Spike-and-wave Discharges Research Articles

Modulation of no signaling pathways in an experimental model of epilepsy: Focus on ictal EEG

One of the EEG hallmarks of homocysteine thiolactone (HcT)-induced epilepsy is spike-and-wave discharges (SWD). Nitric oxide (NO) is gasotransmitter produced by neuronal, endothelial and inducible NO synthesis (NOS). Contribution of NO-mediated signaling in epileptogenesis is unclear. The aim of our experiments were to compare the effects of non-selective (L-NAME) and selective (7-nitroindazole for neuronal and aminoguanidine for inducible) NOS inhibitors on ictal EEG phenomena in a model of HcT-induced epilepsy in rats. Male Wistar rats with implanted EEG-recording electrodes were intraperitoneally treated with HcT (subconvulsive dose of 5.5 mmol/kg) and EEG activity was recorded during next 90 min. L-NAME (700 mg/kg), 7-nitroindazole (75 mg/kg), aminoguanidine (100 mg/kg) or saline were injected 30 min prior to HcT administration. Visual inspection of digital EEG signals and analysis of number and duration of SWDs was performed offline. L-NAME significantly increased the number of SWDs per rat induced by HcT, but did not affect its duration. 7-nitroindazole increased duration, but not the number of SWDs in this model. Aminoguanidine increased both parameters significantly. These results indicated that modulation of NO-singaling pathways could affect EEG manifestations of HcT epilepsy showing contribution of this gasotransmitter in epileptogenesis and prominent effects of iNOS inhibition.

Carbamazepine aggravates absence seizures in two dedicated mouse models.

The aim of this study was to evaluate the effect of carbamazepine (CBZ) upon chemically induced absence seizures and in a genetic absence seizures model in the mouse. The γ-butyrolactone (GBL)-induced acute absence seizures and the stargazer spontaneous absence seizures mice models were used to characterize the aggravation of absence seizures induced by oral CBZ treatment. The effect of CBZ upon GABA inward-currents in Ltk cells expressing human recombinant α1β2γ2, α2β2γ2, α3β2γ2 and α5β2γ2 GABAA receptors was evaluated by means of patch clamp. GBL administration induced motor impairment in NMRI mice. High dose CBZ (25mg/kg body weight) had no effect on motor performance but exacerbated the behavioral incoordination observed for GBL. Also, coadministration of a high dose CBZ and GBL impaired spontaneous locomotion. Moreover, CBZ was investigated after oral administration to evaluate the potential to aggravate GBL-induced acute spike-and-wave discharges (SWD) in the electroencephalogram. High dose CBZ significantly aggravated SWD induced by GBL. Likewise, in the stargazer mouse model of genetic spontaneous absence seizures, CBZ significantly aggravated SWD frequency and duration. Pre-treatment with the T-type Ca(2+) channel blocker ethosuximide (200mg/kg body weight) prevented the CBZ aggravation of SWD induced by GBL and in the stargazer mouse. CBZ increased in a concentration dependent manner sub-maximal α1β2γ2 and α3β2γ2 GABA currents. CBZ aggravates absence seizures as assessed in two dedicated mouse models of absence seizures. Facilitation of sub-maximal α1β2γ2, and α3β2γ2 GABA currents by CBZ may play a role in CBZ-induced GABA-mediated aggravation of absence seizures.

Role of Laterodorsal Thalamic Nucleus during Absence Seizure Attacks

Introduction: A typical absence epilepsy is a type of nonconvulsive and generalized epilepsy. The main feature of these attacks is a sudden brief impairment of consciousness. The disturbances in thalamocortical loop play an important role in pathogenesis of absence seizures. However, it is not clear that which part of this network triggers the seizure. This study was aimed to investigate the role of latrodorsal (LD) thalamic neurons during spike and wave discharges (SWDs) in WAG/Rij rats, as the most valid animal model of absence epilepsy. Materials and Methods: Single unit activities in the LD thalamic nucleus and electrocorticogram of somatosensory cortex were simultaneously recorded in six-month-old WAG/Rij rats. Results: During SWDs, unit activity in the LD thalamic nucleus showed burstlike discharges, which were started before the peak component of SWDs. In SWD-free periods, burst like activity in the LD was reduced. Conclusion: Our findings suggest that the burst firing of LD may stimulate the neocortex to exhibit SWDs. It can be concluded that inhibition of

