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B Lefèvre

Publications and source records attributed to B Lefèvre.

At least 19 recordsLinked to original sources
PubMed2006

Lead cations affect the control of both meiosis arrest and meiosis resumption of the mouse oocyte in vitro at least via the PKC pathway.

The aim of this study was to determine in vitro whether lead has a direct cytotoxic effect on the female gamete or through its surrounding somatic cells. We had previously demonstrated that it partly accumulates in the mouse ovary and induces follicle and oocyte apoptosis. The data reported here demonstrate for the first time that low levels of Pb(NO3)2 (<or=10 pM) affect oocyte meiosis in vitro. On the one hand, in condition similar to the in vivo one, i.e. in hypoxanthine (HX)-maintained meiotic arrest, Pb(NO3)2 was able to significantly release the oocytes from this arrest. On the other hand, when meiosis occurred spontaneously in vitro, Pb(NO3)2 inhibits meiosis. Whereas PMA, an agonist of PKC was able to prevent the first lead effect, calphostin C, an antagonist, was able to significantly prevent lead inhibition of spontaneous GVBD. And, similarly to Pb2+, the inhibition of PKC by calphostin C prevented HX to maintain the meiotic arrest whereas its activation by PMA inhibited spontaneous GVBD. No significant differences in the effects of Pb(NO3)2 on the oocytes were observed whatever the cumulus cells were present or absent. Moreover, lead did not seem to affect the metaphase plate formation. We concluded that Pb2+ may disturb the control of oocyte meiosis at least in part through its ability to interfere with the PKC pathway in taking place of Ca2+ ions.

Animals↗
PubMed2004

[The effect of similar speed's walking and functional classification of foot contact on variability of the vertical ground reaction force].

INTRODUCTION: The variability of the normal ground reaction force (F(z)) is a restrictive factor for the clinical analyse of kinetics parameters recorded during walking. OBJECTIVE: The aim of this study is the decrease of the inter-individual variability of the normal ground reaction force: F(z). MATERIAL AND METHOD: The method tested consists in imposing a similar speed to the subjects during walking tests, then to class foot according to their function: loading or propulsive foot. A group of seven young adults walk at spontaneous speed (VSpon) for the first walking test then at similar speed (Vsim = N(Fr) x square root of (g x li); where N(Fr) is the Froud's number, g is the gravitational acceleration and li is the length of the lower limb) for the second walking test. Two forces platforms register the F(z) of two consecutive steps. The normal ground reaction force and the mean coefficient of variability are retained to test for speed (VSim and VSpon) and functional classification effects. RESULTS: The CoV of F(z) decreases from 13% to 8% when the subjects walk at similar speed rather than at spontaneously chosen speed. The variability decreases by 1-1.5% when the data are classified according to functional criterion. The inter-individual variability of the F(z) significantly reduces when the tests are performed at similar speed and when the loading or propulsive factors are used for functional classification. CONCLUSION: The coupling of the methods described must permit to the clinician to constitute a data base which, tainted of less variability, should make easier the detection of pathology affecting the ground reaction force.

Adult↗
PubMed2004

Higher intake of DK265 corn silage by dairy cattle.

In this experiment, intake of DK265 3-way corn hybrid by dairy cattle was compared specifically with intake 1) of its bm3 isogenic form, 2) of its 2 related single-way hybrids, and 3) of 2 controls that were registered hybrids of similar earliness. Both dry matter (DM) and lignin contents were similar in all hybrids except for the bm3 hybrid, which was less lignified. There was a tendency for lower starch content and, correlatively, higher neutral detergent fiber content in DK265 and in the 2 related single-way hybrids. Significant intake differences were observed between hybrids; the highest intake was recorded for the bm3 hybrid. Among normal hybrids, DK265 and one of its related single-way hybrids registered significantly higher intakes than other hybrids. Among normal hybrids, cell wall digestibility and/or lignin content did not explain all of the variations observed for intake, whereas the higher intake of DK265 bm3 could be related to its lower lignin content as compared with isogenic DK265. It was hypothesized that the higher intake observed for the DK265 hybrid was probably related to specific friability traits that are not relevantly measured through the usual tests used in corn breeding.

