2.15 Morris water maze
The Morris water maze (MWM) was performed as described in our previous study with some modifications (Fan et al., 2019). Briefly, mice at the age of 10 months old were trained for 2 days and subsequently tested for 5 days using MWM. The mice were trained 3 times a day for 2 days to find the visible platform (5 cm dia.) above the water, and then were tested 3 trails a day for 5 days to find the hidden platform (1 cm below the water surface). A total of 1 min was given for the mice to find the platform. The escape latency and the path length during MWM were recorded using SMART 3.0 software to evaluate their spatial learning scores. For the probe trail test, 24 h after the last trail of the hidden platform test, the platform was removed, and the number of times that the mice crossed the platform region during 1 min was recorded by the SMART 3.0 software.