Differential localization of dopamine D1 and D2 receptors in rat retina

Dopamine interacts with distinct receptors on different target neurons in the rat retina. Dopamine receptors were labeled in the rat retina by autoradiography using 3H-SCH-23390 and 3H-spiperone binding to retinal sections. The 3H-SCH-23390 binding to D1 receptors was most concentrated in the inner plexiform, inner nuclear, and ganglion cell layers; it was absent from the outer nuclear layer and the photoreceptor inner and outer segments. Competition studies indicated that 3H-SCH-23390 binding to the inner retina was inhibited with high affinities by the D1-specific agonist and antagonist, SKF-38393 and SCH-23390. The D2-specific compounds were ineffective in competing for 3H-SCH-23390 binding. The 3H-spiperone binding to D2 receptors, however, was most concentrated in the photoreceptor inner and outer segments and in the outer nuclear layer. The D2-specific agonist and antagonists, such as quinpirole, sulpiride, and eticlopride, competed for 3H-binding with high affinities; SCH-23390 and SKF-38393 were ineffective. The D2 receptors on the photoreceptors had a high affinity for clozapine but lower affinities for the modified benzamides. This is characteristic of a novel subtype of D2 receptors. Thus, D1 and D2 dopamine receptors are localized differentially in the rat retina to mediate different physiologic effects of dopamine.