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Self-administration of 0.05 and 0.4 mg/kg/injection cocaine alone (shaded bars) and after PB pretreatment by monkeys responding under a PR schedule of reinforcement. The labels on the X-axis are the self-administered dose of cocaine and the pretreatment doses of PB in mg/kg/injection. Each bar is the mean value for four monkeys and vertical lines are s.e.m. Numbers in bars are mean session duration in minutes.
