Amygdala kindling in the WAG/Rij rat model of absence epilepsy

PURPOSE: The kindling model in rats with genetic absence epilepsy is suitable for studying mechanisms involved in the propagation and generalization of seizure activity in the convulsive and nonconvulsive components of epilepsy. In the present study, we compared the amygdala kindling rate and afterdischarge characteristics of the nonepileptic Wistar control rat with a well-validated model of absence epilepsy, the WAG/Rij rat, and demonstrated the effect of amygdala kindling on spike-and-wave discharges (SWDs) in the WAG/Rij group. METHODS: Electrodes were stereotaxically implanted into the basolateral amygdala of rats for stimulation and recording and into the cortex for recording. After a recovery period, the animals were stimulated at their afterdischarge thresholds. EEG was recorded to analyze SWDs and afterdischarge durations. The seizure severity was evaluated by using Racine's 5-stage scale. RESULTS: All nonepileptic control and four of seven WAG/Rij animals reached a stage 5 seizure state, whereas three animals failed to reach stage 3, 4, or 5 and stayed at stage 2 after application of 30 stimulations. Interestingly, WAG/Rij rats, resistant to kindling, demonstrated a significantly longer duration of SWDs on the first day of the experiment before kindling stimulation than did the kindled WAG/Rij animals. Additionally, the cumulative total duration and the number of SWDs after the kindling stimulation were statistically increased compared with SWDs before kindling stimulation. CONCLUSIONS: The results of our study demonstrate that the progress of amygdala kindling is changed in rats with genetic absence epilepsy, perhaps as a consequence of the hundreds of daily SWDs.     

Audiogenic kindling in Wistar and WAG/Rij rats: kindling-prone and kindling-resistant subpopulations

Purpose: Audiogenic kindling (AK) is a model of naturally occurring epileptogenesis triggered by repeated sound stimulation of rats genetically prone to audiogenic seizures. It is accepted that limbic seizure networks underlie progressive changes in behavioral seizure pattern during AK. The present study investigated AK progression in rats susceptible and unsusceptible to absence seizures. Methods: Progression of AK as indicated by an appearance and intensification of limbic clonus was examined in Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats with genetic absence epilepsy and in Wistar rats. Results: Subpopulations of kindling‐prone and kindling‐resistant rats were found in both Wistar and WAG/Rij strains. Despite identical seizure responses to the first sound stimulation, AK progression dramatically differed between the two subpopulations. AK‐prone rats exhibited rapid kindling development up to maximal stage‐5 severity. In AK‐resistant rats, limbic clonus did not appear after 30 stimulations or if it appeared, it did not progress beyond stage 2. The proportions of AK‐prone and AK‐resistant animals within Wistar and WAG/Rij strains were similar. Comparison of Wistar and WAG/Rij rats within the kindling‐prone and kindling‐resistant groups did not reveal a significant strain effect on AK progression. However, within the WAG/Rij strain, a significantly higher incidence of absence seizures was found in AK‐resistant rats compared to AK‐prone rats. Conclusions: The present study demonstrates that sensitivity to sound‐induced epileptogenesis differs dramatically within Wistar and WAG/Rij strains, whereas genetic susceptibility to absence seizures does not change AK progression significantly. It is supposed that an increased incidence of nonconvulsive seizures and resistance to kindling result from a common seizure modulating mechanism.     

Resistance to propagation of amygdaloid kindling seizures in rats with genetic absence epilepsy

PURPOSE: The existence of absence epilepsy and temporal partial seizure pattern in the same patient is an uncommon state. In the present study, we aimed to evaluate whether the process of kindling as a model of complex partial seizures with secondary generalization is altered in rats with genetic absence epilepsy. METHODS: Six- to 12-month-old nonepileptic control Wistar rats and genetic absence epileptic rats from Strasbourg (GAERS) were used in the experiments. One week before the experiments, bilateral stimulation and recording electrodes were implanted stereotaxically into the basolateral amygdala and cortex, respectively. Animals were stimulated at their afterdischarge threshold current twice daily for the process of kindling and accepted as fully kindled after the occurrence of five grade 5 seizures. Bilateral EEGs from amygdala and cortex were recorded continuously during 20 min before and 40 min after each stimulus. RESULTS: All control Wistar rats were fully kindled after stimulus 12 to 15. Although the maximal number of stimulations had been applied, GAERS remained at stage 2, and no motor seizures were observed. The afterdischarge duration in bilateral amygdala and the cortex after the kindling stimulus was shorter in GAERS when compared with control rats. CONCLUSIONS: Occurrence of only grade 2 seizures and no observation of grade 3-5 seizures in GAERS with the maximal number of stimulations would suggest that the generalized absence seizures may be the reason of the resistance in the secondary generalization of limbic seizures during amygdala kindling.     

