Biomedical subjects

R F Smith

Publications and source records attributed to R F Smith.

At least 19 recordsLinked to original sources

PubMed2006

Immunization of cattle with live tachyzoites of Neospora caninum confers protection against fetal death.

Neospora caninum is an obligate intracellular protozoan parasite that causes abortion in cattle. It is normally found as a latent infection controlled by a T-helper-cell type 1 response involving CD4(+) cytotoxic T cells and gamma interferon. Cattle may be infected by two different routes: transplacentally as a result of activation of the latent infection in the mother causing congenital infection or abortion and by ingestion of oocysts, which, if it occurs during gestation, can also result in abortion. Here, for the first time, we establish proof that live vaccination protects against fetal death, whereas immunization using whole-tachyzoite lysate in different adjuvants fails to protect against fetal death. Strong antibody responses were induced in all the vaccinated groups, and the quality and magnitude of these responses were similar in the live- and the lysate-vaccinated groups. In contrast, only the group immunized with live tachyzoites had strong cellular and gamma interferon responses prior to challenge, and these responses correlated with protection against fetopathy. These results suggest that a cellular immune response may be important in the mechanisms involved in protection against N. caninum-associated abortions.

Animals↗

PubMed2006

Oestradiol stimulates the release of AVP and GnRH from the ewe hypothalamus in vitro.

Oestradiol (E(2)) sensitizes the stress and reproductive axes in vivo. Our current aim is to investigate whether E(2) directly influences hypothalamic AVP and GnRH release in vitro. Within 10 min of ewe killing, saggital midline hypothalamic slices (from the anterior preoptic area to mediobasal hypothalamus, 2 mm thick, two per sheep) were dissected, placed in oxygenated MEM-alpha at 4 degrees C and within next 2 h were singly perifused at 37 degrees C with oxygenated MEM-alpha (pH 7.4; flow rate 150 microl/min) alone (vehicle; n = 15), with low (6 pg/ml; n = 14) or high E(2) (24 pg/ml; n = 13). After 5 h equilibration, 10 min fractions were collected for 3 h with exposure to 100 mm KCl for 10 min within the last hour. Concentrations of AVP and GnRH were measured by RIA. Baselines for AVP and GnRH were 7.0 +/- 1.1 and 17.4 +/- 0.8 pg/ml respectively. Basal values with low E(2) were similar to vehicle for AVP (7.5 +/- 1.2 pg/ml) and GnRH (17.5 +/- 1.1 pg/ml). However, high E(2) increased basal AVP (11.7 +/- 1.4 pg/ml; p < 0.05) and GnRH (23.7 +/- 1.4 pg/ml; p < 0.05). After KCl, AVP and GnRH respectively, increased (p < 0.05) to 25.6 +/- 7.5 and 38.2 +/- 5.6 (vehicle), 26.3 +/- 7.5 and 23.6 +/- 2.1 (low E(2)) and 24.1 +/- 5.4 and 41.3 +/- 6.6 pg/ml (high E(2)). After KCl, maximum values of AVP occurred at 20 and GnRH at 30 min. In conclusion, high E(2) concentration augments AVP and GnRH release by direct action on the ewe hypothalamus.

Animals↗

PubMed2005

Plasma conditions for improved energy coupling into the gain region of the Ni-like Pd transient collisional x-ray laser.

We have directly probed the conditions in which the Ni-like Pd transient collisional x-ray laser is generated and propagates by measuring the near-field image and by utilizing picosecond resolution soft x-ray laser interferometry of the preformed Pd plasma gain medium. The electron density and gain region of the plasma have been determined experimentally and are found to be in good agreement with simulations. We observe a strong dependence of the laser pump-gain medium coupling on the laser pump parameters. The most efficient coupling occurs with the formation of lower density gradients in the preformed plasma and when the duration of the main heating pulse is comparable to the gain lifetime (approximately 10 ps for mid- Z Ni-like schemes). This increases the output intensity by more than an order of magnitude relative to the commonly utilized case where the same pumping energy is delivered within a shorter heating pulse duration (<3 ps) . In contrast, the higher intensity heating pulses are observed to be absorbed at higher electron densities and in regions where steep density gradients limit the effective length of the gain medium.

Journal Article↗

PubMed2005

The usefulness of a single measurement of insulin-like growth factor-1 as a predictor of embryo yield and pregnancy rates in a bovine MOET program.

