Expression of GRK2 and D1 receptor phosphorylation. Expression levels of GRK2 were decreased in cytosol preparation (A) and increased in membrane preparation (B) from the cultures of Fmr1 KO mice as compared with KO neurons. Synergistic addition of DL-AP3 (10 μM) and SKF81297 (5 μM) reversed redistribution of GRK2 between membrane and cytosol in Fmr1 KO neurons. (C) Synergistic addition of DL-AP3 (10 μM) and SKF81297 (5 μM) reduced the increase of D1 receptor phosphorylation at serine sites to a level similar to WT neurons. n = 4 dishes. * p < 0.05, ** p < 0.01 compared between Fmr1 WT and KO neurons; # p < 0.05 compared with KO control.