Biomedical subjects

D H Anderson

Publications and source records attributed to D H Anderson.

At least 73 records · Page 4Linked to original sources

PubMed1988

Tunicamycin-induced degeneration in cone photoreceptors.

Tunicamycin (TM), an inhibitor of dolichylphosphate-mediated protein glycosylation, was injected intravitreally into the eyes of diurnal rodents with cone-dominated retinas. Injection of 1 microgram of the B2 isomer led to a progressive degeneration of the photoreceptor outer segments and disruption of the RPE-photoreceptor interface that took place over a 10-day period. Cone outer segments were shortened by postinjection day 6 and virtually absent by day 9. The microvilli that normally protrude from the apical surface of the retinal pigment epithelium were replaced by a fringe of shortened processes. The other retinal layers showed no morphological evidence of disruption. Retinal sensitivity, as measured by electroretinographic b-wave threshold, showed a significant and progressive decline over the 10-day course of the experiment that paralleled the disruption of retinal morphology. These results suggest that TM leads to similar morphological and electrophysiological effects on rod and cone photoreceptors.

Animals↗

PubMed1988

Laccase-mediated detoxification of phenolic compounds.

The ability of a polyphenoloxidase, the laccase of the fungus Rhizoctonia praticola, to detoxify phenolic pollutants was examined. The growth of the fungus could be inhibited by phenolic compounds, and the effective concentration was dependent on the substituents of the phenol. A toxic amount of a phenolic compound was added to a fungal growth medium in the presence or absence of a naturally occurring phenol, and half of the replicates also received laccase. The medium was then inoculated with R. praticola, and the levels of phenols in the medium were monitored by high-performance liquid chromatography analysis. The addition of the laccase reversed the inhibitory effect of 2,6-xylenol, 4-chloro-2-methylphenol, and p-cresol. Other compounds, e.g., o-cresol and 2,4-dichlorophenol, were detoxified only when laccase was used in conjunction with a natural phenol such as syringic acid. The toxicity of p-chlorophenol and 2,4,5-trichlorophenol could not be overcome by any additions. The ability of the laccase to alter the toxicity of the phenols appeared to be related to the capacity of the enzyme to decrease the levels of the parent compound by transformation or cross-coupling with another phenol.

Chlorophenols↗

PubMed1987

Glial fibrillary acidic protein increases in Müller cells after retinal detachment.

Retinal detachment, separation of the neural retina from the retinal pigment epithelium (RPE), initiates a series of changes in the eye which result in loss of vision if the retina is not rapidly reattached to the RPE. Many of the complex effects of this separation on the cell biology of the retina have yet to be determined. We report here a change in the amount and location of a specific cytoskeletal protein, glial fibrillary acidic protein (GFAP), within Müller cells after retinal detachment. Cat neural retina and RPE were separated by injecting fluid into the extracellular space between the retina and RPE. Normal retinas and retinas detached for 30 days were fixed and embedded for conventional electron microscopy or immunocytochemistry, or homogenized and processed by SDS-PAGE for immunoblot analysis with anti-GFAP. In normal retinas and in attached retinal regions of eyes with retinal detachment, GFAP was detected only in the end feet of the Müller cells as 10 nm diameter filaments and as a diffuse component over the cytoplasm. By contrast, in regions where the retina was detached from the RPE, GFAP was localized throughout the Müller cells in both of these forms. Immunoblots revealed a significant increase in anti-GFAP labeling of a 51,000 MW band from the detached retina.

Animals↗

PubMed1987

Structural basis for regulation in gram-negative bacterial citrate synthases.

The citrate synthases of Gram-negative bacteria, unlike those of eukaryotes, are inhibited allosterically by NADH, but the two kinds of citrate synthase are about 30% homologous in amino acid sequence--the two Gram-negative citrate synthase sequences so far determined, from Escherichia coli and Acinetobacter anitratum, are about 70% identical. A model for the NADH-sensitive E. coli citrate synthase has been constructed using sequence homology and the known structure of the pig heart enzyme. The most reactive cysteine in the E. coli enzyme, which probably marks the NADH binding site, has now been identified as Cys-206. The model places this residue far from the active site. An E. coli citrate synthase mutant, from which a stretch of 24 amino acids has been deleted near the active site, still binds NADH normally. Two active site missense mutants of this enzyme, generated by oligonucleotide-directed mutagenesis, have lower affinities for one substrate, oxaloacetate, but also are much less sensitive to 2-oxoglutarate, an oxaloacetate analogue hitherto believed to be an allosteric inhibitor. These results confirm that NADH binds to a truly allosteric site in E. coli citrate synthase, the features of which are still to be defined; while 2-oxoglutarate is really an active-site directed inhibitor, although it may still play a regulatory role in vivo.

