title: Extracellular dopamine levels in striatal subregions track shifts in motivation and response cost during instrumental conditioning.
abstract: Tonic dopamine (DA) signaling is widely regarded as playing a central role in effort-based decision making and in the motivational control of instrumental performance. The current study used microdialysis to monitor changes in extracellular DA levels across subregions of the nucleus accumbens and dorsal striatum of rats as they lever pressed for food reward on a probabilistic schedule of reinforcement, a procedure that ensured they would experience variation in the amount of effort needed to earn rewards across tests. Each rat was given three tests. Rats were hungry for the first and last test, but were sated on food before the middle test, allowing us to assess the effects of a downshift in motivational state on task performance and conditioning-induced DA efflux. During hungry tests, DA levels rose in both the shell and core of the accumbens and, to a lesser degree, in both the medial and lateral divisions of the dorsal striatum. Interestingly, changes in DA efflux across hungry tests in the accumbens core were negatively correlated with changes in the effort required to obtain rewards. We also found that--across regions--the DA response to instrumental conditioning was attenuated when rats were sated before testing. Furthermore, the effect of satiety on DA efflux in the accumbens shell was positively correlated with its effect on task performance. Together, the results indicate that tonic DA contributes to the control of instrumental performance by conveying information about the costs and benefits of responding to different striatal subregions.
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, Semel Institute for Neuroscience and Human Behavior, University of California, Los Angeles, Los Angeles, California 90024, USA. sostlund@ucla.edu
authors.forename: Sean B
authors.initials: SB
authors.lastname: Ostlund
authors.forename: Kate M
authors.initials: KM
authors.lastname: Wassum
authors.forename: Niall P
authors.initials: NP
authors.lastname: Murphy
authors.forename: Bernard W
authors.initials: BW
authors.lastname: Balleine
authors.forename: Nigel T
authors.initials: NT
authors.lastname: Maidment
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D003216:Conditioning, Operant / Q000502:physiology*; D003342:Corpus Striatum / Q000166:cytology / Q000378:metabolism*; D004298:Dopamine / Q000378:metabolism*; D004563:Electrochemistry / Q000379:methods; D045604:Extracellular Fluid / Q000378:metabolism*; D005215:Fasting / Q000502:physiology; D016014:Linear Models; D008297:Male; D017551:Microdialysis / Q000379:methods; D009042:Motivation / Q000502:physiology*; D009714:Nucleus Accumbens / Q000378:metabolism; D051381:Rats; D020318:Rats, Long-Evans; D012527:Satiation / Q000502:physiology
chemical_list: D004298:Dopamine