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

We investigated the effects of exogenous corticosterone on the locomotor ac tivity of captive red-eared slider turtles, Trachemys scripta elegans. An i ncrease in plasma corticosterone often increases locomotor activity in mamm als and birds, but there are no reported findings for turtles. In this stud y 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 tu rtles exhibited no such increase, validating the effectiveness of our impla nts to deliver corticosterone. Although corticosterone remained high at the end of the activity trials, the increase in activity was ephemeral in natu re, 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 th ere are underlying physiological mechanisms, perhaps mediated at the recept or level in the brain, involved in locomotor activity behavior in slider tu rtles. Environmental perturbations that cause a reduction in available food resources may cause the organism to increase its level of locomotor activi ty to increase food encounter rate but later reduce activity to conserve en ergy reserves. These data are important when considering behavioral and phy siological mechanisms involved in a turtle's response to changing condition s in habitat quality, J. Exp. Zool. 284:637-644: 1999. (C) 1999 Wiley-Liss, Inc.