Figure 5.

Self-administration of cocaine alone (●) and in combination with 0.001 mg/kg/inj nicotine (◑), 0.0032 mg/kg/inj nicotine (◮), and 0.01 mg/kg/inj nicotine (◨) in a group of three monkeys. Abscissae: Saline or drug unit dose (mg/kg/injection). Ordinates: Total injections obtained on the last three days of each dose condition. Points above ‘S’ represent number of injections when saline was available for self-administration and points above ‘N’ represent number of injections when only nicotine (0.001, 0.0032, and 0.01 mg/kg/inj) was available for self-administration. The cocaine alone dose-effect curve is repeated on each graph for comparison with the cocaine + nicotine combinations. Asterisks indicate unit doses of cocaine + nicotine that were significantly different from corresponding doses of cocaine alone (* P < 0.05).