Murine urocortin 3 (mUcn 3), a member of the corticotropin releasing factor (CRF) peptide family, was recently identified. Of known agonists, this neuropeptide displays the highest degree of selectivity in binding to the CRF(2) receptor. These experiments sought to test the hypothesis that CRF(2) receptors have a role in modulating stress by examining intracerebroventricular (i.c.v.) administration of mUcn 3 in animal models of activation and anxiety. To investigate the effects of mUcn 3 on motor activity, rats were injected with mUcn 3 (0, 0.1, 1.0 or 10 microg, i.c.v.) 10 min prior to testing and activity was monitored for 6 h. To determine changes in novelty-induced exploration, rats were injected with mUcn 3 (0, 0.1, 1.0 or 10 microg, i.c.v.) 10 min prior to testing and examined in the elevated plus maze. Finally, delayed effects of mUcn 3 were tested in rats injected with 1.0 microg of mUcn 3 or vehicle 30 or 60 min prior to testing in the elevated plus maze. Injections of mUcn 3 significantly decreased locomotor activity in rats during the first hour of testing. In the elevated plus maze, mUcn 3 injections significantly increased open arm preference compared to vehicle when tested using a 10-min pretreatment interval. mUcn treated rats tested in the elevated plus maze following the delayed pretreatment interval did not differ from controls. These data demonstrate that injection of mUcn 3 leads to acute locomotor suppressive effects and decreases in stress-like behaviors, indicating an anxiolytic-like action for mUcn 3, and suggests a possible role of the CRF(2) receptor in the regulation of stress-related behavior.