Blockade of “antiabsence” activity of sodium valproate by THIP in rats with petit mal-like seizures

Summary Wistar rats from our laboratory spontaneously present frequent epileptic seizures whose clinical semeiology, EEG signs and pharmacological reactivity resemble absence seizures in humans. In these rats, GABAmimetics such as THIP enhance the duration of seizures in a dose-dependent fashion. In contrast to the action of these drugs, valproate sodium (VPA), which potentiates GABAergic transmission, abolishes the seizures. VPA injected in association with THIP completely loses its therapeutic effects; moreover, VPA potentiates the aggravating effects of THIP. Ethosuximide which does not interact with GABA, was still effective when given in association with THIP. These findings raise questions as to 1. the role of GABAergic neurotransmission in the occurrence of spontaneous petit mal-like seizures in the rat, and 2. the mode of action of antiepileptics against these seizures.     

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.     

Social behavior impairment in offspring exposed to maternal seizures in utero

Human and animal models have demonstrated that maternal seizures in utero could be deleterious to the development of the offspring. This study focused on the social behavior of offspring exposed to seizures in utero. A pilocarpine model of temporal lobe epilepsy was induced in female Wistar rats that were mated after the first spontaneous seizure. Early after birth, pups from an epileptic mother were reared by a control mother. To evaluate the influence of the adoption process, two other groups were added: rat pups from control mothers cross-fostered with other control mothers, and rat pups reared by their birth mother. Animals exposed to seizures in utero showed impaired social behavior with no signs of anxiety-like behavior. This study demonstrated that epileptic seizures during pregnancy could be harmful to brain development and may increase the risk of developing neurodevelopmental disorders. The mechanisms underlying the abnormalities of social behavior are not well understood, and further studies in this field are warranted.     

Effects of the novel antiepileptic drug levetiracetam on spontaneous recurrent seizures in the rat pilocarpine model of temporal lobe epilepsy

PURPOSE: Animal models in which seizures are elicited by chemical or electrical means are commonly used for identification and preclinical testing of novel antiepileptic drugs (AEDs). Such models have been successful in discovering all the new AEDs. However, despite the high efficacy of AEDs against elicited seizures in rodent models, a significant proportion of epilepsy patients with spontaneous recurrent seizures is resistant to these drugs. It is not known whether drug testing in rodent models with spontaneous recurrent seizures would yield a more predictive result with respect to AED efficacy in the clinic. This led us to test one of the novel AEDs, levetiracetam (LEV), in a rat model of temporal lobe epilepsy (TLE) with spontaneous recurrent seizures. METHODS: Wistar rats were subjected to pilocarpine-induced status epilepticus and recorded for spontaneous recurrent seizures in the months after pilocarpine treatment. A group of rats with frequent spontaneous seizures was used for the drug trial with LEV. The experimental protocol for drug testing in these rats was as follows. For 2 weeks, rats received subcutaneous implantation of osmotic minipumps filled with saline (predrug control period), followed by a 2-week period with implantation of LEV-filled minipumps (drug period), after which pumps were replaced by drug-free pumps for 2 weeks (postdrug control period). The LEV concentration in the pumps during the drug period was adjusted to give daily doses resulting in the maximal plasma concentration range determined previously in patients with TLE during prolonged treatment with LEV. During the 6 weeks of the experiment in epileptic rats, seizures were recorded by video monitoring. RESULTS: Average seizure frequency during the pre- and postdrug control period in a group of eight epileptic rats was 21 and 25 seizures. This was reduced to an average seizure frequency of 8 seizures during the 2 weeks of treatment with LEV. However, the individual response of rats to LEV varied markedly from complete seizure control to no effect at all, although plasma drug levels were within the therapeutic range in all rats. When seizure frequency was separately calculated for the first and second week of treatment, the significant anticonvulsant effect determined in the first week was partially diminished in the second week, suggesting that tolerance may have developed in some of the rats. CONCLUSIONS: The data demonstrate that interesting results can be obtained by drug testing in epileptic rats, giving a more realistic prediction of clinical efficacy than results from drug testing in animal models with elicited seizures. Thus, although drug trials in rats with spontaneous recurrent seizures are laborious and time-consuming, such trials should be added to the preclinical characterization of novel AEDs.     

