Diminution of nicotinic receptor alpha 3 subunit mRNA expression in aged rat brain

Losses in nicotinic acetylcholine receptors (nAChRs) have been linked to a decline in cognitive function in patients with neurodegenerative diseases, but the impact of normal aging on the different neuronal nicotinic receptor subunits has yet to be fully characterized. The expression pattern of nine nAChR subunits mRNA (alpha 2-7 and beta 2-4) was investigated in this study in young and aged rat brains, 5 weeks and 30 months old, respectively. Microtissue samples were dissected from brain slices and nAChR subunit mRNA expression was analyzed by reverse transcription polymerase chain reaction (RT-PCR) from eight different brain areas. In several regions, a loss of PCR signal was found for the alpha 3, and to a lesser extent, for alpha 2 subunit mRNA in aged rat brain. A relative quantification of alpha 3 and alpha 4 mRNA expression was then carried out in four of these brain regions. A significant diminution of alpha 3 expression level was observed in all regions tested while, in comparison, much less modification in alpha 4 mRNA was detected. This decrease in alpha 3 subunit mRNA may represent a selective degradation of neurons expressing the alpha 3 subunit or a diminution of alpha 3-containing nAChR subtypes in those neurons during aging. (C) 1999 Elsevier Science B.V. All rights reserved.