Units in tegmental nuclei responding to stimulation of gastric vagal and greater splanchnic fibers in the cat.

The response of neurons in the ventral and dorsal tegmental nuclei during electrical stimulation of the gastric vagal fibers which serve the proximal stomach and the left greater splanchnic fibers were evaluated in chloralose-anesthetized cats. The mean latency of 181 gastric vagally evoked unitary responses recorded in the tegmental nuclei was 352.2 ms, whereas the latency of the left greater splanchnic-evoked tegmental response was significantly less (63.2 ms). The unitary responses to the gastric vagal and greater splanchnic fibers stimulation were bilaterally distributed in the ventral and dorsal tegmental nuclei. Convergence of the gastric vagal input from the proximal stomach and the left greater splanchnic input was observed in 151 units (83 percent). Stimulation of the greater splanchnic nerve usually resulted in a short latency excitation followed by an inhibitory effect on gastric vagally evoked responses. The results suggested that some convergent splanchnic inhibition of gastric vagally evoked responses was mediated via an interneuron. Projections from the nucleus tractus solitarius and the parabrachial nucleus to the tegmental nuclei were also identified electrophysiologically by direct microstimulation of the two former areas. The significant number of gastric vagal and splanchnic evoked unitary responses recorded in the ventral and dorsal tegmental nuclei suggested that they may serve as an important pontine site for processing of visceral information between the nucleus tractus solitarius and forebrain sites.