Expression of α4-1 and α5 Nicotinic Cholinoceptor mRNA in the Aging Rat Cerebral Cortex

Although important in neurodegeneration, systematic studies of nicotinic acetylcholine receptor expression in normal aging human brains are difficult to perform. We have studied the expression of nicotinic receptor α4-1 and α5 mRNA in the frontal and parietal isocortex of 3-(young adult), 24- (late middle aged), and 33-month-old (old) rats by nonisotopic in situ hybridization. In all groups transcripts were mainly present in layer II/III and V pyramidal neurons. The numerical densities of α4-1 mRNA-containing neurons with respect to those of cresyl violet-stained neurons decreased with aging in the rat frontal and parietal cortex, while those of α5 mRNA-containing neurons were not affected. These findings point to an age-related decrease of the percentages of numerical densities of α4-1 mRNA-containing neurons, which has to be taken into account as a possible substrate for the well-known decrease of nicotine binding sites in the aging cerebral cortex.