170 research outputs found
Habenular expression of rare missense variants of the β4 nicotinic receptor subunit alters nicotine consumption
The CHRNA5-CHRNA3-CHRNB4 gene cluster, encoding the {alpha}5, {alpha}3, and {beta}4 nicotinic acetylcholine receptor (nAChR) subunits, has been linked to nicotine dependence. The habenulo-interpeduncular (Hb-IPN) tract is particularly enriched in {alpha}3{beta}4 nAChRs. We recently showed that modulation of these receptors in the medial habenula (MHb) in mice altered nicotine consumption. Given that {beta}4 is rate-limiting for receptor activity and that single nucleotide polymorphisms (SNPs) in CHRNB4 have been linked to altered risk of nicotine dependence in humans, we were interested in determining the contribution of allelic variants of {beta}4 to nicotine receptor activity in the MHb. We screened for missense SNPs that had allele frequencies >0.0005 and introduced the corresponding substitutions in Chrnb4. Fourteen variants were analyzed by co-expression with {alpha}3. We found that {beta}4A90I and {beta}4T374I variants, previously shown to associate with reduced risk of smoking, and an additional variant {beta}4D447Y, significantly increased nicotine-evoked current amplitudes, while {beta}4R348C, the mutation most frequently encountered in sporadic amyotrophic lateral sclerosis (sALS), showed reduced nicotine currents. We employed lentiviruses to express {beta}4 or {beta}4 variants in the MHb. Immunoprecipitation studies confirmed that {beta}4 lentiviral-mediated expression leads to specific upregulation of {alpha}3{beta}4 but not {beta}2 nAChRs in the Mhb. Mice injected with the {beta}4-containing virus showed pronounced aversion to nicotine as previously observed in transgenic Tabac mice overexpressing Chrnb4 at endogenous sites including the MHb. Habenular expression of the {beta}4 gain-of-function allele T374I also resulted in strong aversion, while transduction with the {beta}4 loss-of function allele R348C failed to induce nicotine aversion. Altogether, these data confirm the critical role of habenular {beta}4 in nicotine consumption, and identify specific SNPs in CHRNB4 that modify nicotine-elicited currents and alter nicotine consumption in mice
Arecibo HI Absorption Measurements of Pulsars and the Electron Density at Intermediate Longitudes in the First Galactic Quadrant
We have used the Arecibo telescope to measure the HI absorption spectra of
eight pulsars. We show how kinematic distance measurements depend upon the
values of the galactic constants R_o and Theta_o, and we select our preferred
current values from the literature. We then derive kinematic distances for the
low-latitude pulsars in our sample and electron densities along their lines of
sight. We combine these measurements with all others in the inner galactic
plane visible from Arecibo to study the electron density in this region. The
electron density in the interarm range 48 degrees < l < 70 degrees is [0.017
(-0.007,+0.012) (68% c.l.)] cm^(-3). This is 0.75 (-0.22,+0.49) (68% c.l.) of
the value calculated by the Cordes & Lazio (2002) galactic electron density
model. The model agrees more closely with electron density measurements toward
Arecibo pulsars lying closer to the galactic center, at 30 degrees<l<48
degrees. Our analysis leads to the best current estimate of the distance of the
relativistic binary pulsar B1913+16: d=(9.0 +/- 3) kpc.
