Electrophysiological responses to vagus nerve stimulation in rats

Vagus nerve stimulation (VNS) for refractory epilepsy requires optimization of stimulation parameters to improve outcome. Measuring electrophysiological activity from the vagus nerve in response to electrical stimulation may provide an objective tool to evaluate the effects of various stimulation parameters in an experimental set-up. Rats were implanted with a stimulation electrode around the left cervical vagus nerve. Electrophysiological recordings were performed using thin point electrodes placed on the vagus nerve 2 and 4mm rostrally to the cathode. Reference/ground electrode was placed in the wound. The vagus nerve was stimulated with a biphasic, charge-balanced pulse. Silk wire was strapped along the vagus nerve to cause reversible lesions of the nerve. VNS induced an electrophysiological response consisting of a fast and a slow component. The threshold intensity was 2490±240µA and 2067±247µA respectively. The components reached their maximum amplitude at 3875±530µA and 3000±935 µA. Mean latency, at 2mm, was 0.4±0.1ms and 2.6±0.3ms. Conduction velocity for the fast component was 25m/s. The fast component disappeared by afferent lesioning the vagus nerve. The slow component disappeared by efferent lesioning, by lesioning the recurrent laryngeal nerve and by applying Vecuronium to the larynx muscles. A short, single electrical pulse activates fast conducting afferent fibers. Also efferent fibers of the recurrent laryngeal nerve are activated resulting in contraction of larynx muscles. A far field potential was recorded on the vagus nerve. Our set-up can be used to evaluate the effect of stimulation parameters at the cervical vagus nerve in rat epilepsy models.

Jaar van publicatie:2011