Changes of cortical epileptic afterdischarges after status epilepticus in immature rats

Status epilepticus (SE) in developing rats leads to neuronal degeneration in many brain structures including neocortex but the functional consequences of cortical damage were studied only exceptionally. Lithium-pilocarpine SE was elicited in 12- (P12) and 25-day-old (P25) rats, convulsions were interrupted after 2h by paraldehyde. Cortical electrodes were implanted 3, 6, 9, 13 and/or 26 days after SE. Low-frequency stimulation of sensorimotor cortex was repeated with at least 10-min intervals with a stepwise increasing intensity (0.2-14 mA). Thresholds for movements elicited by stimulation, spike-and-wave afterdischarges (ADs), clonic seizures, mixed ADs (transition into a limbic type of ADs) and recurrent ADs as well as duration of ADs were evaluated. The first three phenomena were not influenced by SE with the exception of lower thresholds for movements during stimulation. Transition into limbic seizures and recurrent seizures were delayed in both age groups and threshold intensities for limbic ADs were at some intervals higher in SE than in control animals. Duration of ADs was changed only at short intervals after SE; it was shortened at 3 and 6 days in P25 and 3 days in P12 rats, respectively. P12 group then exhibited a transient increase in duration of ADs 6 days after SE. Our results did not prove a higher cortical excitability after SE in either age group. On the contrary, there were some signs of a decreased excitability.     

Does status epilepticus induced at early postnatal period change excitability after cortical epileptic afterdischarges?

Possible changes of cortical excitability after status epilepticus (SE) elicited in 12‐day‐old rats were studied by means of paired cortical afterdischarges (ADs). Consequences of lithium‐pilocarpine status were studied in animals with implanted electrodes 3, 6, 9, 13, and 26 days after SE. Paired low‐frequency stimulation with a 1‐min interval was repeated after 10 min, and duration of ADs was measured. Control rats received saline instead of pilocarpine; other treatments were the same as in SE group. Postictal refractoriness (i.e., the testing response significantly shorter than the conditioning one) appeared at the age of 18 days in lithium‐paraldehyde controls, whereas SE animals exhibited this phenomenon since postnatal day 21. The only significant difference between SE and lithium‐paraldehyde controls was found in the second conditioning AD in the oldest group studied–it was longer in 38‐day‐old SE animals. Our results demonstrated moderate signs of higher excitability of SE rats in comparison with control ones long before appearance of spontaneous seizures.     

Does Status Epilepticus Influence the Motor Development of Immature Rats?

Summary: Purpose : To study the effect of severe status epilepticus (SE) on the motor development of rats.
Methods : SE was induced in 12-day-old rats (P12 group) and 25-day-old rats (P25 group) using the lithium-pilocarpine model. Seizures were interrupted after 2 hours by paraldehyde with an intraperitoneal dose of 0.3 or 0·6 mL/kg, respectively. Starting 3 days after SE, all animals were repeatedly exposed to a battery of motor and behavioral tests, including the bar-holding test, rotarod test, and open field test.
Results : In P12 animals, motor impairment occurred 2 months after SE, when significantly worse performance in the rotarod test was found. No difference between controls and experimental rats was found in any other test used. In contrast, P25 animals were significantly poorer in the bar-holding test from postnatal day 34 until adulthood. In open field study, P25 rats were found to be hyperactive during the whole period of testing, whereas P12 animals exhibited an initial period of hypoactivity (in the first test) that was replaced by hyperactivity that lasted until 2 months of age. In the last test performed at the age of 98 days, experimental P12 animals were again less active than age-matched controls.
Conclusions : Animals of both age groups exhibited permanent changes of motor performance; however, both the pattern and the time course of these changes was related to age when SE was elicited.     

