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Biomedical subjects

V B Meyer-Rochow

Publications and source records attributed to V B Meyer-Rochow.

At least 55 records · Page 3Linked to original sources
PubMed1989

Comparative fine structure of the axial skeleton inside the regenerated tail of some lizard species and the tuatara (Sphenodon punctatus).

The regenerated tail of the New Zealand gecko Hoplodactylus maculatus is equipped with an elastic cartilaginous tube as skeletal axis. Other lizard species and Sphenodon punctatus possess variably developed hyaline cartilaginous tubes. Moreover, H. maculatus enhances the functional performance of its tail by long elastic fibres, which are arranged all around the central regenerated spinal cord. The different characteristics of the regenerated skeleton could be related to the different environments that the species studied occupy in nature.

Animals↗
PubMed1987

Near infra-red sensitivity of the eye of the crustacean Mysis relicta?

When individuals of the crustacean Mysis relicta are fully dark-adapted and preparations for electroretinogramme recordings are performed in infra-red light of wavelength greater than 730 nm, responses to 300 ms flashes of light can be recorded. Though this is the first time that responses to such long wavelengths have ever been reported for any invertebrate photoreceptor, the authors suggest that near infra-red sensitivity in arthropods could be more widespread, and that because of very long adaptation and sensitivity regeneration times preparations should not be carried out in red light, hitherto deemed invisible to most arthropods, but with the aid of an infra-red image converter and a filter at wavelengths greater than 800 nm.

Animals↗
PubMed1986

Morphology of the compound eye of the giant deep-sea isopod Bathynomus giganteus.

The structural organization of the compound eye of the largest known isopod, Bathynomus giganteus, is described from four specimens maintained in the laboratory for as long as two months. Living specimens have not previously been available for study. The two triangular compound eyes measure about 18 mm on the dorsal edge and are separated by an interocular distance of 25 mm. They face forward and slightly downward and may have significant overlap in visual fields. Each eye contains about 3,500 ommatidia in animals of body lengths from 22.5 cm to 37.5 cm. The packing of ommatidia is not uniform across the retina, but is nearly hexagonal in the dorsal central region and nearly square in the ventral and lateral periphery. The dioptric elements in each ommatidium consist of a laminar cornea, which is flat externally and convex internally, and a bipartite crystalline cone. Sometimes seven and sometimes eight retinular cells closely appose the proximal tip of the cone and bear the microvilli of the rhabdom. Proximal to the rhabdom the retinular cells form thin pillars near the periphery of the ommatidium, and the central portion along the optic axis at this level is occupied by interstitial cells that contain massive arrays of clear vesicles thought to serve as reflective elements. The arhabdomeral segments of the retinular cells and the interstitial cells rest on a basement membrane. Within each ommatidium the basement membrane has two extensions with cylindrical cores and thin sheets of dense material and collagen-like filaments. These sheets occupy spaces between adjacent interstitial cells up to the level of the rhabdomeral segments of the retinular cells. Arrays of pigment cells with relatively weak light-screening properties separate adjacent ommatidia. Animals were fixed both in light within a week of being brought from depth into daylight, and after 2 months of maintenance in constant darkness following such daylight exposure. In both cases, microvilli of the rhabdom were severely disrupted and the retinular cytoplasm contained numerous multivesicular bodies. Exposure to natural daylight appears to cause irreversible structural damage to the photoreceptors of these animals.

Animals↗
PubMed1984

The effects of temperature and light on particles associated with crayfish visual membrane: a freeze-fracture analysis and electrophysiological study.

