Vestibular inputs mask the directional specificity of neck proprioceptor afferent signals in sympathetic cardiovascular regulation during postural changes

During postural changes, arterial blood pressure is regulated by multiple sensory systems, including vestibular and cervical proprioceptive inputs, but their interaction remains poorly understood. We examined the involvement and interaction of these inputs in urethane-anesthetized rabbits (n = 24). Responses to 45° head-down tilt (HDT), passive neck flexion (NF), and passive neck extension (NE) were compared between control and bilateral vestibular lesion (VL) groups. In control animals, HDT evoked transient, second-to-second suppression of renal sympathetic nerve activity (RSNA) during the early phase after postural change, accompanied by a decrease in mean arterial pressure (MAP). The HDT-evoked MAP decrease was no longer observed after hexamethonium bromide administration, consistent with involvement of autonomic ganglionic transmission. Both the RSNA and MAP responses were significantly attenuated after VL, suggesting that vestibular afferents make a major contribution to the sympathoinhibitory cardiovascular response to HDT. Heart rate did not change significantly. Although absolute MAP and RSNA responses to NF and NE did not differ significantly from baseline in either group, within-animal comparison revealed a significant directional difference in MAP after VL (NE > NF in all six animals), whereas no such difference was evident in controls. These findings are consistent with the hypothesis that vestibular inputs normally mask the directional specificity of cervical proprioceptive influences on blood pressure regulation. This interaction may contribute to cardiovascular adjustments during the early phase of postural change and thereby potentially to the maintenance of cerebral perfusion.