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Biomedical subjects

G Orr

Publications and source records attributed to G Orr.

12 recordsLinked to original sources
PubMed1992

Thrombospondin as a component of the extracellular matrix of epiretinal membranes: comparisons with cellular fibronectin.

We compared the distribution of the adhesive extracellular matrix glycoproteins thrombospondin and cellular fibronectin in epiretinal membranes. A total of nine membranes were investigated with immunohistochemical techniques. Thrombospondin and cellular fibronectin immunoreactivity were observed in seven of the specimens and immunostaining for the two glycoproteins was co-localised in four of the membranes. The findings indicate that thrombospondin contributes to the extracellular glycoprotein content of epiretinal membranes and is frequently co-distributed with cellular fibronectin in the tissue. As a consequence, thrombospondin may play a role in the assembly of the extracellular matrix of epiretinal membranes.

Diabetic Retinopathy↗
PubMed1992

Four-quadrant local anaesthesia technique for vitreoretinal surgery.

We report our experience of a recently described local anaesthetic technique which seeks to avoid risk of perforation of the globe, damage to the optic nerve, or injection into the subarachnoid space, whilst providing prolonged and reliable anaesthesia. A prospective series of 19 patients who underwent vitreoretinal surgery using this technique were compared with 19 patients who had retrobulbar anaesthesia for cataract extraction. The vitreoretinal group had excellent akinesia and very good anaesthesia, allowing prolonged retinal reattachment surgery lasting up to 3 hours. Patient evaluation of discomfort or pain experienced in the two groups was assessed using a visual analogue pain score chart. The pain scores for the two groups were not significantly different (p = 0.03) and 16 of 19 patients in each group (84%) experienced only slight pain or less. Satisfaction with local anaesthesia, in both groups, was also assessed by asking patients which method of anaesthesia they would prefer if future surgery were to be performed. In the vitreoretinal group, 18 of 19 patients expressed a preference for local anaesthesia and in the cataract group 17 ot 19 also favoured local anaesthesia. The vitreoretinal patients' median pain score was 0 compared with 1 for the cataract patients. This study demonstrates that local anaesthesia provides pain relief for vitreoretinal surgery which is comparable to the experience of patients undergoing cataract surgery by retrobulbar anaesthesia. The technique described can provide successful local anaesthesia for vitreoretinal procedures. The success of this technique for pain relief and akinesia calls for a reappraisal of the number of patients suitable for vitreoretinal surgery under local anaesthesia.

Anesthesia, Local↗
PubMed1992

Determinants of bone density in young women. I. Relationships among pubertal development, total body bone mass, and total body bone density in premenarchal females.

Bone mass accretion during puberty appears to be critical in the development of peak bone mass, which, in turn, is believed to be a major determinant of osteoporosis risk. Although genetics may be the primary determinant of peak bone mass, modifiable secondary factors, such as nutrition and hormone exposure, may significantly affect bone mass accretion during the second decade of life. As part of a longitudinal study of major determinants of bone development during puberty, we obtained cross-sectional measurements from 112 premenarchal caucasian females (mean +/- SD age, 11.9 +/- 0.49 yr at study entry). Total body bone mineral density (TBBMD) and total body bone mineral content (TBBMC) were measured by dual energy x-ray absorptiometry and compared to anthropometric, pubertal development, urinary steroid and gonadotropin levels, and nutrient intake. An integrated estrogen exposure index was developed and used to evaluate the cumulative effect of circulating estrogen levels on both development. Compared to normative reference data for adults, our subjects possessed 90% of adult height, 68% of adult weight, 83% of adult TBBMD, and 53% of TBBMC. The strongest combined predictors of prepubertal TBBMD and TBBMC were body weight, followed by height and pubertal development. Urinary estradiol levels were positively correlated with dietary intake of iron and vitamin B6.

Adolescent↗
PubMed1990

Purification and characterization of fatty acid beta-oxidation enzymes from Caulobacter crescentus.

Acetoacetyl coenzyme A (acetoacetyl-CoA) thiolase, an enzyme required for short-chain fatty acid degradation, has been purified to near homogeneity from Caulobacter crescentus. The relative heat stability of this enzyme allowed it to be separated from beta-ketoacyl-CoA thiolase. The purification scheme minus the heating step also permitted the copurification of crotonase and 3-hydroxyacyl-CoA dehydrogenase. These activities are in a multienzyme complex in Escherichia coli, but a similar complex was not observed in C. crescentus. Instead, separate proteins differing in enzymatic activity were detected, analogous to the beta-oxidation enzymes that have been isolated from Clostridium acetobutylicum and from mitochondria of higher eucaryotes. In these cells, as appears to be the case with C. crescentus, the individual enzymes form multimers of identical subunits.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1990

Construction of a protoglomerular template by olfactory axons initiates the formation of olfactory glomeruli in the insect brain.

