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.     

Onset and propagation of spike and slow wave discharges in human absence epilepsy: A MEG study

Purpose: A nonlinear association and a source localization technique were used to describe the onset and propagation of spike‐and‐slow‐wave discharges (SWDs) in children with absence seizures. Previous studies have emphasized a leading cortical role in the generation of absence seizures in genetic epileptic rats. Methods: Synchronization between all magnetoencephalography (MEG) sensor‐couples before and during SWDs in five patients was investigated over time. A source localization [beamformer, SAM(g₂)] technique was used to find brain regions associated with the origin of the spikes of the SWDs. Results: The onset of SWDs was characterized by high associations at left and right frontal regions. An alternating pattern of high synchronization was found during trains of SWDs: generalized during the wave and localized during the spike; the origin of the spike was different from the onset of SWDs, more frontal lateral and medial parietal. The localization of this latter region was confirmed with SAM(g₂). Discussion: The outcome of the nonlinear association techniques demonstrated that SWDs have a local cortical onset, whereas the association and beamformer technique support a local or even a focal cortical involvement in the occurrence of the spike in a train of SWDs. In all, the cortex contains local frontal and parietal sites relevant before the onset of the generalized pattern of SWDs and other ones that might contain the driving force behind the spike in trains of 3–4 Hz SWDs.     

NIRS‐measured oxy‐ and deoxyhemoglobin changes associated with EEG spike‐and‐wave discharges in a genetic model of absence epilepsy: The GAERS

Purpose: Absence epilepsy may be severe and is frequently accompanied by cognitive delay, yet its metabolic/hemodynamic aspects have not been established. The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are an isomorphic, predictive, and homologous model of human absence epilepsy. We studied hemodynamic changes related to generalized spike‐and‐wave discharges (GSWDs) in GAERS by using a technique with high temporal resolution: near‐infrared spectroscopy (NIRS). We hypothesized that conflicting results from other techniques might be due to the averaging of a biphasic response such as the one we described in children. Methods: NIRS is particularly suitable for monitoring changes in the concentrations of oxy‐, deoxy‐, and total hemoglobin (HbO₂, HHb, and HbT), using the specific absorption properties of living tissues in the near infrared range. We obtained concomitant high quality electroencephalography (EEG)–NIRS recordings in six GAERS (total of 444 seizures), and tested whether the discharges were related to changes in cardiac or respiration rates. Results: The onset of GSWDs was preceded by a deactivation, followed by an activation that was possibly due to seizure‐suppression mechanisms. The end was marked by a deactivation. The onset of GSWDs was associated with a decrease and the end with a brief increase in respiratory rate. Discussion: Our results differ partially from those of previous studies on hemodynamic aspects of GSWDs (many of which describe a simple deactivation), probably due to differences in temporal resolution and data processing; however, they are consistent with metabolic studies, functional magnetic resonance imaging (fMRI) studies on WAG/Rij rats, and some results in children with absence epilepsy.     

WAG/Rij rats show a reduced expression of CB1 receptors in thalamic nuclei and respond to the CB1 receptor agonist,R(+)WIN55,212‐2, with a reduced incidence of spike‐wave discharges

Purpose: Genetically epileptic WAG/Rij rats develop spontaneous absence‐like seizures after 3 months of age. We used WAG/Rij rats to examine whether absence seizures are associated with changes in the expression of type‐1 cannabinoid (CB₁) receptors. Methods: Receptor expression was examined by in situ hybridization and western blot analysis in various brain regions of “presymptomatic” 2‐month old and “symptomatic” 8‐month‐old WAG/Rij rats relative to age‐matched nonepileptic control rats. Furthermore, we examined whether pharmacologic activation of CB₁ receptor affects absence seizures. We recorded spontaneous spike‐wave discharges (SWDs) in 8‐month old WAG/Rij rats systemically injected with the potent CB₁ receptor agonist, R(+)WIN55,212‐2 (3–12 mg/kg, s.c.), given alone or combined with the CB₁ receptor antagonist/inverse agonist, AM251 (12 mg/kg, s.c.). Results: Data showed a reduction of CB₁ receptor mRNA and protein levels in the reticular thalamic nucleus, and a reduction in CB₁ receptor protein levels in ventral basal thalamic nuclei of 8‐month‐old WAG/Rij rats, as compared with age‐matched ACI control rats. In vivo, R(+)WIN55,212‐2 caused a dose‐dependent reduction in the frequency of SWDs in the first 3 h after the injection. This was followed by a late increase in the mean SWD duration, which suggests a biphasic modulation of SWDs by CB₁ receptor agonists. Both effects were reversed or attenuated when R(+)WIN55,212‐2 was combined with AM251. Discussion: These data indicate that the development of absence seizures is associated with plastic modifications of CB₁ receptors within the thalamic‐cortical‐thalamic network, and raise the interesting possibility that CB₁ receptors are targeted by novel antiabsence drugs.     

