Capsaicin‐Sensitive Vagal Afferent Fibers and Gastric Motility: Evidence for an “Axon Reflex” Mechanism

Abstract

The role of capsaicin‐sensitive afferent fibers in gastric motility has been studied in normal rats and in rats treated at birth with the sensory neurotoxin capsaicin, a procedure known to destroy up to 90% of unmyelinated afferent fibers. Gastric motility was measured as intragastric pressure changes evoked by the distention of the stomach with 8 to 10 ml of normal (154 mM) or 1 M saline solution. No differences were observed between the motility patterns evoked by gastric distention with these two solutions. Distention of the stomach evoked a significantly lower basal tone and a reduced number and amplitude of phasic contractions in capsaicin‐treated rats compared to control rats. Intravenous administration of the ganglionic blocker hexamethonium substantially reduced phasic motility in both groups of animals. Subsequent bilateral vagotomy had little extra effect. After bilateral vagotomy, electrical stimulation at supramaximal intensities of the peripheral end of the cut right vagus in the presence of hexamethonium produced an inhibition of the gastric basal tone in both groups of rats and, on cessation of stimulation, a series of rebound contractions in most control animals, but not in those treated at birth with capsaicin. These results provide evidence for an efferent role of vagal afferent fibers in the control of gastric motility, possibly via an axon reflex mechanism.