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Biomedical subjects

J Howard

Publications and source records attributed to J Howard.

At least 109 records · Page 6Linked to original sources

Transmission of feline immunodeficiency virus in domestic cats via artificial insemination.

The objective of this study was to determine whether semen from male domestic cats infected with feline immunodeficiency virus (FIV) can transmit virus to females. Twelve inseminations were performed by an intrauterine laparoscopic technique with fresh or cryopreserved electroejaculates from asymptomatic males chronically infected with the NCSU1 strain of FIV. Of six inseminations performed with fresh semen, three resulted in infection of queens, as indicated by seroconversion, expression of FIV gag provirus in peripheral blood leukocytes, and reduced peripheral CD4+/CD8+ T-lymphocyte ratios. None of the six inseminates with thawed cryopreserved semen resulted in infection. Two infected queens and one uninfected queen became pregnant. Virus was not evident in the seven offspring. We conclude that FIV can be transmitted horizontally by artificial insemination with fresh semen.

Animals↗

The movement of kinesin along microtubules.

The molecular motor kinesin is a homodimer containing two heads-globular domains each of which has an ATP- and a microtubule-binding site. It is argued by analogy to other proteins with coiled-coil dimerization domains that the kinesin dimer has an approximate axis of rotational symmetry. The path kinesin follows along the surface of the microtubule is parallel to the protofilaments, and the steps are likely separated by 8 nm, the length of the tubulin dimer. Micromechanical recordings from single kinesin molecules indicate that one motor can exert a force as great as 5 pN. The efficiency of kinesin probably is in the order of 50%, considering the free energy available from ATP hydrolysis. Structural, mechanical, and biochemical experiments suggest that in order not to let go of a microtubule, the two heads of kinesin might move in a coordinated manner, perhaps undergoing a rotary motion.

Animals↗

Issues in subject recruitment and retention with pregnant and parenting substance-abusing women.

To advance knowledge about the treatment of addiction among pregnant women and other women of childbearing age, investigators must adhere to the requirements of a strict experimental research design while concurrently providing clinical services. This means that researchers must address a variety of difficult questions, including the following: Was the sample large enough? Were the criteria for subject inclusion and exclusion well defined? Did the process of recruitment result in a sample that could be generalized to a larger population, or was the sample biased in some way? Was assignment to groups clearly random? What was the attrition rate? Was attrition the same in both experimental and comparison groups? Did baseline measures collect enough information to permit a description of the facts that were associated with attrition in each group? Was the attrition rate so high that the retained sample had special characteristics? If so, what were these features? This chapter highlights several problems related to these questions, describes the difficulties that investigators have faced in meeting clinical and research challenges to date, and suggests strategies for overcoming some obstacles. In establishing the Perinatal-20 project, the National Institute on Drug Abuse took an informed first step in organizing a substantial research effort to investigate treatment modalities that incorporate services specific to the needs of substance-abusing women who have children. This initial effort has resulted in a beginning knowledge base that can be used to refine and expand future treatment efforts. Even the issue of the "study unit" for this population is evolving. Today's researchers are attempting to determine whether the mother alone or the mother along with her dependent children constitutes the study unit. This question also has led professionals in the field to examine a range of specific outcome priorities, and investigators just now are beginning to determine exactly what needs to be evaluated in gauging the effectiveness of treatment. Is success measured on the basis of the woman's progress with abstinence alone, or does it also include her role with her children? Is it determined on the basis of her relationship with her children or the children's growth and development? Compared with providing services for and studying single adult subjects, developing treatment for women and their children presents researchers with a more complex task and requires expanded clinical services (Gallagher 1990, pp. 540-559). As in most fields of study, initial research data in substance abuse treatment for pregnant and parenting women are derived from samples of convenience, as described above. To put this information in perspective, future research will require a wider and more representative spectrum of the population. Furthermore, tensions between clinical needs and research requirements must be considered in advance, and methods for relaxing these tensions will be critical to the success of future efforts. For example, members of both the research and clinical staff teams must be absolutely clear about the study design and the requirements of reliable research. Where possible, potential ambiguities about group assignment, project services, subjects' responsibilities, and so forth must be incorporated into subject consent forms so that the subjects also are apprised of potential problems and their solutions. A final caution to future investigators is to be aware of the economic, physical, and personnel limitations of the range of treatment services that can be provided in a research demonstration study involving this population. Because of these limitations and the extensive range of services the subjects of the studies require, treatment components must be discrete and carefully defined to prevent programs from becoming impractically diverse and unclear. Research goals must be attainable and measurable.(ABSTRACT TRUNCATED)

