Transfer of an avian genetic reflex epilepsy by embryonic brain graft: a tissue autonomous process?

Electroencephalographic characteristics and clinical symptoms of an avian genetic reflex epilepsy have been transferred from Fayoumi epileptic (Fepi) chickens to non-epileptic chickens by embryonic homotopic grafts of brain neuroepithelium. Transplanted tissues belonging to the prosencephalic vesicle transferred epileptic electrical features while tissues from the mesencephalic vesicle were responsible for seizure motor manifestations of the disease. Thus each of these tissues can express their own specificity when grafted separately in a normal host, but they co-operate to produce the complete epileptic phenotype when grafted together.     

Epilepsy caused by an abnormal alternative splicing with dosage effect of the SV2A gene in a chicken model

Photosensitive reflex epilepsy is caused by the combination of an individual's enhanced sensitivity with relevant light stimuli, such as stroboscopic lights or video games. This is the most common reflex epilepsy in humans; it is characterized by the photoparoxysmal response, which is an abnormal electroencephalographic reaction, and seizures triggered by intermittent light stimulation. Here, by using genetic mapping, sequencing and functional analyses, we report that a mutation in the acceptor site of the second intron of SV2A (the gene encoding synaptic vesicle glycoprotein 2A) is causing photosensitive reflex epilepsy in a unique vertebrate model, the Fepi chicken strain, a spontaneous model where the neurological disorder is inherited as an autosomal recessive mutation. This mutation causes an aberrant splicing event and significantly reduces the level of SV2A mRNA in homozygous carriers. Levetiracetam, a second generation antiepileptic drug, is known to bind SV2A, and SV2A knock-out mice develop seizures soon after birth and usually die within three weeks. The Fepi chicken survives to adulthood and responds to levetiracetam, suggesting that the low-level expression of SV2A in these animals is sufficient to allow survival, but does not protect against seizures. Thus, the Fepi chicken model shows that the role of the SV2A pathway in the brain is conserved between birds and mammals, in spite of a large phylogenetic distance. The Fepi model appears particularly useful for further studies of physiopathology of reflex epilepsy, in comparison with induced models of epilepsy in rodents. Consequently, SV2A is a very attractive candidate gene for analysis in the context of both mono- and polygenic generalized epilepsies in humans.     

Listen carefully: positional cloning of an audiogenic seizure mutation may yield Frings benefits.

Neurologists have long sought to understand what precipitates individual seizures in epileptic patients. Studies of reflex epilepsies seem well suited to this task. In this issue of Neuron, Skradski et al. describe a mutation in a novel gene underlying audiogenic seizures in the Frings mouse, providing a valuable resource for elucidating the pathophysiological mechanisms of this inherited form of reflex epilepsy.     

Energetic,oxidative and ionic exchange in rat brain and liver mitochondria at experimental audiogenic epilepsy (Krushinsky–Molodkina model)

The role of brain and liver mitochondria at epileptic seizure was studied on Krushinsky-Molodkina (KM) rats which respond to sound with an intensive epileptic seizure (audiogenic epilepsy). We didn't find significant changes in respiration rats of brain and liver mitochondria of KM and control rats; however the efficiency of АТР synthesis in the KM rat mitochondria was 10% lower. In rats with audiogenic epilepsy the concentration of oxidative stress marker malondialdehyde in mitochondria of the brain (but not liver) was 2-fold higher than that in the control rats. The rate of H₂O₂ generation in brain mitochondria of КМ rats was twofold higher than in the control animals when using NAD-dependent substrates. This difference was less pronounced in liver mitochondria. In KM rats, the activity of mitochondrial ATP-dependent potassium channel was lower than in liver mitochondria of control rats. The comparative study of the mitochondria ability to retain calcium ions revealed that in the case of using the complex I and complex II substrates, permeability transition pore is easier to trigger in brain and liver mitochondria of KM and КМs rats than in the control ones. The role of the changes in the energetic, oxidative, and ionic exchange in the mechanism of audiogenic epilepsy generation in rats and the possible correction of the epilepsy seizures are discussed.     

