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B Robertson

Publications and source records attributed to B Robertson.

At least 109 records · Page 6Linked to original sources
PubMed1997

A standardized mouse model of Helicobacter pylori infection: introducing the Sydney strain.

BACKGROUND & AIMS: Currently available Helicobacter pylori models show variable and, in some instances, poor colonization. There is a need for a strain with high colonizing ability to act as a standard for animal studies. METHODS: After screening a range of fresh clinical isolates and long-term adaptation in mice, a strain of H. pylon has been isolated with a very good colonizing ability. RESULTS: This strain, named the Sydney strain of H. pylori (strain SS1), is cagA and vacA positive. High levels of colonization (10(6)-10(7) colony-forming units/g tissue) were achieved consistently in C57BL/6 mice. Colonization levels varied depending on the mouse strain used with BALB/c, DBA/2, and C3H/He, all being colonized but in lower numbers. In all strains of mice, bacteria were clearly visible at the junctional zone between the antrum and the body. The phenotype was stable with colonizing ability remaining after 20 subcultures in vitro. The bacterium attached firmly to gastric epithelium. During 8 months, a chronic active gastritis slowly developed, progressing to severe atrophy in both C57BL/6 and BALB/c mice. CONCLUSIONS: The Sydney strain of H. pylori is available to all and will provide a standardized mouse model for vaccine development, compound screening, and studies in pathogenesis.

Animals↗
PubMed1997

The real life of voltage-gated K+ channels: more than model behaviour.

The past ten years have provided an embarrassment of riches for those interested in cloned voltage-gated K+ (Kv) channels. Details of their physiology and pharmacology in expression systems, and their precise cellular location abound, making them excellent targets for pharmacologists. However, there is still a considerable and important gap in our knowledge between the behaviour of expressed Kv channels and K+ currents in vivo. In this review Brian Robertson focuses on a few of the recent developments in the field of Kv channels, namely modulation of their behaviour by accessory subunits, their control, and localization of identified Kv subunits.

Animals↗
PubMed1997

Optical and electrical characterization of bacteriorhodopsin films.

The lifetime of the M-state of bacteriorhodopsin (BR) is increased by genetic and chemical modifications and by solubilizing purple membranes (PMs) with detergent. Chemically modified D96E films as well as D96N films, possess close to 100% bleaching efficiency which makes them attractive for use as image storage media. The mutant S35C has spectral and kinetic properties identical to the WT, both in aqueous suspensions and in films. This indicates that substitution of Ser-35 with Cys has an insignificant effect on the photocycling activity of BR. This substitution provides an attachment site that does not interfere with the function of BR. The magnitude of photocurrent transients generated by mutant BR proteins is used to measure the efficiency of the ground-to-M-state transitions.

Bacteriorhodopsins↗
PubMed1997

The relative potencies of dendrotoxins as blockers of the cloned voltage-gated K+ channel, mKv1.1 (MK-1), when stably expressed in Chinese hamster ovary cells.

1. The mKv1.1 voltage-gated K+ channel has been expressed stably in Chinese hamster ovary cells and whole-cell currents recorded by the patch-clamp method. 2. A range of structurally related peptide toxins (dendrotoxins) from the venom of green mamba (Dendroaspis angusticeps) and black mamba (Dendroaspis polylepis polylepis) snakes were tested for mKv1.1 channel blocking activity. Their potencies were compared based on EC50s derived from their respective concentration-inhibition relationships. 3. The rank order of potency, thus determined was: Toxin K > 7-dendrotoxin(7-Dtx) > delta-Dtx > Toxin I = alpha-Dtx > beta-Dtx. 4. Block was independent of voltage and no effects of the toxins on the kinetics of activation were observed. These results are consistent with a mechanism involving the block of closed channels. 5. A wide range of activity was observed even between toxins with an extremely high degree of sequence homology. Toxin K, in particular was an exquisitely potent blocker of the mKv1.1 channel, having an EC50 of 30 pM compared with 1.8 nM for delta-Dtx in spite of 95% sequence identity.

Animals↗
PubMed1997

The edentulous Le Fort fracture.

A retrospective review of 328 Le Fort fractures has identified 20 (6.1%) of these fractures as edentulous. A review of treatment of the patients was conducted. Conservative (nonsurgical treatment methods) and classic open reductions produce aesthetic and functional results that lead to posterior and oblique positioning of the maxillary occlusal segment in comminuted fractures. Attention to positioning the maxilla by relating it to the mandible through maxillomandibular fixation minimized these deformities. Establishing maxillary-mandibular relationships in edentulous fractures, therefore, seems to have the same importance as establishing occlusion in dentulous patients as an important initial step in the treatment of comminuted Le Fort fractures.

