Search PubMed⌕ Search

Biomedical subjects

A Vincent

Publications and source records attributed to A Vincent.

At least 181 records · Page 10Linked to original sources
PubMed1997

Identification of phospholipase A2 and neurotoxic activities in the venom of the New Guinean small-eyed snake (Micropechis ikaheka).

The Papua New Guinean small-eyed snake (Micropechis ikaheka) is recognised as a cause of life-threatening envenoming in certain parts of New Guinea. The clinical features suggest the presence of toxins acting at the neuromuscular junction and on muscle. We have used the mouse phrenic nerve hemidiaphragm preparation, a phospholipase A2 assay, and 125I-neurotoxin-binding radioimmunoassays to look for toxic activities in the crude venom and in preliminary high-performance liquid chromatography (HPLC) fractions. Micropechis ikaheka venom at 1 and 3 micrograms/ml completely abolished nerve-evoked muscle twitch within 70 min at 37 degrees C. There was also a sustained contracture of the muscle and some reduction in twitch tension evoked by direct stimulation; these were explained by the presence of phospholipase A2 activity. The venom inhibited the binding of 125I-alpha-bungaro-toxin to detergent-extracted human muscle acetylcholine receptor (AChR), and inhibited acetylcholine receptor function in a muscle cell line. It also inhibited binding of 125I-omega-conotoxin GVIA to detergent-extracted human frontal cortex voltage-gated calcium channels, but this appeared to be dependent on the phospholipase A2 activity. Identification of the main neurotoxic fractions following HPLC are shown.

Animals↗
PubMed1997

Lack of effect of Miller Fisher sera/plasmas on transmitter release from PC12 cells.

IgG antibodies to GQ1b ganglioside are found in > 90% of patients with the Miller Fisher Syndrome (MFS). MFS sera or IgG preparations have marked effects on neurotransmitter release at the neuromuscular junction, but their mode(s) of action remain unclear. To establish a cell-based system for investigating the mechanism of action of MFS serum preparations, we looked at neurotransmitter release from three cell lines. We failed to demonstrate substantial 14C-acetylcholine release from two motor-neuronal cell lines, VSC4.1 and NSC19, and therefore studied 3H-noradrenaline release from NGF-differentiated PC12 cells, a neural-crest derived catecholaminergic cell line. K(+)-induced release was inhibited by botulinum toxin and basal release was enhanced by alpha-latrotoxin, resembling that at the neuromuscular junction, although K(+)-induced release was dependent on L-type rather than P/Q-type calcium channels. The cells expressed polysialylated gangliosides on the cell surface. Incubation in heat-inactivated or untreated MFS preparations did not, however, affect basal or K(+)-induced release. Thus the PC12 cells do not appear to be sensitive to the effects of serum antibodies from MFS patients.

Animals↗
PubMed1997

Genes at the junction--candidates for congenital myasthenic syndromes.

The neuromuscular junction is the site of several myasthenic (mys, muscle; aesthenia, weakness) disorders of autoimmune and genetic origin. The acquired autoimmune conditions are mainly adult-onset and caused by antibodies to specific neuronal and muscle ion channels, but can occur neonatally due to placental transfer of maternal antibodies. This review focuses on the rarer genetic conditions, called congenital myasthenic syndromes (CMS), that often present at birth. Mutations have yet to be characterized for familial infantile myasthenia, acetylcholinesterase deficiency and ACh-receptor deficiency; but genes encoding both structural and functional NMJ protiens should be considered. Other syndromes have recently been shown to involve defects in the functioning of the ACh receptor itself. In particular, eight different mutations have been reported in cases of the slow channel syndrome, a dominant condition associated with point mutations that generate single amino acid changes within the ACh receptor and result in prolonged channel activations. These investigations are providing new insights into the structure and function of the ACh receptor. Further studies of CMS should pave the way for analysis and treatment of disorders involving other synapses in the peripheral and central nervous system.

