Biomedical subjects

R A Hall

Publications and source records attributed to R A Hall.

At least 73 records · Page 4Linked to original sources

PubMed1996

Circulatory management with retrograde cerebral perfusion for acute type A aortic dissection.

BACKGROUND: Cerebral circulation during urgent repair of acute type A aortic dissection has traditionally been managed with cardiopulmonary bypass and aortic cross clamping proximal to the innominate artery or by the use of hypothermic circulatory arrest (HCA). The more recently introduced retrograde cerebral perfusion (RCP) may confer additional cerebral protection during elective aortic arch reconstruction. The purpose of this study was to demonstrate the efficacy of RCP in the urgent repair of acute type A aortic dissection. METHODS AND RESULTS: We evaluated 60 consecutive patients who underwent repair of acute type A aortic dissection over a 6-year period. Patients were grouped according to intraoperative circulatory management strategies. Group 1 consisted of 41 patients operated on early in the series who were managed by cardiopulmonary bypass and standard aortic cross clamping (n = 21) with conversion to HCA (n = 20) if the intimal tear extended into the aortic arch. Since 1993, 19 patients, who make up group 2, were managed with routine open distal anastomosis and HCA with RCP. Data were analyzed for clinically evident, radiographically confirmed cerebrovascular accidents and 60-day mortality and evaluated by chi 2 analysis. Stroke and mortality rates of patients managed with either cardiopulmonary bypass or HCA were 26.3% and 29.3%, respectively. Patients undergoing RCP experienced statistically significant reductions in rates of confirmed cerebrovascular accidents (0%, P = .015) and mortality (5.3%, P = .04). CONCLUSIONS: We conclude that the introduction of circulatory management using RCP with HCA during urgent operative repair of acute type A aortic dissection has significantly improved both stroke and mortality rates.

Acute Disease↗

PubMed1996

Effects of heparin on the properties of solubilized and reconstituted rat brain AMPA receptors.

Heparin was found to bind to alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors and to alter their functional properties. AMPA receptors solubilized in 0.4% Triton X-100 bound to a heparin-agarose column and were eluted by 0.4 M NaCl. Soluble heparin inhibited 10 nM [3H]AMPA binding to detergent-solubilized receptors by 75% (IC50 = 10 micrograms/ml), but had little effect on binding to membrane-associated receptors. The inhibition of [3H]AMPA binding to detergent-solubilized receptors was not observed when binding was measured in the presence of 0.4 M NaCl, and no effect of heparin was observed on binding of the AMPA receptor antagonist [3H]6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Scatchard analyses of [3H]AMPA binding to solubilized receptors revealed that the inhibition induced by heparin was caused by a decrease in the apparent affinity of a portion of the total binding sites. Studies on AMPA receptors reconstituted in artificial lipid bilayers indicated that 10 micrograms/ml heparin enhanced cooperativity between channels and prolonged the lifetime of the open channel, but did not affect the amplitude of single channel currents. Thus, heparin may be added to the list of compounds known to modulate AMPA receptor function. These data also raise the possibility that heparin-containing proteoglycans, which are known to be concentrated at synaptic junctions, might be able to bind AMPA receptors and influence their functional characteristics.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed1996

Molecular characterization of the Japanese encephalitis serocomplex of the flavivirus genus.

