Reversible inactivation of the medial septal area impairs consolidation but not retrieval of passive avoidance learning in rats

Involvement of the medial septal area (MSA) in consolidation and retrieval of passive avoidance response (PAR) was investigated with functional suppression of this area by tetrodotoxin (TTX). Rats carrying a chronically implanted cannula aimed at the MSA were trained on a step-through passive avoidance task and received intraseptal injection of 5 ng TTX dissolved in 1 mu l saline 5, 90 and 360 min after the acquisition trial or 60 min before the retrieval test. TTX injected 5 and 90 min after the acquisition trial significantly reduced avoidance of the dark compartment in comparison with the control group injected with saline. PAR was not impaired by septal TTX injected 360 min after acquisition or 60 min before the retrieval test. Step-through latency of naive rats was not affected by septal blockade. The results indicate that the MSA contributes to PAR consolidation at least 90 min after acquisition but its involvement in PAR retrieval is unlikely. It is concluded that functional ablation of the MSA may disrupt integrity of subcortical circuits participating in PAR learning.