CAPSAICIN-RESISTANT VAGAL AFFERENT-FIBERS IN THE RAT GASTROINTESTINAL-TRACT - ANATOMICAL IDENTIFICATION AND FUNCTIONAL INTEGRITY

The presence and distribution of vagal fibers and terminals throughout esophagus and gastrointestinal tract that could be anterogradely labe led by nodose ganglion tracer injections was quantitatively assessed i n capsaicin- and vehicle-pretreated adult rats, in order to identify t he capsaicin-resistant population. Up to 90% of the intraganglionic la minar endings (IGLEs) in the myenteric plexus of the esophagus, and 70 -90% in the stomach, as well as 57% of the intramuscular endings or ar rays (IMAs) in the fundic stomach survived the capsaicin treatment, wh ile in the upper small intestine only few and in the lower small intes tine, the cecum and colon, virtually no IGLEs survived capsaicin treat ment. Intramucosal terminals were not assessed. Furthermore, gastric b alloon distension-induced c-Fos expression in the dorsal vagal complex was not significantly decreased in capsaicin-treated rats. It is conc luded that among primary vagal afferents there is a capsaicin-resistan t population that primarily innervates the esophagus and upper gastroi ntestinal tract, and a capsaicin-sensitive population that innervates mainly the lower tract. At least vagal gastric tension-sensitive affer ents also seem to be functionally intact in that they may be capable o f synaptically activating second-order neurons in the brainstem.