Distribution of PACAP-like immunoreactivity in the nervous system of oligochaeta

The marked similarity between the primary structures of human, other vertebrate, and the invertebrate tunicate PACAP suggests that PACAP is one of the most highly conserved peptides during the phylogeny of the metazoans. We investigated the distribution of PACAP-like immunoreactivity in the nervous system of three oligochaete (Annelida) worms with immunocytochemistry. The distribution pattern of immunoreactivity was similar in all three species (Lumbricus terrestris, Eisenia fetida, and Lumbricus polyphemus). The cerebral ganglion contains numerous immunoreactive cells and fibers. A few cells and fibers were found in the medial and lateral parts of the subesophageal and ventral cord ganglia. In the peripheral nervous system, immunoreactivity was found in the enteric nervous system, in epidermal sensory cells, and in the clitellum.     

Ultrastructure of midgut endocrine cells in the adult mosquito, Aedes aegypti

The ultrastructure of endocrine cells in the midgut of the adult mosquito, Aedes aegypti, resembled that of endocrine cells in the vertebrate gastro-intestinal tract. Midgut endocrine cells, positioned basally in the epithelium as single cells, were cone-shaped and smaller than the columnar digestive cells. The most distinctive characteristic of endocrine cells was numerous round secretory granules along the lateral and basal plasma membranes where contents of the granules were released by exocytosis. Secretory granules in each individual cell were exclusively of one type, either solid or 'haloed', and for all cells observed, the range in granule diameter was 60-120 nm. The cytoplasm varied in density from clear to dark. Lamellar bodies were prominent in the apical and lateral cellular regions and did not exhibit acid phosphatase activity. The basal plasma membrane was smooth adjacent to the basal lamina, whereas in digestive cells the membrane formed a labyrinth. Some endocrine cells reached the midgut lumen and were capped by microvilli; a system of vesicles and tubules extended from beneath the microvilli to the cell body. An estimated 500 endocrine cells were distributed in both the thoracic and abdominal regions of the adult midgut. In one midgut, we classified a sample of endocrine cells according to cytoplasmic density and granule type and size; endocrine cells with certain types of granules had specific distributions within the midgut.     

Gastrin- and cholecystokinin-like immunoreactivities in the nervous system of the earthworm.

The distribution of cholecystokinin and gastrin-like immunoreactive cell bodies and fibers in the nervous system of 2 annelid worms, Lumbricus terrestris and Eisenia fetida, has been studied by means of immunohistochemistry. The cerebral ganglion contains 170-250, the subesophageal ganglion contains 120-150, and the ventral ganglia contain 50-75 cholecystokinin immunoreactive cells, that represent 8-12%, 8-10% and 4-5% of the total cell number, respectively. The anti-gastrin serum stained 330-360 nerve cells in the cerebral, 32-46 in the subesophageal and 7-25 in the ventral cord ganglia, representing 15-16%, 2-3% and 0.5-2% of the total cell number. Immunopositivity was found with both antisera in the enteric nervous system, where the stomatogastric ganglia and the enteric plexus contain immunoreactive cells and fibers. Immunopositive cells were found in the epithelial and subepithelial cells, as well as in nerve cells innervating the muscular layer of the gastrointestinal tube. Various epidermal sensory cells also displayed strong immunoreactivity. According to our findings and the results of several functional studies, it is suggested that in annelids cholecystokinin- and gastrin-like peptides may be involved in digestive regulation, sensory processes and central integrating processes.     

A fourth type of neuroglial cell in the adult central nervous system

Labeling central nervous tissue from mature animals with antibodies to NG2 chondroitin sulfate proteoglycan reveals the existence of large numbers of NG2 positive cells, at least some of which are oligodendroglial progenitors. It is generally agreed that these cells differ from the classically defined neuroglia, since they are antigenetically different from astrocytes, oligodendrocytes, or microglial cells. Although the NG2 positive cells have been well characterized in light microscopic preparations, examination of the labeled cells by electron microscopy have not led to general agreement about their morphological features. The basic reason for this is that it is difficult to obtain good preservation of the fine structure of NG2 labeled neurons. Since these NG2 positive cells are abundant in the central nervous system, it was decided to examine routinely prepared tissue from the brains of mature monkeys and rats by electron microscopy to determine if there is a neuroglial cell type whose presence has been overlooked. It soon became evident that there is a fourth type of neuroglial cell. These cells have pale, irregular shaped nuclei with a thin rim of heterochromatin beneath the nuclear envelope, and they have pale cytoplasm. Superficially they resemble astrocytes, which is the probable reason why the presence of this fourth type of neuroglial cell has been largely overlooked. However, the fourth type of neuroglial cell, here referred to as a ß neuroglial cell, has no intermediate filaments in its cytoplasm, the mitochondria are thinner than those of astrocytes, centrioles are frequently encountered in their cytoplasm, and when they are adjacent to capillaries they are always separated from the basal membrane by an astrocytic processes.     

