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R Hillenbrand

Publications and source records attributed to R Hillenbrand.

13 recordsLinked to original sources
PubMed2003

Performance of visible and mid-infrared scattering-type near-field optical microscopes.

We describe the principles of two scattering-type near-field optical microscopes (s-SNOMs), one operating at 633 nm wavelength, the other at selectable wavelengths in the range 7.3-11.3 micro m, and compare the measurement experience. Both use interferometric detection of scattered radiation, and are therefore capable of amplitude and phase-contrast imaging. In this study both instruments use the same or even identical commercial probe tips, and measure a single, three-component, test sample. Our results show that the imaging process of s-SNOM is wavelength-independent, namely, that the resolution is determined by the properties of the tip only, and that the contrast is given by the complex refractive index of the sample, predictable from a simple, analytical model of tip-sample interaction. A novel, 'edge-darkening' artefact is described which may appear in s-SNOM and that is wavelength-independent.

Journal Article↗
PubMed2002

Phonon-enhanced light matter interaction at the nanometre scale.

Optical near fields exist close to any illuminated object. They account for interesting effects such as enhanced pinhole transmission or enhanced Raman scattering enabling single-molecule spectroscopy. Also, they enable high-resolution (below 10 nm) optical microscopy. The plasmon-enhanced near-field coupling between metallic nanostructures opens new ways of designing optical properties and of controlling light on the nanometre scale. Here we study the strong enhancement of optical near-field coupling in the infrared by lattice vibrations (phonons) of polar dielectrics. We combine infrared spectroscopy with a near-field microscope that provides a confined field to probe the local interaction with a SiC sample. The phonon resonance occurs at 920 cm(-1). Within 20 cm(-1) of the resonance, the near-field signal increases 200-fold; on resonance, the signal exceeds by 20 times the value obtained with a gold sample. We find that phonon-enhanced near-field coupling is extremely sensitive to chemical and structural composition of polar samples, permitting nanometre-scale analysis of semiconductors and minerals. The excellent physical and chemical stability of SiC in particular may allow the design of nanometre-scale optical circuits for high-temperature and high-power operation.

Journal Article↗
PubMed2001

Pure optical contrast in scattering-type scanning near-field microscopy.

We have enhanced the apertureless scattering-type scanning near-field optical microscope by two improvements which together achieve a recording of the true near field without any height-induced artefact. These are the use of interferometric detection of the scattered light on one hand, and the use of higher-harmonic dither demodulation of the scattered signal on the other. Here we present the basic rationale for these techniques, and give examples measured with two different experiments, one in the infrared (10 microm wavelength), the other in the visible (633 nm). The latter operates in a fully heterodyne mode and displays simultaneous images of optical near-field phase and amplitude, at below 10 nm resolution.

Journal Article↗
PubMed2000

Complex optical constants on a subwavelength scale.

Optical phase contrast has for the first time been observed on a nanometer scale, with a near-field microscope of scattering type that maps the complete optical field of amplitude and phase. Backed by quasielectrostatic theory, we demonstrate the significance and experimental accessibility of even complex optical constants on a subwavelength scale. Further, our method can separate the near-field response from background artifacts and thus is expected to enable nanoscale optical mapping of even topography-rich objects such as resonant clusters and macromolecules.

Journal Article↗
PubMed1999

Role for myelin-associated glycoprotein as a functional tenascin-R receptor.

The expression of the immunoglobulin superfamily member myelin-associated glycoprotein (MAG) and the extracellular matrix glycoprotein tenascin-R (TN-R) by oligodendrocytes overlaps in time and space. The two molecules can be neurite outgrowth-inhibitory or -promoting depending on the neuronal cell type and the environment in which they are presented. Here we show that the two molecules directly bind to each other in vitro and that binding sites on TN-R localize to two domains, the fibrinogen domain and the epidermal growth factor-like repeat domain with the N-terminal cysteine-rich stretch. We further show by a functional assay, namely the repulsion of MAG-transfected Chinese hamster ovary cells (CHO) cells from a TN-R substrate, that MAG is part of the signalling pathway of TN-R for cell repulsion. When coated as a uniform substrate, MAG was inhibitory for neurite outgrowth of hippocampal and cerebellar neurons in vitro, when compared to poly-L-lysine, while TN-R enhanced neurite outgrowth. When added to MAG, TN-R neutralized the neurite outgrowth-inhibitory effects of MAG, presumably by blocking the neurite outgrowth-inhibitory domain of MAG.

Animals↗
PubMed1999

The close homologue of the neural adhesion molecule L1 (CHL1): patterns of expression and promotion of neurite outgrowth by heterophilic interactions.

