Heightened PKC-mediated serine phosphorylation of mGluR1 in prenatal cocaine- exposed brains is responsible for the reduced mGluR1 coupling to G_q/11 and Homer1.

<p>(<b>A</b>) Levels of mGluR1 - G_q/11 and mGluR1 - Homer1 coupling as well as serine-phosphorylated mGluR1 (pS-mGluR1) on purified mGluR1 signaling complexes. FCX synaptosomal membranes from prenatal cocaine- and saline-exposed P21 rats were incubated with either vehicle 100 µM alkaline phosphatase, 30 µM ATP containing Kreb’s-Ringer (K-R) or 162 nM PMA (20 µg phosphoatidylserine). Following completion of dephosphorylation by addition of phosphatase inhibitors, phosphate-free mGluR1 from prenatal saline-treated rats was phosphorylated by recombinant γPKC in the presence of ATP. The reaction was terminated by specific PKC inhibitor, celestrine. The resultant synaptic membranes containing differentially phosphorylated mGluR1 were then incubated with K-R or 1 µM glutamate. The mGluR1 purified by anti-mGluR1 immunoprecipitation was analyzed for phosphoserine by Western blotting. The interaction between mGluR1 and G_q/11 or Homer1 with different phosphorylation states was assessed by the levels of Gα_q/11 and Homer1 in the anti-mGluR1 immunoprecipitates by Western blotting. (<b>B</b>) Densitometric quantification of mGluR1-associated Gα_q/11 and Homer1 as well as pS-mGluR1 levels. Data are represented as means ± s.e.m. of the ratios of Gα_q/11, Homer1 or pS-mGluR1/total mGluR1 optical intensities. <i>n</i> = 4 for each group. *<i>p</i><0.01 comparing the glutamate-induced to basal mGluR1-G_q/11 complex levels by two-tailed Student’s <i>t</i> test. #<i>p</i><0.01 comparing the respected levels in prenatal cocaine- to saline-treated rats. No between-group differences in the levels of mGluR1were detected.