Diurnal variations in depression-like behavior of Wistar and spontaneously hypertensive rats in the kainate model of temporal lobe epilepsy

The purpose of this study was to explore whether the kainate (KA) model of temporal lobe epilepsy (TLE) can be used as a model of comorbid epilepsy and depression to study diurnal behavioral variations in rats. Development of chronic epilepsy was confirmed by the detection of spontaneous motor seizures (SMS) with video monitoring (24 hours/3-5 months after status epilepticus [SE]). KA-treated spontaneously hypertensive rats (SHRs) exhibited higher seizure frequency than Wistar rats during the light phase in the fourth and fifth months after SE. Although epileptic Wistar rats showed depression-like behavior and reduced anxiety mostly during the light phase, there were no diurnal variations in depression-like patterns in SHRs. Anxiety levels of control and epileptic SHRs were similar. Decreases in serotonin, tryptophan, and dopamine concentrations in the hippocampus were detected in epileptic Wistar rats compared with naive controls. However, monoamine levels of epileptic SHRs were close to those of their controls. Wistar rats and SHRs develop stable depression-like behavior during the chronic epileptic phase with strain-dependent diurnal differences.     

A genetic form of petit mal absence in Wistar rats

One-third of the Wistar rats bred in the Centre of Neurochemistry in Strasbourg, France, develop spontaneous epileptic seizures which from their clinical manifestations, pharmacological responses, and electroencephalographic findings are suggestive of Petit Mal absences. These fits are genetically determined since in two lines selected from affected animals they occurred in 90 p. cent of three generations. The selection of a pure strain should assist in the use of this pharmacologic and neurophysiologic model of Petit Mal epilepsy.     

Ontogeny of spontaneous petit mal-like seizures in Wistar rats

Wistar rats spontaneously presenting electroclinical signs of petit mal-like epileptic seizures were inbred until all offspring were affected, and the ontogeny of this inherited phenotype was studied in the offspring from 30-60 days of age to 18 months. The first EEG spike and wave discharges appeared at 40-120 days. Their number and duration increased progressively with age.     

Dynamic fMRI and EEG recordings during spike-wave seizures and generalized tonic-clonic seizures in WAG/Rij rats.

Generalized epileptic seizures produce widespread physiological changes in the brain. Recent studies suggest that "generalized" seizures may not involve the whole brain homogeneously. For example, electrophysiological recordings in WAG/Rij rats, an established model of human absence seizures, have shown that spike-and-wave discharges are most intense in the perioral somatosensory cortex and thalamus, but spare the occipital cortex. Is this heterogeneous increased neuronal activity matched by changes in local cerebral blood flow sufficient to meet or exceed cerebral oxygen consumption? To investigate this, we performed blood oxygen level-dependent functional magnetic resonance imaging (fMRI) measurements at 7T with simultaneous electroencephalogram recordings. During spontaneous spike-wave seizures in WAG/Rij rats under fentanylhaloperidol anesthesia, we found increased fMRI signals in focal regions including the perioral somatosensory cortex, known to be intensely involved during seizures, whereas the occipital cortex was spared. For comparison, we also studied bicuculline-induced generalized tonic-clonic seizures under the same conditions, and found fMRI increases to be larger and more widespread than during spike-and-wave seizures. These findings suggest that even in regions with intense neuronal activity during epileptic seizures, oxygen delivery exceeds metabolic needs, enabling fMRI to be used for investigation of dynamic cortical and subcortical network involvement in this disorder.     

Developmental brain damage after chemically induced epileptic seizures.

25 Wistar rats were subjected twice daily to epileptic seizures induced by the convulsant gaz Flurothyl. Compared with littermates of the same sex and birth weight, the brain of seizure-treated rats showed a reduction of 6% (5.2 million cells) after 5 days and 17.6% (33.4 million cells) after 10 days of treatment.     