Reduced susceptibility to induced seizures in the Neuroligin-3R451C mouse model of autism

Epilepsy is a common comorbidity in patients with autism spectrum disorder (ASD) and several gene mutations are associated with both of these disorders. In order to determine whether a point mutation in the gene for the synaptic protein, Neuroligin-3 (Nlgn3, R451C), identified in patients with ASD alters seizure susceptibility, we administered the proconvulsant pentylenetetrazole (PTZ) to adult male Neuroligin-3R451C (NL3R451C) and wild type (WT) mice. It has previously been reported that NL3R451C mice show altered inhibitory GABAergic activity in brain regions relevant to epilepsy, including the hippocampus and somatosensory cortex. PTZ administration induces absence-seizures at low dose, and generalised convulsive seizures at higher dose. Susceptibility to absence seizures was examined by analysing the frequency and duration of spike-and-wave discharge (SWD) events and accompanying motor seizure activity induced by subcutaneous administration of low dosage (20 or 30mg/kg) PTZ. Susceptibility to generalised convulsive seizures was tested by measuring the response to high dosage (60mg/kg) PTZ using a modified Racine scale. There was no change in the number of SWD events exhibited by NL3R451C compared to WT mice following administration of both 20mg/kg PTZ (1.17±0.31 compared to 16.0±11.16 events/30min, NL3R451C versus WT, respectively) and 30mg/kg PTZ (7.5±6.54 compared with 27.8±19.9 events/30min, NL3R451C versus WT, respectively). NL3R451C mice were seizure resistant to generalised convulsive seizures induced by high dose PTZ compared to WT littermates (median latency to first >3s duration clonic seizure; 14.5min versus 7.25min, 95% CI: 1.625–2.375, p=0.0009, NL3R451C versus WT, respectively). These results indicate that the R451C mutation in the Nlgn3 gene, associated with ASD in humans, confers resistance to induced seizures, suggesting dysfunction of PTZ-sensitive GABAergic signalling in this mouse model of ASD.

Effect of caffeine and adenosine receptor ligands on the expression of spike-and-wave discharges in Genetic Absence Epilepsy Rats from Strasbourg (GAERS)

The influence of caffeine on epileptic seizures remains a matter of debate. Here we tested on Genetic Absence Epilepsy Rats from Strasbourg (GAERS) the consequences of acute and chronic exposure to caffeine on the expression of spike-and-wave discharges (SWDs). Since caffeine is a mixed nonspecific A(1) and A(2A) adenosine receptor antagonist, we measured also the influence of antagonists and agonists of these receptors on SWD expression. GAERS were equipped with four cortical electrodes over the frontoparietal cortex and the cumulated duration and number of SWDs were recorded for 120 min after the injection of increasing doses of caffeine, specific antagonists and agonists of A(1) and A(2A) adenosine receptors. The effects of chronic caffeine were also studied. In GAERS, caffeine dose-dependently reduced the cumulated number and duration of SWDs which almost disappeared after the injection of the two highest doses of caffeine, 5 and 10 mg/kg. Likewise, the A(1) and A(2A) adenosine receptor antagonists led to a dose-dependent reduction of SWD expression while the agonists dose-dependently increased SWD expression. Conversely, the chronic exposure to caffeine via drinking water for 15 days did not influence SWD expression. With the exception of the two highest doses of caffeine that largely enhanced activity, all compounds including low doses of caffeine had no effect on locomotor activity of GAERS. These data show that the acute exposure to low doses of caffeine, or A(1) and A(2A) adenosine receptor antagonists reduces SWD expression in GAERS, independently from any effect on motor activity. The chronic exposure of GAERS to caffeine does not affect the expression of epilepsy.

Oxcarbazepine and its active metabolite, (S)-licarbazepine, exacerbate seizures in a mouse model of genetic generalized epilepsy.

Oxcarbazepine (OXC), widely used to treat focal epilepsy, is reported to exacerbate seizures in patients with generalized epilepsy. OXC is metabolized to monohydroxy derivatives in two enantiomeric forms: (R)-licarbazepine and (S)-licarbazepine. Eslicarbazepine acetate is a recently approved antiepileptic drug that is rapidly metabolized to (S)-licarbazepine. It is not known whether (S)-licarbazepine exacerbates seizures. Here, we test whether OXC or either of its enantiomers exacerbates the number of spike-and-wave discharges (SWDs) in mice harboring the human γ-aminobutyric acid A receptor (GABAA)γ2(R43Q) mutation. OXC (20 mg/kg), (S)-licarbazepine (20 mg/kg), and (R)-licarbazepine (20 mg/kg) all significantly increased the number of SWDs, while their duration was unaffected. The potential for (S)-licarbazepine to exacerbate SWDs suggests that eslicarbazepine acetate should be used with caution in generalized epilepsy. Furthermore, generalized seizure exacerbation for first-, second-, and third-generation carbamazepine-based compounds is likely to occur through a common mechanism.

