Long-term alteration of calcium homeostatic mechanisms in the pilocarpine model of temporal lobe epilepsy

Dantrolene paradoxically exacerbates short-term brain glucose hypometabolism, hippocampal damage and neuroinflammation induced by status epilepticus in the rat lithium-pilocarpine model

Status epilepticus (SE) is a neurologic emergency characterized by prolonged or rapidly recurring seizures. Increased intracellular calcium concentration ([Ca2+]i) occurring after SE is a key mediator of excitotoxicity that contributes to the brain damage associated with the development of epilepsy. Accumulated evidence indicates that dantrolene, a ryanodine receptor (RyR) blocker may have protective effects against the SE-induced damage. We evaluated whether dantrolene (10 mg/kg, i.p.) administered twice, 5 min and 24 h after the lithium-pilocarpine-induced SE in rats, had neuroprotective effects. Dantrolene by itself had no effects on control rats. However, it exacerbated the signs of damage in rats that underwent SE, increasing brain glucose hypometabolism as measured by PET neuroimaging 3 days after SE. Likewise, the neurohistochemical studies revealed that dantrolene aggravated signs of hippocampal neurodegeneration, neuronal death and microglia-induced neuroinflammation. Besides, the damaging effects were reflected by severe body weight loss. Overall, our results point towards a deleterious effect of dantrolene in the lithium-pilocarpine-induced SE model. Nonetheless, our results are in opposition to the reported neuroprotective effects of dantrolene. Whether the mechanisms underlying [Ca2+]i increase might significantly differ depending on the particularities of the model of epilepsy used and general experimental conditions need further studies. Besides, it is yet to be determined which isoform of RyRs significantly contributes to Ca2+-induced excitotoxicity in the lithium-pilocarpine SE rat model.

Parvalbumin Regulates GAD Expression through Calcium Ion Concentration to Affect the Balance of Glu-GABA and Improve KA-Induced Status Epilepticus in PV-Cre Transgenic Mice

Aims: the study aimed to (i) use adeno-associated virus technology to modulate parvalbumin (PV) gene expression, both through overexpression and silencing, within the hippocampus of male mice and (ii) assess the impact of PV on the metabolic pathway of glutamate and γ-aminobutyric acid (GABA). Methods: a status epilepticus (SE) mouse model was established by injecting kainic acid into the hippocampus of transgenic mice. When the seizures of mice reached SE, the mice were killed at that time point and 30 min after the onset of SE. Hippocampal tissues were extracted and the mRNA and protein levels of PV and the 65 kDa (GAD65) and 67 kDa (GAD67) isoforms of glutamate decarboxylase were assessed using real-time quantitative polymerase chain reaction and Western blot, respectively. The concentrations of glutamate and GABA were detected with high-performance liquid chromatography (HPLC), and the intracellular calcium concentration was detected using flow cytometry. Results: we demonstrate that the expression of PV is associated with GAD65 and GAD67 and that PV regulates the levels of GAD65 and GAD67. PV was correlated with calcium concentration and GAD expression. Interestingly, PV overexpression resulted in a reduction in calcium ion concentration, upregulation of GAD65 and GAD67, elevation of GABA concentration, reduction in glutamate concentration, and an extension of seizure latency. Conversely, PV silencing induced the opposite effects. Conclusion: parvalbumin may affect the expression of GAD65 and GAD67 by regulating calcium ion concentration, thereby affecting the metabolic pathways associated with glutamate and GABA. In turn, this contributes to the regulation of seizure activity.

Regulation of specific abnormal calcium signals in the hippocampal CA1 and primary cortex M1 alleviates the progression of temporal lobe epilepsy

Temporal lobe epilepsy is a multifactorial neurological dysfunction syndrome that is refractory, resistant to antiepileptic drugs, and has a high recurrence rate. The pathogenesis of temporal lobe epilepsy is complex and is not fully understood. Intracellular calcium dynamics have been implicated in temporal lobe epilepsy. However, the effect of fluctuating calcium activity in CA1 pyramidal neurons on temporal lobe epilepsy is unknown, and no longitudinal studies have investigated calcium activity in pyramidal neurons in the hippocampal CA1 and primary motor cortex M1 of freely moving mice. In this study, we used a multi-channel fiber photometry system to continuously record calcium signals in CA1 and M1 during the temporal lobe epilepsy process. We found that calcium signals varied according to the grade of temporal lobe epilepsy episodes. In particular, cortical spreading depression, which has recently been frequently used to represent the continuously and substantially increased calcium signals, was found to correspond to complex and severe behavioral characteristics of temporal lobe epilepsy ranging from grade II to grade V. However, vigorous calcium oscillations and highly synchronized calcium signals in CA1 and M1 were strongly related to convulsive motor seizures. Chemogenetic inhibition of pyramidal neurons in CA1 significantly attenuated the amplitudes of the calcium signals corresponding to grade I episodes. In addition, the latency of cortical spreading depression was prolonged, and the above-mentioned abnormal calcium signals in CA1 and M1 were also significantly reduced. Intriguingly, it was possible to rescue the altered intracellular calcium dynamics. Via simultaneous analysis of calcium signals and epileptic behaviors, we found that the progression of temporal lobe epilepsy was alleviated when specific calcium signals were reduced, and that the end-point behaviors of temporal lobe epilepsy were improved. Our results indicate that the calcium dynamic between CA1 and M1 may reflect specific epileptic behaviors corresponding to different grades. Furthermore, the selective regulation of abnormal calcium signals in CA1 pyramidal neurons appears to effectively alleviate temporal lobe epilepsy, thereby providing a potential molecular mechanism for a new temporal lobe epilepsy diagnosis and treatment strategy.

Modulating Expression of Endogenous Interleukin 1 Beta in the Acute Phase of the Pilocarpine Model of Epilepsy May Change Animal Survival

The pilocarpine-induced (PILO) model has helped elucidate the electrophysiological and molecular aspects related to mesial temporal lobe epilepsy. It has been suggested that the extensive cell death and edema observed in the brains of these animals could be induced by increased inflammatory responses, such as the rapid release of the inflammatory cytokine interleukin 1 beta (Il1b). In this study, we investigate the role of endogenous Il1b in the acute phase of the PILO model. Our aim is twofold. First, we want to determine whether it is feasible to silence Il1b in the central nervous system using a non-invasive procedure. Second, we aim to investigate the effect of silencing endogenous Il1b and its antagonist, Il1rn.We used RNA interference applied non-invasively to knockdown Il1b and its endogenous antagonist Il1rn. We found that knocking down Il1b prior to pilocarpine injection increased the mortality rate of treated animals. Furthermore, we observed that, when exposing the animals to more Il1b by silencing its endogenous antagonist Il1rn, there was a better response to status epilepticus with decreased animal mortality in the acute phase of the PILO model. Thus, we show the feasibility of using a novel, less invasive approach to study genes involved in the inflammatory response in the central nervous system. Furthermore, our results provide suggestive evidence that modulating endogenous Il1b improves animal survival in the acute phase of the PILO model and may have effects that extend into the chronic phase.

