Hippocampus-Dependent Retrieval and Hippocampus-Independent
Extinction of Place Avoidance Navigation, and Stress-Induced Out-of-Context
Activation of a Memory Revealed by Reversible Lesion Experiments
in Rats
K. JEŽEK1, M. WESIERSKA2, A. A. FENTON1,3
1Institute of Physiology, Academy of Sciences of the
Czech Republic, Prague, Czech Republic,
2Nencki Institute of Experimental Biology, Warsaw,
Poland and 3Department of Physiology and Pharmacology,
State University of New York, Downstate Medical Center, New
York, USA
Summary
The use of reversible lesion techniques in memory research was
pioneered in the laboratory of Jan Bureš and Olga Burešova. We
use the occasion of Jan’s 75th birthday to briefly review the
experimental utility of this approach. Two experiments from our
current research are reported in which reversible lesioning
methods are used to ask otherwise experimentally untenable
questions about memory retrieval. The first experiment used
intra-hippocampal injections of tetrodotoxin to temporarily
inactivate the hippocampus during retrieval of a well-learned
place avoidance navigation memory. This revealed that the
hippocampus is necessary for place avoidance retrieval but that
the extinction of place avoidance can occur independently of
retrieving the memory and intact hippocampal function. The
second experiment used KCl-induced cortical spreading depression
in an interhippocampal transfer paradigm to demonstrate that a
Y-maze memory that is learned by only one cortical hemisphere
can be made to transfer to the other hemisphere by forcing the
rat to swim, a unique stressful experience that occurred in a
different apparatus, different behavioral context, and involved
different behaviors than the Y-maze training. This demonstrates,
we believe for the first time behaviorally, that memories can be
activated outside of the behavioral context of their acquisition
and expression in rats.
Reprint
requests
Dr. André Fenton, Institute of Physiology, Academy of Sciences
of the Czech Republic, Videnska 1083, 142 20 Prague 4, Czech
Republic. Fax: +420 2 4106 24 88. email:
fenton@biomed.cas.cz
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