NIRS-measured oxy- and deoxyhemoglobin changes associated with EEG spike-and-wave discharges in children

Purpose: Absence epilepsy is characterized by 3‐Hz generalized spike‐and‐wave discharges (GSWD) on the electroencephalogram, associated with behavioral arrest. It may be severe, and even in childhood benign absence epilepsy cognitive delay is frequent, yet the metabolic/hemodynamic aspects of this kind of epilepsy have not been established. We aimed to determine if the GSWD were related to hemodynamic changes by using a new technique with high temporal resolution: near infrared spectroscopy (NIRS). Methods: NIRS is gaining acceptance as a technique particularly suitable for routine follow‐up in children, using the specific absorption properties of living tissues in the near infrared range to measure changes in the concentrations of oxy‐, deoxy‐ and total hemoglobin (HbO₂, HHb, and HbT, respectively). We performed simultaneous electroencephalography (EEG) and left frontal NIRS recordings in six children with GSWD. We also tested if the discharges were related to changes in cardiac or respiratory rates. Results: GSWD were associated in the frontal area with an oxygenation (beginning 10 s before the GSWD) followed by strong deoxygenation, then oxygenation again with [HbT] increase, and a return to baseline. We did not identify any relationship between the onset of the GSWD and heart or respiratory rates. Discussion: Our results partially differ from previous studies on GSWD hemodynamic aspects (many of which described a simple deactivation), probably due to differences in temporal resolution and data processing. Simultaneous acquisition of EEG and NIRS can optimize the use of both techniques and help shed light on the mechanisms underlying spike‐and‐wave discharges.     

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.     

Participation of cortical recurrent inhibition in the genesis of spike and wave discharges in feline generalized penicillin epilepsy

Cortical recurrent inhibition (RI) evoked in pericruciate cortex by antidronic stimulation of the cerebral peduncle (CP) was studied in normal cats and in cats exhibiting the signs of feline generalized penicillin epilepsy (FGPE) following the i.m. injection of penicillin. Two measures of RI evoked by antidromic CP stimulation were used: (i) the averaged focal potential in the pericruciate gyrus: and (ii) the duration of the suppression or diminution of extracellularly recorded action potential (ap) discharge of antidromically activated pericruciate neurons measured in peristimulus time histograms (PSTHs). After i.m. injection of 350,000 IU/kg of penicillin RI remained preserved as long as only generalized spike and wave (SW) discharges appeared in the EEG, although in 5/17 neurons a modest to moderate reduction in the duratuon of RI occurred once SW discharges had appeared in the EEG. This inconstant reduction was probably not caused by a direct anti-inhibitory action of penicillin, but is a consequence of the increased number of ap discharges curtailing RI. At the small concentrations of penicillin existing in brain in FGPE its anti-inhibitory action evident with larger concentrations cannot be demonstrated.When focal or generalized tonic-clonic (T-C) seizured occurred, RI was reduced in slightly more than half of the instances for a few minutes before the onset of these seizures. This suggests that the transition from SW discharge to T-C seizure may be caused by a breakdown of RI.     

Focal administration of neuropeptide Y into the S2 somatosensory cortex maximally suppresses absence seizures in a genetic rat model

Purpose: Neuropeptide Y (NPY) is an inhibitory neurotransmitter that suppresses focal and generalized seizures in animal models. In this study, we investigated the sites within the thalamocortical circuit that NPY acts to suppress seizures in genetic absence epilepsy rats from Strasbourg (GAERS). Methods: In conscious freely moving GAERS, NPY was administered via intracerebral microcannulae implanted bilaterally into one of the following regions: primary somatosensory cortex (S1), secondary somatosensory cortex (S2), the primary motor cortex (M1), caudal nucleus reticular thalamus (nRT), or ventrobasal thalamus (VB). Animals received vehicle and up to three doses of NPY, in a randomized order. Electroencephalography (EEG) recordings were carried out for 30 min prior to injection and 90 min after the injection of NPY or vehicle. Key Findings: Focal microinjections of NPY into the S2 cortex suppressed seizures in a dose‐dependent manner, with the response being significantly different at the highest dose (1.5 mm ) compared to vehicle for total time in seizures postinjection (7.2 ± 3.0% of saline, p < 0.01) and average number of seizures (9.4 ± 4.9% of saline, p < 0.05). In contrast NPY microinjections into the VB resulted in an aggravation of seizures. Significance: NPY produces contrasting effects on absence‐like seizures in GAERS depending on the site of injection within the thalamocortical circuit. The S2 is the site at which NPY most potently acts to suppress absence‐like seizures in GAERS, whereas seizure‐aggravating effects are seen in the VB. These results provide further evidence to support the proposition that these electroclinically “generalized” seizures are being driven by a topographically restricted region within the somatosensory cortex.     

