PARABRACHIAL NUCLEUS - NEURONAL EVOKED-RESPONSES TO GASTRIC VAGAL AND GREATER SPLANCHNIC NERVE-STIMULATION

Unitary responses were recorded extracellularly in the parabrachial nucleus (PBN) in anesthetized cats during electrical stimulation of the 1) gastric branches of the ventral and dorsal vagal trunks which serve the proximal stomach, and 2) left greater splanchnic nerve. The gastric vagally evoked parabrachial responses consisted of phasic single and multiple spike orthodromic discharges, which were bilaterally distributed, with a mean latency of 349 ms (S.D. +/- 38.5). The parabrachial-evoked splanchnic unitary responses had a much shorter latency with a bimodal distribution (mean latencies, 53 and 128 ms, respectively). Convergence of gastric vagal input from the proximal stomach and the left greater splanchnic nerve upon single neurons in the PBN was electrophysiologically demonstrated in 132 units. Eighty-seven percent of the gastric vagally evoked parabrachial unitary responses were inhibited by simultaneous electrical stimulation of the splanchnic nerve. The condition-test paradigm was used to evaluate the time course of the splanchnic inhibition of the gastric vagally evoked parabrachial response. Reciprocal connections between neuronal populations in the nucleus tractus solitarius (NTS) which received gastric vagal input and the PBN were also identified electrophysiologically by direct microstimulation of the former structure. The density and characteristics of the gastric vagal and greater splanchnic input to the PBN suggested that this nucleus receives and processes a substantial amount of visceral afferent input. The PBN may serve as an important site for integrating visceral information governing the proximal stomach and ingestive processes.