An autoradiographic survey of mouse brain nicotinic acetylcholine receptors defined by null mutants

Nine nicotinic receptor subunits are expressed in the central nervous system indicating that a variety of nicotinic acetylcholine receptors (nAChR) may be assembled. A useful method with which to identify putative nAChR is radioligand binding. In the current study the binding of [I-125]alpha-bungarotoxin, [I-125]alpha-conotoxinMII, 5[I-125]-3-((2S)-azetidinylmethoxy)pyridine (A-85380), and [I-125]epibatidine has been measured autoradiographically to provide data on many nAChR binding sites. Each binding site was evaluated semi-quantitatively for samples prepared from wild-type and alpha 2, alpha 4, alpha 6, alpha 7, beta 2, beta 4, alpha 5 and beta 3 null mutant mice. Deletion of the alpha 7 subunit completely and selectively eliminated [I-125]alpha- bungarotoxin binding. The binding of [I-125]alpha-conotoxinM11 was eliminated in most brain regions by deletion of either the a6 or 132 subunit and is reduced by deletion of either the a4 or 133 subunit. The binding of 5[I-125]A-85380 was completely eliminated by deletion of the beta 2 subunit and significantly reduced by deletion of the alpha 4 subunit. Most, but not all, alpha 4-independent sites require expression of the alpha 6 subunit. The effect of gene deletion on total [I-125]epibatidine binding was very similar to that on [I-125]A-85380 binding. [I-125]Epibatidine also labels beta 4* nAChR, which was readily apparent for incubations conducted in the presence of 100 nM cytisine. The effects of alpha 3 gene deletion could not be evaluated, but persistence of residual sites implies the expression of alpha 3* nAChR. Taken together these results confirm and extend previously published evaluations of the effect of nAChR gene deletion and help to define the nAChR subtypes measurable by ligand binding. (C) 2011 Elsevier Inc. All rights reserved.