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Biomedical subjects

J N Shelton

Publications and source records attributed to J N Shelton.

At least 19 recordsLinked to original sources
PubMed1998

Multidimensional model of racial identity: a reconceptualization of African American racial identity.

Research on African American racial identity has utilized 2 distinct approaches. The mainstream approach has focused on universal properties associated with ethnic and racial identities. In contrast, the underground approach has focused on documenting the qualitative meaning of being African American, with an emphasis on the unique cultural and historical experiences of African Americans. The Multidimensional Model of Racial Identity (MMRI) represents a synthesis of the strengths of these two approaches. The underlying assumptions associated with the model are explored. The model proposes 4 dimensions of African American racial identity: salience, centrality, regard, and ideology. A description of these dimensions is provided along with a discussion of how they interact to influence behavior at the level of the event. We argue that the MMRI has the potential to make contributions to traditional research objectives of both approaches, as well as to provide the impetus to explore new questions.

Journal Article↗
PubMed1993

Effect of culture systems on mouse early embryo development.

The amount of oxygen available to embryos in drop cultures under paraffin may be limited by the gas mixture employed, the method of equilibration or by the use of positive or negative pressure filtration. When these factors were varied, in experiments using Swiss outbred (SO) embryos, the only significant difference detected was the poorer development of embryos from the 1-cell to blastocyst stage when cultured in medium without prior equilibration. Also under these conditions, the inclusion of glucose in the medium did not increase the incidence of 2-cell block, and glutamine in the presence of glucose enhanced the development of 1-cell embryos to blastocysts. One-cell (C57BL/6 x SJL) F1 x SO embryos were successfully cultured in HEPES buffered CZB medium with added bicarbonate, under an atmosphere of air. The proportion of blastocysts formed in this medium, with a concentration of 10 mM sodium bicarbonate, was not different from that developed in CZB under 5% CO2 in air.

Animals↗
PubMed1993

Vitrification of preimplantation stages of mouse embryos.

Three vitrification solutions (VS) namely VS1 (5.5 mol ethylene glycol l-1 and 2.5 mol glycerol l-1), VS11 (6.0 mol ethylene glycol l-1 and 1.8 mol glycerol l-1) and VS14 (5.5 mol ethylene glycol l-1 and 1 mol sucrose l-1) were tested for cryopreservation by vitrification of all developmental stages of mouse preimplantation embryos. In these experiments all preparative work was at room temperature (25 degrees C). VS1 was toxic to embryos at and earlier than the eight-cell stage, whereas VS11 was toxic to the four-cell and earlier stages. VS14 was the least toxic VS. All three VS resulted in good viability of vitrified Swiss Outbred day-4 embryos (morulae, early blastocysts and blastocysts) in vitro and vitrification with VS14 resulted in no loss of viability in all preimplantation stage Swiss Outbred embryos except one-cell embryos. One-cell F1 embryos were vitrified successfully with VS14 and VS1. The minimal equilibration time essential for successful vitrification of embryos suggests that concentration of the intracellular solutes by dehydration has a major role in establishing conditions conducive to intracellular vitrification. Studies in vitro suggested that sucrose dilution was not necessary in the removal of cryoprotectant from vitrified eight-cell and day-4 mouse embryos but, in contrast, development of vitrified day-4 embryos in vivo was better when the VS was diluted with sucrose.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Successful vitrification of day-6 sheep embryos.

The aim of the experiments described here was to investigate cryopreservation of day-6 sheep embryos by vitrification methods in which the preliminary procedures can be performed at room temperature using VS1 (5.5 mol ethylene glycol l-1 and 2.5 mol glycerol l-1), VS11 (6.0 mol ethylene glycol l-1 and 1.8 mol glycerol l-1) and VS14 (5.5 mol ethylene glycol l-1 and 1.0 mol sucrose l-1). None of the day-6 sheep embryos vitrified with VS1 survived. Day-6 sheep embryos with the exception of blastocysts were vitrified with VS11 with no loss of viability in vitro. The viability of transferred day-6 embryos vitrified with VS11 was however extremely poor. Osmotic damage was avoided by initially exposing the embryos to one of four dilutions (20%, 30%, 40% and 50%) of VS11 for 5 min at 25 degrees C and then vitrifying with the undiluted VS11. The highest survival (88.2%) in vitro was obtained when embryos were exposed to 30% VS11 before vitrification with the undiluted VS11. Survival of transferred embryos exposed to 30% VS11 and then vitrified with undiluted VS11 was 55% (16 of 29) for morulae and 62% (18 of 29) for blastocysts. The pregnancy rate for recipients that received two vitrified sheep embryos of these developmental stages per ewe was 79% (22 of 28). In a small study performed with VS14 the survival of day-6 sheep embryos vitrified with VS14 (in one-step) was 100% in vitro and 50% after transfer.