Cortical and limbic excitability in rats with absence epilepsy

The classical cortico-reticular theory on absence epilepsy suggests that a hyperexcitable cortex is a precondition for the occurrence of absence seizures. In the present experiment seizure thresholds and characteristics of cortical and limbic epileptic afterdischarges (AD) were determined in a comparative cortical stimulation study in young and old adult genetically epileptic WAG/Rij, congenic ACI and Wistar rats. Fifteen-second series of 8Hz stimulation of the sensory-motor cortex were applied in 80- and 180-day-old rats with implanted electrodes. Strain differences were found for the threshold for movements directly induced by stimulation, low frequency spike-and-wave AD, maximal clonic intensity of seizures accompanying direct stimulation, and frequency characteristics of low frequency AD. None of these results agreed with a higher cortical excitability exclusively in WAG/Rij rats. However, WAG/Rij rats had the longest duration of the low frequency AD, and the lowest threshold for the transition to the limbic type of AD. The decrease of this threshold correlated with the increase of the incidence and total duration of spontaneous SWDs in WAG/Rij rats. It is concluded that the elevated excitability of the limbic system or pathways mediating the spread of the epileptic activity into this system can be attributed to the development of genetic epileptic phenotype in WAG/Rij rats.     

Spike–wave discharges are necessary for the expression of behavioral depression-like symptoms

Purpose:   The WAG/Rij strain of rats, a well-established model for absence epilepsy, has comorbidity for depression. These rats exhibit depression-like behavioral symptoms such as increased immobility in the forced swimming test and decreased sucrose intake and preference (anhedonia). These depression-like behavioral symptoms are evident in WAG/Rij rats, both at 3–4 and 5–6 months of age, with a tendency to aggravate in parallel with an increase in seizure duration. Here we investigated whether the behavioral symptoms of depression could be prevented by the suppression of absence seizures.
Methods:   Ethosuximide (ETX; 300 mg/kg/day, in the drinking water) was chronically applied to WAG/Rij rats from postnatal day 21 until 5 months. Behavioral tests were done before the cessation of the treatment. Electroencephalography (EEG) recordings were made before and after cessation of treatment to measure seizure severity at serial time-points.
Results:   ETX-treated WAG/Rij rats exhibited no symptoms of depression-like behavior in contrast to untreated WAG/Rij rats of the same age. Moreover, treated WAG/Rij rats did not differ from control age-matched Wistar rats. ETX treatment led to almost complete suppression of spike-wave discharges (SWDs) in 5–6 month old WAG/Rij rats. Discontinuation of chronic treatment was accompanied by a gradual emergence of SWDs; however, a persistent reduction in seizure activity was still present 47 days after discontinuation of the chronic treatment.
Discussion:   The results suggest that seizure activity is necessary for the expression of depression-like behavioral symptoms and confirm that epileptogenesis can be prevented by early and chronic treatment.     

The relationship between age-related development of spike-and-wave discharges and the resistance to amygdaloid kindling in rats with genetic absence epilepsy

Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are resistant to amygdaloid kindling. Since in GAERS the characteristics of spike-and-wave discharges (SWDs) change with age, we have studied the relation between SWD maturation and the development of kindling resistance. Non-epileptic Wistar rats and GAERS were stimulated in basolateral amygdala with 400 μA at 20 min intervals until they reached stage 5 seizures or for a maximum of 36 stimulations. All of the Wistar rats, the postnatal (PN) day 20 GAERS and the (kindling-prone) subgroups of GAERS at PN30 and PN60 reached stage 5 seizures; at PN20, PN30 and PN60 kindling rates were significantly slower in GAERS compared to Wistar rats. At PN30 and PN60, 41% and 69% of GAERS, respectively, showed no stage 3, 4 or 5 seizures after 36 stimulations (kindling-resistant subgroups). The SWD maturation involves changes in spectral patterns and correlate with age-related increases in kindling resistance in GAERS.     

