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Figure 4: Photomicrographs (20x magnification) of neurons in the granule cell layer of the dentate gyrus expressing Arc and zif268 protein. Arc (green), zif268 (red), and merged images are shown for unstimulated home cage animals (a)–(c) and for animals killed 30 min (d)–(f) and 90 min (g)–(i) following fear conditioning. The number of Arc-positive neurons increased following fear conditioning (a), (d), (g), and the degree of zif268 immunoreactivity is greatest in the 30 min condition (e). Arc and zif268 are co-localized in dentate gyrus granule cells, which appear yellow when Arc and zif268 images are merged (c), (f), and (i). Example neurons co-expressing Arc and zif268 protein are indicated with arrows in the merged images.