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Biomedical subjects

H J Wagner

Publications and source records attributed to H J Wagner.

At least 163 records · Page 9Linked to original sources
PubMed1987

Amacrine cells with neurotensin- and somatostatin-like immunoreactivities in three species of teleosts with different color vision.

Neurotensin- and somatostatin-like immunoreactivities were localized by pre-embedding techniques in retinal whole-mounts and radial sections of a monochromatic glass catfish (Kryptopterus bicirrhis), a dichromatic cichlid species (Aequidens pulcher), and the tetrachromatic roach (Rutilus rutilus). Both neuropeptides were observed in perikarya and processes of amacrine cells. For a precise identification of cell types, tangential and radial views were correlated with Golgi-impregnated material. The dendritic pattern defining the morphological subtype of amacrine cells was determined by the given neuropeptide or by the species-specific degrees of complexity of retinal structure and function. Neurotensin-like immunoreactivity was localized in amacrine cells of intermediate size, radial symmetry and dendrites with numerous varicosities; they were monostratified in sublayer 3 of the inner plexiform layer. This cell type was common to all three species. In the mono- and dichromatic retinas, a single type of amacrine cell with somatostatin-like immunoreactivity was found with radially oriented, varicose dendrites in sublayer 5. In the tetrachromatic roach retina, two somatostatin-positive amacrine cell types were found with very different patterns of ramification; furthermore, both of these types occurred in more than one sublayer. Possible functional implications for color vision of neuropeptide-specific amacrine cells with uniform morphology in all three species and those with a more varied morphology in the tetrachromatic roach are discussed.

Animals↗
PubMed1987

Retinal neurones of cyprinid fish: intracellular marking with horseradish peroxidase and correlative morphological analysis.

An isolated retinal preparation from the cyprinid fish, roach, is described, in which neurones have been labelled ionophoretically with horseradish peroxidase (HRP), and then processed in a variety of steps to provide anatomical information concerning their form, structural relationships and synaptic contacts. This includes the use of computer graphics for 3D visualisation of fine structural features and generation of views from various angles. The practical procedures that have been devised should be useful for efficient and quantitative correlation of electrophysiological and morphological properties of retinal neurones.

Animals↗
PubMed1986

Destruction of the preganglionic nerves by beta-bungarotoxin does not interfere with normal embryonic development of the rat adrenal medulla.

Using beta-bungarotoxin (beta-BTX) as a tool to eliminate the preganglionic cholinergic nerve supply to the embryonic rat adrenal gland, we have investigated whether or not these nerves affect the differentiation of embryonic chromaffin cells (pheochromoblasts). Rat fetuses received a single injection of 1 or 2 micrograms beta-BTX or an identical volume of saline at embryonic day (E) 17 and were taken for morphological and biochemical analyses at E 21. Administration of beta-BTX caused a 15 to 20% reduction in body weight, crown-rump-length and adrenal weight. Spinal cord development was reduced and acetylcholinesterase-positive cells in ventral and lateral columns were virtually absent in toxin-treated animals. In adrenal glands, a decrease of choline acetyltransferase activity to 13% of control levels and a concomitant decrease of ultrastructurally identifiable nerve fibers and axon terminals revealed that application of 2 micrograms beta-BTX effectively reduced the neuronal input to E 21 adrenal glands. Values for total adrenal catecholamines, relative amounts of adrenaline and noradrenaline, tyrosine hydroxylase and phenylethanolamine N-methyltransferase activities were unaltered. All ultrastructural features of pheochromoblasts (except the lack of synapse-like axon terminals) were inconspicuous. Corticosterone levels in adrenals and plasma were identical to controls. These data strongly suggest that normal embryonic development of adrenal chromaffin cells does not require an intact nerve supply.

Adrenal Medulla↗
PubMed1985

The cellular origin of an unusual type of S-potential: an intracellular horseradish peroxidase study in a cyprinid fish retina.

