N-METHYL-D-ASPARTATE RECEPTORS IN THE NUCLEUS-ACCUMBENS ARE INVOLVED IN DETECTION OF SPATIAL NOVELTY IN MICE

The aim of this study was to investigate the role played by intra-accu mbens N-methyl-D-aspartate (NMDA) receptors in spatial information enc oding. For this purpose, the effect of local administration of both co mpetitive (AP-5) and non-competitive (MK-801) NMDA antagonists was ass essed in a task designed to estimate the ability of rodents to encode spatial relationships between discrete stimuli. The task consists of p lacing mice in an open field containing five objects and, after three sessions of habituation, examining their reactivity to object displace ment (spatial novelty) and object substitution (object novelty). The r esults show that both doses of MK-801 (0.15 and 0.3 mu g/side) induced a selective impairment in the capability of mice to detect spatial no velty. A similar effect was obtained by injecting the low dose of the competitive antagonist AP-5 (0.1 mu g/side), whereas the high dose (0. 15 mu g/side) abolished detection of both spatial and object novelty T aken together, these results show that intra-accumbens injections of l ow doses of competitive and non-competitive NMDA antagonists can produ ce selective deficits in processing spatial information resembling tho se observed after hippocampal damage. Moreover, the fact that pharmaco logical treatments spare memory processes involved in habituation sugg ests that NMDA antagonists may interfere with the formation of spatial representations rather than producing memory deficits per se.