Anticonvulsant effect of unilateral anterior thalamic high frequency electrical stimulation on amygdala-kindled seizures in rat

Deep brain stimulation (DBS) is an emerging treatment of epilepsy. Anterior nucleus of the thalamus (ANT) is considered to be an attractive target due to its close connection to the limbic structures and wide regions of neocortex. In this study, we examined the effect of unilateral high frequency stimulation (HFS) of the ANT on amygdala-kindled seizures in Wistar rats. When fully-kindled seizures were achieved by daily amygdala kindling, HFS (15 min train of 100 μs pulses at 200 Hz and 450-800 μA) was delivered to the ipsilateral or contralateral ANT immediately before the kindling stimulation for 15 days. HFS of the ipsilateral ANT significantly decreased the incidence of generalized seizures and the mean behavioral seizure stage and afterdischarge duration (ADD), and shortened cumulative ADD and cumulative generalized seizure duration. Furthermore, HFS of the ipsilateral ANT significantly increased the afterdischarge threshold (ADT). Our data suggest that unilateral HFS of the ANT may be an effective method of inhibiting kindled seizures by suppressing the susceptibility to seizures and generating long lasting anti-epileptic effect preventing the recurrence of kindled seizures, providing an alternative to bilateral ANT DBS for refractory epilepsy.     

Aminophylline and kindled seizures

The effects of aminophylline on amygdaloid and cortically kindled rats was studied. Rats implanted with chronic amygdaloid electrodes received either saline or 150 mg/kg, i.p., aminophylline 20 min prior to their first stimulation. On the first stimulation, aminophylline-treated rats had dramatically longer afterdischarge durations and more severe seizure ranks. When fully kindled, the animals were retested with saline or aminophylline. Again, the aminophylline-treated animals had longer afterdischarge durations than the saline-treated rats. In a second experiment, fully amygdaloid kindled rats were pretreated with various doses of aminophylline and stimulated 20 min later. With suprathreshold stimulation, a dose-dependent increase was noted in the afterdischarge duration. During seizure threshold determinations, aminophylline pretreatment markedly prolonged afterdischarge durations without significantly changing seizure severity or threshold. When animals were treated with the adenosine agonist, 2-chloroadenosine, prior to kindled amygdaloid stimulation, the elicited afterdischarge was shortened. The effect was antagonized where treatment with both 2-chloroadenosine and aminophylline occurred prior to amygdaloid stimulation. Rats with neocortical electrodes were also exposed to various doses of aminophylline while in a stable, partially developed kindled stage and again when fully kindled. At both stages, afterdischarge duration was increased by aminophylline in a dose-dependent manner. The partially developed, cortically kindled animals were more responsive to aminophylline than were those fully kindled and they tended to have greater increases in afterdischarge duration and seizure rank. These data demonstrate that aminophylline acts to prolong afterdischarges elicited at various stages of kindling from both amygdaloid and cortical sites.     

Anticonvulsant action of fluzinamide (AHR-8559) on kindled amygdaloid seizures

The anticonvulsant properties of fluzinamide (AHR-8559) were evaluated in the kindled amygdaloid seizure model in rats. Fluzinamide significantly attenuated afterdischarge durations and the severity of the accompanying convulsive responses in previously kindled rats at doses that did not cause sedation or ataxia. After acute intraperitoneal injections, the maximum anticonvulsant effectiveness against suprathreshold (400 microA) stimulation was seen at 30 min. Fluzinamide (10-80 mg/kg i.p.) was also evaluated in previously kindled rats using threshold (20-microA increments) seizures. Low doses of fluzinamide significantly elevated seizure threshold and reduced both elicited afterdischarge durations and seizure severity. When administered daily during kindling acquisition, fluzinamide (20 and 40 mg/kg i.p.) significantly increased the number of trials necessary to complete kindling. The duration and the severity of the responses induced by stimulations during the acquisition period were reduced. Previous studies have shown that the anticonvulsant profile for fluzinamide, as determined by traditional electrical and clinical models of epilepsies, most closely resembled phenobarbital and valproic acid, and differed from phenytoin and ethosuximide. The current study is consistent with this profile, with fluzinamide--like phenobarbital and valproic acid--significantly modifying both acquisition of kindling and the fully kindled amygdaloid seizure.     

