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N G Cooper

Publications and source records attributed to N G Cooper.

45 records · Page 3Linked to original sources
PubMed1986

Lectins demarcate the barrel subfield in the somatosensory cortex of the early postnatal mouse.

Plant lectins were used to examine the disposition of glycosylated molecules in vibratome sections through the barrel subfield of mouse somatosensory cortex at selected times during postnatal development. The peroxidase conjugates of peanut agglutinin (PNA, specific for N-acetylgalactosamine), concanavalin A (specific for mannose), and wheat germ agglutinin (specific for N-acetylglucosamine and N-acetylneuraminic acid) were used to study lectin binding in aldehyde-fixed tissue sections of cortex. Following peroxidase cytochemistry and light microscopy, it was found that all three lectins bound in the region of the barrel subfield as early as postnatal day 3 (day of birth = postnatal day 1). The lectins bound to the prospective sides and/or septae of individual barrels in preference to the prospective hollows. This lectin demarcation of the barrel field occurred prior to the detection of this region with cresyl violet staining and was still demonstrable on postnatal day 6, when the individual barrels became discernible with cresyl violet. This suggests that the lectin binding material is present before the barrel field becomes a fully formed and organized region. A decrease in lectin affinity for binding sites in these tissue sections occurs during postnatal development (Cooper and Steindler: Soc. Neurosci. (Abstr.) 10: 43a, '84) and this study demonstrates that lectins do not delineate the barrel field of more mature animals (2-3 months old), whereas barrels can be detected with cresyl violet at this time. A preliminary electron microscope analysis of the postnatal day 6 somatosensory cortex demonstrates that the lectin PNA binds to elements of the forming neuropil and also to Golgi apparatus intermediate saccules in neuronal cells. The prospective barrel field can be detected with lectins during a critical period in development in which alterations can occur in the barrel field in response to peripheral deprivation (Jeanmonod et al: Neuroscience 6:1503-35, '81) and therefore we suggest that the glycans visualized with lectin-peroxidase conjugates denote possible candidates for molecules involved in shaping barrel structure.

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PubMed1986

Wheat germ agglutinin binding sites in the adult mouse cerebellum: light and electron microscopic studies.

The binding properties of derivatized wheat germ agglutinin (WGA) have been examined in fixed tissue sections from the adult mouse cerebellum and also in axonal tracing paradigms following cerebellar injections. The aim of these studies is to begin to distinguish the roles different binding sites may play in generating diverse biological activities which lead to neuronal uptake and axonal transport of lectins or glycoconjugates. Vibratome sections from aldehyde-fixed cerebellum were incubated in N-[acetyl-3H] WGA or WGA conjugated to horseradish peroxidase (WGA-HRP). Sections from this in vitro binding paradigm and those from cerebellar pressure injection cases using those tracers (in vivo binding paradigm) were processed for light microscopic autoradiography, histochemistry, and electron microscopy. Blocking experiments were also performed with various sugar haptens to confirm the binding specificity of these lectin preparations. Light microscopy of lectin binding patterns within the cerebellar cortex has revealed that both derivatized WGA preparations bind most intensely to the molecular layer. Within the deep cerebellar nuclei, binding is unique and produces a punctate delineation of cell bodies and dendrites. Electron microscopy revealed that these binding sites are associated with glial processes which abut the plasma membrane of deep nuclei cells. Cerebellar WGA-HRP injection sites contain labeled profiles involved in uptake and axonal transport of the labeled lectin (e.g., multivesicular and dense bodies) in addition to label associated with synapses, glia, undetermined components of the extracellular space, and neuronal plasma membranes. These sites are therefore presumed to possess a high affinity or capacity for binding derivatized WGA. Binding studies performed here thus reveal, for the first time, the existence of discrete glial sites that display an extraordinary attraction for lectins such as WGA. The roles such glial glycoconjugates play in diverse biological activities including neuronal uptake and transport of macromolecules need further study.

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PubMed1985

Calmodulin-dependent protein phosphatase: immunocytochemical localization in chick retina.

