The effects of response operandum and prior food training on intravenous nicotine self-administration in rats.

RATIONALE: Nicotine intravenous self-administration (IVSA) in rats has been conducted using a variety of methodological procedures with equally variable results.
OBJECTIVES: Here, we addressed the importance of the type of response operandum and prior instrumental training with a natural reinforcer on nicotine IVSA and reinstatement.
METHODS: Rats were tested for spontaneous acquisition of IVSA using either nose poke (NP) or lever press (LVR) operandum. A dose-response test was then conducted, followed by extinction and cue- and nicotine-induced reinstatement.
RESULTS: The use of the NP operandum resulted in markedly higher levels of IVSA across acquisition and across dose-response testing compared with the LVR group. Whereas both groups reinstated following a nicotine prime, only the LVR group demonstrated cue-induced reinstatement. As a positive control, the experiment was repeated with cocaine as the reinforcer: equivalent levels of IVSA were observed across all tests, irrespective of operandum. When rats self-administering nicotine received instrumental training with a sucrose reinforcer prior to IVSA, a facilitated acquisition of IVSA was observed in both LVR and NP groups to a similar extent (the effect of operandum remained), but had little effect on responding thereafter. During reinstatement testing, both groups now displayed cue- and nicotine-induced reinstatement, but this was also evident in saline control animals that had never received nicotine.
CONCLUSIONS: These results suggest that, unlike cocaine, an increased physical response requirement can decrease nicotine intake. It also indicates that operandum and prior sucrose training may influence the role that visual cues play in nicotine dependence.