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Biomedical subjects

D L Marshall

Publications and source records attributed to D L Marshall.

At least 19 recordsLinked to original sources
PubMed1997

Presynaptic nicotinic modulation of dopamine release in the three ascending pathways studied by in vivo microdialysis: comparison of naive and chronic nicotine-treated rats.

The modulation of dopamine release by presynaptic nicotinic receptors in vitro is well established, but the significance of this effect in vivo is unclear. We have characterised the effect of nicotine, locally applied via a microdialysis probe, on dopamine release from the terminal regions of three ascending dopaminergic pathways in conscious, freely moving rats. Nicotine caused a dose-dependent increase in dopamine release in the striatum, the nucleus accumbens, and, to a lesser extent, the frontal cortex. Metabolite levels were unaltered by any concentration of nicotine. Prior administration of mecamylamine via the probe abolished the nicotine-evoked increase in dopamine release, confirming the mediation of nicotinic receptors. The dose dependence of mecamylamine-sensitive, nicotine-evoked dopamine release was similar in all three brain regions. However, 10(-5) M tetrodotoxin totally blocked nicotine-stimulated dopamine release in the striatum and the accumbens but not the cortex. Daily subcutaneous injections of nicotine (0.4 mg kg-1 for 7 days) increased the response to a subsequent local application of nicotine in the striatum, and a similar trend was found in the other brain areas. The same daily dose of nicotine given as a continuous infusion had no effect, whereas infusion of 4 mg kg-1 day-1 increased the response to a subsequent nicotine challenge. The localisation and regulation of nicotinic receptors in the terminal fields of dopaminergic pathways are discussed.

Animals↗
PubMed1996

Effect of monolaurin and lactic acid on Listeria monocytogenes attached to catfish fillets.

The purpose of this study was to determine the effects of monolaurin and lactic acid, singly or combined, on Listeria monocytogenes attached to catfish fillets. Skinless catfish fillets were inoculated with L. monocytogenes and dip treated in monolaurin and/or lactic acid solution for various time periods. Results showed that monolaurin up to 400 micrograms/ml had no influence on counts. Conversely, lactic acid-treated fillets had reduced counts compared to controls. Dipping in 0.85, 1.70, or 2.55% lactic acid for 30 min reduced counts by 0.9, 1.4, or 1.3 logs, respectively. Extending the dipping time to 60 min resulted in little additional decrease in counts. Combining monolaurin with lactic acid yielded results similar to lactic acid alone. Hence, population reduction ability resides with lactic acid and not monolaurin.

Animals↗
PubMed1996

Antimicrobial susceptibility and plasmid-mediated streptomycin resistance of Plesiomonas shigelloides isolated from blue crab.

Five Plesiomonas shigelloides strains isolated from retail or wild-catch Louisiana blue crabs (Callinectes sapidus) were examined for resistance to selected antibiotics and presence of plasmids. Three agar media, MacConkey, Salmonella-Shigella and a modification of inositol brilliant green bile salt (IBB), were evaluated for isolation of P. shigelloides. Of these, IBB was most satisfactory for distinguishing between P. shigelloides and the related species Aeromonas hydrophila. Isolates were susceptible to gentamicin, nalidixic acid and tetracycline, and were resistant to ampicillin, carbenicillin, kanamycin and streptomycin. Each isolate carried three plasmids of approximately 2.5 kb, 3.8 kb and 5.3 kb. Plasmid curing with ethidium bromide and elevated temperature linked the streptomycin resistance determinant with the 3.8 kb and/or 5.3 kb plasmids. These results provide the first description of small size plasmids in P. shigelloides. Identical antibiotic resistance patterns of the isolates indicated they share a common environment and likely share a common mode for developing antibiotic resistance. Furthermore, emergence of antibiotic-resistant P. shigelloides may imply contamination of Louisiana aquatic environments by wastewater.

Animals↗
PubMed1994

Neuromuscular effects of some potassium channel blocking toxins from the venom of the scorpion Leiurus quinquestriatus hebreus.

The scorpion venom Leiurus quinquestriatus hebreus was fractionated by chromatography in order to isolate toxins that affected binding of radiolabelled dendrotoxin to K+ channel proteins on synaptosomal membranes and that facilitated acetylcholine release in chick biventer cervicis nerve-muscle preparations. In addition to the previously characterized charybdotoxin, three toxins were isolated: 14-2, 15-1 and 18-2. Toxin 14-2 has a blocked N-terminus and because of low quantities, it has not been sequenced; 15-1 is a newly sequenced toxin of 36 residues with some overall homology to charybdotoxin and noxiustoxin; 18-2 is identical to charybdotoxin-2. The apparent Ki against dendrotoxin binding were: charybdotoxin, 3.8 nM; 14-2, 150 nM; 15-1, 50 nM; and 18-2, 0.25 nM. Toxin 14-2 (75 nM-1.5 microM) had a presynaptic facilitatory effect on neuromuscular preparations. Toxin 15-1 augmented responses to direct muscle stimulation, probably because it blocked Ca(2+)-activated K+ currents in muscle fibres. Toxin 18-2 (charybdotoxin-2) had a potent presynaptic facilitatory action, with less effect on direct muscle stimulation. This contrasts with the relatively weak neuromuscular effects of the highly homologous charybdotoxin. On a Ca(2+)-activated K+ current in mouse motor nerve endings, charybdotoxin and toxin 18-2 produced maximal block at around 100 nM, whereas 15-1 was inactive at 300 nM. Charybdotoxin can increase quantal content, but this is more likely to result from block of voltage-dependent K+ channels than Ca(2+)-activated channels: the increase in transmitter release occurred in conditions in which little IKCa would be present; higher concentration of charybdotoxin and longer exposure times were required to increase transmitter release than those needed to block IKCa, and the facilitatory effects of charybdotoxin and toxin 18-2 correlated more with their effects on dendrotoxin binding than on block of IKCa.

Acetylcholine↗
PubMed1994

Mechanism of inhibited growth of Bacillus pumilus by Propionibacterium freudenreichii subsp. shermanii.

Physiological studies were conducted in an attempt to elucidate the mechanism of inhibition of Bacillus pumilus by Propionibacterium freudenreichii subsp. shermanii. Inhibition of B. pumilus by P. shermanii occurred in media supplemented with 1% glucose, indicating that glucose utilization by the latter bacterium was not responsible for growth inhibition of the former bacterium. The medium pH in which P. shermanii inhibited the growth of B. pumilus was 4.3. Propionic acid was positively identified in the culture medium in which B. pumilus was inhibited by P. shermanii. The presence of propionic acid and a low medium pH may account for the inhibition of B. pumilus by P. shermanii. Sodium lactate concentrations of 0.8-1.0% were essential for the continuous growth of and propionic acid production by P. shermanii. Thus, use of P. shermanii to inhibit B. pumilus in foods would likely require a lactate source.

Antibiosis↗
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↗