Capsaicin Injection in Neonatal Period Potentiates Intensity and Duration of Atopic Dermatitis of Rats.

Background: Atopic dermatitis (AD) is a chronically relapsing inflammatory skin disease, characterized by severe itching and dysfunction of skin homeostasis. Previously, new AD model was established through capsaicin injection to neonatal rats, which displayed itching behavior and skin inflammation from 3 weeks after injection.

Methods: Rats were injected with capsaicin and AD skins were analyzed using immunohistochemistry, RT-PCR, and immunoblot analysis.

Results: We showed that alteration of filaggrin and corneodesmosin (CDSN) proteolytic processing was co-related with AD development. New-borne rat showed well-developed epidermis, which became thinner till 2 week-age when hair began to grow. After that, epidermal thickness gradually increased, which was co-related with expression of epidermal differentiation markers, suggesting of U-shape epidermal development. To investigate relationship between AD and epidermal development, neonate, 2 and 4 week-age rats were injected with capsaicin and AD symptoms were monitored. A more late injection produced earlier development of AD but AD symptoms were less severe and shorter duration, suggesting of stimulation in neonatal period potentiated AD symptoms. Subsequent immunohistochemical staining showed increase of Lgr6 expression, which is known as epidermal stem cell marker.

Conclusions: These results suggested that postnatal epidermal development may influence on AD development.