Fos expression in the mPFC following immediate extinction. A, Representative photomicrographs showing Fos expression in the IL, PL, and M2. Fos expression was identified using CY3 fluorescence (red), and nuclei were identified by DAPI staining (blue). Scale bar, 10 μm. B, Schematic diagram illustrating the IL, PL, and M2. C–E, Percentages of Fos-IR neurons in the IL, PL, and M2. Fos-IR neurons in both the IL and PL were found in significantly greater numbers in the D-EXT group than in other groups. Numbers of Fos-IR neurons in the I-EXT group were not different from the controls. D-EXT, Delayed extinction group; I-EXT, immediate extinction group; I-NO-EXT, immediate no extinction group; D-NO-EXT, delayed no extinction group; I-UNPAIRED, immediate unpaired conditioning group; D-UNPAIRED, delayed unpaired conditioning group. *p < 0.05. All data are presented as means ± SEM.