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Biomedical subjects

D L Marshall

Publications and source records attributed to D L Marshall.

At least 37 records · Page 2Linked to original sources
PubMed1993

Improved method for the routine analysis of acetylcholine release in vivo: quantitation in the presence and absence of esterase inhibitor.

An improved high-performance liquid chromatographic (HPLC) method using electrochemical detection (ED) is described capable of routinely measuring the low levels of acetylcholine (ACh) typically found in rat brain microdialysis samples. Microdialysis was performed in the striatum of the urethane anesthetized rat using a 4-mm membrane length, high recovery (40% at 1.0 microliters/min; ambient conditions), loop-design probe perfused with an artificial cerebrospinal fluid (aCSF) solution containing physiologically normal calcium levels (1.2 mM). The HPLC method utilizes a polymeric stationary phase to resolve choline (Ch) from ACh. These analytes are then converted to hydrogen peroxide (H2O2) by a solid-phase reactor (containing immobilized choline oxidase and acetylcholinesterase enzymes). The H2O2 is detected amperometrically and quantitated on a platinum (Pt) working electrode (+300 mV; with a unique analytical cell featuring a solid-state palladium reference electrode). Two designs of the Pt working electrode were examined, differing only in the support material used (Kel-F or PEEK). The Kel-F/Pt electrode had a limit of detection (LOD) for both analytes of < 30 fmol per 10 microliters with a signal-to-noise ratio of 3:1. Striatal microdialysis perfusates were monitored for ACh and Ch over a 0-1000 nM range of neostigmine (NEO) in the CSF perfusion medium. Using the 4-mm probe, basal ACh and Ch levels were detected with a NEO level as low as 10 nM and were found to be 37 +/- 3 fmol and 22 +/- 1 pmol per 10 microliters (mean +/- S.E.M., n = 6 replicates) respectively. In similar experiments using 3-mm concentric probes comparable (lower) levels of ACh were found with the 50 and 1000 nM NEO doses (n = 4-21 animals). ACh could not be reliably quantitated when animals were perfused with the 10 nM dose of NEO (n = 4). The PEEK/Pt electrode had an improved LOD of < 20 fmol per 10 microliters due to a two- to three-fold decrease in the background noise component. Basal striatal levels of ACh in the absence of NEO approached the LOD and were found to be 15 +/- 2 fmol per 10 microliters; Ch was 5 +/- 1 pmol per 10 microliters (n = 2, mean of five basal samples). The analytical system requires very little maintenance; a simple electrochemical electrode cleaning step eliminates the need for routine polishing of the Pt electrode and the mobile phase is stable for up to one week.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1993

Effect of choline on basal and stimulated acetylcholine release: an in vivo microdialysis study using a low neostigmine concentration.

Using in vivo microdialysis, we examined the ability of choline (Ch) chloride (120 mg/kg i.p.) to amplify basal and stimulated acetylcholine (ACh) release from rat striatum in the presence of high (10(-5) M) and low (5 x 10(-8) M) neostigmine concentration. High concentrations might suppress ACh release, and thus Ch dependence, by excessively stimulating presynaptic cholinergic receptors; alternatively, they could enhance Ch dependence by depriving the cholinergic terminals of Ch that would otherwise be formed intrasynaptically from the hydrolysis of ACh. Both basal and stimulated ACh release were found to be tetrodotoxin (TTX) sensitive. The concentration of neostigmine in the microdialysis fluid positively affected basal ACh levels, but had no effect on Ch levels. Ch administration significantly increased ACh release (to 136% of basal values; P < 0.01) in the presence of the low neostigmine concentration, but failed to significantly increase ACh release following local electrical depolarization of striatal neurons. In contrast, Ch failed to affect basal ACh release in the presence of the high neostigmine concentration, but did increase electrically evoked release to 408% of basal values, as compared with 250% in rats receiving saline instead of the Ch (P < 0.05). Ch administration significantly increased microdialysate Ch levels in the presence of both of the neostigmine concentrations. Local administration of oxotremorine, a muscarinic agonist, to animals receiving the lower neostigmine concentration reduced basal ACh release and reduced the increase in basal release produced by Ch administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

A potassium channel toxin from the secretion of the sea anemone Bunodosoma granulifera. Isolation, amino acid sequence and biological activity.

A peptide toxin affecting potassium channels was isolated from the sea anemone Bunodosoma granulifera. It facilitates acetylcholine release at avian neuromuscular junctions, competes with dendrotoxin I, a probe for voltage-dependent potassium channels, for binding to synaptosomal membranes of rat brain with a Ki of 0.7 nM and suppresses K+ currents in rat dorsal root ganglion neurones in culture. It represents a new structural type of potassium channel toxin with the sequence V1RCDWFKETA10CRHAKSLGNC20RTSQKYRANC30AKTLQCC37 (M(r) 4275, three disulfides).

