A light and electron microscopic investigation of the digestive system of the Ophiuroid ophiuroiderma panamensis (Brittle Star)

The Brittle Star digestive system is composed of buccal, pharyngeal, esophageal and stomach cavities. The buccal and pharyngeal cavities are lined by columnar cells covered by a cuticle, and are apparently concerned with mucous production. Coelomocytes and tall columnar cells are described in the esophagus and stomach epithelia. The columnar cells are adapted for nutrient absorption, enzyme synthesis, and lipid storage. Nerves are found beneath the epithelia within a connective tissue layer. Smooth muscle and coelomic layers lie external to the connective tissue layer. The coelomic layer lines a perivisceral space and has diverse modifications of its perivisceral surface; a pedicle-cuticle modification perhaps having general significance in echinoderms.     

Structural insights into the secretin PulD and its trypsin-resistant core

Limited proteolysis, secondary structure and biochemical analyses, mass spectrometry, and mass measurements by scanning transmission electron microscopy were combined with cryo-electron microscopy to generate a three-dimensional model of the homomultimeric complex formed by the outer membrane secretin PulD, an essential channel-forming component of the type II secretion system from Klebsiella oxytoca. The complex is a dodecameric structure composed of two rings that sandwich a closed disc. The two rings form chambers on either side of a central plug that is part of the middle disc. The PulD polypeptide comprises two major, structurally quite distinct domains; an N domain, which forms the walls of one of the chambers, and a trypsin-resistant C domain, which contributes to the outer chamber, the central disc, and the plug. The C domain contains a lower proportion of potentially transmembrane beta-structure than classical outer membrane proteins, suggesting that only a small part of it is embedded within the outer membrane. Indeed, the C domain probably extends well beyond the confines of the outer membrane bilayer, forming a centrally plugged channel that penetrates both the peptidoglycan on the periplasmic side and the lipopolysaccharide and capsule layers on the cell surface. The inner chamber is proposed to constitute a docking site for the secreted exoprotein pullulanase, whereas the outer chamber could allow displacement of the plug to open the channel and permit the exoprotein to escape.     

Paracloacal glands of Alligator mississippiensis: A histological and histochemical study

The histology of the paracloacal 'musk' glands of adult American alligators ( Alligator mississippiensis ) is described. The gland is a single secretory sac with a single duct and a central lumen partially occluded by a central, cylindrical conglomerate of cells and secretion product. The capsule of the gland consists of an outer layer of smooth muscle and an inner layer of connective tissue containing collagen and elastin fibres. Septa carrying blood vessels radiate from the connective tissue layer of the capsule to the border of the central conglomerate. Parenchymal cells containing lipid droplets enlarge from the periphery to the centre of the gland. Secretions formed by degeneration of cells in the central cylinder are concentrated near the secretory duct. Histochemical tests indicate lipids but not mucopolysaccharides in the glandular exudate.     

Lineage analysis in the chicken inner ear shows differences in clonal dispersion for epithelial, neuronal, and mesenchymal cells

The epithelial components of the vertebrate inner ear and its associated ganglion arise from the otic placode. The cell types formed include neurons, hair-cell mechanoreceptors, supporting cells, secretory cells that make endolymphatic fluid or otolithic membranes, and simple epithelial cells lining the fluid-filled cavities. The epithelial sheet is surrounded by an inner layer of connective and vascular tissues and an outer capsule of bone. To explore the mechanisms of cell fate specification in the ear, retrovirus-mediated lineage analysis was performed after injecting virus into the chicken otocyst on embryonic days 2.5-5.5. Because lineage analysis might reveal developmental compartments, an effort was made to study clonal dispersion by sampling infected cells from different parts of the same ear, including the auditory ganglion, cochlea, saccule, utricle, and semicircular canals. Lineage relationships were confirmed for 75 clones by amplification and sequencing of a variable DNA tag carried by each virus. While mesenchymal clones could span different structural parts of the ear, epithelial clones did not. The circumscribed epithelial clones indicated that their progenitors were not highly migratory. Ganglion cell clones, in contrast, were more dispersed. There was no evidence for a common lineage between sensory cells and their associated neurons, a prediction based on a proposal that the ear sensory organs and fly mechanosensory organs are evolutionarily homologous. As expected, placodal derivatives were unrelated to adjacent mesenchymal cells or to nonneuronal cells of the ganglion. Within the otic capsule, fibroblasts and cartilage cells could be related by lineage.     

