PubMed Health⌕ Search

Biomedical subjects

J A Davies

Publications and source records attributed to J A Davies.

At least 19 recordsLinked to original sources
PubMed2006

A method for cold storage and transport of viable embryonic kidney rudiments.

Organ culture of mouse embryonic kidneys is a powerful system for studying normal renal development and for researching the developmental effects of experimental perturbations (drugs, antibodies, interfering RNA, and so on). In standard protocols, embryonic kidneys are isolated by delicate micro-dissection and placed in organ culture as soon as possible after the death of the donor mouse, before there is time to genotype them or to transport them elsewhere. This report demonstrates that fully viable embryonic kidneys can be isolated and cultured from crudely dissected caudal portions of embryos that have been stored on ice or at 4 degrees C for several days. This very simple technique can save considerable resources in laboratories that culture kidneys of transgenic mice: (i) cold storage allows embryos to be genotyped before their kidneys are cultured, and (ii) cold transport allows kidney research laboratories to study kidneys of transgenic mice raised elsewhere without the need for expensive importing of the mouse line itself. It will therefore substantially augment the ability of kidney research labs to perform pilot experiments on large numbers of different transgenic animals and to collaborate in new ways.

Animals↗
PubMed2006

Innexins in the lobster stomatogastric nervous system: cloning, phylogenetic analysis, developmental changes and expression within adult identified dye and electrically coupled neurons.

Gap junctions play a key role in the operation of neuronal networks by enabling direct electrical and metabolic communication between neurons. Suitable models to investigate their role in network operation and plasticity are invertebrate motor networks, which are built of comparatively few identified neurons, and can be examined throughout development; an excellent example is the lobster stomatogastric nervous system. In invertebrates, gap junctions are formed by proteins that belong to the innexin family. Here, we report the first molecular characterization of two crustacean innexins: the lobster Homarus gammarus innexin 1 (Hg-inx1) and 2 (Hg-inx2). Phylogenetic analysis reveals that innexin gene duplication occurred within the arthropod clade before the separation of insect and crustacean lineages. Using in situ hybridization, we find that each innexin is expressed within the adult and developing lobster stomatogastric nervous system and undergoes a marked down-regulation throughout development within the stomatogastric ganglion (STG). The number of innexin expressing neurons is significantly higher in the embryo than in the adult. By combining in situ hybridization, dye and electrical coupling experiments on identified neurons, we demonstrate that adult neurons that express at least one innexin are dye and electrically coupled with at least one other STG neuron. Finally, two STG neurons display no detectable amount of either innexin mRNAs but may express weak electrical coupling with other STG neurons, suggesting the existence of other forms of innexins. Altogether, we provide evidence that innexins are expressed within small neuronal networks built of dye and electrically coupled neurons and may be developmentally regulated.

Amino Acid Sequence↗
PubMed2004

Designing follow-up intervals.

When an examination is needed to determine if an event has occurred there will be a loss of efficiency in using the resulting interval-censored data instead of the exact event times. In designing follow-up intervals this loss for longer intervals needs to be weighed against extra visits required by shorter intervals. We obtain results to quantify this for the estimation of the median and mean survival and for covariates in parametric regression models with equally spaced examination times. Asymptotic information loss for the log-normal and Weibull distributions are similar when comparisons are made between corresponding members of the two families. For distributions with coefficients of variation of 50 per cent or more, a choice of interval from 0.25 to 0.7 times the median is recommended.

Administration, Topical↗
PubMed2003

Effects of bilobalide on cerebral amino acid neurotransmission.

Bilobalide is one of many active constituents found in EGb 761 (definition see editorial), which is extracted from Ginkgo biloba leaves. Whilst there is good, sound evidence that bilobalide exhibits neuroprotective actions in a variety of model systems, there is currently no consensus on its mechanism of action. This present communication summarises the results we have obtained with this compound on excitatory amino acid neurotransmission in the central nervous system using both neurochemical and electrophysiological techniques. Bilobalide was shown to reduce glutamate and aspartate release elicited by both high potassium-containing artificial cerebrospinal fluid (aCSF) or veratridine from mouse cortical slices. In addition, bilobalide had a very potent effect (IC (50) 2.7 microM) on glutamate release elicited by hypoxia/hypoglycaemia-induced release from rat cortical slices. Electrophysiologically, bilobalide also decreased the frequency of gamma-aminobutyric acid (GABA) uptake inhibitor-induced depolarisations in mouse cortical slices, an effect probably mediated by a decrease in glutamate release. No definitive conclusions can be reached concerning the mechanism of action of bilobalide, but an ability to decrease excitotoxic amino acid release, particularly glutamate, would suggest that this is a probable mechanism to account for its neuroprotective properties.

