Selective effects of low-dose dopamine D1 and D2 receptor antagonists on rat information processing

It is well established that the dopaminergic system influences simple reaction time (RT) performance. However, the role of this system in more complex information processing remains to be clarified. The present study was aimed at addressing this issue. To this end, we used an inferential method that relies on choice RT procedures and allows one to identify information processing stages in both humans and rats. Long-Evans rats responded to lateral visual cues (left or right). Two task factors, signal intensity and foreperiod duration, were manipulated. Low doses of two pharmacological agents, SCH 23390 (a D-1 receptor antagonist; 0.015 and 0.025 mumol/kg) and eticlopride (a D-2 receptor antagonist; 0.01 and 0.02 mumol/kg), were administrated systemically. Both drugs increased choice RT: eticlopride interacted with signal intensity on RT, showing that D-2 receptors mediate at least the sensory stage of stimulus preprocessing. In addition, eticlopride interacted with signal intensity on omission rate, thereby suggesting an involvement of D-2 receptors in attentional processes; and SCH 23390 interacted with foreperiod duration on RT, indicating that D-1 receptors specifically mediate the response adjustment stage. The effect of this drug on RT rests entirely in its interaction with foreperiod duration, allowing us to conclude that this D-1 antagonist affects the response adjustment stage while sparing all other processing stages.