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 CCK 2 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 CCK 2 receptors mediate habituation to an anxiety-inducing stimulus in PVG hooded rats and further suggest that differential expression of these CCK 2 receptors underlies this strain difference.
- PVG hooded and Sprague-Dawley