Figure 1.

(A) Experimental time-line of METH SA, footshocks and withdrawal tests. (B) METH infusions during the training period of 22 days (9-h /day). Rats escalate their METH intake during the training phase of the experiment. METH SA rats were segregated into two distinct phenotypes post facto based on their responses to footshocks, namely rats that continue to take METH despite negative outcomes (shock-resistant, SR) and rats that significantly reduce their METH intake (shock-sensitive, SS). Both SR (n=7) and SS (n=9) rats significantly increased their METH intake during escalation phase of SA training. During the maintenance phase of SA training, both SR and SS rats reached similar plateaus of METH intake. SR rats are denoted in black circles, SS rats are denoted in white circles while saline controls (n=5) rats are shown in white squares. Data are represented as means ± SEM of number of METH infusions (0.1 mg/kg/infusion). Key to statistics: *p<0.05. (C) Shock-resistant (SR) and shock-sensitive (SS) phenotypes take most METH infusions during the first hour of the three daily 3-hour sub-interval on sessions 6, 11, and 22 of METH SA. Rats did not take much METH at the beginning of METH SA training. Key to statistics: *P<0.05, **P<0.01, ***P<0.001, in comparison to first day of training.