L2-type S-potentials are mainly blue/green-sensitive hyperpolarizing responses with a red-sensitive depolarizing component which is either weak or absent. They were first described in the retina of the roach, a cyprinid fish, by Djamgoz (1978, 1984) and Djamgoz & Ruddock (1978, 1979a). The cellular origin of these responses has been determined and characterized by intracellular recording, horseradish peroxidase staining, and light and electron microscopy. They were found to arise in horizontal cells with H2-like morphologies on average (Stell & Lightfoot, 1975). The dendrites of these cells contacted green- and blue-sensitive cone pedicles within which both lateral and central contacts were made at ribbon synapses. The laterally-positioned dendrites had incompletely formed spinules associated with them. A number of similarities between these units and the biphasic, chromaticity (Cb)-type S-potentials have been outlined and it is suggested that L2 units are essentially Cb-units with a weak depolarizing component. In turn, it is suggested that the depolarizing component is reduced as a consequence of the relatively dark-adapted states of the retinae. It is concluded that the negative feed-back pathway that subserves the generation of depolarizing (Cb-type) S-potentials is weak or absent in dark-adapted retinae and that spinules may be the site of this feed-back interaction.

Animals↗
PubMed1985

Relation of retinomotor responses and contractile proteins in vertebrate retinas.

Photoreceptors of many nonmammalian vertebrate species display pronounced light-dependent movements which are absent in mammalian species. In order to further analyze the molecular basis of receptor movements and of simultaneous migration of melanin granules in pigment epithelial processes, we investigated the distribution of actin, myosin and the actin-binding muscular proteins alpha-actinin and vinculin in the retina of various vertebrate species. The species investigated can be divided in two groups (i) those possessing retinomotor capacity (fish, frog, turtle, chick) and (ii) those in which retinomotor activities are negligible or absent (gecko, mouse, rat). Prominent bundles of actin filaments extending throughout the long axis of photoreceptor inner segments were only found in species possessing retinomotor capacity, while comparable actin filament bundles were absent or poorly developed in photoreceptors of species lacking significant retinomotor capacity. In all species examined, a well developed circumferential band of actin filaments was associated with the zonula adhaerens-like junctions between photoreceptors and Müller (glial) cells forming the external limiting membrane. This area was also identified as the exclusive site of myosin, alpha-actinin and vinculin (only in the chick, alpha-actinin-like immunoreactivity was also found along the photoreceptor actin filament bundles). Thus, the external limiting membrane may be important for both structural support and for providing a possible site of filament sliding for photoreceptor movements. In pigment epithelium actin, myosin, alpha-actinin and vinculin were concentrated circumferentially in the area of the terminal bar which has been previously shown to be contractile. In all species apical pigment-epithelial processes displayed actin-like fluorescence of varying intensities. Another site of actin-like staining were photoreceptor synaptic complexes which represent a well known site for synaptic plasticity. Immunoblotting studies on the avascular chick retina revealed polypeptide bands at Mr approximately 130 000, approximately 100 000, and 42 000 which were specific for vinculin, alpha-actinin and actin, respectively. A faint polypeptide band comigrating with thymus myosin heavy chain indicates myosin to be only a minor component of the retina (chick and fish).

Actins↗
PubMed1984

Light-dependent change of cone-horizontal cell interactions in carp retina.

Carp H2 horizontal cells were investigated at various stages of dark and light adaptation. Their state of adaptation was verified by evaluating in computer reconstructed serial sections the number of small, fingerlike protrusions originating from H1 processes. These so-called spinules are absent in the dark-adapted state and are reformed during light adaptation. Intracellular recordings showed that long-wave-induced depolarization thought to be mediated by sign-inverted feedback from H1 horizontal cells onto green-sensitive cones could not be demonstrated in completely dark-adapted specimens. This type of response only developed with increasing light adaptation. Following electrophysiological characterization, the cells were injected with horseradish peroxidase and identified light and electronmicroscopically. Our results show a good correlation between the number of spinules and the degree of electrophysiological feedback suggesting that the spinules may be the sites of the feedback synapses in teleost retinas. Several models of synaptic transmission from H1 terminals to cone pedicles are discussed.

Animals↗
PubMed1984

Double labelling of retinofugal projections in the cat: a study using anterograde transport of 3H-proline and horseradish peroxidase.