The objective was to determine if a single measurement of plasma insulin-like growth factor-1 (IGF-1) could predict the number of viable embryos obtained from donors and the likelihood of pregnancy in recipients in multiple ovulation and embryo transfer (MOET) programs in cattle. The embryo yields from 101 embryo recoveries were examined in maiden Holstein heifers (n=75) and multiparous Holstein cows (lactating cows n=20, dry cows n=6). Donors were super stimulated with FSH and embryo recovery was done non-surgically 7 days after artificial insemination. Embryos were classified according to the IETS criteria. Pregnancy rates in 100 maiden Holstein heifer recipients were analysed. Recipients were on day 7+/-1 of the estrous cycle at transfer. Pregnancy diagnosis was carried out at day 30 (PD 30) and rechecked at day 60 (PD 60) after transfer. Blood samples from coccygeal vessels taken at the time of embryo recovery (donors) and transfer (recipients) were analysed for IGF-1, insulin, beta-hydroxybutyrate (beta-OHB), non-esterified fatty acids (NEFA), urea and cholesterol. There was a negative correlation between the number of viable embryos and insulin (r=-0.33, P=0.025) in donor heifers. In donor cows, the number of viable embryos was correlated with IGF-1 (r=0.43, P=0.028) and cholesterol (r=-0.43, P=0.027). In recipients, PD30 and PD 60 were not affected by any of the circulating parameters analysed. Insulin, IGF-1 and cholesterol only explained 8.9, 13.9 and 15.8% of the variation in the production of viable embryos, respectively. Several factors affect MOET programs and under the circumstances of the present study the usefulness of hormonal and metabolic profiles as predictors of the outcome of this biotechnology was limited.

3-Hydroxybutyric Acid↗

PubMed2005

High-repetition-rate grazing-incidence pumped x-ray laser operating at 18.9 nm.

We have demonstrated a 10 Hz Ni-like Mo x-ray laser operating at 18.9 nm with 150 mJ total pump energy by employing a novel pumping scheme. The grazing-incidence scheme is described, where a picosecond pulse is incident at a grazing angle to a Mo plasma column produced by a slab target irradiated by a 200 ps laser pulse. This scheme uses refraction of the short pulse at a predetermined electron density to increase absorption to pump a specific gain region. The higher coupling efficiency inherent to this scheme allows a reduction in the pump energy where 70 mJ long pulse energy and 80 mJ short pulse energy are sufficient to produce lasing at a 10 Hz repetition rate. Under these conditions and by optimizing the delay between the pulses, we achieve strong amplification and close to saturation for 4 mm long targets.

Journal Article↗

PubMed2005

Observation of a multiply ionized plasma with index of refraction greater than one.

We present clear experimental evidence showing that the contribution of bound electrons can dominate the index of refraction of laser-created plasmas at soft x-ray wavelengths. We report anomalous fringe shifts in soft x-ray laser interferograms of Al laser-created plasmas. The comparison of measured and simulated interferograms shows that this results from the dominant contribution of low charge ions to the index of refraction. This usually neglected bound electron contribution can affect the propagation of soft x-ray radiation in plasmas and the interferometric diagnostics of plasmas for many elements.

Journal Article↗

PubMed2004

Metabolic and histological analysis of mesenchymal stem cells grown in 3-D hyaluronan-based scaffolds.

Sheep mesenchymal stem cells (MSCs) were isolated and expanded using the principle of plastic adherence. Their identity as progenitor cells was confirmed by induction along the osteoblastic lineage using osteogenic supplements and observation of calcific deposits by von Kossa staining. MSCs were seeded onto two types of hyaluronan-based cylindrical scaffolds in high concentrations and cultured for varying time points up to three weeks. Culture medium was supplied using the following conditions: statically, on a shaker, by stirring with a magnetic stirrer or by perfusion in a tubular flow circuit. Total cell metabolism was assessed by MTT assay and the quality of cell coverage and matrix formation observed by SEM and histological analysis of thin sections of the constructs. Perfusion culture was established as the most appropriate culturing conditions, with cell metabolism increasing by approximately 300% over three weeks. The coverage of the scaffold surface was very good and the deposition of collagenous matrix was superior in these conditions compared to the, static and other dynamic culture conditions.

Animals↗

PubMed2004

Heterogeneity in proliferative potential of ovine mesenchymal stem cell colonies.

