The graded and quantal nature of opioid analgesia in the rat tailflick assay

Byron C. Yoburn, Alan Cohen, Jason G. Umans, Geoffrey S.F. Ling, Charles E. Inturrisi

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Opioid agonists routinely increase the latency to respond in the rodent tailflick assay. The nature of this effect was investigated in 5 experiments using several parametric variations and routes of administration. Morphine and methadone were found to produce both quantal and graded effects in all experiments. In cases where quantal effects were observed, the majority of animals also responded in a graded manner during subsequent testing. The increase in latency to respond in the tailflick assay produced by opioid agonists is not accurately characterized as predominantly quantal.

Original languageEnglish (US)
Pages (from-to)327-336
Number of pages10
JournalBrain research
Issue number2
StatePublished - Apr 8 1985


  • analgesia
  • graded response
  • methadone
  • morphine
  • opioids
  • quantal response
  • tailflick assay

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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