Vagus nerve stimulation elevates seizure threshold in the kindling model

Vagus nerve stimulation (VNS) provides partial relief of medically refractory partial seizures in a subset of patients. The optimal pattern of stimulation and the mechanism of the antiseizure effects are uncertain. Establishing the efficacy of VNS in an animal model of epilepsy would provide an experimental preparation with which to address these questions. We sought to determine whether VNS exerted antiseizure effects in the kindling model of epilepsy.

We implanted adult rats with bipolar stimulating electrodes in the right amygdala and VNS devices around the left vagus nerve. Following induction of kindling, electrographic seizure threshold (EST) was determined by quantifying the amygdala electrode current required to evoke a seizure. Once stable ESTs were established, VNS devices were programmed to deliver U.S. Food and Drug Administration (FDA)-approved, clinically used (standard) or an experimental (microburst) pattern of stimulation of variable intensity. VNS devices were programmed identically in control animals except that no current was delivered. EST was examined at 60 min and 1 week in the control and vagus nerve stimulated groups.

Significant reductions of EST values were detected in control animals when tested both 60 min and 1 week following device programming. Both clinically used and experimental patterns of VNS prevented the reduction of EST evident in control animals when tested either 60 min or 1 week after device programming.

These findings establish an experimental preparation with which to elucidate the antiseizure mechanisms of VNS and to determine patterns of VNS most effective at elevating seizure threshold.