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Eur J Neurosci. 2014 Oct;40(7):3041-3054. doi: 10.1111/ejn.12709. Epub 2014 Sep 11.

Rapid dopamine transmission within the nucleus accumbens: dramatic difference between morphine and oxycodone delivery.

Author information

1
Department of Psychology, University of Michigan, Ann Arbor, MI 48109.
2
Departments of Chemistry and Pharmacology, University of Michigan, Ann Arbor, MI 48109.
3
Program in Neuroscience, University of Michigan, Ann Arbor, MI 48109.
#
Contributed equally

Abstract

While most drugs of abuse increase dopamine neurotransmission, rapid neurochemical measurements show that different drugs evoke distinct dopamine release patterns within the nucleus accumbens. Rapid changes in dopamine concentration following psychostimulant administration have been well studied; however, such changes have never been examined following opioid delivery. Here, we provide novel measures of rapid dopamine release following intravenous infusion of two opioids, morphine and oxycodone, in drug-naïve rats using fast-scan cyclic voltammetry and rapid (1 min) microdialysis coupled with high-performance liquid chromatography - tandem mass spectrometry (HPLC-MS). In addition to measuring rapid dopamine transmission, microdialysis HPLC-MS measures changes in GABA, glutamate, monoamines, monoamine metabolites and several other neurotransmitters. Although both opioids increased dopamine release in the nucleus accumbens, their patterns of drug-evoked dopamine transmission differed dramatically. Oxycodone evoked a robust and stable increase in dopamine concentration and a robust increase in the frequency and amplitude of phasic dopamine release events. Conversely, morphine evoked a brief (~ 1 min) increase in dopamine that was coincident with a surge in GABA concentration and then both transmitters returned to baseline levels. Thus, by providing rapid measures of neurotransmission, this study reveals previously unknown differences in opioid-induced neurotransmitter signaling. Investigating these differences may be essential for understanding how these two drugs of abuse could differentially usurp motivational circuitry and powerfully influence behavior.

KEYWORDS:

addiction; motivation; opioid; reward

PMID:
25208732
PMCID:
PMC4358739
DOI:
10.1111/ejn.12709
[Indexed for MEDLINE]
Free PMC Article

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