The Japanese encephalitis (JE) serocomplex of flaviviruses comprises 10 members, 9 of which: Alfuy (ALF); Koutango (KOU); Kokobera (KOK); Kunjin (KUN); Murray Valley encephalitis (MVE); JE; Stratford (STR); Usutu (USU); and West Nile (WN) have been isolated from Africa, southern Europe, Middle East, Asia, and Australia. The tenth member, St. Louis encephalitis (SLE) virus, is confined to North, Central, and South America. For ALF, KOK, KOU, STR, and USU, no sequence data have as yet been reported, and little molecular phylogeny has been determined for this complex as a whole. Using a rapid, one-step RT-PCR and universal primers, we have amplified and sequenced a 450-600 base pair region of the virus genome encompassing the N terminus of the nonstructural protein NS5 and the 5' end of the 3' noncoding region, for several strains of all of these viruses, except USU and SLE viruses. These data, as well as published sequence data for other flaviviruses, were analyzed with the ClustalW and Phylip computer packages. The resultant phylogenetic data were consistent with some of the current flavivirus serological classification, showing a close relationship between ALF and MVE viruses and between KOK and STR viruses, but suggested that KOK and STR are distantly related to the other viruses and should perhaps be reclassified in their own serocomplex. The data also confirmed the close relationship between KUN and WN viruses and showed that an isolate of KUN virus from Sarawak may represent a "link" between these two virus species. In addition, the primary sequence data revealed a polymorphic region just downstream of the stop codon in the 3' end of the viral genomes.

Amino Acid Sequence↗

PubMed1996

Ultraviolet radiation, thiol reagents, and solubilization enhance AMPA receptor binding affinity via a common mechanism.

The binding properties of membrane-bound or solubilized AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid)-type glutamate receptors from rat brain were tested following exposure to ultraviolet (UV) radiation or incubation with the thiol reagent p-chloromercuriphenyl-sulfonic acid (PCMBS). Brief exposure to UV radiation (254 nm) increased [3H]AMPA binding to brain membranes, while binding to soluble fractions decreased. The increase in brain membrane binding was caused by an apparent interconversion of low-affinity [3H]AMPA binding sites into a higher-affinity state. Incubation with PCMBS caused a significant increase in [3H]AMPA binding to brain membranes but had no significant effect on [3H]AMPA binding to solubilized receptors. There was an interaction between the PCMBS and UV effects in the brain membranes such that prior exposure to one of the treatments reduced the relative magnitude of the other's effects. The present results suggest that ultraviolet radiation, PCMBS and solubilization all increase AMPA receptor binding affinity via a common mechanism.

4-Chloromercuribenzenesulfonate↗

PubMed1996

Distinct distributions of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunits and a related 53,000 M(R) antigen (GR53) in brain tissue.

Polyclonal antibodies against specific carboxy-terminal sequences of known alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor subunits (GluR-4) were used to screen regional homogenates and subcellular fractions from rat brain. Affinity purified anti-GluR1 (against amino acids 877-899), anti-GluR2/3 (850-862), and anti-GluR4a and anti-GluR4b (868-881) labeled distinct subunits with the expected molecular weight of approximately 105,000. These antigens were shown to have distinct distributions in the brain. While GluR2/3 epitopes had a distribution profile similar to that of the presynaptic marker synaptophysin, GluR1 was notable for its abundance in the hippocampus and its relatively low density in neocortical areas, and GluR4 was highly enriched in cerebellar tissue. An additional antigen (glutamate receptor-related, GR53) of lower molecular weight (50,000-59,000) was recognized in rat, human, frog, chick and goldfish brain samples by anti-GluR4a as well as by anti-GluR1 at, an antibody that specifically recognizes the extracellular aminoterminal domain of GluR1 (amino acids 163-188). Both antibodies also labeled antigens of approximately 105,000 mol. wt in brain tissue from all species tested. The approximately 53,000 mol. wt antigen was concentrated 10-20-fold in synaptic membranes vs homogenates across rat brain regions. Both the 105,000 and the 53,000 mol. wt proteins were also concentrated in postsynaptic densities, and neither of the two antigens were evident in seven non-brain tissue samples. These data indicate that AMPA receptors have regionally different subunit combinations and that some AMPA receptor composites include proteins other than the conventional 105,000 mol. wt GluR subunits.

Amino Acid Sequence↗

PubMed1996

Protective immune responses to the E and NS1 proteins of Murray Valley encephalitis virus in hybrids of flavivirus-resistant mice.

