bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphometrical relationships between South‐east Asian deer (Cervidae, tribe Cervini): evolutionary and biogeographic implications
Authors: Meijaard E. , Groves C. P.
Published: May 2004

Two hundred and fourteen skulls of Asian deer species (Cervini) were measured and the resulting craniometric data analysed using multivariate statistics. Our results suggest that elements of skull shape as determined by morphometrics can be used as phylogenetic characters and depict phylogenetic relationships among Cervini deer species that is not far removed from the picture given by molecular studies and other characters. Morphometrics‐based phylogeny was used in combination with other phylogenies and palaeoenvironmental reconstructions to investigate factors that may have influenced evolutionary changes. Our data indicate the need for a revision of the genus and subgenus level taxonomy of the Cervini.
Enamel hypoplasia provides insights into early systemic stress in wild and captive giraffes (Giraffa camelopardalis)
Authors: Franz‐Odendaal Tamara A.
Published: May 2004

Enamel hypoplasia, a developmental tooth defect, provides a permanent record of systemic stress during early life. The incidence and distribution of linear enamel hypoplasia has been used by anthropologists and palaeontologists to assess the health status of past populations but has not been applied by wildlife biologists studying extant animals. This study investigates enamel hypoplasia in 23 Giraffa camelopardalis skulls from wild and captive animals of various ages and sex to determine whether any systemic stress events are unique to life in captivity. Results indicate that wild giraffes are relatively stress‐free as they do not have linear defects. Based on the distribution of linear defects in other giraffes, three key stress periods during the first 6 years of giraffe life were identified. The first stress event occurs during weaning, the second at about 3 years of age and the third, which is the least common, at 4–5 years of age. All three stress events were observed in both male and female giraffes. This study highlights the usefulness of assessing enamel hypoplasia in both wild and captive animals as well as the need for further research on tooth developmental timings in many wild ungulates. Some left–right asymmetry was observed in the development of linear and non‐linear defects, which has implications for the aetiology of these defects.
Editorial
Authors: Fields R. Douglas
Published: May 2004

“Of what use a newborn babe?” was Oersted's response to
a question from the audience as to the value of electromagnetism
following his demonstration that a compass needle
could be deflected by passing current through a nearby wire.
Such is the immediate reaction anytime something new is
encountered: What is it, and why do we need it? This perplexity
arises from the certain conclusion of a proof derived from the
objective facts: we seem to have managed quite well up to now
without it. But as functional as a world before cell phones and
email seemed, how dysfunctional would the world now appear
without them? Time changes, and Science is change. Scientific
journals track and pioneer those changes.
Astrocytic Connectivity in the Hippocampus
Authors: SUL JAI-YOON , OROSZ GEORGE , GIVENS RICHARD S. , HAYDON PHILIP G.
Published: May 2004

Little is known about the functional connectivity between astrocytes in the CNS. To explore this issue we photo-released glutamate onto a single astrocyte in murine hippocampal slices and imaged calcium responses. Photo-release of glutamate causes a metabotropic glutamate receptor (mGluR)-dependent increase in internal calcium in the stimulated astrocyte and delayed calcium elevations in neighboring cells. The delayed elevation in calcium was not caused by either neuronal activity following synaptic transmission or by glutamate released from astrocytes. However, it was reduced by flufenamic acid (FFA), which is consistent with a role for adenosine triphosphate (ATP) release from astrocytes as an intercellular messenger. Exogenous ligands such as ATP (1 µM) increased the number of astrocytes that were recruited into coupled astrocytic networks, indicating that extracellular accumulation of neurotransmitters modulates neuronal excitability, synaptic transmission and functional coupling between astrocytes.
Glial cell inclusions and the pathogenesis of neurodegenerative diseases
Authors: MILLER DAVID W. , COOKSON MARK R. , DICKSON DENNIS W.
Published: May 2004

In this review, we discuss examples that show how glial-cell pathology is increasingly recognized in several neurodegenerative diseases. We also discuss the more provocative idea that some of the disorders that are currently considered to be neurodegenerative diseases might, in fact, be due to primary abnormalities in glia. Although the mechanism of glial pathology (i.e. modulating glutamate excitotoxicity) might be better established for amyotrophic lateral sclerosis (ALS), a role for neuronal–glial interactions in the pathogenesis of most neurodegenerative diseases is plausible. This burgeoning area of neuroscience will receive much attention in the future and it is expected that further understanding of basic neuronal–glial interactions will have a significant impact on the understanding of the fundamental nature of human neurodegenerative disorders.
Adenosine: an activity-dependent axonal signal regulating MAP kinase and proliferation in developing Schwann cells
Authors: STEVENS BETH , ISHIBASHI TOMOKO , CHEN JIANG-FAN , FIELDS R. DOUGLAS
Published: May 2004