Role of the brain-stem reticular formation in tonic-clonic seizures: lesion and pharmacological studies

Bilateral lesions of the pontine tegmentum involving the superior cerebellar peduncles and the nucleus reticularis pontis oralis have been shown to attenuate the tonic components of maximal seizures induced by electroshock, sound stimulation (audiogenic), or pentylenetetrazol, although having no effect on clonus in three separate seizure models. The pontine tegmental lesion also abolishes the clonus of minimal audiogenic seizures that have a motor pattern different from that of other clonic models, and are believed to originate in the brain stem. The preponderant suppression of tonus by the pontine tegmental lesion as well as the inhibition of clonus in audiogenic seizures is strikingly similar to the effects of phenytoin in these same seizure models. The findings presented are consistent with the hypothesis that the pontine reticular formation (RF) plays a key role in the generation and/or expression of tonic convulsions. Additional findings are presented that suggest that serotonin may attenuate the tonic components of maximal electroshock seizures by an action on the brain stem. Thus, it seems likely that pontine tegmental lesions as well as antiepileptic drugs and neurotransmitters with preferential effects on tonic seizures act on a common neural substrate that appears to include the brain-stem RF.     

Correlation between tectum formation and expression of two PAX family genes, PAX7 and PAX6, in avian brains

Heterotopic transplantation of brain vesicles between chick and quail were performed, and the correlation between tectum formation and the expression of two PAX family genes, PAX7 and PAX6 , analyzed. Reciprocal transplantation between the prosencephalon and mesencephalon showed that formation of the tectum always coincided with induction/maintenance of PAX7 and suppression of PAX6 , indicating that switch-on or -off of these two PAX family genes in region specific manners are responsible for the differentiation of brain vesicles into the tectum. On the other hand, transplantation of the mesencephalic floor plate into the dorsal mesencephalon suppressed PAX7 expression in the dorsal mesencephalon and changed its fate from the tectum to the tegmentum, indicating that factors in the mesencephalic floor plate suppress PAX7 and limit tectum territory to the dorsal part of the mesencephalon.     

The effect of acetyldexphenmetrazine and dexphenmetrazine on the susceptibility to audiogenic seizures in mice.

The antiepileptic effect of dexphenmetrazine (DP) and acetyldexphenmetrazine (ADP) was tested on audiogenic seizures in a 100% susceptible strain of mice. DP had no antiepileptic effect, however, it markedly suppressed the postparoxysmal motor inhibition. ADP had a distinct anticonvulsive effect--it suppressed the convulsive component of the seizure, leaving its running component unaffected. The results are compared with the effect of both drugs on electrographic epileptic phenomena in the turtle brain (Servít and Strejcková 1976).     

脑电超慢涨落图技术在癫痫研究中的应用

目的：观察脑内多种神经递质对癫痫发作的影响。方法：以癫痫患者和ＳＤ大鼠为实验对象,用脑功能检测的最新脑电超电涨落图分析仪（ｅｎｃｅｐｈａｌｏｆｌｕｃｔｕｏｇｒａｍ ｔｅｃｈｎｏｌｏｇｙ,ＥＴ）长时程采集脑电信号,提取在脑电中载有脑神经递质调节系统的震荡信息（即Ｓ谱线）,分析癫痫发作时的脑神经递质的变化。结果：患儿癫痫发作时,Ｓ谱线中Ｓ２（谷氨酸）增高;Ｓ１（γ－氨基丁酸）降低,造成Ｓ１＜Ｓ２。Ｓ５     

Study of Uridine Effect on the Development of Audiogenic Tonic Seizures in Krushinsky–Molodkina Strain Rats

The latency of tonic seizure in response to loud sound (in rats of the Krushinsky–Molodkina strain with audiogenic epilepsy) had been slightly (although statistically significantly) longer after chronic uridine injections (100 mg/kg, i.p., three times a day during 9 or 12 days). The recovery time from the tonic seizure was shorter after 12 days of injections in comparison to the 9-day injection period. At the same time, the intensity of tonic seizures provoked by loud sound did not change after chronic uridine injections. The lack of uridine anticonvulsive effect demonstrated in the audiogenic epilepsy model contradicts the anticonvulsant effects of uridine in experiments with other seizure models, in which the epileptic foci were localized in the forebrain structures.     

