Responses of neurons in the caudal medullary lateral tegmental field to visceral inputs and vestibular stimulation in vertical planes

Abstract

The dorsolateral reticular formation of the caudal medulla, or lateral tegmental field (LTF), has been classified as the brain's “vomiting center” as well as an important region in regulating blood pressure. We examined in cats the responses of LTF neurons to rotations of the body that activate vertical semicircular canals and otolith organs, as well as to stimulation of baroreceptors and gastrointestinal receptors (through the intragastric administration of the emetic compound copper sulfate). Half of the LTF neurons exhibited graviceptive responses to vestibular stimulation, similar to primary afferents innervating otolith organs. The other half of the neurons had complex responses, suggesting that they received convergent inputs from a variety of vestibular receptors, as expected for neurons that contribute to the generation of motion sickness. The administration of copper sulfate often modulated the gain of responses of LTF neurons to vestibular stimulation, particularly for units whose spontaneous firing rate was altered by infusion of drug (median of 459%). The present results thus raise the prospect that emetic signals from the gastrointestinal tract modify the processing of vestibular inputs by LTF neurons, thereby affecting the probability that vomiting will occur as a consequence of motion sickness.