Caenorhabditis elegans est un modèle animal de choix pour l'identification à partir d'animaux mutants des gènes intervenant dans différents comportements. En revanche, la caractérisation des mutants à l'échelle cellulaire a longtemps été limitée par la taille restreinte de l'animal. La mise au point de la dissection et l'application de la technique de patch-clamp et d'imagerie Ca2+ sur la cellule musculaire striée de C. elegans nous ont permis de caractériser pour la première fois les principales conductances ioniques de cette cellule. Nous avons montré le rôle crucial que jouaient les canaux Ca2+ EGL-19 dans le couplage excitation-contraction et mis en évidence les propriétés d'activation de canaux K+ voltage-dépendants et Ca2+-activés. Nous avons aussi démontré que le canal Na+ UNC-105, de la famille des dégénérines, n'était pas mécanosensible comme le supposaient les études génétiques, tandis qu'un autre membre de cette famille s'est avéré sensible à l'acidification extracellulaire

<p>The development of the avian embryo is dependent of heat provisioning from the parents. To increase the heat transfer to a cooled egg the Zebra finch females develop a brood patch. Mild cooling generally constricts the blood vessels but the Arterio-venous anastomoses (AVA) in the brood patch in birds dilate. This is called cold-induced vasodilation CIVD. The Zebra finches were anesthetized with isoflurane and the brood patch was stimulated with a cooling probe set at 20-21 °C. Differences in the vascular changes to cooling in broody and non- broody birds were studied by comparing males and broody females. The brood patch skin was cooled, but no cold-induced vasodilation (CIVD) was documented for the males or the broody females. Isoflurane anesthesia depresses the sympathetic nervous system activity and the results support that the mechanism for CIVD in the brood patch of Zebra finches depends on a neural pathway, but does not exclude a local non-neural mechanism.</p>

<p>During the breeding season Zebra finch, Taeniopygia guttata, females develops a brood patch on the ventral surface which facilitates heat exchange between the incubating bird and the egg. The brood patch has to be sensitive to changes in temperature, so that the eggs can be kept at an optimal temperature for embryo development. If the egg temperature drops it has to be re-warmed. Mild cooling of the brood patch has been shown to cause cold induced vasodilation, but the responsible mechanism for this is not known. In this study we investigated if known thermoreceptors, TRPV3 and TRPV4, could be involved in the alteration of blood flow. To activate TRPV3 and TRPV4 two agonists, carvacrol and 4α-PDD respectively, were applied on the brood patch. Changes in skin temperature and vascularity were then examined. The results obtained did not reveal any changes in the vascularity. Temperature changes in the skin that could be caused by an alteration in blood flow did not significantly change either. Still, a role of these channels in the brood patch cannot be excluded.</p>

<p>In this work suitable habitats for hazel grouse (<i>Bonasa bonasia</i>) were identified using ecological niche factor analysis (ENFA). The results from ENFA reveal that hazel grouse utilize a different and more restricted niche than what is generally available in the study area. When a landscape is fragmented the amount of edge increases, which is negative for many species and thus will affect the amount of available area. The perimeter-area ratio was used to analyze the relative importance of geometric shape. In order to estimate a correlation between incidence of hazel grouse and landscape features census data and land cover maps were analyzed with logistic regression models. It is concluded that hazel grouse is tied to coniferous forest and avoid open areas. However, the result indicates that there is a scale effect that should be considered. The amount of edge in a landscape seems to be important and shape of patches could be a better measure in metapopulation dynamics. In this study the Incidence function model was used to estimate occupancy levels and capacity of a landscape to sustain a metapopulation according to four different area measurement scenarios. Results from the simulations indicate that perimeter-area related measures of patch size combined with capacity could be a more important measure for estimation of population dynamics compared to a basic area measurement. Using a landscape genetic approach, hazel grouse genetic structure, neighbourhood size and dispersal distance were estimated. Genetic estimates of dispersal were in concordance with previous ecological estimates. The results indicate evidence of a population structure reminiscent of what has been found in many other Scandinavian animals with a basic north-south divide. No evidence was found that geographic and environmental structures affected gene flow and dispersal patterns for the hazel grouse.</p>

