The Agnathan Enteropancreatic Endocrine System: Phylogenetic and Ontogenetic Histories, Structure, and Function

The extant jawless fishes (Agnatha) include the hagfishes and lampreys whose ancestry can be traced through a conserved evolution to the earliest of vertebrates. This review traces the study of the enteropancreatic (EP), endocrine cells and their products in hagfishes and lampreys over the past two centuries. Erika Plisetskaya is one of several prominent comparative endocrinologists who studied the development, distribution or function of the agnathan EP system. Her physiological studies in Russia laid the foundation for her subsequent isolation in North America of the first lamprey EP peptides (insulin and somatostatin) and providing the first homologous radioimmunoassay for agnathan (lamprey) insulin. This review also emphasizes the nature and the method of development of the agnathan endocrine pancreas (islet organ), for it reflects the earliest vertebrate endocrine pancreas originating from intestinal and/or bile-duct epithelia. The lamprey life cycle includes a protracted larval period and a metamorphosis when the adult EP system develops. Differences in morphogenesis during metamorphosis of southern- and northern-hemisphere lampreys dictate that a single cranial mass (islet organ) appear in the former and both a cranial and a caudal principal islet comprises most of the islet organ in holarctic species. There are differences in distribution of cell types and in the primary structure of the peptides in the definitive islet organ of hagfishes and lampreys. The primary structures of insulin, somatostatins, glucagons, glucagon-like peptide, and peptide tyrosine tyrosine are now available for three lamprey species representing three genera and two of the three families. Differences in structure of peptides within, and between, families is providing support for earlier views on the time of divergence of the families and the different genera. It is concluded that due to the ancient lineage and successful habitation of lampreys and hagfishes, and the importance of the EP system to their survival, that their EP systems should be a research focus well into the next century

A comparison of the thyroid follicular cells of young and old rats in the light and electron microscope.

In scientific discourse aging implies "a determined chain of events occupying a significant portion of the lifespan after maturity" (Birren, 1959). This definition suggests changes within an organism, or object, with time. Another term used quite frequently is "senescence", defined as "a process of unfavorable progressive change, usually correlated with the passage of time, becoming apparent after maturity and terminating invariably in death of the individual" (Lansing, 1951). [...

Metamorphosis of the olfactory organ of the sea lamprey (Petromyzon marinus L.): Morphological changes and morphometric analysis

In larval sea lampreys (Petromyzon marinus), a small, relatively inconspicuous olfactory organ sac contains small, densely packed olfactory receptor neurons and sustentacular cells. During metamorphosis, the larval organ transforms into a prominent lamellar structure with large distinct olfactory epithelial cells that is characteristic of the adult lamprey. In the present study, scanning electron microscopy and light microscopy are used to examine changes during the seven stages (1–7) of metamorphosis. The magnitude of growth over the course of metamorphosis is evident from the doubling of the relative weight of the nasal sac. During early metamorphosis (stages 1 and 2), the larval olfactory organ enlarges, and by stage 3 specific adult structures begin to form, namely a nasal valve between the nasal tube and the organ, lamellar folds, and diverticuli of the accessory olfactory organ. Subsequent development involves widening of the cells lining the lamellar folds to the form characteristic of postmetamorphic lampreys. Although the cells in the troughs initially retain numerical density values that are significantly higher than those on the lamellar surfaces, by stage 7 values decline both in troughs and along lamellar surfaces to those observed in adults. These results show that although expansion of the olfactory organ is ongoing throughout metamorphosis, remodeling occurs early (by stage 3). This timing provides space for extensive olfactory receptor neuron neurogenesis and differentiation and correlates with the transformation of some organs that were previously examined. This is the first report in any species of olfactory receptor neuron zonation based on morphometric characteristics. J. Morphol. 231:41–52, 1997. © 1997 Wiley-Liss, Inc