Activity patterns of cardiac vagal motoneurons in rat nucleus ambiguus

Abstract

Extracellular recordings were made in the right nucleus ambiguus of urethane-anesthetized rats from 33 neurons that were activated at constant latency from the craniovagal cardiac branch. Their calculated conduction velocities were in the B-fiber range (1.6-13.8 m/s, median 4.2), and most (22/33) were silent. Active units were confirmed as cardiac vagal motoneurons (CVM) by the collision test for antidromic activation and by the presence of cardiac rhythmicity in their resting discharge (9/9). Brief arterial pressure rises of 20-50 mmHg increased the activity in five of five CVM by 0.1 ± 0.02 spikes·s-1·mmHg-1 from a resting 3.8 ± 1.2 spikes/s; they also recruited activity in two of four pre..