Nonsynaptic release of ATP from electrically stimulated dorsal root gangion (DRG) axons inhibits Schwann cell (SC) proliferation and arrests SC development at the premyelinating stage, but the specific types of purinergic receptor(s) and intracellular signaling pathways involved in this form of neuron–glia communication are not known. Recent research shows that adenosine is a neuron–glial transmitter between axons and myelinating glia of the CNS. The present study investigates the possibility that adenosine might have a similar function in communicating between axons and premyelinating SCs. Using a combination of pharmacological and molecular approaches, we found that mouse SCs in culture express functional adenosine receptors and ATP receptors, a far more complex array of purinergic receptors than thought previously. Adenosine, but not ATP, activates ERK/MAPK through stimulation of cAMP-linked A2A adenosine receptors. Both ATP and adenosine inhibit proliferation of SCs induced by platelet-derived growth factor (PDGF), via mechanisms that are partly independent. In contrast to ATP, adenosine failed to inhibit the differentiation of SCs to the O4+ stage. This indicates that, in addition to ATP, adenosine is an activity-dependent signaling molecule between axons and premyelinating Schwann cells, but that electrical activity, acting through adenosine, has opposite effects on the differentiation of myelinating glia in the PNS and CNS.
Myelin associated glycoprotein cross-linking triggers its partitioning into lipid rafts, specific signaling events and cytoskeletal rearrangements in oligodendrocytes
Authors: MARTA C.B. , TAYLOR C.M. , CHENG S. , QUARLES R.H. , BANSAL R. , PFEIFFER S.E.
Published: May 2004

Myelin-associated glycoprotein (MAG) has been implicated in inhibition of nerve regeneration in the CNS. This results from interactions between MAG and the Nogo receptor and gangliosides on the apposing axon, which generates intracellular inhibitory signals in the neuron. However, because myelin–axon signaling is bidirectional, we undertook an analysis of potential MAG-activated signaling in oligodendrocytes (OLs). In this study, we show that antibody cross-linking of MAG on the surface of OLs (to mimic axonal binding) leads to the redistribution of MAG into detergent (TX-100)-insoluble complexes, hyperphosphorylation of Fyn, dephosphorylation of serine and threonine residues in specific proteins, including lactate dehydrogenase and the β subunit of the trimeric G-protein-complex, and cleavage of α-fodrin followed by a transient depolymerization of actin. We propose that these changes are part of a signaling cascade in OLs associated with MAG function as a mediator of axon–glial communication which might have implications for the mutual regulation of the formation and stability of axons and myelin.
Remyelination of spinal cord axons by olfactory ensheathing cells and Schwann cells derived from a transgenic rat expressing alkaline phosphatase marker gene
Authors: AKIYAMA YUKINORI , LANKFORD KAREN , RADTKE CHRISTINE , GREER CHARLES A. , KOCSIS JEFFERY D.
Published: May 2004

Transplantation of cell suspensions containing olfactory ensheathing cells (OECs) has been reported to remyelinate demyelinated axons in the spinal cord with a Schwann cell (SC)-like pattern of myelination. However, questions have been raised recently as to whether OECs can form SC-like myelin. To address this issue we prepared SCs and OECs from transgenic rats in which a marker gene, human placental alkaline phosphatase (hPAP), is linked to the ubiquitously active promoter of the R26 gene. SCs were prepared from the sciatic nerve and OECs from the outer nerve-fiber layer of the olfactory bulb. Positive S100 and p75 immunostaining indicated that >95% of cells in culture displayed either SC or OEC phenotypes. Suspensions of either SCs or OECs were transplanted into an X-irradiation/ethidium bromide demyelinating lesion in the spinal cord. We observed extensive SC-like remyelination following either SC or OEC transplantation 3 weeks after injection of the cells. Alkaline phosphatase (ALP) chromagen reaction product was associated clearly with the myelin-forming cells. Thus, cell suspensions that are enriched in either SCs or OECs result in peripheral-like myelin when transplanted in vivo.
Control of axonophilic migration of oligodendrocyte precursor cells by
Eph–ephrin interaction
Authors: PRESTOZ LAETITIA , CHATZOPOULOU ELLI , LEMKINE GREGORY , SPASSKY NATHALIE , LEBRAS BARBARA , KAGAWA TETSUSHI , IKENAKA KATZUHIRO , ZALC BERNARD , THOMAS JEAN-LÉON
Published: May 2004

The migration of oligodendrocyte precursor cells (OPCs) is modulated by
secreted molecules in their environment and by cell–cell and matrix–cell
interactions. Here, we ask whether membrane-anchored guidance cues, such as
the ephrin ligands and their Eph receptors, participate in the control of
OPC migration in the optic nerve. We postulate that EphA and EphB receptors,
which are expressed on axons of retinal ganglion cells, interact with ephrins
on the surface of OPCs. We show the expression of ephrinA5, ephrinB
2 and ephrinB3 in the migrating OPCs of the optic nerve as
well as in the diencephalic sites from where they originate. In addition,
we demonstrate that coated EphB2-Fc receptors, which are specific
for ephrinB2/B3 ligands, induce dramatic changes
in the contact and migratory properties of OPCs, indicating that axonal EphB
receptors activate ephrinB signaling in OPCs. Based on these findings, we
propose that OPCs are characterized by an ephrin code, and that Eph–ephrin
interactions between axons and OPCs control the distribution of OPCs in the
optic axonal tracts, and the progress and arrest of their migration.
Satellite cells of dorsal root ganglia are multipotential glial precursors
Authors: SVENNINGSEN ÅSA FEX , COLMAN DAVID R. , PEDRAZA LILIANA
Published: May 2004