Binding Sites↗

PubMed1986

A concentration of fucosylated glycoconjugates at the base of cone outer segments: quantitative electron microscope autoradiography.

Rod photoreceptors show a discrete band of labeled molecules at the outer segment base shortly after the administration of radioactive protein precursors (Young, 1967). The band signifies the insertion of radiolabeled protein, primarily opsin, into rod disc membrane (Basinger, Bok and Hall, 1976). In contrast, the autoradiographic labeling pattern in cones is characteristically diffuse (Young, 1971), although cones as well as rods are now thought to replace their disc membranes continually (Anderson, Fisher, and Steinberg, 1978). Using grain count analysis in conjunction with electron microscope autoradiography, we demonstrate for the first time that the initial cone outer segment (COS) labeling pattern in the retinas of cone-dominant rodents is not random or diffuse after intraocular injection of [3H]-fucose--a specific glycoprotein precursor. Thirty minutes after [3H]-fucose injection, the Golgi complex is heavily labeled in both rods and cones. At 1.5 hr, labeling first appears in the periciliary region and in the basal portion of the COS. We detected a basal concentration of fucosylated molecules up to 12 hr after injection; thereafter, we found no differential distribution of labeled product molecules in COS. In rods, we observed no band of labeled protein at any of the time points sampled. The low level of labeling in rods is uniformly distributed between the basal and apical portion of the outer segments. Although the identity of the fucosylated material remains unknown, the early labeling of the Golgi complex--followed by labeling over the periciliary region and the basal portion of the outer segment--suggests that newly synthesized membrane protein is transported from sites of synthesis in the inner segment and inserted into disc membrane at the COS base. However, in contrast to rods, the protein is apparently capable of diffusing longitudinally throughout the interconnected membrane network.

Animals↗

PubMed1986

Neurogenic diabetes insipidus in a sheep.

A 7-month-old Suffolk-cross ram was examined because of polydipsia and polyuria of 2 months" duration. Neurogenic diabetes insipidus was diagnosed on the basis of failure to concentrate urine of low specific gravity in response to water deprivation and a positive response to antidiuretic hormone administration. Post-mortem examination of the brain revealed degeneration in the cerebral peduncles, an absence of pituitary neural tissue and evidence suggesting external pressure as the cause.

Animals↗

PubMed1986

Disc shedding and autophagy in the cone-dominant ground squirrel retina.

The temporal pattern of cone outer-segment disc shedding was examined in the retina of the California ground squirrel, Spermophilus beecheyi, under two different lighting conditions. Squirrels were entrained to either 10-180 lx (room lighting) or 1,400 lx. Cone shedding during the dark period was biphasic in both conditions, with increases occurring at 2-3 hr and 5-6 hr after light offset. Entrainment to 1400 lx resulted in an increase in shedding at 2 hr after light offset and a slight advance in the timing of both peaks. Dense granules were often found in photoreceptors, retinal neurons, Müller cells, microglia and vascular cells. These granules, which were found primarily during the dark period and early light period, were lipofuscin-like in their lipophilia, size and autofluorescence. Many of the granules were probably autophagic in origin, but some within Müller cells may have originated via endocytosis of extracellular material which was exocytosed by photoreceptors.

Animals↗

PubMed1986

In vitro maintenance of a pure-cone retina.

The retina of the lizard, Sceloporus occidentalis, appears to have only cone photoreceptors. Eyecups from this animal were incubated in media containing Earle's Balanced Salts, supplemented with amino acids and vitamins, and gassed with 5% CO2/95% O2. Under these conditions, good morphology, protein synthesis, and normal cyclic AMP and cyclic GMP levels were maintained for 1-2 days. This in vitro preparation is likely to be useful for pharmacological studies of cone photoreceptors.

Amino Acids↗

PubMed1986

Retinoid-binding proteins in cone-dominant retinas.