Outcome of Status Epilepticus in Immature Rats Varies According to the Paraldehyde Treatment

Summary:  Purpose: To test effects of paraldehyde on behavioral outcome of status epilepticus (SE) in developing rats.
Methods: Motor SE was induced by LiCl-pilocarpine in rats on postnatal (P) day 12 or 25. Two hours after SE onset, animals were injected with a single dose of paraldehyde (0.07 and 0.3 ml/kg in the P12 group and 0.3 and 0.6 ml/kg in the P25 group). Effects on seizure severity and mortality were evaluated. Growth of animals and their motor abilities were monitored until the adulthood. Three months after SE, cognitive abilities were tested by using the Morris water maze.
Results: Both tested doses of paraldehyde equally affected motor seizures. Convulsions continued until the paraldehyde administration, but then they quickly subsided in all groups. During the subsequent 24 h, occasional clonic seizures occurred in P25 animals treated with the lower dose of paraldehyde. Only hyperactivity and/or automatisms were observed in the other experimental groups. Mortality was not affected by the dosage of paraldehyde. The higher dosage of paraldehyde improved recovery after SE in both age groups. No difference was found in motor abilities between controls and SE animals, except shortening of time spent on the rod in the rotarod test in the P12 group. In P25 rats, treatment with a higher dosage of paraldehyde improved learning abilities compared with the lower dosage. In the P12 group, animals treated with the lower dosage exhibited slightly impaired learning compared with controls and animals receiving the higher dosage.
Conclusions: Paraldehyde injected 2 h after SE onset modulates long-term outcome in immature rats in a dose-related manner.     

Proechimys guyannensis: An Animal Model of Resistance to Epilepsy

Summary:  Purpose: The potential interest of Proechimys guyannensis (PG), a spiny rat species living in the Amazonian region, as an animal model of anticonvulsant mechanisms, prompted the investigation of the susceptibility of this animal species to different epileptogenic treatments.
Methods: Adult male Wistar and PG animals were submitted to amygdala kindling, the pilocarpine model and the intrahippocampal kainic acid (KA) model. Electrographic, behavioral, and neuropathological changes were compared between Wistar and PG animals.
Results: PG animals demonstrated a striking resistance to reaching stage 5 of kindling. Of the 43 PG rats submitted to the kindling process, only three animals reached stage 5. In the pilocarpine and KA models, doses lower than those used in Wistar rats were able to induce status epilepticus (SE) in PG animals. Pilocarpine-induced SE in PG had a shorter duration, rarely exceeding 2 h, in contrast to the 8- to 12- h long SE in the Wistar rat. Of the 61 PG animals injected with pilocarpine, 48 presented with SE and only two presented with some spontaneous seizures after silent periods of 60 and 66 days. KA elicited self-sustained electrographic SE in PG animals, which lasted for 72 h. None of the surviving animals presented with spontaneous seizures in the long-term observation period (up to 120 days).
Conclusions: These findings indicate that the PG animal may have natural endogenous anticonvulsant mechanisms and also may be an animal model that is resistant to epileptogenic treatments.     

Changes in NADPH-diaphorase positivity induced by status epilepticus in allocortical structures of the immature rat brain

The distribution and time course of changes of nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) positivity were studied in immature rats (12 and 25 days old) surviving motor status epilepticus (SE) induced by a high dose of pilocarpine. Motor SE characterized by continuous convulsions was interrupted after 2 h by an injection of clonazepam (0.5 mg/kg or 1 mg/kg in 12- and 25-day-old rats, respectively) in order to reduce mortality. Correlation between electroencephalographic and behavioral seizure activity was confirmed using animals with electrodes implanted bilaterally in the hippocampus and sensorimotor cortex. Brains were examined 2, 6, 13, and 21 days after motor SE using NADPH-diaphorase histochemistry. Two types of changes were found in both age groups: (a) decrease of NADPH-d positivity occurred in both neuropil and cell bodies in piriform, periamygdalar, and entorhinal cortices; and (b) NADPH-d positivity was induced in the cell bodies in the hippocampal fields CA1/2, CA3, and dentate gyrus. These changes were more intense in animals surviving SE at postnatal day 25 than in younger age group, and they peaked 2 days after SE. The changes observed after SE disappeared quickly in 12-day-old rat pups, where only moderate changes could be observed in piriform, periamygdalar, and entorhinal cortices 6 days after SE, whereas the changes in the histochemical positivity persisted in older animals even 21 days after SE.     

