Search PubMed⌕ Search

Biomedical subjects

J C Rodger

Publications and source records attributed to J C Rodger.

At least 37 records · Page 2Linked to original sources
PubMed1997

Arachidonic acid-induced acrosomal loss in the spermatozoa of a marsupial, the tammar wallaby (Macropus eugenii).

Tammar wallaby spermatozoa were induced to undergo acrosomal loss when incubated with arachidonic acid (AA). Ultrastructural examination indicated that the AA-induced acrosomal loss occurred via multiple point fusions between the outer acrosomal membrane and the overlying plasma membrane. This form of acrosomal loss mimicked the physiological acrosome reaction (AR) seen in the sperm of eutherian mammals. The fusion event was limited to the acrosomal region of the plasma membrane and did not proceed past the peri-acrosomal ring. The entire acrosome was lost after AA treatment leaving no evidence of a persistent equatorial segment-like region. Ultrastructural evidence of AR-like membrane fusion was seen immediately on addition of 50 microg mL(-1) AA and a large proportion of sperm examined after five min incubation were in the late stages of membrane fusion. Longer-term incubation with AA had deleterious effects on wallaby sperm motility. It remains to be determined whether the AA-induced membrane fusion observed here indicates that AA is involved in the marsupial AR. However, pretreatment of sperm with the protein kinase C (PKC) inhibitor HMG significantly reduced AA-induced acrosomal loss suggesting that AA may have acted via PKC. If this is so, AA is probably physiologically significant and a novel pathway may be operating during AR induction in marsupials.

Acrosome↗
PubMed1997

Likely targets for immunocontraception in marsupials.

There is a growing need to manage marsupial populations as a means to mitigate economic and environmental damage and resolve animal welfare problems. In Australia, the problems of population management are highly specific and localized. In contrast, in New Zealand the problem is the control of the many millions of widely-distributed brushtail possums which are the country's major vertebrate pest. The needs of the two countries are thus very different but immunocontraception may provide an effective and humane alternative to current lethal control strategies. This paper discusses the features of marsupial reproduction and development that offer potential as targets for immunocontraceptive interference, including: (1) sperm production and maturation in the male; (2) sperm transport and maturation in the female; and (3) sperm and egg antigens and the early embryo. Some of these antigen targets are shared with eutherian mammals but others are likely to be unique to marsupials.

Animals↗
PubMed1996

Capacitation and the acrosome reaction in marsupial spermatozoa.

Although yet to be established definitively, it appears that marsupial spermatozoa require a process of capacitation and that the mechanisms involved may be quite different between the Australian and American species. For Australian species, failure to induce this functional event in culture has meant that in vitro fertilization (IVF) is yet to be achieved. However, in the American species with paired spermatozoa, IVF and subsequent embryo development have been obtained under quite simple culture conditions. Our understanding of the interactions of marsupial spermatozoa with the female tract, and in particular the oviduct, the most likely site of capacitation, is discussed. Although the acrosome reaction (AR) is an equally critical event in marsupial fertilization it appears to be regulated quite differently. The uniquely stable character of the marsupial acrosome is examined as well as our current understanding of the regulation of the marsupial sperm AR in vivo and in vitro.

Acrosome↗
PubMed1996

Hormones of oestrus and ovulation and their manipulation in marsupials.

Oestrus and ovulation occur spontaneously in the majority of marsupials, with behavioural oestrus usually occurring 1-2 days before ovulation. The hormone changes that occur at this time have been described in the most detail for the monovular tammar wallaby Macropus eugenii. The respective roles of the Graafian follicle, corpus luteum and the pituitary in the events leading up to oestrus and ovulation in this species are also reviewed. Recently, various protocols have been developed for superovulation of marsupials, including Australian species, such as the brush-tailed possum, fat-tailed dunnart, brush-tailed bettong and tammar wallaby, and the American laboratory opossum, Monodelphis domestica. These protocols provide an opportunity for studying the regulation of ovarian activity and for the collection of larger quantities of material for the study of gamete maturation, in vitro fertilization and embryonic development.

