Modulation of seizure threshold by vagus nerve stimulation in an animal model for motor seizures

Objective - The precise mechanism of action of vagus nerve stimulation (VNS) in suppressing epileptic seizures remains to be elucidated. This study investigates whether VNS modulates cortical excitability by determining the threshold for provoking focal motor seizures by cortical electrical stimulation before and after VNS. Material and methods - Male Wistar rats (n = 8) were implanted with a cuff-electrode around the left vagus nerve and with stimulation electrodes placed bilaterally on the rat motor cortex. Motor seizure threshold (MST) was assessed for each rat before and immediately after 1 h of VNS with standard stimulation parameters, during two to three sessions on different days. Results - An overall significant increase of the MST was observed following 1 h of VNS compared to the baseline value (1420 mu A and 1072 mu A, respectively; P < 0.01). The effect was reproducible over time with an increase in MST in each experimental session. Conclusions - VNS significantly increases the MST in a cortical stimulation model for motor seizures. These data indicate that VNS is capable of modulating cortical excitability.