Adult↗
PubMed1997

Pulmonary clearance of 99mTc-DTPA in experimental surfactant dysfunction treated with surfactant instillation.

BACKGROUND: Breakdown of the alveolo-capillary barrier is a characteristic feature of respiratory distress syndrome. Restoration of alveolo-capillary barrier function may be an important aspect of surfactant replacement therapy. We examined the effect of surfactant instillation on alveolo-capillary barrier function in an experimental model of surfactant dysfunction by measuring pulmonary clearance of 99mTc-DTPA. METHODS: Nineteen rabbits were tracheotomized and mechanically ventilated. Surfactant dysfunction was induced by administration of a synthetic detergent in aerosol form. Detergent was given to 13 rabbits; seven rabbits were then treated with instillation of natural surfactant, whereas six rabbits received saline. Six rabbits were used as untreated controls. An aerosol of 99mTc-DTPA was administered to all animals and the pulmonary clearance was measured with a gamma camera. RESULTS: 99mTc-DTPA cleared from the lungs with a half-life of 71 +/- 22 min in the control animals, 21.4 +/- 7.4 min in the surfactant-treated animals and 5.8 +/- 1.5 min in the saline-treated animals. The difference in half-life between groups was highly significant (P < 0.001). There was no change in arterial oxygenation or compliance in controls or in animals treated with saline. In animals treated with surfactant, a small transient reduction in arterial oxygen tension and a more long-standing reduction in compliance were observed. CONCLUSION: Surfactant treatment thus significantly attenuated the effect of detergent treatment but did not restore alveolo-capillary transfer of 99mTc-DTPA to normal.

Animals↗
PubMed1997

A randomized trial of group outpatient visits for chronically ill older HMO members: the Cooperative Health Care Clinic.

OBJECTIVE: To compare the impact of group outpatient visits to traditional "physician-patient dyad" care among older chronically ill HMO members on health services utilization and cost, self-reported health status, and patient and physician satisfaction. DESIGN: A 1-year randomized trial. SETTING: A group model HMO in the Denver Metropolitan area. PARTICIPANTS: Three hundred twenty-one members aged 65 and older, randomized to a group visit intervention (n = 160) or to usual care (n = 161). INTERVENTION: Patients with high health services utilization and one or more chronic conditions had monthly group visits with their primary care physician and nurse. Visits included health education, prevention measures, opportunities for socialization, mutual support, and for one-to-one consultations with their physician, where necessary. MEASUREMENTS: Health services utilization and associated cost, health status, and patient and physician satisfaction. RESULTS: Outcome measures obtained after a 1-year follow-up period showed that group participants had fewer emergency room visits (P = .009), visits to subspecialists (P = .028), and repeat hospital admissions per patient (P = .051). Group participants made more visits (P = .021) and calls (P = .038) to nurses than control group patients and fewer calls to physicians (P = .019). In addition, a greater percentage of group participants received influenza and pneumonia vaccinations (P < .001). Group participants had greater overall satisfaction with care (P = .019), and participating physicians reported higher levels of satisfaction with the groups than with individual care. No differences were observed between groups on self-reported health and functional status. Cost of care per member per month was $14.79 less for the group participants. CONCLUSIONS: Group visits for chronically ill patients reduce repeat hospital admissions and emergency care use, reduce cost of care, deliver certain preventive services more effectively, and increase patient and physician satisfaction.

Aged↗
PubMed1997

Surfactant improves lung function and mitigates bacterial growth in immature ventilated rabbits with experimentally induced neonatal group B streptococcal pneumonia.

AIMS: To study the influence of surfactant on lung function and bacterial proliferation in immature newborn rabbits with experimental group B streptococcal (GBS) pneumonia. METHODS: Preterm rabbit fetuses (gestational age 28 days) underwent tracheotomy and were mechanically ventilated in a warmed body plethysmograph that permitted measurement of lung-thorax compliance. Fifteen minutes after the onset of ventilation the animals received either GBS or saline intratracheally; at 30 minutes, a bolus of saline or 200 mg/kg of a porcine surfactant (Curosurf) was administered via the airway. Bacterial proliferation was evaluated in lung homogenate at the end of the experiments and the results expressed as mean log10 cfu/g lung (SD). Animals receiving only saline (n = 20) or saline and surfactant (n = 20) served as controls. RESULTS: The average survival time was about three hours in all groups. Infected animals receiving surfactant (n = 22) had significantly less bacterial growth (9.09 (0.45) vs 9.76 (0.91)) and improved lung function (compliance: 0.61 (0.14) vs 0.34 (0.19) ml/kg. cm H2O) than infected rabbits receiving saline at 30 minutes (n = 22). CONCLUSION: Surfactant improves lung function and mitigates bacterial growth in preterm rabbits infected with group B streptococci.

