| Summary: | 碩士 === 輔仁大學 === 營養科學系 === 97 === Docosahexaenoic acid (DHA) is one of the major polyunsaturated fatty acids accumulated in the nervous system. It is now well recognized that DHA is essential for normal brain development in animals and humans. The intake of 20 mg DHA/kg body weight/day has been recommended for full-term baby by the World Health Organization. Thus, DHA has been added in infant formulas at various levels. However, the effective dosage of the dietary DHA supplementation is unknown. Therefore, the purposes of this study were (1) to determine how much dietary DHA actually getting into the brain tissue; (2) to evaluate the effects of different level of DHA on the cortex and hippocampus development by determination the expression of N-methyl-D- aspartat receptor (NMDARs) and Choline acetyltransferase (ChAT) in neonatal rat brain. Three-day-old neonatal rat pups were tube-fed by gastrostomy with artificial rat’s milk in various levels of DHA, i.e. 0, 5, 300 mg DHA/dL respectively, for a period of 6, 8, 10, 12 and 14 days. DHA concentration in brain of pups fed artificial milk for 14 days was determined by Gas Chromatography (GC). NMDAR subunits 1A and 2A/B proteins expression in hippocampus and cortex of gastrostomy tube-fed neonatal rat pups for 6, 8, 10, 12 and 14 days were measured respectively by Western blotting. The result showed that there were no significant effects of DHA intake on body weight gains and relative organ weights. The amount of total milk intake was significantly smaller in high-DHA group, while the DHA levels in various brain tissues were significantly higher than other groups (p＜0.05). Although the observation of the variation of protein expression of NMDAR 1A, 2A/B subunits and ChAT in neonatal brain only lasted for a week (6, 8, 10, 12 and 14 days), the expression of each protein positively correlated with the duration of gastrostomy tube-feeding by adequate and high level DHA supplementation in rat milk. The protein expression of NMDAR 1A subunit in hippocampus of gastrostomy tube-fed neonatal rat pups for 14 days was significantly increased with the adequate and high-DHA supplementation (p＜0.05), meanwhile this phenomenon also occurred in the protein expression of NMDAR 1A, 2A/B subunit and ChAT in cortex. In addition to a significantly higher NMDAR 2A/B subunits expression in hippocampus of high-DHA animals compared with the control, there is a dose dependent response on NMDAR 2A/B subunits expression in cortex of neonates. In conclusion, the average DHA concentration in neonatal pups’ brains is not significantly increased by the level of DHA added with adequate dosage; however, the protein expression of the neuron makers related to cognition, behavior, learning and/or memory were significantly enhanced in neonates.
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