Ventral hippocampal dopamine D1 and D2 systems and spatial working memory in rats

The hippocampus has long been known to be important for memory function. However, the involvement of hippocampal dopamine systems with memory has received little attention. In the current study, dopamine D-1 and D-2 hippocampal receptor system involvement with memory was assessed in female Sprague-Dawley rats by local infusion of D-1 and D-2 agonists and antagonists into the ventral hippocampus. Working memory performance was assessed on the radial-arm maze. Neither the D-1 agonist dihydrexidine (1.1-10 mu g/side) nor the D-1 antagonist SCH 23390 (0.19-1.67 mu g/side) was effective in significantly altering radial-arm maze choice accuracy. In contrast, there were significant and opposite effects of D-2 agonist and antagonist treatments. The D-2 agonist quinpirole caused a significant (P<0.05) dose-related improvement in choice accuracy over a dose range of 1.1-10 mu g/side. In a complementary fashion, the D-2 antagonist raclopride caused a significant (P<0.05) dose-related choice accuracy deficit over a range of 0.19-1.67 mu g/side. This study provides clear evidence that hippocampal D-2 activity is positively related to working memory performance, while evidence for D-1 systems is less compelling. Dopamine D-2 receptors in the ventral hippocampus were shown to have important influences on spatial working memory. In a consistent pattern of effects ventral hippocampal infusion of the D-2 agonist quinpirole improved working memory performance in the radial-arm maze, while ventral hippocampal infusion of the D-2 antagonist raclopride impaired performance. (C) 1999 IBRO. Published by Elsevier Science Ltd.