Animals↗
PubMed2003

Non-selective and cyclo-oxygenase-2-specific non-steroidal anti-inflammatory drugs impair the hyperaemic response of skin to brief axillary artery occlusion.

BACKGROUND: Cyclo-oxygenase-2 (COX-2)-specific inhibitors are marketed as safer analgesics than non-selective non-steroidal anti-inflammatory drugs. However, there has been conflicting evidence concerning endothelial function and cardiovascular risk after COX-2 inhibitor use. We investigated forearm skin vascular reactivity to brief axillary artery occlusion in healthy volunteers after a single dose of the non-steroidal anti-inflammatory drugs ibuprofen (non-selective) and rofecoxib (COX-2 specific). METHODS: Ten healthy male volunteers were studied. Forearm skin blood flow was measured using laser Doppler flowmetry. Two non-invasive probes were placed on the volar surface of the forearm. The magnitude of hyperaemic response to brief (20 s) and prolonged (5 min) occlusion of the axillary artery was measured before and 2-3 h after administration of ibuprofen 800 mg or rofecoxib 25 mg. The transient hyperaemic response ratio (THRR), defined as the net peak hyperaemic flow-flux divided by the net baseline flow-flux, was calculated. Each volunteer received both drugs in random order at least 1 week apart. RESULTS: Ibuprofen and rofecoxib increased net baseline blood flow (median (range): ibuprofen, from 23.3 (12.1-40.8) to 31.5 (17.4-77.3); rofecoxib, from 22.0 (14.6-41.0) to 29.9 (19.5-112.0); P<0.01). The net hyperaemic peak flow-flux after brief and prolonged occlusion was unchanged after both drugs. THRR was reduced by both drugs (ibuprofen, from 2.92 (2.38-3.86) to 2.09 (1.45-3.54); rofecoxib, from 3.36 (2.06-5.16) to 2.67 (1.15 -3.84); P<0.01). CONCLUSIONS: Both COX-2 and non-selective non-steroidal anti-inflammatory drugs, when given to healthy volunteers as single therapeutic doses, decrease skin microvascular tone but do not impair maximal vasodilatory ability.

Adult↗
PubMed2002

Effects of bilobalide on amino acid release and electrophysiology of cortical slices.

This study investigated the effects of bilobalide, a constituent of Ginkgo biloba, on potassium and veratridine-induced release of glutamate and aspartate from mouse cortical slices. We also studied its effects on spontaneous and N-methyl-D-aspartate (NMDA)-induced depolarizations elicited in magnesium-free artificial cerebrospinal fluid (aCSF) as well as its effect on NO-711 (a gamma-aminobutyric acid (GABA) uptake inhibitor)-induced depolarizations. Bilobalide, 100 microM significantly reduced both glutamate and aspartate release elicited by potassium or veratridine. Bilobalide (5-100 microM) also significantly reduced the frequency of NO-711 induced depolarizations, however, it had no effect on spontaneous or on NMDA-induced depolarizations at 5-200 microM. These results suggest that the neuroactive properties of bilobalide may be mediated by a reduction in excitatory amino acid neurotransmitter release.

Animals↗
PubMed2001

The infrequency of transmission of herpesviruses between humans and animals; postulation of an unrecognised protective host mechanism.

The infrequency of natural transmission of herpesviruses between humans and animals is surprising as there is extensive contact between humans and non-human species with unequivocal evidence that host cells from non-susceptible species will support replication of herpesviruses which do not seem to naturally infect that species. This review examines natural cross-infections between human and other species and suggests that, firstly, it is possible that humans and animals do become asymptomatically or symptomatically cross-infected from other species, but the infection is not diagnosed or not diagnosable by conventional methods; secondly, an as yet unidentified novel mechanism(s) may operate to prevent infection using chemical, electrical or as yet unidentified pathways and may even be 'switched on' by exposure to the virus.

Animals↗
PubMed2001

Glycosaminoglycans in the study of mammalian organ development.

Glycosaminoglycans (GAGs) are linear polymers of amino sugar uronic acid disaccharides, and are generally attached to protein cores to form proteoglycans. GAGs interact with a large number of proteins and can participate in matrix organization, cell adhesion, differentiation, growth and apoptosis. Proteoglycans are expressed in tightly regulated spatio-temporal patterns during organ development, and changes in expression frequently correlate with developmental events. Here we review the evidence that GAGs play important roles in the development of mouse kidneys, which are organs that will undergo organotypic development in simple culture conditions and that are therefore highly accessible to experimentation. Depleting kidneys of GAGs, either biochemically or genetically, blocks the development of the urinary collecting-duct system, probably because critical signalling molecules require GAGs to form stable associations with their receptors. The insensitivity of GAG-deprived organ rudiments to physiological concentrations of growth factors can be used to screen candidate signalling molecules for morphoregulatory activity; candidate growth factors are applied at supraphysiological levels to GAG-deprived kidneys and assessed for their ability to rescue normal development. This approach has assisted the identification of four collecting-duct morphogens: hepatocyte growth factor, glial cell line-derived neurotrophic factor, nerturin and persephin.

