Morphine-induced modulation of nociceptive spinal dorsan horn neuronal activities after formalin-induced inflammatory pain

Joo Min Park, Kang Wu Li, Sung Jun Jung, Jun Kim, Sangjeong Kim

Research output: Contribution to journalArticleResearchpeer-review

Abstract

In this study, we examined the morphine-induced modulation of the nociceptive spinal dorsal horn neuronal activities before and after formalin-induced inflammatory pain. Intradermal injection of formalin induced time-dependent changes in the spontaneous activity of nociceptive dorsal horn neurons. In naïve cats before the injection of formalin, iontophoretically applied morphine attenuated the naturally and electrically evoked neuronal responses of dorsal horn neurons. However, neuronal responses after the formalin-induced inflammation were significantly increased by morphine. Bicuculline, GABAA antagonist, increased the naturally and electrically evoked neuronal responses of dorsal horn neurons. This increase in neuronal responses due to bicuculline after the formalin-induced inflammation was larger than that in the naïve state, suggesting that basal GABAA tone increased after the formalin injection. Muscimol, GABAA agonist, reduced the neuronal responses before the treatment with formalin, but not after formalin treatment, again indicating an increase in the GABAergic basal tone after the formalin injection which saturated the neuronal responses to GABA agonist. Morphine-induced increase in the spinal nociceptive responses after formalin treatment was inhibited by co-application of muscimol. These data suggest that formalin-induced inflammation increases GABAA basal tone and the inhibition of this augmented GABAA basal tone by morphine results in a paradoxical morphine-induced increase in the spinal nociceptive neuronal responses after the formalin-induced inflammation.

Original languageEnglish
Pages (from-to)77-86
Number of pages10
JournalKorean Journal of Physiology and Pharmacology
Volume9
Issue number2
StatePublished - 1 Apr 2005

Fingerprint

Horns
Morphine
Formaldehyde
Pain
Posterior Horn Cells
Inflammation
Muscimol
Bicuculline
Injections
GABA-A Receptor Agonists
GABA Agonists
GABA-A Receptor Antagonists
Intradermal Injections
Nociceptors
Cats
Therapeutics

Keywords

  • GABA basal tone
  • Morphine
  • Nociceptive dorsal horn neurons
  • Spinal cord
  • Subacute inflammatory state

Cite this

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title = "Morphine-induced modulation of nociceptive spinal dorsan horn neuronal activities after formalin-induced inflammatory pain",
abstract = "In this study, we examined the morphine-induced modulation of the nociceptive spinal dorsal horn neuronal activities before and after formalin-induced inflammatory pain. Intradermal injection of formalin induced time-dependent changes in the spontaneous activity of nociceptive dorsal horn neurons. In na{\"i}ve cats before the injection of formalin, iontophoretically applied morphine attenuated the naturally and electrically evoked neuronal responses of dorsal horn neurons. However, neuronal responses after the formalin-induced inflammation were significantly increased by morphine. Bicuculline, GABAA antagonist, increased the naturally and electrically evoked neuronal responses of dorsal horn neurons. This increase in neuronal responses due to bicuculline after the formalin-induced inflammation was larger than that in the na{\"i}ve state, suggesting that basal GABAA tone increased after the formalin injection. Muscimol, GABAA agonist, reduced the neuronal responses before the treatment with formalin, but not after formalin treatment, again indicating an increase in the GABAergic basal tone after the formalin injection which saturated the neuronal responses to GABA agonist. Morphine-induced increase in the spinal nociceptive responses after formalin treatment was inhibited by co-application of muscimol. These data suggest that formalin-induced inflammation increases GABAA basal tone and the inhibition of this augmented GABAA basal tone by morphine results in a paradoxical morphine-induced increase in the spinal nociceptive neuronal responses after the formalin-induced inflammation.",
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Morphine-induced modulation of nociceptive spinal dorsan horn neuronal activities after formalin-induced inflammatory pain. / Park, Joo Min; Li, Kang Wu; Jung, Sung Jun; Kim, Jun; Kim, Sangjeong.

In: Korean Journal of Physiology and Pharmacology, Vol. 9, No. 2, 01.04.2005, p. 77-86.

Research output: Contribution to journalArticleResearchpeer-review

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