Cyclic histological changes of the oviductal-cloacal junction in the viviparous snake Toluca lineata

The structure and seasonal changes of the oviductal-cloacal junction remain poorly understood in most squamates. This study was undertaken to describe the histology of the oviductal-cloaca junction of a female viviparous snake Toluca lineata, during gestation, previtellogenesis, and vitellogenesis. The oviductal-cloacal junction exhibits a wider lumen and thicker layers of connective tissue, smooth muscle layers, and total wall width compared to the posterior vagina. The lining is characterized by thick, short longitudinal mucosal folds. The luminal epithelia differ morphologically from anterior to posterior portions of the oviductal-cloacal junction. The anterior portion is lined with a simple columnar epithelium composed of nonciliated cells. The middle portion is lined with stratified epithelium that contains an apical columnar cell layer that undergoes morphological changes coincident with the reproductive cycle. The posterior portion is lined with a stratified squamous epithelium. The connective tissue underlying the epithelium contains numerous ovoid cells having abundant acidophilic cytoplasmic granules—eosinophils. Copulation occurs during the previtellogenic stage, as evidenced by the presence of abundant spermatozoa in the lumen of the anterior portion and of a copulatory plug in the middle and posterior portion of the oviductal-cloacal junction. J. Morphol. 237:91–100, 1998. © 1998 Wiley-Liss, Inc.     

Network organization of interstitial connective tissue cells in the human endolymphatic duct.

The human endolymphatic duct (ED) and sac of the inner ear have been suggested to control endolymph volume and pressure. However, the physiological mechanisms for these processes remain obscure. We investigated the organization of the periductal interstitial connective tissue cells and extracellular matrix (ECM) in four freshly fixed human EDs by transmission electron microscopy and by immunohistochemistry. The unique surgical material allowed a greatly improved structural and epitopic preservation of tissue. Periductal connective tissue cells formed frequent intercellular contacts and focally occurring electron-dense contacts to ECM structures, creating a complex tissue network. The connective tissue cells also formed contacts with the basal lamina of the ED epithelium and the bone matrix, connecting the ED with the surrounding bone of the vestibular aqueduct. The interstitial connective tissue cells were non-endothelial and non-smooth muscle fibroblastoid cells. We suggest that the ED tissue network forms a functional mechanical entity that takes part in the control of inner ear fluid pressure and endolymph resorption.     

Sonic hedgehog regulates otic capsule chondrogenesis and inner ear development in the mouse embryo

Development of the cartilaginous capsule of the inner ear is dependent on interactions between otic epithelium and its surrounding periotic mesenchyme. During these tissue interactions, factors endogenous to the otic epithelium influence the differentiation of the underlying periotic mesenchyme to form a chondrified otic capsule. We report the localization of Sonic hedgehog (Shh) protein and expression of the Shh gene in the tissues of the developing mouse inner ear. We demonstrate in cultures of periotic mesenchyme that Shh alone cannot initiate otic capsule chondrogenesis. However, when Shh is added to cultured periotic mesenchyme either in combination with otic epithelium or otic epithelial-derived fibroblast growth factor (FGF2), a significant enhancement of chondrogenesis occurs. Addition of Shh antisense oligonucleotide (AS) to cultured periotic mesenchyme with added otic epithelium decreases levels of endogenous Shh and suppresses the chondrogenic response of the mesenchyme cells, while supplementation of Shh AS-treated cultures with Shh rescues cultures from chondrogenic inhibition. We demonstrate that inactivation of Shh by targeted mutation produces anomalies in the developing inner ear and its surrounding capsule. Our results support a role for Shh as a regulator of otic capsule formation and inner ear development during mammalian embryogenesis.     