Animals↗
PubMed1996

Pellet-freezing spermatozoa of two marsupials: the tammar wallaby, Macropus eugenii, and the brushtail possum, Trichosurus vulpecula.

A protocol was developed for pellet-freezing spermatozoa of the tammar wallaby and the brushtail possum. Seren was collected by electro-ejaculation and wallaby spermatozoa were washed by 'swim-up' into phosphate-buffered saline (PBS), whereas possum spermatozoa were not washed. Wallaby spermatozoa were screened for toxicity in diluents containing a range of cryoprotectants (0-10%): dimethyl sulfoxide (DMSO), ethylene glycol and propanediol. Possum spermatozoa were tolerant of diluents containing 17.5% glycerol. Wallaby and possum spermatozoa were diluted 1:1 with the most promising cryoprotective diluents (final concentrations in PBS: possum, 17.5% glycerol; wallaby, 7.5% glycerol + 10% DMSO) and, after 5 min equilibration at room temperature, were pellet-frozen. Pellets were thawed (35 degrees C) and wallaby spermatozoa were washed by centrifugation (200 g for 5 min) and resuspended in PBS to minimize cryoprotectant toxicity. A high proportion of possum spermatozoa was recovered after freezing (67.5%), having good progressive motility (3.6 on a 0-5 scale). The progressive motility of frozen-thawed wallaby spermatozoa was also high (3.0), but only 10% of motile spermatozoa were recovered. The pellet-freezing method in conjunction with the post-thaw washing procedure (wallaby) may produce a viable population of cryopreserved marsupial spermatozoa suitable for use in assisted-breeding techniques such as in vitro fertilization and artificial insemination.

Animals↗
PubMed1994

Fluorescent localization of thiols and disulfides in marsupial spermatozoa by bromobimane labelling.

The acrosome of marsupial spermatozoa is a robust structure which, unlike its placental counterpart, resists disruption by detergent or freeze/thawing and does not undergo a calcium ionophore induced acrosome reaction. In this study specific fluorescent thiol labels, bromobimanes, were used to detect reactive thiols in the intact marsupial spermatozoon and examine whether disulfides play a role in the stability of the acrosome. Ejaculated brushtail possum (Trichosurus vulpecula) and tammar wallaby (Macropus eugenii) spermatozoa were washed by swim up and incubated with or without dithiothreitol (DTT) in order to reduce disulfides to reactive thiols. Spermatozoa were then washed by centrifugation and treated with monobromobimane (mBBr), a membrane-permeable bromobimane, or with monobromotrimethylammoniobimane (qBBr), a membrane-impermeable bromobimane. Labelled spermatozoa were examined by fluorescence microscopy and sperm proteins (whole sperm proteins and basic nuclear proteins) were analysed by gel electrophoresis. The membrane-permeable agent mBBr lightly labelled the perimeter of the acrosome of non-DTT-treated possum and wallaby spermatozoa, indicating the presence of peri-acrosomal thiol groups. After reduction of sperm disulfides by DTT, mBBr labelled the entire acrosome of both species. The membrane-impermeable agent qBBr did not label any part of the acrosome in non-DTT or DTT-treated wallaby or possum spermatozoa. Thiols and disulfides are thus associated with the marsupial acrosome. They are not found on the overlying plasma membrane but are either in the acrosomal membranes and/or matrix. The sperm midpiece and tail were labelled by mBBr, with increased fluorescence observed in DTT-treated spermatozoa.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Prefertilization gamete maturation events in marsupials.

Despite many fundamental similarities between the gametes of marsupials and placental mammals, the regulation and timing of prefertilization gamete maturation are quite different. The marsupial acrosome is remarkably stable and an acrosome reaction (AR) is not induced by reagent effective for the sperm of placental mammals. The ultrastructure of the marsupial sperm AR is essentially similar to that of placental mammals, however, whether an equatorial segment (ES) persists to serve as the site of sperm-egg membrane fusion is unclear. Diacylglycerol induction of the AR suggests that the sperm of Australian species lack an ES, yet an ES-like region appears to be involved in fertilization in the opossum Monodelphis. The marsupial oocyte, unlike those of placentals, continues to grow throughout follicular life and major cytoplasmic maturation events occur late in oocyte development. Cortical granules only become evident shortly before ovulation and mature dark granules may only appear after ovulation. Further, the zona pellucida (ZP) changes in character and function during the peri-ovulatory period. In vitro fertilization has been achieved for an opossum but not for any Australian marsupial, owing to failure of sperm-ZP binding. Requirement for a sperm maturation process is likely, but capacitation treatments used for placental sperm in vitro have been ineffective. Since it is now feasible to experimentally manipulate marsupial gametes in vitro major advances in our understanding of their function can be expected.

