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Changes of learning, memory and levels of CaMKII, CaM mRNA, CREB mRNA in the hippocampus of chronic multiple‐stressed rats

Background The effect of chronic stress on cognitive functions has been one of the hot topic in neuroscience. But there has been much controversy over its mechanism. Such single stressor applied in the past could not simulate complicated living circumstances that people confronted with. The aim of this study was to investigate the effects of chronic multiple‐stress on learning and memory as well as on the levels of calcium/calmodulin‐dependent protein kinase II (CaMKII), calmodulin (CaM) mRNA, and cAMP‐response element binding protein (CREB) mRNA in the hippocampus of rats. Methods The rats were divided randomly into stressed and control groups. The stressed group was given chronic multiple‐stress for 6 weeks to set up a chronic multiple‐stressed model. The rats' performance of spatial learning and memory was tested using Morris Water Maze (MWM) and Y‐maze. Meanwhile, the expressions of CaMKII, CaM mRNA and CREB mRNA of rats' hippocampus were detected by immunohistochemistry, Western blot and reverse transcription‐polymerase chain reaction (RT‐PCR), respectively. In addition, the width of synaptic cleft and the thickness of post‐synaptic densities (PSD) were observed in the hippocampal CA3 region of rats by electron microscopy. Results After exposure to chronic multiple‐stress for 6 weeks, the ability of learning and memory of the stressed group was higher than that of the control group (P<0.05, P<0.01). The width of synaptic cleft was smaller and the thickness of PSD was larger in the hippocampal CA3 region of the stressed group than in that of the control group (P<0.01). The CaMKII immunostaining of the stressed group was stronger than that of the control group in the stratum radiatum and oriens of the hippocampal CA1 and CA3, especially in the stratum oriens. Quantitative analysis indicated that the expression of CaMKII, CaM mRNA, and CREB mRNA in the hippocampus of the stressed group was higher than that of the control group (P<0.05, P<0.01). Conclusions The capacity of learning and memory can be enhanced after chronic multiple‐stress. The increased levels of CaMKII, CaM mRNA, and CREB mRNA may contribute to the enhancing effect of chronic multiple‐stress on learning and memory.