Changes Of The Brain-derived Neurotrophic Factor Lysis Pathway And Synaptic Plasticity In Rats After Chronic Stress And Escitalopram Treatment

Part Ⅰ Effects of chronic stress and escitalopram treatment on the tPA-BDNF-TrkB pathway in rat brain regions associated with moodBackground:Despite progress in studies of the etiology and treatment of depression, a clear understanding of its pathophysiology and mechanisms critical to the effectiveness of existing antidepressant drugs are still lacking. In the recent decade, more and more attentions were paid on the "neurutrophic factor" and "neurogenesis" hypotheses. Brain-derived neurotrophic factor (BDNF) is the key factor of the hypothesis. It has been indicated BDNF play crucial roles on neuroplasticity and neurogenesis. The p11-tPA-BDNF pathway is the main extra cellular lysis pathway of BDNF.Objective:To investigate the effects of p11-tPA-BDNF on the pathophysiology of depressed rats and the anti-depression treatment of escitalopram.Methods:Rats were performed chronic unpredicted mild stress for four weeks. Behavior tests were employed to assess the rats’ performance both after stress and only the depressed rats were used in the following studies. After that, depressed rats received stress and escitalopram or saline treatment for four weeks. Changed expression of some key factors in the p11-tPA-BDNF lysis pathway in several regions of depression circuits, including prelimbic cortex, area 1 of cingulate cortex, amygdala, CA1, CA3 and DQ were tested by western blot and real-time PCR. Meanwhile, neurogenesis in DG were tested by immunofluorescence technique. After knock down of pll in hippocampus by LV-siRNA, rats’behavior tests were performed and changed BDNF expression in hippocampus were investigated.Results:(1) Compared with the normal rats, significant decreased body weight (p< 0.0001), sucrose preference (p< 0.0001), total distance and rearing times in open-field test (p< 0.0001), as well as increased immobile time in forced swimming test (p< 0.0001) in depressed ones were observed. Escitalopram treatment did not affect body weight, but could significantly improve the body weight (p< 0.0001), sucrose preference (p< 0.0001), total distance (p=0.0053) and rearing times (p= 0.0353) in open-field test, and decrease immobile time in forced swimming test (p< 0.0001). (2) Compared with the normal ones, the expression of key factors in p11-tPA-BDNF lysis pathway significantly changed among the mode regions such as cingulate gyrus, prefrontal cortex, amygdala and hippocampus in the depressed rats. Escitalopram could improve the changes caused by stress in the regions; (3) neuronal proliferation is significantly decreased in depressed rats, while escitalopram could reverse the decrease; (4) Most of the rats died one day after injection with LV-p11shRNAi in hippocampus. Rats that survived after virus injection failed to show any changes in depressive-like behaviors and expression of proteins.Conclusions:The changed expression of key factors in the pll-tPA-BDNF lysis pathway among the depression circuits including prelimbic cortex, area 1 of cingulate cortex, amygdala, and hippocampus involved in the pathophysiology of depression and the anti-depression of escitaloprm in rats. Thus, pll-tPA-BDNF lysis pathway may provide a target in anti-depression therapy in the future.Part II Changes of Gray’s Type I synaptic plascity in rat mPFC network after stress and/or escitalopram treatmentBackground:The pathophysiology of depression is still largely unknown, although preclinical and clinical observations suggest that the disorder is associated with impaired adaptive plasticity ability in neural systems. In the synaptogenic hypothesis of depression, it is believed synaptic dysfunction plays crucial roles in the pathophysiological process of depression.Objective:To investigate morphological changes of Gray type I synapses and changed expression of synaptic proteins in depression circuit in rats in order to provide supports for the synaptogenic hypothesis.Methods:Rats were performed chronic unpredicted mild stress for four weeks. Behavior tests were employed to assess the rats’performance both after stress and only the depressed rats were used in the following studies. After that, depressed rats received stress and escitalopram or saline treatment for four weeks. Ultrastructural analysis, including mean width of synaptic cleft, mean and maximal PSD thickness, and length of active zone and synaptic curvature, was used to explore precise morphological changes of excitatory synapses in depression circuit by transmission electron microscope. The altered expression of synapse-related proteins accompanied with the morphologic changes, including PSD93, PSD95, Spinophilin, Synaptophysin, Synapsin I and Arc, were determined by western blot.Results:(1) Compared with the normal rats, significant decreased body weight (p< 0.0001), sucrose preference (p< 0.0001), total distance and rearing times in open-field test (p< 0.0001), as well as increased immobile time in forced swimming test (p< 0.0001) in depressed ones were observed. Escitalopram treatment did not affect body weight, but could significantly improve the sucrose preference (p= 0.0157), total distance (p=0.0002) and rearing times (p=0.0002) in open-field test, and decrease immobile time in forced swimming test (p=0.0003). (2) Compared with normal rats, excitatory synapses in the depressed ones-length of active zone in area 1 of cingulate cortex (Cgl), CA1 and dentate gyrus (DG) significantly decreased (p= 0.0427,0.007,0.0448), but increased in BLA (p= 0.029); mean PSD thickness in CA1 decreased significantly (p= 0.049); maximal PSD thickness in PrL and CA1 decreased (p= 0.0113,0.0157), but increased in BLA (p= 0.036); mean width of synaptic cleft in Cgl increased remarkably (p= 0.0427); convex-formed of synapses in Cg1, CA1, CA3 and DG decreased significantly (p= 0.0444,0.0245,0.0385, 0.0343), but increased in BLA (p= 0.0346). Escitalopram could improve or reverse the above-mentioned changes significantly. (3) Compared with that of synapse-associated proteins in subareas of normal rats, the expression of PSD93, PSD95, spinophilin, synapsin I and synaptophysin was observed to be decreased significantly in AC of depressed rats compared with that of normal ones (p=0.0005、 < 0.0001、= 0.0023、= 0.0007 and< 0.0001, respectively); expression of PSD93, PSD95 and spinophilin in PrL of depressed rats was detected (p<0.0001、<0.0001 and=0.0002, respectively); expression of PSD93 in amygdala was dereased sharply (p=0.0142); expression of PSD95 in the CA1 subarea of depressed rats’ hippocampus decreased significantly (p=0.0339); expression of all the five proteins decreased significantly in CA3 (p= 0.0033、< 0.0001、=0.0009、= 0.0002 and= 0.0035); expression of PSD93、 PSD95、synapsin I and synaptophysin in DG subarea decreased significantly (p= 0.0291、= 0.0417、 0.0001 and< 0.0001, respectively). Escitalopram could increase or reverse the above-mentioned changes significantly.Conclusions:The changed synaptic morphology and expression of synaptic proteins may play important roles in the pathophysiology of depression and anti-depression effects of escitalopram in rats.