Biomedical subjects

Yvon Le Maho

Publications and source records attributed to Yvon Le Maho.

At least 19 recordsLinked to original sources

PubMed2006

Innate immunity, assessed by plasma NO measurements, is not suppressed during the incubation fast in eiders.

Immunity is hypothesized to share limited resources with other physiological functions and may mediate life history trade-offs, for example between reproduction and survival. However, vertebrate immune defense is a complex system that consists of three components. To date, no study has assessed all of these components for the same animal model and within a given situation. Previous studies have determined that the acquired immunity of common eiders (Somateria mollissima) is suppressed during incubation. The present paper aims to assess the innate immune response in fasting eiders in relation to their initial body condition. Innate immunity was assessed by measuring plasma nitric oxide (NO) levels, prior to and after injection of lipopolysaccharides (LPS), a method which is easily applicable to many wild animals. Body condition index and corticosterone levels were subsequently determined as indicators of body condition and stress level prior to LPS injection. The innate immune response in eiders did not vary significantly throughout the incubation period. The innate immune response of eiders did not vary significantly in relation to their initial body condition but decreased significantly when corticosterone levels increased. However, NO levels after LPS injection were significantly and positively related to initial body condition, while there was a significant negative relationship with plasma corticosterone levels. Our study suggests that female eiders preserve an effective innate immune response during incubation and this response might be partially determined by the initial body condition.

Animals↗

PubMed2006

Marine animal behaviour: neglecting ocean currents can lead us up the wrong track.

Tracks of marine animals in the wild, now increasingly acquired by electronic tagging of individuals, are of prime interest not only to identify habitats and high-risk areas, but also to gain detailed information about the behaviour of these animals. Using recent satellite-derived current estimates and leatherback turtle (Dermochelys coriacea) tracking data, we demonstrate that oceanic currents, usually neglected when analysing tracking data, can substantially distort the observed trajectories. Consequently, this will affect several important results deduced from the analysis of tracking data, such as the evaluation of the orientation skills and the energy budget of animals or the identification of foraging areas. We conclude that currents should be systematically taken into account to ensure the unbiased interpretation of tracking data, which now play a major role in marine conservation biology.

Animals↗

PubMed2006

Effect of physical inactivity on the oxidation of saturated and monounsaturated dietary Fatty acids: results of a randomized trial.

OBJECTIVES: Changes in the way dietary fat is metabolized can be considered causative in obesity. The role of sedentary behavior in this defect has not been determined. We hypothesized that physical inactivity partitions dietary fats toward storage and that a resistance exercise training program mitigates storage. DESIGN: We used bed rest, with randomization to resistance training, as a model of physical inactivity. SETTING: The trial took place at the Space Clinic (Toulouse, France). PARTICIPANTS: A total of 18 healthy male volunteers, of mean age +/- standard deviation 32.6 +/- 4.0 y and body mass index 23.6 +/- 0.7 kg/m(2), were enrolled. INTERVENTIONS: An initial 15 d of baseline data collection were followed by 3 mo of strict bed-rest alone (control group, n = 9) or with the addition of supine resistance exercise training every 3 d (exercise group, n = 9). OUTCOME MEASURES: Oxidation of labeled [d(31)]palmitate (the main saturated fatty acid of human diet) and [1-(13)C]oleate (the main monounsaturated fatty acid), body composition, net substrate use, and plasma hormones and metabolites were measured. RESULTS: Between-group comparisons showed that exercise training did not affect oxidation of both oleate (mean difference 5.6%; 95% confidence interval [95% CI], -3.3% to 14.5%; p = 0.20) and palmitate (mean difference -0.2%; 95% CI, -4.1% to 3.6%; p = 0.89). Within-group comparisons, however, showed that inactivity changed oxidation of palmitate in the control group by -11.0% (95% CI, -19.0% to -2.9%; p = 0.01) and in the exercise group by -11.3% (95% CI, -18.4% to -4.2%; p = 0.008). In contrast, bed rest did not significantly affect oleate oxidation within groups. In the control group, the mean difference in oleate oxidation was 3.2% (95% CI, -4.2% to 10.5%; p = 0.34) and 6.8% (95% CI, -1.2% to 14.7%; p = 0.08) in the exercise group. CONCLUSIONS: Independent of changes in energy balance (intake and/or output), physical inactivity decreased the oxidation of saturated but not monounsaturated dietary fat. The effect is apparently not compensated by resistance exercise training. These results suggest that Mediterranean diets should be recommended in sedentary subjects and recumbent patients.

