Immunohistochemical analysis of c-Fos protein expression after auditory fear conditioning with different intensities of unconditioned stimuli in the striatum. (A) Two hours after auditory fear conditioning with a footshock at 0 mA, 0.3 mA, or 1.0 mA, brains were sectioned and immunostained with anti-c-Fos antibody (upper panels, green). The nuclei were stained with SYTOX orange (middle panels, red). Representative images of coronal sections of NAc are shown as separate images (upper and middle panels) and merged images (lower panels). (B) Quantitative analysis of c-Fos-immunoreactive cell density in NAc. n = 18 slices from 3 mice each. Scale bar: 100 μm. * and **, P < 0.05 and P < 0.01.