Characterization of lithium potentiation of pilocarpine-induced status epilepticus in rats

A modification to the Kuramoto model to simulate epileptic seizures as synchronization

The Kuramoto model was developed to describe the coupling of oscillators, motivated by the natural synchronization phenomena. We are interested in modeling an epileptic seizure considering it as the synchronization of action potentials using and modifying this model. In this article, we propose to modify this model, changing the constant coupling force for a function with logistic growth to simulate the onset and epileptic seizure level in an adult male rat caused by the administration of lithium-pilocarpine. Later, we select some frequencies and their respective amplitude values using an algorithm based on the fast Fourier transform (FFT) from an electroencephalography signal when the rat is in basal conditions. Then, we take these values as the natural frequencies of the oscillators in the modified Kuramoto model, considering every oscillator as a single neuron to simulate the emergence of an epileptic seizure numerically by increasing the synchronization value in the coupling function. Finally, using Dynamic Time Warping algorithm, we compare the simulated signal by the Kuramoto model with an FFT approximation of the epileptic seizure.

Dapsone Protects Against Lithium-Pilocarpine-Induced Status Epilepticus in Rats through Targeting Tumor Necrosis Factor-α and Nitrergic Pathway

Background and Purpose

Status epilepticus (SE) results in permanent neuronal brain damage in the central nervous system. One of the complex etiologies underlying SE pathogenesis is neuroinflammation. Dapsone has been recently considered as a potential neuroprotective agent in neuroinflammatory conditions. Therefore, the present study aims to investigate effects of dapsone on lithium-pilocarpine-induced SE in rats and assess whether tumor necrosis factor-alpha (TNF-α) and nitric oxide (NO) pathway participate in this effect.

Methods

SE was established by injecting lithium chloride (127 mg/kg, intraperitoneally [i.p.]) and pilocarpine (60 mg/kg, i.p.). The animals received pre-treatment dapsone (2, 5, 10, and 20 mg/kg, oral gavage) and post-treatment dapsone (10 mg/kg). Subsequently, seizure score and mortality rate were documented. To assess the underlying signaling pathway, L-Nω-Nitro-L-arginine methyl ester hydrochloride (a non-specific NO synthase [NOS] inhibitor), 7-nitroindazole (a specific neuronal NOS inhibitor), and aminoguanidine (a specific inducible NOS inhibitor) were administered 15 minutes before dapsone (10 mg/kg) pre- or post-treatment. Hippocampal tissue TNF-α and NO concentrations were quantified using the enzyme-linked immunosorbent assay method.

Results

Dapsone (10 mg/kg) pre-and post-treatment significantly attenuated the increased seizure score and mortality rate due to lithium-pilocarpine-induced SE. The development of SE in animals was associated with higher TNF-α and NO metabolites levels, which notably decreased in the dapsone-treated rats. Moreover, co-administration of NOS inhibitors with dapsone markedly reversed the anti-epileptic effects of dapsone and caused an escalation in TNF-α level but a significant reduction in NO concentration level.

Conclusions

It seems that dapsone may exert an anti-epileptic effect on lithium-pilocarpine-induced SE through TNF-α inhibition and modulation of the nitrergic pathway.

Possible mechanisms involved in the neuroprotective effect of Trans,trans-farnesol on pilocarpine-induced seizures in mice

This study aimed to investigate, through in vivo and in vitro methodologies, the effect of acute trans,trans-farnesol (12.5, 25, 50 or 100 mg/kg, p.o.) administration on behavioral and neurochemical parameters associated with pilocarpine-induced epileptic seizure (300 mg/kg, i.p.) in mice. The initial results showed that the compound in question presents no anxiolytic-like or myorelaxant effects, despite reducing locomotor activity in the animals at all doses tested. In addition, the lowest dose increased the latency to onset of the first epileptic seizure, and the time to death. In addition to decreasing the mortality percentage in mice submitted to the pilocarpine model. In this same model, pretreatment with the lowest dose of the compound decreased the hippocampal concentrations of thiobarbituric acid and nitrite, and partially restored striatal concentrations of noradrenaline, dopamine, and serotonin. Taken together, the results suggest that trans,trans-farnesol presents a central depressant effect which contributes to its antiepileptic action which, in turn, seems to be mediated by the antagonism of muscarinic cholinergic receptors, reduction of oxidative stress. and modulation of noradrenaline, dopamine and serotonin concentrations in the central nervous system.

Modulation of Gq/PLC-Mediated Signaling by Acute Lithium Exposure

Although lithium has long been one of the most widely used pharmacological agents in psychiatry, its mechanisms of action at the cellular and molecular levels remain poorly understood. One of the targets of Li+ is the phosphoinositide pathway, but whereas the impact of Li+ on inositol lipid metabolism is well documented, information on physiological effects at the cellular level is lacking. We examined in two mammalian cell lines the effect of acute Li+ exposure on the mobilization of internal Ca2+ and phospholipase C (PLC)-dependent membrane conductances. We first corroborated by Western blots and immunofluorescence in HEK293 cells the presence of key signaling elements of a muscarinic PLC pathway (M1AchR, Gq, PLC-β1, and IP3Rs). Stimulation with carbachol evoked a dose-dependent mobilization of Ca, as determined with fluorescent indicators. This was due to release from internal stores and proved susceptible to the PLC antagonist U73122. Li+ exposure reproducibly potentiated the Ca response in a concentration-dependent manner extending to the low millimolar range. To broaden those observations to a neuronal context and probe potential Li modulation of electrical signaling, we next examined the cell line SHsy5y. We replicated the potentiating effects of Li on the mobilization of internal Ca, and, after characterizing the basic properties of the electrical response to cholinergic stimulation, we also demonstrated an equally robust upregulation of muscarinic membrane currents. Finally, by directly stimulating the signaling pathway at different links downstream of the receptor, the site of action of the observed Li effects could be narrowed down to the G protein and its interaction with PLC-β. These observations document a modulation of Gq/PLC/IP3-mediated signaling by acute exposure to lithium, reflected in distinct physiological changes in cellular responses.

Effects of the putative lithium mimetic ebselen on pilocarpine-induced neural activity

Lithium, commonly used to treat bipolar disorder, potentiates the ability of the muscarinic agonist pilocarpine to induce seizures in rodents. As this potentiation by lithium is reversed by the administration of myo-inositol, the potentiation may be mediated by inhibition of inositol monophosphatase (IMPase), a known target of lithium. Recently, we demonstrated that ebselen is a 'lithium mimetic' in regard to behaviours in both mice and man. Ebselen inhibits IMPase in vitro and lowers myo-inositol in vivo in the brains of mice and men, making ebselen the only known inhibitor of IMPase, other than lithium, that penetrates the blood-brain barrier. Our objective was to determine the effects of ebselen on sensitization to pilocarpine-induced seizures and neural activity. We administered ebselen at different doses and time intervals to mice, followed by injection of a sub-seizure dose of pilocarpine. We assessed seizure and neural activity by a subjective seizure rating scale, by monitoring tremors, and by induction of the immediate early gene c-fos. In contrast to lithium, ebselen did not potentiate the ability of pilocarpine to induce seizures. Unexpectedly, ebselen inhibited pilocarpine-induced tremor as well as pilocarpine-induced increases in c-fos mRNA levels. Both lithium and ebselen inhibit a common target, IMPase, but only lithium potentiates pilocarpine-induced seizures, consistent with their polypharmacology at diverse molecular targets. We conclude that ebselen does not potentiate pilocarpine-induced seizures and instead, reduces pilocarpine-mediated neural activation. This lack of potentiation of muscarinic sensitization may be one reason for the lack of side-effects observed with ebselen treatment clinically.

