Behavioral dissociations between C57BL/6 and DBA/2 mice on learning and memory tasks: A hippocampal-dysfunction hypothesis

We recently demonstrated that C57BL/6 (C57) mice are capable of spatial learning in the Morris water task whereas DBA/2 (DBA) mice are impaired. There may be a number of reasons why the DBA mice are impaired in the Morris task. The main objective of this study was to understand the nature of the DBA impairment. First, we showed that DBA mice do not have a general learning impairment, since they can solve two different discrimination problems. Using a water-filled plus maze and a modified version of the Morris task, we showed that DBA mice can (1) see distal cues, (2) attend to the extramaze environment, and (3) learn the place of a hidden platform if training allows them to utilize only part of the distal environment. Probe data indicate, however, that in contrast to C57 mice, DBA mice do not form a complete representation of the extra-maze environment. Final experiments demonstrate that DBA mice are also impaired on a task that requires conditional learning but perform as well as C57 mice on a response-tendency task and a nonconditional learning task. The results of these and other studies suggest that learning and memory processes in DBA mice may be disrupted as a result of impaired hippocampal function.