Animals↗
PubMed2000

Cytoplasmic and nuclear phospholipase C-beta 1 relocation: role in resumption of meiosis in the mouse oocyte.

The location of the phospholipase C beta 1-isoform (PLC-beta 1) in the mouse oocyte and its role in the resumption of meiosis were examined. We used specific monoclonal antibodies to monitor the in vitro dynamics of the subcellular distribution of the enzyme from the release of the oocyte from the follicle until breakdown of the germinal vesicle (GVBD) by Western blotting, electron microscope immunohistochemistry, and confocal microscope immunofluorescence. PLC-beta 1 became relocated to the oocyte cortex and the nucleoplasm during the G2/M transition, mainly in the hour preceding GVBD. The enzyme was a 150-kDa protein, corresponding to PLC-beta 1a. Its synthesis in the cytoplasm increased during this period, and it accumulated in the nucleoplasm. GVBD was dramatically inhibited by the microinjection of anti-PLC-beta1 monoclonal antibody into the germinal vesicle (GV) only when this accumulation was at its maximum. In contrast, PLC-gamma 1 was absent from the GV from the time of release from the follicle until 1 h later, and microinjection of anti-PLC-gamma 1 into the GV did not affect GVBD. Our results demonstrate a relationship between the relocation of PLC-beta 1 and its role in the first step of meiosis.

Animals↗
PubMed1999

Calmodulin, gametes and fertilisation.

The role of calmodulin in fertilisation events was examined in a zona-free mouse system by using a selective calmodulin inhibitor, calmidazolium (1 microM). The effects of this antagonist were studied either on the ooplasmic calcium oscillations induced by fertilisation by using the Ca2+ indicator, fluo-3/AM, or on pronucleus formation 4 h later by using the nucleic acid stain, Syto-15. When the calmidazolium treatment was applied to one or the other gamete before insemination, the fertilisation process was affected only when spermatozoa were treated: most of the oocytes were partially fertilised as demonstrated by the profile of Ca2+ oscillations and the presence of polar bodies with no typical male and female pronuclei. When the treatment was applied during insemination, more than half the oocytes were unfertilised and only a few were partially fertilised. These results demonstrate that: (1) the calmodulin-dependent events taking place in spermatozoa before insemination appear essential at least for regular Ca2+ oscillations and for pronucleus formation; (2) the inhibition of calmodulin by calmidazolium applied to metaphase II oocytes before insemination has no major impact on their fertilising ability; and (3) at the time of gamete fusion calmodulin, either from the oocyte or from the spermatozoon, is essential for fertilisation to occur.

Acrosome Reaction↗
PubMed1999

Age and gonadotropins control Ca2+-spike acquisition in mouse oocytes isolated from early preantral follicles.

The action of gonadotropins upon the oocyte is known to be crucial at later stages of follicular development in mammals. However, its influence on oocytes at early preantral stages is still a matter of debate. In the present study we evaluated the onset of mouse oocyte's capacity to exhibit calcium spikes during preantral stages of follicular development, prior to meiotic competence acquisition. In particular, through the use of confocal microscopy, we probed for the specific effects of age and gonadotropin stimulation upon the calcium dynamics of preantral follicle oocytes. We found that important developmental changes on the Ca2+ signalling mechanisms take place early during follicular development. Specifically we demonstrate that both age and gonadotropin stimulation increase the capacity of oocytes recovered from preantral follicles to exhibit calcium spikes. We propose that a strictly morphological staging of follicular development is insufficient to predict oocyte behaviour and must take in consideration animal age and gonadotropin environment.

Aging↗
PubMed1998

Nuclear calcium release by InsP3-receptor channels plays a role in meiosis reinitiation in the mouse oocyte.

