Responses of neurons in the rostral ventrolateral medulla (RVLM) to moderate‐amplitude tilts: comparisons in conscious and decerebrate cats

Abstract

Studies in decerebrate or anesthetized animals have shown that the RVLM integrates a variety of inputs, including those from baroreceptor and vestibular afferents; the latter signals are presumably involved in regulating blood distribution in the body during postural alterations. However, no prior studies have considered activity of RVLM neurons in conscious animals. The goal of the present study was to compare responses of RVLM neurons to moderate-amplitude (<15°) body tilts (MABT) in conscious and decerebrate cats. Carotid blood flow or blood pressure was also measured to determine if the units examined received baroreceptor inputs. A large fraction of RVLM neurons (51/110) responded to MABT in decerebrate cats; ~20% of these cells also responded to stretch of the carotid artery. In contrast, the activity of only 2/135 RVLM neurons in conscious cats was modulated by MABT (0/5 neurons with cardiac-related activity). Fisher's exact test confirmed that responses to MABT were less frequent in conscious animals (p<0.001). These data suggest that responses of RVLM neurons to MABT are masked in conscious animals, perhaps because they are not beneficial during postural changes that are too small to compromise blood pressure.