Effects of MPEP on avoidance learning in rats.

In recent years metabotropic glutamate receptors (mGluRs) have received considerable attention as a potential target for psychotropic drugs, but their influence on learning and memory is still unclear. The aim of the present study was to examine whether intraperitoneal (i.p.) administration of selective mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyrydine (MPEP), injected prior to, immediately after or 30 min after training, affects acquisition and/or retrieval of the inhibitory step-down and active shuttle-box avoidance in rats. Our results indicate that 5 or 10 mg/kg i.p. MPEP in all tested groups impaired memory consolidation of step-down training without affecting acquisition and had no effect on learning and retention in shuttle-box trained rats. The data are in agreement with the statement that mGluR5s may contribute very little and task-dependently to the actual acquisition of new information, but memory formation, appears to require mGluR5s through modulation of consolidation and/or recall.