Animals↗
PubMed1997

Role of nitric oxide and superoxide anion in spontaneous lung chemiluminescence.

Inhibition of nitric oxide (.NO) synthase by nitro-L-arginine (NLA) decreased baseline chemiluminescence in a dose-dependent fashion up to 78% at 300 microM NLA. This inhibition was prevented by pretreatment with 1 mM arginine. Similarly, addition of superoxide dismutase (SOD; 200 U/ml) to the perfusion buffer inhibited spontaneous light emission by 57%. Addition of NLA after SOD or vice versa did not inhibit light emission any further, suggesting that both .NO and O2.- were precursors of the same oxidant. Production of additional extracellular O2.- by neutrophils activated with phorbol 12-myristate 13-acetate increased light emission by >200%, but this increase was insensitive to NLA. Increasing the intracellular steady-state O2.- concentration by perfusion of control lungs with the Cu and Zn-containing SOD inhibitor diethyldithiocarbamate (1 mM) stimulated light emission up to fourfold, but this spontaneous chemiluminescence was also insensitive to NLA. In experiments using cultured endothelial cells supplemented with extracellular bovine serum albumin (BSA), 5 microM of the Ca2+ ionophore A-23187 (a stimulant of .NO synthase) stimulated chemiluminescence by 40%. This increase was again SOD and NLA sensitive. Addition of NLA after SOD or vice versa did not change light emission. These results suggest that the background chemiluminescence of isolated-perfused intact lungs may result from the constant release of small amounts of O2.- and .NO by endothelial cells into the capillary lumen, which in turn react with BSA in the perfusion buffer.

Animals↗
PubMed1997

Pathophysiology of neonatal lung injury induced by monoclonal antibody to surfactant protein B.

Near-term newborn rabbits were exposed via the airways to a monoclonal antibody to surfactant protein B and ventilated for 0-120 min. Control animals received nonspecific rabbit or mouse immunoglobulin G, saline, or no material via the airways. Administration of the antibody at > or = 40 mg/kg elicited an immediate, significant fall in lung-thorax compliance associated with progressive intra-alveolar edema and/or alveolar collapse and necrosis and desquamation of airway epithelium, and hyaline membranes. The vascular-to-alveolar leak of human albumin and human immunoglobulin G, injected intravenously at birth and determined in lung lavage fluid 60-120 min after instillation of the antibody, was 1.8% for the left lung, with no difference between the markers. The average leak in control animals ventilated for 120 min was < 0.3% (P < 0.05). Cytospin preparations of lung lavage fluid from animals exposed to the antibody showed significantly increased recruitment of neutrophilic granulocytes. The pathology and pathophysiology of neonatal lung injury induced by the monoclonal antibody to surfactant protein B probably reflect a combination of direct inactivation of surfactant and an inflammatory response triggered by the immune reaction.

Animals↗
PubMed1997

Surfactant dysfunction makes lungs vulnerable to repetitive collapse and reexpansion.

Reexpansion of collapsed lung creates intrapulmonary shear forces. In an earlier study we showed that application of a negative end-expiratory airway pressure (NEEP) to normal rabbit lungs in vivo produced tidal collapse and reexpansion with transient changes in compliance and gas exchange but no histologic damage. In the present study we examined NEEP in a model of surfactant perturbation produced by an inhaled aerosol of 2% and 5% dioctyl sodium sulfosuccinate (DOSS). DOSS increased alveolocapillary permeability without affecting compliance or oxygenation. Repeated collapse and reexpansion (RECOREX), caused by NEEP for 3 h was compared with ventilation with positive-end expiratory pressure (PEEP). Groups ventilated with PEEP maintained normal lung mechanics and morphology even if pretreated with DOSS. NEEP disturbed lung mechanics and gas exchange with persistent dose-related histologic damage in animals pretreated with DOSS. Lungs subjected to NEEP without DOSS had normal morphology. We conclude that perturbation of the surfactant system makes lungs vulnerable to injury by RECOREX. The combination of DOSS and NEEP might lead to leakage of plasma proteins into alveoli, causing inactivation of surfactants and increased shear forces with resulting lung damage. Similar mechanisms may accelerate lung damage in the respiratory distress syndrome.

