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C B Allen

Publications and source records attributed to C B Allen.

16 recordsLinked to original sources
PubMed1990

Distributions of elements in the human retinal pigment epithelium.

Distributions of elements above the atomic number of sodium were mapped in the retinal pigment epithelia of eight human eyes. X-ray energy spectra and maps were collected from cryofixed, freeze-dried, and epoxy-embedded tissues using energy-dispersive x-ray microanalysis. All eyes had high concentrations of phosphorus in the nuclei of retinal pigment epithelial cells. Melanosomes were rich in sulfur, zinc, calcium, and iron. Lipofuscin and cytoplasm contained only phosphorus and sulfur in detectable amounts. Drusen, when present, contained phosphorus and calcium. Six eyes had a prominent aluminum peak recorded from melanosomes, nuclei, and Bruch's membrane. In one pair of 90-year-old eyes, small, electron-dense deposits surrounded many melanosomes and contained mercury and selenium. Retinal pigment epithelial melanosomes may bind and accumulate metals and other potentially toxic ions over time, preventing them from reaching the neural retina.

Aged↗
PubMed1987

Macular degeneration in a community of rhesus monkeys. Ultrastructural observations.

The eyes of 29 aged adult, (mean age, 20 years) rhesus monkeys were examined for the presence of age-related macular degeneration (AMD). This sample represented approximately 25% of the aged population in the seminatural colony at the Caribbean Primate Research Center (CPRC) of the University of Puerto Rico. Approximately 75% of the animals examined had drusen in the posterior pole. Ultrastructural analysis was used to determine whether the pathologic alteration of Bruch's membrane and drusen in the colony resembled those noted in aged or AMD-afflicted human retinas. There were abnormalities in all layers of Bruch's membrane. Deposits of heterogeneous material, comprised of membranous, granular, and cellular components, were seen in both the inner collagenous zone (ICZ) and the outer collagenous zone (OCZ). Accumulation of this drusenoid material in the ICZ produced a scalloping of the basal border of the retinal pigment epithelium (RPE). Dense bodies were seen in both Bruch's membrane and RPE cytoplasm near the basal infoldings. Cytoplasmic processes, as well as whole cells, were seen with regularity within the drusenoid material. In one case there was a cell with a basement membrane crossing the middle elastic layer of Bruch's membrane. These changes are consistent with those reported in human aging and AMD. Aged individuals in this colony appear to be predisposed to macular degenerative changes and may prove to be an invaluable animal model for studying AMD in humans.

Animals↗
PubMed1987

Scanning electron microscopy of human drusen.

Drusen are small, yellowish deposits that form under the retinal pigment epithelium (RPE) with senescence or under certain pathological conditions. The present study examined these structures under the scanning electron microscope. Tissue came from four eyes of 66- and 75-year-old donors who demonstrated widespread drusen of the posterior fundus noted on postmortem examination. Specimens were prepared by either detaching the RPE from Bruch's membrane, or by cryofracturing the tissue for cross-sectional views. Drusen appeared to be composed of irregularly-shaped globular masses and of distinct spherical entities. These particles varied greatly in size, and were situated between the RPE's basement membrane and the outer collagenous zone of Bruch's membrane. Surface views showed drusen components to be embedded in the collagenous zone of Bruch's membrane. Pits corresponding to the sizes of the globular and spherical masses imply that some particles were lost during tissue processing. Fractured cross sections of the irregularly-shaped globular masses revealed a homogeneous, granular matrix with no distinct ultrastructural features, while some of the fractured spherical components demonstrated an internal core. Transmission electron microscopic analysis on the same specimens that were subjected to SEM corroborated these observations. Analytical x-ray microanalysis (Kevex, Foster City, CA) in the SEM revealed major peaks for calcium and phosphorous in the crystalline spherical components, and primarily potassium and chloride in the globular structures.

Aged↗
PubMed1987

Scanning electron microscopic analysis of intraocular ossification in advanced retinal disease.

Chicken eyes from congenic blind (rd/rd) animals showing early, intermediate, and final stages of ossification, similar to the phthisis bulbi condition in man, were examined using scanning and transmission electron microscopy as well as light microscopy and X-ray microanalysis. Early stages of ossification were devoid of mineralized calcium apatite while intermediate and end stages of the disorder contained large amounts of calcium and phosphorus. This process resulted in metaplastic bone formation. An intact Bruch's membrane appeared to separate the choroid from the degenerated pigment epithelium and the developing bone suggesting that its possible origin was metaplasia of the retinal pigment epithelium and the degenerated sensory retina. The end-stage ossification resulted in "phthisic bone" formation which completely filled the vitreous cavity in a manner very similar to the human condition of phthisis bulbi.

