Functional Classification of the Vagal Afferent Discharges in the Dog's Stomach

Differences of discharge patterns in various vagal afferent fibers from gastric wall were studied to assess the accuracy of the transformation of the applied stimulation into afferent discharge.The right vagus nerve (partly left) was divided at the peripheral end of Ggl. nodosum and afferent impulses from gastric wall were recorded in the functionally isolated single units.In the vagus, the most effective source of afferent activity was the area extending from the lesser curvature to the posterior wall of antrum, only rarely was stimulation at the other parts effective. The discharges of 23 single units isolated from the vagus nerve were classified to three types as follows.(1) The discharges corresponded with the change in gastric volume and gastric peristalsis, were recorded in the nerve from antrum (including lesser curvature) and seemed to carry the information of tension change.(2) The discharges corresponded with the change in gastric volume and not gastric peristalsis, were recorded in the nerve from cardiac portion and seemed to carry the information of stretch change.(3) The discharges, in the form of transient brief burst, occurred immediately after the increase of the gastric volume but disappeared soon, responded neither to the constant holding of air volume in the stomach nor to frequently occurring gastric peristalsis. Furthermore, this type of fibers carried tonic discharges and the discharge frequencies increased in accordance with the increase in the acidity of insufflated HCl acid.The τ-S relations in the discharges of the second type suggested that the firing patterns were quite stable to the applied stimulation.