2.5. Passive Avoidance Test

The passive avoidance (PA) test is widely used to test memory. The test was performed using a Shuttle Box Avoidance Basic Test Package (Med Associates Inc., Fairfax, VT, USA) composed of four reaction chambers. The apparatus was divided into two rooms, an illuminated room and a dark room, that were connected together via an automatic door. The dark room was equipped with a grid floor through which an electronic shock could be delivered. In the training trial, the mice were initially placed into the light room; after 30 s of habituation, the automatic door was opened to allow the mice to move to the dark room. The door was closed quickly after the mice passed into the dark room, and an electric shock (0.35 mA, 3 s) was delivered. The test trial was performed the next day, during which each mouse was reevaluated in the same manner without an electronic shock. The latency times for the mice moving from the light room to the dark room were recorded up to a maximum of 3 min. The PA test was conducted in accordance with a previous study [15].