REGIONAL AND FUNCTIONAL DIFFERENCES IN THE DISTRIBUTION OF VESTIBULOSYMPATHETIC REFLEXES

Although considerable evidence suggests that the vestibular system reg ulates sympathetic outflow during movement and changes in posture, lit tle is known about relative vestibular influences on activity of diffe rent sympathetic nerves and sympathetic efferents with different funct ions. In the present study, we demonstrated that; electrical stimulati on of the vestibular nerve in the cat elicited responses in sympatheti c nerves innervating the head and abdominal viscera. This observation suggests that activity of sympathetic efferents innervating multiple b ody regions is affected by vestibular signals. These responses were at tenuated by >80% when blood pressure was increased to >160 mmHg. Becau se raising blood pressure decreases the responsiveness of vasoconstric tor fibers, the simplest explanation tion for these data is that the v estibular system provides particularly strong inputs to components of the sympathetic nervous system that regulate peripheral vascular resis tance. Furthermore, the relative magnitude of vestibule sympathetic re flexes was over four times larger in one sympathetic nerve composed ma inly of vasoconstrictor efferents (renal nerve) than another nerve (ex ternal carotid nerve) containing similar types of fibers. Collectively , these data indicate that the vestibular system has selective influen ces on sympathetic outflow to particular tissues and body regions.