Regional differences in dopamine receptor blockade affect timing impulsivity that is altered by d-amphetamine on differential reinforcement of low-rate responding (DRL) behavior in rats

The ability to control when to start an action and when to stop is crucial in human and animal behavior. A failure to suppress premature behavior or to carry out an action in a timely manner is commonly seen in several neuropsychological disorders. Despite the phenomenon, the exact neural mechanisms underlying this timing impulsivity remain to be elucidated. Systemic injection of d-amphetamine (AMP) has been shown to disrupt rat's performance in the differential reinforcement of low-rate (DRL) task that requires both optimal timing and proper impulsive control as measured by peak time and non-reinforced responses, respectively. By directly infusing selective D1 or D2 receptor antagonists (SCH23390 and raclopride, respectively) into three brain areas, we aimed to uncover which brain regions and which dopamine receptor subtypes are involved in counteracting the rat's deficit of DRL performance induced by the systemic injection of AMP. We found that D1, but not D2 receptors in the dorsal hippocampus (dHIP) and nucleus accumbens (NAC) played an important role in impulsive control as well as in timing. In the medial prefrontal cortex (mPFC), both D1 and D2 receptors played an equal role in impulsive control, but only mPFC D1 was critical in the control of timing. Together, our data revealed a regional-dependent and dopamine receptor subtype specific effect across each region tested in the mesocorticolimbic circuits on the deleterious effect of AMP in the DRL task. The current findings further advance our understanding of the neurobehavioral mechanisms involved in timing impulsivity.