92 research outputs found
Elastic anomaly of heavy fermion systems in a crystalline field
An elastic anomaly, observed in the heavy fermi liquid state of Ce alloys
(for example, CeCu and CeTe), is analyzed by using the infinite-
Anderson lattice model. The four atomic energy levels are assumed for
f-electrons. Two of them are mutually degenerate. A small crystalline splitting
is assumed between two energy levels. The fourfold degenerate
conduction bands are also considered in the model. We solve the model using the
mean field approximation to slave bosons, changing the Fermi energy in order to
keep the total electron number constant. The nonzero value of the mean field of
the slave bosons persists over the temperatures much higher than the Kondo
temperature. This is the effect of the constant electron number. Next, the
linear susceptibility with respect to is calculated in order to obtain
the renomalized elastic constant. The resulting temperature dependence of the
constant shows the downward dip. We point out the relation of our finding with
the experimental data.Comment: submitted to J. Phys.: Condens. Matter, please request figure copies
to [email protected]
Optical and transport properties of heavy fermions: theory compared to experiment
Employing a local moment approach to the periodic Anderson model within the
framework of dynamical mean-field theory, direct comparison is made between
theory and experiment for the dc transport and optical conductivities of
paramagnetic heavy fermion and intermediate valence metals. Four materials,
exhibiting a diverse range of behaviour in their transport/optics, are analysed
in detail: CeB6, YbAl3, CeAl3 and CeCoIn5. Good agreement between theory and
experiment is in general found, even quantitatively, and a mutually consistent
picture of transport and optics results.Comment: 21 pages, 10 figures; Replacement with minor style changes made to
avoid postscript file error
The role of GDNF family ligand signalling in the differentiation of sympathetic and dorsal root ganglion neurons
The diversity of neurons in sympathetic ganglia and dorsal root ganglia (DRG) provides intriguing systems for the analysis of neuronal differentiation. Cell surface receptors for the GDNF family ligands (GFLs) glial cell-line-derived neurotrophic factor (GDNF), neurturin and artemin, are expressed in subpopulations of these neurons prompting the question regarding their involvement in neuronal subtype specification. Mutational analysis in mice has demonstrated the requirement for GFL signalling during embryonic development of cholinergic sympathetic neurons as shown by the loss of expression from the cholinergic gene locus in ganglia from mice deficient for ret, the signal transducing subunit of the GFL receptor complex. Analysis in mutant animals and transgenic mice overexpressing GFLs demonstrates an effect on sensitivity to thermal and mechanical stimuli in DRG neurons correlating at least partially with the altered expression of transient receptor potential ion channels and acid-sensitive cation channels. Persistence of targeted cells in mutant ganglia suggests that the alterations are caused by differentiation effects and not by cell loss. Because of the massive effect of GFLs on neurite outgrowth, it remains to be determined whether GFL signalling acts directly on neuronal specification or indirectly via altered target innervation and access to other growth factors. The data show that GFL signalling is required for the specification of subpopulations of sensory and autonomic neurons. In order to comprehend this process fully, the role of individual GFLs, the transduction of the GFL signals, and the interplay of GFL signalling with other regulatory pathways need to be deciphered
Threshold-Free Population Analysis Identifies Larger DRG Neurons to Respond Stronger to NGF Stimulation
Sensory neurons in dorsal root ganglia (DRG) are highly heterogeneous in terms of cell size, protein expression, and signaling activity. To analyze their heterogeneity, threshold-based methods are commonly used, which often yield highly variable results due to the subjectivity of the individual investigator. In this work, we introduce a threshold-free analysis approach for sparse and highly heterogeneous datasets obtained from cultures of sensory neurons. This approach is based on population estimates and completely free of investigator-set parameters. With a quantitative automated microscope we measured the signaling state of single DRG neurons by immunofluorescently labeling phosphorylated, i.e., activated Erk1/2. The population density of sensory neurons with and without pain-sensitizing nerve growth factor (NGF) treatment was estimated