The dopamine D2 agonist quinpirole disrupts attention to temporal signals without selectively altering the speed of the internal clock

Abstract

Three groups of rats were trained to discriminate between 2 sec and 8 sec of darkness by responding to either the left or the right lever. Following acquisition of this temporal discrimination, psychophysical functions were obtained by presenting unreinforced signals of intermediate duration. Two groups of rats were trained with saline and subsequently tested with the specific D2 dopamine agonist quinpirole (0.08 mg/kg). One of these groups was naive to the drug prior to testing (DN), whereas the other had exposure to the drug but not during training sessions (DE). A third group (DT) was trained under quinpirole and tested with saline. The temporal discrimination was acquired rapidly and equivalently in Groups DN and DE. However, rats in Group DT were severely impaired in acquiring the discrimination. During psychophysical testing, quinpirole disrupted the accuracy of temporal discrimination equivalently in Groups DN and DE. Both the Weber fraction (WF) and the difference limen (DL) increased significantly in Groups DN and DE; however, the point of subjective equality (PSE) was not affected. In Group DT, the shift to saline during psychophysical testing did not result in any changes to the PSE, DL, or WF. These findings are not consistent with the hypothesis that the speed of the internal clock is selectively affected by D2 dopaminergic manipulations. Prior exposure to the drug does not appear to be a critical variable in the failure to observe a selective adjustment of the internal clock. The D2 agonist quinpirole appears to affect the accuracy of temporal discriminations generally, without altering the speed of the internal clock.