bluuebunny/crossref_metadata_2025 huggingface dataset:
Localization of GABA- and GAD-like immunoreactivity in the turtle retina
Authors: Hurd Lawrence B. , Eldred William D.
Published: June 2009

γ-aminobutyric acid (GABA) has been reported to be an important neurotransmitter in the retinas of many species. This immunocytochemical study detailed the localization of antigens resembling GABA and glutamic acid decarboxylase (GAD, an enzyme involved in the synthesis of GABA), in retinal neurons in the turtle, Pseudemys scripta elegans. GABA-like immunoreactivity was present within somata in the inner and outer regions of the inner nuclear layer, within somata in the ganglion cell layer, and in processes in the outer plexiform layer, inner plexiform layer, and ganglion cell axon layer. GAD-like immunoreactivity was found in somata in the inner and outer regions of the inner nuclear layer and in processes in the inner and outer plexiform layers. Cell counts indicated more somata with GABA-like than GAD-like immunoreactivity in the inner nuclear layer. Double-label studies showed that every somata in the inner nuclear layer which had GAD-like immunoreactivity also had GABA-like immunoreactivity, but that many somata had only GABA-like immunoreactivity.

The stratification of immunoreactivity within the inner plexiform layer was analyzed using a scanning densitometer. We described the strata within the inner plexiform layer such that S0 represented the inner nuclear layer/inner plexiform layer border and S100 represented the inner plexiform layer/ganglion cell layer border. Analysis of GAD-like labeling yielded seven distinct strata with peak densities at positions S8, S19, S28, S42, S59, S75, and S93. GABA-like labeling provided five distinct strata with peak densities at positions S17, S28, S67, S84, and S95. The strata with peaks of GABA-like immunoreactivity at S17 and S28 were in statistically identical locations to corresponding strata with GAD-like immunoreactivity. The strata with GABA-like immunoreactivity at S67, S84, and S95 did not have statistically identical peaks of correlated GAD-like immunoreactivity, although there were corresponding strata with GAD-like immunoreactivity nearby. Antiserum directed against GABA failed to produce labeled strata at positions corresponding to the strata with GAD-like immunoreactivity at S8 and S42.

In summary, our results indicated that the antisera we used, which were directed against GABA and GAD, produced significantly different labeling in the inner nuclear layer, inner plexiform layer, and the ganglion cell body and axon layers of the turtle retina. Until the physiological significance of these differences is resolved, studies employing these markers to investigate the function of GABA in the turtle retina should be interpreted with caution.
A double-labeling investigation of the pretectal visuo-vestibular pathways
Authors: Magnin M. , Kennedy H. , Hoffmann K. P.
Published: June 2009

The projections of the nucleus of the optic tract were studied in the cat by simultaneous use of two distinct retrograde tracers (Fast Blue and Diamidino Yellow) injected in the inferior olive and the prepositus hypoglossi nucleus. Following injections of diamidino yellow in one structure and fast blue in the other, a significant number of retrogradely labeled neurons projecting to either target were observed dispersed in the nucleus of the optic tract. Three populations of labeled cells were found: one which projected to the inferior olive, a second to the nucleus prepositus hypoglossi, and a third which projected by means of a bifurcating axon to both of these structures. Quantification of these results reveals that 72% of the total number of labeled neurons are labeled by the IO injection, the remaining cells being labeled by the NPH injection. Double-labeled neurons represent more than 7% of the total number of the labeled cells. Tentative inferences as to the electrophysiological properties of the nucleus of the optic tract are discussed in the context of the optokinetic system.
Organization of visual cortex in the mouse revealed by correlating callosal and striate-extrastriate connections
Authors: Olavarria Jaime , Montero Vicente M.
Published: June 2009

In this study, we have investigated the organization of mouse visual cortex by correlating in detail the distribution of striate-extrastriate projections with the pattern of callosal connections revealed by the transport of horseradish peroxidase from the contralateral hemisphere. Single injections of 3H-proline into striate cortex produce 8–9 discrete projection fields in the belt of cortex surrounding area 17. The number and arrangement of these fields closely resemble the pattern of extrastriate visual areas in the rat. The callosal pattern is also very similar to that in the rat, and provides a set of landmarks for the location of the striate-recipient zones. Thus, cortical regions containing dense aggregations of callosal cells and terminations surround totally or partially the sparsely callosal striate-recipient zones. By comparing our results with previous accounts of the rat visual plan, we were able to identify in lateral extrastriate cortex of the mouse areas anterolateral (AL), lateromedial (LM), laterointermediate (LI), laterolateral (LL), posterolateral (PL), and posterior (P). We also observed 1–2 projections fields into anteromedial (AM) extrastriate cortex, and one field (S) into the posteromedial border of the head representation in primary somatosensory cortex. Our results support the notions that the visual cortex in the mouse is subdivided into multiple visual areas, and that these areas are arranged according to a plan that is common in rodents.
An improved retinal densitometer: Design concepts and experimental applications
Authors: Baker Howard D. , Henderson Ross , O'Keefe Lawrence P.
Published: June 2009

