Plasma and brain angiotensin concentrations associated with water response behavior in the desert anuran, Scaphiopus couchii under natural conditions in the field

Terrestrial amphibians obtain water by absorption across a specialized region of the ventral skin and exhibit a behavior, the water absorption response (WR) to place that region in contact with moist surfaces. Spadefoot toads (Scaphiopus couchii) spend dry months of the year in burrows, then emerge during brief periods of summer rainfall and seek water sources for rehydration and reproduction. We tested the hypothesis that these toads have changes in plasma and/or central angiotensin concentrations that are associated with seasonal emergence and WR behavior. Immunoreactive concentrations of combined angiotensin II and III (ir-ANG) were measured in plasma samples and microdissected regions of brain tissue taken from toads moving across the road or toads showing WR behavior in shallow puddles on the road. Plasma ir-ANG concentrations were not significantly different between these groups, but were significantly higher in the periventricular region of the hypothalamus in toads showing WR behavior. Concentrations in other brain regions, while highly variable among individuals, were not different between groups. Within the context of the natural history of a specialized desert toad, these results support the hypothesis that ir-ANG is associated with WR behavior in spadefoot toads in a manner analogous to oral drinking exhibited by other vertebrate clades.