The evolutionary origin of myelinating cells in the vertebrate nervous system remains a mystery. A clear delineation of the developmental potentialities of neuronal support cells in the CNS and PNS might aid in formulating a hypothesis about the origins of myelinating cells. Although a glial-precursor cell in the CNS can differentiate into oligodendrocytes (OLs), Schwann cells (SCs) and astrocytes, a homologous multipotential cell has not yet been found in the PNS. Here, we identify a cell type of embryonic dorsal root ganglia (DRG) of the PNS – the satellite cell – that develops into OLs, SCs and astrocytes. Interestingly, satellite-cell-derived OL precursors were found in cultures prepared from embryonic day 17 (E17) to postnatal day 8 (P8) ganglia, but not from adult DRGs, revealing a narrow developmental window for multipotentiality. We suggest that compromising the organization of the ganglia triggers a differentiation pathway in a subpopulation of satellite cells, inducing them to become myelinating cells with either a CNS or PNS phenotype. Our data provide an additional, novel piece in the myelinating-cell-precursor puzzle, and lead to the concept that cells in the CNS and PNS that function to ensheath neuronal cell bodies and axons can differentiate into OLs, SCs and astrocytes. In sum, it appears that glial fate might be determined over and above the CNS/PNS dichotomy. Last, we suggest that primordial ensheathing cells form the original cell population in which the myelination program first evolved.
The shape of auroral backscatter spectra
Authors: Moorcroft D. R.
Published: May 2004

Recent observations of auroral backscatter at frequencies from 10 to 933 MHz have found spectral shapes which are intermediate between Lorentzian and Gaussian. To account for these observations a model has been developed consisting of a random distribution of scatterers in the radar field of view. Spectral shape is discussed in terms of the shape of the magnitude of the temporal autocorrelation function (ACF–the Fourier transform of the spectrum), and within the assumptions of the model it is shown that the observed shapes arise from either the average ACF associated with the signal from individual scatterers or from the Doppler spread in the scattering volume. The observed spectral shapes are easily accounted for by a model for the individual scatterer signals consisting of an exponential growth, a quasi‐steady section and an exponential decay.
Plasmaspheric plumes: CRRES observations of enhanced density beyond the plasmapause
Authors: Moldwin M. B. , Howard J. , Sanny J. , Bocchicchio J. D. , Rassoul H. K. , Anderson R. R.
Published: May 2004

CRRES plasma wave receiver density data were used to study the distribution and properties of dense plasmaspheric‐like plasma observed outside the plasmapause. Our study indicates that outer plasmaspheric structure, often called plasmaspheric plumes, blobs, tails, or detached plasma regions, can exist at all local times under all levels of geomagnetic activity. Of the 558 CRRES orbits that had at least one clearly defined plasmapause, 169 (or 30%) had plasmaspheric‐like density structures at higher L shells than the plasmapause. Most of the occurrences of plasmaspheric‐like plasma observed by CRRES were in the noon‐to‐dusk sector in the aftermath of enhanced geomagnetic activity consistent with plasmaspheric plume models.
Analyzing earthquake clustering features by using stochastic reconstruction
Authors: Zhuang Jiancang , Ogata Yosihiko , Vere‐Jones David
Published: May 2004

On the basis of the epidemic‐type aftershock sequence (ETAS) model and the thinning procedure, this paper gives the method about how to classify the earthquakes in a given catalogue into different clusters stochastically. The key points of this method are the probabilities of one event being triggered by another previous event and being a background event. Making use of these probabilities, we can reconstruct the functions associated with the characteristics of earthquake clusters to test a number of important hypotheses about the earthquake clustering phenomena. We applied this reconstruction method to the shallow seismic data in Japan and also to a simulated catalogue. The results show the following assertions: (1) The functions for each component in the formulation of the space‐time ETAS model are good enough as a first‐order approximation for describing earthquake clusters; (2) a background event triggers less offspring in expectation than a triggered event of the same magnitude; (3) the magnitude distribution of the triggered event depends on the magnitude of its direct ancestor; (4) the diffusion of the aftershock sequence is mainly caused by cascades of individual triggering processes, while no evidence shows that each individual triggering process is diffusive; and (5) the scale of the triggering region is still an exponential law, as formulated in the model but not the same one for the expected number of offspring.
Suspended minerogenic particle distributions in high‐energy coastal environments: Optical implications
Authors: Stavn Robert H. , Keen Timothy R.
Published: May 2004

This paper examines suspended minerogenic particle distributions in the near‐coastal ocean, Oceanside, California. The environment is dominated by resuspension of particles from a well‐sorted sandy sediment. We obtain information on the suspended mineral matter from the relocatable numerical sedimentation model, TRANS98. Inputs for the model include bottom particle size distribution, wind speed, wave period and height, and near‐bottom current speed. Model output is a vertical profile of mineral particle concentrations and size distributions at selected depths. The mineral particle size distribution allows the calculation of the total scattering coefficient of suspended minerogenic matter. The particle size distribution for the bed at Oceanside is approximately Gaussian lognormal in character. The predicted size distribution near bottom is a skewed Gaussian lognormal; then the distribution shifts toward the increasing importance of smaller size classes as we approach the water surface. Deeper stations maintain a lognormal character up into the surface layers while the shallower stations switch to a particle size distribution of the smallest size class being the modal class in the surface layers. Hyperbolic size distributions have been proposed for the Oceanside site from optical observations. These distributions would have a slope of 2.1 for coastal water which would decrease to as low as 1.3 for shallow nearshore stations and near the bottom. None of the proposed hyperbolic slopes provides an adequate approximation of the particle distributions predicted by TRANS98. The larger particle size classes are significantly overestimated by hyperbolic models, which causes the total scattering coefficient of the minerogenic matter to be overestimated. These results indicate that hyperbolic slope models cannot be used to retrieve particle size distributions by inversions involving the total scattering coefficient nor are they accurate estimators of the minerogenic scattering coefficient.
Determination of the surface geostrophic velocity field from satellite altimetry
Authors: Park Young‐Hyang
Published: May 2004