Journal Article↗

PubMed2006

Body temperature changes induced by huddling in breeding male emperor penguins.

Huddling is the key energy-saving mechanism for emperor penguins to endure their 4-mo incubation fast during the Antarctic winter, but the underlying physiological mechanisms of this energy saving have remained elusive. The question is whether their deep body (core) temperature may drop in association with energy sparing, taking into account that successful egg incubation requires a temperature of about 36 degrees C and that ambient temperatures of up to 37.5 degrees C may be reached within tight huddles. Using data loggers implanted into five unrestrained breeding males, we present here the first data on body temperature changes throughout the breeding cycle of emperor penguins, with particular emphasis on huddling bouts. During the pairing period, core temperature decreased progressively from 37.5 +/- 0.4 degrees C to 36.5 +/- 0.3 degrees C, associated with a significant temperature drop of 0.5 +/- 0.3 degrees C during huddling. In case of egg loss, body temperature continued to decrease to 35.5 +/- 0.4 degrees C, with a further 0.9 degrees C decrease during huddling. By contrast, a constant core temperature of 36.9 +/- 0.2 degrees C was maintained during successful incubation, even during huddling, suggesting a trade-off between the demands for successful egg incubation and energy saving. However, such a limited drop in body temperature cannot explain the observed energy savings of breeding emperor penguins. Furthermore, we never observed any signs of hyperthermia in huddling birds that were exposed to ambient temperatures as high as above 35 degrees C. We suggest that the energy savings of huddling birds is due to a metabolic depression, the extent of which depends on a reduction of body surface areas exposed to cold.

Animals↗

PubMed2006

Huddling behavior in emperor penguins: Dynamics of huddling.

Although huddling was shown to be the key by which emperor penguins (Aptenodytes forsteri) save energy and sustain their breeding fast during the Antarctic winter, the intricacies of this social behavior have been poorly studied. We recorded abiotic variables with data loggers glued to the feathers of eight individually marked emperor penguins to investigate their thermoregulatory behavior and to estimate their "huddling time budget" throughout the breeding season (pairing and incubation period). Contrary to the classic view, huddling episodes were discontinuous and of short and variable duration, lasting 1.6+/-1.7 (S.D.) h on average. Despite heterogeneous huddling groups, birds had equal access to the warmth of the huddles. Throughout the breeding season, males huddled for 38+/-18% (S.D.) of their time, which raised the ambient temperature that birds were exposed to above 0 degrees C (at average external temperatures of -17 degrees C). As a consequence of tight huddles, ambient temperatures were above 20 degrees C during 13+/-12% (S.D.) of their huddling time. Ambient temperatures increased up to 37.5 degrees C, close to birds' body temperature. This complex social behavior therefore enables all breeders to get a regular and equal access to an environment which allows them to save energy and successfully incubate their eggs during the Antarctic winter.

Animals↗

PubMed2006

Phytohemagglutinin response and immunoglobulin index decrease during incubation fasting in female common eiders.

To maximize their fitness, long-lived species face trade-offs between survival and reproduction. The cost of reproduction, which is defined as the negative effect of current parental investment on chances of adult survival and future reproduction, may affect immune function, possibly through hormonal changes. In this study, components of acquired immunity and plasma corticosterone levels of female eiders (Somateria mollissima) have been measured throughout the incubation period as a function of clutch size. These precocial birds lay up to six eggs and fast completely during incubation. Birds were sampled early and late in the incubation period, with clutches ranging from one to four eggs. T-cell-mediated immune response and humoral immunity were assessed by phytohemagglutinin (PHA) skin tests (a challenging method) and measurements of serum immunoglobulins (a monitoring method), respectively. During incubation, responses to PHA injection and immunoglobulin index significantly decreased, by about 40% and 25%, respectively. These observed decreases occurred independently of the number of eggs laid by the females. Corticosterone did not vary significantly during incubation, whatever the clutch size. We conclude that female eiders seem to reallocate their resources from immune function to reproductive effort independently of clutch size or corticosterone levels.

