Conditioned Fear Paradigm for Mice

The conditioned flight paradigm^{24 (link)} is a Pavlovian fear conditioning paradigm in which an SCS is used as the conditioning stimulus (CS) that is paired with the unconditioned stimulus, a shock. The SCS consists of a 10-s pure tone period (7.5 kHz, 75 dB, 500 ms beeps and 1 Hz) followed by a 10-s white noise period (1–20 kHz, 75 dB, 500 ms bursts and 1 Hz). On the first day (pre-exposure), the SCS alone is presented four times in a white cylinder (27 cm diameter). The conditioning was then performed on two consecutive days, with five SCS/US pairings on each day after a 3-min baseline period (pseudorandomized inter-stimulus interval (ITI): 170–230 s). The conditioning context was a red transparent square box (30 × 30 cm) with a grid floor through which footshocks were delivered. For each SCS/US pairing, a 1-s footshock (0.9 mA; Model 2,100 Isolated Pulse Stimulator, A-M System) immediately followed the last white noise burst. On the fourth day, animals underwent cue retrieval in a transparent cylinder (30 cm diameter), to receive 16 SCS presentations, without US pairings (pseudorandomized ITI: 80–140 s). One group of mice was placed into their HC while replaying the SCS tones instead a new context. A subset of mice underwent an additional day of recording and were placed back in the conditioning context for 15 min on the fifth day of the protocol (context retrieval).
Days 1 and 4 of the conditioned flight paradigm (pre-exposure and cue retrieval) and OF, EPM and LDB recordings were performed in context A (acetic acid smell, dim light), while recordings for days 2, 3 and optionally 5 of the conditioned flight paradigm (conditioning, context retrieval) were made in context E (ethanol smell, brighter light).