Dietary Docosahexanoic Acid (DHA) Effects on Rat Pup Myelin

Abstract

The lipid composition of neural membranes can be altered by diet during development, and effects on membrane fluidity, enzyme systems, and measures of neural function have been reported. The fatty acids docosahexanoic acid (DHA) and arachidonic acid (AA) are present in large amounts in neuronal membranes. Dietary supplementation with DHA alone, which has been recommended for pregnant and lactating women, results in higher milk levels of DHA. However, little is known regarding the effects of maternal DHA supplementation on neural development of offspring. We investigated the effects of increasing levels of DHA on the lipid composition of myelin membranes and on electrophysiologic function of neural membranes. Methods: Timed pregnant dams were fed, beginning on day 2 of gestation and throughout lactation, a purified diet whose fat source (22% of kcals) was a vegetable blend supplemented with different levels of DHA. Final concentrations of DHA in the maternal diets were 0%, 0.3%, 0.7% and 3% of total acids. On postnatal day 3, pups were culled to 10 per dam and were randomly cross fostered among dams of the same diet group to minimize litter effects. On postnatal day 15, the latency of the acoustic startle reflex was recorded from needle electrodes placed in the muscle of the thigh. This latency is a measure of conduction time through the brainstem auditory pathway, spinal cord and peripheral nerve, and myelination of these pathways is the primary determinant of its latency. Pups were killed on postnatal day 24, brains were removed, and myelin was isolated. Myelin fatty acid composition, and the cholesterol content of myelin were measured. Results: DHA constituted 5.4%, 6.0%, 6.6% and 6.7% of total fatty acids in brain myelin of pups of dams fed 0%, 0.3%, 0.7% and 3% DHA diets, respectively. There was a significant positive correlation between the myelin content of DHA and latency of the reflex (r=0.592; p=0.008), and a significant negative correlation between the myelin content of DHA and the myelin content of cholesterol (r=0.635; p=0.004) (Figs). Conclusion: Diet-induced alterations in the fatty acid composition of developing myelin may have significant effects on the content of cholesterol -the predominant lipid constituent of myelin -and on a myelin-dependent electrophysiologic response.