A new method is described for combining 3H-proline and horseradish peroxidase (HRP) as anterograde neuronal tracers. By this method the presence of both substances can be demonstrated in the same histological section. We developed this method to investigate the retinofugal projections from the two eyes in the cat. One eye was injected with 3H-proline the other with HRP. Cryostat sections of the brain were mounted on emulsion coated slides in the dark. Sections were first exposed to the emulsion for 2-3 weeks at -40 degrees C and developed for autoradiography. Only then they were reacted for HRP-activity with tetramethylbenzidine (TMB). Keeping to this sequence autoradiographic procedures could not abolish the HRP-reaction product and silver grains and TMB can be visualized on the same slide. The wellknown projection pattern in the lateral geniculate nuclei was confirmed as a control for the new method. In the superior colliculus and in the pretectum a clear overlap of retinal terminals from the two eyes could be demonstrated for the first time.

Afferent Pathways↗
PubMed1984

Action spectrum of photomechanical cone contraction in the catfish retina.

The action spectrum for the photomechanical contraction of catfish single cones was found to fit the absorbance spectrum of the visual pigment they contain (determined by microspectrophotometry). This indicates that cone contraction is brought about by a direct effect of light on the cones themselves and not, as is the case for the epithelial pigment, by an indirect effect via the rods.

Animals↗
PubMed1984

[Microsomal glucose 6-phosphate dehydrogenase in the rat testis--an testis--specific isoenzyme?].

Mammalian tissues contain cytosolic and microsomal glucose 6-phosphate dehydrogenase (G6PD). In the present study it was examined whether the microsomal G6PD in liver and testis of the rat are homologous. Kinetic parameters and immunological reactivity were estimated using rabbit antiserum against mice erythrocyte G6PD. Kinetic parameters allow to distinguish cytosolic and microsomal G6PD in rat liver but not in testis, whereas the immunological properties of the testis enzymes are different. The cytosolic G6PDs from liver and testis of the rat are identical enzymes having extremely similar properties to mice erythrocyte G6PD. The microsomal G6PD of both organs are not homologous enzymes. Testicular microsomal G6PD is likely to be an organ specific G6PD-isoenzyme.

Animals↗
PubMed1983

Endogenous control of spinule formation in horizontal cells of the teleost retina.

The process of horizontal cells invaginating teleost cone pedicles are studded with small finger-like projections which are present only in the light-adapted state. The aim of this study was to investigate whether the formation and degradation of these so-called spinules, which are thought to function as feed-back synapses onto the cones, is endogenously controlled. Three types of experiment were carried out involving fish entrained to a 12 h light/dark cycle: 1) The number of spinules was determined in goldfish at various times during exposure to either constant darkness (36 h) or constant light (57 h). 2) The time course of spinule formation and degradation in goldfish was investigated following exposure to light or darkness at various times during the light/dark cycle. 3) The time course of flash-induced spinule formation in tench following dark adaptation at noon was compared to that following dark adaptation at midnight. The results of these experiments show that spinule formation and degradation are partially under endogenous control but that they need light and full expression. This endogenous rhythm is reflected in the time courses of spinule formation and breakdown during different phases of the light/dark cycle.

Adaptation, Physiological↗
PubMed1983

Permeability of the external glial limiting membrane of rat parietal cortex.

As the relevance of previous reports demonstrating the permeability of the glia limitans appears to be not generally accepted, the problem is reinvestigated by examination of the ultrastructure of the glia limitans in combination with tracer studies using Ruthenium Red. The results clearly show that gap junctions are the only type of intercellular contact present in this layer. Measurements of the lengths of cross-sections of junctional regions reveal a decrease in size in absolute terms as well as in relation to total astrocytic surface if one proceeds from the more superficial layers into the depth of the tissue. The intercellular clefts leading from the subarachnoidal space into the interspaces of brain tissue are patent thus allowing the tracer to penetrate to a depth of 0.4-0.6 mm in one hour. Although these observations confirm the idea of an ultimate communication between the cerebrospinal fluid compartments and the extracellular space of brain the discussion shows how the particular arrangement of the intercellular channels and the cells bordering them may be suited to control the local composition of interstitial fluid independently from that of the cerebrospinal fluid.