Calcium dysregulation and compensation in cortical pyramidal neurons of the R6/2 mouse model of Huntington's disease

Huntington's disease (HD) is a fatal, hereditary neurodegenerative disorder that predominantly affects striatal medium-sized spiny neurons and cortical pyramidal neurons (CPNs). It has been proposed that perturbations in Ca²⁺ homeostasis could play a role in CPN alterations. To test this hypothesis, we used the R6/2 mouse model of juvenile HD at different stages of disease progression; presymptomatic, early symptomatic, and late symptomatic. We combined whole-cell patch-clamp recordings of layer 2/3 CPNs with two-photon laser scanning microscopy to image somatic and dendritic Ca²⁺ transients associated with evoked action potentials (APs). We found that the amplitude of AP-induced Ca²⁺ transients recorded at the somata of CPNs was significantly reduced in presymptomatic and late symptomatic R6/2 mice compared with wild-type (WT) littermates. However, reduced amplitudes were compensated by increases in decay times, so that Ca²⁺ transient areas were similar between genotypes. AP-induced Ca²⁺ transients in CPN proximal dendrites were variable and differences did not reach statistical significance, except for reduced areas in the late symptomatic group. In late symptomatic mice, a specific store-operated Ca²⁺ channel antagonist, EVP4593, reduced somatic Ca²⁺ transient amplitude similarly in WT and R6/2 CPNs. In contrast, dantrolene, a ryanodine receptor (RyR) antagonist, and nifedipine, an L-type Ca²⁺ channel blocker, significantly reduced both somatic Ca²⁺ transient amplitude and area in R6/2 but not WT CPNs. These findings demonstrate that perturbations of Ca²⁺ homeostasis and compensation occur in CPNs before and after the onset of overt symptoms, and suggest RyRs and L-type Ca²⁺ channels as potential targets for therapeutic intervention.NEW & NOTEWORTHY We used two-photon microscopy to examine calcium influx induced by action potentials in cortical pyramidal neurons from a mouse model of Huntington's disease (HD), the R6/2. The amplitude of somatic calcium transients was reduced in R6/2 mice compared with controls. This reduction was compensated by increased decay times, which could lead to reduced calcium buffering capacity. L-type calcium channel and ryanodine receptor blockers reduced calcium transient area in HD neurons, suggesting new therapeutic avenues.

Neurochemical abnormalities in the hippocampus of male rats displaying audiogenic seizures, a genetic model of epilepsy

BACKGROUND

Epilepsy is a disorder characterized by recurrent seizures that affects 1% of the population. However, the neurochemical alterations observed in epilepsy are not fully understood. There are different animal models of epilepsy, such as genetic or drug induced. In the present study, we utilize Wistar Audiogenic Rats (WAR), a murine strain that develops seizures in response to high intensity audio stimulation, in order to investigate abnormalities in glutamatergic and GABAergic systems.

METHODS

Synaptosomes and glial plasmalemmal vesicles were prepared from hippocampus and cortex, respectively. Glutamate and GABA release and uptake were assayed by monitoring the fluorescence and using L-[³H]-radiolabeled compounds. Glutamate and calcium concentration in the synaptosomes were also measured. The expression of neuronal calcium sensor 1 (NCS-1) was determined by western blot.

RESULTS

Glutamate and GABA release evoked by KCl was decreased in WAR compared to control Wistar rats. Calcium independent release was not considerably different in both groups. The total amount of glutamate of synaptosomes, as well as glutamate uptake by synaptosomes and GPV were also decreased in WAR in comparison with the controls. In addition, [Ca²⁺]_i of hippocampal synaptosomes, as well as NCS-1 expression in the hippocampus, were increased in WAR in comparison with controls.

CONCLUSION

In conclusion, our results suggest that WAR have important alterations in the glutamatergic and GABAergic pathways, as well as an increased expression of NCS-1 in the hippocampus and inferior colliculus. These alterations may be linked to the spreading of hyperexcitability and recruitment of various brain regions.

The actin binding protein α-actinin-2 expression is associated with dendritic spine plasticity and migrating granule cells in the rat dentate gyrus following pilocarpine-induced seizures

α-actinin-2 (α-actn-2) is an F-actin-crosslinking protein, localized in dendritic spines. In vitro studies suggested that it is involved in spinogenesis, morphogenesis, actin organization, cell migration and anchoring of the NR1 subunit of the N-methyl-D-aspartate (NMDA) receptors in dendritic spines. However, little is known regarding its function in vivo. We examined the levels of α-actn-2 expression within the dentate gyrus (DG) during the development of chronic limbic seizures (epileptogenesis) induced by pilocarpine in rats. In this model, plasticity of the DG glutamatergic granule cells including spine loss, spinogenesis, morphogenesis, neo-synaptogenesis, aberrant migration, and alterations of NMDA receptors have been well characterized. We showed that α-actn-2 immunolabeling was reduced in the inner molecular layer at 1-2 weeks post-status epilepticus (SE), when granule cell spinogenesis and morphogenesis occur. This low level persisted at the chronic stage when new functional synapses are established. This decreased of α-actn-2 protein is concomitant with the recovery of drebrin A (DA), another actin-binding protein, at the chronic stage. Indeed, we demonstrated in cultured cells that in contrast to DA, α-actn-2 did not protect F-actin destabilization and DA inhibited α-actn-2 binding to F-actin. Such alteration could affect the anchoring of NR1 in dendritic spines. Furthermore, we showed that the expression of α-actn-2 and NR1 are co-down-regulated in membrane fractions of pilocarpine animals at chronic stage. Last, we showed that α-actn-2 is expressed in migrating newly born granule cells observed within the hilus of pilocarpine-treated rats. Altogether, our results suggest that α-actn-2 is not critical for the structural integrity and stabilization of granule cell dendritic spines. Instead, its expression is regulated when spinogenesis and morphogenesis occur and within migrating granule cells. Our data also suggest that the balance between α-actn-2 and DA expression levels may modulate NR1 anchoring within dendritic spines.

Genetic Landscape of Common Epilepsies: Advancing towards Precision in Treatment

Epilepsy, a neurological disease characterized by recurrent seizures, is highly heterogeneous in nature. Based on the prevalence, epilepsy is classified into two types: common and rare epilepsies. Common epilepsies affecting nearly 95% people with epilepsy, comprise generalized epilepsy which encompass idiopathic generalized epilepsy like childhood absence epilepsy, juvenile myoclonic epilepsy, juvenile absence epilepsy and epilepsy with generalized tonic-clonic seizure on awakening and focal epilepsy like temporal lobe epilepsy and cryptogenic focal epilepsy. In 70% of the epilepsy cases, genetic factors are responsible either as single genetic variant in rare epilepsies or multiple genetic variants acting along with different environmental factors as in common epilepsies. Genetic testing and precision treatment have been developed for a few rare epilepsies and is lacking for common epilepsies due to their complex nature of inheritance. Precision medicine for common epilepsies require a panoramic approach that incorporates polygenic background and other non-genetic factors like microbiome, diet, age at disease onset, optimal time for treatment and other lifestyle factors which influence seizure threshold. This review aims to comprehensively present a state-of-art review of all the genes and their genetic variants that are associated with all common epilepsy subtypes. It also encompasses the basis of these genes in the epileptogenesis. Here, we discussed the current status of the common epilepsy genetics and address the clinical application so far on evidence-based markers in prognosis, diagnosis, and treatment management. In addition, we assessed the diagnostic predictability of a few genetic markers used for disease risk prediction in individuals. A combination of deeper endo-phenotyping including pharmaco-response data, electro-clinical imaging, and other clinical measurements along with genetics may be used to diagnose common epilepsies and this marks a step ahead in precision medicine in common epilepsies management.

Ryanodine receptors drive neuronal loss and regulate synaptic proteins during epileptogenesis

Status epilepticus (SE) is a clinical emergency that can lead to the development of temporal lobe epilepsy (TLE). The development and maintenance of spontaneous seizures in TLE are linked to calcium (Ca⁺²)-dependent processes such as neuronal cell loss and pathological synaptic plasticity. It has been shown that SE produces an increase in ryanodine receptor-dependent intracellular Ca⁺² levels in hippocampal neurons, which remain elevated during the progression of the disease. However, the participation of ryanodine receptors (RyRs) in the neuronal loss and circuitry rewiring that take place in the hippocampus after SE remains unknown. In this context, we first investigated the functional role of RyRs on the expression of synaptic and plasticity-related proteins during epileptogenesis induced by pilocarpine in Wistar rats. Intrahippocampal injection of dantrolene, a selective pharmacological blocker of RyRs, caused the increase of the presynaptic protein synapsin I (SYN) and synaptophysin (SYP) 48 h after SE induction. Specifically, we observed that SYN and SYP were regulated in hippocampal regions known to receive synaptic inputs, revealing that RyRs could be involved in network changes and/or neuronal protection after SE induction. In order to investigate whether the changes in SYN and SYP were related to neuroplastic changes that could contribute to pathological processes that occur after SE, we evaluated the levels of activity-regulated cytoskeleton-associated protein (ARC) and mossy fiber sprouting in the dentate gyrus (DG). Interestingly, we observed that although SE induced the appearance of intense ARC-positive cells, dantrolene treatment did not change the levels of ARC in both western blot and immunofluorescence analyses. Accordingly, in the same experimental conditions, we were not able to detect changes in the levels of both pre- and post-synaptic plasticity-related proteins, growth associated protein-43 (GAP-43) and postsynaptic density protein-95 (PSD-95), respectively. Additionally, the density of mossy fiber sprouting in the DG was not increased by dantrolene treatment. We next examined the effects of intrahippocampal injection of dantrolene on neurodegeneration. Notably, dantrolene promoted neuroprotective effects by decreasing neuronal cell loss in CA1 and CA3, which explains the increased levels of synaptic proteins, and the apparent lack of positive effect on pathological plasticity. Taken together, our results revealed that RyRs may have a major role in the hippocampal neurodegeneration associated to the development of acquired epilepsy.

