Biomedical subjects

A Reichenbach

Publications and source records attributed to A Reichenbach.

At least 91 records · Page 5Linked to original sources

PubMed1995

Expression of glial fibrillary acidic protein (GFAP), glutamine synthetase (GS), and Bcl-2 protooncogene protein by Müller (glial) cells in retinal light damage of rats.

In retinal light damage, degeneration of photoreceptors may cause alterations of glial (Müller) cells. We performed immunocytochemical studies on Müller cells isolated from retinae of rats exposed to enhanced illumination for 24 months, a procedure which leads to complete loss of photoreceptor cells. One group of rats was fed daily with Ginkgo biloba extract (EGb 761, an established free radical-scavenger) during the last 8 months of life when the remaining photoreceptors (about 50%) die. We found that (1) Müller cells respond to photoreceptor damage by increased expression of glial fibrillary acidic protein, (2) Müller cells reduce expression of glutamine synthetase when the major glutamate-releasing neurons are lost, and (3) the application of exogenous free radical scavengers prevents the expression by Müller cells of the protooncogene protein Bcl-2, a molecule assumed to activate endogenous free radical-scavenging activities.

Animals↗

PubMed1995

Effects of enhanced extracellular ammonia concentration on cultured mammalian retinal glial (Müller) cells.

Müller (glial) cells of the neonatal rabbit retina were cultured as confluent monolayers and exposed to enhanced concentrations of ammonia (0.25, 0.5, 1, 3, 7, and 10 mM) in medium for various periods (30 min to 10 d). This caused, in a time- and dose-dependent manner, similar changes in the Müller cells as had previously been described in cultured astrocytes. The most conspicuous events were 1) an increasing size of cell nuclei, 2) an accumulation of phagocytotic vacuoles, and 3) a rearrangement of intermediate filaments. 4) A considerable number of cells died when higher ammonia concentrations were applied for more than 1 h. Simultaneous application of dibutyryl-cyclic adenosine monophosphate (dBcAMP) prevented almost completely both the increase in cell nucleus size and the changes of intermediate filaments, but only partly the early cell death of a subpopulation of cells, and the accumulation of phagocytotic vacuoles. Further changes evoked by enhanced ammonia concentration were 5) an accumulation of lipofuscin-like material ("fatty degeneration") revealed by lipophilic stain, 6) reduced immunoreactivity for cathepsin D, and increased immunoreactivity for 7) glial fibrillary acidic protein, 8) glutamine synthetase, and 9) bcl-2 protooncogene protein. These findings are discussed in respect to the possible underlying pathophysiological mechanisms.

Ammonia↗

PubMed1995

Hepatic retinopathy: morphological features of retinal glial (Müller) cells accompanying hepatic failure.

More than 80 years ago, Alzheimer described changes in the brains of patients who had suffered hepatic failure. Astrocytes are primarily affected; their nuclei become swollen, their intermediate filament protein composition is altered and their cytoplasm becomes vacuolated. Cells with these features are called Alzheimer type II astrocytes and these changes have been attributed to the toxic effects of elevated ammonia levels. The present study investigates whether the dominant glia of another part of the central nervous system, the Müller cells of the retina, undergo similar changes. Retinae of patients who had died with symptoms of hepatic failure were processed for histology, histochemistry, and immunocytochemistry. Cell nuclei were measured from brain astrocytes (insula cortex), Müller cells, and retinal bipolar neurons. Hepatic failure resulted in the enlargement of nuclei in astrocytes and Müller cells, and the enhanced expression in Müller cells of glial fibrillary acidic protein, cathepsin D, and the beta-subunit of prolyl 4-hydroxylase (glial-p55). In some retinae, signs of gliosis were also observed. We conclude that increased levels of serum ammonia resulting from hepatic insufficiency cause changes in Müller cells that are similar to those seen in brain astrocytes. We term this condition hepatic retinopathy.

Adult↗

PubMed1995

Alterations of Müller (glial) cells in dystrophic retinae of RCS rats.

