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Biomedical subjects

J C Blanks

Publications and source records attributed to J C Blanks.

At least 37 records · Page 2Linked to original sources
PubMed1989

Uptake of tritiated thymidine in mitochondria of the retina.

Light microscopic autoradiography with 3H-thymidine was used as a probe for DNA synthesis on the retinas of the guinea pig, rabbit, and monkey. Relatively heavy labeling was found in the ganglion cell and inner nuclear layers as well as in the photoreceptor inner segments in the guinea pig and monkey. Electron microscopic autoradiography demonstrated that in the ganglion cells and photoreceptor inner segments in the monkey, 89% of silver grains, representing thymidine uptake, were on or near the mitochondria.

Animals↗
PubMed1989

Retinal light damage in rats exposed to intermittent light. Comparison with continuous light exposure.

Visible light-induced photoreceptor cell damage resulting from exposure to multiple intermittent light-dark periods was compared with damage resulting from continuous light in albino rats maintained in a weak cyclic-light environment or in darkness before light treatment. The time course of retinal damage was determined by correlative measurements of rhodopsin and visual cell DNA at various times after light exposure, and by histopathological evaluation. The effect of intense light exposures on rhodopsin regeneration and on the level of rod outer segment docosahexaenoic acid was also determined. For rats previously maintained in weak cyclic light, 50% visual cell loss was measured 2 weeks after 12 1 hr light/2 hr dark periods, or following 24 hr of continuous light. A comparable 50% loss of visual cells was found in dark-reared rats after only 5 hr of continuous illumination or 2-3 hr of intermittent light. As judged by histology, cyclic-light-reared rats incurred less retinal pigment epithelial cell damage than dark-reared animals. In both experimental rat models intermittent light exposure resulted in greater visual cell damage than continuous exposure. Visual cell damage from intermittent light was found to depend on the duration of light exposure and on the number of light doses administered. Measurements of rhodopsin and DNA 2 hr and 2 weeks after light exposure of up to 8 hr duration revealed that visual cell loss occurs largely during the 2 week dark period following light treatment. The loss of docosahexaenoic acid from rod outer segments was also greater in rats exposed to intermittent light than in animals treated with continuous light. It is concluded that intermittent light exposure exacerbates Type I light damage in rats (involving the retina and retinal pigment epithelium) and the schedule of intense light exposure is a determinant of visual cell death.

Animals↗
PubMed1988

Ultrastructural visualization of primate cone photoreceptor matrix sheaths.

Glycoconjugates, including glycolipids, glycoproteins, and proteoglycans, are present in the plasma membrane of photoreceptor cells and in the interphotoreceptor matrix surrounding photoreceptor cell ellipsoids and outer segments. Although the precise function of these molecules is unknown, they may be important in mediating photoreceptor-pigment epithelial cell interactions, outer segment membrane assembly, and/or disc shedding. Lectins, affinity ligands for defined carbohydrate sequences, have proven particularly useful in studying the glycoconjugate composition of the interphotoreceptor matrix. The peanut lectin selectively binds to domains of the interphotoreceptor matrix surrounding cone ("cone matrix sheaths"), but not rod inner and outer segments. This is evidence for the existence of chemical and structural heterogeneity within the interphotoreceptor matrix. The studies described herein utilized ultrastructural pre-embedding histochemical labeling to assess whether, in addition to the surrounding interphotoreceptor matrix, peanut lectin binding is associated directly with that plasma membrane of cone inner and outer segments. This study confirms that ferritin-conjugated peanut agglutinin binds to cone matrix sheaths, and, in addition, provides ultrastructural evidence for the presence of binding to the plasma membrane surrounding cone inner and outer segments. The data suggest that cone membrane-associated peanut agglutinin-binding molecules may differ from those located within cone matrix sheaths.

Animals↗
PubMed1988

Monoclonal antibodies react with neuronal subpopulations in the human nervous system.

Monoclonal antibody probes were used to identify antigenic cross reactivities among neuronal subpopulations and to dissect the human nervous system at several levels of organization. Six monoclonal antibodies, prepared with immunogens from Drosophila melanogaster or human nervous tissue, were used to localize antigens immunocytochemically in normal adult human neocortex, hippocampus, cerebellum, spinal cord, and retina. Four of the six antibodies were neural specific in their reactivity and each stained a unique combination of neurons. The antibodies reacted with at least three subpopulations of cerebral cortical neurons, including discrete populations of pyramidal and nonpyramidal cells. Components of a widely distributed functional system within the spinal cord and cerebellum were labelled by one antibody, which reacted with neurons in the nucleus dorsalis of Clarke, deep cerebellar nuclei, and Purkinje cells. At the single-cell level, three of the monoclonals differentially labelled the photoreceptor cell outer segment, inner segment, and perikaryon. Three of the six antibodies were reactive with specific protein bands on immunoblots of tissue homogenates. This monoclonal antibody panel provides a novel and potentially useful method of analysis of the organization of the normal and diseased human nervous system.

