Biomedical subjects

L Peichl

Publications and source records attributed to L Peichl.

At least 37 records · Page 2Linked to original sources

PubMed1990

Dye-induced 'photo-degeneration' and 'photo-permeabilization' of mammalian neurons in vivo.

Dyes are known to induce neuronal 'photo-degeneration' and 'photo-permeabilization' in fly photoreceptor cells in vivo. In the present study, we attempted to generalize this photodynamic damage to vertebrate neurons, using the rat retina, a brain part which is optically accessible in vivo. After intravitreal injection of the photosensitizing dye Rose Bengal (RB), irradiation of the retina of a living rat with a T-shaped microbeam was found to induce striking 'optograms' which could be observed on the excised retina. The T-shaped pattern which was to be seen in the translucent retina under transmitted light was attributed to neuronal degeneration of the neurons irradiated in the presence of RB, as attested by classical degenerative features such as a cytoplasmic darkening or a drastic swelling. The T-shaped pattern could also be observed on adding the dye Lucifer yellow to the extracellular space of the retina either in vitro or in vivo, showing that the cells irradiated in the presence of RB became permeable. These structural reactions were observed in the cells in the inner nuclear layer (INL) and ganglion cell layer (GCL), in the processes in both plexiform layers, and in the ganglion cell axons crossing this area, whereas the photoreceptors in the outer retina appeared to be undamaged. From these reactions, due to photo-degeneration and photo-permeabilization, it was possible to identify the photodynamic damage to the nervous system histologically at the macroscopic, cellular and ultrastructural levels. In view of its accuracy and reproducibility, the photo-lesion technique holds great potential as a tool for investigating various nervous systems.

Animals↗

PubMed1989

Alpha and delta ganglion cells in the rat retina.

In the rat retina a distinctive class of large ganglion cell was demonstrated by intracellular staining with Lucifer Yellow and with reduced silver staining. They are referred to as alpha cells because they resemble the alpha cells of other mammalian retinae. A second class, called delta cells, is also described. Both classes belong to the type I group defined by Perry (Proc. R. Soc. Lond. [Biol.] 204:363-375, '79). The dendritic trees of both classes stratify in either an inner or outer lamina of the inner plexiform layer which presumably corresponds to an on/off dichotomy in the response to light. Rat alpha cells constitute 2-4% of all ganglion cells, and their density, size, and detailed morphological appearance change with retinal location. Inner and outer stratifying alpha cells of the rat show significant differences compared to those of other mammals. In central retina (at the large cell density maximum) the densities and dendritic field sizes of inner and outer alpha cells are approximately equal. However, in peripheral retina outer alpha cells are up to three times more numerous and have dendritic field areas only one-third the size of those of the inner alpha cells. The maximal density is about 110 alpha cells/mm2; peripheral densities are about 30/mm2. The smallest central dendritic field diameters are 220 microns. Peripheral dendritic field diameters are 350-550 microns for outer and 570-790 microns for inner alpha cells. Each subpopulation is distributed in a regular mosaic, and the territorial arrangement of the dendritic fields provides a homogeneous coverage of the retina. The dendritic coverage is three- to 3.6-fold for each subpopulation, irrespective of their other quantitative differences. Eccentricity-dependent receptive field sizes of the alpha cells are predicted from the morphological data.

Animals↗

PubMed1989

Topography of cones and rods in the tree shrew retina.

The topographical distribution of cones and rods in the tree shrew retina was analysed quantitatively in whole-mounted retinae and horizontal semithin sections stained with cresyl violet or toluidine blue. The outer nuclear layer consists of a single layer of photoreceptor nuclei with the rod nuclei slightly displaced towards the outer plexiform layer. This facilitated quantification of the photoreceptor populations. The density of cones ranges from 12,000/mm2 in the peripheral retina to a maximum of 36,000/mm2 in the inferior retina. Unlike ganglion cell density, the density of cones does not peak in the temporal retina. Rod density, between 500/mm2 and 3,500/mm2, also peaks in the inferior retina, but not in the same region as cone density. Rods constitute from 1 to 14% of the photoreceptor population, depending on retinal location, and have a local minimum at the central area. Amongst the cones a regularly arrayed subpopulation of presumed blue-sensitive cones is distinguished by its special staining properties. These cones constitute between 4 and 10% of the cone population depending on retinal location. A second, irregularly spaced, subpopulation of possibly pathological cones is also described.

