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Biomedical subjects

P A Stein

Publications and source records attributed to P A Stein.

11 recordsLinked to original sources
PubMed2002

The effects of ivermectin and moxidectin on egg viability and larval development of ivermectin-resistant Haemonchus contortus.

The in vivo effects of ivermectin and moxidectin on egg viability and larval development of ivermectin-resistant Haemonchus contortus were examined over time after anthelmintic treatment of sheep. Twenty merino sheep, (12 months old) were allocated to five treatment groups and infected with ivermectin-resistant H. contortus. Thirty one days later, the sheep were treated with intraruminal ivermectin capsules, oral ivermectin, oral moxidectin or injectable moxidectin at the manufacturer's recommended dosages, or left untreated. At various times up to 112 days after treatment, faecal egg counts (FEC) were determined and development rates of infective larvae (L3) cultured in faeces or on agar were measured. Eggs in faecal cultures from ivermectin capsule treated sheep showed reduced L3 development percentages in comparison to faecal cultures from untreated sheep. Eggs from ivermectin capsule treated sheep, isolated from faeces, and cultured on agar showed similar L3 development to eggs from control sheep. These results demonstrate an inhibitory effect of excreted ivermectin in faeces on larval development of ivermectin-resistant H. contortus. L3 development in faecal culture from animals receiving oral ivermectin were reduced for only 3 days after treatment. Faecal egg counts and development of L3 larvae in both culture systems from moxidectin treated sheep were low, due to the high efficacy of the drug. Egg counts in moxidectin treated sheep were reduced by approximately 90% 24h after treatment, before decreasing to almost 100% at 48h, suggesting that the current quarantine recommendation of holding sheep off pasture for 24h after treatment may still lead to some subsequent pasture contamination with worm eggs.

Animals↗
PubMed2001

Selection of different genotype larvae and adult worms for anthelmintic resistance by persistent and short-acting avermectin/milbemycins.

To understand the factors that influence selection for anthelmintic resistance, it is necessary to examine the impact of drug treatment, particularly persistent drugs, on all phases of the worm life cycle. The efficacy of various avermectin/milbemycin anthelmintics was determined against resident worms, incoming larvae (L3) and development of eggs in faecal culture. Homozygote-resistant and maternal and paternal F1-heterozygote genotypes of Haemonchus contortus were used to infect sheep before or after treatment with ivermectin (IVM) oral, IVM capsule, moxidectin (MOX) oral or MOX injectable. Total worm count and quantitative larval culture were used to determine efficacy against parasitic and free-living stages, respectively. Selection for resistance by IVM capsules occurred at the adult and L3 stages because of poor efficacy against these stages for all resistant genotypes. However, the selective advantage of these surviving worms was reduced due to the low development of their eggs to L3 in faecal culture. For MOX, selection for resistance predominantly occurred after treatment because of high efficacy against resident adult worms of all resistant genotypes but poor efficacy against resistant L3 ingested after drug administration. The results indicated no evidence of sex-linked inheritance for IVM resistance. Mean IVM efficacies against homozygous and heterozygous resistant adult worms were not different, and IVM capsule efficacy against incoming L3 was approximately 70% for all resistant genotypes, consistent with a dominant trait. MOX was highly effective against adults of all resistant genotypes and approximately 76% effective against incoming L3 regardless of resistance genotype, also consistent with a dominant trait. These results will enable the impact of persistent drugs on worm control and anthelmintic resistance to be estimated. The results indicate that IVM capsules should not be used in populations where avermectin/milbemycin resistance is present.

Administration, Oral↗
PubMed2001

A new model for nuclear envelope breakdown.

Nuclear envelope breakdown was investigated during meiotic maturation of starfish oocytes. Fluorescent 70-kDa dextran entry, as monitored by confocal microscopy, consists of two phases, a slow uniform increase and then a massive wave. From quantitative analysis of the first phase of dextran entry, and from imaging of green fluorescent protein chimeras, we conclude that nuclear pore disassembly begins several minutes before nuclear envelope breakdown. The best fit for the second phase of entry is with a spreading disruption of the membrane permeability barrier determined by three-dimensional computer simulations of diffusion. We propose a new model for the mechanism of nuclear envelope breakdown in which disassembly of the nuclear pores leads to a fenestration of the nuclear envelope double membrane.

