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Biomedical subjects

W Reichelt

Publications and source records attributed to W Reichelt.

At least 55 records · Page 3Linked to original sources
PubMed1991

Development of the rabbit retina. IV. Tissue tensility and elasticity in dependence on topographic specializations.

A method is introduced for the quantification of specific compliance and the elasticity of small pieces of living retinal tissue. These pieces are fixed at their margins by means of tissue glue, and loaded with a small iron spherule the bending force of which can be gradually enhanced by the action of an electromagnet. Retinal bending caused by such calibrated forces is measured by a horizontal light microscope, and used for estimations of specific compliance and elasticity of the tissue. Three different particular regions of the rabbit retina--periphery, visual streak, and (prospective) medullary rays--were tested at several post-natal developmental stages. From very early stages on (day 2 p.p.) up to adulthood the peripheral retina was found to be significantly more tensile than the two other central regions. This can be shown to depend greatly on the thickness of the tissue which is lower in the retinal periphery. During early post-natal development, all retinal regions except the (prospective) medullary rays become thinner. The tensility of the tissue increases, with the exception of the medullary rays which reduce their compliance strongly. In the adult retina, however, the tensility of all retinal regions is reduced as compared with the neonatal tissue. This seems to be caused by a constant gradual increase of the elasticity of the retina during development which, in turn, may be caused by several developmental parameters, e.g. the formation of synapses, the outgrowth of glial side branches ensheathing neighbouring neuronal cells, or a reduction in extracellular clefts. It is proposed that these differences in tensility between different retinal regions, may be the cause for differential retinal expansion driven by the intraocular pressure. Thus, simple mechanical features of the tissue may contribute to the formation of important topographic specializations of the retina, e.g. the visual streak as the site of highest visual acuity.

Aging↗
PubMed1990

Rabbit retinal Müller cells in cell culture show gap and tight junctions which they do not express in situ.

Retinae of early postnatal rabbits were enzymatically dissociated and explanted in a culture system. The prospective myelinated region was discarded in order to avoid the presence of astrocytic or mesenchymal cells. After about 14 days in vitro (DIV), outgrowing glial (Müller) cells formed what light optically appeared to be confluent monolayers but by electron microscopy was shown to consist of flat epithelioid cells which overlapped considerably by extension of cytoplasmic tongues. Applying the freeze-fracture technique, apposed membranes of these cells were demonstrated to express infrequently but consistently both gap and tight junctions. This kind of junctions has never been observed on the membrane of rabbit Müller cells in situ. In comparison with Müller cell membranes in situ, the density of intramembrane particles was considerably reduced. Orthogonal arrays of particles which are characteristic elements of Müller cells in situ were not detected. Our results suggest that in homogeneous cell culture, Müller cells form some kind of epithelium-like specialized intercellular junctions. This situation resembles that of closely related glial cell types which form homogeneous layers in situ as e.g. retinal pigment epithelium cells expressing tight junctions, and marginal astrocytes being coupled by extensive gap junctions.

Animals↗
PubMed1990

Orthogonal arrays of intramembranous particles in the Müller cell and astrocyte endfoot membrane of rabbit retina. Postnatal development and adulthood.

The freeze-fracture technique was applied to the retina of early postnatal and adult rabbits to investigate the distribution and density of orthogonal arrays of intramembrane particles (OAP) within the vitread endfoot membranes. In adult animals, two distinct types of endfoot membranes were observed within the central myelinated retina but not in the retinal periphery. One type of endfoot membranes contained low density of individual 'background' particles, and a more or less stripe-like pattern of OAP; this type was found only within the myelinated centre and is concluded to represent membranes of retinal astrocytes. The other type of endfoot membranes was rather tightly packed with individual 'background' particles, and contained OAP which formed rows only at the margins of footplates; this kind of membrane was found throughout the whole retina, and represents Müller cell endfeet. The density of OAP in both types of endfoot membranes was higher within the central myelinated retina than in the Müller cell endfeet of the retinal periphery. In early postnatal retinae, a discrimination between the two types of endfeet was impossible. At the day of birth, only very few OAP were observed, and the majority of footplates were free of OAP. Within the next 10 days, both density and size of OAP were found to increase but fail to reach adult levels. Quantitative data are presented with the hope of providing a basis for future correlation with functional maturation of rabbit retinal glia.

Animals↗
PubMed1990

Does isoflurane lead to a higher incidence of myocardial infarction and perioperative death than enflurane in coronary artery surgery? A clinical study of 1178 patients.