Presently available marine geoid models are not accurate enough to extract the mean surface circulation directly from satellite altimetry. A novel method for estimating the mean velocity field of major ocean current systems is derived from the free surface boundary condition. With a given quasi‐geostrophic balance for the horizontal surface flow, a scaling analysis of this boundary condition indicates that although the vertical velocity w is mostly balanced by the local change of the free surface, ∂η′/∂t, useful information on the mean current (, ) is contained in a small ageostrophic departure (∂η′/∂t − w). Our method consists in the development of a simple algebraic equation with two unknowns (, ) and an adjustable parameter associated with ∂η′/∂t, assuming that the latter is proportional to (∂η′/∂t − w). Most interestingly, ∂η′/∂t and all other coefficients of the equation can be determined from altimetry. The altimeter data used is combined TOPEX/Poseidon‐ERS gridded data, and the solution is obtained by least squares, minimizing the contribution from the time‐variable part of the parameter and prescribing the zonal direction of the mean current. The method, which is found to be particularly useful for quasi‐zonal high‐energy current systems, has been validated against direct observations in the Gulf Stream and Southern Ocean. Comparisons with direct observations and Monte Carlo experiments suggest an overall solution error of about 10 cm s−1. Once calibrated against regional velocity statistics, this method will be able to determine from altimetry the mean or instantaneous surface velocity field down to the frontal scale, with a realism that has been inaccessible because of the geoid constraint.
Variability in vertical distributions of planktonic foraminifera in the California Current: Relationships to vertical ocean structure
Authors: Field David B.
Published: May 2004

Geochemical records from planktonic foraminifera are among the few means available to infer past changes in the upper ocean, although interpretations can be confounded by variability in foraminifera habitat depths. The principal environmental factors affecting foraminiferal vertical distributions were examined through 28 vertically stratified plankton tows taken off southern California in winter, spring, and summer. Each species has a dynamic range of preferred habitat depth, from the mixed layer to the thermocline, characterized by a unique relationship with environmental properties. Globigerina bulloides, Neogloboquadrina pachyderma (dextral), and Neogloboquadrina dutertrei can live near the surface but frequently live deeper as stratification increases and a particular isotherm deepens. Globigerinoides ruber and Orbulina universa vary more closely with the depth of the thermocline than the depth of a given isotherm. The shifts in habitat depth are of sufficient magnitude to affect δ18O records. The effects of such shifts are observed for G. bulloides and N. pachyderma in Santa Barbara Basin sediments. Geochemical signatures from multiple species of foraminifera, each with a different predicted response to environmental change, can permit the detection of changes in habitat depth of a given species and thus more accurately indicate past changes in hydrographic structure.
Tectonic processes during oblique collision: Insights from the St. Elias orogen, northern North American Cordillera
Authors: Pavlis Terry L. , Picornell Carlos , Serpa Laura , Bruhn Ronald L. , Plafker George
Published: May 2004

Oblique convergence in the St. Elias orogen of southern Alaska and northwestern Canada has constructed the world's highest coastal mountain range and is the principal driver constructing all of the high topography in northern North America. The orogen originated when the Yakutat terrane was excised from the Cordilleran margin and was transported along margin‐parallel strike‐slip faults into the subduction‐transform transition at the eastern end of the Aleutian trench. We examine the last 3 m.y. of this collision through an analysis of Euler poles for motion of the Yakutat microplate with respect to North America and the Pacific. This analysis indicates a Yakutat‐Pacific pole near the present southern triple junction of the microplate and predicts convergence to dextral‐oblique convergence across the offshore Transition fault, onland structures adjacent to the Yakutat foreland, or both, with plate speeds increasing from 10 to 30 mm/yr from southeast to northwest. Reconstructions based on these poles show that NNW transport of the collided block into the NE trending subduction zone forced contraction of EW line elements as the collided block was driven into the subduction‐transform transition. This suggests the collided block was constricted as it was driven into the transition. Constriction provides an explanation for observed vertical axis refolding of both earlier formed fold‐thrust systems and the collisional suture at the top of the fold‐thrust stack. We also suggest that this motion was partially accommodated by lateral extrusion of the western portion of the orogen toward the Aleutian trench. Important questions remain regarding which structures accommodated parts of this motion. The Transition fault may have accommodated much of the Yakutat‐Pacific convergence on the basis of our analysis and previous interpretations of GPS‐based geodetic data. Nonetheless, it is locally overlapped by up to 800 m of undeformed sediment, yet elsewhere shows evidence of young deformation. This contradiction could be produced if the overlapping sediments are too young to have accumulated significant deformation, or GPS motions may be deflected by transient strains or strains from poorly understood fault interactions. In either case, more data are needed to resolve the paradox.
The impact of institutional constraints on the Limarí River Valley water market
Authors: Hadjigeorgalis Ereney , Lillywhite Jay
Published: May 2004

