Transdermal delivery of corticosterone in terrestrial amphibians

Stressors elicit allostatic responses that allow animals to cope with changing and challenging environments and also cause release of glucocorticoid hormones (GCs). Compared to other vertebrate classes, relatively little is known about amphibian behavioral and physiological responses to GCs. To understand the effects of elevated plasma GCs in amphibians, exogenous application of GCs is necessary, but traditional methods to elevate GCs require handling and/or anesthesia which themselves are stressors. A less invasive alternative successfully used in birds and reptiles utilizes transdermal delivery by applying GCs via a dermal patch. We asked whether dermal patches containing corticosterone (CURT, the main GC in amphibians) would elevate plasma CURT in terrestrial salamanders and frogs. We explored the use of the dermal patch to deliver CURT in an acute, sustained, and repeated manner. Patches adhered well to the amphibians' moist skin and were easily removed to regulate the time course of CURT delivery. Application of CURT treated patches elevated plasma CURT concentrations compared to vehicle patches in all species. Patches delivered physiological levels of plasma CURT in ecologically relevant time frames. Repeated application and removal of CURT patches were used to simulate exposure to repeated stressors. Application of patches did not represent a stressor because plasma CURT concentrations were similar between animals that received vehicle patches and untreated animals. Thus, transdermal delivery of GCs represents a potentially useful tool to better understand amphibian allostatic responses to stressors, and perhaps amphibian population declines. (C) 2010 Elsevier Inc. All rights reserved.