Number of synaptophysin-immunoreactive presynaptic boutons (SIPBs) in the prelimbic area (PRL), the cingulate gyrus (GC), and the stratum radiatum (SR), stratum lucidum (SL) and the inner (IML) and outer molecular layer (OML) of the dentate gyrus in the hippocampus. In female mice, there was a significant effect of genotype on the number of SIPBs in the IML (/group, ). ApoE4 female mice have less SIPBs than female wild-type mice (*). In other brain regions, no significant differences were found (/group, ). In male mice, there were no significant effects found in any of the brain regions ( = 6–8/group, ). Error bars show mean ± SEM.