An autoradiographic study of the distribution of binding sites for the novel α7-selective nicotinic radioligand [3H]methyllycaconitine in the mouse brain

被引:110
作者
Whiteaker, P
Davies, ARL
Marks, MJ
Blagbrough, IS
Potter, BVL
Wolstenholme, AJ
Collins, AC
Wonnacott, S [1 ]
机构
[1] Univ Bath, Dept Biol & Biochem, Bath BA2 7AY, Avon, England
[2] Univ Bath, Dept Pharm & Pharmacol, Bath BA2 7AY, Avon, England
[3] Univ Colorado, Inst Behav Genet, Boulder, CO 80309 USA
基金
英国惠康基金;
关键词
acetylcholine; autoradiography; alpha-bungarotoxin; MLA; nicotine; receptor;
D O I
10.1046/j.1460-9568.1999.00685.x
中图分类号
Q189 [神经科学];
学科分类号
071006 ;
摘要
[H-3]-Methyllycaconitine ([H-3]-MLA) is a new radioligand with selectivity for alpha 7-type neuronal nicotinic acetylcholine receptors (nAChRs). In our previous study [Davies, A.R.L., Hardick, D.J., Blagbrough, I.S., Potter, B.V.L., Wolstenholme, A.J. & Wonnacott, S. (1999) Neuropharmacology, 38, 679-690], this radioligand labelled a single class of site in rat brain membranes; its pharmacology and distribution in crudely dissected brain regions closely paralleled that of the well-established alpha 7-ligand [I-125]-alpha-bungarotoxin. However, a small population of [H-3]-MLA binding sites was apparently insensitive to alpha-bungarotoxin. Here we have extended the study to mouse brain, using autoradiography to examine the distribution of [H-3]-MLA and [I-125]-alpha-bungarotoxin binding sites. [H-3]-MLA labelled a single class of site in mouse brain membranes with a K-D of 2.2 nM and a B-max of 45.6 fmol/mg protein. Specific binding, defined by unlabelled MLA (K-i = 0.69 nM), was completely inhibited by (-)-nicotine (K-i = 1.62 mu M), whereas alpha-bungarotoxin inhibited only 85% of specific binding (K-i = 3.5 nM). The distributions of [I-125]-alpha-bungarotoxin and [H-3]-MLA binding sites were compared by autoradiography, and binding was quantitated in 72 brain regions. Binding of both radioligands was highly correlated, with highest densities in the dorsal tegmental nucleus of the pons, colliculi and hippocampus. Serial sections labelled with [H-3]-MLA in the absence or presence of unlabelled MLA or alpha-bungarotoxin provided no evidence for any alpha-bungarotoxin-resistant binding. The results are discussed in terms of binding sites that are inaccessible to alpha-bungarotoxin in membrane preparations. This study demonstrates the utility of [H-3]-MLA for characterization of alpha 7-type nicotinic receptors in mammalian brain, and suggests that it labels a population identical to that defined by [I-125]-alpha-bungarotoxin.
引用
收藏
页码:2689 / 2696
页数:8
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