Photomicrographs of the prelimbic region from representative control, acquisition (footshock), and expression animals. Rats previously adapted to the testing chamber underwent a 2 d test session. On day 1, rats were placed into the chamber for 30 min and received randomized 10 tones alone (Control) or paired with footshock (Acquisition). After this first session, all rats were returned to the home cages, and, after 90 min, rats in the acquisition group and some control rats were killed, and the brain tissues were prepared to visualize Fos-li. On the second day, the remaining rats were returned to the test chamber and exposed to 10 tones without footshock. Rats previously exposed to footshock on day 1 made up the conditioned fear group (Extinction). Ninety minutes after the end of the session, these rats were killed, and Fos-li was visualized in brain tissues. Scale bar, 100 μm.