The lack of an effective animal model has been a major obstacle in attempts to define the role of humoral and cellular immune responses in protection against flavivirus infection. We have used F1 hybrid mice (BALB/c x C3H/RV) that are heterozygous for the flavivirus resistance allele F1vr and show reduced virus replication in the brain after intracerebral inoculation. F1 hybrid mice challenged by intracerebral inoculation with Murray Valley encephalitis (MVE) virus developed encephalitis 2-3 days later than a genetically susceptible strain (BALB/c) but showed a similar mortality rate. This delay in the onset of disease provided more opportunity for virus clearance by primed immune responses. Using F1 hybrid mice we were able to demonstrate protective immunity induced by structural and non-structural proteins of MVE virus by immunization with pure NS1 protein or recombinant vaccinia viruses that expressed various regions of the MVE genome. These constructs included VV-STR (C-prM-E-NS1-NS2A), VV-delta C (prM-E-Ns1-NS2A) and VV-NS1 (NS1-NS2A). VV-delta C vaccinated mice were completely protected (100% survival)from challenge with 1000 infectious units of MVE virus, while mice inoculated with VV-STR, VV-NS1 or pure NS1 were partially protected (40%, 47% and 85% respectively). Analysis of prechallenge sera and in vivo depletion studies revealed that the solid protection induced by VV-delta C was mediated by neutralizing antibody to the E protein and did not require a CD8+ T cell response. The partial protection provided by VV-STR, VV-NS1 and pure NS1 occurred after induction of antibody to NS1. However, depletion of CD8+ cells prior to virus challenge ablated the protection provided by VV-NS1 indicating some requirement for class I restricted cytotoxic T cells.

Animals↗

PubMed1996

Alphavirus infection in mosquitoes at the Ross River reservoir, north Queensland, 1990-1993.

This study addresses the potential problem of alphavirus infection associated with recreational use of the Ross River reservoir in north Queensland, Australia. From 1990 to 1993, 51,497 adult female mosquitoes were collected mainly by CO2-supplemented light traps. Four localities within the reservoir were considered and compared with mosquitoes collected during 1991 from 2 public localities around Townsville City. Ten isolates of Ross River virus, one of Barmah Forest virus, and 2 of Sindbis virus were recovered from Aedes normanensis, Anopheles amictus, and Culex annulirostris. All isolates were collected during the wet seasons of 1991 and 1992 using an enzyme immunoassay and cross-checked using a polymerase chain reaction assay Estimation of relative hazard was based on total mosquito abundance, prevalence of vector species, and on mosquito infection rates. Based on 1990-93 data, it was concluded that the Big Bay area of the Ross River dam, currently being considered as a primary recreational locality, was relatively safer than Antill Creek, Ross River, and Toonpan and presented no greater hazard than localities around urban Townsville, away from the reservoir. However, because of the changing ecology of the reservoir and lack of a full understanding of annual alphavirus activity, periodic surveillance is recommended.

Aedes↗

PubMed1995

Glycosylation and antigenic variation among Kunjin virus isolates.

Previous studies have found Kunjin (KUN) virus isolates from within Australia to be genetically homogenous and that the envelope protein of the type strain (MRM61C) was unglycosylated and lacked a potential glycosylation site. We investigated the extent of antigenic variation between KUN virus isolates from Australia and Sarawak using an immunoperoxidase assay and a panel of six monoclonal antibodies. The glycosylation status of the E protein of each virus was also determined by N glycosidase F (PNGase F) digestion and limited sequence analysis. The results showed that KUN viruses isolated within Australia oscillated between three antigenic types defined by two epitopes whose expression was influenced by passage history and host cell type. In contrast an isolate from Sarawak formed a stable antigenic type that was not influenced by passage history and was distinct from all Australian isolates. PNGase F digestions of KUN isolates indicated that 19 of the 33 viruses possessed a glycosylated E protein. Nucleotide sequence of the 5' third of the E gene of selected KUN isolates revealed that a single base change in PNGase F sensitive strains changed the tripeptide N-Y-F (amino acids 154-156 of the published sequence) to the potential glycosylation site N-Y-S. Further analysis revealed that passage history also had a significant influence on glycosylation.

