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W R Allen

Publications and source records attributed to W R Allen.

At least 19 recordsLinked to original sources
PubMed2004

Influence of insulin-like growth factor-I on cytoplasmic maturation of horse oocytes in vitro and organization of the first cell cycle following nuclear transfer and parthenogenesis.

In vitro maturation of horse oocytes cultured with or without IGF-I supplementation and their first cell cycle organization were studied in reconstructed horse oocytes made by somatic cell nuclear transfer versus intact oocytes stimulated parthenogenetically. The rates of metaphase II oocytes (47% and 45%) and of reconstructed oocytes that developed to the two-cell (27% and 25%) and blastocyst stages (11% and 3%) were not different between the media, with or without IGF-I, respectively. However, significantly more parthenogenetic embryos exhibited two-cell development with IGF-I (P < 0.05). The results also demonstrated that the first cell cycle organization in the reconstructed oocytes involved two different ways of nuclear remodeling. The donor nucleus in the Type I embryo showed normal nuclear remodeling that resulted in normal embryonic development. In the Type II embryos, however, the donor nucleus formed a polyploid nucleus or the embryo fragmented. Addition of IGF-I to the maturation medium significantly increased the rate of normal Type I embryonic development from the reconstructed oocytes (45% vs. 28%, P < 0.05). Maturation-promoting factor (MPF; including cdc2 and cyclin B) and mitogen-activated protein kinase (MAPK; including ERK1 and ERK2) were present at the beginning of culture, just after the oocytes had been harvested from the ovaries. The quantities of cyclin B remained stable no matter how long a period of in vitro culture the oocytes underwent, whereas cdc2 showed a tendency to accumulate in the oocytes toward the end of the 30-h culture period. Addition of IGF-I to the medium may induce a bigger accumulation of MAPK in the cytoplasm of the horse oocyte, especially in the ERK2 component, which might, in turn, increase the chance of the reconstructed oocyte undergoing nuclear remodeling to form a Type I embryo following nuclear transfer.

Animals↗
PubMed2004

Fetomaternal glycosylation of early placentation events in the African elephant Loxodonta africana.

During implantation in the African elephant (Loxodonta africana), fetal trophoblast displaces the surface uterine epithelium and superficially penetrates the uterine glands. This limited invasion is followed by the upgrowth of blunt fingers of endometrial stroma, covered with trophoblast and containing capillaries that subsequently vascularize the growing placenta. We have used lectin histochemistry to compare the glycosylation of maternal endothelial cells in the endometrium with those growing within the trophoblastic processes of a 2 g embryo (approximately 125 days' gestation), and also examine changes in the endometrial glands associated with trophoblastic invasion. Maternal vessels at the apices of the trophoblast-covered stromal upgrowths showed increased expression of terminal N-acetyl galactosamine, N-acetyl glucosamine oligomers, some sialic acids, and tri/tetra-antennate non-bisected complex N-linked glycan, as indicated by increased lectin staining. The areas of increased staining were also more resistant to neuraminidase digestion. Invaded glands had distended walls composed of flattened epithelial cells, some of which showed heavy lectin staining suggestive of intracellular glycan accumulation. The vascular changes suggest that new maternal capillary growth is accompanied by alterations in surface glycosylation. This may be the result of increased glycosyl transferase activity associated with cell proliferation and may also indicate the expression of significantly increased anti-adhesive molecules preventing blood stasis and egress of maternal immunocompetent cells into the fetal compartment.

Animals↗
PubMed2004

The influence of maternal size on pre- and postnatal growth in the horse: III Postnatal growth.