A photon-counting retinal densitometer is described that has been designed optically and electronically for improved sensitivity and reliability. The device allows measurement of visual pigments through the undilated natural pupils of subjects at relatively low levels of measuring lights, and serves also as an adaptometer for direct comparisons between pigment bleaching or regeneration and light or dark adaptation. Instrumental control and data collection are by computer to permit rapid and simple data analysis and comparisons between subjects. The methods by which the sensitivity and reliability have been enhanced are described in detail, and some examples of experimental results are presented.
A 221-bp fragment of the mouse opsin promoter directs expression specifically to the rod photoreceptors of transgenic mice
Authors: Quiambao Alexander B. , Peachey Neal S. , Mangini Nancy J. , Röhlich Pal , Hollyfield Joe G. , Al-Ubaidi Muayyad R.
Published: June 2009

Mutations in the human rod opsin gene have been shown to segregate with autosomal dominant retinitis pigmentosa (ADRP) and photoreceptor degeneration in transgenic mice. While these degenerations are characterized by the primary degeneration of rods, cones eventually die as well. To determine whether this subsequent cone degeneration is the result of expression of mutant rod opsin in the cones, the retinal cell-type specificity of a 221-bp fragment of the mouse rod opsin promoter was evaluated. Two transgenic mouse lines generated by injecting a fusion gene comprised of a 221-bp fragment of the mouse rod opsin promoter and the simian virus 40 large tumor antigen gene (Tag) were examined. The expression of Tag causes photoreceptor cell degeneration in members of both transgenic lines. However, the two lines differed with respect to the level of Tag expression and the rate and extent of photoreceptor cell degeneration. Immunocytochemical localization of opsin and Tag in surviving photoreceptor cells was determined and the results were confirmed by reverse transcriptase polymerase chain reaction (RT-PCR). Rod- and cone-mediated function was evaluated by electroretinography (ERG). In the higher Tag-expressing transgenic line only one row of nuclei remained in the outer nuclear layer at postnatal day (P) 150. While these nuclei showed no antigenicity for rod opsin or Tag, they did stain with an antibody that reacts with both rod and cone S-antigens (arrestins), indicating that these cells were surviving photoreceptor nuclei. Positive staining with peanut agglutinin, which uniquely decorates matrix domains surrounding cones in the normal retina, confirmed that the surviving photoreceptor nuclei were of cone origin. RT-PCR substantiated the results from immunostaining; amplification product was obtained using blue cone opsin transcripts but not from either Tag or rod opsin transcripts. The second transgenic mouse line exhibited a much slower photoreceptor cell death that was associated with low levels of Tag transgene transcript. At P120, ~50% of photoreceptors remained and an ~45% reduction in the rod ERG a-wave was observed. Cone-mediated ERGs, however, were normal. The results demonstrate the rod-specific expression of Tag as directed by the 221-bp fragment of the mouse rod opsin promoter and suggest that the cone degeneration in ADRP or transgenic mice associated with mutations in the rod opsin gene is a secondary effect of rod degeneration.
Functional consequences of oncogene-induced horizontal cell degeneration in the retinas of transgenic mice
Authors: Peachey Neal S. , Roveri Luisa , Messing Albee , McCall Maureen A.
Published: June 2009

Visual function was evaluated in transgenic mice expressing the simian virus 40 early region under the control of the promoter for phenylethanolamine-N-methyltransferase. These transgenic mice undergo a degeneration of the retinal horizontal cells and the outer plexiform layer. Electroretinograms (ERGs) were recorded under stimulus conditions chosen to elicit both receptoral and postreceptoral responses. The dark-adapted a-waves obtained from transgenic mice were not different from control recordings, indicating that the degenerative process does not interfere with function of the rod photoreceptors. In comparison, the ERG b-wave was markedly reduced in transgenic mice under both dark- and light-adapted conditions. Reproducible visual evoked potentials (VEPs) were recorded from transgenic mice in response to both low luminance stimuli that isolate rod function, and to higher luminance stimuli, indicating that retinal activity is transmitted centrally to the visual cortex. However, VEPs were delayed at all stimulus luminances compared to controls. Analysis of luminance-response functions suggests that the VEP delays could reflect the combination of a decrease in synaptic efficacy and an overall loss in visual sensitivity. These functional abnormalities correlate well with the anatomical abnormalities that have been previously observed in the transgenic retina (Hammang et al., 1993), namely a reduced number of synapses between photoreceptors and second-order neurons.
Interlaminar connections of the superior colliculus in the tree shrew. III: The optic layer
Authors: Hall William C. , Lee Psyche
Published: June 2009

These experiments were designed to test the idea that the optic layer in the tree shrew, Tupaia belongeri, is functionally distinct and provides a link between the visuosensory superficial and the premotor intermediate layers of the superior colliculus. First, cells in the optic layer were intracellularly labeled with biocytin in living brain slices. Compared to cells in the adjacent lower part of the superficial gray layer, which have apical dendrites that ascend toward the tectal surface, optic layer cells have dendritic fields that are restricted for the most part to the optic layer itself. The differences in dendritic-field location imply that superficial gray and optic layer cells have different patterns of input. The axons of optic layer cells terminate densely within the optic layer and, in addition, project in a horizontally restricted fashion to the overlying superficial gray and subjacent intermediate gray layers. This pattern also is different from the predominantly descending interlaminar projections of lower superficial gray layer cells. Next cells in the intermediate gray layer were labeled in order to examine the relationships between optic layer cells and these subjacent neurons that project from the superior colliculus to oculomotor centers of the brain stem Neurons in the upper part of the intermediate gray layer send apical dendrites into the optic layer and therefore can receive signals from the superficial gray layer either directly, from descending axons of lower superficial gray layer cells, or indirectly, through intervening optic layer cells. In contrast, lower intermediate gray layer cells have more radiate dendritic fields that are restricted to the intermediate gray layer. Thus, these lower cells must depend on descending projections from optic or upper intermediate gray layer cells for signals from the superficial gray layer. Together, these results support the idea that the optic layer is a distinct lamina that provides a link between the superficial and intermediate gray layers. They also are consistent with the traditional view that descending intracollicular projections play a role in the selection of visual targets for saccades.
A gradient of basic fibroblast growth factor in rod photoreceptors in the normal human retina
Authors: Li Zong-Yi , Chang Jean H. , Milam Ann H.
Published: June 2009