Piperidine and piperazine inhibitors of fatty acid amide hydrolase targeting excitotoxic pathology

FAAH inhibitors offer safety advantages by augmenting the anandamide levels "on demand" to promote neuroprotective mechanisms without the adverse psychotropic effects usually seen with direct and chronic activation of the CB1 receptor. FAAH is an enzyme implicated in the hydrolysis of the endocannabinoid N-arachidonoylethanolamine (AEA), which is a partial agonist of the CB1 receptor. Herein, we report the discovery of a new series of highly potent and selective carbamate FAAH inhibitors and their evaluation for neuroprotection. The new inhibitors showed potent nanomolar inhibitory activity against human recombinant and purified rat FAAH, were selective (>1000-fold) against serine hydrolases MGL and ABHD6 and lacked any affinity for the cannabinoid receptors CB1 and CB2. Evaluation of FAAH inhibitors 9 and 31 using the in vitro competitive activity-based protein profiling (ABPP) assay confirmed that both inhibitors were highly selective for FAAH in the brain, since none of the other FP-reactive serine hydrolases in this tissue were inhibited by these agents. Our design strategy followed a traditional SAR approach and was supported by molecular modeling studies based on known FAAH cocrystal structures. To rationally design new molecules that are irreversibly bound to FAAH, we have constructed "precovalent" FAAH-ligand complexes to identify good binding geometries of the ligands within the binding pocket of FAAH and then calculated covalent docking poses to select compounds for synthesis. FAAH inhibitors 9 and 31 were evaluated for neuroprotection in rat hippocampal slice cultures. In the brain tissue, both inhibitors displayed protection against synaptic deterioration produced by kainic acid-induced excitotoxicity. Thus, the resultant compounds produced through rational design are providing early leads for developing therapeutics against seizure-related damage associated with a variety of disorders.

Novel therapeutics for treating organophosphate-induced status epilepticus co-morbidities, based on changes in calcium homeostasis

Organophosphate (OP) chemicals include pesticides such as parathion, and nerve gases such as sarin and soman and are considered major chemical threat agents. Acute OP exposure is associated with a cholinergic crisis and status epilepticus (SE). It is also known that the survivors of OP toxicity exhibit neurobehavioral deficits such as mood changes, depression, and memory impairment, and acquired epilepsy. Our research has focused on addressing the need to develop effective therapeutic agents that could be administered even after prolonged seizures and would prevent or lessen the chronic morbidity associated with OP-SE survival. We have developed rat survival models of OP pesticide metabolite paraoxon (POX) and nerve agent sarin surrogate diisopropyl fluorophosphate (DFP) induced SE that are being used to screen for medical countermeasures against an OP attack. Our research has focused on studying neuronal calcium (Ca²⁺) homeostatic mechanisms for identifying mechanisms and therapeutics for the expression of neurological morbidities associated with OP-SE survival. We have observed development of a "Ca²⁺ plateau" characterized by sustained elevations in neuronal Ca²⁺ levels in OP-SE surviving rats that coincided with the appearance of OP-SE chronic morbidities. These Ca²⁺ elevations had their origin in Ca²⁺ release from the intracellular stores such that blockade with antagonists like dantrolene, carisbamate, and levetiracetam lowered OP-SE mediated Ca²⁺ plateau and afforded significant neuroprotection. Since the Ca²⁺ plateau lasts for a prolonged period, our studies suggest that blocking it after the control of SE may represent a unique target for development of novel countermeasures to prevent long term Ca²⁺ mediated OP-SE neuropsychiatric comorbidities such as depression, anxiety, and acquired epilepsy (AE).

Hypothermia Reduces Mortality, Prevents the Calcium Plateau, and Is Neuroprotective Following Status Epilepticus in Rats

Status Epilepticus (SE) is a major neurological emergency and is considered a leading cause of Acquired Epilepsy (AE). We have shown that SE produces neuronal injury and prolonged alterations in hippocampal calcium levels ([Ca²⁺]_i) that may underlie the development of AE. Interventions preventing the SE-induced Ca²⁺ plateau could therefore prove to be beneficial in lowering the development of AE after SE. Hypothermia is used clinically to prevent neurological complications associated with Traumatic Brain Injury, cardiac arrest, and stroke. Here, we investigated whether hypothermia prevented the development of Ca²⁺ plateau following SE. SE was induced in hippocampal neuronal cultures (HNC) by exposing them to no added MgCl₂ solution for 3 h. To terminate SE, low Mg²⁺ solution was washed off with 31°C (hypothermic) or 37°C (normothermic) physiological recording solution. [Ca²⁺]_i was estimated with ratiometric Fura-2 imaging. HNCs washed with hypothermic solution exhibited [Ca²⁺]_i ratios, which were significantly lower than ratios obtained from HNCs washed with normothermic solution. For in vivo SE, the rat pilocarpine (PILO) model was used. Moderate hypothermia (30–33°C) in rats was induced at 30-min post-SE using chilled ethanol spray in a cold room. Hypothermia following PILO-SE significantly reduced mortality. Hippocampal neurons isolated from hypothermia-treated PILO SE rats exhibited [Ca²⁺]_i ratios which were significantly lower than ratios obtained from PILO SE rats. Hypothermia also provided significant neuroprotection against SE-induced delayed hippocampal injury as characterized by decreased FluoroJade C labeling in hypothermia-treated PILO SE rats. We previously demonstrated that hypothermia reduced Ca²⁺ entry via N-methyl-D-aspartate and ryanodine receptors in HNC. Together, our studies indicate that by targeting these two receptor systems hypothermia could interfere with epileptogenesis and prove to be an effective therapeutic intervention for reducing SE-induced AE.

Evidence for a role of plasma membrane calcium pumps in neurodegenerative disease: Recent developments

Plasma membrane Ca2+ ATPases (PMCAs) are a major system for calcium extrusion from all cells. Different PMCA isoforms and splice variants are involved in the precise temporal and spatial handling of Ca2+ signals and the re-establishment of resting Ca2+ levels in the nervous system. Lack or inappropriate expression of specific PMCAs leads to characteristic neuronal phenotypes, which may be reciprocally exacerbated by genetic predisposition through alleles in other genes that modify PMCA interactions, regulation, and function. PMCA dysfunction is often poorly compensated in neurons and may lead to changes in synaptic transmission, altered excitability and, with long-term calcium overload, eventual cell death. Decrease and functional decline of PMCAs are hallmarks of neurodegeneration during aging, and mutations in specific PMCAs are responsible for neuronal dysfunction and accelerated neurodegeneration in many sensory and cognitive diseases.

Profound deficits in hippocampal synaptic plasticity after traumatic brain injury and seizure is ameliorated by prophylactic levetiracetam

Aim

To determine the precise effects of post-traumatic seizure activity on hippocampal processes, we induced seizures at various intervals after traumatic brain injury (TBI) and analyzed plasticity at CA1 Schaffer collateral synapses.

Material and Methods

Rats were initially separated into two groups; one exposed solely to fluid percussion injury (FPI) at 2 Psi and the other only receiving kainic acid (KA)-induced seizures without FPI. Electrophysiological (ePhys) studies including paired-pulse stimulation for short-term presynaptic plasticity and long-term potentiation (LTP) of CA1 Schaffer collateral synapses of the hippocampus for post-synaptic function survey were followed at post-event 1 hour, 3 and 7 days respectively. Additional rats were exposed to three seizures at weekly intervals starting 1 week or 2 weeks after TBI and compared with seizures without TBI, TBI without seizures, and uninjured animals. An additional group placed under the same control variables were treated with levetiracetam prior to seizure induction. The ePhys studies related to post-TBI induced seizures were also followed in these additional groups.