The growth parameters exhibited by seven Thoroughbred (Tb) foals that had experienced a 'restricted' in utero existence following transfer as embryos to the uteri of smaller Pony (P) mares (Tb-in-P) and, conversely, six P foals that experienced a 'luxurious' in utero existence after transfer to larger Tb mares (P-in-Tb), were compared from birth to 3 years of age with those exhibited by six normal Tb-in-Tb and six P-in-P foals conceived by within-breed artificial insemination. Bodyweight, height at the withers, girth, poll-to-nose length, crown-rump length and three foreleg longbone measurements were made at regular intervals. At birth, an approximate 15% reduction or increase in parameters was observed in the Tb-in-P and P-in-Tb respectively, which declined to 5% by 3 years of age. Growth post partum was affected by restricted or enhanced growth in utero. In the first 6 months post partum, growth rate was enhanced in the previously restricted Tb-in-P foals and curbed in the previously enhanced P-in-Tb foals compared with their respective controls. Overall, the similarity of the responses of the offspring to both 'restriction' and 'luxury' in utero ensured that no major changes to conformation resulted from either treatment. Thus, the Thoroughbreds carried by the Pony mares were merely scaled down versions of the Tb-in-Tb controls while the Ponies carried by the Thoroughbred mares were scaled up versions of the P-in-P controls.

Animals↗
PubMed2004

Postnatal insulin secretion and sensitivity after manipulation of fetal growth by embryo transfer in the horse.

This study examined the effects of intrauterine growth on insulin secretion and resistance in newborn foals. Embryo transfer between small pony and large Thoroughbred mares was used to produce four groups of foals with different birth weights (pony in pony n=7; pony in Thoroughbred n=7; Thoroughbred in Thoroughbred n=8; Thoroughbred in pony n=8). On day 2 after birth, glucose (0.5 g/kg) was administered intravenously to the foal and blood samples were taken for 2 h to determine plasma glucose and insulin concentrations. On day 3, insulin sensitivity was assessed by giving insulin (0.75 U/kg i.v.) and measuring the decrement in plasma glucose in the foals. There were no significant differences in insulin secretion, insulin sensitivity or glucose tolerance between the control and growth-retarded Thoroughbred foals. Overgrown pony foals delivered by Thoroughbred mares had higher basal insulin levels and greater beta cell responses to glucose than the other groups of foals. The relationship between plasma glucose and insulin was also significantly steeper in overgrown pony foals than in the other groups. Variations in intrauterine growth rate, therefore, affect postnatal insulin secretion in the horse. More specifically, it is overgrowth, not growth retardation in utero that alters equine beta cell function in the immediate neonatal period.

Animals↗
PubMed2003

The beta3 nicotinic receptor subunit: a component of alpha-conotoxin MII-binding nicotinic acetylcholine receptors that modulate dopamine release and related behaviors.

Nigrostriatal dopaminergic neurons express many nicotinic acetylcholine receptor (nAChR) subunits capable of forming multiple nAChR subtypes. These subtypes are expressed differentially along the neuron and presumably mediate diverse responses. beta3 subunit mRNA has restricted expression but is abundant in the substantia nigra and ventral tegmental areas. To investigate the potential role(s) of nicotinic receptors containing the beta3 subunit in dopaminergic tracts, we generated mice with a null mutation in the beta3 gene. We were thereby able to identify a population of beta3-dependent alpha-conotoxin MII-binding nAChRs that modulate striatal dopamine release. Changes were also observed in locomotor activity and prepulse inhibition of acoustic startle, behaviors that are controlled, in part, by nigrostriatal and mesolimbic dopaminergic activity, respectively, suggesting that beta3-containing nAChRs modulate these behaviors.

Animals↗
PubMed2003

Free amino-acid concentrations in the equine placenta: relationship to maternal and fetal plasma concentrations.

Free amino-acid concentrations were measured in maternal venous and fetal umbilical vein plasma, and in the allantochorion, of Thoroughbred mares at term. Concentrations in maternal and fetal plasma were similar to those reported previously in equids. The concentrations of free amino-acids in the allantochorion were higher than those in the maternal and fetal plasmas and were characterised by high levels of the nonessential amino-acids as observed in other species. Fourteen of the 20 amino-acids measured had similar allantochorion/umbilical vein concentration ratios suggesting that simple gradient diffusion might play a part in their transfer from the placenta to the fetus.