Amino Acid Sequence↗
PubMed1993

Potentiation by choline of basal and electrically evoked acetylcholine release, as studied using a novel device which both stimulates and perfuses rat corpus striatum.

We examined the release of acetylcholine (ACh) and dopamine (DA) using a novel probe through which striatal neurons could be both superfused and stimulated electrically in both anesthetized and freely moving awake animals. Optimal stimulation parameters for eliciting ACh release from cholinergic neurons differed from those required for eliciting DA release from dopaminergic terminals: at 0.6 ms pulse duration, 20 Hz and 200 microA, ACh release increased to 357 +/- 30% (P < 0.01) of baseline and was blocked by the addition of tetrodotoxin (TTX). Pulse durations of 2.0 ms or greater were required to increase DA release. Unlike ACh release, DA release showed no frequency dependence above 5 Hz. The maximal evoked releases of ACh and DA were 556 +/- 94% (P < 0.01) and 254 +/- 38% (P < 0.05) of baseline, respectively. Peripheral administration of choline (Ch) chloride (30-120 mg/kg) to anesthetized animals caused dose-related (r = 0.994, P < 0.01) increases in ACh release; basal release rose from 117 +/- 7% to 141 +/- 5% of initial baseline levels (P < 0.05) and electrically evoked ACh release rose from 386 +/- 38% to 600 +/- 34% (P < 0.01) in rats given 120 mg/kg. However, Ch failed to affect basal or evoked DA release although neostigmine (10 microM) significantly elevated basal DA release (from 36.7 fmol/10 min to 71.5 fmol/10 min; P < 0.05). In awake animals, Ch (120 mg/kg) also elevated both basal (from 106 +/- 7% to 154 +/- 17%; P < 0.05) and electrically evoked (from 146 +/- 13 to 262 +/- 16%; P < 0.01) ACh release.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1993

Interactive behavior of Saccharomyces cerevisiae, Bacillus pumilus and Propionibacterium freudenreichii subsp. shermanii.

Prevention of ropy bread caused by mucoid variants of certain bacilli presents a major problem for developing countries where cost of preservatives is prohibitive. Control of ropiness may be achieved by using propionic acid-producing bacteria in mixed culture with leavening yeasts. Therefore, interaction studies between Propionibacterium freudenreichii subsp. shermanii, Bacillus pumilus and Saccharomyces cerevisiae were conducted in a chemically defined medium to test the relevance of such an approach. Growth of vegetative cells and germination of spores of B. pumilus were inhibited in media preincubated with P. shermanii at 30 degrees C for 13 h. Inhibition was bacteriostatic for the first 6 h of incubation, becoming bactericidal between 6 and 12 h. Inhibition of B. pumilus spore germination was greater than inhibition of growth of vegetative cells of the bacterium. Culturing of either P. shermanii with S. cerevisiae or B. pumilus with S. cerevisiae did not produce inhibitory effects on any of the organisms. Inhibition of B. pumilus by P. shermanii may be useful for prevention of ropiness in bread prepared by the sponge method, involving fermentation of a portion of the dough.

Bacillus↗
PubMed1993

Antimicrobial activity of ethanol, glycerol monolaurate or lactic acid against Listeria monocytogenes.

Minimal inhibitory concentrations (MIC) and antimicrobial effects of glycerol monolaurate (monolaurin), ethanol and lactic acid, either alone or in combination, against Listeria monocytogenes in tryptic soy broth were determined. Ethanol at concentrations up to 1.25% did not inhibit growth, but growth was strongly inhibited in the presence of 5% ethanol. MIC values of monolaurin and ethanol alone were 10 micrograms/ml (0.001%) and 50,000 micrograms/ml (5%), respectively. However, MIC values were not changed when monolaurin was combined with ethanol. When 5 micrograms/ml monolaurin was combined with 5% ethanol, the inhibitory effect of the combination was similar to the most active compound alone after 24 h incubation. These data indicate little interaction between monolaurin and ethanol against L. monocytogenes. MIC value of lactic acid alone was 5000 micrograms/ml (0.5%), but was lower when 1.25% ethanol was combined with 0.25% lactic acid. When 2.5% ethanol was combined with 0.25% lactic acid, the combination did not increase the inhibitory effect of the most active single compound alone. This result also indicates that there was little interaction between ethanol and lactic acid.

Culture Media↗
PubMed1993

Structural features important for the biological activity of the potassium channel blocking dendrotoxins.

