John Daly's Compound, Epibatidine, Facilitates Identification of Nicotinic Receptor Subtypes

J Mol Neurosci (2010) 40:96104 DOI 10.1007/s12031-009-9264-x

John Dalys Compound, Epibatidine, Facilitates Identification of Nicotinic Receptor Subtypes

Michael J. Marks & Duncan S. Laverty &

Paul Whiteaker & Outi Salminen & Sharon R. Grady &

J. Michael McIntosh & Allan C. Collins

Received: 6 July 2009 /Accepted: 20 July 2009 /Published online: 12 August 2009 # Humana Press 2009

Abstract The diversity of nicotinic acetylcholine receptor (nAChR) subtypes was explored by measuring the effects of gene deletion and pharmacological diversity of epibati-dine binding sites in mouse brain. All epibatidine binding sites require expression of either the 7, 2, or 4 subunit. In agreement with general belief, the 42*-nAChR and 7-nAChR subtypes are major components of the epibati-dine binding sites. 42*-nAChR sites account for approximately 70% of total high- and low-affinity epibati-dine binding sites, while 7-nAChR accounts for 16% of the total sites all of which have lower affinity for epibatidine. The other subtypes are structurally diverse. Although these minor subtypes account for only 14% of total binding in whole brain, they are expressed at relatively high concentrations in specific brain areas indicating unique functional roles.

Keywords Neuronal nicotinic acetylcholine receptors . Epibatidine . Null mutant mice . -Bungarotoxin . Cytisine . -Conotoxin MII

Introduction

Ligand binding assays have been used for over 40 years to identify and characterize nicotinic cholinergic receptors (nAChRs) in brain. Indeed, the first studies that showed that [125I]--bungarotoxin (Patrick and Stallcup 1977) and [3H]-nicotine (Romano and Goldstein 1980) bind with high affinity to membranes derived from rat brain provided some of the first evidence that suggested that nAChRs might be expressed in brain. Subsequent studies that compared the anatomical distributions and biochemical properties of these binding sites in rat (Clarke et al. 1985) and mouse (Marks and Collins 1982) brain yielded the first evidence that more than one nAChR subtype is expressed in brain. When the nine nAChR subunit genes that are expressed in mammalian brain (27, 24) were cloned and sequenced nearly 20 years ago, the number of potential subtypes expanded dramatically. Much of the recent research in the nAChR field is attempting to identify the subunit compositions of those receptor subtypes that are actually expressed (i.e., native receptors) in brain as well as other tissues (reviewed in Millar and...