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M Kuehn

Publications and source records attributed to M Kuehn.

At least 19 recordsLinked to original sources
PubMed2005

Olivocochlear activity and temporary threshold shift-susceptibility in humans.

STUDY OBJECTIVES: Animal studies (guinea pig, cat, chinchilla) have shown that activity of the medial olivocochlear efferents can exert noise-protective effects on the cochlea. It is not yet known whether such effects are also existent in humans. Olivocochlear activity can be estimated indirectly by contralateral suppression (CS) of otoacoustic emissions (OAE). MATERIAL AND METHODS: We measured Input/Output functions of distortion products of OAE (DPOAE), with and without contralateral acoustic stimulation by white noise, in 94 normal hearing young male subjects. Seven stimuli with L2 between 20 and 60 dB SPL and L1 = 39 dB + 0.4 L2 ("scissor paradigm") were used at f2 = 2, 3, 4, 5, and 6 kHz. The measurement was repeated 2 weeks later. In 83 subjects of the same group, pure tone audiometry was registered before and 6 minutes after shooting exercises to evaluate individual susceptibility to develop a temporary threshold shift (TTS). RESULTS: Test-retest repeatability of CS was generally good. CS averaged 0.98 dB SPL (SD 1.19 dB, median 0.56 dB). As expected, CS was greatest at low stimulus levels (median 1.06 dB at L2 = 20 dB, as compared with 0.33 dB at L2 = 60 dB). The smallest average CS was found at 4 kHz, and the greatest CS appeared at 2 kHz. A TTS occurred in 7 of 83 (8.5%) subjects. Statistical analysis did not reveal any correlation between the amount of CS and individual TTS susceptibility. CONCLUSIONS AND OUTLOOK: 1) Measurement of CS of DPOAE using an extensive measurement paradigm revealed good test-retest repeatability, confirming the reliability of this audiologic tool. 2) CS of DPOAE does not predict individual susceptibility to mild TTS induced by impulse noise in humans. Possible explanations for the missing association are discussed. Future perspectives include longitudinal studies to further elucidate the association between medial olivocochlear bundle-activity and permanent threshold shift in humans. The goal is to develop a diagnostic tool for the prediction of individual noise vulnerability in humans, thereby preventing noise-induced hearing loss.

Acoustic Impedance Tests↗
PubMed2005

Architecture of a nascent Sphingomonas sp. biofilm under varied hydrodynamic conditions.

The architecture of a Sphingomonas biofilm was studied during early phases of its formation, using strain L138, a gfp-tagged derivative of Sphingomonas sp. strain LB126, as a model organism and flow cells and confocal laser scanning microscopy as experimental tools. Spatial and temporal distribution of cells and exopolymer secretions (EPS) within the biofilm, development of microcolonies under flow conditions representing varied Reynolds numbers, and changes in diffusion length with reference to EPS production were studied by sequential sacrificing of biofilms grown in multichannel flow cells and by time-lapse confocal imaging. The area of biofilm in terms of microscopic images required to ensure representative sampling varied by an order of magnitude when area of cell coverage (2 x 10(5) microm(2)) or microcolony size (1 x 10(6) microm(2)) was the biofilm parameter under investigation. Hence, it is necessary to establish the inherent variability of any biofilm metric one is attempting to quantify. Sphingomonas sp. strain L138 biofilm architecture consisted of microcolonies and extensive water channels. Biomass and EPS distribution were maximal at 8 to 9 mum above the substratum, with a high void fraction near the substratum. Time-lapse confocal imaging and digital image analysis showed that growth of the microcolonies was not uniform: adjacently located colonies registered significant growth or no growth at all. Microcolonies in the biofilm had the ability to move across the attachment surface as a unit, irrespective of fluid flow direction, indicating that movement of microcolonies is an inherent property of the biofilm. Width of water channels decreased as EPS production increased, resulting in increased diffusion distances in the biofilm. Changing hydrodynamic conditions (Reynolds numbers of 0.07, 52, and 87) had no discernible influence on the characteristics of microcolonies (size, shape, or orientation with respect to flow) during the first 24 h of biofilm development. Inherent factors appear to have overriding influence, vis-a-vis environmental factors, on early stages of microcolony development under these laminar flow conditions.

Biofilms↗
PubMed2003

Radiotherapy with 16 Gy may fail to eradicate testicular intraepithelial neoplasia: preliminary communication of a dose-reduction trial of the German Testicular Cancer Study Group.

