Figure 2.

Nicotine-induced enhancement of METH self-administration persists in male adolescent rats. Mean day 4–5 2-hour responses ± SEM in (A) female adolescent, (B) female adult, (C) male adolescent, and (D) male adult Sprague-Dawley rats. **p < .01, ***p < .01 adolescent Nic versus adolescent Sal Reinf or Non-Reinf responses; ⁺p < .05, ⁺⁺p < .01 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; NR = nonreinforced; Reinf = reinforced; Sal = saline.