778 Fig. 2 Effect of altering reward size, α-flupenthixol, and reward omission on responding for cocaine under an ST(PR) schedule in rats. a Breakpoints for different unit doses of cocaine (n = 7). b Effect of α-flupenthixol on breakpoints for cocaine (n = 10). c Effects of reward omission and reacquisition on breakpoints; baseline response (session 0; closed symbol) followed by three reward omission sessions (sessions 1–3; open symbols), after which reacquisition took place (session 4; closed symbols) (n = 8). Data are presented as mean breakpoints ± SEM. *p < 0.05 for difference between groups (a, b) or sessions (c) (Wilcoxon signed ranks test) Table 1). Furthermore, 0.5 mg/kg α-flupenthixol suppressed seeking to a greater extent than that seeking was suppressed during the first reward omission session (Z17=−2.417, p< 0.05). Figure 2c shows that the breakpoint was reduced during the first reward omission session compared to the last baseline session (Z7=−2.521, p<0.05). Over the next two sessions, the breakpoint did not change further (χ(2)2= 2.400, NS). When cocaine was reintroduced, the breakpoint returned to pre-reward omission levels (Z7=−2.521, p< 0.05). There was no difference between the last baseline session before the omission sessions and the first session in which cocaine was reintroduced (Z7=−0.169, NS). ST(RI) schedule with sucrose reinforcement For the ST(RI) experiments with sucrose reinforcement, baseline responding averaged 9.1±0.2 rewards/session (range 7.6–10 rewards/session). Figure 3a shows that varying the reward magnitude by changing the amount of sucrose pellets per reward did not affect the seeking and taking responses when rats were lever pressing under an ST(RI) schedule of reinforcement (seeking, F2, 18=2.432, NS; taking, F2, 18= 0.172, NS; Fig. 3a, b). Panels c and d of Fig. 3 show that α- flupenthixol decreased sucrose seeking and taking (seeking, F3, 27= 6.939, p= 0.01; taking, F1, 9= 5.949, p< 0.05). Post Psychopharmacology (2012) 220:771–785 hoc analyses showed no significant between-group effects on taking, but seeking under 0.5 mg/kg α-flupenthixol differed from all other treatments (0 vs. 0.5 mg/kg, t9= 3.743, p< 0.01; 0.05 vs. 0.5 mg/kg, t9= 4.541, p= 0.001; 0.25 vs. 0.5 mg/kg, t9= 3.255, p=0.01). There was no effect of α- flupenthixol on responding during the consecutive self- administration session (seeking, F3, 27=2.140, NS; taking, F3, 27= 1.898, NS; Table 1). Furthermore, α-flupenthixol treatment suppressed seeking and taking to a comparable extent as the first reward omission (seeking—0 mg/kg vs. first extinction session t17=−0.651 NS; 0.05 mg/kg vs. first extinction session, t17=−0.123, NS; 0.25 mg/kg vs. first extinction session, t17 = 0.121, NS; 0.5 mg/kg vs. first extinction session, t17=1.498, NS; taking—0 mg/kg vs. first extinction session, t17=−0.415, NS; 0.05 mg/kg vs. first extinction session, t17=−1.102, NS; 0.25 mg/kg vs. first extinction session, t17 = 0.344, NS; 0.5 mg/kg vs. first extinction session, t17=1.492, NS). Both the seeking and taking rates were reduced when animals were exposed to reward omission (Fig. 3e, f). Seeking decreased as soon as sucrose was no longer delivered (t8 = 2.555, p < 0.05; Fig. 3a) and seeking and taking continued to gradually decline during further reward omission sessions (seeking, F9, 72= 13.117, p<0.001; taking, F9, 72= 5.836, p< 0.001). When sucrose was reintroduced, seeking and taking rates increased (seeking, t8 = −2.373, p < 0.05; taking, t8 = −2.646, p < 0.05). During the second reacquisi- tion session, seeking levels were again comparable to pre- reward omission sessions (baseline vs. first reacquisition session, t8 = 4.071, p < 0.05; baseline vs. second reacquisi- tion session, t8 = 1.305, NS; baseline vs. third reacquisition session, t8 = 1.996, NS; baseline vs. fourth reacquisition session, t8 = 0.537, NS), but taking responses did not return to pre-reward omission levels during the four reacquisition sessions (baseline vs. first reacquisition session, t8 = 2.475, p < 0.05; baseline vs. second reacquisition session, t8 = 2.626, p < 0.05; baseline vs. third reacquisition session, t8= 2.530, p<0.05; baseline vs. fourth reacquisition session, t8= 2.443, p< 0.05). ST(PR) schedule with sucrose reinforcement For the ST(PR) experiments with sucrose reinforcement, baseline responding averaged at 15.0 ± 0.4 rewards/session (range 10.3–19 rewards/session). Baseline sessions lasted on average for 136.7 ± 8.3 min, which is nearly 2 h longer than the ST(RI) schedules with sucrose reinforcement. Varying the reward magnitude by changing the number of sucrose pellets per reward did not alter seeking rates under the ST(PR) schedule (χ(2)2 = 6.000, NS; Fig. 4a). Figure 4b shows that α-flupenthixol treatment dose- dependently altered sucrose seeking (χ(3)2 = 10.800, p < 0.05). Post hoc analysis showed that saline pretreatment