A comparison of endocrine pancreatic tissue in adults of four species of lampreys in British Columbia: A morphological and immunohistochemical study

Abstract

Histological techniques and immunohistochemistry with antisera against insulin and somatostatin were used in a study of the identification and the distribution of endocrine pancreatic tissue in adults of four species of lampreys in British Columbia. The fine structure of the pancreatic cells of one of the species was also examined. The four species ( Lampetra ayresi, Lampetra tridentata, Lampetra macrostoma, and Lampetra richardsoni) all possess cranial and caudal pancreatic masses and an intervening intermediate cord, but there are variations in amount and deposition of the pancreatic tissue with respect to the alimentary canal and the liver which appear to be species specific. There is also some variation in the distribution of pancreatic tissue between L. richardsoni of different stream populations. A newly identified parasitic variety of L. richardsoni in Morrison Creek, called L. richardsoni var. marifuga, usually has no cranial pancreas but has an extensive intermediate cord. The distribution of pancreatic tissue in these lampreys is of relevance to taxonomy and to variations in development of the endocrine pancreas during lamprey metamorphosis. The pancreatic tissue of all species and var. marifuga is composed of cells which are immunoreactive to either insulin or somatostatin antisera. The fine structure of cells from the cranial and caudal pancreatic tissue from L. ayresi does not vary with saltwater and fresh-water acclimation. Insulin-containing B cells and somatostatin-containing D cells are present in equal numbers in both pancreatic regions and the cells each have characteristic cytoplasmic granules. A third cell type is most abundant in the cranial pancreas but it is of unknown function.