Institutional constraints on water and water rights trades are usually implemented to reduce the potential costs of free trade in water rights, but these constrains are themselves not without cost. Using data on permanent water rights and annual spot water transactions in the Limarí River Valley of northern Chile, we test for trade barrier‐induced price differences in the constrained permanent water rights market versus the unconstrained spot water market and then estimate the welfare losses generated as a result of these restrictions. We find that trade barriers in the permanent water rights market cause prices to diverge across adjacent irrigation districts for homogenous water rights despite the fact that prices equalize across irrigation districts in the unconstrained spot water market. The resulting estimates of welfare losses from these barriers in the permanent water rights market are found to be significant.
Unsaturated flow through a spherical inclusion
Authors: Warrick A. W. , Knight J. H.
Published: May 2004

Unsaturated flow is considered through a spherical inclusion. The hydraulic conductivity is of the form Kiexp(αh), where the saturated conductivity Ki is different in the main flow regime, the inclusion α is a constant in the entire flow domain, and h is the pressure head. The solution technique is analogous to that used by the authors previously to analyze flow through circular inclusions for two‐dimensional flow by reducing Richards' equation to the Helmholtz equation and applying the analytic element method. Comparisons show differences between the two‐dimensional case (circles) and three‐dimensional case (spheres) in terms of flow enhancement and exclusion through the inclusions. When the inclusion permeability is less than the background conductivity, a lesser fraction of flow occurs through the three‐dimensional case than for the two‐dimensional case; conversely, when the permeability is higher within the inclusion, there is a higher enhancement of flow through that region in the case of the three‐dimensional inclusion.
High‐resolution Sr/Ca records in modern Porites lobata corals: Effects of skeletal extension rate and architecture
Authors: Allison Nicola , Finch Adrian A.
Published: May 2004

We used ion microprobe analysis to determine the Sr/Ca composition of fasciculi (deposited during the day) and centers of calcification (COCs, deposited at night) across transects of two Porites lobata corals, of different linear extension rates, from Oahu, Hawaii. The COCs of both corals contained significantly higher Sr/Ca than the fasciculi (at the 95% confidence level). We observed no significant differences between the Sr/Ca ratios of the fasciculi (or of the COCs) of the fast and slow growing corals, and we conclude that variations in the extension rate of each colony have not affected Sr incorporation in these corals. The fasciculi and COCs in both corals exhibit large Sr/Ca heterogeneity, which is not temperature dependent. Our data do not support the hypothesis that COC analyses provide a SST signature which is unaffected by biological or kinetic effects. The heterogeneity of both features may reflect short‐term (daily to weekly) variations in calcification rate which are known to occur during the day and night and which influence the relative transport rates of Sr and Ca through the coral tissue. We plotted running means through the fasciculi and COC chronologies and compared maximum and minimum Sr/Ca values in each annual cycle with the corresponding minimum and maximum mean sea surface temperature (SST) values (calculated over equivalent time periods). We found that the constants C and M of the linear equation Sr/Ca = C + (M × SST) became smaller as the time interval used to calculate the running means increased from 1 day to ∼77 days. This decrease in C and M reflects the gradual removal of the short‐term Sr heterogeneity (dependent on biological and/or kinetic processes) from the data set as progressively larger numbers of data points are used to calculate the Sr/Ca running mean. We hypothesize that variations in M and C between different published Sr/Ca‐SST calibrations may reflect the relative importance of biological or kinetic processes in corals at different locations.
The dominant influence of the Icelandic Low on the position of the Gulf Stream northwall
Authors: Hameed Sultan , Piontkovski Sergey
Published: May 2004

The location where the Gulf Stream separates from the American coast and turns eastward is called its northwall. The interannual fluctuations of the northwall are significantly correlated with the North Atlantic Oscillation with a lag of two years. When the Azores High and the Icelandic Low pressures are taken as independent variables, the latter dominates the relationship with the northwall, and the influence of the Azores High pressure is insignificant. This is consistent with the hypothesis that the major oceanic control of the northwall is in the southward flow of Labrador Sea Water into the Slope Sea. The alternative mechanism that the interaction of westward propagating Rossby waves with the American coast is responsible for northwall fluctuations is considered less likely because its initiation requires perturbations of the eastward winds in the mid‐Atlantic region, and they are very likely dependent on the Azores High. The analysis suggests that the time lag between perturbations of the Icelandic Low and the northwall varies between one and three years.
Electron quasi‐viscous effects in collisionless slow‐mode shocks
Authors: Yin L. , Winske D. , Daughton W. , Coroniti F. V.
Published: May 2004

The dynamics of collisionless slow‐mode shocks are examined using one‐dimensional full particle (kinetic ions and electrons) and hybrid (kinetic ions, massless fluid electrons) simulations. Full particle simulations indicate that the downstream electron temperature becomes anisotropic (T∥e > T⊥e) at very oblique angles. The anisotropy results from both the large mirror effects and the electron heating due to the parallel electric field of very obliquely propagating kinetic Alfvén waves; it gives rise to finite off‐diagonal electron pressure tensor terms in the simulation frame. Inclusion of these electron quasi‐viscous effects in hybrid simulations allows slow shocks to be set up at very oblique angles, as observed in the distant tail, where dissipation from ion‐ion streaming becomes much weaker.
The Adriatic region: An independent microplate within the Africa‐Eurasia collision zone
Authors: Battaglia Maurizio , Murray Mark H. , Serpelloni Enrico , Bürgmann Roland
Published: May 2004

