Seeking–taking chain schedules of cocaine and sucrose self-administration: effects of reward size, reward omission, and α-flupenthixol

RATIONALE: In heterogeneous seeking–taking (ST) chain schedules of self-administration, seeking rewards and taking rewards are distinct actions, giving animals explicit control over their intake of the reward. However, the neurobehavioral characteristics of ST chain schedules are relatively unexplored. OBJECTIVES: This study was made to evaluate two variants of ST chain schedules of self-administration to measure seeking and taking of sucrose and cocaine in rats. METHODS: Rats had to respond on one lever (seeking lever) under a random interval (RI) or under a progressive ratio (PR) schedule, to gain access to a second lever (taking lever), responding on which under a fixed-ratio 1 (FR-1) schedule of reinforcement delivered the reward. We assessed the effects of reward size, reward omission, and administration of the dopamine receptor antagonist α-flupenthixol. The effects of α-flupenthixol on responding for cocaine or sucrose under an FR-1 schedule of reinforcement were also assessed. RESULTS: Cocaine seeking under both schedules was reduced by decreasing reward size, reward omission, and α-flupenthixol treatment. Cocaine taking was decreased by α-flupenthixol treatment and reward omission, but not by altering reward size. Sucrose seeking was not affected by reward size, but was reduced by α-flupenthixol and reward omission. Sucrose taking was diminished by reward omission only. α-Flupenthixol increased cocaine but not sucrose intake under an FR-1 schedule of reinforcement. CONCLUSIONS: Both ST(PR) and ST(RI) schedules can be used to assess seeking and taking of sucrose and cocaine. Dopaminergic neurotransmission mediates the positive subjective properties of cocaine but not sucrose and the motivational properties of both sucrose and cocaine.