Low-dose radiotherapy to the testis is effective in eradicating testicular intraepithelial neoplasia (TIN, carcinoma in situ of the testis) at the risk of androgenic deficiency. The present trial was designed to define the lowest dose effective to control TIN assuming a dose-response relation of radiation-induced endocrinological damage. Patients with TIN in a solitary testicle or with bilateral TIN were treated with 18 Gy (14 patients) and 16 Gy (26 patients) (5 x 2 Gy per week). Biopsies to ascertain clearance of TIN were performed after 6 and 24 months. The median time of follow-up is 20.5 months. There were three adverse events. In one patient, relapse of TIN along with microinvasive seminoma was observed 2 years after 16 Gy irradiation. In two other patients, persistent spermatogonia were observed with the 16 and 18 Gy regimen after 6 and 24 months, respectively. All other post-treatment biopsies showed the Sertoli cell-only pattern. These results confirm that TIN is a radiosensitive lesion efficiently controlled in most cases with doses below 20 Gy. However, sporadic failures may occur. A dose of 16 Gy is probably unsafe and should no longer be used. Future investigations should not only focus on total dosage of irradiation but also on fractionation schedules.

Adult↗
PubMed2003

Biopharmaceutical characterization of some synthetic purine drugs.

Hydrophilic-lipophilic properties (water solubility, n-octanol/water partition coefficient, transport across membranes) of some mercaptopurines (6-MP, 6-TG, AZA and a new AZA derivative--metazathioprine (MAZA) were determined. MAZA is the most lipophilic compound due to low aqueous solubility and high n-octanol/water partition coefficient. The fluxes from the donor medium into the membrane and from the membrane into the acceptor medium are highest for MAZA as well. The partition coefficients of the other purines decrease in the order: AZA > 6-TG > 6-MP.

Absorption↗
PubMed2001

Time-resolved study of biofilm architecture and transport processes using experimental and simulation techniques: the role of EPS.

Cellular material and extracellular polymeric substances are the basic structural elements in biofilm systems. The structure and role of EPS for biofilm development and metabolic processes have not been precisely determined and, therefore, have not yet been included as a necessary element in modelling and simulation studies. This is due to the difficulty of experimentally detecting the extracellular polymeric substances in situ and differentiating them from cellular material on the one hand, and to the subsequent uncertainty about appropriate models--e.g. rigid hindrances, porous microstructure or visco-elastic structure--on the other hand. In this work, we report on the use of confocal laser scanning microscopy to monitor the development of a monoculture biofilm of Sphingomonas sp. grown in a flow cell. The bacterial strain was genetically labelled resulting in strong constitutive expression of the green fluorescent protein. The development of extracellular polymeric substances was followed by binding of the lectin concavalin A to cell exopolysaccharides. The growth of the resulting strain was digitally recorded by automated confocal laser scanning microscopy. In addition, local velocity profiles of fluorescent carboxylate-modified microspheres were observed on pathlines throughout the biofilm. The CLSM image stacks were used as direct input for the explicit modelling and three-dimensional numerical simulation of flow fields and solute transport processes based on the conservation laws of continuum mechanics. At present, a strongly simplifying EPS-model is applied for numerical simulations. The EPSs are preliminarily assumed to behave like a rigid and dense hindrance with diffusive-reactive solute transport.

Biofilms↗
PubMed1999

Foreign travel.

Explore the source record for details and available documents.

Journal Article↗
PubMed1998

Nutrient intake and growth of infants with phenylketonuria undergoing therapy.

BACKGROUND: Because of reports of poor growth, a study was conducted for 6 months in 35 infants with classic phenylketonuria diagnosed during the neonatal period who were fed Phenex-1 Amino Acid Modified Medical Food With Iron (Ross Products Division, Columbus, OH, U.S.A.).as their primary protein source. METHODS: Diet diaries and anthropometric measures were obtained monthly as part of a larger study in which nutrition status was evaluated. RESULTS: In 6-month-old infants, mean percentiles for crown-heel length (59.14+/-4.31 SEM), head circumference (63.88+/-4.50) and weight (71.51+/-4.25) were normal. Mean (+/- SEM) daily intake of medical food was 79+/-4 g; protein and energy intakes were 17.3+/-0.6 g and 2772+/-75.6 kJ (660+/-18 kcal). Mean daily phenylalanine and tyrosine intakes per kilogram of body weight were 40+/-1 mg and 219+/-9 mg. Intakes of protein, energy, and tyrosine were positively correlated with crown-heel length, head circumference, and weight at 3 months of study. Overall plasma phenylalanine and tyrosine concentrations during the 6-month study were 297+/-41 micromol/l and 58+/-5 micromol/l, respectively. Neither plasma phenylalanine nor tyrosine concentration was correlated with growth. CONCLUSION: Phenex-1 supports normal growth when fed in adequate amounts. These data support those of the Medical Research Council Working Party on Phenylketonuria for 3 g/kg per day of amino acids from medical food.