Retinitis pigmentosa (RP) is an inherited disease that causes primary degeneration of rod photoreceptors in the retina. Although the causal gene (e.g. rhodopsin) is thought to be expressed in all rods across the retina, the degeneration is typically nonuniform, with rods in the far periphery surviving significantly longer than those in the midperiphery and macula. Basic fibroblast growth factor (bFGF) is a putative survival factor for photoreceptors, and the characteristic regional pattern of rod cell survival in RP suggested that bFGF might be distributed nonuniformly in the human retina. We performed double-label immunocytochemistry on 15 normal human retinas, using anti-bFGF and other antibody markers for retinal neurons and glia. Immunoreactivity for bFGF was consistently absent from cones but was present in rods, populations of cone bipolar and amacrine cells, Müller glial cells, and astrocytes. In the macula, the percentage of bFGF-reactive rods was very low (~0.5%) but it increased in a central to peripheral gradient, accounting for up to ~88% of the rods in the far periphery. These findings suggest that a central to peripheral gradient of rod bFGF is present in normal human retina and may influence the pattern of photoreceptor degeneration in RP. The absence of bFGF in cones and the low number of bFGF-positive rods in the macula may correlate with the vulnerability of these cells in RP, age-related macular degeneration, and other retinal diseases.
The distribution and morphology of LGN K pathway axons within the layers and CO blobs of owl monkey V1
Authors: Ding Y. , Casagrande V.A.
Published: June 2009

The lateral geniculate nucleus (LGN) of primates contains three classes of relay cells, the magnocellular (M), parvocellular (P), and koniocellular (K) cells. At present, very little is known about either the structure or function of the K relay cells in New or Old World monkeys (simian primates). In monkeys, K cells are located between the main LGN layers and adjacent to the optic tract. For convenience, these intercalated cell layers are numbered K1-K4 starting closest to the optic tract with K1. The objective of this study was to examine the details of K axon morphology in the primary visual cortex (V1) of owl monkeys and to determine if different K layers give rise to distinct axon types. For this purpose, injections of WGA-HRP or PHA-L were made into specific K LGN layers and the distribution and morphology of the resulting labeled axons were analyzed. Injections of fluorescent tracers also were made within the superficial layers of V1 to further document connections via analysis of the patterns of retrogradely labeled cells in the LGN. Our main finding is that K axons in owl monkeys terminate as delicate focused arbors within single cytochrome oxidase (CO) blob columns in cortical layer III and within cortical layer I. Overall, the morphology of the K axons in these monkeys is quite similar to what we described previously for K geniculocortical axons in the distantly related bush baby (prosimian primate), suggesting that the basic features of this pathway are common to all primates. Our results also provide evidence that the axon arbors from different K layers are morphologically distinct; axons from LGN layer K1 project mainly to cortical layer I, while axons from LGN layer K3 chiefly terminate in cortical layer III. Taken together, these results imply that the basic features of axons within the K pathway are conserved across primates, and that the K axons from different K layers are likely to differ in function based upon their different morphologies.
Tyrosine hydroxylase expression in the Cebus monkey retina
Authors: Guimarães Marília Zaluar P. , Hokoç Jan Nora
Published: June 2009

Tyrosine hydroxylase (TH) expression was used as a marker to study the dopaminergic cells in the Cebus monkey retina. Two types of dopaminergic cells were identified by cell body size and location, level of arborization in the inner plexiform layer, and amount of immunolabeling. Type 1 cells displayed intense immunoreactivity and larger somata (12–24 μm) located in the inner nuclear layer or ganglion cell layer, whereas type 2 had smaller cell bodies (8–14 μm) found either in the inner plexiform layer or ganglion cell layer and were more faintly labeled. Interplexiform cells were characterized as type 1 dopaminergic cells. Immunoreactive axon-like processes were seen in the nerve fiber layer, and a net of fibers was visible in the foveal pit and in the extreme periphery of the retina. The population of TH+ cells was most numerous in the temporal superior quadrant and its density peaked at 1–2 mm from the fovea. Type 1 TH+ cells were more numerous than type 2 cells at any eccentricity. Along the horizontal meridian, type 1 cell density was slightly higher in temporal (29 cells/mm2) than in nasal (25 cells/mm2) retina, while type 2 cells had a homogeneous distribution (4.5 cells/mm2). Along the vertical meridian, type 1 cells reached lower peak density (average 17.7 cells/mm2) in the inferior retina (central 4 mm), compared to the superior portion (23.7 cells/mm2). Type 2 cell density varied from 4.5 cells/mm2 in the superior region to 9.4 cells/mm2 in the inferior region. The spatial density of the two cell types varied approximately inversely while the total density of TH+ cells was virtually constant across the retina. No correlation between dopaminergic cells and rod distribution was found. However, we suggest that dopaminergic cells could have a role in mesopic and/or photopic vision in this species, since TH+ fibers are present in cone-dominated regions like the foveola and extreme nasal Periphery.
An adaptive Reichardt detector model of motion adaptation in insects and mammals
Authors: Clifford Colin W.G. , Ibbotson Michael R. , Langley Keith
Published: June 2009