To examine if the choice of volatile agents influences cardiac outcome in coronary artery surgery, 1178 patients undergoing elective coronary artery bypass grafting without additional operations received enflurane (608) or isoflurane (570) as their primary anesthetics. The inspired concentration of volatile agent (administered with 50% nitrous oxide) was adjusted depending on the level of blood pressure at the discretion of the anesthesiologist. In addition to the volatile agent assigned, each patient received small doses of fentanyl at induction and before sternotomy (total 0.006-0.008 mg/kg). The groups did not differ in preoperative and surgical characteristics except for a more frequent history of renal dysfunction in patients given isoflurane. The rates of postoperative myocardial infarction, administration of positive inotropic agents at the time of weaning from cardiopulmonary bypass, and in-hospital deaths in the enflurane and isoflurane groups were 1.8% and 4.0% (P less than 0.05), 4.9% and 8.1% (P less than 0.05%), and 0.3% and 2.1% (P less than 0.01), respectively. Although the mechanism of the adverse effects of isoflurane could not be clarified in this study, these results demonstrate that the use of isoflurane could be inappropriate in patients undergoing coronary artery bypass grafting.

Aged↗
PubMed1989

The structure of rabbit retinal Müller (glial) cells is adapted to the surrounding retinal layers.

Radial glial (Müller) cells of the rabbit retina were studied by various techniques including Golgi impregnation, scanning electron microscopy, horseradish peroxidase application, and staining of enzymatically isolated cells. This combination of methods produced detailed information on the specialized morphology of the Müller cells within the different topographical regions of the retina, and of the Müller cell processes within the various retinal layers. As a general rule, the retinal periphery contains short thick Müller cells with big endfeet, whereas the thick central retina is occupied by long slender cells with small endfeet. Independent of their location within the retina, Müller cell processes were found to be adapted to the structure of the surrounding retinal layers. Within the outer and inner nuclear layers, Müller cell processes (and somata) extend thin cytoplasmic "bubbles" ensheathing the neuronal somata, as do the "velate" astrocytes in the brain. In the plexiform layers, Müller cells extend many fine side branches between the neuropil, comparable to the protoplasmic astrocytes of the brain. In the thick myelinated nerve fibre layer of the central retina the Müller cell processes are rather smooth, similar to those of fibrous astrocytes. It is concluded that the neuronal microenvironment determines the morphology of a given glial process, or even of a part of a glial process running through a specialized neuronal compartment.

Animals↗
PubMed1989

Potassium as a signal for both proliferation and differentiation of rabbit retinal (Müller) glia growing in cell culture.

Retinal glial (Müller) cells were grown from explants of early postnatal rabbit retinae. The resulting monolayers of flat cells were exposed to control media (containing 5.85 mM K+), and to media with enhanced K+ concentrations (10 and 20 mM) or arginine-vasopressin (AVP, 20 micrograms/ml) or epithelial growth factor (EGF, 10 ng/ml). Autoradiographically, protein synthesis was quantified as L-[3H]-lysine incorporation, and DNA synthesis as [3H]-thymidine incorporation. Furthermore, the activity of Na+,K(+)-ATPase was measured radiochemically. Short exposure to either moderately enhanced K+ concentrations (10 mM) or to AVP, stimulated L-[3H]-lysine incorporation into the cells. Long-lasting exposure to either high K+ concentrations (20 mM) or to EGF stimulated [3H]-uptake. The Na+,K(+)-ATPase activity of cell cultures increased with increasing K+ concentration of the media. It is suggested that release of K+ by active neuronal compartments stimulates local protein synthesis of glial cells, resulting in the formation of glial sheaths with active K+ uptake capacity. Strong K+ release may even induce glial proliferation.

Animals↗
PubMed1989

[Bronchial obstruction caused by incorrect positioning of a temperature probe].

In a case of open heart surgery a temperature probe was inserted orally to monitor the temperature in the esophagus. After insertion, the arterial oxygen tension decreased. Fiberoptic examination of the bronchial system revealed an obstruction in the right main bronchus by the temperature probe. After removal of the probe normal oxygenation was restored.

Adult↗
PubMed1989

The course of axons within the postnatal rabbit retina.

The course of optic axons within the postnatal rabbit retina was studied by scanning electron microscopy (SEM) of the nerve fibre layer exposed by HCl and collagenase treatment, and by freeze-fracture electron microscopy. In the first days after birth, axon bundles were found to run along a rather tortuous way in between the developing Müller cell endfeet. Later on and in adults, the axon bundles show a more straight course. Single axons running into a bundle show a very irregular course before they assume their path in parallel to the other fibres of the bundle. These results support the idea that the course of growing axons is somehow determined by free "channels" in between the endfeet of glial cells.

