Search PubMed⌕ Search

Biomedical subjects

C Baumann

Publications and source records attributed to C Baumann.

At least 73 records · Page 4Linked to original sources
PubMed1992

[Ewald Hering's opponent colors. History of an idea].

Ewald Hering (1834-1918) was one of the founders of modern visual science. Among his contributions, his color concept gave rise to mostly fruitless controversies, because it appeared to be incompatible with the trivariance of vision theory put forward by Young and Helmholtz. It is now clear that the two color concepts can be reconciled with one another. Hering's theory is based upon an analysis of visual perception. Experience indicates that a conscious subject needs four unique colors in order to characterize perception: blue, yellow, red and green. Usually, two of these hues, but never more, constitute a color sensation, e.g., orange contains red and yellow while blue and green are the components of turquoise. The central idea in Hering's concept was that red and green are opposite hues because they are never elicited simultaneously by a color stimulus; the same is true for blue and yellow. Hering also postulated that the perception of opponent colors is mediated by opponent processes in certain elements of the nervous system, i.e., that there are neurons that respond in a qualitatively different way to spectral stimuli of different frequencies. Today we know that, in fact, the majority of neurons in the retina and the visual pathway is capable of opponent-type responses as anticipated by Hering. It was, however, a long way until his concept was understood and finally accepted by the science community. Among those who helped to acknowledge it were the German physiologist von Kries, the Austrian physicist Schrödinger, the Finnish neurophysiologist Svaetichin, and the American psychophysicists Hurvich and Jameson. In 1906, the German Ophthalmological Society honored Ewald Hering by awarding him the Albrecht von Graefe Medal.

Color Perception↗
PubMed1991

[Primary and secondary neonatal negative coagulase staphylococcus infections].

As a rule, coagulase-negative staphylococcal infections in the neonate is an acquired iatrogenic infection. It usually occurs in premature infants with an in-dwelling catheter. Clinical and laboratory criteria are used to differentiate contaminated samplings from true infection. the frequency of methicillin-resistant strains justifies the use of vancomycin combined with an aminoglycoside and, in the first days, with rifampicin, all drugs administered in doses calculated for the post-conception age. This treatment is also administered in mother-to-foetus infections caused by CNS.

Anti-Bacterial Agents↗
PubMed1990

[Cystic fibrosis: a gene at the end of the road].

The authors first give an account of the work undertaken jointly by two Canadian and one American groups, which lead to the cloning and identification of the cystic fibrosis gene. To achieve this aim, it was necessary to clone a large region amounting to 500 kb, using chromosome walking and jumping. The gene was located from a cross-hybridization signal with two probes from the cloned region and bovine cDNA. The CF gene is made of 24 exons giving a messenger of 6,500 nucleotides and a protein of about 1,500 aminoacids. The protein structure has been deduced from its composition in aminoacids. However, the localization of the protein in the cell and its true function remain an open question. At the same time workers from those groups identified the prevalent mutation in CF. These outstanding achievements will help unravelling the physiopathology of the disease. They increase the possibilities of prevention, but it is fanciful to think that they can lead to its eradication.

Chromosome Mapping↗
PubMed1990

Effect of luminance and contrast on stereoscopic acuity.

The threshold of binocular depth perception was measured in 11 healthy volunteers. A three-rod arrangement was employed in which both the luminance of the rods and that of the adapting field could be adjusted independently. This allowed fixing the contrast when the effect of luminance was studied or fixing the luminance when the effect of contrast was investigated. The observation distance was 400 mm. Thresholds were expressed as angular disparities and were based on 75% correct responses. Points of subjective equality were also determined. Lowest thresholds (2.85 +/- 0.67 s of arc) were found for a moderate contrast of 0.5 whereas low (0.05) and high (0.95) contrast both produced significantly higher thresholds (luminance 250 cd/m2). Altering the field luminance (50, 250, 1600 cd/m2) under constant contrast conditions (0.95) did not measurably influence stereoscopic acuity.

Adult↗
PubMed1990

Effect of intracellularly applied sodium ions on the dark voltage of isolated retinal rods.

Isolated retinal rods of the frog consisting of the outer segment and the ellipsoid were patch-clamped and recorded in the whole-cell mode. The recording pipettes were filled with solutions of different composition in order to alter the cytoplasmic content of sodium, phosphate, and calcium ions, and guanine nucleotides. When a simple medium with potassium as the principal cation was used, the dark voltage slowly approached more negative values. This tendency of spontaneous hyperpolarization was reduced significantly when cGMP or GTP were present in the pipette medium. Sodium ions, on the other hand, clearly increased the speed of hyperpolarization. In the presence of sodium (20 mM), the stabilizing effect of GTP did not occur and that of cGMP was clearly diminished. Phosphate (20 mM) neutralized the sodium effect. High calcium levels (100 microM) did not measurably influence the time course of hyperpolarization. We conclude that the normal cytoplasmic sodium level in rods does not exceed 10 mM and that higher internal sodium concentrations interfere with the sodium-calcium exchange mechanism.

