Ultrastructural Study of Melanocytic Lesions in Albino Guinea Pigs Induced with 7,12-Dimethyl-Benzanthracene

Abstract

We studied the fine structure of benign, premalignant and malignant melanocytic lesions induced in Dunkin—Hartley guinea pigs by means of topical application of 7,1 2-dimethyl-benzanthracene (DMBAI. The most noteworthy characteristics of the atypical melanocytes (melanocytic dysplasia and melanomas) were the variable morphology and structure, and, in particular, the aberrant character of the melanosomes. The melanocytes presented irregularity of nuclear outlines with requent lobulation. The heterochromatin was usually found in thick clumps reinforcing the nuclear membrane, and the nucleoli were usually multiple. The melanosomes were ellipsoidal and spherical with a pattern that was lamellar, concentric, incomplete, and even microgranular and microvesicular. The melanization was usually in thick, irregular clumps. Melanosome complexes were always present.

Key Words:

• ultrastructure
• melanocytic carcino-genesis
• aberrant melanosomes