On the physicochemical properties, setting chemical reaction, and in vitro bioactivity of aragonite–chitosan composite cement as a bone substitute

A chitosan gel additive modulates the initial vaterite dissolution–recrystallisation in injectable aragonite-based composite cement and promotes its in vitro bioactivity.

Self-reported mental health symptoms, quality of life and coping strategies in French health sciences students during the early stage of the COVID-19 pandemic: An online survey

Introduction

Health sciences students usually report high rates of mental health problems. The COVID-19 pandemic context may have serious psychological impacts in this at-risk population. We aimed to assess the self-reported mental health status, health-related quality of life and coping strategies of health sciences students during the early stage of the pandemic.

Method

An online 128-item questionnaire sent to 17,673 health sciences students from the Claude Bernard University Lyon 1 in April 2020 assessed: a) sociodemographic characteristics, b) conditions of lockdown, c) depressive (Beck Depression Inventory- Short Form, BDI-SF), anxiety (State-Trait Anxiety Inventory-A, STAI-A) and traumatic symptoms (Impact of Event Scale -Revised, IES-R), d) health-related quality of life (SF12) and e) coping strategies (Brief Coping Orientation to Problems Experienced, Brief COPE).

Results

The participation rate was 9.9% (n = 1,765). A total of 19.5% of participants reported an IES-R > 33, 11.6% depressive symptoms, 58.1% anxiety symptoms, and 4.4% suicidal ideation. Their mental health-related quality of life was significantly poorer than for physical health. Female gender, COVID-like symptoms, social isolation due to the lockdown, pandemic-related financial restraint and exams-related stress were significantly associated with poorer self-reported mental health conditions. Volunteering in the healthcare system was significantly associated with lower mental health scores. Coping strategies were mostly oriented toward avoidance and positive appraisal.

Conclusion

French health sciences students exhibited high levels of self-reported mental health problems and a poor mental health-related quality of life during the early stage of the COVID-19 pandemic. Specific risk factors related to the pandemic partly explain the observed prevalence.

Suicidal Ideation among French Adolescents: Separation Anxiety and Attachment according to Sex

The present study explored the links between the quality of adolescents' attachment to their mother and their father, separation anxiety and suicidal ideation. Self-report questionnaires were completed by French adolescents (n = 455; M_age = 15.78 years, SD = 1.61) to probe their attachment styles, separation anxiety (related to school phobia, a secure base, and family members), and suicidal ideation. Avoidantly attached adolescents displayed greater school phobia than securely attached adolescents. Female adolescents with an avoidant attachment to their father tended to report less fear related to family members than their secure counterparts. Male adolescents who were insecurely attached to their mother reported more separation anxiety than securely attached males. The structural models were significant for both boys and girls (R² = .38 and .44, p < .001) with good fit indices. Mediation analyses revealed that separation anxiety partially mediated the negative effect of attachment to mother (especially alienation) on suicidal ideation for both girls and boys, and partially mediated the negative effect of attachment to father (especially alienation) on suicidal ideation for boys. These results support an individuated conception of attachment patterns, with a differential influence of dyadic relationships, and could provide a better understanding of adolescents' suicidal ideation.

Gout and pseudo-gout-related crystals promote GLUT1-mediated glycolysis that governs NLRP3 and interleukin-1β activation on macrophages

OBJECTIVE

Macrophage activation by monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals mediates an interleukin (IL)-1β-dependent inflammation during gout and pseudo-gout flare, respectively. Since metabolic reprogramming of macrophages goes along with inflammatory responses dependently on stimuli and tissue environment, we aimed to decipher the role of glycolysis and oxidative phosphorylation in the IL-1β-induced microcrystal response.

METHODS

Briefly, an in vitro study (metabolomics and real-time extracellular flux analysis) on MSU and CPP crystal-stimulated macrophages was performed to demonstrate the metabolic phenotype of macrophages. Then, the role of aerobic glycolysis in IL-1β production was evaluated, as well in vitro as in vivo using ¹⁸F-fluorodeoxyglucose positron emission tomography imaging and glucose uptake assay, and molecular approach of glucose transporter 1 (GLUT1) inhibition.