Our purpose was to investigate the presence of nuclear specific elements of the phosphoinositide pathway, and the link between nuclear calcium events and the first step of meiosis resumption, i.e. germinal vesicle breakdown (GVB) in mouse immature oocytes. Using confocal laser scanning microscopy, we analyzed the effects of nuclear microinjection of inositol 1,4,5-trisphosphate (InsP3), heparin and anti-InsP3 receptor monoclonal antibodies on both spontaneous nuclear and cytoplasmic calcium oscillations, as well as the effects of these components on the GVB. First we observed that nuclear Ca2+ events were dependent upon both nucleoplasmic and cytoplasmic InsP3 levels, highlighting a cross-talk between the GV and the cytoplasm concerning the Ca2+/InsP3 pathway. We demonstrated also that: 1) type 1 InsP3 receptors were localized at the nuclear membrane level while type 3 were absent from the nucleus; 2) calcium release from nuclear stores was mediated by type 1 rather than type 3 InsP3 receptor associated channels; 3) the anti-InsP3 R-1 mAB microinjected into the nucleus inhibited the GVB. These results demonstrate that reinitiation of meiosis requires an increase in nuclear phosphoinositide dependent Ca2+. Thus, the role of nuclear Ca2+ homeostasis is discussed with particular emphasis on nuclear envelope dynamics.

Animals↗
PubMed1997

Acquisition of meiotic competence is related to the functionality of the phosphoinositide/calcium signaling pathway in the mouse oocyte.

The meiosis resumption process has been related to spontaneous cytoplasmic InsP3-dependent calcium oscillations in fully grown mouse oocytes. Our purpose was to determine whether the acquisition of meiotic competence during the growth phase of oogenesis was associated with that of Ca2+ oscillations and whether these oscillations were dependent on the phosphoinositide cycle. We used confocal laser scanning microscopy to image free calcium ions in fluo-3/AM-loaded oocytes recovered from 12- to 26-day-old mice for 15 min following follicular release. As expected, oocytes isolated from 12-day-old mice were totally incompetent to undergo GVB in vitro, whereas the GVB rate increased progressively with mouse age and oocyte diameter. The percentage of oocytes exhibiting spontaneous calcium oscillations and that of oocytes resuming meiosis were similarly correlated with the female age, with incompetent oocytes failing to exhibit spontaneous Ca2+ oscillations. It is noteworthy that regardless of the stage of growth, thapsigargin induced an ooplasmic calcium release from the InsP3-sensitive stores when it was added to the culture medium. However, intracytoplasmic microinjection of InsP3 induced a shorter sequence of Ca2+ oscillations in 12-day-old mouse oocytes than in 15-day-old mouse oocytes and, whereas InsP3 increased the GVB rate at 15 days, it was unable to induce GVB at 12 days. These data lead us to conclude that the acquisition of meiotic competence is related to the functionality of the InsP3 pathway and, correspondingly, to the oocyte's ability to generate spontaneous cytoplasmic InsP3-dependent calcium oscillations.

Age Factors↗
PubMed1995

Cytoplasmic and nucleic calcium oscillations in immature mouse oocytes: evidence of wave polarization by confocal imaging.

Using confocal laser scanning microscopy and time-lapse reconstruction, we monitored [Ca2+]i in living mouse oocytes loaded with the calcium-sensitive fluorescent dyes fluo-3/AM or NuCa Green (specific for nuclear calcium) at the time of meiosis reinitiation. Our data confirm that spontaneous Ca2+ oscillations occurred in most of the immature fully grown mouse oocytes at least during the first half hour after release of the follicle and these oscillating oocytes underwent GVB in a large proportion after 1 h of culture. These spontaneous oscillations were disrupted when GVB was inhibited by dbcAMP and suppressed in the absence of external calcium. They were dependent on intracellular InsP3-sensitive Ca2+ stores since they were inhibited by heparin, an InsP3-receptor antagonist, or thapsigargin, which depletes InsP3-sensitive Ca2+ stores. A relation appeared between the germinal vesicle chromatin appearance and the oocyte's ability to exhibit calcium oscillations. NuCa Green-loaded oocytes exhibited clear fluorescence oscillations in the nuclear region which lead us to discuss the implication of the nuclear calcium in the meiotic process. Moreover, the observation of a clear polarization of the Ca2+ waves in 30% of the oocytes permits us to hypothesize the existence of a predetermined localization for the initial point of the calcium wave.