Adult↗
PubMed1988

Cellular proliferation induced by subretinal injection of vitreous in the rabbit.

A new experimental model of subretinal cellular proliferation, based on injection of autologous vitreous into the subretinal space of rabbits, was studied by light and electron microscopy. As early as five days after injection, proliferation of retinal pigment epithelial (RPE) and retinal glial cells was observed in the subretinal space. These morphologically distinct proliferating cells were sometimes joined by junctional complexes. Morphologically, the proliferating RPE cells resembled either RPE cells or fibroblasts. Some proliferating RPE cells also retained their epithelial characteristics (ie, basement membranes and cell junctions), while others were partially dedifferentiated and showed some embryonic features. New formation of melanin could be identified within the proliferated RPE cells, which could account, in part, for the hyperpigmentation at the site of the bleb caused by the injection of vitreous. The results demonstrated that injection of autologous vitreous into the subretinal space can lead to subretinal proliferation of retinal glial and RPE cells in the rabbit.

Animals↗
PubMed1987

Monoclonal antibody identification of subpopulations of cerebral cortical neurons affected in Alzheimer disease.

Neuronal degeneration is one of the hallmarks of Alzheimer disease (AD). Given the paucity of molecular markers available for the identification of neuronal subtypes, the specificity of neuronal loss within the cerebral cortex has been difficult to evaluate. With a panel of four monoclonal antibodies (mAbs) applied to central nervous system tissues from AD patients, we have immunocytochemically identified a population of vulnerable cortical neurons; a subpopulation of pyramidal neurons is recognized by mABs 3F12 and 44.1 in the hippocampus and neocortex, and clusters of multipolar neurons in the entorhinal cortex reactive with mAb 44.1 show selective degeneration. Closely adjacent stellate-like neurons in these regions, identified by mAB 6A2, show striking preservation in AD. The neurons recognized by mAbs 3F12 and 44.1, to the best of our knowledge, do not comprise a single known neurotransmitter system. mAb 3A4 identifies a phosphorylated antigen that is undetectable in normal brain but accumulates early in the course of AD in somas of vulnerable neurons. Antigen 3A4 is distinct from material reactive with thioflavin S or antibody generated against paired helical filaments. Initially, antigen 3A4 is localized to neurons in the entorhinal cortex and subiculum, later in the association neocortex, and, ultimately in cases of long duration, in primary sensory cortical regions. mAb 3F12 recognizes multiple bands on immunoblots of homogenates of normal and AD cortical tissues, whereas mAb 3A4 does not bind to immunoblots containing neurofilament proteins or brain homogenates from AD patients. Ultrastructurally, antigen 3A4 is localized to paired helical filaments. Using these mAbs, further molecular characterization of the affected cortical neurons is now possible.

Alzheimer Disease↗
PubMed1987

Appearance of PNA-binding cells within the outer nuclear layer coinciding with photoreceptor degeneration in rd mice.

Peanut agglutinin (PNA), a lectin with affinity for galactose-galactosamine disaccharides, has been employed to monitor alterations in carbohydrate expression in retinal degenerative (rd) mice. Mice homozygous for the rd gene exhibit a rapid loss of rod photoreceptor cells in the first postnatal month; outer segment degeneration is first detected between postnatal days (P) 12-P14 and most rod photoreceptors degenerate by P30. In the rd mouse, PNA-binding cells are observed in the outer nuclear layer (ONL) between P10 and P18, a time corresponding to the intense phase of photoreceptor cell death (LaVail et al., 1982). At no time are PNA-positive cells identified within the ONL of control retinas. PNA-binding cells typically occur in groups and binding of the lectin appears to be restricted to granular elements of the cytoplasm. This report represents the first documentation of changes in the expression and/or accessibility of glycoconjugates in the degenerating ONL of the rd retina. Further analysis of the relationship between regional distribution of PNA-binding cells in the ONL and degenerating photoreceptors of the rd may lead to a better understanding of the mechanism of cell death induced by this mutation.

Animals↗
PubMed1986

Vascular atrophy in the retinal degenerative rd mouse.