Animals↗

PubMed2006

Fasting-induced changes of immunological and stress indicators in breeding female eiders.

One adaptive significance of immunosuppression during reproduction can be explained by the immunopathology-avoidance hypothesis. This hypothesis states that since heat shock proteins (HSP) are highly conserved proteins found in both pathogen and host, and are expressed at a higher level during reproduction, the risk of autoimmunity is then increased, HSP being the target of the host's immune response. Reduced immunocompetence has been attributed to hormonal regulation, in particular by glucocorticoids. The current study aimed at testing the immunopathology-avoidance hypothesis and the implication of corticosterone in incubating fasting common eiders (Somateria mollissima). To this end, we have measured immunological and stress indicators including immunoglobulin (IgY), HSP70, HSP60, and corticosterone levels in breeding females. A multivariate general linear model analysis showed that female body condition, IgY, HSP70, and HSP60 levels were the main variables explaining the model. Females showed a significant decrease by 15% of their IgY index during incubation. Conversely, HSP70 and HSP60 levels significantly increased by 12 and 10%, respectively throughout incubation. Moreover, there was a positive significant relationship between both HSP whereas HSP60 levels were negatively correlated to IgY index. Plasma corticosterone levels showed a tendency to decrease during incubation. We conclude that these findings are consistent with the immunopathology-avoidance hypothesis in breeding eiders. Nevertheless, the long-term reproductive costs and the underlying mechanisms of such an immunosuppression remain to be determined and will require further experiments.

Animals↗

PubMed2005

Reliability in estimates of body composition of birds: oxygen-18 versus deuterium dilution.

Body composition in birds was evaluated indirectly by 18O and 2H dilution. Body composition was determined by whole-body chemical analysis of eight adult roosters (Gallus gallus). In vivo measurements of total body water (TBW) were carried out using doubly labeled water (2H2 18O). Estimated dilution spaces using both the plateau and intercept approaches were compared with the results obtained by carcass lyophilization. Both 18O and 2H slightly overestimated TBW compared with the results obtained by lyophilization, by 2.2%+/-1.9% and 5.7%+/-0.2%, respectively; both differences were statistically significant (P<0.01). The difference between these isotope estimations was significant (P<0.001). However, isotope dilution spaces and TBW were highly correlated. There was a strong inverse relationship between total body fat and TBW percentages (r2=0.98, P<0.0001). The relation between TBW and body protein was significant. Water content in lean body mass (72.8%) obtained in our study was very close to that reported in mammals, demonstrating no fundamental difference in tissue water content between birds and mammals. Estimated body fat and protein values from isotopic dilution did not significantly differ from values obtained by direct chemical analysis (P>0.05), except for body fat in the Pace and Rathbun approach (Table 3). Although estimation of TBW and body composition by isotope dilution is time consuming and expensive, deuterium offers a reliable and low-cost alternative compared with 18O. The advantage of in vivo estimation of TBW with isotopic dilution in combination with the regression approach is that it permits repeated measurements of body composition on the same birds under laboratory and free-living conditions.

Animals↗

PubMed2005

Intestinal apoptotic changes linked to metabolic status in fasted and refed rats.