Cholinergic and Glutaminergic Excitation of Neuronal Cells

Excessive cholinergic or glutaminergic brain stimulation may result in seizures, excitotoxicity and neuronal damage. Cholinergic neuronal excitation is mediated via muscarinic receptors which couple with GTP-binding proteins (G–proteins), activate phospholipase C, and produce the inositol lipid second messengers, inositol-1,4,5,-trisphosphate (InsP3) and diacyl-glycerol (DG). InsP3 facilitates intracellular Ca2+ metabolism and DG activates protein kinase C (PKC). Glutaminergic neuronal stimulation is mediated through ionotropic N-methyl-D-aspartate (NMDA) receptors, which increase Ca2+ influx, and kainate α-amino-3-hydroxy-5-methyl-4-isoxalolproprionic acid receptors, which mainly regulate Na+ fluxes. Glutaminergic metabotropic receptors are also coupled to a G-protein, and their stimulation activates neurons through increased production of InsP3 and DG. A salient feature in glutamate-induced excitotoxicity is the induction of an oxidative burst, subsequent oxidative stress, and damage to the neurons. The glutamate-induced oxidative burst can be amplified by lead, a direct activator of PKC, and the oxidative burst can be blocked by a PKC inhibitor, suggesting an important role for PKC. Carbachol also induces an oxidative burst in neuronal cells and this is associated with elevations of free intracellular calcium. The ability of an NMDA receptor antagonist, AP-5, to block carbachol-induced elevations of free intracellular calcium, suggests that activation of muscarinic receptors is associated with a simultaneous glutamate receptor activation. Thus, cross-talk between cholinergic muscarinic and glutaminergic receptors may be an important contributing factor in cholinergic and glutaminergic excitotoxicity.

Sumatriptan reduces severity of status epilepticus induced by lithium-pilocarpine through nitrergic transmission and 5-HT1B/D receptors in rats: A pharmacological-based evidence

Status epilepticus (SE) is a life-threatening neurologic disorder that can be as both cause and consequence of neuroinflammation. In addition to previous reports on anti-inflammatory property of the anti-migraine medication sumatriptan, we have recently shown its anticonvulsive effects on pentylenetetrazole-induced seizure in mice. In the present study, we investigated further (i) the effects of sumatriptan in the lithium-pilocarpine SE model in rats, and (ii) the possible involvement of nitric oxide (NO), 5-hydroxytryptamin 1B/1D (5-HT_1B/1D ) receptor, and inflammatory pathways in such effects of sumatriptan. Status epilepticus was induced by lithium chloride (127 mg/kg, i.p) and pilocarpine (60 mg/kg, i.p.) in Wistar rats. While SE induction increased SE scores and mortality rate, sumatriptan (0.001-1 mg/kg, i.p.) improved it (P < 0.001). Administration of the selective 5-HT_1B/1D antagonist GR-127935 (0.01 mg/kg, i.p.) reversed the anticonvulsive effects of sumatriptan (0.01 mg/kg, i.p.). Although both tumor necrosis factor-α (TNF-α) and NO levels were markedly elevated in the rats' brain tissues post-SE induction, pre-treatment with sumatriptan significantly reduced both TNF-α (P < 0.05) and NO (P < 0.001) levels. Combined GR-127935 and sumatriptan treatment inhibited these anti-inflammatory effects of sumatriptan, whereas combined non-specific NOS (L-NAME) or selective neuronal NOS (7-nitroindazole) inhibitors and sumatriptan further reduced NO levels. In conclusion, sumatriptan exerted a protective effect against the clinical manifestations and mortality rate of SE in rats which is possibly through targeting 5-HT_1B/1D receptors, neuroinflammation, and nitrergic transmission.

The evolution of the pilocarpine animal model of status epilepticus

The pilocarpine animal model of status epilepticus is a well-established, clinically translatable model that satisfies all of the criteria essential for an animal model of status epilepticus: a latency period followed by spontaneous recurrent seizures, replication of behavioural, electrographic, metabolic, and neuropathological changes, as well as, pharmacoresistance to anti-epileptic drugs similar to that observed in human status epilepticus. However, this model is also characterized by high mortality rates and studies in recent years have also seen difficulties in seizure induction due to pilocarpine resistant animals. This can be attributed to differences in rodent strains, species, gender, and the presence of the multi-transporter, P-glycoprotein at the blood brain barrier. The current paper highlights the various alterations made to the original pilocarpine model over the years to combat both the high mortality and low induction rates. These range from the initial lithium-pilocarpine model to the more recent Reduced Intensity Status Epilepticus (RISE) model, which finally brought the mortality rates down to 1%. These modifications are essential to improve animal welfare and future experimental outcomes.

Early endocannabinoid system activation attenuates behavioral impairments induced by initial impact but does not prevent epileptogenesis in lithium-pilocarpine status epilepticus model

Mood and anxiety disorders, as well as memory impairments, are important factors affecting quality of life in patients with epilepsy and can influence the antiepileptic therapy. Clinical studies of psychiatric comorbidities are quite complicated to design and interpret, so animal studies of behavioral impairments associated with seizures can be of use. We investigated the effect of early administration of endocannabinoid receptor agonist WIN-55,212-2 on the development of spontaneous seizures, long-term behavioral and memory impairments, and neurodegeneration in the hippocampus on the lithium-pilocarpine model of status epilepticus (SE). We also studied the role of spontaneous seizures in the development of pathologic consequences of the SE. Our results showed that behavioral impairments found in the elevated plus maze test depended mostly on the consequences of SE itself and not on the development of spontaneous seizures while hyperactivity in the open-field test and light-dark chamber was more prominent in rats with spontaneous seizures. Administration of WIN-55,212-2 decreased emotional behavior in the elevated plus maze but did not affect hyperactive behavior in the open-field test. Spatial memory impairment developed both in the presence or absence of spontaneous seizures and was not affected by administration of WIN-55,212-2. Both administration of endocannabinoid receptor agonist WIN-55,212-2 and the presence of spontaneous seizures affected SE-induced neuronal loss in the hippocampus.

Treatment of early life status epilepticus: What can we learn from animal models?

