Cysts and tumour‐like lesions in the endocrine pancreas of the lamprey (Lampetra fluviatilis)

Abstract

Histological observations on the endocrine pancreas of the upstream migrant stage of the River lamprey, Lamperra fluviatilis, have revealed a relatively high incidence of cysts and other tumour‐like lesions, remarkably similar to the hamartomas described in the Atlantic hagfish, Myxine glufinosa. The frequency of these lesions increases throughout the migratory period from autumn to spring. In the most common type the cysts are surrounded by an intensely granular, single‐layered epithelium and both the epithelial cells and the cyst contents show a marked reaction to aldehyde‐fuchsin staining. In more extreme forms the breakdown of the epithelial walls of neighbouring cysts leads to the formation of large multi‐locular structures occupying almost the whole of the islet organ, but no consistent evidence of changes in blood sugar levels has been obtained in animals where the islet tissue is severely affected. A smaller proportion of the animals display neoplastic developments, frequently associated with hyperplasia and vacuolization of the foregut epithelium. In such cases, there is evidence of invasiveness and the development of epithelioid nodules within the adjoining islet tissue. Cavitation within these nodules leads to the formation of cyst‐like structures containing cell debris which reacts to aldehyde‐fuchsin staining. The development of cysts and hyperplasia is interpreted as a renewal in the sexually mature lamprey of inherent trends towards epithelial proliferation and vacuolization that are involved during metamorphosis in the morphogenetic processes that lead to the formation of the adult foregut and cranial islet tissue.