2,276 research outputs found
Early Changes in Hippocampal Eph Receptors Precede the Onset of Memory Decline in Mouse Models of Alzheimer’s Disease
Abstract. Synapse loss occurs early in Alzheimer’s disease (AD) and is considered the best pathological correlate of cognitive
decline. Ephrins and Eph receptors are involved in regulation of excitatory neurotransmission and play a role in cytoskeleton
remodeling. We asked whether alterations in Eph receptors could underlie cognitive impairment in an AD mouse model
overexpressing human amyloid-β protein precursor (hAβPP) with familial mutations (hAβPPswe-ind mice). We found that
EphA4 and EphB2 receptors were reduced in the hippocampus before the development of impaired object recognition and spatial
memory. Similar results were obtained in another line of transgenic AβPP mice, Tg2576. A reduction in Eph receptor levels
was also found in postmortem hippocampal tissue from patients with incipient AD. At the time of onset of memory decline
in hAβPPswe-ind mice, no change in surface expression of AMPA or NMDA receptor subunits was apparent, but we found
changes in Eph-receptor downstream signaling, in particular a decrease in membrane-associated phospho-cofilin levels that may
cause cytoskeletal changes and disrupted synaptic activity. Consistent with this finding, Eph receptor activation in cell culture
increased phospho-cofilin levels. The results suggest that alterations in Eph receptors may play a role in synaptic dysfunction in
the hippocampus leading to cognitive impairment in a model of AD
Overexpression of wild-type human APP in mice causes cognitive déficits and pathological features unrelated to Abeta levels
Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent
amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type
human APP (hAPPwt) we found an early memory impairment, particularly in the water maze and to a lesser
extent in the object recognition task, but β-amyloid peptide (Aβ42) was barely detectable in the
hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP
carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the
levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was
also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and
NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in
the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2
immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Aβ42 were found in the
hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Aβ-
independent pathogenic pathways in Alzheimer's disease
Observation of resonances consistent with pentaquark states in decays
Observations of exotic structures in the channel, that we refer to
as pentaquark-charmonium states, in decays are
presented. The data sample corresponds to an integrated luminosity of 3/fb
acquired with the LHCb detector from 7 and 8 TeV pp collisions. An amplitude
analysis is performed on the three-body final-state that reproduces the
two-body mass and angular distributions. To obtain a satisfactory fit of the
structures seen in the mass spectrum, it is necessary to include two
Breit-Wigner amplitudes that each describe a resonant state. The significance
of each of these resonances is more than 9 standard deviations. One has a mass
of MeV and a width of MeV, while the second
is narrower, with a mass of MeV and a width of MeV. The preferred assignments are of opposite parity, with one
state having spin 3/2 and the other 5/2.Comment: 48 pages, 18 figures including the supplementary material, v2 after
referee's comments, now 19 figure
Study of and decays and determination of the CKM angle
We report a study of the suppressed and favored
decays, where the neutral meson is detected
through its decays to the and CP-even and
final states. The measurement is carried out using a proton-proton
collision data sample collected by the LHCb experiment, corresponding to an
integrated luminosity of 3.0~fb. We observe the first significant
signals in the CP-even final states of the meson for both the suppressed
and favored modes, as well as
in the doubly Cabibbo-suppressed final state of the decay. Evidence for the ADS suppressed decay , with , is also presented. From the observed
yields in the , and their
charge conjugate decay modes, we measure the value of the weak phase to be
. This is one of the most precise
single-measurement determinations of to date.Comment: 22 pages, 9 figures; All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-020.htm
Measurement of the lifetime
Using a data set corresponding to an integrated luminosity of ,
collected by the LHCb experiment in collisions at centre-of-mass energies
of 7 and 8 TeV, the effective lifetime in the
decay mode, , is measured to be ps. Assuming
conservation, corresponds to the lifetime of the light
mass eigenstate. This is the first measurement of the effective
lifetime in this decay mode.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-017.htm
Study of boson production in association with beauty and charm
The associated production of a boson with a jet originating from either a
light parton or heavy-flavor quark is studied in the forward region using
proton-proton collisions. The analysis uses data corresponding to integrated
luminosities of 1.0 and collected with the LHCb detector
at center-of-mass energies of 7 and 8 TeV, respectively. The bosons are
reconstructed using the decay and muons with a transverse
momentum, , larger than 20 GeV in the pseudorapidity range
GeV
and . The sum of the muon and jet momenta must satisfy
GeV. The fraction of jet events that originate from beauty
and charm quarks is measured, along with the charge asymmetries of the
and production cross-sections. The ratio of the jet to
jet production cross-sections is also measured using the
decay. All results are in agreement with Standard Model predictions
Measurement of the mass and lifetime of the baryon
A proton-proton collision data sample, corresponding to an integrated
luminosity of 3 fb collected by LHCb at and 8 TeV, is used
to reconstruct , decays. Using the , decay mode for calibration, the lifetime ratio and absolute
lifetime of the baryon are measured to be \begin{align*}
\frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\
\tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the
uncertainties are statistical, systematic and from the calibration mode (for
only). A measurement is also made of the mass difference,
, and the corresponding mass, which
yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm
MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2.
\end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm
Search for hidden-sector bosons in decays
A search is presented for hidden-sector bosons, , produced in the decay
, with and
. The search is performed using -collision data
corresponding to 3.0 fb collected with the LHCb detector. No significant
signal is observed in the accessible mass range
MeV, and upper limits are placed on the branching fraction product
as
a function of the mass and lifetime of the boson. These limits are of
the order of for lifetimes less than 100 ps over most of the
range, and place the most stringent constraints to date on many
theories that predict the existence of additional low-mass bosons.Comment: All figures and tables, along with supplementary material, are
available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-036.htm
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