Passive Avoidance Test

On PND 22, the memory of animals was tested by a passive avoidance test. The apparatus (Gemini; SD Instruments, San Diego, CA, USA) consisted of a shuttle box equipped with a door to restrict access between equal-sized (25×25×35 cm) illuminated and dark compartments. In the training trial, rats were individually placed in the illuminated compartment for 180 seconds and allowed to enter the dark compartment through an opened door between the two compartments. After some time, the animal spontaneously entered the dark compartment. The door was shut one second after the crossing, and the rat was given an unavoidable scrambled electric foot shock (1 mA/2 seconds) through the grid floor of the dark compartment. Then 24 hours later, the same procedure was repeated without an electric foot shock. A latency of entry greater than 300 seconds was a criterion for successful learning. Controls (n=10) and VPA treated group (n=10) were used for this analysis.