2,056 research outputs found
Alpha1 -adrenergic stimulation selectively enhances endothelium-mediated vasodilation in rat cremaster arteries.
We have systematically investigated how vascular smooth muscle α1 -adrenoceptor activation impacts endothelium-mediated vasodilation in isolated, myogenically active, rat cremaster muscle 1A arteries. Cannulated cremaster arteries were pressurized intraluminally to 70 mmHg to induce myogenic tone, and exposed to vasoactive agents via bath superfusion at 34°C. Smooth muscle membrane potential was measured via sharp microelectrode recordings in pressurized, myogenic arteries. The α1 -adrenergic agonist phenylephrine (25-100 nmol/L) produced further constriction of myogenic arteries, but did not alter the vasorelaxant responses to acetylcholine (0.3 μmol/L), SKA-31 (an activator of endothelial Ca2+ -dependent K+ channels) (3 μmol/L) or sodium nitroprusside (10 μmol/L). Exposure to 0.25-1 μmol/L phenylephrine or 1 μmol/L norepinephrine generated more robust constrictions, and also enhanced the vasodilations evoked by acetylcholine and SKA-31, but not by sodium nitroprusside. In contrast, the thromboxane receptor agonist U46619 (250 nmol/L) dampened responses to all three vasodilators. Phenylephrine exposure depolarized myogenic arteries, and mimicking this effect with 4-aminopyridine (1 mmol/L) was sufficient to augment the SKA-31-evoked vasodilation. Inhibition of L-type Ca2+ channels by 1 μmol/L nifedipine decreased myogenic tone, phenylephrine-induced constriction and prevented α1 -adrenergic enhancement of endothelium-evoked vasodilation; these latter deficits were overcome by exposure to 3 and 10 μmol/L phenylephrine. Mechanistically, augmentation of ACh-evoked dilation by phenylephrine was dampened by eNOS inhibition and abolished by blockade of endothelial KCa channels. Collectively, these data suggest that increasing α1 -adrenoceptor activation beyond a threshold level augments endothelium-evoked vasodilation, likely by triggering transcellular signaling between smooth muscle and the endothelium. Physiologically, this negative feedback process may serve as a "brake" to limit the extent of vasoconstriction in the skeletal microcirculation evoked by the elevated sympathetic tone
Variational inference for large-scale models of discrete choice
Discrete choice models are commonly used by applied statisticians in numerous
fields, such as marketing, economics, finance, and operations research. When
agents in discrete choice models are assumed to have differing preferences,
exact inference is often intractable. Markov chain Monte Carlo techniques make
approximate inference possible, but the computational cost is prohibitive on
the large data sets now becoming routinely available. Variational methods
provide a deterministic alternative for approximation of the posterior
distribution. We derive variational procedures for empirical Bayes and fully
Bayesian inference in the mixed multinomial logit model of discrete choice. The
algorithms require only that we solve a sequence of unconstrained optimization
problems, which are shown to be convex. Extensive simulations demonstrate that
variational methods achieve accuracy competitive with Markov chain Monte Carlo,
at a small fraction of the computational cost. Thus, variational methods permit
inferences on data sets that otherwise could not be analyzed without
bias-inducing modifications to the underlying model.Comment: 29 pages, 2 tables, 2 figure
High Velocity Cloud Edges and Mini-HVCs
Arecibo mapping is reported of the neutral hydrogen distribution along
selected directions out from the centers of two small High Velocity Clouds
(HVC), W486 and W491. Both HVCs have a small inner region where the neutral
hydrogen column density N_HI decreases slowly and a larger outer region where
N_HI declines more rapidly, smoothly and exponentially from ~ 2 X 10^19 atoms
cm^-2 down to < 10^18 atoms cm^-2. Line widths, and presumably temperature and
turbulence, do not increase in the outermost regions. Therefore pressure
decreases smoothly, making confinement by dark matter gravity more likely than
confinement by external pressure.
The more extended HVC, W491, has a superimposed small cloud (which we dub a
``mini-HVC''), offset by 66 km s^-1 in velocity along the line of sight with
peak column density about 5 X 10^18 atoms cm^-2. Preliminary data toward future
mapping of two more HVCs reveals two more mini-HVCs of similarly small size and
central column density a bit less than 1 X 10^19 atoms cm^-2. We suggest that
these three mini-HVCs are not physically associated with the HVCs on which they
are superimposed, but are either very small outlyers of the extended Magellanic
Stream HVC complex or more distant and/or smaller isolated CHVCs.