Electroencephalographic and behavioral effects of intracerebroventricular or intraperitoneal injections of toxic honey extract in adult Wistar rats and GAERS.

Toxic honey, containing grayanotoxin, is obtained from nectar and polen of rhododendron. Consumed in excess it produces seizures and convulsions. In order to investigate whether the toxic honey extract can be used as a seizure model, we examined the electroencephalographic (EEG) and motor effects of intracerebroventricular (icv) or intraperitoneal (ip) injection of toxic honey extract in Wistar rats or in genetic absence epilepsy rats from Strasbourg (GAERS). Male Wistar rats or GAERS were stereotaxically implanted with bilateral cortical recording electrodes in all ip groups and cannula in the icv groups. Based on the previous study, an extract was obtained from the non-toxic and toxic honey. After the injection of the non-toxic or toxic honey extract, seizure stages and changes in EEG were evaluated from 9 am to noon. The icv administration of toxic honey extract produced stage 4 seizures and bilateral cortical spikes within 30-60 min and these effects disappeared after 120 min in Wistar rats or GAERS. The mean of bilateral cortical spike acitivity in EEG of Wistar rats was 804.2 ± 261.0 s in the 3-h period. After the icv administration of toxic honey extract to GAERS, the mean duration of spike-and-wave discharges (SWDs) in GAERS significantly decreased during the first 60 min and then returned to baseline level. Ip injection of toxic honey extract caused no seizure and no change in EEG in either GAERS or Wistars. These results suggest that the icv administration of toxic honey extract can be used as a seizure model.

Rebound burst firing in the reticular thalamus is not essential for pharmacological absence seizures in mice.

Intrinsic burst and rhythmic burst discharges (RBDs) are elicited by activation of T-type Ca(2+) channels in the thalamic reticular nucleus (TRN). TRN bursts are believed to be critical for generation and maintenance of thalamocortical oscillations, leading to the spike-and-wave discharges (SWDs), which are the hallmarks of absence seizures. We observed that the RBDs were completely abolished, whereas tonic firing was significantly increased, in TRN neurons from mice in which the gene for the T-type Ca(2+) channel, CaV3.3, was deleted (CaV3.3(-/-)). Contrary to expectations, there was an increased susceptibility to drug-induced SWDs both in CaV3.3(-/-) mice and in mice in which the CaV3.3 gene was silenced predominantly in the TRN. CaV3.3(-/-) mice also showed enhanced inhibitory synaptic drive onto TC neurons. Finally, a double knockout of both CaV3.3 and CaV3.2, which showed complete elimination of burst firing and RBDs in TRN neurons, also displayed enhanced drug-induced SWDs and absence seizures. On the other hand, tonic firing in the TRN was increased in these mice, suggesting that increased tonic firing in the TRN may be sufficient for drug-induced SWD generation in the absence of burst firing. These results call into question the role of burst firing in TRN neurons in the genesis of SWDs, calling for a rethinking of the mechanism for absence seizure induction.

Anxiety and locomotion in Genetic Absence Epilepsy Rats from Strasbourg (GAERS): inclusion of Wistar rats as a second control.

