Regulatory Effects Of 4-methylresidin On Primary Neuronal Damage And Chronic Stress-induced Depression

Major depressive disorder(MDD)is a commonm mental disorder which major symptoms are low mood,slow thought and mental disorder,but the underlying mechanisms are largely unknown.Depression not only threatens the health and quality of life of patients,but also brings a huge mental and economic burden on the families of patients.The causes of depression are complex,and currently known pathogenic factors include the environment,genetics,and neurobiochemistry.The hippocampus(HPC)has recently attracted tremendous for the study of depression.When the body is subjected to various types of stress or stimuli,the hippocampus exhibits a high degree of plasticity in terms of structure and function.Clinical and neuroimaging studies show that patients with major depression have reduced structure and function of the hippocampusContinuous and large doses of corticosterone can damage the structure of hippocampal neurons,thereby inflicting damage on learning and memory and cognitive function.Although scholars at home and abroad have done a lot of research on the pathogenesis of depression,its exact mechanism remains to be further explored.The aim of this study was to investigate whether 7,8-dihydroxy-4-methylcoumarin(Dhmc)could protect cortieosterone-induced neurotoxieity in primary cultured rat neuronal cell.To evaluate if the Dhmc can relieve chronic unpredictable stress(CUMS)-induced depressive-like behaviors,and to investigate the effect of Dhmc on the plasticity of hippocampal pyramidal neurons and neuronal plasticity related protein kalirin7(Kal7)and GluR1.To generate depression-like behaviors,rats randomly received one or two stressors every day for 28 days to make depression model.Stressors included the following:inversion of the light/dark cycle,food or water deprivation,crowded group housing shaking,cold water swimming,hot water swimming,wet bedding,tilted cage,tail nip,restraint stress,strobe light,light off during the day for 3h.The behavioral tests were used to determine whether the CUMS model was successful and the effect of Dhmc on CUMS-induced depression-like behavior;Golgi staining was used to investigate the effect of Dhmc on stress-induced alteration in dendritic spines in the apical dendrites of hippocampal CA3 pyramidal neurons;The effect of Dhmc on the neuroplasticity-related proteins Kalirin7(Kal7)and GluR1 was studied by Western-Blot.The main research results are as follows:1.Neurotoxicity analysis of Dhmc experiment showed that different concentrations of Dhmc(2,4,8,16,32 and 64 μM)were used to treat cultured neurons for 24h,cell viability assay with MTT showed that there concentrations are safe.2.The morphological results showed that treatment of culture neurons with 560μM corticosterone for 24h caused obvious neuronal damage.The results of MTT were in accordance with the results of cell imaging,showing that the best condition of CORT to damage neurons was 560 μM with 24h treatment.3.The Dhmc pretreatment of neurons for 30min with 2,4,8,16,32 and 64 μM did not have significant protective effect on neuronal damage induced by treatment with 560 μM corticosterone for 24h.4.A 4-week of CUMS exposure resulted in an apparently reduction in the body weight gain,sucrose cunsumption,the number of rearings,crossings and total moving distance in rats as compared to the controls,while the immobility time of CUMS group significantly increased indicating that CUMS-induced depressive-like behavior model was established successfully.Long-term treatment of CUMS-exposed rats with Dhmc(10 mg/kg)for 18 days resulted in significant increases in the body weight gain,the percentage of sucrose consumption,the number of rearings,crossings and total moving distance while the immobility time significantly decreased when compared with CUMS-exposed rat.5.Spine density in the apical dendrites of hippocampal CA1 pyramidal neurons in the CON group,CUMS group,VF group and Dhmc group were analyzed by Golgi staining.Interestingly,nosignificant change was found in each group.We counted the dendritic spine density of hippocampal CA3 pyramidal neurons in the CON group,CUMS group,VF group and Dhmc group by Golgi staining.The CUMS group showed a significant reduction in spine density in CA3 apical dendrites in comparison with the CON group.Injection of Dhmc or VF prevented CUMS-mediated reduction in spine density in CUMS-exposed rats compared with CUMS group received saline injection only.The levels of GluRl and Kal7 proteins in the HPC were determined by Western blot analysis.The levels of GluR1 and Kal7 proteins were significantly reduced after CUMS compared with CON group.This reduction was reversed by treating with Dhmc or VF in the CUMS-exposed animals in comparison with CUMS group received saline treatment.In addition,although Dhmc has no obvious protective effect on neuronal damage induced corticosterone,Dhmc has the effect of regulating depression-like behavior caused by CUMS.Dhmc regulates the reduction of dendritic spine density in the hippocampal CA3 pyramidal neurons induced by stress.Neuroplasticity related proteins GluRl and Kal7 have important role in the pathogenesis and treatment of depression.