DIETARY ALPHA-LINOLENATE LINOLEATE BALANCE INFLUENCES LEARNING AND MEMORY IN THE SENESCENCE-ACCELERATED MOUSE (SAM)

The senescence-accelerated mouse (SAMP8) is a model of age-related deterioration of memory and learning ability. A semipurified diet supplemented either with safflower oil (rich in linoleate) or with perilla oil (rich in alpha-linolenate) was fed to SAMP8 mouse dams and their pups. The offspring (males from several mothers) at 28 weeks of age were used for behavioral tests. The proportions of n-3 and n-6 highly unsaturated fatty acids in brain phospholipids reflected the n-3/n-6 balance of the diets. The learning and memory abilities of the two dietary groups were tested with the Sidman active avoidance task and the light and dark discrimination learning test. The group given perilla oil showed much greater improvement in learning in the Sidman active avoidance task than did the group fed safflower oil. In the light and dark discrimination learning test, the total number of responses to positive and negative stimuli was lower in those fed perilla oil, and their responses to positive stimuli were higher than to negative stimuli after the 10th session. Consequently, the correct response ratios of discrimination were higher in the perilla oil group than in the safflower oil group. In the open field test, the total amount of locomotor activity during 5 min was lower in the perilla oil group at 7 months of age than in the group fed safflower oil. Observations of the circadian rhythm of spontaneous motor activity (SMA) indicated that the mice in the safflower oil group tended to be more active than those in the perilla oil group in both light and dark periods, and SMA counts in the safflower group were significantly higher in the second half of the light period than in the first half. These results indicate that in the SAMP8 mouse, the dietary alpha-linolenate/linoleate balance affects the n-3/n-6 ratio of brain phospholipid acyl chains and this may influence learning, memory and behavior.