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The Journal of Neuroscience, August 27, 2008, 28(35):8821-8831; doi:10.1523/JNEUROSCI.2225-08.2008

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Behavioral/Systems/Cognitive
Preferential Enhancement of Dopamine Transmission within the Nucleus Accumbens Shell by Cocaine Is Attributable to a Direct Increase in Phasic Dopamine Release Events

Brandon J. Aragona,^1,2 Nathan A. Cleaveland,² Garret D. Stuber,² Jeremy J. Day,² Regina M. Carelli,^2,3 and R. Mark Wightman^1,3

Departments of ¹Chemistry and ²Psychology and ³Neuroscience Center and Curriculum in Neurobiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290

Correspondence should be addressed R. Mark Wightman, Department of Chemistry, Campus Box 3290, Venable and Kenan Laboratories, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290. Email: rmw{at}unc.edu

Preferential enhancement of dopamine transmission within the nucleus accumbens (NAc) shell is a fundamental aspect of the neural regulation of cocaine reward. Despite its importance, the nature of this effect is poorly understood. Here, we used fast-scan cyclic voltammetry to examine specific transmission processes underlying cocaine-evoked increases in dopamine transmission within the NAc core and shell. Initially, we examined altered terminal dopamine concentrations after global autoreceptor blockade. This was the first examination of autoreceptor regulation of naturally occurring phasic dopamine transmission and provided a novel characterization of specific components of dopamine neurotransmission. Comparison of increased dopamine signaling evoked by autoreceptor blockade and cocaine administration allowed robust resolution between increased frequency, concentration, and duration of phasic dopamine release events after cocaine delivery. Cocaine increased dopamine transmission by slowed uptake and increased concentration of dopamine released in the core and shell. However, an additional increase in the number phasic release events occurred only within the NAc shell, and this increase was eliminated by inactivation of midbrain dopaminergic neurons. This represents the first evidence that cocaine directly increases the frequency of dopamine release events and reveals that this is responsible for preferentially increased dopamine transmission within the NAc shell after cocaine administration. Additionally, cocaine administration resulted in a synergistic increase in dopamine concentration, and subregion differences were abolished when cocaine was administered in the absence of autoregulation. Together, these results demonstrate that cocaine administration results in a temporally and regionally specific increase in phasic dopamine release that is significantly regulated by dopamine autoreceptors.

Key words: in vivo voltammetry; neurotransmission; carbon-fiber microelectrode; drug abuse; addiction; reward

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Received May 16, 2008; revised July 10, 2008; accepted July 24, 2008.

Correspondence should be addressed R. Mark Wightman, Department of Chemistry, Campus Box 3290, Venable and Kenan Laboratories, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290. Email: rmw{at}unc.edu

This article has been cited by other articles:

				L. A. Sombers, M. Beyene, R. M. Carelli, and R. Mark Wightman Synaptic Overflow of Dopamine in the Nucleus Accumbens Arises from Neuronal Activity in the Ventral Tegmental Area J. Neurosci., February 11, 2009; 29(6): 1735 - 1742. [Abstract] [Full Text] [PDF]

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