Biomedical subjects

K C Marshall

Publications and source records attributed to K C Marshall.

At least 37 records · Page 2Linked to original sources

PubMed1993

Conjugative Plasmid Transfer between Bacteria under Simulated Marine Oligotrophic Conditions.

Marine Vibrio S14 strains and an Escherichia coli strain were starved in artificial seawater (NSS) with no added carbon, nitrogen, or phosphorus. The broad-host-range plasmid RP1 was transferred between the starving S14 strains and also from the E. coli donor to the S14 recipient under oligotrophic conditions, in which mixtures of donor and recipient cells were held on Nuclepore filters either floated on NSS or held such that NSS flowed through the filter. Transconjugants were obtained from S14 donors and recipients starved for at least 15 days before being mixed together for conjugation, whereas transconjugants were recovered from the E. coli donor and S14 recipient for up to 3 days of prestarvation, but not after 5 days. Transconjugants were obtained when there were as few as about 10 and 10 cells of starving S14 donors and recipients, respectively, per ml held on the filters. Starved donor and recipient mixtures incubated at 4 or 26 degrees C, as well as those allowed to mate for 2, 5, or 24 h, all yielded numbers of transconjugants which were not significantly (P > 0.05) different.

Journal Article↗

PubMed1991

Developmental aspects of the locus coeruleus-noradrenaline system.

The locus coeruleus-noradrenaline (LC-NA) system exhibits an early developmental pattern, so that its nerve terminals are present in target areas before formation of most synapses. Several properties of the source neurons in the LC change substantially during early postnatal periods: spontaneous activity patterns, responsiveness to sensory stimulation, and responsiveness to NA. The effect may be to confer enhanced responsiveness of LC neurons, and an enhanced release of NA in target areas, during early postnatal development. Developmental changes in density of adrenoceptors or adrenergic responsiveness in target areas have also been documented. The usual pattern is a progressive increase in adrenergic ligand binding, with some reduction during later phases of development. However, there are a number of examples of receptor subtypes and region-specific transient binding during the first few weeks of postnatal life, followed by reductions to very low levels. These observations may reflect developmentally transient adrenergic responsiveness in certain target areas. NA and the LC-NA system have been implicated in the control of morphological and functional properties of neurons in target areas, and in the control of developmentally important biochemical systems (ornithine decarboxylase). NA, as well as other neurotransmitters, may individually, or in cooperation, exert important trophic influences during a restricted developmental period.

Action Potentials↗

PubMed1991

Modulation of amino acid neurotransmitter actions by other neurotransmitters: some examples.

Developments in the field of central neurotransmission indicate that amino acids serve as important and widespread transmitters throughout the central nervous system. There are increasing indications from recent experimental studies that several of the other central neurotransmitters may exert potent effects on central neurons by modulating the actions of amino acids. Noradrenaline and serotonin have received particular attention as potential modulators, and a wide variety of actions has been reported for them. Modulatory actions have been reported at both pre- and post-synaptic levels, including both short- and long-term effects and facilitation or inhibition of amino acid actions. Selectivity has been found both for specific receptor subtypes of the neuromodulator and for specific effects of amino acids. Examples of such selectivity are modification of actions of an amino acid with little effect on spontaneous activity or membrane properties of the target cell, or in comparison to the actions of other neurotransmitters, or even other selective amino acid analogs. Modulatory actions on amino acids have also been reported for several other neurotransmitters including acetylcholine and various peptides. Recent studies of angiotensin II demonstrate that when iontophoretically applied, it can potently and selectively block the depolarizing action of glutamate on locus coeruleus neurons. It is possible that physiological influences of these various transmitter substances are expressed through modification of amino acid actions, rather than through direct effects on central neurons.

Amino Acids↗

PubMed1990

Angiotensin II modulation of glutamate excitation of locus coeruleus neurons.

The effects of iontophoretically applied angiotensin II (AII) have been tested on intracellularly recorded locus coeruleus neurons in an in vitro brain slice preparation. In most neurons, AII strongly depressed the depolarizing effect of L-glutamate in the absence of other effects on membrane properties. This action was specific, in that AII had no effect on depolarizations caused by current injection or application of acetylcholine, and it was blockable by the AII antagonist saralasin. These results appear to demonstrate a potent and previously unreported neuromodulatory action of AII in the central nervous system.

Acetylcholine↗

PubMed1990

Effects of respiratory activity on starvation survival of marine vibrios.

The marine bacterium Vibrio fluvialis NCTC11328 responded to nutrient depletion by a reduction in cell volume, and this was prevented by conditions that eliminated respiration as a source of energy. Addition of the protonophore, CCCP, removal of oxygen and introduction of mutations leading to defects of the respiratory chain prevented size reduction during periods of nutrient limitation. Further, survival of the wild-type strain during starvation was reduced under anaerobic conditions and survival of respiratory mutants under aerobic conditions was reduced compared with that of the parent strain. Removal by mutation of the respiratory Na+ pump from Vibrio alginolyticus did not inhibit size reduction or lead to reduced viability in starved cultures.

