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Biomedical subjects

D Bruce

Publications and source records attributed to D Bruce.

At least 55 records · Page 3Linked to original sources
PubMed1997

The origins of nonphotochemical quenching of chlorophyll fluorescence in photosynthesis. Direct quenching by P680+ in photosystem II enriched membranes at low pH.

In most plants and algae, a down-regulation of photosynthesis under "excess" light conditions occurs which is associated with a quenching of chlorophyll a fluorescence. This nonphotochemical quenching of chlorophyll a fluorescence most likely arises from a mechanism which protects photosystem II from excessive excitation and resulting photoinhibition. In this report, nonphotochemical quenching of variable chlorophyll a fluorescence was induced by low pH in photosystem II enriched spinach thylakoid membranes. The origin of quenching was investigated with picosecond fluorescence decay spectroscopy in samples suspended in buffers ranging from pH 6.5 to pH 4.0. The yield of a relatively slow (approximately 1.5 ns) fluorescence decay process associated with the photosystem II reaction center decreased with decreasing pH. There were no significant changes in the yield of faster decay components associated with photosystem II antenna chlorophyll a processes. These results suggest a reaction center based rather than antenna chlorophyll based mechanism for nonphotochemical quenching in these preparations. Measurements of the photosystem II absorption cross section revealed no decrease in the functional antenna size at low pH which also supports a reaction center quenching mechanism. The kinetics of electron transfer in photosystem II were investigated using a pump probe spectrometer which measured simultaneously the flash-induced absorbance change at 820 nm (formation of oxidized photosystem II reaction center pigment, P680+) and the variable fluorescence yield (formation of reduced photosystem II, electron acceptor, QA-). A large increase in the lifetime of P680+ at low pH was correlated with fluorescence quenching. After flash excitation of photosystem II the loss of fluorescence quenching occurred with the same kinetics as the reduction of P680+. In conflict with reaction center based quenching mechanisms based on charge recombination between P680+ and QA-, the oxidation rate of QA- was unaffected by low pH and under all conditions occurred at a slower rate than the reduction of P680+. Our data are discussed in terms of a model for low pH dependent nonphotochemical quenching in photosystem II based on direct quenching by P680+.

Chlorophyll↗
PubMed1997

Magnetic resonance imaging in relation to functional outcome of pediatric closed head injury: a test of the Ommaya-Gennarelli model.

OBJECTIVE: To characterize late neuropathological findings of pediatric closed head injury (CHI), to assess depth of brain lesion in relation to acute severity, and to assess long-term outcome to test the Ommaya-Gennarelli model. METHODS: Magnetic resonance imaging (MRI) at least 3 months postinjury in a prospective sample (n 5 169) and at least 3 years after CHI in a retrospective sample (n 5 82) was studied. Lesion volume was measured by planimetry. Acute CHI severity was measured by the Glasgow Coma Scale. Patients were classified according to the depth of the deepest parenchymal lesion into no lesion, subcortical, and deep central gray/brain stem groups. The outcomes were assessed by the Glasgow Outcome Scale and the Vineland Adaptive Behavior Scale, which were performed at the time of the MRI in the retrospective sample and up to 3 years postinjury in the prospective sample. RESULTS: Focal brain lesions were present in 55.4% of the total sample. Depth of brain lesion was directly related to severity of acute impairment of consciousness and inversely related to outcome, as measured by both the Glasgow Outcome Scale and the Vineland Adaptive Behavior Scale. A rostrocaudal gradient of hemispheric lesion frequency was observed, whereas the posterior lesions of the corpus callosum were particularly common. Total lesion volume could not explain the depth of lesion effect. CONCLUSION: Our findings extend support for the Ommaya-Gennarelli model to pediatric CHI, indicating that depth of brain lesion is related to functional outcome. The relative frequency of focal brain lesions revealed by late MRI is higher than that of previous findings using acute computed tomography. Future investigations could explore whether depth of lesion observed using late MRI is sensitive to neuroprotective interventions.

