Effect Of Schisandrin B On Learning And Memory Function In Rats With Chronic Aluminum Poisoning And Its Mechanism

Objective:To study the effect of Schisandrin B（Sch B）on learning and memory function in rats with chronic aluminum poisoning,and explore the mechanism of Schisandrin B in improving learning and memory impairment in rats with chronic aluminum poisoning,providing theoretical and experimental evidence for the prevention and treatment of learning and memory impairment caused by chronic aluminum poisoning.Methods:（1）Prepare an aqueous solution with a concentration of 16 g·L^-1of Al Cl₃.According to the daily body weight and feed intake of rats,mix the aqueous solution of Al Cl₃into the feed at a dose of 120 mg·kg^-1per day to feed the rats.Make sure that the aluminum-stained feed is fed every day and then feed the normal feed to ensure the intake of aluminum.Feed the aluminum-stained feed continuously for 3 months to establish an animal model of chronic aluminum poisoning.According to the method of statistical random grouping,the animal model of chronic aluminum poisoning was divided into five groups,namely model group,positive control group,low dose group of Schisandrin B,medium dose group of Schisandrin B,high dose group of Schisandrin B.The positive control group was gavaged with piracetam at a dose of 40 mg·kg^-1,and the low dose group,medium dose group,and high dose group of Schisandrin B were gavaged with Schisandrin B at a dose of 10mg·kg^-1,20 mg·kg^-1,and 40 mg·kg^-1,respectively,Each group was gavaged once a day for 30days;Another blank control group was set up,with 10 rats in each group.（2）Morris water maze test was used to test the learning and memory ability of rats in each group.（3）The apoptosis of neurons in cerebral cortex and hippocampus was detected by TUNEL.（4）The ultrastructure pictures of synapses in hippocampal CA1 area were observed and collected by transmission electron microscope,and the number of synapses,the thickness of postsynaptic dense substance and the width of synaptic gap in hippocampal CA1 area were measured.（5）Immunohistochemistry was used to detect the expression of postsynaptic density protein-95（PSD-95）and synaptophysin（SYN）in hippocampus CA1 region of rats in each group.（6）Western blot was used to detect the expression of PSD-95 and SYN protein in the hippocampus of rats in each group.（7）RT-PCR was used to detect the expression of Bcl-2associated X protein（Bax）,B-cell lymphoma/leukemia 2（Bcl-2）m RNA in the hippocampus of rats in each group.Results:（1）Morris water maze test results show that:The swimming path trajectory map of the positioning navigation experiment shows that the movement trajectory of the rats in the aluminum poisoning model group has a poor tendency,and the movement trajectory in the target quadrant is also significantly reduced,deviating from the platform;Compared with the model group,rats in each dose group of Sch B tended to move more towards the target platform.On the 3rd and 4th days of positioning navigation experiment training,the incubation period of the model group was significantly increased compared to that of the normal group（P<0.01）;The incubation period of the positive control group was significantly shorter than that of the model group（P<0.01）;The incubation period of the high dose experimental group of Sch B was significantly shorter than that of the model group（P<0.01）.The incubation period of the spatial exploration experiment in the high dose group of Sch B was shorter than that in the model group,and the number of platform crossings was increased compared to that in the model group（P<0.05）.（2）The results of in situ cell apoptosis assay showed that:compared with the control group,the apoptosis rates of neurons in the cerebral cortex and hippocampus of the aluminum poisoning model group were significantly increased（P<0.01）;Compared with the aluminum poisoning model group,the apoptosis rates of neural cells in the cerebral cortex and hippocampus of the middle and high dose Sch B groups were significantly lower than those of the model group（P<0.01）.（3）Transmission electron microscopy showed that the synapses ultrastructure in hippocampal CA1 of the model group was blurred,some synaptic structures were fused,the pre synaptic membrane and post synaptic membrane were discontinuous,synaptic vesicles were significantly reduced,synaptic bodies were severely edematous,and mitochondrial cristae in the synapse were swollen and broken.The synaptic structure of each dose of Sch B experimental group was clear,the pre synaptic membrane and the post synaptic membrane existed,the number of synaptic vesicles in the pre synaptic membrane increased,and the edema of synaptic bodies decreased.The number of synapses,the width of synaptic gaps,and the thickness of postsynaptic dense matter in the model group were significantly lower than those in the normal group（P<0.01）;The number of synapses,the width of synaptic gaps,and the thickness of postsynaptic dense matter in the positive control group were significantly higher than those in the model group（P<0.01）;The number of synapses,the width of synaptic gaps,and the thickness of postsynaptic dense matter in the hippocampal CA1 region in the high dose group of Sch B were significantly higher than those in the model group（P<0.01）.（4）Immunohistochemical results show that:Compared with the blank control group,the expression levels of SYN and PSD-95 in the hippocampus and cerebral cortex of the aluminum poisoning model group were significantly lower than those of the blank group（P<0.01）;Compared with the aluminum poisoning model group,the expression levels of SYN and PSD-95 in the hippocampus and cerebral cortex of the high dose Sch B group were significantly higher than those of the model group（P<0.01）.（5）Western Blot result show that:Compared with the blank control group,the relative expressions of SYN and PSD-95 proteins in the hippocampus and cerebral cortex of the aluminum poisoning model group were significantly reduced（P<0.01）;Compared with the aluminum poisoning model group,the relative expression levels of PSD-95 and SYN proteins in the high dose group of Sch B were significantly increased（P<0.01）.（6）RT-PCR results showed that:compared with the blank control group,The expression of Bax m RNA in aluminum poisoning model group was significantly increased（P<0.01）,while the expression of Bcl-2 m RNA was significantly decreased（P<0.01）;Compared with the aluminum poisoning model group,the expression of Bax m RNA in the positive control group was significantly decreased（P<0.01）,while the expression of Bcl-2 m RNA was significantly increased（P<0.01）;The relative expression of Bcl-2 m RNA in the hippocampus of the middle and high dose groups of Sch B was significantly increased（P<0.05 or P<0.01）;The relative expression of Bax m RNA in the hippocampus of the high dose group of Sch B significantly decreased（P<0.01）.Conclusion:Sch B can upregulate the expression of PSD-95 and SYN proteins in the hippocampus of rats,improve the changes in synaptic ultrastructure and abnormal changes in synaptic structural parameters of the hippocampus,thereby affecting the synaptic plasticity of hippocampal neurons,and thereby improving the learning and memory abilities of aluminum poisoned rats.