Drugs and dose ranges are listed in Table 1. Pramipexole was generously provided by Drs. Jianyong Chen and Shaomeng Wang (University of Michigan, Ann Arbor, MI), sumanirole by Benjamin Greedy and Dr. Stephen Husbands (University of Bath, Bath, UK), GBR 12909 by Novo Industri (Bagsvaerd, Denmark), ABT-724 by Dr. Kenner Rice (Chemical Biology Research Branch, National Institute on Drug Abuse, Bethesda, MD), and PG01037 was synthesized according to the procedure in the literature (Grundt et al., 2005 (link)) by Dr. Peter Grundt (University of Minnesota – Duluth, Duluth, MN) and Ms. J Cao (Medicinal Chemistry Section – National Institute on Drug Abuse, Baltimore, MD). Haloperidol, SKF 81297, SCH 23390, and apomorphine were obtained from Sigma-Aldrich (St. Louis, MO), L-741,626 and L-745,870 were obtained from Tocris (Ellisville, MO), and d-amphetamine was obtained from the National Institute on Drug Abuse (Bethesda, MD). All drugs were dissolved in sterile saline except L-741,626, which was dissolved in 5% ethanol, and PG01037, which was dissolved in 20% β-cyclodextrin. All injections were administered s.c. in a volume of 1.0 ml/kg except 56 mg/kg PG01037 which was administered in of volume of 1.75 ml/kg due to solubility limits.