Figure 1.

Activation of cFos and pErk within the nuclei of pyramidal CA1 cells after contextual fear conditioning and extinction. A, Freezing behavior is robustly induced by a single training (T) trial but progressively decreases with repeated extinction (E1–E5) trials (*p < 0.05; **p < 0.01 vs E1). n = 10; error bars = mean ± SEM. B, Within CA1 cells, nuclear cFos was maximal after training and declined during extinction. Significant increase of nuclear pErk, however, was observed only during extinction (*p < 0.05; **p < 0.001 vs naive; ^#p < 0.05; ^##p < 0.01 vs T). n = 32 (4 per group); error bars = mean ± SEM. C, Representative micrographs demonstrating cFos and pErk signals 1 h after training (T, right) or after the second extinction test 2 (E2, middle) and the fifth extinction test (E5).