The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is a genetic model, derived from Wistar rats by selective breeding. In all previous studies, GAERS were compared to their paired selected strain not expressing spike-and-wave discharges (SWDs), namely nonepileptic controls (NECs). Because the occurrence/absence of SWDs is of polygenic origin, some other traits could have been selected along with occurrence/absence of SWDs. Therefore, we explored the importance of using a second control group consisting in Wistar rats, the strain of origin of GAERS, in addition to NECs, on locomotion and anxiety in GAERS. A test battery encompassing home-cage, open-field, beam-walking and elevated plus-maze evaluations was used. In addition, stereologic analyses were performed to assess the volume of thalamus, amygdala, and hippocampus. The occurrence/absence of SWDs was determined in all three strains by electroencephalography (EEG) recording. When compared to NECs and Wistars, GAERS displayed lower exploratory activity and fastened habituation to novelty. In the plus-maze, scores of GAERS and Wistars were similar, but NECs appeared significantly less anxious (possibly in association with increased amygdala volume); evidence for weaker anxiety in NECs was also found in the open-field evaluation. The volumetric study revealed increased thalamic volume in GAERS compared to both control groups. SWDs were present in all GAERS and in 80% of Wistars. Compared to the original Wistar strain as an additional control group, the selective breeding that generated the GAERS has no incidence on anxiety-related behavior, conversely to the selection of SWD suppression in NECs, in which anxiety is attenuated. These findings point to the importance of using a second control group composed of Wistar rats in studies characterizing the behavioral profile of GAERS. Thereby, possible confusions between occurrence/absence of SWDs and other features that come along with selection and/or differential brain development induced by the genetic mutations are reduced.

Thalamocortical neurons display suppressed burst-firing due to an enhanced Ih current in a genetic model of absence epilepsy.

Burst-firing in distinct subsets of thalamic relay (TR) neurons is thought to be a key requirement for the propagation of absence seizures. However, in the well-regarded Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model as yet there has been no link described between burst-firing in TR neurons and spike-and-wave discharges (SWDs). GAERS ventrobasal (VB) neurons are a specific subset of TR neurons that do not normally display burst-firing during absence seizures in the GAERS model, and here, we assessed the underlying relationship of VB burst-firing with Ih and T-type calcium currents between GAERS and non-epileptic control (NEC) animals. In response to 200-ms hyperpolarizing current injections, adult epileptic but not pre-epileptic GAERS VB neurons displayed suppressed burst-firing compared to NEC. In response to longer duration 1,000-ms hyperpolarizing current injections, both pre-epileptic and epileptic GAERS VB neurons required significantly more hyperpolarizing current injection to burst-fire than those of NEC animals. The current density of the Hyperpolarization and Cyclic Nucleotide-activated (HCN) current (Ih) was found to be increased in GAERS VB neurons, and the blockade of Ih relieved the suppressed burst-firing in both pre-epileptic P15–P20 and adult animals. In support, levels of HCN-1 and HCN-3 isoform channel proteins were increased in GAERS VB thalamic tissue. T-type calcium channel whole-cell currents were found to be decreased in P7–P9 GAERS VB neurons, and also noted was a decrease in CaV3.1 mRNA and protein levels in adults. Z944, a potent T-type calcium channel blocker with anti-epileptic properties, completely abolished hyperpolarization-induced VB burst-firing in both NEC and GAERS VB neurons.

Regionally specific expression of high-voltage-activated calcium channels in thalamic nuclei of epileptic and non-epileptic rats.

The polygenic origin of generalized absence epilepsy results in dysfunction of ion channels that allows the switch from physiological asynchronous to pathophysiological highly synchronous network activity. Evidence from rat and mouse models of absence epilepsy indicates that altered Ca(2+) channel activity contributes to cellular and network alterations that lead to seizure activity. Under physiological circumstances, high voltage-activated (HVA) Ca(2+) channels are important in determining the thalamic firing profile. Here, we investigated a possible contribution of HVA channels to the epileptic phenotype using a rodent genetic model of absence epilepsy. In this study, HVA Ca(2+) currents were recorded from neurons of three different thalamic nuclei that are involved in both sensory signal transmission and rhythmic-synchronized activity during epileptic spike-and-wave discharges (SWD), namely the dorsal part of the lateral geniculate nucleus (dLGN), the ventrobasal thalamic complex (VB) and the reticular thalamic nucleus (NRT) of epileptic Wistar Albino Glaxo rats from Rijswijk (WAG/Rij) and non-epileptic August Copenhagen Irish (ACI) rats. HVA Ca(2+) current densities in dLGN neurons were significantly increased in epileptic rats compared with non-epileptic controls while other thalamic regions revealed no differences between the strains. Application of specific channel blockers revealed that the increased current was carried by L-type Ca(2+) channels. Electrophysiological evidence of increased L-type current correlated with up-regulated mRNA and protein expression of a particular L-type channel, namely Cav1.3, in dLGN of epileptic rats. No significant changes were found for other HVA Ca(2+) channels. Moreover, pharmacological inactivation of L-type Ca(2+) channels results in altered firing profiles of thalamocortical relay (TC) neurons from non-epileptic rather than from epileptic rats. While HVA Ca(2+) channels influence tonic and burst firing in ACI and WAG/Rij differently, it is discussed that increased Cav1.3 expression may indirectly contribute to increased robustness of burst firing and thereby the epileptic phenotype of absence epilepsy.