We use GPS measurements and block modeling to investigate the present‐day deformation of the Adriatic region, whose kinematics within the Nubia‐Eurasia plate boundary zone is not well constrained and remains controversial. Block modeling allows us to compute rigid‐plate angular velocities while accounting for elastic strain accumulation along block‐bounding faults. Results suggest that the Adriatic is a microplate (Adria) and that the southern boundary with the Nubia plate and the Aegean domain may be located along the Apulia Escarpment and the Kefallinia fault. Geodetic data alone cannot discriminate between a single block (AP) or a two blocks (GDAP) description of Adria, but the GDAP model predicts boundary slip rates that are in better agreement with observations from previous studies.
Fluctuation dissipation theorem in a general circulation model
Authors: Cionni I. , Visconti G. , Sassi F.
Published: May 2004

We use the Fluctuation Dissipation Theorem (FDT) as formulated by Leith [1975] and Bell [1980] to asses the climatic sensitivity of the Whole Atmosphere Community Climate Model (WACCM). The lagged covariance matrix is evaluated from the “natural” (unperturbed) variability of the model. Perturbation in both the carbon dioxide content and the solar constant are used to obtain the response function from which the sensitivity matrix is calculated for different level and at the surface of the model. We show that even if the perturbed model does not reach equilibrium the FDT gives reliable values for the climate sensitivity for both the solar radiative and the carbon dioxide forcing.
Power‐law scaling behavior of crustal density and gravity
Authors: Pilkington Mark , Todoeschuck John P.
Published: May 2004

The scale invariant nature of crustal heterogeneity has been established through direct measurements of rock properties and inferences from geophysical observations. We examine the behavior of crustal density variations over length scales from centimeters to hundreds of kilometers using well‐logs, surface rock samples and observed gravity data. The three data types support a simple model of an isotropic, scaling crust with density characterized by a power‐law spectral behavior.
Summertime water masses off the northern Larsen C Ice Shelf, Antarctica
Authors: Nicholls K. W. , Pudsey C. J. , Morris P.
Published: May 2004

We report on oceanographic observations made at the northern end of Larsen C Ice Shelf in the western Weddell Sea. It appears that the Larsen C continental shelf is flushed not by High Salinity Shelf Water from the southern continental shelf, but by Modified Weddell Deep Water (MWDW) flowing across the shelf break. MWDW is observed at the ice front, having tracked west along the northward facing slopes of depressions that reach to the shelf break. Ice Shelf Water observed near the ice front is not, however, derived from MWDW directly, but from MWDW pre‐conditioned by winter cooling and by salinification from sea ice production. If the ice shelf base generally is being melted only by pre‐conditioned MWDW, then, contrary to recent suggestions, changes in the temperature of the deep Weddell Sea are unlikely to have a major impact on melt rates at the base of Larsen C Ice Shelf.
Bv8, the amphibian homologue of the mammalian prokineticins, modulates ingestive behaviour in rats
Authors: Negri Lucia , Lattanzi Roberta , Giannini Elisa , Felice Milena De , Colucci Antonella , Melchiorri Pietro
Published: May 2004

The small protein Bv8, secreted by the skin of the frog Bombina variegata, belongs to a novel family of secreted proteins whose mammalian orthologues have been identified and named prokineticins (PK‐1 and PK‐2).

Bv8 (from 2.5 to 60 pmol) injected into the lateral ventricles of rat brain suppressed diurnal, nocturnal, deprivation‐induced and neuropeptide Y‐stimulated feeding and stimulated diurnal drinking. Nocturnal drinking was increased only in fasted rats.

PK‐2 mRNA is expressed in discrete areas of the rat brain, including the suprachiasmatic nucleus (SCN), medial preoptic area (MPA) and nucleus of the solitary tract (NTS). In the SCN neurons, PK‐2 mRNA is highest during the light phase of the circadian cycle and undetectable during the dark phase.

The G‐protein‐coupled receptor prokineticin receptor 2 (PKR‐2), which binds Bv8 and PK‐2 with high affinity, is mainly expressed in the piriform cortex, paraventricular thalamic nucleus, parataenial nucleus (PT), SCN, hypothalamic paraventricular (PVH) and dorsomedial (DMH) nuclei, arcuate nucleus (ARC) and subfornical organ (SFO) of the rat brain.

Bv8 microinjected into the ARC, at doses from 0.02 to 2.0 pmol during night‐time or from 0.2 to 5 pmol in 24‐h‐fasted rats, selectively suppressed feeding without affecting drinking. When injected into the SFO, Bv8 (from 0.2 to 2 pmol) stimulated drinking but did not affect feeding. Bv8 injections into other brain areas left rat ingestive behaviours unchanged.

We hypothesize that PK‐2‐rich projections from SCN neurons to PKR‐expressing ARC neurons could transmit the circadian rhythm of feeding, whereas inputs from the PK‐2‐expressing NTS neurons to the PKR‐2‐expressing SFO neurons could transmit visceral information on the water–electrolyte balance and osmotic regulation.