Kainic acid dose affects delayed cell death mechanism after status epilepticus

Kainic acid (KA)-induced status epilepticus (SE) produces hippocampal neuronal death, which varies from necrosis to apoptosis or programmed cell death (PCD). We examined whether the type of neuronal death was dependent on KA dose. Adult rats were induced SE by intraperitoneal injection of KA at 9 mg/kg (K9) or 12 mg/kg (K12). Hippocampal neuronal death was assessed by TUNEL staining, electron microscopy, and Western blotting of caspase-3 on days 1, 3 and 7 after SE induction. K12 rats showed higher a mortality rate and shorter latency to the onset of SE when compared with K9 rats. In both groups, acidophilic and pyknotic neurons were evident in CA1 at 24h after SE and neuronal loss developed from day 3. The degenerated neurons became TUNEL-positive on days 3 and 7 in K9 rats but not in K12 rats. Caspase-3 activation was detected on days 3 and 7 in K9 rats but was undetectable in K12 rats. Ultrastructural study revealed shrunken neurons exhibiting pyknotic nuclei containing small and dispersed chromatin clumps 24h after SE in CA1. No cells exhibited apoptosis. On days 3 and 7, the degenerated neurons were necrotic with high electron density and small chromatin clumps. There were no ultrastructural differences between the K9 and K12 groups. These results revealed that differences in KA dose affected the delayed cell death (3 and 7 days after SE); however, no effect was seen on the early cell death (24h after SE). Moderate-dose KA induced necrosis, while low-dose KA induced PCD.     

Increased persistent sodium currents in rat entorhinal cortex layer V neurons in a post-status epilepticus model of temporal lobe epilepsy

PURPOSE: Spontaneous seizures in rats emerge several weeks after induction of status epilepticus with pharmacologic treatment or electrical stimulation, providing an animal model for human temporal lobe epilepsy. In this study, we investigated whether status epilepticus caused changes in the function of voltage-gated sodium channels in entorhinal cortex layer V neurons, a cellular group important for the genesis of limbic seizures. METHODS: We induced status epilepticus in rats, by using lithium-pilocarpine, and then 2-12 weeks later, used whole-cell voltage-clamp to examine voltage-activated sodium currents of acutely dissociated layer V neurons. RESULTS: Transient sodium currents of entorhinal cortex layer V neurons isolated from 9- to 12-week post-status epilepticus rats were similar to currents in age-matched controls; however, low-threshold persistent sodium currents were significantly larger. This increase in persistent activity was not seen 2-3 weeks after pilocarpine treatment; thus it occurred after a delay comparable to the delay in the appearance of spontaneous seizures. CONCLUSIONS: Increased persistent currents are expected to accentuate neuronal excitability and thus may contribute to the genesis of spontaneous seizures after status epilepticus.     

Status Epilepticus Causes Long-Term NMDA Receptor-Dependent Behavioral Changes and Cognitive Deficits

Summary: Purpose: The role of N -methyl- d -aspartate (NMDA)-receptor activation on behavioral and cognitive changes after status epilepticus (SE) is unknown. In this study, behavioral and cognitive changes after SE were evaluated in the short and long term and in rats in which the NMDA receptor was inactivated during SE.
Methods: Pilocarpine (350 mg/kg) was injected to induce SE. Inhibition of the NMDA receptor during SE was achieved with MK-801 (4 mg/kg). Seizure intensity during SE was monitored by electroencephalography (EEG). After SE, behavioral studies were performed to identify abnormal behavior by using behavioral tests adapted from Moser's funetional observational battery. Cognitive changes were assessed by using the Morris Water Maze (MWM).
Results: Pilocarpine–treated animals scored significantly higher on two of the behavioral tests: the Touch test and the Pick-Up test. These behavioral changes occurred very soon after SE, with the earliest changes observed 2 days after SE and persisting for the life of the animal. Inhibition of the NMDA receptor with MK-801 completely inhibited these behavioral changes under conditions that did not alter the duration of SE. In addition, pilocarpine-treated animals exhibited cognitive deficits as determined by using the MWM. Six weeks after SE, the animals displayed significantly longer latencies to locate the hidden platform on this test. The impaired performance on the MWM also occurred as early as 5 days after SE. These cognitive deficits were prevented in animals treated with MK-801 during SE.
Conclusions: The results indicate that behavioral and cognitive changes occur soon after SE, are permanent, and are dependent on NMDA-receptor activation during SE. NMDA receptor activation may play an important role in causing cognitive and behavioral morbidity after recovery from SE.     