Results

Seizures affected the short- and long-term synaptic plasticity of the hippocampal CA3-CA1 pathway. FPI itself suppressed LTP and field excitatory post synaptic potentials (fEPSP) in the CA1 Schaffer collateral synapses; KA-induced seizures that followed FPI further suppressed synaptic plasticity. The impairments in both short-term presynaptic and long-term plasticity were worse in the rats in which early post-TBI seizures were induced than those in which later post-TBI seizures were induced. Finally, prophylactic infusion of levetiracetam for one week after FPI reduced the synaptic plasticity deficits in early post-TBI seizure animals.

Conclusion

Our data indicates that synaptic plasticity (i.e., both presynaptic and postsynaptic) suppression occurs in TBI followed by a seizure and that the interval between the TBI and seizure is an important factor in the severity of the resulting deficits. Furthermore, the infusion of prophylactic levetiracetam could partially reverse the suppression of synaptic plasticity.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

P-gp Protein Expression and Transport Activity in Rodent Seizure Models and Human Epilepsy

A cure for epilepsy is currently not available, and seizure genesis, seizure recurrence, and resistance to antiseizure drugs remain serious clinical problems. Studies show that the blood-brain barrier is altered in animal models of epilepsy and in epileptic patients. In this regard, seizures increase expression of blood-brain barrier efflux transporters such as P-glycoprotein (P-gp), which is thought to reduce brain uptake of antiseizure drugs, and thus, contribute to antiseizure drug resistance. The goal of the current study was to assess the viability of combining in vivo and ex vivo preparations of isolated brain capillaries from animal models of seizures and epilepsy as well as from patients with epilepsy to study P-gp at the blood-brain barrier. Exposing isolated rat brain capillaries to glutamate ex vivo upregulated P-gp expression to levels that were similar to those in capillaries isolated from rats that had status epilepticus or chronic epilepsy. Moreover, the fold-increase in P-gp protein expression seen in animal models is consistent with the fold-increase in P-gp observed in human brain capillaries isolated from patients with epilepsy compared to age-matched control individuals. Overall, the in vivo/ex vivo approach presented here allows detailed analysis of the mechanisms underlying seizure-induced changes of P-gp expression and transport activity at the blood-brain barrier. This approach can be extended to other blood-brain barrier proteins that might contribute to drug-resistant epilepsy or other CNS disorders as well.

Z944, a Novel Selective T-Type Calcium Channel Antagonist Delays the Progression of Seizures in the Amygdala Kindling Model

Temporal lobe epilepsy (TLE) is the most common form of drug resistant epilepsy. Current treatment is symptomatic, suppressing seizures, but has no disease modifying effect on epileptogenesis. We examined the effects of Z944, a potent T-type calcium channel antagonist, as an anti-seizure agent and against the progression of kindling in the amygdala kindling model of TLE. The anti-seizure efficacy of Z944 (5mg/kg, 10mg/kg, 30mg/kg and 100mg/kg) was assessed in fully kindled rats (5 class V seizures) as compared to vehicle, ethosuximide (ETX, 100mg/kg) and carbamazepine (30mg/kg). Each animal received the seven treatments in a randomised manner. Seizure class and duration elicited by six post-drug stimulations was determined. To investigate for effects in delaying the progression of kindling, naive animals received Z944 (30mg/kg), ETX (100mg/kg) or vehicle 30-minutes prior to each kindling stimulation up to a maximum of 30 stimulations, with seizure class and duration recorded after each stimulation. At the completion of drug treatment, Ca_V3.1, Ca_V3.2 and Ca_V3.3 mRNA expression levels were assessed in the hippocampus and amygdala using qPCR. Z944 was not effective at suppressing seizures in fully kindled rats compared to vehicle. Animals receiving Z944 required significantly more stimulations to evoke a class III (p<0.05), IV (p<0.01) or V (p<0.0001) seizure, and to reach a fully kindled state (p<0.01), than animals receiving vehicle. There was no significant difference in the mRNA expression of the T-type Ca²⁺ channels in the hippocampus or amygdala. Our results show that selectively targeting T-type Ca²⁺ channels with Z944 inhibits the progression of amygdala kindling. This could be a potential for a new therapeutic intervention to mitigate the development and progression of epilepsy.

Decreased expression of hippocampal Na⁺/Ca²⁺ exchanger isoform-1 by pentylenetetrazole kindling in mice

Previous studies have shown that inhibitors of the Na(+)/Ca(2+) exchanger (NCX) attenuate seizure activity in drug-induced epilepsy models, but the role of NCX in epilepsy is not fully understood. The present study examined the effects of pentylenetetrazole (PTZ)-induced kindling on the mRNA expression of NCX isoforms (NCX1, NCX2 and NCX3) in mouse brain. Chronic administration of PTZ at 40mg/kg resulted in kindling seizure development. It caused decreases in the mRNA levels of NCX1 and NCX2, but not NCX3, in the hippocampus. Changes in NCX isoform expression levels were not observed in the prefrontal cortex or striatum. Acute PTZ at 40mg/kg, which caused little seizure activity, also decreased NCX2, but not NCX1 mRNA levels in the hippocampus. These results suggest that down-regulation of hippocampal NCX1 expression is associated with PTZ-induced kindling seizure development.

Anti-epileptic effect of Ganoderma lucidum polysaccharides by inhibition of intracellular calcium accumulation and stimulation of expression of CaMKII α in epileptic hippocampal neurons

Purpose

To investigate the mechanism of the anti-epileptic effect of Ganoderma lucidum polysaccharides (GLP), the changes of intracellular calcium and CaMK II α expression in a model of epileptic neurons were investigated.

Method

Primary hippocampal neurons were divided into: 1) Control group, neurons were cultured with Neurobasal medium, for 3 hours; 2) Model group I: neurons were incubated with Mg²⁺ free medium for 3 hours; 3) Model group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with the normal medium for a further 3 hours; 4) GLP group I: neurons were incubated with Mg²⁺ free medium containing GLP (0.375 mg/ml) for 3 hours; 5) GLP group II: neurons were incubated with Mg²⁺ free medium for 3 hours then cultured with a normal culture medium containing GLP for a further 3 hours. The CaMK II α protein expression was assessed by Western-blot. Ca²⁺ turnover in neurons was assessed using Fluo-3/AM which was added into the replacement medium and Ca²⁺ turnover was observed under a laser scanning confocal microscope.

Results

The CaMK II α expression in the model groups was less than in the control groups, however, in the GLP groups, it was higher than that observed in the model group. Ca²⁺ fluorescence intensity in GLP group I was significantly lower than that in model group I after 30 seconds, while in GLP group II, it was reduced significantly compared to model group II after 5 minutes.

Conclusion

GLP may inhibit calcium overload and promote CaMK II α expression to protect epileptic neurons.

