Roles and mechanisms of metformin in improving cognitive dysfunction induced by chronic cerebral hypoperfusion in rats / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To explore the roles and mechanisms of metformin in the improvement of cognitive dysfunction induced by chronic cerebral hypoperfusion in rats.Methods:Total 82 SD male rats (SPF grade) aged 3-4 months were randomly divided into four groups sham operation control group (Con group, n=15), sham operation with metformin treatment group (Met group, n=20), 2-vessel occlusion group (2VO group, n=22), and 2-vessel occlusion with metformin administration group (2VO+ Met group, n=25). The chronic cerebral hypoperfusion model was established by bilateral common carotid artery ligation, and the carotid arteries of rats in Con group and Met group were only separated without ligation.After 2VO operation, rats in 2VO+ Met group and Met group were given metformin solution in drinking water at a dose of 100 mg/kg per day for 4 weeks.After 4-week continuous intervention with metformin, Morris water maze was performed to test the spatial cognitive function of the rats, in vivo electrophysiological technology was used to detect the long-term potential of the rats, and enzyme-linked immunosorbent assay(ELISA) was used to detect the concentrations of inflammatory factor tumor necrosis factor-α(TNF-α), interleukin-1β(IL-1β) and interleukin-6(IL-6) in the hippocampus.The density of dendritic spines of hippocampal neurons was observed by Golgi staining, and the synaptic structure of hippocampal neurons, especially the vesicle density, was observed by transmission electron microscopy.SPSS 16.0 software was used for statistical analysis.Repetitive measurement ANOVA was used for the escape latency data of 7 days repeated learning training in water maze.One-way ANOVA was used for the comparison of other data among multiple groups, and Dunnett's t test was used for further pairwise comparison. Results:Morris water maze results showed that during 7 days of learning training, the time and group interaction for escape latency was not significant in the 4 groups of rats ( F=0.93, P>0.05), but the time main effect ( F=25.90, P<0.05) and group main effect ( F=13.20, P<0.05) were significant.Morris water maze test showed that from the 3rd to 7th day, the escape latencies in 2VO group were significantly longer than those in Con group and 2VO+ Met group(all P<0.05). The short-term memory of rats was detected after 1 day of rest.The results showed that the escape latency in 2VO group was significantly longer than that in Con group and 2VO + Met group( P<0.01). The retention time and crossing times in the platform area of 2VO rats were less than those in Con group and 2VO + Met group ( P<0.01). Electrophysiological results showed that the relative field excitatory postsynaptic potential slope of 2VO group (1.29±0.09) was significantly lower than that in Con group (2.07±0.09) and 2VO + Met group (1.69±0.08)( P<0.01). ELISA results showed that TNF-α level in hippocampal tissue of 2VO group was significantly higher than that in Con group and 2VO+ Met group; IL-1β and IL-6 levels in hippocampal tissue of 2VO group were significantly higher than those in Con group and 2VO + Met group.Density of dendritic spines in hippocampal neurons of 2VO group was significantly lower than that in Con group and 2VO+ Met group.The density and proportion of immature dendritic spines in hippocampal neurons of 2VO group were significantly higher than those in Con group and 2VO + Met group.Synaptic vesicle density of neurons in CA1 area of hippocampus in 2VO group ((230.29±19.44) vescicles/μm 2) was significantly lower than that in the Con group ((414.52±13.17) vescicles/μm 2) and 2VO+ Met group ((313.19±12.42) vescicles/μm 2). Conclusion:Metformin can reduce neuroinflammation of hippocampus with chronic cerebral hypoperfusion and improve synaptic plasticity and cognitive dysfunction.It may have potential application value in the treatment of vascular cognitive dysfunction.