Pharmacology Biochemistry and Behavior, Vol. 59, No. 3, pp. 557–566, 1998 © 1998 Elsevier Science Inc. Printed in the USA. All rights reserved 0091-3057/98 $19.00 + .00 PII S0091-3057(97)00544-3 557 The Role of Accumbens Dopamine in Lever Pressing and Response Allocation: Effects of 6-OHDA Injected into Core and Dorsomedial Shell J. D. SOKOLOWSKI AND J. D. SALAMONE Department of Psychology, University of Connecticut, Storrs, CT 06269-1020 Received 17 January 1997; Revised 19 May 1997; Accepted 19 June 1997 SOKOLOWSKI, J. D. AND J. D. SALAMONE. The role of accumbens dopamine in relative response allocation: Effects of 6-OHDA injected into core and dorsomedial shell. PHARMACOL BIOCHEM BEHAV 59(3) 557–566, 1998.—Three ex- periments investigated the behavioral effects of injections of the neurotoxic agent 6-hydroxydopamine (6-OHDA) into the core or shell of the nucleus accumbens. In the first experiment, it was observed that injections of 6-OHDA into either core or shell had no significant effect on variable interval 30-s responding. In Experiment 2, responding on a fixed ratio 5 (FR5) schedule was impaired by 6-OHDA injections in the core, but not the shell. Rats with core injections of 6-OHDA showed sig- nificant alterations in the relative distribution of interresponse times, which were indicative of reductions in the maximal rate of responding and increases in the number of pauses. In the third experiment, rats were tested using a lever-pressing/chow- feeding procedure, in which a preferred food (Bioserve pellets) was available by pressing a lever on a FR5 schedule, but a less preferred food (lab chow) was also available concurrently in the test chamber. Untreated rats usually pressed the lever at high rates to obtain the food pellets and ate little of the lab chow. After training, dopamine depletions were produced by in- jections of 6-OHDA directly into the core or dorsomedial shell subregions. Injections of 6-OHDA into the core significantly decreased lever pressing for food pellets, increased lab chow consumption, and decreased the relative amount of food ob- tained by lever pressing. Dorsomedial shell injections of 6-OHDA had no significant effects on either lever pressing or lab chow consumption. Neurochemical results indicate that injections of 6-OHDA in the shell produced substantial depletions in the shell that were somewhat selective; however, injections of 6-OHDA into the core tended to deplete both core and shell. Correlational analyses revealed that decreases in FR5 lever pressing were associated with dopamine levels in the core, but not the shell. The present results indicate that substantial depletions of dopamine in the dorsomedial shell are not sufficient for suppressing reinforced lever pressing, and indicate that dopamine depletions must include the core area to impair perfor- mance on these tasks. The lack of effect of accumbens dopamine depletions on VI30 responding are consistent with the no- tion that accumbens dopamine depletions affect responding on schedules that generate a high rate of responding (FR5), but not those that generate a moderate rate of responding (e.g., VI30 s). The results of the concurrent FR5/chow-feeding experi- ment indicate that rats with accumbens dopamine depletions remain directed towards the acquisition and consumption of food. These results suggest that dopamine in the core region of accumbens sets constraints upon the selection of food-related behaviors, and that core dopamine depletions alter the relative allocation of food-related responses. © 1998 Elsevier Sci- ence Inc. Dopamine Reinforcement Operant Motivation Movement Behavioral economics SEVERAL studies have shown that antagonism of brain dopamine (DA) receptors impairs instrumental lever pressing (15,47–52,69–72). Depletions of DA in the ventrolateral neo- striatum lead to severe motor impairments that are associated with deficits in lever pressing (10,11,55). In addition, deple- tions of DA in the nucleus accumbens have been shown to re- duce lever pressing on some schedules [e.g., fixed ratio 5; (55)], while responding on other schedules is relatively unaf- Requests for reprints should be addressed to John D. Salamone, Department of Psychology, University of Connecticut, 406 Babbidge Road, U-20, Storrs, CT 06269-1020.