Observational fear response (Social Transfer of Fear)

Observational fear response assays were performed as described previously (1) with slight modifications. Two fear-conditioning shock chambers, made by different manufacturers, in two entirely separate rooms were used as the two separate contexts (Context A: Ugo Bassile passive avoidance chamber, and Context B: Med Associate self-administration chambers with shock floor additions) . To enhance the magnitude of the social transfer of fear (2,3), 24 h prior to the social transfer procedure (Day 1; Fig. 4A), BY mice were administered a shock experience by being placed in one of the fear-conditioning chambers (context A, Fig 4A) for 5 minutes at which time they received 2 unpredicted, un-cued, footshocks (0.4 mA, for 2 sec, 1 min interval) and then transferred back to their home cage with treatment matched cagemates. The following day (Day 2), a naive mouse was placed in the other fear-conditioning chamber (Context B) while a BY mouse was placed in an adjacent homemade plexiglass observation chamber, which allowed for the communication of visual, auditory and olfactory cues through a transparent, perforated plexiglass divider. After a 5 min habituation period, the naive mouse received 24 unpredicted, un-cued, footshocks (0.7 mA, for 2 sec, 10 sec intervals over 4 min). The entire session was recorded with a high definition camera (Logitech) and the time spent freezing was scored manually using a stop watch. Mice were then housed in pairs for 24 h with treatment-matched cagemates. The following day (Day 3), contextual observational fear memory was assessed by placing the BY mice back into the observation chamber in the same context (Context B) for 10 min.

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