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. Author manuscript; available in PMC: 2011 Jul 26.
Published in final edited form as: Exp Clin Psychopharmacol. 2011 Jun;19(3):203–214. doi: 10.1037/a0023373

Figure 3.

Figure 3

Self-administration of cocaine alone (●) and nicotine alone (▼) in a group of three monkeys. Abscissa: Saline or drug unit dose (mg/kg/injection). Ordinate: Mean (±SEM) injections obtained on the last three days of each dose condition. The point above ‘S’ represents the number of injections when saline was available for self-administration. Asterisks indicate drug unit doses that differed significantly from saline self-administration (* P < 0.05; ** P < 0.01; *** P < 0.001). Daggers indicate unit doses of nicotine that maintained levels of responding that were significantly different from corresponding unit doses of cocaine († P < 0.05; †† P < 0.01; ††† P < 0.001).