Animals↗

PubMed1989

Opsin- and S-antigen-like immunoreactions in photoreceptors of the tree shrew retina.

In the tree shrew retina individual rod and cone photoreceptors can be readily identified and quantified because their perikarya are arranged in a single layer. This retina is therefore an ideal system for testing the specificity of photoreceptor-directed antibodies. Here we describe the staining properties of polyclonal antibodies against (rhod)opsin and retinal S-antigen in the tree shrew retina. The (rhod)opsin antibody exclusively and completely labelled the rod population. The antibody against S-antigen also labelled all rods and, in addition, a regularly arrayed subpopulation of cones, which we argue to be the blue-sensitive cones. In the context of our findings, the labelling of pinealocytes with these antibodies is discussed.

Animals↗

PubMed1989

[Organization of the retina: structure/function relations and a species comparison of retinal ganglion cells].

The retina contains a range of ganglion cell types that differ in morphology and in their response to visual stimuli. They extract different image parameters and transmit them to the brain in independent parallel channels. One type, the alpha cells, shows a phasic response to light stimuli and covers a relatively large retinal area of about 1 degree to 3 degrees diameter. They are important for the detection of movement and global form, but not for high visual acuity. In a comparative study, alpha cells were found in all mammalian species investigated. They comprise only 1%-4% of all ganglion cells. However, with their large dendritic fields and regular soma spacing they provide complete coverage of the retina and contribute to image analysis at each retinal location. As alpha cells are a consistent component of mammalian retinae, they are most likely also a functional constituent of the human retina. The functional properties of different ganglion cell types have a bearing on the clinical diagnosis, because retinal damage (e.g., in glaucoma patients) may be specific to the cell type.

Animals↗

PubMed1988

Neurofibrillar long-range amacrine cells in mammalian retinae.

A distinct population of wide-field, unistratified amacrine cells are shown to be selectively stained by using neurofibrillar methods in rabbit and cat retinae. Their cell bodies may be located in the inner nuclear, inner plexiform or ganglion cell layers and they branch predominantly in stratum 2 of the inner plexiform layer. Characteristically, each cell has two or more long-range distal processes which extend for 2-3 mm beyond a more symmetrical, proximal dendritic field of 0.6-0.8 mm diameter. Although the neurofibrillar long-range amacrines account for less than 1 amacrine in 500, they achieve effective coverage of the retina by both the proximal and distal dendrites.

Animals↗

PubMed1988

A concept for detecting unexpected changes in the environment early.

A project was established under the auspices of the German Federal Ministry of Research and Technology with the task of developing a concept for the early recognition of signals for unexpected deleterious changes in the environment. Predictive assessments of products (e.g., chemicals) and technologies as regards their potential environmental impacts contain numerous sources of error and uncertainties. Therefore, appropriate observation systems are needed in order to detect unexpected developments in the environment and in human health. Long-term storage of samples (environmental specimen banking) is the third basic activity that must be undertaken within an early warning system. When monitoring the environment for unwanted changes, it is not sufficient to trace some individual agents, preselected for their well-known capacity to inflict harm. The following avenues of identifying symptoms of change in the environment were identified: development and deployment of "key indicators"; acquisition and correlative treatment of conventional monitoring data from different sources; and execution of concise studies in environmental problem areas. Key indicators are defined as scientific measurement and observation methods which respond to early stages of anthropogenically induced environmental changes and are capable of responding to a multitude of simultaneously present agents. A series of examples is discussed. Approaches concerning how the statistical evaluation of available sets of environment-related data could reveal unexpected developments are presented.