RESULTS

We observed that MSU and CPP crystals led to a metabolic rewiring toward the aerobic glycolysis pathway explained by an increase in GLUT1 plasma membrane expression and glucose uptake on macrophages. Also, neutrophils isolated from human synovial fluid during gout flare expressed GLUT1 at their plasma membrane more frequently than neutrophils isolated from bloodstream. Both glucose deprivation and treatment with either 2-deoxyglucose or GLUT1 inhibitor suppressed crystal-induced NLRP3 activation and IL-1β production, and microcrystal inflammation in vivo.

CONCLUSION

In conclusion, we demonstrated that GLUT1-mediated glucose uptake is instrumental during the inflammatory IL-1β response induced by MSU and CPP crystals. These findings open new therapeutic paths to modulate crystal-related inflammation.

Psychiatric and physical outcomes of long-term use of lithium in older adults with bipolar disorder and major depressive disorder: A cross-sectional multicenter study

OBJECTIVE

Although lithium is widely used in current practice to treat bipolar disorder (BD) and treatment-resistant major depressive disorder (MDD) among older adults, little is known about its efficacy and tolerability in this population, which is generally excluded from randomized clinical trials. The objective of this study was to evaluate the efficacy and tolerability of long-term use of lithium among older adults with BD and MDD.

METHOD

Data from the Cohort of individuals with Schizophrenia and mood disorders Aged 55 years or more (CSA) were used. Two groups of patients with BD and MDD were compared: those who were currently receiving lithium versus those who were not. The effects of lithium on psychiatric (i.e., depressive symptoms severity, perceived clinical severity, rates of psychiatric admissions in the past-year), geriatric (overall and cognitive functioning) and physical outcomes (i.e., rates of non-psychiatric medical comorbidities and general hospital admissions in the past-year) were evaluated. All analyses were adjusted for age, sex, duration of disorder, diagnosis, smoking status, alcohol use, and use of antipsychotics, antiepileptics or antidepressants.

RESULTS

Among the 281 older participants with BD or MDD, 15.7% were taking lithium for a mean duration of 12.5(SD = 11.6) years. Lithium use was associated with lower intensity of depressive symptoms, reduced perceived clinical global severity and lower benzodiazepine use (all p < 0.05), without being linked to greater rates of medical comorbidities, except for hypothyroidism.

LIMITATIONS

Data were cross-sectional and data on lifetime history of psychotropic medications was not assessed.

CONCLUSION

Our results suggest that long-term lithium use may be efficient and relatively well-tolerated in older adults with BD or treatment-resistant MDD.

[Anemia, a new severity factor in young infants with acute viral bronchiolitis?]

INTRODUCTION

The role of anemia is raised as a risk of low respiratory infection of the child, but there are no data on anemia as a severity factor in acute viral bronchiolitis (AVB) in infants.

METHODS

All infants less than 16 weeks old admitted to Montpellier University Hospital from 2015/10/01 to 2016/04/01 for AVB were included in a retrospective observational study. The primary objective was to determine whether the hemoglobin (Hb) concentration on admission was an independent factor of clinical severity, judged by the modified Wood's clinical asthma score (m-WCAS). The secondary objective was to assess the impact of Hb level on the characteristics of hospitalization, including the type and duration of respiratory support.

RESULTS

The m-WCAS was used at least once during hospitalization in 180 out of 220 patients (82%), making it possible to distinguish patients with mild AVB (maximum m-WCAS<2, n=81) from patients with severe AVB (maximum m-WCAS>2, n=99). A logistic regression model indicated that the Hb concentration, for every 1g/dL decrement, was an independent factor of AVB severity (OR 1.16 [1.03-1.29], P=0.026). A level under 10g/dL on admission was associated with a higher use of continuous positive airway pressure (P<0.001), as well as a longer duration of respiratory support (P=0.01).