1. Dendrotoxins from mamba snake venoms are small proteins that block neuronal K+ channels. In order to investigate structural features associated with their biological activity, partially folded versions of dendrotoxins I and K from black mamba (Dendroaspis polylepis) were prepared by selectively reducing one or more of their three S-S bonds. 2. The modified toxins were tested for ability to compete with 125I-labelled native toxin I to high affinity binding sites on rat brain synaptosomal membranes and for the ability to increase acetylcholine release in a neuromuscular preparation. 3. Binding affinity increased progressively as the toxins folded to the native conformation and the most biologically active of the modified species were those in which only the disulphide bond between residues 14 and 38 was not formed. These intermediates had native-like conformations as determined by circular dichroism but still had about 5-10 times lower affinity than native toxins. 4. Addition of negatively charged groups to block the free sulthydryls at positions 14 and 38 caused a further, marked loss of activity. 5. The results are consistent with the existence of two important regions in the dendrotoxin molecules. The region containing two of the disulphide bonds (around Cys5-Cys55 and Cys30-Cys51) and much of the secondary structure is essential for the binding affinity of the toxins, while the region around Cys14 and Cys38, equivalent to part of the antiprotease site of the homologous protease inhibitor from bovine pancreas (BPTI), plays an important role in the potency of dendrotoxins.

Animals↗
PubMed1993

Proceedings of the Alaska-Russia Native Peoples Health and Social Issues Conference. May 1992, Alaska.

An Alaska-Russia Native People's Health and Social Issues Conference, sponsored by the Alaska Department of Health and Social Services, the Alaska Native Foundation, the University of Anchorage Institute for Circumpolar Health Studies, the International Scientific Center "ARTIKA" (Magadan, Russia), the Associations of Native People of Chukotka and Kolyma, and the Magadan Native Association, was held in Wasilla, Alaska in May, 1992. The conference brought together Native people, primarily health and social services workers, to discuss differences and similarities in issues and approaches, and to lay the foundation for future collaboration. The primary participants came mostly from rural villages and small regional cities, and represented Native Health Corporations, Native Associations, and villages. Additional participants came from the University of Alaska, the Alaska Department of Health and Social Services, the Indian Health Service, the Magadan Health Department, the Inuit Circumpolar Conference, and the International Union for Circumpolar Health. A Total of 39 people participated, including: eight Russian Natives (Chukchi, Even, and Siberian Yup'ik); three non-Native Russians; 18 Alaska Natives (Aleut, Athabaskan, Inupiat, Siberian Yup'ik, Yup'ik); nine non-Native Alaskans; one Canadian. The issues discussed in individual and panel presentations, and in small groups, included history, demography, settlement patterns, the cash and subsistence economies, mental and physical health (epidemiology, etiology, treatment and prevention), education, governance, culture and language. As the conference participants came to know each other better, the discussions became increasingly open, and, particularly around shared feelings of cultural oppression and loss, emotional.(ABSTRACT TRUNCATED AT 250 WORDS)

Alaska↗
PubMed1992

Dendrotoxin-like effects of noxiustoxin.

Noxiustoxin from the Mexican scorpion (Centruroides noxius Hoffmann) is known to block neuronal K+ channels. Noxiustoxin facilitated acetylcholine release in chick biventer cervicis nerve-muscle preparations, but not in mouse phrenic nerve-hemidiaphragm preparations. Noxiustoxin displaced binding of a radiolabelled dendrotoxin from synaptosomal membranes from rat brain, with a Ki of 10(-10) M. It is concluded that noxiustoxin shares some pharmacological properties with the K+ channel blocking dendrotoxins.

Animals↗
PubMed1992

Protease inhibitor homologues of dendrotoxin do not bind to dendrotoxin acceptors on synaptosomal membranes or facilitate neuromuscular transmission.

The dendrotoxins are a homologous group of potassium channel-blocking polypeptides found in mamba snake venom. They are similar in sequence and structure to Kunitz-type serine protease inhibitors. Modified and native protease inhibitors were assayed for dendrotoxin-like activity using radioligand-binding and twitch tension-recording methods. Despite the large number and high concentration of compounds tested, no protease inhibitor displayed dendrotoxin-like activity. The results indicate that the protease-inhibiting and potassium channel-blocking activities of these two groups of polypeptides are not linked.

Amino Acid Sequence↗
PubMed1991

Physiological evaluation of stimulated growth of Listeria monocytogenes by Pseudomonas species in milk.

Experiments were designed to elucidate a possible physiological mechanism for stimulated growth of Listeria monocytogenes by Pseudomonas fluorescens in milk. The ability of L. monocytogenes to grow in milk under aerobic and microaerophilic environments was compared. Neither environment favored the growth of the organism at 10 degrees C. Autoclaved whole milk was inoculated with P. fluorescens P26 and preincubated for 3 days at 10 degrees C followed by inoculation with L. monocytogenes Scott A and further incubation for 8 days at 10 degrees C. Changes in selected milk components were monitored over the 8-day period. The amount of lactose in the milk was determined, as well as the extent of proteolysis and lipolysis. Both L. monocytogenes and P. fluorescens were able to hydrolyze milk fat but were unable to use lactose. Milk protein was hydrolyzed by P. fluorescens but not by L. monocytogenes. Whole milk partially proteolyzed by treatment with purified protease was inoculated with L. monocytogenes. Results indicated that the growth of L. monocytogenes was stimulated in proteolyzed milk. This is the first report to provide evidence describing a likely mechanism for commensalism between L. monocytogenes and Pseudomonas spp.