In this work suitable habitats for hazel grouse (Bonasa bonasia) were identified using ecological niche factor analysis (ENFA). The results from ENFA reveal that hazel grouse utilize a different and more restricted niche than what is generally available in the study area. When a landscape is fragmented the amount of edge increases, which is negative for many species and thus will affect the amount of available area. The perimeter-area ratio was used to analyze the relative importance of geometric shape. In order to estimate a correlation between incidence of hazel grouse and landscape features census data and land cover maps were analyzed with logistic regression models. It is concluded that hazel grouse is tied to coniferous forest and avoid open areas. However, the result indicates that there is a scale effect that should be considered. The amount of edge in a landscape seems to be important and shape of patches could be a better measure in metapopulation dynamics. In this study the Incidence function model was used to estimate occupancy levels and capacity of a landscape to sustain a metapopulation according to four different area measurement scenarios. Results from the simulations indicate that perimeter-area related measures of patch size combined with capacity could be a more important measure for estimation of population dynamics compared to a basic area measurement. Using a landscape genetic approach, hazel grouse genetic structure, neighbourhood size and dispersal distance were estimated. Genetic estimates of dispersal were in concordance with previous ecological estimates. The results indicate evidence of a population structure reminiscent of what has been found in many other Scandinavian animals with a basic north-south divide. No evidence was found that geographic and environmental structures affected gene flow and dispersal patterns for the hazel grouse.

During the breeding season Zebra finch, Taeniopygia guttata, females develops a brood patch on the ventral surface which facilitates heat exchange between the incubating bird and the egg. The brood patch has to be sensitive to changes in temperature, so that the eggs can be kept at an optimal temperature for embryo development. If the egg temperature drops it has to be re-warmed. Mild cooling of the brood patch has been shown to cause cold induced vasodilation, but the responsible mechanism for this is not known. In this study we investigated if known thermoreceptors, TRPV3 and TRPV4, could be involved in the alteration of blood flow. To activate TRPV3 and TRPV4 two agonists, carvacrol and 4α-PDD respectively, were applied on the brood patch. Changes in skin temperature and vascularity were then examined. The results obtained did not reveal any changes in the vascularity. Temperature changes in the skin that could be caused by an alteration in blood flow did not significantly change either. Still, a role of these channels in the brood patch cannot be excluded.

Nickel stands out as the main cause of contact allergy in both children and adults, which has given rise to concern and the introduction of regulations by official bodies. Today´s youths are frequently exposed to body piercing and orthodontic treatment. Changes in youth lifestyle practices are also likely to influence nickel exposure and thus, the occurrence of nickel allergy. However, against patient and parental concern regarding nickel exposure to orthodontic appliances, often evoked by allergies following piercing, stand results from studies indicating that early orthodontic appliance treatment may reduce, rather than increase, prevalence of nickel allergy; a finding that has been suggested to result from tolerance induction by early exposure to nickel via the oral route. The objective of the present thesis was to investigate the association between nickel allergy and exposure to different orthodontic appliances and lifestyle, in particular piercing, as well as to study nickel release from orthodontic appliances into the oral cavity. Furthermore, one objective was to establish baseline prevalence data of nickel allergy in a Swedish adolescent population. Data was generated from a cross-sectional survey, in which about 6000 youths completed a questionnaire and almost 4500 of these were patch-tested for contact allergy. Information on exposure to orthodontic appliances was verified by dental records, whilst nickel content in saliva and dental biofilm was measured in a clinical study. Questionnaire data demonstrated a reduced risk of nickel allergy when orthodontic treatment preceded piercing (OR 0.5; 95 % CI 0.3-0.8) and similar results were found for data verified from dental records, however statistical significance was lost when adjusting for background factors (OR 0.6, 95 % CI 0.4-1.0). Exposure to full fixed appliances with NiTi-containing alloys, as well as a pooled ‘high nickel-releasing’ appliance group prior to piercing correlated with a significantly reduced risk of nickel allergy and a trend towards a reduced risk with exposure duration. Nickel could also be found in significantly higher concentrations from dental plaque samples, but not saliva samples, in orthodontic patients who were well into treatment compared to patients who had not been exposed to orthodontic appliances. The effect was not found to be due to differences in estimated dietary nickel intake between the two groups. Significantly more girls than boys (13.3 % versus 2.5 %) were found to be patch-test positive to nickel. Positive nickel tests were also most prevalent in occupational programmes and least prevalent in natural science programmes, indicating differences in lifestyle and exposure to nickel. Dropout from testing was handled using a missing-value analysis. This internal validation showed that our results overestimated the occurrence of nickel allergy to a minor degree. More girls than boys reported piercing, vegetarian/vegan diet, and smoking practices, whereas an interesting shift in tattooing prevalence was observed with a larger proportion of girls reporting this practice compared to boys. Sex, number of piercings, smoking and orthodontic appliance treatment prior to piercing were found to influence weighted risk estimates of nickel allergy. To conclude, although orthodontic patients are exposed to nickel intraorally, we found no increased risk of sensitising adolescents to nickel by the use of oral orthodontic appliances. On the contrary, early orthodontic treatment preceding piercing reduced the risk of nickel allergy by a factor of 1.5-2.0. This reduced risk appears to be associated with estimated nickel release of the appliance and duration of treatment, in all supporting a hypothesised induction of immunological tolerance via oral administration of nickel. Our study also showed a strong association between lifestyle and nickel allergy. Although there have been changes in lifestyle over time, as indicated by the strong shift in tattooing practices, no large change in nickel allergy prevalence was found compared with previous Swedish data. Our data will serve as a baseline for future studies of the effect of nickel exposure regulations, such as the Nickel Directive, and for studies of lifestyle changes and their effects on nickel allergy.

