Potential evidence of parasite avoidance in an avian malarial vector

Epidemiological studies of malaria or other vector-transmitted diseases often consider vectors as passive actors in the complex life cycle of the parasites, assuming that vector populations are homogeneous and vertebrate hosts are equally susceptible to being infected during their lifetime. However, some studies based on both human and rodent malaria systems found that mosquito vectors preferentially selected infected vertebrate hosts. This subject has been scarcely investigated in avian malaria models and even less in wild animals using natural host-parasite associations. We investigated whether the malaria infection status of wild great tits, Parus major, played a role in host selection by the mosquito vector Culex pipiens. Pairs of infected and uninfected birds were tested in a dual-choice olfactometer to assess their attractiveness to the mosquitoes. Plasmodium-infected birds attracted significantly fewer mosquitoes than the uninfected ones, which suggest that avian malaria parasites alter hosts' odours involved in vector orientation. Reaction time of the mosquitoes, that is, the time taken to select a host, and activation of mosquitoes, defined as the proportion of individuals flying towards one of the hosts, were not affected by the bird's infection status. The importance of these behavioural responses for the vector is discussed in light of recent advances in related or similar model systems.

Efficacy of iclaprim against wild-type and thymidine kinase-deficient methicillin-resistant Staphylococcus aureus isolates in an in vitro fibrin clot model.

Iclaprim is a novel diaminopyrimidine antibiotic that is active against methicillin-resistant Staphylococcus aureus (MRSA). However, it is known that the activity of diaminopyrimidines against S. aureus is antagonized by thymidine through uptake and conversion to thymidylate by thymidine kinase. Unlike with humans, for whom thymidine levels are low, thymidine levels in rodents are high, thus precluding the accurate evaluation of iclaprim efficacy in animal models. We have studied the bactericidal activity of iclaprim against an isogenic pair of MRSA isolates, the wild-type parent AW6 and its thymidine kinase-deficient mutant AH1252, in an in vitro fibrin clot model. Clots, which were aimed at mimicking vegetation structure, were made from human or rat plasma containing either the parent AW6 or the mutant AH1252, and they were exposed to homologous serum supplemented with iclaprim (3.5 microg/ml), trimethoprim-sulfamethoxazole (TMP-SMX; 8/40 microg/ml), vancomycin (40 microg/ml), or saline, each of which was added one time for 48 h. In rat clots, iclaprim and TMP-SMX were bacteriostatic against the parent, AW6. In contrast, they were bactericidal (> or = 3 log10 CFU/clot killing of the original inoculum) against the mutant AH1252. Vancomycin was the most active drug against AW6 (P < 0.05), but it showed an activity similar those of iclaprim and TMP-SMX against AH1252. In human clots, iclaprim was bactericidal against both AW6 and AH1252 strains and was as effective as TMP-SMX and vancomycin (P > 0.05). Future studies of animals using simulated human kinetics of iclaprim and thymidine kinase-deficient MRSA, which eliminate the thymidine-induced confounding effect, are warranted to support the use of iclaprim in the treatment of severe MRSA infections in humans.

A constitutively active mutant of the alpha 1B-adrenergic receptor can cause greater agonist-dependent down-regulation of the G-proteins G9 alpha and G11 alpha than the wild-type receptor.