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

Animal models of status epilepticus and temporal lobe epilepsy: a narrative review

Temporal lobe epilepsy (TLE) is the chronic and pharmacoresistant form of epilepsy observed in humans. The current literature is insufficient in explicating the comprehensive mechanisms underlying its pathogenesis and advancement. Consequently, the development of a suitable animal model mimicking the clinical characteristics is required. Further, the relevance of status epilepticus (SE) to animal models is dubious. SE occurs rarely in people; most epilepsy patients never experience it. The present review summarizes the established animal models of SE and TLE, along with a brief discussion of the animal models that have the distinctiveness and carries the possibility to be developed as effective models for TLE. The review not only covers the basic requirements, mechanisms, and methods of induction of each model but also focuses upon their major limitations and possible modifications for their future use. A detailed discussion on chemical, electrical, and hypoxic/ischemic models as well as a brief explanation on the genetic models, most of which are characterized by development of SE followed by neurodegeneration, is presented.

A Novel Neuroprotective Mechanism for Lithium That Prevents Association of the p75NTR-Sortilin Receptor Complex and Attenuates proNGF-Induced Neuronal Death In Vitro and In Vivo

Neurotrophins play critical roles in the survival, maintenance and death of neurons. In particular, proneurotrophins have been shown to mediate cell death following brain injury induced by status epilepticus (SE) in rats. Previous studies have shown that pilocarpine-induced seizures lead to increased levels of proNGF, which binds to the p75NTR-sortilin receptor complex to elicit apoptosis. A screen to identify compounds that block proNGF binding and uptake into cells expressing p75 and sortilin identified lithium citrate as a potential inhibitor of proNGF and p75NTR-mediated cell death. In this study, we demonstrate that low, submicromolar doses of lithium citrate effectively inhibited proNGF-induced cell death in cultured neurons and protected hippocampal neurons following pilocarpine-induced SE in vivo. We analyzed specific mechanisms by which lithium citrate afforded neuroprotection and determined that lithium citrate prevented the association and internalization of the p75NTR-sortilin receptor complex. Our results demonstrate a novel mechanism by which low-dose treatments of lithium citrate are effective in attenuating p75NTR-mediated cell death in vitro and in vivo.

The relevance of inter- and intrastrain differences in mice and rats and their implications for models of seizures and epilepsy

It is becoming increasingly clear that the genetic background of mice and rats, even in inbred strains, can have a profound influence on measures of seizure susceptibility and epilepsy. These differences can be capitalized upon through genetic mapping studies to reveal genes important for seizures and epilepsy. However, strain background and particularly mixed genetic backgrounds of transgenic animals need careful consideration in both the selection of strains and in the interpretation of results and conclusions. For instance, mice with targeted deletions of genes involved in epilepsy can have profoundly disparate phenotypes depending on the background strain. In this review, we discuss findings related to how this genetic heterogeneity has and can be utilized in the epilepsy field to reveal novel insights into seizures and epilepsy. Moreover, we discuss how caution is needed in regards to rodent strain or even animal vendor choice, and how this can significantly influence seizure and epilepsy parameters in unexpected ways. This is particularly critical in decisions regarding the strain of choice used in generating mice with targeted deletions of genes. Finally, we discuss the role of environment (at vendor and/or laboratory) and epigenetic factors for inter- and intrastrain differences and how such differences can affect the expression of seizures and the animals' performance in behavioral tests that often accompany acute and chronic seizure testing.

Which component of treatment is important for changes of cortical epileptic afterdischarges after status epilepticus in immature rats?

Role of lithium chloride and paraldehyde in acute changes after lithium-pilocarpine status epilepticus (SE) induced at postnatal day 12 was studied in 15-day-old rats. In addition to SE group four other groups were formed: naïve animals without any injection, lithium chloride group, paraldehyde group and lithium-paraldehyde group. Cortical epileptic afterdischarges (CxADs) induced by increasing intensities of stimulation current were used as a measure of excitability. SE animals did not exhibit any change in duration of CxADs with increasing stimulation intensity in contrast to naïve control with a progressive prolongation of CxAD. LiCl group was similar to SE rats whereas paraldehyde and lithium-paraldehyde groups exhibited some progress in duration of ADs. Lithium chloride participates in short-term changes of CxADs after SE. Paraldehyde and combination of lithium and paraldehyde are similar to naïve controls.

Anticonvulsive Effects of Licofelone on Status Epilepticus Induced by Lithium-pilocarpine in Wistar Rats: a Role for Inducible Nitric Oxide Synthase

Background and Purpose

Status epilepticus (SE) is a neurological disorder with high prevalence and mortality rates, requiring immediate intervention. Licofelone is a cyclooxygenase (COX) and 5-lipoxygenase (5-LOX) inhibitor, which its effectiveness to treat osteoarthritis has been approved. Increasing evidence suggests an involvement of COX and LOX enzymes in epileptic disorders. Thus, in the present study we investigate possible effects of licofelone on prevention and termination of SE. We also evaluated whether the nitrergic system could participate in this effect of licofelone.

Methods

We have utilized lithium-pilocarpine model of SE in adult Wistar rats to assess the potential effect of licofelone on seizure susceptibility. Licofelone was administered 1 h before pilocarpine. To evaluate probable role of nitric oxide (NO) system, L-arginine (60 mg/kg, i.p.), as a NO precursor; L-NAME (15 mg/kg, i.p.), as a non-selective nitric oxide synthase (NOS) inhibitor; aminoguanidine (100 mg/kg, i.p.), as an inducible NOS (iNOS) inhibitor and 7-nitroindazole (60 mg/kg, i.p.), as a neuronal NOS inhibitor were injected 15 min before licofelone. Also, licofelone and diazepam 10 mg/kg were administered 30 minutes after onset of SE.

Results

Pre-treatment with licofelone at the dosage of 10 mg/kg, significantly prevented the onset of SE in all subjects (p < 0.001). L-arginine significantly inverted this anticonvulsant effect (p < 0.05). However, L-NAME and aminoguanidine, potentiated the anticonvulsant effect of licofelone (p < 0.05, p < 0.01). Licofelone could not terminate seizures after onset which was terminated by diazepam.

Conclusions

Our findings showed that anticonvulsive effects of licofelone on SE could be mediated by iNOS. Also, we suggest that COX/5-LOX activation is possibly required in the initial stage of onset but SE recruits extra excitatory pathways with prolongation.

The pilocarpine model of temporal lobe epilepsy: Marked intrastrain differences in female Sprague-Dawley rats and the effect of estrous cycle

Rat strains such as Sprague-Dawley (SD) or Wistar are widely used in epilepsy research, including popular models of temporal lobe epilepsy in which spontaneous recurrent seizures (SRS), hippocampal damage, and behavioral alterations develop after status epilepticus (SE). Such rats are randomly outbred, and outbred strains are known to be genetically heterogeneous populations with a high intrastrain variation. Intrastrain differences may be an important reason for discrepancies between studies from different laboratories, but the extent to which such differences affect the development of seizures, neurodegeneration, and psychopathology in post-SE models of epilepsy has received relatively little attention. In the present study, we induced SE by systemic administration of pilocarpine (following pretreatment with lithium) in SD rats from different breeders (Harlan, Charles River [CRL], Taconic) as well as different breeding locations of the same breeder (Harlan-Winkelmann [HW] in Germany vs. Harlan Laboratories [HL] in the Netherlands). Some experiments were also performed in Wistar rats. Pilocarpine was administered by a ramp-up dosing protocol that allows determining interindividual differences in susceptibility to the convulsant. Marked intrastrain differences in induction of SE and its long-term consequences were found. Sprague-Dawley rats from HW were significantly more sensitive to SE induction than all other SD substrains. The majority of SD rats from different vendors developed SRS after SE except SD rats from HL. The CRL-SD rats markedly differed in basal behavior and SE-induced behavioral alterations from other SD substrains. Susceptibility to pilocarpine was hardly affected by the estrous cycle. The marked intrastrain differences provide an interesting tool to study the impact of genetic and environmental factors on seizure susceptibility, epileptogenesis, and relationship between behavior and epilepsy and vice versa.