Acrosome↗
PubMed1994

Cardiac tamponade as the initial presentation of malignancy: is it as rare as previously supposed?

Advanced malignant disease frequently involves the heart and pericardium, and pericardial effusion is a common postmortem finding in such patients. Identification of pericardial effusions in life is uncommon, however, even when symptomatic. Cardiac tamponade occurring as the first presentation of malignancy appears to be uncommon. We present five cases of cardiac tamponade due to undiagnosed malignancy which presented to a general medical unit over 18 months. The availability of echocardiography was an important factor in correct diagnosis, since clinical features were non-specific. Bronchial adenocarcinoma was the cause in three of the five cases. Review of the literature confirms adenocarcinomas of the bronchus as the most common cause of this complication. The majority of cases have presented with large volume, haemorrhagic effusions, and cytology (with or without carcinoembryonic antigen measurement) was diagnostic in most patients. Immediate treatment with subxiphoid pericardiotomy is recommended; the role of balloon catheter pericardiotomy remains to be established. Combined chemotherapy and radiotherapy appears to extend survival, which in some cases may be prolonged. We recommend that early echocardiography should be obtained in all patients presenting with apparent cardiac failure, since early treatment of malignant effusions provides symptomatic relief.

Adenocarcinoma, Bronchiolo-Alveolar↗
PubMed1993

In vitro maturation of oocytes from a marsupial, the tammar wallaby (Macropus eugenii).

This study examined the competence of oocytes from the tammar wallaby, Macropus eugenii to mature in vitro. Oocytes were collected from follicles > 1 mm diameter 24 h after pregnant mare serum gonadotrophin (PMSG) treatment and incubated in Eagle's minimum essential medium supplemented with 10% fetal calf serum, at 35 degrees C in 5% CO2 in air for 24, 36, or 48 h. Oocytes were incubated either granulosa cell-intact or granulosa cell-free or in the presence of 10 IU ml-1 PMSG or 10 micrograms ml-1 porcine luteinizing hormone (LH) + 10 micrograms ml-1 porcine follicle stimulating hormone (FSH). The ability of oocytes recovered from small (< 1.5-mm-diameter) and large (> or = 1.5 mm-diameter) follicles to mature in vitro was also examined. The nuclear status of oocytes was assessed using the DNA-specific dye Hoechst 33342. Initially, all oocytes examined contained a germinal vesicle. After 24 h of culture, 60% of oocytes had progressed to metaphase I or anaphase I. After 36 h, approximately 20% of oocytes possessed metaphase II chromosomes, and 20% of oocytes were at metaphase I or anaphase I. At the completion of the 48 h culture period, 40% of oocytes had completed maturation to the metaphase II stage. In vitro oocyte maturation after 48 h was not affected by the presence of granulosa cells, PMSG, or LH and FSH. More oocytes from large follicles (55%) completed maturation by 48 h than from small follicles (20%). Approximately 50% of oocytes remained at the GV stage at all times under all conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Lysophosphatidylcholine disrupts the acrosome of tammar wallaby (Macropus eugenii) spermatozoa.