We use the high-latitude pulsars to search for small-scale structure in the
interstellar hydrogen observed in absorption over multiple epochs. PSR B0301+19
exhibited significant changes in its absorption spectrum over 22 yr, indicating
HI structure on a ~500 AU scale.Comment: Accepted by Astrophysical Journal September 200
Multi-Frequency Synthesis of VLBI Images Using a Generalized Maximum Entropy Method
A new multi-frequency synthesis algorithm for reconstructing images from
multi-frequency VLBI data is proposed. The algorithm is based on a generalized
maximum-entropy method, and makes it possible to derive an effective spectral
correction for images over a broad frequency bandwidth, while simultaneously
reconstructing the spectral-index distribution over the source. The results of
numerical simulations demonstrating the capabilities of the algorithm are
presented.Comment: 17 pages, 8 figure
Sco X-1: The Evolution and Nature of the Twin Compact Radio Lobes
The radio components associated with the LMXB Sco X-1 have been monitored
with extensive VLBI imaging at 1.7 and 5.0 GHz over four years, including a
56-hour continuous VLBI observation in 1999 June. We often detected one strong
and one weak compact radio component, moving in opposite directions from the
radio core. We suggest that the moving components are radio lobes generated by
the disruption of energy flow in a twin-beam from the binary system. The
average lifetime of a lobe-pair, the space motion of the lobes and the measured
energy flow in the beam are discussed in arXiv:astro-ph/0104325. The lobe has a
flux density that is variable over a time-scale of one hour, a measured minimum
size of 1 mas (2.8 au), and is extended perpendicular to its motion. This short
electron radiative lifetime may be caused by synchrotron losses if the lobe
magnetic field is 300 G, or by adiabatic expansion of the electrons as soon as
they are produced at the working surface. The lobes also show periods of slow
expansion and a steepening radio spectrum, perhaps related to the
characteristics of the beam energy flow. The radio morphology for Sco X-1 is
more simple than for most other Galactic jet sources. The lobes of Sco X-1 are
similar to hot-spots found in many extragalactic double sources. Scaling the
phenomena observed in Sco X-1 to extragalactic sources implies hot-spot
variability time-scales of 10^4 yr and hot-spot lifetimes of 10^5 yr. The
recurrent formation of lobes in Sco X-1 probably does not occur for
extragalactic radio sources.Comment: 22 pages of text + 16 figures. ApJ, in pres
Optimal Image Reconstruction in Radio Interferometry
We introduce a method for analyzing radio interferometry data which produces
maps which are optimal in the Bayesian sense of maximum posterior probability
density, given certain prior assumptions. It is similar to maximum entropy
techniques, but with an exact accounting of the multiplicity instead of the
usual approximation involving Stirling's formula. It also incorporates an Occam
factor, automatically limiting the effective amount of detail in the map to
that justified by the data. We use Gibbs sampling to determine, to any desired
degree of accuracy, the multi-dimensional posterior density distribution. From
this we can construct a mean posterior map and other measures of the posterior
density, including confidence limits on any well-defined function of the
posterior map.Comment: 41 pages, 11 figures. High resolution figures 8 and 9 available at
http://www.astro.uiuc.edu/~bwandelt/SuttonWandelt200
Instruments of RT-2 Experiment onboard CORONAS-PHOTON and their test and evaluation III: Coded Aperture Mask and Fresnel Zone Plates in RT-2/CZT Payload
Imaging in hard X-rays of any astrophysical source with high angular
resolution is a challenging job. Shadow-casting technique is one of the most
viable options for imaging in hard X-rays. We have used two different types of
shadow-casters, namely, Coded Aperture Mask (CAM) and Fresnel Zone Plate (FZP)
pair and two types of pixellated solid-state detectors, namely, CZT and CMOS in
RT-2/CZT payload, the hard X-ray imaging instrument onboard the CORONAS-PHOTON
satellite. In this paper, we present the results of simulations with different
combinations of coders (CAM & FZP) and detectors that are employed in the
RT-2/CZT payload. We discuss the possibility of detecting transient Solar
flares with good angular resolution for various combinations. Simulated results
are compared with laboratory experiments to verify the consistency of the
designed configuration.Comment: 27 pages, 16 figures, Accepted for publication in Experimental
Astronomy (in press
Ascl1 (Mash1) Defines Cells with Long-Term Neurogenic Potential in Subgranular and Subventricular Zones in Adult Mouse Brain
Ascl1 (Mash1) is a bHLH transcription factor essential for neural differentiation
during embryogenesis but its role in adult neurogenesis is less clear. Here we
show that in the adult brain Ascl1 is dynamically expressed during neurogenesis
in the dentate gyrus subgranular zone (SGZ) and more rostral subventricular zone
(SVZ). Specifically, we find Ascl1 levels low in SGZ Type-1 cells and SVZ B
cells but increasing as the cells transition to intermediate progenitor stages.
In vivo genetic lineage tracing with a tamoxifen (TAM) inducible
Ascl1CreERT2 knock-in mouse strain shows
that Ascl1 lineage cells continuously generate new neurons over extended periods
of time. There is a regionally-specific difference in neuron generation, with
mice given TAM at postnatal day 50 showing new dentate gyrus neurons through 30
days post-TAM, but showing new olfactory bulb neurons even 180 days post-TAM.
These results show that Ascl1 is not restricted to transit amplifying
populations but is also found in a subset of neural stem cells with long-term
neurogenic potential in the adult brain
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