Cyclicity of spontaneous recurrent seizures in pilocarpine model of temporal lobe epilepsy in rat

Pilocarpine administration to rats results in status epilepticus (SE) and after a latency period to the occurrence of spontaneous seizures. The model is commonly used to investigate mechanisms of epileptogenesis as well as the antiepileptic effects of novel compounds. Surprisingly, there have been no video-EEG studies determining the duration of latency period from SE to the appearance of the first spontaneous seizures or the type and frequency of spontaneous seizures at early phase of pilocarpine-induced epilepsy even though such information is critical for design of such studies. To address these questions, we induced SE with pilocarpine in 29 adult male Wistar rats with cortical electrodes. Rats were continuously video-EEG monitored during SE and up to 23 days thereafter. The first spontaneous seizures occurred 7.2+/-3.6 days after SE. During the follow-up, the mean daily seizure frequency was 2.6+/-1.9, the mean seizure duration 47+/-7 s, and the mean behavioral seizure score 3.2+/-0.9. Typically first seizures were partial (score 1-2). Interestingly, spontaneous seizures occurred in clusters with cyclicity, peaking every 5 to 8 days. These data show that in the pilocarpine model of temporal lobe epilepsy the latency period is short. Because many of the early seizures are partial and the seizures occur in clusters, the true phenotype of epilepsy triggered by pilocarpine-induced SE may be difficult to characterize without continuous long-term video-EEG monitoring. Finally, our data suggest that the model can be used for studies aiming at identifying the mechanisms of seizure clustering.     

Pilocarpine-induced status epilepticus results in mossy fiber sprouting and spontaneous seizures in C57BL/6 and CD-1 mice

Several rodent models are available to study the cellular mechanisms associated with the development of temporal lobe epilepsy (TLE), but few have been successfully transferred to inbred mouse strains commonly used in genetic mutation studies. We examined spontaneous seizure development and correlative axon sprouting in the dentate gyrus of CD-1 and C57BL/6 mice after systemic injection of pilocarpine. Pilocarpine induced seizures and status epilepticus (SE) after systemic injection in both strains, although SE onset latency was greater for C57BL/6 mice. There were also animals of both strains which did not experience SE after pilocarpine treatment. After a period of normal behavior for several days after the pilocarpine treatment, spontaneous tonic-clonic seizures were observed in most CD-1 mice and all C57BL/6 that survived pilocarpine-induced SE. Robust mossy fiber sprouting into the inner molecular layer was observed after 4-8 weeks in mice from both strains which had experienced SE, and cell loss was apparent in the hippocampus. Mossy fiber sprouting and spontaneous seizures were not observed in mice that did not experience a period of SE. These results indicate that pilocarpine induces spontaneous seizures and mossy fiber sprouting in both CD-1 and C57BL/6 mouse strains. Unlike systemic kainic acid treatment, the pilocarpine model offers a potentially useful tool for studying TLE development in genetically modified mice raised on the C57BL/6 background.     

Repeated low-dose treatment of rats with pilocarpine: low mortality but high proportion of rats developing epilepsy.

Systemic administration of pilocarpine in rats can result in a chronic behavioral state that is similar to human temporal lobe epilepsy. The pilocarpine model of epilepsy is widely used for studying the factors that contribute to the development of epilepsy as a consequence of status epilepticus (SE). For this purpose, pilocarpine is either administered alone at a high systemic dose or in combination with lithium, which markedly potentiates the convulsant effect of pilocarpine. Both experimental protocols, however, are associated with high mortality rates. In the present study, we evaluated whether mortality rate in rats can be decreased by repeated administration of low doses of pilocarpine. The time the rats spent in SE was limited by diazepam. Preliminary experiments in lithium-free rats indicated that repeated low-dose administration of pilocarpine is too time-consuming to produce SE compared to single high-dose administration. All subsequent experiments were performed in lithium-pretreated rats. Single-dose injection of 30 mg/kg pilocarpine produced SE in approximately 70% of the animals, but 45% of the rats died although SE was interrupted by diazepam after 90 min. Repeated i.p. administration of 10 mg/kg pilocarpine at 30-min intervals resulted in SE after 2-4 injections; the mean dose of pilocarpine needed to induce SE was 26 mg/kg. When SE was interrupted after 90 min, mortality rate was below 10%, which was significantly lower compared to the protocol with one single administration of 30 mg/kg pilocarpine. In contrast to mortality rate, the development of spontaneous recurrent seizures did not differ between experimental protocols. Almost all rats which had experienced a SE of at least 60 min developed chronic epilepsy. Average latency to the first spontaneous seizure was approximately 40 days. The frequency and severity of spontaneous seizures was not significantly different between protocols, although animal groups with repeated low-dose treatment tended to have higher frequencies of spontaneous seizures compared to single-dose administration. The present study demonstrates that systemic treatment of lithium-pretreated rats with several low doses of pilocarpine efficiently produces SE and chronic epilepsy with much lower mortality rates than single-dose pilocarpine.     