Amino Acids↗
PubMed2003

Placentation in the African elephant (Loxodonta africana): II morphological changes in the uterus and placenta throughout gestation.

The gross and microscopic development of the zonary endotheliochorial placenta in the African elephant was studied in 22 gravid uteri that ranged in gestational stage from 0.5 to 20.6 months. The conceptus only ever occupies one horn of the uterus and is associated with 2-5 large corpora lutea that persist in the ipsilateral ovary throughout gestation. Initially, the trophoblast in the equatorial region of the conceptus completely replaces the lumenal epithelium of the endometrium to which it is apposed. Blunt upgrowths of endometrial stroma then develop, each closely invested by trophoblast, and containing the capillaries that will vascularize this maternal component of the resulting placental band. With advancing gestation the lamellate stromal upgrowths increase markedly in length and become much thinner, thereby bringing the trophoblast into intimate contact with the endothelium of the maternal capillaries. They also become folded or pleated to increase the total area of intimate feto-maternal contact. At the lateral edges of the placental band the lamellae bend over towards the endometrium to form a blind cleft. Leakage of blood into this area creates haemophagous zones in which phenotypically specialized trophoblast cells phagocytose the blood components. The presence of large resorbing blood clots and circumferential scars in the uteri of three post parturient animals initiated the hypothesis that, when the standing elephant gives birth at term, the passage of the 120 kg fetus through the vagina may wrench the placenta off the endometrium by severing its very narrow maternal placental hilus. The resulting intrauterine haemorrhage may then play a role in preventing further conception for around 2 years.

Animals↗
PubMed2003

Successful non-surgical transfer of horse embryos to mule recipients.

Mules, hybrids resulting from the mating of a horse mare (Equus caballus, 2n = 64) to a Jack donkey (E. asinus, 2n = 62), are generally infertile. Five horse embryos were transferred non-surgically to two cyclic and one acyclic recipient mules. In the mares and cycling mules, oestrus and ovulation were induced with, respectively, d-cloprostenol and human chorionic gonadotrophin (hCG). The acyclic mule, on the other hand, received oestradiol benzoate when the embryo donor was showing oestrus and progesterone after the donor had ovulated and until pregnancy diagnosis. Non-surgical embryo collections were attempted on day 7 after ovulation and recovered embryos were transferred transcervically into the mules' uteri. Mules that became pregnant were blood sampled serially for equine chorion gonadotrophin (eCG), progestagen and total conjugated oestrogen concentrations until around 6 months of gestation. The three embryos transferred to the acyclic mule did not produce any pregnancies whereas both embryos transferred to the cycling mules resulted in the birth of live foals. The peak concentration and duration of secretion of eCG differed markedly between the two pregnant mules, although both animals appeared to develop secondary corpora lutea beyond day 40 of gestation, as in normal intraspecies horse pregnancy. Moreover, the rise in serum oestrogen concentrations from around day 90 was also similar to that seen in normal pregnant mares. Parturition occurred spontaneously on day 348 of gestation in both mules and the resulting colt foals developed normally to weaning. Thus, cycling mules can carry a horse conceptus after non-surgical embryo transfer and give birth to a normal mature foal.

Animals↗
PubMed2003

Developmental changes in localization of steroid synthesis enzymes in camelid placenta.

The uninucleate trophoblast of epitheliochorial camelid placenta produces multinucleate giant cells starting between day 30 and day 35 of pregnancy. The giant cells are found scattered along the trophoblast at similar frequency throughout gestation. Light microscope immunocytochemistry indicates that the four steroid synthesis enzymes (cholesterol side chain cleavage, 3beta-hydroxysteroid de-hydrogenase, 17alpha-hydroxylase and aromatase) are present in all uninucleate trophoblast cells between day 14 and day 30 of pregnancy, but are found only in the giant cells once they are established, and that this localization persists until term. The giant cells show massive amounts of smooth endoplasmic reticulum and numerous small mitochondria, again as has been shown in other steroid-producing cells. As progesterone from the corpus luteum is necessary throughout gestation in camels, the capacity for oestrogen production by the trophoblast presumably has an important role, but one limited mostly to the immediate vicinity of the fetomaternal interface.

