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Biomedical subjects

M Levasseur

Publications and source records attributed to M Levasseur.

At least 19 recordsLinked to original sources
PubMed2002

Particle size fractionation of paralytic shellfish toxins (PSTs): seasonal distribution and bacterial production in the St Lawrence estuary, Canada.

We determined the seasonal distribution of paralytic shellfish toxins (PSTs) and PST producing bacteria in > 15, 5-15, and 0.22-5 microm size fractions in the St Lawrence. We also measured PSTs in a local population of Mytilus edulis. PST concentrations were determined in each size fraction and in laboratory incubations of sub-samples by high performance liquid chromatography (HPLC), including the rigorous elimination of suspected toxin 'imposter' peaks. Mussel toxin levels were determined by mouse bioassay and HPLC. PSTs were detected in all size fractions during the summer sampling season, with 47% of the water column toxin levels associated with particles smaller than Alexandrium tamarense (< 15 microm). Even in the > 15 microm size fraction, we estimated that as much as 92% of PSTs could be associated with particles other than A. tamarense. Our results stress the importance of taking into account the potential presence of PSTs in size fractions other than that containing the known algal producer when attempting to model shellfish intoxication, especially during years of low cell abundance. Finally, our HPLC results confirmed the presence of bacteria capable of autonomous PST production in the St Lawrence as well as demonstrating their regular presence and apparent diversity in the plankton.

Animals↗
PubMed2000

Thalamic microglial activation in ischemic stroke detected in vivo by PET and [11C]PK1195.

Using quantitative PET, the authors studied the binding of [11C]PK11195, a marker of activated microglia, in the thalamus of patients with chronic middle cerebral artery infarcts. All patients showed increased [11C]PK11195 binding in the ipsilateral thalamus, indicating the activation of microglia in degenerating projection areas remote from the primary lesion. A persistent increase in [11C]PK11195 binding suggests active, long-term thalamic microstructural changes after corticothalamic connection damage.

Adult↗
PubMed2000

Population-based study of the pattern of molecular markers of minimal residual disease in childhood and adult acute lymphoblastic leukemia: an assessment of the practical difficulty of representative sampling for trial purposes. Northern Region Haematology Group.

BACKGROUND: The prevalence, in unselected patients with acute lymphoblastic leukaemia (ALL), of clonal rearrangements suitable for minimal residual disease (MRD) studies has not been formally investigated. PROCEDURE: This was a prospective, demographic study of the frequency of molecular markers of MRD in all patients with ALL presenting over 5 years within the Northern Health Region of England (population 3.1 million). Presentation marrow samples were examined to detect informative markers. RESULTS: One hundred twenty-four children (age <15 years) developed non-Burkitt ALL. No material was available for study in 21. Eighty-six had clonal gene rearrangements (BCR/ABL, immunoglobulin heavy chain (IGH) and/or T cell receptor (TCR) gene rearrangements). All entered remission; 84 (68% of the original cohort) survived to become eligible for MRD studies. One hundred sixteen adults developed ALL, of whom 48 were not studied due to insufficient cellular material in the bone marrow aspirate or to logistical problems in central referral of samples from other hospitals. Material from elderly adults (age >55 years) was less likely to be sent for analysis, 36% vs. 59% (P = 0.024). Thirty-eight had BCR/ABL and/or IGH/TCR gene rearrangements. Thirty-one (27% of the original cohort) entered remission and became eligible for MRD studies. Informative gene rearrangements were more common in children than adults (83% vs. 63%, P < 0.003). CONCLUSIONS: The results reveal substantial potential, unintentional, selection bias. Large-scale multicentre studies of MRD in children may well produce clinically relevant and representative data. Those who mount similar studies in adults should not assume they will be similarly representative or as successful in accrual of material.

Adolescent↗
PubMed2000

[Non-medical factors in perinatal health. A study of socioeconomic anc cultural features of women admitted to the maternity hospital in Lens (Pas-de-Calais)].

BACKGROUND: The aim of this study was to determine the influence of medical and non-medical factors on perinatal health in an underpriviledged area, the ex-coal mines of Lens (Pas-de-Calais). POPULATION AND METHODS: This prospective study concerned 1,000 women who delivered in the maternity hospital of Lens between January 5, 1993 and May 13, 1993. The relationships between preterm delivery, low birth weight and maternal socioeconomic and cultural characteristics were analyzed. RESULTS: The women included presented adverse pregnancy outcomes. Preterm delivery, low birth weight and neonatal transfer rates were respectively 6.9%, 7.3% and 12.7% higher than the average regional rates. In contrast with these results, antenatal care could be considered correct or even better. The poor socioeconomic status of the population appeared to be a very significant perinatal risk factor. CONCLUSION: At present, in an unfavourable regional conjuncture, socioeconomic and cultural factors have adverse effects on perinatal morbidity and mortality independent of medical factors like prenatal care. The prevention of poor perinatal outcome should be based on these data. Not the access to the health care system but the manner of dispensing health care should require great consideration.