CONCLUSION

This study suggested that anemia may influence the clinical expression of AVB in young infants.

Where do human schistosomes come from? An evolutionary approach

Schistosomiases affect between 200 and 400 million people, mainly in the tropical and poorly developed zones of the globe. They are often considered as the 'second' disease of mankind, just after malaria. One important question regarding human parasites is: are they the descendants of parasites that used to infect our primate ancestors and have had an evolution parallel to that of the human lineage, or are they the result of lateral transfers of parasites that evolved in different hosts? Recently, knowledge of the biology of schistosomes has dramatically increased, and answers to this and other questions are beginning to emerge.

A comparative physico-chemical study of chlorapatite and hydroxyapatite: from powders to plasma sprayed thin coatings

Due to their bioactivity and osteoconductivity, hydroxyapatite (HA) plasma sprayed coatings have been widely developed for orthopedic uses. However, the thermodynamic instability of HA leads frequently to a mixture of phases which limit the functional durability of the coating. This study investigates the plasma spraying of chlorapatite (ClA) powder, known to melt without decomposition, onto pure titanium substrates using a low energy plasma spray system (LEPS). Pure ClA powder was prepared by a solid gas reaction at 950 °C and thermogravimetric analysis showed the good thermal stability of ClA powder in the range 30-1400 °C compared to that of the HA powder. Characterization of ClA coating showed that ClA had a very high crystalline ratio and no other crystalline phase was detected in the coating. HA and ClA coatings composition, microstructure and in vitro bioactivity potential were studied, compared and discussed. In vitro SBF test on HA and ClA coatings revealed the formation of a poorly crystalline apatite on the coating surface suggesting that we could expect a good osteoconductivity especially for the ClA coating prepared by the LEPS system.

Neonatal mortality and morbidity in preterm infants born from assisted reproductive technologies

AIM

Premature birth is frequent in infants conceived with assisted reproductive technologies (ART). We sought to determine whether neonatal outcome in ART preterm infants differs from that of spontaneously conceived (SC) preterm infants.

METHODS

Data were prospectively collected in infants born ≤ 32 weeks after ART or SC. We calculated a composite index of severe morbidity (based on occurrences of severe necrotizing enterocolitis, severe intraventricular haemorrhage, periventricular leukomalacia or bronchopulmonary dysplasia). Survival rate without severe morbidity was compared between the two groups.

RESULTS

Six hundred and twelve preterm infants were hospitalized in our tertiary care centre: 81 in ART group and 521 in SC group. In the ART group, twin pregnancy (69.1% vs. 15.9%, p < 0.001) and inborn delivery (98.8% vs. 90.0%, p < 0.01) were more frequent. Gestational age (29 vs. 28 weeks, p < 0.05) and birth weight (1100 vs. 1020 g, p < 0.001) were also higher. Survival without severe morbidity was significantly higher in ART infants (76.5% vs. 55.2%, p < 0.001), with the difference mainly observed in infants born ≤ 28 weeks (22.9% vs. 55.7%, p < 0.001).

CONCLUSION

Assisted reproductive technologies was not associated with adverse neonatal outcome. Differences in pregnancy and neonatal characteristics probably explain the increased survival without severe morbidity in ART infants.

Co-grinding significance for calcium carbonate-calcium phosphate mixed cement. Part I: effect of particle size and mixing on solid phase reactivity

In part I of this study we aim to evaluate and control the characteristics of the powders constituting the solid phase of a vaterite CaCO(3)-dicalcium phosphate dihydrate cement using a co-grinding process and to determine their impact on cement setting ability. An original methodology involving complementary analytical techniques was implemented to thoroughly investigate the grinding mechanism of separated or mixed reactive powders and the effects on solid phase reactivity. We showed that the association of both reactive powders during co-grinding improves the efficiency of this process in terms of the particle size decrease, thus making co-grinding adaptable to industrial development of the cement. For the first time the usefulness of horizontal attenuated total reflection Fourier transform infrared spectroscopy to follow the chemical setting reaction at 37°C in real time has been demonstrated. We point out the antagonist effects that co-grinding can have on cement setting: the setting time is halved; however, progress of the chemical reaction involving dissolution-reprecipitation is delayed by 30 min, probably due to the increased contact area between the reactive powders, limiting their hydration. More generally, we can take advantage of the co-grinding process to control powder mixing, size and reactivity and this original analytical methodology to better understand its effect on the phenomena involved during powder processing and cement setting, which is decisive for the development of multi-component cements.

