Abstract
The density (Bmax) and apparent dissociation constant (KD) of dopamine D1 and D2 receptors in striatum was estimated in rats of different ages (from 3.5 to 25 months) using 3H-SCH 23390 and 3H-spiperone as ligands. The density of D1 and D2 receptors decreases with age attaining 70 and 69% of the 3.5 months'' value, respectively, whereas the KD''s remain constant. The decreases in density of D1 and D2 receptors are parallel. Thus, throughout life the ratio between the density of D1 and D2 receptors remains constant.