Bone marrow biopsies were taken from the iliac crest of 28 individual sheep from three different breeds, ranging in age from 4 months to 8 years and mesenchymal stem cells (MSCs) isolated using selection due to plastic adherence. Cells were cultured in medium that had been selected for its effect on observed MSC proliferation, until populations of greater than 50 million had been obtained from each biopsy. The identity of the isolated cell populations as progenitors of the mesenchymal lineage was verified by deriving both osteoblastic and chondrocytic phenotypes when cultured in osteogenic and chondrogenic medium supplements, respectively. The rate of cell proliferation for each marrow biopsy was measured at each passage and the number of initial stem cells in each sample estimated. There was no statistically significant correlation between the age of the sheep and MSC proliferative potential, or age and estimated initial MSC number. There was no apparent significant difference between proliferation rate and sheep breed and colonies established from frozen cells grew at similar rates to pre-frozen cells. Counter intuitively, there appeared to be a negatively correlated trend between proliferation rate and MSC concentration in the samples. It is concluded that no initial descriptive statistics of the marrow biopsies can assist in estimating the proliferative potential, and therefore the timing of future surgeries, of MSCs sampled for the purposes of tissue engineering.

Aging↗

PubMed2003

First demonstration of protective immunity against foetopathy in cattle with latent Neospora caninum infection.

The parasite Neospora caninum is an important cause of abortion in cattle world-wide. Chronically infected dams transmit the parasite transplacentally and infected foetuses may be aborted or born chronically infected but clinically normal. Chronically infected cows repeatedly transmit the parasite to foetuses in several pregnancies and some may abort more than once suggesting that the immune response in these cattle is compromised during pregnancy. To investigate the nature of the immune response in chronically infected cattle, five naturally, chronically infected cows were challenged with N. caninum tachyzoites at 10 weeks of gestation. No foetopathy occurred and all five delivered live calves at full-term. In four naive pregnant cows challenged at the same time, all four foetuses died within 3-5 weeks of challenge. Of the five live calves born to the chronically infected challenged cows, three were transplacentally infected with N. caninum. The kinetics of the maternal anti-N. caninum antibody responses during gestation suggested that these transplacental infections were not the result of the superimposed challenge, but the result of the recrudescence of the maternal chronic infection-which occurred concurrently in non-challenged, chronically infected pregnant controls. These data provide the first experimental evidence that protective immunity occurs in neosporosis. They also suggest that whilst immunity to a pre-existing infection will protect against an exogenous challenge, this protective immunity will not prevent transplacental infection. This implies that a subtle form of concomitant immunity exists in chronically infected cattle and has important implications for vaccine development.

Abortion, Veterinary↗

PubMed2003

Identification of stimulatory and inhibitory inputs to the hypothalamic-pituitary-adrenal axis during hypoglycaemia or transport in ewes.

This study used the novel approach of statistical modelling to investigate the control of hypothalamic-pituitary-adrenal (HPA) axis and quantify temporal relationships between hormones. Two experimental paradigms were chosen, insulin-induced hypoglycaemia and 2 h transport, to assess differences in control between noncognitive and cognitive stimuli. Vasopressin and corticotropin-releasing hormone (CRH) were measured in hypophysial portal plasma, and adrenocorticotropin hormone (ACTH) and cortisol in jugular plasma of conscious sheep, and deconvolution analysis was used to calculate secretory rates, before modelling. During hypoglycaemia, the relationship between plasma glucose and vasopressin or CRH was best described by log10 transforming variables (i.e. a positive power-curve relationship). A negative-feedback relationship with log10 cortisol concentration 2 h previously was detected. Analysis of the "transport" stimulus suggested that the strength of the perceived stimulus decreased over time after accounting for cortisol facilitation and negative-feedback. The time course of vasopressin and CRH responses to each stimulus were different However, at the pituitary level, the data suggested that log10 ACTH secretion rate was related to log10 vasopressin and CRH concentrations with very similar regression coefficients and an identical ratio of actions (2.3 : 1) for both stimuli. Similar magnitude negative-feedback effects of log10 cortisol at -110 min (hypoglycaemia) or -40 min (transport) were detected, and both models contained a stimulatory relationship with cortisol at 0 min (facilitation). At adrenal gland level, cortisol secretory rates were related to simultaneously measured untransformed ACTH concentration but the regression coefficient for the hypoglycaemia model was 2.5-fold greater than for transport. No individual sustained maximum cortisol secretion for longer than 20 min during hypoglycaemia and 40 min during transport. These unique models demonstrate that corticosteroid negative-feedback is a significant control mechanism at both the pituitary and hypothalamus. The amplitude of HPA response may be related to stimulus intensity and corticosteroid negative-feedback, while duration depended on feedback alone.

Adrenal Cortex Hormones↗

PubMed2003

Stress and the control of LH secretion in the ewe.

