Neonatal capsaicin treatment in rats results in scratching behavior with skin damage: potential model of non-painful dysesthesia.
We administered capsaicin or vehicle in 2-day-old rat pups, and for over 6 months examined the rats for damaged skin and for the behaviors of scratching, gnawing and biting their skin. By 35 days of age, all rats in the capsaicin group (n = 10) had damaged skin (i.e., lesions, hair loss and red skin) on the rostral half of their bodies. Skin damage remained prevalent over 6 months, whereas vehicle-treated rats (n = 8) had virtually no skin damage. Gnawing and biting behaviors were rarely observed, however, rats in the capsaicin group frequently scratched themselves. There was a significant positive correlation between the frequency at which rats scratched themselves and the total area of skin damage. Morphine (3.0 mg/kg, i.p.) greatly increased scratching behavior in only the capsaicin-treated rats and naloxone (0.5 mg/kg, i.p.) significantly reduced scratching in these rats. Thus, neonatal capsaicin, in its destruction of the majority of primary afferent C-fibers, is capable of inducing opioid-sensitive scratching behavior.
Thomas
D A
DA
Neurobiology and Anesthesiology Branch, National Institute of Dental Research, National Institutes of Health, Bethesda, MD.
Dubner
R
R
Ruda
M A
MA
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D001522:Behavior, Animal / Q000187:drug effects*; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D004195:Disease Models, Animal; D007278:Injections, Spinal; D007279:Injections, Subcutaneous; D008297:Male; D009020:Morphine / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009412:Nerve Fibers / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D012652:Self Mutilation / Q000139:chemically induced* / Q000473:pathology / Q000523:psychology; D012867:Skin / Q000473:pathology*; D013373:Substance P / Q000008:administration & dosage / Q000494:pharmacology
D013373:Substance P; D009270:Naloxone; D009020:Morphine; D002211:Capsaicin