AFFERENT INNERVATION OF GASTROINTESTINAL-TRACT SMOOTH-MUSCLE BY THE HEPATIC BRANCH OF THE VAGUS

To survey the vagal hepatic branch afferent projections to and the ter minal specializations in the gastrointestinal tract, male Sprague-Dawl ey rats were given subdiaphragmatic vagotomies, sparing only the commo n hepatic branch, and were injected with 3 mu l of 8% wheat germ agglu tinin-horseradish peroxidase in the left nodose ganglion. The nodose g anglia, the stomach, the first 8 cm of duodenum, and the cecum were pr epared as wholemounts and were processed with tetramethyl benzidine. H epatic afferent innervation of the ventral stomach consisted of one or more bundles entering at the lower esophageal sphincter and coursing to the forestomach, where they branched into distinct terminal fields. The only fibers on the dorsal forestomach were distal branches and te rminals that wrapped around the greater curvature from the ventral sid e. Hepatic afferents supplied the forestomach with both intraganglioni c laminar endings (IGLEs; putative mechanosensors that coordinate peri stalsis) and intramuscular arrays (IMAs; considered tension receptors) . IGLEs were located primarily on the ventral wall of the stomach, whe reas IMAs were distributed symmetrically. Afferents were also supplied to the distal antrum and the pylorus, with pyloric innervation consis ting almost exclusively of IMAs. Innervation of the proximal duodenum was denser in the first 3 cm and decreased progressively caudally, wit h only meager innervation after 6 cm. Cecal innervation consisted of a few fibers at the ileocecal junction. Duodenal and cecal endings were predominately IGLEs. These results indicate that the hepatic branch c arries sensory information from the forestomach, antrum, pylorus, duod enum, and cecum. Furthermore, the different terminals it supplies sugg est that the branch mediates a multiplicity of gastrointestinal functi ons. (C) 1997 Wiley-Liss, Inc.