AMNESIC EFFECTS OF PREACQUISITION, POSTACQUISITION, OR PRERETRIEVAL TETRODOTOXIN ADMINISTRATION INTO THE MEDIAL SEPTAL AREA ON RATS PASSIVE-AVOIDANCE MEMORIZATION

By means of local administration of tetrodotoxin (TTX) fully reversibl e functional inactivation of the medial septal area (MSA) of the rat w as obtained in order to define the role of this structure in the reten tion of a conditioned passive avoidance response (PAR). In permanently cannulated animals, TTX (5 ng in 0.5 mu l saline) or saline (0.5 mu l ) was injected in the MSA. TTX or saline was administered to six diffe rent groups of rats, respectively 1 h before PAR acquisition, immediat ely after PAR acquisition, and 1 h before PAR retrieval, performed 48 h after the acquisition trial. It was shown that MSA preacquisition an d preretrieval TTX injections were followed by significant PAR retenti on impairment, while postacquisition TTX administration had no effect on PAR retention. The results indicate a well-defined mnemonic role of MSA during the acquisition and retrieval periods but not during the c onsolidation of PAR engram. The experimental evidence is discussed in relation to other reports and to MSA connectivity with other subcortic al structures, (C) 1996 Academic Press, Inc.