The effects of the immature rat model of febrile seizures on the occurrence of later generalized tonic-clonic and absence epilepsy

This study was designed to investigate whether the intensity of experimental febrile seizures reduces the threshold to generalized tonic-clonic epilepsy and its effects on the development of generalized absence epilepsy in adulthood. For the evaluation of absence epilepsy, WAG/Rij rats and for the tonic-clonic seizures, PTZ injected Wistar rats were used. Our results showed that while the frequency of the experimental febrile seizures facilitates PTZ-induced generalized tonic-clonic seizures, it does not influence the properties of absence epileptic seizures in adulthood.     

Cardiovascular effects of intracerebroventricular bicuculline in rats with absence seizures

Gamma-aminobutyric acid (GABA) plays an important role in both central cardiovascular homeostasis and pathogenesis of epileptic seizures. Previous studies have indicated a critical role of the amygdala in the spread of seizures from brainstem to forebrain and in the regulation of autonomic responses such as blood pressure and heart rate. The purpose of the present study was to examine blood pressure and heart rate effects of bicuculline, a GABA(A) antagonist, and the effect of lesions of the central or the basolateral nuclei of the amygdala on bicuculline-induced cardiovascular responses in conscious WAG/Rij rats with absence epilepsy. Intracerebroventricular administration of 0.3 and 0.5 nmol of bicuculline produces an increase in blood pressure and a slight bradycardia in non-epileptic Wistar rats. The blood pressure response to intracerebroventricular bicuculline is significantly potentiated in epileptic WAG/Rij rats. Bilateral lesions of the basolateral nucleus of the amygdala of WAG/Rij rats completely prevent the pressor response to 0.5 nmol of bicuculline, whereas unilateral lesion of the basolateral nucleus does not affect blood pressure changes in epileptic WAG/Rij rats. Additionally, the pressor effect of 0.5 nmol of bicuculline is not attenuated by bilateral electrolytic ablation of the central nucleus of the amygdala in WAG/Rij rats. Heart rate response to bicuculline is not significantly changed in the lesioned groups. These findings indicate (a) altered GABAergic function in blood pressure regulation; and (b) a critical role of the basolateral nucleus in GABA(A)-mediated blood pressure control in epileptic WAG/Rij rats.     

Diurnal rhythms of spontaneous recurrent seizures and behavioral alterations of Wistar and spontaneously hypertensive rats in the kainate model of epilepsy

Attention deficit hyperactivity disorder (ADHD) can coexist with epilepsy. Spontaneously hypertensive rats (SHRs) are considered to model ADHD with overactivity, impulsiveness, deficient sustained attention, and alterations in circadian autonomic profiles. The present study explored spontaneous recurrent seizures (SRSs) and behavioral diurnal activity rhythms in normotensive Wistar rats and SHRs in the kainate model of epilepsy. Rats were video monitored (24 h/3 months) to detect SRSs. SHRs manifested a lower seizure frequency during the light phase in the 8th and 10th weeks and a lower frequency of SRSs during the night phase accompanied by attenuated responses in hyperexcitability tests. Both epileptic strains were hyperactive, with lower anxiety levels, and their diurnal rhythms were abolished. Epileptic Wistar rats and SHRs exhibited less exploration during the dark phase. This study suggests that SHRs may be useful in modeling some aspects (particularly hypertension-related diurnal rhythm disturbance) of behavior associated with epilepsy.     

Effects of subcutaneous injections of zinc chloride on seizures induced by noise and by kainic acid

Several lines of evidence implicate zinc in the pathogenesis of epileptic seizures, and administration of zinc salts has been shown to affect seizure susceptibility. In the present work, we studied the effects of subcutaneous (s.c.) injections of ZnCl2 on seizures induced by intraperitoneal (i.p.) kainic acid (10 mg/kg) in rats and by noise (80-120 dB) in the DBA/2J mouse. Previous administration of zinc salt (20-200 mg/kg) substantially reduced the frequency of noise-induced running fits, clonic and tonic seizures, and deaths in mice, but had no significant effect on the incidence or severity of kainic acid-induced seizures in rats. Together with findings in the literature, our results suggest that zinc plays multiple, sometimes antagonistic roles in seizure development.     

