Figure 2: Expression of Arc protein in the dorsal hippocampus following fear conditioning. (a) The temporal expression profile for Arc protein shows a noticeable increase in expression at 30 min, continuing through 90 min post training. The rise in Arc protein diminishes over time, reaching basal levels by 4 hr post training. Bar graph represents the group means ± SEM. Representative western blot images are presented for each group directly below the corresponding graph plot. Significant differences from home cage (HC) controls are denoted with asterisks: P*<.05, P**<.01. (b) Brightfield photomicrograph (2× magnification) of the dorsal hippocampus. The boxed area indicates the region depicted in the immunofluorescence images of C and D (10× magnification). (c) Basal expression of Arc protein in the dentate gyrus is low in the home cage control animal. (d) Arc protein expression is significantly increased in granule cells of the dentate gyrus 90 min after fear conditioning. (e, f) Higher magnification photomicrographs (20× magnification) of the boxed regions from (c) and (d), respectively.