The Effects Of Running Exercise On The Oligodendrocytes Of Medial Prefrontal Cortex In Depression Model Rats

Part one The effects of running exercise on the behavioral changes and the total volume of medial prefrontal cortex in depression model rats induced by CUSObjective:Running exercise has been proven to prevent or relieve depression,however,the therapeutic effects of exercise on depression are still controversial and the structural basis for antidepressant action of exercise is not clear.Medial prefrontal cortex(MPFC)is one of the main brain areas affected by depression.Many previous studies have demonstrated that there was a significant shrinkage of the MPFC in depression patients.Therefore,the effects of running exercise on the behavioral changes and the total volume of the medial prefrontal cortex in the depression model rats induced by chronic unpredictable stress were investigated in the present study.Methods:Male SD rats aged six to eight weeks were used.After adaptation for two weeks,the rats were randomly divided into non-stressed group(n = 23)and CUS model group(n = 113).The CUS model group rats were given CUS intervention for five weeks.Then,37 successful depression model rats were randomly divided into stressed group(n = 17)and stressed + running group(n = 20).The stressed + running group rats were given a six-week forced running exercise,5 days per week,20 min per day.During the first week,the rats ran at a speed of 10 m/min on the first day,followed by an increase of 2 m/min per day.For the rest of 5 weeks,the running speed was maintained 20 m/min.During the experiment,non-stressed group rats were housed in normal conditions with four or five rats per cage,and the rats in stressed group and stressed + running group were still housed with one rat per cage.The body mass of the rats in each group was recorded at the same time frame per week.Sucrose preference test was done at the same time frame per week to evaluate the state of anhedonia.During the last week of running exercise,the elevated plus maze test was performed to detect the state of anxiety of each group rats.After behavior tests,five rats from each group were randomly selected and perfused transcardially with 4% paraformaldehyde.The brains were removed and split into two hemispheres by a midsagittal section.The right or left hemisphere from each rat was sampled at random and was dehydrated in sucrose dilution with gradient concentration.Then,the hemispheres were embedded with OCT and coronally sectioned into 60-μm on a cryostat microtome.The sections were kept in anatomical series.From the sections containing area MPFC,every sixth section was sampled in a systematic-random manner and six sets of sampled sections were acquired in the end.One sets of sampled sections was radomly chosen.The sampled sections were stained with cresyl violet and the boundaries of MPFC were delineated according to the cytoarchitectionics under optical microscope.The total volume of MPFC in each rat was estimated according to Cavalieri’s principle.Results: 1.Before CUS intervention,there was not significant difference in the body mass between the non-stressed group rats and the CUS model rats.However,from the first weekend of the CUS intervention to the end of five-week CUS intervention,the body mass of the CUS model group rats was significantly lower than that of the non-stressed group rats(p < 0.01).During the phase of running exercise,the body mass of rats in the stressed group and the stressed + running group were still significantly lower than that of the non-stressed rats(p < 0.01).There was no significant difference in the body mass between the stressed group rats and the stressed + running group rats.2.Before CUS intervention,there was no significant difference in the sucrose preference between the non-stressed group rats and CUS model rats.After five-week CUS intervention,the sucrose preference of the CUS model group rats was significantly lower than that of the non-stressed group rats(p < 0.01).After six-week running exercise,the sucrose preference of rats in the stressed group was still significantly lower than that of non-stressed rats(p < 0.01).However,the sucrose preference of rats in the stressed + running group was significantly higher than that of the stressed rats(p < 0.01).There was no significant difference in the sucrose preference between the non-stressed group rats and the stressed + running group rats.3.In the elevated plus maze test,there were no significant differences in the number of open arm entries,open arm time,the number of closed arm entries,closed arm time,the total number of arm entries,the percentage of open arm entries and the percentage of time spending in the open arms among the non-stressed group rats,the stressed group rats and the stressed + running group rats.4.The stereological results showed that there was a significant decrease in the total volume of the MPFC in the stressed group rats when compared to that of the non-stressed group rats(p < 0.05).However,the total volume of the MPFC of stressed + running group rats was significantly higher than that of stressed group rats(p < 0.01).There was no significant difference in the total volume of the MPFC between the non-stressed group rats and the stressed + running group rats.Conclusion:1.Six-week treadmill running exercise could improve the state of anhedonia of depression model rats induced by CUS,but it could not affect the state of anxiety detected with elevated plus maze test.2.The stereological results indicated that the total volume of the MPFC in the depression model rats induced by CUS was significantly reduced.3.Six-week treadmill exercise could reverse the decrease in the total volume of the MPFC of the depression model rats induced by CUS.Part two The effects of running exercise on the oligodendrocyte in medial prefrontal cortex of the depression model rats induced by CUSObjective:Running exercise has been proven to prevent or relieve depression,however,the underlying cellular mechanisms are unclear.In the present study,the effects of running exercise on the oligodendrocytes in the medial prefrontal cortex of the depression model rats induced by CUS were investigated and the results might provide experimental evidence for the antidepressant effect of running exercise.Methods: From the