Passive avoidance test

The test apparatus consisted of a light and a dark chamber (17 × 22 × 20 cm), each equipped with a shock-grid floor and a door between the two chambers. During the first day of testing, each mouse was placed in the light chamber and left to habituate to the apparatus for 5 min, while allowing it to explore the light and dark rooms. On the second day, the mice were placed in the light chamber. After 20 sec, the door was opened, and the mice were allowed to enter into the dark chamber such that all four paws were inside. When the mice entered the dark room, the door was closed, and one successive electric foot-shock (0.1 mA, 2 sec) was delivered through the grid floor. After training, the mice were then returned to their home cages. After 7 days, the mice were individually replaced in the light chamber, and the latency to enter the dark chamber was measured, which was recorded as the posttest latency⁶². The cut-off time for the entry into the dark chamber was 180 sec.