3-Hydroxysteroid Dehydrogenases↗
PubMed2003

The effects of maternal age and parity on placental and fetal development in the mare.

REASONS FOR PERFORMING STUDY: The normality of equine placentation is essential for fetal health and development. Substantial information exists on the gross morphological status of the placenta but few studies have addressed the problem of degenerative lesions that interfere with placental morphology and placental efficiency. HYPOTHESIS: Degenerative changes in the endometrium with increasing age and parity are reflected in the morphology and density of the placental microcotyledons. OBJECTIVE: To assess placental efficiency on the basis of foal birthweight as a function of total microscopic area of fetomaternal contact. METHODS: Stereology was used to examine the placentae of 84 Thoroughbred mares grouped on the basis of age and parity. Placental efficiency, assessed by expressing foal birthweight as a function of total microscopic area of fetomaternal contact, was also determined. RESULTS: Mare age and parity influenced the development of the microcotyledons and microcotyledon surface density (Sv) was lowest in aged multiparous mares, presumably due to degenerative changes in their endometrium. However, primiparous mares also showed significantly lower Sv values than young multiparous mares, despite the virginal endometrium of the former group. This apparent 'priming' effect of a first pregnancy on microcotyledonary Sv was illustrated further by 11 maiden mares followed in 2 successive pregnancies. They all showed significant increases in Sv values in their second parity, with equivalent improvements in foal birthweight. CONCLUSIONS: Foal birthweight is a reflection of the balance between fetomaternal contact and placental efficiency. Increases in fetomaternal contact are correlated to reductions in placental efficiency, which may reflect the ability of the placenta to modify its exchange capabilities. POTENTIAL RELEVANCE: Further work is needed to elucidate how such changes in microcotyledon morphology and efficiency are brought about.

Age Factors↗
PubMed2003

Pregnancy rates in mares after a single fixed time hysteroscopic insemination of low numbers of frozen-thawed spermatozoa onto the uterotubal junction.

REASONS FOR PERFORMING STUDY: To compensate for the wide variation in the freezability of stallion spermatozoa, it has become common veterinary practice to carry out repeated ultrasonography of the ovaries of oestrous mares in order to be able to inseminate them within 6-12 h of ovulation with a minimum of 300-500 x 10(6) frozen-thawed spermatozoa. Furthermore, in order to achieve satisfactory fertility, this requirement for relatively high numbers of spermatozoa currently limits our ability to exploit recently available artificial breeding technologies, such as sex-sorted semen, for which only 5-20 x 10(6) spermatozoa are available for insemination. OBJECTIVES: This study was designed to evaluate and compare the efficacy of hysteroscopic vs. conventional insemination when low numbers of spermatozoa are used at a single fixed time after administration of an ovulation-inducing agent. METHODS: In the present study, pregnancy rates were compared in 86 mares inseminated once only with low numbers of frozen-thawed spermatozoa (3-14 x 10(6)) at 32 h after treatment with human chorionic gonadotrophin (hCG), either conventionally into the body of the uterus or hysteroscopically by depositing a small volume of the inseminate directly onto the uterotubal papilla ipsilateral to the ovary containing the pre-ovulatory follicle. RESULTS: Pregnancy rates were similarly high in mares inseminated conventionally or hysteroscopically with 14 x 10(6) motile frozen-thawed spermatozoa (67% vs. 64%). However, when the insemination dose was reduced to 3 x 10(6) spermatozoa, the pregnancy rate was significantly higher in the mares inseminated hysteroscopically onto the uterotubal junction compared to those inseminated into the uterine body (47 vs. 15%, P < 0.05). CONCLUSIONS: When inseminating mares with <10 x 10(6) frozen-thawed stallion spermatozoa, hysteroscopic uterotubal junction deposition of the inseminate is the preferred method. POTENTIAL CLINICAL RELEVANCE: Satisfactory pregnancy rates are achievable after insemination of mares with frozen-thawed semen from fertile stallions 32 h after administration of human chorionic gonadotrophin (Chorulon). Furthermore, these results were obtained when mares were inseminated with 14 x 10(6) progressively motile frozen-thawed spermatozoa from 2 stallions of proven fertility.

