COMPARISON OF THE REGIONAL EXPRESSION OF NICOTINIC ACETYLCHOLINE-RECEPTOR ALPHA-7 MESSENGER-RNA AND [I-125] ALPHA-BUNGAROTOXIN BINDING IN HUMAN POSTMORTEM BRAIN

Neuronal nicotinic acetylcholine receptors are expressed in the human central nervous system. A specific subtype of this receptor family, th e alpha 7 nicotinic acetylcholine receptor, is thought to be the princ ipal alpha-bungarotoxin (alpha BTX)-binding protein in mammalian brain . Although the expression of this receptor subtype has been characteri zed in rat, no study has specifically compared the expression of both the alpha 7 gene and the localization of BTX binding sites in human br ain. Expression of alpha 7 mRNA and receptor protein in human postmort em brain tissue was examined by in situ hybridization and [I-125]-alph a-bungarotoxin autoradiography, respectively, with particular emphasis on regions associated with sensory processing. Regions with high leve ls of both alpha 7 gene expression and [I-125]-alpha BTX binding inclu de the nucleus reticularis of the thalamus, the lateral and medial gen iculate bodies, the basilar pontine nucleus, the horizontal limb of th e diagonal band of Broca, the nucleus basalis of Meynert, and the infe rior olivary nucleus. High-to-moderate levels of alpha 7 probe hybridi zation were also seen in the hippocampus and the cerebral cortex; howe ver, there was a reduced or variable degree of [I-125]-alpha BTX bindi ng in these regions compared with the level of probe hybridization. In most brain regions, [I-125]-alpha BTX binding was localized to neuron al cell bodies similar in morphology to those that exhibited alpha 7 h ybridization, suggesting that the high-affinity [I-125]-alpha BTX bind ing sites in the human brain are likely to be principally composed of alpha 7 receptor subtypes. (C) 1997 Wiley-Liss, Inc.