There are marked similarities in the adaptation to motion observed in wide-field directional neurons found in the mammalian nucleus of the optic tract and cells in the insect lobula plate. However, while the form and time scale of adaptation is comparable in the two systems, there is a difference in the directional properties of the effect. A model based on the Reichardt detector is proposed to describe adaptation in mammals and insects, with only minor modifications required to account for the differences in directionality. Temporal-frequency response functions of the neurons and the model are shifted laterally and compressed by motion adaptation. The lateral shift enhances dynamic range and differential motion sensitivity. The compression is not caused by fatigue, but is an intrinsic property of the adaptive process resulting from interdependence of temporal-frequency tuning and gain in the temporal filters of the motion detectors.
Neuropeptide Y and enkephalin immunoreactivity in retinorecipient nuclei of the hamster pretectum and thalamus
Authors: Morin L.R. , Blanchard J.H.
Published: June 2009

This investigation was stimulated by the historical confusion concerning the identity of certain pretectal nuclei and by large differences reported between species with respect to which nuclei receive retinal innervation. Subcortical visual nuclei were studied using immunohistochemistry to identify retinal projections labeled following intraocular injection of cholera toxin, b fragment. In addition, neuropeptide Y (NPY) or enkephalin (ENK) immunoreactive cells and fibers were also evaluated in the retinorecipient pretectal and thalamic areas. The results confirm the established view that the retina directly innervates the nucleus of the optic tract (NOT), posterior (PPT) and olivary pretectal (OPT) nuclei. However, the retina also innervates the hamster medial (MPT) and anterior (APT; dorsal division) pretectal nuclei, results not previously reported in rodents. A commissural pretectal area (CPT) sparsely innervated by retina is also described. The data show for the first time that the posterior limitans nucleus (PLi) receives a moderately dense, direct retinal input. The PLi does not project to the cortex and appears to be a pretectal, rather than thalamic, nucleus. All retinal projections are bilateral, although predominantly contralateral The PLi contains a moderately dense plexus of NPY- and ENK-IR fibers and terminals. However, peptidergic fibes also traverse the APT and connect with the dorsomedial pretectum. The OPT contains ENK- and NPY-IR neurons and fibers, but is specifically identifiable by a moderately dense plexus of ENK-IR terminals. Numerous ENK-IR neurons are found in the NOT and PPT. The latter also has moderate numbers of ENK-IR fibers and terminals b few NPY-IR neurons or fibers. The MPT contains modest numbers of ENK-IR fibers. The APT has no NPY-IR neurons or terminals, but an occasional ENK-IR neuron is seen and there is sparse ENK-IR innervation Peptidergic innervation of the visual nuclei does not appear to be derived from the retina. The results show a set of retinally innervated, contiguous nuclei extending from the thalamic ventrolateral geniculate nucleus dorsomedially to the midbrain CPT. These nuclei plus the superior colliculus comprise a dorsal “visual shell” embracing a central core of caudal thalamus and rostral midbrain.
Dendritic development of retinal ganglion cells after prenatal intracranial infusion of tetrodotoxin
Authors: Campbell Gregor , Ramoa Ary S. , Stryker Michael P. , Shatz Carla J.
Published: June 2009

The dendritic form of a cell may be established by many factors both intrinsic and environmental. Blockade of action potentials along the course of axons and in their postsynaptic targets dramatically alters the development of axonal morphology. The extent to which blockade of target cell activity retrogradely alters the dendritic morphology of the presynaptic cells is unknown. To determine whether the establishment of dendritic form by developing retinal canclion cells depends on activity within their targets, the sodium channel blocker, tetrodotoxin (TTX), was administeredviaminipumps to the diencephalon of cat fetuses from embryonic day 43 (E43) to E57. At E57 retinae were removed and living retinal ganglion cells injectedin vitrowith Lucifer yellow to reveal their dendritic morphology. In the TTX-treated animals both alpha and beta types of retinal ganglion cells were present, as were putative gamma cells. Overall, the dendrites of retinal ganglion cells in TTX-treated animals appeared qualitatively and Quantitatively similar to those of untreated animals. The only significant change in the TTX-treated cases was a small increase in the number of dendritic spines on the non-beta cells. These results indicate that the acquisition of basic dendritic form of developing ganglion cells is not influenced by the action potential activity within their targets, and that it is also independent of the terminal branching patterns of their axons.
Relationships between Müller cells and neurons in a primitive tetrapod, the Australian lungfish
Authors: Robinson Stephen R.
Published: June 2009