A Low Mortality, High Morbidity Reduced Intensity Status Epilepticus (RISE) Model of Epilepsy and Epileptogenesis in the Rat

Animal models of acquired epilepsies aim to provide researchers with tools for use in understanding the processes underlying the acquisition, development and establishment of the disorder. Typically, following a systemic or local insult, vulnerable brain regions undergo a process leading to the development, over time, of spontaneous recurrent seizures. Many such models make use of a period of intense seizure activity or status epilepticus, and this may be associated with high mortality and/or global damage to large areas of the brain. These undesirable elements have driven improvements in the design of chronic epilepsy models, for example the lithium-pilocarpine epileptogenesis model. Here, we present an optimised model of chronic epilepsy that reduces mortality to 1% whilst retaining features of high epileptogenicity and development of spontaneous seizures. Using local field potential recordings from hippocampus in vitro as a probe, we show that the model does not result in significant loss of neuronal network function in area CA3 and, instead, subtle alterations in network dynamics appear during a process of epileptogenesis, which eventually leads to a chronic seizure state. The model’s features of very low mortality and high morbidity in the absence of global neuronal damage offer the chance to explore the processes underlying epileptogenesis in detail, in a population of animals not defined by their resistance to seizures, whilst acknowledging and being driven by the 3Rs (Replacement, Refinement and Reduction of animal use in scientific procedures) principles.

Single versus combinatorial therapies in status epilepticus: Novel data from preclinical models

Drug-refractory status epilepticus (RSE) is a major medical emergency with a mortality of up to 40% and the risk of severe long-term consequences. The mechanisms involved in RSE are incompletely understood. Animal models are important in developing treatment strategies for more effective termination of SE and prevention of its long-term outcomes. The pilocarpine and lithium-pilocarpine rat models are widely used in this respect. In these models, resistance to diazepam and other antiseizure drugs (ASDs) develops during SE so that an SE that is longer than 30 min is difficult to suppress. Furthermore, because all ASDs used in SE treatment are much more rapidly eliminated by rodents than by humans, SE recurs several hours after ASD treatment. Long-term consequences include hippocampal damage, behavioral alterations, and epilepsy with spontaneous recurrent seizures. In this review, different rational polytherapies for SE, which are more effective than monotherapies, are discussed, including a novel polytherapy recently developed by our group. Based on data from diverse seizure models, we hypothesized that cholinergic mechanisms are involved in the mechanisms underlying ASD resistance of SE. We, therefore, developed an intravenous drug cocktail, consisting of diazepam, phenobarbital, and the anticholinergic scopolamine. This drug combination irreversibly terminated SE when administered 60, 90, or 120 min after SE onset. The efficacy of this cocktail in terminating SE was comparable with the previously reported efficacy of polytherapies with the glutamate receptor antagonist ketamine. Furthermore, when injected 60 min after SE onset, the scopolamine-containing cocktail prevented development of epilepsy and hippocampal neurodegeneration, which was not observed with high doses of diazepam or a combination of phenobarbital and diazepam. Our data add to the existing preclinical evidence that rational polytherapy can be more effective than monotherapy in the treatment of SE and that combinatorial therapy may offer a clinically useful option for the treatment of RSE. This article is part of a Special Issue entitled "Status Epilepticus".

Pilocarpine-induced convulsive activity is limited by multidrug transporters at the rodent blood-brain barrier

As a result of the growing availability of genetically engineered mouse lines, the pilocarpine post-status epilepticus (SE) model of temporal lobe epilepsy is increasingly used in mice. A discrepancy in pilocarpine sensitivity in FVB/N wild-type versus P-glycoprotein (PGP)-deficient mice precipitated the investigation of the interaction between pilocarpine and two major multidrug transporters at the blood-brain barrier. Doses of pilocarpine necessary for SE induction were determined in male and female wild-type and PGP-deficient mice. Brain and plasma concentrations were measured following low (30-50 mg⋅kg(-1) i.p.) and/or high (200 mg⋅kg(-1) i.p.) doses of pilocarpine in wild-type mice, and mice lacking PGP, breast cancer resistance protein (BCRP), or both transporters, as well as in rats with or without pretreatment with lithium chloride or tariquidar. Concentration equilibrium transport assays (CETA) were performed using cells overexpressing murine PGP or BCRP. Lower pilocarpine doses were necessary for SE induction in PGP-deficient mice. Brain-plasma ratios were higher in mice lacking PGP or PGP and BCRP, which was also observed after pretreatment with tariquidar in mice and in rats. Lithium chloride did not change brain penetration of pilocarpine. CETA confirmed transport of pilocarpine by PGP and BCRP. Pilocarpine is a substrate of PGP and BCRP at the rodent blood-brain barrier, which restricts its convulsive action. Future studies to reveal whether strain differences in pilocarpine sensitivity derive from differences in multidrug transporter expression levels are warranted.

Rapid throughput analysis demonstrates that chemicals with distinct seizurogenic mechanisms differentially alter Ca2+ dynamics in networks formed by hippocampal neurons in culture

Primary cultured hippocampal neurons (HN) form functional networks displaying synchronous Ca(2+) oscillations (SCOs) whose patterns influence plasticity. Whether chemicals with distinct seizurogenic mechanisms differentially alter SCO patterns was investigated using mouse HN loaded with the Ca(2+) indicator fluo-4-AM. Intracellular Ca(2+) dynamics were recorded from 96 wells simultaneously in real-time using fluorescent imaging plate reader. Although quiescent at 4 days in vitro (DIV), HN acquired distinctive SCO patterns as they matured to form extensive dendritic networks by 16 DIV. Challenge with kainate, a kainate receptor (KAR) agonist, 4-aminopyridine (4-AP), a K(+) channel blocker, or pilocarpine, a muscarinic acetylcholine receptor agonist, caused distinct changes in SCO dynamics. Kainate at <1 µM produced a rapid rise in baseline Ca(2+) (Phase I response) associated with high-frequency and low-amplitude SCOs (Phase II response), whereas SCOs were completely repressed with >1 µM kainate. KAR competitive antagonist CNQX [6-cyano-7-nitroquinoxaline-2,3-dione] (1-10 µM) normalized Ca(2+) dynamics to the prekainate pattern. Pilocarpine lacked Phase I activity but caused a sevenfold prolongation of Phase II SCOs without altering either their frequency or amplitude, an effect normalized by atropine (0.3-1 µM). 4-AP (1-30 µM) elicited a delayed Phase I response associated with persistent high-frequency, low-amplitude SCOs, and these disturbances were mitigated by pretreatment with the KCa activator SKA-31 [naphtho[1,2-d]thiazol-2-ylamine]. Consistent with its antiepileptic and neuroprotective activities, nonselective voltage-gated Na(+) and Ca(2+) channel blocker lamotrigine partially resolved kainate- and pilocarpine-induced Ca(2+) dysregulation. This rapid throughput approach can discriminate among distinct seizurogenic mechanisms that alter Ca(2+) dynamics in neuronal networks and may be useful in screening antiepileptic drug candidates.

