Failure of dark adaptation to upregulate D-1 dopamine receptors in retina of senescent rats.
The effect of aging on the binding parameters of 3H-SCH 23390, the most selective ligand of D-1 DA receptors, was studied in membrane preparations from the rat retina. DA-stimulated adenylate cyclase activity was also measured in order to better characterize the changes in retinal D-1 DA receptors induced by aging. The binding studies revealed that the density of 3H-SCH 23390 was increased (34 and 73%) in the retina of 14- and 26-month-old rats, when compared to young adult animals, respectively. In contrast, aging failed to alter the sensitivity of the adenylate cyclase to the action of DA. In fact, DA (10(-6) M to 10(-4) M) elicited a similar enhancement in cyclic AMP formation in retinal homogenates of both adult and senescent rats. Since dark adaptation increases the density of D-1 DA receptors in the retina of adult rats we studied the effect of light deprivation on 3H-SCH 23390 binding and DA-sensitive adenylate cyclase activity in the retina of senescent rats. As previously shown (25) light deprivation increased 3H-SCH 23390 binding and enhanced DA-sensitive adenylate cyclase activity in the retina of young adult rats. On the contrary, dark adaptation failed to increase 3H-SCH 23390 binding and to enhance DA-sensitive adenylate cyclase activity in the retina of senescent rats. Taken together these results indicate that D-1 DA receptors in the retina of aged rats have biochemical and functional properties different from those found in the retina of adult animals; these changes may result in an altered response to the physiological stimuli elicited by environmental lighting.
Department of Experimental Biology, University of Cagliari, Italy.
M L
ML
Porceddu
G
G
De Montis
S
S
Pepitoni
G
G
Toffano
G
G
Biggio
D000262:Adenylyl Cyclases / Q000502:physiology; D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D001665:Binding Sites / Q000502:physiology; D003623:Dark Adaptation; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D011954:Receptors, Dopamine / Q000502:physiology*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D015854:Up-Regulation
D001552:Benzazepines; D011954:Receptors, Dopamine; D000262:Adenylyl Cyclases