APP and Alzheimer disease: Sildenafil improved cognition in several mouse models of AD, including scopolamine-induced dementia [96], NO synthase N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced dementia [97, 98], the APP/PS1 mouse model of AD [51, 99–101], the Tg2576 transgenic mouse model of AD [47], SAMP-8 mice [46, 49, 52], age-related AD models [102, 103] and aluminium-induced AD models [50].