Rat 1 fibroblasts transfected to express either the wild-type hamster alpha 1B-adrenergic receptor or a constitutively active mutant (CAM) form of this receptor resulting from the alteration of amino acid residues 288-294 to encode the equivalent region of the human beta 2-adrenergic receptor were examined. The basal level of inositol phosphate generation in cells expressing the CAM alpha 1B-adrenergic receptor was greater than for the wild-type receptor, The addition of maximally effective concentrations of phenylephrine or noradrenaline resulted in substantially greater levels of inositol phosphate generation by the CAM alpha 1B-adrenergic receptor, although this receptor was expressed at lower steady-state levels than the wild-type receptor. The potency of both phenylephrine and noradrenaline to stimulate inositol phosphate production was approx. 200-fold greater at the CAM alpha 1B-adrenergic receptor than at the wild-type receptor. In contrast, endothelin 1, acting at the endogenously expressed endothelin ETA, receptor, displayed similar potency and maximal effects in the two cell lines. The sustained presence of phenylephrine resulted in down-regulation of the alpha subunits of the phosphoinositidase C-linked, pertussis toxin-insensitive, G-proteins G9 and G11 in cells expressing either the wild-type or the CAM alpha 1B-adrenergic receptor. The degree of down-regulation achieved was substantially greater in cells expressing the CAM alpha 1B-adrenergic receptor at all concentrations of the agonist. However, in this assay phenylephrine displayed only a slightly greater potency at the CAM alpha 1B-adrenergic receptor than at the wild-type receptor. There were no detectable differences in the basal rate of G9 alpha/G11 alpha degradation between cells expressing the wild-type or the CAMalpha 1B-adrenergic receptor. In both cell lines the addition of phenylephrine substantially increased the rate of degradation of these G-proteins, with a greater effect at the CAM alpha 1B-adrenergic receptor. The enhanced capacity of agonist both to stimulate second-messenger production at the CAM alpha 1B-adrenergic receptor and to regulate cellular levels of its associated G-proteins by stimulating their rate of degradation is indicative of an enhanced stoichiometry of coupling of this form of the receptor to G9 and G11.

Light-induced retinal degeneration correlates with changes in iron metabolism gene expression, ferritin level, and aging.

PURPOSE: Retinal degeneration is associated with iron accumulation in several rodent models in which iron-regulating proteins are impaired. Oxidative stress is catalyzed by unbound iron. METHODS: The role of the heavy chain of ferritin, which sequesters iron, in regulating the thickness of the photoreceptor nuclear layer in the 4- and 16-month-old wild-type H ferritin (HFt(+/+)) and heterozygous H ferritin (HFt(+/-)) mice was investigated, before and 12 days after exposure to 13,000-lux light for 24 hours. The regulation of gene expression of the various proteins involved in iron homeostasis, such as transferrin, transferrin receptor, hephaestin, ferroportin, iron regulatory proteins 1 and 2, hepcidin, ceruloplasmin, and heme-oxygenase 1, was analyzed by quantitative (q)RT-PCR during exposure (2, 12, and 24 hours) and 24 hours after 1 day of exposure in the 4-month-old HFt(+/+) and HFt(+/-) mouse retinas. RESULTS: Retinal degeneration in the 4-month-old HFt(+/-) mice was more extensive than in the HFt(+/+) mice. Yet, it was more extensive in both of the 16-month-old mouse groups, revealing the combined effect of age and excessive light. Injury caused by excessive light modified the temporal gene expression of iron-regulating proteins similarly in the HFt(+/-) and HFt(+/+) mice. CONCLUSIONS: Loss of one allele of H ferritin appears to increase light-induced degeneration. This study highlighted that oxidative stress related to light-induced injury is associated with major changes in gene expression of iron metabolism proteins.

A metapopulation model for the introgression from genetically modified plants into their wild relatives

Most models on introgression from genetically modified (GM) plants have focused on small spatial scales, modelling gene flow from a field containing GM plants into a single adjacent population of a wild relative. Here, we present a model to study the effect of introgression from multiple plantations into the whole metapopulation of the wild relative. The most important result of the model is that even very low levels of introgression and selection can lead to a high probability that the transgene goes to fixation in the metapopulation. Furthermore, the overall frequency of the transgene in the metapopulation, after a certain number of generations of introgression, depends on the population dynamics. If there is a high rate of migration or a high rate of population turnover, the overall transgene frequency is much higher than with lower rates. However, under an island model of population structure, this increased frequency has only a very small effect on the probability of fixation of the transgene. Considering these results, studies on the potential ecological risks of introgression from GM plants should look not only at the rate of introgression and selection acting on the transgene, but also at the metapopulation dynamics of the wild relative.

Morphological and physiological species-dependent characteristics of the rodent Grueneberg ganglion.