Adult↗

p53-independent tumor growth and in vitro cell survival for F-MuLV-induced erythroleukemias.

Retroviral insertional activation of the Fli-1 proto-oncogene is the first genetic event associated with the induction of erythroleukemias by the Friend murine leukemia virus (F-MuLV). Mutations within p53, which are only detected in cell lines established from transplanted tumors, have been previously shown to be associated with the immortalization of erythroleukemic cells in culture. In this study, we have demonstrated that primary erythroleukemic cells grown in liquid culture undergo rapid apoptosis independent of the stabilization of wild-type p53 protein. Further confirmation that the programmed cell death observed for liquid-cultured F-MuLV-induced primary erythroleukemic cells is largely p53 independent was provided by experimentation with a transgenic mouse line containing multiple copies of the dominant negative mutant p53Pro-193 allele. Erythroleukemic cells taken from tumor-bearing transgenic mice expressing high levels of the mutant p53Pro-193 undergo programmed cell death in culture in a manner that is largely identical to that observed for tumor cells derived from nontransgenic littermates. Furthermore, the rate of development of F-MuLV-induced erythroleukemias for both p53Pro-193-transgenic and nontransgenic littermates are similar. Moreover, cytogenetic analysis indicates that primary erythroleukemia cells are diploid, whereas chromosomal aberrations were observed in all established cell lines. These results are consistent with the notion that mutations within the p53 tumor suppressor gene affect genomic stability, subsequently leading to changes in gene expression that are associated with the immortalization of erythroid progenitor cells.

Animals↗

Use of random amplified polymorphic DNA (RAPD) technique in inheritance studies of Plasmodium falciparum.

Effectiveness of random amplified polymorphic DNA (RAPD), a technique using 1 10-base primer to amplify random segments of genomic DNA, and some of its possible uses were tested in the A + T-rich genome of Plasmodium falciparum. The best concentrations of MgCl2, 60% G + C primer, and DNA were determined to be 4.0 mM, 0.4 microM, and 90-180 ng/15 microliters reaction, respectively. Use of 30% G + C primers did not allow amplification to occur. Application of RAPD to DNA of parent and progeny clones from a P. falciparum cross showed that polymorphisms identified in the parentals and tracked in the progeny were inherited in a Mendelian fashion and that RAPD-identified polymorphisms could be used as genetic markers. Some of these polymorphic markers were located on more than 1 chromosome, whereas others were specific for a single chromosome. Two of these markers, each located on chromosome 3 of 1 of the parental parasites, were missing from 2 of the 18 progeny, suggesting that deletions, or crossover events had occurred. RAPD markers also identified a higher number of nonparental-type progeny than expected, thus confirming previous observations for high genetic variability in malaria parasites.

Animals↗

Hypertrophic cardiomyopathy associated with tacrolimus in paediatric transplant patients.

Reported side-effects of tacrolimus, a potent immunosuppressive agent, have not included cardiotoxicity. We describe 5 consecutive paediatric transplant recipients (3 small bowel with or without liver and 2 liver) who received tacrolimus. 2 developed congestive heart failure and hypertrophic obstructive cardiomyopathy which resolved after changing to cyclosporin. In the other 3 patients the cardiomyopathy regressed or improved with a lower dose of tacrolimus or after stopping the drug.

Blood Pressure↗

The force generated by a single kinesin molecule against an elastic load.

