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Neuroscience. 2018 Feb 21;372:306-315. doi: 10.1016/j.neuroscience.2017.12.003. Epub 2017 Dec 15.

Inhibiting Mesolimbic Dopamine Neurons Reduces the Initiation and Maintenance of Instrumental Responding.

Author information

1
Neuroscience Graduate Program, University of California at San Francisco, San Francisco, CA 94158, USA.
2
Department of Neurology, University of California at San Francisco, San Francisco, CA 94158, USA.
3
Department of Psychological and Brain Sciences, Krieger School of Arts and Sciences, Johns Hopkins University, Baltimore, MD 21218, USA; The Solomon H. Snyder Department of Neuroscience, Johns Hopkins School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA. Electronic address: patricia.janak@jhu.edu.

Abstract

Mesolimbic dopamine perturbations modulate performance of reward-seeking behavior, with tasks requiring high effort being especially vulnerable to disruption of dopamine signaling. Previous work primarily investigated long-term perturbations such as receptor antagonism and dopamine depletion, which constrain the ability to assess dopamine contributions to effort expenditure in isolation from other behavior events, such as reward consumption. Also unclear is if dopamine is required for both initiation and maintenance when a sequence of multiple instrumental responses is required. Here we used optogenetic inhibition of midbrain TH+  neurons to probe the role of dopamine neuron activity during instrumental responding for reward by varying the time epoch of neural inhibition relative to the time of response initiation. Within a fixed-ratio procedure, requiring eight nosepoke responses per reinforcer delivery, or a progressive ratio (PR) procedure, in which within-session response requirements increased exponentially, inhibiting dopamine neurons while mice were engaged in response bouts decreased the probability of continued responding. If inhibition occurred during each attempted bout, the effect was to decrease total responses, and thus amount of rewards earned, over a session. In contrast, if inhibition was applied only during some bouts, mice increased the number of bouts initiated to earn control levels of reward. Inhibiting dopamine neurons while mice were not responding decreased the probability of initiating an instrumental response but had no effect on the amount of effort exerted over the entire session. We conclude that midbrain dopamine signaling promotes initiation of instrumental responding and maintains motivation to continue ongoing bouts of effortful responses.

KEYWORDS:

instrumental learning; motivation; optogenetics; progressive ratio; ventral tegmental area

PMID:
29248527
PMCID:
PMC5942212
[Available on 2019-02-21]
DOI:
10.1016/j.neuroscience.2017.12.003
[Indexed for MEDLINE]

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