Animals↗
PubMed2003

Effect of the number of passages of fetal and adult fibroblasts on nuclear remodelling and first embryonic division in reconstructed horse oocytes after nuclear transfer.

The effects of repeated passage in vitro of fetal fibroblast cells (FFC) and adult fibroblast cells (AFC) on nuclear remodelling and first embryonic division when used to reconstruct horse oocytes, and the reasons for the developmental block in progression to the two-cell stage were investigated. A total of 463 metaphase II oocytes produced 427 fibroblast-cytoplasm couplets after nuclear transfer, which finally resulted in 319 reconstructed oocytes. With increasing numbers of passages, the rates of nuclear remodelling decreased in both types of donor cell; about half of the fused donor cell nuclei showed the S-G2-prometaphase stages of the first embryonic division 18-20 h after cell-fusion treatment, irrespective of the number of donor cell passages (FFC: 49%; AFC: 53%). The rates of first embryonic division in the reconstructed oocytes fell with increasing age of the donor cells (FFC: 32%-26%-23%; AFC: 27%-23%-24%) and these rates were significantly lower than those obtained from metaphase II oocytes activated parthenogenetically (79%, P < 0.05). Microscopic analysis of the organization of the first embryonic division in the developmentally blocked oocytes reconstructed with either FFC or AFC showed that most of these (FFC: 78%; AFC: 92%) could not form the mitotic spindle and the metaphase plate of chromosomes. These findings indicate that either fetal or adult fibroblasts that have undergone relatively few passages in vitro are most suitable as donors. However, both types of cell have lower potential to restart first embryonic development after nuclear transfer than do the equivalent cells in other species. Improvement in the rate of donor cell nuclear progression from S-G2-prometaphase to beyond the metaphase stage, and the normal organization of first embryonic development in reconstructed horse oocytes, would seem to be the key to the production of cloned embryos in this species.

Animals↗
PubMed2002

Postnatal cardiovascular function after manipulation of fetal growth by embryo transfer in the horse.

This study used between-breed embryo transfer in the horse to investigate the effects of maternal size and uterine capacity on fetal growth and postnatal cardiovascular and neuroendocrine functions. Equine embryos were transferred to establish eight Thoroughbred-in-Thoroughbred (TinT), seven Pony-in-Pony (PinP), five Thoroughbred-in-Pony (TinP) and eight Pony-in-Thoroughbred (PinT), pregnancies. Maternal and foal weights and placental microscopic area were measured at birth. At 6 days of postnatal life, arterial blood pressure and heart rate were monitored and blood samples were taken for hormone analysis before, during and after a 10 min period of nitroprusside-induced hypotension. Values for maternal and foal weights and placental area at birth were larger in TinT than in PinP pregnancies (P < 0.05). PinT pregnancies resulted in larger placentae and heavier foals relative to PinP (P < 0.05). TinP had smaller placentae and lighter foals relative to TinT (P < 0.05). Growth-enhanced (PinT) foals showed elevated basal arterial blood pressure and baroreflex threshold, reduced baroreflex sensitivity, diminished plasma catecholamine responses to acute stress, and increased cortisol responsiveness to ACTH. Conversely, growth-restricted (TinP) foals showed no change in basal arterial blood pressure, baroreflex threshold or adrenocortical responsiveness to ACTH, but had enhanced baroreflex sensitivity and augmented plasma catecholamine responses to acute stress. The data show that fetal growth acceleration as well as fetal growth restriction, resulting from between-breed embryo transfer in the horse, leads to altered postnatal regulation of blood pressure and the circulating concentrations of cortisol. These findings suggest that deviations in the pattern and rate of fetal growth both above and below the normal trajectory may influence cardiovascular function in postnatal life.

