Endocytosis following dopamine D 2 receptor activation is critical for neuronal activity and dendritic spine formation via Rabex-5/PDGFRβ signaling in striatopallidal medium spiny neurons.

Aberrant dopamine D2 receptor (D2 R) activity is associated with neuropsychiatric disorders, making those receptors targets for antipsychotic drugs. Here, we report that novel signaling through the intracellularly localized D2 R long isoform (D2L R) elicits extracellular signal-regulated kinase (ERK) activation and dendritic spine formation through Rabex-5/platelet-derived growth factor receptor-β (PDGFRβ)-mediated endocytosis in mouse striatum. We found that D2L R directly binds to and activates Rabex-5, promoting early-endosome formation. Endosomes containing D2L R and PDGFRβ are then transported to the Golgi apparatus, where those complexes trigger Gαi3-mediated ERK signaling. Loss of intracellular D2L R-mediated ERK activation decreased neuronal activity and dendritic spine density in striatopallidal medium spiny neurons (MSNs). In addition, dendritic spine density in striatopallidal MSNs significantly increased following treatment of striatal slices from wild-type mice with quinpirole, a D2 R agonist, but those changes were lacking in D2L R knockout mice. Moreover, intracellular D2L R signaling mediated effects of a typical antipsychotic drug, haloperidol, in inducing catalepsy behavior. Taken together, intracellular D2L R signaling through Rabex-5/PDGFRβ is critical for ERK activation, dendritic spine formation and neuronal activity in striatopallidal MSNs of mice.