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

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

Dynamics of hippocampal acetylcholine release during lithium-pilocarpine-induced status epilepticus in rats

The lithium-pilocarpine model is a rat model of epilepsy that mimics status epilepticus in humans. Here, we report changes of acetylcholine (ACh) release in the hippocampus before, during and after status epilepticus as monitored by microdialysis in unanesthetized rats. Administration of pilocarpine (30 mg/kg s.c.) to rats pretreated with lithium chloride (127 mg/kg i.p.) caused a massive, six-fold increase of hippocampal ACh release, paralleling the development of tonic seizures. When seizures were stopped by administration of diazepam (10 mg/kg i.p.) or ketamine (75 mg/kg i.p.), ACh levels returned to normal. Extracellular concentrations of glutamate remained unchanged during this procedure. Administration of atropine (1 mg/kg i.p.) 2 h after pilocarpine caused a further increase of ACh but did not affect seizures, whereas injection of mecamylamine (5 mg/kg i.p.) reduced ACh levels and seizures in a delayed fashion. Local infusion of tetrodotoxin, 1 μM locally) or hemicholinium (10 μM locally) strongly reduced ACh release and had delayed effects on seizures. Administration of glucose or inositol (250 mg/kg each i.p.) had no visible consequences. In parallel experiments, lithium-pilocarpine-induced status epilepticus also enhanced striatal ACh release, and hippocampal ACh levels equally increased when status epilepticus was induced by kainate (30 mg/kg i.p.). Taken together, our results demonstrate that seizure development in status epilepticus models is accompanied by massive increases of extracellular ACh, but not glutamate, levels. Treatments that reduce seizure activity also reliably reduce extracellular ACh levels.

A potassium leak channel silences hyperactive neurons and ameliorates status epilepticus

OBJECTIVE

To develop a constitutively active K(+) leak channel using TREK-1 (TWIK-related potassium channel 1; TREK-M) that is resistant to compensatory down-regulation by second messenger cascades, and to validate the ability of TREK-M to silence hyperactive neurons using cultured hippocampal neurons. To test if adenoassociated viral (AAV) delivery of TREK-M could reduce the duration of status epilepticus and reduce neuronal death induced by lithium-pilocarpine administration.

METHODS

Molecular cloning techniques were used to engineer novel vectors to deliver TREK-M via plasmids, lentivirus, and AAV using a cytomegalovirus (CMV)-enhanced GABRA4 promoter. Electrophysiology was used to characterize the activity and regulation of TREK-M in human embryonic kidney (HEK-293) cells, and the ability to reduce spontaneous activity in cultured hippocampal neurons. Adult male rats were injected bilaterally with self-complementary AAV particles composed of serotype 5 capsid into the hippocampus and entorhinal cortex. Lithium-pilocarpine was used to induce status epilepticus. Seizures were monitored using continuous video-electroencephalography (EEG) monitoring. Neuronal death was measured using Fluoro-Jade C staining of paraformaldehyde-fixed brain slices.

RESULTS

TREK-M inhibited neuronal firing by hyperpolarizing the resting membrane potential and decreasing input resistance. AAV delivery of TREK-M decreased the duration of status epilepticus by 50%. Concomitantly it reduced neuronal death in areas targeted by the AAV injection.

SIGNIFICANCE

These findings demonstrate that TREK-M can silence hyperexcitable neurons in the brain of epileptic rats and treat acute seizures. This study paves the way for an alternative gene therapy treatment of status epilepticus, and provides the rationale for studies of AAV-TREK-M's effect on spontaneous seizures in chronic models of temporal lobe epilepsy.

Experimental models of status epilepticus and neuronal injury for evaluation of therapeutic interventions

This article describes current experimental models of status epilepticus (SE) and neuronal injury for use in the screening of new therapeutic agents. Epilepsy is a common neurological disorder characterized by recurrent unprovoked seizures. SE is an emergency condition associated with continuous seizures lasting more than 30 min. It causes significant mortality and morbidity. SE can cause devastating damage to the brain leading to cognitive impairment and increased risk of epilepsy. Benzodiazepines are the first-line drugs for the treatment of SE, however, many people exhibit partial or complete resistance due to a breakdown of GABA inhibition. Therefore, new drugs with neuroprotective effects against the SE-induced neuronal injury and degeneration are desirable. Animal models are used to study the pathophysiology of SE and for the discovery of newer anticonvulsants. In SE paradigms, seizures are induced in rodents by chemical agents or by electrical stimulation of brain structures. Electrical stimulation includes perforant path and self-sustaining stimulation models. Pharmacological models include kainic acid, pilocarpine, flurothyl, organophosphates and other convulsants that induce SE in rodents. Neuronal injury occurs within the initial SE episode, and animals exhibit cognitive dysfunction and spontaneous seizures several weeks after this precipitating event. Current SE models have potential applications but have some limitations. In general, the experimental SE model should be analogous to the human seizure state and it should share very similar neuropathological mechanisms. The pilocarpine and diisopropylfluorophosphate models are associated with prolonged, diazepam-insensitive seizures and neurodegeneration and therefore represent paradigms of refractory SE. Novel mechanism-based or clinically relevant models are essential to identify new therapies for SE and neuroprotective interventions.

Optogenetic delay of status epilepticus onset in an in vivo rodent epilepsy model

Epilepsy is a devastating disease, currently treated with medications, surgery or electrical stimulation. None of these approaches is totally effective and our ability to control seizures remains limited and complicated by frequent side effects. The emerging revolutionary technique of optogenetics enables manipulation of the activity of specific neuronal populations in vivo with exquisite spatiotemporal resolution using light. We used optogenetic approaches to test the role of hippocampal excitatory neurons in the lithium-pilocarpine model of acute elicited seizures in awake behaving rats. Hippocampal pyramidal neurons were transduced in vivo with a virus carrying an enhanced halorhodopsin (eNpHR), a yellow light activated chloride pump, and acute seizure progression was then monitored behaviorally and electrophysiologically in the presence and absence of illumination delivered via an optical fiber. Inhibition of those neurons with illumination prior to seizure onset significantly delayed electrographic and behavioral initiation of status epilepticus, and altered the dynamics of ictal activity development. These results reveal an essential role of hippocampal excitatory neurons in this model of ictogenesis and illustrate the power of optogenetic approaches for elucidation of seizure mechanisms. This early success in controlling seizures also suggests future therapeutic avenues.

