bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for glutamatergic mechanisms in the vagal sensory pathway initiating cardiorespiratory reflexes in the shorthorn sculpinMyoxocephalus scorpius
Authors: Sundin L. , Turesson J. , Taylor E. W. 
Published: January 2003

SUMMARYGlutamate is a major neurotransmitter of chemoreceptor and baroreceptor afferent pathways in mammals and therefore plays a central role in the development of cardiorespiratory reflexes. In fish, the gills are the major sites of these receptors, and, consequently, the terminal field (sensory area)of their afferents (glossopharyngus and vagus) in the medulla must be an important site for the integration of chemoreceptor and baroreceptor signals. This investigation explored whether fish have glutamatergic mechanisms in the vagal sensory area (Xs) that could be involved in the generation of cardiorespiratory reflexes.The locations of the vagal sensory and motor (Xm) areas in the medulla were established by the orthograde and retrograde axonal transport of the neural tract tracer Fast Blue following its injection into the ganglion nodosum. Glutamate was then microinjected into identified sites within the Xs in an attempt to mimic chemoreceptor- and baroreceptor-induced reflexes commonly observed in fish. By necessity, the brain injections were performed on anaesthetised animals that were fixed by `eye bars' in a recirculating water system. Blood pressure and heart rate were measured using an arterial cannula positioned in the afferent branchial artery of the 3rd gill arch, and ventilation was measured by impedance probes sutured onto the operculum.Unilateral injection of glutamate (40-100 nl, 10 mmol l-1) into the Xs caused marked cardiorespiratory changes. Injection (0.1-0.3 mm deep) in different rostrocaudal, medial-lateral positions induced a bradycardia, either increased or decreased blood pressure, ventilation frequency and amplitude and, sometimes, an initial apnea. Often these responses occurred simultaneously in various different combinations but, occasionally, they appeared singly, suggesting specific projections into the Xs for each cardiorespiratory variable and local determination of the modality of the response. Response patterns related to chemoreceptor reflex activation were predominantly located rostral of obex, whereas patterns related to baroreceptor reflex activation were more caudal, around obex.The glutamate-induced bradycardia was N-methyl-D-aspartate (NMDA)receptor dependent and atropine sensitive. Taken together, our data provide evidence that glutamate is a putative player in the central integration of chemoreceptor and baroreceptor information in fish.
Ontogeny of feeding function in the gray short-tailed opossumMonodelphis domestica: empirical support for the constrained model of jaw biomechanics
Authors: Thompson Elicia N. , Biknevicius Audrone R. , German Rebecca Z. 
Published: January 2003

SUMMARYThe constrained model of masticatory function enables specific predictions of bite force potentials in skulls of differing craniodental configurations. In this study, empirical support for the constrained model is provided using maximum voluntary bite force data along Region I and II of the jaws of gray short-tailed opossums Monodelphis domestica. Then, growth series of M. domestica are used to assess how bite force potential changes with growth by evaluating craniodental changes using longitudinal sets of dorsoventral radiographs and by assessing maximal bite force potential at the Region I-II boundary of the jaw in juveniles (aged 70-80 days) and adults. Our findings show that, while juveniles and adults alike enclose at least three molariform teeth within Region II (the area of highest bite force potential along the jaw), age-dependent elongation of the masticatory muscle resultant lever arm and narrowing of the palate relative to jaw length especially enhance the mechanical advantage of the adductor muscle resultant in adults. While maximal bite forces at the Region I-II boundary are absolutely greater in adults, these bite forces scale isometrically with body mass, which suggests that mass-specific forces exerted by jaw adductor muscles of larger(adult) opossums are disproportionately smaller than those exerted by smaller(juvenile) opossums.
Cardiovascular responses to hypoxia and anaemia in the toadBufo marinus
Authors: Andersen Johnnie B. , Hedrick Michael S. , Wang Tobias 
Published: January 2003

