慢性应激增加大鼠海马齿状回的多巴胺水平并损伤空间学习记忆能力

Chronic stress increases dopamine levels in hippocampal dentate gyrus and impairs spatial learning and memory in rats

本研究旨在揭示慢性应激(chronic stress,CS)对空间学习和记忆活动过程中大鼠海马齿状回(dentate gyrus,DG)的多巴胺(dopamine,DA)水平及突触效能的影响。Sprague Dawley(SD)大鼠随机分成对照组和CS组(n=10),CS组大鼠接受慢性温和不可预知应激原处理,对照组不给予应激处理,用酶联免疫吸附法测定大鼠血清中肾上腺素和皮质酮(corticosterone,CORT)的水平,用Morris水迷宫(Morris water maze,MWM)评估大鼠的空间学习和记忆能力;用在体生物电记录法、脑部微量透析结合高效液相色谱法检测大鼠在学习和记忆活动中DG区场兴奋性突触后电位(field excitatory postsynaptic potential,fEPSP)幅值及细胞外液中DA水平的动态变化;用免疫组织化学染色或免疫蛋白印迹法检测DA的D1受体(D1 receptor,D1R)和下游通路关键蛋白在DG区的表达变化。结果显示,CS大鼠处于应激状态,表现为血清中肾上腺素和CORT水平明显升高(P<0.05);CS大鼠的空间学习和记忆能力下降,其学习过程中DG区突触传递效能也显著降低,表现为MWM训练第3天时,对照组大鼠DG区的fEPSP幅值与训练前比较显著升高(P<0.05),而CS组却无明显改变,与对照组比较有显著差异(P<0.05);CS大鼠DG区的DA水平在学习的第1、2、3天均明显升高,与训练前及对照组比较均有显著差异(P<0.05);和对照组相比,CS组大鼠海马DG区的D1R表达显著上调,其下游通路中磷酸化的蛋白激酶A(protein kinase A,PKA)、cAMP反应元件结合蛋白(cyclic AMP-response element binding protein,CREB)和脑源神经营养因子(brain derived neurotrophic factor,BDNF)的表达水平显著下调(P<0.05)。以上结果提示,CS可能通过影响海马DG区突触传递效能和DA水平损伤大鼠的空间学习和记忆功能。

The objective of this study was to elucidate the effect of chronic stress(CS)on dopamine(DA)level and synaptic efficiency in the hippocampal dentate gyrus(DG)during spatial learning and memory.Sprague Dawley(SD)male rats were randomly divided into control group and CS group(n=10).CS group was treated with chronic mild unpredictable stress,and control group did not receive any treatments.The levels of epinephrine and corticosterone(CORT)in serum were measured by using enzyme-linked immunosorbent assay(ELISA);the spatial learning and memory abilities of rats were measured by Morris water maze(MWM)test.Meanwhile,the amplitude of field excitatory postsynaptic potential(fEPSP)and concentration of DA in the DG region were determined by in vivo electrophysiology,microdialysis and HPLC techniques during MWM test in rats.After that,the DAD1 receptor(D1R)and its key downstream members in DG were examined by immunohistochemistry or Western blot assay.The results showed that the levels of epinephrine and CORT in the serum of the rats in CS group were significantly increased compared with those in the control group(P<0.05).In CS group rats,the escape latency was significantly prolonged and the number of platform crossing was markedly decreased during MWM test,compared with those in control group(P<0.05).Furthermore,the amplitude of fEPSP in the DG was not changed during MWM test in CS rats,while it was significantly increased on the 3 rd day of MWM test in control group(P<0.05).Compared with baseline or control group,CS group showed significantly increased DA level from the 1 st to 3 rd days of MWM test in the DG(P<0.05).In addition,the protein expression of D1R was markedly up-regulated in the DG in CS group,while the protein expression levels of p-PKA,p-CREB and BDNF were significantly reduced,compared with those in control group.These results suggest that CS may impair spatial learning and memory abilities in rats through the enhancement of the DA levels in the hippocampal DG.