Biomedical subjects
Publications and source records attributed to J D Evans.
A case of compression of the common peroneal nerve caused by a ganglion herniating from the superior tibio-fibular joint is reported. MR imaging was partially helpful in making the diagnosis. The patient has made an almost complete recovery 3 months after excision of the lesion. Early diagnosis and treatment is required to ensure recovery.
The multicylinder somatic shunt cable model for passive neurones with differing time constants in each cylinder is considered in this paper. The solution to the model with general inputs is developed, and the parameteric dependence of the voltage response is investigated. The method of analysis is straightforward and follows that laid out in Evans et al. (1992, 1994): (i) The dimensional problem is stated with general boundary and initial conditions. (ii) The model is fully non-dimensionalised, and a dimensionless parameter family which uniquely governs the behaviour of the dimensionless voltage response is obtained. (iii) The fundamental unit impulse problem is solved, and the solutions to problems involving general inputs are written in terms of the unit impulse solution. (iv) The large and small time behaviour of the unit impulse solution is examined. (v) The parametric dependence of the unit impulse upon the dimensionless parameter family is explored for two limits of practical interest. A simple expression for the principle relationship between the dimensionless parameter family is derived and provides insight into the interaction between soma and cylinders. A well-posed method for the solution of the dimensional inverse problem is presented.
Solutions for transients in arbitrarily branching passive cable neurone models with a soma are extended to models with nonuniform electrical parameters and multiple dendritic shunts. The response to an injected current can again be represented as an infinite series of exponentially decaying components with system time constants obtained from the roots of a recursive transcendental equation. The reciprocity relations and global parameter dependencies are the same as for uniform models. Infinitely many "raw" electro-morphological models map onto a given "core" electrotonic model; local as well as global raw parameter trade-offs are now possible. The solutions are illustrated by means of biologically relevant examples: (i) the effects of nonuniform electrical parameters in a two-cylinder + soma cortical pyramidal cell model, (ii) the errors that can occur when uniformity is incorrectly assumed in a single cylinder model, (iii) nonsumming interactions between cells and electrodes that can dramatically increase the duration of the effective capacitative electrode artefact, and (iv) shunting inhibition and double impalements in a hippocampal CA1 pyramidal cell "cartoon" representation. These solutions should complement compartmental modelling techniques.
An analytical solution is derived for voltage transients in an arbitrarily branching passive cable neurone model with a soma and somatic shunt. The response to injected currents can be represented as an infinite series of exponentially decaying components with different time constants and amplitudes. The time constants of a given model, obtained from the roots of a recursive transcendental equation, are independent of the stimulating and recording positions. Each amplitude is the product of three factors dependent on the corresponding root: one constant over the cell, one varying with the input site, and one with the recording site. The amplitudes are not altered by interchanging these sites. The solution reveals explicitly some of the parameter dependencies of the responses. An efficient recursive root-finding algorithm is described. Certain regular geometries lead to "lost" roots; difficulties associated with these can be avoided by making small changes to the lengths of affected segments. Complicated cells, such as a CA1 pyramid, produce many closely spaced time constants in the range of interest. Models with large somatic shunts and dendrites of unequal electrotonic lengths can produce large amplitude waveform components with surprisingly slow time constants. This analytic solution should complement existing passive neurone modeling techniques.
Analytical solutions are derived for arbitrarily branching passive neurone models with a soma and somatic shunt, for synaptic inputs and somatic voltage commands, for both perfect and imperfect somatic voltage clamp. The solutions are infinite exponential series. Perfect clamp decouples different dendritic trees at the soma: each exponential component exists only in one tree; its time constant is independent of stimulating and recording position within the tree; its amplitude is the product of a factor constant over that entire tree and factors dependent on stimulating and recording positions. Imperfect clamp to zero is mathematically equivalent to voltage recording with a shunt. As the series resistance increases, different dendritic trees become more strongly coupled. A number of interesting response symmetries are evident. The solutions reveal parameter dependencies, including an insensitivity of the early parts of the responses to specific membrane resistivity and somatic shunt, and an approximately linear dependence of the slower time constants on series resistance, for small series resistances. The solutions are illustrated using a "cartoon" representation of a CA1 pyramidal cell and a two-cylinder + soma model.
