The day after steady nicotine self-administration (FR1) had been achieved, animals received (±)TCP (3 mg/kg, i.p.; black bars) or (+)TCP (1.5 mg/kg, i.p.; white bars) pretreatment and 45 min later a ketanserin (1 mg/kg, s.c.) injection. Ketanserin caused a drop in responding in the (±)TCP-treated group (*p=0.008 vs. baseline, n=6), but not in the (+)TCP-trained group (n=5). Mean reinforced responses (+SEM) were plotted for each treatment group.