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. 2006;29(3):186–192.

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Unless otherwise noted in the text, all material appearing in this journal is in the public domain and may be reproduced without permission. Citation of the source is appreciated.

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A P rats (closed symbols), which are genetically selected for high alcohol drinking, self-administer more nicotine intravenously than do NP rats (open symbols), which are selected for low drinking. The animals were allowed to self-administer nicotine during the daily 1-hour sessions under different reinforcement schedules^†. The number of nicotine infusions earned by the animals during the first 24 days of nicotine self-administration (0.03 mg/kg per infusion) is shown. B The two strains do not differ in the amount of cocaine they self-administer intravenously. The number of cocaine infusions during the first 14 days of cocaine self-administration (0.75 mg/kg per infusion) is shown.

SOURCE: Modified from Le et al., 2006. © 2006, Society for Neuroscience.

^*Days when P rats self-administered significantly more nicotine that NP rats.

^†With the FR-1 schedule, animals had to press a lever once to receive the infusion, with the FR-2 schedule they had to press the lever twice, and with the FR-5 schedule they had to press the lever five times.