sampled sections acquired in the part one,two separate sets of serial sections containing area MPFC of each group rats were randomly chosen.The sections were immunoreacted with anti-NG2 antibody and anti-CNPase antibody,respectively,for the stereological analyses of the total number of OPCs and the total number of the mature oligodendrocytes in MPFC.Then,from another set of sampled sections,every second section was sampled again in a systematic random fashion to obtain two series of sections.The adjacent series of sections were immunofluorescence labeled with antibodies Olig2/NG2 against the OPCs and immunofluorescence labeled with antibody MBP against the myelin-forming cells and myelin sheaths.Fluorescent images were collected on a laser confocal scanning microscope.The number of Olig2+cells,NG2+ cells and Olig2+/NG2+ cells per unit area in MPFC of each rats were quantified.Quantification of MBP immunofluorescence staining was performed using the Image-Pro Plus software 5.0.Then,eight rats from each group in the part one were randomly chosen.The rats were anesthetized and MPFC tissue were rapidly removed.One side MPFC of each rat was randomly selected.The proteins were extracted and the protein expression levels of CNPase,MBP,Olig2 and NG2 in MPFC were detected using western blot.Results: 1.Stereological results showed that the total number of CNPase+ cells in the MPFC of the stressed group rats was significantly decreased compared with that of the non-stressed group rats(p < 0.05).However,the total number of the CNPase+ cells in the MPFC of the stressed + running group rats was significantly increased compared with that of the stressed group rats(p < 0.05).There was no significant difference in the total number of the CNPase+ cells of the MPFC between the non-stressed group rats and the stressed + running group rats.2.The results of western blot showed that the protein expression level of CNPase in the MPFC of the stressed group rats was significantly lower than that of the non-stressed group rats(p < 0.01).However,the protein expression level of the CNPase in the MPFC of the stressed + running group rats was significantly higher than that of the stressed group rats(p < 0.01).There was no significant difference in the protein expression level of the CNPase in the MPFC between the non-stressed group rats and the stressed + running group rats.3.After quantifying of the MBP immunofluorescence staining,we found that the MBP intensity in the MPFC of the stressed group rats was significantly lower than that of the non-stressed group rats(p < 0.01).However,the MBP intensity in the MPFC of the stressed + running group rats was significantly higher than that of the stressed group rats(p < 0.05).There was no significant difference in the MBP intensity in the MPFC between the non-stressed group rats and the stressed + running group rats.4.The results of western blot showed that the protein expression level of MBP in the MPFC of the stressed group rats was significantly lower than that of the non-stressed group rats(p < 0.01).However,the protein expression level of the MBP in the MPFC of the stressed + running group rats was significantly higher than that of the stressed group rats(p < 0.05).There was no significant difference in the protein expression level of the MBP in the MPFC between the non-stressed group rats and the stressed + running group rats.5.Stereological results showed that there was no significant difference in the total number of the NG2+ cells of the MPFC among the non-stressed group rats,the stressed group rats and the stressed + running group rats.6.The quantitative results of in the number of Olig2+ cells,NG2+ cells and Olig2+/NG2+ cells per unit area in the MPFC of each rat showed that the number of the Olig2+ cells per unit area in the MPFC of the stressed group rats was significantly decreased compared with that of the non-stressed group rats(p < 0.05).However,the number of the Olig2+ cells per unit area in the MPFC of the stressed + running group rats was significantly increased compared with that of the stressed group rats(p < 0.05).There was no significant difference in the number of the Olig2+ cells per unit area in the MPFC between the non-stressed group rats and the stressed + running group rats.In addition,the ratio between Olig2+/NG2+ cell number and Olig2+ cell number in the MPFC of the stressed group rats was significantly highrt than that of the non-stressed group rats(p < 0.05).However,the ratio between Olig2+/NG2+ cell number and Olig2+ cell number in the MPFC of the stressed + running group rats was significantly lower than that of the stressed group rats(p < 0.05).There was no significant difference in the ratio between Olig2+/NG2+ cell number and Olig2+ cell number of the MPFC between the non-stressed group rats and the stressed + running group rats.There were no significant difference in the number of NG2+ cells and Olig2+/NG2+ cell per unit area and the ratio between Olig2+/NG2+ cell number and NG2+ cell number of the MPFC among the three group rats.7.The results of western blot showed that the protein expression level of the Olig2 in the MPFC of the stressed group rats was significantly lower than that of the non-stressed group rats(p < 0.01).However,the protein expression level of the Olig2 in the MPFC of the stressed + running group rats was significantly higher than that of the stressed group rats(p < 0.05).There was no significant difference in the protein expression level of the Olig2 in the MPFC between the non-stressed group rats and the stressed + running group rats.There was no significant difference in the protein expression level of the NG2 in the MPFC among the three group rats.Conclusion: 1.There was a significant decrease in the number of mature oligodendrocytes and the myelin forming ability of in the MPFC of the depression model rats induced by CUS.2.Six-week running exercise could promote the differenciation of the oligodendrocytes and myelin forming ability,but it could not promote the proliferation of OPCs,to alleviating the pathological changes of oligodendrocytes in the MPFC of the depression model rats induced by CUS.3.The positive effects of running exercise on the oligodendrocytes of MPFC might be one of the important cellular mechanisms for the anti-depression of running exercise.