D-1 dopamine receptors labelled with 3H-SCH 23390: decrease in the striatum of aged rats.

The effects of age on the binding parameters of 3H-SCH 23390, the most selective D-1 dopamine receptor ligand available at present, were studied in membrane preparations from rat striatum. When compared with 3 month old animals, there was a significant decrease in the density of 3H-SCH 23390 binding sites in 20 month old (-37%) and in 26 month old (-44%) rats, without alterations in the apparent dissociation constant values. No significant changes in the density or affinity of D-1 DA receptors were observed in 14 month old rats. In view of the behavioural effects mediated by D-1 DA receptors recently described (i.e., grooming, stereotypies and EEG desynchronization), the decrease in the density of these receptors in senescent rats may underlie some of the age-related alterations in dopaminergic functions in the rat brain.