Differential effect of aging on3H-SCH 23390 binding sites in the retina and in distinct areas of the rat brain

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Abstract
The effects of age on the binding parameters of the selective D-1 dopamine (DA) receptor antagonist3H-SCH 23390 were studied in membrane preparations from rat striatum, substantia nigra, olfactory tubercle, prefrontal cortex and retina. When compared with 3-month-old animals, there was a significant decrease in the density of3H-SCH 23390 binding sites in the striatum (−25%), substantia nigra (−24%), and olfactory tubercle (−23%), but not in the prefrontal cortex of senescent (23-month-old) rats. The affinity of3H-SCH 23390 for D-1 DA receptors did not change with age in any of the brain areas analyzed. In contrast, the density of3H-SCH 23390 binding sites was higher (+53%) in the retina of aged rats that in 3-month-old controls. Confirming previous studies, we observed that light deprivation induced a significant increment in the density of3H-SCH 23390 binding sites in the retina of adult rats (+31%) but not in the retina of aged animals. The ability of light exposure to activate DAergic neurons in the rat retina was not altered by normal aging. In fact, a similar increase in the concentration of DOPAC was observed in the retina of light-adapted adult and senescent rats when compared to their respective dark-adapted controls (+94% and +95%, respectively). The results indicate that aging has a differential effect on D-1 DA receptors in the retina and different areas of the rat brain. Finally, the age-related increment in the density of retinal D-1 DA receptors does not appear to depend on presynaptic mechanisms, since DA metabolism is increased by light to the same extent in young and aged rats.