Intra-ventricular infusion of the NMDA antagonist AP5 impairs performance on a non-spatial operant DRL task in the rat

Rats were trained to lever press on a differential reinforcement of low rates (DRL-18 s) schedule. They were then allocated to four treatment groups. These were: hippocampal aspiration lesions [HIPP]; implantation of osmotic minipumps for intraventricular infusion of either (a) the NMDA receptor antagonist 30 mM D, L-2-amino-5-phosphonopentanoic acid [AP5] or (b) vehicle [VEH]; and an unoperated control group [UNOP]. In subsequent DRL testing, the HIPP group showed a profound and enduring loss of efficiency, resulting from an increased tendency to respond too early; the AP5 group showed a qualitatively similar, but less severe, impairment followed by full recovery once the minipumps had expired; the VEH and UNOP groups both maintained their pre-operative levels of efficiency. We conclude that AP5 infusion disrupts temporary memory storage in the hippocampus, and that the hippocampus is concerned with the retention of memories outside the purely spatial domain.