Novel aspects of the nervous system of Bonellia viridis (Echiura) revealed by the combination of immunohistochemistry, confocal laser-scanning microscopy and three-dimensional reconstruction

The Echiura have been placed in close phylogenetic affinity to the Annelida on the basis of numerous homologous characters including the mode of development, the nearly identical formation of a trochophore larva, as well as the development and ultrastructure of chaetae and spermatozoa. Furthermore, phylogenetic analysis of elongation factor-1 gene sequences supports placement of the Echiura within the Annelida. Nevertheless, the Echiura are generally excluded from the Annelida due to their lack of segmentation. However, it must be considered that this lack could represent a secondary condition and that Echiura are derived from formerly segmented ancestors. In the present study, the combination of methods applied reveals several novel aspects of the central nervous system in developmental stages of Bonellia viridis. The most important of these is the metameric organization of the ventral nerve cord. Antibodies against different neurotransmitters label discrete repetitive units of perikarya in the ventral nerve cord. This organisation is additionally supported by the distribution of peripheral nerves as shown by labelling of neurotubules. These nerves are clearly paired and are evenly distributed, corresponding to the serial units of serotoninergic neurons. Different methods of computer-aided three-dimensional reconstruction display the precise spatial distribution of perikarya and peripheral nerves allowing the repetitive units to be discerned on the basis of relative size, position and number of labelled cells. The repetitive units in the nervous system of B. viridis correspond to segmental ganglia of various Annelida and are interpreted as an indication that Echiura are derived from formerly segmented ancestors, thus supporting the systematic inclusion of the Echiura within the Annelida.     

BMP and Delta/Notch signaling control the development of amphioxus epidermal sensory neurons: insights into the evolution of the peripheral sensory system

The evolution of the nervous system has been a topic of great interest. To gain more insight into the evolution of the peripheral sensory system, we used the cephalochordate amphioxus. Amphioxus is a basal chordate that has a dorsal central nervous system (CNS) and a peripheral nervous system (PNS) comprising several types of epidermal sensory neurons (ESNs). Here, we show that a proneural basic helix-loop-helix gene (Ash) is co-expressed with the Delta ligand in ESN progenitor cells. Using pharmacological treatments, we demonstrate that Delta/Notch signaling is likely to be involved in the specification of amphioxus ESNs from their neighboring epidermal cells. We also show that BMP signaling functions upstream of Delta/Notch signaling to induce a ventral neurogenic domain. This patterning mechanism is highly similar to that of the peripheral sensory neurons in the protostome and vertebrate model animals, suggesting that they might share the same ancestry. Interestingly, when BMP signaling is globally elevated in amphioxus embryos, the distribution of ESNs expands to the entire epidermal ectoderm. These results suggest that by manipulating BMP signaling levels, a conserved neurogenesis circuit can be initiated at various locations in the epidermal ectoderm to generate peripheral sensory neurons in amphioxus embryos. We hypothesize that during chordate evolution, PNS progenitors might have been polarized to different positions in various chordate lineages owing to differential regulation of BMP signaling in the ectoderm.     

Microanatomy of the digestive system of Supachai's caecilian,Ichthyophis supachaii Taylor, 1960 (Amphibia: Gymnophiona)

The gross anatomy and microanatomy of the digestive system of Ichthyophis supachaii were investigated. The microscopic structures of the digestive system are similar to those in other caecilians. Functional and developing teeth are present in adults. The tongue contains the genioglossus muscle. The digestive tract is elongated and consists of the mucosa, submucosa, muscularis and adventitia/serosa. The oesophagus contains longitudinal folds and lacks oesophageal glands. We report for the first time the caecilian gastric rugae and specific localization of oxynticopeptic cells in the anterior gastric region. The intestinal folds are exclusively present in the anterior intestinal region. The liver comprises 30–40 incomplete hepatic lobes, lying in an imbricate manner. Each lobe is enveloped by haematopoietic tissue that produces and delivers blood cells into sinusoids. Hepatic parenchyma is organized into anastomosing, two‐cell‐thick plates, having sinusoids at the basal domain and bile canaliculi at the apical domain of hepatocytes. Pigment cells are scattered inside sinusoids. The pancreas contains pancreatic acini interspersed with islets of Langerhans. The gallbladder proper is thin and continuous with the cystic duct wall. Neutral and carboxylated acid mucosubstances are secreted along the digestive tract, while sulphated mucosubstances are not produced by the stomach and anterior intestinal regions.     