Stress influences the activity of the reproductive system at several sites. One of the most significant effects is at level of the GnRH secretory system to reduce GnRH pulsatility and thus LH pulsatility. This in turn reduces the oestradiol signal that stimulates the GnRH-LH surge in the follicular phase. Three sequential phases have been identified in the induction of the GnRH-LH surge by oestradiol: (i) activation, (ii) transmission and (iii) surge secretion. There is evidence that administration of endotoxin prevents activation but not transmission, hypoglycaemia blocks both activation and transmission, whereas truck transport is effective during the late, but not early, transmission phase. Opioids mediate the suppressive effects of hypoglycaemia on both LH pulsatility and the delayed onset of the LH surge in ewes. The exact neurocircuitry used in sheep is yet to be identified but many of the connections that are proposed as important in rats are present in sheep. Corticotrophin-releasing hormone (CRH) neurones in the paraventricular nucleus that project axons to the median eminence probably do not directly inhibit GnRH, but either afferent or parallel central pathways are involved. New members of the CRH peptide and receptor families have been identified, but roles in the control of reproduction have yet to be determined.

Adrenocorticotropic Hormone↗

PubMed2002

Neospora caninum: oocyst challenge of pregnant cows.

Three pregnant cows were each orally challenged at 10 weeks of gestation with 600 sporulated oocysts of Neospora caninum. The number of oocysts was limited by those available. In concurrent bioassays, one oocyst per os infected each of two gerbils. Challenged cattle developed Neospora-specific antibody, cell proliferation and gamma-interferon responses. N. caninum specific PCR demonstrated persisting infection in the brains of cows 4 months after calving. Abortion was not induced and there was no evidence of transplacental infection in the healthy calves born at full-term. This experiment suggests that the dose threshold for induction of abortion exceeds 600 oocysts.

Animals↗

PubMed2002

Picosecond x-ray laser interferometry of dense plasmas.

We present the first results from picosecond interferometry of dense laser-produced plasmas using a soft x-ray laser. The picosecond duration and short wavelength of the 14.7 nm Ni-like Pd laser mitigates effects associated with motion blurring and refraction through millimeter-scale plasmas. This enables direct measurement of the electron-density profile to within 10 microm of the target surface. A series of high-quality two-dimensional (2D) density measurements provide unambiguous characterization of the time evolution in a fast-evolving plasma suitable for validation of existing 1D and 2D hydrodynamic codes.

Journal Article↗

PubMed2002

Habitat suitability modelling for calcareous grassland restoration on the South Downs, United Kingdom.

The South Downs Area of Outstanding Natural Beauty, UK, is an internationally and nationally important landscape, which contains a significant proportion (28%) of the southeast of England's calcareous grassland resource. The traditional calcareous grassland habitats characteristic of the downland landscape have suffered significant losses since the Second World War, and the remaining sites are small, fragmented and confined to the more marginal areas, often steeper slopes. The re-creation and restoration of these species rich grasslands has become a central aim of national and regional conservation organisations, however, the methods and mechanism by which restoration sites could be identified has not been clarified. The purpose of this work was to study the landscape characteristics of the calcareous grassland systems, and by use of GIS-based modelling approaches identify those sites on the downland most suited to the re-establishment and expansion of calcareous grasslands. Using a weighted scoring approach, a GIS-based Habitat Suitability Model is developed for use as a tool to support strategic landscape evaluation and to provide a method of identifying sites for targeted restoration. The approach models the relationship between specific grassland communities and topographic variables, and is applied to the South Downs landscape in order to predict the nature of grassland communities likely to result from restoration efforts at specific sites.

Conservation of Natural Resources↗

PubMed2002

Hormonal interactions within the hypothalamus and pituitary with respect to stress and reproduction in sheep.