In ants of genus Myrmica, female progeny may be the offspring of one to several different queens. In addition, both workers and queens are capable of producing haploid male offspring. Even in such complex colonies, parentage can be assigned on the basis of genotypic variation at highly polymorphic simple sequence repeat loci. Methods are described for isolating and screening dinucleotide repeat loci in ants. Three independent loci, Myrt2, Myrt3 and Myrt4, show expected heterozygosities of 0.94, 0.92 and 0.95, respectively. When used in parallel these loci should be sufficient to establish parentage in the vast majority of screened colonies. An initial screening indicates that males are produced by workers in the subalpine ant Myrmica 'near tahoensis'.
The somatic shunt cable model for neurones is extended to the case in which several equivalent cylinders, not necessarily of the same electrotonic length, emanate from the cell soma. The cable equation is assumed to hold in each cylinder and is solved with sealed end conditions and a lumped soma boundary condition at a common origin. A Green's function (G) is defined, corresponding to the voltage response to an instantaneous current pulse at an arbitrary point along one of the cylinders. An eigenfunction expansion for G is obtained where the coefficients are determined using the calculus of residues and compared with an alternative method of derivation using a modified orthogonality condition. This expansion converges quickly for large time, but, for small time, a more convenient alternative expansion is obtained by Laplace transforms. The voltage response to arbitrary currents injected at arbitrary sites in the dendritic tree (including the soma) may then be expressed as a convolution integral involving G. Illustrative examples are presented for a point charge input.
On 22 August 1985 a fire occurred on a Boeing 737 jet airliner at take off at Manchester Airport. One hundred and thirty seven passengers and crew were on board. Fifty two passengers died on the aircraft, 85 escaped. Most survivors had minor physical injuries, but 15 required admission to hospital because of smoke inhalation and two of these had severe burns. At presentation only one survivor required ventilation but within 12 hours a further five required ventilation. Although initially patients suffering from smoke inhalation may seem relatively well, lung function may deteriorate rapidly in the first 24 hours. Careful organisation and regular practice of procedures to deal with a major accident are essential to be able to respond adequately to such an event.
Purified lipoteichoic acids (LTAs) from several gram-positive organisms have been shown, by methods involving spectral changes of an added merocyanine dye probe, to have critical micelle concentrations in the range of 1 to 10 micrograms/ml, suggesting that acylated LTAs in their monomer forms may represent the major configuration of extracellular LTAs in bacterial culture fluids. The critical micelle concentrations obtained did not differ markedly with degree of carbohydrate substitution of the polymers. The significance of these findings in relation to the biological properties of LTA is discussed.
Streptococcus sanguis G9B was grown in continuous culture at different generation times and pH values in media containing either glucose or fructose and differing in the concentrations of Na+ and K+. The growth pH, carbohydrate, and cation concentration each affected the yield of organisms, their ability to adhere to saliva-coated hydroxyapatite beads, and their hydrophobicity, as measured by adhesion to hexadecane. There was no correlation between adhesion to saliva-coated hydroxyapatite beads and hydrophobicity, the values for hydrophobicity varying between 44 and 83% for organisms that adhered poorly and between 24 and 75% for those that adhered effectively. For organisms grown in batch culture at pH 6.0 or 7.0 there was similarly no correlation between adhesion and hydrophobicity. The growth conditions also had a considerable influence on the production of extracellular protein. The total amount was greater at pH 7.5 than at other pH values, and there were also differences in the individual components in response to changes in generation time, pH, carbohydrate source, and cation concentration. Two protein bands were identified, namely, glucosyltransferase and protein P1 (also called antigen B or I/II). However, there was no correlation between a particular protein component and adhesion.