using a kernel density estimator (KDE). By subtraction of both densities and integration of the positive part, a robust estimate for the size of the responsive subpopulations was obtained. To assure sufficiently large datasets, we determined the number of cells required for reliable estimates using a bootstrapping approach. The proposed methods were employed to analyze response kinetics and response amplitude of DRG neurons after NGF stimulation. We thereby determined the portion of NGF responsive cells on a true population basis. The analysis of the dose dependent NGF response unraveled a biphasic behavior, while the study of its time dependence showed a rapid response, which approached a steady state after less than five minutes. Analyzing two parameter correlations, we found that not only the number of responsive small-sized neurons exceeds the number of responsive large-sized neurons—which is commonly reported and could be explained by the excess of small-sized cells—but also the probability that small-sized cells respond to NGF is higher. In contrast, medium-sized and large-sized neurons showed a larger response amplitude in their mean Erk1/2 activity
Identification of S-nitrosated mitochondrial proteins by S-nitrosothiol difference in gel electrophoresis (SNO-DIGE): implications for the regulation of mitochondrial function by reversible S-nitrosation
The S-nitrosation of mitochondrial proteins as a consequence of NO metabolism is of physiological and pathological significance. We previously developed a MitoSNO (mitochondria-targeted S-nitrosothiol) that selectively S-nitrosates mitochondrial proteins. To identify these S-nitrosated proteins, here we have developed a selective proteomic methodology, SNO-DIGE (S-nitrosothiol difference in gel electrophoresis). Protein thiols in control and MitoSNO-treated samples were blocked, then incubated with copper(II) and ascorbate to selectively reduce S-nitrosothiols. The samples were then treated with thiol-reactive Cy3 (indocarbocyanine) or Cy5 (indodicarbocyanine) fluorescent tags, mixed together and individual protein spots were resolved by 2D (two-dimensional) gel electrophoresis. Fluorescent scanning of these gels revealed S-nitrosated proteins by an increase in Cy5 red fluorescence, allowing for their identification by MS. Parallel analysis by Redox-DIGE enabled us to distinguish S-nitrosated thiol proteins from those which became oxidized due to NO metabolism. We identified 13 S-nitrosated mitochondrial proteins, and a further four that were oxidized, probably due to evanescent S-nitrosation relaxing to a reversible thiol modification. We investigated the consequences of S-nitrosation for three of the enzymes identified using SNO-DIGE (aconitase, mitochondrial aldehyde dehydrogenase and α-ketoglutarate dehydrogenase) and found that their activity was selectively and reversibly inhibited by S-nitrosation. We conclude that the reversible regulation of enzyme activity by S-nitrosation modifies enzymes central to mitochondrial metabolism, whereas identification and functional characterization of these novel targets provides mechanistic insight into the potential physiological and pathological roles played by this modification. More generally, the development of SNO-DIGE facilitates robust investigation of protein S-nitrosation across the proteome
Effectiveness of acupuncture, special dressings and simple, low-adherence dressings for healing venous leg ulcers in primary healthcare: study protocol for a cluster-randomized open-labeled trial
<p>Abstract</p> <p>Background</p> <p>Venous leg ulcers constitute a chronic recurring complaint that affects 1.0–1.3% of the adult population at some time in life, and which corresponds to approximately 75% of all chronic ulcers of the leg. Multilayer compression bandaging is, at present, the only treatment that has been proved to be effective in treating this type of ulcer. There is no consensus, however, about the dressings that may be applied, beneath the compression, to promote the healing of this type of ulcer, as there does not seem to be any added benefit from using special dressings rather than simple, low-adherence ones. As well as analgesia, acupuncture provokes peripheral vasodilation, in skin and muscles – which has been demonstrated both experimentally and in clinical practice – probably due to the axon reflex, among other mechanisms. The aim of the present study is to measure the effectiveness and cost of compression treatment for venous leg ulcers combined with special dressings, in comparison with low-adherence ones and acupuncture.