Vagal interactions on brain stem neurons receiving input from the proximal stomach in cats.

Gastric vagal fibers on the proximal stomach that join the dorsal and ventral vagal trunks were electrically stimulated to localize and evaluate brain stem neuronal interactions in anesthetized cats. The brain stem responses were located in nucleus tractus solitarius in the dorsomedial, caudal region of the medulla oblongata. There was no significant difference in the mean latency of the gastric vagally evoked brain stem response between the dorsal and ventral vagal trunks. The responses consisted of single or multiple spikes with a mean latency of approximately 290 +/- 50 (SD) ms. Forty-one percent, or 168 unitary responses of the 406 total responses recorded, showed convergence of proximal gastric vagal input from both the dorsal and ventral vagal trunks on the same recording site or on the same cell. Of those unitary responses that received convergent proximal gastric vagal input, 95 unitary responses (57%) showed convergence of input to the same area, on different cells at the same recording site during a single trial. Seventy-three single units (43%) received convergent input from proximal gastric vagal afferent fibers in both the dorsal and ventral trunks. Fifty-two, or 71%, of the single unit convergent responses were excitatory in nature, whereas the remaining 29% were inhibitory. These data demonstrated that proximal gastric vagal afferent fibers that join the dorsal and ventral trunks converged on a significant number of single neurons in the brain stem. The convergent response was synaptically secure and exerted an identifiable biasing effect on the response of the brain stem neuron.(ABSTRACT TRUNCATED AT 250 WORDS)