Changes in electroencephalographic characteristics and blood-brain barrier permeability in WAG/Rij rats with cortical dysplasia

PurposeThis study investigated the effects of cortical dysplasia (CD) on electrophysiology and blood-brain barrier (BBB) permeability in WAG/Rij rats with genetic absence epilepsy.MethodsPregnant WAG/Rij rats were exposed to 145 cGy of gamma-irradiation on embryonic day 17 to induce CD. An electroencephalogram was recorded from cortices subdurally in the offspring of the pregnant animals. Horseradish peroxidase (HRP) was used as determinant of BBB permeability.ResultsA massive tissue loss in the cerebral cortex was seen in WAG/Rij rats with CD (p < 0.05). There was a significant decrease in the number and duration of spike-and-wave discharges (SWDs) and an increase in the frequency of SWDs in the WAG/Rij rats with CD when compared with the properties of SWDs in intact WAG/Rij rats (p < 0.01). Ultrastructurally, the accumulation of HRP reaction products in the cerebral cortex and thalamus of WAG/Rij rats was significantly higher than that of control values (p < 0.01). The accumulation of HRP reaction products in the cerebral cortex and thalamus regions of WAG/Rij rats with CD increased and was higher than that of the control and WAG/Rij animals (p < 0.01).ConclusionIn our study, we showed that number and duration of SWDs decreased and SWD frequency increased in WAG/Rij rats with CD, suggesting a shift in seizure pattern. The association of these alterations with significant loss of cortical thickness and increased BBB permeability to HRP tracer may represent a causal relation of the EEG abnormalities with cerebral structural changes in these animals.     

Effect of intracranial administration of ethosuximide in rats with spontaneous or pentylenetetrazol-induced spike-wave discharges

Purpose: Generalized absence seizures are characterized by bilateral spike‐wave discharges (SWDs), particularly in the frontoparietal cortical region. In WAG/Rij and GAERS rats with absence epilepsy, recent evidence indicates that SWDs arise first from the lateral somatosensory cortex (LSC), that is, the cortical focus theory. To further understand the cortical role in SWD generation, two epileptic rat models were assessed. Methods: Two models, Long‐Evans rats with spontaneous SWDs and Wistar rats with low‐dose pentylenetetrazol‐induced SWDs (20 mg/kg, i.p.), were administered intracortical or intrathalamic ethosuximide (ESM) or saline. Electroencephalographic recordings were analyzed before and after intracranial microinfusion to evaluate onset, frequency, and duration of SWDs. Key Findings: In both epileptic rat models, ESM in the LSC significantly reduced SWD number, shortened SWD duration, and delayed SWD onset compared to saline. By contrast, ESM in the medial somatosensory cortex had little effect compared to saline. Intrathalamic infusion of ESM only delayed SWD onset. Significance: These findings suggest that the LSC may be essential for the occurrence of SWDs. Our data support the cortical focus theory for the generation of absence seizures.     

Thalamic kindling: electrical stimulation of the lateral geniculate nucleus produces photosensitive grand mal seizures

