Spatial Memory Evaluation in Mice

Spatial learning and memory were evaluated using a conventional MWM as previously described [39 (link),40 (link),41 (link)]. During the MWM training, an escape platform (10 cm in diameter) made of white plastic was submerged 1.0 cm below the water level. The swim path of each mouse during each trial was recorded by a video camera connected to a video tracking system (Noldus, Wageningen, Netherlands). On the day prior to the spatial training, all mice underwent pretraining to assess their swimming ability and acclimatize the mice to the pool (n = 12–15 per group). The mice that floated in the pool during the pretraining stage were excluded from the experiment. A 4-day training session consisting of four 60-s training trials (inter-trial interval: 20–30 min) per day was conducted with a hidden platform placed at the same location in the pool (northeast quadrant). The mice that failed to locate the platform within 60 s were placed on the platform for 20 s during the training period. The escape latency time to reach the platform was recorded in each trial. Three probe trials were performed 48 h after the final training trial. During the probe trial, the mice were allowed to swim for 60 s after the platform was removed from the pool. The platform-crossing frequencies were recorded to evaluate the changes in long-term spatial memory in each group.