[Molecular diversity and properties of brain nicotinic acetylcholine receptor].
To date, cDNA studies and purification of nicotinic acetylcholine receptors (nAChRs) have shown that there are many different subtypes of the receptors in the central and peripheral nervous systems. This review focuses on the animal and avian brain nAChRs, their diversity, pharmacological properties, distribution and regulation. nAChR subtypes are classified as alpha beta types and alpha-bungarotoxin binding proteins. Each subtype contains two or more subunits. Each subunit combination leads to a distinct pattern of sensitivity to nicotinic agonists in reconstituted systems of Xenopus oocytes. Nicotine has been shown to increase the levels of intracellular free Ca through both nAChR types. The mRNAs for each subunit are uniquely expressed in animal and avian brains, although beta 2 is expressed in most regions of the brains. This shows somewhat overlapping patterns of gene expression. Monoclonal antibodies against each subunit make it possible to investigate the distribution of the subunits in brains and neurons. nAChRs have been shown to be regulated by nicotine administration and phosphorylation of the receptors. The regulatory mechanisms have been extensively studied, but still remain obscure. The structural and functional diversity of neuronal nAChRs is probably important in nicotine addiction, tolerance and reverse tolerance.