The close homologue of L1 (CHL1), a member of the L1 family of neural adhesion molecules, is first expressed at times of neurite outgrowth during brain development, and is detectable in subpopulations of neurons, astrocytes, oligodendrocyte precursors and Schwann cells of the mouse and rat. Aggregation assays with CHL1-transfected cells show that CHL1 does not promote homophilic adhesion or does it mediate heterophilic adhesion with L1. CHL1 promotes neurite outgrowth by hippocampal and small cerebellar neurons in substrate-bound and soluble form. The observation that CHL1 and L1 show overlapping, but also distinct patterns of synthesis in neurons and glia, suggests differential effects of L1-like molecules on neurite outgrowth.

Animals↗
PubMed1998

An adhesion test system based on Schneider cells to determine genotype-phenotype correlations for mutated P0 proteins.

Myelin protein zero (MPZ, P0) is well known as the adhesion molecule responsible for the compaction of the myelin sheath of peripheral nerves. Mutations are linked to Charcot-Marie-Tooth syndrome type 1B (CMT1B) and the more severe Dejerine-Sottas syndrome (DSS). Three mutations leading to phenotypes of increasing severity (Ser34del/CMT1B, Ser34Cys/DSS, INS663GC/DSS) were expressed in S2 insect cells and resulted in a decreased adhesion capability in correlation with their respective phenotypes.

Animals↗
PubMed1997

Signaling events following the interaction of the neuronal adhesion molecule F3 with the N-terminal domain of tenascin-R.

Interaction between the extracellular matrix protein tenascin-R and the neuronal adhesion molecule F3 might be involved in the formation of neuronal networks. In this study, the fragment of tenascin-R comprising epithelial growth factor (EGF)-like repeats and the cysteine-rich NH2 terminal stretch (EGF-L), known to be inhibitory for growing neurites and repellent for growth cones, was used to investigate the signaling events following the F3/EGF-L interaction. We addressed this question using an in vitro test with F3-transfected Chinese hamster ovary (CHO) cells that allowed us to measure the kinetics, magnitude and specificity of the repellent effect resulting from the specific F3/EGF-L interaction. We showed that the repellent effect was counteracted by addition of the serine/threonine kinase and -phosphatase modulators (staurosporine, okadaic acid and H7) but not by modulators of tyrosine kinase or -phosphatases. This result indicates that the intracellular signals activated by the repellent effect involve a serine/threonine kinase pathway. Furthermore, the repellent effect of the EGF-L fragment for growth cones of cultured cerebellar neurons was also abolished by the identical modulators of serine/threonine kinase and -phosphatases. The inhibition of neurite outgrowth from hippocampal neurons by EGF-L was abolished in the presence of the serine threonine-kinase inhibitor H7. These results strongly suggest that the F3/tenascin-R interaction through EGF-L involves an intracellular activation of serine/ threonine kinase(s) in all F3-expressing cells tested.

Animals↗
PubMed1997

Interaction of N-tosyl-L-phenylalanylchloromethane with Thermus thermophilus elongation factor Tu.

The interaction of N-tosyl-L-phenylalanylchloromethane (TosPheCH2Cl) with Thermus thermophilus elongation factor Tu (EF-Tu) was studied by affinity labelling and NMR spectroscopy. TosPheCH2Cl binds to GDP and GTP conformers of EF-Tu. The interaction of TosPheCH2Cl with EF-Tu x GDP leads to alkylation of Cys82, while interaction of TosPheCH2Cl with EF-Tu x GTP does not lead to covalent labelling. [A82]EF-Tu, in which the Cys82 is replaced by Ala, has similar properties to wild-type EF-Tu with respect to GTPase activity, binding of guanine nucleotides, interaction with elongation factor Ts (EF-Ts) and interaction with ribosomes. This structural change did not lead to changes, compared with wild-type EF-Tu in the functionality of [A82]EF-Tu, either in the GTP or in the GDP conformation. TosPheCH2Cl binds to EF-Tu x GTP with a dissociation constant of 10 microM. The interaction of TosPheCH2Cl with EF-Tu promotes the hydration of the carbonyl group of TosPheCH2Cl. TosPheCH2Cl competes with aminoacyl-tRNA for its binding site on EF-Tu x GTP. Covalent modification of Cys82 by TosPheCH2Cl does not prevent nucleotide binding and GTPase activity, but interferes with the interaction with aminoacyl-tRNA. TosPheCH2Cl probably mimics the aminoacyl residue of the aminoacyl-tRNA and binds to its binding site on EF-Tu x GTP. This rather specific interaction with EF-Tu x GTP does not allow the modification of Cys82, whereas the loose interaction of TosPheCH2Cl with EF-Tu x GDP leads to alkylation of this residue.

