Trafficking of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors is an important determinant of synaptic strength. Our prior work suggests that D1 dopamine (DA) receptors regulate AMPA receptor trafficking. This is a possible mechanism by which amphetamine and cocaine, which indirectly stimulate D1 receptors, may alter synaptic strength in addiction-related neuronal circuits. Post-natal rat nucleus accumbens (NAc) cultures were used to study the role of protein kinase A (PKA) in D1 receptor regulation of the surface expression of the AMPA receptor subunit GluR1. Using an immunocytochemical assay that selectively detects newly externalized GluR1, we found that the rate of GluR1 externalization is enhanced by the D1 agonist SKF 81297 (100 nm-1 microm). This was blocked by a D1 receptor antagonist (SCH 23390; 10 microm) and by two different cell-permeable PKA inhibitors, KT5720 (2 and 10 microm) and RpcAMPS (10 microm). Conversely, the PKA activator SpcAMPS increased the rate of GluR1 externalization in a concentration-dependent manner. A maximally effective concentration of SpcAMPS (10 microm) occluded the effect of SKF 81297 (1 microm) on GluR1 externalization. Using similar cultures, we showed previously that D1 receptor stimulation increases GluR1 phosphorylation at the PKA site. Together, our findings suggest that PKA phosphorylation of GluR1 is required for GluR1 externalization in response to D1 receptor stimulation.