Kindling is traditionally viewed as a chronic, focal epilepsy model which consistently induces complex partial seizures from limbic structures in animals. This study revealed that primary or exceedingly rapid secondary generalized seizures could also be kindled when stimulation was applied to the lateral geniculate nucleus, a thalamic region involved in sleep regulation and possibly also photosensitive epilepsy. Two experiments were conducted in cats. Experiment 1 compared the development of generalized tonic-clonic convulsions and associated sleep disorders following electrical stimulation of the lateral geniculate nucleus (N = 4) and the amygdala (N = 4). Experiment 2 described the effects of intermittent light stimulation on seizure thresholds in both groups. Three primary findings distinguished the epileptogenic process in those two brain regions. First, generalized electroencephalographic and clinical seizures accompanied the first afterdischarge obtained with thalamic stimulation. In contrast, focal seizures with secondary generalization appeared during a 3- to 4-week period of afterdischarge elicitations from the amygdala. Second, amygdala-kindled cats showed fewer sleep spindles during slow-wave sleep whereas cats kindled in the lateral geniculate nucleus had abnormal sleep spindles approaching spike wave-like activity. Third, only the latter cats showed reduced seizure thresholds in response to photic stimulation. Based on the anatomic substrates involved, the clinical and electrographic profiles observed during kindling and the type of sleep disturbance shown, we concluded that lateral geniculate nucleus kindling may represent primary generalized epilepsy, possibly of a photosensitive nature; alternatively, the rapid propagation of abnormal discharge was also consistent with the important role of the thalamus in secondary seizure generalization.     

Anticonvulsant action of a non-competitive antagonist of NMDA receptors (MK-801) in the kindling model of epilepsy

Anticonvulsant action of MK-801, a novel non-competitive antagonist of N-methyl-d-aspartate (NMDA) receptors, was investigated in the kindling model of epilepsy in rats. The results obtained were as follows. (1) Both the seizure stage and afterdischarge duration of previously kindled seizures from the amygdala were significantly suppressed following systemic injection of MK-801 (0.25–4 mg/kg) in a dose-dependent manner. The maximum effects were observed between 2 and 4 h after the injection. (2) The MK-801 also showed significant anticonvulsant effedts on kindled seizures from the frontal cortex and the ventral and dorsal hippocampus. The efficacy however, significantly differed between these kindled sites. (3) Daily treatment of MK-801 (0.25 and 1 mg/kg) prior to each electrical stimulation of the amygdala significantly retarded kindling seizure development and increased the total amount of afterdischarge (accumulated AD) required to reach the first stage 5 seizure. During drug sessions of 1 mg/kg MK-801 for 19 days, all rats showed only partial seizures and the growth of afterdischarge was strongly prevented. (4) Pretreatment with reserpine did not antagonize the anticonvulsant effects of MK-801 on previously kindled seizures from the amydala, suggesting that the effects may not be mediated by catecholaminergic systems. These results indicate that MK-801 has potent anticonvulsant actions on kindled seizures from both limbic and cortical foci, the NMDA system may play a critical role in the seizure-triggering mechanism of kindling. The possible application of NMDA antagonists in clinical epilepsy is suggested.     

The midline thalamus: alterations and a potential role in limbic epilepsy

PURPOSE: In limbic or mesial temporal lobe epilepsy, much attention has been given to specific regions or cell populations (e.g., the hippocampus or dentate granule cells). Epileptic seizures may involve broader changes in neural circuits, and evidence suggests that subcortical regions may play a role. In this study we examined the midline thalamic regions for involvement in limbic seizures, changes in anatomy and physiology, and the potential role for this region in limbic seizures and epilepsy. METHODS: Using two rat models for limbic epilepsy (hippocampal kindled and chronic spontaneous limbic epilepsy) we examined the midline thalamus for evidence of involvement in seizure activity, alterations in structure, changes in the basic in vitro physiology of the thalamic neurons. We also explored how this region may influence limbic seizures. RESULTS: The midline thalamus was consistently involved with seizure activity from the onset, and there was significant neuronal loss in the medial dorsal and reuniens/rhomboid nuclei. In addition, thalamic neurons had changes in synaptically mediated and voltage-gated responses. Infusion of lidocaine into the midline thalamus significantly shortened afterdischarge duration. CONCLUSIONS: These observations suggest that this thalamic region is part of the neural circuitry of limbic epilepsy and may play a significant role in seizure modulation. Local neuronal changes can enhance the excitability of the thalamolimbic circuits.     