The effects of phenytoin and phenobarbital on seizures induced by imipenem/cilastatin in rats

The effects of phenytoin (PHT) and phenobarbital (PHB) on EEG activity and behavior was studied in the model of epilepsy induced by intracerebroventricular (i.c.v.) administration of imipenem/cilastatin (Imi/Cil). Under intraperitoneal (i.p.) sodium pentobarbital anesthesia adult male Wistar albino rats were implanted with electrodes and cannulas were placed into the right lateral ventricle. Animals were divided into groups: 1) Imi/Cil (100/100 microg, i.c.v.), 2) PHT (40 mg/kg) + Imi/Cil (100/100 microg, i.c.v), 3) PHT (80 mg/kg) + Imi/Cil (100/100 microg, i.c.v.), 4) PHT (160 mg/kg) + Imi/Cil (100/100 microg, i.c.v.), 5) PHB (50 mg/kg) + Imi/Cil (100/100 microg, i.c.v.), and 6) PHB (80 mg/kg) + Imi/Cil (100/100 microg, i.c.v.). PHT and PHB were injected intraperitoneally (i.p.) 1 h before Imi/Cil. Seizures were scored according to the scale: 0--normal behavior; 1--twitching, 2--head nodding, forelimb clonus, 3--rearing, and 4--clonic-tonic convulsions. Imi/Cil provoked maximal seizures in all animals, and all rats died 10 - 18 min after the injection. Epileptiform activity preceded behavioral seizures. Clonic-tonic seizures were associated with continuous bursts of high-frequency high-amplitude spikes in the EEG. PHT and PHB suppressed Imi/Cil-induced seizures dose-dependently. PHB reduced epileptiform discharges during behavioral seizures elicited by Imi/Cil, while PHT had no effect on EEG epileptic phenomena. These results suggest that PHT acts as anticonvulsant, and PHB as anticonvulsant and antiepileptic agent in the model of epilepsy induced by Imi/Cil.     

Influence of antioxidants on the blood-brain barrier permeability during epileptic seizures.

Pentylenetetrazol-induced seizures in rats lead to the breakdown of the blood-brain barrier. We compared the disruption of the blood-brain barrier during epileptic seizure in untreated rats and in rats treated with vitamin E or selenium. The rats were supplemented with nontoxic doses of sodium selenite (4 pp) in drinking water for 3 months, or vitamin E (70 mg/kg) was given intraperitoneally for 30 min before the pentylenetetrazole injection. Evans-blue was used as a blood-brain barrier tracer and was given intravenously at a dose of 4 ml/kg of a 2% solution. The rats were divided into four experimental groups. Group I: control (n = 24); Group II: pentylenetetrazole-induced seizure (n = 12); Group III: vitamin E injected + seizure (n = 12); Group IV: Selenium supplemented + seizure (n = 12). The rats subjected to epileptic seizures showed Evans-blue albumin extravasations especially in the thalamic nuclei, brainstem, occipital, and frontal cortex. Mean values for Evans-blue dye were found to be 0.28 +/- 0.04 mg % brain tissue in control rats and 1.6 +/- 0.2 mg % brain tissue after epileptic seizures (P < 0.01). The magnitude of distribution of the blood-brain barrier during epileptic seizures was significantly less in rats treated with vitamin E or selenium. The mean value for Evans-blue dye was found to be 1.2 +/- 0.1 mg % brain tissue in selenium supplemented rats and 1.2 +/- 0.1 mg % brain tissue in vitamin E injected rats after epileptic seizures. This difference between treated and untreated animals was found to be significant (P < 0.05). The findings of the present study suggest that free radicals contribute to disruption of the blood-brain barrier during pentylenetetrazol-induced seizures.     