SUMMARYAmphibians exhibit cardiorespiratory responses to hypoxia and, although several oxygen-sensitive chemoreceptor sites have been identified, the specific oxygen stimulus that triggers these responses remains controversial. This study investigates whether the cardiovascular response to oxygen shortage correlates with decreased oxygen partial pressure of arterial blood(PaO2) or reduced oxygen concentration([O2]) in toads. Toads, equipped with blood flow probes and an arterial catheter, were exposed to graded hypoxia [fraction of oxygen in the inspired air (FIO2)=0.21, 0.15, 0.10, 0.07 and 0.05] before and after reductions in arterial [O2] by isovolemic anaemia that reduced haematocrit by approximately 50%. Toads responded to hypoxia by increasing heart rate (fH) and pulmocutaneous blood flow(Q̇pc) and reducing the net cardiac right-to-left-shunt. When arterial [O2] was reduced by anaemia, the toads exhibited a similar cardiovascular response to that observed in hypoxia. While arterial CO2 partial pressure(PaCO2) decreased significantly during hypoxia,indicative of increased alveolar ventilation, anaemia did not alter PaCO2). This suggests that reductions in[O2] mediate cardiovascular adjustments, while ventilatory responses are caused by reduced PaO2.
norpAanditprmutants reveal roles for phospholipase C and inositol (1,4,5)- trisphosphate receptor inDrosophila melanogasterrenal function
Authors: Pollock Valerie P. , Radford Jonathan C. , Pyne Susan , Hasan Gaiti , Dow Julian A. T. , Davies Shireen-A. 
Published: January 2003

SUMMARYMutants of norpA, encoding phospholipase Cβ (PLCβ), and itpr, encoding inositol (1,4,5)-trisphosphate receptor(IP3R), both attenuate response to diuretic peptides of Drosophila melanogaster renal (Malpighian) tubules. Intact tubules from norpA mutants severely reduced diuresis stimulated by the principal cell- and stellate cell-specific neuropeptides, CAP2b and Drosophila leucokinin (Drosokinin), respectively, suggesting a role for PLCβ in both these cell types. Measurement of IP3production in wild-type tubules and in Drosokinin-receptor-transfected S2 cells stimulated with CAP2b and Drosokinin, respectively, confirmed that both neuropeptides elevate IP3 levels.In itpr hypomorphs, basal IP3 levels are lower,although CAP2b-stimulated IP3 levels are not significantly reduced compared with wild type. However,CAP2b-stimulated fluid transport is significantly reduced in itpr alleles. Rescue of the itpr90B.0 allele with wild-type itpr restores CAP2b-stimulated fluid transport levels to wild type. Drosokinin-stimulated fluid transport is also reduced in homozygous and heteroallelic itpr mutants.Measurements of cytosolic calcium levels in intact tubules of wild-type and itpr mutants using targeted expression of the calcium reporter,aequorin, show that mutations in itpr attenuated both CAP2b- and Drosokinin-stimulated calcium responses. The reductions in calcium signals are associated with corresponding reductions in fluid transport rates.Thus, we describe a role for norpA and itpr in renal epithelia and show that both CAP2b and Drosokinin are PLCβ-dependent, IP3-mobilising neuropeptides in Drosophila. IP3R contributes to the calcium signalling cascades initiated by these peptides in both principal and stellate cells.
Feeding mechanisms in carp: crossflow filtration, palatal protrusions and flow reversals
Authors: Callan W. Todd , Sanderson S. Laurie 
Published: January 2003

SUMMARY
It has been hypothesized that, when engulfing food mixed with inorganic particles during benthic feeding, cyprinid fish use protrusions of tissue from the palatal organ to retain the food particles while the inorganic particles are expelled from the opercular slits. In crossflow filtration, the particle suspension is pumped parallel to the filter surface as filtrate exits through the filter pores, causing the suspension to become more concentrated as it travels downstream along the filter. We used high-speed video endoscopy to determine whether carp Cyprinus carpio use crossflow filtration and/or palatal protrusions during benthic feeding. We found that carp use crossflow filtration to concentrate small food particles in the pharyngeal cavity while expelling small dense inorganic particles through the opercular slits and via spits. Our results suggest that, during feeding on small food particles, palatal protrusions serve a localized chemosensory function rather than a mechanical particle-sorting function. However, palatal protrusions did retain large food particles while large inorganic particles were spit anteriorly from the mouth. We also investigated whether flow is continuous and unidirectional during suspension feeding in carp. As reported previously for ventilation in hedgehog skates and for certain industrial crossflow filtration applications, we observed that flow is pulsatile and bidirectional during feeding. These results have implications for hydrodynamic models of crossflow filtration in suspension-feeding fishes.
Comparative analysis of nitric oxide and SALMFamide neuropeptides as general muscle relaxants in starfish
Authors: Melarange Richard , Elphick Maurice R. 
Published: January 2003

