8,040 research outputs found
Self-reinoculation with fecal flora changes microbiota density and composition leading to an altered bile-acid profile in the mouse small intestine
Background: The upper gastrointestinal tract plays a prominent role in human physiology as the primary site for enzymatic digestion and nutrient absorption, immune sampling, and drug uptake. Alterations to the small intestine microbiome have been implicated in various human diseases, such as non-alcoholic steatohepatitis and inflammatory bowel conditions. Yet, the physiological and functional roles of the small intestine microbiota in humans remain poorly characterized because of the complexities associated with its sampling. Rodent models are used extensively in microbiome research and enable the spatial, temporal, compositional, and functional interrogation of the gastrointestinal microbiota and its effects on the host physiology and disease phenotype. Classical, culture-based studies have documented that fecal microbial self-reinoculation (via coprophagy) affects the composition and abundance of microbes in the murine proximal gastrointestinal tract. This pervasive self-reinoculation behavior could be a particularly relevant study factor when investigating small intestine microbiota. Modern microbiome studies either do not take self-reinoculation into account, or assume that approaches such as single housing mice or housing on wire mesh floors eliminate it. These assumptions have not been rigorously tested with modern tools. Here, we used quantitative 16S rRNA gene amplicon sequencing, quantitative microbial functional gene content inference, and metabolomic analyses of bile acids to evaluate the effects of self-reinoculation on microbial loads, composition, and function in the murine upper gastrointestinal tract.
Results: In coprophagic mice, continuous self-exposure to the fecal flora had substantial quantitative and qualitative effects on the upper gastrointestinal microbiome. These differences in microbial abundance and community composition were associated with an altered profile of the small intestine bile acid pool, and, importantly, could not be inferred from analyzing large intestine or stool samples. Overall, the patterns observed in the small intestine of non-coprophagic mice (reduced total microbial load, low abundance of anaerobic microbiota, and bile acids predominantly in the conjugated form) resemble those typically seen in the human small intestine.
Conclusions: Future studies need to take self-reinoculation into account when using mouse models to evaluate gastrointestinal microbial colonization and function in relation to xenobiotic transformation and pharmacokinetics or in the context of physiological states and diseases linked to small intestine microbiome and to small intestine dysbiosis
On How to Extend the NIR Tully-Fisher Relation to be Truly All-Sky
Dust extinction and stellar confusion by the Milky Way reduce the efficiency
of detecting galaxies at low Galactic latitudes, creating the so-called Zone of
Avoidance. This stands as a stumbling block in charting the distribution of
galaxies and cosmic flow fields, and therewith our understanding of the local
dynamics in the Universe (CMB dipole, convergence radius of bulk flows). For
instance, ZoA galaxies are generally excluded from the whole-sky Tully-Fisher
Surveys () even if catalogued. We show here that by
fine-tuning the near-infrared TF relation, there is no reason not to extend
peculiar velocity surveys deeper into the ZoA. Accurate axial ratios ()
are crucial to both the TF sample selection and the resulting TF distances. We
simulate the effect of dust extinction on the geometrical properties of
galaxies. As expected, galaxies appear rounder with increasing obscuration
level, even affecting existing TF samples. We derive correction models and
demonstrate that we can reliably reproduce the intrinsic axial ratio from the
observed value up to extinction level of about mag (
mag), we also recover a fair fraction of galaxies that otherwise would fall out
of an uncorrected inclination limited galaxy sample. We present a
re-calibration of the 2MTF relation in the NIR , , and -bands for
isophotal rather than total magnitudes, using their same calibration sample.
Both TF relations exhibit similar scatter at high Galactic latitudes. However,
the isophotal TF relation results in a significant improvement in the scatter
for galaxies in the ZoA, and low surface brightness galaxies in general,
because isophotal apertures are more robust in the face of significant stellar
confusion.Comment: 12 pages, 10 figures, 4 tables, accepted for publication in MNRA
The HI mass function in the Parkes HI Zone of Avoidance survey
An HI mass function (HIMF) was derived for 751 galaxies selected from the
deep Parkes HI survey across the Zone of Avoidance (HIZOA). HIZOA contains both
the Great Attractor Wall and the Local Void, two of the most extreme
environments in the local Universe, making the sample eminently suitable to
explore the overall HIMF as well as its dependence on local environment. To
avoid any selection bias because of the different distances of these
large-scale structures, we first used the two-dimensional stepwise
maximum-likelihood method for the definition of an average HIMF. The resulting
parameters of a Schechter-type HIMF for the whole sample are , , and Mpc. We then used the -th
nearest-neighbour method to subdivide the sample into four environments of
decreasing local density and derived the Schechter parameters for each
subsample. A strong trend is observed, for the slope of the low-mass
end of the HIMF. The slope changes from being nearly flat, i.e. for galaxies residing in the densest bin, to the steep value of
in the lowest density bin. The characteristic mass,
however, does not show a clear trend between the highest and lowest density
bins. We find similar trends in the low-mass slope when we compare the results
for a region dominated by the Great Attractor, and the Local Void, which are
found to be over-, respectively underdense by 1.35 and 0.59 compared to the
whole sample.Comment: 10 pages, 13 figures, 4 tables, accepted for publication in MNRA
Lung Circulation Modeling: Status and Prospect
Mathematical modeling has been used to interpret anatomical and physiological data obtained from metabolic and hemodynamic studies aimed at investigating structure-function relationships in the vasculature of the lung, and how these relationships are affected by lung injury and disease. The indicator dilution method was used to study the activity of redox processes within the lung. A steady-state model of the data was constructed and used to show that pulmonary endothelial cells may play an important role in reducing redox active compounds and that those reduction rates can be altered with oxidative stress induced by exposure to high oxygen environments. In addition, a morphometric model of the pulmonary vasculature was described and used to detect, describe,and predict changes in vascular morphology that occur in response to chronic exposure to low-oxygen environments, a common model of pulmonary hypertension. Finally, the model was used to construct simulated circulatory networks designed to aid in evaluation of competing hypotheses regarding the relative contribution of various morphological and biomechanical changes observed with hypoxia. These examples illustrate the role of mathematical modeling in the integration of the emerging metabolic, hemodynamic, and morphometric databases
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