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. Author manuscript; available in PMC: 2014 Oct 1.
Published in final edited form as: Neurobiol Dis. 2013 May 30;58:132–143. doi: 10.1016/j.nbd.2013.05.009

Figure 1.

Figure 1

Rats escalated METH intake over the course of self-administration. Symbols show an average METH intake per 15-h session in the group of rats euthanized 24 h after cessation of self-administration. Rats increased METH intake on session 2 compared with session 1, and on session 5 compared with session 2. Animals further escalated their drug intake on session 6 in comparison to session 3 and stayed at this level until cessation of METH self-administration. METH intake by rats in the 24-h group reached 14.2 mg/kg/day. Data were analyzed by one-way ANOVA for repeated measures, followed by Tukey's multiple comparison test. N = 12. * p < 0.05, ** p < 0.01, *** p < 0.001 compared with session 1; # p < 0.05, ## p < 0.01 compared with session2; ! p < 0.05 compared with session 3.