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Cerebral Cortex Advance Access originally published online on January 28, 2009
Cerebral Cortex 2009 19(10):2411-2427; doi:10.1093/cercor/bhn258
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© The Author 2009. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org

Involvement of Nicotinic and Muscarinic Receptors in the Endogenous Cholinergic Modulation of the Balance between Excitation and Inhibition in the Young Rat Visual Cortex

Estelle Lucas-Meunier1, Cyril Monier2, Muriel Amar1, Gérard Baux1, Yves Frégnac2 and Philippe Fossier1

1 Laboratoire de neurobiologie cellulaire et moléculaire, UPR CNRS 9040, 91198 Cedex, Gif-sur-Yvette, France, 2 Unité de neurosciences intégratives et computationnelles, UPR CNRS 2191, 91198 Cedex, Gif-sur-Yvette, France

Address correspondence to email: mamar{at}nbcm.cnrs-gif.fr.

This study aims to clarify how endogenous release of cortical acetylcholine (ACh) modulates the balance between excitation and inhibition evoked in visual cortex. We show that electrical stimulation in layer 1 produced a significant release of ACh measured intracortically by chemoluminescence and evoked a composite synaptic response recorded intracellularly in layer 5 pyramidal neurons of rat visual cortex. The pharmacological specificity of the ACh neuromodulation was determined from the continuous whole-cell voltage clamp measurement of stimulation-locked changes of the input conductance during the application of cholinergic agonists and antagonists. Blockade of glutamatergic and {gamma}-aminobutyric acid (GABAergic) receptors suppressed the evoked response, indicating that stimulation-induced release of ACh does not directly activate a cholinergic synaptic conductance in recorded neurons. Comparison of cytisine and mecamylamine effects on nicotinic receptors showed that excitation is enhanced by endogenous evoked release of ACh through the presynaptic activation of {alpha}*β4 receptors located on glutamatergic fibers. DHβE, the selective {alpha}4β2 nicotinic receptor antagonist, induced a depression of inhibition. Endogenous ACh could also enhance inhibition by acting directly on GABAergic interneurons, presynaptic to the recorded cell. We conclude that endogenous-released ACh amplifies the dominance of the inhibitory drive and thus decreases the excitability and sensory responsiveness of layer 5 pyramidal neurons.

Key Words: acetylcholine • cortical network • patch-clamp • pyramidal neuron • rat visual cortex • synaptic integration

Estelle Lucas-Meunier and Cyril Monier have contributed equally to this work.


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