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Biomedical subjects

L Griffiths

Publications and source records attributed to L Griffiths.

At least 55 records · Page 3Linked to original sources
PubMed1993

Regulation and sequence of the structural gene for cytochrome c552 from Escherichia coli: not a hexahaem but a 50 kDa tetrahaem nitrite reductase.

The structural gene, nrfA, for cytochrome c552, which is the terminal reductase of the formate-dependent pathway for nitrite reduction to ammonia, has been located at co-ordinate 4366 on the physical map of the Escherichia coli chromosome. The DNA sequence of nrfA encodes a tetrahaem c-type cytochrome with a predicted M(r) for the unprocessed product of 53,788. Cleavage of the putative signal peptide at Ala-26 would result in a mature, periplasmic cytochrome of M(r) 50,580 rather than a larger hexahaem cytochrome, as has been widely reported previously. A cytochrome of this size was detected by staining SDS-polyacrylamide gels for covalently bound haem. This cytochrome was partially purified by anion exchange chromatography and confirmed to be cytochrome c552 by difference spectroscopy. Similar cytochromes were detected in five other E. coli strains including strain ST 249, which was used previously to purify and characterize the protein. A plasmid with an in-phase deletion within nrfA directed the synthesis of a truncated haemoprotein of the predicted mass. In-phase translational fusions to lacZ were used to locate the nrfA translation start, and the transcription start site was found by S1 mapping. Expression from the FNR-dependent nrfA promoter was almost totally repressed during aerobic growth, partially induced during anaerobic growth in the absence of nitrite or in the presence of nitrate, but fully induced only during anaerobic growth in the presence of nitrite. No nitrate repression was detected in a narL mutant, but nitrite induction was unaffected, indicating that the nitrite-sensing mechanism is independent of the NarL protein. Expression from the nrfA promoter was subject to glucose repression but regulation was independent of the CRP-cAMP complex.

Aerobiosis↗
PubMed1992

Arteriovenous fistula after arthroscopic synovectomy in a patient with haemophilia.

Arteriovenous fistula is a rare complication of arthroscopy. We report a human immunodeficiency virus-positive person with haemophilia who 19 months after an arthroscopic synovectomy of the knee presented with increasingly frequent haemarthroses and a palpable thrill over the knee. Angiography confirmed an arteriovenous fistula. The patient was successfully treated by surgical ligation of the communicating vessels. The literature regarding vascular injuries after arthroscopy of the knee is reviewed.

Adolescent↗
PubMed1992

Latent equid herpesviruses 1 and 4: detection and distinction using the polymerase chain reaction and co-cultivation from lymphoid tissues.

The polymerase chain reaction (PCR) and co-cultivation were used to identify the lymphoreticular system as the site of latency of equid herpesvirus I (EHV-1). Primers for PCR were designed from aligned nucleotide sequences of the glycoprotein gB genes to amplify the same region of both the EHV-1 and EHV-4 genomes. Subsequent restriction digests using specific enzymes distinguished the amplified fragments of the EHV-1 genome from those of the EHV-4 genome. Ten weeks following an experimental infection of five ponies with EHV-1, latent virus was detected by PCR and recovered by co-cultivation, predominantly from lymphoid tissues draining the respiratory tract. Significantly, latent EHV-1 also persisted in peripheral blood leukocytes (PBL). Latent EHV-4, presumably from a preceding natural infection, was also detected in some tissues, including PBL, from all animals. Of additional interest was the recovery of EHV-1 and -4 only in the presence of the ubiquitous EHV-2.

Acute Disease↗
PubMed1992

Transcriptional control, translation and function of the products of the five open reading frames of the Escherichia coli nir operon.

Five open reading frames designated nirB, nirD, nirE, nirC and cysG have been identified from the DNA sequence of the Escherichia coli nir operon. Complementation experiments established that the NirB, NirD and CysG polypeptides are essential and sufficient for NADH-dependent nitrite reductase activity (EC 1.6.6.4). A series of plasmids has been constructed in which each of the open reading frames has been fused in-phase with the beta-galactosidase gene, lacZ. Rates of beta-galactosidase synthesis during growth in different media revealed that nirB, -D, -E and -C are transcribed from the FNR-dependent promoter, p-nirB, located just upstream of the nirB gene: expression is co-ordinately repressed by oxygen and induced during anaerobic growth. Although the nirB, -D and -C open reading frames are translated into protein, no translation of nirE mRNA was detected. The cysG gene product is expressed from both p-nirB and a second, FNR-independent promoter, p-cysG, located within the nirC gene. No NADH-dependent nitrite reductase activity was detected in extracts from bacteria lacking either NirB or NirD, but a mixture of the two was as active as an extract from wild-type bacteria. Reconstitution of enzyme activity in vitro required stoichiometric quantities of NirB and NirD and was rapid and independent of the temperature during mixing. NirD remained associated with NirB during the initial stages of purification of the active enzyme, suggesting that NirD is a second structural subunit of the enzyme.

