Apolipoprotein E deficiency effects on learning in mice are dependent uponthe background strain

Apolipoprotein E (apoE) deficient mice were bred onto the C57BL/6 and FVB/N strain backgrounds. The cognitive behavior of food-restricted apoE-deficie nt and wildtype male mice from these strains was assessed in an olfactory c ued 8-arm radial maze. At 6 weeks of age, all four types of mice improved i n maze performance over the course of 5 days. However, at 6 months of age, only the apoE-deficient mice on the C57BL/6 background failed to improve th eir maze performance over the 5 day course, as gauged by the number of inco rrect choices made before retrieving both food rewards. Thus, an age-depend ent and strain-specific effect of apoE deficiency on cognitive behavior was observed in these mice. The background strain affected activity levels in the maze? as well as in an open field assay. Plasma corticosterone levels w ere assessed in control, fasted, and post-restraint stress states. Fasting and restraint stress led to increases in plasma corticosterone levels. Alth ough there were strain specific effects on fasting corticosterone levels, a nd the effect of apoE deficiency on post-stress corticosterone levels, ther e was no association between fasted corticosterone levels and impaired cogn itive behavior in the 8-arm radial maze assay. (C) 2001 Elsevier Science B. V. All rights reserved.