Aniline Compounds↗
PubMed1994

Mouse oocyte maturation is affected by lithium via the polyphosphoinositide metabolism and the microtubule network.

The incubation of mechanically denuded mouse oocytes in medium containing LiCl delayed both germinal vesicle breakdown (GVBD) and polar body extrusion in a dose-dependent and reversible manner. When myo-inositol alone was added to the culture medium, we observed that it accelerated GVBD and increased the rate of polar body extrusion, whereas, when combined with LiCl, the normal timing of GVBD was recovered. In the same way, when inositol trisphosphate (InsP3) was microinjected into the ooplasma, we observed an important improvement of the rate of GVBD, as compared to control oocytes, and prevention of lithium inhibition. However, neither myo-inositol nor InsP3 were able to rescue totally the oocytes from the negative effect of lithium on polar body extrusion. Moreover, lithium induced some important changes in microtubule and chromosome organizations. Before extrusion of the first polar body, the reduction of the spindle size or the appearance of short individualized chromosomes dispersed around a large aster of microtubules were often observed, whereas, after polar body extrusion, the spindle appeared smaller and chromosomes were often trapped in the midbody. Thus lithium affects mouse oocyte maturation at two different levels: GVBD and polar body extrusion. Whereas the former seems to be affected via polyphosphoinositide turnover, the latter is InsP3-independent and seems to be influenced negatively via underdevelopment of microtubular structures.

Actin Cytoskeleton↗
PubMed1992

Protein kinase C modulators influence meiosis kinetics but not fertilizability of mouse oocytes.

The role of protein kinase C (PKC) in the successive steps of mouse oocyte meiotic process was investigated. We have used either OAG, an analog of diacylglycerol, or mezerein, a nonphorbol ester diterpene, less tumor promoting than phorbol esters, as PKC activators, and staurosporine as PKC inhibitor. Cumulus-free oocytes were cultured in minimum essential medium with each of these PKC modulators and maturation stages were screened every two hours until the end of the process. Both PKC activators prevented GVBD at each tested dose for 4 hr (OAG) and 8 hr (mezerein), and decreased the frequencies of PB oocytes. The inhibitory effects of both activators were dose dependent and reversible. The addition of OAG to the culture medium after GVBD occurrence (i.e., after 4 hrs) did not affect PB extrusion whereas similar addition of mezerein significantly decreased the frequency of PB oocytes. Inhibition of PKC by staurosporine accelerated GVBD and increased the frequency of PB extrusion. When staurosporine was added after GVBD, PB extrusion occurred earlier but PB oocyte frequency was not increased. Fertilizability was not affected when oocyte maturation occurred in the presence of any of these substances despite the delay in maturation process. These results clearly indicate that the PKC pathway is involved in mouse oocyte meiotic process: activation of the enzyme would arrest meiotic process whereas its inhibition would participate in meiosis induction.

Alkaloids↗
PubMed1992

Influence of a gonadotrophin-releasing hormone agonist and gonadotrophins on morphometric characteristics of the population of small ovarian follicles in cynomolgus monkeys (Macaca fascicularis).

Small follicles, less than or equal to 100 microns, in monkey ovaries were divided into four types based on the morphological characteristics of the granulosa cells that surrounded the oocyte: primordial, intermediary, primary and secondary follicles. The proportion of primordial follicles positively correlated, whereas those of intermediary, primary and secondary follicles negatively correlated, with the total number of follicles less than or equal to 100 microns. There was no relationship between the population of nongrowing follicles (primordial and intermediary) and that of early-growing follicles (primary and secondary). Administration of exogenous gonadotrophins did not induce significant changes in the population of small follicles, whereas there was a significant increase in the number of intermediary follicles when gonadotrophins were associated with a gonadotrophin-releasing hormone agonist, buserelin. Buserelin can therefore partly inhibit the initiation of ovarian follicular growth in monkeys.

Animals↗
PubMed1992

Comparison of nalbuphine and fentanyl as intravenous analgesics for medically compromised patients undergoing oral surgery.

