Isobolographic analysis of interaction between spinal endomorphin-1, a newly isolated endogenous opioid peptide, and lidocaine in the rat formalin test

Shuanglin Hao, Osamu Takahata, Hiroshi Iwasaki

Research output: Contribution to journalArticle

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Endomorphin-1, a newly isolated endogenous opioid ligand, has a potential affinity with mu-opioid receptor. We investigated antinociception of intrathecal endomorphin-1 and lidocaine in the rat formalin test and examined the interaction between the two agents using isobolographic analysis. Intrathecal endomorphin-1 caused dose-dependent suppression of the formalin-induced biphasic behavioral response. Intrathecal lidocaine produced dose-dependent inhibition of phase-2 behavioral response. Isobolographic analysis confirmed that combination of intrathecal endomorphin-1 and lidocaine, given at a fixed dose ratio, produced synergistic suppression of phase-2 behavioral response. These data demonstrate that spinal endomorphin-1synergistically interacts with local anesthetic lidocaine in producing antinociception in the formalin test. Copyright (C) 1999 Elsevier Science Ireland Ltd.

Original languageEnglish (US)
Pages (from-to)177-180
Number of pages4
JournalNeuroscience Letters
Issue number3
StatePublished - Dec 10 1999
Externally publishedYes



  • Endomorphin-1
  • Formalin test
  • Isobolographic analysis
  • Lidocaine

ASJC Scopus subject areas

  • Neuroscience(all)

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