ANPEP and Cognitive impairment: To determine whether cognitive deficits are also present in our middle‐aged APN‐KO mice, we performed an open field test, light‐dark test, elevated plus maze (EPM), forced swim test (FST), Tail suspension test (TST), Y‐maze, novel object recognition (NOR) and Morris water maze tests with 12‐month‐old APN‐KO mice.