Fear conditioning (referred to here as the ‘CS–US’ group) and extinction training was conducted as above, with the addition of an unconditioned group (as above for ‘Pre-extinction treatment in unconditioned mice’) that received CS-only trials during conditioning (referred to here as the ‘CS’ group). AM3506 was administered at a dose of 0 or 1.0 mg/kg 60 min before extinction training.