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 wa s found that systemic pretreatment with the D2 agonist quinpirole before pa iring 2 conditioned stimuli (CSs; CS2-CS1) dose dependently blocked the acq uisition of second-order fear conditioning. Quinpirole's actions were not d ue to nonspecific impairments in the ability to perceive the CSs, or form a nd store an association, because the identical drug pretreatment before pai ring the same 2 CSs had no effect on the acquisition of sensory preconditio ning. In a separate study, rats were given fear conditioning while untreate d and then received extinction sessions while under the influence of quinpi role or its vehicle. Quinpirole pretreatment blocked extinction. Findings s uggest that quinpirole decreased fear by blocking the retrieval of a learne d 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.