GABAA and dopamine receptors in the nucleus accumbens shell differentially influence performance of a water-reinforced progressive ratio task

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Abstract

Several authors have shown that injections of the GABAA agonist muscimol into the medial shell region of the nucleus accumbens (AcbSh) result in large increases in food, but not water, intake. In previous studies we demonstrated that intra-AcbSh injections of either muscimol or of the indirect dopamine agonist amphetamine increase response output on a food-reinforced progressive ratio schedule. In the current experiment we extended these observations by examining the effects of muscimol and amphetamine injections on the performance of a water-reinforced progressive ratio task in mildly deprived animals. We found that muscimol did not affect the number of responses made in the water-reinforced task, even though a marked increase in responding was observed after amphetamine. Muscimol did, however, significantly increase food intake in the same animals. The results suggest that the enhancing effects of intra-AcbSh muscimol differ from those of amphetamine in that they are selective for food-reinforced behaviors.

Highlights

▸ Progressive ratio performance examined after drug injections in accumbens shell. ▸ Amphetamine increased responding for water reward. ▸ The amphetamine effect was due to increased duration of sessions. ▸ Muscimol increased food intake, but did not increase responding for water. ▸ We conclude that inactivation of the shell does not increase willingness to work for water.

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