Characterization of Benzodiazepine Receptor Binding in Immature Rat Brain After Kainic Acid Administration

Summary: Purpose : To evaluate the effects of status epilepticus on benzodiazepine (BDZ) receptor binding in immature rat brain.
Methods : Twenty-four immature (15 days old) and six adult (90 days old) rats were used in this study. Status epilepticus was induced in immature animals by administration of kainic acid (7 mg/kg intraperitoneal), whereas adults rats received saline. Animals were killed 72 hours or 35 days after treatment, and their brains were used for in vitro autoradiography experiments to determine BDZ binding.
Results : In basal conditions and compared with the adult group, immature animals presented reduced BDZ binding in the entorhinal cortex, substantia nigra pars reticulata, and periaqueductal gray. Seventy-two hours after kainic acid–induced status epilepticus, immature rats showed significantly increased BDZ in the frontal (48%), cingulate (39%), sensorimotor (39%), piriform (57%), and entorhinal (59%) cortices, the medial (84%) and basolateral (27%) amygdaloid nuclei, the dentate gyrus (51%), and the substantia nigra pars reticulata (43%). Thirty-five days after status epilepticus, immature rats displayed decreased BDZ binding in the entorhinal cortex (48%), dentate gyrus (36%), and fields CA1, CA2, and CA3 of Ammon's horn (30%).
Conclusions : The present study demonstrates that status epilepticus and temporal lobe epilepsy produce a characteristic pattern of BDZ binding changes in the immature rat brain that differs from the one previously seen in adults.     

Persistent reduction of hippocampal glutamine synthetase expression after status epilepticus in immature rats

Mesiotemporal sclerosis (MTS), the most frequent form of drug‐resistant temporal lobe epilepsy, often develops after an initial precipitating injury affecting the immature brain. To analyse early processes in epileptogenesis we used the juvenile pilocarpine model to study status epilepticus (SE)‐induced changes in expression of key components in the glutamate–glutamine cycle, known to be affected in MTS patients. SE was induced by Li⁺/pilocarpine injection in 21‐day‐old rats. At 2–19 weeks after SE hippocampal protein expression was analysed by immunohistochemistry and neuron damage by FluoroJade staining. Spontaneous seizures occurred in at least 44% of animals 15–18 weeks after SE. As expected in this model, we did not observe loss of principal hippocampal neurons. Neuron damage was most pronounced in the hilus, where we also detected progressive loss of parvalbumin‐positive GABAergic interneurons. Hilar neuron loss (or end‐folium sclerosis), a common feature in patients with MTS, was accompanied by a progressively decreased glutamine synthetase (GS)‐immunoreactivity from 2 (?15%) to 19 weeks (?33.5%) after SE. Immunoreactivity for excitatory amino‐acid transporters, vesicular glutamate transporter 1 and glial fibrillary acidic protein was unaffected. Our data show that SE elicited in 21‐day‐old rats induces a progressive reduction in hilar GS expression without affecting other key components of the glutamate–glutamine cycle. Reduced expression of glial enzyme GS was first detected 2 weeks after SE, and thus clearly before spontaneous recurrent seizures occurred. These results support the hypothesis that reduced GS expression is an early event in the development of hippocampal sclerosis in MTS patients and emphasize the importance of astrocytes in early epileptogenesis.     