Aerobiosis↗

PubMed1990

Genes Responsible for Size Reduction of Marine Vibrios during Starvation Are Located on the Chromosome.

In a survey of 21 marine Vibrio spp., all responded to nutrient deprivation by undergoing a reduction in size (dwarfing). However, only 43% of these strains possessed one or more plasmids, suggesting that the genes responsible for dwarfing were located on the chromosome rather than on the plasmids. This conclusion was confirmed by the observation that fragmentation and subsequent size reduction occurred in three strains from which the plasmids had been removed by curing. The cured strains lost certain characteristics, such as resistance to some heavy metals and antibiotics, that were restored when the plasmids were reintroduced by either transformation or electroporation.

Journal Article↗

PubMed1990

The alpha 1- and alpha 2-adrenoceptor and muscarinic responses of normal and axotomized bullfrog sympathetic ganglia.

When neurones in bullfrog paravertebral sympathetic ganglia are studied by means of the sucrose-gap technique, muscarinic agonists produce a biphasic response (an initial hyperpolarization of ganglionic C cells followed by a depolarization of ganglionic B cells). Activation of ganglionic alpha 2-adrenoceptors promotes hyperpolarization. The present experiments with selective alpha 1- and alpha 2-adrenoceptor agonists and antagonists provided evidence for the existence of hitherto undescribed alpha 1-adrenoceptors, which are responsible for the production of depolarizing responses in these ganglia. Fifteen to twenty-five days after cutting postganglionic axons (axotomy), there was a nonselective depression of both alpha 1- and alpha 2-adrenoceptor mechanisms but little change in muscarinic responses. These results argue against the hypothesis that C cells assume all the properties of B cells after axotomy. Since the alpha-selective agonist phenylephrine failed to depolarize axotomized ganglia, it is unlikely that an alpha 1-adrenoceptor mechanism is prominent in axotomized neurones as it is in some immature adrenergic neurones. The data are consistent with the idea that axotomy selectively affects the properties of certain types of cation channels and raise questions as to the mechanisms involved in regulating the expression and maintenance of specific neurotransmitter responses on ganglionic neurones.

Animals↗

PubMed1990

Bacterial polymers: physicochemical aspects of their interactions at interfaces.

How do bacteria stick to a surface? There is still not enough information about to answer this question especially at the molecular level. This question only gives rise to more questions. What is the structure of the true adhesive bacterial polymer? Is only one bacterial polymer or several polymers involved in the adhesion process? What is the role of proteins associated with the bacterial polysaccharides? What type of polymer is produced for the adhesion to hydrophobic surfaces? Is the polymer produced as a response to the surface? This review is an attempt to summarize the physicochemical aspects of bacterial polymers and their interaction with surfaces. It was tried to give an overview of the literature published in this field. The article is divided into the following sections: first, the forces involved in bacterial adhesion are discussed. Third, different fluid conditions are investigated. Fourth, the nature of different bacterial polymers which are important for the interaction with a surface is elaborated. Fifth, the current knowledge about biological polymers at interfaces is shown. And sixth, the role of polymers in the adhesion of bacteria available to date is highlighted.

Bacterial Adhesion↗

PubMed1988

Synchronous bursting of locus coeruleus neurons in tissue culture.

Synchronous bursts of firing of locus coeruleus neurons have been observed in unanesthetized rats, particularly in response to various sensory stimuli. In explant tissue cultures, synchronous bursting activity of locus coeruleus neurons was also observed and the possible mechanisms responsible for this synchronous activation have been investigated. Barrages of depolarizing events apparently initiated and continued throughout spontaneous bursts of spikes in the cultured neurons. Simultaneous intracellular recordings from pairs of neurons show a very high degree of synchrony of such barrages between cells. On the basis of tests for electrical coupling in simultaneously recorded cell pairs, and tests for dye coupling with Lucifer Yellow, it was concluded that the synchrony is not due to electrical coupling of locus coeruleus neurons. Small non-synaptic interactions between cell pairs that may reflect elevated extracellular potassium levels have been observed on some occasions. Spontaneous and evoked depolarizations similar to those initiating the bursts appear to be synaptically mediated events, suggesting that locus coeruleus neurons are synchronously activated by a common excitatory input. It was concluded that the neurons providing this common excitation are located within or very close to the locus coeruleus, at least at birth. The synchronization of activation of many locus coeruleus neurons could result in almost simultaneous release of neurotransmitter in the widespread target areas of locus coeruleus projections.