Acetylcholinesterase↗
PubMed1997

Effect of a stemless femoral implant for total hip arthroplasty on the bone mineral density of the proximal femur. A prospective longitudinal study.

After total hip arthroplasty with a medullary stem, significant loss of bone mineral density (BMD) has been demonstrated in the proximal-medial femoral cortex. In an attempt to prevent bone loss, a stemless femoral component was designed. Owing to promising experimental results, a prospective clinical trial was undertaken in a limited group of patients, all below the age of 50. Yearly BMD measurements were carried out in the vicinity of the implant and compared with the BMD values obtained in the immediate perioperative period and with the values on the unaffected side. The follow-up period in this study was 4 to 6 years, involving 32 hips in 31 patients. Maintenance of BMD in the operated femur was demonstrated. A statistically significant increase in the BMD of the proximal medial femoral cortex was observed in those patients who had low initial values. In active patients with a life expectancy greater than 30 years, preservation of the proximal bone stock after total hip arthroplasty appears beneficial, as these patients are most likely to need revision surgery, which is more difficult if significant bone loss has occurred. The data further reinforce the crucial role of mechanical stress in BMD maintenance.

Absorptiometry, Photon↗
PubMed1997

Mechanisms of action of anti-GM1 and anti-GQ1b ganglioside antibodies in Guillain-Barré syndrome.

Anti-GM1 and anti-GQ1b ganglioside antibodies are found in association with acute and chronic peripheral neuropathies, including Guillain-Barré syndrome. They are believed to arise as a result of molecular mimicry with immunogenic microbial polysaccharides. Although anti-ganglioside antibodies are suspected to play a causal role in neuropathy pathogenesis, the details of this have yet to be proven. The approach in this laboratory to solving this issue has been to generate anti-GM1 and anti-GQ1b monoclonal antibodies from peripheral blood lymphocytes of affected patients and to study their immunolocalization in peripheral nerve and their electrophysiologic effects in animal models in which peripheral nerve sites are exposed to anti-ganglioside antibodies. These data show that anti-ganglioside antibody-reactive epitopes are widely distributed in peripheral nerve and can cause electrophysiologic abnormalities in a variety of model systems; thus, these data support the view that anti-ganglioside antibody-reactive epitopes may directly contribute to neuropathy pathogenesis.

Animals↗
PubMed1997

Utrophin abundance is reduced at neuromuscular junctions of patients with both inherited and acquired acetylcholine receptor deficiencies.

Congenital myasthenic syndromes are a heterogeneous group of conditions in which muscle weakness resulting from impaired neuromuscular transmission is often present from infancy. One form of congenital myasthenic syndrome is due to a reduction of the number of acetylcholine receptors (AChRs) at the neuromuscular junction. We describe four new cases of AChR deficiency, characterized by a reduction in both miniature endplate potential amplitude and AChR abundance accompanied by elongation of the neuromuscular junction and some decrease in postsynaptic folding. A number of cytoplasmic proteins are normally associated with the postsynaptic membrane and may contribute to the clustering of AChRs at the neuromuscular junction. We therefore investigated the expression of several of these proteins in these AChR-deficiency patients. In each patient, immunolabelling of the neuromuscular junction for rapsyn, dystrophin, beta-dystroglycan and a form of beta-spectrin was strong but that for utrophin was markedly reduced or absent. This suggested that a defect in utrophin expression might underlie the congenital AChR deficiency. However, a reduction in utrophin labelling was also seen in three patients with adult acquired autoimmune myasthenia gravis in whom AChR loss results directly from the extracellular binding of autoantibodies. We conclude that the loss of AChRs in AChR deficiency does not result from the absence of rapsyn or beta-dystroglycan and that reduction of utrophin is probably secondary to the loss of AChRs. The possible role of AChRs and/or utrophin in determining the extent of postsynaptic folding is discussed.

Action Potentials↗
PubMed1997

Mutations in different functional domains of the human muscle acetylcholine receptor alpha subunit in patients with the slow-channel congenital myasthenic syndrome.