Body Height↗
PubMed1998

Automated confocal laser scanning microscopy and semiautomated image processing for analysis of biofilms.

The purpose of this study was to develop and apply a quantitative optical method suitable for routine measurements of biofilm structures under in situ conditions. A computer program was designed to perform automated investigations of biofilms by using image acquisition and image analysis techniques. To obtain a representative profile of a growing biofilm, a nondestructive procedure was created to study and quantify undisturbed microbial populations within the physical environment of a glass flow cell. Key components of the computer-controlled processing described in this paper are the on-line collection of confocal two-dimensional (2D) cross-sectional images from a preset 3D domain of interest followed by the off-line analysis of these 2D images. With the quantitative extraction of information contained in each image, a three-dimensional reconstruction of the principal biological events can be achieved. The program is convenient to handle and was generated to determine biovolumes and thus facilitate the examination of dynamic processes within biofilms. In the present study, Pseudomonas fluorescens or a green fluorescent protein-expressing Escherichia coli strain, EC12, was inoculated into glass flow cells and the respective monoculture biofilms were analyzed in three dimensions. In this paper we describe a method for the routine measurements of biofilms by using automated image acquisition and semiautomated image analysis.

Automation↗
PubMed1997

Selenocysteine tRNA[Ser]Sec levels and selenium-dependent glutathione peroxidase activity in mouse embryonic stem cells heterozygous for a targeted mutation in the tRNA[Ser]Sec gene.

To investigate the effect of a reduced level of selenocysteine (Sec) tRNA[Ser]Sec in selenoprotein biosynthesis, two mouse embryonic stem (ES) cell lines heterozygous for the corresponding gene were generated by homologous recombination of the host genome with targeting vectors encoding a deleted or a disrupted tRNA[Ser]Sec gene. The presence of a single functional gene in ES cells afforded us an opportunity to determine directly in the cell line the effect of reduced gene dosage on (1) the levels of the Sec tRNA[Ser]Sec population, (2) the distributions of the isoacceptors within the Sec tRNA population, and (3) selenoprotein biosynthesis. We therefore determined the amounts and distributions of the two major tRNA[Ser]Sec isoacceptors, designated mcm5U and mcm5Um, within the Sec tRNA population and determined the activity of the anti-oxidant, selenium-containing glutathione peroxidase (GPx) in the heterozygotes and in wild type cells grown in media with and without added selenium. The level of the Sec tRNA[Ser]Sec population in the heterozygotes was approximately 60% of that of wild type cells grown in media under normal conditions, while the ratio of the mcmU isoacceptor in wild type vs mutant cells was approximately 2:1 and of the mcmUm isoacceptor approximately 1:1. In the presence of media supplemented with selenium, the Sec tRNA[Ser]Sec population increased about 20% in wild type cells and virtually not all in heterozygous cells, and the level of the Sec tRNA[Ser]Sec population was, therefore, approximately 50% of that of wild type cells. GPx activity was indistinguishable among these cell lines in either selenium-supplemented or unsupplemented media, indicating that the resultant changes in tRNA[Ser]Sec levels did not have a measurable effect on GPx biosynthesis.

Animals↗
PubMed1997

The expression pattern of nodal and lefty in the mouse mutant Ft suggests a function in the establishment of handedness.

We have investigated the expression of left/right (L/R) asymmetry markers, nodal and lefty, in the situs inversus mouse mutant Fused toes (Ft). Both genes exhibited bilateral expression in the lateral plate mesoderm (LPM) at developmental stages whereas in wildtype embryos these genes were found to be expressed exclusively in the left LPM. Inspection of tail location and primitive heart tube looping, structures known to be handed in their orientation, documented a random orientation of these structures. Crossing of the Ft mutation into a different genetic background resulted in a strong reduction of this random orientation. Although the major fraction of these individuals still displayed nodal and lefty on both sides of the LPM, expression was almost always found to be weaker in the right LPM. These results suggest that the establishment of asymmetry is independent of nodal or lefty signals. However, handed asymmetry, which means consistent L/R differences, such as the dextral looping of the primitive heart tube or the right-oriented tail, is directed by differences in the L/R expression pattern of these two genes.