Brain regional heterogeneity and toxicological mechanisms of organophosphates and carbamates

The brain is a well-organized, yet highly complex, organ in the mammalian system. Most investigators use the whole brain, instead of a selected brain region(s), for biochemical analytes as toxicological endpoints. As a result, the obtained data is often of limited value, since their significance is compromised due to a reduced effect, and the investigators often arrive at an erroneous conclusion(s). By now, a plethora of knowledge reveals the brain regional variability for various biochemical/neurochemical determinants. This review describes the importance of brain regional heterogeneity in relation to cholinergic and noncholinergic determinants with particular reference to organophosphate (OP) and carbamate pesticides and OP nerve agents.

Exposure to nerve agents: from status epilepticus to neuroinflammation, brain damage, neurogenesis and epilepsy

Epilepsy is a common neurological disorder characterized by an initial injury due to stroke, traumatic brain injury, brain infection, or febrile seizures causing status epilepticus (SE). This phenomenon precedes recurrent (secondary) seizures, the latent period (period without seizures) and downstream appearance of spontaneous recurrent seizures (SRS). Epilepsy inducers include the organophosphorous (OP) compounds modified as chemical warfare nerve agents, such as soman. SE induced by soman is a result of cholinergic system hyperactivity caused by the irreversible inhibition of acetylcholinesterase, and the subsequent increase in the amount of the neurotransmitter acetylcholine at central and peripheral sites. SE leads to profound, permanent, complex and widespread brain damage and associated cognitive and behavioral deficits, accompanied by impaired neurogenesis. Several anticonvulsant and neuroprotective strategies have been studied in order to avoid the epileptogenesis which occurs after SE caused by soman exposure. In recent studies, we showed that SRS occur post-soman exposure and neuropathology can be reduced with diazepam (DZP) and valproic acid (VPA) when administered in combination treatment. These effects are accompanied by neurogenesis seen 15 days post-exposure in the hippocampal dentate gyrus (DG). This review discusses several findings about epilepsy induced by soman exposure such as behavioral changes, EEG anomalies, neuropathology, neuroinflammation, neurogenesis, possible circuitry changes and current strategies for treatment. The soman seizure model is an important model of temporal lobe epilepsy (TLE) and comparable in certain respects with well studied models in the literature such as pilocarpine and kainic acid. All these models together allow for a greater understanding of the different mechanisms of seizure induction, propagation and options for treatment. These studies are very necessary for current military and civilian treatment regimens, against OP nerve agent exposure, which fail to prevent SE resulting in severe neuropathology and epilepsy.

Selective loss and axonal sprouting of GABAergic interneurons in the sclerotic hippocampus induced by LiCl-pilocarpine

In this study, we performed immunohistochemistry for somatostatin (SS), neuropeptide Y (NPY), and parvalbumin (PV) in LiCl-pilocarpine-treated rats to observe quantitative changes and axonal sprouting of GABAergic interneurons in the hippocampus, especially in the sclerotic hippocampus. Fluoro-Jade B (FJB) was performed to detect the specific degeneration of GABAergic interneurons. Compared with age-matched control rats, there were fewer SS/NPY/PV-immunoreactive (IR) interneurons in the hilus of the sclerotic hippocampus in pilocarpine-treated rats; hilar dentritic inhibitory interneurons were most vulnerable. FJB stain revealed degeneration was evident at 2 months after status epilepticus. Some SS-IR and NPY-IR interneurons were also stained for FJB, but there was no evidence of degeneration of PV-IR interneurons. Axonal sprouting of GABAergic interneurons was present in the hippocampus of epileptic rats, and a dramatic increase of SS-IR fibers was observed throughout all layers of CA1 region in the sclerotic hippocampus. These results confirm selective loss and degeneration of a specific subset of GABAergic interneurons in specific subfields of the hippocampus. Axonal sprouting of inhibitory GABAergic interneurons, especially numerous increase of SS-IR neutrophils within CA1 region of the sclerotic hippocampus, may constitute the aberrant inhibitory circum and play a significant role in the generation and compensation of temporal lobe epilepsy.

Lessons from the laboratory: the pathophysiology, and consequences of status epilepticus

Status epilepticus (SE) is the most common neurologic emergency of childhood. Experimental models parallel several clinical features of SE including (1) treatment is complicated by an increasing probability that benzodiazepines will fail with increasing seizure duration and (2) outcome varies with age and etiology. Studies using these models showed that the activity-dependent trafficking of GABA(A) receptors contributes in part to the progressive decline in GABA-mediated inhibition and the failure of the benzodiazepines. Furthermore, laboratory studies have provided evidence that age and inciting stimulus interact to determine the neuronal circuits activated during SE (ie, functional anatomy) and that differences in functional anatomy can partially account for variations in SE outcome. Future laboratory studies are likely to provide an additional understanding of the cellular and molecular mechanisms that underlie SE and its consequences. Such studies are necessary in the development of rational emergent therapy for SE and its long-term outcomes.

Neuronal damage and memory deficits after seizures are reversed by ascorbic acid?

The objective of the present study was to evaluate the neuroprotective effects of ascorbic acid (AA) in rats, against the neuronal damage and memory deficit caused by seizures. Wistar rats were treated with 0.9% saline (i.p., control group), ascorbic acid (500 mg/kg, i.p., AA group), pilocarpine (400 mg/kg, i.p., pilocarpine group), and the association of ascorbic acid (500 mg/kg, i.p.) plus pilocarpine (400 mg/kg, i.p.), 30 min before of administration of ascorbic acid (AA plus pilocarpine group). After the treatments all groups were observed for 24 h. Pilocarpine group presented seizures which progressed to status epilepticus in 75% of the animals. Pretreatment with AA led to a reduction of 50% of this rate. Results showed that pretreatment with AA did not alter reference memory when compared to a control group. In the working memory task, we observed a significant day's effect with important differences between control, pilocarpine and AA plus pilocarpine groups. Pilocarpine and AA plus pilocarpine groups had 81 and 16% of animals with brain injury, respectively. In the hippocampus of pilocarpine animals, it was detected an injury of 60%. As for the animals tested with AA plus pilocarpine, the hippocampal region of the group had a reduction of 43% in hippocampal lesion. Our findings suggest that seizures caused cognitive dysfunction and neuronal damage that might be related, at least in part, to the neurological problems presented by epileptic patients. AA can reverse cognitive dysfunction observed in rats with seizures as well as decrease neuronal injury in rat hippocampus.