Congenital myasthenic syndromes are a group of rare genetic disorders that compromise neuromuscular transmission. A subset of these disorders, the slow-channel congenital myasthenic syndrome (SCCMS), is dominantly inherited and has been shown to involve mutations within the muscle acetylcholine receptor (AChR). We have identified three new SCCMS mutations and a further familial case of the alpha G153S mutation. Single channel recordings from wild-type and mutant human AChR expressed in Xenopus oocytes demonstrate that each mutation prolongs channel activation episodes. The novel mutations alpha V156M, alpha T254I and alpha S269I are in different functional domains of the AChR alpha subunit. Whereas alpha T254I is in the pore-lining region, like five of six previously reported SCCMS mutations, alpha S269I and alpha V156M are in extracellular domains. alpha S269I lies within the short extracellular sequence between M2 and M3, and identifies a new region of muscle AChR involved in ACh binding/channel gating. alpha V156M, although located close to alpha G153S which has been shown to increase ACh binding affinity, appears to alter channel function through a different molecular mechanism. Our results demonstrate heterogeneity in the SCCMS, indicate new regions of the AChR involved in ACh binding/channel gating and highlight the potential role of mutations outside the pore-lining regions in altering channel function in other ion channel disorders.

Adolescent↗
PubMed1997

Diverse Fab specific for acetylcholine receptor epitopes from a myasthenia gravis thymus combinatorial library.

The muscle weakness in myasthenia gravis (MG) is caused by heterogeneous high-affinity IgG autoantibodies to the nicotinic acetylcholine receptor (AChR), a complex ion channel glycoprotein. These antibodies are clearly responsible for reducing AChR numbers at the neuromuscular junction in myasthenia; however, the origins, diversity, specificity and pathogenicity of individual antibodies have not yet been established. We have cloned and characterized four different AChR-specific Fab from an MG patient's thymus by screening an IgG1/kappa gene combinatorial lambda phage library with soluble human AChR labeled with [125I] alpha-bungarotoxin. Unlike most previously cloned human antibodies, all four Fab immunoprecipitated soluble human muscle AChR. Two Fab strongly inhibited binding of mAb to the main immunogenic region on the alpha subunits and one Fab bound to an epitope on the fetal-specific gamma subunit. In sensitivity and fine specificity, these Fab resembled the anti-AChR antibodies found in many MG patients, including the donor. The closest germline counterparts for their heavy chains were in VH families 1, 3 and 4; however, there were many differences consistent with an antigen-driven response of diverse B cell clones. The combinatorial approach holds promise for further analysis of human autoantibodies.

Adult↗
PubMed1997

Pharmacokinetics and bronchial diffusion of single daily dose amikacin in cystic fibrosis patients.

A single daily dose of amikacin 35 mg/kg by i.v. infusion over 30 min in 18 cystic fibrosis patients achieved mean serum peak and trough concentrations of 121.4 mg/L (+/- 37.3) and 0.88 mg/L (+/- 0.62), respectively. Pharmacokinetic parameters and bronchial diffusion of amikacin showed marked inter-patient variability. The highest concentrations in sputum were obtained at 2 h (10.95 +/- 7.55 mg/L) and decreased slowly to reach a mean concentration of 2.14 mg/L (range 0.2-3.8 mg/L) just before the following infusion. An increase in the body clearance of amikacin and a decrease in the volume of distribution according to age were observed.

Adolescent↗
PubMed1997

Distractibility and processing resource deficit in major depression. Evidence for two deficient attentional processing models.

Performance on the Stroop Color-Word Test is impaired in depression, but it is not clear whether this impairment reflects a distractor inhibition disturbance or a reduction of processing resources. In this study, untreated major depressives were evaluated using a modified computerized Stroop Test composed of three tasks: to name the color of XXXXXs, of nonconflicting words, and of conflicting color words. It was hypothesized that, unlike color words, nonconflicting word distractors would disturb the color naming task only in the presence of a primary distractor inhibition disturbance. The slow reaction time (RT) depressives and normal RT depressives, according to their color naming speed without distractors, were contrasted to distinguish depressives with and without clear signs of resource deficit. It was found that interference produced by nonconflicting words was greater in normal RT depressives than in either slow RT depressives or control subjects, while interference caused by color words was dramatically stronger in slow RT depressives than in other groups. Results suggest the existence of two different attentional deficit patterns in clinical depression: some depressives have a distractor inhibition disturbance while others are deficient in processing resources.

