Opioid-induced transfer of Gα subunits to RGSZ2 and RGS9 proteins. Groups of 6 to 8 mice, icv-injected with 10 nmol morphine or 100 pmol DAMGO, were sacrificed at different intervals post-opioid administration. Their PAG P2 fractions were then obtained and solubilized under nondenaturing conditions. The MOR, RGSZ2 and RGS9 proteins were immunoprecipitated with specific antibodies from different aliquots of the same solubilized material. The presence of Gαi2 subunits was then analyzed in Western blots in which equal loading was verified by probing anti-MOR or anti-RGSZ2 IgGs in parallel blots using the same immunoprecipitated material. The data corresponding to the co-precipitation of MORs or RGSZ2 with Gαi2 subunits were then normalized and are shown as the mean ± SEM from three determinations (two for RGS9 and Gαi2) performed in different PAG samples.