Nucleus Accumbens shell and core dopamine responsiveness during operant responding for sucrose: nose poking versus lever pressing

In our study we investigated by microdialysis the responsiveness of dopamine (DA) transmission in the nucleus accumbens shell and core in rats responding for sucrose using two different operant schedules: nose poking versus lever pressing. In rats trained to respond for sucrose pellets on nose poking fixed ratio 1 (FR1) schedule, dialysate DA increased in the shell but not in the core during active responding as well as under extinction in the presence of sucrose cues. In rats responding for sucrose on lever pressing FR1 schedule we observed a strengthening of DA transmission both in the shell and in the core. Non-contingent sucrose presentation and feeding in nose poking and lever pressing FR1 trained animals increased dialysate DA to a similar extent in the shell and in the core. We can conclude that while non contingent sucrose feeding activates dopamine transmission in the shell and core, response-contingent feeding activates without habituation dopamine transmission selectively in the shell in nose poking FR1 trained rats as a result of the action of sucrose conditioned cues. In lever pressing trained rats during responding for sucrose we found an increase of DA in both areas as a result of the higher effort required to obtain the reward. These findings can explain most of the discrepancies existing in the literature on the responsiveness of shell and core DA during food self administration.