Neuronal nicotinic acetylcholine receptors (nAChRs) are likely candidate genes to be involved in mediating nicotine dependence. These pentameric ion channels are present in the peripheral and central nervous systems, including dopaminergic neurons, and are activated by endogenous acetylcholine and exogenous nicotine (Mineur and Picciotto, 2008). The CHRNA6 and CHRNB3 genes coding for the α6 and β3 receptor subunits are located contiguously in a tail to tail configuration on chromosome 8. Their protein products are co-localized in nicotinic receptors in the substantia nigra, ventral tegmental area, striatum, and locus coeruleus (Gotti et al, 2006). Located on chromosome 8 at position 8p11.21, CHRNA6 spans 16.01 kb (NCBI Build 35) and has at least three alternatively spliced transcripts. CHRNB3 is located on chromosome 8 at position 8p11.2, and spans 39.99 kb. Six exons can be alternatively spliced into at least three different transcripts (GeneCards: http://www.genecards.org (Rebhan et al, 1998)).