Intestinal apoptosis and expression of apoptosis inducers--the cytokines TNFalpha, TGFbeta1--and the intestinal transcription factor Cdx2, were studied according to two different metabolic and hormonal phases which characterize long-term fasting: the long period of protein sparing during which energy expenditure is derived from lipid oxidation (phase II), and the later phase characterized by a rise in body protein utilization and plasma corticosterone (phase III). Apoptosis was further studied in 2, 6, and 24 h refed rats. Morphological apoptotic events were observed by environmental and conventional scanning electron microscopy and a TUNEL test was used to characterize the final stages of apoptotic death. The gene and protein expressions of TNFalpha, TGFbeta1, and Cdx2 were measured. Apoptotic events and TNFalpha, TGFbeta1, and Cdx2 gene and protein expressions did not vary significantly during phase II as compared to the normally fed animals. However, a phase III fasting induced a delay in intestinal epithelial apoptosis, along with a 92, 58, and 25% decrease in TNFalpha, TGFbeta1, and Cdx2 mRNAs, respectively. The amounts of TNFalpha, TGFbeta1, and Cdx2 proteins decreased by 70, 36, and 25%, respectively. Apoptosis was restored rapidly after a 2 h refeeding following the phase III, accompanied by a significant increase in TNFalpha, TGFbeta1, and Cdx2 mRNA and the protein levels, compared to the phase III fasting values. The concomitant decreases in cytokines and Cdx2 and in apoptotic cells during phase III suggest the preservation of enterocytes during this critical fasting period in order to optimize nutrient absorption as soon as food is available and thus, to rapidly restore body mass.

Animals↗

PubMed2005

Recurrent evolution of host-specialized races in a globally distributed parasite.

The outcome of coevolutionary interactions is predicted to vary across landscapes depending on local conditions and levels of gene flow, with some populations evolving more extreme specializations than others. Using a globally distributed parasite of colonial seabirds, the tick Ixodes uriae, we examined how host availability and geographic isolation influences this process. In particular, we sampled ticks from 30 populations of six different seabird host species, three in the Southern Hemisphere and three in the Northern Hemisphere. We show that parasite races have evolved independently on hosts of both hemispheres. Moreover, the degree of differentiation between tick races varied spatially within each region and suggests that the divergence of tick races is an ongoing process that has occurred multiple times across isolated areas. As I. uriae is vector to the bacterium responsible for Lyme disease Borrelia burgdorferi sensu lato, these results may have important consequence for the epidemiology of this disease. With the increased occurrence of novel interspecific interactions due to global change, these results also stress the importance of the combined effects of gene flow and selection for parasite diversification.

Animals↗

PubMed2005

Intestinal gluconeogenesis and glucose transport according to body fuel availability in rats.

Intestinal hexose absorption and gluconeogenesis have been studied in relation to refeeding after two different fasting phases: a long period of protein sparing during which energy expenditure is derived from lipid oxidation (phase II), and a later phase characterized by a rise in plasma corticosterone triggering protein catabolism (phase III). Such a switch in body fuel uses, leading to changes in body reserves and gluconeogenic precursors, could modulate intestinal gluconeogenesis and glucose transport. The gene and protein levels, and the cellular localization of the sodium-glucose cotransporter SGLT1, and of GLUT5 and GLUT2, as well as that of the key gluconeogenic enzymes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (Glc6Pase) were measured. PEPCK and Glc6Pase activities were also determined. In phase III fasted rats, SGLT1 was up-regulated and intestinal glucose uptake rates were higher than in phase II fasted and fed rats. PEPCK and Glc6Pase mRNA, protein levels and activities also increased in phase III. GLUT5 and GLUT2 were down-regulated throughout the fast, but increased after refeeding, with GLUT2 recruited to the apical membrane. The increase in SGLT1 expression during phase III may allow glucose absorption at low concentrations as soon as food is available. Furthermore, an increased epithelial permeability due to fasting may induce a paracellular movement of glucose. In the absence of intestinal GLUT2 during fasting, Glc6Pase could be involved in glucose release to the bloodstream via membrane trafficking. Finally, refeeding triggered GLUT2 and GLUT5 synthesis and apical recruitment of GLUT2, to absorb larger amounts of hexoses.

Amino Acids↗

PubMed2005

Avian uncoupling protein expressed in yeast mitochondria prevents endogenous free radical damage.