Adenine↗
PubMed1999

A visual screen of a GFP-fusion library identifies a new type of nuclear envelope membrane protein.

The nuclear envelope (NE) is a distinct subdomain of the ER, but few membrane components have been described that are specific to it. We performed a visual screen in tissue culture cells to identify proteins targeted to the NE. This approach does not require assumptions about the nature of the association with the NE or the physical separation of NE and ER. We confirmed that screening a library of fusions to the green fluorescent protein can be used to identify proteins targeted to various subcompartments of mammalian cells, including the NE. With this approach, we identified a new NE membrane protein, named nurim. Nurim is a multispanning membrane protein without large hydrophilic domains that is very tightly associated with the nucleus. Unlike the known NE membrane proteins, it is neither associated with nuclear pores, nor targeted like lamin-associated membrane proteins. Thus, nurim is a new type of NE membrane protein that is localized to the NE by a distinct mechanism.

Amino Acid Sequence↗
PubMed1999

Investigation of intestinal nematode responses to naphthalophos and pyrantel using a larval development assay.

Responses of several nematode species to naphthalophos and pyrantel/levamisole were examined using a larval development assay in order to determine the potential of this assay for detection of resistance. Haemonchus contortus and Ostertagia circumcincta showed concentration-dependent responses to naphthalophos, however, the assay was unsuitable for Trichostrongylus colubriformis due to the low toxicity of the drug to the larval stages of this nematode. Measurement of concentration-dependent response to pyrantel in susceptible T. colubriformis was limited by a reduced toxicity against larvae at high drug concentrations, resulting in a parabolic response with a development-inhibition maxima of less than 100%. This limits the usefulness of the assay to detect pyrantel resistance in this species as the presence of a small resistant fraction in a field isolate may be indistinguishable from the parabolic susceptible response. On the other hand, responses of susceptible T. colubriformis to levamisole, and susceptible H. contortus to pyrantel and levamisole showed 100% development inhibition over a range of drug concentrations, indicating that the appearance of a resistant fraction in a field population would be readily discernible from the susceptible response, allowing resistance detection for these drug/parasite combinations. This study has highlighted the varied suitability of the larval development assay technique for resistance detection with different combinations of drugs and parasite species.

Animals↗
PubMed1993

FGF signalling in the early specification of mesoderm in Xenopus.

We have examined the role of FGF signalling in the development of muscle and notochord and in the expression of early mesodermal markers in Xenopus embryos. Disruption of the FGF signalling pathway by expression of a dominant negative construct of the FGF receptor (XFD) generally results in gastrulation defects that are later evident in the formation of the trunk and tail, though head structures are formed nearly normally. These defects are reflected in the loss of notochord and muscle. Even in embryos that show mild defects and gastrulate properly, muscle formation is impaired, suggesting that morphogenesis and tissue differentiation each depend on FGF. The XFD protein inhibits the expression of the immediate early gene brachyury throughout the marginal zone, including the dorsal side; it does not, however, inhibit the dorsal lip marker goosecoid, which is expressed in the first involuting mesoderm at the dorsal side that will underlie the head. The XFD protein also inhibits Xpo expression, an immediate early marker of ventral and lateral mesoderm. These results suggest that FGF is involved in the earliest events of most mesoderm induction that occur before gastrulation and that the early dorsal mesoderm is already composed of two cell populations that differ in their requirements for FGF.

Animals↗
PubMed1991

A DNA transformation-competent Arabidopsis genomic library in Agrobacterium.