Animals↗
PubMed1997

Biophysical and physiological properties of a modified porcine surfactant enriched with surfactant protein A.

Surfactant protein A (SP-A), a major protein component of natural pulmonary surfactant, is absent in exogenous surfactants currently used in clinical practice. We investigated the physical and physiological properties of one of these modified natural surfactants (Curosurf) after enrichment with 5% SP-A (SP-A-Curosurf). A pulsating bubble system was used for in vitro assessments and ventilated newborn rabbits for evaluation of in vivo effects. In the presence of various potential inhibitors (meconium 5 mg.mL-1, fibrinogen 5 mg.mL-1, albumin 25 mg.mL-1, or whole serum proteins 25 mg.mL-1), Curosurf at a concentration of 5 mg.mL-1 was inactivated while SP-A-Curosurf and natural porcine surfactant at the same concentration had normal maximum and minimum surface tension. This protective effect of SP-A was calcium dependent. In immature newborn rabbits, the improvement of lung-thorax compliance observed after treatment with 100 mg.kg-1 of SP-A-Curosurf was equivalent to that obtained with 200 mg.kg-1 of Curosurf. Similarly, in near-term newborn rabbits with respiratory failure induced by instillation of fibrinogen via the airways, the increase in compliance after administration of 100 mg.kg-1 of SP-A-Curosurf corresponded to that seen after treatment with 200 mg.kg-1 of Curosurf, whereas Curosurf at a dose of 100 mg.kg-1 had no substantial effect. Our data thus indicate that surfactant protein A increases the resistance of Curosurf to inactivation under in vivo conditions.

Albumins↗
PubMed1997

Manual ventilation with a few large breaths at birth compromises the therapeutic effect of subsequent surfactant replacement in immature lambs.

The reason why some infants with respiratory distress syndrome fail to respond to surfactant, or respond only transiently, is incompletely understood. We hypothesized that resuscitation with large breaths at birth might damage the lungs and blunt the effect of surfactant. Five pairs of lamb siblings were delivered by cesarean section at 127-128 d of gestation. One lamb in each pair was randomly selected to receive six manual inflations of 35-40 mL/kg ("bagging") before the start of mechanical ventilation, a volume roughly corresponding to the inspiratory capacity of lamb lungs after prophylactic surfactant supplementation. Both siblings were given rescue porcine surfactant, 200 mg/kg, at 30 min of age. Blood gases and deflation pressure-volume (P-V) curves of the respiratory system were recorded until the lambs were killed at 4 h. The P-V curves became steeper after surfactant in the control group, but no such effect was seen in those subjected to bagging. At 4 h, inspiratory capacity and maximal deflation compliance were almost three times higher (p < 0.01) in the controls than in the bagged lambs. The latter were also more difficult to ventilate and tended to have less well expanded alveoli and more widespread lung injury in histologic sections. We conclude that a few inflations with volumes that are probably harmless in other circumstances might, when forced into the surfactant-deficient lung immediately at birth, compromise the effect of subsequent surfactant rescue treatment. Our findings challenge current neonatal resuscitation practice of rapidly establishing a normal lung volume by vigorous manual ventilation.

Animals↗
PubMed1997

Speed, sex, gay men, and HIV: ecological and community perspectives.

Fifteen years into the HIV/AIDS epidemic, a great deal is now known about the different populations impacted by the disease, including those affected directly or indirectly by drug use. Anthropology has played a critical role in assisting with this task by identifying hidden populations, developing new methodological approaches, and targeting outreach efforts. In spite of this considerable body of ethnographic knowledge, men who have sex with other men (i.e., MSM, or gay and bisexual men) who use drugs have not received the same research attention as other drug users, despite the fact that they represent nearly one-fifth of AIDS cases in the U.S. with injection drug histories. In response to the alarming increase in HIV seroprevalence among this population, this ethnographic project provides preliminary data about those who are at dual risk for HIV through both homosexual behavior and injection drug use.

Adult↗
PubMed1997

Apoptosis in chronic myelogenous leukemia: studies of stage-specific differences.