Lipoic acid effects on monoaminergic system after pilocarpine-induced seizures

Systemic injection of pilocarpine has been shown to induce recurrent seizures and epileptic discharges demonstrated by EEG monitoring. It also has been reported that antioxidants are able to diminish or prevent the occurrence of epileptic discharges induced by pilocarpine through the inhibition of free radical formation and neurotransmitter metabolic alterations. The purpose of this work was to determine the effects of lipoic acid (LA) on the levels of dopamine (DA), serotonin (5-HT), norepinephrine (NE) and subsequent metabolites in the hippocampus of rats after seizure induction by pilocarpine. Seizures dramatically decreased the levels of DA, 5-hydroxyindoleacetic acid (5-HIAA) and NE, whereas significantly increased the levels of neurotransmitter metabolites. The administration of lipoic acid before seizure induction resulted in normalized levels of DA and 5-HA. However, the lipoic acid administration in similar conditions produced a reduction of the metabolites levels when compared with the pilocarpine group. These results suggest that the establishment of acute phase of seizures induced by pilocarpine might be produced by consequent the activation of serotonergic neurons. In addition, the lipoic acid inhibits hyperactivity of this system during the installation of pilocarpine-induced seizures.

Epileptogenesis in the immature brain: emerging mechanisms

Epileptogenesis is defined as the process of developing epilepsy-a disorder characterized by recurrent seizures-following an initial insult. Seizure incidence during the human lifespan is at its highest in infancy and childhood. Animal models of epilepsy and human tissue studies suggest that epileptogenesis involves a cascade of molecular, cellular and neuronal network alterations. Within minutes to days following the initial insult, there are acute early changes in neuronal networks, which include rapid alterations to ion channel kinetics as a result of membrane depolarization, post-translational modifications to existing functional proteins, and activation of immediate early genes. Subacute changes occur over hours to weeks, and include transcriptional events, neuronal death and activation of inflammatory cascades. The chronic changes that follow over weeks to months include anatomical changes, such as neurogenesis, mossy fiber sprouting, network reorganization, and gliosis. These epileptogenic processes are developmentally regulated and might contribute to differences in epileptogenesis between adult and developing brains. Here we review the factors responsible for enhanced seizure susceptibility in the developing brain, and consider age-specific mechanisms of epileptogenesis. An understanding of these factors could yield potential therapeutic targets for the prevention of epileptogenesis and also provide biomarkers for identifying patients at risk of developing epilepsy or for monitoring disease progression.

Acute neuroprotection to pilocarpine-induced seizures is not sustained after traumatic brain injury in the developing rat

Following CNS injury there is a period of vulnerability when cells will not easily tolerate a secondary insult. However recent studies have shown that following traumatic brain injury (TBI), as well as hypoxic-ischemic injuries, the CNS may experience a period of protection termed "preconditioning." While there is literature characterizing the properties of vulnerability and preconditioning in the adult rodent, there is an absence of comparable literature in the developing rat. To determine if there is a window of vulnerability in the developing rat, post-natal day 19 animals were subjected to a severe lateral fluid percussion injury followed by pilocarpine (Pc)-induced status epilepticus at 1, 6 or 24 h post TBI. During the first 24 h after TBI, the dorsal hippocampus exhibited less status epilepticus-induced cell death than that normally seen following Pc administration alone. Instead of producing a state of hippocampal vulnerability to activation, TBI produced a state of neuroprotection. However, in a second group of animals evaluated 20 weeks post injury, double-injured animals were statistically indistinguishable in terms of seizure threshold, mossy fiber sprouting and cell survival when compared to those treated with Pc alone. TBI, therefore, produced a temporary state of neuroprotection from seizure-induced cell death in the developing rat; however, this ultimately conferred no long-term protection from altered hippocampal circuit rearrangements, enhanced excitability or later convulsive seizures.

Intrastrain differences in seizure susceptibility, pharmacological response and basal neurochemistry of Wistar rats

Reliable well-characterised animal models of seizures are necessary in order to better understand the underlying pathophysiological mechanisms as well as to screen potential anticonvulsant drugs. We currently use the focal pilocarpine model as an acute limbic seizure model. Due to breeding problems at the vendor, and apparent changes in pilocarpine-induced seizure susceptibility, we were forced to change breeding locations and vendors over a period of 2 years. Male Wistar rats were either purchased from two breeding locations of Charles River Laboratories (France and Germany), or obtained from Harlan Laboratories (The Netherlands). In the present retrospective study we evaluated the impact of these vendor changes on ketamine dosing to establish anaesthesia, on pilocarpine-induced seizure susceptibility, and on basal extracellular hippocampal noradrenaline, dopamine, serotonin, gamma-amino butyric acid, and glutamate levels of all pilocarpine-treated rats included in our studies. Significant differences were present in all of the parameters analyzed. This study clearly illustrates that intrastrain differences do exist from one vendor/breeding location to another, or even between rats from the same breeding location.

Pilocarpine vs. lithium-pilocarpine for induction of status epilepticus in mice: development of spontaneous seizures, behavioral alterations and neuronal damage

In recent years, the pilocarpine model of temporal lobe epilepsy has become the most popular and widely used rodent model of this common and difficult-to-treat type of epilepsy. In this model, the cholinomimetic convulsant pilocarpine is used to induce a status epilepticus, which is followed by hippocampal damage and development of spontaneous recurrent seizures. In rats, pilocarpine is either administered alone or in combination with lithium, which allows a conspicuous reduction of the pilocarpine dose required to induce status epilepticus and results in a higher percentage of animals developing status epilepticus. In mice, lithium has only rarely been used in association with pilocarpine, which prompted us to directly compare the pilocarpine and lithium-pilocarpine models in this species. In contrast to rats, pretreatment with lithium in mice did not potentiate the convulsant effect of pilocarpine. The sequence of behavioral changes observed in mice undergoing a status epilepticus was very similar for lithium-pilocarpine compared to pilocarpine administered alone. All mice that survived status epilepticus developed epilepsy with spontaneous recurrent seizures. Epileptic mice exhibited significant increases of anxiety-related behavior and impaired learning and memory. Neuronal damage resulting from status epilepticus was essentially similar in the lithium-pilocarpine and pilocarpine models and was characterized by severe neurodegeneration in the hippocampal formation, resembling hippocampal sclerosis in mesial temporal lobe epilepsy. Mice in which pilocarpine or lithium-pilocarpine did not induce status epilepticus but only single brief seizures did not show any significant differences in behavior, spatial learning or hippocampal histology from controls. Our data demonstrate that the syndromes produced by pilocarpine and lithium-pilocarpine in mice are behaviorally and neuropathologically indistinguishable, and that both models can be used to study the relationship between seizures, neuronal damage and psychopathology.

Neonatal status epilepticus alters prefrontal-striatal circuitry and enhances methamphetamine-induced behavioral sensitization in adolescence

Neonatal seizures may alter the developing neurocircuitry and cause behavioral abnormalities in adulthood. We found that rats previously subjected to lithium-pilocarpine (LiPC)-induced neonatal status epilepticus (NeoSE) exhibited enhanced behavioral sensitization to methamphetamine (MA) in adolescence. Neurochemically, dopamine (DA) and metabolites were markedly decreased in prefrontal cortex (PFC) and insignificantly changed in striatum by NeoSE, but were increased in both PFC and striatum by NeoSE+MA. Glutamate levels were increased in both PFC and striatum in the NeoSE+MA group. DA turnover, an index of utilization and activity, was increased by NeoSE but reversed by MA in PFC. Gene expression of the regulator of G-protein signaling 4 (RGS4) was downregulated in PFC and striatum by NeoSE and further suppressed by MA. These findings suggest NeoSE affects both dopaminergic and glutamatergic systems in the prefrontal-striatal circuitry that manifests as enhanced behavioral sensitization to MA in adolescence.