We identified and localized interphotoreceptor (or interstitial) retinoid-binding protein (IRBP) and cellular retinaldehyde-binding protein (CRALBP) in the cone-dominant retinas of diurnal squirrels. Western blots were prepared from sodium dodecyl sulfate polyacrylamide gels (SDS-PAGE) from whole retina, and from retina proximal and distal to the photoreceptor nuclei. Blots were incubated with purified rabbit IgG's specific for the bovine retinal antigens, and the labeled components were visualized using immunoperoxidase techniques. Anti-bovine IRBP and anti-bovine CRALBP recognized single components on gels of retinal supernatants that corresponded to the electrophoretic migration of the bovine antigens. The component recognized by anti-bovine IRBP on blots of outer retinal proteins (Mr 146,000) was absent on blots of inner retinal proteins. Twelve and 24 hr after intravitreal injection of 3H-L-fucose, electropherograms showed one major peak of radioactivity that coincided with the component recognized by anti-bovine IRBP. By immunoelectron microscopy, anti-bovine CRALBP labeling was restricted to the cytoplasm of both RPE and Muller cells, with light labeling of nuclear euchromatin in both cell types. In contrast, anti-bovine IRBP recognized antigenic sites primarily in the interphotoreceptor space (IPS). Intracellular labeling was limited to occasional granules in the photoreceptor myoids and the apical RPE cytoplasm. Extracellular labeling with anti-bovine IRBP was strongly associated with patches or small clumps of amorphous, electron opaque material distributed throughout the IPS. This material was particularly prominent near the cone outer segment plasma membranes, and was tentatively identified as the residual interphotoreceptor matrix that remained after exposure to the solvents used during tissue processing. In general, the results are consistent with those obtained in rod-dominant species. In addition, they imply that cones as well as rods are responsible for IRBP synthesis in the ground squirrel.

Animals↗

PubMed1986

Morphological recovery in the reattached retina.

After experimental retinal detachment in the cat, a number of morphological changes take place in retinal and RPE cells. Following reattachment, the ultrastructural relationship between the photoreceptors and the RPE is re-established, but it does not return to the predetachment state even after short detachment episodes coupled with prolonged recovery periods. All of the reattached retinae show some degree of abnormality, ranging from subtle changes in photoreceptor ultrastructure to dramatic degenerative effects in the outer retina. Abrupt transitions in morphology from one reattached area to an adjacent area are not unusual. Photoreceptor recovery varies widely between animals, and between adjacent regions within the same retina. Ensheathment of outer segments by RPE apical processes is abnormal. In some reattached areas rod outer segment dimensions and disc structure are near normal as is the displacement rate of rod outer segment discs. In others, especially in areas of RPE or Müller cell proliferation and hypertrophy, the outer segments are shortened or absent completely, and there is a reduction of cell bodies in the outer nuclear layer. In some retinae, recovery in cones is inferior to that in rods. At short detachment durations (less than 1 wk) morphological recovery in the reattached retina is optimal while at long intervals (greater than 1 month) recovery is poor. The changes at the photoreceptor-RPE interface identified in the reattached cat retina probably have adverse effects on visual recovery when they occur within the human macula.

Animals↗

PubMed1985

Factor analysis of the aftereffects of drinking in alcoholics.

Research that deals with the causes of alcoholism has been hampered by the absence of factor analyses that deal specifically with ethanol's aftereffects. We factor analyzed 100 alcoholics' reports of the effects that they experience after alcohol consumption. Five factors emerged--Hangover, Euphoria, Flushing, Seizures, and Sleepiness. They are described and discussed. Future investigators may find them helpful in assessing theories on the etiology of alcoholism and in studies of ethanol's effects on subsets of alcohol abusers.

Adult↗

PubMed1985

Cluster analytic methods applied to the Minnesota Multiphasic Personality Inventory in a psychiatric population.

Cluster analysis and the MMPI were used together to determine whether the heterogeneous diagnostic groups could be identified in an inpatient psychiatric population. The effectiveness of four clustering techniques in separating diagnostic groups was compared using percent of coverage, between-sample replication, between-method replication, cluster differences on age, and cluster differences on diagnosis. The results showed cluster analysis to be a poor diagnostic discriminator when compared to diagnostic groups, which were considered the "true" clusters of the sample. The final conclusion of the study was that cluster analysis should not be used to form groups that would be diagnostically labeled because each analytic technique produced misleading results.