The longevity of birds is surprising since they exhibit high metabolic rates and elevated blood sugar levels compared with mammals of the same body size, which presumably expose them to higher rates of free oxygen radical production, which is implicated in accelerated senescence. Uncoupling proteins (UCPs) are transporters of the inner mitochondrial membrane and their physiological activity is still a subject of debate. Avian UCP was found in birds but data on its activity are scarce. Avian UCP (Gallus gallus) was overexpressed in yeast and we assessed its ability to prevent mitochondrial reactive oxygen species (ROS) production by measuring ROS damage (aconitase activity) and antioxidant defences (MnSOD activity). We show that avian UCP protects yeast mitochondria against the deleterious impact of ROS, but without stimulation of superoxide dismutase activity. Avian UCP protein was specifically immunodetected and retinoic acid, which belongs to the carotenoid family, was found to trigger its activity. These data show that avian UCP basal activity protects against ROS damage. However, when activated by retinoic acid, avian UCP can also operate as the mammalian thermogenic UCP1. The hypothesis that avian UCP activities are state- and species-dependent is further discussed.

Aconitate Hydratase↗

PubMed2005

Year-round recordings of behavioural and physiological parameters reveal the survival strategy of a poorly insulated diving endotherm during the Arctic winter.

Warm-blooded diving animals wintering in polar regions are expected to show a high degree of morphological adaptation allowing efficient thermal insulation. In stark contrast to other marine mammals and seabirds living at high latitudes, Arctic great cormorants Phalacrocorax carbo have very limited thermal insulation because of their partly permeable plumage. They nonetheless winter in Greenland, where they are exposed to very low air and water temperatures. To understand how poorly insulated diving endotherms survive the Arctic winter, we performed year-round recordings of heart rate, dive depth and abdominal temperature in male great cormorants using miniature data loggers. We also examined the body composition of individuals in the spring. Abdominal temperatures and heart rates of birds resting on land and diving showed substantial variability. However, neither hypothermia nor significantly lower heart rate levels were recorded during the winter months. Thus our data show no indication of general metabolic depression in great cormorants wintering in Greenland. Furthermore, great cormorants did not reduce their daily swimming time during the coldest months of the year to save energy; they continued to forage in sub-zero waters for over an hour every day. As birds spent extended periods in cold water and showed no signs of metabolic depression during the Arctic winter, their theoretical energy requirements were substantial. Using our field data and a published algorithm we estimated the daily food requirement of great cormorants wintering in Greenland to be 1170+/-110 g day(-1). This is twice the estimated food requirement of great cormorants wintering in Europe. Great cormorants survive the Arctic winter but we also show that they come close to starvation during the spring, with body reserves sufficient to fast for less than 3 days. Lack of body fuels was associated with drastically reduced body temperatures and heart rates in April and May. Concurrent, intense feeding activity probably allowed birds to restore body reserves. Our study is the first to record ecophysiological parameters in a polar animal on a year-round basis. It challenges the paradigm that efficient thermal insulation is a prerequisite to the colonization of polar habitats by endotherms.

Acclimatization↗

PubMed2005

Mercury concentrations in king penguin (Aptenodytes patagonicus) feathers at Crozet Islands (sub-Antarctic): temporal trend between 1966--1974 and 2000--2001.

Remote sub-Antarctic islands and their wildlife may be contaminated by mercury via atmospheric and oceanic currents. Because of mercury's high toxicity and its capacity to be biomagnified in marine food chains, top predators like seabirds may be threatened by secondary poisoning. The present study provides data regarding mercury concentrations in breast feathers sampled in 2000 and 2001 on king penguins (Aptenodytes patagonicus) living at Crozet Islands. These contemporary concentrations were compared to those measured in feathers of king penguins sampled in the same colony between 1966 and 1974 and preserved in a museum (1970s sample). The average concentration of the contemporary sample is 1.98 microg g(-1) (dry mass) and is significantly different than the concentrations reported in some other penguin species. The concentration of the contemporary sample is significantly lower than the concentration of the 1970s sample (2.66 microg g(-1)). This suggests that mercury concentrations in southern hemisphere seabirds do not increase, which conflicts with the trends observed in the northern hemisphere. This difference in temporal trends between the northern and southern hemispheres usually is attributed mainly to a higher degree of pollutant emission in the northern hemisphere. Parameters that may explain the interspecies differences in mercury concentrations are discussed. These first results may constitute a basis for further ecotoxicological and/or biomonitoring studies of king penguins in these remote ecosystems.

