Absence epilepsy in male and female WAG/Rij rats: A longitudinal EEG analysis of seizure expression

Effect of Vagus Nerve Stimulation on the GASH/Sal Audiogenic-Seizure-Prone Hamster

Vagus nerve stimulation (VNS) is an adjuvant neuromodulation therapy for the treatment of refractory epilepsy. However, the mechanisms behind its effectiveness are not fully understood. Our aim was to develop a VNS protocol for the Genetic Audiogenic Seizure Hamster from Salamanca (GASH/Sal) in order to evaluate the mechanisms of action of the therapy. The rodents were subject to VNS for 14 days using clinical stimulation parameters by implanting a clinically available neurostimulation device or our own prototype for laboratory animals. The neuroethological assessment of seizures and general behavior were performed before surgery, and after 7, 10, and 14 days of VNS. Moreover, potential side effects were examined. Finally, the expression of 23 inflammatory markers in plasma and the left-brain hemisphere was evaluated. VNS significantly reduced seizure severity in GASH/Sal without side effects. No differences were observed between the neurostimulation devices. GASH/Sal treated with VNS showed statistically significant reduced levels of interleukin IL-1β, monocyte chemoattractant protein MCP-1, matrix metalloproteinases (MMP-2, MMP-3), and tumor necrosis factor TNF-α in the brain. The described experimental design allows for the study of VNS effects and mechanisms of action using an implantable device. This was achieved in a model of convulsive seizures in which VNS is effective and shows an anti-inflammatory effect.

Optogenetic stimulation of the superior colliculus suppresses genetic absence seizures

While anti-seizure medications are effective for many patients, nearly one-third of individuals have seizures that are refractory to pharmacotherapy. Prior studies using evoked preclinical seizure models have shown that pharmacological activation or excitatory optogenetic stimulation of the deep and intermediate layers of the superior colliculus (DLSC) display multi-potent anti-seizure effects. Here we monitored and modulated DLSC activity to suppress spontaneous seizures in the WAG/Rij genetic model of absence epilepsy. Female and male WAG/Rij adult rats were employed as study subjects. For electrophysiology studies, we recorded single unit activity from microwire arrays placed within the DLSC. For optogenetic experiments, animals were injected with virus coding for channelrhodopsin-2 or a control vector, and we compared the efficacy of continuous neuromodulation to that of closed-loop neuromodulation paradigms. For each, we compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). For closed-loop stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of spike-and-wave discharges (SWDs). We quantified the number and duration of each SWD during each 2 h-observation period. Following completion of the experiment, virus expression and fibre-optic placement was confirmed. We found that single-unit activity within the DLSC decreased seconds prior to SWD onset and increased during and after seizures. Nearly 40% of neurons displayed suppression of firing in response to the start of SWDs. Continuous optogenetic stimulation of the DLSC (at each of the three frequencies) resulted in a significant reduction of SWDs in males and was without effect in females. In contrast, closed-loop neuromodulation was effective in both females and males at all three frequencies. These data demonstrate that activity within the DLSC is suppressed prior to SWD onset, increases at SWD onset, and that excitatory optogenetic stimulation of the DLSC exerts anti-seizure effects against absence seizures. The striking difference between open- and closed-loop neuromodulation approaches underscores the importance of the stimulation paradigm in determining therapeutic effects.

Alpha2 Adrenergic Modulation of Spike-Wave Epilepsy: Experimental Study of Pro-Epileptic and Sedative Effects of Dexmedetomidine

In the present report, we evaluated adrenergic mechanisms of generalized spike-wave epileptic discharges (SWDs), which are the encephalographic hallmarks of idiopathic generalized epilepsies. SWDs link to a hyper-synchronization in the thalamocortical neuronal activity. We unclosed some alpha2-adrenergic mechanisms of sedation and provocation of SWDs in rats with spontaneous spike-wave epilepsy (WAG/Rij and Wistar) and in control non-epileptic rats (NEW) of both sexes. Dexmedetomidine (Dex) was a highly selective alpha-2 agonist (0.003-0.049 mg/kg, i.p.). Injections of Dex did not elicit de novo SWDs in non-epileptic rats. Dex can be used to disclose the latent form of spike-wave epilepsy. Subjects with long-lasting SWDs at baseline were at high risk of absence status after activation of alpha2- adrenergic receptors. We create the concept of alpha1- and alpha2-ARs regulation of SWDs via modulation of thalamocortical network activity. Dex induced the specific abnormal state favorable for SWDs-"alpha2 wakefulness". Dex is regularly used in clinical practice. EEG examination in patients using low doses of Dex might help to diagnose the latent forms of absence epilepsy (or pathology of cortico-thalamo-cortical circuitry).

