Effects Of Acute And Chronic Stress On Spatial Learning And Memory In Mice And Expression Of Wnt3a In Brain

Objective and Methods: This study used single stressor(foot shock) to build the acute stress animal model. The chronic stress model of mice was induced by stimulation of ice swimming, crowd, food deprivation, overnight lighting, water deprivation, hathpace, randomly select one each day, these work need about 21 days. And this study was to explore the changes in the spontaneous behavior and the ability of spatial learning-memory in mice after acute stress and chronic stress and the expression of Wnt3 a and β-catenin in the brain. The spatial learning-memory ability of mice were measured by Morris Water maze task, and the morphology of neurons changes and the expression of Wnt3 a and β-catenin in the hippocampus(HP) and prefrontal cortex(PFC) were detected by HE staining method and immunohistochemical method. Result: 1. Open field test. Compared with the control group mice, after acute stress immediately, the number of rearing and square crossing of stress group mice were increased significantly, and the central cell residence time were significantly reduced, however, the number of modification had no obvious changed. After acute stress 7th day, these had no obvious changes. Compared with the control group mice, after chronic stress immediately, the number of rearing and square crossing of stress group mice were decreased significantly, and the defecation and central cell residence time were significantly increased. After chronic stress 7th day, these index had obvious changed, but central cell residence time had no obvious changes.2. Morris water maze. After acute stress, the escape latency of stress group mice were significantly shortened than control group mice. In the spatial search test, compared with control group mice, the swimming time of first quadrant(i.e. platform quadrant) in stress group mice were obviously higher after acute stress. After acute stress 7th day, the data had no significant difference. After chronic stress, the escape latency of stress group mice were significantly higher than control group mice. After chronic stress 7th day, the data had no significant difference but in second trial. In the spatial search test, compared with control group mice, the swimming time of first quadrant in stress group mice were obviously shortened after chronic stress. After chronic stress 7th day, the data had no significant difference.3. HE staining. After acute stress instantly, respectively compared with control group mice, morphology of neurons in stress group mice didn’t change significantly. After 7 day, they had no significant deference. After chronic stress instantly, the stress group mice showed obviously morphological changes in HP and PFC, such as the neurons number reducing, a loose arrangement, most cells dyeing shallow, dyed uneven and some cells atrophy. After 7 days they had better.4. Immunohistochemistry. After acute stress immediately and 7th day, the number of Wnt3 a and β-catenin positive cells in HP didn’t see clearly expression or change significantly in stress or control group mice, the average target gray value was not obvious difference. But after acute stress immediately, the number of Wnt3 a and β-catenin positive cells expression in PFC can see clearly in stress group mice, and the expression of Wnt3 a and β-catenin were significantly higher. And it was not obvious difference after acute stress 7th day. After chronic stress immediately and 7th day, the expression of Wnt3 a and β-catenin was not significant in HP of stress or control group mice, and the average target gray value was not obvious difference too. In PFC, the expression of Wnt3 a and β-catenin in stress group mice was significantly lower. Conclusions:1.The acute stress can enhance the spontaneous behaviors of mice, and significantly increase the spatial learning-memory ability of mice. However, the chronic stress can weaken the spontaneous behaviors of mice and impair the spatial learning-memory ability of mice.2. The acute stress did not cause significant changes in neuronal morphology of mice, but the chronic stress significant changed in neuronal morphology.3. In acute stress and chronic stress, the expression of Wnt3 a and β-catenin was not found in HP of mice. After the acute stress the expression of Wnt3 a and β-catenin obviously up-regulate in PFC of mice brain. However after the chronic stress, the expression of Wnt3 a and β-catenin obviously reduce in PFC of mice brain.4. The changes of behavior and learning-memory ability in mice after stress is closely related to the expression of Wnt3 a in PFC.