The dopaminergic modulation of fear: quinpirole impairs the recall of emotional memories in rats.

Past studies examining the contributions of dopamine to fear have produced inconsistent results. The present experiments reevaluated this issue. It was found that systemic pretreatment with the D2 agonist quinpirole before pairing 2 conditioned stimuli (CSs; CS2-CS1) dose dependently blocked the acquisition of second-order fear conditioning. Quinpirole's actions were not due to nonspecific impairments in the ability to perceive the CSs, or form and store an association, because the identical drug pretreatment before pairing the same 2 CSs had no effect on the acquisition of sensory preconditioning. In a separate study, rats were given fear conditioning while untreated and then received extinction sessions while under the influence of quinpirole or its vehicle. Quinpirole pretreatment blocked extinction. Findings suggest that quinpirole decreased fear by blocking the retrieval of a learned association between a CS and unconditioned stimulus (US), rather than by devaluing the US, which would have resulted from summation of quinpirole's appetitive properties with the aversive properties of fear.