The morphology of the gills of the freshwater African crab Potamon niloticus (Crustacea: Brachyura: Potamonidae): A scanning and transmission electron microscopic study

The gills of the African freshwater crab Potamon niloticus -Ortmann have been investigated by scanning and transmission electron microscopy. Potamon has seven pairs of phyllobranchiate gills contained in the branchial chambers. From the central axis of the gills arise bilaterally situated thin flaps, the lamellae. The afferent branchial vessel (the epibranchial vessel) is located on the dorsal aspect of the gill arch and the efferent vessel (the hypobrancial vessel) on the ventral side. Between these two blood vessels, the blood percolates through the lamellar vascular channels where it is oxygenated. The lamellae consist of an epithelial cell layer covered by a thin cuticle which consists of tightly fused but distinct layers. The epithelial cells approach each other at regular intervals and fuse in the middle of the lamellar sinus delineating the vascular channels. Apical profuse membranous infoldings and numerous mitochondria characterize the epithelial cells, features typical of cells involved in active transport of macro- and micromolecules. In Potamon , however, there were no distinct gas exchange and osmoregulatory regions of the gills. On average, the cuticle was 0.78 μm thick while the epithelial cell was 6 μm. Cells that were morphologically similar to the renal glomerular podocytes of the vertebrates were observed in the efferent gill vessel of Potamon. These cells have been said to be phagocytic and may play an important defensive role in the crustaceans. Although basically the morphology of the gills of Potamon is similar to that of the other decapods, fine structural differences were evident as would be intuitively expected in a group of animals that has undergone such remarkable adaptive radiation.     

A scanning and transmission electron microscopic study of the lung of a caecilian Boulengerula taitanus

The lung of an apodan amphibian Bouiengerula taitanus has been investigated by scanning and transmission electron microscopy. This caecilian has only a single, long tubular lung that tapers towards the caudal end of the body. The lung has a central air duct which radially opens into a single stratum of alveoli lined by well developed septa that attach to two diametrically opposite trabeculae. The trabeculae carry the pulmonary artery and vein. The septa have blood capillaries on both surfaces and supportive and contractile elements like collagen, smooth muscle, elastic tissue and fibrocytes. The alveolar surface has only a single population of pneumocytes that combine the morphological features of the mammalian type 1 and 2 cells, i.e. they contain the osmiophilic, lamellated bodies and are squamous in form. Through subepithelial cytoplasmic invaginations, the pneumocytes, together with their basement lamina, were observed to be firmly attached to the septa1 tissue elements, presumably to avoid mechanical detachment during the rapid respiratory movements. The compartmentation of the whole lung in this species is viewed as a means of increasing the surface area available for gas exchange which, coupled with other already established cardiovascular adaptations in this species, may be of significance in its fossorial mode of life, an environment that is usually hypoxic and hypercarbic.     

A covalently bound photoisomerizable agonist. Comparison with reversibly bound agonists at electrophorus electroplaques

After disulphide bonds are reduced with dithiothreitol, trans-3- (α-bromomethyl)-3’-[α- (trimethylammonium)methyl]azobenzene (trans-QBr) alkylates a sulfhydryl group on receptors. The membrane conductance induced by this “tethered agonist” shares many properties with that induced by reversible agonists. Equilibrium conductance increases as the membrane potential is made more negative; the voltage sensitivity resembles that seen with 50 [mu]M carbachol. Voltage- jump relaxations follow an exponential time-course; the rate constants are about twice as large as those seen with 50 μM carbachol and have the same voltage and temperature sensitivity. With reversible agonists, the rate of channel opening increases with the frequency of agonist-receptor collisions: with tethered trans-Qbr, this rate depends only on intramolecular events. In comparison to the conductance induced by reversible agonists, the QBr-induced conductance is at least 10-fold less sensitive to competitive blockade by tubocurarine and roughly as sensitive to “open-channel blockade” bu QX-222. Light-flash experiments with tethered QBr resemble those with the reversible photoisomerizable agonist, 3,3’,bis-[α-(trimethylammonium)methyl]azobenzene (Bis-Q): the conductance is increased by cis {arrow} trans photoisomerizations and decreased by trans {arrow} cis photoisomerizations. As with Bis-Q, ligh-flash relaxations have the same rate constant as voltage-jump relaxations. Receptors with tethered trans isomer. By comparing the agonist-induced conductance with the cis/tans ratio, we conclude that each channel’s activation is determined by the configuration of a single tethered QBr molecule. The QBr-induced conductance shows slow decreases (time constant, several hundred milliseconds), which can be partially reversed by flashes. The similarities suggest that the same rate-limiting step governs the opening and closing of channels for both reversible and tethered agonists. Therefore, this step is probably not the initial encounter between agonist and receptor molecules.     