One hour of pilocarpine-induced status epilepticus is sufficient to develop chronic epilepsy in mice, and is associated with mossy fiber sprouting but not neuronal death

Determining the minimal duration of status epilepticus (SE) that leads to the development of subsequent spontaneous seizures (i.e., epilepsy) is important, because it provides a critical time-window for seizure intervention and epilepsy prevention. In the present study, male ICR (Imprinting Control Region) mice were injected with pilocarpine to induce acute seizures. SE was terminated by diazepam at 10 min, 30 min, 1 h, 2 h and 4 h after seizure onset. Spontaneous seizures occurred in the 1, 2 and 4 h SE groups, and the seizure frequency increased with the prolongation of SE. Similarly, the Morris water maze revealed that the escape latency was significantly increased and the number of target quadrant crossings was markedly decreased in the 1, 2 and 4 h SE groups. Robust mossy fiber sprouting was observed in these groups, but not in the 10 or 30 min group. In contrast, Fluoro-Jade B staining revealed significant cell death only in the 4 h SE group. The incidence and frequency of spontaneous seizures were correlated with Timm score (P = 0.004) and escape latency (P = 0.004). These data suggest that SE longer than one hour results in spontaneous motor seizures and memory deficits, and spontaneous seizures are likely associated with robust mossy fiber sprouting but not neuronal death.     

Effects of herbimycin A in the pilocarpine model of temporal lobe epilepsy

Pilocarpine-induced status epilepticus (SE) causes widespread tyrosine phosphorylation in the brain. It has been postulated that this intracellular signal may mediate potentially epileptogenic changes in the morphology and physiology of particular brain regions, including the hippocampus. The present study evaluated the effects of herbimycin A, a protein tyrosine kinase (PTK) inhibitor, over the acute (during which intense biochemical and electrophysiological activation occurs) and the chronic phase (characterized by spontaneous and recurrent epileptic seizures and the presence of synaptic reorganization, e.g., mossy fiber sprouting) of the pilocarpine model of epilepsy. The administration of a single dose of 1.74 nmol of herbimycin A (i.c.v., 5 microL) 5 min after the onset of SE did not change the acute behavioral manifestation of seizures despite significantly decreasing c-Fos immunoreactivity in different areas of the hippocampus and of the limbic cortex. Herbimycin-treated animals developed spontaneous recurrent seizures, as did control animals, with a similar latency for the appearance of the first seizure and similar seizure frequency. Neo-Timm staining revealed that all animals experiencing SE, regardless of whether or not injected with herbimycin, showed aberrant mossy fiber sprouting in the supragranular region of the dentate gyrus. Herbimycin did not obviously affect neuronal cell death as evaluated in Nissl-stained sections. These results indicate that the PTK blockade achieved with the current dose of herbimycin reduced the acute c-Fos expression but failed to alter the spontaneous seizure frequency or to attenuate the morphological modifications triggered by the SE.     

Effect of long-term spontaneous recurrent seizures or reinduction of status epilepticus on the development of supragranular mossy fiber sprouting.

In a recent report we have shown that a protein synthesis inhibitor, cycloheximide (CHX), is able to block the mossy fiber sprouting (MFS) that would otherwise be triggered by pilocarpine (Pilo)-induced status epilepticus (SE), and also gives relative protection against hippocampal neuronal death. Under this condition animals still showed spontaneous recurrent seizures (SRS) which led us to question the role played by sprouted mossy fibers in generating those seizures. In both patients and animal models of epilepsy the relative contribution of SE (when present) and/or SRS for the development of MFS is not known. In the present study we investigated the relationship between MFS, SE and SRS, and evaluated whether the CHX-induced blockade of MFS was transient or permanent in nature. We performed a chronic study which included animals subject to Pilo-induced SE in the presence of CHX and sacrificed between 8 and 10 months later, and animals that were subject to Pilo-induced SE in the presence of CHX and underwent a reinduction of SE with Pilo, 45 days after the first induction, but this time in the absence of CHX. Re-induction of SE or a long period of chronic seizures, were able to trigger supragranular MFS even in animals where the first (or only) SE event was triggered in the presence of CHX. MFS did not show any association with the frequency of SRS, and thus seemed to depend more critically on time. Our current findings allow us to suggest that MFS are neither the cause nor the consequence of SRS in the pilocarpine model.     

