Mao Chun-ting, Li Ting-yu, Qu Ping, Zhao Yong, Wang Rong, Liu You-xue
Department of Child Health Care, Children's Hospital, Chongqing University of Medical Sciences, Chongqing 400014, China.
Zhonghua Er Ke Za Zhi. 2006 Jan;44(1):15-20.
In recent years, some experiments on vitamin A-deprived animals reveal a progressive and ultimately profound impairment of hippocampal CA1 area's long-term potentiation and these losses are fully reversible by dietary vitamin A replenishment in vivo. Our previous study revealed that marginal vitamin A deficiency (MVAD) beginning from embryonic period impairs learning, memory and long-term potentiation (LTP) in young rats. But the losses might not be reversible if the vitamin A supplementation is late, especially when the critical period of hippocampus development is missed. The present study aimed to observe the recovery of learning and memory in vitamin A marginally deficient young rats after early intervention with vitamin A supplementation and begin to study the mechanism.
Rats were divided into control, MVAD, vitamin A intervention 1 (VAI1) and VAI2 groups in this study. In control group (10 young rats) the dams and pups were fed with normal diet (VA 6500 U/kg). In MVAD group (19 young rats) the dams and pups were fed with MVAD diet (VA 400 U/kg). In VAI1 group (10 young rats) the dams were fed with MVAD diet till day 14 of pregnancy, then were fed with normal diet and the pups were fed with normal diet. In VAI2 group (13 young rats) the dams were fed with MVAD diet till delivery, then were fed with normal diet and the pups were fed with normal diet too. All the young rats were killed at the age of 7 weeks. During the last week of the experiment, the shuttle box active avoidance reaction tests were carried out. At week 7, the hippocampal CA1 LTP was detected by electrophysiological technique. The expression of RAR-alpha, RAR-beta, RXR-beta, RXR-gamma, RC3 and tTG mRNA was detected by using semi-quantified RT-PCR in hippocampus.
(1) The times to reach the learning standard in MVAD group (45.6 +/- 12.1) were more than those in control group (17.1 +/- 4.4) (P < 0.01), in both VAI1 group (20.8 +/- 3.1) and VAI2 group (22.1 +/- 4.0) were more than those in group MVAD (P < 0.01), and there were no significant differences among groups VAI1, VAI2 and control (P > 0.05) in active avoidance reaction tests. (2) The changes of field excitatory postsynaptic potentials (fEPSP) slope for MVAD group [(22.9 +/- 9.4)%] and VAI2 group [(39.1 +/- 4.33)%] were less than that of control group [(57.5 +/- 27.3)%], respectively (P < 0.05). No significant difference was found between VAI1 and control group (P > 0.05). (3) The expression of RAR-beta and RXR-beta mRNA decreased by 48.72% and 37.84% respectively (P < 0.05) compared with control, but the expression of RAR-beta mRNA in group VAI1 was higher than that in group MVAD (P = 0.065). The expression of RC3 mRNA in MVAD group was lower than that in control (P = 0.061) and RAR-alpha mRNA in MVAD group was higher than that in control (P = 0.061). The expression of RXR-gamma and tTG mRNA had no significant difference among different groups as determined with semi-quantified RT-PCR in hippocampus.
Early vitamin A intervention may make the impaired learning and memory behavior due to marginal vitamin A deficiency recover to the normal level in young rats, but lip losses in group VAI2 might not be reversible. Vitamin A may modulate the expression of RC3 mRNA by affecting RAR-alpha, RAR-beta and RXR-beta to influence the LTP, learning and memory.
近年来，一些对维生素A缺乏动物的实验显示，海马CA1区的长期增强作用出现渐进性且最终严重受损，而通过在体内补充膳食维生素A可完全逆转这些损伤。我们之前的研究表明，从胚胎期开始的边缘性维生素A缺乏（MVAD）会损害幼鼠的学习、记忆和长期增强作用（LTP）。但如果维生素A补充过晚，尤其是错过海马发育的关键期，这些损伤可能无法逆转。本研究旨在观察早期补充维生素A对边缘性维生素A缺乏幼鼠学习和记忆的恢复情况，并开始研究其机制。
本研究将大鼠分为对照组、MVAD组、维生素A干预1组（VAI1）和VAI2组。对照组（10只幼鼠）的母鼠和幼鼠喂食正常饮食（VA 6500 U/kg）。MVAD组（19只幼鼠）的母鼠和幼鼠喂食MVAD饮食（VA 400 U/kg）。VAI1组（10只幼鼠）的母鼠在怀孕第14天前喂食MVAD饮食，之后喂食正常饮食，幼鼠也喂食正常饮食。VAI2组（13只幼鼠）的母鼠在分娩前喂食MVAD饮食，之后喂食正常饮食，幼鼠也喂食正常饮食。所有幼鼠在7周龄时处死。在实验的最后一周，进行穿梭箱主动回避反应测试。在第7周，通过电生理技术检测海马CA1区的LTP。采用半定量RT-PCR检测海马中RAR-α、RAR-β、RXR-β、RXR-γ、RC3和tTG mRNA的表达。
（1）MVAD组（45.6±12.1）达到学习标准的次数多于对照组（17.1±4.4）（P<0.01），VAI1组（20.8±3.1）和VAI2组（22.1±4.0）达到学习标准的次数均多于MVAD组（P<0.01），且VAI1组、VAI2组与对照组在主动回避反应测试中无显著差异（P>0.05）。（2）MVAD组（22.9±9.4）%和VAI2组（39.1±4.33）%的场兴奋性突触后电位（fEPSP）斜率变化分别小于对照组（57.5±27.3）%（P<0.05）。VAI1组与对照组之间无显著差异（P>0.05）。（3）与对照组相比，RAR-β和RXR-β mRNA的表达分别下降了48.72%和37.84%（P<0.05），但VAI1组中RAR-β mRNA的表达高于MVAD组（P=0.065）。MVAD组中RC3 mRNA的表达低于对照组（P=0.061），MVAD组中RAR-α mRNA的表达高于对照组（P=0.061）。通过海马半定量RT-PCR测定，不同组间RXR-γ和tTG mRNA的表达无显著差异。
早期维生素A干预可能使边缘性维生素A缺乏导致的幼鼠学习和记忆行为损伤恢复至正常水平，但VAI2组的损伤可能无法逆转。维生素A可能通过影响RAR-α、RAR-β和RXR-β来调节RC3 mRNA的表达，从而影响LTP、学习和记忆。