Metal ion- and phosphate-mediated transport of glucose by insulin.

Insulin, in the presence of Mg²⁺ and Pi, can transport D-glucose across a bulk phase separating two aqueous phases. All three molecular species (Mg²⁺, Pi, D-glucose) are transported simulataneously in 1:1:1 stoichiometry. The same system will transport D-galactose and L-arabinose, but not L-glucose, D-arabinose, D-mannitol, D-fructose and 3-0-methyl glucose. Phloridzin completely suppresses transport, not only of glucose, but also of Mg²⁺ and Pi. Other divalent metal ions are less efficient (Mg²⁺ >Mn²⁺ >Ca²⁺ >Zn²⁺). The capability of insulin for transport of D-glucose is not duplicated by proinsulin or glucagon. Amino acids and citric cycle substrates are also transported, some as rapidly as D-glucose. Pi is replaceable by phosphate esters such as AMP, ADP and ATP, less efficiently with Mg²⁺, but more efficiently with Ca²⁺ as metal ion. The transport of D-glucose in the systems formed by insulin, Ca²⁺ and nucleotide is less sensitive to phloridzin than the standard Mg²⁺, Pi system.     

Relationships of reproductive performance indicators in black rhinoceros (Diceros bicornis michaeli) with plant available moisture,plant available nutrients and woody cover

Plant available moisture and plant available nutrients in soils influence forage quality and availability and subsequently affect reproductive performance in herbivores. However, the relationship of soil moisture, soil nutrients and woody forage with reproductive performance indicators is not well understood in mega‐browsers yet these three are important in selecting suitable areas for conservation of mega‐browsers. Here, the eastern black rhinoceros (Diceros bicornis michaeli), a mega‐browser, was studied in seven geographically distinct populations in Kenya to understand the relationships between its reproductive performance indicators and plant available moisture, plant available nutrients and woody cover. Reproductive parameters showed a complex relationship with plant available moisture and plant available nutrients. We found an increase in the predicted yearly percentage of females calving as plant available nutrients decreased in areas of high levels of plant available moisture but no relationship with plant available nutrients in areas of low plant available moisture. Age at first calving was earlier, inter‐calving interval was longer and yearly percentage of females calving was higher at higher woody cover. Woody plant cover contributes positively to black rhino reproduction performance indicators, whereas plant available moisture and plant available nutrients add to the selection of conservation areas, in more subtle ways.     

First demonstration of the neuroepithelial cells and their chemical code in the accessory respiratory organ and the gill of the sharptooth catfish,Clarias gariepinus: A preliminary study

Available studies that have examined O₂ sensing in fish have indicated that oxygen-sensitive neuroepithelial cells (NECs) are O₂ sensors in the gills and initiate cardiorespiratory reflexes in aquatic vertebrates. This is the first study describing the occurrence of NECs in accessory respiratory organs in the air-breathing catfish Clarias gariepinus. Immunocytochemical stainings with specific neuronal markers such as nNOS, VAchT, 5-HT and TH have been shown to be very useful for location and distribution of these cells in the gill fans and suprabranchial chamber that take origin from the transformation of the gill tissue. But the response of these putative O₂ chemoreceptors, their role in the respiratory reflexes and their innervation await investigation.     

Systematic analysis of hematopoietic, vasculogenetic, and angiogenetic phases in the developing embryonic avian lung, Gallus gallus variant domesticus

