Selective labeling of vagal sensory nerve fibers in the lower esophageal sphincter with anterogradely transported WGA-HRP.

Wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) injected into the nodose ganglion was anterogradely transported into the vagal sensory terminal fibers that were further visualized in the lower esophageal sphincter (LES) of the cat. The distribution pattern of the labeled fibers in the LES wall was investigated. All the labeled fibers came from the serosa and penetrated between the bundles of longitudinal muscle fibers. Then the labeled fibers took two different pathways: they either ran, and probably ended, between the longitudinal and circular muscle layers, or they ran directly from the longitudinal to the circular muscle layer. Between the longitudinal and circular muscle layers, they followed a sinuous pathway. In contrast, when they crossed the circular muscle layer toward the mucosa, they ran perpendicular to the orientation of the muscle fibers. After having entered the mucosa, they became twisted and penetrated deeply into the epithelium. These two populations of vagal sensory labeled fibers might correspond respectively to the muscular and mucosal receptors classically described in previous electrophysiological studies.