The effects of UVB and 7, 12, dimethylbenz(alpha)anthracene (DMBA) on epidermal melanocytes of the tail in C57BL mice

Abstract

The morphological and numerical changes in the epidermal melanocyte system of the tail of C57BL mice were studied after exposure to 7, 12 dimethylbenz(alpha)anthracene (DMBA) followed by UVB irradiation. The dorsal aspect of the tail was exposed for 5 days per week, for a total duration of 10 weeks, to a daily dosage of 0.1 J/cm2 UVB (peak 310 nm). Once a week, 0.2 ml of 0.15% DMBA in acetone was locally applied to the irradiated areas. Biopsies were studied by the combined skin-splitting DOPA and electron microscopic techniques. After 10 weeks of DMBA treatment the following changes were observed: DMBA treatment the following changes were observed: the original brick-like arrangement of melanocytes became confluent, melanocytes were irregularly shaped, dendrites shortened and clumped together, and the outer root sheaths of the hair follicles became covered with melanocytes. There was a significant increase in the number of DOPA positive melanocytes at the end of the first week in DMBA and DMBA + UVB treated skin. Ultrastructurally, an increase in melanosome formation in melanocytes and transfer into keratinocytes was found, as well as redistribution of melanosomes from singlets and doublets into larger groups. Damage of melanocytes by the DMBA treatment was seen, but no inflammation or tumor formation was observed.