Increased Nicotinic Acetylcholine Receptor Protein Underlies Chronic Nicotine-Induced Up-Regulation Of Nicotinic Agonist Binding Sites In Mouse Brain

Department

neurobiology

Document Type

Article

Abstract

Chronic nicotine treatment elicits a brain region-selective increase in the number of high-affinity agonist binding sites, a phenomenon termed up-regulation. Nicotine-induced up-regulation of α4β2-nicotinic acetylcholine receptors (nAChRs) in cell cultures results from increased assembly and/or decreased degradation of nAChRs, leading to increased nAChR protein levels. To evaluate whether the increased binding in mouse brain results from an increase in nAChR subunit proteins, C57BL/6 mice were treated with nicotine by chronic intravenous infusion. Tissue sections were prepared, and binding of [ 125I]3-((2S)-azetidinylmethoxy)-5-iodo-pyridine (A85380) to β2*-nAChR sites, [ 125I]monoclonal antibody (mAb) 299 to α4 nAChR subunits, and [ 125I]mAb 270 to β2 nAChR subunits was determined by quantitative autoradiography. Chronic nicotine treatment dose-dependently increased binding of all three ligands. In regions that express α4β2-nAChR almost exclusively, binding of all three ligands increased coordinately. However, in brain regions containing significant β2*-nAChR without α4 subunits, relatively less increase in mAb 270 binding to β2 subunits was observed. Signal intensity measured with the mAbs was lower than that with [ 125I]A85380, perhaps because the small ligand penetrated deeply into the sections, whereas the much larger mAbs encountered permeability barriers. Immunoprecipitation of [1 25I] epibatidine binding sites with mAb 270 in select regions of nicotine-treated mice was nearly quantitative, although somewhat less so with mAb 299, confirming that the mAbs effectively recognize their targets. The patterns of change measured using immunoprecipitation were comparable with those determined autoradiographically. Thus, increases in α4β2*-nAChR binding sites after chronic nicotine treatment reflect increased nAChR protein. Copyright © 2011 by The American Society for Pharmacology and Experimental Therapeutics.

Publication Date

4-1-2011

Publication Title

Journal of Pharmacology and Experimental Therapeutics

ISSN

00223565

Volume

337

Issue

1

First Page

187

Last Page

200

Digital Object Identifier (DOI)

10.1124/jpet.110.178236

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