[Drug compliance and health locus of control in schizophrenia]

Schizophrenia is a frequent disorder since it affects about 1% of the general population. Drug compliance, that is to say patients' adherence to their treatment, remains rather poor concerning this disease with, on an average, one patient out of two not complying with his/her medication. Among the factors influencing drug compliance, we focused on patients' beliefs in terms of health control, a concept known as health locus of control. This is a concept that originated from social psychology and derived from the Rotters' original concept of locus of control: it corresponds to the type of connexion established by an individual between subsequent events in the history of his/her disease and internal (personal abilities) or external factors (chance, powerful others). Nowadays, the tridimensional structure of this concept is commonly admitted as being in three dimensions: internality, chance externality and powerful others externality, the latter group being divided between doctors and others. We have assumed that there is a correlation between the degree of drug compliance and the internal and/or doctors' external health locus of control. For this purpose, we have determined the quality of drug compliance by using the Medical Adherence Rating Scale (MARS) and the type of health locus of control by using the Multidimensional Health Locus of Control (MHLC) scale among 65 schizophrenic patients. We have also considered it was important to evaluate patients' insight by using the Amador's scale (Scale of Unawareness of Mental Disorder) because many researchers have established a strong correlation between insight and drug compliance in schizophrenia. Associations between the four dimensions of health locus of control ("internal", "chance external", "others external" and "doctors' external") and drug compliance were assessed by estimating Spearman's rank correlation coefficient (r) and its degree of significance (p). These associations were judged significant at an alpha threshold of 5%, which corresponded to a level of p inferior to 0.05. Our results tend to confirm a statistically significant positive correlation between internal (r=0.25; p=0.043) and/or doctors' external (r=0.27; p=0.027) health locus of control and drug compliance. Conversely, there is no correlation between chance external or others' external health locus of control and drug compliance (p>0.05). This means that the more patients believe that their schizophrenia can be controlled by themselves and/or by doctors, the more they follow their prescriptions. Furthermore, the link between health locus of control and drug compliance appears to be confused by two dimensions of insight, namely awareness of the response to the treatment and perceived need for treatment. An application of these results is that, in the case of patients whose health locus of control is chance or others' external, it can be beneficial to attempt to change their beliefs in order to improve drug compliance. These results hold particular interest in the field of psycho-education and can be directly applied to cognitive therapy for beliefs among stabilized schizophrenic patients.

Amorphous calcium phosphates: synthesis, properties and uses in biomaterials

This review paper on amorphous calcium phosphates (ACPs) provides an update on several aspects of these compounds which have led to many studies and some controversy since the 1970s, particularly because of the lack of irrefutable proof of the occurrence of an ACP phase in mineralised tissues of vertebrates. The various synthesis routes of ACPs with different compositions are reported and the techniques used to characterise this phase are reviewed. We focus on the various physico-chemical properties of ACPs, especially the reactivity in aqueous media, which have been exploited to prepare bioactive bone substitutes, particularly in the form of coatings and cements for orthopaedic applications and composites for dental applications.

[Lymphoma of the pituitary stalk]

INTRODUCTION

Tumors of the pituitary stalk are rare and their diagnosis is sometimes difficult.

