Dissociation of the striatal D-2 dopamine receptor from adenylyl cyclase following 6-hydroxydopamine-induced denervation

Abstract

Intracellular cyclic AMP accumulation following exposure to dopamine (DA) agonists and and antagonists was measured in striatal slices from rats with a unilateral 6-hydroxydopamine (6-OHDA) lesion of the nigrostriatal pathway and which showed contralateral circling to apomorphine. Both DA (10-320 microM) and the D-1 agonist SKF 38393 (0.1-32 microM) increased cyclic AMP accumulation in striatal slices from the lesioned and intact hemispheres. The EC50 for DA to increase cyclic AMP accumulation in slices was greater in the 6-OHDA-lesioned striata compared to the intact striatum, but the EC50 for SKF 38393 was not affected. The D-1 antagonist SCH 23390 (10 microM) completely inhibited the ability of DA and SKF 38393 to increase cyclic AMP accumulation in striatal slices from both denervated and intact sides of the brain. In slices from the intact hemisphere the increase in DA-induced cyclic AMP accumulation was enhanced by the D-2 antagonist (+/-)-sulpiride (50 microM) but (+/-)-sulpiride had no effect on the DA response in slices from the lesioned side. Similarly, the ability of SKF 38393 to enhance cyclic AMP accumulation was blocked by the D-2 agonist quinpirole (10 microM) in striatal slices from the intact hemisphere but not in tissue from the lesioned side. The density of striatal D-1 and D-2 receptors assessed by [3H]SCH 23390 and [3H]spiperone binding did not differ between the hemispheres although there was an increase in the affinity of D-1 receptors for [3H]SCH 23390 in the lesioned striatum. After striatal deafferentiation there appears to be an uncoupling of the "inhibitory" D-2 receptor from the D-1 receptor-associated adenylyl cyclase.