Itch Specific C fibers were not Destroyed by Neonatal Capsaicin Treatment in Rats

Deafferentation can be achieved by neonatal capsaicin treatment in rats. We estimated that itchy sensation would be attenuated by neonatal capsaicin treatment, because itchy sensation is transmitted to the central nervous system via primary afferent C-fibers in the spinothalamic tract. To reveal neonatal deafferentation modify the scratching behavior induced by pruritogenic agents in rats, we treated neonatal rats with capsaicin to deafferent C-fibers and performed behavioral tests using pruritogenic agents. Deafferentation by capsaicin was successful, as evidenced by the decreased number of eye wipings induced by NaOH compared with the control rats. Histamine or compound 48/80, mast cell degranulationg agent, was injected subcutaneously as a pruritogenic agents and then scratching behavior was monitored over 30 min. No significant differences were detected between capsaicin-treated and control groups. These results suggest that neonatal deafferentation does not modify scratching behavior induced by pruritogenic agents in rats and itch-specific C-fibers are not destroyed by neonatal capsaicin treatment or deafferentation activates other itchy pathway.