Comparative morphology of the amphibian opercularis system: I. General design features and functional interpretation

The morphology of the opercularis system of anuran and caudate amphibians suggests that it acts to produce motion of the operculum that in turn produces fluid motion within the inner ear. The operculum and opercularis muscle form a lever system, with a narrow connection between the operculum and otic capsule acting as a fulcrum about which the operculum moves in response to forces applied via the muscle. The opercula of many species possess a muscular process on which the muscle inserts, thereby increasing the moment arm through which the muscle acts. The tonicity of the opercularis muscle allows tensile forces produced by substrate vibration or other mechanical energy applied to the forelimb to be effectively transmitted to the operculum; the elasticity of the connective tissue holding the operculum in place should act to return the operculum to its original position. The opercularis systems of frogs and non-plethodontid salamanders are similar structurally and functionally; that of plethodontid salamanders is structurally distinct but also functions as a lever system. Fluid motion produced by opercular motion could stimulate various end organs of the inner ear; the saccule, lagena, and amphibian papilla are in close approximation and wave energy could directly affect their otoconial or tectorial structures. In those anurans with a tympanic ear, the stapedial footplate and operculum articulate, but this articulation allows both to move independently. The stapes-tympanum complex and opercularis system therefore appear to be independent functional systems, and it is unlikely that the opercularis system modulates middle ear responsiveness. The general design of the opercularis system is consistent with a function in reception of substrate vibrations.     

扬子鳄皮肤腺结构与发育的初步观察

扬子鳄有三种皮肤腺:背腺、泄殖腔麝腺和下颌腺。背腺位于背中线左右两侧第二行鳞片下方,其确切位置个体间差异很大,如表1。幼鳄背腺形态多种多样,但显示出是一种退化器官,未观察到腺开口,也未观察到半成鳄和成鳄的背腺,因此扬子鳄背腺可能不具功能。泄殖腔麝腺位于泄殖腔腹唇内,梨形,腺管开口于泄殖腔腹壁,成体腺腔很大,腺的底部壁较厚,腺细胞明显地分成若干小叶,其它部位壁较薄,小叶不明显,属全泌腺,分泌油脂物,繁殖期特别发达,但性未成熟个体亦具功能,是一种信息素下颌腺位于下颌后方两侧皮肤内,圆柱状,脉管开口于下颌腹侧皮肤表面,成体腺腔不规则,腺壁厚,从包囊到腺腔,腺细胞可明显地分成三个区,属全泌腺,分泌油脂物,在繁殖期特别发达,此腺到性成熟才具功能。     

Ultrastructure of the Feeding Apparatus of Rhabdodemania minima Chitwood, 1936 (Enoplida: Rhabdodemaniidae)

The feeding apparatus of the marine nematode Rhabdodemania minima Chitwood, 1936 has been examined with light and transmission electron microscopy. The buccal capsule consists of a posterior region with smooth walls bearing three sets of three minute denticles at its posterior end and three large onchia in its mid region; a middle region with grooved walls; and an anterior region with costae and six odontia. The anterior and middle portions of the buccal capsule are enveloped by the cephalic cuticle, whereas the posterior region, which is set off from the middle region by a buccal seam, is partially enveloped by the anterior end of the esophagus. Two subventral esophageal glands open into the lumen of the esophagus. Secretions of each of three paraesophageal glands are conveyed through a duct in each of the three corresponding corners of the buccal wall to an opening between labia. A pair of wing-like thickenings, termed pterons, embraces the duct of each paraesophageal gland in the posterior and middle regions of the buccal capsule. A model of how the buccal capsule operates is proposed and tested. Morphological and functional aspects of the buccal apparatus and cephalic cuticle are compared with those of other taxa of the Enoplida, and their phylogenetic implications are discussed.     

