Recording of spontaneous vagus nerve activity during Pentylenetetrazol-induced seizures in rats

Background: Vagus nerve stimulation is a treatment for refractory epilepsy. The vagus nerve carries para-sympathetic information and innervates multiple organs. As seizures are commonly associated with autonomic manifestations, we believe that biomarkers for diseases affecting autonomic functions such as epilepsy can be found in vagus nerve signals. New method: We present a method to record vagus nerve electroneurogram (VENG) and detect in the VENG single unit activity in anesthetized rats during Pentylenetetrazol induced seizures using a true tripolar cuff electrode. Results: The VENG consisted of high amplitude bursts and lower amplitude bursts synchronous to respiration and heartbeat respectively. The average spikes exhibited a triphasic shape with duration below 1.5ms and root mean square amplitude varied between 5.5 +/- 0.2 mu V and 11.4 +/- 3.1 mu V depending on the type of recording. An increase of the contact distance resulted in a signal amplitude increase. Application of Lidocaine led to a total disappearance of the recorded spontaneous spiking of the nerve. Comparison with existing methods: True tripolar cuff electrodes exhibited a better performance in terms of artefact rejection, stability and reproducibility of the signal compared to commonly used hook electrodes which is of special interest in seizures where important motion and EMG artifacts are expected. Conclusion: We present a new method to record single unit activity of the vagus nerve during acute chemically induced seizures in rats and verified the neural origin of the recorded signals. This recording method might be a powerful tool to develop seizure biomarkers based on VENG.