THE WATER-ABSORPTION RESPONSE - A BEHAVIORAL ASSAY FOR PHYSIOLOGICAL PROCESSES IN TERRESTRIAL AMPHIBIANS

Terrestrial amphibians take up water by abducting the hind limbs and p ressing a specialized portion of the ventral skin to a moist surface, using a characteristic behavior called the water absorption response. An assay of the water absorption response was used to quantify physiol ogical factors associated with thirst and water uptake. Dramatic chang es in the water absorption response resulted from subtle changes in hy dration state and from altering the reserve water supply in the urinar y bladder. The water absorption response could be induced by intraperi toneal and intracerebroventricular injection of angiotensin II, demons trating that components of the renin-angiotensin system on both sides of the blood-brain barrier have a dipsogenic function in amphibians. T hese experiments also demonstrated that the water absorption response could be influenced by changes in barometric pressure. Toads avoided t he water absorption response on hyperosmotic substrates, and behaviora l experiments showed that the amphibian skin served, a sensory functio n similar to that of the lingual epithelium of mammals. The water abso rption response assay has enormous potential as a tool for the investi gation of physiological processes and sensory capabilities of amphibia ns.