| Part I The study on the changes of the myelinated fibers and myelin sheaths in the hippocampal formation of the depression model ratsObjective:To investigate the changes of the myelinated fibers and myelin sheaths in the CA1 and DG in CUS rat model of depression.Methods:Male SD rats (age 4-5 weeks, weight 100-150 g, n= 120) were used. At the start of the experiment, rats were first trained to consume a 1% sucrose solution. Sucrose consumption and body weight were monitored throughout the experiment once per three days. During a two-week period of adaptation, sucrose preference baseline tests were performed for all animals in order to make rats familiarize with the sucrose preference procedure. On the basis of the sucrose preference in the final baseline test, the rats with the sucrose preference lower than the baseline were abandoned. Remaining rats were divided into control group (24 rats), CUS group (72 rats). CUS rats were subjected to a 4-week CUS procedure. Open field test and elevated plus maze test were performed in the 4th week of CUS procedure. Sucrose preference test, weighing were performed once per week. After CUS intervention period, the changes of myelin ultrastructures were qualitatively investigated. Then, the total volumes of hippocampal formation, CA1 and DG, the total length of the myelinated fiber, the total volume of the myelinated fibers and the total volume of myelin sheaths and axons in these areas were investigated with the modern stereological methods and transmission electron microscope technique.Results:1. CUS induced a decrease in sucrose preference, relative to control conditions. The CUS group gradually reduced the sucrose preference from the 2nd week to the 4th week of CUS procedure. In open feild test, the travelled distance in the inner area, the percentages of the inner area time and the percentages of inner area distance of CUS group exhibited significant decrease compared to control group (p< 0.05). The results of the elevated plus maze test were non-significantly different between control group and CUS group (p> 0.05).2. The pathological alterations of myelin sheaths including splitting lamellae and segmental demyelization in the hippocampal formation subregions of the CUS rats were observed. The ratio of the injured myelinated nerve fibers in the CA1 of CUS rats (22.42±4.24%) was significantly higher than the control rats (3.84±1.35%) (p< 0.01). The ratio of the injured myelinated nerve fibers in the DG of CUS rats (7.21±1.24%) did not show a significant difference when compared to the control rats (4.84±1.55%) (p> 0.05).3. When compared to the control group, the total length, the total volume of the myelinated fibers and the total volumes of the myelin sheaths and axons in CAl of CUS group were significantly decreased (p< 0.05). The total volumes of the HF, CA1 and DG, the total length and the total volume of the myelinated fibers, and the total volumes of the myelin sheaths and the axons in the DG of CUS group were not significantly different when compared to the control group (p> 0.05). The inner diameter and outer diameter, the inner perimeter and outer perimeter of the myelinated nerve fibers of the CA1 and DG in CUS group were not significantly different when compared to the control group (p> 0.05). The decrease of the total length of the myelinated nerve fibers in the CA1 of the CUS rats was mainly due to the decrease of the myelinated fibers with the myelin sheath thickness of 0.15 μm～0.20μm.Conclusions:The present study demonstrated that the depression-like behaviors and demyelization in the CA1 of CUS rats. These results provided further evidence of hippocampal formation deficits in depression and meantime indicated that CUS was a good model for the study for biological mechanisms of the etiology of depression. These structural changes suggested that the demyelination changes in the CA1 induced by 4-week CUS might be one of the important structural bases for the depression-like behaviors.Part II The effects of fluoxetine on the myelinated fibers and myelin sheaths in the hippocampal formation of the depression model ratsObjective:To investigate the effects of the SSRI representative drug, fluoxetine, on the changes of the behaviors, the myelinated fibers and myelin sheaths in the hippocampal formation of CUS rats.Methods:Male Sprague-Dawley rats (age 4-5 weeks, weight 120-160 g, n= 150) were used. Rats were first trained to consume a 1% sucrose solution for two weeks. On the basis of the sucrose preference in the final baseline test, the rats with the sucrose preference lower than the baseline were abandoned. Remaining rats were divided into control group (24 rats), CUS group (113 rats). Then CUS rats were subjected to a 7-week CUS procedure. After 4th week CUS procedure, On the basis of the sucrose preference in the final sucrose preference test, CUS rats with lower sucrose preference were randomly divided into CUS group (n= 15) and CUS/fluoxetine group (n= 15). From 5th week to 7th week CUS procedure, drug injection lasted for 21 consecutive days. The control group and the CUS group were intraperitoneally treated with saline at dose of 1 ml/kg/d. The CUS/fluoxetine group was treated with fluoxetine at dose of 5 mg/kg/d. During the 7-week CUS procedure, sucrose preference test and weighing were performed once per week. At the 3 rd week of the fluoxetine intervention, all rats were tested with sucrose preference test, the open field test and the elevated plus maze test, which were used to test the behavioral changes of these rats. The changes of myelin ultrastructure were also qualitatively investigated. The total volume of hippocampal formation, CA1, CA3 and DG, the total length and the total volume of the myelinated fiber, as well as the total volumes of myelin sheaths and axons in these areas were investigated with the modern stereological methods and transmission electron microscope technique.Results:1. We found that the rats with fluoxetine administration showed increased sucrose preference (p= 0.045< 0.05). In open feild test, the total movement distance and the mean speed in CUS group exhibited significant decrease compared to control group (p< 0.05). In the elevated plus maze test, time spent in open arms and the percentage of time in open arms were significantly decreased and the percentage of time in close arms was significantly increased compared to control group, respectively (p= 0.047< 0.05, p= 0.044< 0.05, p= 0.024< 0.05).2. The pathological alterations of the myelin sheaths including splitting lamellae and segmental demyelization in the CA1, CA3 and DG both CUS group and fluoxetine group were observed. The ratio of the injured myelinated nerve fibers in the CA1 of CUS rats (22.18±4.26%) was significantly higher than control rats (5.33±1.36%) (p< 0.01). The ratio of the injured myelinated nerve fibers in the CA3 and DG of CUS rats did not show a significant difference when compared to control rats (p> 0.05).3. The CA1 volume in CUS rats was significantly decreased compared to the control rats treated with saline (F= 3.21, p= 0.019< 0.05) and the CA1 volume of fluoxetine group were not significantly different from the other groups (p> 0.05). The volumes of the HF, CA3 and DG among three groups were not significantly different (p> 0.05).3. The total length of the myelinated fibers in the CA1 of CUS group was significantly decreased compared to control group (F= 4.112,p=0.027 < 0.05). The total volume of the myelinated fibers in the CA1 of CUS group was significantly decreased compared to control group (F= 4.192, p = 0.015< 0.05); The total volumes of the myelin sheaths and the axons in the CA1 of CUS group were not significantly different (p> 0.05). The total length and total volume of the myelinated fibers, the total volumes of the myelin sheaths and the axons in the CA3 and DG among three groups were not significantly different (p> 0.05). The inner diameter and outer diameter, the inner perimeter and outer perimeter of the myelinated nerve fibers of the CA1, CA3 and DG among three groups were not significantly different (p> 0.05). The decrease of the total length of the myelinated nerve fibers in the CA1 of CUS rats was mainly due to the decrease of the myelinated fibers with the myelin sheath thickness of 0.20 μm～0.30 μm.Conclusions:The present study demonstrated that after the fluoxetine intervention, the depression-like behaviors caused by the chronic stress were reversed. Even though 3 week fluoxetine intervention could improve depression-like behaviours,3 week fluoxetine intervention could not repair the demyelization of CUS rats. |
PDF Full Text Request