Effect of activating α7 nicotinic acetylcholine receptor on learning and memory function and microglia in traumatic brain injury model rat / 中华行为医学与脑科学杂志

ABSTRACT

Objective:To explore the effects of activating α7 nicotinic acetylcholine receptor(α7nAChR)on cognitive function and polarization of hippocampal microglia in traumatic brain injury (TBI) rats.Methods:Totally 36 male SD rats with 6-8 weeks old were randomly divided into Sham group ( n=12), TBI group ( n=12), TBI+ α7nAChR agonist group ( n=6) and TBI+ α7nAChR antagonist group( n=6). The TBI model was established by the " free fall impact" method. From the 4th to 6th day after modeling, mice in the TBI+ α7nAChR agonist group were intraperitoneally injected with α7nAChR agonist PNU-282987 (3 mg/kg). Rats in TBI+ α7nAChR antagonist group were intraperitoneally injected with α7nAChR antagonist methyllycaconitine citrate (5 mg/kg) first, then 45 minutes later they were injected with α7nAChR agonist PNU-282987 (3 mg/kg). Rats in the TBI group and Sham group were intraperitoneally injected with an equal volume of 0.9% sodium chloride solution. Morris water maze test was used to evaluate the learning and memory function of rats. Immunofluorescence staining was used to observe the ionized calcium binding adapter molecule 1 (Iba-1)(a marker for microglia) and arginase 1 (Arg-1)(a marker for M2 microglia). Western blot was used to detect the protein level of Arg-1 in hippocampal tissue. Statistical analysis was performed using GraphPad Prism 9 software. Independent sample t test was used for comparison between two groups, one-way ANOVA was used for comparison among multiple groups, and Tukey test was used for multiple comparison. Results:The results of the water maze test showed that after 7 days of modeling, there was a statistical difference in the escape latency among the 4 groups of rats ( F=6.134, P<0.05). There was no statistical difference in the escape latency between the TBI group and the TBI+ α7nAChR antagonist group( P>0.05), but the both were higher than that of the Sham group (both P<0.05). The escape latency of the TBI+ α7nAChR agonist group((31.87±9.01)s) was shorter than that of the TBI group((56.75±2.62)s) and the TBI+ α7nAChR antagonist group((60.00±0.00)s) (both P<0.05). The results of immunofluorescence staining showed that there were statistical differences in the fluorescence intensity and cell numbers of Arg-1 + /Iba-1 + among the four groups ( F=17.37, 9.33, both P<0.05). The immune fluorescence intensity (0.27±0.03) and cell numbers (21.67±4.41) of Arg-1 + /Iba-1 + in the TBI+ α7nAChR agonist group were higher than those in the TBI group((0.14±0.03), (11.33±2.60)) and TBI+ α7nAChR antagonist group((0.10±0.03), (7.67±1.20)) (all P<0.05). The results of Western blot showed that there was a statistical difference in the level of Arg-1 protein in hippocampus among the 4 groups ( F=8.323, P=0.001). There was no significant difference in the level of Arg-1 protein between the TBI group and the TBI+ α7nAChR antagonist group( P>0.05), and the level of Arg-1 protein in the TBI+ α7nAChR agonist group(1.06±0.22) was higher than that in the TBI group(0.60±0.13) and TBI+ α7nAChR antagonist group(0.35±0.10) (both P<0.05). Conclusion:Activating α7nAChR can promote the polarization of M2 type microglia in rat hippocampal tissue and improve the learning and memory function of TBI rats.