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Biomedical subjects

M Larsen

Publications and source records attributed to M Larsen.

At least 109 records · Page 6Linked to original sources
PubMed1996

Biological control. Aspects of biological control--with special reference to arthropods, protozoans and helminths of domesticated animals.

Biological control describes situations in which a living antagonist (a predator, parasite, parasitoid or a pathogen) is distributed by man to lower pest (parasite) populations to acceptable sub-clinical densities or to keep the population at a non-harmful level. Ideally, biological control has no negative effects on the environment, whereas chemical control is not always so harmless. Laboratory and field observations have revealed many organisms, such as viruses, bacteria, fungi, protozoans, turbellarians, nematodes, earthworms, tardigrades, insects, copepods and mites as antagonists to parasitic arthropods, protozoans and helminths of domesticated animals. However, only very few of these antagonists have shown promising qualities as biological control agents within veterinary science. The lack of success should be linked to the lack of knowledge about complex natural biological systems and the antagonists that may be found there. This situation has restricted the interest of industry in developing biological products. In the future, however, industry may become more interested in biological control considering the increasing problems with parasite resistance to drugs in combination with the increasing cost of developing new chemical products, and because of increasing public concern about chemical residues in animal products and in the environment.

Animals↗
PubMed1996

Induction of traps by Ostertagia ostertagi larvae, chlamydospore production and growth rate in the nematode-trapping fungus Duddingtonia flagrans.

Biological control of parasitic nematodes of domestic animals can be achieved by feeding host animals chlamydospores of the nematode-trapping fungus Duddingtonia flagrans. In the host faeces, D. flagrans develop traps that may catch nematode larvae. In experiments on agar, D. flagrans had a growth rate between 15 and 60 mm/week at temperatures between 20 and 30 degrees C. The presence of nematodes induces the fungus to produce traps. The rate of trap formation in D. flagrans has an optimum at 30 degrees C, producing 700-800 traps/cm2/2 days, when induced by 20 nematodes/cm2 on agar. Approaching 10 and 35 degrees C the ability to produce traps is gradually reduced. The response of chlamydospore production on agar to changes in temperature is the same as that for trap formation. On agar, at 10, 20 and 30 degrees C D. flagrans loses its trap inducibility after 2-3 weeks. During the ageing process, increasing numbers of chlamydospores are produced up to a certain limit. The time for reaching maximum chlamydospore concentration coincided with the time for loss of induction potential. The implications of these results in relation to biological control in faeces are discussed.

Animals↗
PubMed1996

The capacity of the fungus Duddingtonia flagrans to prevent strongyle infections in foals on pasture.

A field trial was conducted to evaluate the potential of the nematode-destroying fungus Duddingtonia flagrans to control free-living stages of horse strongyles. In late Spring 2 groups of horses (yearlings) with mixed infections of strongyles were allowed to contaminate 2 equal-sized pastures. One of the groups (F) received a daily dose of D. flagrans mixed in a feed supplement, while the other (C) received a similar amount of supplement without fungus. During a 3-month contamination period strongyle egg counts in faeces and number of infective strongyle larvae harvested from faecal cultures were determined. Grass samples were collected fortnightly. After the contamination period the yearlings were removed and 2 groups of young tracer foals (TF and TC) grazed the fungus and control pastures respectively for 4 weeks, housed for another 15 weeks and then killed to determine their worm burdens. The number of larvae in cultures from group TF was significantly lower than that in TC and herbage infectivity was reduced to a very low level on the pasture grazed by horses fed fungi. The number of Strongylus vulgaris and Strongylus edentatus larvae was also significantly lowered in group TF. Cyathostome larvae recovered from the mucosa of the ventral and dorsal colon and from the caecum were significantly lowered in group TF foals. Also, the number of strongyles found in the gut contents of group TF foals were significantly reduced in the dorsal colon, but numbers of worms in the ventral colon and in the caecum were similar to those of the controls.

Animal Feed↗
PubMed1996

Androgen-regulated proliferation and gene transcription in a prostate smooth muscle cell line (PS-1).

