Mean (± SEM) number of cocaine (0.4 mg/kg) infusions over the last 5 days of acquisition for the rats that met the acquisition criterion in each group. Filled symbols indicate adolescents, and open symbols indicate adults. LoS rats are represented by circles, and HiS rats are represented by triangles. On Day 3, LoS adults self-administered significantly more cocaine infusions than HiS adults (# p < 0.05), and on Day 5, HiS adults self-administered significantly more cocaine infusions than all other groups (* p < 0.05).