SUMMARY
Previous studies have established that the gaseous signalling molecule nitric oxide (NO) and the SALMFamide neuropeptides S1 and S2 cause cardiac stomach relaxation in the starfish Asterias rubens. Here we show that S1, S2 and the NO donor SNAP also cause relaxation of two other preparations from Asterias — tube feet and the apical muscle of the body wall. The rank order of effectiveness as muscle relaxants when tested at a concentration of 10 μmol l-1 was SNAP&gt;S2&gt;S1 for both tube feet and apical muscle whereas for cardiac stomach it was S2&gt;S1&gt;SNAP. Significantly, these data indicate that NO and SALMFamide neuropeptides function as general muscle relaxants in starfish but vary in their relative importance in different organ systems.
The molecular mechanisms by which NO and SALMFamides cause muscle relaxation in starfish are not known, but previous pharmacological studies on the cardiac stomach using the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazol[4,3-a]quinoxalin-1-one (ODQ) indicate that the cyclic nucleotide second messenger cGMP may mediate effects of NO. Consistent with this hypothesis, here we report that ODQ also causes partial inhibition of the relaxing effect of SNAP on tube foot and apical muscle preparations. To further investigate the involvement of cyclic nucleotides as mediators of the effects of NO and SALMFamides on starfish muscle, we have measured both cGMP and cAMP in cardiac stomach and in apical muscle after treatment with S1, S2 or SNAP. However, no significant changes in cyclic nucleotide content were observed compared with controls. Further experiments were performed on apical muscle tissue in the presence of the cyclic-nucleotide-phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX), a drug that also causes cardiac stomach relaxation in starfish. Treatment with IBMX caused a 2-3-fold increase above basal levels for cGMP and cAMP, but co-treatment with IBMX and S1 or S2 or SNAP resulted in no significant further increase above the level observed with IBMX alone. We conclude from these data that the relaxing action of NO on starfish muscle may be mediated by both cGMP-dependent and cGMP-independent pathways. However, the mechanisms by which SALMFamides cause muscle relaxation in starfish remain unknown and, although our results do not rule out the involvement of cGMP or cAMP, other signalling pathways may now need to be investigated.
Dynamical aspects of the life cycle of the winter storm ‘Lothar’ (24–26 December 1999)
Authors: Wernli Heini , Dirren Sebastien , Liniger Mark A. , Zillig Matthias 
Published: January 2003

AbstractDynamical aspects of the life cycle of the winter storm ‘Lothar’ (24–26 December 1999) are investigated with the aid of the European Centre for Medium‐Range Weather Forecasts analysis data and mesoscale model simulations. Neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds, but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event. The analysis and interpretation is primarily based upon the evolution of the lower‐ and upper‐level potential vorticity (PV) field complemented by three‐dimensional trajectory calculations.‘Lothar’ originated in the western Atlantic and travelled as a shallow low‐level cyclone of moderate intensity towards Europe. This translation took place below and slightly to the south of a very intense upper‐level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low‐level PV anomaly (not unlike the concept of a ‘diabatic Rossby wave’). No significant PV anomalies were evident at the tropopause level during this early phase of the life cycle. The surface cyclone intensified rapidly when the shallow cyclone approached the jet‐stream axis. The circulation induced by the diabatically produced low‐tropospheric PV anomaly on steeply sloping isentropic surfaces that transect the intense upper‐level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold. This stratospheric PV anomaly virtually merged with the diabatically produced ephemeral PV feature to form a vertically aligned tower of positive PV at the time of maximum storm intensity. A sensitivity study with a dry adiabatic hindcast simulation shows no PV‐tower configuration (and only a very weak surface development) and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid ‘bottom‐up’ intensification of ‘Lothar’.A comparison of the anomalously high Atlantic sea surface temperatures in December 1999 with the water‐vapour source regions for the latent‐heat release that accompanied the rapid intensification phase of ‘Lothar’ shows a close relationship. This is of importance when discussing the possible implications of climate variability and change on the development of North Atlantic winter storms. Copyright © 2002 Royal Meteorological Society
Idealized numerical simulations of shallow föhn
Authors: Zängl G. 
Published: January 2003

