Figure 6.

Training-induced expression of Arc/Arg3.1 is impaired by intra-LA infusion of a MEK inhibitor. a, Schematic of the behavioral protocol. Rats were given intra-LA infusion of either 50% DMSO vehicle (0.5 μl; n = 10) or the MEK inhibitor U0126 (1 μg/side/0.5 μl; n = 10) 30 min before fear conditioning consisting of 3 tone-shock pairings. Rats were killed 2 h after fear conditioning by either decapitation or perfusion. b, Western blot analysis of Arc protein (black bars) and phospho-ERK protein in the LA of Vehicle and U0126-infused groups after fear conditioning. *p < 0.05 relative to Vehicle group. Representative blots can be seen in the inset. c, d, Representative 10× photomicrographs of immunolabeled Arc/Arg3.1 neurons in the LA of rats receiving vehicle or U0126 infusion, respectively. Higher-level magnification of Arc/Arg3.1 labeled neurons from the box in c is shown in the inset. e, Quantification of Arc/Arg3.1 labeled cells in the LA of Vehicle (n = 4) and U0126-treated rats (n = 4). *p < 0.05 relative to the Vehicle group. f, Histological verification of cannula placements for rats infused with vehicle (black circles) or U0126 (white circles). Panels were adapted from Paxinos and Watson (1997).