Nucleus accumbens dopamine receptors in the consolidation of spatial memory

Nucleus accumbens dopamine is known to play an important role in motor activity and in behaviours governed by drugs and natural reinforcers, as well as in nonassociative forms of learning. At the same time, activation of D-1 and D-2 dopamine receptors has been suggested to promote intracellular events related to neural plasticity. Therefore, in this study we wished to investigate the role of the two classes of dopamine receptors within the nucleus accumbens on the consolidation of spatial information. On day 1, CD1 male mice were placed in an open field containing five different objects and, immediately after three sessions of habituation, the animals were focally injected within the nucleus accumbens with either the D-1 antagonist SCH 23390 (12.5, 25 or 50 ng/side), or the D-2 antagonist sulpiride (25, 50, 75 or 100 ng/side). Twenty-four hours later the ability of mice to discriminate an object displacement was assessed. Both the D-1 and the D-2 antagonists impaired the ability of mice to detect the spatial change. If the highest doses of the two antagonists were injected 2 h after the end of the last of the habituation sessions, no effect was observed in the reactivity to spatial change examined 24 h later. These data demonstrate that activation of both D-1 and D-2 receptors within the accumbens is necessary in the early stages of the consolidation of spatial information. The data are discussed in terms of involvement of nucleus accumbens dopamine in information processing in the absence of explicit reinforcers. (C) 2004 Lippincott Williams Wilkins.