Endogenously produced apoE4 causes loss of somatostatin-positive interneurons. A, Representative images of anti-somatostatin-immunostained sections of the dentate gyrus of 17-month-old female apoE3-fKI, apoE4-fKI, apoE3-fKI/Syn-1-Cre, apoE4-fKI/Syn-1-Cre, apoE3-fKI/GFAP-Cre, and apoE4-fKI/GFAP-Cre mice. Scale bar, 250 μm. B, Quantification of somatostatin-positive hilar interneurons in 17-month-old female apoE3-fKI, apoE4-fKI, apoE3-fKI/Syn-1-Cre, apoE4-fKI/Syn-1-Cre, apoE3-fKI/GFAP-Cre, and apoE4-fKI/GFAP-Cre mice (n = 8 for each group of mice). C, Representative images of anti-somatostatin immunostained sections of the dentate gyrus of 17-month-old female apoE3-fKI, apoE4-fKI, apoE3-fKI/Dlx-Cre, and apoE4-fKI/Dlx-Cre mice. Scale bar, 250 μm. D, Quantification of somatostatin-positive hilar interneurons in 17-month-old female apoE3-fKI, apoE4-fKI, apoE3-fKI/Dlx-Cre, and apoE4-fKI/Dlx-Cre mice (n = 8 for each group of mice). **p < 0.01 (t test).