Quantitative trait locus on distal chromosome 1 regulates the occurrence of spontaneous spike-wave discharges in DBA/2 mice

Purpose: Most common forms of human epilepsy result from a complex combination of polygenetic and environmental factors. Quantitative trait locus (QTL) mapping is a first step toward the nonbiased discovery of epilepsy-related candidate genes. QTL studies of susceptibility to induced seizures in mouse strains have consistently converged on a distal region of chromosome 1 as a major phenotypic determinant; however, its influence on spontaneous epilepsy remains unclear. In the present study we characterized the influence of allelic variations within this QTL, termed Szs1, on the occurrence of spontaneous spike-wave discharges (SWDs) characteristic of absence seizures in DBA/2 (D2) mice. Methods: We analyzed SWD occurrence and patterns in freely behaving D2, C57BL/6 (B6) and the congenic strains D2.B6-Szs1 and B6.D2-Szs1. Key Findings: We showed that congenic manipulation of the Szs1 locus drastically reduced the number and the duration of SWDs in D2.B6-Szs1 mice, which are homozygous for Szs1 from B6 strain on a D2 strain background. However, it failed to induce the full expression of SWDs in the reverse congenic animals B6.D2-Szs1. Significance: Our results demonstrate that the occurrence of SWDs in D2 animals is under polygenic control and, therefore, the D2 and B6 strains might be a useful model to dissect the genetic determinants of polygenic SWDs characteristic of typical absence seizures. Furthermore, we point to the existence of epistatic interactions between at least one modifier gene within Szs1 and genes within unlinked QTLs in regulating the occurrence of spontaneous nonconvulsive forms of epilepsies.     

The primary somatosensory cortex and the insula contribute differently to the processing of transient and sustained nociceptive and non‐nociceptive somatosensory inputs

Transient nociceptive stimuli elicit consistent brain responses in the primary and secondary somatosensory cortices (S1, S2), the insula and the anterior and mid‐cingulate cortex (ACC/MCC). However, the functional significance of these responses, especially their relationship with sustained pain perception, remains largely unknown. Here, using functional magnetic resonance imaging, we characterize the differential involvement of these brain regions in the processing of sustained nociceptive and non‐nociceptive somatosensory input. By comparing the spatial patterns of activity elicited by transient (0.5 ms) and long‐lasting (15 and 30 s) stimuli selectively activating nociceptive or non‐nociceptive afferents, we found that the contralateral S1 responded more strongly to the onset of non‐nociceptive stimulation as compared to the onset of nociceptive stimulation and the sustained phases of nociceptive and non‐nociceptive stimulation. Similarly, the anterior insula responded more strongly to the onset of nociceptive stimulation as compared to the onset of non‐nociceptive stimulation and the sustained phases of nociceptive and non‐nociceptive stimulation. This suggests that S1 is specifically sensitive to changes in incoming non‐nociceptive input, whereas the anterior insula is specifically sensitive to changes in incoming nociceptive input. Second, we found that the MCC responded more strongly to the onsets as compared to the sustained phases of both nociceptive and non‐nociceptive stimulation, suggesting that it could be involved in the detection of change regardless of sensory modality. Finally, the posterior insula and S2 responded maximally during the sustained phase of non‐nociceptive stimulation but not nociceptive stimulation, suggesting that these regions are preferentially involved in processing non‐nociceptive somatosensory input. Hum Brain Mapp 36:4346–4360, 2015. © 2015 Wiley Periodicals, Inc.     