CASE REPORT

We report a case of a primary lymphoma of the pituitary stalk in a 78-year-old patient. To our knowledge, only seven similar cases have been previously published: prominent symptoms were headache, fatigue and diplopia; biologically, anterior pituitary low secretion or hyperprolactinemia were found in the majority of cases; regarding the imaging, only three patients presented an initial and isolated lesion of the stalk; histological evidence was obtained by a trans-sphenoidal biopsy in case of hypothalamic or pituitary associated lesion or by a trans-cranial biopsy in the event of an isolated lesion. As an alternative, a lumbar puncture could be performed; although less invasive, its diagnostic performance is lower.

CONCLUSION

Current treatment relies on chemotherapy with intravenous methotrexate associated with intrathecal methotrexate infusion if cerebrospinal showed abnormal cells. Unfortunately, the results remain poor with a median survival of 9 months.

Surface characteristics of nanocrystalline apatites: effect of mg surface enrichment on morphology, surface hydration species, and cationic environments

The incorporation of foreign ions, such as Mg2+, exhibiting a biological activity for bone regeneration is presently considered as a promising route for increasing the bioactivity of bone-engineering scaffolds. In this work, the morphology, structure, and surface hydration of biomimetic nanocrystalline apatites were investigated before and after surface exchange with such Mg2+ ions, by combining chemical alterations (ion exchange, H2O-D2O exchanges) and physical examinations (Fourier transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM)). HRTEM data suggested that the Mg2+/Ca2+ exchange process did not affect the morphology and surface topology of the apatite nanocrystals significantly, while a new phase, likely a hydrated calcium and/or magnesium phosphate, was formed in small amount for high Mg concentrations. Near-infrared (NIR) and medium-infrared (MIR) spectroscopies indicated that the samples enriched with Mg2+ were found to retain more water at their surface than the Mg-free sample, both at the level of H2O coordinated to cations and adsorbed in the form of multilayers. Additionally, the H-bonding network in defective subsurface layers was also noticeably modified, indicating that the Mg2+/Ca2+ exchange involved was not limited to the surface. This work is intended to widen the present knowledge on Mg-enriched calcium phosphate-based bioactive materials intended for bone repair applications.

Calcium carbonate–calcium phosphate mixed cement compositions for bone reconstruction

The feasibility of making calcium carbonate-calcium phosphate (CaCO(3)-CaP) mixed cements, comprising at least 40% (w/w) CaCO(3) in the dry powder ingredients, has been demonstrated. Several original cement compositions were obtained by mixing metastable crystalline CaCO(3) phases with metastable amorphous or crystalline CaP powders in aqueous medium. The cements set within at most 1 h at 37 degrees C in atmosphere saturated with water. The hardened cement is microporous and exhibits weak compressive strength. The setting reaction appeared to be essentially related to the formation of a highly carbonated nanocrystalline apatite phase by reaction of the metastable CaP phase with part or almost all of the metastable CaCO(3) phase. The recrystallization of metastable CaP varieties led to a final cement consisting of a highly carbonated poorly crystalline apatite analogous to bone mineral associated with various amounts of vaterite and/or aragonite. The presence of controlled amounts of CaCO(3) with a higher solubility than that of the apatite formed in the well-developed CaP cements might be of interest to increase resorption rates in biomedical cement and favors its replacement by bone tissue. Cytotoxicity testing revealed excellent cytocompatibility of CaCO(3)-CaP mixed cement compositions.

Exploration de l’hypotension de liquide cérébro-spinal à l’étage rachidien en IRM

We propose studying signs of cervicothoracic CSF hypotension by MRI. Axial T1-weighted GRE sequence with and without saturation bands positioned above and below the selected image plane, MR venography and MR Angiography with contrast administration are helpful to confirm the venous nature of the epidural thickening and to make the differential diagnosis with infectious or neoplastic epiduritis.

[Rhabdomyolysis induced by fenofibrate monotherapy]

INTRODUCTION

Rhabdomyolysis with fibrate have been reported when fibrate are associated with statin or during renal insufficiency or hypothyroidism.

CASE RECORD

We describe one patient with diabetes mellitus treated by fenofibrate monotherapy since several years; 48 h after gliclazide therapy was introduced, rhabdomyolysis occurred.