Parallel changes in the promoter methylation of voltage-gated T-type calcium channel alpha 1 subunit G and histone deacetylase activity in the WAG/Rij model of absence epilepsy

Objective: In the last two decades, research on epigenetic mechanisms has expanded dramatically. Recent studies demonstrated that epigenetic mechanisms regulate epilepsy and epileptogenic pathologies. In this study, we aimed to investigate changes in the promoter methylation status of the voltage-gated T-type calcium channel alpha 1 subunit G (CACNA1G) gene and total histone deacetylase activity in Wistar Albino Glaxo/Rijswijk (WAG/Rij) rats which is one of the commonly used genetic absence rat models of epilepsy in the three different age groups (3, 6, and 9 months old) on both sexes. Material and Method: Evaluation of changes in the spike-wave discharges (SWDs) was performed with electrocorticography (ECoG). The promoter methylation status of the CACNA1G gene was determined by methylation-specific PCR (MSP), and histone deacetylase (HDAC) activity was determined spectrophotometrically. Results: Our results demonstrated that the number of SWDs increased time-dependent in WAG/Rij. Additionally, it was observed that CACNA1G promoter methylation decreased, and total HDAC activity increased with age in both sexes. Conclusion: Our results provide further support for epigenetic regulation in the absence epilepsy phenotype and suggest that the underlying mechanism behind the increase in the number of SWDs with age in the WAG/Rij animals might be regulated by CACNA1G promoter methylation or HDAC activity.

C-Met Receptors Deficiency Was Involved in Absence Seizures Development in WAG/Rij Rats

Background: A variety of receptors may be involved in the pathogenesis of absence seizures. The c-Met receptors have a critical role in modulating the GABAergic interneurons and creating a balance between excitatory and inhibitory neurotransmission, sensorimotor gating, and normal synaptic plasticity. Objectives: This study aimed to assess the changes of the c-Met receptor during the appearance of absence attacks in the experimental model of absence epilepsy. Methods: A total of 48 animals were divided into four groups of two- and six-month-old WAG/Rij and Wistar rats. Epileptic WAG/Rij rats showing SWP in electrocorticogram (ECoG) were included in the epileptic group. The two-month-old WAG/Rij rats as well as two- and six-month-old Wistar rats not exhibiting SWP in ECoG were selected as the non-epileptic. Gene (RT-PCR) and protein expression (western blotting) of c-Met receptors as well as c-Met protein distribution (immunohistochemistry) in the somatosensory cortex and hippocampus were assessed during seizure development of the absence attacks. Results: According to the study findings, a lower c-Met gene and protein expression, as well as a lower protein distribution, were observed in the hippocampus (P < 0.001, P < 0.05, and P < 0.001, respectively) and cortex (P < 0.01, P < 0.001 and P < 0.001, respectively) of the two-month-old WAG/Rij rats compared to the same-age Wistar rats. Moreover, the data revealed a reduction of hippocampal and cortical c-Met protein expression (P < 0.001, for both) in six-month-old WAG/Rij rats compared to two-month-old ones. Six-month-old WAG/Rij rats had a lower cortical c-Met gene (P < 0.05) and protein expression (P < 0.001) as well as lower hippocampal and cortical protein distribution (P < 0.05 and P < 0.001) than the same-age Wistar rats. Conclusions: In sum, the c-Met receptor was found to play a significant role in the development of absence epilepsy. This receptor, therefore, may have been considered as an effective goal for absence seizure inhibition.

Spike-Wave Seizures, NREM Sleep and Micro-Arousals in WAG/Rij Rats with Genetic Predisposition to Absence Epilepsy: Developmental Aspects

The current study was done in Wistar Albino Glaxo Rijswijk (WAG/Rij) rats, which are genetically prone to develop spontaneous spike-wave discharges (SWDs) and are widely used as a genetic model of absence epilepsy. Here, we examined functional links between sleep and spike-wave epilepsy in aging WAG/Rij rats using advanced techniques of EEG analysis. SWDs, periods of NREM sleep and micro-arousals were automatically detected in three-channel epidural EEG recorded in freely moving WAG/Rij rats consequently at the age 5, 7 and 9 months. We characterized the developmental profile of spike-wave epilepsy in drug-naïve WAG/Rij rats and defined three epi-phenotypes—severe, mild and minor epilepsy. Age-related changes of SWDs were associated with changes in NREM sleep. Several signs of NREM sleep fragmentation were defined in epileptic WAG/Rij rats. It seems that spike-wave epilepsy per se promotes micro-arousals during NREM sleep. However, subjects with a higher number of micro-arousals (and NREM sleep episodes) at the age of 5 months were characterized by a reduction of SWDs between 5 and 7 months of age.

Sleep Disturbances in Rats With Genetic Pre-disposition to Spike-Wave Epilepsy (WAG/Rij)

Wistar Albino Glaxo Rijswijk (WAG/Rij) rats are widely used in basic and pre-clinical studies as a valid genetic model of absence epilepsy. Adult WAG/Rij rats exhibit generalized 8–10-Hz spike-wave discharges (SWDs) in the electroencephalogram. SWDs are known to result from thalamocortical circuit dysfunction, and this implies an intimate relationship between slow-wave EEG activity, sleep spindles, and SWDs. The present mini review summarizes relevant research on sleep-related disturbances associated with spike-wave epilepsy in WAG/Rij rats in the domain of slow-wave sleep EEG and microarousals. It also discusses enhancement of the intermediate stage of sleep. In general, sleep EEG studies provide important information about epileptogenic processes related to spike-wave epilepsy.