The current status and implications of the neurohumoral hypothesis of motion-induced vomiting are reviewed. Data show that squirrel monkey subjects vomit only once if horizontal rotation is terminated immediately on the occurrence of the emetic response. Refractory periods for multiple vomiting episodes concurrent with continued rotation are sufficiently brief to suggest that the expected presence of the hypothetical neurochemical agent in the cerebrospinal fluid of the fourth ventricle should continue to evoke more than one vomiting response even after cessation of motion stimulation. In its present form, the hypothesis is conceptually vague and should be developed further to account for a mechanism by which the expected recurrent emesis is inhibited during the period when the alleged agent is a potentially effective stimulant.
Animals Cerebral Ventricles