Endocrine systems may be used as indicators of stress in two ways. The primary role of a hormone may be as part of the homeostatic response to a stimulus (e.g., adrenaline, corticosteroids). The amplitude of hormone response may correlate with the severity of the stimulus and any change indicate that the body is responding. Alternatively, a hormone may have a key role in normal body function (e.g., reproduction) and stress may deleteriously alter the hormone signal prevent normal function. This demonstrates that the stimulus was sufficiently severe that homeostatic mechanisms were unable to maintain normal function. Stress may effect reproduction by reducing both LH pulse amplitude and frequency. The LH surge may also be delayed. Several mechanisms may account for these effects both at the hypothalamus and pituitary. Corticosteroids have a broad, yet fundamental, role in homeostasis and have been used as primary indicators of stress for many years. Excess corticosteroid can be detrimental so the concentration is controlled via the hypothalamus-pituitary-adrenal (HPA) axis by multi-level feedback mechanisms. Under field and experimental conditions, after an initial large response prolonged stimulation leads to a gradually reducing plasma corticosteroid concentrations. This has been interpreted as a reduction in perceived stimulus severity or habituation to the stimulus and the animal deemed "less stressed" and its welfare "better." However, this reduction may be due to the intrinsic control mechanisms designed to prevent prolonged increases in corticosteroid concentrations. The stress signal at higher brain levels may still be present and the animal may still be experiencing the stimulus as aversive. Thus, the welfare interpretation of a corticosteroid concentration may differ during the time course of a stress response. A greater understanding of the mechanisms controlling corticosteroid secretion at each level of the HPA is required to determine what is the correct interpretation at any time point. To address these issues, we have used mathematical modelling to produce representations of possible control mechanisms at each level of the HPA. The starting point was to measure AVP and CRH concentrations in hypophysial portal blood and ACTH and cortisol concentrations in jugular blood in conscious sheep during 2h road transport (a cognitive stimulus). Modelling identified the signal inputs that were most likely to explain the secretion rate of each hormone. Modelling suggested that the reduction in AVP and CRH secretion observed during transport was most likely due to a reduction in stimulus input, with a significant contribution from cortisol negative feedback only on AVP secretion. At the pituitary level, ACTH secretion was stimulated more by AVP than by CRH (ratio 2.3:1) and there was also a stimulatory effect related to cortisol concentration at the time of sampling. However, the responses to both stimuli were curtailed by cortisol negative feedback and an inhibitory effect of prior CRH concentration. These are complex effects, but the modelling does suggest that while "stress" inputs may reduce over time hormone negative feedback is a major factor reducing hormone responses. When interpreting hormone data for animal welfare purposes, it is important not to interpret a reduction in hormone concentration due to intrinsic hormone control mechanisms as a reduction due to a decrease in the stress stimulus.

Adrenal Glands↗

PubMed2001

Neospora caninum in persistently infected, pregnant cows: spontaneous transplacental infection is associated with an acute increase in maternal antibody.

Nine cows which were naturally and persistently infected with Neospora caninum were housed and observed intensively throughout pregnancy. No recrudescence of a latent infection was detected by PCR tests on maternal blood but fetal infection, implying a recrudescence of maternal parasitosis, was associated with a marked increase in maternal antibody. The increase occurred in the second half of pregnancy in five cows which infected their calves, and before mid-pregnancy in one cow which aborted. There was no change in the avidity of the antibody, which remained high and characteristic of long-term infection. In three infected cows that gave birth to uninfected calves there was no marked increase in maternal antibody. Antigen-specific interferon gamma responses of peripheral blood mononuclear cells were observed in all the infected cattle but they did not vary significantly either during pregnancy, or whether the cows did or did not infect their calves, although the responses were consistently higher in the latter. There was no change in the plasma concentrations of cortisol or acute phase proteins associated with the recrudescence of the parasite. Three uninfected cows housed with the infected cows remained uninfected throughout the experiment. No immunosuppressive event was detected which might have provoked parasite recrudescence but the acute antibody rise associated with transplacental infection provides a valuable, non-invasive marker for further studies to investigate the cause and consequences of parasite recrudescence in N caninum infection in cattle.

Animals↗

PubMed2001

Is stress really all that important?

There is growing concern in many parts of the world that fertility of dairy cattle is reducing as milk yields increase. Stress could be one important cause. As an example, fertility is lower after caesarian operations. Delayed uterine involution after dystocia is associated with abnormal ovarian cyclicity and prolonged intervals to the next pregnancy. There is a greater reduction in fertility as the clinical conditions of lameness, milk fever or mastitis worsen. Changes in social groupings greatly increase the number of inseminations required per pregnancy. Transport reduces the number of CL after superovulation, and can interfere with pregnancy rates after estrous synchronization. Embryos collected from heat-stressed donors are less viable and have delayed trophoblast function. Human-animal interactions influence stress-responses in cattle--the behavior of stockman and embryo transfer personnel could affect success. Putting aside financial aspects, exposure of an animal to avoidable stress compromises welfare, whether application of biotechnology is involved or not. The fact that stressors can be deleterious to such an important function as reproduction, emphasizes that stress is very important and should be minimized whenever possible.

Adrenocorticotropic Hormone↗

PubMed2001

Separation of nicotine metabolites by capillary zone electrophoresis and capillary zone electrophoresis/mass spectrometry.

The use of capillary zone electrophoresis (CZE) and capillary zone electrophoresis/mass spectrometry (CZE/MS) has been demonstrated, in principle, for the separation of nicotine and nicotine metabolites. The buffer system developed for separation and detection by CZE/UV was modified for use in CZE/MS analysis. Several of the metabolites are isobaric and tandem mass spectrometric (MS/MS) techniques have been used to differentiate such analytes.

Electrophoresis, Capillary↗