In the wild, when an animal is exposed to predators or harsh conditions, the stress response is often associated with fleeing behaviors, which are seen as increased locomotor behavior. Handling-stress procedures and intracerebroventricular (icy) injection of corticotropin-releasing factor (CRF) have both been shown to cause an increase in locomotor activity in roughskin newts (Taricha granulosa). The present experiments were designed to determine if icv administration of corticosterone (CORT) prevents stress-induced locomotor increases in activity, if it prevents CRF-induced increases in locomotor activity, and if the time-course and pharmacological specificity of the CORT effects on locomotor activity fit the model for intracellular or membrane receptors. In experiment 1, newts which had been injected with CORT or dexamethasone (DEX) received a standardized handling-stress procedure. Corticosterone administration was able to suppress the increase in locomotor activity in newts exposed to handling-stress at 20 minutes after administration. This effect was transient (no longer present at 2 hours after the injection) and not mimicked by DEX, a synthetic glucocorticoid that binds to intracellular and not membrane receptors. In experiments 2 and 3, either CORT or DEX was administered in the same icy injection with CRF. CORT suppressed CRF-induced locomotor activity in some cases, but this action of CORT seems to be context dependent. Results for DEX-injected newts were confounded the failure of CRF to induced significant increases in locomotor activity. There was variability in the effect of CRF on locomotor activity across seasons. Based on time-course and specificity, it appears that CORT can modulate locomotor activity in newts through mechanisms involving the membrane receptor. Variability in the effects of CRF on locomotor activity in newts suggests there may be seasonal differences in responses to stress. / Graduation date: 1998