(A,B) Immunoblot analysis of Aβ peptide levels. Soluble (A) and insoluble (B) protein extracts were prepared as described in Materials and Methods. Proteins (175 and 2 μg for soluble and insoluble respectively) were separated by SDS-PAGE and membranes were probed with anti-Aβ Abs. Aβ levels in the soluble fraction were normalized to a ~12 KDa band in the Ponceau staining (lower panels). (C, D) Quantification of immunoblot results of soluble (C) and insoluble (D) Aβ levels (*p < 0.05, **p < 0.005, ***p < 0.0005, Student’s t test). (n = 8). (E, G) Immunoblot analysis of APP levels. Cortical protein extracts were prepared from brains of APP.PS and APP.PS.Cd38−/− mice at 8 (E) and 14 (G) months of age. Proteins (50 μg) were separated on SDS-PAGE and membranes were probed with anti-APP Abs as described in Materials and Methods. The membranes were cut into two parts and each part was stained separately for either APP or for cytochrome c for normalization. APP levels were normalized to cytochrome c (Cyt c). (F, H) Quantification of APP immunoblot results at 8 (F) and 14 (H) months of age. (NS, not significant; Student’s t test) The quantified values shown are presented as the mean ± SEM (bars). (n = 8 for each genotype).