Characteristics of Vagal Esophageal Tension-Sensitive Afferent Fibers in the Cat

Bang, Yoon Kyung; song, Chi Wook; Han, Hee Chul; Hong, Seung Kil; Hyun, Jin Hae

Abstract

BACKGROUND/AIMS: Activation of tension-sensitive receptors in the esophagus evokes spike discharges in vagal and sympathetic afferent axons. These tension-sensitive afferent fibers play irnportant roles in esophageal reflex activities, including the activation of peristalsis and contraction of the upper esophageal sphincter, as well as in the central mediation of esophageal pain. To understand the properties of vagal esophageal tension-sensitive afferents we studied the raponse of vagal afferents to balloon distension in the lower esophagus of the cat using the single fiber recording technique. We also studied whether these afferent fibers were sensitized by acid infusion or not.
METHODS
Under an alpha-chloralose anesthesia, the cat was dissected along the aidline of the neck and 21 vagal afferent fibers were separated. Electrophysiological activity was then measured during rest and during latex balloon distentions. Next, acid(0.1N HC1) was infused into the lurnen of the esopahgus and changes in baseline discharges and response to distention of vagal afferents were compared before and after the acid infusion.
RESULTS
Of the 21 esophageal afferents, 18 were A6 and 3 were C fibers. During the resting state, 19 of the 21 fibers showed spontaneous discharge activity, the mean was found to be 3.6+5.4 imp/second. Esophageal distention produced a reproducible increase in discharge rate that adapted slowly to sustained distention. The average threshold pressure of the endings was 10.4+5 mmHg. The saturation pressure was 97.8+10.2 mmHg with graded, discrete distentions. After intraesophageal acid infusion, the discharge rate showed no significant changes when compared to base line discharges.
CONCLUSIONS
Esophageal tension-sensitive vagal afferent fibers showed a reproducible re:sponse to distention, which may provide a new objective methodology in studying afferent sensory nerve fibers. Furthermore these fibers were also not sensitized by intraesophageal acid infusion.