The Water Absorption Response: A Behavioral Assay for Physiological Processes in Terrestrial Amphibians

Abstract

Terrestrial amphibians take up water by abducting the hind limbs and pressing 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 physiological factors associated with thirst and water uptake. Dramatic changes in the water absorption response resulted from subtle changes in hydration state and from altering the reserve water supply in the urinary bladder. The water absorption response could be induced by intraperitoneal and intracerebroventricular injection of angiotensin II, demonstrating that components of the renin-angiotensin system on both sides of the blood-brain barrier have a dipsogenic function in amphibians. These experiments also demonstrated that the water absorption response could be influenced by changes in barometric pressure. Toads avoided the water absorption response on hyperosmotic substrates, and behavioral experiments showed that the amphibian skin served a sensory function similar to that of the lingual epithelium of mammals. The water absorption response assay has enormous potential as a tool for the investigation of physiological processes and sensory capabilities of amphibians.

The water-absorption region of ventral skin of several semiterrestrial and aquatic anuran amphibians identified by aquaporins

“…The tissue electrolyte content was diluted in nonperfused skin, indicating the circulation removed water as it was absorbed to prevent diminution of the osmotic gradient across the epidermis. Water absorption by anurans occurs in conjunction with a behavior, termed the water absorption response (16,26), during which the skin is pressed to a moist surface and there is a large increase in blood flow to the absorbing area of the seat patch (33,34), in conjunction with the insertion of AQPs into the apical membranes of the FRC layer of the skin (27). A better understanding of adaptations for semiterrestrial vs. semiaquatic species will require an understanding of all three parameters from a physiological and phylogenetic perspective.…”

Comparative Physiology of Body Fluid Regulation in Vertebrates with Special Reference to Thirst Regulation

“…The relative importance of these stimuli varies among different classes of vertebrates or among species in different habitats. Thirst motivates oral drinking behavior in terrestrial animals, but it induces cutaneous drinking behavior in amphibians [34]. Angiotensin II is more intimately related to extracellular dehydration because hypovolemia invariably stimulates renin secretion in all of the species examined, while an increase in plasma osmolarity generally inhibits renin secretion in most species examined [35].…”

“…Furthermore, angiotensin II seems to induce a sensation of thirst in amphibians. Hillyard and his colleagues [34,47] showed that angiotensin II stimulates water drive in the terrestrial toad, Bufo punctatus; it then induces hind limb abduction to bring a specialized portion of the ventral skin to a moist surface, the so-called "cutaneous drinking behavior." Therefore, it seems that angiotensin II in-Japanese Journal of Physiology Vol.…”

“…In the quail, hypovolemic stimulus increased plasma angiotensin II concentration (Table 3), and the inhibition of angiotensin II formation by SQ14225 inhibited hemorrhage-induced drinking. Hemorrhage did not induce oral drinking in the frog [45], but increased plasma angiotensin II and vasotocin after hemorrhage may induce cutaneous drinking behavior [34] and increase cutaneous uptake of water and Na ϩ [44].…”

Cardiovascular and behavioural changes during water absorption in toads, Bufo alvarius and Bufo marinus

“…This chamber also allowed us to evaluate the effect of different immersion levels on BCF and water absorption from deionised water (DI) and salt solutions. Because the toads were conscious and unrestrained, we were able to observe whether the time course for behaviours associated with water absorption (Hillyard et al, 1998) corresponded to the physiological response to water contact (increase in BCF).…”