AbstractIdealized numerical simulations are performed in order to get a deeper dynamical understanding of the so‐called shallow föhn. This is a southerly gap flow which sometimes occurs in north–south oriented Alpine valleys under approximately westerly synoptic‐scale flow conditions. Observations indicate that shallow föhn is primarily driven by a hydrostatic pressure difference between relatively cold air to the south of the Alps and warmer air to the north. A recent study suggested that the meridional pressure gradient associated with geostrophically balanced westerly wind also has the potential to induce significant shallow föhn. While this study is restricted to an infinitely long mountain ridge with a gap, various isolated ridges are considered in the present work.It is found that replacing the infinite ridge by an isolated one leads to fundamental changes in the behaviour of the gap flow if surface friction is excluded and the large‐scale flow is taken to be uniform westerly. While strong southerly gap flow is found for the infinite ridge, weak northerly gap flow prevails for the isolated mountains. This is primarily because flow splitting and Coriolis effects yield—in the parameter range relevant for the Alps—strong anticyclonic flow around an isolated mountain. Due to ageostrophy, this anticyclonic flow is associated with a northerly flow component towards the northern side of the mountain, piling up some air there and compensating for or even reversing the geostrophic pressure gradient across the mountain. From that it follows that the mere presence of a geostrophic pressure gradient is not sufficient to induce shallow föhn. Surface friction yields a southerly flow component in the boundary layer and reinforces the pressure gradient across the mountain. Therefore, friction supports southerly gap flow and reduces the differences between infinite and isolated ridges. However, additional simulations with an arc‐shaped mountain similar to the real Alps indicate a further reduction of the tendency towards southerly gap flow. This is due to a weak lee cyclone which forms to the east of the arc and reduces the cross‐Alpine pressure gradient. A southerly component in the large‐scale flow appears to be necessary to obtain southerly gap flow for the arc‐shaped mountain. In this case, potentially cold low‐level air is piled up on the southern side of the Alps, and a hydrostatic pressure difference across the Alps is established in accordance with observations. Copyright © 2002 Royal Meteorological Society
Properties of embedded convection in warm‐frontal mixed‐phase cloud from aircraft and polarimetric radar
Authors: Hogan R. J. , Field P. R. , Illingworth A. J. , Cotton R. J. , Choularton T. W. 
Published: January 2003

