2,112 research outputs found
Extracellular electrophysiological measurements of cooperative signals in astrocytes populations
Astrocytes are neuroglial cells that exhibit functional electrical properties sensitive to neuronal activity and capable of modulating neurotransmission. Thus, electrophysiological recordings of astroglial activity are very attractive to study the dynamics of glial signaling. This contribution reports on the use of ultra-sensitive planar electrodes combined with low noise and low frequency amplifiers that enable the detection of extracellular signals produced by primary cultures of astrocytes isolated from mouse cerebral cortex. Recorded activity is characterized by spontaneous bursts comprised of discrete signals with pronounced changes on the signal rate and amplitude. Weak and sporadic signals become synchronized and evolve with time to higher amplitude signals with a quasi-periodic behavior, revealing a cooperative signaling process. The methodology presented herewith enables the study of ionic fluctuations of population of cells, complementing the single cells observation by calcium imaging as well as by patch-clamp techniques.Portuguese Foundation for Science and Technology (FCT) [PTDC/EEI-AUT/5442/2014]; Instituto de Telecomunicacoes [UID/Multi/04326/2013]; Associated Laboratory - Institute of Nanoscience and Nanotechnology [POCI-01-0145-FEDER-016623]; [PTDC/CTM-NAN/3146/2014]info:eu-repo/semantics/publishedVersio
The sleep-inducing lipid oleamide deconvolutes gap junction communication and calcium wave transmission in glial cells.
Oleamide is a sleep-inducing lipid originally isolated from the cerebrospinal fluid of sleep-deprived cats. Oleamide was found to potently and selectively inactivate gap junction-mediated communication between rat glial cells. In contrast, oleamide had no effect on mechanically stimulated calcium wave transmission in this same cell type. Other chemical compounds traditionally used as inhibitors of gap junctional communication, like heptanol and 18beta-glycyrrhetinic acid, blocked not only gap junctional communication but also intercellular calcium signaling. Given the central role for intercellular small molecule and electrical signaling in central nervous system function, oleamide- induced inactivation of glial cell gap junction channels may serve to regulate communication between brain cells, and in doing so, may influence higher order neuronal events like sleep induction
Large magnetic anisotropy in Ferrihydrite nanoparticles synthesized from reverse micelles
Six-line ferrihydrite(FH) nanoparticles have been synthesized in the core of
reverse micelles, used as nanoreactors to obtain average particle sizes
2 to 4 nm. The blocking temperatures extracted from
magnetization data increased from to 20 K for increasing particle
size. Low-temperature \MOS measurements allowed to observe the onset of
differentiated contributions from particle core and surface as the particle
size increases. The magnetic properties measured in the liquid state of the
original emulsion showed that the \FH phase is not present in the liquid
precursor, but precipitates in the micelle cores after the free water is
freeze-dried. Systematic susceptibility \chi_{ac}(\emph{f},T) measurements
showed the dependence of the effective magnetic anisotropy energies
with particle volume, and yielded an effective anisotropy value of kJ/m.Comment: 8 pages, 10 figures. Nanotechnology, v17 (Nov. 2006) In pres
Pseudobulges in the Disk Galaxies NGC 7690 and NGC 4593
We present Ks-band surface photometry of NGC 7690 (Hubble type Sab) and NGC
4593 (SBb). We find that, in both galaxies, a major part of the "bulge" is as
flat as the disk and has approximately the same color as the inner disk. In
other words, the "bulges" of these galaxies have disk-like properties. We
conclude that these are examples of "pseudobulges" -- that is, products of
secular dynamical evolution. Nonaxisymmetries such as bars and oval disks
transport disk gas toward the center. There, star formation builds dense
stellar components that look like -- and often are mistaken for -- merger-built
bulges but that were constructed slowly out of disk material. These
pseudobulges can most easily be recognized when, as in the present galaxies,
they retain disk-like properties. NGC 7690 and NGC 4593 therefore contribute to
the growing evidence that secular processes help to shape galaxies.
NGC 4593 contains a nuclear ring of dust that is morphologically similar to
nuclear rings of star formation that are seen in many barred and oval galaxies.
The nuclear dust ring is connected to nearly radial dust lanes in the galaxy's
bar. Such dust lanes are a signature of gas inflow. We suggest that gas is
currently accumulating in the dust ring and hypothesize that the gas ring will
starburst in the future. The observations of NGC 4593 therefore suggest that
major starburst events that contribute to pseudobulge growth can be episodic.Comment: 10 pages, 3 Postscript figures; requires emulateapj.cls,
apjfonts.sty, and psfig.sty; accepted for publication in ApJ; for a version
with full resolution figures, see
http://chandra.as.utexas.edu/~kormendy/n7690.pd
Calcium Dynamics of Cortical Astrocytic Networks In Vivo
Large and long-lasting cytosolic calcium surges in astrocytes have been described in cultured cells and acute slice preparations. The mechanisms that give rise to these calcium events have been extensively studied in vitro. However, their existence and functions in the intact brain are unknown. We have topically applied Fluo-4 AM on the cerebral cortex of anesthetized rats, and imaged cytosolic calcium fluctuation in astrocyte populations of superficial cortical layers in vivo, using two-photon laser scanning microscopy. Spontaneous [Ca(2+)](i) events in individual astrocytes were similar to those observed in vitro. Coordination of [Ca(2+)](i) events among astrocytes was indicated by the broad cross-correlograms. Increased neuronal discharge was associated with increased astrocytic [Ca(2+)](i) activity in individual cells and a robust coordination of [Ca(2+)](i) signals in neighboring astrocytes. These findings indicate potential neuron–glia communication in the intact brain
Continuous loading of a magnetic trap
We have realized a scheme for continuous loading of a magnetic trap (MT).
