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Six vs. eight-week old age of onset of nicotine self-administration initial training for nicotine self-administration fixed-ratio-1 (FR1), infusions (mean±sem) per 45-min. session in female rats. There was a significant (p<0.01) main effect of age of onset with the rats that had begun access at six weeks of age self-administering more nicotine than the rats that had begun access at eight weeks of age.
