The effect of aging on rat striatal D1 receptor mRNA-containing neurons

In situ hybridization of a digoxigenin-labeled oligonucleotide probe combined with computer assisted image assessment was used to directly visualize D1 dopamine receptor mRNA-containing neurons in rat striata, and quantify age-related changes in the sizes and relative mRNA content of these neurons. It was found that 1) numbers of D1 mRNA-containing neurons appear to decrease in striata of aged rats; 2) relative amounts of D1 receptor mRNA in individual striatal neurons do not change during aging; and 3) neurons of all sizes appear to be lost, with the greatest absolute decrease in those larger than 150 microns2. These data confirm the age associated loss of D1 dopamine receptors reported for some other rat strains in that species, and further suggest that neuronal loss is responsible for the decrement. The latter finding contrasts with the aging associated loss of D2 dopamine receptors, which additionally involves decreased amounts of mRNA per cell.