We have carried out a light microscopical study of Müller cells in the retinae of rats with inherited retinal dystrophy (Royal College of Surgeons rats). Isolated retinae of both control and Royal College of Surgeons rats were exposed to a Procion Yellow solution which is taken up selectively into Müller cells. The shape of the cells was then studied by confocal microscopy. Enzymatically isolated Müller cells were studied immunocytochemically with antibodies against glial fibrillary acidic protein, cathepsin D, beta-amyloid precursor protein, bcl-2 protooncogene product, and glutamine synthetase. Müller cells from RCS retinae were shorter than those from control retinae, and showed a coarse hypertrophy of their distal (sclerad) processes. In Müller cells isolated from the retinae of Royal College of Surgeon's rats, the expression of glial fibrillary acidic protein, cathepsin D, beta-amyloid precursor protein and bcl-2 protooncogene product was increased, and the expression of glutamine synthetase was reduced. Obviously, loss of neighbouring neurons leads to major alterations of both the shape and metabolism of Müller cells. The expression of enzymes that serve functional glio-neuronal interactions, such as glutamine synthetase, seems to be down-regulated, whereas proteins involved in cell reconstruction (cathepsin D), cell repair (possibly beta-amyloid precursor protein), and protection against apoptotic cell death (bcl-2 protooncogene product), are up-regulated, together with the 'pathological marker' glial fibrillary acidic protein.

Amyloid beta-Protein Precursor↗

PubMed1995

Visualization of Müller (retinal glial) cells by bulk filling with procion yellow.

A method is presented that allows for an easy and reliable demonstration of retinal glial (Müller) cell morphology. When a 3% solution of the fluorescent dye Procion Yellow (reactive yellow, Sigma) is placed on isolated living retinae for 2 hrs, many Müller cells take up the dye. In paraffin sections, the cells can be observed by confocal microscopy in great detail. As the cells are filled throughout their length, the method has advantages over most immunocytochemical methods which label only parts of the cells. The method was applied to retinae of frogs, rats, guinea pigs, and rabbits. The vitread trunks of the cells differed in diameter. Those of frogs and rats were thin (less than 1 to 2 microns diameter) whereas those of guinea pigs and rabbits were thicker (2 to 5 microns). In all species studied the following rule was found. In thick central regions of the retina, Müller cells were long with slender trunks whereas in the thin retinal periphery, the Müller cells had thick short trunks. There was an inverse relationship between length and diameter of Müller cell trunks. Mammalian Müller cells were densely packed and had rather cylindrical endfeet. In the frog retina, Müller cells were more sparsely distributed, and the endfeet formed wide, flat funnels. It is concluded that the higher metabolic rate of mammalian retinae requires more densely packed Müller cells than occur in the amphibian retina.

Animals↗

PubMed1995

Distribution of Bergmann glial somata and processes: implications for function.

We have used immunocytochemistry for glial fibrillary adidic protein and glutamine synthetase to selectively label Bergmann glia in the adult rat cerebellum. From measurements of radial, tangential and en face sections we provide new data on the distribution and disposition of these glial cells. Specifically, Bergmann glia were found to have a mean areal packing density of 8,269 somata/mm2, their radial processes are packed at a mean density of 39,000/mm2, and their endfeet at the pial surface have a mean density of 19,973/mm2. Each Bergmann glial cell ist "responsible" for the equivalent of a column of cerebellar cortex having a base of 11 microns x 11 microns, a height of 170 microns, and a volume of 20,559 microns3. There are 8.1 Bergmann glia for each Purkinje cell, and each glial cell ensheaths between 2,142 and 6,358 Purkinje cell synapses. We use these data to offer insights on the roles of Bergmann glia during development and in the adult brain.

Animals↗

PubMed1995

Surface complexity of human neocortical astrocytic cells: changes with development, aging, and dementia.

Astrocytes from area 11 of the human neocortex were Golgi-impregnated. The material was taken from four human subjects, (1) a neonate without obvious CNS damage, (2) a middle-aged adult serving as control, (3) an aged individual without apparent mental disturbances, and (4) an aged patient with dementia. Camera-lucida drawings of 7 to 26 astrocytic cells from each donor were digitized into a personal computer, and analyzed for their fractal dimension D which is an objective and quantitative measure of the complexity of the cell's borders. Both radial and multipolar astrocytes from neonatal cortex showed a comparatively low fractal dimension (D approximately 1.39), that is, low surface complexity. Adult ("control") astrocytes were characterized by a high fractal dimension (D = 1.57), corresponding to their large surface complexity. Astrocytes from the aged subject showed a somewhat smaller fractal dimension (D = 1.51) and, thus, surface complexity; this difference was however not highly significant. In contrast, astrocytes from the subject with dementia showed a significant reduction in surface complexity (D = 1.47). Parallel changes were observed in the brain volume compartment occupied by the process of individual astrocytes. These data suggest that formation and maintenance of astrocytic processes and/or side branches correlate positively with the degree of information processing within their neuronal environment.

