Biomedical subjects

K C Marshall

Publications and source records attributed to K C Marshall.

At least 55 records · Page 3Linked to original sources

PubMed1984

Adhesion of Leptospira at a solid-liquid interface: a model.

Two strains of the saprophytic Leptospira biflexa serovar patoc display reversible and irreversible adhesion at a solid-liquid interface. Both forms of adhesion are enhanced in the presence of 20 microM carbonyl cyanide meta-chlorophenyl hydrazone (CCCP), an uncoupler which inhibits motility of the bacteria. Microscopic observations also indicated that motility may have a role in adhesion as only actively motile organisms were seen to detach from the substratum. A dynamic model is proposed for adhesion of these organisms at a solid-liquid interface. It is suggested that the level of reversible adhesion is determined by the comparative rates of attachment (ON phase) and detachment (OFF phase). As reversible adhesion is mediated by weak forces of attraction, bacterial motility or gentle washing could promote the OFF phase. When motility is inhibited, the OFF phase is reduced and the ON phase continues (as motility is not required for the ON phase) causing the level of reversible adhesion to increase. Since reversible adhesion is a prerequisite for irreversible adhesion, then increased reversible adhesion leads directly to increased irreversible adhesion. Reversible adhesion appears to be mediated by the weak attractive forces of the "secondary minimum" whereas the mechanism facilitating irreversible adhesion of leptospires is not known.

Leptospira↗

PubMed1984

The triggering effect of surfaces and surfactants on heat output, oxygen consumption and size reduction of a starving marine Vibrio.

The marine Vibrio DW1 exhibited a positive response in heat output to a dialysis membrane surface in the presence of substrate (100 mM sodium glutamate) and, more particularly, in the absence of exogenous substrate (starvation conditions). The latter result paralleled the previously reported decrease in cell volume and increase in oxygen consumption by starving bacteria at a similar surface. Modified Morita's salts (MMS) did not extract nutrients from the dialysis membrane, but an artificial seawater containing tris buffer (ASW-tris) did extract surface active and nutrient materials from the membrane. The ASW-tris membrane extract and a commercial surfactant, Tween 85, were found to mimic the effects of the dialysis membrane surface by inducing a decrease in cell volume, and an increasing oxygen consumption and heat output of Vibrio DW1 even in the bulk liquid. The significance of the adsorption of naturally occurring surfactants at surfaces in relation to the behaviour of bacteria at the surfaces is discussed.

Calorimetry↗

PubMed1984

Hyperpolarizing and age-dependent depolarizing responses of cultured locus coeruleus neurons to noradrenaline.

The electrical activity and responses to noradrenaline (NA) of locus coeruleus (LC) neurons have been studied in organotypic cultures using intracellular recording. Most LC neurons were predominantly quiescent, though occasional bursts of activity were observed; a few cells were tonically active at rates of 0.5-5/s. In most cells tested, iontophoretic application of NA evoked responses which were initially hyperpolarizing, sometimes followed by a depolarizing phase and frequently followed by a period of increased excitatory synaptic activity. The enhanced synaptic activity appeared to be an indirect effect since it was blocked by bath application of tetrodotoxin (TTX). In the presence of TTX, responses to NA of all but one cell were simple hyperpolarizations or biphasic (hyperpolarization/depolarization) responses. The presence of the depolarizing component appeared to be age-dependent, since it was frequently observed in cultures grown in vitro for less than 26 days, while neurons in older cultures exhibited only hyperpolarizing responses. If such age-dependent depolarizing responses are present in vivo, they would represent a unique example of a transmitter response which is present only during a transient developmental phase.

Animals↗

PubMed1984

Noradrenergic actions of Purkinje and locus coeruleus neurons in culture.

Explant cultures prepared from neonatal mice were used to study the actions of iontophoretically applied noradrenaline (NA) on Purkinje and locus coeruleus neurons, with extracellular and intracellular recording respectively. NA depressed spontaneous activity of Purkinje neurons and enhanced excitatory responses to glutamate in 14/16 cells. In cultures older than 26 days, NA hyperpolarized LC neurons but had no effect on or depressed depolarizing responses to glutamate. The hyperpolarizations were blocked by the selective alpha 2 antagonist yohimbine. Enhancement of glutamate responses is not a ubiquitous characteristic of NA action and appears not to be associated with alpha 2 adrenergic receptors.

Animals↗

PubMed1983

Responses of marine bacteria under starvation conditions at a solid-water interface.

Size changes during starvation of 17 marine bacterial isolates at a solid-water interface and in the liquid phase were examined. Twelve rod-shaped, hydrophilic bacteria decreased in size more rapidly at the solid surface than in the liquid phase, a result parallel to that observed previously for one of the strains at an air-water interface. On the other hand, three rod-shaped, hydrophobic bacteria diminished in size more rapidly in the liquid phase than at the solid-water interface. The rapid size decrease (defined here as the dwarfing phase) in either situation appeared to be an active process which occurred more rapidly when the cells were in an early stage of logarithmic growth at the onset of starvation. Dwarfing was reversibly inhibited by low temperature and low pH but was not inhibited by chloramphenicol. Three coccoidal bacteria showed little tendency to become smaller upon starvation in the liquid phase or at a surface.