Biosensing Techniques↗

PubMed1988

Cholinergic amacrine cells of the rabbit retina contain glutamate decarboxylase and gamma-aminobutyrate immunoreactivity.

The transmitters acetylcholine and gamma-aminobutyrate (GABA) play critical roles in the formation of receptive-field properties of retinal ganglion cells. In rabbit retina, cholinergic amacrine and displaced amacrine cells were identified by immunohistochemical staining for the enzyme choline acetyltransferase and by their avid accumulation of the fluorescent dye 4',6-diamidino-2-phenylindole. Several GABA-immunoreactive and glutamate decarboxylase-immunoreactive cell types, including a prominent population of small, round amacrine and displaced amacrine cells, were also identified. Double-label experiments demonstrated that all amacrine and displaced amacrine cells that prominently accumulate 4',6-diamidino-2-phenylindole contain GABA and glutamate decarboxylase immunoreactivity. However, not all GABA-immunoreactive cells accumulate this dye. Quantitative analysis of the ganglion cell layer of whole mount preparations of the retina showed that choline acetyltransferase-immunoreactive cells and the majority of GABA-immunoreactive cells have a small, round shape and similar cell density profiles that parallel that of displaced amacrine cells. These studies establish that cholinergic cells are a major subpopulation of GABA-immunoreactive amacrine and displaced amacrine cells. The role these cells have in the formation of ganglion cell receptive-field properties may be parsimoniously explained by an excitatory postsynaptic action mediated by acetylcholine and an inhibitory presynaptic action mediated by GABA.

Acetylcholine↗

PubMed1988

Postnatal dendritic maturation of alpha and beta ganglion cells in cat retina.

Of the 3 anatomically defined classes of ganglion cell in adult cat retina, the alpha and beta cells are the most well documented, thus providing a basis of comparison for developing ganglion cells. Alpha and beta ganglion cells in cat retinae at various ages from birth (P0) to adult were intracellularly injected with Lucifer yellow. At all ages, both cell types strongly resembled their adult counterparts. However, transient developmental characteristics established their immaturity. These features included spiny protuberances and "rings" along the dendritic surface that were no longer detectable after 3 weeks of age. In a small proportion of both inner and outer stratifying alpha ganglion cells, there was aberrant dendritic arborization. However, by P5 there was no remaining evidence of this deviant stratification pattern and all alpha and beta cells displayed the adult pattern of unistratification (present among the majority of these cells from birth). For both alpha and beta cells, the area of greatest development was the retinal periphery. In this region alpha cell dendritic trees continued to grow until 3 weeks postnatally, when they approached the adult dendritic field size; around this time, the major period of beta cell dendritic expansion began. From birth to adulthood, the distance between alpha cell dendritic branching points increased, while the number of nodes and tips decreased with age. The temporal disparity between alpha and beta cell dendritic expansion suggests that postnatal dendritic development involves an active process of growth, rather than merely passive stretching.

Animals↗

PubMed1987

Dendritic maturation in cat retinal ganglion cells: a Lucifer yellow study.

The dendritic morphology of developing cat alpha- and beta-retinal ganglion cells was investigated by intracellular injection of Lucifer yellow. In both cell classes the basic pattern of adult morphology was present at birth. However, the presence of transient small spiny protrusions along the dendrites was characteristic of early postnatal cells. Many alpha-cells were further distinguished by a small degree of dendritic bi-stratification which disappeared within the first 5 postnatal days. Therefore during the period before the eyes opened (P7-P10) there was a considerable degree of modification and maturation in dendritic morphology in both classes of retinal ganglion cells. alpha- and beta-cells exhibited differing temporal patterns of dendritic growth, which argues against a 'passive-stretching' hypothesis that explains dendritic field enlargement solely as an effect of retinal areal growth.

