Psychopharmacology (2012) 220:771–785 animals when they underwent omission of the cocaine reward, devaluation of the taking link by omitting the cocaine reward did not affect cocaine seeking during a 5 min extinction session (Zapata et al. 2010). In contrast, in our study, animals did receive presentations of the taking lever after they had fulfilled the response requirement on the seeking lever, providing them with explicit feedback of the consequences of their actions (i.e., pressing the taking lever results in infusion with saline instead of cocaine). This may have precluded the expression of any habitual behavior in our animals, perhaps because distal (seeking) actions gain habitual properties more readily with extended training, or under interval schedules, than actions proximal to reward consumption (Dickinson 1985; Dickinson et al. 2002; Miles et al. 2003). Over sessions, animals adapted their expectancy of the reward since seeking levels stabilized at a low level of responding after a few sessions. Thus, omission of the cocaine reward reduced the motiva- tion to seek the drug. Taking responses under the ST(RI) schedule also declined over sessions, but the effect was more gradual and less pronounced than for seeking responses. There are two explanations for this initial absence of a reduction in taking under the ST(RI) schedule. First, the low effort requirement on the taking link and the limited amount of opportunities to respond on the taking lever in an ST(RI) session do not facilitate fast extinction of responding. Second, in a reinforced ST(RI) session, responding on the taking link resulted in the presentation of the reward and reward-associated stimuli, i.e., the presentation of the cue light and the retraction of the taking lever. Thus, the association between the responding on the taking lever and reward-associated stimuli is much stronger for the taking link than for the seeking link. These reward- associated stimuli that were still presented in the reward omission sessions had likely acquired motivational proper- ties that maintained responding on the taking link (Stewart et al. 1984; Everitt and Robbins 2000). In fact, reward- associated conditioned stimuli can support the acquisition of new instrumental responding that is only reinforced with presentation of these conditioned stimuli (Di Ciano and Everitt 2004; Parkinson et al. 2005). In our hands, varying the number of sucrose pellets per reward had no effect on seeking or taking under both the ST(PR) and the ST(RI) schedules. This is surprising since it has been shown that both the traditional PR and the ST(RI) schedules are sensitive to changes in the amount of sucrose delivered (Cheeta et al. 1995; Cleary et al. 1996; Olmstead et al. 2000; Sclafani and Ackroff 2003; Rickard et al. 2009). Interest- ingly, Rickard et al. (2009) showed that the dose–response curve under a PR schedule flattens when sucrose solutions are used that yield more than approximately 20.5 mg sucrose per reward. Since the sucrose pellets we used 781 contained 42.5 mg sucrose per pellet, it may be that the lowest amount of sucrose used in the present study already elicited a maximal response rate. When different amounts of sucrose are offered simultaneously within the same session, such as in a delayed reward task when the delay to the large reward is zero, rats can clearly distinguish between one or four sucrose pellets (e.g., Evenden and Ryan 1996; van Gaalen et al. 2006). Apparently, when the absolute amount of sucrose was varied between sessions, the ST schedules tested in the present study were not sensitive enough to measure the changes in motivation for the sucrose reward. In contrast to varying the reward value from one to four sucrose pellets, the ST schedules did identify a decrease in motivation when the absolute value of the sucrose reinforcer was reduced to zero. Omission of the sucrose reward attenuated sucrose seeking under the ST(RI) schedule already during the first reward omis- sion session, and in consecutive omission sessions, sucrose seeking was suppressed further. Taking responses for sucrose under the ST(RI) schedule showed a similar pattern as when the cocaine reward was omitted. Initially, taking was unaffected but decreased over repeated testing, most likely for the same reasons as described above for the effects of reward omission on cocaine taking. Sucrose seeking under the ST(PR) schedule did not decline until the third reward omission session, indicating a transient resistance to extinction under these circumstances. We also systematically evaluated the role of dopa- mine in the motivation for cocaine and sucrose under ST chain schedules. Johnston et al. (2001) have previously tested the effect of pimozide, a dopamine D2 receptor antagonist, in animals that were trained under an ST(RI) schedule with sucrose reinforcement. Treatment with pimozide reduced reinforced sucrose taking over sessions. Pimozide treatment also resulted in a decreased sucrose seeking rate in a later session in which animals got access to the seeking lever only under drug-free con- ditions. In contrast to the present study, Johnston et al. (2001) tested the effects of pimozide on seeking and taking sucrose in isolation and not during responding under the ST(RI) schedule itself. Our study therefore extends these findings by showing that α-flupenthixol treatment directly decreases cocaine and sucrose seeking under both ST chain schedules as well as cocaine taking under the ST(RI) schedule. This is consistent with previous studies measuring motivation for food rewards (Reilly 1999; Cheeta et al. 1995; Aberman and Salamone 1999; Caul and Brindle 2001; Salamone et al. 2001). As mentioned in the Introduction, it is generally thought that dopamine mediates the willingness to exert effort for food, rather than its positive subjective properties (Baldo and Kelley 2007; Barbano and Cador 2007; Berridge