ABSTRACT: Eight spontaneous orocutaneous papillomas of adult, wild-caught brown bullheads Ictalurus nebulosus and 4 anatomically matching control tissue samples were examined by electron microscopy. Ultrastructural characteristics of normal and neoplastic Malpighian epithelial cells were compared and neoplastic cells were described. Normal Malpighian epithelial cells of brown bullheads were similar to those of other teleosts. Euchromatic nucleus, abundant nuclear pores and numerous ribosomes suggested elevated protein synthetic activity in both normal and neoplastic Malpighian cells. Three morphological alterations were consistently present in neoplastic cells: loss of zonal cytoplasmic distribution of organelles, well-developed vesicular system and disorganization of bundles of intermediate filaments (cytokeratin, presumably) with frequent whorl formation. These changes suggest a high membrane-generating activity and imperfect differentiation in these cells, which would be compatible with their neoplastic nature. There were no other significant morphological differences between normal and neoplastic Malpighian epithelial cells. No virus particles were detected in the 8 papillomas examined.

KEY WORDS: Brown bullhead . Ictalurus nebulosus . Mucosa . Papilloma . Skin . Ultrastructure

Published in DAO Vol. 24, No. 2 (1996) on February 1
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 1996