Capsaicin-induced neuroparalytic keratitis-like corneal changes in the mouse

A single subcutaneous injection of 12.5-100 mg kg-1 capsaicin to newborn mice produced gross corneal changes. The changes were manifest about three weeks after capsaicin treatment and progressed dose-dependently from slight punctate vesiculations in the epithelium to diffuse edematous opacities and vascularizations in the stroma, followed by recovery in several weeks with or without residual scars. Control newborn mice with vehicle solution did not show any corneal abnormality. The most prominent histopathological feature of the affected corneas was a marked loss of nerve axons in the epithelium with associated disorganization of the epithelium. Similar corneal changes were observed with systemic capsaicin treatment to young or adult mice. The pathogenesis of the capsaicin-induced corneal changes was discussed with reference to the trophic action of the trigeminal nerve.