Tolerance development to the arousal effects of nicotine

To determine if repeated daily doses of nicotine induces tolerance to both its EEG and behavioral activating effects, rats implanted with sets of bipolar cortical elecrodes and carotid cannulae received intracarotid injections of either (1) 6 daily doses of nicotine (as tartrate, 30 mug/kg) (Group 1) or (2) 3 daily doses of saline followed by 4 days of nicotine (Group 2). From an exercise-induced resting state, nicotine produced immediate EEG and behavioral arousal, both of which disappeared in Group 1 by Day 6. Saline administered to Group 2 rats produced little or no response but subsequent nicotine resulted in responses similar to those produced by Group 1 animals. It is concluded that tolerance development to nicotine activation is reflected not only in behavior, but also in the EEG.