Inventory and distribution of vagal afferent projections in the muscular wall of the rat gastrointestinal tract

Feng Bin Wang, Purdue University

Abstract

This study was designed to identify unequivocally the vagal afferent endings, bundles, and fibers, and to determine their distribution pattern in the muscular wall of the rat gastrointestinal (GI) tract. Techniques used include intracranial vagal motor rhizotomy, wheat-germ-agglutinin conjugated horseradish peroxidase and Fluorogold tracer injection, and wholemounts and transverse sections of GI tract. The entire GI tract is innervated by vagal afferents. Axon bundles enter the esophagus and the intestines through the connective tissue attachments and project predominantly circumferentially toward the antimesentery; they also tend to project somewhat caudally from their entry. Fiber bundles enter the stomach from the lesser curvature, distribute predominantly radially, and break up into smaller processes which course both longitudinally and circularly in the gastric wall. The esophagus and stomach are ipsilaterally innervated by the nodose ganglia. The proximal duodenum is heavily innervated throughout its entire circumference. The fibers and endings in the rest of the intestine are progressively concentrated near the mesenteric attachment. Vagal endings known as intraganglionic laminar endings (IGLEs) are distributed from the pharynx to the distal colon. IGLEs and intramural vagal processes occur in high density from the esophagus to duodenum; moderate density from the mid jejunum to mid colon; and low density in the distal colon. With their ubiquitous distribution and placement between the muscle layers, IGLEs are the best candidates for detecting GI contractions such as peristalsis and the migrating myoelectric complex. The vagal afferent endings named intramuscular arrays (IMAs) are selectively distributed in the upper and lower esophageal sphincters, pylorus, and the stomach, where they are organized in diverse patterns. IMAs vary widely in density and configuration throughout the stomach. The greatest concentration of IMAs in the GI tract is located in a restricted region of the forestomach, where the endings are consolidated in both longitudinal and circular muscle, producing a unique three-dimensional gridwork. IMAs are also found in smaller numbers in a restricted region in the caudal part of the proximal colon, suggesting the site may serve as a functional sphincter. With their locations and distribution patterns, IMAs may function as stretch receptors.

Degree

Ph.D.

Advisors

Powley, Purdue University.

Subject Area

Neurology|Psychobiology|Physiological psychology

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