Molecular and cellular basis of epileptogenesis in symptomatic epilepsy

Epileptogenesis refers to a process in which an initial brain-damaging insult triggers a cascade of molecular and cellular changes that eventually lead to the occurrence of spontaneous seizures. Cellular alterations include neurodegeneration, neurogenesis, axonal sprouting, axonal injury, dendritic remodeling, gliosis, invasion of inflammatory cells, angiogenesis, alterations in extracellular matrix, and acquired channelopathies. Large-scale molecular profiling of epileptogenic tissue has provided information about the molecular pathways that can initiate and maintain cellular alterations. Currently we are learning how these pathways contribute to postinjury epileptogenesis and recovery process and whether they could be used as treatment targets.

The pilocarpine model of temporal lobe epilepsy

Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

Pentoxifylline ameliorates lithium-pilocarpine induced status epilepticus in young rats

The neuroprotective effects of pentoxifylline (PTX) against lithium-pilocarpine (Li-Pc)-induced status epilepticus (SE) in young rats are described. Animals treated with PTX (0, 20, 40, and 60 mg/kg) before induction of SE were examined for latency to and frequency of SE, behavioral changes, oxidative stress, neurochemical alterations in the hippocampus and striatum, and histological abnormalities in the hippocampus. Treatment with PTX significantly ameliorated the frequency and severity of epileptic seizures in a dose-dependent manner. Our behavioral studies using the elevated plus-maze, rotarod, and water maze tests suggested a significant reduction in anxiety, enhanced motor performance, and improved learning and memory in PTX-treated rats. Li-Pc-induced neuronal cell loss and sprouting of mossy fibers in the hippocampus were also attenuated by PTX. The neuroprotective activity of PTX was accompanied by reduction in oxidative stress and reversal of SE-induced depletion of dopamine and 5-hydroxytryptamine in hippocampus and striatum. The results of this study provide a good rationale to explore the prophylactic/therapeutic potential of PTX in SE.

Mu-calpain mediates hippocampal neuron death in rats after lithium-pilocarpine-induced status epilepticus

Status epilepticus (SE) is a severe clinical manifestation of epilepsy which causes brain damage. The pathological process and underlying mechanisms involved in the programmed cell death (PCD) are still not fully clear. In the current study, rats were induced SE by lithium-pilocarpine administration. Our data showed hippocampal neurons death appeared at 6h after SE and sustained for 7 days. By blotting the activation of mu-calpain and its specific cleavage of nonerythroid alpha-spectrin (alphaSpII) (145 kDa) was evident at 1 and 3 days after SE, which coincided with Bid activation, apoptosis inducing factor (AIF) translocation and cytochrome c release from mitochondria, whereas, activated caspase-3 and caspase-3-specific fragments of alphaSpII (120 kDa) predominantly appeared at 5 and 7 days after SE. Moreover, MDL-28170, a calpain inhibitor, partially rescued the neuron death and attenuated the expression of activated mu-calpain, cleavage of Bid (15 kDa), AIF translocation and cytochrome c release. Taken together, our study indicated that mu-calpain mediated hippocampal neuron PCD is prior to caspase-3 activation. It functioned via translocation of Bid, AIF and cytochrome c release.

Seizures in the developing brain: cellular and molecular mechanisms of neuronal damage, neurogenesis and cellular reorganization

Epilepsy is a common neurological disorder that occurs more frequently in children than in adults. The extent that prolonged seizure activity, i.e. status epilepticus (SE), and repeated, brief seizures affect neuronal structure and function in both the immature and mature brain has been the subject of increasing clinical and experimental research. Earlier studies suggest that seizure-induced effects in the immature brain compared with the adult brain are different. This is manifested as differences in neuronal vulnerability, cellular and synaptic reorganization and regenerative processes. The focus of this review is first to give a short overview of currently used experimental models of epilepsy in immature rats, and then discuss more thoroughly seizure-induced acute and sub-acute cellular and molecular alterations, highlight the contribution of inflammatory-like reactions and intracellular cytoskeleton to the insult, and reveal changes in the structure and function of inhibitory GABA(A) and excitatory glutamate receptors. The role of seizure-activated reparative, plastic processes, synaptic remodelling, neurogenesis as well as the long-term consequences of seizures are briefly outlined. The main emphasis is put on studies carried out in experimental animals, and the focus of interest is the hippocampus, the brain area of great vulnerability in epilepsy. In vitro studies are discussed only to limited extent. Collectively, recent studies suggest that the deleterious effects of seizures may not solely be a consequence of neuronal damage and loss per se, but could be due to the fact that seizures interfere with the highly regulated developmental processes in the immature brain.

Behavioral alterations in the pilocarpine model of temporal lobe epilepsy in mice

Psychiatric disorders frequently occur in patients with epilepsy, but the relationship between epilepsy and psychopathology is poorly understood. Frequent comorbidities in epilepsy patients comprise major depression, anxiety disorders, psychosis and cognitive dysfunction. Animal models of epilepsy, such as the pilocarpine model of acquired epilepsy, are useful to study the relationship between epilepsy and behavioral dysfunctions. However, despite the advantages of mice in studying the genetic underpinning of behavioral alterations in epilepsy, mice have only rarely been used to characterize behavioral correlates of epilepsy. This prompted us to study the behavioral and cognitive alterations developing in NMRI mice in the pilocarpine model of epilepsy, using an anxiety test battery as well as tests for depression, drug-induced psychosis, spatial memory, and motor functions. In order to ensure the occurrence of status epilepticus (SE) and decrease mortality, individual dosing of pilocarpine was performed by ramping up the dose until onset of SE. This protocol was used for studying the consequences of SE, i.e. hippocampal damage, incidence of epilepsy with spontaneous recurrent seizures, and behavioral alterations. SE was terminated by diazepam after either 60, 90 or 120 min. All mice that survived SE developed epilepsy, but the severity of hippocampal damage varied depending on SE length. In all anxiety tests, except the elevated plus maze test, epileptic mice exhibited significant increases of anxiety-related behavior. Surprisingly, a decrease in depression-like behavior was observed in the forced swimming and tail suspension tests. Furthermore, epileptic mice were less sensitive than controls to most of the behavioral effects induced by MK-801 (dizocilpine). Learning and memory were impaired in epileptic mice irrespective of SE duration. Thus, the pilocarpine-treated mice seem to reflect several of the behavioral and cognitive disturbances that are associated with epilepsy in humans. This makes these animals an ideal model to study the neurobiological mechanisms underlying the association between epilepsy and psychopathology.