Development of the pedicle in the articulate brachiopod Terebratalia transversa (Brachiopoda,Terebratulida)

Summary The development of the pedicle in the articulate brachiopod Terebratalia transversa has been examined by electron microscopy. The posterior half of the free-swimming larva comprises a non-ciliated pedicle lobe that contains the primordium of the juvenile pedicle at its distal end. During settlement at five to six days post-fertilization, the pedicle lobe secretes a sticky sheet that attaches the larva to the substratum. As metamorphosis proceeds, the epithelium in the posterior half of the pedicle lobe produces a thin overlying cuticle, and the pedicle primordium develops into a stalk-like anchoring organ. The juvenile pedicle protrudes through the gape that occurs between the posterior margins of the shell valves. A cup-like canopy, called the pedicle capsule, lines the posterior end of the shell and surrounds the newly formed pedicle. The core of the juvenile pedicle is filled with a solid mass of connective tissue. Numerous tonofibrils occur in the pedicle epithelium, and the overlying cuticle consists of amorphous material covered by a thin granular fringe. By one year post-metamorphosis, a body cavity develops anterior to the pedicle. Two pairs of adjustor muscles extend from the posterior end of the shell and traverse the cavity to insert in the pedicle. The connective tissue core of the pedicle in sub-adult specimens lacks muscle cells but contains numerous fibroblasts and collagen fibers. Three regions are recognizable in the connective tissue compartment of the adult pedicle: a subepithelial layer of non-fibrous connective tissue, a central fibrous zone, and a proximal mass of tissue that resembles cartilage.List of abbreviations as adhesive sheet - bc body cavity - bv brachial valve of shell - cf collagen fibrils - ct connective tissue - cu cuticle - di diductor muscle - ec epithelial cell - f fibroblast - fz fibrous zone - g gut - gc granular cell - gd gastric diverticulum - ht hinge tooth - ia interarea of pedicle valve - icl inner cuticular layer - lo lophophore - lu lumen of gut - m mesenchyme - ma mantle - ml mantle lobe - ocl outer cuticular layer - p periostracum - pc pedicle capsule - pce pedicle capsule epithelium - pcl pedicle collar of shell - pcn pedicle connectives - pd pedicle - pe pedicle epithelium - pl pedicle lobe - pv pedicle valve of shell - pzc proximal zone of cartilage-like tissue - s substratum - sel subepithelial layer - t tendon - tf tonofibril - vam ventral adjustor muscle     

Myxobolus cuneus n. sp. (Myxosporea) infecting the connective tissue of Piaractus mesopotamicus (Pisces: Characidae) in Brazil: histopathology and ultrastructure

The characteristics of Myxobolus cuneus n. sp. and its relationship to the host Piaractus mesopotamicus are described based on light and electron microscopy and histological observations. Polysporic plasmodia measuring 20 microm to 2.1 mm in size were found in 63.3 % of the P. mesopotamicus examined. The parasite was found in the gall bladder, urinary bladder, gills, spleen, fins, head surface, liver and heart. Generative cells and disporoblastic pansporoblasts occurred along the periphery of the plasmodia, and mature spores were found in the internal region. The mature spores had a pear shaped body in frontal view, with a total length of 10.0 +/- 0.6 microm and a width of 5.1 +/- 0.3 microm (mean +/- SD). The spore wall was smooth with sutural folds. The polar capsules were elongated, were pear shaped, and equal in size (length 5.7 +/- 03 microm; width 1.7 +/- 0.2 microm), with the anterior ends close to each other. The polar filaments were tightly coiled in 8-9 turns perpendicular to the axis of the capsule. The plasmodia were always found in connective tissue (wall of the arterioles of the gill filaments, serous capsule of the gall bladder, middle layer and subepithelial connective tissue of the urinary bladder, connective tissue between the rays of the fins, subcutaneous tissue of the head surface and fibrous capsule spleen). The parasite caused important damage in the gills, where development occurred in the wall of gill filament arterioles; a mild macrophage infiltrate was also observed. In advanced developmental stages, the plasmodia caused deformation of the arteriole structure, with a reduction and, in some cases, obstruction of the lumen. The parasite was found throughout the period studied and its prevalence was unaffected by host size, season or water properties.     

