Distribution and pharmacology of alpha 6-containing nicotinic acetylcholine receptors analyzed with mutant mice.
The alpha6 subunit of the nicotinic acetylcholine receptor (nAChR) is expressed at very high levels in dopaminergic (DA) neurons. However, because of the lack of pharmacological tools selective for alpha6-containing nAChRs, the role of this subunit in the etiology of nicotine addiction remains unknown. To provide new tools to investigate this issue, we generated an alpha6 nAChR knock-out mouse. Homozygous null mutants (alpha6-/-) did not exhibit any gross neurological or behavioral deficits. A careful anatomic and molecular examination of alpha6-/- mouse brains demonstrated the absence of developmental alterations in these animals, especially in the visual and dopaminergic pathways, where the alpha6 subunit is normally expressed at the highest levels. On the other hand, receptor autoradiography revealed a decrease in [3H]nicotine, [3H]epibatidine, and [3H]cytisine high-affinity binding in the terminal fields of retinal ganglion cells of alpha6-/- animals, whereas high-affinity [125I]alpha-conotoxinMII (alphaCtxMII) binding completely disappeared in the brain. Moreover, inhibition of [3H]epibatidine binding on striatal membranes, using unlabeled alphaCtxMII or cytisine, revealed the absence of alphaCtxMII-sensitive and cytisine-resistant [3H]epibatidine binding sites in alpha6-/- mice, although the total amount of binding was unchanged. Because alphaCtxMII, a toxin formerly thought to be specific for alpha3beta2-containing nAChRs, is known to partially inhibit nicotine-induced dopamine release, these results support the conclusion that alpha6 rather than alpha3 is the partner of beta2 in the nicotinic modulation of DA neurons. They further show that alpha6-/- mice might be useful tools to understand the mechanisms of nicotine addiction, although some developmental compensation might occur in these mice.
Champtiaux
Nicolas
N
Laboratoire de Neurobiologie Moléculaire, Centre National de la Recherche Scientifique, Unité de Recherche Associée 2182, Récepteurs et Cognition, Institut Pasteur 75724 Paris, Cedex 15, France. champtia@pasteur.fr
Han
Zhi-Yan
ZY
Bessis
Alain
A
Rossi
Francesco Mattia
FM
Zoli
Michele
M
Marubio
Lisa
L
McIntosh
J Michael
JM
Changeux
Jean-Pierre
JP
D000470:Alkaloids / Q000378:metabolism / Q000493:pharmacokinetics; D000818:Animals; D001345:Autoradiography; D001392:Azocines; D001665:Binding Sites / Q000502:physiology; D001667:Binding, Competitive / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000166:cytology / Q000378:metabolism; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism / Q000493:pharmacokinetics; D020916:Conotoxins / Q000494:pharmacology; D003342:Corpus Striatum / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism; D006720:Homozygote; D051379:Mice; D018345:Mice, Knockout; D008817:Mice, Mutant Strains; D009538:Nicotine / Q000378:metabolism / Q000493:pharmacokinetics; D018733:Nicotinic Antagonists / Q000494:pharmacology; D009928:Organ Specificity / Q000502:physiology; D021122:Protein Subunits; D011725:Pyridines / Q000378:metabolism / Q000493:pharmacokinetics; D011807:Quinolizines; D011978:Receptors, Nicotinic / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000378:metabolism; D014029:Tobacco Use Disorder / Q000378:metabolism; D014795:Visual Pathways / Q000378:metabolism; D000093843:Quinolizidine Alkaloids
D000470:Alkaloids; D001392:Azocines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D020916:Conotoxins; D004298:Dopamine; D009538:Nicotine; D018733:Nicotinic Antagonists; D021122:Protein Subunits; D011725:Pyridines; D011807:Quinolizines; D011978:Receptors, Nicotinic; C098872:alpha-conotoxin MII; C004712:cytisine; D000093843:Quinolizidine Alkaloids; C082748:epibatidine