Androgens play a key role in directing stromal-epithelial interactions in prostate gland development, in maintenance of adult phenotype, and in disease progression. To address the molecular mechanisms of androgen action in prostate stromal cells and the genes regulated by androgens in this cell type, a stromal cell line (PS-1) was developed from rat ventral prostate. The PS-1 cell line was adapted to chemically defined media and characterized as smooth muscle based on expression of desmin, smooth muscle alpha-actin, and nuclear androgen receptor, markers for prostate smooth muscle. To examine steroid hormone regulation, PS-1 cells were analyzed for response to a panel of steroid hormones in serum-free, chemically defined media. PS-1 cells were significantly growth stimulated by physiological concentrations of androgens (10nM) relative to other steroids tested. To ascertain whether this cell line could be used to examine androgen-regulated gene expression, differential display PCR was used to demonstrate the presence of androgen-regulated transcripts and provide the initial steps in cloning these genes. Replicate differential display PCR analyses showed consistent androgen stimulation of 16 messenger RNA species. Northern analysis confirmed androgen regulation of 6 species. Sequence analysis of each indicated no regions of significant homology or direct matches to existing sequences. Further study of the PS-1 stromal cell line and androgen-regulated genes identified here will provide a novel in vitro system for defining molecular mechanisms of androgen action in prostate stromal cells and the significance of stromal androgen-regulated genes to stromal-epithelial interactions.

Androgens↗
PubMed1995

Structure-dependent induction of CYP2B by polychlorinated biphenyl congeners in female Sprague-Dawley rats.

The dose-response induction of hepatic microsomal pentoxyresorufin O-dealkylase (PROD) activity by phenobarbital (PB) and several polychlorinated biphenyl (PCB) mixtures and congeners was determined in the immature female Sprague-Dawley rat. At a dose of 75 mg/kg/day of PB for 3 days, the microsomal PROD activity was 2154 pmol/min/mg protein. Aroclors 1260, 1254, 1242, and 1016 did not induce maximal PROD activity at doses up to 500 mg/kg, and only Aroclor 1016 induced > a half-maximal response at the 500 mg/kg dose. The relative potencies of eighteen different PCB congeners were also determined, and the structures of these compounds differed with respect to the degree of chlorination (tri- to octochloro) and substitution patterns. The relative potencies of these compounds were estimated by comparing their induced activities at the high dose (150 or 100 mg/kg) with that of PB. The most potent inducers were 2,3,3',4',5,6-hexaCB and 2,2',3,4',5,5',6-heptaCB; at a dose of 150 mg/kg, the PROD activity induced by 2,2'3,4',5,5',6-heptaCB was comparable to that observed for PB. 2,3,3',4',5,6-HexaCB was the most potent inducer, and hepatic PROD activity in rats treated with 150 mg/kg was 4202 pmol/min/mg; this value was higher than that observed for PB at a dose of 75 mg/kg. A second group of congeners including 2,2',3,4,4',5,5'-heptaCB, 2,2',4,4',5,5'-hexaCB, 2,2',3,3',4,4',5,5'-octaCB 2,2',4,4'-tetraCB, 2,2',4,5,5'-pentaCB, 2,2',3,4,4',5',6-heptaCB, 2,2',4,4',5-pentaCB and 2,2',3,3',4',5,5',6-octaCB induced PROD activity > or = 1090 pmol/min/mg at the 150 mg/kg dose, and this value was > 50% of the maximal response observed for PB. The remaining compounds, namely 2,4,4'-triCB, 2,2',3,4'-tetraCB, 2,2',5,5'-tetraCB, 2,3',4,4',5-pentaCB, 2,3,3',4,4'-pentaCB, 2,2',4,4',5,6'-hexaCB, 2,3,3',4,4',5,5'-heptaCB and 2,2',3,3',4,4,5-heptaCB were all relatively weak inducers of hepatic microsomal PROD activity ( < 450 pmol/min/mg). In parallel experiments, western blot analysis of immunoreactive CYP2B1 and CYP2B2 protein showed that PB, the PCB mixtures, and congeners induced both proteins. Previous studies have identified a cis-acting DNA element that plays a role in regulating CYP2B1/B2 gene expression and binds nuclear trans-acting factor(s) induced by PB. The results of gel electrophoretic mobility shift assays with nuclear extracts showed that both PB and 2,2',3,4',5,5',6-heptaCB induce formation of a common retarded band using a 32P-labeled oligonucleotide corresponding the the cis-acting DNA promoter sequence. Both PB and PCBs appear to induce CYP2B1/B2 via a common mechanism. Although the results of this study do not define structure-induction (CYP2B1/B2) relationships for PCBs, two compounds, namely 2,3,3',4',5,6-hexaCB and 2,2',3,4',5,5',6-heptaCB, were identified as highly potent inducers.

