Open field test was done as previously described [47 (link), 58 (link)]. Briefly, mice were allowed to explore a 40 × 40 cm arena (Maze Engineers, # 3201) illuminated at 60 l × for 5 min during which the distance traveled and the time spent in the inner 15 cm-area were measured using the EthoVision tracking system (XT 17, Noldus Information Technology). Contextual fear conditioning was performed as previously described [58 (link)], except that acoustic cue conditioning was not tested on the third day of contextual fear conditioning. Briefly, during the first day of training, mice were allowed to explore a Med Associates’ fear conditioning chamber (Cat # VFC-008) equipped with a grid floor in the presence of a 2% lemon scent for 300 s. After 300 s of free exploration, mice were exposed to 5 shock-tone pairing at variable inter-trial interval (30–180 s). These were presented as 30 s discontinued tones (7500 Hz, 80 dB) that co-terminated with a 1 s 0.65 mA foot shock. There was a 30 s period at the end of the session following the last pairing and freezing behavior recorded using Med Associates’ Video Freeze software. On the second day, mice were returned to the same box and contextual freezing was determined for 300 s in the absence of a tone or a shock.
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