To probe the mechanism by which the motor protein kinesin moves along microtubules, we have developed a highly sensitive technique for measuring the force exerted by a single motor molecule. In this technique, one end of a microtubule is attached to the tip of a flexible glass fiber of calibrated stiffness. The other end of the microtubule makes contact with a surface sparsely coated with kinesin. By imaging the tip of the glass fiber on a photodiode detector, displacement of the microtubule by kinesin through as little as 1 nm can be detected and forces as small as 1 pN resolved. Using this force-fiber apparatus we have characterized the mechanical output of this molecular motor. The speed at which a molecule of kinesin moved along the surface of a microtubule decreased linearly as the elastic force was increased. The force required to stop a single kinesin molecule was 5.4 +/- 1.0 pN (mean +/- SD; n = 16), independent of the stiffness of the fiber, the damping from the fluid, and whether the ATP concentration was high or low.

Adenosine Triphosphate↗

Pathology of pulmonic valve stenosis and pure regurgitation.

Little morphologic information is available on operatively excised pulmonic valves. The causes of pulmonic stenosis are limited to a few conditions: (1) rheumatic and (2) nonrheumatic (congenital, carcinoid, infective endocarditis). Congenital causes of pulmonic stenosis constitute well over 95% of these conditions. Congenital types of pulmonic stenosis include acommissural dome-shaped, dysplastic, and bicuspid. Rare acquired causes of pulmonic stenosis include carcinoid, rheumatic, and infective endocarditis. Of the acquired causes of pulmonic stenosis, carcinoid is the most common condition. In contrast, causes of pure pulmonic regurgitation are multiple. Two major categories of pure pulmonic regurgitation include (1) conditions associated with anatomically abnormal valve cusps (congenital, rheumatic, carcinoid, trauma, and infective endocarditis) and (2) conditions associated with anatomically normal cusps (elevated pulmonary artery systolic pressures, idiopathic dilated pulmonary trunk, and Marfan's syndrome).

Humans↗

Pathology of tricuspid valve stenosis and pure tricuspid regurgitation--Part I.

This three-part article examines the histologic and morphologic basis for stenotic and purely regurgitant tricuspid valves. In Part I, conditions producing tricuspid valve stenosis are reviewed. In over 90% of stenotic tricuspid valves, the etiology is rheumatic disease. In isolated tricuspid stenosis, the etiology is either carcinoid or congenital. Rare causes of tricuspid stenosis include active infective endocarditis, metabolic or enzymatic abnormalities (Fabry's, Whipple's disease), and giant blood cysts.

Carcinoid Heart Disease↗

Pathology of tricuspid valve stenosis and pure tricuspid regurgitation--Part II.

This three-part article examines the histologic and morphologic basis for stenotic and purely regurgitant tricuspid valves. In Part I, conditions producing tricuspid valve stenosis were reviewed. In Part II, conditions producing pure tricuspid regurgitation are discussed. In contrast to the relatively few causes of tricuspid stenosis, the causes of pure (no element of stenosis) tricuspid regurgitation are multiple. Some of the conditions producing pure regurgitation include floppy tricuspid valves, infective endocarditis, papillary muscle dysfunction, rheumatic disease, and Ebstein's anomaly.

Carcinoid Heart Disease↗

Pathology of tricuspid valve stenosis and pure tricuspid regurgitation--Part III.

This three-part article examines the histologic and morphologic basis for stenotic and purely regurgitant tricuspid valves. In Part III, morphometric analysis of tricuspid valve annular circumference, leaflet area, and the product of annular circumference and leaflet area are shown to be useful in establishing etiology for the purely regurgitant tricuspid valves and in assessing the anatomic basis of pure tricuspid regurgitation in the presence of mitral stenosis.

Blood Pressure↗

Kinesin does not support the motility of zinc-macrotubes.

