Interhemispheric difference in susceptibility to epileptogenesis: evidence from the audiogenic kindling model in Wistar rats

Rodent Models of Audiogenic Epilepsy: Genetic Aspects, Advantages, Current Problems and Perspectives

Animal models of epilepsy are of great importance in epileptology. They are used to study the mechanisms of epileptogenesis, and search for new genes and regulatory pathways involved in the development of epilepsy as well as screening new antiepileptic drugs. Today, many methods of modeling epilepsy in animals are used, including electroconvulsive, pharmacological in intact animals, and genetic, with the predisposition for spontaneous or refractory epileptic seizures. Due to the simplicity of manipulation and universality, genetic models of audiogenic epilepsy in rodents stand out among this diversity. We tried to combine data on the genetics of audiogenic epilepsy in rodents, the relevance of various models of audiogenic epilepsy to certain epileptic syndromes in humans, and the advantages of using of rodent strains predisposed to audiogenic epilepsy in current epileptology.

Dynamics of sensorimotor cortex activation during absence and myoclonic seizures in a mouse model of juvenile myoclonic epilepsy

OBJECTIVE

Generalized epilepsy syndromes often confer multiple types of seizures, but it is not known if these seizures activate separate or overlapping brain networks. Recently, we reported that mice with a juvenile myoclonic epilepsy mutation (Gabra1[A322D]) exhibited both absence and myoclonic generalized seizures. Here, we determined the time course of sensorimotor cortex activation and the spatial distribution of spike voltage during these two seizures.

METHODS

We implanted Gabra1^+/A322D mice with multiple electroencephalography (EEG) electrodes over bilateral somatosensory cortex barrel fields (S1) and anterior (aM1) and posterior (pM1) motor cortices and recorded absence seizures/spike-wave discharges (SWDs) and myoclonic seizures. We used nonlinear-association analyses and cross-correlation calculations to determine the strength, leading regions, and time delays of cortical coupling from the preictal to ictal states and within the spike and interspike periods. The distribution of spike voltage was also measured in SWDs and myoclonic seizures.

RESULTS

EEG connectivity among all electrode pairs increased at the onset of both SWDs and myoclonic seizures. Surprisingly, during spikes of both seizure types, S1 led M1 with similar delay times. Myoclonic seizure spikes started more focally than SWD spikes, with a significant majority appearing first only in S1 electrodes, whereas a substantial fraction of SWD spikes were detected first in S1 and at least one M1 electrode. The absolute voltage of myoclonic seizure spikes was significantly higher than that of SWD spikes, and there was a greater relative voltage over M1 during myoclonic seizure spikes than in the first one to two SWD spikes.

SIGNIFICANCE

The leading sites in S1 and similar delay times suggest both SWDs and myoclonic seizures activate overlapping networks in sensorimotor cortex and thus, therapeutically targeting of this network could potentially treat both seizures. Spike focality, absolute voltage, and voltage distribution provide insight into neuronal activation during these two seizure types.

Evaluation of seizure foci and genes in the Lgi1(L385R/+) mutant rat

Mutations in the leucine-rich, glioma inactivated 1 (LGI1) gene have been identified in patients with autosomal dominant lateral temporal lobe epilepsy (ADLTE). We previously reported that Lgi1 mutant rats, carrying a missense mutation (L385R) generated by gene-driven N-ethyl-N-nitrosourea (ENU) mutagenesis, showed generalized tonic-clonic seizures (GTCS) in response to acoustic stimuli. In the present study, we assessed clinically relevant features of Lgi1 heterozygous mutant rats (Lgi1(L385R/+)) as an animal model of ADLTE. First, to explore the focus of the audiogenic seizures, we performed electroencephalography (EEG) and brain Fos immunohistochemistry in Lgi1(L385R/+) and wild type rats. EEG showed unique seizure patterns (e.g., bilateral rhythmic spikes) in Lgi1(L385R/+) rats with GTCS. An elevated level of Fos expression indicated greater neural excitability to acoustic stimuli in Lgi1(L385R/+) rats, especially in the temporal lobe, thalamus and subthalamic nucleus. Finally, microarray analysis revealed a number of differentially expressed genes that may be involved in epilepsy. These results suggest that Lgi1(L385R/+) rats are useful as an animal model of human ADLTE.