Choanocyte-like cells in the digestive system of the starfish Marthasterias glacialis (Echinodermata)

Two types of choanocyte-like cells have been found in the digestive tract of the starfish. Type I choanocytes are in the lining epithelium of all organs of the digestive system. These are narrow, columnar cells strongly anchored basally and expanded apically into a protuberance projecting into the lumen. A prominent flagellum surrounded by microvilli projects from the center of this protuberance. Apical cytoplasm contains numerous mitochondria, secondary lysosomes, and multivesicular bodies. A distinctive characteristic of these cells is a filament bundle that traverses the length of the cell from its region of attachment on the rootlet of the flagellar basal body to its terminus on the basal plasma membrane. Between the attenuated basal ends of type I cells are the nerve fibers of an intraepithelial nerve plexus. Thickness of the plexus is correlated with the quantity of type I cells in the epithelium. Type II choanocytes are in the cuboidal coelomic epithelium that forms the outer layer of digestive tract organs. These cells are smaller than those of type I, and they have an apical collar surmounted by a ring of 13 microvilli. Within the collar is a cup-shaped depression with a central flagellum. Coated vesicles, secondary lysosomes, and phagocytic infoldings are observed in and near the collar cytoplasm. Filament bundles similar to those in type I choanocytes are also observed in coelomic epithelial cells that are sufficiently tall. Injection of peroxidase into the stomach and ferritin into the coelom results in phagocytic uptake of these macromolecules by type I and type II choanocytes, respectively.     

Metameric organisation of the nervous system in developmental stages of Urechis caupo (Echiura) and its phylogenetic implications

The phylogenetic position of Echiura is still in continuous debate. The commonly accepted view regards Echiura as a distinct taxon, often classified as phylum, which forms the sister group of the Articulata. The alternative view considers Echiura to be a subtaxon of Annelida, which is supported by numerous shared characters. The correct systematic position of Echiura is inevitably linked to the presence or absence of true segmentation. The apparent lack of segmentation in Echiura is considered to be either primary, thereby supporting their exclusion from Annelida, or alternatively to be the result of reduction. The latter would clearly substantiate their classification as a subtaxon of Annelida. Immunohistochemical methods and confocal laser-scanning microscopy clearly demonstrate a metameric organisation of the nervous system in different larval stages of Urechis caupo, which corresponds to the segmental arrangement of ganglia in "typical" Annelida. This segmental pattern is reflected in the serially repetitive distribution of neurons containing the neurotransmitter serotonin (5-hydroxytryptamine) and also in the corresponding distribution of strictly paired peripheral nerves. Precisely two pairs of peripheral nerves are associated with each of the repetitive units. This metameric pattern also corresponds to the transient annulation of the trunk, which is found in late larval stages. Other characters of the nervous system including the paired origin of the ventral nerve cord, the anterior-posterior development gradient and the presence of a distinct suboesophageal ganglion are also found accordingly in typical Annelida. These results are interpreted as an indication that Echiura are derived from formerly segmented ancestors, and thus support their systematic inclusion within Annelida.     

Larval development of Myzostoma cirriferum (Myzostomida)

The larval development of Myzostoma cirriferum is described by means of SEM, TEM, and cLSM. It is similar to that of other myzostomids and includes three stages: the protrochophore, the trochophore, and the metatrochophore. The protrochophore is a ball-shaped larva present in culture from 18-48 h after egg laying. It has no internal organs and its body is made of three cell types: covering cells and ciliated cells that are external and surrounded by a cuticle, and resting cells that fill the blastocoel. The trochophore is a pear-shaped larva that develops 20-72 h after egg laying; the body includes the same three cell types as the previous stage. The metatrochophore is a pear-shaped larva that develops between 40 h and 14 days and is characterized by the presence of two bundles of four chaetae. When fully developed, the metatrochophore has a digestive system (made of a pharynx, an esophagus, and a blind digestive pouch), two pairs of protonephridia, and a nervous system composed of a supraesophageal ganglion, circumesophageal connectives, and dorsal and ventral nerves. Metamorphosis generally occurs 7 days after egg laying. At that time, the metatrochophore loses its chaetae and becomes pleated ventrally. This ultrastructural analysis suggests that chaetae and the five ventral longitudinal nerve cords of M. cirriferum metatrochophores are homologous structures to those observed in some polychaete trochophores. Coupled with recent phylogenetic analyses, where the Myzostomida are placed outside the Annelida, homologies between myzostomid and polychaete larvae support the view that a trochophore appeared early during the spiralian evolution.     