We examined the effect of growth conditions in chemostat culture on the quantity and composition of the cell wall teichoic acids of Streptococcus mutans BHT and Lactobacillus plantarum NCIB 7220 and the membrane lipoteichoic acid from S. mutans Ingbritt. With the cell wall teichoic acids, which are covalently linked to peptidoglycan, the amount of teichoic acid is independent of the growth conditions employed. However, the extent of glucosyl substitution of the polymer from L. plantarum was dependent on growth conditions. S. mutans Ingbritt lipoteichoic acid, on the other hand, was little affected by growth conditions in terms of composition or serological activity, but the amount produced was markedly affected by changes in growth conditions.
The group G antigen of lactobacilli was identified as a negatively-charged cell wall polysaccharide. The components of the preparation isolated from cell walls of L. salivarius subsp. salivarius by mild acid hydrolysis were glucose, galactose and lesser amounts of rhamnose, N-acetylglucosamine and phosphate. Quantitative serological studies on acid-released polysaccharide and enzymic lysates of cell walls showed that rhammose was the immunodominant component. The antigen was also detected in L. salivarius subsp. salicinus but not in a recent isolate of L. salivarius, strain IV CL-37.
The lipoteichoic acids (LTA) of gram-positive bacteria are known to bind spontaneously to a variety of animal cell membranes. We investigated the biological and biochemical characteristics of the binding of LTA of Streptococcus pyogenes and S. faecalis to human and sheep erythrocytes. The kinetics of the binding of the radiolabeled LTA ([(3)H]LTA) from each of these organisms to erythrocytes was similar. The dissociation constants for sheep and adult human erythrocytes were 1.6 muM and 4.5 muM, respectively, whereas that of human cord blood erythrocytes was approximately 10-fold higher, 31 muM. The number of binding sites for sheep erythrocytes was calculated to be 7.2 x x 10(6) per cell, and that of human erythrocytes, 29 x 10(6) per cell. Binding was reversible. More than 50% of bound [(3)H]LTA was displaced from erythrocytes by a 50-fold excess of unlabeled LTA. LTA prepared from heterologous species of gram-positive bacteria were all inhibitory to the binding of [(3)H]LTA whether derived from S. pyogenes or from S. faecalis. Among a number of potential receptor analogues and other inhibitors tested, including serum albumin, gangliosides Gm(2) and Gm(3), lipopolysaccharide of gram-negative bacteria, and various sugars, only albumin and the gangliosides significantly inhibited LTA binding. Trypsin or neuraminidase treatment of erythrocytes had no effect on LTA binding. Deacylation of [(3)H]LTA abolished binding ability and binding was restored by esterification of the deacylated material with stearoyl chloride, indicating that ester-linked lipids are necessary for membrane binding.
Streptococcus mutans Ingbritt was grown in a chemostat at defined dilution rates and pH values and under carbohydrate limitation. At a constant dilution rate of D = 0.1 h-1 and with either 0.5% glucose or 0.5% sucrose, the amounts of both cellular and extracellular lipoteichoic acid increased as the culture pH increased from 5.0 to 7.5. At a constant pH of 6.0, the amount of cellular lipoteichoic acid formed by cultures growing in 0.2% or 0.5% glucose was relatively constant over a range of dilution rates, although the amount of extracellular lipoteichoic acid formed in 0.2% glucose at intermediate dilution rates was less than that formed in 0.5% glucose. Organisms grown in 0.5% sucrose at pH 6.0 contained increasing amounts of cellular lipoteichoic acid as the dilution rate was increased. A comparison of the amounts of cellular lipoteichoic acid formed by organisms growing at D = 0.5 h-1 and pH 6.0 in glucose, sucrose, fructose, or mixtures of glucose and fructose in limiting amounts suggested that the enhanced production of lipoteichoic acic by sucrose-grown organisms was due to the fructose component. The culture fluids from both glucose- and sucrose-grown organisms contained detectable amounts of serotype c antigen, whereas glucose-grown cultures also contained significant amounts of an extracellular hexose-containing polymer.
A new type of amphipathic antigen was isolated from culture supernatants and cells of Actinomyces viscosus NY1 and partially characterized as a fatty acid-substituted heteropolysaccharide. Similar components have been detected serologically in other strains of Actinomyces.
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