The Ventrolateral Medulla of the Cat Mediates Vestibulosympathetic Reflexes

Extracellular recordings were made from 94 neurons located in the ventrolateral medulla (VLM) whose firing rate was affected by vestibular nerve (VN) stimulation; 50 of these units were in the subretrofacial (SRF) nucleus, which contains cells that make direct excitatory connections with sympathetic preganglionic neurons. The sample included 12 SRF cells which were antidromically driven from the upper thoracic spinal cord and had conduction velocities of 10 m/s or less; the effect of VN stimulation on all but one of these units was inhibition. The onset latency of the response to VN stimulation was long [20.3 +/- 3.7 (S.E.M.) ms, n = 9, for the antidromically activated neurons and 12.1 +/- 1.2 ms, n = 73, for the others], suggesting that the effects were predominantly polysynaptic. In addition, most of the spontaneously active units tested (33/36) received convergent inputs from the carotid sinus nerve (CSN), as would be expected for neurons which influence sympathetic outflow. Vestibular-elicited inhibition of SRF neurons with projections to the intermediolateral cell column could account for late, long duration inhibition of sympathetic discharges produced by labyrinth stimulation.