Patterning of the basal telencephalon and hypothalamus is essential for guidance of cortical projections

PMID: 11830575We have investigated the mechanisms that control the guidance of corticofugal projections as they extend along different subdivisions of the forebrain. To this aim, we analyzed the development of cortical projections in mice that lack Nkx2-1, a homeobox gene whose expression is restricted to two domains within the forebrain: the basal telencephalon and the hypothalamus. Molecular respecification of the basal telencephalon and hypothalamus in Nkx2-1-deficient mice causes a severe defect in the guidance of layer 5 cortical projections and ascending fibers of the cerebral peduncle. These axon tracts take an abnormal path when coursing through both the basal telencephalon and hypothalamus. By contrast, loss of Nkx2-1 function does not impair guidance of corticothalamic or thalamocortical axons. In vitro experiments demonstrate that the basal telencephalon and the hypothalamus contain an activity that repels the growth of cortical axons, suggesting that loss of this activity is the cause of the defects observed in Nkx2-1 mutants. Furthermore, analysis of the expression of candidate molecules in the basal telencephalon and hypothalamus of Nkx2-1 mutants suggests that Slit2 contributes to this activity.This work was supported by the research grants to J. L. R. R. from Nina Ireland, NARSAD, NIDA (R01DA12462) and NIMH (RO1 MH49428-01, RO1 MH51561-01A1 and K02 MH01046-01). O. M. is a NARSAD Young Investigator Award recipient and a UC Davis MIND Institute Scholar.Peer reviewe

Indeterminacy of Spatiotemporal Cardiac Alternans

Cardiac alternans, a beat-to-beat alternation in action potential duration (at the cellular level) or in ECG morphology (at the whole heart level), is a marker of ventricular fibrillation, a fatal heart rhythm that kills hundreds of thousands of people in the US each year. Investigating cardiac alternans may lead to a better understanding of the mechanisms of cardiac arrhythmias and eventually better algorithms for the prediction and prevention of such dreadful diseases. In paced cardiac tissue, alternans develops under increasingly shorter pacing period. Existing experimental and theoretical studies adopt the assumption that alternans in homogeneous cardiac tissue is exclusively determined by the pacing period. In contrast, we find that, when calcium-driven alternans develops in cardiac fibers, it may take different spatiotemporal patterns depending on the pacing history. Because there coexist multiple alternans solutions for a given pacing period, the alternans pattern on a fiber becomes unpredictable. Using numerical simulation and theoretical analysis, we show that the coexistence of multiple alternans patterns is induced by the interaction between electrotonic coupling and an instability in calcium cycling.Comment: 20 pages, 10 figures, to be published in Phys. Rev.

Measuring the Quantum State of a Large Angular Momentum

We demonstrate a general method to measure the quantum state of an angular momentum of arbitrary magnitude. The (2F+1) x (2F+1) density matrix is completely determined from a set of Stern-Gerlach measurements with (4F+1) different orientations of the quantization axis. We implement the protocol for laser cooled Cesium atoms in the 6S_{1/2}(F=4) hyperfine ground state and apply it to a variety of test states prepared by optical pumping and Larmor precession. A comparison of input and measured states shows typical reconstruction fidelities of about 0.95.Comment: 4 pages, 6 figures, submitted to PR

Multiple stellar populations in the Galactic globular cluster NGC 6752

We have carried out high-precision photometry on a large number of archival HST images of the Galactic globular cluster NGC 6752, to search for signs of multiple stellar populations. We find a broadened main sequence, and demonstrate that this broadening cannot be attributed either to binaries or to photometric errors. There is also some indication of a main-sequence split. No significant spread could be found along the subgiant branch, however. Ground-based photometry reveals that in the U vs. (U-B) color-magnitude diagram the red-giant branch exhibits a clear color spread, which we have been able to correlate with variations in Na and O abundances. In particular the Na-rich, O-poor stars identified by Carretta et al. (2007) define a sequence on the red side of the red-giant branch, while Na-poor, O-rich stars populate a bluer, more dispersed portion of the red-giant branch.Comment: 31 pages, 12 figures; Accepted for Publication in the Astrophysical Journa

Diffusionweighted MR imaging derived apparent diffusion coefficient is predictive of clinical outcome in primary central nervous system lymphoma

BACKGROUND AND PURPOSE: There is evidence that increased tumor cellular density within diagnostic specimens of primary central nervous system lymphoma (PCNSL) may have significant prognostic implications. Because cellular density may influence measurements of apparent diffusion coefficient (ADC) by using diffusion-weighted MR imaging (DWI), we hypothesized that ADC measured from contrastenhancing regions might correlate with clinical outcome in patients with PCNSL

Planck's scale dissipative effects in atom interferometry

Atom interferometers can be used to study phenomena leading to irreversibility and dissipation, induced by the dynamics of fundamental objects (strings and branes) at a large mass scale. Using an effective, but physically consistent description in terms of a master equation of Lindblad form, the modifications of the interferometric pattern induced by the new phenomena are analyzed in detail. We find that present experimental devices can in principle provide stringent bounds on the new effects.Comment: 12 pages, plain-Te

Optical Photometry of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex in IC 5179

We present UBVRIz lightcurves of the Type Ia SN 1999ee and the Type Ib/c SN 1999ex, both located in the galaxy IC 5179. SN 1999ee has an extremely well sampled lightcurve spanning from 10 days before Bmax through 53 days after peak. Near maximum we find systematic differences ~0.05 mag in photometry measured with two different telescopes, even though the photometry is reduced to the same local standards around the supernova using the specific color terms for each instrumental system. We use models for our bandpasses and spectrophotometry of SN 1999ee to derive magnitude corrections (S-corrections) and remedy this problem. This exercise demonstrates the need of accurately characterizing the instrumental system before great photometric accuracies of Type Ia supernovae can be claimed. It also shows that this effect can have important astrophysical consequences since a small systematic shift of 0.02 mag in the B-V color can introduce a 0.08 mag error in the extinction corrected peak B magnitudes of a supernova and thus lead to biased cosmological parameters. The data for the Type Ib/c SN 1999ex present us with the first ever observed shock breakout of a supernova of this class. These observations show that shock breakout occurred 18 days before Bmax and support the idea that Type Ib/c supernovae are due to core collapse of massive stars rather than thermonuclear disruption of white dwarfs.Comment: 55 pages, 15 figures, accepted by the Astronomical Journa