Affinity Labels↗
PubMed1996

Structural features of a close homologue of L1 (CHL1) in the mouse: a new member of the L1 family of neural recognition molecules.

We have identified a close homologue of L1 (CHL1) in the mouse. CHL1 comprises an N-terminal signal sequence, six immunoglobulin (Ig)-like domains, 4.5 fibronectin type III (FN)-like repeats, a transmembrane domain and a C-terminal, most likely intracellular domain of approximately 100 amino acids. CHL1 is most similar in its extracellular domain to chicken Ng-CAM (approximately 40% amino acid identity), followed by mouse L1, chicken neurofascin, chicken Nr-CAM, Drosophila neuroglian and zebrafish L1.1 (37-28% amino acid identity), and mouse F3, rat TAG-1 and rat BIG-1 (approximately 27% amino acid identity). The similarity with other members of the Ig superfamily [e.g. neural cell adhesion molecule (N-CAM), DCC, HLAR, rse] is 16-11%. The intracellular domain is most similar to mouse and chicken Nr-CAM, mouse and rat neurofascin (approximately 60% amino acid identity) followed by chicken neurofascin and Ng-CAM, Drosophila neuroglian and zebrafish L1.1 and L1.2 (approximately 40% amino acid identity). Besides the high overall homology and conserved modular structure among previously recognized members of the L1 family (mouse/human L1/rat NILE; chicken Ng-CAM; chicken/mouse Nr-CAM; Drosophila neuroglian; zebrafish L1.1 and L1.2; chicken/mouse neurofascin/rat ankyrin-binding glycoprotein), criteria characteristic of L1 were identified with regard to the number of amino acids between positions of conserved amino acid residues defining distances within and between two adjacent Ig-like domains and FN-like repeats. These show a collinearity in the six Ig-like domains and four adjacent FN-like repeats that is remarkably conserved between L1 and molecules containing these modules (designated the L1 family cassette), including the GPI-linked forms of the F3 subgroup (mouse F3/chicken F11/human CNTN1; rat BIG-1/mouse PANG; rat TAG-1/mouse TAX-1/chicken axonin-1). The colorectal cancer molecule (DCC), previously introduced as an N-CAM-like molecule, conforms to the L1 family cassette. Other structural features of CHL 1 shared between members of the L1 family are a high degree of N-glycosidically linked carbohydrates (approximately 20% of its molecular mass), which include the HNK-1 carbohydrate structure, and a pattern of protein fragments comprising a major 185 kDa band and smaller fragments of 165 and 125 kDa. As for the other L1 family members, predominant expression of CHL1 is observed in the nervous system and at later developmental stages. In the central nervous system CHL1 is expressed by neurons, but, in contrast to L1, also by glial cells. Our findings suggest a common ancestral L1-like molecule which evolved via gene duplication to generate a diversity of structurally and functionally distinct yet similar molecules.

Animals↗
PubMed1995

Inhibition of PC12 cell attachment and neurite outgrowth by detergent solubilized CNS myelin proteins.

Adhesion and neurite outgrowth of PC12 cells, as well as the spreading of 3T3 fibroblasts, were inhibited in a dose dependent manner by detergent solubilized mouse central nervous system myelin proteins as a tissue culture substrate. These inhibitory effects could be neutralized by the monoclonal antibody IN-1 directed against the neurite growth inhibiting proteins NI-35 and NI-250. Separation of the detergent soluble proteins of bovine spinal cord by an anion exchange column showed that the peaks of inhibitory activity for the two cell lines overlapped, such that the PC12 cells were inhibited by a larger number of fractions comprising those inhibitory for 3T3 cells. Neurite outgrowth of PC12 cells was not influenced by the myelin associated glycoprotein, MAG.

Animals↗
PubMed1995

Lack of evidence that myelin-associated glycoprotein is a major inhibitor of axonal regeneration in the CNS.

The MAG-deficient mouse was used to test whether MAG acts as a significant inhibitor of axonal regeneration in the adult mammalian CNS, as suggested by cell culture experiments. Cell spreading, neurite elongation, or growth cone collapse of different cell types in vitro was not significantly different when myelin preparations or optic nerve cryosections from either MAG-deficient or wild-type mice were used as a substrate. More importantly, the extent of axonal regrowth in lesioned optic nerve and corticospinal tract in vivo was similarly poor in MAG-deficient and wild-type mice. However, axonal regrowth increased significantly and to a similar extent in both genotypes after application of the IN-1 antibody directed against the neurite growth inhibitors NI-35 and NI-250. These observations do not support the view that MAG is a significant inhibitor of axonal regeneration in the adult CNS.

3T3 Cells↗