Bacterial Proteins↗
PubMed1991

Event-related potentials and selective attention in major depressive illness.

Depressive episodes have been frequently characterized by deficits in information processing efficiency which are particularly evident when required to sustain or focus attention. As cerebral event-related potentials (ERPs) have been shown to reflect various aspects of selective attention and attentional dysfunction, this study attempted to examine ERPs in depressed patients performing a selective auditory attention task. Twenty-nine patients with a diagnosis of major depressive disorder (DSM-III) and 15 normal, non-psychiatric controls served as experimental subjects. Auditory potentials were recorded from the vertex of subjects who listened selectively to a series of tone pips in one ear and ignored concurrent tone pips to the other ear. Tone pips were delivered at short (320-500 ms) interstimulus intervals and subjects were required to detect, within the attended ear, rare 'target' tones of a different pitch than the more frequent 'standard' tones. In addition to behavioral indices of 'hits' and 'false alarms', ERP-derived measures included N1 amplitudes to attended and ignored stimuli, 'coefficients of attention' as calculated from N1 amplitude ratios and the latency onset and amplitude of the 'negative difference' (Nd) wave resulting from the subtraction of attended and ignored waveforms. Behavioral measures indicated that depressed patients were as efficient as controls in task performance and in fact they exhibited a significant left ear advantage in the additional task. Although a significant 'N1 effect' was observed with attended tones eliciting larger amplitudes than unattended tones, ERP measures of selective attention did not tend to differentiate the two groups.

Adult↗
PubMed1991

Preparatory brain potentials in major depressive disorder.

1. Psychomotor slowing in depression is frequently reflected by delayed reaction times (RT). 2. The role of central arousal mechanisms in response slowing was examined by comparing scalp-recorded slow negative potentials of depressed patients with normal controls in two separate studies. 3. Varying fore-warned RT conditions elicited contingent negative variation (CNV) waveforms and the resultant mid-point amplitudes of these waveforms together with orienting (O-wave), expectancy (E-wave) and post-imperative negative variation (PINV) component amplitudes and sensory evoked responses (N1, P2) were compared between groups. 4. RTs were significantly slowed in depressed patients and the patient group exhibited consistently larger PINV amplitudes. Depending on the RT condition, patients also exhibited larger mid-point CNV amplitudes and smaller N1 and P2 amplitudes.

Adult↗
PubMed1991

The role of endothelial cell infection in the endometrium, placenta and foetus of equid herpesvirus 1 (EHV-1) abortions.

One of three mares in the last trimester of pregnancy became paraplegic 7 days after experimental infection with EHV-1 and was killed 10 days after infection (d.p.i.). The other two mares aborted foetuses at 12 and 14 d.p.i. In the first mare, virus was detected by immunofluorescence (IIF) and immunoperoxidase (IP) staining in endothelial cells of the endometrium, placenta and umbilical vein, but not in any other foetal tissues. In the experimentally aborted foetuses, and in two other independent field cases of abortions, endothelial cell infection was also detected in the foetuses, both in major blood vessels and in capillaries or sinusoidal cells associated with parenchymal lesions. In these four cases there were also positive endothelial placental lesions detected by IIF or IP, although it was not always possible to isolate virus from these tissues, as it was from the foetuses. The evidence suggests that infection of maternal endothelial cells has a major role in the pathogenesis of abortion, and that endothelial cells are also involved in dissemination of virus within the foetus.

Abortion, Septic↗
PubMed1991

Effects of intra-core mechanical interlocks and cement type on full crown retention.

This study compared the retention of full cast crowns over cores of amalgam or a Bis-GMA composite resin when cemented with a Bis-GMA composite resin cement or a zinc phosphate cement. The surfaces of two groups of Bis-GMA composite cores were mechanically altered with a groove or dimples to provide physical retention; two other groups were either etched with 1.23% acidulated phosphate fluoride (APF) or exposed to a zinc oxide-eugenol interim luting agent before crown cementation. Control groups of unaltered composite or amalgam core served as comparison standards. The zinc phosphate cement provided significantly greater retention with the amalgam core than with any of the composite cores. The APF-treated composite cores had the least retention of any of the zinc phosphate cementations. Cementation failure over the composite cores was at the core surface. Crown retention over the control and dimpled-surface composite core with the resin cement was twice that with zinc phosphate, and significantly greater than retention of castings cemented with the resin cement over amalgam cores. Retention over amalgam cores was significantly greater with zinc phosphate cement than with the composite resin cement.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1990

Different physiological roles of two independent pathways for nitrite reduction to ammonia by enteric bacteria.

