats pre-exposed to hypoxia

Preconditioning can induce a cascade of cellular events leading to neuroprotection against subsequent brain insults. In this study, we investigated the chronic effects of hypoxic preconditioning on spontaneous recurrent seizures (SRS), neuronal death, and spatial memory performance in rats subjected to pilocarpine (Pilo)-induced status epilepticus (SE). Rats underwent a short hypoxic episode (7% O2+93% N2; 30min on two consecutive days) preceding a 4-h SE (HSE group). Control groups were rats submitted to SE only (SE), rats subjected to hypoxia only (H) or normoxia-saline (C). Animals were monitored for the occurrence of SRS, and spatial memory performance was evaluated in the radial-arm maze. Hippocampal sections were analyzed for cell death and mossy fiber sprouting at 1 or 60days after SE. Compared to SE group, HSE had increased SE latency, reduced number of rats with SRS, reduced mossy fiber sprouting at 60days, and reduced cell death in the hilus and the CA3 region 1 and 60days after SE. Additionally, HSE rats had better spatial memory performance than SE rats. Our findings indicated that short hypoxic preconditioning preceding SE promotes long-lasting protective effects on neuron survival and spatial memory.

Protection against cognitive impairment and modification of epileptogenesis with curcumin in a post-status epilepticus model of temporal lobe epilepsy

Epileptogenesis is a dynamic process initiated by insults to the brain that is characterized by progressive functional and structural alterations in certain cerebral regions, leading to the appearance of spontaneous recurrent seizures. Within the duration of the trauma to the brain and the appearance of spontaneous recurrent seizures, there is typically a latent period, which may offer a therapeutic window for preventing the emergence of epilepsy. Previous animal studies have shown that curcumin can attenuate acute seizure severity and brain oxidative stress, but the effect of curcumin on epileptogenesis has not been studied. We examined the effect of continued administration of curcumin during the latent period on epileptogenesis and the deleterious consequences of status epilepticus in adult rats in a post-status epilepticus model of temporal lobe epilepsy induced by kainic acid. We demonstrate that, while administration of curcumin treatment during the latent period does not prevent occurrence of spontaneous recurrent seizures after status epilepticus, it can attenuate the severity of spontaneous recurrent seizures and protect against cognitive impairment. Thus, treatment with curcumin during the latent period following status epilepticus is beneficial in modifying epileptogenesis.

Increased extracellular levels of glutamate in the hippocampus of chronically epileptic rats

An increase in the release of excitatory amino acids has consistently been observed in the hippocampus during seizures, both in humans and animals. However, very little or nothing is known about the extracellular levels of glutamate and aspartate during epileptogenesis and in the interictal chronic period of established epilepsy. The aim of this study was to systematically evaluate the relationship between seizure activity and changes in hippocampal glutamate and aspartate extracellular levels under basal and high K+-evoked conditions, at various time-points in the natural history of experimental temporal lobe epilepsy, using in vivo microdialysis. Hippocampal extracellular glutamate and aspartate levels were evaluated: 24h after pilocarpine-induced status epilepticus (SE); during the latency period preceding spontaneous seizures; immediately after the first spontaneous seizure; in the chronic (epileptic) period. We found that (i) basal (spontaneous) glutamate outflow is increased in the interictal phases of the chronic period, whereas basal aspartate outflow remains stable for the entire course of the disease; (ii) high K+ perfusion increased glutamate and aspartate outflow in both control and pilocarpine-treated animals, and the overflow of glutamate was clearly increased in the chronic group. Our data suggest that the glutamatergic signaling is preserved and even potentiated in the hippocampus of epileptic rats, and thus may favor the occurrence of spontaneous recurrent seizures. Together with an impairment of GABA signaling (Soukupova et al., 2014), these data suggest that a shift toward excitation occurs in the excitation/inhibition balance in the chronic epileptic state.

Spatial memory deficits in juvenile rats with pilocarpine induced temporal lobe epilepsy

Abstract One of the most frequent forms of epilepsy in humans is temporal lobe epilepsy. Characteristic to this form of the disease is the frequent pharmacoresistance and the association with behavioural disorders and cognitive impairment. The objective of our study was to establish the degree of cognitive impairment in a rat model of temporal lobe epilepsy after an initial epileptogenic exposure but before of the onset of the effect of long-duration epilepsy. Methods. For the experiment we used 11 rats. Status epilepticus was induced by systemic administration of a single dose of pilocarpine. The animals were continuously video-monitored to observe the occurrence of spontaneous recurrent seizures; during weeks 9-10 we performed eight-arm radial maze testing in order to assess the cognitive impairment. Results. Animals developed spontaneous recurrent seizures after a 14-21 day latency with a daily average seizure density of 0.79±0.43 during weeks 9-10. Epileptic rats had significantly more working memory errors per session, more reference memory errors and the number of visited arms was also significantly higher. Accuracy was also lower in the pilocarpine treated group. Interestingly significant differences disappeared after six days of trials. Conclusions. Our study shows behavioural deficits occurring after 9-10 weeks of epilepsy in the pilocarpine model of epilepsy applied to juvenile rats. In contrast to previous studies, we showed that juvenile rats with short duration of epilepsy are able to learn the behavioural task, therefore a morphopathological and/or behavioural “no-return point” regarding the development of severe cognitive impairment is not reached by status epilepticus alone.

Impairment of GABA release in the hippocampus at the time of the first spontaneous seizure in the pilocarpine model of temporal lobe epilepsy

The alterations in GABA release have not yet been systematically measured along the natural course of temporal lobe epilepsy. In this work, we analyzed GABA extracellular concentrations (using in vivo microdialysis under basal and high K+-evoked conditions) and loss of two GABA interneuron populations (parvalbumin and somatostatin neurons) in the ventral hippocampus at different time-points after pilocarpine-induced status epilepticus in the rat, i.e. during development and progression of epilepsy. We found that (i) during the latent period between the epileptogenic insult, status epilepticus, and the first spontaneous seizure, basal GABA outflow was reduced to about one third of control values while the number of parvalbumin-positive cells was reduced by about 50% and that of somatostatin-positive cells by about 25%; nonetheless, high K+ stimulation increased extracellular GABA in a proportionally greater manner during latency than under control conditions; (ii) at the time of the first spontaneous seizure (i.e., when the diagnosis of epilepsy is made in humans) this increased responsiveness to stimulation disappeared, i.e. there was no longer any compensation for GABA cell loss; (iii) thereafter, this dysfunction remained constant until a late phase of the disease. These data suggest that a GABAergic hyper-responsiveness can compensate for GABA cell loss and protect from occurrence of seizures during latency, whereas impaired extracellular GABA levels can favor the occurrence of spontaneous recurrent seizures and the maintenance of an epileptic state.

Role of inflammatory mediators in the pathogenesis of epilepsy.

Epilepsy is one of the most common chronic brain disorders worldwide, affecting 1% of people across different ages and backgrounds. Epilepsy is defined as the sporadic occurrence of spontaneous recurrent seizures. Accumulating preclinical and clinical evidence suggest that there is a positive feedback cycle between epileptogenesis and brain inflammation. Epileptic seizures increase key inflammatory mediators, which in turn cause secondary damage to the brain and increase the likelihood of recurrent seizures. Cytokines and prostaglandins are well-known inflammatory mediators in the brain, and their biosynthesis is enhanced following seizures. Such inflammatory mediators could be therapeutic targets for the development of new antiepileptic drugs. In this review, we discuss the roles of inflammatory mediators in epileptogenesis.