Impairment of long-term auditory fear memory by post-training intra-striatum infusion of ifenprodil. (A) Experimental design. Mice were injected with 0.5 μl of ACSF or ifenprodil into the striatum immediately after auditory fear conditioning with a footshock at 0.3 mA or 1.0 mA, and tested 24 h later. (B) Freezing responses of ACSF (n = 17) and ifenprodil (n = 16) groups conditioned with a low-intensity footshock (0.3 mA) on the conditioning (left) and test (right) days. There was a significant difference in the extent of the freezing responses between ACSF- and ifenprodil-treated mice (F1,31 = 7.19, P = 0.01, repeated measures ANOVA). (C) Freezing responses of ACSF (n = 9) and APV (n = 9) groups conditioned with a footshock at 1.0 mA on the conditioning (left) and test (right) days. The freezing responses of two groups of mice were comparable (F1,16 = 0.12, P = 0.74, repeated measures ANOVA). Solid lines and thick arrows represent tone and footshock, respectively.