The Effect Of Acute And Chronic Stress On Spatial Learning And Memory Function In Mice And The Role Of IGF-II

This study used a foot shock stress source establish acute stress animal model, and withseven kinds of stressors (water deprivation, bondage+hot stimulus, food deprivation, hathpace,cold stimulation, foot shock, bondage,21days) to create chronic stress animal model. This studyaims to investigate the effects of acute and chronic stress on the spontaneous behavior and thespatial learning-memory function in different aged mice and its mechanism. We examined thespontaneous behaviors of new environment in mice by open field test, and the ability of spatiallearning memory of mice by Morris water maze. The changes of morphological structure inhippocampus (HP) and prefrontal cortex (PFC) of mice brain were observed by HE dye, and theexpression of insulin-like growth factor (IGF-?) in HP and PFC were detected byimmunohistochemical method.The results of this study are as follows:1. After acute stress instantly, compared with the young control group mice, the squarecrossing and rearing of young stress group mice were remarkably increased, and the central cellresidence time and defecation were significantly decreased. The7th day after stress, comparedwith the young control group mice, the behavior of young stress group mice had no significantdifferences. After stress instantly and the7th day after stress, aged stress group mice in openfield test change trend was consistent with young stress group.After acute stress instantly, compared with the young control group mice, the square crossingand rearing of aged control group mice were remarkably decreased.2. In the place navigation test, after acute stress instantly, compared with the young and agedcontrol group mice, the escape latency to find platform of the young and aged stress group micewere significantly decreased. Compared with young group mice, the escape latency of the agedcontrol and stress group mice were significantly increased. The7th day after stress, comparedwith stress group mice, the escape latency of control group mice had no significant difference.In the space probe test, after acute stress instantly, the swimming time in first quadrant (theoriginal platform quadrant) of young and aged stress group mice were remarkably increasedcompared with control group mice, respectively. Compared with young control group mice, theswimming time in first quadrant of aged control group had no significant difference. The7th dayafter stress, compared with control group mice, the swimming time in first quadrant of stressgroup mice had no significant difference.3. After acute stress instantly and7th day after stress, compared with control group mice,neurons form and structure of young and aged stress group mice had no significant changes.After acute stress instantly, the number of IGF-? positive cells in HP and PFC of stress group mice brain were remarkably increased, and the average target gray value was significantlydecreased. The IGF-?of brain areas were expressed significantly increase. The young stressgroup mice's change was especially remarkable. The7th day after stress, the expression ofIGF-?in stress and control group mice had no significant difference. Compared with youngcontrol and stress group mice, the expression of IGF-?in aged control and stress mice weresignificantly decrease.4. After chronic stress instantly, compared with young control group mice, the squarecrossing, rearing and grooming of young stress group mice were remarkably decreased, and thecentral cell residence time and defecation were significantly increased. The7th day after stress,the square crossing of young stress group mice was still remarkably decreased, and the centralcell residence time and defecation were still significantly increased. After stress and the7th dayafter stress, the change tendency of aged group mice was consistent with the young group, andmore obvious changes.After chronic stress instantly, compared with young control group mice, the rearing andgrooming of aged control group were remarkably decreased.5. After chronic stress and7th day after stress, in the place navigation test, compared withcontrol group mice, the escape latency to find platform of the young and aged stress group weresignificantly lower. Compared with young group mice, the escape latency to find platform of theaged group was significantly extend.In the space probe test, after chronic stress instantly, the swimming time in first quadrant (theoriginal platform quadrant) of young and aged stress group mice were remarkably decreasedcompared with control group mice, respectively. Compared with young control group mice, theswimming time in first quadrant of aged control group had no significant difference.6. After chronic stress instantly, compared with young control group mice, the stress groupmice displayed obviously morphologic changes such as the number of cells reducing,arrangement loose and sparse, cells dyeing shallow?cell dyed uneven and cell atrophy in HP andPFC. Compared with young control group mice, neurons distribution of aged control group indifferent brain regions had a little sparse, but cells had complete structure and orderly rows.Compared with young stress group mice, neurons injury of aged stress group was more serious,and there was still no significant change after7th day after stress.After chronic stress instantly, the number of IGF-? positive cells in HP and PFC of stressgroup mice brain were remarkably decreased, and the average target gray value was significantlyincreased. The IGF-?of brain areas were expressed significantly decrease. The aged stressgroup mice's change was especially remarkable. Compared with young control and stress groupmice, the expression of IGF-?in aged control and stress mice were significantly decrease. The conclusion of this study are as follows:1. As growth of the age, the spontaneous behaviors and the spatial learning-memory abilityof mice was significantly reduced.2. The acute stress treatments enhanced the spontaneous behavior of mice, and prominentlyenhance the spatial learning-memory ability of mice. The chronic stress treatments reduced thespontaneous behavior of mice, and significantly damage the spatial learning-memory ability ofmice.3. The acute stress treatments has no significant effect on neuronal morphology of mice, andthe chronic stress cause obvious morphological changes of neurons in HP and PFC of mice brain,aged mice change is more apparent.4. The acute stress treatments cause obvious increase of IGF-? expression in HP and PFC ofmice brain. The chronic stress induce obvious reduction of IGF-? expression in HP and PFC ofmice brain.5. The brain aging and the changes of the spatial learning-memory ability which may benearly related to the expression of IGF-? in HP and PFC.