Time-dependent effect of low-frequency stimulation on amygdaloid-kindling seizures in rats

Low-frequency stimulation (LFS) has been considered as a new option for the treatment of intractable epilepsy. The present study was designed to determine whether LFS of the kindling focus given at different time points after seizures exert different roles on kindling seizures. Our results showed that: (i) In kindling animals, LFS delivered immediately after cessation of the kindling stimulus inhibited the seizure stage during kindling acquisition, whereas LFS delivered after the cessation of afterdischarge accelerated the kindling progression to stages 1 and 2. (ii) In fully kindled animals, when using the generalized seizure threshold current as the kindling stimulus, immediate LFS decreased the incidence of generalized seizures and the average seizure stage as well as shortened the cumulative generalized seizure duration (GSD). However, delayed LFS prolonged the cumulative GSD and afterdischarge duration. Our study indicates that there is a time-dependent aspect of LFS treatment, and immediate LFS has anti-epileptogenic action.     

Neocortical and thalamic spread of amygdala kindled seizures

PURPOSE: Amygdala kindling is an epilepsy model involving long-term network plasticity in the nervous system. In this model, repeated weak stimulation of the amygdala eventually leads to severe motor seizures. The mechanisms for worsening behavioral seizures, and the possible role of enhanced connectivity between the amygdala and other structures have not been thoroughly investigated. METHODS: We performed simultaneous field potential recordings from the amygdala, frontal cortex, and medial thalamus during kindling in rats. Seizures were analyzed for signal power compared with baseline and for correlation between recording sites. Interictal signals were analyzed for changes in coherence between electrode contacts in kindled animals compared with sham kindled controls. RESULTS: We found that increased behavioral severity of seizures was related to increased seizure duration and to increased signal power in the frontal cortex and medial thalamus. Kindling was associated with increased connectivity between the amygdala and frontal cortex, based on increased amygdala-frontal signal correlation during seizures. In addition, during the interictal period, increased coherence was noted between amygdala and frontal contacts in kindled animals compared with controls. CONCLUSIONS: We found evidence for increased connectivity between the amygdala and frontal cortex both during seizures and in the interictal period, as a result of kindling. Enhanced connections between limbic and neocortical circuits may be important for the development of epilepsy, as well as for normal long-range network plasticity in the nervous system.     

Effects of levetiracetam on spike and wave discharges in WAG/Rij rats

Effects of the novel anti-epileptic drug levetiracetam (50 and 100 mg/kg) on spike and wave discharges (SWDs) of WAG/Rij rats were studied. Levetiracetam decreased the incidence, average duration, total duration and peak frequency of the SWDs. There was no difference between the two doses. These results agree with results obtained in Genetic Absence Epilepsy Rat from Strasbourg (GAERS). Furthermore, the decrease of the SWD peak frequency might support the suggestions that levetiracetam might have a GABAergic mechanism of action.     

Modulation of neurogenesis by targeted hippocampal irradiation fails to affect kindling progression

Changes in the rate of dentate granule cell neurogenesis and in the fate of newborn granule cells have been implicated in the development and progression of epilepsies. Strategies to normalize neurogenesis in chronic epilepsy models are thought to increase our understanding of the functional consequences of aberrant neurogenesis in the epileptic brain. Therefore, we modulated neurogenesis in an amygdala kindling paradigm in rats by targeted irradiation of the hippocampus using a medical linear accelerator device. Selective irradiation normalized the hippocampal cell proliferation rate in kindled animals. Both, in kindled and nonkindled rats the number of BrdU/NeuN‐labeled newborn neurons was reduced in response to irradiation. Whereas kindling resulted in a pronounced increase in the number of neuroblasts identified based on doublecortin‐labeling, irradiation prevented the expansion of the neuroblast population. Moreover, irradiation counteracted the kindling‐associated increase in hilar basal dendrites, and kept the fraction of cells with basal dendrites at control levels. Despite the efficacious modulation of neurogenesis, irradiation did not affect the rate of kindling progression. Both, the number of stimulations as well as the cumulative afterdischarge duration to reach respective seizure stages were comparable in animals with and without irradiation. In addition, pre‐ and postkindling thresholds as well as seizure parameters recorded at threshold stimulation remained unaffected by irradiation. In conclusion, the fact that the efficacious modulation of neurogenesis by irradiation did not exert any effects on kindling acquisition and kindled seizures suggests that newborn neurons do not critically contribute to the hyperexcitable state in the chronic epilepsy model used. © 2010 Wiley‐Liss, Inc.     