Calmodulin-dependent protein phosphatase, previously called CaM-BP80 or calcineurin, is present in high concentrations in the central nervous system. The level of the phosphatase has been shown by radioimmunoassay to increase during development in the retinas of embryonic and hatching chicks (Tallant, E.A., and W.Y. Cheung, 1983, Biochemistry, 22:3630-3635). The aims of this study are to immunocytochemically localize the phosphatase in developing and mature retinas and to determine if the phosphatase is present in fractions of retinal synaptic membranes and synaptic junctions. Vibratome slices of fixed chick retina and Western blots of detergent-solubilized retinal fractions are both treated sequentially with rabbit primary antisera and goat anti-rabbit Fab fragments conjugated to peroxidase, and then reacted with hydrogen peroxide and diaminobenzidine. The tissue slices are further processed for electron microscopy. This paper demonstrates the presence of peroxidase reaction product in the retina just before synapse formation. In the outer plexiform layer the product is confined to photoreceptor synaptic terminals, whereas in the inner plexiform layer it is present in synaptic terminals of bipolar cells and in dendrites of ganglion cells. In this latter site the product is present postsynaptically at bipolar and amacrine synapses. The phosphatase is detected in Western blots of both synaptic plasma membrane and synaptic junction fractions.

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PubMed1984

The distribution of filipin-sterol complexes in photoreceptor synaptic membranes.

The polyene antibiotic filipin, which binds to membrane sterols, has been used to investigate the relative distribution of cholesterol at photoreceptor synaptic junctions in the chick retina. Following anesthesia and aldehyde perfusion fixation, the retina is removed and immersed in fixative solution containing the filipin for 36-48 hours. The retinas are then processed for freeze-fracture. Electron microscopy of freeze-fracture replicas demonstrates that the filipin-sterol complexes are not evident between intramembrane particles of the presynaptic and postsynaptic particle arrays that are present at ribbon and basal junctions. In contrast, the synaptic vesicle fusion zone of ribbon junctions contains large numbers of filipin-sterol complexes which are observed merging with the free margins of the presynaptic particle array. There is a scarcity of such complexes, however, around the free margins of basal junction presynaptic particle arrays. These latter sites do not contain a vesicle fusion zone. Particle-poor areas of membrane that surround postsynaptic particles arrays of ribbon and basal junctions also do not contain filipin binding sites. The nonsynaptic membrane of photoreceptor terminals contains large numbers of filipin-sterol complexes, less tightly packed than in the synaptic vesicle fusion zone. Coated vesicle fusion sites in the presynaptic membrane contain groups of intramembrane particles but the filipin-sterol complexes are excluded from these sites. The observations suggest that synaptic membrane domains which interact with cytoskeletal components, such as clathrin and pre- and postsynaptic densities contain less cholesterol than other domains such as the synaptic vesicle fusion zones.

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PubMed1984

Phagocytosis of lectin-coated beads by dystrophic and normal retinal pigment epithelium.

In the dystrophic pigmented Royal College of Surgeons (RCS) rat, the retinal pigment epithelium (RPE) has a diminished capacity to phagocytose shed photoreceptor outer segments (ROS). An alteration in phagocytic recognition or ligand-receptor interactions between the RPE and ROS's could contribute to this defect. To this end, we have examined whether or not RPE lectin receptors are implicated in phagocytosis in the normal and dystrophic rat RPE by comparing differences in phagocytic uptake of lectin-coated beads. To test this, the following lectins were bound either indirectly to sugar-coated latex beads or directly to activated beads: Concanavalin A (conA), specific for mannose; Ulex europeus (ULEX), specific for fucose; Lens culinaris (LcH), specific for mannose; and wheat germ agglutinin (WGA), specific for N-acetyl glucosamine and sialic acid. The distribution of the lectin binding around beads was visualized and confirmed using lectin-Ferritin conjugates. Lectin-coated beads were fed to normal and dystrophic pigmented RPE tissue explants to determine differences in phagocytic uptake. We found that whether beads were directly or indirectly coated, similar results were obtained, but that there were differences in uptake of two types of lectin-coated beads by dystrophic as compared with normal animals. The dystrophic RPE phagocytosed greater numbers of conA-mannose beads (6.9/cell) than the normal RPE (3.6/cell). LcH-mannose beads were also phagocytosed by dystrophic (2.7/cell) but not by the normal (0/cell). A similar number of ULEX-fucose beads were taken up by dystrophic (3.8/cell) and normal (3.4/cell) RPE and neither took up WGA-N-acetyl glucosamine beads (0/cell). These results showing that the dystrophic RPE takes up greater numbers of conA and LcH-coated beads than the normal RPE suggest that a ligand-receptor interaction involving mannose may contribute to this difference in phagocytic uptake.