Animals↗

PubMed2004

Endangered species: where leatherback turtles meet fisheries.

The dramatic worldwide decline in populations of the leatherback turtle (Dermochelys coriacea) is largely due to the high mortality associated with their interaction with fisheries, so a reduction of this overlap is critical to their survival. The discovery of narrow migration corridors used by the leatherbacks in the Pacific Ocean raised the possibility of protecting the turtles by restricting fishing in these key areas. Here we use satellite tracking to show that there is no equivalent of these corridors in the North Atlantic Ocean, because the turtles disperse actively over the whole area. But we are able to identify a few 'hot spots' where leatherbacks meet fisheries and where conservation efforts should be focused.

Animal Migration↗

PubMed2003

Coordinate upregulation of proteolytic-related genes in rat muscle during late fasting.

The present study examines whether and to what extent the profiles of proteolytic-related genes are altered in atrophying muscle during prolonged food deprivation. Long-term fasted animals exhibited three metabolic phases characterized by changes in lipid and protein utilization. Starvation induced an increase in some proteolytic gene expressions during P2 of fasting, especially for Cat L (by 3-fold). In P3, the fasting-induced enhancement of mRNA expression involved all proteolytic pathways and was much more pronounced than in P2 for pUb, E2(14k), CAPN3, and Cat B, D, and H (by 2- to 4-fold), for C2, C5, and S5a (by 5- to 6-fold), and mainly for Cat L, C3, and C8 (by 10- to 15-fold). At the molecular level, it is concluded that the three proteolytic systems found in skeletal muscle are selectively induced in P2 of fasting and coordinately upregulated in late fasting.

Adaptation, Physiological↗

PubMed2003

Recombinant leptin in the hypothalamic response to late fasting.

The aim of the current study was to gain further insight into the implication of leptin in the regulation of hypothalamic gene expression during long-term food deprivation with emphasis on phase 3 of fasting (P3, late protein breakdown). Among plasma parameters, glucose, non-esterified fatty acids, and insulin levels tended to be decreased by leptin infusion, whilst corticosterone levels remained unchanged. From Northern blot analysis, NPY, AGRP, and MCH mRNA gene expressions were differentially regulated during prolonged fasting in leptin-perfused rats. In comparison with fed animals, NPY, AGRP, and MCH mRNA levels in P3 rats treated with leptin either remained stable or increased slightly. Regarding anorexigenic peptides (CART and POMC) and prepro-OX, fasting with leptin induced only slight changes in gene expression. Similar data have been obtained in leptin-treated fasted rats at various doses within the physiological range. We conclude that leptin and particularly low levels of plasma leptin can reasonably be considered as a constituent of a signal triggering the fasting-induced enhanced drive for refeeding in P3.

Animals↗

PubMed2003

Spheniscins, avian beta-defensins in preserved stomach contents of the king penguin, Aptenodytes patagonicus.

During the last part of egg incubation in king penguins, the male can preserve undigested food in the stomach for several weeks. This ensures survival of the newly hatched chick, in cases where the return of the foraging female from the sea is delayed. In accordance with the characterization of stress-induced bacteria, we demonstrate the occurrence of strong antimicrobial activities in preserved stomach contents. We isolated and fully characterized two isoforms of a novel 38-residue antimicrobial peptide (AMP), spheniscin, belonging to the beta-defensin subfamily. Spheniscin concentration was found to strongly increase during the period of food storage. Using a synthetic version of one of two spheniscin isoforms, we established that this peptide has a broad activity spectrum, affecting the growth of both pathogenic bacteria and fungi. Altogether, our data suggest that spheniscins and other, not yet identified, antimicrobial substances may play a role in the long term preservation of stored food in the stomach of king penguins.

Amino Acid Sequence↗