Animals↗
PubMed1983

Morphologic changes in teleost primary and secondary retinal cells following brief exposure to light.

Light adaptive morphologic changes in the teleost retina, such as movements of rods, cones, and epithelial pigment and spinule formation on horizontal cell terminals, are normally associated with continual exposure to light. Depending on a variety of factors these processes are generally completed within 30-60 min. In this report we show that a brief exposure to light (1-2 min) preceded and followed by darkness is sufficient to elicit these changes in four species of teleost; the trout (Salmo gairdneri), the tench (Tinca tinca), the carp (Cyprinus carpio), and the goldfish (Carassius auratus). A brief pulse is as effective in causing cone migration and an increase in the number of spinules as continual exposure; however, it is sometimes less effective in causing pigment migration. The photomechanical changes following a brief period of light are always completed more quickly and show greater species variability than the formation of spinules. These results show that the various morphologic manifestations of light adaptation are autonomous processes that need only a short pulse of light to trigger the whole sequence of events. This is of interest when considering their control mechanisms and may have consequences for physiologic work involving experiments on dark-adapted eyes.

Adaptation, Physiological↗
PubMed1982

Endogenous patterns of photomechanical movements in teleosts and their relation to activity rhythms.

The retinal rods, cones and epithelial pigment of most lower vertebrates display rhythmic photomechanical (retinomotor) migrations in response to changes in ambient lighting conditions. This study examines the extent of these migrations in the absence of the daily changes in illumination (constant darkness and constant light) in three species of teleosts. Salmo trutta, a crepuscularly active fish, showed two peaks of light adaptation occurring around dawn and dusk when kept in constant darkness. Tinca tinca, a nocturnal species, also showed an endogenous rhythm during extended periods of darkness, but, unlike Salmo trutta, it was light-adapted throughout what would normally have been "day". At the maximal extent of migration under conditions of continual darkness, the pigment migrated 59% as much as it did during a normal light/dark cycle. Nannacara anomala, a tropical diurnally active species, showed a similar but more pronounced rhythm than Tinca tinca for all 3 days of experimental darkness, behaving essentially identically to fish exposed to a light/dark cycle. Nannacara anomala also displayed a weak rhythm when kept in constant light. It is concluded from these and previous results that the pattern of endogenous photomechanical movement depends both on the activity pattern of a species and on the constancy of the lighting conditions to which it has been exposed during its lifetime.

Animals↗
PubMed1981

Layer-specific labelling of cat visual cortex after stimulation with visual noise: a [3H]2-deoxy-d-glucose study.

Tritiated 2-deoxy-D-glucose (2-DG) was used to demonstrate layer specific uptake of 2-DG at the cellular level in the visual cortex of the cat after stimulation with different kinds of visual stimuli. Two-dimensional static Gaussian visual noise drifting across the visual field led to an increased accumulation of 2-DG in layers III and V as compared to the amount of radioactivity in layer IV. In unstimulated control tissue of visual cortex a homogeneous pattern of labelling was found. Horizontal bars moving vertically across the visual field increased the uptake in layer IV more than in all other layers. Analysis of the 2-DG uptake at the cellular level revealed that visual noise activated two bands of cells, one above and one below layer IV, whereas bar stimuli activated cells mainly in layer IV. Accumulation of 2-DG was always higher in the perikarya than in the surrounding neuropil. These results confirm the physiologically recorded properties of cells in different cortical layers.

Animals↗
PubMed1981

Retinal projection to the nucleus of the optic tract in the cat as revealed by retrograde transport of horseradish peroxidase.

Retrograde transport of horseradish peroxidase injected iontophoretically into the nucleus of the optic tract of cats revealed that the direction-selective cells in this pretectal nucleus receive direct retinal projections from small retinal ganglion cells, the so-called gamma-cells. These cells from a horizontal band on the contralateral retina. Few labeled cells are found in the ipsilateral temporal retina. The input from the contralateral retina is 10 times more numerous than from the ipsilateral one. In both retinae the highest concentration of labeled cells is near the area centralis.

Animals↗