Animals↗
PubMed2001

Erk MAP kinase regulates branching morphogenesis in the developing mouse kidney.

Branching morphogenesis of epithelium is a common and important feature of organogenesis; it is, for example, responsible for development of renal collecting ducts, lung airways, milk ducts of mammary glands and seminal ducts of the prostate. In each case, epithelial development is controlled by a variety of mesenchyme-derived molecules, both soluble (e.g. growth factors) and insoluble (e.g. extracellular matrix). Little is known about how these varied influences are integrated to produce a coherent morphogenetic response, but integration is likely to be achieved at least partly by cytoplasmic signal transduction networks. Work in other systems (Drosophila tracheae, MDCK models) suggests that the mitogen-activated protein (MAP) kinase pathway might be important to epithelial branching. We have investigated the role of the MAP kinase pathway in one of the best characterised mammalian examples of branching morphogenesis, the ureteric bud of the metanephric kidney. We find that Erk MAP kinase is normally active in ureteric bud, and that inhibiting Erk activation with the MAP kinase kinase inhibitor, PD98059, reversibly inhibits branching in a dose-dependent manner, while allowing tubule elongation to continue. When Erk activation is inhibited, ureteric bud tips show less cell proliferation than controls and they also produce fewer laminin-rich processes penetrating the mesenchyme and fail to show the strong concentration of apical actin filaments typical of controls; apoptosis and expression of Ret and Ros, are, however, normal. The activity of the Erk MAP kinase pathway is dependent on at least two known regulators of ureteric bud branching; the GDNF-Ret signalling system and sulphated glycosaminoglycans. MAP kinase is therefore essential for normal branching morphogenesis of the ureteric bud, and lies downstream of significant extracellular regulators of ureteric bud development.

Animals↗
PubMed2000

Hypoxia/hypoglycemia-induced amino acid release is decreased in vitro by preconditioning.

The aim of this study was to investigate the effects of preconditioning on amino acid neurotransmitter release, induced by hypoxia/hypoglycaemia, from rat brain cortical slices. Tissue, perfused with artificial cerebrospinal fluid (aCSF) at 37 degrees C with zero glucose and gassed with 95% nitrogen and 5% carbon dioxide, showed a fivefold increase in glutamate release with little effect on gamma-aminobutyric acid (GABA) release. Preconditioning, with three 5-min periods of hypoxia/hypoglycaemia preceding continuous hypoxia/hypoglycaemia, significantly decreased glutamate release whilst significantly elevating GABA release. These results suggest that GABA may reduce the release of glutamate and consequently decrease the neurotoxic effects of glutamate.

Amino Acids↗
PubMed2000

Femtosecond time-resolved photoelectron angular distributions probed during photodissociation of NO2.

Femtosecond time-resolved photoelectron angular distributions (PADs) are measured for the first time in the molecular frame of a dissociating molecule. Various stages of the dissociation process, NO2-->NO(C Pi)+O(P), are probed using ionization of the NO(C Pi) fragment to NO+(X Sigma(+)). The PADs evolve from forward-backward asymmetric with respect to the dissociation axis at short time delays ( < or =500 fs) to symmetric at long time delays (> or = 1 ps). Changes in the PADs directly reflect the time-dependent separation and reorientation of the dissociating photofragments.

Journal Article↗
PubMed2000

An evaluation of the efficacy of in-patient bladder retraining.

This is a retrospective review of 50 consecutive patients with urinary frequency, urgency and urge incontinence, admitted in 1995 and early 1996 for bladder retraining in the form of timed voiding. At discharge 80% of the women were subjectively cured or satisfactorily improved, but this was significantly reduced to 32% of the 37 who replied to a postal survey between 12 and 29 months (mean interval 21.3 months) later. There were no significant associations between outcome and urodynamic diagnosis, reduced cystometric capacity, length of symptomatology, previous treatment or requirement for additional therapy, but this may have been in part due to small numbers. In conclusion, bladder retraining is a method of treatment for patients with both sensory urgency and detrusor instability which appears to be at least as successful as other modes of treatment for these conditions.

