Test Description: Groups of naive mice are trained in conditioning chambers (Med-Associates, St.
Albans, Vermont) that have stainless steel rod floors through which foot shocks could be delivered. For
cued trace fear conditioning mice are placed in training context and left undisturbed for habituation
purposes for 60 seconds. Then a conditioned stimulus (CS: 15 sec duration, 85 dB 3kHz) generated by
white noise is delivered, followed by a trace period of 10 sec and the unconditioned stimulus (US:
foot shock, 2 sec, 0.35 mA). Mice are presented with 5 trials with inter-trial interval (ITI) 3 min and
returned to the home cage 1 minute after the final shock.
Testing is carried out 24 hours later, in a different room and cage, in order to assess the efficacy of
cue (tone) conditioning in the absence of interference from context conditioning. Each mouse is placed
in the plastic cage and carried into a chamber that differs from conditioning chambers in having
different light (red instead of bright), walls (not clear instead of clear) and smooth floor. After
60 seconds of habituation CS (same white noise) is presented for 15 sec, and then mouse left in the
chamber for another 60 seconds.
Memory for cued (white noise) fear conditioning is assessed as a difference in percentage of time that
mice spent freezing after CS (conditioned freezing) and percentage of time they spent freezing before
CS (baseline freezing). |