Plastic Changes and Disease-modifying Effects of Scopolamine in the Pilocarpine Model of Epilepsy in Rats

Summary:  Purpose: We describe the use of a clinically relevant pharmacological intervention that alters the clinical history of status epilepticus (SE)-induced spontaneous recurrent seizures (SRS) in the pilocarpine model and the possible plastic changes underlying such an effect.
Methods: Two hours after pilocarpine-induced SE (320–350 mg/kg, i.p.), rats received scopolamine 1–2 mg/kg i.p. or saline, every 6 h for 3 days. After that, osmotic minipumps were implanted for continuous delivery of scopolamine or saline for an additional 14 days. Animals were video-monitored for 12 h/week during the following 3-month period for the occurrence of SRS and, thereafter, were perfused, processed, and coronal brain sections were stained for acetylcholinesterase (AChE) and for the presence of supragranular mossy fibers (Timm).
Results: Treatment with scopolamine led to significantly fewer SRS. Staining for AChE in the dentate gyrus was significantly more intense in naïve animals. The scopolamine group had the least intense AChE staining of all groups. However, regression analysis of the AChE staining for this group did not correlate with the presence or absence of SRS, or the latency or frequency of SRS. Supragranular mossy fiber sprouting developed in all animals experiencing pilocarpine-induced SE, irrespective of whether or not they were treated with scopolamine.
Conclusions: Pilocarpine-induced SE in the presence of scopolamine might produce animals that, despite mossy fiber sprouting, were not seen to exhibit spontaneous seizures. In addition, our data suggest that the encountered changes in the AChE staining in the dentate gyrus that followed treatment with scopolamine do not help to explain its disease-modifying effects.     

A short episode of seizure activity protects from status epilepticus-induced neuronal damage in rat brain

Kainic acid (KA)-induced status epilepticus (SE) in adult rats results in extensive neuronal damage throughout the limbic system and the loss of selectively vulnerable neuronal populations, particularly CA3 neurons. We investigated the effects of a short episode of seizure activity on neuronal death elicited by a subsequent prolonged SE episode. A short episode of seizure activity was produced by sub-cutaneous (s.c.) injection of KA followed after 1 h by pentobarbital administration. Twenty-four hours later, KA was administered again, and animals were sacrificed 3 days later. Neuronal damage was estimated by visual analysis of neuronal density. Our results show that a short episode of seizure activity did not produce neuronal damage but almost completely protected vulnerable neurons from KA-induced neuronal damage. These results extend to epileptic tolerance the notion of tolerance previously described in the case of ischemia.     

Status epilepticus in immature rats leads to behavioural and cognitive impairment and epileptogenesis

It remains under dispute whether status epilepticus (SE) in the perinatal period or early childhood or the underlying neuropathology is the cause of functional impairment later in life. The present study examined whether SE induced by LiCl-pilocarpine in normal immature brain (at the age of 12 or 25 days; P12 or P25) causes cognitive decline and epileptogenesis, and the data were compared to those of rats undergoing SE as adults. Rats in the P12 group had impaired memory (repeated exposure to open-field paradigm) and emotional behaviour (lower proportion of open-arm entries and higher incidence of risk assessment period in elevated plus-maze) when assessed 3 months after SE, although not as severe as in the older age groups. Importantly, video-electroencephalography monitoring 3 months after SE demonstrated that 25% of rats in the P12 and 50% in P25 group developed spontaneous seizures. Only nonconvulsive seizures (ictal activity in hippocampus accompanied by automatisms) were recorded in the P12 group whereas rats in the P25 group exhibited clonic convulsions. The present findings indicate that SE is harmful to the immature brain as early as P12, which might be compared with early infancy in humans.     