In the mouse, the Grueneberg ganglion (GG) is an olfactory subsystem implicated both in chemo- and thermo-sensing. It is specifically involved in the recognition of volatile danger cues such as alarm pheromones and structurally-related predator scents. No evidence for these GG sensory functions has been reported yet in other rodent species. In this study, we used a combination of histological and physiological techniques to verify the presence of a GG and investigate its function in the rat, hamster, and gerbil comparing with the mouse. By scanning electron microscopy (SEM) and transmitted electron microscopy (TEM), we found isolated or groups of large GG cells of different shapes that in spite of their gross anatomical similarities, display important structural differences between species. We performed a comparative and morphological study focusing on the conserved olfactory features of these cells. We found fine ciliary processes, mostly wrapped in ensheating glial cells, in variable number of clusters deeply invaginated in the neuronal soma. Interestingly, the glial wrapping, the amount of microtubules and their distribution in the ciliary processes were different between rodents. Using immunohistochemistry, we were able to detect the expression of known GG proteins, such as the membrane guanylyl cyclase G and the cyclic nucleotide-gated channel A3. Both the expression and the subcellular localization of these signaling proteins were found to be species-dependent. Calcium imaging experiments on acute tissue slice preparations from rodent GG demonstrated that the chemo- and thermo-evoked neuronal responses were different between species. Thus, GG neurons from mice and rats displayed both chemo- and thermo-sensing, while hamsters and gerbils showed profound differences in their sensitivities. We suggest that the integrative comparison between the structural morphologies, the sensory properties, and the ethological contexts supports species-dependent GG features prompted by the environmental pressure.

Neuron-to-neuron wild-type Tau protein transfer through a trans-synaptic mechanism: relevance to sporadic tauopathies.

BACKGROUND: In sporadic Tauopathies, neurofibrillary degeneration (NFD) is characterised by the intraneuronal aggregation of wild-type Tau proteins. In the human brain, the hierarchical pathways of this neurodegeneration have been well established in Alzheimer's disease (AD) and other sporadic tauopathies such as argyrophilic grain disorder and progressive supranuclear palsy but the molecular and cellular mechanisms supporting this progression are yet not known. These pathways appear to be associated with the intercellular transmission of pathology, as recently suggested in Tau transgenic mice. However, these conclusions remain ill-defined due to a lack of toxicity data and difficulties associated with the use of mutant Tau. RESULTS: Using a lentiviral-mediated rat model of hippocampal NFD, we demonstrated that wild-type human Tau protein is axonally transferred from ventral hippocampus neurons to connected secondary neurons even at distant brain areas such as olfactory and limbic systems indicating a trans-synaptic protein transfer. Using different immunological tools to follow phospho-Tau species, it was clear that Tau pathology generated using mutated Tau remains near the IS whereas it spreads much further using the wild-type one. CONCLUSION: Taken together, these results support a novel mechanism for Tau protein transfer compared to previous reports based on transgenic models with mutant cDNA. It also demonstrates that mutant Tau proteins are not suitable for the development of experimental models helpful to validate therapeutic intervention interfering with Tau spreading.

Heterozygosity-fitness correlations among wild populations of European tree frogs (Hyla arborea) detect fixation load.

Quantifying the impacts of inbreeding and genetic drift on fitness traits in fragmented populations is becoming a major goal in conservation biology. Such impacts occur at different levels and involve different sets of loci. Genetic drift randomly fixes slightly deleterious alleles leading to different fixation load among populations. By contrast, inbreeding depression arises from highly deleterious alleles in segregation within a population and creates variation among individuals. A popular approach is to measure correlations between molecular variation and phenotypic performances. This approach has been mainly used at the individual level to detect inbreeding depression within populations and sometimes at the population level but without consideration about the genetic processes measured. For the first time, we used in this study a molecular approach considering both the interpopulation and intrapopulation level to discriminate the relative importance of inbreeding depression vs. fixation load in isolated and non-fragmented populations of European tree frog (Hyla arborea), complemented with interpopulational crosses. We demonstrated that the positive correlations observed between genetic heterozygosity and larval performances on merged data were mainly caused by co-variations in genetic diversity and fixation load among populations rather than by inbreeding depression and segregating deleterious alleles within populations. Such a method is highly relevant in a conservation perspective because, depending on how populations lose fitness (inbreeding vs. fixation load), specific management actions may be designed to improve the persistence of populations.

Experimental evidence that adult antipredator behaviour is heritable and not influenced by behavioural copying in a wild bird.

