EFFECT OF THE INFUSION OF THE GABA-A RECEPTOR AGONIST, MUSCIMOL, ON THE ROLE OF THE ENTORHINAL CORTEX, AMYGDALA, AND HIPPOCAMPUS IN MEMORY PROCESSES

Rats were bilaterally implanted with cannulae in the entorhinal cortex , amygdala, and hippocampus; after recovery, they were trained in a st ep-down inhibitory avoidance task and tested for retention 24 h later. Muscimol (0.03 mu g) or D-amino-5-phosphonovalerate (5.0 mu g) infuse d in the entorhinal cortex 20 min prior to training inhibited the amne stic effect of the same dose of muscimol infused into this area 100 mi n after training. Thus, memory-relevant information must be processed by the entorhinal cortex at the time of training in order that this co rtex may play a late post-training role in memory processing. Pretrain ing intraentorhinal muscimol administration did not affect the amnesti c effect of the post-training infusion of muscimol into the amygdala a nd hippocampus, or the inhibition of memory expression induced by a pr etest infusion of CNQX into the amygdala and hippocampus or into the e ntorhinal cortex. Pretest intraentorhinal muscimol also did not influe nce the effect of pretest intraamygdala and intrahippocampal CNQX admi nistration. These data indicate that the cells of the entorhinal corte x that are sensitive to pretraining muscimol are not part of the input s that lead to post-training processing by the amygdala and hippocampu s, or to the intervention of the amygdala, hippocampus, and entorhinal cortex in memory expression. The present findings are compatible with the possibility that, instead, the entorhinal cortex may be an output of the amygdala and hippocampus at the time of memory expression. (C) 1994 Academic Press, Inc.