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Biomedical subjects

H Schweizer

Publications and source records attributed to H Schweizer.

At least 19 recordsLinked to original sources
PubMed2005

[Transfusion incidents reports of grade zero: a national and descriptive analysis upon two years of practical survey].

A grade zero transfusion incident is defined as an inappropriate transfusion of blood component due to one or several failures without immediate clinical or biological consequences for the recipient. Two years after the setting up of the mandatory notification of these incidents, Afssaps haemovigilance unit performed a first descriptive national analysis of the data collected in years 2003 and 2004 at the national level. This analysis was based on one part on computarised e-Fit national database and on the other part on investigation results documents and additional surveys set up by the network professionals. From a quantitative point of view, this study reveals differences in notification as well as in the type of analysis from one region to another. Quantitatively, 45% of grade zero transfusion incidents correspond to attribution errors. The site of origin of grade zero incidents is for almost 73% linked to health establishment, clinical unit or hospital blood bank, and for almost 23% linked to blood establishment. Complete analysis has notably shown that 9% of the incidents are due to errors in blood component prescription. This descriptive analysis, which identifies recurrent failure and critical points originating from non-appropriated transfusions, should constitute the starting point of a reflection aiming at optimising and standardising methods of analysis of grade zero transfusion incidents and at elaborating suggestions to better control critical points.

France↗
PubMed2004

Detection of a Landau band-coupling-induced rearrangement of the Hofstadter butterfly.

The spectrum of 2D electrons subjected to a weak 2D potential and a perpendicular magnetic field is composed of Landau bands with a fractal internal pattern of subbands and minigaps referred to as Hofstadter's butterfly. The Hall conductance may serve as a spectroscopic tool as each filled subband contributes a specific quantized value. Advances in sample fabrication now finally offer access to the regime away from the limiting case of a very weak potential. Complex behavior of the Hall conductance is observed and assigned to Landau band-coupling-induced rearrangements within the butterfly.

Journal Article↗
PubMed2004

Characterization of migration behavior of myogenic precursor cells in the limb bud with respect to Lmx1b expression.

Limb buds develop from lateral plate-derived stationary mesenchyme and are invaded by cells from extrinsic regions. The largest populations of these cells are myogenic precursor cells that originate from the lateral dermomyotomes. After detachment under the influence of SF/HGF, myogenic precursor cells migrate in a proximo-distal direction and populate a dorsal and ventral zone. The patterning mechanism leading to the segregation of dorsal and ventral myogenic cells is at present not understood. Lmx1b, a LIM homeodomain transcription factor expressed in the dorsal mesenchyme of the developing limb bud, forms a sharp dorso-ventral boundary of expression within the limb. We have investigated the mechanisms of dorso-ventral patterning of muscle precursor cells in the limb buds with respect to Lmx1b expression using quail-chick chimeras and transgenic mice. Although cells appeared to be capable of migrating either ventrally or dorsally, their migration was restricted to the position they had attained during normal development or in the experimental situation. They were never found to cross the dorso-ventral boundary. Immunohistochemistry and histological analysis of mice carrying a LacZ reporter gene under the control of the endogenous Lmx1b locus confirmed that myogenic precursors in the limb bud were devoid of Lmx1b expression. In addition, it was shown that Lmx1b is not only expressed at early stages of limb development but maintains its pattern, at least until after birth. The present study provides new insights into migratory pathways of myogenic precursor cells and reveals details of Lmx1b expression on a cellular basis within the limb.

Animals↗
PubMed2001

Evidence of Hofstadter's Fractal Energy Spectrum in the Quantized Hall Conductance.

The energy spectrum of a two-dimensional electron system in a perpendicular homogeneous magnetic field and a weak lateral superlattice potential with square symmetry is composed of Landau bands with recursive internal subband structure. The Hall conductance in the minigaps is anticipated to be quantized in integer multiples of e(2)/h that vary erratically from minigap to minigap in accordance with a Diophantine equation. Hall measurements on samples with the requisite properties uncover this long searched for evidence of Hofstadter's butterflylike energy spectrum.

Journal Article↗
PubMed1997

Significance of the paralemniscal tegmental area for audio-motor control in the moustached bat, Pteronotus p. parnellii: the afferent off efferent connections of the paralemniscal area.

