Synaptic levels of GluR1 and GluR2/3 subunits were measured in the VTA and NAcc from wild-type and Girk−/− mice (8-12 wk) via post-embedding immunoelectron microscopy. Tissue was prepared as described (Lujan et al. 1996); sections containing of the VTA and NAcc were then cut at 500 μm incubated in a 1 M sucrose/PBS solution overnight, slammed onto copper blocks cooled in liquid nitrogen, and embedded in Lowicryl HM20 (TAAB Laboratories; Aldermaston, UK) after freeze substitution with methanol. Ultrathin sections (80 nm) from three Lowicryl-embedded blocks were incubated for 45 min on coated nickel grids with drops of blocking solution containing: 0.05 M TBS, 0.9% NaCl, 0.03% Triton X-100, and 2% albumin. Grids were then incubated at room temperature overnight in blocking solution containing rabbit polyclonal antibodies (10 μg/ml each) against GluR1 (AB1504, Millipore; Billerica, MA) or GluR2/3 (AB1506, Millipore). For VTA experiments, a mouse monoclonal antibody directed against TH (mAb 6D7, EMD Biosciences; San Diego, CA) was used to identify DA neurons. After washing in TBS, grids were incubated for 2 hr in drops of goat anti-rabbit IgG conjugated to