The acrosomal status of wallaby spermatozoa was evaluated by light and electron microscopy after incubation in 1-100 microM lysophosphatidylcholine (LPC) for up to 120 min. Treatment with 1 and 10 microM LPC for 120 min did not lead to acrosomal loss, or detectable alteration to the acrosome, as detected by Bryan's staining and light microscopy. Incubation with 25 microM LPC had little effect on acrosomal loss, however statistically significant changes (P < 0.05) in the acrosomal matrix (altered) were detected after 10-min incubation by light microscopy. Around 50% of acrosomes were altered after 20-min incubation in 50 microM LPC (P < 0.001), and 40% of spermatozoa had lost their acrosome after 60-min incubation (P < 0.001). Treatment with 75 and 100 microM LPC led to rapid acrosomal loss from around 50% of spermatozoa within 10 min (P < 0.001), and by 60 min acrosomal loss was 70-80%. LPC, like the diacylglycerol DiC8 (1,2-dioctanoyl-sn-glycerol), is thus an effective agent to induce loss of the relatively stable wallaby sperm acrosome, and it also induces changes within the acrosomal matrix. Ultrastructure of the LPC-treated spermatozoa revealed that the plasma membrane and the acrosomal membranes were disrupted in a manner similar to that seen after detergent treatment (Triton X-100). There was no evidence of point fusion between the plasma membrane overlying the acrosome and the outer acrosomal membrane. The plasma membrane was the first structure to disappear from the spermatozoa. The acrosomal membranes and matrix showed increasing disruption with time and LPC concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrosome↗
PubMed1993

West Nile virus infection induces susceptibility of in vitro outgrown murine blastocysts to specific lysis by paternally directed allo-immune and virus-immune cytotoxic T cells.

Day 3 post-coitum BALB/c and (BALB/c x CBA/H)F1 blastocysts were isolated and hatched in replicate wells. Some were treated with interferon-gamma (IFN-gamma). Whilst others were infected with West Nile Virus (WNV) at 100 plaque-forming units per cell, for 18 h. Controls were mock-treated. Gamma-irradiated (2000 rads) CBA/H, (paternal) WNV-specific and allo(CBA/H)-specific cytotoxic T (Tc) cells were then added to replicates of infected, mock-infected or IFN-gamma-treated cultures for 20 h. [3H]Thymidine was then added for a further 8 h. [3H]Thymidine incorporation was inhibited by 40-50% in WNV-infected cultures exposed to WNV-paternal-specific Tc cells and by 30-40% in WNV-infected cultures exposed to allo-paternal-specific Tc cells compared to similarly exposed, uninfected, or unexposed, WNV-infected, or unexposed, uninfected cultures. No significant differences in [3H]thymidine incorporation were found between these controls and IFN-gamma-treated cultures exposed to allo-paternal-specific Tc cells or IFN-gamma-treated cultures not exposed to Tc cells. Parallel exposure of L929 fibroblasts to the same Tc cells irradiated with 500-8000 rads in doubling doses, showed that irradiation did not alter the efficacy or specificity of the Tc cells. Relevance to maternal anti-viral immune responses during implantation is discussed.

Animals↗
PubMed1993

The unique stability of the marsupial sperm acrosomal membranes examined by unprotected freeze-thawing and treatment with the detergent Triton X-100.

In this study of the unique stability of the marsupial acrosome, experiments were carried out on the acrosomes of spermatozoa of the tammar wallaby (Macropus eugenii), common brushtail possum (Trichosurus vulpecula) and grey short-tailed opossum (Monodelphis domestica). Light microscopy showed that 4% of opossum and 15% of possum and wallaby spermatozoa lost their acrosomes after freeze-thawing. Electron microscopy revealed that freeze-thawing also induced changes in the acrosomal matrix of some acrosome intact spermatozoa. In both possum and wallaby, freeze-thawing increased the number of spermatozoa with vesiculation of the acrosomal matrix. Freeze-thawing disrupted the plasma membrane of spermatozoa but the acrosomal membranes remained intact. Immediately on addition of high concentrations of TX-100 (0.02% and 0.04%) there was significant loss of acrosomes and motility in possum and wallaby spermatozoa. Lower concentrations of TX-100 (< or = 0.01%) did not affect motility for up to 30 min in all three species, and there was no significant loss of acrosomes. Although loss of acrosomes did not occur under mild detergent treatment, 56% of wallaby and 70% of possum spermatozoa had altered acrosomes after 30 min in 0.01% TX-100. Electron microscopy revealed that acrosomes were undergoing a vesiculation process similar to that seen after freeze-thawing. Often the plasma membrane of detergent-treated spermatozoa was disrupted and had formed plasma membrane vesicles. However, the acrosomal membranes remained intact despite major changes to the acrosomal matrix. The study confirmed the remarkable stability of the marsupial acrosome and suggested that this is probably based in the acrosomal membranes.