Depending on the pre-experimental treatment, densities as well as sizes of particles associated with the visual membranes in the eyes of Procambarus clarkii varied. The highest mean particle density (5268 +/- 969 microns -2) and the smallest mean particle diameter (5.57 +/- 1.35 nm) were found in crayfish which had been kept in the dark for 10 weeks in aerated fresh water of 10 degrees C. Crayfish kept under a 12 h dark/light regime in water of 10 degrees C or 30 degrees C for three weeks displayed particle densities of 1076 +/- 180 and 2899 +/- 249 microns -2, respectively; particle diameters were of the order of 8 nm. Temperature did not alter the shape or the slope of the V/log I curves, but ERG recordings show that maximum spectral sensitivity was shifted from lambda max = 560 nm in cold water crayfish (10 degrees C) to lambda max = 580 nm in crayfish from the 30 degrees C tank, and that the 10 degrees C curve was somewhat narrower than the 30 degrees C curve. It is suggested that the observed shift was caused by a combination of factors, of which the following may have played key roles: (1) The filter effect of screening pigment granules and other intracellular components such as vesicles, vacuoles, endoplasmic reticulum, and mitochondria, some of which were developed to a considerably greater extent in 30 degrees C material; (2) increased membrane fluidity due to higher temperature as well as the presence of photoproducts in the light, and the 'countermeasures' taken by the visual pigment molecules to stabilize the lipid bilayer, e.g. higher density, possible 12-s-cis linkages etc.; and (3) increased regeneration or synthesis of rhodopsin due to higher metabolic activity of retinula cells at higher temperatures. Temperature-induced changes of visual pigments in a variety of organisms are discussed and evidence for the rhodopsin-aggregate model of crayfish visual pigment is presented. It is concluded that the retinula cytoplasm is involved in restoring depleted stocks of photopigment, and that the biological sense of possessing an increase in red sensitivity during the warm summer months lies in the correlation of light penetration in the natural habitat of P. clarkii and optimal exploitation of the habitat.

Animals↗
PubMed1984

Fine-structure of the compound eye of the buprestid beetle Curis caloptera (Coleoptera, Buprestidae).

Curis caloptera is a buprestid beetle, which is active in bright sunlight. Its eye, like that of many other diurnal arthropods, is of the apposition type, in which dioptric apparatus and receptor layer are not separated by a region devoid of pigment. Perhaps to prevent damage by U. V.-radiation, the cornea is relatively thick (approximately 90 micron) and crystalline cones are of the "eucone-type". In each ommatidium the cone cell extensions occupy regular positions between the 8 retinula cells and reach down to the basement membrane where they end in bulbous swellings and contain grains of screening pigment. Pigment grains, slightly smaller than those present in the primary pigment cells, are also found within the retinula cells. Although the rhabdom possesses a uniform diameter of approximately 2 micron over its entire length of almost 300 micron, the number of rhabdomeres contributing to the rhabdom varies and depends on the level at which the rhabdom is sectioned. At the distal end, only one retinula cell possesses a rhabdomere; the same holds true for the proximal end, where a different rhabdomere (with microvilli at right angles to those of the distal cell) dominates. One retinula cell, of darker appearance in electron micrographs, occupies a distal position in each ommatidium and remains preferentially oriented within a sector of 60 degrees irrespective of the ommatidial axis. The ommatidial axis itself was found to vary 235 degrees. We provide circumstantial evidence for the view that the cell in question could be a U. V.-receptor with a role to play in an unambiguous determination of the E-vector. Separate bundles, each containing 8 axons, pass through the basement membrane together with 1 or 2 tracheoles. A traceheal tapetum is not developed.

Animals↗
PubMed1983

Trophospongium-like structures in an insect eye: response of retinula cells of Papilio xuthus (Lepidoptera) to irradiation with ultraviolet light.

Presumably, as a consequence of a 3-h exposure to light of 350-nm wavelength (1.5 X 10(15) photons/cm2 sec) followed by a period of 20 h of rest in the dark, the four smaller retinula cells in each ommatidium of the eye of the butterfly Papilio xuthus contain a structure in the peripheral regions of their cytoplasm that resembles a portion of a rhabdom. Evidence for and against the view that this unusual, highly ordered arrangement of membranes represents a trophospongium is presented. In view of the fact that the structure in question only occurred at the same time when rhabdomeres were in a process of disintegration or reformation, the authors conclude that the structure in question is involved in the supply or removal of substances during a period of considerable activity of the retinula cell.

Animals↗
PubMed1982

Comparison between temperature-induced changes and effects caused by dark/light adaptation in the eyes of two species of Antarctic crustaceans.

