ORGANIZATION OF VESTIBULAR INPUTS TO NUCLEUS-TRACTUS-SOLITARIUS AND ADJACENT STRUCTURES IN CAT BRAIN-STEM

The vestibular system is involved in maintaining stable blood pressure and respiration during changes in posture and is essential for elicit ing motion sickness-related vomiting. Because the nucleus tractus soli tarius (NTS) participates in the regulation of sympathetic and inspira tory outflow and the triggering of emesis, we tested the hypothesis th at this region receives vestibular inputs in cats. In one set of exper iments, microinjections of the tracer Phaseolus vulgaris leucoagglutin in into the medial and inferior vestibular nuclei labeled projections to the middle and lateral regions of the NTS. In electrophysiological experiments, electrical stimulation of the vestibular nerve modified t he firing rates of neurons located in the same regions. Some neurons w ith vestibular inputs received convergent signals from the abdominal v agus nerve and could potentially mediate motion sickness-related vomit ing. Others received convergent baroreceptor inputs and could act as a substrate for some components of vestibulosympathetic reflexes. In co ntrast, inspiratory neurons in the dorsal respiratory group received l ittle vestibular input, suggesting that vestibulorespiratory reflexes are mediated by cells located elsewhere.