Maternal dietary docosahexanoic acid content affects the rat pup auditory system

Previous studies of the effects of dietary docosahexanoic acid (DHA), 22:6n3, on neurodevelopment have focused mainly on visual-evoked potentials and indices of visual activity, measures that may be confounded by effects on the retina rather than on neural pathways. We investigated the effect of pre- and postnatal maternal dietary DHA content on auditory brainstem conduction times (ABCTs), the appearance of the auditory startle reflex (ASR), and 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity in brainstem homogenates. Timed pregnant dams were fed, beginning on day 2 of gestation and throughout lactation, a purified diet containing one of three levels of DHA (0, 1, or 3% of total fatty acids, or 0, 0.4 or 1.2% of total energy). On postnatal day (PND) 3, pups were randomly crossfostered within diet groups to minimize litter effects and culled to 10 per litter. Cerebrums and milk from culled pups stomachs were collected for lipid analysis. The timing of appearance of the ASR was determined between PND 10 through 14 and ABCTs were measured in pups on PND 24 and 31. Pups were sacrificed on PND 31 and cerebrums were removed. In each of two replicated studies, pups in the 1% DHA group weighed significantly less on PND 3 and they gained significantly less weight from PND 3 to 31 compared with pups in the 0 or 3% groups (p<0.01). The auditory studies were not conducted on the 1% DHA group since measures of auditory function are in part a function of somatic growth. The tissue fatty acid data for the 1% DHA group did not show unexpected findings. Higher dietary DHA was reflected in milk and pup cerebrums, and levels of arachidonic acid were inversely related to levels of DHA. In the pups of dams fed diets containing 3% versus 0% DHA, the ASR appeared significantly later (p<0.001) and the ABCTs were longer (p<0.05) on PND 31. CNPase activity levels were not different between the 0 and 3% DHA groups. This study demonstrated that the auditory brainstem response is sensitive for identifying effects of diet on neurodevelopment, and that diets supplemented with high levels of DHA may exert a negative influence on central nervous system development, potentially through effects on myelin. This study suggests the need for further studies of pre- and postnatal long chain polyunsaturated fatty acid dietary supplementation.