Acrosome↗
PubMed1993

Ovarian function and its manipulation in the tammar wallaby, Macropus eugenii.

This study aimed to develop a superovulation protocol for the monovulatory tammar wallaby (Macropus eugenii), and examined the regulation of ovarian activity which leads to alternate ovulation in this marsupial. The most effective stimulatory treatment was 20 I.U. pregnant mare serum gonadotrophin (PMSG) given intramuscularly (i.m.) 20 days after the activation of an oestrous cycle by the removal of a sucking pouch young (RPY). Bromocriptine treatment was given at the time of RPY if the animal was in early seasonal quiescence. Mating had generally occurred when animals were examined 2 days after PMSG treatment on the morning of Day 22 RPY. Ovulation occurred only if the animal was treated on Day 22 or 23 (i.e. 2 or 3 days after PMSG) with gonadotrophin releasing hormone (GnRH) to induce a luteinizing hormone (LH) surge. Three 30-micrograms injections of GnRH (in 0.2 mL olive oil) were delivered as i.m. injections at 3-h intervals. Radioimmunoassay confirmed that the PMSG dose used did not elevate circulating steroid hormone concentrations beyond those found in normal cycles and that the GnRH protocol led to an LH surge of at least 6 h. Although multiple ovulation was achieved, the number of ovulations was low (2 or 3 per female). A major factor influencing the low ovulation rate was that generally only one ovary responded. Fertilized eggs and cleaving embryos were obtained. However, the fertility of induced ovulations has not yet been examined systematically. Laparoscopic examination through successive natural cycles confirmed that follicle growth and ovulation in the tammar wallaby alternates between the right and left ovary. Inhibition of follicle development in the corpus luteum (CL)-bearing ovary was also seen in females treated with the exogenous gonadotrophin (PMSG/GnRH) superovulation protocol. Follicle development was inhibited during the first half of the cycle in the non-CL-bearing ovary and during the entire cycle in the CL-bearing ovary. This inhibition seemed to occur at the follicular level because exogenous gonadotrophin was unable to initiate a response during periods of inhibition and the response to gonadotrophin differed in the two ovaries. The number of follicles growing in the non-CL-bearing ovary in response to an exogenous gonadotrophin stimulus was inversely related to the weight of the growing CL for the first 19 days after RPY.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

The value of thallium scintigraphy in a district general hospital.

The usefulness of exercise Tl scintigraphy (combined with electrocardiography) in a district general hospital has been assessed in 80 patients in whom a previous exercise electrocardiogram (ECG) had not been definitive. Seventy-five of the patients presented with chest pain and five with no pain but an abnormal ECG. Case notes and test results were examined to establish the clinicians' judgment of the likelihood of having coronary heart disease (CHD) and the patient's outcome. The mean time of follow-up was 27 months. In the majority of patients the test was found to help the clinician come to a decision on the presence or absence of CHD. It was found to be particularly useful in patients with abnormal resting ECGs. There was a shorter time to discharge for patients classified as highly unlikely of having CHD. Only four patients were re-referred following discharge from the outpatient clinic. Nine patients were referred for coronary angiography with five being found to have significant stenosis. None of the 16 patients in whom the exercise ECG was normal had ischaemic myocardial segments in the Tl scintigraphy.

Coronary Disease↗
PubMed1993

A survey of exercise testing practice in Scottish hospitals.

