Average number of infusions per 2-h METH self-administration session for 15 consecutive days in No Stress (n=6), Adult Stress (n=10), Early Life Stress (n=6), and Early Life Stress + Adult Stress (n=5) rats. Data points represent group mean ± SEM. p≤0.05: * vs. Early Life Stress + Adult Stress, # vs. Adult Stress, and % vs No Stress.