Animals↗
PubMed1995

Purification of a novel protein (ps20) from urogenital sinus mesenchymal cells with growth inhibitory properties in vitro.

Our previous studies have characterized mesenchyme-derived proteins to identify biologically active proteins and novel markers for stromal cell paracrine action relative to stromal-epithelial interactions. Previous reports have characterized properties of a growth inhibitory activity (to bladder and prostatic epithelial cells), secreted by U4F fetal rat urogenital sinus mesenchymal cells, not cross-reactive with antibodies to known cytokines, and provisionally termed UGIF. The present study reports the characterization, purification, and biological properties of a 20-21-kDa protein responsible for UGIF activity. The 20-21-kDa protein (termed ps20) was purified to near homogeneity, the amino-terminal sequence was determined, and biological properties were characterized in vitro. Amino-terminal sequence analysis indicated no direct matches or regions of homology with known proteins. Purified ps20 induced a linear and saturable inhibition of [3H]thymidine incorporation in PC-3 prostatic carcinoma cells (half-maximal activity at 2.6 nM), inhibited cell proliferation (increased population doubling time from 19.8 to 25.8 h), and induced a 210% stimulation in the synthesis of secreted proteins. These data suggest that ps20 may be a candidate paracrine effector protein and may play a role in stromal-epithelial cell interaction in the prostate gland.

Animals↗
PubMed1995

[Nasal myiasis].

Thirty fly maggots were retrieved from the nasal cavity of a 23-year old man who had one week previously received treatment for a nasal fracture. The larvae were identified as Calliphora erythrocephala. These are not a common cause of myiasis as they normally breed on carrion. In myiasis it is important to establish whether the larvae are invasive or not. A brief description of nasal myiasis is given.

Adult↗
PubMed1995

Beta-2 microglobulin is mitogenic to PC-3 prostatic carcinoma cells and antagonistic to transforming growth factor beta 1 action.

Previous studies have identified a M(r) 12,000 protein in rat prostatic stromal cell-conditioned medium with growth stimulatory activity to human prostatic carcinoma cells as a direct match with beta 2-microglobulin (beta 2-m). The present study was conducted to characterize the activities of human beta 2-m directly, using commercially available, purified human beta 2-m. Beta 2-m was assayed for growth stimulatory activity to human PC-3 prostatic carcinoma cells and rat PS-1 prostatic stromal cells and for antagonistic activity to transforming growth factor beta 1 (TGF-beta 1)-induced growth inhibitory actions. Beta 2-m acted to stimulate [3H]thymidine incorporation in PC-3 cells in a linear, concentration-dependent and saturable manner in serum-free medium. Beta 2-m stimulated cell proliferation and significantly decreased population doubling times in both PC-3 and PS-1 cell lines. At half-maximal concentrations of TGF-beta 1 and lower, beta 2-m acted in a concentration-dependent, antagonistic manner, acting to stimulate growth-inhibited PC-3 cells to fully neutralize TGF-B1 activity. In contrast, cells exposed to maximum activity TGF-beta 1 concentrations were refractory to beta 2-m action, regardless of the concentration tested. This represents the first report to demonstrate a growth-stimulatory activity of B2-m with carcinoma/epithelial cells and to show beta 2-m antagonistic activity to TGF-B1 growth-induced inhibition. Beta 2-m has been shown previously to associate with hormone/growth factor receptors. Together, these data suggest that beta 2-m may play a role in modulating cell proliferation, possibly through modification of ligand/receptor kinetics. Owing to the elevation of both beta 2-m and TGF-beta 1 in many dysplastic-neoplastic conditions, beta 2-m may be relevant to mechanisms of abnormal proliferation disorders and in modulating TGF-beta 1 mechanisms of actions.

Cell Division↗
PubMed1995

Interlaboratory reproducibility of yeast protein patterns analyzed by immobilized pH gradient two-dimensional gel electrophoresis.