Animals↗
PubMed1993

Design of vitrification solutions for the cryopreservation of embryos.

A series of experiments was performed to determine the concentrations at which ten cryoprotectants singly and in pairs would vitrify on plunging into liquid nitrogen and remain vitreous when warmed by plunging into a water bath at 25 degrees C. From these tests eight solutions (VS) were selected for testing of toxicity to mouse morulae in vitro. One of these (VS1) was modified as a further five VS of which one (VS11) was tested for toxicity to all stages of mouse embryos and to sheep compacted morulae. The concentrations at which the cryoprotectants vitrified on cooling were: butylene glycol, 3.0 mol l-1; propylene glycol, 4.0 mol l-1; dimethyl sulfoxide (DMSO) and glycerol 5.0 mol l-1; ethylene glycol, 6.5 mol l-1. None of these, at the highest concentration tested, remained vitreous during warming. Methanol and the high molecular weight polymers, dextran, Ficoll, polyethylene glycol and polyvinylpyrrolidone, did not vitrify at the concentrations tested. Toxicity studies showed the order of increasing toxicity to be ethylene glycol, methanol, DMSO, glycerol, propylene glycol and butylene glycol. Of the mixtures composed of two cryoprotectants, those containing ethylene glycol and glycerol were the least toxic at vitrifying concentrations. VS11 (6.0 mol ethylene glycol l-1 and 1.8 mol glycerol l-1) was well tolerated by mouse morulae, less well by eight- and one-cell embryos and poorly by two-cell embryos. Dilution of the VS11 from mouse embryos by exposure to 1.0 mol sucrose l-1 for 10 min did not enhance their survival.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Factors affecting viability of fresh and frozen-thawed sheep demi-embryos.

The addition of 0.1 M sucrose to the medium in which sheep embryos were bisected had no effect (39.5 vs 36.4%) on the survival rate of demi-embryos transferred (one per ewe) to recipients. There was a trend to greater survival of demi-blastocysts (44.7%) compared to demi-morulae (30%), and all the surviving twins were derived from the demi-blastocysts. It is suggested that the survival of demi-morulae is enhanced by the transfer of two demi-morulae to one uterine horn. In three experiments demi-embryos were frozen after the addition of 1.5 M glycerol in three or six steps or after the addition of 1.5 M ethylene glycol in six steps. No treatment resulted in acceptable survival rates of the demi-embryos transferred to recipients after thawing and step-wise removal of the cryoprotectant. Overall, 8 of 142 (5.6%) cryopreserved demi-embryos survived as 50-day fetuses or term lambs compared with 14 of 31 (45.2%) whole embryos.

Journal Article↗
PubMed1991

Natural bone marrow transplantation in cattle with Pompe's disease.

Adding acid alpha-glucosidase to cultures of Pompe's disease muscle has resulted in enzyme uptake and reduction in concentration of glycogen. However, bone marrow transplantation has been unsuccessful as a treatment. Immune rejection may have contributed to this failure. Twin calves share a placenta and carry lymphoreticular cells of each other's type, they become lymphoreticular chimeras in utero and immune rejection does not occur. One natural and three sets of twins produced by embryo transfer were studied in Pompe's disease cattle. Chimerism persisted throughout life and the situation was analogous to a transplant of histocompatible bone marrow stem cells. The activity of acid alpha-glucosidase in leucocytes and in biopsies of the semitendinosus muscle and the mean activity in diaphragm, spleen and lymph node obtained after death from affected twins were significantly higher than in single affected calves. Glycogen concentration was lowered in liver, spleen and lymph node but not in muscles. The affected twins showed clinical signs and changes in muscle similar to those seen in affected single calves. It is concluded that bone marrow transplantation is unlikely to be a successful treatment for Pompe's disease.

Animals↗
PubMed1990

Lymphocyte subpopulations in lymph and blood draining from the uterus and ovary in sheep.

