This study investigated the effects of varying dietary levels of very long-chain polyunsaturated fatty acids on growth, brain fatty acid composition and behavior in mice. Five groups of pregnant and lactating B6D2F1 mice were fed diets with either a very high (n-6):(n-3) ratio of 49 [(n-3) deficient)], a normal ratio of 4.0 or a low ratio of 0.32. The (n-6) fatty acids (FA) were provided either entirely as linoleic acid (LA) or as LA in combination with arachidonic acid (ARA), and the (n-6):(n-3) ratios were adjusted by partial replacement of the (n-6) FA with docosahexaenoic acid (DHA). Offspring were maintained on these diets after weaning. The diets with the low (n-6): (n-3) ratio had no effect on the birth weights of the pups, but after 15 d resulted in a significant 12% reduction in body weights. This effect persisted to adulthood and was apparent in both brain and body weights unless ARA was substituted partially for LA as the source of (n-6) FA. There were significant effects of diet on brain fatty acid composition. Increasing levels of DHA in the diet increased brain DHA and decreased ARA, and there was also retroconversion of DHA in EPA in the mice fed high levels of DHA. Addition of ARA to the diet increased brain ARA, and, at high levels only, decreased DHA. There were no effects of this wide variation in dietary (n-6):(n-3) ratio on the ability of the mice to learn the place of the hidden platform in the Morris water maze. However, in both the cued and the place learning, the mice fed the low (n-6):(n-3) diet swam more slowly, unless ARA substituted partially for LA as the source of (n-6) FA. There were no effects of diet on activity in the spatial open field. These findings show that the effects of a diet with a low (n-6):(n-3) ratio and (n-3) FA provided as DHA, can be overcome if LA is partially replaced by ARA as the source of (n-6) FA.

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The objective of this study was to determine whether an essential fatty acid (EFA)-deficient diet (saturated fat) fed during development would alter the pattern of dendritic growth in pyramidal neurons of mouse occipital cortex. Pregnant and lactating mice were fed either a saturated fat or control diet throughout pregnancy and lactation. At weaning, one female was selected randomly from each litter, and these animals were maintained on their respective diets and reared in an enriched environment for eight weeks. Following this, their brains were processed histologically using a modified Golgi-Cox method, and patterns of dendritic growth were analysed in occipital pyramidal cells. A Sholl concentric circle analysis indicated that, for basilar dendrites, starting at a distance of 62.5 μm, animals fed saturated fat had fewer crossings than controls, which is indicative of either shorter dendrites or of less dendritic branching. Although the analysis of branching order was not significant, the trend seen in these data supports less branching in the saturated fat group, particularly of third- and fourth-order dendrites. Similar effects were seen in the apical dendrites, although to a lesser extent. Covariance analysis indicated that these effects could not be accounted for by the smaller brains in the EFA-deficient group. They can therefore be considered preliminary support for an effect of EFA on the pattern of dendritic development.

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