Late posttraining memory processing by entorhinal cortex: Involvement of NMDA and GABAergic receptors

Abstract

The NMDA receptor antagonist, D-2-amino-5-phosphonopentanoic acid (AP5) (5 μg) and the GABA A receptor agonist, muscimol (0.03 μg) were infused bilaterally into the entorhinal cortex of rats 0, 90, 180, or 360 min after training in habituation to a novel environment or in step-down inhibitory avoidance. Animals were tested for retention 22 h after training in each task. AP5 and muscinol were amnestic for both tasks when given 90 or 180 min after training, but had no effect when given 0 or 360 min after training. In contrast, intraamygdala injections or AP5 or muscimol were amnestic when given 0 but not 90 min after inhibitory avoidance training. The results indicate that the entorhinal cortex plays a late but important role in posttraining memory processing; this role involves glutamatergic NMDA receptors and is inhibited by GABA A receptors. The intervention of the entorhinal cortex in posttraining memory processing is subsequent, and could be secondary, to that of the amygdala and other limbic structures.