Effects of age and cortical infarction on EEG dynamic changes associated with spike wave discharges in F344 rats

Rodent models of absence seizures are used to investigate the network properties and regulatory mechanisms of the seizure's generalized spike and wave discharge (SWD). As rats age, SWDs occur more frequently, suggesting aging-related changes in the regulation of the corticothalamic mechanisms generating the SWD. We hypothesized that brain resetting mechanisms – how the brain “resets” itself to a more normal functional state following a transient period of abnormal function, e.g., a SWD – are impaired in aged animals and that brain infarction would further affect these resetting mechanisms. The main objective of this study was to determine the effects of aging, infarction, and their potential interaction on the resetting of EEG dynamics assessed by quantitative EEG (qEEG) measures of linear (signal energy measured by amplitude variation; signal frequency measured by mean zero-crossings) and nonlinear (signal complexity measured by the pattern match regularity statistic and the short-term maximum Lyapunov exponent) brain EEG dynamics in 4- and 20-month-old F344 rats with and without brain infarction. The main findings of the study were: 1) dynamic resetting of both linear and nonlinear EEG characteristics occurred following SWDs; 2) animal age significantly affected the degree of dynamic resetting in all four qEEG measures: SWDs in older rats exhibited a lower degree of dynamic resetting; 3) infarction significantly affected the degree of dynamic resetting only in terms of EEG signal complexity: SWDs in infarcted rats exhibited a lower degree of dynamic resetting; and 4) in all four qEEG measures, there was no significant interaction effect between age and infarction on dynamic resetting. We conclude that recovery of the brain to its interictal state following SWDs was better in young adult animals compared with aged animals, and to a lesser degree, in age-matched controls compared with infarction-injured animal groups, suggesting possible effects of brain resetting mechanisms and/or the disruption of the epileptogenic network that triggers SWDs.     

Metabotropic glutamate receptors in the thalamocortical network: strategic targets for the treatment of absence epilepsy

Metabotropic glutamate (mGlu) receptors are positioned at synapses of the thalamocortical network that underlie the development of spike-and-wave discharges (SWDs) associated with absence epilepsy. The modulatory role of individual mGlu receptor subtypes on excitatory and inhibitory synaptic transmission in the cortico-thalamo-cortical circuitry makes subtype-selective mGlu receptor ligands potential candidates as novel antiabsence drugs. Some of these compounds are under clinical development for the treatment of numerous neurologic and psychiatric disorders, and might be soon available for clinical studies in patients with absence seizures refractory to conventional medications. Herein we review the growing evidence that links mGlu receptors to the pathophysiology of pathologic SWDs moving from the anatomic localization and function of distinct mGlu receptor subtypes in the cortico-thalamo-cortical network to in vivo studies in mouse and rat models of absence epilepsy.     

Gender and age differences in expression of GABAA receptor subunits in rat somatosensory thalamus and cortex in an absence epilepsy model

Absence epilepsy is more prevalent in females, but reasons for this gender asymmetry are unknown. We reported previously that perinatal treatment of Long–Evans Hooded rats with the cholesterol synthesis inhibitor (CSI) AY9944 causes a life-long increase in EEG spike-wave discharges (SWDs), correlated with decreased expression of GABA_A receptor subunit γ2 protein levels in thalamic reticular and ventrobasal nuclei (SS thalamus) [Li, H., Kraus, A., Wu, J., Huguenard, J.R., Fisher, R.S., 2006. Selective changes in thalamic and cortical GABA(A) receptor subunits in a model of acquired absence epilepsy in the rat. Neuropharmacology 51, 121–128]. In this study, we explored time course and gender different effects of perinatal AY9944 treatment on expression of GABA_A receptor α1 and γ2 subunits in SS thalamus and SS cortex. Perinatal AY9944 treatment-induced decreases in GABA_A γ2 receptor subunits in rat SS thalamus and increases in SS cortex are gender and age specific. The findings suggest a mechanism for the higher prevalence of absence epilepsy in female patients.     

Age‐related changes in metabolic profiles of rat hippocampus and cortices

The time course of metabolic changes was investigated in the hippocampus and the parietal, rhinal and frontal cortices of rats from 4 to 30 months old. Samples were analysed by the solid‐state high‐resolution magic angle spinning nuclear magnetic resonance method. Quantification was performed with the quest procedure of jmrui software. Eighteen metabolites were identified and separated in the spectrum. Six of them were not age sensitive, in particular alanine, glutamine and lactate. In contrast, choline, glycerophosphocholine, myo‐inositol, N‐acetylaspartate, scyllo‐inositol (s‐Ins) and taurine (Tau) were notably altered over aging. Interestingly, each age group showed a specific metabolic profile. The concentration of metabolites such as Tau was altered in middle‐aged rats only, whereas the s‐Ins level decreased in old rats only. Most metabolites showed progressive alteration during the process of aging, which was initiated during the middle‐aged period (18 months). Taken together, these results suggest that cell membrane integrity is perturbed with age. Each brain region investigated had distinctive qualitative and/or quantitative metabolic age‐related features. These age‐related changes would affect network connectivities and then cognitive functions.