Knowledge of the relative importance of genetics and behavioural copying is crucial to appraise the evolvability of behavioural consistencies. Yet, genetic and non-genetic factors are often deeply intertwined, and experiments are required to address this issue. We investigated the sources of variation of adult antipredator behaviour in the Alpine swift (Apus melba) by making use of long-term behavioural observations on parents and cross-fostered offspring. By applying an 'animal model' approach to observational data, we show that antipredator behaviour of adult Alpine swifts was significantly repeatable over lifetime (r = 0.273) and heritable (h(2) = 0.146). Regression models also show that antipredator behaviours differed between colonies and sexes (females were more tame), and varied with the hour and year of capture. By applying a parent-offspring regression approach to 59 offspring that were exchanged as eggs or hatchlings between pairs of nests, we demonstrate that offspring behaved like their biological parents rather than like their foster parents when they were adults themselves. Those findings provide strong evidence that antipredator behaviour of adult Alpine swifts is shaped by genetics and/or pre-hatching maternal effects taking place at conception but not by behavioural copying.

Male reproductive success and multiple paternity in wild, low-density populations of the adder (Vipera berus).

We studied for the first time the occurrence of multiple paternity, male reproductive success, and neonate survival in wild, low-density adder (Vipera berus) populations using 13 microsatellite loci. Paternity was assigned for 15 clutches, collected during 3 years. Our data demonstrated that multiple paternity can occur at a high level (69%) in natural populations of V. berus, even if the density of adults is low. The high proportion of multiple sired clutches was comparable to the proportion observed in captive populations. Male reproductive success significantly increased with body length, and only the largest males successfully sired entire clutches. Finally, no relationship was detected between the number of fathers per clutch and neonate survival. These results suggest that multiple matings could be beneficial in populations with high level of inbreeding or low male fecundity.

The impact of pre- and post-natal contexts on immunity, glucocorticoids and oxidative stress resistance in wild and domesticated grey partridges

Genetic background, prenatal and post-natal early-life conditions influence the development of interconnected physiological systems and thereby shape the phenotype. Certain combinations of genotypes and pre- and post-natal conditions may provide higher fitness in a specific environmental context. Here, we investigated how grey partridges Perdix perdix of two strains (wild and domesticated) cope physiologically with pre- and post-natal predictable vs. unpredictable food supply. Food unpredictability occurs frequently in wild environments and requires physiological and behavioural adjustments. Well-orchestrated and efficient physiological systems are presumably more vital in a wild environment as compared to captivity. We thus predicted that wild-strain grey partridges have a stronger immunity, glucocorticoid (GC) stress response and oxidative stress resistance (OSR) than domesticated birds, which have undergone adaptations to captivity. We also predicted that wild-strain birds react more strongly to environmental stimuli and, when faced with harsh prenatal conditions, are better able to prepare their offspring for similarly poor post-natal conditions than birds of domesticated origin. We found that wild-strain offspring were physiologically better prepared for stressful situations as compared to the domesticated strain. They had a high GC stress response and a high OSR when kept under predictable food supply. Wild-strain parents reacted to prenatal unpredictable food supply by lowering their offspring's GC stress response, which potentially lowered GC-induced oxidative pressure. No such pattern was evident in the domesticated birds. Irrespective of strain and prenatal feeding scheme, post-natal unpredictable food supply boosted immune indices, and GC stress response was negatively related to antibody response in females and to mitochondrial superoxide production. Wild-strain grey partridge showed fitness-relevant physiological advantages and appeared to prepare their offspring for the prospective environment. Negative relationships between GC stress response, immunity and oxidative indices imply a pivotal role of an organism's oxidative balance and support the importance of considering multiple physiological systems simultaneously.