An interlaboratory comparison was conducted on the positional and quantitative reproducibility of yeast proteins resolved by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) using isoelectric focusing with immobilized pH gradient (pH 4-7) in the first dimension. The basic experimental set-up was as follows: one laboratory prepared and distributed a [35S]methionine-labeled total yeast protein extract (Göteborg, Sweden), another laboratory prepared the IPG strips to be used by all labs in this study (Munich, Germany), the third laboratory (Aarhus, Denmark) circulated the protocols and coordinated the modest attempts to unify them. Samples were run horizontally in the first dimension and vertically in the second. The gels were sent to Göteborg for processing by phosphoimager technology and computerized image analysis (PDQuest), and the 2-D PAGE resolved proteins were located and quantified automatically. A subset of 470 spots was manually matched in all gels out of an average of 1328 resolved proteins. The positional interlaboratory comparison revealed great pattern reproducibility, the correlation coefficient in no case being less than 0.9994. In absolute terms an average deviation of 2.8 mm (x-position) and 1.8 mm (y-position) were obtained for all nine gels (three gels per lab). The interlaboratory comparison of protein quantitation displayed higher variability, and the best correlation coefficient generated was 0.975. An average standard deviation of 34.5% was calculated for protein quantitation including all three labs, a value slightly higher than the intralaboratory variation (range 20-28%). Thus, despite differences in protocols, chemicals and equipment, the immobilized pH gradient technology gave extremely high positional and quantitative reproducibility. This will greatly facilitate the exchange of data and the establishment of multi-user image-based 2-D gel databases.

Electrophoresis, Gel, Two-Dimensional↗
PubMed1995

Prevention of clinical trichostrongylidosis in calves by strategic feeding with the predacious fungus Duddingtonia flagrans.

The present investigation showed that strategic feeding of first-season calves with the microfungus Duddingtonia flagrans through the initial 3 months of the grazing season could prevent severe clinical trichostrongylidosis in the late summer. The successful prevention of disease was particularly noteworthy in view of the high stocking rate practiced on this permanent pasture, which was widely contaminated with a range of gastrointestinal nematodes. The results showed that larval populations of Ostertagia and Cooperia were significantly reduced on the pasture grazed by the fungus-treated calves. Numbers of Nematodirus seemed less affected. The present paper discusses the complexity of fungus-nematode interactions in dung pats under natural conditions.

Animals↗
PubMed1995

Biological control of trichostrongyles in calves by the fungus Duddingtonia flagrans fed to animals under natural grazing conditions.

The present study was conducted in the 1993 grazing season with yearling calves exposed to a pasture with a natural mixed trichostrongyle larval infection. It was shown that daily feeding with the microfungus Duddingtonia flagrans during the first 2 months of the season led to a lowered herbage infectivity and a reduced acquisition of Ostertagia sp. and Cooperia sp. later in the season. In addition, the procedure delayed the onset of clinical disease. This was due to the nematode-destroying effects of the fungi in the dung excreted by the fungus-treated calves, as evidenced by results from a parallel in vitro assay on faecal larval cultures. The paper discusses future research needs before practical biological control can be implemented.

Animal Feed↗
PubMed1995

Predacious activity of the nematode-trapping fungus Duddingtonia flagrans against cyathostome larvae in faeces after passage through the gastrointestinal tract of horses.

This study was undertaken to examine the potential of the nematode-trapping microfungus Duddingtonia flagrans to survive passage through the gastrointestinal tract of horses and subsequently to destroy free-living stages of cyathostomes in faecal cultures. Three different oral dose levels were tested, two horses being used for each level. Faeces were collected twice daily and the numbers of parasite eggs per gram of faeces were determined. The numbers of infective third stage larvae which developed in faecal cultures were determined after the cultures had been incubated for 2 weeks at 24 degrees C. Results showed a positive relationship between dose level and reduction in the number of infective larvae. Fungi were recovered in faeces at times which corresponded to high larval reduction.

Animal Feed↗
PubMed1995

Volatile anaesthetics: cellular mechanisms of action.

The mechanisms by which volatile anaesthetics act in the central nervous system are reviewed. The main cellular targets are excitatory synapses and the cell membrane of the neuronal cell body/dendrite, although there also appears to be a significant effect on thin unmyelinated fibres. Experiments quantifying these effects have shown that 1 MAC isoflurane reduces the activity in afferent fibres by 18%, excitatory synapses by 27% and postsynaptic neurones by 24%. Two important effects observed when recording from individual neurones are hyperpolarization of the cell membrane by an enhanced potassium conductance and increased threshold for initiation of action potentials. Excitatory synaptic transmission is most probably reduced due to a decreased release of transmitter from presynaptic terminals. Antagonistic and biphasic effects are often seen, for instance depression of both inhibitory and excitatory transmission and depolarization-hyperpolarization of the postsynaptic membrane.

