Mice were kept in the University of Connecticut Health Center animal facility on a 12 h light/dark cycle (lights on 7:00 am to 7:00 pm) and handled in accordance with University of Connecticut Health Center Institutional Animal Care and Use Committee guidelines. Adult male C57BL/6 mice (Jackson Laboratories; 2-5 months old) were treated daily with cocaine (20 mg/kg/day, i.p.) or saline for 7 days [12] and sacrificed 24 h after the final injection. When tested, the mice exhibited the expected locomotor sensitization to chronic cocaine administration (not shown) [12]. Mice expressing green fluorescent protein (GFP) under the control of the D1-dopamine receptor promoter were from the University of Missouri Mutant Mouse Regional Resource Center (Tg(Drd1a-EGFP)X60Gsat/Mmmh). These mice were bred at least seven generations into C57Bl/6 (Jackson Labs) before use.
