Gastric vagal-splanchnic interactions in the brainstem of the cat

Brainstem unitary responses to gastric vagal-splanchnic nerve interactions were evaluated in anesthetized cats during electrical stimulation of the nerves. The gastric branches of the dorsal and ventral vagal trunks which serve the proximal stomach were electrically stimulated while recording in nucleus solitarius in the brainstem to identify evoked unitary responses. The vagally evoked brainstem responses were orthodromic in nature as evidenced by a slight variability in latency, reduction in the number of spikes upon decreasing stimulus strength and failure to follow higher stimulus frequencies. Interactions between gastric vagal input from the proximal stomach and left greater splanchnic nerve were evaluated by simultaneously stimulating the nerves electrically. Forty-three (16%) of the 265 gastric vagally evoked brainstem responses recorded were inhibited by simultaneously activating the left greater splanchnic nerve. The gastric vagally evoked responses inhibited by splanchnic input were nearly equally divided between the dorsal and ventral vagal trunks. Eighty-eight percent of those vagally evoked brainstem units inhibited by splanchnic input showed complete inhibition suggesting secure synaptic coupling. In addition, 3 gastric vagally activated brainstem units were identified which were also activated by greater splanchnic input. The latency of the splanchnic evoked brainstem response in these 3 units ranged from 55 to 89 ms compared to a mean latency of 290 ms (S.D. +/- 50 ms) for the vagally evoked brainstem response. Splanchnic electrical stimulation usually produced an inhibitory effect upon the vagally evoked brainstem response which persisted for approximately 30 s following termination of splanchnic stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)