The acute and chronic effect of vagus nerve stimulation in genetic absence epilepsy rats from Strasbourg (GAERS).

PURPOSE: The aim of this study was to evaluate the efficacy of acute and chronic vagus nerve stimulation (VNS) in genetic absence epilepsy rats from Strasbourg (GAERS). This is a validated model for absence epilepsy, characterized by frequent spontaneous absences concomitant with spike and wave discharges (SWD) on the EEG. Although absences are a benign form of seizures, it is conceptually important to investigate the efficacy of VNS in a controlled study by using this chronic epilepsy model. METHODS: Both control and stimulated GAERS were implanted with five epidural EEG electrodes and a stimulation electrode around the left vagus nerve. In the first experiment, VNS was given when SWD occurred in the EEG; this was repeated the next day. A randomized crossover design (n = 8) was used. In the chronic experiment, GAERS underwent EEG monitoring during a first baseline week. During the second week, the treated group (n = 18) received VNS; controls (n = 13), on the other hand, only underwent EEG recordings. RESULTS: On day 1 of the acute VNS experiment, the mean duration of the SWD when VNS was applied was higher than in baseline conditions (p < 0.05). However, on day 2, there was no difference in mean duration of the SWD. In the chronic VNS experiment, no statistically significant differences were found between control and stimulated GAERS. CONCLUSIONS: Acute VNS applied shortly after the onset of SWD prolonged the mean duration of SWD in GAERS at least during the first day of VNS. Chronic stimulation hardly affected SWD in GAERS.