We have observed that the lectin Ricinus communis agglutinin I (RCA), which binds to terminal galactose moieties, serves as a marker for vasculature in the mouse retina. The binding of fluorescein-isothiocyanate-conjugated RCA was used to study the development of retinal vasculature in normal mice and in rd (retinal degeneration) mutant mice, which exhibit a massive loss of photoreceptor cells during the first month of life. In the normal mouse, retinal capillaries develop in an ordered manner and are concentrated in three major zones between the inner limiting membrane and the outer plexiform layer. In the rd mouse, the vessels appear to form normally but begin to degenerate by the end of the second postnatal week. By the end of the fourth postnatal week there is approximately a 35% reduction in the total number of vascular profiles in the rd retina compared to normal littermate controls. This reduction in vascularity is temporally associated with the photoreceptor degeneration.

Animals↗
PubMed1986

Optic-nerve degeneration in Alzheimer's disease.

Alzheimer's disease is a dementing disorder of unknown cause in which there is degeneration of neuronal subpopulations in the central nervous system. In postmortem studies, we found widespread axonal degeneration in the optic nerves of 8 of 10 patients with Alzheimer's disease. The retinas of four of the patients were also examined histologically, and three had a reduction in the number of ganglion cells and in the thickness of the nerve-fiber layer. There was no retinal neurofibrillary degeneration or amyloid angiopathy, which are typically seen in the brains of patients with Alzheimer's disease. The changes we observed in the patients with Alzheimer's disease were clearly distinguishable from the findings in 10 age-matched controls and represent a sensory-system degeneration that occurs in Alzheimer's disease. Study of the retina in patients with this disease may be helpful diagnostically, and isolation of the affected ganglion cells may facilitate molecular analysis of the disorder.

Aged↗
PubMed1986

Morphological study of epiretinal membrane following posterior penetrating injury in the monkey eye.

Posterior vitreous detachment (PVD) and epiretinal membranes occur in a number of vitreoretinal diseases. We have developed an experimental model in which we can provide the morphologic correlation of these dynamic processes. The method provides the opportunity to study epiretinal membrane formation with the scanning electron microscope (SEM); with SEM, some epiretinal membranes that could not be readily detected either clinically or by routine light microscopy can now be identified and studied in detail. We performed an experimental posterior penetrating injury with injection of autologous whole blood or blood and lens material into the vitreous. Five eyes with posterior vitreous detachment but no retinal detachment were selected for SEM. A reduction in the cortical vitreous filaments and the presence of epiretinal membranes was apparent with SEM. In most areas the epiretinal membranes were separated from the internal limiting membrane by a narrow cleft; however, limited attachment sites between the epiretinal membranes and retina were observed in areas overlying retinal blood vessels. In two eyes we observed microscopic retinal folds beneath the membranes, demonstrating a possible morphologic correlation between epiretinal cellular contraction and traction on the retina.

Animals↗
PubMed1986

Interphotoreceptor matrix domains ensheath vertebrate cone photoreceptor cells.

The retinal interphotoreceptor matrix (IPM) occupies the space between the neural retina and the retinal pigmented epithelium (RPE), two neuroectoderm-derived epithelia. While the IPM appears to be a major route by which photoreceptor cells receive vital metabolic factors, relatively little is known concerning its structure and function. The studies reported here describe the presence of specialized domains of the IPM that ensheath cone, but not rod, inner and outer segments in pig, monkey, and human retinae. These cone extracellular matrix sheaths are chemically and structurally distinct from the remainder of the IPM as revealed by their specific binding of the lectin peanut agglutinin (PNA) and their structural stability during physical dissociation of the retina. Biochemical studies suggest that the PNA-binding components of the cone matrix sheaths are trypsin-sensitive glycoproteins. These structures may play a role in establishing a specialized microenvironment for cone photoreceptors, maintaining proper orientation of cone outer segments, and/or facilitating cone-RPE interactions.

Animals↗
PubMed1985

Enhancement of (polyA+)RNA synthesis in light in isolated intact photoreceptor cells of the rat.

Incorporation of [3H]-cytidine into messenger RNAs (polyadenylated RNAs) was enhanced in light in isolated intact photoreceptor cells of the rat. The increase in polyadenylated (PolyA+)RNAs appeared selective relative to other photoreceptor RNAs since incorporation of [3H]-cytidine into this fraction was up to 10-fold higher while labeling of total cellular RNAs was only two- to three-fold higher in light compared with dark. The photoreceptor cells were isolated in vivo through destruction of inner retina neurons with injections of combinations of neurotoxic substances during early postnatal development. The photoreceptor cells attained normal adult morphology and function: the alpha-wave of the electroretinogram, as well as the thickness of the outer nuclear layer and the length of photoreceptor inner and outer segments, were found to be within the normal range at 4 and 10 weeks of age. In addition to RNA synthesis, such photoreceptor cell preparations when incubated in vitro demonstrated a capacity for regulating light-dependent sodium fluxes comparable to that within the intact retina. The potential usefulness of this model for exploring the molecular biology of photoreceptor cells is discussed.

Animals↗
PubMed1984

Morphologic evaluation of vitreous collagen after penetrating ocular injury.

