• Hiroshi Nojima, Christopher T Simons, Jason M Cuellar, Mirela Iodi Carstens, Justin A Moore, and Earl Carstens.
• Department of Applied Pharmacology, Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama 930-0194, Japan.
• J. Neurosci. 2003 Nov 26;23(34):10784-90.

AbstractWe investigated a spinal site for opioid modulation of itch-related scratching behavior in rats. Intradermal 5-HT (2%, 10 microl) 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.

36 keywords...

hide…