Aging↗

PubMed1987

Alpha ganglion cells in the rabbit retina.

In the rabbit retina a distinctive morphological class of large ganglion cells was demonstrated by a combination of intracellular staining with Lucifer Yellow and the quantification of reduced silver-stained preparations. The class is called alpha because of the qualitative and quantitative resemblance to the alpha cells of the cat's retina. Rabbit alpha cells change their size with location on the retina. In the high ganglion cell density region of the visual streak, their somata are about 15 micron in diameter, and their dendritic fields have diameters as small as 180-220 micron. The largest alpha cells in the inferior periphery have soma diameters of 30 micron and dendritic field diameters of 960 micron. There is a considerable scatter of sizes at any retinal location. Alpha cell density changes from about 55/mm2 in the streak to about 3/mm2 in far periphery, and the cells make up 1-1.4% of the ganglion cell population. Dendritic trees stratify in either an inner or an outer sublamina of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Each of the inner and outer branching subtypes is distributed in a regular mosaic, and the dendritic trees cover the retina completely and economically. The possibility is discussed that the alpha cells are the brisk transient/Y cells of physiology.

Animals↗

PubMed1987

Alpha ganglion cells in mammalian retinae.

Retinae from species of six orders of mammals (table 1) were processed by an on-the-slide neurofibrillar staining method to establish whether alpha-type ganglion cells are generally present in placental mammals. Alpha cells of the domestic cat, where they were first defined as a type, are used as a standard of reference. Alpha cells were found in all the twenty species examined; characteristically they have the largest somata and large dendritic fields with a typical branching pattern. In keeping with the common morphology there are inner and outer stratifying subpopulations and therefore a presumptive 'on-centre' and 'off-centre' responsiveness to light. Depending on the species, alpha cells form between 1 and 4% of the ganglion-cell population and their dendritic fields cover the retina three to four times. The morphology of alpha ganglion cells, and many of their quantitative features, are conserved in mammals coming from different habitats and having a wide variety of behaviours. Because it is known different habitats and having a wide variety of behaviours. Because it is known from the cat that alpha ganglion cells have brisk-transient or Y receptive fields it is possible that all placental mammals possess this physiological system.

Animals↗

PubMed1986

Morphology of rabbit retinal ganglion cells projecting to the medial terminal nucleus of the accessory optic system.

Rabbit retinal ganglion cells were retrogradely labeled following injection of rhodamine-labeled microspheres into the medial terminal nucleus. The small fraction of rhodamine-labeled neurons reached their peak concentration within the visual streak and then decreased with increasing eccentricity until none were encountered in the far periphery. The same rabbits also received injections of the fluorescent tracer Fast Blue into the superior colliculus. No double-labeled neurons were observed, i.e., ganglion cells projecting to the medial terminal nucleus (MTN) had no axon collaterals to the superior colliculus. In fixed retinae rhodamine-labeled ganglion cells were intracellularly injected with the fluorescent dye Lucifer Yellow to reveal their full dendritic arborization. MTN-projecting cells had medium-sized to large somata with thin and frequently branched dendrites. The large dendritic trees had a distinct morphology and were predominantly unistratified in a narrow band that presumably corresponded to the electrophysiologically determined on-sublamina of the inner plexiform layer. Dendritic field sizes were inversely related to ganglion cell density, thus providing an eccentricity-independent, constant dendritic coverage factor. Approximately five to six dendritic fields from neighboring cells cover every point of the retina. Published reports claim that the physiological class of on-direction-selective ganglion cells provides the sole retinal input to the MTN in the rabbit. In this context morphological features of MTN-projecting cells and their presumed functional correlation with on-direction-selective ganglion cells are discussed.

Animals↗

PubMed1985

Dendritic plasticity in the early postnatal feline retina: quantitative characteristics and sensitive period.