Adolescent↗
PubMed1996

Effects of ectopic overexpression of p21(WAF1/CIP1) on aneuploidy and the malignant phenotype of human brain tumor cells.

p21WAF1/CIP1 is a downstream effector of the p53 tumor suppressor gene and a universal cyclin-dependent kinase (CDK) inhibitor. To determine the ability of p21WAF1/CIP1 to function as a tumor suppressor, we constructed a replication-defective adenovirus vector containing p21WAF1/CIP1 (Adp21WAF1/CIP1) to effect ectopic overexpression in a p53-defective human astrocytoma cell line, U-373MG. We observed a marked decrease in CDC2 and CDK2 kinase activity associated with a corresponding decrease in the amount of CDC2 but not CDK2 protein; a decreased growth potential of Adp21WAF1/CIP1-infected cells demonstrated by diminished [3H]thymidine incorporation, increased cell doubling time and G1-arrested cell cycle; an association between Adp21WAF1/CIP1-infected cells and inhibition of aneuploid cell accumulation; and an alteration of the malignant phenotype of cells was evidenced by the loss of anchorage-independent growth in soft agar and the failure to induce tumorigenesis in both peripheral and intracerebral xenograft models, including the prevention of tumor formation Adp21WAF1/CIP1 infection 2 days post tumor cell implantation. Adp21WAF1/CIP1. Adp21WAF1/CIP1 appears to be a strong candidate for gene therapy studies based on these studies indicating that Adp21WAF1/CIP1 inhibits proliferation, tumorigenicity and aneuploidy in human brain tumor cells.

Aneuploidy↗
PubMed1996

Semantic memory following pediatric head injury: relationship to age, severity of injury, and MRI.

The effects of closed head injury (CHI) severity (mild vs. severe) and age at injury were analyzed in a longitudinal study (3. 12 months postinjury) of semantic memory which used magnetic resonance imaging (MRI) to characterize focal brain lesions. Semantic memory was evaluated by word and category fluency, semantic verification, semantic clustering in word list recall, and vocabulary. Episodic memory was assessed by word list recall. Comparison of normal control (n = 104) data with the patients' data (n = 77) at 3 months postinjury disclosed semantic and episodic memory deficits in the severe CHI patients. Analysis of the longitudinal data revealed significant effects of age at injury for all of the semantic memory measures. The effects of injury severity were confined to the latency of verifying correct statements. Volume of left frontal and extrafrontal lesions was predictive of performance on several semantic memory measures, but less robust for right hemisphere lesions.

Adolescent↗
PubMed1995

Superimposition of PET images using 18F-fluorodeoxyglucose with magnetic resonance images in patients with pancreatic carcinoma.

Six patients with histologically proven adenocarcinoma of the pancreas were studied using 2-deoxy-2-[18F]-fluoro-D-glucose (18F-FDG) using positron emission tomography (PET), and magnetic resonance imaging (MRI). In all six cases there was avid accumulation of 18F-FDG within the pancreatic tumour and clear visualization of the tumour on the MRI images. Delineation of the tumours was aided by superimposition of the images from the two imaging methods, which was achieved by using a system of surface markers.

Adenocarcinoma↗
PubMed1995

Left ventricular thrombi in a patient with the antiphospholipid syndrome.

A 41 year old woman with the antiphospholipid antibody syndrome presented with a cerebral embolus. This was caused by a mobile left ventricular thrombus that later resolved. There was an additional old left ventricular thrombus. Left ventricular thrombi such as these have not been previously described in this syndrome, and may have been under diagnosed.

Adult↗
PubMed1995

Craniofacial trauma in children.

Craniofacial trauma is relatively uncommon in children, but the potential involvement of the structures at the base of the skull and the intracranial space makes it important for physicians to understand the potential dangers presented by such injuries. This report delineates the different types of injury that can damage the upper facial skeleton and the brain of a child. The author reviews initial management and diagnosis of such injuries and examines the approach to definitive reconstructive surgery using three case studies as examples for discussion.

Accidents, Traffic↗
PubMed1994

Reactivity of sera collected from dogs in Mutare, Zimbabwe, to antigens of Ehrlichia canis and Cowdria ruminantium.

Six of 20 sera from apparently healthy dogs in Mutare, Zimbabwe, contained antibodies which were reactive with Cowdria ruminantium and Ehrlichia canis in indirect fluorescent antibody tests at similar titres. In Western blots these sera recognised the immunodominant antigen bands of the two organisms. Sera with high titres (> 1/80) recognised additional antigen bands of each organism. It was not possible to determine whether these dogs had been exposed to C ruminantium, E canis or other Ehrlichia species. In areas where these organisms coexist serological tests for canine ehrlichiosis should be interpreted with caution.

