127 research outputs found
TREM2 deficiency attenuates neuroinflammation and protects against neurodegeneration in a mouse model of tauopathy
Significance
Alzheimerâs disease (AD) is the most common cause of dementia and is a major public health problem for which there is currently no disease-modifying treatment. There is an urgent need for greater understanding of the molecular mechanisms underlying neurodegeneration in patients to create better therapeutic options. Recently, genetic studies uncovered novel AD risk variants in the microglial receptor, triggering receptor expressed on myeloid cells 2 (TREM2). Previous studies suggested that loss of TREM2 function worsens amyloid-ÎČ (AÎČ) plaque-related toxicity. In contrast, we observe TREM2 deficiency mitigates neuroinflammation and protects against brain atrophy in the context of tau pathology. These findings indicate dual roles for TREM2 and microglia in the context of amyloid versus tau pathology, which are important to consider for potential treatments targeting TREM2.</jats:p
Constraints on thick disc and halo parameters from HST photometry of field stars in the Galaxy
We analyse a sample of over 1000 stars from 32 fields imaged in the V and I
bands with the Wide Field and Planetary Camera, on board of the Hubble Space
Telescope. The fields are located at Galactic latitudes | b | >= 15deg and in
various directions on the sky. We consider models for the structure of the
Galaxy with different choices for the main parameters governing the shape and
luminosity function of the thick disk and stellar halo. Comparing model
predictions with the observed colour-magnitude diagram we are able to rule out
an increasing or flat stellar luminosity function at the low-luminosity end. We
also rule out large values of the vertical scale height of the thick disc, z_0,
finding it to be in the range 800 <= z_0 <= 1200 pc. As for the local density
normalization, values within the range 4 % <= n_0 <= 8 % seem to better
reproduce the data. Our data essentially rule out a flattened stellar halo (c/a
<~ 0.5) or models with both large local normalization and effective radii.Comment: 7 pages LaTeX, 9 Postscript figure
Factor XIIIa-positive dermal dendritic cells and HLA-DR expression in radial versus vertical growth-phase melanomas
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72186/1/j.1600-0560.1998.tb01740.x.pd
Stellar Subsystems of the Galaxy NGC 2366
Hubble Space Telescope archive data are used to perform photometry of stars
in seven fields at the center and periphery of the galaxy NGC2366. The
variation of the number density of stars of various ages with galactocentric
radius and along the minor axis of the galaxy are determined. The boundaries of
the thin and thick disks of the galaxy are found. The inferred sizes of the
subsystems of NGC2366 ( kpc and kpc for the thin
and thick disks, respectively) are more typical for spiral galaxies. Evidence
for a stellar halo is found at the periphery of NGC2366 beyond the thick disk
of the galaxy.Comment: 16 pages, 4 figures, Astronomy Reports, 2008,v. 52, n.1, p. 1
Stellar disks and halos of the edge-on spiral galaxies: NGC 891, NGC 4144 and NGC 4244
The results of the stellar photometry of the images ACS/WFC and WFPC2 of the
HST are used to study stellar population and spatial distribution of stars in
three edge-on galaxies: NGC 891, NGC 4144 and NGC 4244. The measuring of the
number density of the old stars revealed two stellar substructures in these
galaxies: thick disk and halo. The borders of these substructures consisting
mainly of red giants, are determined by the change of number density gradient
of the old stars. The revealed halos have flattened shapes and extend up to 25
kpc from the galaxy planes. The obtained results of number density
distributions of different type stars perpendicular to the galaxy planes allow
us to verify our stellar model of spiral galaxies. Using the determination of
the tip of red giant branch (TRGB method) we have derived the following
distances: D = 9.82 Mpc (NGC 891), D = 7.24 Mpc (NGC 4144), D = 4.29 Mpc (NGC
4244).Comment: 18 pages, 9 figures. accepted to Astrofizic
Broadband Observations of the Afterglow of GRB 000926: Observing the Effect of Inverse Compton Scattering and Evidence for a High-Density Environment
GRB 000926 has one of the best-studied afterglows to-date, with multiple
X-ray observations, as well as extensive multi-frequency optical and radio
coverage. Broadband afterglow observations, spanning from X-ray to radio
frequencies, provide a probe of the density structure of the circumburst
medium, as well as of the ejecta energetics, geometry, and the physical
parameters of the relativistic blastwave resulting from the explosion. We
present an analysis of {\em Chandra X-ray Observatory} observations of this
event, along with {\em Hubble Space Telescope} and radio monitoring. We combine
these data with ground-based optical and IR observations and fit the
synthesized afterglow lightcurve using models where collimated ejecta expand
into a surrounding medium. We find that we can explain the broadband lightcurve
with reasonable physical parameters only if the cooling is dominated by inverse
Compton scattering. Excess X-ray emission in the broadband spectrum indicates
that we are directly observing a contribution from inverse Compton scattering.
It is the first time this has been observed in a GRB afterglow, and it implies
that the GRB exploded in a reasonably dense (n~30 cm^{-3}) medium, consistent
with a diffuse interstellar cloud environment.Comment: 16 pages, 5 figures Accepted for publication in the Astrophysical
Journa
GRB 010921: Strong Limits on an Underlying Supernova from HST
GRB 010921 was the first HETE-2 GRB to be localized via its afterglow emission. The low-redshift of the host galaxy, z=0.451, prompted us to undertake intensive multi-color observations with the Hubble Space Telescope with the goal of searching for an underlying supernova component. We do not detect any coincident supernova to a limit 1.34 mag fainter than SN 1998bw at 99.7% confidence, making this one of the most sensitive searches for an underlying SN. Analysis of the afterglow data allow us to infer that the GRB was situated behind a net extinction (Milky Way and the host galaxy) of A_V ~ 1.8 mag in the observer frame. Thus, had it not been for such heavy extinction our data would have allowed us to probe for an underlying SN with brightness approaching those of more typical Type Ib/c supernovae
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