SUMMARY

1. In the present study, we investigated the effect of docosahexaenoic acid (DHA) on spatial memory related learning ability in aged (100 weeks) male Wistar rats.

2. Rats were fed a fish oil-deficient diet through three generations and were then randomly divided into two groups. Over 10 weeks, one group was per orally administered 300 mg/kg per day DHA dissolved in 5% gum Arabic solution and the other group was administered the vehicle alone. Five weeks after the start of the administration, rats were tested with the partially baited eight-arm radial maze to estimate two types of spatial memory related learning ability displayed by reference memory error and working memory error.

3. Chronic administration of DHA significantly decreased the number of reference memory errors and working memory errors.

4. The level of lipid peroxide (LPO) in the hippocampus tended to decrease with chronic DHA administration and demonstrated a positive correlation with the number of reference memory errors.

5. These results suggest that the accumulation of hippocampal LPO reduces spatial memory related learning ability in aged rats. Moreover, chronic administration of DHA was effective in decreasing the level of hippocampal LPO, then improving learning ability.