Figure 9. Activation of α7 nAChR increases the number of synapses and maintains the structural integrity of synapses in the hippocampus of APP/PS1_DT mice. The synapses were visualized using transmission electron microscopy. Control, the WT mice; WP, the WT treated with PNU; APP/PS1, the APP/PS1_DT mice; and AP, the APP/PS1_DT mice treated with PNU. Magnification, (A) x20 and (B) x50. The number and characteristics of synapses in (C–F) 6- and (G–J) 10-months-old mice are presented in the figure. Arrows indicate synapses. The results demonstrated that synapses underwent the following changes: (C and G) The number of synapses in both 6- and 10-month-old mice was decreased; (D and H) the synaptic gap became wider; (E and I) the post-synaptic dense substance in the hippocampus of the APP/PS1 group became thinner (vs. the control group) and the post-synaptic dense substance in the AP groups (either 6- or 10-month-old) were thicker than the APP/PS1 group; and (F and J) the curvature of the synaptic interface became smaller in 10-month-old mice. (D, H, F and J) Moreover, there were no significant differences in synaptic gap width and synaptic interface curvature between the APP/PS1 and AP groups. These results indicate that α7 nAChR is beneficial to maintain the integrity of the synaptic structure and increase the number of synapses, thus could improve synaptic functions. Data are presented as the mean ± standard deviation. *P<0.05, **P<0.01 vs. control group; #P<0.05, ##P<0.01 vs. APP/PS1 group.