Timing of development of the middle ear of Anura (Amphibia)

Summary The opercularis system and tympanum-stapes complex of the anuran middle ear develop at different times relative to metamorphosis. In early larvae, the fenestra ovalis is represented by a large lateral opening in the otic capsule filled with connective tissue. At later larval stages, but well before metamorphosis, a cartilaginous operculum begins to form at the posterior margin of the fenestra ovalis, and proceeds to expand to fill all except the anterior part of the fenestra. The opercularis muscle forms along with the levator scapulae superior muscle at the anteromedial edge of the developing suprascapular cartilage of the shoulder girdle. The muscle fibers extend anteroventrally towards the operculum and otic capsule, and, just before emergence of the forelimbs, that portion that will form the opercularis muscle inserts on the lateral surface of the operculum. At this stage, when the metamorphosing frogs first show terrestrial habits, the opercularis system is complete and presumably functional. Timing of development of the tympanum-stapes complex is more variable. The stapes begins as a cartilaginous condensation in the anterior part of the fenestra ovalis, and develops laterally to eventually contact the epidermis and dermis that together will form the tympanum. Meanwhile a middle ear cavity and tympanic annulus form to complete the complex. In several species, especially those that metamorphose at a smaller body size, the tympanum-stapes complex is quite incomplete by the end of metamorphosis, and in Hyla crucifer it takes about 60 days to fully develop. The presence of a complete opercularis system by the start of terrestrial activity is consistent with an hypothesized seismic function of the system. The independent timing of development of the opercularis system and tympanum-stapes complex does not support functional hypotheses linking the opercularis system with modulation of responsiveness of the tympanum-stapes complex to aerial sound. Newly metamorphosed frogs with poorly developed tympanum-stapes complexes are presumably either insensitive to aerial sound or employ alternate mechanisms for transmission of sound energy to the inner ear, possibly involving the opercularis system.     

Middle ear transmission in the grass frog, Rana temporaria

The anuran middle ear serves to transmit eardrum vibrations to the inner ear. In order to do this efficiently, the eardrum and middle ear must operate as an impedance transformer matching the low impedance of air to the higher impedance of the fluid-filled inner ear. In amniotes, one of the mechanisms used to achieve impedance transformation is to have the middle ear work as a force-amplifying lever system. Here, we present evidence that the grass frog middle ear also implements a lever system. The columellar footplate, which sits in the oval window, is firmly connected to the otic capsule along its ventral edge. Therefore, simple in-out movement of the columella is prevented while a rotational movement around the footplate's ventral edge is possible. The latter movement pattern was confirmed by laser vibrometry measurements of eardrum and footplate vibrations. The results showed that the footplate vibrations were 20–30 dB weaker than those of the eardrum and that the two structures vibrated 180° out of phase (at low frequencies). The lever ratio was approximately 6, i.e. somewhat higher than lever ratios reported for amniotes. Hence, the middle ear lever probably makes a significant contribution to impedance matching in frogs. Accepted: 1 July 1997     

Histological description of the midgut and the pyloric valve of Tropidacris collaris (Stoll, 1813) (Orthopetera: Romaleidae).

The present research describes the histology of the midgut, gastric caeca, and pyloric valve of Tropidacris collaris (Stoll, 1813), (Orthopetera: Romaleidae). We used light microscopy, staining (Gomori's trichrome and periodic acid-Schiff (PAS)), and a routine histological analysis method (hematoxilin-eosin). The insects were obtained from, and also bred in, the Laboratory of Entomology, Department of Biology, of the Rural Federal University of Pernambuco (UFRPE). The collected material was fixed in alcoholic Botüin and embedded in paraplast. The results demonstrated that the midgut wall is composed of an inner epithelial layer and two outer layers of striate muscles: one internal (circular) and the other external (longitudinal), with connective tissue between the muscle fibers. The epithelium is single-layered, with two cell types: regenerative and elongated columnar. The gastric caeca presents muscle layers similar to those of the midgut. Simple columnar epithelium lines the gastric caeca, which presents villi and projects towards the lumen. The pyloric valve is of striate muscle tissue, covered by a single epithelial-cell layer.     