</p> <p>Methods/design</p> <p>Cluster-randomized open-labeled trial, at 15 primary healthcare clinics in the Sevilla-Sur Healthcare District, with a control group treated with compression bandaging and low-adherence dressings; the experiment will consist, on the one hand, of the compression treatment applied in combination with special dressings (Treatment 1), and on the other, the compression treatment applied in association with low-adherence dressings, together with acupuncture (Treatment 2).</p> <p>Discussion</p> <p>The results will be measured and recorded in terms of the median time elapsed until complete healing of the ulcer, and the rate of complete healing at 3 months after beginning the treatment. An economic analysis will also be made.</p> <p>This study, carried out in the context of real clinical practice, will provide information for decision-taking concerning the effectiveness of special dressings. Moreover, for the first time a high-quality study will evaluate the effectiveness of acupuncture in the process of healing venous leg ulcers.</p> <p>Trial registration</p> <p>Current Controlled Trials ISRCTN26438275.</p
Effects of peripheral nerve injury on parvalbumin expression in adult rat dorsal root ganglion neurons
Background: Parvalbumin (PV) is a calcium binding protein that identifies a subpopulation of proprioceptive dorsal root ganglion (DRG) neurons. Calcitonin gene-related peptide (CGRP) is also expressed in a high proportion of muscle afferents but its relationship to PV is unclear. Little is known of the phenotypic responses of muscle afferents to nerve injury. Sciatic nerve axotomy or L5 spinal nerve ligation and section (SNL) lesions were used to explore these issues in adult rats using immunocytochemistry. Results: In naive animals, the mean PV expression was 25 % of L4 or L5 dorsal root ganglion (DRG) neurons, and this was unchanged 2 weeks after sciatic nerve axotomy. Colocalization studies with the injury marker activating transcription factor 3 (ATF3) showed that approximately 24 % of PV neurons expressed ATF3 after sciatic nerve axotomy suggesting that PV may show a phenotypic switch from injured to uninjured neurons. This possibility was further assessed using the spinal nerve ligation (SNL) injury model where injured and uninjured neurons are located in different DRGs. Two weeks after L5 SNL there was no change in total PV staining and essentially all L5 PV neurons expressed ATF3. Additionally, there was no increase in PV-ir in the adjacent uninjured L4 DRG cells. Co-labelling of DRG neurons revealed that less than 2 % of PV neurons normally expressed CGRP and no colocalization was seen after injury. Conclusion: These experiments clearly show that axotomy does not produce down regulation of PV protein in the DRG. Moreover, this lack of change is not due to a phenotypic switch in PV immunoreactive (ir) neurons, or de novo expression of PV-ir in uninjured neurons after nerve injury. These results further illustrate differences that occur when muscle afferents are injured as compared to cutaneous afferents
Magnetotransport of CeRhIn5
We report measurements of the temperature-dependent anisotropic resistivity
and in-plane magnetoresistance on single crystals of the tetragonal
heavy-fermion antiferromagnet (TN = 3.8 K) CeRhIn5. The measurements are
reported in the temperature range 1.4 K to 300 K and in magnetic fields to 18
tesla. The resistivity is moderately anisotropic, with a room-temperature
c-axis to in-plane resistivity ratio rho_c/rho_a(300 K) = 1.7. rho(T)
measurements on the non-magnetic analog LaRhIn5 indicate that the anisotropy in
the CeRhIn5 resistivity stems predominately from anisotropy in Kondo-derived
magnetic scattering. In the magnetically ordered regime an applied field H
reduces TN only slightly due to the small ordered moment (0.37mu_B) and
magnetic anisotropy. The magnetoresistance (MR) below TN is positive and varies
linearly with H. In the paramagnetic state a positive MR is present below 7.5
K, while a high-field negative contribution is evident at higher temperatures.
The positive contribution decreases in magnitude with increasing temperature.
Above 40 K the positive contribution is no longer observable, and the MR is
negative. The low-T positive MR results from interactions with the
Kondo-coherent state, while the high-T negative MR stems from single-impurity
effects. The H and T-dependent magnetotransport reflects the magnetic
anisotropy and Kondo interactions at play in CeRhIn5.Comment: submitted to Physical Review
Substance P antagonists as a therapeutic approach to improving outcome following traumatic brain injury
Role of neurotrophin signalling in the differentiation of neurons from dorsal root ganglia and sympathetic ganglia
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