Hippocampal NMDAR-Wnt-Catenin Signaling Disrupted With Cognitive Deficits In Adolescent Offspring Exposed To Prenatal Hypoxia

Part 1 Prenatal hypoxia impairs brain development andspatial cognition in offspring.Objective:To determine the effects of prenatal hypoxia impairs brain development and cognitive abilities in offspring.Methods: Pregnant rats were randomly divided into the control(C) group and the prenatal hypoxia(PH) group. Animals in the control group were kept in a normoxic chamber(21%O2), while animals in the PH group were exposed to hypoxia(10.5% O2 at normal barometric pressure) from GD4 to 21 in a plexiglass chamber.At gestational day 21,half of the pregnant dams were anesthetized intraperitoneally with 4% chloralhydrate(0.8ml/100g), fetuses were removed through surgical hysterotomy and weighed immediately.The other half of the pregnant rats were allowed to delivernaturally. All rats were raised in the same standard environment. 6 weeks after birth(correlated to the mid-late adolescent stage of human), male offspring were randomly selected(n=15 from 8 litters,each group)and used for behavioral tests by the water maze tests.Results:PH significantly decreased brain weight of the fetuses at GD21 and the offspring 6 weeks after birth. Body weight in the PH group was lower at GD21; however,adolescent body weight in the PH group was not significantly different from controls.PH offspring exhibited longer escape latencies and path length during testing in a hidden platform-learning phase. There was no significant change found with swim speed between two groups. Compared with the control group, the PH group spent less time in the target areas during the probe trails.Conclusion: Prenatal hypoxia impairs brain development and cognitive ability in adolescent offspring.Part 2 Prenatal hypoxia affects NMDAR-Wnt-Catenin signalingpathwayon hippocampus in the adolescent offspringObjective: To investigatethe potential signalingpathwayson hippocampuswith the adolescent offspring as the consequences of hypoxia during pregnancy.Methods:The hippocampus tissues were isolated, frozen in liquid nitrogen, and then stored in the 80 o C freezer for molecular experiments.Total RNA and protein were isolated from the hippocampus, The expression of m RNA grin1,grin2 a,grin2b and Wnt singnaling genes were measured with Real-time Quantitative PCR Detecting System.NR1,NR2 A,NR2B, β-catenin and active-β-catenin protein abundance were measured with Western blotting analysis.Results: Protein and m RNA abundance of three important NMDAR subunits NR1/Grin1, NR2A/Grin2 a and NR2B/Grin2 b were decreased significantly in PH in compared with the control group.Wnt3 a m RNA expression decreased significantly, while other four Wnt ligands m RNA did not change significantly. In addition, no significant changes of Fzd4 and LRP5/6 m RNA expression were observed in the hippocampus in the PH group.In this study, β-catenin m RNA expression did not change significantly in the PH group. However, active form of β-catenin protein was significantly decreased, although total β-catenin protein did not change in the PH group. Fosl1 is a directly downstream gene of β-catenin signaling. Fosl1 m RNA expression was decreased in the hippocampus of the PH group.Conclusion: The expressions of NMDARs and Wnt signaling as well as related downstream signalings play critical roles in prenatal hypoxia brain development associated with learning and memory.