Fig. 4.

A Example of a response record showing the effect of a nicotine injection during an extinction session. Numbers in parentheses indicate the responses made during the 45-min period after the injection. B The effect of nicotine administered during an extinction trial on non-reinforced responding for cocaine in animals previously treated with nicotine 3 min prior to cocaine self-administration sessions. Data are presented as responses per 5 min (mean±SEM). During the extinction session, animals reached near-zero levels of responding. However, when animals were injected with nicotine (arrow) after 45 min of non-reinforced responding, they showed a significant increase in responding during the 5-min period following the injection relative to when they were injected with saline (n=11). C Responding on the inactive lever was not significantly different when animals were treated with nicotine relative to when they were treated with saline. Data are presented as the number of responses per 5 min (mean±SEM). *P<0.001 [Tukey’s HSD after repeated-measures, two-way ANOVA analyses (drug × time) across 90 min]