Adolescent↗
PubMed1997

Congenital myasthenic syndromes.

Congenital myasthenic syndromes are a rare group of heterogeneous disorders affecting neuromuscular transmission. Recent identification and in-vitro functional analysis of some of the genetic mutations that cause these disorders correlates with previous electrophysiological, biochemical, pathological and therapeutic studies, and has advanced our understanding of neuromuscular transmission.

DNA Mutational Analysis↗
PubMed1997

Postnatal changes in electrophysiological properties of rat nucleus tractus solitarii neurons.

Whole-cell recordings in brainstem slices revealed postnatal changes in passive and firing properties in the rat caudal nucleus tractus solitarii (cNTS) neurons. Membrane potential, threshold for Na+ spike and degree of sag were unchanged during development. In the adult, the rheobase was twice that found at birth. The input resistance decreased over the period studied, while time constants declined markedly after the third postnatal week. At all postnatal ages, Na(+)-dependent action potentials (APs) were elicited in response to depolarization. Nevertheless, AP duration gradually decreased by 40% over the developmental period studied. Spike amplitude was smaller at birth than at any other ages and reached a peak two weeks after birth. At all ages, Na(+)-dependent APs were blocked by application of tetrodotoxin. Full APs were replaced by an initial slow oscillation in young cells and by oscillations in older cells. The TTX-resistant oscillations were altered by cobalt (2 mM) and cadmium (100 microM). The spike afterhyperpolarization (AHP) was not altered during development, but was observed in less neurons in adult cells when measured at a holding potential of -60 mV. Neurons were subdivided into one of three classes based on their responses to a hyperpolarizing prepulse: 1) post-inhibitory rebound (PIR) cells, 2) delayed excitation (DE) cells and 3) NON cells expressing neither PIR nor DE. The relative proportions of different cell types varied with age. The mean maximum duration of DE increased three times. Voltage-clamp experiments revealed that the DE was due to the activation of an A-current. In addition, a three-fold increase in its inactivation rate was observed postnatally. The physiological significance of these results is discussed.

Action Potentials↗
PubMed1997

Two types of zinc fingers are required for dimerization of the serendipity delta transcriptional activator.

The serendipity (sry) delta zinc finger protein controls bicoid gene expression during Drosophila melanogaster oogenesis. In addition, sry delta mutants display various zygotic phenotypes, ranging from abnormal embryogenesis to sex-biased adult lethality. We report here that sry delta is a sequence-specific transcriptional activator. A single sry delta consensus binding site (SDCS), in either orientation, is sufficient to promote transcription activation in cell culture, and multiple SDCSs mediate a strong synergistic activation, reflecting the cooperativity of sry delta binding to DNA. Further, several lines of evidence strongly suggest that sry delta binds to DNA as a dimer. While each of three point mutations located in the third zinc finger of sry delta drastically reduces its DNA binding affinity, a fourth mutation, located in the N-terminal region of the protein, specifically affects the cooperativity of DNA binding. This mutation reveals the functional importance of a putative Cys2/Cys2 zinc finger motif of a novel type, located outside the DNA binding domain. A systematic deletion analysis shows that interaction between this proposed Cys2/Cys2 motif and a classical Cys2/His2 zinc finger mediates homodimerization, which is required for DNA binding cooperativity.

Animals↗
PubMed1997

Antibodies to 125I-glutamic acid decarboxylase in patients with stiff man syndrome.