Head-to head comparison of mGlu1 and mGlu5 receptor activation in chronic treatment of absence epilepsy in WAG/Rij rats

Acute treatment with positive allosteric modulators (PAMs) of mGlu1 and mGlu5 metabotropic glutamate receptors (RO0711401 and VU0360172, respectively) reduces the incidence of spike-and wave discharges in the WAG/Rij rat model of absence epilepsy. However, from the therapeutic standpoint, it was important to establish whether tolerance developed to the action of these drugs. We administered either VU0360172 (3 mg/kg, s.c.) or RO0711401 (10 mg/kg, s.c.) to WAG/Rij rats twice daily for ten days. VU0360172 maintained its activity during the treatment, whereas rats developed tolerance to RO0711401 since the 3rd day of treatment and were still refractory to the drug two days after treatment withdrawal. In response to VU0360172, expression of mGlu5 receptors increased in the thalamus of WAG/Rij rats after 1 day of treatment, and remained elevated afterwards. VU0360172 also enhanced mGlu5 receptor expression in the cortex after 8 days of treatment without changing the expression of mGlu1a receptors. Treatment with RO0711401 enhanced the expression of both mGlu1a and mGlu5 receptors in the thalamus and cortex of WAG/Rij rats after 3–8 days of treatment. These data were different from those obtained in non-epileptic rats, in which repeated injections of RO0711401 and VU0360172 down-regulated the expression of mGlu1a and mGlu5 receptors. Levels of VU0360172 in the thalamus and cortex remained unaltered during the treatment, whereas levels of RO0711401 were reduced in the cortex at day 8 of treatment. These findings suggest that mGlu5 receptor PAMs are potential candidates for the treatment of absence epilepsy in humans

Ethosuximide reduces electrographical and behavioral correlates of alcohol withdrawal seizure in DBA/2J mice

Chronic alcohol abuse depresses the nervous system and, upon cessation, rebound hyperexcitability can result in withdrawal seizure. Withdrawal symptoms, including seizures, may drive individuals to relapse, thus representing a significant barrier to recovery. Our lab previously identified an upregulation of the thalamic T-type calcium (T channel) isoform CaV3.2 as a potential contributor to the generation and propagation of seizures in a model of withdrawal. In the present study, we examined whether ethosuximide (ETX), a T-channel antagonist, could decrease the severity of ethanol withdrawal seizures by evaluating electrographical and behavioral correlates of seizure activity. DBA/2J mice were exposed to an intermittent ethanol exposure paradigm. Mice were treated with saline or ETX in each withdrawal period, and cortical EEG activity was recorded to determine seizure severity. We observed a progression in seizure activity with each successive withdrawal period. Treatment with ETX reduced ethanol withdrawal-induced spike and wave discharges (SWDs), in terms of absolute number, duration of events, and contribution to EEG power in the 6–10 Hz frequency range. We also evaluated the effects of ETX on handling-induced convulsions. Overall, we observed a decrease in handling-induced convulsion severity in mice treated with ETX. Our findings suggest that ETX may be a useful pharmacological agent for studies of alcohol withdrawal and treatment of resulting seizures.

The effect of amygdala kindling on neuronal firing patterns in the lateral thalamus in the GAERS model of absence epilepsy

The co-occurrence of absence and mesial temporal lobe epilepsy is rare in both humans and animal models. Consistent with this, rat models of absence epilepsy, including genetic absence epilepsy rats from Strasbourg (GAERS), are resistant to experimental temporal lobe epileptogenesis, in particular by amygdala kindling. Structures within the cortical-thalamocortical system are critically involved in the generation and maintenance of the electrographic spike-and-wave discharges (SWDs) that characterize absence seizures. Using in vivo electrophysiologic recordings, this study investigated the role of thalamocortical circuitry in the generalization of amygdala-kindling induced seizures in the GAERS and the nonepileptic control (NEC) strain of Wistar rats. GAERS and NEC rats were implanted with a stimulating electrode in amygdala and stimulated at afterdischarge threshold twice daily to a maximum number of 30 stimulations. Thereafter extracellular single neuron recordings were performed in vivo under neuroleptanesthesia in the thalamocortical network. In NEC rats, amygdala kindling induced convulsive class V seizures and altered characteristics of neuronal activity in the thalamic reticular nucleus (TRN), in particular decreased firing rates and increased burst firing patterns. Less marked changes were seen in other regions examined: the ventroposteromedial nucleus of thalamus (VPM), the CA3 region of the hippocampus, and the deep layers (V/VI) of the cortex. GAERS did not progress beyond class II seizures, with a matched number of kindling stimulations, and the thalamic neuronal firing alterations observed in NEC rats were not seen. These data suggest that the TRN plays an important role in kindling resistance in GAERS and is central to the control of secondary generalization of limbic seizures.

