Central Fiber Connections of the Vestibulo-Autonomic Reflex Arc in Cats

The fiber connections associated with the vestibulo-autonomic reflex in the brain stem were investigated in cats using electrophysiological and horseradish peroxidase (HRP) methods. When the peripheral labyrinth was stimulated, the stomach constricted, and in some cases this constriction was strong and lasted for a relatively long period. This phenomenon was interpreted as a kind of vomiting triggered by the vestibuloautonomic reflex. When the electrical stimulus was applied to the peripheral labyrinth, the solitary tractus nuclear (SN) neurons, where the vagal nerve cell bodies exist, fired spikes with short latencies. When HRP was injected into the SN region, HRP-labelled cells were found in the parvocellular reticular nucleus (PC) and vestibular nuclei (VN). When HRP was injected into the PC region, HRP-labelled cells were found in the VN. These electrophysiological and histological results indicate the existence of the following fiber connections: (i) vestibular organs-VN-SN-(vagal nerve)-stomach, (ii) vestibular organs-VN-PC-SN-(vagal nerve)-stomach, associated with the vestibulo-autonomic reflex.