Cerebral Cortex Advance Access originally published online on October 26, 2006
Cerebral Cortex 2007 17(8):1948-1957; doi:10.1093/cercor/bhl104
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Extensive Overlap of Mu-Opioid and Nicotinic Sensitivity in Cortical Interneurons
1 Laboratoire de Neurobiologie et Diversité Cellulaire, CNRS UMR 7637, École Supérieure de Physique et de Chimie Industrielles, 75005 Paris, France, 2 Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
Address correspondence to Dr Bertrand Lambolez, NPA, CNRS UMR 7102, UPMC, 9 quai St Bernard, 75005 Paris, France. Email: bertrand.lambolez{at}snv.jussieu.fr.
We studied µ-opioid transmission in acute slices of rat neocortex using whole-cell recordings and single-cell reverse transcriptionpolymerase chain reaction. The µ-opioid receptor (MOR) was found in
-aminobutyric acidergic (GABAergic) interneurons that were either layer I cells frequently expressing neuropeptide Y or layers IIV cells expressing vasoactive intestinal peptide and enkephalin (Enk). We found that µ-opioid agonists inhibit these interneurons that are selectively excited by nicotinic agonists. The extensive overlap of µ-opioid and nicotinic responsiveness allowed µ-opioid agonists to inhibit nicotinic excitation of responsive interneurons and of their GABAergic output onto pyramidal cells. Finally, nicotinic stimulation resulted in a dynamic sequence where GABAergic transmission was first enhanced and then depressed below its baseline. This latter disinhibitory effect was prevented by a µ-opioid antagonist, indicating that excitation of nicotinic-responsive interneurons induced the release of endogenous Enk, which in turn led to MOR activation. Our results suggest that neocortical µ-opioid transmission acts as an inhibitory feedback onto nicotinic-responsive interneurons, which may change network excitability and inhibition patterns during cholinergic excitation.
Key Words: enkephalin GABAergic interneuron µ-opioid receptor neocortex nicotinic receptor
Funding to pay the Open Access publication charges for this article was provided by Grant-in-Aid for Scientific Research on Priority Areas (Molecular Brain Science) from the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 17024055).