Amidohydrolases↗

PubMed1995

Stable maintenance of glutamate receptors and other synaptic components in long-term hippocampal slices.

Cultured hippocampal slices retain many in vivo features with regard to circuitry, synaptic plasticity, and pathological responsiveness, while remaining accessible to a variety of experimental manipulations. The present study used ligand binding, immunostaining, and in situ hybridization assays to determine the stability of AMPA- and NMDA-type glutamate receptors and other synaptic proteins in slice cultures obtained from 11 day postnatal rats and maintained in culture for at least 4 weeks. Binding of the glutamate receptor ligands [3H]AMPA and [3H]MK-801 exhibited a small and transient decrease immediately after slice preparation, but the binding levels recovered by culture day (CD) 5-10 and remained stable for at least 30 days in culture. Autoradiographic analyses with both ligands revealed labeling of dendritic fields similar to adult tissue. In addition, slices at CD 10-20 expressed a low to high affinity [3H]AMPA binding ratio that was comparable with that in the adult hippocampus (10:1). AMPA receptor subunits GluR1 and GluR2/3 and an NMDA receptor subunit (NMDAR1) exhibited similar postcutting decreases as that exhibited by the ligand binding levels, followed by stable recovery. The GluR4 AMPA receptor subunit was not evident during the first 10 CDs but slowly reached detectable levels thereafter in some slices. Immunocytochemistry and in situ hybridization techniques revealed adult-like labeling of subunit proteins in dendritic processes and their mRNAs in neuronal cell body layers. Long-term maintenance was evident for other synapse-related proteins, including synaptophysin, neural cell adhesion molecule isoforms (NCAMs), and an AMPA receptor related antigen (GR53), as well as for certain structural and cytoskeletal components (e.g., myelin basic protein, spectrin, microtubule-associated proteins). In summary, following an initial and brief depression, many synaptic components were expressed at steady-state levels in long-term hippocampal slices, thus allowing the use of such a culture system for investigations into mechanisms of brain synapses.

Amino Acid Sequence↗

PubMed1995

A novel complex formed between the flavivirus E and NS1 proteins: analysis of its structure and function.

We examined the structural features and functional significance of a novel complex which forms between the envelope (E) protein and nonstructural protein NS1 of Murray Valley encephalitis (MVE) virus. Western blot analysis of virus-infected C6/36 cell lysates revealed that the undenatured form of this E-NS1 complex was a heat-sensitive E-(NS1 dimer) complex. Furthermore, the E-NS1 complex was observed in cells infected with Kunjin, Japanese encephalitis, West-Nile and Kokobera viruses which indicates the complex is a common feature of flavivirus infection. E-NS1 complex which had been immunoaffinity purified from MVE-infected cell lysates or eluted from gel slices exhibited partial breakdown into the individual monomers, demonstrating that the complex arose from the association of E and NS1 proteins and was not a single polypeptide created from incomplete gene cleavage. Radioimmunoprecipitation and western blot analysis of MVE-infected cell lysates and culture fluid preparations collected at various times after infection revealed that the E-NS1 complex has a long half life, accumulates in the virus-infected cell with time and is not secreted into the extracellular fluid. We have postulated that the E-NS1 complex, or at least a major portion of the complex, is a non-specific aggregation with no functional significance in the viral life cycle.

Animals↗

PubMed1995

Molecular epidemiology and evolution of mosquito-borne flaviviruses and alphaviruses enzootic in Australia.

Three distinct patterns in the molecular epidemiology and evolution are evident among the alphaviruses and flaviviruses enzootic in Australia. One pattern, exemplified by MVE and KUN viruses, is of a single genetic type evolving slowly and uniformly in geographically widely separated regions of Australia with no evidence of independent divergence. The second pattern, exemplified by RR virus, is of separate genotypes evolving in different geographic regions with significant nucleotide divergence between genotypes. The third pattern, exemplified by SIN virus, is of a succession of temporally related genotypes that extend over most of the Australian continent, with relatively low levels of nucleotide divergence within a genotype, and which are each replaced by the subsequent genotype. These patterns are associated in part due to the nature and dispersal of their vertebrate hosts. Nucleotide divergence rates for Australian alphaviruses are similar to those reported elsewhere. Genomic relationships between Australian flavivirus members of the JE virus serological complex and between Australian alphaviruses are discussed, and evidence is presented for a possible new genomic lineage of SIN virus.

