Figure 3.

Cranial irradiation before cocaine self-administration increases cocaine reward. A, Irradiated rats did not differ from sham rats in the time it took to obtain 100 sucrose pellets during acquisition of an FR1 schedule during food training. B, Cranial irradiation 4 weeks prior increased the amount of cocaine self-administered at a 0.5 mg/kg infusion dose under both FR1 and FR5 schedules. C, Irradiated rats self-administered more cocaine, causing a vertical shift in the dose–response curve. D, Dose–response data converted into dose-intake curves by multiplying infusions by dose show irradiated rats took more significantly more cocaine. E, Irradiated rats worked harder to get their last infusion of cocaine, suggesting that they find cocaine more rewarding. Data are presented as mean ± SEM. *p < 0.05, **p < 0.01, ***p < 0.001.