Journal Article↗

PubMed1983

Initial phases of starvation and activity of bacteria at surfaces.

The activity of the hydrophilic Vibrio sp. strain DW1 and the hydrophobic Pseudomonas sp. strain S9, which both undergo starvation-induced responses, was examined at nutrient-enriched and nutrient-deficient interfaces. The initial period of response to a starvation regime ("dwarfing" phase) is a sequence of two processes: fragmentation and continuous size reduction of the fragmented cells. This dwarfing phase is also one of intense metabolic activity as supported by O(2) uptake measurements of the endogenous metabolism and the use of inhibitors of the proton flow, the electron transport chain, and membrane-bound ATPase. Hydrophilic bacteria become even smaller at nutrient-deficient surfaces than in the liquid phase upon starvation, and this is reflected in a higher endogenous metabolism exhibited by surface-associated cells compared with those in the liquid phase. On the other hand, hydrophobic bacteria dwarfing at surfaces did not exhibit a greater size reduction and exhibited an endogenous metabolism that was only slightly higher than that of cells in the liquid phase. Bacterial scavenging of surface-localized nutrients is related to the degree of irreversible binding of dwarf and starved bacteria, which in turn may be related to the degree of cell surface hydrophobicity.

Journal Article↗

PubMed1983

Synaptic interactions between mammalian central neurons in cell culture. II. Quantal Analysis of EPSPs.

The presynaptic release mechanism involved in excitatory synaptic connections between neurons in cell cultures of fetal mouse spinal cord were studied by statistical analysis of intracellularly recorded postsynaptic responses. Quantal parameters were determined for the EPSPs evoked in spinal cord (SC) neurons by stimulation of either other SC or dorsal root ganglion (DRG) neurons. Transmitter release was manipulated by varying the Ca2+ and Mg2+ content of the culture medium. The release process was represented better by binomial than by Poisson statistics. A method was derived for obtaining the probability of release and the number of release elements. The quantal content and the number of release elements were substantially higher for the SC-SC connection than for the DRG-SC connection. This was partially compensated for by a larger quantal amplitude for the DRG-SC connection. There was some indication that the probability of release was higher for the SC-SC connection. The relationship between transmitter output and effective external Ca2+ ion concentration was approximately linear.

Animals↗

PubMed1982

Effect of interfaces on small, starved marine bacteria.

The copiotrophic marine Vibrio sp. strain DW1, shown previously in batch culture to increase in numbers at the onset of starvation and then to form viable small cells with low endogenous respiration, appears to have a survival advantage at interfaces. Vibrio sp. strain DW1 behaved differently at interfaces compared with the aqueous phase under starvation conditions: (i) small cells were observed at an air-water interface without nutrients, (ii) nutrients added to the air-water interface quickly produced larger cells at the surface, (iii) motility persisted many hours longer at the solid-water interface of a dialysis membrane in a microchamber at the onset of starvation, and (iv) regrowth and division at the solid-liquid interface occurred quickly and at nutrient concentrations too low to permit growth in the aqueous phase. It was concluded that, if small starved cells from copiotrophic bacteria can reach an interface, additional survival mechanisms become available to them: (i) interfaces constitute areas of favorable nutrient conditions, and (ii) interfaces lacking a sufficient amount of nutrient, nevertheless, trigger cells to become smaller, thus increasing their surface/volume ratio and the packing density.

Journal Article↗

PubMed1982

Bubble contact angle method for evaluating substratum interfacial characteristics and its relevance to bacterial attachment.

A bubble contact angle method was used to determine interfacial free-energy characteristics of polystyrene substrata in the presence and absence of potential surface-conditioning proteins (bovine glycoprotein, bovine serum albumin, fatty acid-free bovine serum albumin), a bacterial culture supernatant, and a bacterial exopolymer. Clean petri dish substrata gave a contact angle of 90 degrees , but tissue culture dish substrata were more hydrophilic, giving an angle of 29 degrees or less. Bubble contact angles at the surfaces exposed to the macromolecular solutions varied with the composition and concentration of the solution. Modification by pronase enzymes of the conditioning effect of proteins depended on the nature of both the substratum and the protein, as well as the time of addition of the enzyme relative to the conditioning of the substratum. The effects of dissolved and substratum-adsorbed proteins on the attachment of Pseudomonas sp. strain NCMB 2021 to petri dishes and tissue culture dishes were consistent with changes in bubble contact angles (except when proteins were adsorbed to tissue culture dishes before attachment) as were alterations in protein-induced inhibition of bacterial attachment to petri dishes by treatment with pronase. Differences between the attachment of pseudomonads to petri dishes and tissue culture dishes suggested that different mechanisms of adhesion are involved at the surfaces of these two substrata.