Voltage-gated ion channels are fundamental for electrical signaling in living cells. They are composed of four subunits, each holding six transmembrane helices, S1-S6. Each subunit contains a voltage-sensor domain, S1-S4, and a pore domain, S5-S6. S4 contains several positively charged amino-acid residues and moves in response to changes in membrane voltage. This movement controls the opening and closing of the channel. The structure of the pore domain is solved and demonstrates principles of channel selectivity. The molecular mechanism of how the voltage sensor regulates the opening of the channel is still under discussion. Several models have been discussed. One of the models is the paddle model where S3b and S4 move together. The second one is the helical-twist where S4 makes a small rotation in order for the channel to open. The third one is the helical-screw model where S4 twists around its axis and moves diagonally towards the extracellular side of the channel. The aim of this PhD project was to study the molecular movement of the voltage sensor in the depolarization-activated Shaker K channel. Cloned channels were expressed in Xenopus laevis oocytes, and investigated with several electrophysiological techniques. 1. We show that S4 moves in relation to both S3b and S5. The formation of some disulfide bonds between S4 and neighboring positions, in only the open state, shows that the paddle model cannot be correct. Furthermore, electrostatic and steric effects of residues in S3b suggest that S3b is tilted, with the intracellular part close to S4. 2. We show that the relatively Mg-sensitive Shaker K channel is changed into the less Mg-sensitive Kv2.1 K channel with respect to its sensitivity to extracellularly applied Mg2+ by changing the charge of three extracellularly positioned amino acid residues. One of the residues, F425C, mediates its effect through the neighboring residue K427. 3. We show that oxaliplatin, an anti-cancer drug, has no effect on the Shaker K channel. It has been suggested that a negatively charged monochloro complex of oxaliplatin is the active substance, and also causes the neurotoxic side effects. Neither this complex shows any effect on the channel. Our experiments point towards the helical-screw model. The other models for voltage-sensor movements are incompatible with the results in this study.

The structure of afferent neurons is pseudounipolar. Studies suggest that they relay action potentials (APs) to both directions of the T-junctions to reach the cell body and the spinal cord. Moreover, the somata are electrically excitable and shown to be able to transmit the signals to associated satellite cells. Our study demonstrates that this transmission can go further and pass onto passive neighbouring somata, if they are in direct contact with same satellite cells. The neurons activate the satellite cells by releasing ATP. This triggers the satellite cells to exocytose acetylcholine to the neighbouring neurons. In addition, the ATP inhibits the nicotinic receptors of the neurons by activating P2Y receptors and initiating the G-protein-mediated pathway, thus reducing the signals that return to the neurons that initiated the signals. This “sandwich synapse” represents a unique pathway by the ectopic release between the somata and the satellite cells.

The structure of afferent neurons is pseudounipolar. Studies suggest that they relay action potentials (APs) to both directions of the T-junctions to reach the cell body and the spinal cord. Moreover, the somata are electrically excitable and shown to be able to transmit the signals to associated satellite cells. Our study demonstrates that this transmission can go further and pass onto passive neighbouring somata, if they are in direct contact with same satellite cells. The neurons activate the satellite cells by releasing ATP. This triggers the satellite cells to exocytose acetylcholine to the neighbouring neurons. In addition, the ATP inhibits the nicotinic receptors of the neurons by activating P2Y receptors and initiating the G-protein-mediated pathway, thus reducing the signals that return to the neurons that initiated the signals. This “sandwich synapse” represents a unique pathway by the ectopic release between the somata and the satellite cells.