Effects of exogenous corticosterone on locomotor activity in the red-eared slider turtle, Trachemys scripta elegans

We investigated the effects of exogenous corticosterone on the locomotor activity of captive red-eared slider turtles, Trachemys scripta elegans. An increase in plasma corticosterone often increases locomotor activity in mammals and birds, but there are no reported findings for turtles. In this study turtles implanted with corticosterone-filled Silastic((R)) implants showed a significant increase in caged locomotor activity when compared to control animals with empty implants. Corticosterone-treated turtles also showed a significant increase in plasma corticosterone concentration when pre-trial plasma samples were compared to post-trial plasma samples, while control turtles exhibited no such increase, validating the effectiveness of our implants to deliver corticosterone. Although corticosterone remained high at the end of the activity trials, the increase in activity was ephemeral in nature, peaking within 48 hr after the implant was in place. This suggests that the effects of corticosterone on behavior may be context-dependent (i.e., whether the turtles can find food) and concentration-dependent, and that there are underlying physiological mechanisms, perhaps mediated at the receptor level in the brain, involved in locomotor activity behavior in slider turtles. Environmental perturbations that cause a reduction in available food resources may cause the organism to increase its level of locomotor activity to increase food encounter rate but later reduce activity to conserve energy reserves. These data are important when considering behavioral and physiological mechanisms involved in a turtle's response to changing conditions in habitat quality. J. Exp. Zool. 284:637-644, 1999.