Abstract

Vagal fibers travel inside fascicles and form branches to innervate organs and regulate organ functions. Vagus nerve stimulation (VNS) therapies activate fibers non-selectively, often resulting in reduced efficacy and side effects from non-targeted organs. Transverse and longitudinal arrangement of fibers according to functions they mediate and organs they innervate is unknown, however it is crucial for selective VNS. Using microcomputed tomography, we found that, in swine, fascicles are arranged in 2 overlapping axes, with sensory and motor fascicles separated cephalad and merging caudad, and larynx-, heart- and lung-specific fascicles separated caudad and progressively merging cephalad. Using immunohistochemistry, we found that the distribution of single fibers is highly nonuniform: myelinated afferents and efferents occupy separate fascicles, unmyelinated efferents co-localize with myelinated afferents, and small unmyelinated afferents are widely distributed. Using a multi-contact cuff electrode, we delivered fascicular cervical VNS in anesthetized and awake swine. Compound action potentials, from distinct fiber types, and organ responses, including laryngeal muscle, cough, breathing, heart rate and blood pressure responses are elicited in a radially asymmetric manner, with consistent angular separations. These results indicate that vagal fibers are anatomically organized according to functions they mediate and organs they innervate and can be asymmetrically activated by fascicular cervical VNS.