Intra- and extracellular dehydration-induced thirst-related behavior in anamphibian

The behavioral response to dehydration is critical to an animal's survival. Because of their permeable skin, amphibians are particularly sensitive to dehydrating conditions. We tested the hypothesis that different forms of de hydration induce water absorption response (WR) behavior in the desert spad efoot toad, Scaphiopus couchii. First, we determined the behavioral respons e to intracellular dehydration by treating fully hydrated toads with increa sing concentrations of hypertonic solutions of NaCl or sucrose via intraper itoneal injection (i.p.). Animals that were treated to induce intracellular dehydration with either solute exhibited a significant increase in WR beha vior compared to vehicle-treated controls. To distinguish that the response was a result of an increased osmotic gradient between the intra- and extra cellular compartments, we treated fully hydrated animals i.p. with urea, wh ich freely passes into the intracellular compartment and increases overall animal osmolarity. Urea treatment did not induce WR behavior. To determine the response to extracellular dehydration, the blood volume of fully hydrat ed toads was reduced via cardiac puncture, and the WR behavior was measured . Animals who had a reduction in blood volume exhibited a significant incre ase in WR behavior compared to sham-punctured controls. Our results are the first to demonstrate that multiple forms of dehydration can induce thirst- related behavior in amphibians. (C) 1999 Elsevier Science Inc.