Avian Scale Development XIV: A Study of Cell Proliferation in the Epidermis of the Scaleless, sc/sc, Mutant

Embryonic induction has been demonstrated in numerous studies, yet the molecular basis for induction still eludes investigators. Components of the extracellular matrix (ECM), cell adhesion molecules (CAM), diffusable factors, as well as direct cell-cell contact, have been implicated in the early induction of avian feathers and scales. Although feathers and scales differ in many aspects, they are similar in that they appear initially as discrete and orderly arranged epidermal placodes. In the case of scutate scales, the cells of the epidermal placode are nonproliferative, while the cells of the interplacode regions are highly proliferative. In this study, I compare the proliferative activity of normal scale cells with that of the epidermal cells from embryos of the scaleless (sc/sc) mutant chicken which does not undergo epidermal placode formation and therefore lacks scutate scales. These results show that prior to the time that placodes would normally form, the proliferative activity of the scaleless epidermal cells is similar to that seen in normal epidermal cells. Likewise, the cessation of cell proliferation seen in normal placodes occurs in the epidermal basal cells of the sc/sc shank. It is the high rate of proliferation seen for the epidermal basal cells of the normal interplacode region and the outer surface of the scale ridge that never develops in the sc/sc epidermal cells.     

On the Fine Structure of Rastrognathia macrostoma gen. et sp.n. Placed in Rastrognathiidae fam.n. (Gnathostomulida)

Rastrognathia macrostoma gen. et sp.n. is described as belonging to Rastrognathiidae fam.n. The ultrastructure is described, especially the nervous and digestive systems and the epidermal specializations. In the epidermis the single cilia belong to the choanocyte-like cell type. An epidermal sensory cell with several cilia is described. The intraepithelial nervous system shows an orthogon pattern. Two ventral nerve trunks unite into a buccal ganglion. The jaws are secreted by the buccal epidermis. The endoderm consists of a single cell type. The food consists of bacteria. The mesodermal elements consist of six main longitudinal muscles.     

The endocrine cells in the gastroenteropancreatic system of the bowfin, Amia calva L.: an immunohistochemical, ultrastructural, and immunocytochemical analysis.

The gastroenteropancreatic (GEP) endocrine system of bowfin (Amia calva) was described using light and electron microscopy and immunological methods. The islet organ (endocrine pancreas) consists of diffusely scattered, mostly small islets and isolated patches of cells among and within the exocrine acini. The islets are composed of abundant, centrally located B cells immunoreactive to bovine and lamprey insulin antisera and D cells showing a widespread distribution and specificity to somatostatin antibodies. A and F cells are present at the very periphery of the islets and are immunoreactive with antisera against glucagon (and glucagon-like peptide) and several peptides of the pancreatic polypeptide (PP)-family, respectively. The peptides of the two families usually collocates within the same peripheral islet cells and are the most common immunoreactive peptides present in the extra-islet tissue. Immunocytochemistry and fine structural observations characterised the granule morphology for B and D cells and identified two cell types with granules immunoreactive to glucagon antisera. These two putative A cells had similar granules, which were distinct from either B or D cells, but one of the cells had rod-shaped cytoplasmic inclusions within cisternae of what appeared to be rough endoplasmic reticulum. The inclusions were not immunoreactive to either insulin or glucagon antisera. Only small numbers of cells in the stomach and intestine immunoreacted to antisera against somatostatin, glucagon, and PP-family peptides. The paucity of these cells was reflected in the low concentrations of these peptides in intestinal extracts. The GEP system of bowfin is not unlike that of other actinopterygian fishes, but there are some marked differences that may reflect the antiquity of this system and/or may be a consequence of the ontogeny of this system in this species.     

Histological and ultrastructural studies of the basal disk of Hydra

Summary The gastrodermis and mesoglea of the basal disk of Hydra were investigated to conclude a three-part series of papers. The gastrodermis is composed of digestive cells (most predominant cell type), mucous and nerve cells (both immature and fully differentiated). The principal function of the digestive cells appears to be storage of protein, lipid and glycogen reserves which are utilized by neighboring cells. Mucous cells apparently use some of the reserves to synthesize their secretions which lubricate cells and prevent cell damage during egestion of waste through the aboral pore. The function of the gastrodermal nerve cells is uncertain.The mesoglea of the basal disk, contains the same structural components as seen in other regions of the polyp. It is reasonable to assume that it maintains the same function of cell adhesion and migration. As the mesoglea converges on the aboral pore, it loses its structural integrity and cells are sloughed off the column.This investigation was supported by The National Science Foundation, Grant Number GB-27395.     

