Response of Neurons in the Rostral Ventrolateral Medulla (RVLM) to Anticipated and Passive Movements

Abstract

It is well‐established that the rostral ventrolateral medulla (RVLM) plays a predominant role in regulating the activity of sympathetic outflow to the cardiovascular system. We and others have previously shown that in addition to baroreceptor inputs, RVLM neurons respond to signals from the vestibular system. However, most recordings of RVLM unit activity have occurred in anesthetized or decerebrate preparations, limiting the assessment of cognitive effects on neuronal activity. In this study, felines were instrumented for chronic recordings of the electrocardiogram and/or carotid artery blood flow as well as activity of RVLM neurons during 40° head‐up tilts. RVLM units were identified through stereotaxic coordinates and having activity correlated with changes in blood pressure during the cardiac cycle. Tilts were preceded by a light cue, so animals anticipated the movement. We tested the hypothesis that head‐up tilts elicit an increase in the activity of RVLM neurons that is initiated between the light cue and the onset of movement. We also determined if there is a relationship between RVLM unit activity and heart rate, as would be expected if the changes in firing rate are dictated by baroreceptor signals. Head‐up tilts elicited an increase in firing rate for a third of RVLM units. However, for the majority of these units, there was not a significant change in firing rate following the light cue and prior to head‐up rotations. In addition, linear regression analyses showed that there was no appreciable relationship between unit firing rate and heart rate (R2 values ranged from 0.001–0.29, median of 0.03). These studies suggest that cognitive inputs do not produce feedforward alterations in excitability of RVLM neurons prior to perturbations that can alter blood pressure. In addition, they show that inputs to RVLM neurons are complex such that the firing rate of the units is not simply related to baroreceptor inputs.Support or Funding InformationNIH grant R01‐DC013788This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.