Opposite caudal versus rostral brain nitric oxide synthase response to generalized seizures in a novel rodent model of reflex epilepsy

AimsNitric oxide (NO) is synthesized from L-arginine (L-Arg) by three different isoforms of NO synthase (NOS), i.e. the constitutive neuronal and endothelial NOS (nNOS and eNOS) and the inducible NOS (iNOS). NO has been involved in the pathophysiology of epilepsy, but available data are conflicting and the actual role of NO in epilepsy still remains to be clarified. In this study we investigated the basal and post-seizure levels of constitutive NOS (cNOS) activity as well as the expression of the cNOS isoforms across brain regions in a novel model of epilepsy.Main methodscNOS activity was assessed in various brain areas along the rostro-caudal axis in control wild type hamsters, unstimulated generalized audiogenic seizure prone hamsters, Salamanca strain, GASH:Sal and GASH:Sal after 10 sound-induced epileptic seizures. Additionally, Western blot experiments for nNOS and eNOS were performed in those areas where relevant changes in cNOS activity were found.Key findingsIn the GASH:Sal, cNOS activity increased in the mesencephalic areas studied while cNOS activity decreased in both the striatum and cerebral cortex after 10 sound-induced epileptic seizures. nNOS (but not eNOS) expression paralleled the variations in cNOS activity. The same sound stimulation had no effect on control hamsters.SignificanceThese results suggest a different NOS response in the regions close to the original epileptic focus (caudal, in our auditory model) versus the remote areas (rostral) possibly recruited at later stages or after repeated crises. These findings may account for some of the discrepancies found regarding the role of NO in epilepsy.     

Interaction of Delta Sleep-inducing Peptide and Valproate on Metaphit Audiogenic Seizure Model in Rats

Effects of valproate (VPA), a conventional antiepileptic drug and natural delta sleep-inducing peptide (DSIP) on metaphit (1-[1-(3-isothiocyanatophenyl)-cyclohexyl]-piperidine)-induced audiogenic reflex epilepsy were studied. For the purpose of the study, valproate in the doses of 50 or 75 mg/kg and DSIP (1.0 mg/kg) was i.p. injected either alone or in combination to adult Wistar male rats with fully developed metaphit seizures after eight audiogenic testing. The animals were stimulated using an electric bell (100 ± 3 dB and 5–8 kHz, for 60 s) 60 min after metaphit injection and afterwards at hourly intervals during the experiment. For EEG recording and power spectra analysis, three gold-plated screws were implanted into the scull. In EEGs of metaphit-treated animals polyspikes, spike-wave complexes and sleep-like patterns were recorded, while the power spectra were increased. Combined treatment of metaphit-induced seizures with valproate and DSIP was more effective than drugs alone especially during 4 h after administration. None of the applied dose combinations eliminated the EEG signs of metaphit-provoked epileptiform activity. Taken together, the results of the present study suggest that the combinations of valproate and DSIP should be considered as beneficial polytherapy in metaphit model of epilepsy.     

Moderate body hypothermia alleviates behavioral and EEG manifestations of audiogenic seizures in metaphit-treated rats

We investigated the effects of hypothermia on the incidence and EEG signs of audiogenic seizures in rats treated with metaphit (1-[1(3isothiocyanatophenyl)-cyclohexyl] piperidine), an experimental model of generalized reflex epilepsy. After i.p. injection with metaphit (10 mg/kg) Wistar rats were exposed to audiogenic stimulation at hourly intervals during the time course of the experiment. After intermittent use of an ice pack 8 h after the metaphit treatment, when seizure was fully developed, the body temperature was reduced to 30 +/- 0.5 degrees C in one half of the rats, and maintained at 37 +/- 0.5 degrees C in the other half. Saline-injected rats served as a control group. In the hypothermia group, the incidence of audiogenic seizures induced by metaphit was completely suppressed during the 3 consecutive testing times, while no signs of epileptiform activity were noted in EEG tracings. The termination of hypothermic treatment resulted in the recovery of seizure susceptibility, and during audiogenic stimulation, bursts of spiking activity were recorded in the EEGs of metaphit-treated rats. These findings indicate that moderate body hypothermia is an effective anticonvulsant treatment for audiogenic seizures in metaphit-treated rats.     