Olfactory glomeruli in insects share many features of organization with their vertebrate counterparts, and yet offer distinct advantages for study of neuronal development. Previous studies have revealed that the olfactory lobes of the brain of the moth Manduca sexta arise postembryonically and that glomeruli in the lobe are induced by olfactory afferent axons (Hildebrand et al., 1979; Oland and Tolbert, 1987). In the present study, we have used the Golgi method, intracellular labeling of neurons with Lucifer yellow, and electron microscopy to follow neuronal development in the antennal lobe through the period when glomeruli develop. Our results, taken together with other results from our laboratory, suggest that olfactory sensory axons have the intrinsic ability to form protoglomeruli, and that an interaction between these axons and glial cells (but not the majority of the neurons of the antennal lobe) causes the glial cells to surround the protoglomeruli. Ingrowth of the neurites of most antennal-lobe neurons into the protoglomeruli occurs after a small delay and appears to be constrained to glomerular units by the presence of the glial boundaries. Synapses, initially not detected in the protoglomeruli, begin to appear as soon as the neurites of antennal-lobe neurons appear in the glomeruli. Thus, antennal axons, instead of immediately seeking out postsynaptic targets, first form the template for organization of future glomeruli. The neurites of most of the neurons of the antennal lobe grow outward to meet the olfactory sensory axons, and in doing so, join with these axons to form glomeruli. Preliminary results concerning the development of a second class of neuron in the lobe, the projection neurons, indicate that at least some of these neurons may arborize in the region of the protoglomeruli very early and therefore participate with the afferent axons in laying the foundation for glomeruli.

Afferent Pathways↗
PubMed1988

Calmodulin supports the force-generating function in desensitized muscle fibers.

Externally added calmodulin (CaM) restored Ca2+ regulation for the tension development by skeletal muscle fibers of hamster and rabbit desensitized by the troponin C (TnC) extraction treatment. CaM produced this action by combining with the TnC-denuded sites in the fiber. However, the binding properties differed strikingly from TnC: unlike TnC, CaM binding required the continued presence of Ca2+ and the bound portion was completely released with EGTA in the physiological milieu. The maximal uptake was 1.7 g of CaM/kg of muscle in the present study. The apparent Ca2+ sensitivity for force development with 200 micrograms/ml CaM in the solution was lower than in the native fiber or in the TnC-loaded fiber. The apparent association constant for CaM binding to the TnC-denuded sites was found as 4.9 x 10(5) M-1, and the extrapolated maximum force (Fmax) with CaM was close to PO. The intrinsic CaM level in intact muscle was also measured and was 18.6 mg/kg, amounting to about 1% of the total TnC or the CaM uptake by TnC-denuded fibers. The intrinsic CaM was not dislodged by EDTA treatment, indicating tight binding and suggesting that it exists in a separate pool from the vacated TnC sites adsorbing externally added CaM. The stringent Ca+ dependence of the CaM adsorption to TnC sites in the regulatory complex in the fiber supports the view that the evolutionary replacement of residues in the amino terminus helix portion of the "EF-hand" motif of site IV may be critical for the functional specialization by TnC.

Animals↗
PubMed1987

Morphologic observations on experimental subretinal neovascularization in the monkey.

Subretinal neovascularization is a poorly understood and potentially disastrous feature of many eye diseases. We used light and electron microscopy to study the sequence of events that lead to the formation of new vessels after laser photocoagulation of the retina and choroid of primates. In this animal model there is a rapid development of new blood vessels; one day after photocoagulation, endothelial cell degeneration and thrombus formation were observed in the capillaries, venules and arterioles of the choroid around the center of the lesion. Re-endothelialization began in some thrombosed choroidal vessels, with migration of the activated endothelial cells within the old basement membrane. Two days after photocoagulation, re-endothelialization was observed in almost all thrombosed choroidal vessels, and the initial stage of the endothelial cell budding was observed in the pre-existing choroidal vessels; this was especially prominent in venules with pericytes. Three days after photocoagulation, not only the endothelial cells in pre-existing vessels but also those in re-endothelialized vessels showed budding and lumen formation. The lumen of vessels was formed by the budding of adjacent endothelial cells that were coupled by transient intercellular junctions. Mitotic figures were frequently found in the endothelial cells distal to the growing tip. Five to eight days after photocoagulation, many new vessels extended into the subretinal space.

Animals↗