Animals↗
PubMed1987

Scanning electron microscopic observations on differentiation and maintenance of photoreceptor cells in vitro.

Scanning electron microscopy was performed on cell cultures of embryonic and post-hatch chick retinas co-cultured with optic lobe neurons or in medium that had been pre-conditioned with optic lobe cells. The culture medium consisted of Eagles Basal Medium supplemented with glucose, fetal calf serum, glutamine and bicarbonate. Application of colchicine (5 micrograms/ml) to the cultures, encouraged the dissociation of retinal cell rosettes and optic lobe neuron aggregates, thereby allowing us to examine differentiation of isolated photoreceptor cells. Over time, developing photoreceptor cells gradually took on the morphological characteristics of rods and cones in the post-hatch chick: cells were polarized having a single neurite on one end of the cell and inner and outer segment-like structures on the other end. Developing cone cells elaborated an oil droplet and filopodial-like processes at the apical end of the inner segment. The latter may correspond to the calyceal processes which normally envelop the basal 1/3 of the outer segment. The sequence of events noted in vitro parallel those previously reported in vivo.

Animals↗
PubMed1987

Conditioned medium-mediated photoreceptor differentiation in retina from embryonic rd chickens.

Retina cells from 8-day rd (retinal degenerate) chicken embryos were cultured in media supplemented with optic lobe conditioned medium (OLCM). The morphogenesis of rd photoreceptors is being described. Several differentiating photoreceptors depicted a membranous sac protruding from the apical end of the cell as revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Such structures were found mostly in 8-day-old cultures supplemented with OLCM and were absent in controls. They resembled rudimentary outer segments emanating from a cilium at the apical inner segments. TEM showed a few stacks of free floating disks within the membranous structure which was suggestive of a rudimentary outer segment development. The possible neurotrophic effect of OLCM on rd retina photoreceptor differentiation is being suggested.

Animals↗
PubMed1986

Tunicamycin-induced dysgenesis of retinal rod outer segment membranes. I. A scanning electron microscopy study.

Incubation of Xenopus retinas with tunicamycin has been shown to block the glycosylation of opsin, the rod visual pigment apoglycoprotein, with concomitant accumulation of vesicular membrane material in the compartment between the rod inner and outer segments (i.e., the intersegmental space) (Fliesler et al, J Cell Biol 100:574-587, 1985). To further assess the morphology, topology, and cellular origin of this membranous material, Xenopus retinas were incubated in the presence or absence of tunicamycin and the photoreceptor cells were examined by scanning electron microscopy. The material which accumulated in the intersegmental space appeared to be a complex of membranous structures consisting of cisternae with numerous tubular projections, as well as closely associated individual vesicles of various sizes. This tubulo-vesicular material was exclusively associated with the basal surface of the rod outer segment. The connecting cilium, periciliary ridge complex, and the apical surface of the rod inner segment were devoid of such membrane material. Nascent (open) discs (i.e., evaginations of the plasma membrane at the base of the outer segment) often observed in control retinas were not present in tunicamycin-treated tissue. These results support the hypothesis that the membranous material which accumulates in the intersegmental space of rods in tunicamycin-treated retinas represents incompletely and aberrantly formed nascent disc membranes. The formation of this material is apparently a consequence of a deficiency in newly synthesized, asparagine-linked membrane glycoconjugates (e.g., the oligosaccharide chains of opsin) at the site of disc assembly.

Animals↗
PubMed1985

Hereditary retinal degeneration in the Rhode Island Red chicken: ultrastructural analysis.