T-type Ca2+ channels in absence epilepsy

Absence epilepsy accompanies the paroxysmal oscillations in the thalamocortical circuit referred as spike and wave discharges (SWDs). Low-threshold burst firing mediated by T-type Ca(2+) channels highly expressed in both inhibitory thalamic reticular nuclei (TRN) and excitatory thalamocortical (TC) neurons has been correlated with the generation of SWDs. A generally accepted view has been that rhythmic burst firing mediated by T-type channels in both TRN and TC neurons are equally critical in the generation of thalamocortical oscillations during sleep rhythms and SWDs. This review examined recent studies on the T-type channels in absence epilepsy which leads to an idea that even though both TRN and TC nuclei are required for thalamocortical oscillations, the contributions of T-type channels to TRN and TC neurons are not equal in the genesis of sleep spindles and SWDs. Accumulating evidence revealed a crucial role of TC T-type channels in SWD generation. However, the role of TRN T-type channels in SWD generation remains controversial. Therefore, a deeper understanding of the functional consequences of modulating each T-type channel subtype could guide the development of therapeutic tools for absence seizures while minimizing side effects on physiological thalamocortical oscillations.

Epilepsy and phenylketonuria: a case description and EEG-fMRI findings

Phenylketonuria (PKU) is characterized by phenylalanine accumulation due to phenylalanine hydroxylase deficiency. Up to 50% of PKU patients experience seizures. We evaluated an adult PKU patient who suffered from absences and primarily generalized tonicclonic seizures, associated with generalized spikeand-wave discharges (GSWs) on EEG. An analysis of blood oxygenation level-dependent (BOLD) signal changes during interictal epileptiform discharges showed early activation of the left perirolandic cortex followed by a BOLD signal decrease within cortical regions belonging to the default mode network and left frontoparietal cortex. Moreover, deactivation of the head of the right caudate nucleus and the left thalamus was observed. The fMRI pattern observed in our patient during GSWs is similar but not identical to that observed in idiopathic generalized epilepsy, suggesting different neurophysiological mechanisms. This is the first description of BOLD-fMRI patterns in a PKU patient with epilepsy. Similar studies in more patients might help to uncover the pathophysiology of seizures in this disease.

5% CO2 inhalation suppresses hyperventilation-induced absence seizures in children

Hyperventilation can cause respiratory alkalosis by exhaling CO2, and is often used to confirm diagnosis of absence epilepsy. CO2 has long been known for its anticonvulsant properties since the 1920s. In this pilot study, we aimed to determine whether inhaling medical carbogen containing 5% CO2 and 95% O2 can suppress hyperventilation-induced absence seizures and spike-and-wave discharges (SWDs). We examined 12 patients whose absence seizures were induced by hyperventilation using video electroencephalographic recording for at least 4h. The patients were asked to hyperventilate for 3 min while breathing the following gases: (1) room air (12 patients); (2) carbogen (12 patients); and (3) 100% O2 (8 patients). Eight out of twelve patients were also examined in room air through pretreatment with carbogen for 3 min before the 3 min hyperventilation. Compared with hyperventilation in room air, hyperventilation supplemented with 5% CO2 had the following effects: (a) decrease in the number and duration of seizures; (b) prolonged appearance of epileptic discharges; and (c) reduction in the number and duration of SWDs (P<0.001). However, pretreatment with 5% CO2 and 100% O2 supplement did not yield similar effects. We demonstrated that 5% CO2 could suppress hyperventilation-induced absence seizures and SWDs, supporting the claim that 5% CO2 is an effective anticonvulsant agent. Our pilot study provides clinical basis that 5% CO2 inhalation could be a therapeutic approach for hyperventilation-related seizures.

