Mean (±SEM) latency (in seconds) to cross to the black side of the black–white shuttle box for all groups in experiment 1. Open bars represent the no stress control groups. Darker slashed bars represent the stressed experimental groups. Long latency scores for the No Ext, 0-saline, and 120-CHX groups represent significant fear. Decreased latency scores for the group that did not receive stress before training and extinction (Ext) represent significantly less avoidance (i.e., reduction of fear). Increased latency scores for the group that received stress 48 h before training (0-saline) compared with the no stress extinction group (Ext) represent the stress-induced impairment of extinction. The 0-CHX group's short latencies replicate retrograde amnesia for the stress-induced impairment of extinction. Significantly longer latencies for the group that received cycloheximide 2 h after stress (120-CHX) compared with the shorter latencies for the group that received cycloheximide immediately after stress (0-CHX) represent a temporal gradient of amnesia.