Animals↗
PubMed1983

Tracer uptake by photoreceptor synaptic terminals. I. Dark-mediated effects.

This electron microscope study examines the sites of uptake and subsequent redistribution of the extracellularly applied tracer, horseradish peroxidase (HRP), in photoreceptor synaptic terminals during dark adaptation. First, chicks are sacrificed by perfusion fixation at various intervals after the addition of tracer to in situ eyecups. It is demonstrated that when terminals contain only one tracer-labeled organelle, this may be either a synaptic or a coated vesicle. At later times vacuoles in terminals become labeled. Some of these are seen as involutions of terminal membrane and some are observed in the cell body. Therefore, it seems likely that some involutions of terminal membrane pinch off and are transported retrogradely. Second, chicks are given intraocular injections of HRP at various intervals in a 12-hr dark period and sacrificed 1 hr later. Terminals of chicks sacrificed at 1 hr into the dark period contain predominantly tracer-labeled synaptic vesicles and vacuoles, whereas terminals of chicks sacrificed at 3 hr into the dark period contain tracer-labeled coated vesicles also. Diverticular membrane, thought to be the result of synaptic vesicle fusion and coalescence with the presynaptic membrane, waxes during the first hour of darkness and then wanes over a period of several hours (N. Cooper and B. McLaughlin, 1982, J. Ultrastruc. Res. 79, 58-73). These observations, together with those presented here, suggest that not all synaptic vesicles coalesce to form the diverticular membrane and that during the waxing stage, some synaptic vesicles are recycled rapidly without passing through a coated vesicle intermediate stage. This is discussed in the context of current models of localized synaptic vesicle membrane recycling.

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PubMed1983

Synaptic membrane domains in photoreceptors of chick retina: a thin-section and a freeze-fracture study.

In this freeze-fracture study of synaptic terminals of chick photoreceptors, three regions of synaptic terminal plasmalemma can be distinguished on the basis of intramembrane characteristics. The first region is the synaptic vesicle fusion region in which rows of P-face depressions and E-face mounds are observed. In the absence of exocytotic figures this zone is relatively free of P-face particles and E-face pits. Adjacent to this, a second region is seen, rich in P-face particles and complementary E-face pits. This second region waxes and wanes in size during dark and light stimulation (Cooper and McLaughlin, 1982) and may correspond to similar expansions and contractions of synaptic plasmalemma induced by less physiological modes of stimulation, as observed in other synaptic terminals (Ceccarelli et al., 1979b; Model et al., 1975; Boyne and McLeod, 1979). During the waxing period, P-face particles and E-face pits are present in this membrane, and its expansion gives rise to diverticula of the synaptic terminal. During the waning period when the diverticula begin to disappear, aggregates of P-face particles and complementary patches of E-face pits are seen in the diverticular membrane. The third region, the nonsynaptic plasmalemma enclosing the terminal, contains a high density of P-face particles but does not contain E-face pits. Serial sections of vacuoles within the cytoplasm demonstrate that some vacuoles retain connections with this nonsynaptic plasmalemma. Vacuoles that are connected in this way are depleted of intramembrane particles. Such regions appear to represent separate domains within the photoreceptor terminal and are discussed in the context of membrane addition and retrieval.

Animals↗
PubMed1981

Gap junctions in the outer plexiform layer of te chick retina: thin section and freeze-fracture studies.

Previous studies have established that gap junctions between presumptive retinal neurons of the chick retina disappear during the course of embryogenesis. The present study examines the 2-3-week-old chick retina to determine if gap junctions are present in the outer plexiform layer of the more mature animal as would be in accordance with evidence from morphological and physiological studies on a variety of other vertebrates. Thin section and freeze-fracture techniques are used in a complementary manner to demonstrate that gap junctions are present between horizontal cell processes in the distal regions of the outer plexiform layer. These junctions appear to be between axon terminals and between spines that project from axon terminals to rods and double cones. Gap junctions are also observed between photoreceptors. They are seen on the synaptic terminals of all classes of cones and are located between the cone synaptic terminals and cone basal processes. Gap junctions are also seen between unidentified photoreceptor basal processes within the neuropil of both distal and proximal parts of the outer plexiform layer. Gap junctions are also present between cone synaptic terminals and deeply invaginated, vesicle-containing processes the origin of which remains to be determined.

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