The value of N_HI at the point where the neutral and ionized column densities
are equal is ~ 2 X 10^19 atoms cm^-2 for the two mapped HVCs. Therefore the
angular scalelength of the total hydrogen is appreciably larger than the
observed HI scalelength. Previous distance estimates, related to absolute size
and mass of the total hydrogen cloud, may have to be scaled down because of the
undetected, more extended ionized hydrogen.Comment: 24 pages, 8 figures, ApJ in pres
Effects of cold winters and roost site stability on population development of non-native Asian ring-necked parakeets (Alexandrinus manillensis) in temperate Central Europe – Results of a 16-year census
Asian ring-necked parakeets (Alexandrinus manillensis, formerly Psittacula krameri, hereafter RNP) first bred in Germany in 1969. Since then, RNP numbers increased in all three major German subpopulations (Rhineland, Rhine-Main, Rhine-Neckar) over the period 2003–2018. In the Rhine-Neckar region, the population increased to more than fivefold within only 15 years. Interestingly, there was no significant breeding range expansion of RNP in the period 2010–2018. In 2018, the total number of RNP in Germany amounted to >16,200 birds. Differences in RNP censuses between years were evident. Surprisingly, cold winters (extreme value, −13.7 °C) and cold weather conditions in the breeding season (coldest month average, −1.36 °C) were not able to explain between-year variation. This finding suggests that in general winter mortality is low – with exceptions for winters 2008/2009 and 2009/2010, and a population-relevant loss of broods is low in our study population. Surprisingly, the social behaviour in terms of spatio-temporal stability of roost sites could well explain positive and negative population trends. Years of spatially stable and regularly used roost sites seem to correlate with increasing population sizes. In contrast, known shifts of RNP among different roost sites or the formations of new roost sites by split are related to population stagnation or a decrease in numbers. Climate change may lead to further range expansion as cities not suitable yet for RNP may become so in the near future.
Passive Avoidance Training and Recall are Associated With Increased Glutamate Levels in the Intermediate Medial Hyperstriatum Ventrale of the Day-Old Chick
In the young chick, the intermediate medial hyperstriatum ventrale is involved in learning paradigms, including imprinting and passive
avoidance learning. Biochemical changes in the intermediate medial hyperstriatum ventrale following learning include an up-regulation of
amino-acid transmitter levels and receptor activity. To follow the changes of extracellular amino acid levels during passive avoidance training,
we used an in vivo microdialysis technique. Probes were implanted in chicks before training the animals, either on a methyl- anthranylate-or water-coated bead. One hour later, recall was tested in both groups by presenting a similar bead. An increase of extra-cellular glutamate levels accompanied training and testing in both groups; during training, glutamate release was higher in methylanthranylate- trained than in water-trained chicks. When compared with the methylanthranylate-trained chicks during testing, the water-trained chicks showed enhanced extra-cellular glutamate levels. No other amino acid examined showed significant changes. After testing, the chicks were anesthetized and release- stimulated with an infusion of 50 mM potassium. Extra-cellular glutamate and taurine levels were significantly increased in both methylanthranylate-and water-trained chicks. The presentation of methylanthranylate as an. olfactory stimulus significantly enhanced glutamate levels, especially in methylanthranylate-trained chicks. The results suggest that such changes in extra-cellular
glutamate levels in the intermediate medial hyperstriatum ventrale accompany pecking at either the water- or the methylanthranylate-bead. The taste of the aversant may be responsible for the greater increases found in methylanthranylate-trained birds
Sexual selection on plumage and behavior in an avian hybrid zone: Experimental tests of male-male interactions
