Abstract
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 language | English (US) |
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Pages (from-to) | 10784-10790 |
Number of pages | 7 |
Journal | Journal of Neuroscience |
Volume | 23 |
Issue number | 34 |
State | Published - Nov 26 2003 |
Keywords
- C-fos immunoreactivity
- Itch
- Morphine
- Naltrexone
- Rat
- Scratching
- Serotonin
ASJC Scopus subject areas
- Neuroscience(all)