DISCUSSION

Responsibilities of deshydratation and / or drug interaction with gliclazide. are discussed.

Preparation, physical–chemical characterisation and cytocompatibility of calcium carbonate cements

The feasibility of calcium carbonate cements involving the recrystallisation of metastable calcium carbonate varieties has been demonstrated. Calcium carbonate cement compositions presented in this paper can be prepared straightforwardly by simply mixing water (liquid phase) with two calcium carbonate phases (solid phase) which can be easily obtained by precipitation. An original cement composition was obtained by mixing amorphous calcium carbonate and vaterite with an aqueous medium. The cement set and hardened within 2h at 37 degrees C in an atmosphere saturated with water and the final composition of the cement consisted mostly of aragonite. The hardened cement was microporous and showed poor mechanical properties. Cytotoxicity tests revealed excellent cytocompatibility of calcium carbonate cement compositions. Calcium carbonates with a higher solubility than the apatite formed for most of the marketed calcium phosphate cements might be of interest to increase biomedical cement resorption rates and to favour its replacement by bone tissue.

Ion exchanges in apatites for biomedical application

The modification of the composition of apatite materials can be made by several processes corresponding to ion exchange reactions which can conveniently be adapted to current coatings and ceramics and are an alternative to setting up of new synthesis methods. In addition to high temperature thermal treatments, which can partly or almost totally replace the monovalent OH- anion of stoichiometric hydroxyapatite by any halogen ion or carbonate, aqueous processes corresponding to dissolution-reprecipitation reactions have also been proposed and used. However, the most interesting possibilities are provided by aqueous ion exchange reactions involving nanocrystalline apatites. These apatites are characterised by the existence on the crystal surface of a hydrated layer of loosely bound mineral ions which can be easily exchanged in solution. This layer offers a possibility to trap mineral ions and possibly active molecules which can modify the apatite properties. Such processes are involved in mineralised tissues and could be used in biomaterials for the release of active mineral species.

[Actinic keratosis seborrheic wart and nevus: three distinct cutaneous eyelid skin lesions in a single patient]

A 67-year-old woman had three different tumors of the eyelids. The most prominent one was a nevus of the free margin of the inferior left eyelid. The nevus was followed for 18 months without change while two epidermal papillomatous tumors grew and were surgically removed. Histopathology disclosed that one tumor was a seborrheic keratosis and the other was a pre-epitheliomatous keratosis. Histologic evaluation of the margins showed that surgical removal was complete. A regular examination of the scars was recommended to the patient.

Crystal growth and structure of a new hormonal derived compound

The 17alpha-acetoxy-6-hydroxymethyl-3,20-dioxo-19-nor-pregna-4,6-diene (C(23)H(30)O(5)), a new hormonal derived compound presenting a potential therapeutic interest for a pharmaceutical formulation, raises a problem as it precipitates spontaneously when in contact with an aqueous solution. The solubilization of this potential pharmaceutical drug was investigated to control and/or prevent crystal formation in the presence of water. The solubility limit of this potential drug, either in Cremophor(R) EL or RH40, was determined to be 2.6% (w/w). In addition, crystal growth of this compound solubilized in Cremophor(R) and in contact with aqueous environment was undertaken to improve crystal quality and size and subsequently to determine its three dimensional structure. We used a system that allows slow single crystal growth at room temperature. The crystallization system that we set-up comprised an interface between two solutions: one containing the compound solubilized either in Cremophor(R) RH40 or EL and the other containing water and glycine. The crystal structure was established by single crystal X-ray diffraction analysis. The structure refinement study revealed the presence of one water molecule with strong intermolecular hydrogen bonding leading to an atomic arrangement corresponding to an infinite chain in the [001] direction.