Glutamate receptor GluR1 expression is altered selectively by chronic audiogenic seizures in the Frings mouse brain

The audiogenic seizure-susceptible mouse, Frings, is genetically susceptible to sound-induced seizures and provides a reliable model of reflex epilepsy that lasts throughout the life span of the animal. We used immunohistochemistry to examine if the expression of the non-N-methyl-D -aspartate glutamate receptor (GluR) subunits GluR1, GluR2, or GluR3 were altered subsequent to multiple seizures. Following a regimen of one seizure per day for 3 weeks, GluR1 immunoreactivity, but not GluR2 or GluR3, was substantially elevated in the outer shell of the nucleus accumbens in 21 of 31 chronically seized Frings mice. No other brain regions such as the hippocampus exhibited any qualitative changes in expression of these subunits. In 9 of the 21 Frings mice exhibiting increased GluR1, but in none of the controls, bilateral structural lesions were observed in the lateral hypothalamus. These results support a model where highly localized changes in the expression of GluR1 occur in response to repeated audiogenic seizure. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 209–216, 1998     

Neural Disturbances in Chickens Caused by Dietary T-2 Toxin

Graded concentrations of dietary T-2 toxin (0, 1, 2, 4, 8, and 16 mug/g) were fed to groups of 40 chickens. T-2 toxin was found to cause an abnormal positioning of the wings, hysteroid seizures, and impaired righting reflex in young chickens. The abnormal wing positioning occurred spontaneously or as the result of dropping from a height of 1 meter. The seizures could be elicited by rough handling or loud noises. The seizures and the abnormal wing posture would not occur again when the stimulus was repeated unless a rest period of 3 to 6 h was allowed. The loss of righting reflex could be demonstrated at any time. The total incidence of neural symptoms was dependent on the length of exposure to T-2 toxin and to its concentration. Neural toxicity occurred at dosages of 4, 8, and 16 mug per g of diet, which are the same doses that retard growth. This neural toxicity of T-2 toxin in chickens is similar to the neural disturbances associated with alimentary toxic aleukia, a nutritional toxicosis of humans produced by eating moldy grain. T-2 toxin has been implicated also in moldy corn toxicosis which has neural manifestations in horses and swine.     

Are WAG/Rij rats with genetic absence epilepsy anxious?

Behavior of susceptible and non-susceptible to audiogenic (convulsive) seizures rats from inbred WAG/Rij strain, genetically predisposed to absence epilepsy, and outbred Wistar strain, genetically not predisposed to absence epilepsy, was compared to assess the level of anxiety (in open field, light-dark choice and elevated plus-maze tests) and the level of depressiveness (in the sucrose consumption and forced swimming tests). Increased level of anxiety was found only in susceptible to audiogenic seizures rats both from WAG/Rij and Wistar strain, but increased level of depressiveness was found only in WAG/Rij strain rats as compared with Wistar rats independently of their susceptibility to audiogenic seizures. Results suggest that increased depressiveness in WAG/Rij strain rats is associated with absence epilepsy but increased anxiety with susceptibility to audiogenic seizures.     

Analysis of inherited epilepsy using single locus mutations in mice.

The neurological expression of mutations at defined gene loci in isogenic mice provides a singular opportunity to investigate the developmental pathophysiology of inherited central nervous system (CNS) diseases. Analysis of the single locus mutants that are currently available shows that CNS diseases that include spontaneous seizures as symptoms can be inherited as simple recessive traits. Mutant gene dose is highly correlated with the spontaneous occurrence of seizures. Single gene defects at one of multiple chromosomal loci may give rise to similar epileptic patterns. One mutation, tottering (tg, chromosome 8, recessive) produces in young mice a focal motor seizure pattern with a somatotopic progression, and behavioral absence seizures accompanied by abnormal bursts of bilaterally synchronous, spike-wave discharges in the electrocorticogram. Spontaneous electrographic and clinical seizures of this general pattern bear close resemblance to common forms of human epilepsy. Defined alterations in restricted neuronal pathways of the mouse brain produced by single locus mutations can be used to infer general principles of inherited epileptogenesis, and may provide specific biological test systems for the development of more selective chemical antagonists of seizure activity.     