Female↗
PubMed2000

Two Drosophila innexins are expressed in overlapping domains and cooperate to form gap-junction channels.

Members of the innexin protein family are structural components of invertebrate gap junctions and are analogous to vertebrate connexins. Here we investigate two Drosophila innexin genes, Dm-inx2 and Dm-inx3 and show that they are expressed in overlapping domains throughout embryogenesis, most notably in epidermal cells bordering each segment. We also explore the gap-junction-forming capabilities of the encoded proteins. In paired Xenopus oocytes, the injection of Dm-inx2 mRNA results in the formation of voltage-sensitive channels in only approximately 40% of cell pairs. In contrast, Dm-Inx3 never forms channels. Crucially, when both mRNAs are coexpressed, functional channels are formed reliably, and the electrophysiological properties of these channels distinguish them from those formed by Dm-Inx2 alone. We relate these in vitro data to in vivo studies. Ectopic expression of Dm-inx2 in vivo has limited effects on the viability of Drosophila, and animals ectopically expressing Dm-inx3 are unaffected. However, ectopic expression of both transcripts together severely reduces viability, presumably because of the formation of inappropriate gap junctions. We conclude that Dm-Inx2 and Dm-Inx3, which are expressed in overlapping domains during embryogenesis, can form oligomeric gap-junction channels.

Amino Acid Sequence↗
PubMed2000

Synaptogenesis in the giant-fibre system of Drosophila: interaction of the giant fibre and its major motorneuronal target.

The tergotrochanteral (jump) motorneuron is a major synaptic target of the Giant Fibre in Drosophila. These two neurons are major components of the fly's Giant-Fibre escape system. Our previous work has described the development of the Giant Fibre in early metamorphosis and the involvement of the shaking-B locus in the formation of its electrical synapses. In the present study, we have investigated the development of the tergotrochanteral motorneuron and its electrical synapses by transforming Drosophila with a Gal4 fusion construct containing sequences largely upstream of, but including, the shaking-B(lethal) promoter. This construct drives reporter gene expression in the tergotrochanteral motorneuron and some other neurons. Expression of green fluorescent protein in the motorneuron allows visualization of its cell body and its subsequent intracellular staining with Lucifer Yellow. These preparations provide high-resolution data on motorneuron morphogenesis during the first half of pupal development. Dye-coupling reveals onset of gap-junction formation between the tergotrochanteral motorneuron and other neurons of the Giant-Fibre System. The medial dendrite of the tergotrochanteral motorneuron becomes dye-coupled to the peripheral synapsing interneurons between 28 and 32 hours after puparium formation. Dye-coupling between tergotrochanteral motorneuron and Giant Fibre is first seen at 42 hours after puparium formation. All dye coupling is abolished in a shaking-B(neural) mutant. To investigate any interactions between the Giant Fibre and the tergotroachanteral motorneuron, we arrested the growth of the motorneuron's medial neurite by targeted expression of a constitutively active form of Dcdc42. This results in the Giant Fibre remaining stranded at the midline, unable to make its characteristic bend. We conclude that Giant Fibre morphogenesis normally relies on fasciculation with its major motorneuronal target.

Animals↗
PubMed2000

A study to evaluate the field efficacy of ivermectin, fenbendazole and pyrantel pamoate, with preliminary observations on the efficacy of doramectin, as anthelmintics in horses.

The efficacy of ivermectin, fenbendazole, pyrantel pamoate and doramectin was evaluated under field conditions at 2 sites in the Free State Province of South Africa. The study involved 25 horses at each site, divided into 5 groups of equal size. Ivermectin, fenbendazole and pyrantel pamoate were administered orally at doses of 0.2, 10 and 19 mg/kg respectively. Doramectin was administered by intramuscular injection at a dose of 0.2 mg/kg. Treatment efficacy was based on the mean faecal egg count reduction 14 days post treatment. At site A a faecal egg count reduction of 100% was found after treatment with ivermectin, fenbendazole and doramectin. A 96.1% reduction was found after treatment with pyrantel pamoate. At site B ivermectin and doramectin produced a 100% reduction in faecal egg counts, fenbendazole produced an 80.8% reduction and pyrantel pamoate a 94.1% reduction. Doramectin produced a 100% reduction in faecal egg counts at both sites, despite not being registered for use in horses. In addition, the results indicated reduced efficacy of fenbendazole at site B, which suggested benzimidazole resistance. Larval cultures showed that cyathostomes accounted for between 86 and 96% of pre-treatment parasite burdens at both sites. Other helminths identified in the faecal samples were Strongylus spp. and Trichostrongylus axei.

Animals↗