Animals↗
PubMed1989

Effect of guanine nucleotides on the dark voltage of single frog rods.

Single frog rods consisting of the outer segment and the ellipsoid were investigated by the whole-cell patch-clamp technique. When the recording pipette was filled with a simple intracellular medium containing potassium as the principal cation, a slow increase in dark voltage (hyperpolarization) associated with a decay of the photoresponses was observed. The hyperpolarization started at a dark voltage of -27 +/- 8 mV, followed an exponential course, and leveled out at -52 +/- 6 mV. The time constant was proportional to the access resistance of the preparations. With a pipette medium containing a 0.5 or 1.0 microM cGMP, the initial dark voltage was shifted to more positive values and the tendency of hyperpolarization was clearly attenuated. Similar results were obtained with 1 mM GTP. The effects of GDP and of ATP were less significant. In experiments with 1 mM GTP plus 1 mM ATP, the dark voltage behaved as in experiments with only GTP. The stabilizing action of GTP was amplified by EGTA so that with 1 mM GTP plus 1 mM free EGTA the dark voltage was stable at a level of -15 mV. It is concluded that the preparations lose intracellular components such as cGMP and GTP by diffusion into the recording pipette and that the losses are prevented or reduced when the pipette medium contains these nucleotides in nearly physiological concentrations. For the internal transmitter cGMP, the results suggest that its free concentration does not exceed 1 microM.

Adenosine Triphosphate↗
PubMed1986

ATP-dependent acidification and tonoplast hyperpolarization in isolated vacuoles from green suspension cells of Chenopodium rubrum L.

The tonoplast of isolated vacuoles from photoautotrophic suspension cells of Chenopodium rubrum L. was studied by means of the patch-clamp technique. In a symmetrical K(+) concentration of 46 mM, similar to in vivo conditions, the tonoplast displayed a membrane potential near zero and a linear current-voltage relationship with a mean slope of 1.0 S/m(2). ATP at 2 mM hyperpolarized the tonoplast (vacuole positive) by 15-20 mV and, in a parallel experiment, acidified the vacuole (outside pH 7.0) to pH 5.0, as monitored by accumulation of acridine orange. Analysis of the voltage-clamp current indicates a 2-fold, ATP-dependent increase of the membrane capacitance, from 4 to 8 mF/m(2), and an ATP-independent, unidentified ion channel having a mean opening time of about 5 msec and a conductivity of 0.5-1.0 pS.

Journal Article↗
PubMed1984

Studies on visual transduction in the retinal rods of the frog.

In recent theories of visual transduction, an active form of rhodopsin plays a decisive role. If metarhodopsin II is considered to be a likely candidate for this role, its properties and reactions are of interest. A scheme describes how the various metarhodopsins react with each other. In the electrophysiological experiments, the dark currents and the photocurrents generated by the plasma membrane of the outer segments are analyzed. While the dark currents are computed from voltage gradients and the interstitial resistance in the receptor layer, the photocurrents are directly from single cells under voltage-clamp conditions.

Animals↗
PubMed1983

Mode of origin of large extracellular photovoltages from the retinal rods of the frog.

Arrays of extracellular microelectrodes were advanced into the receptor layer of isolated frog retinae to measure interstitial voltage and resistance. In addition, current was locally injected through one of the micro-electrodes and spatial profiles of local resistance were recorded. A large increase of local resistance in the proximal half of the receptor layer was frequently associated with the occurrence of large extracellular voltages arising from rods. The large responses presumably occur at sites where the micropipette tip makes tight contact with membrane process of the rod inner segment and a quasi-intracellular mode of recording results.

Animals↗
PubMed1982

[Serum angiotensin converting enzyme activity in sarcoidosis. A review of seventy cases].

The serum angiotensin converting enzyme (ACE) activity was assayed in seventy untreated patients with sarcoïdosis. Results were considered abnormal if they exceeded 34,5 U/ml. (SEM + 250). Increased ACE activity was found in 55,7% of the patients. Most of these patients had either Stage II or disseminated disease. Significant decreases in ACE activity always occurred during remission, whether spontaneous or induced by corticosteroids. In most patients with persistant roentgenologic features ACE activity was still high six months after onset. No correlations were found between serum ACE activities and lymphocytosis in bronchial washing samples. We conclude that, while serum ACE activity assays are not of significant diagnostic utility in patients with sarcoidosis, they are helpful for monitoring the course of the disease.

Adult↗