British Journal of Pharmacology (2004) 142, 181–191. doi:10.1038/sj.bjp.0705686
Salicylidene salicylhydrazide, a selective inhibitor ofβ1‐containing GABAAreceptors
Authors: Thompson S A , Wheat L , Brown N A , Wingrove P B , Pillai G V , Whiting P J , Adkins C , Woodward C H , Smith A J , Simpson P B , Collins I , Wafford K A
Published: May 2004

A high‐throughput assay utilizing the voltage/ion probe reader (VIPR) technology identified salicylidene salicylhydrazide (SCS) as being a potent selective inhibitor ofα2β1γ1θGABAAreceptors with a maximum inhibition of 56±5% and an IC50of 32 (23, 45) nM.

Evaluation of this compound using patch‐clamp electrophysiological techniques demonstrated that the compound behaved in a manner selective for receptors containing theβ1 subunit (e.g. maximum inhibition of 68.1±2.7% and IC50value of 5.3 (4.4, 6.5) nMonα2β1γ1 receptors). The presence of aβ1 subunit was paramount for the inhibition with changes betweenα1 andα2,γ1 andγ2, and the presence of aθsubunit having little effect.

On all subtypes, SCS produced incomplete inhibition with the greatest level of inhibition atα1β1γ1θreceptors (74.3±1.4%). SCS displayed no use or voltage dependence, suggesting that it does not bind within the channel region. Concentration – response curves to GABA in the presence of SCS revealed a reduction in the maximum response with no change in the EC50or Hill coefficient. In addition, SCS inhibited pentobarbitone‐induced currents.

Threonine 255, located within transmembrane domain (TM) 1, and isoleucine 308, located extracellularly just prior to TM3, were required for inhibition by SCS.

SCS did not compete with the known allosteric modulators, picrotoxin, pregnenolone sulphate, dehydroepiandrosterone 3‐sulphate, bicuculline, loreclezole or mefenamic acid. Neither was the inhibition by SCS influenced by the benzodiazepine site antagonist flumazenil.

In conclusion, SCS is unique in selectively inhibiting GABAAreceptors containing theβ1 subunitviaan allosteric mechanism. The importance of threonine 255 and isoleucine 308 within theβ1 subunit and the lack of interaction with a range of GABAAreceptor modulators suggests that SCS is interacting at a previously unidentified site.

British Journal of Pharmacology(2004)142, 97–106. doi:10.1038/sj.bjp.0705689
The complexities of the cardiovascular actions of cannabinoids
Authors: Randall Michael D , Kendall David A , O'Sullivan Saoirse
Published: May 2004

The cardiovascular actions of cannbinoids are complex. In general they cause vasorelaxation in isolated blood vessels, while in anaesthetised animals they cause multiphasic responses which involve an early bradycardia and long‐lasting hypotension. However, in conscious animals, the picture is one of bradycardia followed by pressor responses. Clearly, the responses to cannabinoids are dependent on the experimental conditions and synthetic cannabinoids and endocannabinoids exhibit different pharmacologies. In terms of mechanisms involved in the vascular responses to cannabinoids, the following have been implicated: the involvement of ‘classical’ cannabinoid receptors, the involvement of a novel endothelial cannabinoid receptor, the release of nitric oxide, the release of endothelium‐derived hyperpolarising factor (EDHF), the activation of vanilloid receptors, metabolism of endocannabinoids to vasoactive molecules, and both peripheral inhibition and central excitation of the sympathetic nervous system.

British Journal of Pharmacology (2004) 142, 20–26. doi:10.1038/sj.bjp.0705725
Vascular relaxation response to hydrogen peroxide is impaired in hypertension
Authors: Gao Yu‐Jing , Zhang Yongde , Hirota Simon , Janssen Luke J , Lee Robert M K W
Published: May 2004

In phenylephrine (1 μM)‐precontracted rat superior mesenteric arteries (MA), hydrogen peroxide (H2O2, 0.3 and 1 mM) caused a biphasic response: a transient contraction followed by a relaxation. In the presence of thromboxane A2/prostaglandin H2 (TP) receptor antagonist (SQ 29548), the contractile component of the biphasic response was abolished. The relaxation response to H2O2 was smaller in spontaneously hypertensive rats (SHR) when compared with normotensive Wistar–Kyoto rats (WKY).

The mechanisms for the attenuated relaxation to H2O2 in the SHR were studied. KCl (40 mM) prevented the relaxation response. Calcium‐dependent K+ channel (KCa) blockers (tetraethylammonium chloride, TEA; iberiotoxin, and charybdotoxin) showed a greater inhibition of H2O2 relaxation in SHR than in WKY, whereas voltage‐dependent K+‐channel (Kv) blocker 4‐aminopyridine was more effective in inhibiting the relaxation in WKY than in SHR.

H2O2 (1 mM) greatly enhanced the frequency and intensity of the spontaneous transient outward K+ currents in SHR MA, and the effects of H2O2 were inhibited by iberiotoxin, while in WKY MA the K+ currents induced by H2O2 were mainly of the Kv type. The consequence of the activation of different types of K+ channel was that the net increase in mean outward K+ current density in response to H2O2 was smaller in SHR than in WKY, which may account for the attenuated relaxation response to H2O2 in the SHR.