Status epilepticus induced by lithium-pilocarpine in the immature rat does not change the long-term susceptibility to seizures

The causal relationship between early seizures and subsequent temporal lobe epilepsy has not yet been established. Prospective clinical studies reported that seizures occurring early in life rarely result in hippocampal sclerosis. Likewise, in most experimental models, early seizures occurring before the end of the second postnatal week do not lead to neuronal damage and subsequent epilepsy. In some models, this early event decreases latency sensitivity and threshold to seizures. In the present study, we induced lithium and pilocarpine status epilepticus (SE) in 10-day-old (P10) rats. The goal of this study was to determine whether this early life SE altered the sensitivity to convulsants such as pentylenetetrazol (20 and 25 mg/kg), picrotoxin (2.5 and 4.0 mg/kg) and kainate (5 and 8 mg/kg) during adulthood. The occurrence of electrographic seizures (spike-and-wave discharges, SWD) and/or of behavioral seizures was monitored. There was no difference in latency to and duration of SWDs and seizures between lithium-saline and lithium-pilocarpine exposed rats. Thus, SE induced by lithium and pilocarpine early in life does not change the sensitivity to limbic seizures or seizures induced by GABA(A) antagonists during adulthood.     

Castration in female rats modifies the development of the pilocarpine model of epilepsy

Previous studies have shown that the susceptibility to pilocarpine-induced status epilepticus (SE) in female rats changes according to estrous cycle phases. These studies have also shown that following pilocarpine administration changes occur in gonadal, hypophyseal and hypothalamic hormones that could contribute for the sequence of the epileptic events. Accordingly, the present work aimed to investigate the role of sexual hormones withdrawal on the development of the pilocarpine model of epilepsy in female rats. With this purpose, castrated and non-castrated adult female Wistar rats were injected with pilocarpine and some characteristic parameters of the experimental model were observed. The results showed increased mortality after pilocarpine injection in the castrated rats when compared with non-castrated females. The latency period for SE onset and for the first spontaneous seizure was decreased in castrated when compared with non-castrated animals. The mossy fiber sprouting measured by neo-Timm scale during the chronic period, reached grade 3 for castrated epileptic rats while the non-castrated epileptic rats showed grade 2. Our results indicate that castration interferes with the epileptogenesis in the pilocarpine model of epilepsy suggesting that female sexual hormones could have protective effects against pilocarpine-induced SE.     

The course of untreated seizures in the pilocarpine model of epilepsy

The course of untreated epilepsy is not well established. This study uses a model of chronic limbic epilepsy (pilocarpine model of epilepsy) to determine the pattern of occurrence of seizures in untreated animals. Following pilocarpine administration, 21 rats were monitored continuously with a video system for 135 days after the first spontaneous seizure. Animals showed a great variability in seizure numbers and were divided in two subgroups presenting either a low frequency of seizures (n = 9 animals presenting ten or less seizures in the first 15 days of observation) or a high frequency of seizures (n = 12 animals presenting more than ten seizures during this period). Animals with low number of seizures during the first 15 days of observation showed a significant increase in seizure frequency in the following period of analysis (until 105 days). On the other hand, those with initial high number of seizures showed significant changes in seizure frequency only in the first 2 months. The duration of each spontaneous seizure did not change significantly over time. These findings show that in untreated epilepsy there is a maturation process in the early stages and this accelerating process can be of predictive value for the treatment of epilepsy.     

Circuit Mechanisms of Seizures in the Pilocarpine Model of Chronic Epilepsy: Cell Loss and Mossy Fiber Sprouting

