Fig. 4. Rats that self-administered nicotine vapor exhibited addiction-like behaviors after 3 weeks of protracted abstinence.

a Experimental timeline of the behavioral analysis in the nicotine vapor group and vehicle vapor group. b The time spent in the open arms of the elevated plus maze decreased in rats that self-administered nicotine vapor compared with vehicle vapor. Error bars represent the SEM of the time spent on the open arms (n = 24 rats [12–13 females, 11–12 males]). c The percent change in pain thresholds relative to baseline in rats that self-administered nicotine vapor decreased compared with their own baseline (BSL) and with vehicle vapor during protracted abstinence following a 3-week incubation period. Error bars represent the SEM of the percent change in pain thresholds relative to baseline (n = 24 rats [12–13 females, 11–12 males]). d Number of lever presses in the nicotine vapor group (n = 24 rats [12 females, 12 males]) and vehicle vapor group (n = 24 rats [13 females, 11 males]) in a 1-h session before (self-administration [SA]) and after (reexposure [R]) a 3-week incubation period. Error bars represent the SEM of the number of lever presses.