Animals↗
PubMed1988

Vecuronium induced bradycardia following induction of anaesthesia with etomidate or thiopentone, with or without fentanyl.

To define the role of vecuronium in the occurrence of bradyarrhythmia, haemodynamic changes after the induction of anaesthesia were studied in 96 patients undergoing coronary artery bypass grafting. Patients were assigned to one of six groups according to different combinations of induction agents (etomidate 0.3 mg kg-1 or thiopentone 3 mg kg-1, with fentanyl 0.003 mg kg-1; etomidate 0.4-0.5 mg kg-1 or thiopentone 4-6 mg kg-1, without fentanyl) and neuromuscular blocking drugs (vecuronium 0.112 mg kg-1, pancuronium 0.112 mg kg-1 or suxamethonium 1 mg kg-1). Anaesthesia was maintained with enflurane and nitrous oxide in oxygen. After initial diverse changes, heart rate decreased in all groups. Thirty minutes after intubation, the reduction of heart rate showed statistically significant differences between the different combinations of drugs: fentanyl-etomidate-vecuronium (group I) (the largest reduction) greater than etomidate-vecuronium (II) = fentanyl-thiopentone-vecuronium (IV) greater than thiopentone-vecuronium (V) = fentanyl-thiopentone-suxamethonium (VI) = fentanyl-etomidate-pancuronium (III). Five patients in group I, two in group IV and one each in groups II and V had a heart rate slower than 45 beat min-1, whereas a similar value was never seen in groups III and VI. These results indicate that vecuronium has a bradycardic effect. This effect is more pronounced in association with etomidate than in association with thiopentone, and is augmented by the addition of fentanyl.

Adult↗
PubMed1987

High Na+ affinity of the Na+,K+ pump in isolated rabbit retinal Müller (glial) cells.

Rabbit retinal Müller (glial) cells were isolated by means of papain and mechanical dissociation. In a special perfusion chamber, the cells were penetrated with a recording microelectrode. Membrane potential changes were recorded in response to extracellular application of both high-K+ solutions and of ouabain, and that during perfusion with normal and Na+-free solutions, respectively. In other Müller cell preparations, Na+,K+-adenosine triphosphatase (ATPase) activity was measured using a radiochemical method, and its Na+ dependence was determined. All results strongly suggest that the Müller cell's Na+,K+ pump can be activated in the presence of extremely low amounts of Na+. This provides additional evidence for significant differences between the glial and the neuronal enzyme.

Animals↗
PubMed1986

Postnatal development of radial glial (Müller) cells of the rabbit retina.

Radial glial (Müller) cells were isolated from postnatal rabbit retinae by enzymatic dissociation in papain-containing solution, air-dried, and submitted to Pappenheim's panoptic stain. Morphometric data of these cells were evaluated by light microscopy. During postnatal development, the cells become substantially thicker and shorter, their nuclei lose the rod shape and move more toward scleral layers, and the nucleus-cytoplasm volume relation decreases. Whereas the cell volume increases from birth on, substantial outgrowth of fine side branches within the plexiform layers fails to occur before electrical activity is established there, i.e. after postnatal day 9. A model is proposed relating the growth of sheath-bearing glial processes to local protein synthesis stimulated by external K+ accumulation due to neuronal activity. Early myelinated nerve fibers are suggested to bear mechanical resistance to growing radial glial processes thus causing a splitting of these processes when they enter developing nerve fiber layers.

Animals↗
PubMed1986

Asystole and bradycardia in adult patients after a single dose of suxamethonium.

Two cases of cardiac asystole and one case of severe bradycardia were seen following a single injection of suxamethonium in a series of 46 adult patients in whom anaesthesia was induced with fentanyl and etomidate. It is suggested that the vagomimetic effects of fentanyl and, possibly also of etomidate, may contribute to the enhancement of the bradycardic effects of suxamethonium.

Anesthesia, General↗
PubMed1985

Na+,K+-activated adenosine triphosphatase of isolated Müller cells from the rabbit retina shows a K+ dependence similar to that of brain astrocytes.

Müller (glial) cells from the rabbit retina were isolated by means of papain and mechanical dissociation. Their Na+,K+-adenosine triphosphatase (ATPase) activity was measured using a radiochemical method, and its K+ dependence was determined. In contrast to that of photoreceptors (data from the literature), the Na+,K+-ATPase of Müller cells could be shown to increase its activity greatly when the [K+] was enhanced up to 10 mM. The functional implications of this behaviour for the K+ clearance in the retina are discussed.

Animals↗