Adult↗

PubMed1994

Development of the rabbit retina. V. The question of 'columnar units'.

A qualitative and quantitative description of the columnar units in the mammalian retina, and a discussion of their ontogeny and putative functions is given. Columnar arrangements of cells exist in the developing retina which can be observed by means of scanning electron microscopy. In the adult retina, each Müller cell ensheaths a columnar group of neuronal cells. Counting the number of cells in radial H/E stained sections at various developmental stages reveals a constant ratio of neuronal cells per Müller cell, independent of the developmental stage (after postnatal day 9), and independent of the retinal topography. Such groups of cells always consist of one Müller cell, 11 rod photoreceptor cells, about 2 bipolar cells, and 1 to 2 amacrine cells. Retinal ganglion cells, cone photoreceptor cells, and horizontal cells are more sparsely distributed in the retina than these units; since they are known to arise earlier in the ontogenesis than other cell types they are considered to exist independently of the columnar units. It is suggested that the units arise by migration of groups of preneurons along a common Müller (precursor) cell; these preneurons and the corresponding Müller cell may be clonally related. In the adult retina, such columns might constitute metabolic and functional units.

Animals↗

PubMed1994

Immunocytochemical demonstration of astrocytes and microglia in the whale brain.

Whale brains have attracted the attention of neuroscientists but there are only sparse studies on whale glial cells. Here we report on immunolabeling of astrocytes by antibodies to glial fibrillary acidic protein (GFAP) or protein S-100 beta (both by the streptavidin/biotin technique), and labeling of microglial cells by Griffonia simplicifolia agglutinin (GSA I-B4, coupled to horseradish peroxidase), in the neocortex of a harbour porpoise Phocoena phocoena L. Many subpial and perivascular astrocytes were stained; they differed greatly in thickness and length of their processes. Subpial astrocytes were coarse with a few stout stem processes, whereas perivascular astrocytes deeper in the brain had many long and slender processes. Additionally, some long radial astrocytes were observed. Microglia were labeled throughout the brain, and showed similar features as 'resting' (ramified) microglia in the brain of other mammals.

Animals↗

PubMed1994

K(+)-, hypoosmolarity-, and NH4(+)-induced taurine release from cultured rabbit Müller cells: role of Na+ and Cl- ions and relation to cell volume changes.

The release of preloaded radiolabeled taurine (TAU) from cultured rabbit Müller cells [14-21 days in vitro (DIV)] was measured before and after treatment with the following stimuli: 1) isoosmotic 65 mM KCl; 2) a medium made hypoosmotic by uncompensated lowering of Na+ by 40-100 mM; and 3) NH4Cl ranging from 0.25 to 5 mM. The same stimuli were tested for their effect on the cell volume by the 3-O-methyl-D-glucose (OMG) uptake method of Kletzien et al. (Anal Biochem 68:537, 1975). Hypoosmotic media and 65 mM KCl stimulated TAU release, and the release was well correlated with the increase of cell volume. The stimulatory effect of 65 mM KCl was abolished by isotonic removal of Cl- or Na+, and omission of either ion markedly enhanced the basal release of TAU. The results are roughly consistent with the characteristics of the swelling-induced TAU release reported for cultured astrocytes and neurons of various CNS regions, and also for freshly isolated, nondissociated retina. Taken together, the results are indicative of a significant role of TAU release from Müller cells, in the osmosensory response of the retina. Ammonium chloride stimulated TAU release in a dose-dependent manner, a significant stimulation being already observed at 0.5 mM, a concentration that is frequently measured in brain during acute hyperammonemia. The effect of NH4Cl was strictly chloride dependent at 0.5-2 mM, but partly Cl- independent at 5 mM. The Kletzien's method did not appear to be well suited for measuring cell volume in the presence of ammonium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Na+ channels of Müller (glial) cells isolated from retinae of various mammalian species including man.

