Hypothèse : le modèle du lieu de rencontre pour la maladie des prions

Prions are responsible for spongiform diseases such as scrapie and bovine spongiform encephalopathy. It is now generally accepted that the disease mechanism involves the conversion from the normal form, PrP^C, to the pathogenic form, PrP^Sc, and that this isoform is infectious. In the case of scrapie, 15 different forms of the disease have been described and some of these different phenotypes can be conferred by infectious prions that are themselves encoded by normal genes. We propose here that a prion with an altered structure has a correspondingly altered preference for lipids; this altered preference creates a proteolipid domain containing different lipids and other factors such as chaperonins and enzymes responsible for post-translational modifications. Normal prions associated with this abnormal domain adopt the conformation dictated by its lipidic composition (and by the other factors present) and so acquire the lipidic preference of the original pathogenic prions. These transformed prions could then create new proteolipid domains. This process may be considered as semi-conservative replication in which prion and lipids are analogous to the Watson and Crick strands and the proteolipid domain to the double helix itself.     

Analyse des courbes de survie de nématodes phytoparasites selon le modèle de Teissier

Four survival curves of plant parasitic nematodes are analysed with Teissier's model. The model is based upon the assumption of an exponential decrease with time of the life expectancy, E(t) = E₀ exp(−αt), with E₀ the life expectancy at time 0 and α a decay coefficient. By integrating this formula we obtain an expression for the number of survivors at time t, S(t), as a function of the time, t, and S₀, the number of individuals at time 0, and the parameters E₀ and α: S(t) = S₀exp[αt −(exp(αt) −1)/αE₀. S₀ is a scaling parameter, related to the initial number of individuals in the population, thus the form of the curve depends only on the parameters E₀ and α, which are readily understandable in a biological model. These parameters E₀ and α are estimated by fitting the model to experimental data using a non-linear regression based on a least squares procedure. The results show a highly significant fit of the model to the data indicating the ability of the model to describe the plant parasitic nematodes survival curve. Results are discussed and the hypothesis of Teissier is compared with other related hypotheses.     

Le complexe des ennemis naturels des Aphides du Pêcher dans la moyenne vallée du Rhone

Résumé Dans le cadre d’une recherche écologique sur les Aphides du Pêcher soutenue par le Comité Lutte Biologique de la DGRST, en vue d’explorer les modalités d’application à cette culture du concept de la Lutte intégrée, une première étude a présenté l’analyse de la dynamique des populations des pucerons les plus nuisibles et montré l’importance de certains ennemis naturels (Leclant & Remaudière, 1970). L’objet du présent article est de dégager les principaux éléments du complexe biologique intervenant dans la régulation des populations et de préciser les rapports existant entre quelques-uns d’entre eux. Les recherches ont été accomplies de 1968 à 1970 dans plusieurs vergers vergers de Pêcher de la région de Valence (Dr?me) et plus particulièrement au domaine de Gotheron (Saint-Marcel-lès-Valence).

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Summary Samples consisting of about 20 infested twigs of 6 to 8 leaves have been collected periodically and kept alive during a period of 10 days. At this time, most of the predators have achieved their growth and the parasites have mummified their hosts; then they are isolated until hatching. Syrphids play a predominant role in the regulation of the aphid population.Epistrophe balteata andSyrphus vitripennis are the most frequent of the six species obtained. 35% of the Syrphids is destroyed by parasites; however their action at the highth of the orchards is not affected because their number appears to depend on the immigrants. Spiders have a significative impact at the end of the winter when fundatrix larvae hatch. Coccinellids (Col.), Chamaemyiids (Dipt.) and other predators and parasites are not very important factors of regulation. Aphids parasitized by fungi (Entomophthora aphidis andplanchoniana) are found more or less frequently according to the climatic conditions of the year. An epizootic situation occurred in June 1968 which determined a quicker decline of the populations ofMyzus persicae. Cultural practices affect the relative importance of the various natural enemies: in orchards with high weeds the action of Coccinellids may be preponderant.

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Communication présentée à la 2^e réunion du groupe de travail PBI ?Biological Control of Aphids?, Paris, 16–18 septembre 1970.     

Un cas de leishmaniose féline disséminée dans le sud de la France

We report a case of disseminated feline leishmaniasis in a FIV-seropositive 14-year-old male cat (Felis catus) living in the Alpes-Maritimes (south of France). The cat presented with erythematous ulcerated papules on the head and withers, and with an ulcerated proliferative lesion on the left pinnae. The condition was diagnosed, along with a squamous cell carcinoma of the pinnae, after histopathological examination of the cutaneous lesions. Total remission of the cutaneous lesions was obtained after oral administration of 100 mg of allopurinol once a day for four months. Necropsic samples revealed that the parasite was still present in the organism after six months of treatment. This case discusses of the cat sensibility to the leishmaniasis pathology and of his potential ability of being a reservoir host.     

Théorie de la cible: Un modèle markovien pour l'évolution génétique d'une mutation latente

Résumé Chez les individus d'une mÊme espèce, un caractère héréditaire est supposé associé à une cible constituée de plusieurs particules, indépendantes entre elles, et susceptibles de se présenter sous diverses formes. Le phénotype dépend de la répartition de ces différentes formes dans la cible. A la division cellulaire correspond un certain mode de division de la cible, permettant la transmission des particules d'une génération à l'autre, et induisant des règles d'apparition des divers phénotypes. Le problème de la détermination du nombre des particules constituant la cible est examiné ici, et une solution est exposée. Cette solution tient compte à la fois des aspects mathématiques (étude théorique du processus), expérimentaux (observation de l'évolution génétique d'une mutation provoquée par un agent mutagène) et numériques (une technique d'ajustements numériques complète avantageusement l'étude théorique).

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Summary A hereditary character in individuals of the same species is envisaged as belonging to a target made up of several mutually independent particles, which can be manifested in diverse forms. The phenotype depends on the distribution of the different forms in the target. Cell fission then corresponds to a certain mode of division of the target, permitting particle transmission between generations. In this way the rules for appearance of various phenotypes are determined. The problem of determining the number of particles constituting a target is examined and a solution is given. This solution takes into account simultaneously three factors: a) mathematical (theoretical study of the process), b) experimental (observation of the genetic evolution of an artificially induced mutation) and c) numerical (a numerical fitting technique complements the theoretical study).

     

Place de l’embolisation percutanée de la varicocèle dans le traitement de l’infertilité

Objectives

To describe percutaneous embolization of varicocele and to evaluate the effect on fertility disorders.

Materials and methods

One hundred nineteen patients, aged 11 to 48 years, underwent percutaneous embolization for varicocele indicated by a fertility disorder in 23% of cases. Correction of the varicocele and resolution of associated pain, improvement of testicular trophicity and the effect on fertility were studied and a review of the literature was performed.

Results

Percutaneous embolization was performed using neuroleptanalgesia on an outpatient basis. The technique combined venous sclerotherapy and placement of coils in the gonadal vein. The technique was successful in 95% of cases and one complication was observed. At 3 months, the varicocele and related pain had resolved in 98% of treated patients. According to previous reports in the literature, the relations between varicocele and fertility disorders are still unclear, but improvement of fertility (semen quality and conception rates) after varicocele repair has been established.

Conclusion

Although the consequences of varicocele on fertility have not been fully elucidated, treatment of varicocele appears to be beneficial. Percutaneous embolization of varicocele is a safe and effective alternative to surgery. This technique, based on a urological and radiological consensus, is the first-line treatment for varicocele in our institution.