The amphipod, Orchomene plebs, and the isopod, Glyptonotus antarcticus, both adapted to live in seawater of a temperature of -2 degree to 0 degree C, were kept for 7h at the unphysiologically high temperature of +10 degree C. Temperature elevation appeared to mimic light adaptation with regard to the position of the screening pigment granules within the visual cells, but not with respect to ultrastructural changes in the microvillar array of the rhabdom, i.e. the visual membranes. Cellular metabolism, membranous fatty acid composition, and ion fluxes, all known to be readily affected by an increase in temperature, are thought to be responsible for the observed effects. Pigment granules could possibly cause an elevation of intracellular temperatures due to the fact that they are dark and dissipate absorbed energy as heat.

Adaptation, Physiological↗
PubMed1982

Retinal organization of the eyes of three nototheniid fishes from the Ross Sea (Antarctica).

The retinas of 3 nototheniid fishes co-existing in the McMordo Sound (Antarctica), but with different depth preferenda, were studied to establish a correlation between habitat and retinal organization. Light and electron microscopic observations of the retinas of these fishes show the layering typical of most vertebrate retinas. However, the difference in the ratio of rods and cones, and particularly the structure of the rods are related to the amounts and spectral properties of the light available in the depths in which they are meant to operate. D. mawsoni possesses the highest concentration of unusual rods characterized by long cylindrical inner segments (60 microns) and outer segments. T. borchgrevinki has the smallest number of rods, while T. bernacchii possesses an intermediate number. The retinal pigmented epithelium is present in the 3 retinas studied, but it is only in T. borchgrevinki that there is an apparent movement of pigment granules (photomechanical response). Thus, the retinal organization of T. borchgrevinki suggests that this species is able to see in an environment that is relatively bright but in which ambient light levels can change. On the other hand, the apparent lack of photomechanical movements and the greater population of rods in T. bernacchii and especially D. mawsoni suggest that these 2 species are better adapted to an environment of constantly low light intensities.

Animals↗
PubMed1978

The eyes of mesopelagic crustaceans. III. Thysanopoda tricuspidata (Euphausiacea).

The compound eyes of the mesopelagic eupausiid Thysanopoda tricuspidata were investigated by light-, scanning-, and transmission electron microscopy. The eyes are spherical and have a diameter that corresponds to 1/6 of the carapace length. The hexagonal facets have strongly curved outer surfaces. Although there are four crystalline cone cells, only two participate in the formation of the cone, which is 90-120 micrometer long and appears to have a radial gradient of refractive index. The clear zone, separating dioptric structures and retinula, is only 90-120 micrometer wide. In it lie the very large oval nuclei of the seven retinula cells. Directly in front of the 70 micrometer long and 15 micrometer thick rhabdom a lens-like structure of 12 micrometer diameter is developed. This structure, known in only a very few arthropods, seems to be present in all species of Euphausiacea studied to date. It is believed that the rhabdom lens improves near-field vision and absolute light sensitivity. Rod-shaped pigment grains and mitochondria of the tubular type are found in the plasma of retinula cells. The position of the proximal screening pigment as well as the microvillar organization in the rhabdom are indicative of light-adapted material. The orthogonal alignment of rhabdovilli suggests polarization sensitivity. Behind each rabdom there is a cup-shaped homogenous structure of unknown, but possibly optical function. Finally, the structure and the function of the euphysiid eye are reviewed and the functional implications of individual components are discussed.

Biological Evolution↗
PubMed1978

The eyes of mesopelagic crustaceans. II. Streetsia challengeri (amphipoda).