Disruption of Cortical Development as a Consequence of Repetitive Pilocarpine-induced Status Epilepticus in Rats

Summary:  Purpose: The aim of the present study was to observe possible cortical abnormalities after repetitive pilocarpine-induced status epilepticus (SE) in rats during development.
Methods: Wistar rats received intraperitoneal injection of pilocarpine hydrochloride 2% (380 mg/kg) at P7, P8, and P9. All experimental rats displayed SE after pilocarpine injections. Rats were killed at P10 and P35, and immunocytochemistry procedures were performed on 50-μm vibratome sections, by using antibodies against nonphosphorylated neurofilament (SMI-311), parvalbumin (PV), calbindin (CB), calretinin (CR), and glutamate decarboxylase (GAD-65). Selected sections were used for the TUNEL method and double-labeling experiments, with different mixtures of the same markers.
Results: The major findings of the present work were (a) altered intracortical circuitry development; (b) anticipation of PV immunoreactivity in neocortical interneurons; (c) increased GAD-65 immunoreactivity; and (d) reduced neocortical apoptotic process.
Conclusions: From these results, we suggest that previously healthy brain, without genetic abnormalities, might develop an "acquired" disruption of cortical development whose evolution reproduces some characteristics of the childhood epilepsies associated with cognitive impairment.     

Granule Cell Neurogenesis After Status Epilepticus in the Immature Rat Brain

Summary: Purpose : Several experimental paradigms of seizure induction that produce epilepsy as a consequence have been shown to be associated with the proliferation of dentate granule cells. In developing animals, the acute sequela of hilar damage and the chronic sequelae of spontaneous seizures and mossy fiber synaptic reorganization, in response to status epilepticus, occur in an age-dependent manner. We investigated seizure-induced granule cell neurogenesis in developing rat pups to study the association between hilar injury, granule cell neurogenesis, and epilepsy.
Methods : Rat pups of 2 and 3 weeks postnatal age were subjected to lithium-pilocarpine status epilepticus (LiPC SE). Rats were given bromodeoxyuridine (BrdU; 50 mg/kg intra-peritoneal) twice daily for 4 days beginning 3 days after SE to label dividing cells. Routine immunocytochemistry and quantification of BrdU labeling by image analysis were performed. Results were compared with previously reported data on cellular injury, mossy fiber sprouting, and spontaneous seizures in rat pups of these ages after LiPC SE.
Results : In 3-week-old pups, which demonstrate SE-induced hilar damage and develop spontaneous seizures accompanied by mossy fiber sprouting, the BrdU-immunoreactive area (percent) in the subgranular proliferative zone increased to 10·6 ± 2·5 compared with 1·4 ± 0·5 in the control animals (p < 0·05). The 2-week-old animals, which show neither hilar damage nor sprouting and rarely develop spontaneous seizures, also showed a comparable extent of SE-induced neurogenesis [8·0 ± 1·4 (LiPC SE) versus 0·4 ± 0·2 (control), p < 0·05].
Conclusions : Seizure-induced granule cell neurogenesis does not appear to be a function of seizure-induced hilar cellular damage. Granule cell neurogenesis induced by SE does not determine epileptogenesis in the developing rat.     

Changes in midline thalamic recruiting responses in the prefrontal cortex of the rat during the development of chronic limbic seizures

Purpose:   Mesial temporal lobe epilepsy (MTLE) is a common form of epilepsy that affects the limbic system and is associated with decreases in memory and cognitive performance. The medial prefrontal cortex (PC) in rats, which has a role in memory, is associated with and linked anatomically to the limbic system, but it is unknown if and how MTLE affects the PC.
Methods:   We evoked responses in vivo in the PC by electrical stimulation of the mediodorsal (MD) and reuniens (RE) nuclei of the thalamus at several time points following status epilepticus, before and after onset of spontaneous seizures. Kindled animals were used as additional controls for the effect of seizures that were independent of epilepsy.
Results:   Epileptic animals had decreased response amplitudes and significantly reduced recruiting compared to controls, whereas kindled animals showed an increase in both measures. These changes were not associated with neuronal loss in the PC, although there was significant loss in both the MD and RE in the epileptic animals.
Conclusions:   There is a significant reduction in the thalamically induced evoked responses in the PCs of epileptic animals. This finding suggests that physiologic dysfunction in MTLE extends beyond primary limbic circuits into areas without overt neuronal injury.     