Adrenocorticotropic Hormone↗
PubMed2002

Hunting debate.

Explore the source record for details and available documents.

Animal Welfare↗
PubMed2002

An overview of low dose insemination in the mare.

The need for relatively high numbers of spermatozoa for artificial insemination limits our application of recently available technologies such as sex-sorted semen. The fertility of two different methods of low dose insemination using fresh, frozen and sex-sorted semen are compared in this overview. Satisfactory conception rates are described using very low doses of spermatozoa inseminated by either hysteroscopic or deep uterine insemination methods, proving the stallion is fully fertile. The hysteroscopic method appears to give higher conception rates when inseminating fewer than 5 x 10(6) spermatozoa and is therefore, the preferred method of insemination for sex-sorted spermatozoa. However, hysteroscopic deposition of low numbers of spermatozoa from infertile stallions does not appear to improve their fertility.

Animals↗
PubMed2002

Investigation of factors affecting pregnancy rate after embryo transfer in the dromedary camel.

The uteri of 36 adult dromedary camels were flushed non-surgically three times each with 90-120 mL of embryo flushing medium 7 days after ovulation. A total of 242 embryos were recovered, of which 139 were transferred non-surgically to recipient camels that were either at different levels of synchrony with respect to the Day 7 donor (+1 to -3 days; n = 58), or were at Day 6 after ovulation, but received one of the following treatments: (i) none (controls, n = 15); (ii) 150 mg progesterone-in-oil injected intramuscularly once daily during Days 5-20 after ovulation inclusive (n = 16); (iii) 500 mg flunixin meglumine given intravenously 15 min before transfer of the embryo (n = 6); (iv) 20 microg of the gonadotrophin-releasing hormone (GnRH) analogue buserelin given on Day 5 after ovulation (n = 12); or (v) the embryo was cooled to 4 degrees C and held at this temperature in an insulated container for 24 h before being transferred (n = 32). Jugular vein blood samples, taken daily from all the recipient camels during Days 0-20 after ovulation, were assayed for progesterone concentration and closely timed serial samples taken from the camels receiving flunixin meglumine or GnRH were assayed for 13,14-dihydro-15-keto prostaglandin F2alpha (PGFM) or oestradiol concentrations. The pregnancy rate increased to a maximum of 67% when ovulation in the recipient was negatively synchronized to have occurred 1 day behind that in the donor, and it fell dramatically when the level of asynchrony between recipient and donor increased to +1 (9%) or -3 (10%) days. It was not improved by daily injections of progesterone (44%), flunixin meglumine given before transfer (16%), or GnRH given on Day 5 (33%). Of the 32 embryos that were cooled to 4 degrees C before being transferred to Day 6 recipients, 20 resulted in pregnancies (63%) to give a success rate similar to that attained with the control fresh embryos (67%). Serum progesterone concentrations in the recipients increased to a mean +/- SEM of 2.6 +/- 0.8 ng mL(-1) by Day 8 after ovulation and, in those that were pregnant, levels remained elevated at 3-5 ng mL(-1) for the remainder of the sampling period; in non-pregnant recipients the concentrations declined to <1 ng mL(-1) by Day 11. Plasma PGFM concentrations in the flunixin meglumine-treated camels remained low (40-90 pg mL(-1)) compared with those in the untreated control camels, in which peak values of around 180 pg mL(-1) were reached within 10 min after transfer after which a steady decline occurred until resting concentrations of 90-100 pg mL(-1) were reached by 110 min after transfer. Treatment with GnRH on Day 5 after ovulation produced a transitory increase in serum oestradiol-17beta concentrations for 24 h. However, from Day 8, oestradiol concentrations in both the GnRH-treated and the untreated camels increased steadily to reach 2.5-3.5 pg mL(-1) by Day 12.

Animals↗