Integrative responses of neurons in nucleus tractus solitarius to stimulation of visceral and vestibular afferents

Abstract

Although the vestibular nuclei project to nucleus tractus solitarius (NTS), little is known about the effects of vestibular inputs on NTS neuronal activity. Lesions of NTS abolish vomiting elicited by a variety of triggering mechanisms, including vestibular inputs. Thus, an emetic stimulus that activates gastrointestinal (GI) receptors could alter the responses of NTS neurons to vestibular inputs. We examined in decerebrate cats the responses of NTS neurons to rotations of the body before and after the intragastric administration of the emetic compound CuSO4. The activity of > 30% NTS neurons was modulated by vestibular stimulation, with most of the responsive cells having their firing rate altered by rotations in the head‐up or head‐down directions. These responses were aligned with head position in space, as opposed to the velocity of head movements. The activity of NTS neurons with baroreceptor, pulmonary and GI inputs could be modulated by vertical plane rotations. However, injection of CuSO4 into the stomach did not alter the responses to vestibular stimulation of NTS neurons that received GI inputs, suggesting that the stimuli did not have additive effects. These findings show that the detection and processing of visceral inputs by NTS neurons can be altered in accordance with the direction of ongoing movements.