Animals↗

PubMed1988

Noradrenaline induces short and long duration potentiation of glutamate excitations of cultured Purkinje neurons.

The effects of iontophoretic application of noradrenaline on spontaneous or glutamate-evoked activity were studied in Purkinje neurons in explant cultures. The most frequently observed effect of noradrenaline was a depression of glutamate responses, and this was sometimes observed in the absence of apparent changes in spontaneous activity. In 30 out of 80 cells, glutamate responses were increased during or following noradrenaline application. In 21 of the 30 cells, these potentiations were of relatively short duration (less than 4 min), while in the other 9, the potentiations had a much longer duration. beta-Adrenergic antagonists blocked the long duration potentiations in four out of five cells, while short duration potentiation was blocked in only one of eight cells. The alpha-adrenergic antagonist prazosin blocked the short duration potentiations in six of eight cells. The results indicate that long duration potentiations by noradrenaline as reported in the hippocampus are also observable in the cerebellum, and that short and long duration potentials of glutamate responses may be pharmacologically distinct.

Animals↗

PubMed1988

Characterization of a developmentally transient adrenergic depolarizing response in cultured locus coeruleus neurons.

The effects of iontophoretically applied noradrenaline have been tested on intracellularly recorded locus coeruleus neurons grown in explant cultures from neonatal mice. In addition to hyperpolarizing responses mediated by alpha 2-adrenergic receptors, as observed in locus coeruleus neurons in vivo and in brain slices from adult animals, alpha 1-mediated depolarizations were observed to succeed the initial hyperpolarizations in some cultures. It was shown that the depolarizing responses were only present in younger cultures, i.e., less than 26 days in vitro. In cultures less than 20 days old, all cells displayed the biphasic hyperpolarizing-depolarizing responses. Both components of the response appear to be direct, since they were present when synaptic transmission was blocked by including tetrodotoxin or by altering divalent cations in the perfusate. The depolarizing responses were frequently reduced in solutions with altered divalent cation content, and this might reflect a calcium dependency of this response. The hyperpolarizing and depolarizing components of the responses to noradrenaline were progressively blocked by increasing concentrations of the selective antagonists yohimbine and prazosin, respectively, in the dose ranges of 100 mM - 1 microM (yohimbine) and 20-200 nM (prazosin). Recent results from electrophysiological studies of locus coeruleus neurons in brain slices suggest that similar changes occur in the animal as well as in culture. It is possible that the transient depolarizing responses reflect a developmentally important enhanced responsiveness of locus coeruleus neurons during the early postnatal period.

Adrenergic alpha-Agonists↗

PubMed1987

Membrane properties and adrenergic responses in locus coeruleus neurons of young rats.

Intracellular recordings were made from locus coeruleus neurons in slices taken from rats 8-26 d of age. Neurons from these animals exhibited spontaneous action potentials, which were superimposed on slow (0.3-3 Hz) rhythmic depolarizations. The frequency of these potentials was closely related to the age of the animals from which the slice was taken, the slowest frequencies being observed in tissues from the youngest animals. In adult animals, such rhythmic activity was only rarely observed under normal recording conditions. The rhythmic depolarizations had a slow rate of rise and fall, were 3-15 mV in amplitude, were not affected by tetrodotoxin, and were abolished in solutions that contained elevated magnesium content. When the membrane potential was hyperpolarized by passing current through the recording electrode, the depolarizing rhythmic activity persisted even at very negative potentials (-120 mV). These depolarizations appear to be generated by the inward movement of calcium ions, probably in dendritic regions of the neuron. Superfusion of phenylephrine caused membrane depolarizations, increased the frequency of action potentials and of the slow, rhythmic depolarizations in about 80% of the cells from young rats, whereas it had no effect or a depressant action on cells from adults. Noradrenaline hyperpolarized the cells through an alpha 2-adrenoceptor and abolished the slow depolarizations. In cells from young rats, the hyperpolarization produced by noradrenaline reached a maximum and then declined, such that there was a "sag" in the membrane potential toward the resting potential following the peak of the hyperpolarization. Following the washout of noradrenaline, the membrane potential repolarized before moving toward the resting level.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗

PubMed1986

Adsorption and adhesion processes in microbial growth at interfaces.

By considering bacteria as living colloidal particles it is possible to define, at least in part, the physicochemical and biological factors involved in the adhesion of bacteria to apparently inert surfaces. Adhesion is considered in terms of the attraction and repulsion forces operative as the organism approaches a substratum surface, as well as in terms of the surface free energies of the bacterium, the substratum and the liquid phase. Bacterial adhesion at a surface is preceded by molecular adsorption, a process that may alter the substratum surface properties and may provide a concentrated source of nutrients allowing limited growth of the bacteria at the surface.

