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Biomedical subjects

P Monaghan

Publications and source records attributed to P Monaghan.

At least 55 records · Page 3Linked to original sources
PubMed1998

Avian diving, respiratory physiology and the marginal value theorem.

Behavioural studies of diving birds have reported that the ratio of dive duration to the duration of the subsequent period on the surface displays a characteristic relation to dive duration. For short dives, the dive to surface ratio increases with dive duration, whereafter the relation peaks, and for longer dives decreases with increasing dive duration. Such a relationship is not a general prediction of existing marginal value models which have been used to predict optimal diving behaviour. This may be because the smooth curve used to describe the oxygen gain rate of individuals after surfacing is not a good reflection of the respiratory physiology of birds. Here we argue that on physiological grounds, the oxygen gain curve for avian divers will not be smooth, but will have two distinct regions (representing oxygen recovery in the respiratory tract, and in haemoglobin and myoglobin, respectively). Modifying two of the classical diving models by incorporating such a kinked curve causes them to predict the humped relationship between dive to surface ratio and dive duration under many circumstances. We also present data on the duration of dives and surface periods from three species of diving seabirds: the shag, Phalacrocorax aristotelis, the black guillemot, Cepphus grylle and the common guillemot, Uria aalge. All three species showed a humped relationship for dive to surface ratio as a function of dive duration. In line with the predictions of our model, when oxygen stores on surfacing were greatly depleted, the dive to surface ratio peaked at short dive durations. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Differential expression of type XIV collagen/undulin by human mammary gland intralobular and interlobular fibroblasts.

Immunolocalisation of type XIV collagen/undulin in the human mammary gland revealed greater deposition in the interlobular stroma than in the intralobular stroma. The interlobular stroma is located between the breast lobules and their associated intralobular stroma. Fibroblasts isolated from the interlobular stroma synthesised 3- to 5-fold more type XIV collagen/undulin than intralobular fibroblasts, but synthesised type I and type IV collagens in similar amounts. The differential expression of type XIV collagen/undulin was maintained with passage in culture. The results suggest a role for type XIV collagen/undulin in stabilising dense collagen fibrils. The maintenance of two types of structurally distinct stromas may be important during developmental processes in the mammary gland.

Breast↗
PubMed1998

Comparison of four techniques for monitoring the setting kinetics of gypsum.

STATEMENT OF PROBLEM: Setting time of gypsum depends on the method of measurement. PURPOSE: In this study, four methods for ascertaining the setting time of gypsum were compared. MATERIAL AND METHODS: Gypsum setting was evaluated with Gillmore needles, setting expansion, scanning electron microscopy, and x-ray diffraction. Both die stone (Vel-Mix) and fast-setting dental stone (Snap-Stone) were investigated. By using Gillmore needles, both initial set and final set were recorded. Setting expansion was monitored until equilibrium was achieved. For scanning electron microscopy, samples of mixed stone were immersed into liquid nitrogen to stop the reaction. The water was subsequently removed by freeze-drying. Samples were then examined in a scanning electron microscope. For x-ray diffraction, the percentages of dihydrate and hemihydrate crystals were monitored every 1.5 minutes. RESULTS: Setting times for the fast-setting type III stone and for the regular-setting type IV stone were approximately 3 and 10 minutes, respectively, with the Gillmore needle indentation tests; 10 and 20 minutes with scanning electron microscopy; and 20 and 60 minutes with x-ray diffraction. CONCLUSION: Scanning electron microscopy, setting expansion, and x-ray diffraction indicated changes that occurred at times after a clinically relevant set was obtained in the gypsum setting reaction.

Calcium Sulfate↗
PubMed1998

High-pressure freezing for immunocytochemistry.

Ultrastructural immunocytochemistry requires that minimal damage to antigens is imposed by the processing methods. Immersion fixation in cross-linking fixatives with their potential to damage antigens is not an ideal approach and rapid freezing as an alternative sample-stabilization step has a number of advantages. Rapid freezing at ambient pressure restricts the thickness of well-frozen material obtainable to approximately 15 microm or less. In contrast, high-pressure freezing has been demonstrated to provide ice-crystal-artefact-free freezing of samples up to 200 microm in thickness. There have been few reports of high-pressure freezing for immunocytochemical studies and there is no consensus on the choice of post-freezing sample preparation. A range of freeze-substitution time and temperature protocols were compared with improved tissue architecture as the primary goal, but also to compare ease of resin-embedding, polymerization and immunocytochemical labelling. Freeze-substitution in acetone containing 2% osmium tetroxide followed by epoxy-resin embedding at room temperature gave optimum morphology. Freeze-substitution in methanol was completed within 18 h and in tetrahydrofuran within 48 h but the cellular morphology of the Lowicryl-embedded samples was not as good as when samples were substituted in pure acetone. Acetone freeze-substitution was slow, taking at least 6 days to complete, and gave blocks which were difficult to embed in Lowicryl HM20. Careful handling of frozen samples avoiding rapid temperature changes reduced apparent ice-crystal damage in sections of embedded material. Thus a slow warm-up to freeze-substitution temperature and a long substitution time in acetone gave the best results in terms of freezing quality and cellular morphology. No clear differences emerged between the different freeze-substitution media from immunocytochemical labelling experiments.