Within the last few years, the expression of voltage-dependent, TTX-sensitive Na+ channels has been demonstrated in several types of neuroglial cells such as astrocytes and Schwann cells. Recently, we reported the occurrence of such Na+ currents in retinal Müller (glial) cells from dog and cat. This paper deals with the description of the properties of Na+ currents in Müller cells isolated from retinae of several mammalian species, as well as from human retinae. These Na+ currents were eliminated by TTX (1 microM), and by exposure to sodium-free extracellular solution; typically, they were demonstrable only after blocking most of the K+ conductance by Ba2+ (1 mM). Voltage-dependent activation and inactivation characteristics and time constants of the Na+ currents were similar to those of currents carried by neuronal Na+ channels. The estimated number of sodium channels per cell was low (about 1,500 channels per 7,500 microns 2), and the K+ conductance exceeded the peak Na+ conductance by an average factor of 5. Thus, the cells were incapable of generating action-potential-like responses under current clamp. Modelling estimations show that triggering of glial Na+ currents under physiological conditions, if any, can at best occur by emhaptic transmission at perinodal sites of optic axons. It is speculated that glial Na+ channels might be involved in neuroglial signalling events.

Animals↗

PubMed1994

Immunocytochemical demonstration of glycogen phosphorylase in Müller (glial) cells of the mammalian retina.

Glycogen phosphorylase (GP) was immunocytochemically detected in Müller cells of the rabbit and rat retina using a monoclonal antibody raised against bovine brain GP. Immunofluorescence and immunoenzymatic procedure were applied on isolated, Müller cells and sections of paraformaldehyde-fixed, paraffin-embedded retinas. All methods used revealed positive immunostaining. GP immunoreactivity was most intense in the Müller cell endfeet and the pericarya, corresponding to the nerve fibre layer and the inner nuclear layer in the retina. The presence of GP in Müller cells stresses the important role of these glial cells in the energy metabolism of the mammalian retina.

Animals↗

PubMed1994

Morphology of horseradish peroxidase (HRP)-injected glial cells in the myenteric plexus of the guinea-pig.

Glial cells of the myenteric plexus from guinea pig small intestine were intracellularly filled with horseradish peroxidase (HRP), and histochemically stained. Camera lucida-like drawings of twenty cells were morphologically and morphometrically analyzed. The cells have very small ellipsoid somata (8.5 +/- 0.7 microns equivalent diameter, i.e., about 330 micron3 volume), and send up to 20 thin and short processes (less than 26 to about 110 microns in length). The morphology of the cells appears to depend on their location within the plexus. Glial cells located within the ganglia are similar to CNS protoplasmic astrocytes; they are star-shaped, and their very short processes are irregularly branched. In contrast, glial cells within the interganglionic fiber tracts resemble CNS fibrous astrocytes. They extend longer processes that are parallel to the fiber tracts, and show less tendency to branch. We propose that the morphology of enteric glia is determined by the structure of the microenvironment. Both cell types form several flat endfeet at a basal lamina either surrounding blood vessels or at the ganglionic border. Furthermore, the occurrence of "holes" in the glial cell processes suggests that particular neuronal cell processes may be enwrapped in a specific manner. Fractal analysis of camera lucida-like drawings of the cells showed that the cells have a highly complex surface structure, comparable to that of protoplasmic astrocytes in the brain. These tiny cells may possess a membrane surface area of approximately 2000 micron2, almost 90% of which are contributed by the cell processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Three distinct types of voltage-dependent K+ channels are expressed by Müller (glial) cells of the rabbit retina.

There is ample evidence that retinal radial glial (Müller) cells play a crucial role in retinal ion homeostasis. Nevertheless, data on the particular types of ion channels mediating this function are very rare and incomplete; this holds especially for mammalian Müller cells. Thus, the whole-cell variation of the patch-clamp technique was used to study voltage-dependent currents in Müller cells from adult rabbit retinae. The membrane of Müller cells was almost exclusively permeable to K+ ions, as no significant currents could be evoked in K(+)-free internal and external solutions, external Ba2+ (1 mM) reversibly blocked most membrane currents, and external Cs+ ions (5 mM) blocked all inward currents. All cells expressed inwardly rectifying channels that showed inactivation at strong hyperpolarizing voltages (> or = -120 mV), and the conductance of which varied with the square root of extracellular K+ concentration ([K+]e). Most cells responded to depolarizing voltages (> or = -30 mV) with slowly activating outward currents through delayed rectifier channels. These currents were reversibly blocked by external application of 4-aminopyridine (4-AP, 0.5 mM) or tetraethylammonium (TEA, > 20 mM). Additionally, almost all cells showed rapidly inactivating currents in response to depolarizing (> or = -60 mV) voltage steps. The currents were blocked by Ba2+ (1 mM), and their amplitude increased with the [K+]e. Obviously, these currents belonged to the A-type family of K+ channels. Some of the observed types of K+ channels may contribute to retinal K+ clearance but at least some of them may also be involved in regulation of proliferative activity of the cells.