This study compared the efficacy and side effects of equianalgesic doses of nalbuphine and fentanyl as intravenous (IV) analgesics for medically compromised patients undergoing oral surgery with local anesthesia. A total of 24 inpatients scheduled for oral surgery and with an ASA physical status of 3 or 4 were randomly assigned to two treatment groups and received IV analgesia with an injection of either 0.2 mg/kg nalbuphine or 2 micrograms/kg fentanyl. Three minutes later, local anesthesia was administered. Respiratory rate, heart rate, arterial blood pressure, and oxyhemoglobin saturation (SpO2) were recorded before and during surgery. After the operation, the patient, surgeon, and anesthesiologist were asked to complete questionnaires regarding drug effects. Analgesia and sedation appeared sufficient and comparable according to the surgeon, anesthesiologists, and patients in the two groups, and there were no significant differences in blood pressure or heart rate. Respiratory rate and SpO2 were lower in patients treated with fentanyl (P < 0.05), and eight patients of this group experienced episodes of oxygen desaturation (SpO2 < 90%) compared with only two patients who received nalbuphine (P < 0.05). Nalbuphine produced less respiratory depression and should be considered a suitable alternative to fentanyl for use in medically compromised patients undergoing oral surgery.

Adult↗
PubMed1991

Progression of oocyte maturation from metaphase I to metaphase II is disturbed by previous immunological interference with cumulus cell function.

The effects of an antibody preparation reacting with preovulatory mouse cumuli oophori (anticumulus Ig) on oocyte maturation in vivo and in vitro were studied. Continuous presence of anticumulus Ig in culture medium did not impair oocyte maturation in vitro. Similarly, no effect on oocyte maturation in vivo was observed when anticumulus Ig was given to females superovulated with pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) at the time of hCG treatment. However, when administered earlier, anticumulus Ig brought about serious disturbances of oocyte meiotic competence, since only immature oocytes were ovulated after anticumulus Ig injection at the time of PMSG treatment and as much as 70% of the ovulated oocytes were immature when the antibody was applied 24 hr later. Previous absorption of anticumulus Ig with isolated cumulus cells removed the inhibitory effect of this preparation on oocyte meiotic competence to the same extent as absorption with whole cumuli oophori, despite the persistence of a strong reactivity of the cumulus cell-absorbed antibody preparations with the cumulus intercellular matrix. The ability of oocytes obtained from antibody-injected animals to mature in vitro was also considerably impaired when the injection was made at the time of PMSG treatment. In all cases the maturation defect concerned the progression of meiosis from metaphase I to metaphase II, while the ability of oocytes to undergo germinal vesicle breakdown (GVBD) was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1991

Effect of a gonadotropin-releasing hormone agonist and gonadotropins on ovarian follicles in cynomolgus monkey: a model for human ovarian hyperstimulation.

STUDY OBJECTIVE: To examine the effect on large follicles (greater than or equal to 2 mm) of human menopausal gonadotropin (hMG) and buserelin acetate, a gonadotropin-releasing hormone agonist in monkeys. DESIGN: Experimental. SETTING: Reproductive research laboratory. ANIMALS: Fourteen cyclic cynomolgus monkeys receiving hMG alone for 8 days or buserelin acetate plus 8 (group 1), 12 (group 2), or 16 (group 3) days of hMG administration always starting from day 1 of the cycle. RESULTS: The different treatments were effective in over-riding the specific ovulatory quota of 1, and more large follicles developed in treatments involving long duration and higher doses of hMG. In buserelin acetate plus hMG treatments, the frequency of dissociated follicles and follicles in late atresia were, respectively, lower and higher than in hMG alone treatment. The numbers of recoverable mature oocytes (germinal vesicle breakdown) were similar to the numbers of such oocytes recovered after hyperstimulation performed for human in vitro fertilization and embryo transfer (IVF-ET). However, the number of mature oocytes enclosed in typically preovulatory follicles was very low because there were numerous dysmature follicles. CONCLUSION: These data suggest a deleterious effect of buserelin acetate plus hMG treatments on the recruitable follicles at the time when treatments start. The implications of these observations in the field of human IVF-ET are discussed.

Animals↗