Animals↗
PubMed1994

Thromboembolic disease due to thermolabile conformational changes of antithrombin Rouen-VI (187 Asn-->Asp)

A new variant of antithrombin (Rouen-VI, 187 Asn-->Asp) with increased heparin affinity was shown to have normal inhibitory activity which decreased slowly at 4 degrees C and rapidly at 41 degrees C. On electrophoresis the freshly isolated variant had an anodal shift relative to native antithrombin due to the mutation. A further anodal transition occurred after either prolonged storage at 4 degrees C or incubation at 41 degrees C due to the formation of a new inactive uncleaved component with properties characteristic of L-form (latent) antithrombin. At the same time, polymerization also occurred with a predominance of di-, tri-, and tetra-mers. These findings fit with the observed mutation of the conserved asparagine (187) in the F-helix destabilizing the underlying A-sheet of the molecule. Evidence of A-sheet perturbation is provided by the increased rate of peptide insertion into the A-sheet and by the decreased vulnerability of the reactive loop to proteolysis. The spontaneous formation of both L-antithrombin and polymers is consistent with our crystal structure of intact antithrombin where L-form and active antithrombin are linked together as dimers. The nature of this linkage favors a mechanism of polymerization whereby the opening of the A-sheet, to give incorporation of the reactive center loop, is accompanied by the bonding of the loop of one molecule to the C-sheet of the next. The accelerated lability of antithrombin Rouen-VI at 41 versus 37 degrees C provides an explanation for the clinical observation that episodes of thrombosis were preceded by unrelated pyrexias.

Adult↗
PubMed1993

Crystallization and preliminary X-ray diffraction analysis of two conformations of intact human antithrombin.

Human antithrombin has been crystallized by microdialysis at pH 6.7 using 18% (w/v) polyethylene glycol-4000 as precipitant. Under these conditions two crystal forms grew. The first started growing after ten days, diffracted to 3.0 A resolution and belongs to the monoclinic space group P2(1) with two molecules in the asymmetric unit and unit cell dimensions a = 70.1 A, b = 101.5 A, c = 90.5 A and beta = 105.9 A. The other crystal form took more than three months to appear, diffracted to 5.5 A and belongs to the hexagonal space group of either P6(1) or P6(5) with unit cell dimensions of a = b = 99.3 A and c = 152.9 A and two molecules in the asymmetric unit. The antithrombin redissolved from the monoclinic crystals was shown both by SDS-polyacrylamide gel electrophoresis and by protein sequence analysis to be intact while that from the hexagonal crystals was cleaved in the reactive centre loop between the P'2 and P'3 (i.e. Leu-Asn) residues. Further analysis of the intact inhibitor from the monoclinic crystals indicated that the antithrombin was present in two different conformations; an active form which could inhibit thrombin and form a stable complex with the protease, and a form which was inactive as an inhibitor and which also did not act as a substrate for thrombin. This latter form also had a low affinity for heparin and in these ways resembles latent antithrombin. The active material from the monoclinic crystals had an association rate constant with thrombin in the presence of heparin (kass) of 7.5 x 10(7) M-1 s-1 (kass for native antithrombin = 8.2 (+/- 1.0) x 10(7) M-1 s-1) indicating it still had effective heparin cofactor activity. X-ray diffraction analysis also suggests that two different protein conformations exist within the monoclinic crystals. Whereas the rotation function peak heights are equal for both molecules in the asymmetric unit using the structure of intact ovalbumin as a search model, one of the two molecules gives a much clearer signal than the other when the structures of the two cleaved serpins, alpha 1-antitrypsin and alpha 1-antichymotrypsin are used.

Antithrombins↗
PubMed1993

Cognition in relation to magnetic resonance imaging in head-injured children and adolescents.