Increased GABA(A)-receptor alpha1-subunit expression in hippocampal dentate gyrus after early-life status epilepticus

PURPOSE: Previous studies in neonatal (postnatal day 10) and adult rats suggest that status epilepticus (SE) induces changes in the alpha1 subunit of the GABA(A) receptor (GABRA1) in dentate granule neurons (DGNs) that are age dependent and vary inversely with the likelihood of epilepsy development. In the present study, we examined GABRA1 expression after SE at postnatal day 20 (P20), an intermediate age when only a subset of SE-exposed animals develop epilepsy. METHODS: SE was induced with lithium-pilocarpine or kainate at P20. Animals were video-EEG monitored after SE to determine the presence or absence of spontaneous seizures. GABRA1 mRNA and protein levels were determined 7 days or 3 months later in SE-exposed and control animals by using a combination of aRNA amplification, Western blotting, and immunohistochemistry techniques. RESULTS: GABRA1 mRNA levels in DGNs of SE-exposed rats that did not become epileptic were higher than those in control rats, but were not different from DGNs in epileptic SE-exposed rats. GABRA1 protein levels in dentate gyrus were significantly increased in both epileptic and nonepileptic SE-exposed rats compared with controls. GABRA1 mRNA changes were region specific and did not occur in CA1 or CA3 areas of hippocampus. GABRA1 alterations were present by 1 week after P20 SE and were similar whether pilocarpine or kainate was used to induced SE. CONCLUSIONS: P20 SE results in persistent increases in GABRA1 levels selectively in dentate gyrus. These changes preceded the onset of epilepsy, were not model specific, and occurred in both epileptic and nonepileptic animals.     

Seizure frequency in pilocarpine-treated rats is independent of circadian rhythm

Pilocarpine-induced status epilepticus (SE) results in chronic spontaneous recurrent seizures resembling human temporal lobe epilepsy. In this and other experimental models, behaviorally monitored seizure frequency was suggested to vary in a circadian fashion, and to increase with time. We re-addressed those hypotheses using continuous video-electroencephalography (EEG) telemetry in rats with SE at 30 days of age. In 11 chronically epileptic animals monitored up to 300 days after SE in a fixed 12 h light/dark cycle, we found that seizure frequency did not correlate with circadian rhythm.     

Status epilepticus in 12-day-old rats leads to temporal lobe neurodegeneration and volume reduction: a histologic and MRI study

PURPOSE: Whether status epilepticus (SE) in early infancy, rather than the underlying illness, leads to temporal lobe neurodegeneration and volume reduction remains controversial. METHODS: SE was induced with LiCl-pilocarpine in P12 rats. To assess acute neuronal damage, brains (five controls, five with SE) were investigated at 8 h after SE by using silver and Fluoro-Jade B staining. Some brains from the early phase were processed for electron microscopy. To assess chronic changes, brains from nine controls and 13 rats with SE at P12 were analyzed after 3 months by using histology and magnetic resonance imaging (MRI). RESULTS: MRI analysis of the temporal lobe of adult animals with SE at P12 indicated that 23% of the rats had hippocampal, 15% had amygdaloid, and 31% had perirhinal volume reduction. Histologic analysis of sections from the MR-imaged brains correlated with the MRI data. Analysis of neurodegeneration 8 h after SE by using both silver and Fluoro-Jade B staining revealed degenerating neurons located in the same temporal lobe regions as the volume reduction in chronic samples. Electron microscopic analysis revealed irreversible ultrastructural alterations. As with the chronic histologic and MRI findings, interanimal variability was seen in the distribution and severity of acute damage. CONCLUSIONS: Our data indicate that SE at P12 can cause acute neurodegeneration in the hippocampus as well as in the adjacent temporal lobe. It is likely that acute neuronal death contributes to volume reduction in temporal lobe regions that is detected with MRI in a subpopulation of animals in adulthood.