Adult↗

PubMed1983

Fluorouracil therapy for proliferative vitreoretinopathy after vitrectomy.

Fluorouracil effectively inhibits epiretinal membrane formation and traction retinal detachment after vitrectomy surgery. When 0.5 mg of fluorouracil was administered intraocularly every 24 hours for seven days, traction retinal detachment two weeks after the intraocular injection of 200,000 cultured retinal pigment epithelial cells occurred in 12 of 12 control eyes but in only six of 14 eyes treated with fluorouracil (P less than .001). Four weeks after cell injection, eight of 12 eyes treated with fluorouracil had traction retinal detachments whereas 12 of 12 control eyes did (P less than .001). The height of the traction retinal detachment four weeks after intraocular injection of 200,000 cultured retinal pigment epithelial cells was reduced 50% in eyes treated with 0.5 mg of fluorouracil every 24 hours for seven days compared to control eyes (P less than .001). When the number of injected retinal pigment epithelial cells was increased to 400,000 cells and 1.25 mg of fluorouracil was administered intraocularly every 24 hours for seven days, traction retinal detachment two weeks after injection occurred in 15 of 15 eyes in the control group but in none of ten eyes in the treated group. Four weeks after cell injection, eight of eight eyes in the control group and five of five eyes in the fluorouracil-treated group had detachments and the mean height of the detachments in the two groups was equal. Autoradiography of the epiretinal membranes in eyes injected with 200,000 cultured retinal pigment epithelial cells and labeled for two hours with tritiated thymidine showed that 0.8% of the epiretinal cell nuclei were labeled two weeks after cell injection but that no labeled cells were present in the fluorouracil-treated eyes. Tritiated thymidine labeling of epiretinal cells in the fluorouracil-treated eyes was first noted three weeks after the cell injection. The presence of tritiated thymidine labeling in the fluorouracil-treated eyes correlated with an increase in the number of epiretinal cells and an increase in the incidence of traction retinal detachment.

Animals↗

PubMed1983

Ocular toxicity of fluorouracil after vitrectomy.

The retinal and corneal toxicity of fluorouracil in the rabbit eye after lensectomy and vitrectomy depended on both the dosage and the frequency of intraocular injection and was reversible at certain dosages. All eyes in Group 1 (1.25 mg of fluorouracil every 12 hours for four days and then every 24 hours for three days) had opaque corneas by three days; these did not clear for four weeks. Histologic studies showed loss of photoreceptor outer segments and loss of ribosomes in all the retinal cells examined. The electroretinographic b-wave decreased to 0% of the baseline value (no b-wave), and did not recover after three weeks. In Group 2 eyes (1.25 mg of fluorouracil every 24 hours for seven days), corneal opacification increased to a maximum after two weeks and gradually decreased by four weeks. The electroretinographic b-wave diminished to 9.6% of the baseline value at two weeks but later recovered to 62.5% of the baseline value at three weeks. Histologic studies showed loss of photoreceptor outer segments and ribosomes at nine days; both returned to near normal after five weeks. Clinical, electrophysiologic, and histologic studies showed no toxicity in Group 3 eyes (0.5 mg of fluorouracil every 24 hours for seven days). This dosage of fluorouracil exerts a significant antiproliferative effect on injected retinal pigment epithelial cells and is well tolerated by the rabbit eye.

Animals↗

PubMed1983

Both rod and cone disc shedding are related to light onset in the cat.

Nineteen domestic cats were entrained to a 12-hr light/12-hr dark lighting cycle and killed at different times of the cycle. The numbers of rod and cone phagosomes in the retinal pigment epithelium (RPE) were quantified by light microscopy. The number of both rod and cone phagosomes shows a large increase within 2 hrs after light onset. Thereafter, the phagosome count remains low until the latter part of the dark period when the number of rod and cone phagosomes increases slightly. In a few cases, substantial variability in phagosome numbers was found between animals killed at the same times in the lighting cycle. Small (0.4-0.8 microns), dense, membrane-bound granules, that have the ultrastructural features of lysosomes, occur in large numbers in the tapetal RPE cells. The granules may contain only a homogeneous matrix or matrix plus membrane fragments or melanin. Variations in the number of such granules in different animals shows no clear diurnal pattern. Phagosome number, size, and length measurements of outer segments are used to provide estimates of cone outer segment turnover time in the cat.

