Effects of coupled perirhinal cortex and medial septal area, fimbria-fornix, entorhinal cortex tetrodotoxin inactivations on passive avoidance consolidation in the rat.

In order to ascertain the rat perirhinal cortex (PC) function during early consolidation of a passive avoidance response (PAR), and to ascertain whether there are some functional interactions with the medial septal area (MSA), the fimbria-fornix complex (FF) and the entorhinal cortex (EC), PC-MSA, PC-FF, and PC-EC coupled inactivations were performed immediately after the PAR acquisition session. Anesthetized male adult Wistar rats aged 60 days were treated with stereotaxical bilateral injections of TTX (5 ng in 0.5 microl saline) in the appropriate sites. Retrieval testing was performed 48 h later. It was shown that all three coupled inactivations were followed by significant PAR disruption. It may be concluded that PC is somehow active even during the first mnemonic phase following the acquisition session, thus better defining PC mnemonic involvement chronology. These results may be taken as indicating that during initial consolidation the engram is concurrently processed in more than one septal and parahippocampal site, each of which by itself is not absolutely necessary for the final engram formation.