767 research outputs found
Primary cilia regulate proliferation of amplifying progenitors in adult hippocampus: implications for learning and memory
Integration of new neurons into the adult hippocampus has been linked to specific types of learning. Primary cilia were found to be required for the formation of adult neural stem cells (NSCs) in the hippocampal dentate gyrus during development. However, the requirement of cilia in maintenance of adult NSCs is unknown. We developed a genetic mouse model in which fetal/perinatal brain development is unaffected, but adult hippocampal neurogenesis is constantly reduced by conditional ablation of primary cilia in adult GFAP(+) neural stem/progenitor cells. We found that this approach specifically reduces the number of hippocampal amplifying progenitors (also called type 2a cells) without affecting the number of radial NSCs (or type 1 cells). Constant reduction of adult hippocampal neurogenesis produced a delay rather than a permanent deficiency in spatial learning without affecting the retention of long-term memories. Decreased neurogenesis also altered spatial novelty recognition and hippocampus-independent cue conditioning. Here, we propose that adult hippocampal newborn neurons increase the efficiency of generating the new representations of spatial memories and that reduction of adult hippocampal neurogenesis may be biased toward cue-based strategies. This novel mouse model provides evidences that cognitive deficits associated with ciliary defects (ciliopathies) might be, in part, mediated by the deficiency of primary cilia in adult hippocampal stem/progenitor cells
Glueballs, symmetry breaking and axionic strings in non-supersymmetric deformations of the Klebanov-Strassler background
We obtain an analytic solution for an axionic non-supersymmetric deformation
of the warped deformed conifold. This allows us to study D-strings in the
infrared limit of non-supersymmetric deformations of the Klebanov-Strassler
background. They are interpreted as axionic strings in the dual field theory.
Following the arguments of [hep-th/0405282], the axion is a massless
pseudo-scalar glueball which is present in the supergravity fluctuation
spectrum and it is interpreted as the Goldstone boson of the spontaneously
broken U(1) baryon number symmetry, being the gauge theory on the baryonic
branch. Besides, we briefly discuss about the Pando Zayas-Tseytlin solution
where the SU(2) \times SU(2) global symmetry is spontaneously broken. This
background has been conjectured to be on the mesonic branch of the gauge
theory.Comment: 30 pages; V2: minor corrections; V3: section 3 corrected and
misprints corrected to match version published in JHE
Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor
The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25â310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor ( I ds > 1 A mm â1 ) to be defined (0.5 A mm â1 at 300 °C). The vertical breakdown voltage has been determined to be âŒ850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current
Ready ... Go: Amplitude of the fMRI Signal Encodes Expectation of Cue Arrival Time
What happens when the brain awaits a signal of uncertain arrival time, as when a sprinter waits for the starting pistol? And what happens just after the starting pistol fires? Using functional magnetic resonance imaging (fMRI), we have discovered a novel correlate of temporal expectations in several brain regions, most prominently in the supplementary motor area (SMA). Contrary to expectations, we found little fMRI activity during the waiting period; however, a large signal appears after the âgoâ signal, the amplitude of which reflects learned expectations about the distribution of possible waiting times. Specifically, the amplitude of the fMRI signal appears to encode a cumulative conditional probability, also known as the cumulative hazard function. The fMRI signal loses its dependence on waiting time in a âcountdownâ condition in which the arrival time of the go cue is known in advance, suggesting that the signal encodes temporal probabilities rather than simply elapsed time. The dependence of the signal on temporal expectation is present in âno-goâ conditions, demonstrating that the effect is not a consequence of motor output. Finally, the encoding is not dependent on modality, operating in the same manner with auditory or visual signals. This finding extends our understanding of the relationship between temporal expectancy and measurable neural signals
Fetal programming and systemic sclerosis
Objective This study investigated whether birthweight is linked to an increased risk of the development of systemic sclerosis. Study Design This was a multicenter case-control study with perinatal data that were obtained from 332 cases with systemic sclerosis and 243 control subjects. Birthweight was treated as a dichotomous variable (<2500 g vs 652500 g); low birthweight was defined as a weight <2500 g; small for gestational age was defined as birthweight <10th percentile for gestational age adjusted for sex. The relationship between systemic sclerosis and both low birthweight and small for gestational age was expressed with the crude (univariate analysis) and adjusted (multivariate analysis) odds ratio (OR). Results Significantly increased ORs were observed in the univariate analysis for low birthweight (OR, 2.59; 95% confidence interval [CI], 1.39-5.05) and small for gestational age (OR, 2.60; 95% CI, 1.34-5.32) subjects. Similarly increased risks were confirmed for both conditions in the multivariate analysis (OR, 3.93; 95% CI, 1.92-8.07; and OR, 2.58; 95% CI, 1.28-5.19), respectively. Conclusion Low birthweight and small for gestational age at birth are risk factors for the adult onset of systemic sclerosis
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