中文摘要：

目的探讨慢性复合应激对大鼠学习与记忆的影响和cAMP／PKA-CREB信号系统在此机制中的作用。方法将成年雄性Wistar大鼠分为对照组：不作任何处理；慢性单一应激组：每天捆绑6h，持续6周；慢性复合应激组：每天随机暴露于4种应激原中，持续6周。应激结束后，用Morris水迷宫（MWM）测试大鼠空间学习与记忆成绩；免疫组织化学方法观察大鼠海马PKA-Cβ和磷酸化的CREB的表达水平；应用RT-PCR法半定量检测海马组织内BDNF和Bcl．2的mRNAs水平。结果应激后在MWM寻找平台潜伏期，与对照组（18．9±13．0）s相比，慢性复合应激组（14．2±5．8）s明显缩短（P〈0．05），显示其空间记忆明显增强，而慢性单一应激组（20．4±12．8）s无明显差异（P〉0．05）；慢性复合应激组大鼠海马CAl和CA3区PKA-Cβ的表达以及CA1区和齿状回pCREB的表达明显上调（P〈0．05）；而慢性单一应激组海马各亚区PKA-Cβ和pCREB的表达无显著性改变（P〉0．05）。BDNF和Bcl-2 mRNAs的表达水平3组间差别无显著性（P〉0．05）。结论慢性复合应激可增强海马依赖的学习与记忆功能，多元的环境刺激可能是其增强的主要原因。PKA-CREB信号通路在其影响机制中发挥了一定的作用。

英文摘要：

Objective The present study is to explore the effect of the chronic multiple-stress on learning and memory of rats and the role of cAMP/PKA-CREB pathway in its mechanism. Methods Adult male Wistar rats were randomly divided into 3 groups： the control rats were housed in normal situations without any treatment; the chronically single-stressed rats were exposed to restraint stress 6 hours a day for 6 weeks; the chronically multiple-stressed rats were irregularly and alternatively subjected to 4 stressors for 6 weeks. After the stress experiment, all rats were tested for spatial learning and memory in Morris water maze （MWM）. The expression of PKA-Cβ and pCREB in different subfields of the hippocampus was assayed by using immunohistochemistry and the level of BDNF and Bcl-2 mRNAs in hippocampal tissues was determined by RT-PCR. Results The latency to escape from water in MWM after stress, as compared with control （18.9 ± 13.0）s, the latency to escape of the chronically multiple-stressed （ 14.2 ± 5.8 ） s was shorten significantly （ P 〈 0.05 ）, indicating enhanced the spatial memory, while no apparent changes were observed in single-stressed （20.4 ± 12.8）s （P 〉 0.05）. Compared with control, the expression of PKA-Cβ in hippocampal area CA1 and CA3 and the expression of pCREB in area CA1 and dentate gyrus （DG） were distinctively higher in multiple-stressed rats （ P 〈 0.05 ）, while no significant difference of the expression was discovered in single-stressed rats （ P 〉 0.05）. No obvious difference was observed in the expression of hippocampal BDNF and Bcl-2 mRNAs among the 3 groups （P 〉 0.05）. Conclusion These results indicate that chronic multiple stress can enhance the hippocampus-dependent spatial learning and memory function. The stimulation of enriched environment may be the two major factors that lead to this enhancement, and cAMP/PKA-CREB signalling cascade may play a role in the mechanism of the enhanced performance.