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Numbers of 1-mg/kg cocaine infusions self-administered during 3-h sessions by WT (solid line, closed symbols) and heterozygous PTPRD-KO mice (dashed line, open circles) on experimental days shown. (Top) FR1 (1 mg/kg per infusion) and (Bottom) progressive-ratio schedules. Mice received 1-mg/kg cocaine infusions after completing 2, 4, 6, 9, and 12 lever presses on days 1–5, respectively (*P < 0.05, t test).
