Activity of Neurons in the Rostral Ventrolateral Medulla (RVLM) of Conscious Cats

Abstract

Although numerous studies in decerebrate or anesthetized animals of several species have considered the activity of neurons in the RVLM, to date no neurophysiological studies of this region have been conducted in conscious animals. The goal of the present study was to determine the firing patterns of RVLM neurons in conscious cats, and to compare the neuronal activity in this preparation to that previously documented in anesthetized animals. Recovery surgery was performed to implant a recording chamber on the caudal aspect of the skull, as well as a telemetric blood pressure recording device (Data Sciences Intl.) and probes to measure blood flow from the carotid artery (Transonic Systems). Blood pressure and blood flow measurements were used to establish whether units displayed cardiac‐related activity. Few (<25%) RVLM neurons exhibited robust cardiac‐related firing, but the mean coherence value relating unit activity to the arterial pulse (0.45±0.07) was higher than in anesthetized animals. Moreover, the mean spontaneous firing rate of RVLM neurons with cardiac‐related activity was over 6 times higher in awake cats than in anesthetized animals. Many RVLM neurons that lacked cardiac‐related firing displayed multifaceted patterns of rhythmic activity. These data suggest that the activity of RVLM neurons is highly complex in awake felines.