Dopamine, not norepinephrine, is required for trace fear memory formation.
(A) Mice were injected with either propranolol, propranolol and prazosin, or SCH23390 thirty minutes before undergoing trace fear conditioning. The next day, mice were tested for their memory of the tone-shock association in a novel context. (B) Freezing behavior during the tone test did not differ between animals that received propranolol injections (Prop, n=8) and vehicle controls (Veh, n=8) (Drug main effect F(1,14) = 1.15, p>.05; Drug x Epoch interaction F(2, 28) = 0.55, p>.05). (C) Freezing behavior during the tone test did not differ between animals that received propranolol + prazosin (low (n=6) and high (n=6) doses) and in vehicle controls (n=6)(Drug main effect F(2,15) = 2.26, p>.05; Drug x epoch interaction F(4, 30) = 0.59, p>.05). (D) Freezing behavior during the tone test did not differ between animals that received intra-hippocampal propranolol infusions (n=8) prior to training and vehicle controls (n=9) (drug main effect F(1,15) = 0.00, p>.05; drug x epoch interaction F(2,30) = 0.11, p>.05). (E) Animals that received SCH23390 (SCH, n=8) injections froze significantly less than vehicle controls (Veh, n=8) (Main effect of drug F(1,14) = 6.14, p<.05). (F) Animals that received intra-hippocampal infusions of SCH23390 (n=5) froze significantly less than vehicle controls (n=5) (Treatment x Phase interaction F(2,16) = 4.62, p<.05). (G) Mice were injected with SCH23390 immediately after training and tested the next day. (H) There was no significant difference between mice injected with SCH23390 (n=8) after training and vehicle controls (n=8) (Main effect of treatment: F(1, 14) = 0.175, p>.05; Treatment X Phase interaction: F(2,28) = 1.65, p > .05).