Drug uptake in a rodent sarcoma model after intravenous injection or isolated lung perfusion of free liposomal doxorubicin /

Rapport de synthèseDrug uptake in a rodent sarcoma model after intravenous injection or isolated lungperfusion of free/liposomal doxorubicinIntroductionLa distribution de doxorubicine libre et doxorubicin liposomale pegylée (Liporubicin?) a été comparée après administration intraveineuse ou application via perfusion isolée du poumon (ILP) dans le parenchyme pulmonaire et dans la tumeur des poumons de rongeurs, porteurs d'une tumeur sarcomateuse.Matériel et méthodeUne tumeur sarcomateuse unique a été générée dans le poumon gauche de 36 rongeurs (Fisher rats) suivie, 10 jours plus tard, par application de doxorubicine ou Liporubicin? soit par perfusion isolée du poumon (n = 20) ou administration intraveineuse (n = 12). Deux différentes concentrations ont été utilisées (100 μg et 400 pg) à doses équimolaires pour les deux formulations de doxorubicine. La concentration des agents cytostatiques ont été mesurées dans la tumeur et le parenchyme pulmonaire à l'aide de chromatographic (HPLC).RésultatsLes résultats indiquent que pour doxorubicine libre, le taux de concentration dans la tumeur et le parenchyme pulmonaire est 3 fois (dosage de 100 μ§) et 10 fois (dosage de 400 plus élevé après ILP par rapport à l'administration intraveineuse. En revanche, pour Liporubicin , le taux de concentration est similaire dans la tumeur et le parenchyme pulmonaire entre ILP et administration intraveineuse, pour les deux doses appliquées.ConclusionPour ILP et administration intraveineuse, le ratio entre accumulation de l'agent cytostatique dans la tumeur versus dans le parenchyme pulmonaire a été comparé pour les deux formulations de doxorubicine ainsi que pour les deux dosages. Pour les deux formulations et dosages de doxorubicine, ILP aboutit à un ratio plus élevé par rapport à l'administration intraveineuse. Cependant, pour les deux formulations et dosages de doxorubicine, ILP résulte également en une distribution de l'agent cytostatique plus hétérogène dans le parenchyme pulmonaire comparé à l'administration intraveineuse.En résumé, l'application de doxorubicine par ILP aboutit donc à une accumulation tumorale élevée et à une augmentation du ratio tumeur-parenchyme pulmonaire, mais en même temps également à une distribution plus hétérogène dans le parenchyme pulmonaire par rapport à l'application intraveineuse. Ceci a été observé pour les deux formulations de doxorubicine et pour les deux dosages appliqué.

A novel and divergent role of granzyme a and B in resistance to helminth infection.

Granzyme (gzm) A and B, proteases of NK cells and T killer cells, mediate cell death, but also cleave extracellular matrices, inactivate intracellular pathogens, and induce cytokines. Moreover, macrophages, Th2 cells, regulatory T cells, mast cells, and B cells can express gzms. We recently reported gzm induction in human filarial infection. In this study, we show that in rodent filarial infection with Litomosoides sigmodontis, worm loads were significantly reduced in gzmA×B and gzmB knockout mice during the whole course of infection, but enhanced only early in gzmA knockout compared with wild-type mice. GzmA/B deficiency was associated with a defense-promoting Th2 cytokine and Ab shift, enhanced early inflammatory gene expression, and a trend of reduced alternatively activated macrophage induction, whereas gzmA deficiency was linked with reduced inflammation and a trend toward increased alternatively activated macrophages. This suggests a novel and divergent role for gzms in helminth infection, with gzmA contributing to resistance and gzmB promoting susceptibility.

Comparison of [3H]tamsulosin and [3H]prazosin binding to wild-type and constitutively active alpha1B-adrenoceptors.

We have tested the hypothesis that smaller alpha1B-adrenoceptor labeling by [3H]tamsulosin compared to [3H]prazosin is related to differential recognition of agonist low affinity states. Paired saturation binding experiments with [3H]prazosin and [3H]tamsulosin were performed in membrane preparations from rat liver and Rat- fibroblasts stably transfected with wild-type hamster alpha1B-adrenoceptors or a constitutively active mutant thereof. In all three settings [3H]tamsulosin labeled significantly fewer alpha1B-adrenoceptors than [3H]prazosin. In noradrenaline competition binding experiments, the percentage of agonist low affinity sites was smallest for the constitutively active alpha1B-adrenoceptor but the percentage of agonist low affinity sites recognized by [3H]tamsulosin and [3H]prazosin did not differ significantly. We conclude that [3H]tamsulosin labels fewer alpha1B-adrenoceptors than [3H]prazosin but this is not fully explained by a poorer labeling of agonist low affinity sites.