Dopamine-opioid interactions in the rat striatum: a modulatory role for dopamine D-1 receptors in delta opioid receptor-mediated signal transduction

Dopaminergic and opioidergic systems interact in the striatum to modulate locomotor and motivated behaviors. The present study investigated the molecular interactions of these two systems by determining the role of dopamine D-1 and D-2 receptors in the modulation of opioid receptor-mediated signal transduction. Male Fischer rats were injected daily for 10 days with either saline, the D-1 receptor agonist SKF 82958, the D-2 receptor agonist quinpirole, or both SKF 82958 and quinpirole. Administration of SKF 82958 alone or together with quinpirole attenuated the ability of the delta receptor agonist D-Pen(2),D-Pen(5)-enkephalin (DPDPE) to inhibit adenylyl cyclase activity in the caudate putamen and nucleus accumbens. Quinpirole administration alone had no effect. The efficacy and potency of the mu opioid receptor agonist D-Ala(2),N-Me-Phe(4),Gly-ol(5)-enkephalin (DAMGO) to inhibit adenylyl cyclase activity was unaltered following administration of either dopamine receptor agonist. Administration of SKF 82958 had no affect on delta receptor binding, forskolin-stimulated adenylyl cyclase activity, or G protein/adenylyl cyclase coupling. However, the ability of DPDPE to stimulate binding of [S-35]GTP gamma S to inhibitory G proteins was attenuated in animals that received SKF: 82958. These result; suggest that repeated activation of D-1 receptors attenuates the functional coupling of delta opioid receptors with adenylyl cyclase due to decreased coupling between delta receptors and G proteins. (C) 2000 Elsevier Science Ltd. All rights reserved.