We next examined the effects of systemic AM3506 treatment on fear extinction. Mice were trained to fear an auditory CS via repeated pairings of the CS with footshock (US). A control group received CS-alone presentations. The day after conditioning, mice were intraperitoneally injected with AM3506 or vehicle 1 h before an extinction training session comprising 50× presentations of the CS alone.23 To evaluate the efficacy of extinction, a retrieval test was conducted 10 days later. The fear response to the CS during extinction and retrieval was measured by quantifying freezing behavior. This treatment and test design was meant to approximate the adjunctive drug treatment approach used in patients with anxiety disorders undergoing exposure therapy.48