朊病毒对中枢神经系统的影响及其作用机制

本文着重叙述了以几个问题：（１）朊病毒能否从牛转移感染到人;（２）朊病毒的感感染途径是怎样的;（３）朊病毒感染有何条件;（４）正常的朊病毒蛋白在神经元和胶质细胞表面表达有何重要功能;（５）朊病毒蛋白功能的结构基因;（６）朊病毒的可能作用机制。最后,分析了朊病毒影响中枢神经系统的两条可能途径,即破坏正常朊病毒蛋白的功能和与小神经胶质细胞共同作用提高神经元对自由基的敏感性及增加氧化自由基的含量。     

The brain of the horseshoe crab (Limulus polyphemus). I. neuroglia

The brain of the horseshoe crab, Limulus polyphemus, harbors three populations of neuroglial cells, whose distribution and cellular details are best appreciated by a combination of silver impregnation, scanning, and transmission electron microscopy. Stellate astrocytes envelop neurons as satellite cells, permeate the neuropile, and secrete a framework of sustentacular trabeculae throughout the brain. Velate astrocytes are restricted to Kenyon cells, i.e. small association neurons, of which they harbor up to 150 per neuroglial cell. Vascular neuroglia is composed of glycogen and mitochondria-laden, interlocked cells that form an open meshwork in the hemocoelic spaces of the brain. Aside from supportive functions of neuroglia, the vascular neuroglial cells in particular seem to subserve the role of a metabolic reserve cell for the central nervous system.     

Identification of the Schwann cell as a peripheral nervous system cell possessing a differentiation antigen expressed by a human lung tumor.

Recent studies of the plasma membrane antigens of a human lung tumor (oat cell carcinoma) indicated that the tumor expressed at least two normal differentiation antigens undetectable in normal respiratory epithelium. One antigen was characteristic of certain endodermally derived epithelial cells of the digestive system; the other antigen was characteristic of certain neural crest-derived cells in the peripheral nervous system. The present studies were undertaken to identify the reactive cell type in the peripheral nervous system. Since similar cells in the rat peripheral nervous system expressed a cross-reactive form of this antigen, and since pure cultures of different rat nerve cell type were available, the following approach was possible. Cultures of pure neurons, pure Schwann cells, pure fibroblasts, neurons and Schwann cells, and neurons, Schwann cells, and fibroblasts were assayed for this antigen with rabbit anti-oat cell carcinoma plasma membrane antiserum absorbed with normal lung and liver. The indirect immunofluorescence method on both whole, viable cell and fixed cell substrates was used. Only Schwann cells expressed the antigen; Schwann cells in the presence of neurons expressed the antigen much more strongly than did pure Schwann cells. It was concluded that the oat cell carcinoma of the lung expressed a differentiation antigen present on Schwann cells.     

Structure and development of the nephridia of Tomopteris helgolandica (Annelida)

 Nephridial diversity is high in Phyllodocida (Annelida) and ranges from protonephridia to metanephridia. The nephridia of Tomopteris helgolandica (Tomopteridae) can be characterized as metanephridia which bear a multiciliated solenocyte. This cell is medially apposed to the proximal part of the nephridial duct and bears several cilia, each of which is surrounded by a ring of 13 microvilli. An extracellular matrix connects the microvilli and thus leads to the impression of a tube surrounding the central cilium. Each tube separately enters a subjacent duct cell and the cilia extend into a cup-shaped compartment within the duct cell. This compartment is not connected to the duct. The funnel consists of eight multiciliated cells and is connected to the nephridial duct, which initially runs intercellularly and later percellularly. The last duct cell bears a neck-like process which pierces the subepidermal basal membrane and is connected to epidermal cells forming a small invagination, the nephropore. The nephridia of T. helgolandica develop from a band of cells and all structural components are differentiated at an early developmental stage. Further development is characterized by enlargment of the funnel, ciliogenesis in the solenocyte, merging of different sections of the duct and, finally, the formation of the nephropore. An evaluation of the nephridia of T. helgolandica leads to the hypothesis that the nephridial diversity in Phyllodocida can be explained by the retainment of different stages in the transition of protonephridia into metanephridia; this is caused by the formation of a ciliated funnel at different ontogenetic stages. Although the protonephridia in Phyllodocida are regarded as primary nephridial organs, protonephridia are also presumed to have evolved secondarily in progenetic interstitial species of the Annelida by an incomplete differentiation of the nephridial anlage. Accepted: 18 December 1996     

THE ULTRASTRUCTURE OF THE SALT GLANDS OF CYNODON AND DISTICHLIS (POACEAE)

The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask-shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.