Search Results - (Author, Cooperation:S. Landis)

2014-11-21

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

Animals ; Biology/history ; Birds/anatomy & histology/*physiology ; History, 20th Century ; History, 21st Century ; Humans ; Models, Neurological ; Neurosciences/*history ; Psychiatry/history ; Speech/*physiology ; Vocalization, Animal/*physiology

1077-3118

AIP Digital Archive

Physics

Arrays of Si square dots down to 200 nm in size were patterned on silicon substrates, and thin films of different magnetic materials were sputter deposited on these patterned substrates. The magnetic film covers the top of the dots, the bottom of the grooves and to much less extent the sidewalls of the dots. Single domain magnetic dots were obtained for Co/NiO bilayers and Co/Pt multilayers, without significant direct coupling mediated by the magnetic deposit on the sidewalls of the dots. Our results indicate that, in these arrays, the magnetic pinning forces are stronger than the estimated value of the largest demagnetizing magnetostatic field on each individual dot. As a result, any magnetic configuration could in principle be stored in such arrays. This approach seems therefore very promising for the preparation of magnetic storage media with ultrahigh density. © 1999 American Institute of Physics.

Electronic Resource

0018-702X

English, American Studies

0012-1606

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Biology

Electronic Resource

1573-7381

Springer Online Journal Archives 1860-2000

Medicine

Summary While distinct precursors committed to a neuronal or glial cell fate are generated from neural crest cells early in peripheral gangliogenesis, little is known about the subsequent generation and maturation of young satellite glia from restricted glial precursor cells. To examine the division and migration of glial precursor cells and their satellite cell progeny, morphological, immunocytochemical and culture techniques were applied to the developing rat superior cervical ganglion. At embryonic day (E)18.5, numerous clusters of nonneuronal cells appeared transiently in the ganglion. Individual cells with a similar morphology were present in E16.5 ganglia, and are likely to represent the precursor cells which generate these clusters. The clustered cells were distinguishable from neighbouring neurons as well as from endothelial cells and fibroblasts. Morphologically similar cells were present in nerve bundles at E18.5 and surrounding principal neurons and nerve bundles in the adult ganglion. Double-label studies of the E18.5 ganglion with tyrosine hydroxylase to identify noradrenergic neurons and propidium iodide counterstaining to visualize all cell nuclei revealed that the cells in clusters stained with propidium iodide but lacked tyrosine hydroxylase immunoreactivity. To determine if cell clusters arose from division, bromodeoxyuridine, a thymidine analogue, was administered to pregnant mothers between E16.5–E18.5, and ganglionic cells examined at E18.5 bothin vivo andin vitro. Numerous non-neuronal cells divided during this periodin situ and composed portions of clusters. When dissociated, superior cervical ganglion satellite glia reacted with an NGF-receptor antibody (MAb 217c) and possessed a flattened shape, in contrast to bipolar Schwann cells. Over half of the 217c-immunoreactive glia at E18.5 had incorporated bromodeoxyuridine during E16.5–18.5in vivo. At birth, non-neuronal cells were no longer grouped in clusters, but were associated with neuronal cell bodies and processes. These findings suggest that, between E16.5–E18.5, glial precursors divide rapidly to form clusters, and that, after the peak of neurogenesis, daughter cells migrate within the ganglion to associate with nerve cell bodies and processes where proliferation continues at a slower rate. Distinct cellular and molecular interactions are likely to trigger the initial rapid division of glial precursors, initiate their migration and association with neuron cell bodies, and control their subsequent slower division.

Electronic Resource

0091-7419

Life Sciences ; Molecular Cell Biology

Wiley InterScience Backfile Collection 1832-2000

Biology

Chemistry and Pharmacology

Medicine

The three-dimensional structure of the multisubunit allosteric enzyme, aspartate transcarbamylase, has been determined to 5.5 Å resolution. An unusual feature of the molecule is a large central aqueous cavity 50 Å × 50 Å × 25 Å, into which the active sites face. Access to the central cavity and the active site region is provided by six equivalent channels of 15 Å diameter.A complex C6R4, composed of catalytic trimers C3 and of regulatory dimers R2, has been isolated upon treatment of aspartate transcarbamylase (ATCase, C6R6) by mercurials. The specific catalytic activity of C6R4 is essentially the same as that of ATCase, about 70% of that of the catalytic trimers at 30 mM aspartate and saturating carbamyl phosphate. Allosteric interactions are reduced in C6R4 as compared with those in ATCase. In the homotropic interactions the Hill coefficient is reduced from approximately 3.3 to 2.1 at pH 8.3, while the heterotropic interactions of both cytidine triphosphate (CTP) and adenosine triphosphate (ATP) are reduced substantially but not abolished at pH 8.3. Thus, the allosteric transitions involved in the regulatory mechanisms do not require the intact structure C6R6. Also, this regulation is not simply the control of access of substrates or products to or from the large central aqueous cavity in the ATCase molecule.Comparison of electron density maps at 5.5 Å resolution for ATCase and for the complex of ATCase with CTP shows substantial similarities throughout the three-dimensional electron density maps. Significant differences are seen, however, in the region of the regulatory dimers R2 where CTP adds, and near the active sites in the catalytic trimers C3.

16 Ill.

Electronic Resource