Retinal lesions were made in kittens between 3 and 60 days postnatal age and in adult cats. After postlesion survival times ranging from 4 to 11 months the dendritic morphology of retinal ganglion cells was revealed by retrograde labeling with horseradish peroxidase or with neurofibrillar staining techniques. After retinal lesions on the third postnatal day changes of dendritic morphology were observed in retinal ganglion cells adjacent to regions of retrograde degeneration. Originating from eccentrically positioned somata the dendritic fields extended into the regions that were free of neighboring cells. The dendrites oriented toward the ganglion-cell-free region were elongated and thicker than normal. The density of dendrites per unit area was increased in this part of the dendritic trees. Lesions on the 20th, 38th, and 56th postnatal days elicited increasingly weaker changes of dendritic morphology. The sensitive period for the type of dendritic plasticity described ends between 40 and 60 days postnatally.

Animals↗

PubMed1985

Regenerative capacity of retinal axons in the cat, rabbit, and guinea pig.

Long-term signs of axonal regeneration were observed in the adult cat, rabbit, and guinea pig retina to follow mechanical or thermal lesions. The axons of surviving ganglion cells displayed signs of growth beginning at the border of the lesions: multiple bifurcations, changes of caliber, and unoriented random course of the fibers. Inspection of the fiber course and retrograde filling with horseradish peroxidase showed that these attempts of regeneration were not successful in terms of reconnection to the brain. None of these axonal changes occurred after early postnatal lesions. The capacity for long-survival regenerative processes after axotomy begins 20 to 50 days after birth in the developing cat retina.

Animals↗

PubMed1985

Influence of benzene on the phytoplankton and on Daphnia pulex in compartments of an experimental pond.

Benzene, with initial concentrations of 100 and 50 mg per liter, was dosed in duplicates into four compartments of a small pond. The decrease of chemical concentration in the water was exponential with a mean half-life of 4.7 +/- 0.9 days. Following benzene application, the phytoplankton density and diversity slightly increased relative to the controls. Both concentrations were lethal for the daphnids present. During 24-hr in vitro tests with Daphnia pulex (initial benzene concentrations less than 50 mg per liter), a direct correlation between mobility and decreasing chemical concentration was observed.

Animals↗

PubMed1984

Kainic acid induces sprouting of retinal neurons.

The neurotoxin kainic acid caused dose-dependent morphological changes in horizontal cells of the retinas of adult cats and rabbits. High concentrations of kainic acid killed the cells, but when exposed to sublethal doses they contracted their dendritic fields and sent sprouting processes into the inner retina. It appears that kainic acid can induce neuronal growth as well as degeneration and that the potential for morphological plasticity is still present in neurons of the adult mammalian retina.

Animals↗

PubMed1983

A spatial analysis of on- and off-ganglion cells in the cat retina.

Using reduced silver staining methods it was possible to stain all alpha-ganglion cells of the cat retina. The dendritic trees of alpha-cells are unistratified in either of two laminae within the inner plexiform layer. This stratification difference was shown physiologically to correspond to the on-off dichotomy. For all alpha-cells recorded, the dendritic field was covered by the corresponding receptive field centre. In addition the general shape of the receptive field centre corresponded to the shape of the dendritic field. The size of the dendritic tree was always smaller than the receptive field centre. The topographical distribution of on- and off-alpha cells could be studied. They were found to occur in about equal numbers. Both on- and off-alpha-cell perikarya form a regular lattice and both lattices are superimposed independently. The dendritic branches of neighbouring alpha-cells overlap and each retinal point is covered by the dendritic field of at least one on- and one off-alpha-cell. After horseradish peroxidase (HRP) injection into the lateral geniculate nucleus all beta-cells were labelled. In this way it is shown that about 55% of all ganglion cells are beta-cells. The mosaic of on- and off-beta-cells was studied from the HRP-labelled material. It is commonly assumed that beta-cells are associated with the resolution of fine detail in the cat visual system. The mosaic of beta-cells imposes some constraints and permits some predictions to be made with respect to the cat's visual discrimination.

Action Potentials↗