| BackgroundDepression is a kind of mental disease of long-lasting low mood or interest loss as the main characteristics, accompanied by physical symptoms, cognitive impairment, sleep disorders, serious harm to public health. Repetitive transcranial magnetic stimulation(rTMS) is a new type of neural electrophysiological techniques developed recently,widely used in the treatment of depression, but its action mechanism has not yet been fully explained. Studies have shown that, rTMS may be directly or indirectly protect hippocampal cells through multiple pathways, reduce neuronal cell damage or promote the proliferation of hippocampal progenitor cells to resist atrophy or apoptosis of neurons, in order to achieve antidepressant effects. This study intends to observe behavior and hippocampal neuronal morphology changes of chronic depression model rats before modeling, after modeling and rTMS intervention, as well as the expression level variation of apoptosis proteins Bax and brain derived neurotrophic factor(BDNF), explore the protective effect of rTMS on hippocampal neurons in chronic depression model rats and its possible mechanism.Objectives1.To observe the behavioral changes and the changes of hippocampal neuronal morphology of rats before modeling, after modeling and after rTMS intervention.2.To investigate the expressional levels of Bax and BDNF of rat hippocampus, and analyze the relationship between the protective effect of rTMS intervention on hippocampus of depression rats with the expression levels of Bax and BDNF, and explore its possible mechanism.Methods1.40 adult male SD rats were divided into normal control group(n=8) and model preparation group(n=30) randomly after screening.The model preparation group were singly housed and given chronic unpredictable mild stress(CUMS) to build depression model. Exclude unsuccessful modeling rats,the model preparation group was divided into three groups:model group(n=8,without giving any treatment), rTMS group(n=8,with the intervention of lOHz rTMS) and shame group(n=8,simulation of rTMS environment without rTMS stimulus).2.rTMS intervention:Rats in rTMS group were given rTMS intervention for 10 Hz frequency every day, a total of 10 min,500 pulse. Each intervention interval two days after five days, a total of 21 days. Rats in shame group were given the same environment with nothing stimulus.3.Measure the body weight of rats and record their changes; Use the sucrose consumption test to detect the interest, pleasure and reward responsiveness in rats; Use open field test(OFT) to detect the ability of self-exploration, spontaneous movement and stress levels in rats; Assess the model of depression through the above behavioral data.4.Use Nissl’s staining to observe the morphology of neurons and Nissl body in hippocampus of rats.5.Use the immunohistochemical techniques to detect the expression levels of Bax and BDNF protein in hippocampus of rats, use reverse transcription-polymerase chain reaction(RT-PCR) to detect the expression levels of Bax and BDNF mRNA in hippocampus of rats.6.Use independent samples T-test and ANOVA to analyze experimental data, multiple comparison use LST test.Inspection level a is 0.05.Results1.Behavioral score results:Before modeling, the overall weight distribution in rats to meet the normal distribution, the homogeneity is high; Differences of sucrose consumption (t=1.674,P>0.05), horizontal movement distance (t=-1.590,P>0.05), the number of vertical upright (t=-1.218,P>0.05), modification times (t=-1.998,P>0.05), defecation times 0=-0.855,P>0.05) and central residence time (t=1.076,P>0.05)were not statistically.After modeling, compared with the control group, differences of the body weight reduction rate(t=4.114,P<0.01), sucrose consumption (t=-3.515,P<0.01), horizontal movement distance (t=-6.482,P<0.01), the number of vertical upright (t=-1.218,P>0.05), modification times (t=-1.998,P>0.05), defecation times (t=-10.557,P<0.01) and central residence time (t=7.106,P<0.01) in model group were statistically significant,it suggest that model is successful.After rTMS intervention, differences of the body weight reduction rate(F=5.048,P<0.01), sucrose consumption (F=11.812,P<0.01), horizontal movement distance (F=13.594,P<0.01), the number of vertical upright (F=67.667,P<0.01), modification times (F=44.452,P<0.01), defecation times (F=17.144,P<0.01) and central residence time (F=22.129,P<0.01) in four groups were significant statistically. Compared with normal control group, body weight reduction rate, sucrose consumption, horizontal movement distance, the number of vertical upright, modification times, defecation times and central residence time in model group and shame group were decreased significantly, the difference was significant statistically (P< 0.01). Compared with shame group and model group, body weight reduction rate, sucrose consumption, horizontal movement distance, the number of vertical upright, modification times, defecation times and central residence time in rTMS group were increased significantly, the difference was significant statistically (P<0.01).Compared with model group, difference of the shame group was not statistically significant(P>0.05).2.Nissl staining results:Compared with the control group, the number of hippocampal CA3 neurons in model group and shame group was reduced, cell morphology was poor,the number of Nissl bodies was reduced;compared with the model group and the shame group, the number of hippocampal CA3 neurons in rTMS group was increased,cell morphology was integral,the number of Nissl bodies was increased.3.Immunohistochemistry results:Differences of number of Bax positive protein(FCA1=29.377,FCA2=70.929,FcA3=36.551,FDG=23.412,P<0.01) and BDNF positive protein(FCA1=72.484,FCA2=110.640,FcA3=27.152,FDG=52.986,P<0.01)of rats hippocampus in four groups were significant statistically. Compared with normal control group, the number of Bax positive protein in rat hippocampus in model group and shame group were significantly higher,and the number of BDNF positive protein in rat hippocampus in model group and shame group were lower significantly, the difference was significant statistically (P< 0.01). Compared with shame group and model group, the number of Bax positive protein in rat hippocampus in rTMS group were significantly lower,and the number of BDNF positive protein in rat hippocampus in rTMS group were higher significantly, the difference was significant statistically (P<0.01). Compared with model group, the difference of shame group was no significant statistically (P>0.05).4.RT-PCR results:Differences of expression levels of Bax mRNA(F=43.514,P<0.01) and BDNF mRNA(F=105.127,P<0.01) of rats hippocampus in four groups, was significant statistically. Compared with control group, the expression level of Bax mRNA in rat hippocampus in model group and shame group were significantly higher,and the expression level of BDNF mRNA in rat hippocampus in model group and shame group were lower significantly, the difference was significant statistically (P< 0.01). Compared with shame group and the model group, the expression level of Bax mRNA in rat hippocampus in rTMS group were significantly lower, and the expression level of BDNF mRNA in rat hippocampus in rTMS group were higher significantly, the difference was significant (P< 0.01) statistically. Compared with model group, the differences of the shame group were not significant statistically (P> 0.05).Conclusions1.rTMS intervention can improve significantly depression-like behavioral and pathological morphological changes of hippocampal neurons in chronic stress depression rats.2.rTMS may exert its neuroprotective effects by regulating the expression of Bax and BDNF in order to achieve the aim of improving depressive symptoms, which may be one mechanism of rTMS treatment for depression. |
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