1. ¹Department of Neurobiology, Pharmacology and Physiology, The University of Chicago, Chicago, IL, USA
2. ²Department of Psychology, Barnard College of Columbia University, New York, NY, USA
3. ³Department of Biopsychology, New York State Psychiatric Institute, New York, NY, USA
4. ⁴PsychoGenics Inc., Hawthorne, NY, USA

Correspondence: Dr B Cagniard, Department of Neurobiology, Pharmacology and Physiology, The University of Chicago, 924E.57th Street, Room R222, Chicago, IL 60637, USA. Tel: +1 773 834 9006, Fax: +1 773 834 3808, E-mail: Barbara.cagniard@gmail.com

Received 20 July 2005; Revised 6 October 2005; Accepted 7 October 2005; Published online 23 November 2005.

Abstract

Dopamine has been critically implicated in learning and motivation, although its precise role remains to be determined. In order to investigate the involvement of dopamine in learning and motivation for a food reward, we used dopamine transporter knockdown mice (DAT KD) that have chronically elevated levels of extracellular dopamine. The present study demonstrates that chronically elevated dopamine enhances tendency to work for a food reward without apparent effects on Pavlovian and operant learning for this reward. The increase in dopamine is associated with elevated levels of dynorphin and Fos B expression in the dorsal caudate-putamen and the core but not the shell subregion of the nucleus accumbens. These data suggest that motivation to work, but not learning, for a food reward appears to be under the critical influence of tonic dopaminergic activity in discrete brain areas relevant for a reward-directed behavior.