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The average number of responses on the active and inactive levers for the first five progressive-ratio sessions under the 5 and 10 µg/kg nicotine dose conditions. Each data point represents an N of 9 females and 6 males under the 5 µg/kg nicotine dose condition and an N of 14 females and 11 males under the 10 µg/kg nicotine dose condition.