We recently proposed a model of cytogenesis which assumes that primitive ancestral mammals and premammalian vertebrates had a retinal composition that consisted of about seven neurons per Müller cell, comprising 1–2 cone photoreceptors, 1–2 rod photoreceptors, 2–3 bipolar cells, 1–2 amacrine cells, less than 1 ganglion cell, and less than 1 horizontal cell (Reichenbach & Robinson, 1995). The Australian lungfish (Neoceratodus forsten) closely resembles the lobe-finned ancestors of land vertebrates, and has an extremely plesiomorphic nervous system. The present study, therefore, has examined the relative frequencies of retinal neurons and Müller cells (identified by immunolabelling for glutamine synthetase) in the lungfish retina. It was found that for each Müller cell there is an average of 1.9 cone photoreceptors, 1.7 rod photoreceptors, 3.1 amacrine/bipolar/horizontal cells, and 0.6 ganglion cells; amounting to a ratio of 7.3 neurons per Müller cell. These results support our conjecture that the sequence of cytogenesis in mammals is constrained by a developmental program that predates the evolution of mammals. The study also provides the first detailed morphological descriptions of lungfish Müller cells and their relationship with adjacent neurons. It was found that individual Müller cells in lungfish have a volume (more than 12,000 μm3) that is an order of magnitude higher than in mammals, yet the proportion of total retinal volume occupied by these cells (20%) is very similar.
Le rôle des anaphores dans la mise en place des relations de cohérence dans le discours: l'hypothèse de J.R. Hobbs
Authors: CORNISH FRANCIS
Published: June 2009

Pour Hobbs (1979), l'interprétation des anaphoriques inter-phrastiques ‘découle’ (‘falls out’) en tant qu'effet secondaire de l'emploi d'une relation de cohérence pour intégrer deux unités de discours. En essayant de mettre au clair la nature des interactions entre relations de cohérence et fonctionnement des anaphores dans la compréhension de textes multi-propositionnels, l'article cherche à démontrer que l'hypothèse de Hobbs n'est valable qu'en partie.

D'abord, la référence complète des anaphoriques ne ‘découle’ pas seulement du choix de telle ou telle relation de cohérence pour intégrer deux unités de discours: elle est essentielle pour la mise en œuvre effective de cette relation. Ensuite, elle sert également à sélectionner l'unité de discours avec laquelle l'unité arrivante va s'intégrer, ainsi qu’à articuler le discours en une structure hiérarchique. Enfin l'intégration des unités de discours n'a pas lieu d'un seul coup, mais peut être étalée sur au moins trois étapes distinctes.
Titres et intertitres dans l'organisation du discours
Authors: REBEYROLLE JOSETTE , JACQUES MARIE-PAULE , PÉRY-WOODLEY MARIE-PAULE
Published: June 2009

Dans cet article, nous explorons le fonctionnement discursif des titres en nous appuyant sur l'hypothèse qu'ils contribuent à la construction d'un modèle interprétatif du discours. Notre objectif est de montrer que les relations que les titres entretiennent avec le texte qu'ils chapeautent ne se laissent pas décrire avec les mêmes outils théoriques ni avec les mêmes méthodes selon le genre des textes. Parce qu'ils sont uniques, les titres d'articles de presse devraient pouvoir être décrits au travers de relations de cohérence. Parce qu'ils sont multiples, en revanche, les titres qui structurent les textes longs ne peuvent pas être abordés ainsi. La description de leur fonctionnement exige une méthode de linguistique de corpus fondée sur l'annotation systématique d'indices susceptibles de faire émerger des types fonctionnels distincts.
CHEBYSHEV POLYNOMIALS ON JULIA SETS AND EQUIPOTENTIAL CURVES FOR THE FAMILYP(z)=zd−c
Authors: XIAO YINGQING , QIU WEIYUAN
Published: June 2009

It is shown that thednth Chebyshev polynomials on the Julia setJP, and on the equipotential curve ΓP(R), of the polynomialP(z)=zd−c, are identical and exactly equal to thenth iteration ofP(z) itself. As an application, the capacity of the Julia setJPis deduced, a result that was first obtained by Brolin.
ON THE INDEX OF COMPOSITION OF THE EULER FUNCTION AND OF THE SUM OF DIVISORS FUNCTION
Authors: DE KONINCK JEAN-MARIE , LUCA FLORIAN
Published: June 2009

Given an integern≥2, letλ(n):=(logn)/(logγ(n)), whereγ(n)=∏p∣np, denote the index of composition ofn, withλ(1)=1. Letting ϕ andσstand for the Euler function and the sum of divisors function, we show that bothλ(ϕ(n)) andλ(σ(n)) have normal order 1 and mean value 1. Given an arbitrary integerk≥2, we then study the size of min {λ(ϕ(n)),λ(ϕ(n+1)),…,λ(ϕ(n+k−1))} and of min {λ(σ(n)),λ(σ(n+1)),…,λ(σ(n+k−1))} asnbecomes large.
TWO-SIDED ASYMPTOTIC BOUNDS FOR THE COMPLEXITY OF SOME CLOSED HYPERBOLIC THREE-MANIFOLDS
Authors: MATVEEV SERGEI , PETRONIO CARLO , VESNIN ANDREI
Published: June 2009

We establish two-sided bounds for the complexity of two infinite series of closed orientable three-dimensional hyperbolic manifolds, the Löbell manifolds and the Fibonacci manifolds. The manifolds of the two series are indexed by an integernand the corresponding complexity estimates are both linear inn.
VECTOR BUNDLES OVER A NONDEGENERATE CONIC
Authors: BISWAS INDRANIL , NAGARAJ D. S.
Published: June 2009