Lymphocyte subsets in utero-ovarian peripheral lymph and uterine and jugular venous blood were analysed with the aid of monoclonal antibodies, polyclonal antisera and flow microfluorometry. The proportion of various lymphocyte subpopulations, as determined by monoclonal antibodies (mAbs) and polyclonal antisera, was found to vary between utero-ovarian peripheral lymph and jugular and uterine venous blood. T cell levels were higher in utero-ovarian peripheral lymph (approx. 80% CD5+, 50% CD4+ and 23% CD8+) than peripheral blood (approx. 55% CD5+, 18% CD4+ and 12% CD8+). Conversely, in lymph, 10% of lymphocytes were B cells compared to 30% in blood. There were 20-30% MHC II+ cells in utero-ovarian peripheral lymph and 40-50% in blood. The level of CD45R+ cells in utero-ovarian peripheral lymph was low (2%) compared to peripheral blood (approx. 55% in pregnant and 25% in non-pregnant ewes). The proportion of lymphocyte subpopulations in lymph was similar for pregnant and non-pregnant ewes. However, some differences in levels in peripheral blood were evident between uterine and jugular venous blood and pregnant and non-pregnant ewes. CD4+ cells were higher in the uterine vein (14%) than in the jugular vein (11%) of pregnant ewes. The uterine and jugular veins in pregnant ewes contained approx. 50% MHC II+ cells compared to 30% in non-pregnant ewes. Likewise, the proportion of CD45R+ cells was higher in uterine and jugular venous blood of pregnant ewes (approx. 58%) compared to non-pregnant ewes (around 25%).

Animals↗
PubMed1990

Production of interspecies chimeric calves by aggregation of Bos indicus and Bos taurus demi-embryos.

Two experiments were conducted to produce interspecific chimeric calves by aggregation of B. indicus and B. taurus demi-embryos. In the first experiment, morulae, compacted morulae, and early blastocysts were collected nonsurgically from Brahman (B. indicus) and Friesian (B. taurus) donors. Embryos were bisected and one demi-embryo from each species was placed in a single zone pellucida. In the second experiment, Brahman (B. indicus) and Hereford-Shorthorn (HS) (B. taurus) demi-embryos were aggregated. The resulting 'chimeric embryos' were transferred nonsurgically to synchronous recipients immediately following microsurgery. Of 112 recipients of 112 chimeric embryos, 29 (26%) were pregnant at 60 days. Of these, 24 (83%) produced full-term calves and 5 (17%) aborted between 2 and 5 months' gestation. From the 24 full-term pregnancies, two sets of twins and 22 singleton calves were born. Of the 22 singletons, 15 were chimeric including six bull calves (one Brahman-Friesian and five Brahman-HS) that were overt chimeras. All the overt chimeras resulted from aggregation of halves of early morulae (precompaction).

Animals↗
PubMed1990

Reproductive technology in animal production.

Research into physiology and embryology has provided a basis for the development of technologies that increase productivity of farm animals through enhanced control of reproductive function. Progestagens, alone or in combination with luteolysins, are used to control the time of oestrus in cattle, sheep and pigs, thus permitting better use of artificial insemination, providing synchronised recipients for embryos and facilitating management strategies. Treatment with progestagens and pregnant mare serum gonadotrophin (PMSG) or with gonadotrophin releasing hormone induces breeding activity in sheep and goats before the commencement of the breeding season and reduces the duration of postpartum anoestrus in cattle. In pigs, gonadotrophins are used to hasten puberty in gilts, control the time of oestrus in sows and gilts and reduce the interval between farrowing and oestrus. Implants of melatonin hasten the onset of the breeding season in sheep and goats. Success in increasing litter size in sheep and cattle with PMSG has been limited because of the large variation in response between animals. Likewise, immunisation against steroids has not given consistent results. Immunisation against inhibin appears to offer the possibility of increasing farm animal fecundity. Induction of twinning in cattle by embryo transfer is practicable, and recent developments suggest that in vitro fertilisation may provide a source of embryos for this purpose. Real-time ultrasonic scanning has proved to be a reliable method for diagnosing pregnancy in small ruminants and pigs. The identification of pregnancy-specific proteins in cattle and sheep may provide a cheap and practical serological test for pregnancy in these species. Partial segregation of spermatozoa into X- and Y-bearing components has been reported, but the method is not yet practicable for use in conventional artificial insemination of farm animals. The sex of bovine and ovine embryos can be determined reliably by DNA probes specific for the Y chromosome. Monozygous twins can be produced in all farm animal species by microsurgical bisection of embryos and techniques for cloning from embryonic cells are rapidly being developed. There is a need to devise strategies to utilise these clones to best advantage in genetic programmes. Chimeric animals can be produced in the common farm animal species and will play an important role in genetic engineering, particularly when embryonic stem cell lines are produced in these species.