Adult↗
PubMed2000

Sperm-induced calcium oscillations at fertilisation in ascidians are controlled by cyclin B1-dependent kinase activity.

The generation of calcium oscillations at fertilisation and during mitosis appears to be controlled by the cell cycle machinery. For example, the calcium oscillations in oocytes and embryos occur during metaphase and terminate upon entry into interphase. Here we report the manipulation of sperm-triggered calcium oscillations by cyclin-dependent kinase (CDK) activity, the major component of maturation/M phase promoting factor (MPF). To control the CDK activity we microinjected mRNAs encoding full-length GFP-tagged cyclin B1 or a truncated and therefore stabilised form of cyclin B1 ((delta)90) into unfertilised oocytes. In the presence of full-length cyclin B1, the calcium oscillations terminate when cyclin B1 levels fall along with the concomitant fall in the associated CDK activity. In addition, when the CDK activity is elevated indefinitely with (delta)90 cyclin B1, the calcium oscillations also continue indefinitely. Finally, in oocytes that contain low mitogen-activated protein (MAP) kinase activity and elevated CDK activity, the sperm-triggered calcium oscillations are again prolonged. We conclude that the CDK activity of the ascidian oocyte can be regarded as a positive regulator of sperm-triggered calcium oscillations, a finding that may apply to other oocytes that display sperm-triggered calcium oscillations at fertilisation. Furthermore, these findings may have a bearing upon the mitotic calcium signals of early embryos.

Animals↗
PubMed2000

Cell cycle-dependent repetitive Ca(2+ )waves induced by a cytosolic sperm extract in mature ascidian eggs mimic those observed at fertilization.

Sperm-triggered Ca(2+) oscillations occur throughout the animal kingdom. The mechanism sperm use to trigger Ca(2+) oscillations at fertilization has not been resolved in any egg. The temporal, spatial and regulatory characteristics of the Ca(2+) oscillations during fertilization in ascidians offer a unique advantage over other systems for determining the mechanism of fertilization. For example, sperm trigger two phases of Ca(2+) oscillations that are all waves in ascidians. The first of these Ca(2+) waves begins at the point of sperm-egg fusion while a second phase of Ca(2+) waves originates at a vegetal protrusion termed the contraction pole. In addition, cyclin B1-dependent kinase activity provides a form of positive feedback, maintaining the second phase of Ca(2+) waves during meiosis and thereby ensuring meiotic exit. We therefore prepared cytosolic ascidian sperm extracts or MonoQ-fractionated ascidian sperm extracts from this urochordate to investigate if a Ca(2+)-releasing sperm-borne factor was responsible for egg activation. Spatially, ascidian sperm extract induced repetitive Ca(2+) waves that mimicked the spatial pattern displayed during fertilization: all the second-phase Ca(2+) waves originated at a vegetal protrusion termed the contraction pole (thus mimicking fertilisation). We also demonstrated that ascidian sperm extract-induced Ca(2+) oscillations were maintained when CDK activity was elevated and MAP kinase activity was low, as found previously for sperm-triggered Ca(2+) oscillations. As would be predicted, large doses of ascidian sperm extract injected into prophase-stage oocytes, lacking CDK activity, failed to induce any Ca(2+) release even though they responded to microinjection of the Ca(2+)-releasing second messenger inositol 1,4,5-trisphosphate. Finally, since the Ca(2+)-releasing activity from Mono-Q fractionated ascidian sperm extract eluted predominantly as one fraction, this may imply that one factor is responsible for the Ca(2+)-releasing activity. These data support a model of egg activation whereby the sperm introduces a Ca(2+)-releasing cytosolic factor into the egg. We demonstrated that ascidian sperm contain a protein factor(s) that is regulated by the egg CDK activity and can trigger all the Ca(2+ )waves observed at fertilization with a spatial pattern that mimics those initiated by sperm.

Animals↗
PubMed2000

Bacterial dynamics in first year sea ice and underlying seawater of Saroma-ko Lagoon (Sea of Okhotsk, Japan) and resolute passage (High Canadian Arctic): inhibitory effects of ice algae on bacterial dynamics.