We have constructed a nuclear genomic library from the cruciferous plant Arabidopsis thaliana ecotype Columbia in a cosmid vector, pLZO3, and a host organism, Agrobacterium tumefaciens AGL1, which can directly DNA-transform the parent organism, Arabidopsis. The broad host range cosmid pLZO3 carries a gentamicin acetyltransferase gene as bacterial selective marker and tandem, chimeric neomycin and streptomycin phosphotransferase genes as plant selective markers. Agrobacterium AGL1 carries the hypervirulent, attenuated tumor-inducing plasmid pTiBo542 from which T-region DNA sequences have been precisely deleted, allowing optimal DNA transformation of many dicotyledonous plants. Agrobacterium AGL1 also carries an insertion mutation in its recA general recombination gene, which stabilizes the recombinant plasmids. The Arabidopsis genomic library consists of some 21,600 clones gridded onto 96-well microtiter dishes and, if random, carries at least three genomic equivalents. When probed for the presence of several Arabidopsis low copy-number genes, the genomic library seems representative. As with the unicellular organisms Escherichia coli and Saccharomyces cerevisiae, this DNA transformation competent genomic library should expedite gene isolation, by gene rescue, in multicellular organisms like Arabidopsis.

Agrobacterium tumefaciens↗
PubMed1989

Manifest anxiety in children with learning disabilities.

Manifest anxiety scores of students receiving part-time services for learning disabilities, students receiving full-time services for learning disabilities, and a matched group of nonexceptional peers were compared. A significant difference was found between the part-time group and the nonexceptional group in Total Anxiety and Worry-Oversensitivity.

Anxiety↗
PubMed1988

The Azorhizobium caulinodans nifA gene: identification of upstream-activating sequences including a new element, the 'anaerobox'.

From nucleotide sequencing analyses, the A. caulinodans nifA gene seems to be under dual control by the Ntr (in response to available N) and Fnr (in response to available O2) transcriptional activation/repression systems. Because it fixes N2 in two contexts, the Ntr system might regulate A. caulinodans nif gene expression ex planta, while the Fnr system might similarly regulate in planta. As nifA upstream-activating elements, we have identified: (i) a gpNifA binding site allowing autogenous nifA regulation, (ii) an Ntr-dependent transcription start, presumably the target of gpNifA activation, and (iii) an "anaerobox" tetradecameric nucleotide sequence that is precisely conserved among O2 regulated enteric bacterial genes controlled by the gpFnr transcriptional activator. Because it is precisely positioned upstream of enteric bacterial transcriptional starts, the "anaerobox" sequence may constitute the gpFnr DNA binding site. If so, then a second, Ntr-independent nifA transcription start may exist. We have also deduced the A. caulinodans nifA open reading frame and have compared the gene product (gpNifA) with those of other N2-fixing organisms. These proteins exhibit strongly conserved motifs: (i) sites conserved among ATP-binding proteins, (ii) an interdomain linker region, and (iii) a C-terminal alpha-helix-turn-alpha-helix DNA binding site.

Amino Acid Sequence↗
PubMed1975

Ventricular performance and energy of compression, power, and rate of change of power during isovolumic contraction.

During isovolumic contraction, there is a calculabe compression of the blood within the ventricle. Energy is expended by the ventricle during isovolumic contraction, and some of it is transferred to the blood in the form of elastic compression. The rate of energy transfer (power) and acceleration of energy transfer (rate of change of power) during isovolumic contraction were calculated based upon considerations of the energy of compression. In anaesthetized dogs, the isovolumic energy of compression was 42 plus or minus 6 (mean plus or minus SE) dyn cm; peak isovolumic power was 1,400 plus or minus 300 dyn cm sec-1; and peak rate of change of power was 56,000 plus or minus 15,000 dyn cm sec-2. During states of augmented contractility induced by isoproterenol, the peak acceleration of energy expeniditure (peak rate of change of power) increased to 126,000 plus or minus 33,000 dyn cm sec-2 (p smaller than 0.001). Conversely, with a reduction of contractility induced by propranolol, the peak isovolumic rate of change of power decreased to 30,000 plus or minus 5,700 dyn cm sec-2 (p smaller than 0.001). The peak rate of change of power was unaffected by changes of the afterload. A trend, however, suggests that it may be affected by preload. The derivations of the isovolumic energy of compression, power, and rate of change of power are based upon firm principles of fluid dynamics. No assumptions related to ventricular geometry, synergy of contraction, or characteristics of muscle fibers are implied. Because of its physiological meaning and the theoretical validity of its derivation, an expression such as the isovolumic peak rate of change of power, when utilized as an index of ventricular performance, would appear to be of value.

Animals↗