Mechanisms by which dietary oils affect behavioral patterns of rats

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Rats fed through two generations a diet supplemented with safflower oil enriched with linoleic acid (n-6) but deficient in ci-linolenic acid (n-3) exhibited significantly lower learning ability in alpha brightness-discrimination learning test (operant-type) and significantly decreased DHA content than those fed a diet supplemented with perilla oil enriched with alpha-linolenic acid. In this study, we examined whether or not the supplementation of DHA after weaning restores the decreased learning ability observed in the safflower oil group. When DHA was supplemented after weaning (Saf + DHA group), DHA and 22 : 5n-6 contents in brain reached the levels seen in the perilla oil group. However, the learning ability (correct response ratio) of the Saf+DHA group was comparable to that of the safflower oil group, and was significantly lower than in the perilla oil group. Lever pressing responses to the positive and negative stimuli were also similar to those of the safflower oil group. Conten … More ts of monoamines (depamine, serotonin and their metabolites) in brain regions were determined to find no significant difference among the three dietary groups. Acetylcholine content tended to be lower in the frontal cortex and hippocampus of the Saf+DHA group than in the other groups, but was not correlated with learning performance. On the other hand, NGF (nerve growth factor) content was significantly lower in hippocampus but was significantly higher in the piriform cortex of the safflower oil group than in the perilla oil group. When EPA (20 : 5n-3) was supplemented to the safflower oil group after weaning, brain DHA content reached the level of the perilla oil group, but NGF level was comparable to that of the safflower oil group. These results suggest that the decreased learning ability of the safflower oil group is due to irreversible effect of decreased DHA in brain during gestation and lactation. However, some fatty acids in brain such as 20 : 4n-6, 22 : 4n-6 and 22 : 5n-3 did not reach the levels seen in the perilla oil group, and could be involved in the inferior learning performance of the safflower oil group and Saf+DHA group. Less