The seasonal development of bacterial abundance in first year bottom ice and underlying seawater were studied at Saroma-ko Lagoon in Hokkaido, Japan, and at Resolute Passage in the High Canadian Arctic during the algal bloom in spring 1992. The aim of this study was to evaluate whether the high algal concentrations reached during the bloom of ice algae have inhibitory effects on bacterial dynamics. Bacterial abundance (measured as total cell count and colony-forming units CFU) increased with the increase of the algal biomass up to 500 micrograms Chla.L-1 in both locations. Culturable fraction (measured as the percentage of CFU counts versus the total cell counts) was between 7% and 22% at Saroma-ko, and approximately 0.08% at Resolute Passage. When algal biomass exceeded 500 micrograms of Chla.L-1, both bacterial abundance and culturable fraction decreased significantly. There was a maximum threshold of algal biomass (between 500 and 800 micrograms of Chla.L-1) after which bacterial dynamics become negatively coupled to the algal biomass. These results suggest that bactericidal and/or bacteriostatic compounds from these extremely high algal concentrations could explain the decrease in bacterial abundance and culturability in bottom ice observed after the ice algae bloom.

Arctic Regions↗
PubMed1998

Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first pause, restart, then stop: correlations with cell cycle kinase activity.

We have investigated the relationship between the sperm-triggered Ca2+ oscillations and the activities of two cell cycle kinases (MPF activity and MAP kinase activity) at fertilisation of Ascidiella aspersa oocytes. Maturation Promoting Factor (MPF) activity is elevated in the metaphase I (MI)-arrested unfertilised oocyte (as measured by phosphorylation of exogenous histone H1) and falls 5 minutes after fertilisation to remain at low levels for 5 minutes. The first polar body (pb1) is extruded when the MPF activity is low. The MPF activity is elevated again 15 minutes after fertilisation and finally becomes inactivated 25 minutes after fertilisation when the pb2 is extruded. MAP kinase activity increases from an initially elevated level to reach maximal activity 10 minutes after fertilisation and subsequently falls to reach low levels 25 minutes after fertilisation. Sperm trigger a series of Ca2+ oscillations that pause for 5 minutes while only the MPF activity is low and are present when both MPF and MAP kinase activity are elevated. We next attempted to determine whether the second phase of calcium oscillations is required to reactivate the MPF activity that precedes extrusion of the second polar body. To do this, we triggered a monotonic Ca2+ signal. This leads to the inactivation of MPF followed by MPF reactivation. The MPF activity then remains elevated for an extended period of time. During this period, the chromatin remains condensed and a metaphase II (MII) spindle forms. Fertilisation of these MII oocytes triggers extrusion of pb2 in 7 minutes. Interestingly, the second phase of Ca2+ oscillations is completely absent when MII oocytes are fertilised. Thus, in both MI and MII oocytes, the sperm-triggered Ca2+ oscillations follow the MPF activity. Finally we discuss our finding that the Ca2+ release system remains sensitive during the metaphase-like state (including the period when the Ca2+ oscillations pause).

Animals↗
PubMed1998

[Breech presentation: management (304 cases)].

UNLABELLED: BUT: Try to precise the optimal management in 1997 face a breech presentation. METHOD: Between January 1991 and December 1995, 304 cases of breech presentations were listed at the maternity of Pavillon Victor Olivier (Lille). From these 304 breech presentations, all parities blended, the authors have analysed the mode of delivery of these patients, distinguishing the para one from the multiparous women and the preterm babies from the other babies. From this study and a review of the literature, were discussed the criterions which can help the practitioner to determine the mode of delivery of these fetus. RESULTS: The results show a cesarean section (cs) rate of 51% (41% of first intention cs and 10% of second intention cs were realized only for primiparity + breech presentation and 67% of the para one women benefited from a first intention cs 8.72% of vaginal deliveries were complicated, and 5 fetal injuries were noted without sequel. On 296 live new-borns, only 2 cases of fetal death were perhaps due to the vaginal delivery. Fetal mortality is principally reliable at the prematurity and the congenital malformations, but finally, not due to mode of delivery. CONCLUSION: The difficulty is to determine rigorous criterions of selection to authorize a vaginal delivery without spoil the fetal pronostic. The major criterions are a perfect radiopelvimetry, an estimated fetal weight < 3800 g for the para one women and < 4300 g for the multiparous woman, a well flexed fetal head, favorable obstetric conditions ond the absence of maternal or fetal complications. The primiparity is not an indication of systematic cesariean section.

