In amphibians, as in other vertebrates, exposure to stressors triggers an increase in plasma glucocorticoids. Glucocorticoids are believed to mediate behavioral transitions critical to coping with stressors. A common amphibian behavioral response to a variety of different stressors is inactivity. With a series of experiments, we tested the hypothesis that stress-induced decreases in locomotory activity are mediated by the glucocorticoid hormone, corticosterone (CORT). With the use of a plethodontid salamander (Red-legged Salamander, Plethodon shermani), we demonstrated that handling, a stressor, resulted in decreased locomotory activity. Next, subjects were treated with a dermal patch containing either oil vehicle or CORT. The amount of CORT used was chosen to elevate plasma CORT acutely to physiologically relevant levels relative to treatment with oil patches. Activity was measured in response to different amounts of CORT, at different times after CORT exposure, and in the presence of different chemosensory cues. One experiment also included treatment with the glucocorticoid receptor blocker, mifepristone. Although handling resulted in reduced activity, we could discern no effect of acute elevations of CORT on activity. These results suggest that acute stress-induced changes in locomotory activity are not mediated by CORT in Red-legged Salamanders.
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Vol. 69 • No. 2