Changes In Synaptic Structure Of Neurons In Specific Brain Regions Of Diabetic Cognitive Impairment Rats

Objective:By observing the differences in synaptic structures in the hippocampal CA1and prefrontal cortex and the differences in the expression of synaptic plasticity-related proteins at different stages of diabetic（diabetes mellitus,DM）cognitive impairment and diabetic non-cognitive rats The relationship between changes in learning and memory abilities and changes in the plasticity of the hippocampus and prefrontal cortex structure provides a basis for the study of the mechanism of cognitive impairment in diabetes.Methods:212 male Wistar rats were randomly divided into 35d-control group（n=11）,35d-DM group（n=95）,84d-control group（n=10）and 84d-DM group（n=96）according to body weight.A model of diabetes was established by intraperitoneal injection of 60 mg·kg-1of streptozotocin（STZ）.The glucose oxidase method was used to measure fasting blood glucose for 72h.Fasting blood glucose≥16.7 mmol·L^-1was used as the model standard.Using a blood glucose meter to measure the fasting blood glucose of the 35-day batch of rats at0d（before modeling）and 7d,20d,and 35d after modeling,and the 84-day batch of rats at 0d,7d,20d,35d,60d,and 80d Measure the body weight and water consumption of rats in each group before and after modeling,and examine the stability of the DM model during the experiment.The learning and memory abilities of the two groups of rats were measured with Morris water maze on the 35th and 84th day after the model was established,and DM cognitively impaired rats and DM non-cognitive impaired rats were screened.The tissue morphology of hippocampal CA1 and prefrontal cortex in two groups of control group,DM cognitive impairment group and DM non-cognitive impairment group were observed by HE staining.Transmission electron microscope experiments were used to observe the synaptic ultrastructure of hippocampal CA1 and prefrontal cortex in three groups of rats,and measure the number of synapses,synaptic active area length and synapse in the hippocampal CA1 and prefrontal cortex areas Gap width.The expression levels of SYN,PSD-95 and GAP-43proteins in the hippocampal CA1 and prefrontal cortex regions of the three groups were detected by immunohistochemical methods.Results:The moulding rates of DM rats in the 35-day and 84-day batches were 89.5%and91.7%.Compared with the control group,the rats in the DM group at the 35th and 84th days were significantly increased in fasting blood glucose and water consumption（p<0.01）,and their body weight was significantly reduced（p<0.01,p<0.05）.In the 35-day batch water maze experiment,there was no significant difference in swimming speed between the two groups of rats.The escape latency of the DM rats at the 6th,8th,and 9th training sessions was significantly higher than that of the control group（p<0.01,p<0.05）.There was no significant difference in the number of rat platform crossings,and the incidence of cognitive impairment was 26.4%.In the 84-day batch water maze experiment,there was no significant difference in swimming speed between the two groups of rats.The escape latency was significantly higher than that of the control group（p<0.01,p<0.05）.The number of platform crossings of DM rats was significantly lower than that of the control group（p<0.01）.The incidence of cognitive impairment was 46.9%.In the HE staining experiment,compared with the control group,the number of pyramidal cells in the hippocampal CA1 region of the DM non-cognitive disorder group was reduced,loosely arranged,long spindle-shaped,smaller nucleus,and richer in cytoplasm compared to the control group.Normal cells in the prefrontal cortex area were slightly reduced,and some nuclear nuclei were condensed.In the DM cognitive impairment group,the number of pyramidal cells in the hippocampal CA1 area was reduced,loosely arranged,long spindle-shaped,smaller nuclei,and less cytoplasm.Prefrontal cortex area reduced normal cells,disordered cell morphology,nucleus shrinkage,and obvious intercellular space.In the transmission electron microscope experiment,the neuron and organelle morphological changes in the hippocampal CA1 and prefrontal cortex regions of the three groups of rats at 35 days and 84 days were small and there were no significant differences;in the 35-day batch:compared with the control group,DM There was no significant difference in the length of synaptic active regions in hippocampal CA1 region in non-cognitive disorder rats.Compared with DM non-cognitive disorder group,the length of synaptic active regions in hippocampal CA1 region of DM cognitive disorder rats was significantly reduced（p<0.05）;There was no significant difference in the number of synapses and synaptic gap width in the hippocampal CA1 area of the three groups of rats;there was no significant difference in the number of synaptic units,synaptic gap width,and synaptic active area length in the prefrontal cortex area of the three groups of rats.difference.In the 84-day batch:compared with the control group,there was no significant difference in synaptic gap width,synaptic active area length,and prefrontal cortical area synaptic active area length in the hippocampal CA1 region of the DM non-cognitive disorder group.Forehead The synaptic gap width of the cortex area increased significantly（p<0.05）;compared with the DM non-cognitive disorder group,the synaptic gap width of hippocampal CA1 area in the DM cognitive impairment group significantly increased（p<0.05）,and synaptic activity There was no significant difference in the length of the region,the length of the synaptic active region in the prefrontal cortex area was significantly reduced（p<0.05）,and there was no significant difference in the width of the synaptic gap;the number of synapses in the hippocampal CA1 and prefrontal cortex areas of the three groups of rats No significant difference.In the immunohistochemical experiment,in the 35-day batch,compared with the control group,the expression of SYN protein in the hippocampal CA1 region of the DM non-cognitive disorder group was significantly reduced（p<0.05）,and the expression of GAP-43 protein was significantly increased.（p<0.05）;Compared with DM non-cognitive disorder group,the expression levels of SYN and GAP-43protein in hippocampus of DM cognitive impairment group were significantly reduced（p<0.05）;PSD-95 in hippocampal CA1 region of three groups of rats There were no significant differences in the expression of SYN,PSD-95 and GAP-43 in the prefrontal cortex.In the 84-day batch,there were no significant differences in the expression of SYN,PSD-95,and GAP-43 proteins in the hippocampal CA1 and prefrontal cortex regions of the three groups of rats.Conclusion:The DM model established in this experiment has good stability throughout the experiment.With the development of the course of DM,the incidence of cognitive impairment increases.During the 84-day experiment,DM cognitive impairment rats mainly showed synaptic structural damage in the hippocampal CA1 area and prefrontal cortex,and no obvious damage to neurons and their organelles.Among them,the hippocampal CA1 area had more synaptic damage than the prefrontal cortex.Synaptic structural damage occurs early.This may be one of the mechanisms by which DM leads to a decline in learning and memory.The shortening of the length of the synaptic active region caused by the decrease of SYN protein expression may be one of the mechanisms of synaptic structural damage.