Neuroprotective effects of idebenone against pilocarpine-induced seizures: modulation of antioxidant status, DNA damage and Na(+), K (+)-ATPase activity in rat hippocampus

The current study investigated the neuroprotective activity of idebenone against pilocarpine-induced seizures and hippocampal injury in rats. Idebenone is a ubiquinone analog with antioxidant, and ATP replenishment effects. It is well tolerated and has low toxicity. Previous studies reported the protective effects of idebenone against neurodegenerative diseases such as Friedreich's ataxia and Alzheimer's disease. So far, the efficacy of idebenone in experimental models of seizures has not been tested. To achieve this aim, rats were randomly distributed into six groups. Two groups were treated with either normal saline (0.9 %, i.p., control group) or idebenone (200 mg/kg, i.p., Ideb200 group) for three successive days. Rats of the other four groups (P400, Ideb50 + P400, Ideb100 + P400, and Ideb200 + P400) received either saline or idebenone (50, 100, 200 mg/kg, i.p.) for 3 days, respectively followed by a single dose of pilocarpine (400 mg/kg, i.p.). All rats were observed for 6 h post pilocarpine injection. Latency to the first seizure, and percentages of seizures and survival were recorded. Surviving animals were sacrificed, and the hippocampal tissues were separated and used for the measurement of lipid peroxides, total nitrate/nitrite, glutathione and DNA fragmentation levels, in addition to catalase and Na(+), K(+)-ATPase activities. Results revealed that in a dose-dependent manner, idebenone (100, 200 mg/kg) prolonged the latency to the first seizure, elevated the percentage of survival and diminished the percentage of pilocapine-induced seizures in rats. Significant increases in lipid peroxides, total nitrate/nitrite, DNA fragmentation levels and catalase activity, in addition to a significant reduction in glutathione level and Na(+), K(+)-ATPase activity were observed in pilocarpine group. Pre-administration of idebenone (100, 200 mg/kg, i.p.) to pilocarpine-treated rats, significantly reduced lipid peroxides, total nitrate/nitrite, DNA fragmentation levels, and normalized catalase activity. Moreover, idebenone prevented pilocarpine-induced detrimental effects on brain hippocampal glutathione level, and Na(+), K(+)-ATPase enzyme activity in rats. Data obtained from the current investigation emphasized the critical role of oxidative stress in induction of seizures by pilocarpine and elucidated the prominent neuroprotective and antioxidant activities of idebenone in this model.

Hypothermia reduces calcium entry via the N-methyl-D-aspartate and ryanodine receptors in cultured hippocampal neurons

Hypothermia is a powerful neuroprotective method when induced following cardiac arrest, stroke, and traumatic brain injury. The physiological effects of hypothermia are multifaceted and therefore a better knowledge of its therapeutic targets will be central to developing innovative combination therapies to augment the protective benefits of hypothermia. Altered neuronal calcium dynamics have been implicated following stroke, status epilepticus and traumatic brain injury. This study was therefore initiated to evaluate the effect of hypothermia on various modes of calcium entry into a neuron. Here, we utilized various pharmacological agents to stimulate major routes of calcium entry in primary cultured hippocampal neurons. Fluorescent calcium indicator Fura-2AM was used to compare calcium ratio under normothermic (37 °C) and hypothermic (31 °C) conditions. The results of this study indicate that hypothermia preferentially reduces calcium entry through N-methyl-D-aspartate receptors and ryanodine receptors. Hypothermia, on the other hand, did not have a significant effect on calcium entry through the voltage-dependent calcium channels or the inositol tri-phosphate receptors. The ability of hypothermia to selectively affect both N-methyl-D-aspartate receptors and ryanodine receptors-mediated calcium systems makes it an attractive intervention for alleviating calcium elevations that are present following many neurological injuries.

Anticonvulsive effect of paeoniflorin on experimental febrile seizures in immature rats: possible application for febrile seizures in children

Febrile seizures (FS) is the most common convulsive disorder in children, but there have been no clinical and experimental studies of the possible treatment of FS with herbal medicines, which are widely used in Asian countries. Paeoniflorin (PF) is a major bioactive component of Radix Paeoniae alba, and PF-containing herbal medicines have been used for neuromuscular, neuropsychiatric, and neurodegenerative disorders. In this study, we analyzed the anticonvulsive effect of PF and Keishikashakuyaku-to (KS; a PF-containing herbal medicine) for hyperthermia-induced seizures in immature rats as a model of human FS. When immature (P5) male rats were administered PF or KS for 10 days, hyperthermia-induced seizures were significantly suppressed compared to control rats. In cultured hippocampal neurons, PF suppressed glutamate-induced elevation of intracellular Ca²⁺ ([Ca²⁺]_i), glutamate receptor-mediated membrane depolarization, and glutamate-induced neuronal death. In addition, PF partially suppressed the elevation in [Ca²⁺]_i induced by activation of the metabotropic glutamate receptor 5 (mGluR5), but not that mediated by α-amino-3-hydroxy-5-methyl-4-isoxazolpropionic acid (AMPA) or N-methyl-D-aspartate (NMDA) receptors. However, PF did not affect production or release of γ-aminobutyric acid (GABA) in hippocampal neurons. These results suggest that PF or PF-containing herbal medicines exert anticonvulsive effects at least in part by preventing mGluR5-dependent [Ca²⁺]_i elevations. Thus, it could be a possible candidate for the treatment of FS in children.

Endoplasmic reticulum potassium–hydrogen exchanger and small conductance calcium-activated potassium channel activities are essential for ER calcium uptake in neurons and cardiomyocytes

Calcium pumping into the endoplasmic reticulum (ER) lumen is thought to be coupled to a countertransport of protons through sarcoplasmic/endoplasmic reticulum calcium ATPase (SERCA) and the members of the ClC family of chloride channels. However, pH in the ER lumen remains neutral, which suggests a mechanism responsible for proton re-entry. We studied whether cation–proton exchangers could act as routes for such a re-entry. ER Ca2+ uptake was measured in permeabilized immortalized hypothalamic neurons, primary rat cortical neurons and mouse cardiac fibers. Replacement of K+ in the uptake solution with Na+ or tetraethylammonium led to a strong inhibition of Ca2+ uptake in neurons and cardiomyocytes. Furthermore, inhibitors of the potassium–proton exchanger (quinine or propranolol) but not of the sodium–proton exchanger reduced ER Ca2+ uptake by 56–82%. Externally added nigericin, a potassium–proton exchanger, attenuated the inhibitory effect of propranolol. Inhibitors of small conductance calcium-sensitive K+ (SKCa) channels (UCL 1684, dequalinium) blocked the uptake of Ca2+ by the ER in all preparations by 48–94%, whereas inhibitors of other K+ channels (IKCa, BKCa and KATP) had no effect. Fluorescence microscopy and western blot analysis revealed the presence of both SKCa channels and the potassium–proton exchanger leucine zipper-EF-hand-containing transmembrane protein 1 (LETM1) in ER in situ and in the purified ER fraction. The data obtained demonstrate that SKCa channels and LETM1 reside in the ER membrane and that their activity is essential for ER Ca2+ uptake.

Alteration in NCX-3 immunoreactivity within the gerbil hippocampus following spontaneous seizures

Although NCX-3 is highly expressed in the brain, the distribution of NCX-3 in the epileptic hippocampus is still controversial. Therefore, to assess the distribution and pattern of NCX-3 expression in epileptic hippocampus, we performed a comparative analysis of NCX-3 immunoreactivities in the hippocampus of seizure-resistant (SR) and seizure-sensitive (SS) gerbils. In SR gerbils, NCX-3 immunoreactivity was higher than pre-seizure SS gerbils, particularly in the pavalbumin (PV)-positive interneurons. Three h post-ictal, NCX-3 immunoreactivity in the SS gerbil hippocampus was markedly elevated to the level of SR gerbils. Six h post-ictal, the expression of NCX-3 was reduced to the level of pre-seizure SS gerbils. Therefore, the results of the present study suggest that down-regulation of NCX-3 expression in the SS gerbil hippocampus may be involved in the hyperexcitability of SS gerbils due to an imbalance of intracellular Na(+)/Ca(2+) homeostasis and Ca(2+) concentration.

A polymorphism in CALHM1 is associated with temporal lobe epilepsy

A recent study suggests that the P86L polymorphism (rs2986017) in the calcium homeostasis modulator 1 (CALHM1) gene interferes with calcium homeostasis and increases amyloid β (Aβ) levels. Moreover, in vitro and in vivo data show that both calcium homeostasis and high levels of Aβ play an important role in the induction and maintenance of epileptic seizures in hippocampus, indicating CALHM1 might play a potential role in pathophysiological pathways involved in temporal lobe epilepsy (TLE). The aim of this study was to investigate the genetic contribution of CALHM1 to TLE. Five single-nucleotide polymorphisms (SNPs) of CALHM1 were selected and genotyped using polymerase chain reaction restriction fragment length polymorphism in 560 patients with TLE and 401 healthy controls. We found a positive association between rs11191692 and TLE, but a negative result between rs2986017 and TLE. The rs11191692-A allele frequency was found in 32.4% of the patients and in 26.2% of control subjects (OR=1.35, 95% CI=1.10-1.65, uncorrected P=0.003, corrected P=0.015). Furthermore, the positive association between rs11191692 and TLE independent of apolipoprotein E ε4 was supported by five SNPs haplotype analysis. The results of this study provide the first evidence that the SNP rs11191692 in CALHM1 confers highly increased susceptibility to TLE.