Animals↗
PubMed1998

The cross-over effect in unilateral neglect. Modelling detailed data in the line-bisection task.

The line-bisection task is the standard assessment of unilateral visual neglect. It supplies one effect, the crossover effect, that challenges models of neglect: in left neglect, the rightward displacement of the midpoint of the line becomes a left displacement for small lines. We review the various attempts to account for the cross-over effect, before describing a computational model of performance in the line-bisection task that produces a cross-over effect quite naturally in its damaged state. The model trades on aspects of several current theories of neglect, including independent attentional processing in the two hemispheres, each of which possesses an attentional gradient in which the contralateral field is accentuated. We assume a small residual noise, along the same gradient, in the damaged hemisphere. When lesioned to simulate right hemisphere damage, the model produces line bisections similar to human performance, in terms of the relationship with line length, a variable cross-over point for the smaller lines, and an amelioration of performance with leftside, but not rightside cueing.

Animals↗
PubMed1997

An immunohistochemical and morphometric study on astrocytes and microvasculature in the human cerebral cortex.

In this study, astrocytes and microvessels of the human cerebral cortex were analysed morphometrically with the aim of acquiring quantitative information on the glio-vascular relationships, considered to be of great importance in the formation and functioning of the blood-brain barrier. Immunohistochemistry for the astrocytic marker, glial fibrillary acidic protein, was used with a computerized image analysis system. The brain tissue was embedded using the progressive lowering of temperature method, and the image analyser was applied to semithin sections subjected to immunogold-silver staining and viewed by epipolarization microscopy. The results show that, in the human cerebral cortex, astrocytes cover 11.4% of the cortex area and that their perivascular processes are nearly as extensive as the vascular bed (0.8% versus 1.72% of the cortex area). These processes form a virtually continuous sheath around the vascular walls, only 11% of the vessel perimeter lacking this astrocytic glia covering. The present results, compared with previous unpublished data obtained by conventional immunocytochemical procedures on wax sections, indicate that low-temperature methods combined with gold-silver immunolabelling on semithin sections significantly improve the detection of immunoreactivity and the performance of the image analyser.

Astrocytes↗
PubMed1997

Glucose transporter GLUT1 in human brain microvessels revealed by ultrastructural immunocytochemistry.

The brain glucose transporter GLUT1 is a transmembrane glycoprotein belonging to the glucose carrier family comprising five isoforms characterized by different functional properties and tissue specificity. Biochemical and immunohistochemical analyses have demonstrated that GLUT isoform 1 is localised within the brain microvascular endothelium, where it controls glucose uptake through the blood-brain barrier (BBB). In this study the expression of GLUT1 was analysed by means of light and electron immunocytochemistry in the adult human cerebellar cortex. The glucose transporter is strongly expressed in cerebellum microvessels, and is localised not only within endothelial cells but also in microvascular pericytes. Moreover, some glial expression of GLUT1 was observed in the neutrophil and in perivascular glial sheaths. The observations demonstrate that different cellular types are involved in the control of brain glucose homeostasis by GLUT1 expression at the BBB site, and support the postulated highly specialised role of brain microvascular pericytes.

Adult↗
PubMed1996

Gap junction distribution and connexin expression in human breast.

