Tissue response to chronic selective stimulation of the vagus nerve of a dog using multi-electrode spiral cuff

Background and Purpose: Histo-pathological analysis of the left vagus nerve of a dog was carried out after stimulation with an implanted multi-electrode spiral cuff Material and Methods: The silicone cuffs consisting of 33 platinum electrodes were implanted around the left vagus nerve at the neck in two adult Beagle dogs. The superficial regions of vagus that innervated specific internal organs or glands and optimal stimulation intensities were defined by electrical stimulation with each group of three longitudinal electrodes (GTE) within the cuff. Afterwards, all the superficial regions were selectively stimulated for 20 minutes with rectangular, charge-balanced, biphasic, and constant current pulses with parameters: width 200ms, amplitude 1mA,frequency 20Hz, and time delay between biphasic phases 100ms. The stimulation session was repeated every two weeks for the time period of 18 months. The cuff remained implanted for two years but during the last 6 months the nerve was not stimulated. To determine the extent of pathology Of neural tissue and to determine the tissue response to the presence of the cuff, the neural and encapsulation tissue beneath the central group of spiral electrodes and beneath the silicone insulation between the two groups of electrodes were evaluated by light microscopy. Results and Conclusions: Use of the cuff was associated with a buildup of connective tissue encapsulation around the cuff as well as within the cuff. It was observed that there was some mechanical distortion of the nerve and neural damage. Functional deficits were not observed in the animal. At the end of the experiment, the surface of one stimulating electrode was investigated by high resolution Auger Electron Spectroscopy (AES).