Quantitative densitometric analysis of the immunohistochemical stainings. For a quantitative analysis of the immunohistochemical data, obtained with antibodies against APP, P-APP, calbindin, MEK, P-MEK, ERK, Elk-1, and P-Elk1, between 20 and 50 cells per group were densitometrically analyzed. Signal intensities in the control group were set at 100. Whereas APP, phospho-APP, and calbindin levels are not affected by the presence of the L199P transgene [Mann-Whitney U-test: not significant (two-tailed exact significance) comparing transgenic with control mice], significant increases are found for levels of the phosphorylated forms of MEK and Elk-1 [Mann-Whitney U-test: P < 0.001 (two-tailed exact significance) comparing transgenic with control mice].