Analysis of plasma membrane Ca2+-ATPase gene expression during epileptogenesis employing single hippocampal CA1 neurons

Disruption of calcium homeostasis in epileptic cells is characterized by both short- and long-term perturbations of Ca(2+) buffering systems. Along with the Na(+)/Ca(2+) exchanger, the plasma membrane Ca(2+)-ATPase (PMCA) plays an important role in excitable cells. The involvement of PMCAs in epileptogenesis has primarily been studied in brief intervals after various stimuli; however, the specific contribution of this molecule to epileptogenesis is not yet fully understood. Our aim has been to investigate whether PMCA expression in the chronic stages of epilepsy is altered. Through an interdisciplinary approach, involving whole-cell recordings and real-time reverse transcriptase-polymerase chain reaction, we have shown that epileptic neurons in our preparation consistently show changes in electrical properties during the period of chronic epilepsy. These changes included increased spike frequency, altered resting membrane potential and changes in passive membrane properties. Following these observations, which indicate an altered excitability in the epileptic cells studied, PMCA mRNA transcripts were studied. It was found that while PMCA1 transcripts are significantly increased one month following the pilocarpine epileptogenic stimulus, PMCA3, an isoform important in excitable tissues, was significantly, decreased. These findings suggest that, in the long-term, a slow PMCA (PMCA1) plays a role in the reestablishment of a new calcium homeostasis attained by epileptic cells. Overall, this phenomenon points out the fact that in seizure disorders, changes that take place in the balance of the different molecules and their isoforms in charge of maintaining neuronal calcium homeostasis, are fundamental in the survival of affected cells.

New insights on culture and calcium signalling in neurons and astrocytes from epileptic patients

Primary brain cell cultures are a useful tool for understanding the physiopathology of epilepsy and for searching new potential antiepileptic drugs. These cell types are usually prepared from murine species and few human models have been described. The main goal of this study is the establishment of experimental conditions to isolate and culture neurons and astrocytes from human brain and to test its functionality. The tissues came from antiepileptic drug-resistant epileptic patients undergoing surgery. Human neurons and astrocytes were isolated following an enzymatic and mechanical dissociation protocol. Cultures were viable for 3-6 weeks. Cytological characterization was performed by immunocytochemistry using specific antibodies against both neuron (anti-NeuN) and astrocyte (anti-GFAP) protein markers. In order to test their viability and functionality, cells were loaded with the fluorescent calcium probe fura-2 and variations in cytosolic calcium concentrations ([Ca2+]c) were measured by cell imaging. [Ca2+]c increases were evoked upon cell stimulation with high K+ (KCl 75 mM), glutamate (500 μM) or bicuculline (100 μM). Interestingly, spontaneous [Ca2+]c transients were also observed in some neuron-like cells. A novel unreported finding in this study has been the incorporation of human serum that was critical for cell functionality. The setting of these human cultures open the opportunity to new insights on culture and calcium signalling studies on the mechanism(s) of cell resistance to antiepileptic drugs, as well as to studies on plasticity, maturation and possible neurite emission for graft studies.

Differential effects of lysophospholipids on exocytosis in rat PC12 cells

Secretory phospholipase A2 (sPLA2) activity is present in the CNS and the sPLA2-IIA isoform has been shown to induce exocytosis in cultured hippocampal neurons. However, little is known about possible contributions of various lysophospholipid species to exocytosis in neuroendocrine cells. This study was therefore carried out to examine the effects of several lysophospholipid species on exocytosis on rat pheochromocytoma-12 (PC12) cells. An increase in vesicle fusion, indicating exocytosis, was observed in PC12 cells after external infusion of lysophosphatidylinositol (LPI), but not lysophosphatidylcholine or lysophosphatidylserine by total internal reflection microscopy. Similarly, external infusion of LPI induced significant increases in capacitance, or number of spikes detected at amperometry, indicating exocytosis. Depletion of cholesterol by pre-incubation of cells with methyl beta cyclodextrin and depletion of Ca2+ by thapsigargin and incubation in zero external Ca2+ resulted in attenuation of LPI induced exocytosis, indicating that exocytosis was dependent on the integrity of lipid rafts and intracellular Ca2+. Moreover, LPI induced a rise in intracellular Ca2+ suggesting that this could be the trigger for exocytosis. It is postulated that LPI may be an active participant in sPLA2-mediated exocytosis in the CNS.

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

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

Development of the calcium plateau following status epilepticus: role of calcium in epileptogenesis

Status epilepticus is a clinical emergency defined as continuous seizure activity or rapid, recurrent seizures without regaining consciousness and can lead to the development of acquired epilepsy, characterized by spontaneous, recurrent seizures. Understanding epileptogenesis--the transformation of healthy brain tissue into hyperexcitable neuronal networks--is an important challenge and the elucidation of molecular mechanisms can lend insight into new therapeutic targets to halt this progression. It has been demonstrated that intracellular calcium increases during status epilepticus and that these elevations are maintained past the duration of the injury (Ca(2+) plateau). As an important second messenger, Ca(2+) elevations can lead to changes in gene expression, neurotransmitter release and plasticity. Thus, characterization of the post-injury Ca(2+) plateau may be important in eventually understanding the pathophysiology of epileptogenesis and preventing the progression to chronic epilepsy after brain injury.

Complete brain-type creatine kinase deficiency in mice blocks seizure activity and affects intracellular calcium kinetics

PURPOSE

Brain-type creatine kinase (CK-B) and ubiquitous mitochondrial creatine kinase (UbCKmit) act as components of local phosphocreatine ATP shuttles that help in the compartmentalization and maintenance of pools of high-energy phosphate molecules in both neurons and glial cells. We investigated the role of these brain-type creatine kinases during extreme energy-demanding conditions in vivo (generalized tonic-clonic seizures) and in vitro.

METHODS

The physiologic response of wild-types and mice lacking both CK-B and UbCKmit (CK--/--mice) to pentylenetetrazole (PTZ)-induced seizures was measured using electroencephalography (EEG) recordings and behavioral monitoring. In vitro intracellular Ca(2+) kinetics in hippocampal granule neurons were monitored upon single and repetitive depolarizations.

RESULTS

PTZ induced in only a few CK--/-- mice PTZ seizure-like behavior, but in all wild-types a full-blown seizure. EEG analysis showed that preseizure jerking was associated with high-amplitude discharges. Wild-type EEG recordings showed continuous runs of rhythmic 4-6 Hz activity, whereas no rhythmic EEG activities were observed in the few CK--/-- mice that developed a behavioral seizure. All other CK--/-- mice displayed a sudden postictal depression without any development of a generalized seizure. Hippocampal granule neurons of CK--/-- mice displayed a higher Ca(2+) removal speed following repetitive KCl-induced depolarizations.

DISCUSSION

Deficiency for creatine kinase is affecting brain energy metabolism and will likely contribute to the disturbance of seizure development. Because CK--/-- hippocampal neurons exhibited an increase in Ca(2+) removal rate of elevated intracellular levels, we conclude that altered Ca(2+) clearance in CK--/-- neurons could play a role in the abnormal EEG and seizure activity.

