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 10 nm colloidal gold particles (BioCell International; Cardiff, UK) for experiments involving the NAcc, or a mixture of goat anti-rabbit IgG conjugated to 10 nm colloidal gold particles and goat anti-mouse IgG conjugated to 20 nm colloidal gold particles for experiments involving the VTA; in all cases, secondary antibodies were diluted 1:80 in a 0.05 M TBS solution containing 2% normal human serum and 0.5% polyethylene glycol. Grids were then washed in TBS for 30 min and counterstained for electron microscopy with saturated aqueous uranyl acetate and lead citrate.
