Extended access to intravenous meth results in robust self-administration and escalation of meth intake.

<p>(A) Timeline of the experiment as described in detail in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0034299#s2" target="_blank">Materials and Methods</a> section. Animals underwent 21 days of meth self-administration (or received yoked-saline) followed by 14 days of home cage abstinence or 14 daily extinction sessions. Tissues were collected at the end of the experiment. (B) Daily lever responding for meth and yoked-sal animals during self-administration (left graph) and extinction (right graph). (C) Escalation of daily meth intake during short (1 hr) and long (6 hr) self-administration sessions as detected in abstinent and extinction animals. Mean daily meth intake over the course of the first three days vs. last three days of short- and long-access self-administration was analyzed by one-way ANOVA and expressed as mg/kg/day of meth. (D) Total meth intake (mg/kg) in abstinent vs. extinction animals. Data shown as mean ± S.E.M.; n = 8–11 samples per group. **p<0.01 L12–L14 vs. L1–L3.