Figure 3.

The norepinephrine enhancement of acquisition of long-term threat memory depends on the length of ITI during training. (A) Schematic of the experimental design. The conditioning session included two CS–US pairings, which were either 2 min apart (short ITI: light blue) or 40 min apart (long ITI: dark blue). All animals were injected with propranolol (10 mg/kg: Prop: empty symbols) or saline vehicle (1 mL/kg: Sal: filled symbols) 30 min before conditioning. Habituation and LTM test sessions were identical to the other experiments. (B) Percentage of freezing (mean ± SEM) to each CS in the conditioning session for each condition. Post hoc pairwise comparisons showed Prop Short ITI animals froze less to CS2 than their saline controls. (C) Graph showing freezing (mean ± SEM) averaged across all 10 CS presentations in the LTM test. A main effect of group was observed. (D) Analysis of freezing in the LTM test to each CS within each group showed that pretraining propranolol reduced freezing only for the Short ITI group but not for Long ITI. Both conditions showed a main effect of CS, demonstrating within-session extinction learning. (*) P < 0.05, (#) P < 0.05 for CS main effect.