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The Journal of Neuroscience, July 20, 2005, 25(29):6729-6733; doi:10.1523/JNEUROSCI.1498-05.2005

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BRIEF COMMUNICATION
Extended Habit Training Reduces Dopamine Mediation of Appetitive Response Expression

Won Yung Choi,¹ Peter D. Balsam,² and Jon C. Horvitz³

¹Department of Psychology, Columbia University, New York, New York 10027, ²Department of Psychology, Barnard College, Columbia University, New York, New York 10027, and ³Department of Psychology, Boston College, Chestnut Hill, Massachusetts 02467

A wide range of behaviors is impaired after disruption of dopamine (DA) transmission, yet behaviors that are reflexive, automatic, or elicited by salient cues often remain intact. Responses triggered by strong external cues appear to be DA independent. Here, we examined the possibility that a single behavior may become DA independent as a result of extended training. Rats were trained to execute a head-entry response to a cue signaling food delivery. Vulnerability of the response to D₁ or D₂ receptor blockade was assessed on day 3, 7, or 17 of 28-trial-per-day training. During the early stages of training, the D₁ receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH 23390) increased response latencies; however, the same behavior was unaffected by SCH 23390 in animals tested during the later stages of training. Other aspects of behavior such as locomotion and head-entry responses during the uncued intertrial interval remained vulnerable to SCH 23390 throughout the experiment. This D₁-mediated response was unaffected by the D₂ antagonist raclopride, even at a dose that strongly suppressed locomotion. The results provide strong evidence that a D₁-dependent behavior becomes less dependent on DA with extended training. A number of fundamental neurobiological changes occur as behaviors become learned habits; at least for some responses, this change involves a shift from D₁-mediated to D₁-independent responding.

Key words: learning; motor; D₁; SCH 23390; raclopride; rat

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Received Dec 6, 2004; revised May 25, 2005; accepted May 26, 2005.

This article has been cited by other articles:

				J. R. Wickens, J. C. Horvitz, R. M. Costa, and S. Killcross Dopaminergic Mechanisms in Actions and Habits J. Neurosci., August 1, 2007; 27(31): 8181 - 8183. [Abstract] [Full Text] [PDF]

				A. Nelson and S. Killcross Amphetamine exposure enhances habit formation. J. Neurosci., April 5, 2006; 26(14): 3805 - 3812. [Abstract] [Full Text] [PDF]

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