Studies using mice with 4 nicotinic acetylcholine receptor (nAChR) subunit deficiency (4-/- mice) helped reveal the roles of this subunit in bradycardiac response to vagal stimulation, nicotine-induced seizure activity and anxiety. In order to identify genes that might be related to 4-containing nAChRs activity, we compared the mRNA expression profiles of brains from 4-/- and wild-type mice using Affymetrix U74Av2 microarray. Seventy-seven genes significantly differentiated between these two experimental groups. Of them, the two most down-regulated were Spg21 and Pts genes. Since the targeted mutagenesis of 4 nAChR subunit was done by using two mouse strains, 129SvEv and C57BL/6J, it is possible that genes closely linked to the mutated 4 gene represent the 129SvEv allele and not the control C57BL/6J-driven allele. We examined this possibility by using public database and quantitative RT-PCR. The expression levels of Spg21 and Pts genes that, like 4 gene, are localized on chromosome 9, as well as the expression levels of other genes located on this chromosome, were dependent on the mouse background strain. The 67 differentially expressed genes that are not located on chromosome 9 were further analyzed for over-represented functional annotations and transcription regulatory elements compared to the entire microarray. Genes encoding for proteins involved in tyrosine phosphatase activity, calcium ion binding, cell growth and/or maintenance and chromosome organization were over-represented. Our data enhance the understanding of the molecular interactions involved in 4 nAChR subunit function. They also emphasize the need for careful interpretation of expression microarray studies done on genetically manipulated animals.