Relationship of Aβ between CNS compartments. A, There is no correlation between CSF Aβ and hippocampal (Hippo.) ISF eAβ in 3-month-old PDAPP mice (Pearson's r = 0.2192; p = 0.3530; n = 20). B, In 12- to 15-month-old PDAPP mice, there is a significant correlation between CSF Aβ and hippocampal ISF eAβ (Pearson's r = 0.6226; p = 0.023; n = 13). In middle-aged mice, there is a significant correlation between CSF Aβ and percentage Aβ load (C) (Pearson's r = 0.6641; p = 0.0133; n = 13), as well as a positive trend between ISF eAβ and percentage Aβ load in the hippocampus (D) (Pearson's r = 0.3511; p = 0.1582; n = 22).