Ventral hippocampal dopamine D-1 and D-2 systems and spatial working memory in rats

The hippocampus has long been known to be important for memory function. Ho wever, the involvement of hippocampal dopamine systems with memory has rece ived little attention. In the current study, dopamine D-1 and D-2 hippocamp al receptor system involvement with memory was assessed in female Sprague-D awley rats by local infusion of D-1 and D-2 agonists and antagonists into t he ventral hippocampus. Working memory performance was assessed on the radi al-arm maze. Neither the D-1 agonist dihydrexidine (1.1-10 mu g/side) nor t he D-1 antagonist SCH 23390 (0.19-1.67 mu g/side) was effective in signific antly altering radial-arm maze choice accuracy. In contrast, there were sig nificant and opposite effects of D-2 agonist and antagonist treatments. The D-2 agonist quinpirole caused a significant (P<0.05) dose-related improvem ent in choice accuracy over a dose range of 1.1-10 mu g/side. In a compleme ntary 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. T his study provides clear evidence that hippocampal D-2 activity is positive ly related to working memory performance, while evidence for D-1 systems is less compelling. Dopamine D-2 receptors in the ventral hippocampus were sh own to have important influences on spatial working memory. In a consistent pattern of effects ventral hippocampal infusion of the D-2 agonist quinpir ole improved working memory performance in the radial-arm maze, while ventr al hippocampal infusion of the D-2 antagonist raclopride impaired performan ce. (C) 1999 IBRO. Published by Elsevier Science Ltd.