The effects of dopamine and its antagonists on directional delay-period activity of prefrontal neurons in monkeys during an oculomotor delayed-response task

To examine the role of dopamine receptors in the memory field of neurons fo r visuospatial working memory in the prefrontal cortex (PFC), dopamine and its antagonists (SCH23390 for the D1-antagonist and sulpiride for the D2-an tagonist) were applied iontophoretically to neurons of the dorsolateral PFC in monkeys that performed an oculomotor delayed-response task. In this tas k, the subject made a memory-guided saccade to a remembered target location that had been cued by a visuospatial stimulus (right, up, left, or down; 1 5 degrees in eccentricity) prior to a 4-s delay period. We focused here on PFC neurons that showed directional delay-period activity i.e., an increase d activity during the delay period, the magnitude of which varied significa ntly with the target location. Iontophoretic application of SCH23390 (usual ly 50 nA) decreased or increased the activities of most of these neurons (n = 48/62, 77%) most neurons showed a decrease (n = 43/62, 69%). For the neu rons affected by SCH23390, a directional index of directional delay-period activity was attenuated by SCH23390, whereas the preferred direction was no t greatly affected. The decreasing effect of SCH23390 was dose-dependent; t he extent of the decrease was less with a lower dose (20-nA current) than w ith the ordinary dose (50-nA current), although the effect of the lower dos e of SCH23390 on delay-period activity was similar in nature to that of the ordinary dose of SCH23390. Furthermore, the application of dopamine itself augmented directional delay-period activity in most of the neurons tested (n = 12/16, 75%). Sulpiride did not have any significant effects in most of the neurons tested (n = 15/17). These results suggest that the activation of DI-dopamine receptors play a facilitating role in the memory field of PF C neurons for visuospatial working memory processes. (C) 2001 Elsevier Scie nce Ireland Ltd and the Japan Neuroscience Society. All rights reserved.