耳甲腔电刺激对药物难治性癫痫大鼠发作及学习记忆影响的研究

目的探讨耳甲腔刺激对药物难治性癫痫大鼠痫性发作及学习记忆的影响,明确特定频率电刺激癫痫大鼠耳甲腔引起的行为学改变。方法 120只Wistar雄性大鼠氯化锂-匹鲁卡品制备惯常发作的颞叶癫痫大鼠,苯巴比妥诱导建立并筛选药物难治性癫痫大鼠50只,随机分为刺激组(20只)、假刺激组(20只)、非刺激组(10只)。按特定参数进行刺激,刺激参数设定为:电流强度1mA,波宽500μs,频率20Hz,刺激时间30s,间歇5分钟,10h/d(08:00~18:00),连续刺激4周。24小时视频脑电监测大鼠发作情况,刺激结束后,进行Morris水迷宫实验,观察大鼠学习记忆能力变化。三组大鼠断头取脑后切片,HE染色,镜下观察。结果成功建立并筛选药物难治性癫痫大鼠,耳甲腔刺激组大鼠癫痫发作次数明显下降,非刺激组和假刺激组大鼠癫痫情况无明显改变。三组间癫痫发作情况差异有统计学意义(P0.01);非刺激组和假刺激组刺激前后癫痫发作率无统计学意义(P0.05)。与假刺激和非刺激组相比,刺激组大鼠定向航行试验潜伏期明显缩短(P0.01),定向航行试验中刺激组大鼠穿越目标象限频次及目标象限停留时间均显著长于其他两组(P0.01)。HE染色发现假刺激组和非刺激组海马神经元明显变性、减少,刺激组则较轻。结论电刺激耳甲腔不仅能够显著抑制大鼠痫性发作,同时能改善因反复痫性发作而受损的学习记忆能力。     

Forebrain metabolic activation induced by the repetition of audiogenic seizures in Wistar rats

In Wistar rats susceptible to audiogenic seizures (Wistar AS) inbred in our laboratory, the exposure to an intense sound induces an epileptic seizure characterized by a running episode followed by a tonic phase showing the major involvement of brainstem structures. After 10–20 sound-induced seizures, development of facial and forelimb clonus and/or tonic-clonic seizures characterize the generalization from brainstem to the forebrain as a result of seizure repetition. In order to specify the anatomical substrates of repeated audiogenic seizures in Wistar AS, we used the 2-deoxyglucose (2DG) technique over a 5 min period to map the midbrain and forebrain structures activated by audiogenic seizures before and after seizure repetition. In naive Wistar AS, six of the 22 structures showed a significant 20–56% increase in relative optical densities compared to non-epileptic controls; these were central and medial amygdala nuclei, perirhinal cortex, medial septum, subthalamic and caudate nuclei. In kindled Wistar AS, 12 additional structures showed a significant 16–121% increase in 2DG labeling. These structures were the substantia nigra, all layers of the hippocampus, the basolateral amygdala, three thalamic nuclei, the frontal motor and prefrontal cortices. In conclusion, the metabolic activation of midbrain and forebrain areas in kindled versus naive Wistar AS rats reflects the changes in the nature of the seizures and the involvement of these structures in the spread of seizure activity from the brainstem to the forebrain during seizure repetition.     

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.     

痫性放电实现异体间转道并致痫动物的研究报道

目的观察青霉素癫痫模型痫性放电能否被引导电极转道至异体大鼠脑内并致痫。方法实验大鼠海马局部注射青霉素建立癫痫模型,通过引导电极拟将痫性放电导入异体大鼠同侧海马,观察实验大鼠的行为学、脑电图变化。结果致痫组、痫能导出组12只大鼠全部点燃,痫能导入组6只大鼠亦出现痫性发作,痫能导出组痫性发作时程缩短,致痫组、痫能导出组、痫能导入组大鼠脑电图均可记录到痫性波;对照组、电极组无痫性发作。结论实验性痫性放电可通过引导电极在异体大鼠脑组织间传导,脑内痫性放电有可能被电极导出。     

Neuroprotectants FK-506 and cyclosporin A ameliorate the course of pilocarpine-induced seizures

The present study was designed to examine whether neuroprotective agents, FK506 or cyclosporin A (CsA), applied to rats undergoing pilocarpine-induced seizures can minimize further development of the status epilepticus. In order to solve this problem, pilocarpine was injected in 60-day-old Wistar rats to evoke status epilepticus. When epileptic seizures reached a defined, moderate level of intensity, the rats received a single FK506 or CsA injections. During a 6-h period following pilocarpine injection, the animals were observed continuously and motor symptoms were recorded and rated. In epileptic rats injected with FK-506 or CsA, signs of significant amelioration of the course of epilepsy accompanied by longer survival periods were observed. Moreover, some differences between effects of the two agents were seen. The obtained results appear to show that, in addition to neuroprotective action, FK506 and CsA can exert also antiepileptic influences.