Evidence of a true pharyngeal tonsil in birds: a novel lymphoid organ in Dromaius novaehollandiae and Struthio camelus (Palaeognathae)

ABSTRACT: BACKGROUND: Tonsils are secondary lymphoid organs located in the naso- and oropharynx of most mammalian species. Most tonsils are characterised by crypts surrounded by dense lymphoid tissue. However, tonsils without crypts have also been recognised. Gut-associated lymphoid tissue (GALT), although not well-organised and lacking tonsillar crypts, is abundant in the avian oropharynx and has been referred to as the "pharyngeal tonsil". In this context the pharyngeal folds present in the oropharynx of ratites have erroneously been named the pharyngeal tonsils. This study distinguishes between the different types and arrangements of lymphoid tissue in the pharyngeal region of D. novaehollandiae and S. camelus and demonstrates that both species possess a true pharyngeal tonsil which fits the classical definition of tonsils in mammals. RESULTS: The pharyngeal tonsil (Tonsilla pharyngea) of D. novaehollandiae was located on the dorsal free surface of the pharyngeal folds and covered by a small caudo-lateral extension of the folds whereas in S. camelus the tonsil was similarly located on the dorsal surface of the pharyngeal folds but was positioned retropharyngeally and encapsulated by loose connective tissue. The pharyngeal tonsil in both species was composed of lymph nodules, inter-nodular lymphoid tissue, mucus glands, crypts and intervening connective tissue septa. In S. camelus a shallow tonsillar sinus was present. Aggregated lymph nodules and inter-nodular lymphoid tissue was associated with the mucus glands on the ventral surface of the pharyngeal folds in both species and represented the Lymphonoduli pharyngeales. Similar lymphoid tissue, but more densely packed and situated directly below the epithelium, was present on the dorsal, free surface of the pharyngeal folds and represented a small, non-follicular tonsil. CONCLUSIONS: The follicular pharyngeal tonsils in D. novaehollandiae and S. camelus are distinct from the pharyngeal folds in these species and perfectly fit the classical mammalian definition of pharyngeal tonsils. The presence of a true pharyngeal tonsil differentiates these two ratite species from other known avian species where similar structures have not been described. The pharyngeal tonsils in these ratites may pose a suitable and easily accessible site for immune response surveillance as indicated by swelling and inflammation of the tonsillar tissue and pharyngeal folds. This would be facilitated by the fact that the heads of these commercially slaughtered ratites are discarded, thus sampling at these sites would not result in financial losses.     

Biophysics of underwater hearing in the clawed frog,Xenopus laevis

Anesthetized clawed frogs (Xenopus laevis) were stimulated with underwater sound and the tympanic disk vibrations were studied using laser vibrometry. The tympanic disk velocities ranged from 0.01 to 0.5 mm/s (at a sound pressure of 2 Pa) in the frequency range of 0.4–4 kHz and were 20–40 dB higher than those of the surrounding tissue. The frequency response of the disk had two peaks, in the range of 0.6–1.1 kHz and 1.6–2.2 kHz, respectively. The first peak corresponded to the peak vibrations of the body wall overlying the lung. The second peak matched model predictions of the pulsations of the air bubble in the middle ear cavity. Filling the middle ear cavity with water lowered the disk vibrations by 10–30 dB in the frequency range of 0.5–3 kHz.Inflating the lungs shifted the low-frequency peak downwards, but did not change the high-frequency peak. Thus, the disk vibrations in the frequency range of the mating call (main energy at 1.7–1.9 kHz) were mainly caused by pulsations of the air in the middle ear cavity; sound transmission via the lungs was more important at low frequencies (below 1 kHz). Furthermore, the low-frequency peak could be reversibly reduced in amplitude by loading the larynx with metal or tissue glue. This shows that the sound-induced vibrations of the lungs are probably coupled to the middle ear cavities via the larynx. Also, anatomical observations show that the two middle ear cavities and the larynx are connected in an air-filled recess in submerged animals.This arrangement is unique to pipid frogs and may be a structural adaptation to connect all the air spaces of the frog and improve low-frequency underwater hearing. Another function of the recess may be to allow cross-talk between the two middle ear cavities. Thus, the ear might be directional. Our pilot experiments show up to 10 dB difference between ipsi- and contralateral stimulus directions in a narrow frequency range around 2 kHz.