4-Aminopyridine↗

PubMed1994

Quantification of tight junction complexity by means of fractal analysis.

The concept of fractal geometry provides an elegant tool for the quantitative and objective structural description of various objects, the fractal analysis. Fractal analysis quantifies the structural complexity of objects by a characteristic singular value, the fractal dimension (FD). It can be estimated, e.g. by the box-counting method and provides a highly integrated measure in the range 1 < FD < 2 for curves extending within a plane. In this study, fractal analysis is used for the first time to evaluate the complexity of the tight junction network between adjoining cells. Bovine brain endothelial cells were cultured under various experimental conditions and the tight junctions were drawn to scale as visualized by the freeze fracture technique. These drawings were analyzed by fractal analysis, and by two other methods commonly used in this field, viz. the strand counting (SC) and complexity index (CI) methods. In contrast to the latter methods, the FD shows no directional preference and therefore no assumptions on the dynamic properties of the network's complexity are required. Thus, FD is demonstrated to provide the most sensitive, reliable and complete measure of tight junction complexity. In combination with SC and CI, additional information can be achieved concerning the directionality of the altered arrangement of tight junctional strands. Our analysis allows for the following conclusions. (1) Defined experimental influences can modify the complexity of tight junctions that are formed between endothelial cells in vitro, and (2) these structural modifications of the tight junctions are mainly due to an altered strand branching pattern.

Animals↗

PubMed1994

Effect of in vivo application of the ginkgo biloba extract EGb 761 (Rökan) on the susceptibility of mammalian retinal cells to proteolytic enzymes.

Lesions, inflammations, or degenerative insults of the human retina are accompanied by the release of proteolytic enzymes. Their deleterious effect may be enhanced by the release of free radicals. Ginkgo biloba extracts are known to exert protective influences against the action of free radicals, and this prompted us to ask whether the application of such extracts might protect retinal tissue against proteolytic damage. Eighteen adult rabbits were fed for 3 weeks (+/- 3 days) with 40 mg/kg of G. biloba extract (EGb 761) or a terpene-free fraction of this extract, dissolved in their drinking water. Twelve control rabbits received no G. biloba extract. The animals were then euthanatized and their retinae isolated. After appropriate enzymatic treatment, the tissue was dissociated and the number of isolated Müller cells counted as an indication of the strength of the proteolytic effects. There was a significant protective action of EGb 761: in an average control rabbit 5,200 cells per milligram retinal tissue were isolated; application of EGb 761 markedly reduced this number to 2,500 (terpene-free fraction; CP 205) or 3,050 (terpene-containing fraction). It is concluded that G. biloba extracts may have a significant therapeutic value in cases of retinal damage.

Animals↗

PubMed1994

A set of early-born neurons is distinctly labeled by several defined antibodies in the adult rabbit retina.

Retinal ganglion cells, cone photoreceptor cells, and horizontal cells arise earlier in ontogenesis than the other retinal cell types. Although during the first postnatal week of life much cell proliferation occurs in the rabbit retina, 3H-thymidine labeling shows that these particular neurons are already postmitotic in neonatal animals. We show here that, in the adult retina, these early-born neurons express antigens as neuron-specific enolase, HNK-1 epitope of N-CAM, and PGP 9.5 antigen, which are not expressed by the neurons later born. It is concluded that the mammalian retina contains two genotypically different sets of neuronal cells which can be distinguished by immunocytochemistry.

Aging↗

PubMed1993

Quantitative phylogenetic constancy of cerebellar Purkinje cell morphological complexity.

Golgi-stained material of cerebellar cortices from 17 species was examined by measuring the fractal dimensions of the borders of Purkinje cells, which is a quantitative, objective measure of morphological complexity. Nine species (from birds to man) were chosen for a comparison with ANOVA and no statistically significant differences were found in their fractal dimensions. In contrast, a wide range of differences was found in the membrane areas across species lines. The Sholl coefficient, a measure of branch formation and termination away from the soma, showed no consistent pattern for each cell. We interpret our results as indicating a constancy in morphological cellular complexity of Purkinje cells during late evolutionary time.

Analysis of Variance↗