In western Panama, an unusual hybrid zone exists between white-collared manakins, Manacus candei, and golden-collared manakins, M. vitellinus. Unidirectional introgression of plumage traits from vitellinus into candei has created a region in which all definitively plumaged males have a collar that is lemon-colored. These males are nearly indistinguishable from white-collared candei genetically and morphometrically, but strongly resemble golden-collared vitellinus due to the introgression of secondary sexual plumage traits, particularly the lemon-colored collar. The introgression could be explained by sexual selection for golden-collared traits or by a series of mechanisms that do not invoke sexual selection (e.g., neutral diffusion, dominant allele). Sexual selection on male-male interactions implies behavioral differences among the plumage forms - specifically that golden- and lemon-collared males should be more aggressive than white-collared males, In contrast, the nonsexual hypotheses predict behavioral similarity between lemon- and white-collared males, based on their nearly identical genetics. We tested the sexual selection hypothesis experimentally, by presenting males with taxidermic mounts of the three forms. As response variables, we monitored vocalizations and attacks on the mounts by replicate subject males. Both golden-collared and lemon-collared males were more likely to attack than were white-collared males, as predicted under sexual selection but not by the nonsexual hypotheses. Lemon-collared males were more vocally reactive than either parental form, contrary to the prediction of the nonsexual hypotheses. Our study demonstrates that sexual selection on male-male interactions may play an important role in the dynamics of character evolution and hybrid zones
Iron–molybdenum-oxo complexes as initiators for olefin autoxidation with O2
The reaction between [(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) yields the
novel tetranuclear complex [(TPA)Fe(μ-Cp*MoO3)]2(OTf)2, 1, with a rectangular
[Mo–O–Fe–O–]2 core containing high-spin iron(II) centres. 1 proved to be an
efficient initiator/(pre)catalyst for the autoxidation of cis-cyclooctene with
O2 to give cyclooctene epoxide. To test, which features of 1 are essential in
this regard, analogues with zinc(II) and cobalt(II) central atoms, namely
[(TPA)Zn(Cp*MoO3)](OTf), 3, and [(TPA)Co(Cp*MoO3)](OTf), 4, were prepared,
which proved to be inactive. The precursor compounds of 1,
[(TPA)Fe(MeCN)2](OTf)2 and [nBu4N](Cp*MoO3) as well as Cp2*Mo2O5, were found
to be inactive, too. Reactivity studies in the absence of cyclooctene revealed
that 1 reacts both with O2 and PhIO via loss of the Cp* ligands to give the
triflate salt 2 of the known cation [((TPA)Fe)2(μ-O)(μ-MoO4)]2+. The cobalt
analogue 4 reacts with O2 in a different way yielding
[((TPA)Co)2(μ-Mo2O8)](OTf)2, 5, featuring a Mo2O84− structural unit which is
novel in coordination chemistry. The compound [(TPA)Fe(μ-MoO4)]2, 6, being
related to 1, but lacking Cp* ligands failed to trigger autoxidation of
cyclooctene. However, initiation of autoxidation by Cp* radicals was excluded
via experiments including thermal dissociation of Cp2*
Chandra Studies of the X-ray Point Source Luminosity Functions of M31
Three different M31 disk fields, spanning a range of stellar populations,
were observed by Chandra. We report the X-ray point source luminosity function
(LF) of each region, and the LF of M31's globular clusters, and compare these
with each other and with the LF of the galaxy's bulge. To interpret the results
we also consider tracers of the stellar population, such as OB associations and
supernova remnants. We find differences in the LFs among the fields, but cannot
definitively relate them to the stellar content of the fields. We find that
stellar population information, average and maximum source luminosities, X-ray
source densities, and slopes of the LF are useful in combination.Comment: 7 pages, 3 figures, accepted for publication in ApJ.
Higher-resolution figures available on reques
What on Earth have we been burning? Deciphering sedimentary records of pyrogenic carbon
Humans have interacted with fire for thousands of years, yet the utilization of fossil fuels marked the beginning of a new era. Ubiquitous in the environment, pyrogenic carbon (PyC) arises from incomplete combustion of biomass and fossil fuels, forming a continuum of condensed aromatic structures. Here we develop and evaluate 14C records for two complementary PyC molecular markers, benzene-polycarboxylic-acids (BPCAs) and polycyclic-aromatic-hydrocarbons (PAHs) preserved in aquatic sediments from a sub-urban and a remote catchment in the United States (U.S.) from mid-1700s to 1998. Results show that the majority of PyC stems from local sources and is transferred to aquatic sedimentary archives on sub-decadal to millennial time scales. Whereas a small portion stems from near-contemporaneous production and sedimentation, the majority of PyC (<90%) experiences delayed transmission due to ‘pre-aging’ on millennial timescales in catchment soils prior to its ultimate deposition. BPCAs (soot) and PAHs (precursors of soot) trace fossil fuel-derived PyC. Both markers parallel historical records of the consumption of fossil fuels in U.S., yet never account for more than 19% total PyC. This study demonstrates that isotopic characterization of multiple tracers is necessary to constrain histories and inventories of PyC, and that sequestration of PyC can markedly lag its production
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