Let k be a field and X a k-form of the projective line. We classify all the isomorphism classes of vector bundles over X.
Basement interpretations from airborne magnetic and gravity data over the Lambert Rift region of East Antarctica
Authors: McLean M. A. , Wilson C. J. L. , Boger S. D. , Betts P. G. , Rawling T. J. , Damaske D.
Published: June 2009

Geological exposures in the Lambert Rift region of East Antarctica comprise scattered coastal outcrops and inland nunataks sporadically protruding through the Antarctic ice sheet from Prydz Bay to the southernmost end of the Prince Charles Mountains. This study utilized airborne magnetic, gravity, and ice radar data to interpret the distribution and architecture of tectonic terranes that are largely buried beneath the thick ice sheet. Free‐air and Bouguer gravity data are highly influenced by the subice and mantle topography, respectively. Gravity stripping facilitated the removal of the effect of ice and Moho, and the residual gravity data set thus obtained for the intermediate crustal level allowed a direct comparison with magnetic data. Interpretation of geophysical data also provided insight into the distribution and geometry of four tectonic blocks: namely, the Vestfold, Beaver, Mawson, and Gamburtsev domains. These tectonic domains are supported by surface observations such as rock descriptions, isotopic data sets, and structural mapping.
Transport estimates at the western section of the Strait of Gibraltar: A combined experimental and numerical modeling study
Authors: Sánchez‐Román A. , Sannino G. , García‐Lafuente J. , Carillo A. , Criado‐Aldeanueva F.
Published: June 2009

Three‐yearlong time series of Acoustic Doppler Current Profiler (ADCP) observations at a single station in Espartel Sill (Strait of Gibraltar) were used to compute an outflow of Q2 = −0.82 Sv through the main channel. The cross‐strait structure of the velocity field or the outflow through a secondary channel north of the submarine ridge of Majuan in Espartel section is not captured by observations so that an improved version of a numerical model (CEPOM) has been used to fill the observational gap. Previously, the model performance has been checked against historical data sets by comparing harmonic constants of the main diurnal and semidiurnal constituents from observed and modeled data at different sites of the strait. Considering the great complexity of tidal dynamics in the area, the comparison is quite satisfactory and validates the model to infer the exchange at longer timescales. Using a “climatological” April in the simulation, extracting a “single station” from the model at the same position as the monitoring station and processing the data similarly, the model gives an outflow through the southern channel 13% higher than observations. The inclusion of the cross‐strait structure of velocity reduces the computed outflow through the southern channel, whereas the contribution of the northern channel brings the total outflow close to that computed using a single station (5% smaller). If the same correction is applied to observations, the total outflow would reduce to Q2 = −0.78 Sv. The paper also assesses the importance of eddy fluxes to the total outflow, their contribution being negligible (≤5%).
Differentiating geology and tectonics using a spatial autocorrelation technique for the hypsometric integral
Authors: Pérez‐Peña J. V. , Azañón J. M. , Booth‐Rea G. , Azor A. , Delgado J.
Published: June 2009

Hypsometry is thought to be sensitive to tectonic uplift rates and lithology differences. In this study we calculated hypsometric integrals (HIs) using as topographic sources two digital elevation models of 10 and 90 m of pixel resolution in the Granada basin (SE of Spain). The HI spatial distributions do not show clear spatial patterns and do not correlate with basin parameters as mean elevation or relief amplitude. However, when exploratory spatial data analysis is applied to the data distributions through local indices of spatial autocorrelation, clear hot spots are visible that improve the geologic meaning of the HI. The distributions are robust and independent of the model resolution but are scale influenced. The application of this new method to the Granada basin shows a strong correlation between the main distribution of active normal faults in the basin and the clusters of high or low HI values obtained in our analysis. Clusters with high HI values define the uplifted footwalls of these faults and regions uplifted in relation with rollover anticlines or where epeirogenic uplift has not been counteracted by local extension. Once the method was adjusted in the Granada basin, we tested its applicability in an area of known contractive tectonic activity, central Otago, New Zealand, showing that the meaning of HI values is improved by using the autocorrelation techniques.
Validation of revised DNDC model for methane emissions from irrigated rice fields in Thailand and sensitivity analysis of key factors
Authors: Smakgahn Kruamas , Fumoto Tamon , Yagi Kazuyuki
Published: June 2009

The original Denitrification–Decomposition (DNDC) model and a revised version were tested against data from field observations of methane (CH4) emissions from irrigated rice fields in Thailand. The revised DNDC model, which was modified for use in Japanese rice fields by revising the crop growth and soil biogeochemical submodels, yielded better simulation results than the original model. In most cases, daily CH4 fluxes predicted by the revised DNDC model agreed well with observations. Seasonal CH4 emissions simulated by the revised model showed significantly higher correlation with observations than those obtained with the original model. Errors in the simulation appear to have resulted from uncertainties in both the input parameters and the model descriptions. Sensitivity analysis revealed that the revised DNDC model is highly sensitive to the concentration of reducible soil Fe, the rate of rice straw incorporation, and rice root biomass. Therefore, uncertainties in these factors may strongly affect the prediction of CH4 emissions. These results suggest that for reliable prediction of CH4 emissions from Thai rice fields, further work is needed to improve the estimates of reducible soil Fe, to quantify the rate of straw incorporation, and to parameterize the crop submodel for the dominant rice varieties grown in Thailand.
Comparing glacial and Holocene opal fluxes in the Pacific sector of the Southern Ocean
Authors: Bradtmiller Louisa I. , Anderson Robert F. , Fleisher Martin Q. , Burckle Lloyd H.
Published: June 2009