In Streetsia challengeri left and right eyes have fused and become a single cylindrical photoreceptor, which occupies the basal half of a forward directed head projection. This unusual compound eye consists of approximately 2500 ommatidia, which are arranged in such a way that the animal has almost circumferential vision, but cannot look ahead or behind. It is thought that the eye operates on light-guide principles, and that the crystalline cones are the major dioptric component. Ommatidia in anterior-posterior rows show a greater overlap of visual fields than dorso-ventrally arranged ommatidia. Cone layer and retinula are separated by a 4 micrometer thick screen-membrane, which contains tiny pigment granules of 0.15 micrometer diameter. Cells of unknown function and origin, containing unusual multitubular organelles, are regularly found near the proximal ends of the crystalline cone threads. The twisted rhabdoms measure 18--20 micrometer in diameter, and consist of microvilli 0.05 micrometer in width, which belong to five retinula cells and which show no trace of disintegration. The position of interommatidial screening pigment, the density of retinula cell vesicles and inclusions, and the narrowness of the perirhabdomal space all suggest that the eyes have been light-adapted at the time of fixation for electron microscopy. The retinula cell nuclei lie on the proximal side of the heavily pigmented basement membrane. A tapetum or basal retinula cells are not developed. It is concluded that the eye optimally combines acuity with sensitivity, and that for distance estimation parallax may be important.

Animals↗
PubMed1978

Visual behavior, eye and retina of the parasitic fish Carapus mourlani.

1. This is the first transmission electron microscope description of the retina of a parasitic fish. 2. The retina is well supplied with capillaries, some of which occur on the inner surface of the retina. An unusual and possibly primitive type of capillary junction is described. 3. The outer segments of the retina of Carapus mourlani, which measure approximately 2 micron in diameter, are of one type only. A certain degree of banking was observed. Outer segments are not isolated from each other by screening pigments; they are, however, surrounded by about 15 calycal processes. 4. Typical spheroids or conoids were not seen in the outer plexiform layer. The inner nuclear layer consists of only one or two layers of nuclei. The inner plexiform layer is unusually wide and some amacrine synapses can be identified. There are few ganglion cells and the ratio of nuclei in the outer nuclear layer to those of the inner nuclear layer to ganglion cells is approximately 100:10:1. 5. The eye of C. mourlani combines features of degenerated photoreceptors, characteristic of cave-organisms, with adaptations which are commonly found in nocturnal and deep-sea forms. 6. The visual behavior of the animal indicates that the eye is fully functional in spite of its corneal keratosis and small number of optic nerve fibers.

Animals↗
PubMed1977

The eyes of mesopelagic crustaceans: I. Gennadas sp. (penaeidae).

The eye of the deep-sea penaeid shrimp Gennadas consists of approximately 700 square ommatidia with a side length of 15 micrometer. It is hemispherical in shape and is located at the end of a 1.5 mm long eye stalk. The cornea is extremely thin, but the crystalline cone is well-developed. A clear zone between dioptric structures and the rhabdom layer is absent. A few pigment granules are found within the basement membrane; otherwise they, too, are absent from the eye of Gennadas. The rhabdom is massive and occupies 50% of the eye. It consists of orthogonally oriented microvilli (the latter measuring 0.07 micrometer in diameter) and is 75 micrometer long. In cross sections adjacent rhabdoms, all approximately 8 micrometer in diameter, form an almost continuous sheet and leave little space for retinula cell cytoplasm. In spite of a one h exposure to light, rhabdom microvilli show no disintegration or disruption of membranes. Vesicles of various kinds, however, are present in all seven retinula cells near the basement membrane. Bundles of seven axons penetrate the basement membrane. On their way to the lamina they often combine and form larger aggregations.

Animals↗
PubMed1975

Larval and adult eye of the western rock lobster (Panulirus longipes).

A number of differences exists between the compound eyes of larval and adult rock lobsters, Panulirus longipes. The larval eye more closely resembles the apposition type of compound eye, in which retinula cells and rhabdom lie immediately below the cone cells. The adult eye, on the other hand, is a typical clear-zone photoreceptor in which cones and retinula cell layers are separated by a wide transparent region. The rhabdom of the larval eye, if cut longitudinally, exhibits a "banded" structure over its entire length; in the adult the banded part is confined to the distal end, and the rhabdom is tiered. Both eyes have in common an eighth, distally-located retinula cell, which possesses orthogonally-oriented microvilli, and a peculiar lens-shaped "crystal", which appears to focus light onto the narrow column of the distal rhabdom. Migration of screening pigment on dark-light adaptation is accompanied by changes in sensitivity and resolution of the eye. Retinula cells belonging to one ommatidium do not arrange into one single bundle of axons, but interweave with axons of four neighbouring facets in an extraordinarily regular fashion.

Animals↗