In the embryonic lung of the domestic fowl, Gallus gallus variant domesticus, hematogenetic and vasculogenetic cells become ultrastructurally clear from day 4 of development. In the former group of cells, filopodial extensions coalesce, cytoplasm thickens, and accumulating hemoglobin displaces the nucleus peripherally while in the latter, conspicuous filopodial extensions and large nuclei develop as the cells assume a rather stellate appearance. From day 5, erythrocytes and granular leukocytes begin forming from cytoarchitecturally cognate hematogenetic cells. The cells become distinguishable when hemoglobin starts to accumulate in the erythroblasts and electron dense bodies form in the leukoblasts. Vasculogenesis begins from day 7 in different areas of the developing lung: erthrocytes (but not granular leukocytes) appear to attract committed vasculogenetic cells (angioblasts) that form an endothelial lining and vessel wall. Arrangement of angioblasts around forming blood vessels sets the direction along which the vessels sprout (angiogenesis). In some areas of the developing lung, through what seems like an inductive erythropoietic process, arcades of erythrocytes organize. Once endothelial cells surround such continuities, discrete vascular units organize. By day 10, the major parts of the in-built (intrinsic) pulmonary vasculature are assembled. Complete pulmonary circulation (i.e., through the exchange tissue) is not established until after day 18 when the blood capillaries start to develop. Since the precursory erythrocytes do not have a respiratory role, it is imperative that de novo erythropoiesis is essential for vasculogenesis. Diffuse (fragmentary) development and subsequent piecemeal assembly of the pulmonary vascular system may explicate the fabrication of a complex circulatory architecture that grants cross-current, counter-current, and multicapillary serial arterialization designs in the exchange tissue of the avian lung. The exceptional respiratory efficiency of the avian lung is largely attributable to the geometries (physical interfacing) between the bronchial and vascular elements at different levels of morphological organization.     

Novel lipophilic amidate oxorhenium and oxotechnetium complexes as potential brain agents: synthesis, characterization and biological evaluation

Novel oxorhenium and oxotechnetium complexes based on the tetradentate 1-(2-hydroxybenzamido)-2-(pyridinecarboxamido)benzene, H3L, ligand have been synthesized and characterized herein. Thus, by reacting equimolar quantities of the triply deprotonated ligand L3- with the suitable MO3+ precursor, the following neutral MOL complexes could be easily produced following similar synthetic routes: M = Re (1), M = 99gTc (2), and M = 99mTc (3). Complexes 1 and 2, prepared in macroscopic amounts, were chemically characterized and their structure determined by single-crystal X-ray analysis. They are isostructural metal chelates, adopting a distorted square pyramidal geometry around the metal. The N3O donor atom set of the tetradentate ligand defines the basal plane and the oxygen atom of the M = O core occupies the apex of the pyramid. Complex 3 forms quantitatively at tracer level by mixing the H3L ligand with Na99mTcO4 generator eluate in aqueous alkaline media and using tin chloride as reductant in the presence of citrate. Its structure was established by chromatographic comparison with prototypic complexes 1 and 2 using high-performance liquid chromatographic techniques. When challenged with excess glutathione in vitro, complex 3 is rapidly converted to hydrophilic unidentified metal species. Tissue distribution data after administration of complex 3 in vivo revealed a significant uptake and retention of this compound in brain tissue.     

Functional morphology of the gas-gland cells of the air-bladder of Oreochromis alcalicus grahami (teleostei: cichlidae): an ultrastructural study on a fish adapted to a severe, highly alkaline environment

Oreochromis alcalicus grahami is a small cichlid fish that lives in shallow peripheral lagoons of Lake Magadi, Kenya. The internal surface of the air-bladder is highly vascularized, illustrating possible utilization as an accessory respiratory organ. The wall of the bladder consists of five distinct tissue layers. From the outer to the inner surfaces are: a squamous, undifferentiated epithelial cell; a collagen-elastic tissue space; a smooth muscle tissue band; an inner connective tissue space; and columnar gas-gland cells projecting into the lumen. The cell membrane over the perikarya of the gas-gland cells was sporadically broken. The disruptions were ascribed to possible physical damage by discharging gas-bubbles. Juxtaluminally, the gas-gland cells attached across tight junctions. The cells have highly euchromatic nuclei and conspicuously large intracytoplasmic secretory bodies. On the blood capillary facing (basal) aspect, the cell membrane of the gas-gland cells is highly amplified. The cells insert onto a smooth muscle tissue band. The morphological features and the topographical arrangement of the gas-gland cells in O. a. grahami are indicative of an operative exchange of materials between them and the underlying tissue components especially the blood capillaries. For a fish that subsists in hot, highly saline and alkaline water heavily invested by avian predators and where the partial pressure of oxygen diurnally shifts from virtual anoxia to hyperoxia, development of a versatile air-bladder for efficient buoyancy control conforms to the functional demands placed on it by a unique environment. Illustratively, instead of the gas-gland morphology in O. a. grahami resembling that in the freshwater fishes, the group from which the fish has evolved, it compares more closely to that of the marine fish. This similarity suggests amazing parallel evolutionary adaptation to biophysically corresponding aquatic milieus.