Animals↗

PubMed1983

Retinal detachment in the cat: the pigment epithelial-photoreceptor interface.

Twenty-six cat retinae were surgically detached by injecting fluid into the subretinal space (SRS). The retinae were then studied by light and electron microscopy at detachment intervals ranging from 1/2 hr to 14 months. Degenerative and proliferative changes occur at the retinal pigment epithelial (RPE)-photoreceptor interface very soon after detachment, and the severity of these changes depends upon both the duration and height of the detachment. The specialized apical RPE processes that ensheath the outer segments are replaced by a uniform fringe of short, undifferentiated processes. The apical RPE surface becomes mounded, and this mounding becomes more pronounced at longer detachment durations. Labeling experiments with 3H-thymidine showed that some cat RPE cells enter a phase of stimulated DNA synthesis 12-24 hrs after detachment; RPE mitotic figures are first apparent 48 hrs after detachment. In the cat, discrete regions of proliferated RPE cells usually appear in one of several configurations. A number of different cell types, including polymorphonuclear neutrophils, monocytes at various maturational stages, photoreceptor cells, Müller cells, and RPE cells, appear in the expanded SRS of detached retinae. Rod and cone outer segments degenerate rapidly and become membrane bound sacs by 3 days postdetachment; the assembly of new outer segment membrane apparently does not stop completely even at moderately long detachment intervals (ie, 2 months). Degenerative changes in the inner segments do not take place with the same rapidity as those in the outer segments. The changes that occur at the RPE-photoreceptor interface are rapid, progressive, and sometimes irreversible events that have significant implications for photoreceptor recovery following retinal reattachment surgery.

Animals↗

PubMed1983

Retinal detachment in the cat: the outer nuclear and outer plexiform layers.

The retinae of cats were surgically detached for 1/2 hr to 14 months, and the outer nuclear (ONL) and outer plexiform layers (OPL) were studied by light and electron microscopy. The longer the duration or the greater the height of detachment the more likely was the occurrence of cell death. Histologic signs of degeneration were present 1 hr after detachment. The number of photoreceptor nuclei in the ONL decreased significantly by 1 month. Loss of cells in the ONL occurred by necrosis and by the migration of photoreceptor cell bodies into the subretinal space. The OPL degenerated by the necrosis of cell processes and synaptic terminals and by the retraction of the synaptic terminals. By 2 weeks most synaptic terminals were necrotic or in the process of retracting. Photoreceptor synaptic contact with second order neurons was diminished by 30 days and was essentially absent by 50 days. Müller cells proliferated and hypertrophied; their nuclei and cell processes filled the intraretinal spaces left by the degenerating photoreceptors. In addition, Müller cells protruded into the subretinal space and formed multiple layers of cell bodies and processes between the retina and retinal pigment epithelium. By 14 months these subretinal Müller cell processes covered the entire detached retina, and appeared morphologically like an astroglial scar. Similar changes in human retinal detachments may significantly influence the degree of visual recovery after retinal reattachment, especially in retinae detached for more than a few days.

Animals↗

PubMed1982

Epiretinal membrane formation after vitrectomy.

Our experimental model of epiretinal membrane formation in the rabbit eye after lensectomy and vitrectomy provides a way of studying pharmacologic and surgical approaches to inhibiting epiretinal cellular proliferation and contraction in the eye that has undergone vitrectomy. We injected 400,000 tissue-cultured retinal pigment epithelial cells onto the retinal surface of rabbit eyes that had undergone lensectomy, vitrectomy, and fluid-gas exchange. By one week, a funnel-shaped detachment of the medullary rays had occurred in 100% of the injected eyes. Histologically, the cells formed an epiretinal membrane by six hours after injection and caused major wrinkling of the inner retina after 24 to 48 hours. The percentage of tritiated-thymidine-labeled epiretinal cells increased dramatically 24 hours after injection and then declined. Cellular membranes bridging the optic nerve, followed by growth and contraction of the epiretinal cells on the detached internal limiting membrane, were responsible for the closed funnel appearance of the medullary rays.

Animals↗