The CCK2agonist BC264 reverses freezing behavior habituation in PVG hooded rats on repeated exposures to a cat

Abstract

Our previous studies (NeuroReport 12 (2001) 2717) showed that PVG hooded and not Sprague-Dawley (SD) rats exhibit remarkable freezing behavior on exposure to a cat in the cat freezing test apparatus. In the present study, we further examined the differences between these two strains of rats in response to repeated daily exposure to a cat in the cat freezing test apparatus. Freezing behavior habituation was observed in both PVG hooded (days 5-7) and SD rats (days 3-7). A selective CCK2 agonist (BC264, 0.3 μg/kg, i.p.) on day 8 reversed habituated freezing behavior and locomotor activity in PVG hooded rats, but not in SD rats. These results suggest that CCK2 receptors mediate habituation to an anxiety-inducing stimulus in PVG hooded rats and further suggest that differential expression of these CCK2 receptors underlies this strain difference. © 2003 Elsevier Ireland Ltd. All rights reserved.