场景恐惧记忆泛化小鼠海马CA1区AMPA受体及NMDA受体亚基表达变化

Altered expression of AMPAR and NMDAR subunits in hippocampal CA1 area with contextual fear memory generalization in mice

目的探讨小鼠在场景恐惧记忆泛化过程中海马CA1区AMPA受体及NMDA受体亚基表达水平变化情况。方法8周龄雄性C57BL/6小鼠共35只，随机选择7只作为蛋白测定对照组（Naive组），无需进行行为学训练与测试；另28只小鼠进行场景恐惧训练和场景转化测试，并根据测试结果分成未泛化组和泛化组；完成测试后处死小鼠，提取海马CA1区蛋白，Western blot检测AMPA受体亚基GluR1、GluR2及NMDA受体亚基NR1、NR2A及NR2B表达情况。结果（1）经历同一强度应激后，7只小鼠（区分率：0.52±0.08）出现场景恐惧记忆泛化，余21只（区分率：0.75±0.07）未出现场景恐惧记忆泛化（P〈0.01），但两组小鼠在场景记忆获得过程僵住反应时间百分比差异无统计学意义。（2）AMPA受体亚基GluR1、GluR2表达在Naive组、未泛化组、泛化组中差异无统计学意义（P〉0.05）。（3）NMDA受体NR1表达在三组中差异无统计学意义（P〉0.05）；NR2A亚基表达在未泛化组（1.11±0.20）、泛化组（1.09±0.20）中差异无统计学意义，但二者较Naive组（0.95±0.17）均显著上升（P〈0.05）；NR2B亚基表达在Naive组（0.83±0.19）、未泛化组（0.80±0.14）中差异无统计学意义，但泛化组（1.05±0.17）中较该两组均显著上升（P〈0.05）；NR2A/NR2B未泛化组（1.23±0.25）较Naive组（0.89±0.31）和泛化组（0.86±0.17）均显著上升（P〈0.05）。结论（1）同一应激强度下仅部分个体出现场景恐惧记忆泛化，且此种泛化情况与场景恐惧记忆获得过程无关。（2）海马CA1区AMPA受体亚基GluR1、GluR2表达在泛化过程中未见明显差异；而NMDA受体亚基表达主要表现为NR2B表达增加，NR2A/NR2B比值下降；由此引起的突触可塑性改变可能是恐惧记忆泛化形成的机制之一。

ObjectiveTo investigate the alteration of subunit expression of AMPAR and NMDAR in hippocampal CA1 area of mice with contextual fear memory generalization.Methods35 male C57BL/6 mice, aged 8 weeks, were involved in the experiment.Seven mice were randomly selected as the naive group, which didn＇t receive the behavioral training.28 mice experienced the context fear conditioning and contextual shift task were divided into generalization group and non generalization group according to the result.Then Western blot was used to measure the expression of AMPAR and NMDAR subunits in CA1 in the naive group, non generalization group and generalization group.Results（1）Seven mice （discrimination ratio： 0.52±0.08） showed contextual generalization when undergoing the same stress level, while the other 21 mice （discrimination ratio： 0.75±0.07） didn’t （P〈0.01）, however, these two group showed similar freezing（%） in the memory acquisition process.（2）The subunit composition of AMPA receptors had no significant difference in CA1 area among the Naive group, non generalization group and generalization group（P〉0.05）. （3）NR1 subunit was similar in the three groups（P〉0.05）. NR2A expression was significantly increased in the non generalization group（1.11±0.20） and generalization group （1.09±0.20 ） compared with that in the naive group（0.95±0.17） （both P〈0.05）. The expression of NR2B was significantly increased in generalization group（1.05±0.17） compared with that in the naive group（0.83±0.19） and non generalization group（0.80±0.14 ）（both P〈0.05）. The ratio of NR2A/NR2B was significantly increased in non generalization group（1.23±0.25） compared with that in the naive group（0.89±0.31） and generalization group （0.86±0.17）（both P〈0.05）.Conclusion（1）Only part of the individuals show contextual fear memory generalization after the same stress, and this contextual generalization progress is not related to the acquisition of context fear memory.（2）There is no significant change in expression of AMPAR subunits in CA1 of mice with the contextual generalization.The rise of NR2B and the decline of ratio of NR2A/NR2B are the main changes, suggesting that consequently the alternation of synaptic plasticity maybe one of the mechanisms of contextual fear memory generalization.