Figure 2.

Inhibition of de novo protein synthesis after memory reactivation does not permanently erase the fear memory. A, Fear-conditioned mice exposed to a reminder shock 24 hr after the last extinction trial reinstated freezing behavior. In contrast, nonconditioned mice did not show freezing after the reminder shock. B, Representative immunoblots demonstrating the biochemical effects of anisomycin and puromycin injected intrahippocampally immediately after training. Both inhibitors completely prevented the production of the cFos protein, as determined 1 hr after training. In addition, anisomycin increased the level of p-cJun [percentage increase (mean ± SEM) vs vehicle, 212 ± 28%) and p-ATF2 (percentage increase vs vehicle, 57 ± 11%), whereas puromycin did not exert a significant effect. The experiment was replicated twice with three mice per group. C, Injection of anisomycin (50 μg, i.h.) or puromycin (25 μg, i.h.) after training prevented the consolidation of contextual fear. A reminder shock failed to reinstate freezing behavior in this group. D, A reminder shock reinstated freezing behavior of mice injected with anisomycin or puromycin after the first nonreinforced memory test. Statistical differences: ^*p < 0.01 versus vehicle control; ^ap<0.01 versus test 1; ^bp < 0.01 versus conditioning context. RS, Reminder shock.