Vigabatrin in low doses selectively suppresses the clonic component of audiogenically kindled seizures in rats

PURPOSE: The effect of systemic administration of the gamma-aminobutyric acid (GABA)-transaminase inhibitor vigabatrin (VGB) on different components of convulsions was tested in the model of audiogenically kindled seizures, which consist of brainstem (running, tonus) and forebrain (clonus) elements. METHODS: Audiogenically susceptible rats of Krushinsky-Molodkina (KM), Wistar, and WAG/Rij strains received repeated sound stimulation (60 dB, 10-80 kHz) until kindled audiogenic seizures were reliably elicited. Kindled audiogenic seizures consisted of running, tonic, and generalized clonic phases in KM rats (severe audiogenic seizures) and of running and Racine stage 5 facial/forelimb clonus in Wistar and WAG/Rij rats (moderate seizures). Vehicle, 100, or 200 mg/kg of VGB was intraperitoneally injected 2, 4 and 24 h before the induction of kindled audiogenic seizures. RESULTS: At both doses, VGB did not change the seizure latency and the duration of running and tonic convulsions, but suppressed clonic ones in all rat strains. In KM rats, the mean duration of posttonic clonus was significantly reduced at 24 h after 100 mg/kg and from 4 h after 200 mg/kg. In Wistar and WAG/Rij rats, the mean duration of facial/forelimb clonus was reduced from 4 and 2 h after 100- and 200-mg/kg administration, respectively; 24 h after the high-dose injection, clonus was completely blocked in all rats of both strains. No difference in efficacy of VGB between Wistar and WAG/Rij rats was observed. CONCLUSIONS: VGB more effectively suppresses clonic convulsions than running and tonic ones in audiogenically kindled rats. It is supposed that this selective anticonvulsive effect of VGB results from different sensitivities of forebrain and brainstem epileptic networks to the presumed GABA enhancement.     

Seizure suppression in kindling epilepsy by grafts of fetal GABAergic neurons in rat substantia nigra

Compared with studies on models of neurodegenerative diseases, considerably less work has been performed with neural grafts in experimental epilepsy. The potential value of this approach, however, is already shown by evidence that noradrenergic grafts implanted bilaterally into the hippocampus or amygdala-piriform cortex can suppress seizure development in the kindling model of temporal lobe epilepsy. We previously showed that amygdala kindling results in a significant decrease of GABA and its synthesizing enzyme glutamate decarboxylase in substantia nigra (SN), i.e., a region thought to be critically involved in seizure propagation in various models of epilepsy. Thus, transplantation of fetal GABAergic neurons into SN might be an effective means of permanently blocking seizure generalization in kindling epilepsy and probably also other types of epilepsy. To test this hypothesis, three groups of female Wistar rats (n = 10 per group) were kindled by electrical stimulation via a bipolar electrode in the basolateral amygdala. After all rats were fully kindled, one group was implanted with GABA-rich cells prepared from the striatal eminence of Wistar rat fetuses at embryonic day 14. The striatal neurons were bilaterally microinjected at various sites over the anterior-posterior axis of the SN, aimed at the pars reticulata. The second group received microinjections of spinal cord cell preparations, whereas the third group received microinjections of cell-free medium only. In all rats, the threshold for focal discharges (afterdischarge threshold [ADT]) as well as afterdischarge duration and severity and duration of seizures occurring at ADT current were determined once weekly before and after transplantation. Eleven to 12 weeks following transplantation, the rats were killed, and location and integration of grafts were examined by immunohistological methods. Rats with GABAergic grafts in SN exhibited a significant increase in ADT and marked reduction in seizure severity compared with pretransplantation values, whereas no such alteration was seen in the other groups. However, the seizure-suppressing effect of GABAergic grafts was not permanent but slowly disappeared over the weeks after transplantation. Although the data indicate that intranigral transplantation of GABA-producing cells is no effective means of inducing long-lasting anticonvulsant effects in experimental epilepsy, this approach may be an initial step to develop more efficient strategies for seizure suppression. J. Neurosci. Res. 51:196–209, 1998. © 1998 Wiley-Liss, Inc.