Aerobiosis↗
PubMed1989

Interactions between dendrotoxin, a blocker of voltage-dependent potassium channels, and charybdotoxin, a blocker of calcium-activated potassium channels, at binding sites on neuronal membranes.

Dendrotoxin I (DpI) from black mamba venom (Dendroaspis polylepis) has high affinity binding sites on rat brain synaptic membranes. Native DpI displaced [125I]-DpI binding with a Ki of 1 x 10(-10) M, and over 90% of specific binding was displaceable. Charybdotoxin isolated from the Israeli scorpion venom (Leiurus quinquestriatus hebraeus), also displaced [125I]-DpI binding, with a Ki of approximately 3 x 10(-9) M, although the displacement curve was shallower than with native DpI. Both toxins are thought to be high affinity blockers of specific K+ currents. Charybdotoxin selectively blocks some types of Ca2+-activated K+ channels, whereas dendrotoxins only block certain voltage-dependent K+ channels. The interaction between the two types of toxin at the DpI binding site is unexpected and may suggest the presence of related binding sites on different K+ channel proteins.

Animals↗
PubMed1989

Block of potassium channels and facilitation of acetylcholine release at the neuromuscular junction by the venom of the scorpion, Pandinus imperator.

Venom from the scorpion Pandinus imperator potently and selectively blocks voltage-gated K+ channels in bullfrog neurones (Pappone, P. A. and Cahalan, M. D. 1987, J. Neurosci. 7, 3300-3305). Its effects on neuromuscular transmission have now been assessed. Twitch tension studies on chick biventer cervicis preparations showed that the venom (1 microgram/ml and above) significantly augmented responses to nerve but not muscle stimulation; there was little change in postjunctional sensitivity to cholinoceptor agonists or K+-induced depolarization. Electrophysiological studies on mouse triangularis sterni preparations revealed that the venom had no effect on spontaneous transmitter release, but increased evoked transmitter release. Extracellular recordings of nerve terminal action potentials showed that the venom selectively reduced the component of the waveform associated with K+ currents. These results confirm that this venom can selectively block neuronal K+ currents, and they show that this can facilitate the release of acetylcholine at the neuromuscular junction.

4-Aminopyridine↗
PubMed1989

Gene flow by pollen into small populations: Data from experimental and natural stands of wild radish.

Gene flow can have an especially strong impact on the evolution of small populations. However, empirical studies on the actual rates and patterns of gene flow into small populations are few. Thus, we sought to measure gene flow into small populations of wild radish. Raphanus sativus. We found significant differences in gene flow receipt among experimental populations and within those populations over a season. A maximum-likelihood estimate revealed that almost all of the gene flow into these synthetic populations had its origin in relatively distant (>650 m), large natural populations rather than the proximal (255-400 m), small synthetic populations. We also estimated rates of interpopulation mating from simple paternity analysis of progeny produced by seven small (ca. 50 plants) natural populations. Again, we found significant heterogeneity in gene flow receipt. Although these populations varied 10-fold in their range of isolation distances (100-1000 m), gene flow rates did not vary with distance. The magnitude of gene flow rates estimated in all but one population was great enough for gene flow to play an important role in the evolution of these small populations.

Journal Article↗
PubMed1988

Clinical laboratory applications of monoclonal antibodies.

Monoclonal antibody (MAb) technology is well recognized as a significant development for producing specific serologic reagents to a wide variety of antigens in unlimited amounts. These reagents have provided the means for developing a number of highly specific and reproducible immunological assays for rapid and accurate diagnosis of an extensive list of diseases, including infectious diseases. The impact that MAbs have had in characterizing infectious disease pathogens, as well as their current and future applications for use in clinical microbiology laboratories, is reviewed. In addition, the advantages (and disadvantages) of the use of MAbs in a number of immunoassays, such as particle agglutination, radioimmunoassays, enzyme-linked immunosorbent assays, immunofluorescent-antibody assays, and immunohistology, are explored, including the use of these reagents in novel test system assays. Also, nucleic acid probe technology is compared with the use of MAbs from the perspective of their respective applications in the diagnosis of infectious disease agents. There is no question that hybridoma technology has the potential to alter significantly the methods currently used in most clinical microbiology laboratories.

Antibodies, Monoclonal↗