The paralemniscal tegmental area has been determined in the brain of the New World moustached bat, Pteronotus p. parnellii, by electrical microstimulation eliciting echolocation calls and pinna movements. It is located in the dorsal tegmentum rostral and medial to the dorsal nucleus of the lateral lemniscus and is characterized by medium sized and large neurons. Tracer injections (WGA-HRP) showed that the most intense input to the paralemniscal tegmental area originates in the intermediate and deep layers of the homolateral superior colliculus. The strong projections from the ipsi- and contralateral nucleus praepositus hypoglossus most probably contributes vestibular information. Further inputs in descending order of intensity are from the substantia nigra, the contralateral paralemniscal tegmental area, the putamen, the ventral reticular formation in its lateral portions, the medial cerebellar nucleus and the dorsal reticular formation. Efferent projections of the paralemniscal tegmental area reach the putamen bilaterally, the nucleus accumbens and other parts of the basal ganglia, the pretectal area, the substantia nigra, the intermediate and deep layers of the superior colliculus bilaterally and the tegmental area ventral to it. Connections to the dorsal part of the periaqueductal grey, the cuneiform nucleus and the parabrachial region are important in the context of vocal control, whereas projections to the medial portion of the contralateral facial nucleus may interfere with the control of pinna movement. The findings suggest that the paralemniscal tegmental area is involved in audio-motor control of vocalization and pinna movements in bats; connectional and functional similarities and disparities to tegmental regions described in other mammals are discussed.

Afferent Pathways↗
PubMed1995

Molecular cloning and characterization of the rfc gene of Pseudomonas aeruginosa (serotype O5).

Previous work from our laboratory has shown that cosmid clone pFV100, containing a 26 kb insert, is able to restore O-antigen synthesis in serotype O5 rough mutants of Pseudomonas aeruginosa. Mobilization of pFV100 into two P. aeruginosa semi-rough (SR) mutants, AK14O1 and rd7513, resulted in O-antigen expression, indicating that pFV100 may contain an O-polymerase (rfc) gene. pFV.TK6, a subclone of pFV100 that contains a 5.6 kb chromosomal insert, was able to complement O-antigen expression in these SR mutants. Mutagenesis of pFV.TK6 using Tn1000 exposed a 1.5 kb region that was essential for complementing O-antigen expression in AK14O1. A 2.0 kb XhoI-HindIII fragment, containing this region, was cloned into vector pUCP26 and the resulting plasmid called pFV.TK8. In Southern analysis of the 20 P. aeruginosa serotypes using a probe generated from the 1.5 kb XhoI fragment of pFV.TK8, the rfc probe hybridized to a common fragment of the cross-reactive O2-O5-O16-O18-O20 serogroup, suggesting that these serotypes may share a common O-polymerase gene. In functional studies of the rfc gene, the PAO1 (serotype O5) chromosomal rfc was mutated using a gene-replacement strategy. These knockout mutants expressed the SR lipopolysaccharide (LPS) phenotype, which indicated that they were no longer producing a functional O-polymerase enzyme. Nucleotide sequence analysis of the insert DNA of pFV.TK8 revealed one open reading frame (ORF), designated ORF48.9, which could code for a 48.9 kDa protein. In comparisons of the P. aeruginosa rfc nucleotide and amino acid sequences with DNA and protein databases, no significant homology was found. However, the deduced structure of the P. aeruginosa Rfc protein indicated that it is very hydrophobic and contains 11 putative membrane-spanning domains. Therefore, the predicted structure is similar to that of other reported Rfc proteins. Furthermore, comparison of the amino acid composition and codon usage of the P. aeruginosa Rfc with other Rfc proteins revealed significant similarity between them.

Amino Acid Sequence↗
PubMed1994

Anatomy and projection patterns of the superior olivary complex in the Mexican free-tailed bat, Tadarida brasiliensis mexicana.

The superior olivary complex (SOC) is the first station in the ascending auditory pathway that receives binaural projections. Two of the principal nuclei, the lateral superior olive (LSO) and the medial superior olive (MSO), are major sources of ascending projections to the inferior colliculus. Whereas almost all mammals have an LSO, it has traditionally been thought that only animals that hear low frequencies have an MSO. Recent reports, however, suggest that the medial part of the SOC in bats is highly variable and that at least some bats have a well-developed MSO. Thus, the main goal of this study was to evaluate the cytoarchitecture and connections of the principal superior olivary nuclei of the Mexican free-tailed bat, with specific attention directed at the MSO. Cell and fiber stained material revealed that the LSO and the medial nucleus of the trapezoid body (MNTB) are similar to those described for other mammals. There are two medial nuclei we refer to as dorsomedial periolivary nucleus (DMPO) and MSO. Tracer experiments exhibited that the DMPO receives bilateral projections from the cochlear nucleus, and additional projections from the ipsilateral MNTB. The DMPO sends a strong projection to the ipsilateral inferior colliculus. Positive staining for acetylcholinesterase indicates that the DMPO is a part of the olivocochlear system, as it is in other animals. The MSO in the free-tailed bat meets many of the criteria that traditionally define this nucleus. These include the presence of bipolar and multipolar principal cells, bilateral innervation from the cochlear nucleus, a strong projection from the ipsilateral MNTB, and the absence of cholinergic cells. The major difference from traditional MSO features is that it projects bilaterally to the inferior colliculus. Approximately 30% of its cells provide collateral projections to the colliculi on both sides. Functional implications of the MSO for the free-tailed bat are considered in the Discussion.

Acetylcholinesterase↗