Age related decrease in the density of dopamine D1 and D2 receptors in corpus striatum of rats.

The densities (Bmax) and apparent dissociation constants (Kd) of D1 and D2 receptors in striatum and of 5-HT2 receptors in cortex of rats aged 1, 3, 7 and 12 months have been determined using 3H-SCH 23390, 3H-spiperone and 3H-ketanserin, respectively, as ligands. No changes in Kd's were seen. The density of D1 receptors decreases continuously from 1 month, attaining approximately 65% at 12 months of age. The density of D2 receptors increases slightly from 1 to 3 months, followed by a decrease until 12 months of age, where the level is approximately 80% of the 1 month value. The rise D2 receptor density is less apparent when calculated on a protein basis due to a concomitant increase in protein content of corpus striatum. The ratio between D1 and D2 receptors remains constant, approximately 4.2, from 1 to 12 months of age. The density of 5-HT2 receptors decreased from 1 to 7 months and remained at this level also after 12 months.