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Cerebral Cortex Advance Access published online on March 4, 2008
Cerebral Cortex, doi:10.1093/cercor/bhn020
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© The Author 2008. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Learning-Dependent, Transient Increase of Activity in Noradrenergic Neurons of Locus Coeruleus during Slow Wave Sleep in the Rat: Brain Stem–Cortex Interplay for Memory Consolidation?

Oxana Eschenko1 and Susan J. Sara2

Neuromodulation, Neuroplasticity & Cognition, CNRS, UMR 7102, University of P & M Curie, Paris, France

Address correspondence to Dr. Susan J. Sara, LPPA, CNRS, UMR 7252, Collège de France, 75005, Paris, France. Email: sjsara{at}ccr.jussieu.fr.

Memory consolidation during sleep is regaining attention due to a wave of recent reports of memory improvements after sleep or deficits after sleep disturbance. Neuromodulators have been proposed as possible players in this putative off-line memory processing, without much experimental evidence. We recorded neuronal activity in the rat noradrenergic nucleus locus coeruleus (LC) using chronically implanted movable microelectrodes while monitoring the behavioral state via electrocorticogram and online video recording. Extracellular recordings of physiologically identified noradrenergic neurons of LC were made in freely behaving rats for 3 h before and after olfactory discrimination learning. On subsequent days, if LC recording remained stable, additional learning sessions were made within the olfactory discrimination protocol, including extinction, reversals, learning new odors. Contrary to the long-standing dogma about the quiescence of noradrenergic neurons of LC, we found a transient increase in LC activity in trained rats during slow wave sleep (SWS) 2 h after learning. The discovery of learning-dependent engagement of LC neurons during SWS encourages exploration of brain stem–cortical interaction during this delayed phase of memory consolidation and should bring new insights into mechanisms underlying memory formation.

Key Words: cortical replay • electrophysiology • memory consolidation • neuromodulation • noradrenaline • slow wave sleep

1 Present address: Max Planck Institute for Biological Cybernetics, Department of Physiology of Cognitive Processes, Spemannstr. 38, D-72076 Tübingen, Germany.

2 Present address: College de France, Centre National de la Recherche Scientifique, UMR 7152, F-75005, Paris, France.


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