Journal Article↗

PubMed1982

Catecholamine neurons of the central nervous system in organotypic culture.

A standardized dissection has been designed to produce explants from the locus coeruleus of the newborn mouse brain. This area, termed the peduncular region, may be explanted with or without cerebellar neurons. Organotypic cultures with peduncular cells contain a cluster of 20-50 (or more) closely-packed large neurons, characterized by intracellular refractile granules in the living state. When treated with the glyoxylic acid method, somata of the granule-containing neurons exhibited catecholamine fluorescence, and a profuse plexus of varicose fluorescent fibers permeated the explant and its outgrowth. Intracellular staining of these cells with horseradish peroxidase demonstrated bipolar and multipolar neurons (25-30 micrometers), with stout dendrites and varicose axons. Granule-containing neurons stained for acetylcholinesterase. Electron microscopically, large dense granules were seen, which appear to correspond to the granules seen in living neurons. Cultures with these cells also have a high concentration of catecholamines in the medium. It is concluded that the granule-bearing neurons of the living culture are in fact neurons of the locus coeruleus.

Acetylcholinesterase↗

PubMed1981

A coeruleo-spinal system in culture.

In combined cultures of dissociated spinal neurons and explants from the region of locus coeruleus, rich catecholamine-containing fiber projections from the explant to the surrounding regions of spinal neurons were demonstrated by fluorescence histochemistry. Electrical stimulation of the explant resulted in slow depolarizing responses in many of the spinal neurons. Cells exhibiting this type of response were also usually depolarized by local application of noradrenaline, whereas other, unresponsive neurons usually were not. The depolarizing responses to electrical stimulation and to noradrenaline were both increased by depolarizing current injection and decreased by hyperpolarizing current. These and other data suggest that the depolarizing responses of the spinal neurons to explant stimulation are mediated by noradrenaline released from axons of locus coeruleus neurons.

Animals↗

PubMed1981

Attachment and rosette formation by hyphomicrobia.

The processes of reversible and irreversible sorption of Hyphomicrobium sp. strain ZV580 to solid surfaces was investigated with the use of swarmer cell populations. Various compounds and physical conditions were examined for their effect on the cell-cell interactions which lead to the formation of rosette-like cell aggregates. The monosaccharides galactose and mannose were able to completely inhibit rosette formation. Concanavalin A and chloramphenicol were also able to prevent rosette formation, and both trypsin and pronase caused the disassociation of rosettes. The results indicate that the adhesin is a glycoprotein or a peptido-polysaccharide and that the flagellum may act as a vehicle for the transport of this adhesin from the cell to a surface.

Journal Article↗

PubMed1981

Specific Adhesion of Bacteria to Heterocysts of Anabaena spp. and Its Ecological Significance.

Two bacterial isolates, Pseudomonas sp. SL10 and Zoogloea sp. SL20, attach to heterocysts of Anabaena spp. with a high degree of selectivity, and this attachment can be expressed quantitatively in terms of adsorption isotherms. Adhesion of Pseudomonas sp. SL10 was restricted to a monolayer and exhibited a type I (Langmuir) isotherm, whereas adhesion of Zoogloea sp. SL20 involved multilayer attachment and exhibited a type II isotherm. The degree of adhesion by the bacteria to heterocysts of different Anabaena species may reflect the distribution and abundance of binding sites on the surface of different heterocysts. Both Pseudomonas sp. SL10 and Zoogloea sp SL20 promoted higher rates of acetylene reduction by Anabaena spp. under oxygenated culture conditions when compared with a cyanobacterial control. At ambient oxygen levels, however, only Zoogloea sp. SL20 stimulated acetylene reduction by Anabaena spp.

Journal Article↗

PubMed1980

Acetylcholinesterase activity and acetylcholine effects in the cerebello-rubro-thalamic pathway of the cat.

Unilateral transections of the brachium conjunctivum (BC) of cats resulted, after 2-3 weeks, in marked loss of acetylcholinesterase (AChE) activity from the contralateral red nucleus (RN) and ventral tier nuclei of the thalamus (VA-VL). Significant changes in activity were not observed in other locations. Sensitivity of RN neurons to iontophoretically applied acetylcholine (ACh) was studied under conditions which should maximize ACh sensitivity, including AChE inhibition, but ACh was found to have only a weak depressant effect on excitability or no effect at all. Intravenous physostigmine usually increased spontaneous activity of RN neurons, and sometimes increased potentials evoked by electrical stimulation of cerebellar nuclei, to a small extent. Anticholinergic drugs were found not to influence such evoked responses, except to reverse the effects of physostigmine. It is concluded that ACh is not a major transmitter in the excitatory cerebello-rubral tract in spite of the relationship of AChE to this pathway.

Acetylcholine↗

PubMed1980