AbstractResults are presented from a case‐study in which the macrophysical and microphysical characteristics of a warm‐frontal mixed‐phase cloud were investigated using simultaneous aircraft and polarimetric‐radar measurements. A region of embedded convection was located and sampled at various stages of its ascent through the cloud from −5° to −11°, and evidence is presented that it was triggered by Kelvin–Helmholtz instability near the melting layer. High concentrations of small crystals were observed in and above narrow convective turrets, around 1 km across, that contained supercooled liquid‐water droplets with an effective diameter of 24 µm and riming ice particles. The area surrounding the turrets was found to contain pristine columns, and was strikingly visible to the radar as a broad plume of high differential reflectivity ZDR (around 3 dB), contrasting with the 0–0.5 dB range usually found in ice clouds. The columns observed in situ had axial ratios of around 5:1, in close agreement with the values predicted theoretically from ZDR assuming horizontal alignment of the crystals. We argue that the high concentrations of small ice crystals (up to 103 l−1) observed in this case were splinters produced via the Hallett–Mossop mechanism in the riming process, and these then grew rapidly by deposition in the water‐saturated environment into pristine columns. Later in the ascent the picture was complicated by the presence of a fallstreak containing large, low‐ZDR aggregates which appeared to rapidly accrete the columns. A number of plumes of high ZDR were observed by the radar on the same day, each of which persisted for at least half an hour. In the vicinity of cloud top −15°, the regions of high ZDR tended to spread out horizontally, and attain values as high as 7 dB. At these temperatures plates and dendrites are known to grow, so these ZDR observations are in good agreement with our theoretical finding that columns alone cannot produce values of ZDR greater than 4 dB, no matter how extreme their axial ratios, whereas planar crystals can attain values up to 10 dB. Embedded convection could clearly be important in determining the distribution of ice and liquid water in frontal clouds, which affects both cloud glaciation and the radiation budget, and is important for aircraft icing. Copyright © 2002 Royal Meteorological Society
Cloud‐top striations above ana‐cold frontal circulations
Authors: Browning K. A. , Wang C.‐G. 
Published: January 2003

AbstractSatellite images occasionally show regular arrays of cloud‐top striations within mesoscale cloud features associated with vigorous ana‐cold frontal circulations. Observational case‐studies with a variety of types of radar are presented to show that the striations are due to bands of upright upper‐level convective cells. These convective cells form at the top of the rearward‐sloping‐ascent part of a transverse frontal circulation which, in one of the cases studied, had a multi‐layered structure fed in turn by upright line convection lifting air from the boundary layer. This coexistence and interdependence of upright and slantwise forms of convection may not in itself be uncommon; what is less usual in these results is the way in which the upper‐level convection is manifested as bands, or striations, orientated roughly parallel to the wind shear at cloud‐top level but almost perpendicular to the strong thermal‐wind shear in the underlying frontal zone—a behaviour that may be specific to vigorous ana‐cold frontal systems. The striations have a large wavelength (30 to 55 km) but we are unaware of any simple dynamical mechanism that can account for the convection being organized on this scale. The striations are regarded as an important indicator of accompanying adverse weather. Earlier studies have suggested that such striations are associated with rapid cyclogenesis and surface gusts. One of the cases presented here falls into this category; the other, more detailed, case‐study is notable for the rainfall associated with the vigorous frontal circulations. Copyright © 2002 Royal Meteorological Society
Effects of in‐cloud nucleation and turbulence on droplet spectrum formation in cumulus clouds
Authors: PINSKY M. B. , Khain A. P. 
Published: January 2003

AbstractDrop spectrum evolution is investigated using a moving mass grid microphysical cloud parcel model containing 2000 mass bins and allowing turbulent effects on droplet collisions. Utilization of precise methods of diffusion and collision drop growth eliminates any artificial droplet spectrum broadening. Simulation of continental, intermediate and maritime clouds is conducted using different concentrations of cloud condensation nuclei and different vertical velocities at the cloud base.An increase of the collision kernel in turbulent surroundings is found to be an important factor in the acceleration of large droplet and raindrop formation. Droplet spectrum formation was found to be affected by three stages of in‐cloud droplets' nucleation: (a) nucleation near the cloud base, forming the primary mode of the droplet spectrum; (b) nucleation within a parcel, where supersaturation exceeds its maximum at the cloud base, this type of nucleation forming the secondary spectral mode; and (c) nucleation within the zone of intensive collisions, when a rapid decrease in drop concentration leads to an increase in supersaturation.It is shown that the secondary mode in the droplet spectrum contributes significantly to raindrop formation, therefore the absence of the secondary mode (the single‐mode spectrum) can reduce or even inhibit formation of raindrops.The contributions of diffusion and collision growth to drop spectrum formation are compared. Effective collisions are found to start when the effective radius attains about 15 µm. The level where the effective radius attains 15 µm can be considered as the level of the first radar echo. This height is shown to crucially depend on cloud dynamics (in particular, on the vertical velocity at the cloud base) and on the concentration of aerosol particles. Copyright © 2002 Royal Meteorological Society