Expression of the gap junction proteins (connexins) in human breast epithelium was studied in vivo and in vitro. A panel of sequence-specific anti-peptide antibodies was used to examine four connexin (Cx) isoforms by indirect immunofluorescence labeling. Antibodies to Cx43 readily detected gap junctions between the basal cells in major ducts, but less so within lobular/alveolar structures. Cx26 immunoreactivity was less abundant in beast epithelium but was observed between the luminal cells in major ducts and to a lesser extent in lobular/alveolar structures. Ultrastructural studies of normal human breast showed gap junctions between basal cells in ducts and lobules, but not between luminal cells or between luminal and basal cells. Immunomagnetically separated luminal and basal cells were grown in vitro. Basal cells expressed Cx43 at cell-cell attachment points whereas luminal cells showed only small amounts of immunolabeling with the Cx26 antibody which was generally not associated with the cell borders. Microinjection of Lucifer yellow into cultured luminal or basal cells indicated that basal cells have high levels of gap junctional communication, but dye transfer between luminal cells was difficult to detect by transfer of Lucifer yellow. Western blot analysis of purified luminal and basal cells indicated the presence of mainly Cx43 in both cell types. Polymerase chain reaction analysis of breast mRNA identified message for CX43 and to a lesser extent for Cx26; Cx32 was not detected in human breast, although it was present in mouse mammary gland. mRNA extracted from cloned cultures of human luminal and basal cells contained message for Cx43 and Cx26 in both cell types.

Animals↗
PubMed1996

Connexin expression and gap junctions in the mammary gland.

Gap junctional communication plays a vital role in embryogenesis, cell differentiation and the co-ordination of tissue responses. Gap junctions are formed by a family of closely-related proteins called connexins which show tissue-specific patterns of expression. The role of gap junctions in the mammary gland remains unclear. The lumena of mammary gland ducts are lined by luminal cells with an outer layer of basal cells. In rodents, the luminal cells express connexin26 only during pregnancy and lactation and the basal cells, in some reports, express connexin43. In the normal human breast the basal cells express connexin43, although human mammary epithelial cells in vitro have been reported to express both connexin26 and connexin43. Analysis of connexin expression at the molecular level is now bringing new insights into the structure and function of gap junctions in a range of normal and pathological cell systems.

Animals↗
PubMed1996

The influence of simulated clinical handling on the flexural and compressive strength of posterior composite restorative materials.

OBJECTIVES: The aim of this study was to investigate the influence of clinical handling on the flexural and compressive strengths of two commercially available posterior composites. METHODS: Since the manufacturing of test specimens in a truly clinical situation presents many problems, an in vitro model was developed, consisting of a phantom-head set-up in a clinical operatory. Two composite materials, recommended for use in posterior teeth, were used: P50 APC (3M Dental Products) and Herculite XRV (Kerr, Dental Manufacturing). Beam specimens for 3-point bending tests of both materials and cylindrical specimens for compression test of P50 were made both under ideal laboratory circumstances and under simulated clinical circumstances. RESULTS: The difference in mean flexural strength between laboratory prepared and the quasi-clinically prepared specimens was highly significant for both the specimens handled in a clinical manner was 15% of the flexural strength of the P50 specimens made under laboratory conditions, and the difference for Herculite XRV was 29%. No difference in compressive strength could be shown between the laboratory-fabricated and the quasi-clinically made specimens of P50. SIGNIFICANCE: The relative flexural strength of composite materials in a clinical situation may differ significantly from that predicted from mechanical properties measured in vitro.

Bicuspid↗
PubMed1995

Freeze-drying and scanning electron microscopy of setting dental gypsum.

OBJECTIVES: The initial and final forms of reactive gypsum products have been photomicrographed previously. However, the purpose of this project was to document the microscopic morphology of setting dental stone at various stages during the reaction. METHODS: Two dental products, a conventional (Type IV) die stone and a fast-setting (Type III) stone, were investigated. At selected times ranging from 1 min to 24 h after mechanically mixing the stone under vacuum, the conversion of calcium sulfate hemihydrate to a dihydrate was suspended by immersion into liquid nitrogen. Water was immediately removed by freeze-drying the specimen to prevent any further reaction so that the specimen could be returned to room temperature for examination in a scanning electron microscope (SEM). RESULTS: Crystal formation appeared to be nearly complete at the 20 min interval for the die stone and at the 10 min interval for the fast-setting dental stone. Transitions noted during these times include the nucleation and growth of small needle-like crystals on and near the larger prismatic-shaped hemihydrate crystals, the concurrent decrease in size and number of the hemihydrate crystals, and the progressive entanglement of the growing dihydrate crystals. SIGNIFICANCE: The two-step process of suspending the reaction, then freeze-drying the specimen made it possible to observe and document the intermediate stages during crystal growth of dental stone. These observations should be helpful in understanding the structural dynamics of crystal growth during the setting of gypsum dental products. This procedure should be applicable to the study of other water-based dental materials.

Calcium Sulfate↗
PubMed1995

Treatment of over-reduction of the nose and subsequent deformities.