^{52}Cr atoms are continuously captured and cooled in a magneto-optical trap
(MOT). Optical pumping to a metastable state decouples atoms from the cooling
light. Due to their high magnetic moment (6 Bohr magnetons), low-field seeking
metastable atoms are trapped in the magnetic quadrupole field provided by the
MOT. Limited by inelastic collisions between atoms in the MOT and in the MT, we
load 10^8 metastable atoms at a rate of 10^8 atoms/s below 100 microkelvin into
the MT. After loading we can perform optical repumping to realize a MT of
ground state chromium atoms.Comment: 4 pages, 4 figures, version 2, modified references, included
additional detailed information, minor changes in figure 3 and in tex
Mapping the spatiotemporal dynamics of calcium signaling in cellular neural networks using optical flow
An optical flow gradient algorithm was applied to spontaneously forming net-
works of neurons and glia in culture imaged by fluorescence optical microscopy
in order to map functional calcium signaling with single pixel resolution.
Optical flow estimates the direction and speed of motion of objects in an image
between subsequent frames in a recorded digital sequence of images (i.e. a
movie). Computed vector field outputs by the algorithm were able to track the
spatiotemporal dynamics of calcium signaling pat- terns. We begin by briefly
reviewing the mathematics of the optical flow algorithm, and then describe how
to solve for the displacement vectors and how to measure their reliability. We
then compare computed flow vectors with manually estimated vectors for the
progression of a calcium signal recorded from representative astrocyte
cultures. Finally, we applied the algorithm to preparations of primary
astrocytes and hippocampal neurons and to the rMC-1 Muller glial cell line in
order to illustrate the capability of the algorithm for capturing different
types of spatiotemporal calcium activity. We discuss the imaging requirements,
parameter selection and threshold selection for reliable measurements, and
offer perspectives on uses of the vector data.Comment: 23 pages, 5 figures. Peer reviewed accepted version in press in
Annals of Biomedical Engineerin
Individual participant data meta-analysis of continuous outcomes: A comparison of approaches for specifying and estimating one-stage models
One-stage individual participant data meta-analysis models should account for within-trial clustering, but it is currently debated how to do this. For continuous outcomes modeled using a linear regression framework, two competing approaches are a stratified intercept or a random intercept. The stratified approach involves estimating a separate intercept term for each trial, whereas the random intercept approach assumes that trial intercepts are drawn from a normal distribution. Here, through an extensive simulation study for continuous outcomes, we evaluate the impact of using the stratified and random intercept approaches on statistical properties of the summary treatment effect estimate. Further aims are to compare (i) competing estimation options for the one-stage models, including maximum likelihood and restricted maximum likelihood, and (ii) competing options for deriving confidence intervals (CI) for the summary treatment effect, including the standard normal-based 95% CI, and more conservative approaches of Kenward-Roger and Satterthwaite, which inflate CIs to account for uncertainty in variance estimates. The findings reveal that, for an individual participant data meta-analysis of randomized trials with a 1:1 treatment:control allocation ratio and heterogeneity in the treatment effect, (i) bias and coverage of the summary treatment effect estimate are very similar when using stratified or random intercept models with restricted maximum likelihood, and thus either approach could be taken in practice, (ii) CIs are generally best derived using either a Kenward-Roger or Satterthwaite correction, although occasionally overly conservative, and (iii) if maximum likelihood is required, a random intercept performs better than a stratified intercept model. An illustrative example is provided
Decision Support Tools for Coronary Artery Calcium Scoring in the Primary Prevention of Cardiovascular Disease Do Not Meet Health Literacy Needs: A Systematic Environmental Scan and Evaluation
A shared decision-making approach is considered optimal in primary cardiovascular disease (CVD) prevention. Evidence-based patient decision aids can facilitate this but do not always meet patients’ health literacy needs. Coronary artery calcium (CAC) scans are increasingly used in addition to traditional cardiovascular risk scores, but the availability of high-quality decision aids to support shared decision-making is unknown. We used an environmental scan methodology to review decision support for CAC scans and assess their suitability for patients with varying health literacy. We systematically searched for freely available web-based decision support tools that included information about CAC scans for primary CVD prevention and were aimed at the public. Eligible materials were independently evaluated using validated tools to assess qualification as a decision aid, understandability, actionability, and readability. We identified 13 eligible materials. Of those, only one qualified as a decision aid, and one item presented quantitative information about the potential harms of CAC scans. None presented quantitative information about both benefits and harms of CAC scans. Mean understandability was 68%, and actionability was 48%. Mean readability (12.8) was much higher than the recommended grade 8 level. Terms used for CAC scans were highly variable. Current materials available to people considering a CAC scan do not meet the criteria to enable informed decision-making, nor do they meet the health literacy needs of the general population. Clinical guidelines, including CAC scans for primary prevention, must be supported by best practice decision aids to support decision-making
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