Animals↗
PubMed1997

Color vision tests for early detection of antiepileptic drug toxicity.

A previous suggestion that antiepileptic drugs may induce color vision deficiencies prompted us to examine whether color vision deficiencies may occur at lower drug serum concentrations than those associated with symptoms of neurotoxicity. Eighty patients presenting with epilepsy received monotherapies of valproic acid, phenytoin, or carbamazepine; 18 patients did not receive antiepileptic drug therapy. Color vision was tested by the Farnsworth-Munsell 100-hue test, spectral sensitivity, and the newly developed tritan screening plates. Patients treated with phenytoin or carbamazepine developed blue-yellow color vision deficiencies. In contrast, patients exposed to valproic acid or receiving no drug treatment showed normal color vision. There was a significant correlation (p < 0.0001) between signs of neurotoxicity induced by phenytoin or carbamazepine and blue-yellow color vision deficiencies. In contrast, we found no correlation between these signs of neurotoxicity and the drug serum concentrations (p = 0.0637). Color vision testing in epileptic patients treated with phenytoin or carbamazepine appears to be a sensitive method for early detection and monitoring of clinical neurotoxicity.

Adolescent↗
PubMed1995

A molecular pathway determining left-right asymmetry in chick embryogenesis.

While significant progress has been made in understanding the molecular events underlying the early specification of the antero-posterior and dorso-ventral axes, little information is available regarding the cellular or molecular basis for left-right (LR) differences in animal morphogenesis. We describe the expression patterns of three genes involved in LR determination in chick embryos: activin receptor IIa, Sonic hedgehog (Shh), and cNR-1 (related to the mouse gene nodal). These genes are expressed asymmetrically during and after gastrulation and regulate the expression of one another in a sequential pathway. Moreover, manipulation of the sidedness of either activin protein or Shh expression alters heart situs. Together, these observations identify a cascade of molecular asymmetry in that determines morphological LR asymmetry in the chick embryo.

Activins↗
PubMed1994

Congenital diaphragmatic hernia: the hidden morbidity.

It is often thought that survivors of congenital diaphragmatic hernia (CDH) have an isolated problem related to lung hypoplasia, and little data exist regarding the extrapulmonary problems of high-risk CDH patients who do survive. In 1990, the authors began a multidisciplinary follow-up clinic for CDH patients. Members of the program include representatives from the departments of surgery, pulmonary medicine, development, nursing, and nutrition. Since this program began, the authors have followed up on 33 infants who survived after treatment of high-risk CDH, ie, those who were symptomatic within 6 hours of birth. Twenty patients were treated with extracorporeal membrane oxygenation (ECMO). Neurological problems were common in these patients: seven children (21%) required hearing aids, and seven others had abnormal results with brain-stem auditory evoked response (BAER) testing. Extraaxial fluid collections or enlarged ventricles were present on head computed tomography scans of 10 children, and four children had clinical seizure activity. Fifteen patients had developmental delays, which improved rapidly once the children began to thrive. Six patients required eyeglasses or had strabismus, and one patient is congenitally blind. There were a variety of problems related to growth and nutrition, with six patients needing fundoplications, and 13 patients below the fifth percentile for weight. Of 10 patients with patch repairs, two had recurrent hernias. Six others required surgery for bowel obstruction. Eleven patients had pectus excavatum, usually mild, and four had mild to moderate degrees of scoliosis. There were undescended testicles in five boys, vesicoureteral reflux in two patients, and kidney stones in two patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalography↗
PubMed1993

A novel secretion apparatus for the assembly of adhesive bacterial pili.

The biogenesis of most types of bacterial pili requires two specialized proteins: a chaperone that caps the pilus subunits in the periplasm, and an outer membrane usher that receives the subunits and serves as an assembly platform. This secretion and assembly machinery is proposed to be a novel export apparatus found widely in Gram-negative pathogens.

Bacterial Adhesion↗
PubMed1992

Gene-centromere linkage mapping by PCR analysis of individual oocytes.

We describe a general method of determining the recombination fraction between a polymorphic locus and the centromere in any species where single oocytes can be obtained. After removal of the first polar body, each oocyte is analyzed by PCR. The frequency of oocytes heterozygous at the polymorphic locus is used to estimate the recombination fraction. We estimate a recombination fraction of 0.15 between the mouse major histocompatibility complex (H-2) and the centromere of chromosome 17.

Animals↗