Study On The Changes Of Monamine Transmitters And Their Receptors In Post-stroke Depression Rats And Protective Mechanisms Of Mirtazapine

Post-stroke depression (PSD) is a common complication of cerebral vascular disease with high morbidity, which affects the rehabilitation of neurologic function and life quality of the patients, and increases the mortality. Its pathogenesis is not well known, and the treatment is hampered. With the progression of population aging, the morbidity of stroke increases, and the morbidity of PSD turns to an increasing trend. At present, there are mainly two theories of PSD pathogenesis, which are primary endogenous mechanism and responsiveness mechanism. It has been shown that neurotrophic factors are involved in the pathogensis of depression. Mirtazapine, a new anti-depression drug, is an antagonist of 5-hydroxytryptamine, norepinephrine receptor. It surpasses other anti-depression drugs in quicker treatments, and less side effects. Furthermore, it has double treatments in depression and anxiety, and could be more suitable for elder people. To further study the pathogensis of PSD, the study established the PSD rat model with the combination methods, studied the changes of neurotrophic factors, monamine transmitters and their receptors in PSD group and the mirzatapin group, which provided better theoretical basis for the treatment of PSD.1. The establishment of PSD rat model and effects of mirzatapine on animal ethology The establishment of PSD model generally adopted the combination of cerebral ischemia, raising alone and stress exertion, which embodied the endogenous mechanism and responsiveness mechanism. Firstly, the model of focal cerebral ischemia was set up by thread occlusion through arteria carotis interna and reperfusion. Then the rats were raised alone and given chronic unpredicable modest stress to establish the PSD model. Weight, sucroese solution consumption test, open-field test and Morris labyrinth were used to estimate the changes of animal ethology in PSD rats, and observed the effects of mirzatapine.150 rats with similar score of open-field were divided into 7 groups: sham control group, depression group, PSD group, fluoxetine group, low-dose mirtazapine group(2.8mg/kg), moderate-dose mirtazapine group(10mg/kg), and high-dose mirtazapine group(20mg/kg). The rats of depression group were raised alone and given stress. The rats of control group were given sham operation. The rats of PSD group and every treatment groups were given tread occlusion and 1 week later raised alone and given stress for 4 weeks. During the period, the rats of every treatment group were lavaged with different dose of mirtazapine and fluoxetine, and rats of sham control group and depression group were lavaged with distilled water under the same consideration. At 1 day before the operation, 1,8,15,22,29 days afer the operation, the behaviors of the rats was measured. The rats of PSD group and depression group lost weight, the sucroese solution consumption, horizontal movement and vertical movement became less than sham control group, and the difference was significant(P<0.01). There was no difference between depression group and PSD group. These results showed that PSD rats had the trait of depression, thus which had the trait of cerebral ischemia and depression. The weight, sucroese solution consumption, horizontal and vertical movements of open-field test of every treatment group were improved, and the differences were remarkabke(P<0.01). Rats of each group were tested with Morris water labyrinth for 3 days at the the 29th day of given stress. The results showed that mean escape latencies of PSD group and depression group rats were much longer than that of the sham control group, and the difference was remakable. There were no difference beween depression group and PSD group, and there were no difference among sham control group and treatment groups, which meant rats of PSD model had a bad study abililty.PSD model rats had the traits of both cerebral ischemia and depression, and the symptoms were improved by mirtazapine, which means the PSD model is successful and mirtazapine is effective for PSD.2. The effect of mirtazapine for monamine transmitters in PSD model ratsNow it has been considered that the etiology of PSD is that the local cerebral impairment injuries NE and(or) 5-HT project fiber, which makes imbalance of NE and 5-HT, and causes PSD. It has been domumented that the levels of monamine transmitters and their metabolites in patients of PSD is lower than normal, and SSRIs is effctive for PSD treatment, which tells there is a change of monamine transmitter in PSD patients. This experiment is designed to explore the changes of monamine transmitters in PSD model rats brain, and observe the effects of mirtazaping for treating PSD.Every group rats were executed by decapitation after animal ethology test, strip frontal cortex and hippocampus above the ice, after weighing the cerebral tissue, which is put in EPP tube and conserved in -80℃refrigerator. Fluorometry was adopted to test monamine transmitter in cortex and hippocampus of rats. The statistic analysis showed that : 5-HT, NE, DA in the right frontal cortex of PSD model rats and depression group rats was lower than the normal controls, and the difference is remarkable(P<0.01). There was no difference between depression group and PSD model group. After the treatment of mirtazapine, 5-HT, NE increased remakably(P<0.01), while 5-HT increased significantly after the treatment of fluoxetine. The content of DA in the hippocampus in the low-dose mirtazapine group increased significantly. Fluoxetine is better than mirtazapine in improving 5-HT, while mirtazapine is better than fluoxetine in improving NE.The results of the experiment showed that monamine transmitter decreased in PSD, which proves the endogenous mechanism, the mechanism of new type of anti-depressive drug may be different from fluoxtine.3. The effect of mirtazapine for the expression of monamine transmitter receptor in PSD rats.It is considered that the occurrence of depression is related to neurologic transmitter receptor abnormal abnormality in new theories and it's also the causative factor for depression. At present, it's seldom in probing pathogensis of PSD from the receptor level, so this experiment talk about PSD pathogensis in the aspect of monamine transmitter receptor. RT-PCR is adopted in this experiment to test 5-HT1A, 5-HT2A, 5-HT3,α2–adrenaline receptor in hippocampus of PSD rats.The results showed that the expression of 5-HT2A receptor in hippocampus of PSD rats was low, while the expressions of 5-HT2,5-HT3,α2–adrenaline receptor became high. While the expression of 5-HT1A in hippocampus of fluoxetine group was higher than that in PSD group, and the expression of 5-HT2A receptor was lower, which showed that fluoxetine could up-regulate 5-HT1A receptor and down-regulate 5-HT2A receptor. The expressions of 5-HT2A, 5-HT3,α2–adrenaline receptor in hippocampus in mirtazapine group was down-regulated compared with PSD group, which showed that mirtazapine could antagonise 5-HT2A , 5-HT2A, 5-HT3, α2–adrenaline receptor.The results showed that the occurrence of PSD was related to the abnormalities of monoamine transmitter receptors. Mirtazapine excercised the treatment effects through antagonising 5-HT2A, 5-HT3,α2–adrenaline receptors, while fluoxetine could not alter the levles of 5-HT3,α2–adrenaline receptor mRNA significantly.4. The effect of mirtazapine for BDNF, GFAP in PSD model rats"Neurotrophy theory"thought the occurrence of depression was mainly related to neuron synapsis plasticity, besides the change of NE,5-HT. The expression level of BDNF down-regulates in depression patients, which may be the basic pathology change of depression. It is related to apoptosis of hippocampus neuron, and the decrease of hippocampus volume is related to descent of the ablility of neuron intaking neurotrophy factors. So immunohistochemistry was adopted to test the expression of BDNF, GFAP in hippocampus of PSD rats. The results showed BDNF,GFAP expression positive cells was much lower in the frontal cortex and hippocampus of PSD rats than that in normal control rats. And after treatment of anti-depressive drugs , BDNF,GFAP expression positive cells in the frontal cortex and hippocampus increased, and there is no difference among these groups in BDNF expression. It's remarkable in low-dose mirtazapine treated rats in GFAP.It's showed that there is low neurotrophy factors in PSD rats, after anti-depressive treatment, and the neurotrophy factors expression increases. That is to say, neurotrophy theory is involved in the PSD pathogensis.