Nor-binaltorphimine: An ultra-long acting kappa-opioid antagonist in pigeons

D. C. Jewett, J. H. Woods

Research output: Contribution to journalArticlepeer-review

21 Scopus citations


This study assessed the ability of naltrexone and nor-binaltorphimine (NBNI) to antagonize the rate-decreasing effects of opioid agonists. Food-restricted pigeons were trained to peck a lit key under a fixed-ratio (FR) 20 schedule of food reinforcement. Bremazocine, a kappa-opioid agonist, decreased food-reinforced responding ED50 = 0.02 mg/kg), and naltrexone (5.6 mg/kg) reduced the potency of bremazocine six-fold. The effect of naltrexone lasted less than 24 h. A single injection of NBNI (1 mg/kg) was given to four pigeons, and the time course of antagonism of the rate-decreasing effects of bremazocine was measured. One hour after NBNI[ was given, it was ineffective. Eight days later, NBNI produced a five-fold reduction in the potency of bremazocine. Between 12 and 20 days after NBNI, it reduced the potency of bremazocine 14-fold. NBNI continued to antagonize bremazocine for 11 weeks. Smaller doses of NBNI (0.001-0.1 mg/kg) were ineffective. The effect of NBNI was not due to tolerance to bremazocine, since tolerance failed to develop to bremazocine administered repeatedly. NBNI (1 mg/kg) did not antagonize the response rate-decreasing effects of morphine, a mu-opioid agonist, or BW373U86, a delta-opioid agonist. NBNI was an effective and extremely long-lasting kappa-opioid antagonist in the pigeon. The duration of action of NBNI is among the longest yet described in any species.

Original languageEnglish (US)
Pages (from-to)815-820
Number of pages6
JournalBehavioural pharmacology
Issue number8
StatePublished - 1995
Externally publishedYes


  • BW373U86
  • Bremazocine
  • Morphine
  • Naltrexone
  • Nor-binaltorphimine
  • Opioids
  • Pigeon
  • Schedule-controlled behavior

ASJC Scopus subject areas

  • Pharmacology
  • Psychiatry and Mental health


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