Morris water maze test

Morris water maze (MWM) test was used to assess the long-term spatial learning and memory ability of mice [20]. Briefly, MWM test was performed in a white circular tank (120 cm in diameter, 50 cm in height), filled with tap water (22 ± 3 °C) and divided into four equal virtual quadrants. Non-toxic white paint was added into the water until it became opaque. Some different geometric cues were mounted on the white curtain surrounding the tank. In the place navigation training phase (four 60-s trials/day for five consecutive days), a circular escape platform (10 cm in diameter) was placed in the center of a targeted quadrant, submerged 1 cm beneath the surface of the water. Each mouse was placed in the water facing the wall of the tank from different release positions and allowed to search for the escape platform. Once the mouse escaped onto the platform, it was allowed to remain on the platform for 5 s. The escape latency to climb onto the escape platform was recorded. If the mouse failed to find the platform within 60 s, it was guided to climb on the platform and remained on it for 30 s. On the 6th day of probe test, mice were allowed to swim freely in the water without the platform for 60 s. The percentage of time spent in the target quadrant and the number of platform crossing were measured. Mice that floated in the maze were not enrolled in the test. Lastly, a visible platform test was performed to detect the visual ability of mice. The swimming speed was also measured during the MWM test to exclude the mice with motor deficits. The swimming tracks were monitored and analyzed by a computer-based video tracking system (Ethovision software, Noldus Information Technology).