SEQUENTIAL ROLE OF HIPPOCAMPUS AND AMYGDALA, ENTORHINAL CORTEX AND PARIETAL CORTEX IN FORMATION AND RETRIEVAL OF MEMORY FOR INHIBITORY AVOIDANCE IN RATS

The hippocampus and amygdala, the entorhinal cortex and the parietal c ortex participate, in that sequence, both in the formation and in the expression of memory for a step-down inhibitory avoidance task in rats . Bilateral infusion of AP5 or muscimol caused retrograde amnesia when given 0 min after training into both hippocampus and amygdala, when g iven or 180 min after training into the entorhinal cortex, or when giv en 180 min after training into the parietal cortex. Therefore, memory formation requires the sequential and integrated activity of all these areas mediated by glutamate NMDA receptors in each case. Pre-test adm inistration of CNQX 1 day after training into hippocampus and amygdala , 1 or 31 days after training in entorhinal cortex, or 1, 31 or 60 day s after training in the parietal cortex temporarily blocked retention test performance. Therefore, 1 day after training, all these brain str uctures are necessary for retrieval; 1 month later, the hippocampus an d amygdala are no longer necessary for retrieval but the entorhinal an d parietal cortex still are; and 60 days after training only the parie tal cortex is needed. In all cases the mechanisms of retrieval require intact glutamate AMPA receptors.