Behavioral and histological assessment of the effect of intermittent feeding in the pilocarpine model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most resistant type of epilepsy. Currently available drugs for epilepsy are not antiepileptogenic. A novel treatment for epilepsy would be to block or reverse the process of epileptogenesis. We used intermittent feeding (IF) regimen of the dietary restriction (DR) to study its effect on epileptogenesis and neuroprotection in the pilocarpine model of TLE in rats. The effect of IF regimen on the induction of status epilepticus (SE), the duration of latent period, and the frequency, duration, severity and the time of occurrence of Spontaneous Recurrent Seizures (SRS) were investigated. We also studied the effect of IF regimen on hippocampal neurons against the excitotoxic damage of prolonged SE (about 4h) induced by pilocarpine. The animals (Wistar, male, 200-250g) were divided into four main groups: AL-AL (ad libitum diet throughout), AL-IF (PfS) [IF post-first seizure], AL-IF (PSE) [IF post-SE] and IF-IF (IF diet throughout), and two AL and IF control groups. SE was induced by pilocarpine (350mg/kg, i.p.) and with diazepam (6mg/kg, i.p.) injected after 3h, the behavioral signs of SE terminated at about 4h (AL animals, n=29, 260.43+/-8.74min; IF animals, n=19, 224.32+/-20.73min). Behavioral monitoring was carried out by 24h video recording for 3 weeks after the first SRS. Rat brains were then prepared for histological study with Nissl stain and cell counting was done in CA1, CA2 and CA3 regions of the hippocampus. The results show that the animals on IF diet had significantly less SE induction and significantly longer duration of latent period (the period of epileptogenesis) was seen in IF-IF group compared to the AL-AL group. The severity of SRS was significantly more in AL-IF (PfS) compared to the AL-IF (PSE) group. These results indicate that IF diet can make rats resistant to the induction of SE and can prolong the process of epileptogenesis. The results of the histological study show that the number of pyramidal neurons was statistically less in CA1, CA2 and CA3 of the hippocampus in the experimental groups compared to the control groups. However, IF regimen could not protect the hippocampal neurons against the excitotoxic injury caused by a prolonged SE. We conclude that IF regimen can significantly influence various behavioral characteristics of pilocarpine model of TLE. Further studies can elaborate the exact mechanisms as well as its possible role in the treatment of human TLE.

Carisbamate prevents the development and expression of spontaneous recurrent epileptiform discharges and is neuroprotective in cultured hippocampal neurons

PURPOSE

Although great advances have been made in the development of treatments for epilepsy, acquired epilepsy following brain injury still comprises approximately 50% of all the cases of epilepsy. Thus, development of drugs that would prevent or decrease the onset of epilepsy following brain injury represents an important area of research.

METHODS

Here, we investigated effects of carisbamate (RWJ 333369) on the development and expression of spontaneous recurrent epileptiform discharges (SREDs) and its neuroprotective potential in cultured hippocampal neurons. This model utilizes 3 h of low Mg(2+) treatment to mimic status epilepticus (SE-like) injury in vitro. Following the injury, networks of neurons manifest synchronized SREDs for their life in culture. Neuronal cultures were treated with carisbamate (200 microM) for 12 h immediately after the SE-like injury. The drug was then removed and neurons were patch clamped 24 h following drug washout.

RESULTS

Treatment with carisbamate after neuronal injury prevented the development and expression of epileptiform discharges. In the few neurons that displayed SREDs following carisbamate treatment, there was a significant reduction in SRED frequency and duration. In contrast, phenytoin and phenobarbital, when used in place of carisbamate, did not prevent the development and expression of SREDs. Carisbamate was also effective in preventing neuronal death when administered after SE-like injury.

CONCLUSIONS

Carisbamate prevents the development and generation of epileptiform discharges and is neuroprotective when administered following SE-like injury in vitro and may offer a novel treatment to prevent the development of epileptiform discharges following brain injuries.

Long-term decrease in calbindin-D28K expression in the hippocampus of epileptic rats following pilocarpine-induced status epilepticus

Acquired epilepsy (AE) is characterized by spontaneous recurrent seizures and long-term changes that occur in surviving neurons following an injury such as status epilepticus (SE). Long-lasting alterations in hippocampal Ca(2+) homeostasis have been observed in both in vivo and in vitro models of AE. One major regulator of Ca(2+) homeostasis is the neuronal calcium binding protein, calbindin-D28k that serves to buffer and transport Ca(2+) ions. This study evaluated the expression of hippocampal calbindin levels in the rat pilocarpine model of AE. Calbindin protein expression was reduced over 50% in the hippocampus in epileptic animals. This decrease was observed in the pyramidal layer of CA1, stratum lucidum of CA3, hilus, and stratum granulosum and stratum moleculare of the dentate gyrus when corrected for cell loss. Furthermore, calbindin levels in individual neurons were also significantly reduced. In addition, the expression of calbindin mRNA was decreased in epileptic animals. Time course studies demonstrated that decreased calbindin expression was initially present 1 month following pilocarpine-induced SE and lasted for up to 2 years after the initial episode of SE. The results indicate that calbindin is essentially permanently decreased in the hippocampus in AE. This decrease in hippocampal calbindin may be a major contributing factor underlying some of the plasticity changes that occur in epileptogenesis and contribute to the alterations in Ca(2+) homeostasis associated with AE.

Epileptogenesis causes an N-methyl-d-aspartate receptor/Ca2+-dependent decrease in Ca2+/calmodulin-dependent protein kinase II activity in a hippocampal neuronal culture model of spontaneous recurrent epileptiform discharges

Alterations in the function of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) have been observed in both in vivo and in vitro models of epileptogenesis; however the molecular mechanism mediating the effects of epileptogenesis on CaM kinase II has not been elucidated. This study was initiated to evaluate the molecular pathways involved in causing the long-lasting decrease in CaM kinase II activity in the hippocampal neuronal culture model of low Mg2+-induced spontaneous recurrent epileptiform discharges (SREDs). We show here that the decrease in CaM kinase II activity associated with SREDs in hippocampal cultures involves a Ca2+/N-methyl-d-aspartate (NMDA) receptor-dependent mechanism. Low Mg2+-induced SREDs result in a significant decrease in Ca2+/calmodulin-dependent substrate phosphorylation of the synthetic peptide autocamtide-2. Reduction of extracellular Ca2+ levels (0.2 mM in treatment solution) or the addition of dl-2-amino-5-phosphonovaleric acid (APV) 25 microM blocked the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. Antagonists of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainic acid receptor or L-type voltage sensitive Ca2+ channel had no effect on the low Mg2+-induced decrease in CaM kinase II-dependent substrate phosphorylation. The results of this study demonstrate that the decrease in CaM kinase II activity associated with this model of epileptogenesis involves a selective Ca2+/NMDA receptor-dependent mechanism and may contribute to the production and maintenance of SREDs in this model.

Traumatic brain injury causes a long-lasting calcium (Ca2+)-plateau of elevated intracellular Ca levels and altered Ca2+ homeostatic mechanisms in hippocampal neurons surviving brain injury

Traumatic brain injury (TBI) survivors often suffer chronically from significant morbidity associated with cognitive deficits, behavioral difficulties and a post-traumatic syndrome and thus it is important to understand the pathophysiology of these long-term plasticity changes after TBI. Calcium (Ca2+) has been implicated in the pathophysiology of TBI-induced neuronal death and other forms of brain injury including stroke and status epilepticus. However, the potential role of long-term changes in neuronal Ca2+ dynamics after TBI has not been evaluated. In the present study, we measured basal free intracellular Ca2+ concentration ([Ca2+](i)) in acutely isolated CA3 hippocampal neurons from Sprague-Dawley rats at 1, 7 and 30 days after moderate central fluid percussion injury. Basal [Ca2+](i) was significantly elevated when measured 1 and 7 days post-TBI without evidence of neuronal death. Basal [Ca2+](i) returned to normal when measured 30 days post-TBI. In contrast, abnormalities in Ca2+ homeostasis were found for as long as 30 days after TBI. Studies evaluating the mechanisms underlying the altered Ca2+ homeostasis in TBI neurons indicated that necrotic or apoptotic cell death and abnormalities in Ca2+ influx and efflux mechanisms could not account for these changes and suggested that long-term changes in Ca2+ buffering or Ca2+ sequestration/release mechanisms underlie these changes in Ca2+ homeostasis after TBI. Further elucidation of the mechanisms of altered Ca2+ homeostasis in traumatized, surviving neurons in TBI may offer novel therapeutic interventions that may contribute to the treatment and relief of some of the morbidity associated with TBI.

