Endogenous κ-opioid receptor systems regulate mesoaccumbal dopamine dynamics and vulnerability to cocaine

Vladimir I. Chefer, Traci Czyzyk, Elizabeth A. Bolan, Jose Moron, John E. Pintar, Toni S. Shippenberg

Research output: Contribution to journalArticlepeer-review

121 Scopus citations

Abstract

Genetic and pharmacological approaches were used to examine κ-opioid receptor (KOR-1) regulation of dopamine (DA) dynamics in the nucleus accumbens and vulnerability to cocaine. Microdialysis revealed that basal DA release and DA extraction fraction (Ed), an indirect measure of DA uptake, are enhanced in KOR-1 knock-out mice. Analysis of DA uptake revealed a decreased Km but unchanged Vmax in knock-outs. Knock-out mice exhibited an augmented locomotor response to cocaine, which did not differ from that of wild-types administered a behavioral sensitizing cocaine treatment. The ability of cocaine to increase DA was enhanced in knock-outs, whereas c-fos induction was decreased. Although repeated cocaine administration to wild types produced behavioral sensitization, knock-outs exhibited no additional enhancement of behavior. Administration of the long-acting KOR antagonist nor-binaltorphimine to wild-type mice increased DA dynamics. However, the effects varied with the duration of KOR-1 blockade. Basal DA release was increased whereas Ed was unaltered after 1 h blockade. After 24 h, release and Ed were increased. The behavioral and neurochemical effects of cocaine were enhanced at both time points. These data demonstrate the existence of an endogenous KOR-1 system that tonically inhibits mesoaccumbal DA neurotransmission. Its loss induces neuroadaptations characteristic of "cocaine-sensitized" animals, indicating a critical role of KOR-1 in attenuating responsiveness to cocaine. The increased DA uptake after pharmacological inactivation or gene deletion highlights the plasticity of mesoaccumbal DA neurons and suggests that loss of KOR-1 and the resultant disinhibition of DA neurons trigger short- and long-term DA transporter adaptations that maintain normal DA levels, despite enhanced release.

Original languageEnglish (US)
Pages (from-to)5029-5037
Number of pages9
JournalJournal of Neuroscience
Volume25
Issue number20
DOIs
StatePublished - May 18 2005

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)

Keywords

  • Cocaine
  • Dopamine
  • Microdialysis
  • Nor-binaltorphimine
  • Nucleus accumbens
  • κ-opioid receptor

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