Figure 1.

Nicotine-induced enhancement of 5-day METH self-administration in male adolescent rats. Mean 2-hour response ± SEM in (A) female adolescent, (B) female adult, (C) male adolescent, and (D) male adult Sprague-Dawley rats. *p ≤ .05, **p < .01, ***p < .001 adolescent Nic versus adolescent Sal Reinf responses; ⁺p < .05, ⁺⁺p < .01, ⁺⁺⁺p < .001 Reinf versus Non Reinf responses. n = 8–11/group. Open and closed circles represent individual female animals, open and closed squares represent individual male animals. METH = methamphetamine; Nic = nicotine (blue); NR = nonreinforced; Reinf = reinforced; Sal = saline (gray).