We used the pilocarpine model of chronic spontaneous recurrent seizures to evaluate the time course of supragranular dentate sprouting and to assess the relation between several changes that occur in epilep tic tissue with different behavioral manifestations of this experimental model of temporal lobe epilepsy. Pilo carpine-induced status epilepticus (SE) invariably led to cell loss in the hilus of the dentate gyrus (DG) and to spontaneous recurrent seizures. Cell loss was often also noted in the DG and in hippocampal subfields CA1 and CA3. The seizures began to appear at a mean of 15 days after SE induction (silent period), recurred at variable frequencies for each animal, and lasted for as long as the animals were allowed to survive (325 days). The granule cell layer of the DG was dispersed in epileptic animals, and neo-Timm stains showed supra-and intragranular mossy fiber sprouting. Supragranular mossy fiber sprout ing and dentate granule cell dispersion began to appear early after SE (as early as 4 and 9 days, respectively) and reached a plateau by 100 days. Animals with a greater degree of cell loss in hippocampal field CAS showed later onset of chronic epilepsy (r= 0.83, p < 0.0005), suggest ing that CA3 represents one of the routes for seizure spread. These results demonstrate that the pilocarpine model of chronic seizures replicates several of the fea tures of human temporal lobe epilepsy (hippocampal cell loss, suprar and intragranular mossy fiber sprouting, den tate granule cell dispersion, spontaneous recurrent sei zures) and that it may be a useful model for studying this human condition. The results also suggest that even though a certain amount of cell loss in specific areas may be essential for chronic seizures to occur, excessive cell loss may hinder epileptogenesis.     

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.     

Seizures in the intrahippocampal kainic acid epilepsy model: characterization using long‐term video‐EEG monitoring in the rat

Objective – Intrahippocampal injection of kainic acid (KA) in rats evokes a status epilepticus (SE) and leads to spontaneous seizures. However to date, precise electroencephalographic (EEG) and clinical characterization of spontaneous seizures in this epilepsy model using long‐term video‐EEG monitoring has not been performed. Materials and Methods – Rats were implanted with bipolar hippocampal depth electrodes and a cannula for the injection of KA (0.4 μg/0.2 μl) in the right hippocampus. Video‐EEG monitoring was used to determine habitual parameters of spontaneous seizures such as seizure frequency, severity, progression and day–night rhythms. Results – Spontaneous seizures were detected in all rats with 13 out of 15 animals displaying seizures during the first eight weeks after SE. A considerable fraction (35%) of the spontaneous seizures did not generalize secondarily. Seizure frequency was quite variable and the majority of the KA‐treated animals had less than one seizure per day. A circadian rhythm was observed in all rats that showed sufficient seizures per day. Conclusions – This study shows that the characteristics of spontaneous seizures in the intrahippocampal KA model display many similarities to other SE models and human temporal lobe epilepsy.     

Study of spontaneous recurrent seizures and morphological alterations after status epilepticus induced by intrahippocampal injection of pilocarpine

Epileptic seizures are clinical manifestations of neuronal discharges characterized by hyperexcitability and/or hypersynchrony in the cortex and other subcortical regions. The pilocarpine (PILO) model of epilepsy mimics temporal lobe epilepsy (TLE) in humans. In the present study, we used a more selective approach: microinjection of PILO into the hilus of the dentate gyrus (H-PILO). Our main goal was to evaluate the behavioral and morphological alterations present in this model of TLE. Seventy-six percent of all animals receiving H-PILO injections had continuous seizures called status epilepticus (SE). A typical pattern of evolution of limbic seizures during the SE with a latency of 29.3 ± 16.3 minutes was observed using an analysis of behavioral sequences. During the subsequent 30 days, 71% of all animals exhibited spontaneous recurrent seizures (SRSs) during a daily 8-hour videotaping session. These SRSs had a very conspicuous and characteristic pattern detected by behavioral sequences or neuroethiological analysis. Only the animals that had SE showed positive Neo-Timm staining in the inner molecular layer of the dentate gyrus (sprouting) and reduced cell density in Ammon's horn pyramidal cell subfield CA1. However, no correlation between the intensity of sprouting and the mean number and total number of SRSs was found. Additionally, using Fluoro-Jade staining, we observed neurodegeneration in the hilus and pyramidal cell subfields CA3 and CA1 24 hours after SE. These data indicate that H-PILO is a reliable, selective, efficient, low-mortality model that mimics the acute and chronic behavioral and morphological aspects of TLE.     