Alphavirus↗

PubMed1995

Thoracoscopic removal of mediastinal parathyroid adenoma.

Mediastinal parathyroid tissue hyperfunctions in as much as 25% of the patients with primary hyperparathyroidism, and this may be responsible for causing conventional operative procedures to fail in as much as one-third of the cases. When lesions prove to not be accessible through a cervical incision, or when a mediastinal adenoma is diagnosed before cervical procedures, median sternotomy and angiographic ablation have been considered the only options for removal. However, thoracoscopy has theoretic advantages over both. Two patients underwent successful thoracoscopic removal of a hyperfunctioning ectopic mediastinal parathyroid adenoma and their cases are presented here.

Adenoma↗

PubMed1995

Fungal pulmonary abscess in an adult secondary to hyperimmunoglobulin E (Job's) syndrome.

Job's syndrome is characterized by recurring bacterial infections of the skin and sinopulmonary tract. Laboratory evaluation reveals consistent elevation of circulating immunoglobulin E levels. The syndrome has been reported as a rare cause of bacterial pulmonary abscess and pneumatocele formation in childhood; here we present a case of cavitating fungal abscess in an adult with Job's syndrome.

Adult↗

PubMed1995

Retrograde cerebral and distal aortic perfusion during ascending and thoracoabdominal aortic operations.

BACKGROUND: Several alternative circulatory management techniques during thoracic aortic reconstruction have been implemented at this institution. This study was performed to assess whether retrograde cerebral perfusion during proximal aortic operations and distal aortic perfusion during thoracoabdominal aortic operations have improved outcomes. METHODS: A retrospective review of 156 patients undergoing elective and emergent operations of the thoracic aorta over the past 7 years was performed. Seventy-five patients underwent proximal aortic procedures: 22 with ascending aneurysms, 45 with type A dissections, and 8 with arch reconstructions. Eighty-one patients underwent descending thoracic or thoracoabdominal procedures: 26 with Crawford type I aneurysms, 18 with type II, 8 with type III, 8 with type IV, 11 with traumatic transections, and 10 with type B dissections. Outcomes measured were neurologic injury, renal failure, and mortality. RESULTS: For proximal aortic procedures, the stroke rate was 12% using cardiopulmonary bypass and 48% using hypothermic circulatory arrest. The addition of retrograde cerebral perfusion decreased the stroke rate to 0% (p < 0.01) and the mortality rate to 7.1% compared with 37% for hypothermic circulatory arrest (p < 0.05). For thoracic and thoracoabdominal aortic operations, straight cross-clamping resulted in a 27% rate of spinal cord injury and a 24% rate of renal failure, whereas the addition of distal aortic bypass resulted in a statistically significant reduction (p < 0.01) in neurologic injury to 7% and a notable, but not statistically significant, decrease in renal failure to 13%. Distal aortic bypass also reduced the mortality rate from 22% to 7% (p < 0.05). CONCLUSIONS: Retrograde cerebral perfusion decreases the stroke rate and mortality rate in proximal aortic operations and distal aortic perfusion decreases the rates of neurologic injury, renal failure, and mortality in thoracoabdominal aortic operations.

Aortic Dissection↗

PubMed1995

Immunodominant epitopes on the NS1 protein of MVE and KUN viruses serve as targets for a blocking ELISA to detect virus-specific antibodies in sentinel animal serum.

