1,835 research outputs found
A study of the effects of the neurokinin peptides on respiratory function in sheep
The respiratory responses, including changes in pulmonary resistance (RL) and
dynamic compliance (Cdyn), to the neurokinin peptides substance P (SP), neurokinin A
(NKA) and neurokinin B (NKB) were assessed in anaesthetised normal Suffolk-cross and
conscious Texel-cross asthmatic sheepIn normal sheep (n=l 1) intravenous SP was a more potent bronchoconstrictor than
NKA (n=9) and this was similar to findings in sheep with a naturally acquired airway
allergy to Ascaris suum antigen (asthmatic) (n=5) where peptides were administered by
inhalation. NKB (n=4) was assessed only in normal sheep and caused insignificant
changes in bronchomotor tone. Intravenous SP and NKA, in normal anaesthetised sheep,
caused a dose-dependent reduction in respiratory rate and this was similar for both
peptides.The bronchomotor response to SP in normal sheep demonstrated age-related changes.
In sheep under 6 months of age there was a pronounced bronchoconstriction, with a
subsequent reduction in the response as animals approach maturity. In old sheep, aged
approximately four years, there was minimal bronchomotor response, however, there was
dose-dependent apnoea.The bronchomotor response to SP in anaesthetised normal sheep was significantly
antagonised after pre-treatment with atropine (lmg/kg; n=6), hexamethonium (20mg/Kg;
n=3) and the NK-1 antagonist CP 96,345 (0.1 and 0.5mg/Kg; n=5), but not by the HI
receptor antagonist chlorpheniramine (2mg/Kg; n=5) or the neurokinin antagonist
spantide (lOug/kg/min; n=3). The anti-asthma drug nedocromil sodium (0.1 and
l.Omg/kg; n=4) had a variable effect on the response. In the isolated sheep trachealis
muscle preparation the contractile effect of SP was inhibited by atropine (n=4) and the
Ml receptor antagonist pirenzepine (n=8), with IC₅₀ values of
5.6xl0⁻⁸ and 5xl0⁻¹⁰ M respectively, while spantide (n=7) and the NK-2 receptor
antagonist L-659,874 (n=6) were ineffective.In several normal sheep (n=10) intravenous SP consistently caused augmented
breaths. Bilateral vagotomy (n=7) abolished, and cooling of the right cervical vagus
(n=7), after section of the left vagus, to temperatures below 7° C significantly attenuated
the bronchomotor response to SP in normal sheep.The conclusion of this study is that the order of potency for the bronchomotor effects
of the neurokinins is similar to rabbits and pigs but different from that reported for most
other species, including man. The mechanism of action of SP is largely indirect,
involving activation of vagal reflex mechanisms and/or modulation of ganglionic
neurotransmission and acetylcholine release from cholinergic nerve endings
Migratory Bird Treaty Act: Strict Criminal Liability for Non-Hunting, Human Caused Bird Deaths
Shocked, Crushed and Poisoned: Criminal Enforcement in Non-Hunting Cases under the Migratory Bird Treaties
A Sea Change in Eta Carinae
Major stellar-wind emission features in the spectrum of Eta Car have recently
decreased by factors of order 2 relative to the continuum. This is
unprecedented in the modern observational record. The simplest, but unproven,
explanation is a rapid decrease in the wind density.Comment: 11 pages, 3 figures, accepted for publication in ApJ
Spiralling out of control: 3D hydrodynamical modelling of the colliding winds in Carinae
Three dimensional (3D) adaptive-mesh refinement (AMR) hydrodynamical
simulations of the wind-wind collision between the enigmatic super-massive star
\etacar and its mysterious companion star are presented which include radiative
driving of the stellar winds, gravity, optically-thin radiative cooling, and
orbital motion. Simulations with static stars with a periastron passage
separation reveal that the preshock companion star's wind speed is sufficiently
reduced that radiative cooling in the postshock gas becomes important,
permitting the runaway growth of non-linear thin shell (NTSI) instabilities
which massively distort the WCR. However, large-scale simulations which include
the orbital motion of the stars, show that orbital motion reduces the impact of
radiative inhibition, and thus increases the acquired preshock velocities. As
such, the postshock gas temperature and cooling time see a commensurate
increase, and sufficient gas pressure is preserved to stabilize the WCR against
catastrophic instability growth. We then compute synthetic X-ray spectra and
lightcurves and find that, compared to previous models, the X-ray spectra agree
much better with {\it XMM-Newton} observations just prior to periastron. The
narrow width of the 2009 X-ray minimum can also be reproduced. However, the
models fail to reproduce the extended X-ray mimimum from previous cycles. We
conclude that the key to explaining the extended X-ray minimum is the rate of
cooling of the companion star's postshock wind. If cooling is rapid then
powerful NTSIs will heavily disrupt the WCR. Radiative inhibition of the
companion star's preshock wind, albeit with a stronger radiation-wind coupling
than explored in this work, could be an effective trigger.Comment: 25 pages, 20 figures, accepted for publication in Ap
Precession and Nutation in the eta Carinae binary system: Evidences from the X-ray light curve
It is believed that eta Carinae is actually a massive binary system, with the
wind-wind interaction responsible for the strong X-ray emission. Although the
overall shape of the X-ray light curve can be explained by the high
eccentricity of the binary orbit, other features like the asymmetry near
periastron passage and the short quasi-periodic oscillations seen at those
epochs, have not yet been accounted for. In this paper we explain these
features assuming that the rotation axis of eta Carinae is not perpendicular to
the orbital plane of the binary system. As a consequence, the companion star
will face eta Carinae on the orbital plane at different latitudes for different
orbital phases and, since both the mass loss rate and the wind velocity are
latitude dependent, they would produce the observed asymmetries in the X-ray
flux. We were able to reproduce the main features of the X-ray light curve
assuming that the rotation axis of eta Carinae forms an angle of 29 degrees
with the axis of the binary orbit. We also explained the short quasi-periodic
oscillations by assuming nutation of the rotation axis, with amplitude of about
5 degrees and period of about 22 days. The nutation parameters, as well as the
precession of the apsis, with a period of about 274 years, are consistent with
what is expected from the torques induced by the companion star.Comment: 9 pages, 8 figures, MNRAS accepte
Determinants of post-school choices of young people: the workforce, university or vocational studies?
Labour market outcomes and educational and occupational pathways of young movers starting off in regional Victoria
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