Animal Husbandry↗
PubMed1989

Osmotic characteristics of sheep and cattle embryos.

Ten minutes of exposure to increasing concentrations of sucrose caused a proportional decrease in the volume of sheep late morulae, their relative volume changed as a linear function of the reciprocal of the osmolality of the medium. Day 6 sheep and Day 7 cattle embryos responded to the addition of permeating cryoprotectants by an initial shrinkage which was followed by gradual reexpansion. After 1.25 min exposure the relative volumes of sheep and cattle embryos respectively were 20 and 25% smaller in glycerol than in ethylene glycol. The volumes of cattle and sheep embryos remained smaller in glycerol than in ethylene glycol up to the final observation at 30 min. The osmotic response of sheep late morulae to 2.0 M propylene glycol was intermediate between their response to 2.0 M glycerol and to 2.0 M ethylene glycol. These results indicate that Day 6 sheep and Day 7 cattle embryos are more permeable to ethylene glycol than to glycerol.

Animals↗
PubMed1988

Survival of sheep demi-embryos in vivo and in vitro.

Sheep embryos (morulae and blastocysts) were bisected either by microscalpel or by microneedle after dissolving the zona pellucida with acidified Tyrode's solution. Fourteen and 11 cryopreserved demi-embryos failed to develop when transferred to recipients or placed in culture, respectively. When fresh demi-embryos were cultured in Dulbecco's phosphate buffered saline (DPBS) plus fetal calf serum (FCS) or Whitten's medium, the survival rate was 26% compared to 68% for whole embryos (P<0.01), and there was a suggestion that the presence of a zona pellucida was beneficial to survival. When two demi-embryos each within a zona pellucida were transferred into each of 10 ewes, six of them lambed to produce a total of eight lambs, including two sets of identical twins. Of 10 ewes receiving two demi-embryos without zonae pellucidae, three lambed to produce a total of four lambs, including one set of identical twins. Of 10 ewes that each received two whole embryos, 10 lambed to produce a total of 16 lambs. There was a suggestion that the zona pellucida might enhance the survival of demi-morulae but not demi-blastocysts.

Journal Article↗
PubMed1988

Flow and composition of lymph from the ovary and uterus of cows during pregnancy.

Ovarian or uterine lymph was collected continuously for periods of up to 25 days from 16 cows cannulated at stages of pregnancy ranging from 96 to 278 days post coitum. Blood samples were taken acutely from the ovarian and uterine veins during surgery and periodically from the jugular vein during the course of lymph collection. The flow rate and cell content of lymph was measured and blood and lymph plasma samples were analysed for progesterone, pregnenolone, pregnenolone sulphate, androstenedione, testosterone, oestrone, oestrone sulphate, oestradiol-17 beta, prostaglandin (PG) F-2 alpha, total protein and albumin. There was a high flow rate of protein-rich lymph from luteal ovaries with rates up to 101.7 ml/h occurring in individual lymphatics over short periods. Peripheral ovarian and uterine lymph contained a low concentration of cells (mean less than 10(5) cells/ml) comprising about 82-87% lymphocytes, 11-14% macrophages and monocytes and 2-4% other cells. At all stages of pregnancy, the concentration of progestagens and androgens was higher in ovarian lymph than in uterine lymph or blood plasma. The differences were greatest for progesterone and androstenedione which occurred at 200-fold and 60-fold greater concentration respectively in ovarian lymph than in jugular plasma. When serial 10 min samples were collected over a 12-h period, the concentration and output of progesterone in ovarian lymph varied in a phasic manner, ranging from 3.5 to 7.6 microM and from 31.7 to 293.1 nmol/h respectively. There was a positive correlation between the output of progesterone in lymph and the progesterone concentration in jugular blood samples taken every 20 min. During most of pregnancy there was little difference between the concentration of oestrogens in ovarian lymph, ovarian venous plasma and jugular plasma but, during the 3-5 days before calving, these hormones occurred at slightly higher concentration in ovarian lymph. Apart from pregnenolone and androstenedione, all steroids occurred at lower concentrations in uterine lymph than in jugular plasma. Shortly before parturition there was an abrupt increase in the concentration of PGF-2 alpha in uterine lymph. Lymph reflects more accurately the milieu of tissue cells than efferent blood and further analysis of differences in the concentration of substances in lymph relative to the output in the ovarian and uterine arterial and venous blood may lead to the identification of factors important in local regulatory mechanisms in the reproductive tract.