Antibodies to glutamic acid decarboxylase (GAD) are found in about 40% of patients with stiff man syndrome. A new assay involving immunoprecipitation of (125)I-glutamic acid decarboxylase was used to measure anti-GAD antibodies in 18 patients with stiff man syndrome. Of the eight serum samples from patients with stiff man syndrome, that had previously been found positive by immunoprecipitation of (35)S-GAD, seven were strongly positive with (125)I-GAD and one gave an equivocal result. Other serum samples from patients with stiff man syndrome and from controls were negative except one from a patient who had a thymoma, acquired neuromyotonia, and myasthenia gravis. Nine of 35 serum samples referred for testing were positive; in two of these the serum titre was 20-50 times higher than that in the CSF. This assay should prove useful in the diagnosis, management, and investigation of stiff man syndrome.

Antibodies↗
PubMed1997

Integration of the head and trunk segmentation systems controls cephalic furrow formation in Drosophila.

Genetic and molecular analyses of patterning of the Drosophila embryo have shown that the process of segmentation of the head is fundamentally different from the process of segmentation of the trunk. The cephalic furrow (CF), one of the first morphological manifestations of the patterning process, forms at the juxtaposition of these two patterning systems. We report here that the initial step in CF formation is a change in shape and apical positioning of a single row of cells. The anteroposterior position of these initiator cells may be defined by the overlapping expression of the head gap gene buttonhead (btd) and the primary pair-rule gene even-skipped (eve). Re-examination of the btd and eve phenotypes in live embryos indicated that both genes are required for CF formation. Further, Eve expression in initiator cells was found to be dependent upon btd activity. The control of eve expression by btd in these cells is the first indication of a new level of integrated regulation that interfaces the head and trunk segmentation systems. In conjunction with previous data on the btd and eve embryonic phenotypes, our results suggest that interaction between these two genes both controls initiation of a specific morphogenetic movement that separates two morphogenetic fields and contributes to patterning the hinge region that demarcates the procephalon from the segmented germ band.

Animals↗
PubMed1997

Judging the time to collision with a simulated textured object: effect of mismatching rate of expansion of object size and of texture element size.

We measured the accuracy with which subjects estimated the time to collision with a simulated textured object approaching at constant speed along the line of sight. The independent variable was the ratio R, where R = (rate of dilation of the texture elements that covered the simulated object)/ (rate of dilation of object size). When matching was perfect (i.e., R = 1.0), the mean of 12 settings was close to the nominal value of 2,000 msec for the 2 subjects. In addition, the standard error of 12 settings was only 25 and 52 msec in 2,000 msec for the 2 subjects. Discrimination threshold for time to collision was not significantly affected by R over the range investigated between R = 0 and R = 2.0. However, the accuracy of estimating time to collision was significantly affected by R. Estimated time to collision was a monotonic function of R. For example, when the mismatch was only 10% (i.e., R = 0.9) subjects judged time to collision would occur 178 msec later than the true time to collision of 2,000 msec.

Adult↗
PubMed1997

Molecular approaches to improved pig fertility.

Geneticists have made limited progress in improving reproductive traits in pigs through traditional selection and crossbreeding systems. Recent advances in molecular genetics and the human genome project have allowed progress in gene identification and gene mapping in pigs. The pig genetic linkage map now has over 1700 genetic markers, and about 200 of these are genes. Furthermore, comparative genomic maps are improving and are becoming useful tools. Molecular approaches such as candidate gene identification and genomic scans permit new genes and chromosomal regions to be discovered which may influence reproduction. One significant finding is that the oestrogen receptor locus (ESR) is associated with increased litter size. Differences between female Chinese pig ESR BB and AA homozygotes have averaged 2.3 pigs born alive for first parity, and in commercial Large White crosses the differences are about 0.9 pigs per litter. Additional new genes have been discovered which may significantly affect litter size. Initial genome scans have revealed that there may be a gene or genes influencing ovulation rate and litter size on chromosome 8. Approaches such as positional comparative candidate gene analysis and eventually positional cloning will probably identify the genes controlling reproduction in pigs.

Animals↗