A 1989 survey (unpublished) of exercise testing practice in Scotland suggested that there were important differences in the practice of exercise testing between hospitals. A postal questionnaire was sent to 30 teaching and district general hospitals in 1991 and followed up by telephone questioning of consultants. The numbers of exercise tests performed had increased to 22,012 in 1990, and a greater proportion were performed in district general hospitals. General practitioners had very limited access to the service but hospital doctors of any grade had almost free access. Rationing of early post myocardial infarction testing led to attempts to define "high risk" post infarction patients and this included inappropriate patients in many hospitals. A variety of different protocols was used. Eighteen out of 30 hospitals surveyed discontinued beta blockers but only four hospitals took account of antianginal, antihypertensive or other medication, and all but one exercised patients while on digoxin. In the majority of hospitals decisions regarding drug therapy were taken by individual physicians. A variety of personnel reported tests, many without specialist training in cardiology. Even among consultants there was no concerns on the degree of ST depression which was significant. Exercise tests performed in different hospitals in Scotland are not comparable due to the wide variation in patient selection, test conditions, and interpretation of tests. This problem is likely to be exacerbated by the multiple personnel involved in all aspects of testing. It seems probable that there is a problem throughout the United Kingdom, and that there is a need for guidelines.

Exercise Test↗
PubMed1993

Induction of the marsupial sperm acrosome reaction in vitro by treatment with diacylglycerols.

The diacylglycerol DiC8 (1,2-dioctanoyl-sn-glycerol; 100 mumol l-1) was found to induce acrosomal loss in 70% of wallaby spermatozoa and 40% of possum spermatozoa after incubation for 120 min. If 10 mumol calcium ionophore l-1 was present, the time required to reach these end points was reduced to 30 and 60 min, respectively. The diacylglycerol OAG (1-oleoyl-2-acetyl-sn-glycerol; 100 mumol l-1) produced some acrosomal loss, particularly when 10 mumol calcium ionophore l-1 was present, but when the ionophore was absent, results were equivocal. The other diacylglycerol tested DOG (1,2-dioleoyl-sn-glycerol; 100 mumol l-1) did not induce significant acrosomal loss in possum or wallaby spermatozoa. The concentration of DiC8 required to induce acrosomal loss in marsupial spermatozoa (50-100 mumol l-1) was relatively high compared with that for placental mammals, suggesting a less specific mode of action than enzyme activation. Of the diacylglycerols tested alone, only DiC8 led to significant loss of motility. In wallabies, this was detectable after incubation for 60 min and in possums after incubation for 120 min. The ultrastructure of the DiC8-induced acrosomal loss was essentially identical to the acrosome reaction described for a broad range of placental mammals. A membrane vesicle shroud covered the acrosomal surface of the sperm head. The vesicles appeared to be formed by multiple point fusions between the plasma membrane and the outer acrosomal membrane. The mechanism of DiC8-induced acrosomal loss remains to be established.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrosome↗
PubMed1993

Role of diacylglycerols and calcium in the marsupial acrosome reaction.

Acrosomal loss was induced in marsupial spermatozoa by an intermediate of the phosphoinositide pathway. The diacylglycerol, 1,2-dioctanoyl-sn-glycerol (DiC8; 100 mumol l-1) induced acrosomal loss in 70% of brushtail possum (Trichosurus vulpecula) spermatozoa and in 80% of tammar wallaby (Macropus eugenii) spermatozoa. The DiC8-induced acrosomal loss was not enhanced by co-incubation with calcium ionophore A23187 and occurred in Ca(2+)-free medium and in the presence of the calcium chelator EGTA (3 mmol l-1). There was no evidence of uptake of 45Ca2+ during the DiC8-induced acrosomal loss. Inhibitors of protein kinase C [1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine] and phospholipase A2 [dexamethasone] did not effect DiC8-induced acrosomal loss in wallaby spermatozoa. The phorbol ester, phorbol 12-myristate 13-acetate, at a concentration of 10 mumol l-1 had no effect on possum spermatozoa and induced acrosomal loss in only 6% of wallaby spermatozoa. It appears that the DiC8-induced acrosome reaction is not mediated by activation of the phosphoinositide pathway and that extracellular calcium is not required for the membrane fusion event. As acrosomal loss was seen only at relatively high concentrations of diacylglycerol (> 50 mumol l-1) and there is no evidence of involvement of other phosphoinositide intermediates or analogues, it is likely that its role is as a direct membrane fusogen.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