Water maze task
Spatial learning was assessed by three variants of the Morris water maze task [27] adapted for mice. Hidden platform task: The pool was divided into four quadrants with four starting locations, called north, east, south and west, at equal distances to the rim. A circular, transparent acrylic platform (diameter 8 cm) was submerged 1 cm below the surface of the water in the centre of the southeast quadrant for each trial of this task. Each mouse was allowed to swim for 60 sec and the time required to reach the platform (escape latency) was recorded in each trial. In total this task consisted of four trials per day over 9 days (1 min inter-trial intervals). Each trial was initiated by randomly placing an animal in one of the four starting locations. Probe trial: A single probe trial was carried out after the hidden platform task had been completed. In this trial, the platform was removed and the movement of each mouse was monitored using a computer-based video tracking system (BTA-2; Muromachi Kikai Co., Ltd., Tokyo, Japan). Each mouse was placed into the northwest quadrant of the pool and allowed to swim for 60 sec. Swim path length and the time spent in the trained (southeast) quadrant were calculated. Visible platform task: In this task, the circular platform was made visible by attaching a black board to it and the mouse was required to locate the visible platform. The mouse was allowed to swim for 60 sec and this task consisted of four trials per day for three consecutive days (1 min inter-trial intervals). Each trial was initiated by randomly placing an animal in one of the four starting locations.