DESCENDING PATHWAYS NECESSARY FOR VESTIBULAR INFLUENCES ON SYMPATHETIC AND INSPIRATORY OUTFLOW

The objective of this study was to determine which brain stem regions that have projections to sympathetic preganglionic neurons or phrenic motoneurons are necessary for vestibulosympathetic or vestibulorespiratory responses in decerebrate cats. Bilateral kainic acid injections into the rostral ventrolateral medulla abolished splanchnic nerve responses to electrical stimulation of the vestibular nerve, suggesting that this region is critical for the production of vestibulosympathetic responses. In contrast, injections into the caudal medullary raphe nuclei had no apparent effect on the responses. Neither the dorsal nor the ventral respiratory group appears to be necessary for mediating vestibular influences on the phrenic nerve, suggesting that nonrespiratory neurons (such as vestibulospinal neurons) may be important for producing vestibulorespiratory responses.