Rats fed diets high in n3 fatty acids have lower whole brain levels of myelin basic protein, lower activities of 2′-3′cyclic nucleotide 3′-phosphodiesterase(an indicator of myelination) (DiBiase & Salvati, 1997), and longer auditory brainstem conduction times (ABCTs) (Saste et al., in press). We investigated the effects of varying levels of the n3 fatty acid DHA upon development of the rat pup auditory system.Methods: Dams were fed, from day 2 of gestation and throughout lactation, a purified diet whose fat source (22% of cals) was a vegetable oil blend supplemented with an algae oil containing 0% or 3% DHA. On postnatal day(pnd) 3, pups were culled to 10 per dam and were randomly cross fostered among dams of the same diet group to minimize litter effects (n=6 dams per diet group, 60 pups per diet group). Milk from culled pup stomachs was used for fatty acid analysis. On pnd 15, auditory electromyelographic reflexes (AEMR) to 130 db peak sound pressure level clicks were recorded from needle electrodes placed in the muscle of the thigh of 20 pups per diet group; pups were then sacrificed and brainstems removed for fatty acid analysis. For the remaining 40 pups per diet group, ABCTs were measured on pnd 24 and 31, and the postnatal day of appearance of the auditory startle reflex was determined. An additional group of dams fed 1% DHA diet had pups whose weight gains were 2/3 that of dams fed the 0% or 3% DHA diets; data from these pups are not presented. Results: Length of gestation, maternal weight gains and pup weights on pnd 3 did not differ between diet groups. Weight gains to pnd 12 were slightly lower among pups of dams fed the 3% DHA diet. The fatty acid composition of dam milk and pup brainstems reflected maternal diet. AEMRs were not different, however, ABCTs on pnd 24 were longer and the time of appearance of the auditory startle reflex was later in pups of dams fed 3% DHA.Conclusion: High levels of dietary DHA during development may be associated with delays in myelination of the central nervous system as suggested by longer ABCTs and a delay in appearance of the auditory startle reflex. Similar AEMRs between diet groups suggest minimal effects upon the peripheral nervous system. Table

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