Failures after rhinoplasty are the result of both technical mistakes and of errors of judgement. One of the most common errors is resection of too much tissue from the components of the nose: the dorsum, alar cartilages, or septum. Such deformities may have both cosmetic and functional effects. The defects that most commonly make a nose look unnatural are: a shallow nasofrontal angle, a nose that has been shortened too much, an over-reduced dorsum which emphasises a parrot's beak deformity, and a round nasal tip with a short interdomal length that lacks definition. The purpose of this paper is to describe the most common deformities associated with excessive resection of the nose, and to suggest the appropriate procedures for correcting the defects. Grafting is usually necessary. We will deal first with deformities of the dorsum and septum and then of the nasal base, but it must be borne in mind that a defect in one area is likely to affect the other areas because they are interrelated-for example, over-resection of the dorsum may also effect the tip of the nose. In addition, not all deformities are the result of excessive reduction; some may result from inadequate resection.

Bone Transplantation↗
PubMed1995

Malignant myoepithelioma (myoepithelial carcinoma) of the breast: a detailed cytokeratin study.

AIMS: To study the expression of a range of cytokeratins by malignant myoepithelioma of the breast. METHODS: Immunophenotyping was carried out using a panel of antibodies on paraffin wax embedded and frozen material using immunohistochemistry and double-labelled immunofluorescence. Electron microscopy was also performed. RESULTS: The tumour cells were positive for CAM 5.2, actin, vimentin, and cytokeratin 14 and negative for cytokeratins 18 and 19. Electron microscopy showed well formed desmosomes and hemidesmosomes together with pinocytic vesicles, plentiful rough endoplasmic reticulum and 6 nM microfilaments with focal densities. CONCLUSIONS: The pattern of cytokeratin expression provides further evidence that tumours with a specific myoepithelial phenotype occur rarely in the breast.

Actins↗
PubMed1995

Immunolocalization of type III collagen in human articular cartilage prepared by high-pressure cryofixation, freeze-substitution, and low-temperature embedding.

We localized Type III collagen by immunogold electron microscopy in resin sections of intact normal and osteoarthritic human articular cartilage. Comparisons of antibody staining between tissue prepared by high-pressure cryofixation and freeze-substitution without fixatives and that exposed to conventional mild chemical fixation with paraformaldehyde showed that dedicated cryotechniques yielded superior preservation of epitopes that are modified by chemical fixation, and simultaneously provided good ultrastructural preservation. Type III collagen was detected with two polyclonal antibodies, one against the triple-helical domain of the molecule and a second against the more antigenic, globular amino pro-peptide domain, which in this collagen is retained in the extracellular matrix after secretion. Positive labeling was seen in association with the major interstitial fibrils, suggesting co-polymerization of Types III and II collagen in cartilage. Type III collagen could not be detected in aldehyde-fixed normal cartilage. In fixed osteoarthritic cartilage, Type III was detectable only when the antibody to the amino pro-peptide was employed. In contrast, high-pressure cryofixation and freeze-substitution preserved epitopes for both antibodies, permitting immunodetection of Type III collagen in normal and osteoarthritic cartilage. Cryotechniques offer exciting possibilities for significantly improving the immunolocalization of collagens and other fixative-sensitive antigens in situ.

Cartilage, Articular↗
PubMed1995

Ultrastructural localization of ras-related proteins using epitope-tagged plasmids.

To determine the ultrastructural distribution of H-ras, the rho proteins rho-A, rho-B, rho-C, and the rac1 protein (members of the ras GTP-binding protein family), we used cDNA expression plasmids in which a short sequence coding for the epitope recognized by the anti c-myc monoclonal antibody 9E10 has been inserted at the N-terminus. Each of the expressed proteins has this epitope as a tag, allowing its localization by light and electron microscopy by the same antibody. After nuclear microinjection of these plasmids into MDCK or Rat 2 cells, expression of the protein (6-18 hr later) was confirmed by immunofluorescence labeling with 9E10 imaged by confocal microscopy. For ultrastructural localization of these tagged proteins, a method was devised to process microinjected cells in situ into low-temperature resin. The proteins were localized on the sections using 9E10 detected with colloidal gold conjugates. Ha-ras protein was localized almost exclusively on the cell membranes. Rho-A and rho-C were predominantly associated with the submembraneous actin network, and rho-B was found in association with multivesicular bodies. Rac1 protein induces the formation of large pinocytotic vesicles and was detected on the cytoplasmic face of these vacuoles. These experiments demonstrate the successful use of this approach for detection of de novo synthesized proteins from microinjected plasmids by both light and electron microscopy on a small (< 50 cells) sample size.

Animals↗