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Figure 1

From: Increased expression of proenkephalin and prodynorphin mRNAs in the nucleus accumbens of compulsive methamphetamine taking rats

Figure 1

Effects of prolonged methamphetamine self-administration and contingent footshocks in rats.

(a) Timeline of the experiment. (b) Escalation of methamphetamine intake during the training phase of the experiment. N = 6 (control group) and 12 (methamphetamine self-administration group). (c) Suppression of lever pressing by footshocks in shock-sensitive (SS) rats but not in shock-resistant (SR) compulsive methamphetamine takers. N = 6 per group. Data are means + SEM of infusions (b) or percentage suppression (c). During the footshock phase, shock intensity was increased from 0.18 to 0.36 mA, with 50% of rewarded lever presses being accompanied by footshocks. #Significantly different from the SR group, p < 0.001.

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