The silicic acid leakage hypothesis (SALH) predicts that during glacial periods excess silicic acid was transported from the Southern Ocean to lower latitudes, which favored diatom production over coccolithophorid production and caused a drawdown of atmospheric CO2. Downcore records of 230Th‐normalized opal (biogenic silica) fluxes from 31 cores in the Pacific sector of the Southern Ocean were used to compare diatom productivity during the last glacial period to that of the Holocene and to examine the evidence for increased glacial Si export to the tropics. Average glacial opal fluxes south of the modern Antarctic Polar Front (APF) were less than during the Holocene, while average glacial opal fluxes north of the APF were greater than during the Holocene. However, the magnitude of the increase north of the APF was not enough to offset decreased fluxes to the south, resulting in a decrease in opal burial in the Pacific sector of the Southern Ocean during the last glacial period, equivalent to approximately 15 Gt opal ka−1. This is consistent with the work of Chase et al. (2003a), and satisfies the primary requirement of the SALH, assuming that the upwelled supply of Si was approximately equivalent during the Holocene and the glacial period. However, previous results from the equatorial oceans are inconsistent with the other predictions of the SALH, namely that either the Corg:CaCO3 ratio or the rate of opal burial should have increased during glacial periods. We compare the magnitudes of changes in the Southern Ocean and the tropics and suggest that Si escaping the glacial Southern Ocean must have had an alternate destination, possibly the continental margins. There is currently insufficient data to test this hypothesis, but the existence of this sink and its potential impact on glacial pCO2 remain interesting topics for future study.
Lundquist Receives 2008 Cryosphere Young Investigator Award
Authors: Dozier Jeff , Lundquist Jessica D.
Published: June 2009

Jessica D. Lundquist received the 2008 Cryosphere Young Investigator Award at the 2008 AGU Fall Meeting Honors Ceremony, held 17 December in San Francisco, Calif. The award is for a significant contribution to cryospheric science and technology.
Source analysis using regional empirical Green's functions: The 2008 Wells, Nevada, earthquake
Authors: Mendoza C. , Hartzell S.
Published: June 2009

We invert three‐component, regional broadband waveforms recorded for the 21 February 2008 Wells, Nevada, earthquake using a finite‐fault methodology that prescribes subfault responses using eight MW∼4 aftershocks as empirical Green's functions (EGFs) distributed within a 20‐km by 21.6‐km fault area. The inversion identifies a seismic moment of 6.2 x 1024 dyne‐cm (5.8 MW) with slip concentrated in a compact 6.5‐km by 4‐km region updip from the hypocenter. The peak slip within this localized area is 88 cm and the stress drop is 72 bars, which is higher than expected for Basin and Range normal faults in the western United States. The EGF approach yields excellent fits to the complex regional waveforms, accounting for strong variations in wave propagation and site effects. This suggests that the procedure is useful for studying moderate‐size earthquakes with limited teleseismic or strong‐motion data and for examining uncertainties in slip models obtained using theoretical Green's functions.
Effective radius and droplet spectral width from in‐situ aircraft observations in trade‐wind cumuli during RICO
Authors: Arabas S. , Pawlowska H. , Grabowski W. W.
Published: June 2009

This paper presents statistics of cloud microphysical properties of shallow tropical cumuli observed by a research aircraft during RICO field campaign. Cloud properties are derived from 10 Hz (about 10 m spatial distance) Fast‐FSSP data in four different flights. The motivation comes from similar analyses of either aircraft data from stratocumulus clouds or remote‐sensing data of tropical cumuli. In the lowest few hundred meters, the standard deviation of the droplet size distribution σr and the relative dispersion, the ratio of σr and the mean radius, are similar to stratocumulus clouds, but they are significantly larger in the upper half of the cloud field depth. The frequency distribution of the effective radius is significantly narrower than in the remote‐sensing observations in the middle and upper third of the cloud field. These results can be used in parameterizations and validations of cloud microphysics in numerical models of various complexity.
Intravenous immunoglobulin up‐regulates the expression of the inhibitory FcγIIB receptor on B cells
Authors: Nikolova Kalina A , Tchorbanov Andrey I , Djoumerska‐Alexieva Iglika K , Nikolova Maria , Vassilev Tchavdar L
Published: June 2009

Intravenous immunoglobulin (IVIg) preparations are known to modulate autoimmune/inflammatory diseases through several F(ab')2‐ and Fc‐dependent mechanisms. In this study, we show that the in vitro and the in vivo exposure of B lymphocytes from lupus‐prone and from healthy mice to IVIg results in an increased expression of their surface inhibitory FcγIIB receptors. Further, this exposure enhanced the ability of a chimeric antibody, cross‐linking FcγRIIB and immunoglobulin receptors on DNA‐specific B lymphocytes, to suppress IgG anti‐DNA antibody production. F(ab')2 fragments of IVIg had a similar activity as the intact preparation, whereas Fc fragments had no effect. This study describes a novel approach with clinical relevance for modulating B lymphocyte activity.
Protection from EAE by IL‐4Rα−/− macrophages depends upon T regulatory cell involvement
Authors: Keating Paula , O'Sullivan David , Tierney Joanna B , Kenwright Diane , Miromoeini Sara , Mawasse Lina , Brombacher Frank , La Flamme Anne C
Published: June 2009

