Two Types of Gastric Excitatory Responses to Stimulation of the Vagal Trunk in Cats: Efferent and Afferent Responses

Abstract

Experiments were performed on cats anesthetized with pentobarbital sodium and gallamine triethiodide. Gastric motility was recorded by a balloon method. The excitatory response to electrical stimulation of the vagal trunk was composed of an initial response during the stimulation period and a late response following stimulation. The maximal excitation of the initial response was elicited by a short pulse duration and that of the late response by a long pulse duration. The initial response was inhibited by treatment with hexamethonium or atropine. The late response was hexamethonium-resistant. This hexamethonium-resistant response was inhibited by atropine, hemicholinium and morphine, and enhanced by physostigmine. Treatment with (D-Pro2, D-Trp7,9)-substance P did not affect the hexamethonium-resistant response. Treatment with morphine inhibited the late response without affecting the initial response. From these results, it was suggested that the initial excitatory response was probably due to the activation of the parasympathetic cholinergic fibers. The late response might be due to the activation of the vagal afferent cholinergic fibers, since the pharmacological nature of the late response was similar to that in the cat with supranodose vagotomy (surviving afferent fibers) in our previous reports.