Hemispheric lateralization of microstructural white matter abnormalities in children with active benign childhood epilepsy with centrotemporal spikes (BECTS): a preliminary DTI study

PURPOSE

The deficit of white matter is reported to be involved during the disease progression in patients with benign childhood epilepsy with centrotemporal spikes (BECTS). The aim of this study is to investigate patterns of white matter damage in children with BECTS with left- or right-hemispheric focus by using diffusion tensor imaging (DTI), and its relationship with the cofactors such duration, seizure frequency and handedness.

METHODS

Diffusion tensor imaging (DTI) was performed in twenty-eight children with BECTS and eighteen healthy controls. The data were analyzed using both tract-based spatial statistics (TBSS) and region of interest (ROI) analyses. Correlations were investigated between the fractional anisotropy (FA) values of the identified altered regions and clinical features such as age, age of onset and seizure frequency.

RESULTS

The TBSS analysis revealed that white matter impairment in children with rolandic spikes on the ipsilateral hemisphere was much wider. The FA value was significantly lower in the body of the corpus callosum and forceps minor in BECTS patients with spikes on the ipsilateral hemisphere. The seizure frequency correlated positively with the FA values of body of corpus callosum (CC), bilateral cingulate gyrus and left uncinate fasciculi (UA).

CONCLUSION

The impaired WM integrity in patients with BECTS was greater in patients with spikes on the dominant hemisphere, possibly due to the greater vulnerability of the left hemisphere and excitotoxic effects of seizures.

Lateral asymmetry of early seizure manifestations in experimental generalized epilepsy

Reorganization of seizure networks during epileptogenesis involves cortico-subcortical and interhemispheric interactions. In the audiogenic kindling (AK) model of generalized tonic-clonic seizures, upstream seizure propagation along ascending brainstem-to-forebrain pathways determines progressive intensification of repeated sound-induced convulsions. Full-blown audiogenic seizures are bilaterally symmetric and their repetition results in bisynchronous recruiting the cortex in secondary epileptogenesis. The present study describes lateral asymmetry of initial behavioral and EEG manifestations of audiogenic seizures and AK in Wistar and WAG/Rij rats with acoustic hypersensitivity. These rats exhibit consistent individual lateralization of running seizures (run directionality) induced by repeated binaural stimulation. Since this initial preconvulsive running reflects seizure onset in the auditory brainstem, the running asymmetry suggests non-symmetric early epileptic activation of brainstem substrates by sound in these rats. Repetition of the asymmetric brainstem seizures led to asynchronous recruiting the cortex into seizure network and lateralization of running seizures was predictive for asymmetry of early cortical seizure manifestations in Wistar and WAG/Rij rats. Both electrographic markers of AK, spreading depression (SD) and post-running afterdischarge, first appeared in the cortex ipsilateral to run direction, suggesting lateralized brainstem-to-forebrain seizure generalization during AK. At the population level, no bias in lateralization of running and SD was found in Wistar and WAG/Rij rats but incidence of secondary cortical seizures varied, depending on strain and run laterality. Among Wistar rats, cortical seizures developed more rarely in right-runners than in left-runners, suggesting enhanced resistance of the right hemisphere to epileptogenesis in rats of this strain. WAG/Rij rats with mixed (absence and audiogenic) epilepsy showed weak lateralization of early cortical seizures and no left-right difference in their incidence during AK. Present findings suggest (1) lateralized brainstem-to-forebrain seizure propagation and hemispheric difference in its facility in Wistar rats, (2) alterations of intra- and interhemispheric seizure propagation in WAG/Rij rats with genetic absence epilepsy.