Ketogenic diet exhibits neuroprotective effects in hippocampus but fails to prevent epileptogenesis in the lithium‐pilocarpine model of mesial temporal lobe epilepsy in adult rats

Purpose: Although the number of antiepileptic drugs (AEDs) is increasing, none displays neuroprotective or antiepileptogenic properties that could prevent status epilepticus (SE)–induced drug‐resistant epilepsy. Ketogenic diet (KD) and calorie restriction (CR) are proposed as alternative treatments in epilepsy. Our goal was to assess the neuroprotective or antiepileptogenic effect of these diets in a well‐characterized model of mesial temporal lobe epilepsy following initial SE induced by lithium‐pilocarpine in adult rats. Methods: Seventy‐five P50 male Wistar rats were fed a specific diet: normocalorie carbohydrate (NC), hypocalorie carbohydrate (HC), normocalorie ketogenic (NK), or hypocalorie ketogenic (HK). Rats were subjected to lithium‐pilocarpine SE, except six NC to constitute a control group for histology (C). Four rats per group were implanted with epidural electrodes to record electroencephalography (EEG) during SE and the next six following days. From the seventh day, the animals were video‐recorded 10 h daily to determine latency to epilepsy onset. Neuronal loss in hippocampus and parahippocampal cortices was analyzed 1 month after the first spontaneous seizure. Results: After lithium‐pilocarpine injection, neither KD nor CR modified SE features or latency to epilepsy. In hippocampal layers, KD or CR exhibited a neuroprotective potential without cooperative effect. Parahippocampal cortices were not protected by the diets. Conclusion: The antiepileptic effect of KD and/or CR is overwhelmed by lithium‐pilocarpine injection. The isolated protection of hippocampal layers induced by KD or CR or their association failed to modify the course of epileptogenesis.     

Strain differences in seizure-induced cell death following pilocarpine-induced status epilepticus

Mouse strains differ from one another in their susceptibility to seizure-induced excitotoxic cell death. Previously, we have demonstrated that mature inbred strains of mice show remarkable genetic differences in susceptibility to the neuropathological consequences of seizures in the kainate model of status epilepticus. At present, while the cellular mechanisms underlying strain-dependent differences in susceptibility remain unclear, some of this variation is assumed to have a genetic basis. However, it remains unclear whether strain differences in susceptibility to seizure-induced cell death observed following kainate administration are observed following systemic administration of other chemoconvulsants. In rodents, the cholinomimetic convulsant pilocarpine is widely used to induce status epilepticus (SE), followed by hippocampal damage and spontaneous recurrent seizures, resembling temporal lobe epilepsy. This model has initially been described in rats, but is increasingly used in mice. We characterized neuronal pathologies after pilocarpine-induced status epilepticus (SE) in eight inbred strains of mice focusing on the hippocampus. A ramping-up dose protocol for pilocarpine was used and behavior was monitored for 4-5 h. While we did not observe any significant differences in seizure latency or duration to pilocarpine among the inbred strains, we did observe a significant difference in susceptibility to the neuropathological consequences of pilocarpine-induced SE. Of the eight genetically diverse mouse strains screened for pilocarpine-induced status, BALB/cJ and BALB/cByJ were the only two strains that were resistant to the neuropathological consequences of seizure-induced cell death. Additional studies of these murine strains may be useful for investigating genetic influences on pilocarpine-induced status epilepticus.     

Effect of lamotrigine treatment on epileptogenesis: an experimental study in rat

Prevention of epileptogenesis in patients with acute brain damaging insults like status epilepticus (SE) is a major challenge. We investigated whether lamotrigine (LTG) treatment started during SE is antiepileptogenic or disease-modifying. To mimic a clinical study design, LTG treatment (20 mg/kg) was started 2 h after the beginning of electrically induced SE in 14 rats and continued for 11 weeks (20 mg/kg per day for 2 weeks followed by 10 mg/kg per day for 9 weeks). One group of rats (n = 14) was treated with vehicle. Nine non-stimulated rats with vehicle treatment served as controls. Outcome measures were occurrence of epilepsy, severity of epilepsy, and histology (neuronal loss, mossy fiber sprouting). Clinical occurrence of seizures was assessed with 1-week continuous video-electroencephalography monitoring during the 11th (i.e. during treatment) and 14th week (i.e. after drug wash-out) after SE. LTG reduced the number of electrographic seizures during SE to 43% of that in the vehicle group (P < 0.05). In the vehicle group, 93% (13/14), and in the LTG group, 100% (14/14) of the animals, developed epilepsy. In both groups, 64% of the rats had severe epilepsy (seizure frequency >1 per day). The mean frequency of spontaneous seizures, seizure duration, or behavioral severity of seizures did not differ between groups. The severity of hippocampal neuronal damage and density of mossy fiber sprouting were similar. In LTG-treated rats with severe epilepsy, however, the duration of seizures was shorter (34 versus 54s, P < 0.05) and the behavioral seizure score was milder (1.4 versus 3.4, P < 0.05) during LTG treatment than after drug wash-out. LTG treatment started during SE and continued for 11 weeks was not antiepileptogenic but did not worsen the outcome. These data, together with earlier studies of other antiepileptic drugs, suggest that strategies other than Na(+)-channel blockade should be explored to modulate the molecular cascades leading to epileptogenesis after SE.     