Adsorption of proteins and calcium phosphate materials bioactivity

The behaviour of calcium phosphate (CaP) based biomaterials in biological environments determines how they can be used in vivo. The prime requirement for CaP materials to be bioactive and bond to living bone is the formation of a bone-like apatite layer on their surface. This phenomenon can be reproduced in vitro using simulated body fluid (SBF): a protein-free solution with ion concentrations similar to those of human blood plasma. Although proteins are unanimously considered as important actors in CaP material bioactivity and biomineralization processes, a certain confusion exists about their role as promotors or inhibitors of mineral crystal formation or both. The adsorption of proteins on the mineral surface can alter the nucleation rate and lead to antagonistic effects depending on the concentration of the adsorbed proteins. The ambiguity of this general effect is illustrated by the action of albumin on calcium phosphate crystallization on type I collagen and several other examples found in the literature.

The origin of cultivated Coffea arabica L. varieties revealed by AFLP and SSR markers

Molecular markers were used to assess polymorphism between and within the genetic bases of coffee (i.e. Typica and Bourbon) spread from Yemen since the early 18th century that have given rise to most arabica cultivars grown world-wide. Eleven Coffea arabica accessions derived from the disseminated bases were evaluated by amplified fragment length polymorphism (AFLP) using 37 primer combinations and simple-sequence repeats (SSRs) produced by six microsatellites. Four cultivars growing in Yemen and 11 subspontaneous accessions collected in the primary centre of diversity of the species were included in the study in order to define their relationship with the accessions derived from the genetic bases of cultivars. One hundred and seven AFLP markers were used to calculate genetic distances and construct a dendrogram. The accessions derived from the disseminated bases were grouped separately, according to their genetic origin, and were distinguished from the subspontaneous accessions. The Yemen cultivars were classified with the Typica-derived accessions. Except for one AFLP marker, all AFLP and SSR markers present in the cultivated accessions were also detected in the subspontaneous accessions. Polymorphism among the subspontaneous accessions was much higher than among the cultivated accessions. It was very low within the genetic bases, confirming the historical documentation on their dissemination. The results enabled a discussion of the genetic diversity reductions that successively occurred during the dissemination of C. arabica from its primary centre of diversity.

Needle in a haystack: involvement of the copepod PARACARTIA grani in the life-cycle of the oyster pathogen Marteilia refringens

Marteilia refringens is a major pathogen of the European flat oyster, Ostrea edulis Linnaeus. Since its description, the life-cycle of this protozoan parasite has eluded discovery. Attempts to infect oysters experimentally have been unsuccessful and led to the hypothesis of a complex life-cycle involving several hosts. Knowledge of this life-cycle is of central importance in order to manage oyster disease. However, the exploration of M. refringens life-cycle has been previously limited by the detection tools available and the tremendous number of species to be screened in enzootic areas. In this study, these two restrictions were circumvented by the use of both molecular detection tools and a mesocosm with low biodiversity. Screening of the entire fauna of the pond for M. refringens DNA was systematically undertaken using PCR. Here, we show that the copepod Paracartia (Acartia) grani is a host of M. refringens. Not only was DNA of M. refringens consistently detected in P. grani but also the presence of the parasite in the ovarian tissues was demonstrated using in situ hybridization. Finally, successful experimental transmissions provided evidence that P. grani can be infected from infected flat oysters.

Do parasites live in extreme environments? Constructing hostile niches and living in them

We develop the hypothesis that parasites do not invade extreme environments, i.e. hostile hosts, but rather 'create' them. We argue that parasites may have driven the evolution of the constitutive and adaptive immune system. This leads to several implications. First, parasites respond to 'genes to kill' by 'genes to survive' and this triggers an indefinite selection of measures and counter-measures. Second, these coevolutionary arms races may lead to local adaptation, in which parasite populations perform better on local hosts. Third, the evolution of the immune system, whose responses are predictable, may allow parasites to specialize, to evade and even to manipulate. Finally we show that the correlations between the increase in the antibody repertoire, the expansion of MHC loci and parasite pressures support our hypothesis that both host complexity and parasite pressures can be invoked to explain the diversity of antibodies, T-receptors and MHC molecules.