Causal influence of epileptic network during spike-and-wave discharge in juvenile myoclonic epilepsy

Electroencephalographic (EEG) characteristic of juvenile myoclonic epilepsy (JME) is spike-and-wave discharge (SWD), which is dominant in the frontal region. However, activity in the parietal area, including the precuneus, has also been documented for several seconds before and during SWD. The aim of this study was to identify the role of the parietal region, especially the precuneus, and to clarify the causal dynamics among cortical regions during SWD. EEGs were obtained from seven patients with JME. Each SWD was divided into six distinct temporal phases: spike onset, spike peak, slow-wave onset, slow-wave ascending, slow-wave peak, and slow-wave descending phases. Based on the cortical current source distribution and the results of a previous study, we selected the medial frontal, orbitofrontal, anterior cingulate, and mesial temporal cortices and the precuneus as regions of interest (ROIs). To assess epileptic networks and the causal relationships among ROIs during SWD, the directed transfer function (DTF), a measure of multivariate causality, was calculated for each phase of SWD. During spike onset, the maximal outdegree region in all patients was the precuneus. The spike-peak and slow-wave onset phases did not show a consistently dominant outflow region. Outflow from the anterior cingulate cortex was dominant in four patients during the slow-wave ascending phase, and the precuneus showed the maximal outdegree in six patients during the slow-wave peak. In the slow-wave descending phase, four patients showed maximal outflow from the temporal cortex. Our findings suggest that the precuneus is likely a key region for SWD despite the small amount of neural activity observed. The precuneus was the region with the maximal outdegree during both the spike onset and slow-wave peak phases, indicating that SWD in JME is initiated and sustained by a network involving the frontal cortex, precuneus, and thalamus.

Exercise Decreases Susceptibility to Homocysteine Seizures: the Role of Oxidative Stress

The aim of the study was to examine the effects of chronic exercise training on seizures induced by homocysteine thiolactone (HCT) in adult rats. Rats were assigned to: sedentary control; exercise control; sedentary+HCT; exercise+HCT group. Animals in the exercise groups ran 30 min daily on a treadmill for 30 consecutive days (belt speed 20 m/min), while sedentary rats spent the same time on the treadmill (speed 0 m/min). On the 31st day, the HCT groups received HCT (8.0 mmol/kg), while the control groups received vehicle. Afterwards, convulsive behavior and EEG activity were registered. Lipid peroxidation, superoxide dismutase (SOD) and catalase (CAT) activity were ascertained in the rat hippocampus. No signs of seizures were registered in sedentary and exercise control rats. Seizure latency was increased, while number of seizure episodes and spike-and-wave discharges (SWD) in EEG were decreased in the exercise+HCT compared to the sedentary+HCT group. Seizure incidence, the severity thereof and duration of SWDs were not significantly different between these groups. Exercise partly prevented increase of lipid peroxidation and decrease of the SOD and CAT activity after HCT administration. These results indicate beneficial effects of exercise in model of HCT-induced seizures in rats, what could be, at least in part, a consequence of improved antioxidant enzymes activity.

Homocysteine thiolactone-induced seizures in adult rats are aggravated by inhibition of inducible nitric oxide synthase

Homocysteine and its metabolites (homocysteine thiolactone (HT)) induce seizures via different but still not well-known mechanisms. The role of nitric oxide (NO) in epileptogenesis is highly contradictory and depends on, among other factors, the source of NO production. The aim of the present study was to examine the effects of aminoguanidine, selective inhibitor of inducible NO synthase (iNOS), on HT-induced seizures. Aminoguanidine (50, 75, and 100mg/kg, intraperitoneally (i.p.)) was injected to rats 30min prior to inducing HT (5.5mmol/kg, i.p.). Seizure behavior was assessed by seizure incidence, latency time to first seizure onset, number of seizure episodes, and their severity during observational period of 90min. Number and duration of spike and wave discharges (SWDs) were determined in electroencephalogram (EEG). Seizure latency time was significantly shortened, while seizure incidence, number, and duration of HT-induced SWD in EEG significantly increased in rats receiving aminoguanidine 100mg/kg before subconvulsive dose of HT. Aminoguanidine in a dose-dependent manner also significantly increased the number of seizure episodes induced by HT and their severity. It could be concluded that iNOS inhibitor (aminoguanidine) markedly aggravates behavioral and EEG manifestations of HT-induced seizures in rats, showing functional involvement of iNOS in homocysteine convulsive mechanisms.