Expression of morphine-conditioned hyperactivity is attenuated by naloxone and pimozide

J. L. Neisewander, M. T. Bardo

Research output: Contribution to journalArticlepeer-review

28 Scopus citations


The present experiments assessed whether morphine-conditioned hyperactivity could be attenuated by either the opiate antagonist naloxone or the dopamine antagonist pimozide. Both of these antagonists were shown to block the unconditioned hyperactivity induced by 2 mg/kg morphine (Experiment 1). Rats were then conditioned by pairing this dose of morphine repeatedly with a distinctive environment (Experiment 2). Following several drug-environment pairings, rats displayed a hyperactive conditioned response (CR) when exposed to the environment in the absence of the drug. CR expression was counteracted by 1 mg/kg naloxone and was attenuated by pimozide (0.25, 0.33, and 0.4 mg/kg) in a dose-related manner. These findings suggest that the unconditioned and conditioned hyperactive responses produced by morphine may involve similar neuropharmacologic substrates.

Original languageEnglish (US)
Pages (from-to)314-319
Number of pages6
Issue number3
StatePublished - Nov 1987
Externally publishedYes


  • Classical conditioning
  • Conditioned hyperactivity
  • Morphine
  • Naloxone
  • Pimozide

ASJC Scopus subject areas

  • Pharmacology


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