Effects of CP94253 (5.6 mg/kg, s.c.) on the cocaine self-administration dose-response function expressed as the mean number of reinforcers in a 2-hour test session ± standard error of the mean (SEM). Animals (n = 8/group) were tested twice at each dose of cocaine presented in descending order, receiving vehicle (squares) pre-treatment 15 minutes prior to one test, and CP94253 (triangles) 15 minutes before the other test, with order of presentation counterbalanced. * Represents a difference from CP94253 pre-treatment test day (Newman–Keuls, P < 0.01)