Androgens↗
PubMed1988

Traffic and proliferative responses of recirculating lymphocytes in fetal calves.

The thoracic duct or efferent prescapular duct was cannulated in four fetal calves aged 121-259 days post-conception. The duration of lymph flow ranged from 2 to 20 days and the mean flow rates sustained over these collection periods varied from 5.4 to 48.8 ml/hr. Lymphocyte output ranged from 4.4 x 10(6) cells/hr in thoracic duct lymph from a 121-day fetus to 3.9 x 10(8) cells/hr in efferent prescapular lymph from a 259-day fetus. The circulating lymphocyte pool in fetal calves of about 120 and 190 days gestational age was calculated to contain, respectively, 4 x 10(8) cells and 2 x 10(10) cells. The proportion of lymphocytes bearing surface immunoglobulin detected in fetal lymph ranged from 2.1% to 8.7%. Recirculating lymphocytes from fetal calves produced strong proliferative responses when stimulated by T-cell mitogens but responded poorly to B-cell mitogens. Fetal lymphocytes also responded to stimulation by allogeneic cells and stimulated other cells to proliferate during mixed lymphocyte culture. When stimulated with Con A, fetal lymphocytes secreted IL-2 to a degree that was indistinguishable from the secretory behaviour of lymphocytes from adult animals. The results presented in this paper show that chronic lymphatic fistulae can be established successfully in fetal calves to give access to recirculating lymphocytes. This provides a new experimental approach for studying the development of the bovine immune system.

Animals↗
PubMed1988

Embryo manipulation in research and animal production.

Research in developmental biology has resulted in techniques to accelerate changes in gene frequency and to interfere directly in the genome. Procedures already in use or being adapted to livestock include embryo transfer, chimera production, embryo splitting, gene transfer and nuclear transplantation. Experiments with mouse embryos are revealing the principles governing embryonic development and differentiation and illustrate the need for these investigations to be extended to embryos of livestock. The optimal combination of these technologies in animal production strategies will depend upon further research and the role of animal products in society.

Animal Husbandry↗
PubMed1988

Analysis of ovine peripheral blood lymphocyte subsets following Ficoll-Hypaque separation or erythrocyte lysis.

Peripheral blood lymphocyte subsets were analysed with the aid of monoclonal antibodies and flow microfluorometry following separation by either the Ficoll-Hypaque method or erythrocyte lysis of the buffy coat. The percentage of lymphocytes labelled by the monoclonal antibodies SBU-T1, SBU-T4 and SBU-T8 were significantly greater (P less than 0.05) in samples obtained by erythrocyte lysis. In contrast, a lower percentage of lymphocytes was labelled by SBU-T6 following erythrocyte lysis (P less than 0.02). These data suggest caution when choosing a method for separation of peripheral blood lymphocytes.

Animals↗
PubMed1987

Prospects for the use of embryos in the control of disease and the transport of genotypes.

Transfer and low temperature storage of embryos are now proven techniques for a number of mammalian species. These techniques are useful in control of disease and in saving genotypes from infected animals. The place of embryos in the epidemiology of disease depends upon whether the causative organism can gain entry to the oocyte before or at fertilisation and on whether the young embryo can be invaded by organisms in the uterine environment. There is little evidence that important live-stock diseases are transmitted via gametes. The zona pellucida surrounding the embryo is an effective barrier against a number of important disease organisms; in some cases the embryo is susceptible once it has hatched from the zona pellucida. It is important therefore in considering the use of embryos in disease control, to ensure that virus is not attached to the surface of the zona pellucida from where it can infect the recipient and/or the embryo after hatching. Washing procedures have been devised together with the use of enzymes and antisera to remove virus from the surface of embryos. Some viruses enter pores and sperm tracks in the zona and removal of these may present a problem. African swine fever virus has been shown to resist removal by treatment with enzymes. There are no guidelines as to the likely interaction between a certain virus and embryos. Therefore each virus of interest must be tested to determine whether it can be transmitted via washed embryos. Nevertheless there are numerous instances of the use of embryo transfer to eradicate a specific disease or to save valuable genetic material from infected animals without transmitting disease.

Animal Diseases↗