Opioid Modulation of Scratching and Spinal c-fos Expression Evoked by Intradermal Serotonin

Hiroshi Nojima, Christopher T. Simons, Jason M. Cuellar, Mirela Iodi Carstens, Justin A. Moore, Earl Carstens

Research output: Contribution to journalArticlepeer-review

48 Scopus citations


We investigated a spinal site for opioid modulation of itch-related scratching behavior in rats. Intradermal 5-HT (2%, 10 μl) elicited intermittent bouts of hindlimb scratching directed toward the injection site (nape of neck) beginning within minutes and lasting >1 hr. 5-HT-evoked scratching was significantly reduced by systemic administration of the opiate antagonist naltrexone but was not affected by systemic morphine at a dosage (3 mg/kg) that induces analgesia. Intradermal 5-HT elicited a significant increase in c-fos-like immunoreactivity (FLI) in superficial laminas I-III at the lateral aspect of the cervical C3-C6 dorsal horn compared with controls receiving intradermal saline. Neither systemic morphine nor naltrexone significantly affected counts of 5-HT-evoked FLI. The lack of effect of morphine suggests that intradermal 5-HT activates dorsal horn neurons, signaling itch but not pain. Attenuation of 5-HT-evoked scratching but not spinal FLI by naltrexone suggests a supraspinal site for its antipruritic action. In contrast, morphine significantly attenuated FLI elicited by intradermal capsaicin, a chemical that induces pain but not scratching.

Original languageEnglish (US)
Pages (from-to)10784-10790
Number of pages7
JournalJournal of Neuroscience
Issue number34
StatePublished - Nov 26 2003


  • C-fos immunoreactivity
  • Itch
  • Morphine
  • Naltrexone
  • Rat
  • Scratching
  • Serotonin

ASJC Scopus subject areas

  • Neuroscience(all)


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