Receptor binding assays.

D₂ and D₃ dopamine receptor binding was determined using radioligand binding assays as previously described (Davis et al., 2010). Crude membranes were prepared from NAc and dorsal striata (caudate putamen, CPu). Due to the limited quantity of ventral striatal tissue and the low density of D₃ sites, the binding analyses were performed using a single concentration of radioligand. D₂ binding was assessed using [³H]spiperone (0.23 nM; 60 Ci/mmol; American Radiolabeled Chemicals, St. Louis, MO, USA) with non-specific binding defined by 1 μM (+)-butaclamol. D₃ receptor binding was assessed using [³H]7-OH-DPAT (0.15 nM; 143 Ci/mmol; PerkinElmer, Waltham, MA, USA) and 1 μM spiperone to define non-specific binding. Specific binding is expressed as fmol/mg protein. Concentrations of [³H]spiperone and [³H]7-OH-DPAT were based on previously published studies (Davis et al., 2010) and approximately correspond to K_D values for each compound_.