Receptor recycling mediates plasma membrane recovery of dopamine D1 receptors in dendrites and axons after agonist-induced endocytosis in primary cultures of striatal neurons

The pharmacological stimulation of G-protein-coupled receptor induces receptor internalization. Receptor's fate after the step of internalization remains poorly characterized despite its incidence on the neuronal responsiveness. In this context, we studied the dopamine (DA) D1 receptor (D1R) trafficking in a model of striatal neuronal culture that endogenously express the D1R. We first characterized by immunohistochemistry the spatial distribution of the compartments involved in the endocytic pathways and then the D1R trafficking in dendrites and axons. In dendrites, immunohistochemical analys, is showed that acute stimulation by the D1R agonist SKF 82958 (1 gM) induces an internalization of D1R in early endosomes labeled with Alexa-488-conjugated transferrin. We show that, 20 min after removal of the agonist, the D1R immunolabeling pattern returns to the basal state in dendrites and in axons. Recovery was unaffected by cycloheximide (70 M) but was prevented by monensin (100 mu M) that inhibits endosomal acidification and receptor recycling. These data suggest that dendritic and axonal D1Rs are internalized after agonist stimulation and targeted to the recycling pathway demonstrating that the machinery involved in GPCR endocytosis and recycling is functional both in dendrites and in axons. Temporal characteristics observed for the recovery of D1R density to the basal state and those observed for the resensitization process strongly suggest that D1R recycling supports the receptor resensitization.