The administration of Th2 cytokines or immune deviation to a Th2 phenotypic response has been shown to protect against the autoimmune pathology of experimental autoimmune encephalomyelitis (EAE). To better understand the function of Th2 cytokines in the induction stage of EAE in the absence of an overt Th2 response, we immunized IL‐4 receptor alpha‐deficient (IL‐4Rα−/−) mice, which are unable to respond to either IL‐4 or IL‐13. Contrary to expectations, mice lacking IL‐4Rα had a lower incidence of EAE and a delayed onset compared to WT BALB/c mice; however, this delay did not correlate to an alteration in the Th1/Th17 cytokine balance. Instead, IL‐4Rα‐responsive macrophages were essential promoters of disease as macrophage‐specific IL‐4Rα‐deficient (LysMcreIL‐4Rα−/lox) mice were protected from EAE. The protection afforded by IL‐4Rα‐deficiency was not due to IL‐10‐, IFN‐γ‐, NO‐ or IDO‐mediated suppression of T‐cell responses but was dependent upon the presence of regulatory T cells (Tregs). This investigation highlights the importance of macrophages and Tregs in regulating central nervous system inflammation and demonstrates that macrophages activated in the absence of Th2 cytokines can promote disease suppression by Tregs.
Isolation and characterization of a secreted, cell-surface glycoprotein SCUBE2 from humans
Authors: Tsai Ming-Tzu , Cheng Chien-Jui , Lin Yuh-Charn , Chen Chun-Chuan , Wu Ann-Ru , Wu Min-Tzu , Hsu Cheng-Chin , Yang Ruey-Bing
Published: June 2009

SCUBE2 [signal peptide, CUB domain, EGF (epidermal growth factor)-like protein 2] belongs to an evolutionarily conserved SCUBE protein family, which possesses domain organization characteristic of an N-terminal signal peptide sequence followed by nine EGF-like repeats, a spacer region, three cysteine-rich repeat motifs, and one CUB domain at the C-terminus. Despite several genetic analyses suggesting that the zebrafish orthologue of the mammalian SCUBE2 gene participates in HH (Hedgehog) signalling, the complete full-length cDNA and biochemical function for mammalian SCUBE2 on HH signalling remains uninvestigated. In the present study, we isolated the full-length cDNA and studied the role of human SCUBE2 in the HH signalling cascade. When overexpressed, recombinant human SCUBE2 manifests as a secreted surface-anchored glycoprotein. Deletion mapping analysis defines the critical role of the spacer region and/or cysteine-rich repeats for membrane association. Further biochemical analyses and functional reporter assays demonstrated that human SCUBE2 can specifically interact with SHH (Sonic Hedgehog) and SHH receptor PTCH1 (Patched-1), and enhance the SHH signalling activity within the cholesterol-rich raft microdomains of the plasma membranes. Together, our results reveal that human SCUBE2 is a novel positive component of the HH signal, acting upstream of ligand binding at the plasma membrane. Thus human SCUBE2 could play important roles in HH-related biology and pathology, such as during organ development and tumour progression.
Introduction: Charles Darwin's plant biology
Authors: Purdie Rosemary
Published: June 2009

The year 2009 marks the bicentenary of Charles Darwin’s birth and 150 years since publication of his theory of evolution, the seeds of which were sown while he was Naturalist during the voyage of the Beagle. Darwin’s botanical observations during that five-year long trip and his thousands of experiments with plants after his return to England provided much of the evidence he used to develop and substantiate his theory. Botany became a time-consuming passion that spanned topics as diverse as plant physiology, plant breeding and domestication, pollination biology, plant morphology and ecology. This paper provides an overview of his experimental work on plants, carried out at his home, Down House, using household items as equipment and working with hundreds of different species from across the flowering plant kingdom. Darwin communicated the results of his work in scientific and popular journals and in seven books, the last of which was published when he was 74 years old. In his autobiography, Darwin attributed his success as a scientist to his love of science, unbounded patience, industry in observing and collecting facts, invention, and common sense. Darwin remains an inspiration for the budding scientists of the 21st century.
Sexual and asexual (apomictic) seed development in flowering plants: molecular, morphological and evolutionary relationships
Authors: Tucker Matthew R. , Koltunow Anna M. G.
Published: June 2009

Reproduction in the flowering plants (angiosperms) is a dynamic process that relies upon the formation of inflorescences, flowers and eventually seed. Most angiosperms reproduce sexually by generating gametes via meiosis that fuse during fertilisation to initiate embryo and seed development, thereby perpetuating the processes of adaptation and evolution. Despite this, sex is not a ubiquitous reproductive strategy. Some angiosperms have evolved an alternate form of reproduction termed apomixis, which avoids meiosis during gamete formation and leads to the production of embryos without paternal contribution. Therefore, apomixis results in the production of clonal progeny through seed. The molecular nature and evolutionary origin of apomixis remain unclear, but recent studies suggest that apomixis evolved from the same molecular framework supporting sex. In this review, we consider physical and molecular relationships between the two pathways, with a particular focus on the initial stages of female reproduction where apomixis deviates from the sexual pathway. We also consider theories that explain the origin of apomictic processes from sexual progenitors. Detailed characterisation of the relationship between sex and apomixis in an evolutionary and developmental sense is an important step towards understanding how apomixis might be successfully integrated into agriculturally important, but currently sexual crops.