Two mosquito-borne flaviviruses, Murray Valley encephalitis (MVE) and Kunjin (KUN), are the aetiological agents of Australian encephalitis. MVE causes a severe and potentially fatal form of the disease while KUN is responsible for only a few relatively mild cases. Therefore it is important that serological tests used in flavivirus surveillance differentiate between infections with these two viruses. However, this has been hampered in the past by the close antigenic relationships between flaviviruses in traditional serological assays. An epitope blocking ELISA using MVE-specific and KUN-specific monoclonal antibodies (mAb) reacting to the non-structural protein NS1 of these viruses and a flavivirus group-specific mAb reacting to the envelope (E) protein was assessed for testing sentinel animals for seroconversion to specific flavivirus infections. Using these assays we were able to detect serum antibodies to a variety of flavivirus in laboratory infected rabbits, and naturally infected chickens and in the case of primary infections, differentiate those caused by KUN or MVE. These assays are now used routinely in our laboratory for testing chicken sera from sentinel flocks in the Kimberley and Pilbara regions of north Western Australia.

Animals↗

PubMed1995

Specific enzyme immunoassays for the rapid detection of Ross River virus in cell cultures inoculated with infected mosquito homogenates.

BACKGROUND: Ross River (RR) virus is a mosquito-borne alphavirus and one of the aetiological agents of epidemic polyarthritis in humans. Early detection of increased virus activity in mosquito populations enables public health authorities to implement measures to reduce the number of human infections during epidemics. However, current surveillance techniques require a minimum of four weeks for viruses to be isolated and identified. OBJECTIVES: This study was carried out to assess the use of enzyme immunoassays (EIA) as rapid alternatives to traditional cell culture techniques for detection of RR virus in mosquitoes. STUDY DESIGN: Enzyme immunoassays and immunoperoxidase assays were developed using RR-specific monoclonal antibodies and compared to traditional methods for detection of RR virus in field-caught mosquito samples. RESULTS: By inoculation of C6/36 cell cultures with mosquito homogenates and testing monolayers and culture supernatant by EIA, RR virus was detected and identified in all infected samples within 6 days. CONCLUSIONS: The use of EIA provides a rapid, sensitive and specific alternative to traditional methods for the detection of RR virus in mosquito vectors.

Journal Article↗

PubMed1994

Effects of cyclothiazide on synaptic responses in slices of adult and neonatal rat hippocampus.

The effects of cyclothiazide, a drug that blocks AMPA receptor desensitization, on synaptic responses were studied in field CA1 of hippocampal slices from adult and neonatal rats. Cyclothiazide (100 microM) reliably increased AMPA receptor-mediated field EPSP decay times in adult slices but only after prolonged (60-120 min) applications. In neonatal slices, 30 min applications of cyclothiazide were sufficient to produce large and long-lasting increases in response decay times. Since the effects of cyclothiazide on AMPA receptor binding properties were similar in adult and neonatal forebrain membranes, the data indicate that the slow action of the drug in adult slices is probably due to diffusion barriers. The prolongation of EPSP decay by cyclothiazide suggests that AMPA receptor-mediated synaptic responses in hippocampus are terminated by receptor desensitization.

Animals↗

PubMed1994

Kainate binding to the AMPA receptor in rat brain.

Displacement of [3H]AMPA and [3H]CNQX by kainate was measured in membranes and solubilized fractions from rat brain. In soluble fractions, plots of [3H]AMPA and [3H]CNQX binding displaced by kainate resulted in one-site fits with Ki values in the range of 1-3 microM. In membranes, plots of [3H]AMPA binding displaced by kainate resulted in graphs which were better fit by two-site regression analysis than by a one-site fit. The Ki value for the high-affinity component of these two-site fits was 3-9 microM and the low-affinity component Ki was in the range of 70-120 microM; similar values were determined for kainate displacement of [3H]CNQX. The presence of thiocyanate ions had no effect on kainate displacement of [3H]CNQX. Since the affinity for kainate of the presumed synaptic AMPA receptor is in the range of EC50 values for kainate determined from physiological studies, these data contribute further evidence for the idea that kainate binding to synaptic AMPA receptors may be responsible for many of kainate's physiological effects.

6-Cyano-7-nitroquinoxaline-2,3-dione↗