The contractile responses of MA to TEA, iberiotoxin, and charybdotoxin were greater in SHR than in WKY.

In summary, an attenuated relaxation response to H2O2 was found in SHR MA when compared to WKY. In contrast to the activation of Kv channels in WKY, H2O2 markedly enhanced KCa activity in SHR, resulting in an attenuation of the increase in mean outward K+ current density in response to H2O2. These results suggest that alteration in K+ channel activation by reactive oxygen species may play a role in the development of hypertension in SHR.

British Journal of Pharmacology (2004) 142, 143–149. doi:10.1038/sj.bjp.0705727
Effect of acute and chronic lamotrigine on basal and stimulated extracellular 5‐hydroxytryptamine and dopamine in the hippocampus of the freely moving rat
Authors: Ahmad Shagufta , Fowler Leslie J , Whitton Peter S
Published: May 2004

We have studied the effects of acute and chronic treatment with the anticonvulsant lamotrigine (LTG) on basal and stimulated extracellular 5‐hydroxytryptamine (5‐HT), dopamine (DA) and their metabolites in the hippocampus of freely moving rats using in vivo microdialysis.

Acute LTG (10 and 20 mg kg−1) decreased extracellular 5‐HT, but had no effect on its metabolite 5‐hydroxyindoleacetic acid (5‐HIAA). Dialysate DA was also decreased by LTG as were its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). When transmitter release was stimulated by either 50 μM veratridine or 100 mM K+, marked increases in the release of both transmitters occurred, but LTG was entirely without effect on this.

In chronic experiments, rats were dialysed after 2, 4, 7, 14 and 21 days of LTG treatment (5 mg kg−1, twice daily). During this period a progressively different response to the drug was seen. After 2 days, basal extracellular 5‐HT was significantly greater in treated rats than control rats. This effect persisted up to 14 days, but by 21 days 5‐HT levels had returned to control values. 5‐HIAA levels were unaltered and there was no effect of LTG on veratridine or K+ stimulated 5‐HT release.

Similarly, DA concentrations significantly increased after 2–7 days of LTG treatment, but returned and remained at basal values thereafter. During the treatment period LTG had no effect on extracellular DOPAC, but HVA followed a similar pattern to its parent transmitter. As with 5‐HT, at no time point did LTG have any effect on stimulated DA release.

These neurochemical findings observed in these experiments are considered in relation to the use of LTG in bipolar disorder.

British Journal of Pharmacology (2004) 142, 136–142. doi:10.1038/sj.bjp.0705737
Bradykinin‐induced relaxation of coronary microarteries: S‐nitrosothiols as EDHF?
Authors: Batenburg Wendy W , Popp Rüdiger , Fleming Ingrid , Vries René de , Garrelds Ingrid M , Saxena Pramod R , Danser A H Jan
Published: May 2004

To investigate whether S‐nitrosothiols, in addition to NO, mediate bradykinin‐induced vasorelaxation, porcine coronary microarteries (PCMAs) were mounted in myographs.

Following preconstriction, concentration–response curves (CRCs) were constructed to bradykinin, the NO donors S‐nitroso‐N‐penicillamine (SNAP) and diethylamine NONOate (DEA‐NONOate) and the S‐nitrosothiols L‐S‐nitrosocysteine (L‐SNC) and D‐SNC. All agonists relaxed PCMAs. L‐SNC was ∼5‐fold more potent than D‐SNC.

The guanylyl cyclase inhibitor ODQ and the NO scavenger hydroxocobalamin induced a larger shift of the bradykinin CRC than the NO synthase inhibitor L‐NAME, although all three inhibitors equally suppressed bradykinin‐induced cGMP responses.

Complete blockade of bradykinin‐induced relaxation was obtained with L‐NAME in the presence of the large‐ and intermediate‐conductance Ca2+‐activated K+‐channel (BKCa, IKCa) blocker charybdotoxin and the small‐conductance Ca2+‐activated K+‐channel (SKCa) channel blocker apamin, but not in the presence of L‐NAME, apamin and the BKCa channel blocker iberiotoxin.

Inhibitors of cytochrome P450 epoxygenase, cyclooxygenase, voltage‐dependent K+ channels and ATP‐sensitive K+ channels did not affect bradykinin‐induced relaxation.

SNAP‐, DEA‐NONOate‐ and D‐SNC‐induced relaxations were mediated entirely by the NO‐guanylyl cyclase pathway. L‐SNC‐induced relaxations were partially blocked by charybdotoxin+apamin, but not by iberiotoxin+apamin, and this blockade was abolished following endothelium removal. ODQ, but not hydroxocobalamin, prevented L‐SNC‐induced increases in cGMP, and both drugs shifted the L‐SNC CRC 5–10‐fold to the right.

L‐SNC hyperpolarized intact and endothelium‐denuded coronary arteries.

Our results support the concept that bradykinin‐induced relaxation is mediated via de novo synthesized NO and a non‐NO, endothelium‐derived hyperpolarizing factor (EDHF). S‐nitrosothiols, via stereoselective activation of endothelial IKCa and SKCa channels, and through direct effects on smooth muscle cells, may function as an EDHF in porcine coronary microarteries.

British Journal of Pharmacology (2004) 142, 125–135. doi:10.1038/sj.bjp.0705747