The Physiology, Morphology, and Ontogeny of Emetic Behavior in Anuran Amphibians

Publisher Website
Google Scholar
Abstract
We examined the responses of Rana catesbeiana, Rana clamitans, and Xenopus laevis to a variety of emetic drug treatments. No treatment caused regurgitation or any emetic behavior (i. e., retching) in any premetamorphic tadpoles. The ability to vomit first appeared during metamorphosis, precisely when the transforming froglets were first able to swallow a large bolus of food. Postmetamorphic frogs exhibited intergeneric differences in their sensitivity to different emetics. The emetic behavior of Rana did not change when it was transferred from a terrestrial to an aquatic environment. Mechanical stimulus, that is, distention of the foregut, alone can induce regurgitation. Movements of the torso, along with contraction of the abdominal wall, appear to be essential for raising abdominal pressure during emesis in anurans. Rana and Xenopus differ in the body movements they exhibit during emesis: Rana dorsiflexes its presacral vertebral column on its sacroiliac joint; Xenopus instead telescopes its torso by sliding the ilia rostrocaudally on the sacral vertebra. These same sacroiliac movements have been previously related to differences in the locomotion of these two frogs. Our data suggest that the sacroiliac musculoskeletal complex of frogs is as important to the elevation of abdominal pressure during actions such as emesis, oviposition, micturition, etc., as it is to adult locomotion. Anurans do not develop their elongated ilia and their sacroiliac joints until metamorphosis. The inability to deform the torso may be one mechanistic reason why tadpoles neither vomit nor display any of the other behaviors requiring abrupt elevation of abdominal pressure.