2.5. Morris Water Maze Test

All the rats were given spatial memory assessment by using Morris water maze (MWM), which mainly includes a 1.5 m diameter pool filled with opaque water and a 10 cm round platform that placed 1 cm below the surface of the water at the center of one quadrant. The whole experiment lasted for 6 days. The first 5 days were the place navigation test, which was used to test the spatial learning and memory functions of rats. During the first 5 days, each rat was gently released into the water at four different locations on opposite sides of the platform for four swimming trials per day. Rats that failed to find the platform within 60 s were manually guided to the platform and allowed to stay for 15 s. The probe trial proceeded on the 6th day, which was tested for spatial memory. On the 6th day, the platform was removed, the contralateral side of the platform was selected as the entry point, and the rats were free to swim in the tank for 60 s. The swimming trace, latency to the platform, the time spent in each quadrant, and the platform crossing times were recorded by a computerized video imaging analysis system (AVTAS Animal Video Tracking Analysis System, Wuhan YiHong Sci. & Tech. Co., Ltd).