Adsorption↗

PubMed1986

Locus coeruleus neurons in culture have a developmentally transient alpha 1 adrenergic response.

Intracellular recordings from locus coeruleus neurons grown in explant cultures reveal age-related differences in the responses to iontophoretically applied noradrenaline. Cells grown in culture for more than 26 days exhibit a simple hyperpolarizing response while cells cultured for less than 26 days often have biphasic hyperpolarizing-depolarizing responses. Pharmacological studies with selective adrenergic agonists and antagonists show that the hyperpolarizations and hyperpolarizing parts of biphasic responses are mediated by alpha 2 adrenergic receptors while the depolarizing responses are mediated by alpha 1 receptors. These observations may reflect a population of neurotransmitter receptors which is transiently present during early postnatal development.

Animals↗

PubMed1986

6-Hydroxydopamine treatment enhances excitation of cultured cerebellar neurons by glutamate.

Explant cultures containing identifiable cerebellar cortical neurons and locus coeruleus neurons were treated with 500 microM 6-hydroxydopamine. At this concentration, locus coeruleus neurons were usually degenerated after 48 h, while the cerebellar cortical neurons had a normal appearance. Extracellular recording and iontophoresis of noradrenaline and glutamate were used to test for changes in electrical activity or neurotransmitter responsiveness of the cerebellar neurons. At 4-5 days following the toxin exposure, spontaneous spiking activity appeared similar to that in control cultures. Mean iontophoretic currents required to give noradrenaline-induced depressions of activity were somewhat lower for the toxin-treated cultures than for controls but not significantly so. The mean currents for glutamate excitations, however, were markedly lower in the treated cultures. Noradrenaline potentiations of glutamate responses were observed in both treated and control cultures. The greatly increased sensitivity of cerebellar neurons to glutamate does not seem related to degeneration of granule cells in the treated cultures but might be explained by disruption of astrocytic uptake mechanisms for glutamate.

Action Potentials↗

PubMed1985

Growth and myelination of explant cultures in defined medium.

The purpose of this study was to compare the development of organotypic cultures in defined medium versus nutrient containing serum and embryo extract (EE). Explant cultures of cerebellum with or without locus ceruleus were grown in the Maximow system and monitored in the living state and with histological stains. Thinner explants, fibronectin and a more frequent feeding schedule were required to overcome the growth differences encountered using a defined medium. The final medium formulation was arrived at by evaluation of living cultures and consisted of a basal medium (Dulbecco's minimal essential medium), a number of hormones and other supplements, and a final glucose concentration of 750 mg%. Using a Golgi stain and histofluorescence, it was shown that the three major types of neurons - Purkinje, deep nuclear, and locus ceruleus - developed similarly in the defined medium and in serum-EE cultures. Myelination occurred in virtually all cerebellar cultures in defined medium and the onset was earlier than in serum-EE cultures. These results indicate that differentiation of oligodendroglia and maturation of neurons occur in a defined medium. Elimination of thyroid hormone delayed the maturation of the cultures, both neurons and myelin, by 3-4 days.

Animals↗

PubMed1985

Bacterial adhesion in oligotrophic habitats.

Oligotrophic and copiotrophic bacteria can act as primary colonizers of surfaces in low nutrient habitats. Adhesion in copiotrophs provides an opportunity to change from a starvation-survival existence in the aqueous phase to an active growth mode at the solid surface. Healthy daughter cells are released from the surface to colonize other surfaces or to resume starvation-survival in the aqueous phase. Non-adhesive copiotrophs scavenge nutrients at surfaces, a fact seldom recognized in studies on the partitioning of bacteria between particulates and the aqueous phase.

Bacteria↗

PubMed1985

Noradrenergic responses of spinal neurons in locus coeruleus-spinal cord co-cultures.

Locus coeruleus (LC) explants were co-cultured with dissociated spinal neurons of mice. Nerve fibers exhibiting catecholamine fluorescence radiated from the explants and frequently invested spinal cord (SC) neurons close to the explants. Electrical stimulation of the explant and iontophoretic application of norepinephrine evoked a spectrum of slow depolarizing, hyperpolarizing, and biphasic responses in the SC cells. The responses to LC stimulation and to application of norepinephrine were usually similar in a given cell. The depolarizing responses were associated with an increase in apparent input resistance and pharmacologic tests indicated that the responses were mediated by alpha-receptors. Neurons in regions innervated by catecholamine-containing fibers usually gave depolarizing responses to LC stimulation and such neurons had a very high probability of exhibiting depolarizing responses to applied norepinephrine. It would appear that either locus coeruleus explants favored the survival of cells with alpha-receptors or expression of these receptors in SC neurons was induced by innervation of the neurons by locus coeruleus axons.

Action Potentials↗