Severe learning deficits in apolipoprotein E-knockout mice in a water maze task.

Recent studies on apolipoprotein E (apoE) have stressed the importance of this protein in neuronal viability, especially in the hippocampal area. In the present study, we used the Morris water maze to assess spatial learning and memory in 6-month-old homozygous apoE-deficient and heterozygous control mice. The apoE status was checked by genotyping and immunocytochemistry. ApoE-knockout mice were not able to learn the task at all, developed neither spatial nor other strategies to locate the platform, but rather an unusual repetitive behavioral pattern of 'wall bumping'. Heterozygous control mice did not experience any difficulty with the task. Swimming ability and general locomotor activity of both groups were comparable. These results indicate that absence of apoE in these animals might be critical for spatial learning and memory abilities.