Lesions of the fornix but not the entorhinal or perirhinal cortex interfere with contextual fear conditioning.
Bilateral infusion of CNQX (1.0 micrograms) into the entorhinal cortex 10 min before retention tests blocked the expression of habituation to a novel environment and of step-down inhibitory avoidance in rats. Memory expression was found to be recovered in a second test session carried out 120 min after the infusions in the avoidance task; this was not measured in the habituation task. The data suggest that memory expression of these two tasks depends on non-NMDA receptor-mediated mechanisms, perhaps the expression of LTP, in the entorhinal cortex. Previous experiments had suggested similar mechanisms in the hippocampus and the amygdala. It is possible that, under normal conditions, memory expression may depend on the coordinated activity of the three brain structures.