Moving along a microtubule, kinesin follows a course parallel to the protofilaments; but it is not known whether kinesin binds exclusively on a single protofilament. The presence of zinc during tubulin polymerization induces sheets where neighboring protofilaments are antiparallel. If kinesin could support the motility of these zinc-sheets, then the binding site for a kinesin molecule would be limited to a single protofilament. Kamimura and Mandelkow [1992: J. Cell Biol. 118:865-75] reported that kinesin moves along zinc-sheets. We found that zinc-sheets grown under their conditions often had a microtubule-like structure along one edge. We confirmed the possibility that the motility observed by Kamimura and Mandelkow [1992: J. Cell Biol. 118:865-75] is attributed to the microtubule-like structure rather than the zinc-sheet. To resolve the question of whether kinesin can recognize an antiparallel protofilament lattice, we investigated the kinesin-mediated motility of zinc-macrotubes. At higher free zinc concentrations, zinc-sheets roll up as macrotubes, free of edges. In the presence of 10 microM taxol and 100 nM free Zn2+ at pH 6.8, the samples were shown by electron microscopy to contain only macrotubes. Under these buffer conditions, kinesin could bind strongly to axonemal doublets in the presence of AMP-PNP, and generate motility in the presence of ATP, but kinesin did not bind to nor move the macrotubes. This shows that kinesin cannot bind efficiently to nor move on the anti-parallel lattice; it is possible (though not necessary) that the groove between two parallel protofilaments is required for kinesin's motility.

Animals↗

Spermatology for understanding, managing and conserving rare species.

Most conventional spermatology research involves common mammalian species including livestock, laboratory animals and humans. Yet, there are more than 4500 mammalian species inhabiting the planet for which little is known about basic reproductive biology, including sperm characteristics and function. This information is important, not just as adjunct knowledge, but because the majority of these species are threatened with extinction, largely due to human-induced pressures. The field of conservation is changing rapidly, and global cooperation is emerging among a variety of wildlife enthusiasts, ranging from management authorities of nature reserves to curators of rare zoological collections. Conservation progress depends on systematic, multidisciplinary research first to answer basic questions, with new data then applied to endangered species management plans. The reproductive physiologist is a crucial component of this scheme. Reproduction is the essence of species survival, and enormous effort needs to be directed at these 'untraditional' research species, subspecies and populations. Spermatology research combined with simultaneous efforts in endocrinology, embryology and cryopreservation (among others) can lead to the successful application of assisted reproduction. Examples from this laboratory include an array of wild felid species and a rare cervid and mustelid. Obstacles to success are formidable, including unique species-specificities, diminished genetic diversity and a general lack of resources. Nonetheless, the field offers tremendous opportunities for generating unique knowledge of comparative interest and with conservation utility.

Animals↗

Rigidity of microtubules is increased by stabilizing agents.

Microtubules are rigid polymers that contribute to the static mechanical properties of cells. Because microtubules are dynamic structures whose polymerization is regulated during changes in cell shape, we have asked whether the mechanical properties of microtubules might also be modulated. We measured the flexural rigidity, or bending stiffness, of individual microtubules under a number of different conditions that affect the stability of microtubules against depolymerization. The flexural rigidity of microtubules polymerized with the slowly hydrolyzable nucleotide analogue guanylyl-(alpha, beta)-methylene-diphosphonate was 62 +/- 9 x 10(-24) Nm2 (weighted mean +/- SEM); that of microtubules stabilized with tau protein was 34 +/- 3 x 10(-24) Nm2; and that of microtubules stabilized with the antimitotic drug taxol was 32 +/- 2 x 10(-24) Nm2. For comparison, microtubules that were capped to prevent depolymerization, but were not otherwise stabilized, had a flexural rigidity of 26 +/- 2 x 10(-24) Nm2. Decreasing the temperature from 37 degrees C to approximately 25 degrees C, a condition that makes microtubules less stable, decreased the stiffness of taxol-stabilized microtubules by one-third. We thus find that the more stable a microtubule, the higher its flexural rigidity. This raises the possibility that microtubule rigidity may be regulated in vivo. In addition, the high rigidity of an unstabilized, GDP-containing microtubule suggests that a large amount of energy could be stored as mechanical strain energy in the protein lattice for subsequent force generation during microtubule depolymerization.

Animals↗