Circadian dentate gyrus excitability in a rat model of temporal lobe epilepsy

In human mesial temporal lobe epilepsy (mTLE), seizure occurrence peaks in the late afternoon and early evening. This temporal binding of seizures has been replicated in animal models of mTLE following electrically-induced status epilepticus (SE). We hypothesized that in chronic epilepsy, alterations of circadian excitatory and inhibitory functions of the dentate gyrus (DG), which is believed to regulate the generation of limbic seizures, pathophysiologically contribute to the temporal binding of ictogenesis. We performed electrophysiological single and paired pulse measurements hourly over 24h in the DG of epileptic rats (n=8) 8 weeks after electrically induced SE. Results were compared to individual data obtained before induction of SE and to those of control animals (n=3). Pre and post SE data were analyzed in two distinct phases of the day, i.e. a high-seizure phase between 2p.m. and 10p.m. and a low-seizure phase between 10p.m. and 2p.m. In chronic epileptic animals, latency of evoked potentials was significantly reduced in the high-seizure phase (p=0.027) but not in the low-seizure phase. Compared to baseline values, paired pulse inhibition was significantly increased during the low-seizure phase (interpulse interval (IPI) 25ms, p=0.003; IPI 30ms; p<0.001) but not in the high-seizure phase. Similarly, when compared to controls, inhibition at IPI 20ms was diminished only in the high-seizure phase (p=0.027). Thus, in chronic epileptic animals, DG excitability is increased in the afternoon and early evening possibly contributing to the time of day-dependency of spontaneous seizures in this model system of mTLE. Alterations of circadian DG excitability in epileptic animals may be influenced by changes in hypothalamus-regulated superordinate functions such as excretion of endocrine hormones but further studies are needed.     

Epileptogenesis in immature rats following recurrent status epilepticus

Strong evidences link status epilepticus (SE) in childhood with the later development of epilepsy. Pilocarpine-induced SE in developing rats leads to late appearance of spontaneous epileptic seizures only when SE is induced after the 18th day of life. We examined the possibility that 3 consecutive episodes of pilocarpine-induced SE on postnatal days 7, 8 and 9 could induce behavioral, electrographic and histological epileptic changes in adult life. The animals also underwent behavioral tests (inhibitory step-down avoidance, skinner box, rota-rod, open field and elevated plus-maze). EEG recordings made at the age of 30, 60 and 90 days showed the occurrence of several episodes of spikes and/or polyspikes appearing simultaneously in hippocampus and cortex. Only three isolated spontaneous seizures were observed during the whole period of observation (120 days). The long-term effects of three consecutive episodes of SE include increased spontaneous exploratory activity, learning impairment, and reduced anxiety when tested on P60. Our findings provide evidence for EEG changes and cognitive deficits in adult life following recurrent SE on postnatal days 7–9.     

Consequences of prolonged caffeine administration and its withdrawal on pilocarpine- and kainate-induced seizures in rats

PURPOSE: To investigate the consequences of caffeine consumption on epileptic seizures, we used the pilocarpine and the kainate models of epilepsy. We hypothesized that prolonged caffeine consumption or its withdrawal would alter adenosine levels and hence alter seizure susceptibility. METHODS: We administered a 0.1% caffeine solution in the drinking water of adult male Wistar rats over a 2-week period. We challenged another group of animals with the same doses of pilocarpine or kainate 12 h after the withdrawal of the same caffeine-administration protocol. RESULTS: This did not alter the threshold for the induction of seizures by a subconvulsant dose of pilocarpine (200 mg/kg, i.p.) or kainic acid (8 mg/kg, i.p.). Similarly, challenging another group of animals with the same doses of pilocarpine or kainate 12 h after the withdrawal of the same caffeine-administration protocol did not lead to any significant changes in seizures. CONCLUSIONS: With the pilocarpine model of epilepsy, we were not able to find any significant difference in seizure profile that could stem from either caffeine administration or its withdrawal. Despite the extensive laboratory evidence on the convulsant properties of xanthine derivatives in animal models of epilepsy, such strong evidence is lacking in clinical settings. Our current findings with the administration of caffeine at doses similar to those of daily life both support and confirm the clinical experience.