Down-regulation of BK channel expression in the pilocarpine model of temporal lobe epilepsy

In the hippocampus, BK channels are preferentially localized in presynaptic glutamatergic terminals including mossy fibers where they are thought to play an important role regulating excessive glutamate release during hyperactive states. Large conductance calcium-activated potassium channels (BK, MaxiK, Slo) have recently been implicated in the pathogenesis of genetic epilepsy. However, the role of BK channels in acquired mesial temporal lobe epilepsy (MTLE) remains unknown. Here we used immunohistochemistry, laser scanning confocal microscopy (LSCM), Western immunoblotting and RT-PCR to investigate the expression pattern of the alpha-pore-forming subunit of BK channels in the hippocampus and cortex of chronically epileptic rats obtained by the pilocarpine model of MTLE. All epileptic rats experiencing recurrent spontaneous seizures exhibited a significant down-regulation of BK channel immunostaining in the mossy fibers at the hilus and stratum lucidum of the CA3 area. Quantitative analysis of immunofluorescence signals by LSCM revealed a significant 47% reduction in BK channel immunofluorescent signals in epileptic rats when compared to age-matched non-epileptic control rats. These data correlate with a similar reduction in BK channel protein levels and transcripts in the cortex and hippocampus. Our data indicate a seizure-related down-regulation of BK channels in chronically epileptic rats. Further functional assays are necessary to determine whether altered BK channel expression is an acquired channelopathy or a compensatory mechanism affecting the network excitability in MTLE. Moreover, seizure-mediated BK down-regulation may disturb neuronal excitability and presynaptic control at glutamatergic terminals triggering exaggerated glutamate release and seizures.

Carbamazepine prevents breakdown of neurotransmitter release induced by hyperactivation of ryanodine receptor

To clarify the mechanisms of the pharmacological action of carbamazepine (CBZ), we determined the effect of CBZ on GABA and glutamate release associated with the ryanodine receptor (Ryr)-sensitive Ca(2+)-induced Ca(2+)-releasing system (CICR) in the rat hippocampus using microdialysis. The therapeutically relevant concentration of CBZ increased basal GABA release without affecting basal glutamate release; however, K(+)-evoked releases were concentration-dependently reduced by CBZ. Lower-concentration ryanodine increased basal and K(+)-evoked releases of GABA and glutamate in a concentration dependent manner, whereas higher-concentration ryanodine reduced them. These inflection points in the concentration-response curves of ryanodine for neurotransmitter release (critical concentrations) were shifted to the left by K(+)-evoked stimulation. The critical concentration of ryanodine in GABA release was lower than that in glutamate release. During the resting stage, the critical concentrations of ryanodine were unaffected by inhibition of L-type, N-type and P-type voltage-sensitive Ca(2+) channels (VSCCs) but were prevented by CBZ; however, during the neuronal hyperexcitable stage, the critical concentration was increased by CBZ, L-type and P-type VSCC inhibitors but not the N-type VSCC inhibitor. Therefore, a therapeutically relevant concentration of CBZ protects against the breakdown of the neurotransmitter release mechanism induced by hyperactivation of Ryr via inhibition of L-type and P-type VSCCs as well as inhibition of Ryr-sensitive CICR. These actions of CBZ appear to be involved, at least partially, in its anti-seizure mechanisms.

Aging is associated with elevated intracellular calcium levels and altered calcium homeostatic mechanisms in hippocampal neurons

Aging is associated with increased vulnerability to neurodegenerative conditions such as Parkinson's and Alzheimer's disease and greater neuronal deficits after stroke and epilepsy. Emerging studies have implicated increased levels of intracellular calcium ([Ca(2+)](i)) for the neuronal loss associated with aging related disorders. Recent evidence demonstrates increased expression of voltage gated Ca(2+) channel proteins and associated Ca(2+) currents with aging. However, a direct comparison of [Ca(2+)](i) levels and Ca(2+) homeostatic mechanisms in hippocampal neurons acutely isolated from young and mid-age adult animals has not been performed. In this study, Fura-2 was used to determine [Ca(2+)](i) levels in CA1 hippocampal neurons acutely isolated from young (4-5 months) and mid-age (12-16 months) Sprague-Dawley rats. Our data provide the first direct demonstration that mid-age neurons in comparison to young neurons manifest significant elevations in basal [Ca(2+)](i) levels. Upon glutamate stimulation and a subsequent [Ca(2+)](i) load, mid-age neurons took longer to remove the excess [Ca(2+)](i) in comparison to young neurons, providing direct evidence that altered Ca(2+) homeostasis may be present in animals at significantly younger ages than those that are commonly considered aged (> or =24 months). These alterations in Ca(2+) dynamics may render aging neurons more vulnerable to neuronal death following stroke, seizures or head trauma. Elucidating the functionality of Ca(2+) homeostatic mechanisms may offer an understanding of the increased neuronal loss that occurs with aging, and allow for the development of novel therapeutic agents targeted towards decreasing [Ca(2+)](i) levels thereby restoring the systems that maintain normal Ca(2+) homeostasis in aged neurons.

Activation of a novel injury-induced calcium-permeable channel that plays a key role in causing extended neuronal depolarization and initiating neuronal death in excitotoxic neuronal injury

Protracted elevation in intracellular calcium caused by the activation of the N-methyl-d-aspartate receptor is the main cause of glutamate excitotoxic injury in stroke. However, upon excitotoxic injury, despite the presence of calcium entry antagonists, calcium unexpectedly continues to enter the neuron, causing extended neuronal depolarization and culminating in neuronal death. This phenomenon is known as the calcium paradox of neuronal death in stroke, and it represents a major problem in developing effective therapies for the treatment of stroke. To investigate this calcium paradox and to determine the source of this unexpected calcium entry after neuronal injury, we evaluated whether glutamate excitotoxicity activates an injury-induced calcium-permeable channel responsible for conducting a calcium current that underlies neuronal death. We used a combination of whole-cell and single-channel patch-clamp recordings, fluorescent calcium imaging, and neuronal cell death assays in a well characterized primary hippocampal neuronal culture model of glutamate excitotoxicity/stroke. Here, we report activation of a novel calcium-permeable channel upon excitotoxic glutamate injury that carries calcium current even in the presence of calcium entry inhibitors. Blocking this injury-induced calcium-permeable channel for a significant time period after the initial injury is still effective in preventing calcium entry, extended neuronal depolarization, and delayed neuronal death, thereby accounting for the calcium paradox. This injury-induced calcium-permeable channel represents a major source for the initial calcium entry following stroke, and it offers a new target for extending the therapeutic window for preventing neuronal death after the initial excitotoxic (stroke) injury.

An in vitro model of Stroke‐Induced Epilepsy: Elucidation of The roles of Glutamate and Calcium in The induction and Maintenance of Stroke‐Induced Epileptogenesis

Stroke is a major risk factor for developing acquired epilepsy (AE). Although the underlying mechanisms of ischemia-induced epileptogenesis are not well understood, glutamate has been found to be associated with both epileptogenesis and ischemia-induced injury in several research models. This chapter discusses the development of an in vitro model of epileptogenesis induced by glutamate injury in hippocampal neurons, as found in a clinical stroke, and the implementation of this model of stroke-induced AE to evaluate calcium's role in the induction and maintenance of epileptogenesis. To monitor the acute effects of glutamate on neurons and chronic alterations in neuronal excitability up to 8 days after glutamate exposure, whole-cell current-clamp electrophysiology was employed. Various durations and concentrations of glutamate were applied to primary hippocampal cultures. A single 30-min, 5-microM glutamate exposure produced a subset of neurons that died or had a stroke-like injury, and a larger population of injured neurons that survived. Neurons that survived the injury manifested spontaneous, recurrent, epileptiform discharges (SREDs) in neural networks characterized by paroxysmal depolarizing shifts (PDSs) and high-frequency spike firing that persisted for the life of the culture. The neuronal injury produced in this model was evaluated by determining the magnitude of the prolonged, reversible membrane depolarization, loss of synaptic activity, and neuronal swelling. The permanent epileptiform phenotype expressed as SREDs that resulted from glutamate injury was found to be dependent on the presence of extracellular calcium. The "epileptic" neurons manifested elevated intracellular calcium levels when compared to control neurons, independent of neuronal activity and seizure discharge, demonstrating that alterations in calcium homeostatic mechanisms occur in association with stroke-induced epilepsy. Findings from this investigation present the first in vitro model of glutamate injury-induced epileptogenesis that may help elucidate some of the mechanisms that underlie stroke-induced epilepsy.