EXCITATORY AMINO-ACID RECEPTORS WITHIN NUCLEUS-ACCUMBENS SUBREGIONS DIFFERENTIALLY MEDIATE SPATIAL-LEARNING IN THE RAT

The present experiments investigated the effects of excitatory amino a cid antagonists, infused into core and shell subregions of the nucleus accumbens, on spatial behavior in the rat. A food-search task was use d, in which animals learn a specific pattern of food gathering; durati on of each trial (time taken to gather all four pellets) and number of errors (visits to empty holes) were measured. In experiment 1, animal s first underwent training, and subsequently were given microinfusions of either D-2-amino-5 phosphonopentanoic acid (AP-5), an N-methyl-D-a spartate (NMDA) antagonist (0, 0.2, 1.0 mu g/0.5 mu l), or 6,7-dinitro quinoxaline-2,3-dione (DNQX), an antagonist of lpha-amino-3-hydroxy-5- methylisoxazole-4-propionic acid (AMPA) and kainate receptors (0, 0.07 5, 0.75 mu g/0.5 mu l). AP-5 significantly increased trial duration in both core and shell groups, but increased errors only in the core gro up. DNQX treatment also impaired performance in both groups, but the e ffect was greater in the core group compared with the shell group. In experiment 2, animals were treated during acquisition. Rats infused wi th AP-5 (1 mu g/0.5 mu l) took significantly longer to finish trials, made more errors and showed a marked learning impairment across days. AP-5 impaired learning in both core and shell groups, but the disrupti on was significantly greater in the core group. DNQX (0.75 mu g/0.5 mu l) also impaired learning when infused into the core during acquisiti on; however the pattern of disruption contrasted markedly with that of AP-5. DNQX in the shell had no effect on trial duration during learni ng. It is hypothesized that both NMDA and non-NMDA receptors in the nu cleus accumbens mediate spatial learning and performance, and that NMD A receptors may have a relatively more important role in memory or ret rieval mechanisms. Moreover, the core subregion may be preferentially involved in the control of spatial behavior.