CNQX INFUSED INTO ENTORHINAL CORTEX BLOCKS MEMORY EXPRESSION, AND AMPA REVERSES THE EFFECT

Rats were trained in a step-down inhibitory avoidance task using a 0.8 -mA foot shock and tested for retention 26 days later. Three to five d ays prior to the retention test they were bilaterally implanted with c annulae aimed at the entorhinal cortex. Ten minutes before testing the y received an infusion, into the entorhinal cortex, of vehicle, ciano- nitro-quinoxaline-dione (CNQX; 0.5 mu g), amino-hydroxy-methyl-isoxalo ne-propionate (AMPA; 1.0 or 2.5 mu g), or AMPA (1.0 mu g) plus CNQX (0 .5 mu g). CNQX blocked memory expression; the effect lasted less than 90 min. AMPA had no effect of its own, but at the lower dose level it counteracted the depressant influence of CNQX. It is not likely that t he effect of CNQX could have been due to an influence on performance: In separate sets of experiments the bilateral intraentorhinal infusion of CNQX (0.5 mu g) 10 min before training did not affect either acqui sition or retention of the avoidance task or general activity during 3 min of free exploration in the training box. The results indicate tha t the integrity of AMPA receptors in the entorhinal cortex is necessar y for memory expression.