Operon fusion strains and mutants of Escherichia coli K-12 lacking the NADH-dependent nitrite reductase have been used to determine the regulation and physiological roles of two independent pathways for nitrite reduction to ammonia. Both the formate- and NADH-dependent pathways (Nrf and Nir, respectively) were totally repressed during aerobic growth, partially active during anaerobic growth in the absence of nitrite and further induced anaerobically by nitrite. Both were dependent upon a functional Fnr protein (a transcription activator of genes for anaerobic respiration). During anaerobic growth in the presence of nitrate, the Nir pathway was fully induced but Nrf was strongly repressed. Mutants defective in the NarL protein, which induces transcription of nitrate reductase genes but represses fumarate reductase genes in the presence of nitrate, were derepressed for Nrf activity during growth with nitrate, but the Nir enzyme was less active. The synthesis of Nrf components was also sensitive to glucose repression and weak activation by NarL during growth in the absence of nitrate. These data indicate that the Nir pathway provides a mechanism for detoxifying nitrite formed in the cytoplasm as a product of nitrate reduction. In contrast, the electrogenic reduction of nitrite by the Nrf pathway provides a secondary source of energy during anaerobic growth and is consequently repressed by the NarL protein when the thermodynamically more favourable electron acceptor, nitrate, is available. Two short DNA sequences, 5'-TACCAT-3' and 5'-CTCCTT-3', were found in the promoters of operons known to be activated or repressed by the NarL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Aerobiosis↗
PubMed1990

Earth benefits from space life sciences.

Contributions of space exploration which are widely recognized are those dealing with the impact of space technology on public health and medical services in both urban and remote rural areas. Telecommunications, image enhancement, 3-dimensional image reconstructions, miniaturization, automation, and data analysis, have transformed the delivery of medical care and have brought about a new impetus to the field of biomedicine. Many areas of medical care and biological research have been affected. These include technological breakthroughs in such areas as: (1) diagnosis, treatment, and prevention of cardiovascular diseases, (2) new approaches to the understanding of osteoporosis, (3) early detection of genetic birth defects, (4) emergency medical care, and (5) treatment of chronic metabolic disorders. These are but a few examples where technology originally developed to support space medicine or space research has been applied to solving medical and health care delivery problems on Earth.

Aerospace Medicine↗
PubMed1989

Further investigations of equine interferons in vitro.

Following a published procedure, preparations of equine interferon (EqIFN) were prepared. Equine mononuclear leukocytes were induced with equine influenza virus to yield a preparation designated EqIFN-alpha, or with phytohemagglutinin to yield a preparation designated EqIFN-gamma. A preparation designated EqIFN-beta was obtained from equine embryo kidney cells treated with poly(rI):poly(rC) and DEAE Dextran. The pH and heat stability of these preparations were studied, and also their activity on various equine and ovine cells challenged with difference viruses. Unexpectedly, the EqIFN-gamma preparation was found to be stable at pH 2 and to heat at 60 degrees C for 2 h, whereas the EqIFN-beta preparation was labile under these conditions.

Animals↗
PubMed1989

Equine interferons following exposure to equid herpesvirus-1 or -4.

When 23 ponies were infected with equid herpesvirus-1 or -4 (EHV-1 or EHV-4), nasal shedding of interferon (IFN) correlated closely with the duration of viral excretion. Equine interferon (EqIFN) was detected in the serum only from animals infected with the EHV-1 virus, and here high levels correlated with clinical symptoms of locomotor disorder and indicated a poor prognosis. Low levels of IFN were detected in explanted mononuclear cells from ponies infected with either virus.

Animals↗
PubMed1989

Subarachnoid haemorrhage--can we do better?

Patients with subarachnoid haemorrhage often have warning symptoms which are unrecognized. Specific neurological signs such as cranial nerve palsies due to aneurysm expansion may occur. Sudden and severe 'out-of-the-blue' headache following minor haemorrhage may be misinterpreted as migraine. Focal neurological signs from secondary ischaemia may be misinterpreted as thromboembolic events. Computed tomography (CT) head scans can be misleading especially if performed too late.

Adult↗
PubMed1987

Lack of redox control of the anaerobically-induced nirB+ gene of Escherichia coli K-12.

Operon fusion strains of Escherichia coli K-12 have been used to demonstrate that transcription of the structural gene for NADH-dependent nitrite reductase is regulated by oxygen repression and induction by its substrate, nitrite. This two-stage regulation of nirB is totally dependent upon a functional Fnr protein. Unlike the Fnr-dependent fumarate reductase operon, nirB transcription is not repressed by nitrate. These results suggest that the Fnr protein is simply a positive control protein essential for the derepression of some, but not all, anaerobically-induced operons rather than a more general redox-sensitive regulator, as suggested by the redox control hypothesis for the regulation of gene expression in facultatively anaerobic bacteria.

Anaerobiosis↗
PubMed1984

Equine adenovirus 1 isolated from cauda equina neuritis.

Equine adenovirus 1 was recovered after four to six passages from two out of three cases of cauda equina neuritis (CEN) using kidney monolayers. Similar treatment of lumbo-sacral spinal cord from six normal horses did not yield adenovirus. All three cases of CEN had antibodies to the neuritogenic myelin protein P2 while immunofluorescence demonstrated that autologous IgG bound to the myelin of affected nerves. Adenovirus was not detected in neural tissue by immunofluorescence.

Adenoviridae↗