During the past decade, the availability of radiolabeled nicotine with high specific activity has led to the discovery and mapping of nicotine binding sites in the mammalian brain. These data suggested that the mammalian brain contains an important nicotinic receptor system. This chapter discusses the family of brain nicotinic acetylcholine receptors that have discovered in the past few years through the use of the molecular genetic approach. It identifies seven genes in the rat or mouse genome that code for proteins with homology to the nicotinic acetylcholine receptor. These genes are expressed in the mammalian brain and in some peripheral neurons. The primary structures of the brain nicotinic receptor subunits expressed in the brain have been deduced from the sequences of the cDNA clones. Analysis of the hydrophobicity profiles of the brain nicotinic receptor subunits suggests that they fold through the membrane in an identical manner to the Torpedo fish nicotinic receptor.
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