Condensation and contraction of the vitreous have been implicated in the development of vitreoretinal traction and traction retinal detachment after penetrating ocular injury. In this study, using the inorganic dye ruthenium-red, we studied ultrastructural changes in vitreous in the rabbit eye after standard penetrating injury and intravitreal blood injection. In normal rabbit vitreous the collagen fibrils have a regular arrangement. In contrast, after a penetrating injury the collagen fibrils appear focally condensed. While it appears unlikely that such a network could alone produce tractional or directional forces, these alterations along the collagen fibrils could provide a scaffold along which contractile cells migrate into the vitreous.

Animals↗
PubMed1984

Application of acrylamide as an embedding medium in studies of lectin and antibody binding in the vertebrate retina.

The use of acrylamide as an embedding medium for vertebrate retinal tissue and its applicability to lectin and antibody-based cytochemical studies is described. The acrylamide technique has numerous advantages over those using fresh-frozen or paraffin embedded material. The morphological integrity of retinal tissue prepared in acrylamide is equivalent to that obtainable with paraffin and superior to that of fresh-frozen material. In addition, this technique alleviates problems often encountered with the thermal and chemical treatments required in the paraffin method. The acrylamide technique allows the localization of lectin and antibody-binding sites essentially unaltered by the fixation and embedding protocol, as in frozen sections, while maintaining tissue morphology similar to that of paraffin-embedded tissue. It is hoped that this approach will be useful to other workers in vision research employing lectin, antibody or other cytochemical approaches to the study of cellular structure and function.

Acrylamide↗
PubMed1984

Topographic variations in the rabbit and primate internal limiting membrane.

The internal limiting membrane (ILM) and cortical vitreous of the rabbit and primate were studied with transmission electron microscopy following staining with the cationic dye, Alcian blue GX. An unusual feature of the cortical vitreal collagen fibril was its displacement from the ILM: it did not insert into the lamina densa. The separation between vitreal collagen and the ILM was especially noticeable in the rabbit eye, which possessed an extremely strong vitreal retinal attachment in the posterior fundus. The lack of fibril insertion was observed in rabbit tissue that had been fixed by quick freezing on a helium-cooled copper block. The similarity in the appearance of tissue fixed by glutaraldehyde, glutaraldehyde supplemented with Alcian blue, or by quick freezing suggested that the lack of collagen fibril insertion into the ILM was an accurate representation of the relationship between collagen and the ILM. It was found that these two animal species had radically different ILM's; the rabbit ILM was a thin basement membrane throughout all areas of the posterior fundus, whereas the ILM of the cynomolgus monkey was a thick basement membrane in the peripapillary region and a thin basement membrane in the region of the fovea centralis. The topographic variations in the primate ILM thickness and appearance followed the pattern observed in human eyes. Like man, the thickening of the cynomolgus ILM in the posterior fundus was age related. The similarity between the cynomolgus and human ILM suggests that this animal would be more suitable than the rabbit for studying age-related changes or alterations in the strength of vitreal attachment following trauma.

Alcian Blue↗
PubMed1984

Specific binding of peanut lectin to a class of retinal photoreceptor cells. A species comparison.

Although lectins have been used to study surface oligosaccharides of photoreceptor cells in intact retinas and dissociated retinal cells, the specificity of lectin binding to cones versus rods in a variety of species has not been examined closely. The authors previously found that application of fluorescein isothiocyanate (FITC)-conjugated peanut agglutinin (PNA), a lectin with high affinity for galactose-galactosamine disaccharide residues, to cryostat sections of unfixed mouse retina results in staining that is confined to synaptic regions and a subpopulation of photoreceptor cells. To further investigate the possibility that PNA binding is specific for cone photoreceptors, the authors extended their studies to include the duplex retinas of fish, rabbit, monkey, and human in addition to the cone-dominant retina of the chick. These studies show that PNA binding is specific for cone inner and outer segments and also is likely to be associated with the large synaptic pedicles of cone photoreceptor cells. In addition, the authors compared PNA binding with that of Ricinus communis agglutinin I (RCA), another lectin that preferentially binds terminal D-galactose moieties. While RCA does bind to cones in the species examined, it also binds to a lesser extent to rod photoreceptor inner segments. The pattern of binding of RCA in other regions of the retina differs markedly from that of PNA. Significantly, RCA serves as a specific marker for retinal vasculature in the human, monkey, and mouse. These results suggest that certain PNA-binding macromolecules may be important in defining the molecular and cellular specificity of cone photoreceptor cells and that PNA may provide a means for the isolation of cones and cone-specific molecules. RCA may prove to be of value in monitoring vascular changes associated with normal development and pathologic conditions.

Animals↗