To investigate the relationship between cognitive sequelae and magnetic resonance imaging (MRI) findings following closed head injury of varying severity in the pediatric age range, 76 head-injured children and adolescents were studied at least 3 months after trauma and compared with 57 normal controls. Problem solving, planning, verbal and design fluency, memory, and response modulation were assessed. Significant effects of injury were obtained on all of the cognitive measures. Cognitive impairment was more consistently present on the various outcome measures in children who were 6 to 10 years old at the time of the study than in the older children and adolescents. Magnetic resonance imaging disclosed areas of abnormal signal in the frontal lobes of 42 patients, whereas focal lesions restricted to the extrafrontal region were found in 15 children. Regression analyses disclosed that taking into account the size of frontal lobe lesion enhanced the relationship between cognitive performance and the severity of injury.

Adolescent↗
PubMed1993

Collaborative practice: a shared success.

A community hospital reflects on changes made when implementing a collaborative practice theory. Using a philosophy that called both professional groups to "share and work together to provide thorough and consistent patient care," a successful joint practice was operational within a year.

Colorado↗
PubMed1992

Late MRI after head injury in children: relationship to clinical features and outcome.

To characterize the brain pathology in relation to long-term outcome after pediatric head injury, 55 children were studied by magnetic resonance imaging (MRI) at least 3 months after sustaining moderate to severe closed head injury (CHI). Thirty-nine of the patients had abnormal signal intensity consistent with residual brain lesions, including 28 children with lesions involving the frontal lobes. The clinical features of children with frontal lesions, extrafrontal lesions, and diffuse injury were compared. The analysis disclosed that children with frontal lobe lesions were more frequently disabled than children who sustained diffuse injury. Our MRI findings indicate that residual brain lesions are more common after moderate to severe CHI in children than previously thought and that the frontal lobes are most frequently involved. Further investigation is indicated to elucidate whether distinctive cognitive and behavioral sequelae are associated with frontal lobe lesions in children.

Adolescent↗
PubMed1992

Corpus callosum lesions after closed head injury in children: MRI, clinical features and outcome.

Thirty-four children who sustained moderate to severe closed head injury underwent magnetic resonance imaging (MRI). Eight (24%) had MRI evidence of corpus callosum injury, most commonly within the posterior body and splenium. In contradistinction to reports in adults, there was no definite relationship between callosal injury and lower initial Glasgow Coma Scale scores, nor was there a significantly higher incidence of primary brain-stem lesions, diffuse axonal shear injury or intraventricular hemorrhage. In none of these 8 children did the initial admission computed tomography show evidence of callosal injury. Callosal injuries on MRI are not necessarily a poor prognostic finding, the majority of the 8 children showing good functional recovery.

Adolescent↗
PubMed1992

Narrative discourse after closed head injury in children and adolescents.

This study examined narrative discourse in 20 children and adolescents at least 1 year after sustaining a head injury. Narratives were analyzed along the dimensions of language structure, information structure, and flow of information. Severity of impaired consciousness was associated with a significant reduction in the amount of language and information. The most important finding which emerged was the disruption in information structure. This pattern confirms the impression of disorganized discourse in severely injured children. Explanations for the disruption in information structure are explored in terms of the role of vocabulary, memory, and localization of lesion according to magnetic resonance imaging. In view of recent evidence that frontal lobe damage is associated with discourse formulation deficits in adults and is the most common site of focal lesion in closed head injury, we examined discourse patterns in individual patients with frontal lobe lesions. Preliminary data from our single-case studies suggest discourse patterns similar to those reported for adults with frontal lobe injuries.

Adolescent↗
PubMed1992

Molecular biology for platelet alloantigen typing.

Hitherto, full investigation of patients with alloimmunization to platelet-specific antigens has been difficult due to the limited availability of both typing reagents and panels of typed platelets. Following recent advances in the understanding of the molecular and genetic basis of platelet alloantigens, it is now possible to genotype individuals for the alleles coding for the epitopes of four platelet antigen systems (HPA-1-4). This is based on the finding that the two alleles differ by only a single base pair substitution, resulting in one amino acid difference in the relevant platelet glycoprotein. The technique involves amplification of the relevant segments of genomic DNA from any nucleated cell by the polymerase chain reaction, followed by restriction fragment length polymorphism analysis. The technique allows investigation of thrombocytopenic individuals and fetuses/neonates, and can be readily applied to large-scale typing of platelet donors.

Alleles↗