Abstracts

The precise mechanism of action of vagus nerve stimulation (VNS) in suppressing seizures remains to be elucidated. This study investigated whether VNS affects the threshold for provoking focal motor seizures using cortical electrical stimulation., Male Wistar rats (n=8) were implanted with a custommade cuff-electrode around the left vagus nerve. Stainless steel electrodes were bilaterally implanted on the rat motor cortex for stimulation and recording of EEG. Motor cortex stimulation (50 Hz, biphasic current pulses) with increasing amplitude (0 to max 2000 [mu]A) was performed. At the time of the first clinical seizure symptoms, the stimulation train was acutely aborted and the threshold intensity was determined by means of continuous video-EEG monitoring. The vagus nerve was stimulated for one hour with an intensity of 0,75 mA and a maximum duty cycle. For each rat, seizure thresholds (ST) were assessed before and immediately after VNS during 2 or 3 sessions on different days., In 7/8 rats, ST increased after one hour of VNS. In 1/8 rat ST remained unchanged. In total, 21 sessions of VNS were performed in the 8 rats; for each session, ST were assessed at least 3 times before and 3 times after VNS. There was a significant increase (99% CI) of the ST after one hour of VNS (mean: 1424 [mu]A; SD: 315; range: 869-1999 [mu]A) compared to the baseline value (mean: 1077 [mu]A; SD: 244; range: 673-1754 [mu]A)., In this study VNS significantly increased ST in a cortical stimulation model used for evaluating efficacy of antiepileptic treatment for motor seizures. These data indicate that VNS is capable of modulating cortical excitability., (Supported by V. De Herdt is supported by a grant ([apos]aspirant[apos]) from the FWO-Flanders.)