An electron microscopic analysis of photoreceptor degeneration in a congenitally blind strain of chickens is presented. The mutation was named rd, meaning 'retinal degeneration'. Although the chicks were behaviorally and electrophysiologically blind at the time of hatching, their retinas appeared morphologically comparable to normal chicks at this stage. Both groups had well-developed photoreceptor cells, although outer segments were typically disoriented or misaligned. In the normal, and to some degree in the rd, retina, outer segments became organized within the first week posthatching. In the rd retina at that time, however, more outer segments were disorganized and disoriented. Disc-like membranes were also seen in some inner segments. Many photoreceptors had distended inner segment tips containing a granular cytoplasm. Membraneous debris was present in the subretinal space. Over the next 2-3 weeks there was a reduction in number of inner segments, outer segments and photoreceptor nuclei of both rods and cones. Photoreceptor cell bodies in the outer nuclear layer were replaced by Mueller cell processes. By the end of the second month, a larger cone:rod ratio was apparent, and a large proportion of the remaining cones were double cones. Intact outer segments were rarely seen at that time. Few and sporadic cone cells, identified by a pale-staining oil droplet, were the predominant surviving photoreceptors by 6 months of age. At the later stages examined, the pigment epithelium (PE) appeared to be undergoing degenerative changes. A general thinning of cells and hypopigmentation of PE cells was apparent, although hyperpigmented, hypertrophied PE cells were also present which bulged into the subretinal space. Pigmented cells of unknown origin were also noted in the subretinal space at the later time points.

Animals↗
PubMed1985

Ultrastructural changes in the retinal pigment epithelium of congenitally blind chickens.

Pathological changes in the retinal pigment epithelium (RPE) in a strain of chickens having hereditary blindness and retinal degeneration were described at the ultrastructural level. Photoreceptors in the retinal degenerate (rd) chicken had previously been noted to degenerate within a week after hatching. Affected chicks have neural retinas that are morphologically comparable to normal animals prior to that time despite an obvious lack of vision. In the present study, no pathological changes were noted in rd RPE prior to the time of photoreceptor degeneration. However, while mitochondria in the normal chick's RPE underwent diurnal changes in morphology within a few days of hatching, pleomorphic or ring mitochondria were not seen with high frequency in the rd chick. After photoreceptors began degenerating, changes were seen in the rd RPE. By 2 weeks of age, we noted a reduction in the depth and number of basal infoldings, an increase in number and size of autophagic vacuoles and large whorls of membranous material within rd RPE cells. Membranous debris and what appeared to be broken off outer segments were seen in the subretinal space at that time. These phenomena became more prominent and prevalent with time. In 3-4 week old specimens, nearly intact outer segments were seen within RPE cytoplasm. At the same time very few intact outer segments were present on photoreceptors. After this time degenerative changes were seen in the RPE: a thinning of cells (apical to basal cell width), spreading out of cells (increased distance between intercellular junctional complexes), hypopigmentation of cells and presence of free cells in the sub-retinal space. Some RPE cells appeared in a rounded up configuration, bulging into the subretinal space and making junctional complexes with remaining photoreceptor inner segments or Mueller cell processes. Many RPE cells did appear to maintain their phagocytic abilities, as evidenced by presence of many microvilli and pinocytotic vacuoles in the apical cytoplasm.

Aging↗
PubMed1984

Scanning electron microscopy of the retina in an animal model of hereditary blindness.

Scanning electron microscopy was performed on retinas from normal and a mutant strain of chickens suffering from congenital blindness with retinal degeneration. Both surface and cryofractured transverse views of the retina were examined. Photoreceptors were generally seen to degenerate along a central to peripheral gradient: the more damaged receptors located centrally while areas of normal appearing photoreceptors were located toward the ora serrata. Pathological changes included deformed and missing outer segments and short, swollen inner segments. Reactive changes in overlying pigment epithelium (PE) were also noted over areas displaying advanced photoreceptor degeneration. PE changes included both hypertrophy and dystrophy of cells, detached cells, and formation of clusters or nodules along Bruch's membrane or in the sub-retinal space among photoreceptor inner segments. Among the 6 types of photoreceptors in the chicken retina (1 type of rod and 5 types of cones), more intact double cones were identified in areas undergoing retinal degeneration than other types. Double cones may be more resistant to the factor(s) involved in cellular death.

Animals↗
PubMed1982

Coccidiosis in swine: dose and age response to Isospora suis.

Coccidiosis is a disease of the young piglet due to infection with Isospora suis and is characterized by diarrhea which is nonresponsive to antibacterial therapy. There is variable morbidity and mortality. Piglets develop a more severe clinical illness and enteritis when infected with I. suis at one to three days of age than when infected at two weeks of age. Microscopic lesions range from villous atrophy and mild erosion to severe fibrinonecrotic enteritis.

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PubMed1974

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