Action Potentials↗
PubMed1994

The effect of the volatile anesthetic isoflurane on Ca(2+)-dependent glutamate release from rat cerebral cortex.

A major effect of volatile anesthetics is to reduce excitatory synaptic transmission. In the present study the stimulated release of glutamate under the influence of increasing concentrations of isoflurane was studied in vitro by utilizing hippocampal slices from Wistar rats. Ca(2+)-dependent release was calculated by subtracting stimulated release with blocked synaptic transmission (50 mM K+, 0 mM Ca2+ and 4 mM Mg2+) from total evoked release (50 mM K+, 2 mM Ca2+ and 1 mM Mg2+). Isoflurane 0.5, 1.5 and 3% reduced Ca(2+)-dependent release of glutamate to 69, 58 and 49%, respectively (P < 0.05 for all related to control). These results are in agreement with the possibility of reduced release of transmitter as a mechanism of action of volatile anesthetics.

Animals↗
PubMed1994

A novel approach to express a heterologous gene on Kluyveromyces lactis linear killer plasmids: expression of the bacterial aph gene from a cytoplasmic promoter fragment without in-phase fusion to the plasmid open reading frame.

Using the cytoplasmically localized killer plasmids pGKL1 and pGKL2 of Kluyveromyces lactis a new linear hybrid plasmid (pWKL1) was constructed. It consists of pGKL1 into which, in addition to the previously developed cytoplasmically expressible LEU2* selection marker, a phosphotransferase encoding bacterial antibiotic resistance gene has been integrated. In the hybrid plasmid pWKL1 this gene was preceded by a putative transcriptional signal from pGKL2, i.e., the upstream conserved sequence of ORF5 (UCS5). All foreign genes, so far integrated and expressed in linear plasmids, required in addition to a cytoplasmic promoter (UCS) an in phase fusion to the corresponding open reading frame. In this study the UCS5, not containing the translational start of ORF5, and the aph coding region were intentionally not combined in phase, in order to check whether expression can occur under these conditions. Kluyveromyces lactis transformants carrying pWKL1 were highly resistant against the antibiotic geneticine (G418) and exhibited elevated levels of APH activity. Expression of the aph gene was due to the presence of the UCS5 containing fragment (110 bp). Thus, an in phase fusion was not required for expression. This is the first report that, concomitant with a selectable marker gene, foreign DNA can be integrated in a linear plasmid via homologous recombination and more importantly, that in phase fusions are not required generally for expression of heterologous genes in linear plasmids.

Base Sequence↗
PubMed1994

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: in vitro and in vivo studies.

Following in vitro screening investigations on approximately 100 nematophagous fungi reported previously, eight species were selected for further investigation. Fungal elements (mycelium and conidia) were subjected to in vitro stress selection designed to simulate rumen and abomasal conditions. From these studies, three species, namely, Arthrobotrys oligospora, Arthrobotrys oviformis and Geniculifera eudermata, were selected for in vivo survival studies in sheep surgically fitted with abomasal and ileal cannulae. Doses of fungal conidia were administered orally or via the abomasal cannulae and samples of digesta were taken from the abomasum, the terminal ileum and faeces. The viability of the three fungal species at these sites was demonstrated. The abundance of fungi throughout the gut was dose-dependent but in all cases only very small volumes of fungal suspension containing unprotected conidia were used. These results demonstrate that a practical means of orally administering nematophagous fungi to control free-living stages of nematodes in faeces may become an achievable objective.

Abomasum↗
PubMed1994

The potential of nematophagous fungi to control the free-living stages of nematode parasites of sheep: survey for the presence of fungi in fresh faeces of grazing livestock in Australia.

In the course of 12 months, 1742 fresh faecal samples from grazing livestock, principally ruminants, from various States of Australia were examined for the presence of nematophagous fungi. In total, 48 separate isolations were made representing various species from the genus Arthrobotrys and also 16 isolates of the single Duddingtonia species, Duddingtonia flagrans. These isolates will be used in continuing studies to select the most suitable species, on the basis of nematophagous capability and ruminant gut survival capacity, for development of a biological means of controlling nematode parasites of livestock.

Animal Husbandry↗