Effects of presession treatments with σR antagonists or dopamine uptake inhibitors on cocaine self-administration in rats trained to self-administer cocaine. Ordinates, responses per second; abscissae, cocaine injection dose in milligrams per kilogram. Each point represents the mean ± S.E.M. (n = 6). AC927 was administered intraperitoneally at 15 min before sessions, whereas the other drugs were administered at 5 min before sessions. A, effects of the σR antagonist AC927 (1.0, 3.2, and 10 mg/kg) on cocaine self-administration. B, effects of NE-100 (1.0, 3.2, and 10 mg/kg) on cocaine self-administration. C, effects of WIN 35,428 (0.1, 0.32, and 1.0 mg/kg) on cocaine self-administration. D, effects of methylphenidate (1.0, 3.2, and 10 mg/kg) on cocaine self-administration. E, effects of nomifensine (0.32, 1.0, and 3.2 mg/kg) on cocaine self-administration.