Breech Presentation↗
PubMed1996

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, genetic homogeneity, and mapping of the locus within a 2-cM interval.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is a recently identified autosomal dominant cerebral arteriopathy characterized by the recurrence of subcortical infarcts leading to dementia. A genetic linkage analysis conducted in two large families recently allowed us to map the affected gene on chromosome 19 in a 12-cM interval bracketed by D19S221 and D19S215. In the present study, these first 2 families and 13 additional ones, including a total of 199 potentially informative meiosis, have been genotyped with eight polymorphic markers located between D19S221 and D19S215. All families were linked to chromosome 19. The highest combined lod score (Zmax = 37.24 at theta = .01) was obtained with marker D19S841, a new CAn microsatellite marker that we isolated from chromosome 19 cosmids. The recombinant events observed within these families were used to refine the genetic mapping of CADASIL within a 2-cM interval that is now bracketed by D19S226 and D19S199 on 19p13.1. These data strongly suggest the genetic homogeneity of this recently identified condition and establish the value of its clinical and neuroimaging diagnostic criteria. Besides their importance for the ongoing positional cloning of the CADASIL gene, these data help to refine the genetic mapping of CADASIL relative to familial hemiplegic migraine and hereditary paroxysmal cerebellar ataxia, conditions that we both mapped within the same chromosome 19 region.

Cerebral Arterial Diseases↗
PubMed1995

c-MYC gene abnormalities in high grade and centroblastic-centrocytic non-Hodgkins lymphoma.

Fifty nine cases of high grade and centroblastic-centrocytic (cc) Non Hodgkins Lymphoma (NHL) were investigated for mutations and gross gene rearrangements in the 5' region of the c-MYC gene. Mutations in this region, and the presence of hypermutated c-MYC genes, have been associated with poor prognostic groups. All cases showed normal c-MYC gene organisation on Southern blot analysis indicating absence of gross gene rearrangements. PCR amplification and restriction digest analysis of the exon 1/intron 1 region revealed point mutations in 7 cases. No evidence for hypermutation was found. Mutations were relatively more common in high grade NHL (6/39) than in cc-NHL (1/20). There was no correlation with disease status at presentation or relapse or the presence of extranodal disease. The cc-NHL case with a c-MYC mutation subsequently transformed to high grade disease. These data suggest that hypermutation of the c-MYC gene is a relatively rare event in cc-NHL and high grade NHL and does not contribute to the aetiology in the majority of cases. Mutation of c-MYC in cc-NHL may predict transformation to high grade disease.

Adolescent↗
PubMed1994

Marchiafava-Bignami disease with dementia: severe cerebral metabolic depression revealed by PET.

The Cerebral Metabolic Rate of Glucose (CMRGlu) was measured with positron emission tomography and 18F-FDG in a patient with Marchiafava-Bignami Disease (MBD)-related dementia. Despite MRI evidence of lesions essentially limited to the corpus callosum (CC), but consistent with the cognitive pattern of cortical dementia, the CMRGlu was markedly reduced in the frontal and temporo-parieto-occipital association cortices. Disruption of cortico-cortical networks crossing the CC presumably contributed to, but may not in and by itself explain, the severity of the clinical-metabolic findings in this patient. An additional role could be played by microscopic white matter lesions and/or neocortical neuronal loss, which have been occasionally observed in post-mortem studies of MBD patients.

Adult↗
PubMed1994

Relapse of acute lymphoblastic leukaemia 14 years after presentation: use of molecular techniques to confirm true re-emergence.

Late relapse after successful treatment of acute lymphoblastic leukaemia (ALL) in children is well-recognized but rare. It is often uncertain whether this represents a true relapse of the original disease or a second malignancy. We present the case of a patient who relapsed 14 years after the original diagnosis of childhood ALL in whom both the original leukaemic cells and those taken at relapse had an identical T cell receptor gamma (TCRG) gene rearrangement. This analysis confirms that this relapse is a true re-emergence of the patient's original disease. The term 'cure' should be used with caution in childhood ALL, even after long periods in continuous remission.

Base Sequence↗
PubMed1994

Brain metabolism after recurrent insulin induced hypoglycaemic episodes: a PET study.

Neuropsychological testing was carried out and the rate of oxygen metabolism in the brain was measured by PET in 15 highly selected patients with type 1 diabetes. The aim was to investigate the impact on the brain of hypoglycaemic comas resulting from insulin treatment. No significant difference was found between nine patients with a history of more than 10 hypoglycaemic comas and six others who denied any history of such events. These data suggest that intensified insulin treatment, although increasing the frequency of hypoglycaemic coma, may not always be harmful for the brain. This may be explained by the limited duration of hypoglycaemic coma induced by conventional insulin treatment.

Adult↗