Synaptic and extrasynaptic GABA transporters as targets for anti-epileptic drugs

Inhibition of the GABA transporter subtype GAT1 by the clinically available anti-epileptic drug tiagabine has proven to be an effective strategy for the treatment of some patients with partial seizures. In 2005, the investigational drug EF1502 was described as possessing activity at both GAT1 and BGT-1. When combined with the GAT1 selective inhibitor tiagabine, EF1502 was found to possess a synergistic anti-convulsant action in the Frings audiogenic seizure-susceptible mouse model of reflex epilepsy. This effect was subsequently attributed to inhibition of BGT-1. In this study, the anti-convulsant effect of the GAT2/3 inhibitor SNAP-5114 was assessed in the Frings audiogenic seizure-susceptible mouse alone, and in combination with tiagabine and EF1502. The results showed that SNAP-5114 produced a synergistic anti-convulsant effect in combination with EF1502 but not when used in combination with tiagabine. These findings support anatomical evidence that GAT2/3 are most likely located at the synapse in close proximity to GAT1; whereas BGT-1 is located some distance away from the synapse and GAT1 and GAT2/3. Lastly, EF1502 and tiagabine were evaluated alone, and in combination, in the corneal kindled mouse model of partial epilepsy. The results of this evaluation provide further evidence in support of a role for BGT-1 in the control of seizure activity. In addition, they suggest that the combined inhibition of GAT1 and BGT-1 may afford some advantage over inhibiting either transporter alone.     

Epileptiform seizures in domestic fowl. V. The anticonvulsant activity of delta9-tetrahydrocannabinol.

The anticonvulsant activity of delta9-tetrahydrocannabinol (delta9-THC) has been determined against seizures induced in epileptic chickens by intermittent photic stimulation (IPS) and in epileptic and nonepileptic chickens by Metrazol. Intravenous administration of the drug reduced both the severity and incidence of seizures evoked by IPS in epileptic chickens. This anticonvulsant action was accompanied by a reduction in frequency of inter-ictal slow-wave high-voltage electroencephalographic activity and by the absence of spiking during IPS. delta9-THC did not affect the incidence of Metrazol-induced seizures in epileptic or nonepileptic chickens.     

Neuroanatomical localization of structures responsible for seizures in the GEPR: lesion studies

Identification of the neural substrates subserving audiogenic convulsions in the GEPR is an important task and while it is not yet complete, many laboratories employing various techniques have contributed importantly to our current understanding. The present review focuses on the use of lesions to identify the neural substrates of audiogenic convulsions. Lesions in brain stem nuclei appear to have a much greater ability to attenuate audiogenic convulsions than do forebrain lesions. In fact, some forebrain lesions (dorsal hippocampus, caudate, intralaminar thalamic nuclei) appear to enhance the severity of audiogenic seizures. On the other hand, bilateral lesions in the inferior colliculus (IC) have been shown to completely abolish audiogenic convulsions, while lesions in the pontine reticular formation (PRF nucleus) abolish all aspects except the running episode suggesting that these two brain stem structures are important neural substrates involved in the expression of audiogenic convulsions. Large bilateral lesions of the substantia nigra also appear to attenuate audiogenic convulsions. The effect of lesions on audiogenic convulsions is basically similar to their effect on other generalized seizure models and the data appear to support the hypothesis that there are two anatomical systems involved in the expression of all generalized convulsions: a forebrain system responsible for the expression of face and forelimb clonus; and a brain stem system responsible in the expression of running-bouncing clonus and tonus.     

Comparative study of appearance of water-soluble antigens and brain esterase fractions in ontogenesis of two strains of rats

By means of immunoelectrophoresis of rat brain, 12 water-soluble antigens were detected, five of which were found to be specific to the brain. Histochemical reactions have identified two antigens that are not specific to the brain, lactate dehydrogenase and esterase. By means of enzymoelectrophoresis, 14 esterase fractions were determined. An immunoautoradiographic study of the synthesis of some antigens specific to the brain was carried out. It was found that rats responding to sound by epileptic seizures develop more slowly than normal rats. In particular, in rats resistant to auditory stimulus the antigenic spectrum typical of the brain of the adult rat (12 antigens) is formed by day 14 of postnatal life, while in rats of the sensitive strain this pattern takes 17 days to completely form. The last brain-specific antigen for rats susceptible to audiogenic epilepsy appears on day 17, while this antigen is present in normal rats on day 14. Fast-moving esterase fractions are detected earlier in ontogenesis in rats resistant to sound than in sensitive rats.