In this study we compared rates of apoptosis, survival and metabolic activity from CML peripheral blood neutrophils with peripheral blood and bone marrow neutrophils from healthy volunteer donors and studied the influence of the disease stage and of cytokines including G-CSF, GM-CSF and IL-1beta on these parameters. Quantification of apoptosis by morphology, diphenylamine DNA fragmentation assay and by gel electrophoresis showed similar rates of apoptosis in chronic phase CML and normal peripheral blood neutrophils when the cells were incubated in RPMI + FCS or in serum-free medium. However, there were lower rates of apoptosis in accelerated and blast phase CML neutrophils (p < .001) and in normal bone marrow neutrophils (p < .001) compared to normal peripheral blood neutrophils (incubated in RPMI + FCS). Survival among neutrophils from chronic phase or accelerated/blast phase CML patients was significantly longer (p < 0.002 and p < 0.001, respectively) than among normal peripheral blood neutrophils but neutrophils purified from normal bone marrow had a survival rate which fell between that of normal peripheral blood and chronic phase CML patients. When the cells were incubated in RPMI + autologous sera, neutrophils from chronic phase CML patients showed markedly lower rates of apoptosis (p < 0.001) and maintained higher metabolic activities (p < 0.002) compared to normal neutrophils. G-CSF and GM-CSF were found to considerably decrease the rate of apoptosis in chronic phase CML neutrophils (p < 0.001 and p = 0.008 respectively) while IL-1beta did not show any antiapoptotic effect. It is suggested that the endogenous production of growth factors may therefore participate in delaying apoptotic cell death, during the progression of CML.

Adult↗
PubMed1996

Studies on the blocking action of human Kv3.4 inactivation peptide variants in the mouse cloned Kv1.1 K+ channel.

1. Whole-cell patch clamp recordings were made from Chinese hamster ovary (CHO) cells stably expressing homomeric mouse Kv1.1 (delayed rectifier K+; mKv1.1) channels. The effects of internal application of a number of different peptides, based on part of the amino terminal sequence of the human Kv3.4 channel subunit (hKv3.4), were examined in order to determine their influence on N-type inactivation. 2. For the native hKv3.4 peptide, the association rate constant (kon) increased with membrane depolarization, whilst the dissociation rate constant (koff) had little dependence on voltage. This resulted in the apparent dissociation constant (KD) of the hKv3.4 peptide tending to increase with depolarization. 3. In general, kon increased and apparent KD decreased with positive charge of the hKv3.4 peptide variants; in peptides lacking a hydrophobic amino terminal this correlation was not maintained. In contrast, the rate of dissociation of the variant peptides (koff) was independent of net charge. 4. The blocking activity of the hKv3.4 peptide was not dependent on a disulphide bridge between cysteine residues C6 and C24 and the presence of cysteine residues in the hKv3.4 peptide was not a prerequisite for rapid inactivation. All cysteine-substituted variants, especially at C6, showed a more rapid recovery from inactivation than the hKv3.4 peptide. Substitutions at C24, and not C6, reduced kon. 5. The present results concerning the action of the mammalian hKv3.4 channel inactivation particle on mKv1.1 channels complement earlier models for the invertebrate Shaker K+ channel. It is proposed that the hydrophobic amino terminal region of the hKv3.4 inactivation peptide blocks the channel pore, whilst the adjacent positively charged region interacts with negative charges on the channel protein.

Animals↗
PubMed1996

Neurogenesis of subpopulations of rat lumbar dorsal root ganglion neurons including neurons projecting to the dorsal column nuclei.

The time of birth of subpopulations of dorsal root ganglion (DRG) neurons was studied with immunohistochemistry for 5-bromodeoxyuridine (BrdU). Pregnant rats were injected with BrdU i.p. to label the neurons on one of the embryonic days (E) E11-E16. When they were adults, the rats were given injections of Fluoro-Gold (FG) into the gracile nucleus to identify DRG neurons projecting to this structure. Following a 5 day survival period, the animals were perfused with aldehyde fixative. Sections from the L3-L5 DRGs were processed for BrdU immunohistochemistry followed by either immunostaining for the antineurofilament antibody RT97, as marker of the light neuronal subpopulation, or histochemical staining for the B4 isolectin from Griffonia simplicifolia I, as marker of the small dark subpopulation. The results indicated that the DRG neurons were generated between E12 and E16. The RT97+ neurons were generated on E12-E15, with a peak at E13. FG+ neurons, the majority of which were RT97+, were also generated on E12-E15. The B4+ neurons were generated on E13-E16, with a peak around E14. The overall pattern of neurogenesis of the DRG neurons showed that the RT97+ neurons were produced prior to the B4+ neurons. These findings are in agreement with earlier observations that the large DRG neurons are generated earlier than the small dark neurons. Our findings also suggest the existence of a third neuronal subpopulation that might be produced at the latest period of DRG neurogenesis at E15-E16.

Animals↗