Effects of Degraded Optical Conditions on Behavioural Responses to Alarm Cues in a Freshwater Fish

Prey organisms often use multiple sensory cues to gain reliable information about imminent predation threat. In this study we test if a freshwater fish increases the reliance on supplementary cues when the reliability of the primary cue is reduced. Fish commonly use vision to evaluate predation threat, but may also use chemical cues from predators or injured conspecifics. Environmental changes, such as increasing turbidity or water colour, may compromise the use of vision through changes in the optical properties of water. In an experiment we tested if changes in optical conditions have any effects on how crucian carp respond to chemical predator cues. In turbidity treatments we added either clay or algae, and in a brown water colour treatment we added water with a high humic content. We found that carp reduced activity in response to predator cues, but only in the turbidity treatments (clay, algae), whereas the response in the brown water treatment was intermediate, and not significantly different from, clear and turbid water treatments. The increased reliance on chemical cues indicates that crucian carp can compensate for the reduced information content from vision in waters where optical conditions are degraded. The lower effect in brown water may be due to the reduction in light intensity, changes in the spectral composition (reduction of UV light) or to a change in chemical properties of the cue in humic waters

Voting and turning out for monetary integration: the case of the French referendum on the Maastricht treaty

This article analyses the voting and abstention patterns in French departments in the 1992 referendum on the Maastricht treaty, in light of the potential impact of monetary union. We observe that departmental characteristics implying either greater benefits or lower costs from monetary union are significantly correlated with the approval rate. This supports the view that the voting behaviour of individual agents depended on their self-interest. The impact of economic characteristics on the abstention rate is less clear. Indeed, the variable that is most significantly correlated with abstention in the referendum is average abstention in other elections.

Tyrosine kinase Flt3/Flt3-ligand signaling in the modulation of immune responses in experimental arthritis

Rheumatoid arthritis (RA) is an autoimmune, chronic systemic inflammatory disorder that primarily affects flexible joints resulting in severe joint destruction and disability if left untreated. Today, advances in treatment have significantly improved the outcome for patients, although the pathogenesis of RA remains relatively unknown. Signaling through the tyrosine kinase receptor fms-like tyrosine kinase 3 (Flt3) has been suggested to play a part in the RA pathogenesis. Flt3 is primarily expressed on hematopoietic stem cells and lymphoid progenitors in the bone marrow and has an important role in early B-cell development and formation of dendritic cells (DC). Furthermore, the ligand for Flt3 (Flt3L) serves as a regulator of regulatory T-cell (Treg) homeostasis and has been suggested to support differentiation of bone-resorbing osteoclasts. This thesis aimed to investigate the effect of Flt3/Flt3L signaling on the immune system during development of arthritis using an experimental animal model of human RA. Our study shows that Flt3 signaling supports formation of DCs and Treg cells during arthritis development. Treg expansion associated with Flt3L treatment resulted in a reduced production of inflammatory cytokines, reduced levels of antigen-specific antibodies and reduced bone destruction. On the contrary, lack of Flt3L was associated with reduced Treg formation resulting in loss of control over T-cell proliferation, and bone destruction during arthritis. Flt3L was found to positively influence the transcription of the osteoclast-regulating factor IRF8, and could by this mechanism influence osteoclast formation. Impaired signaling through Flt3 resulted in low IRF8 expression, accumulation of osteoclasts in the arthritic joint and an increased loss of femoral trabecular bone. Conversely, Flt3L treatment was associated with increased IRF8 expression, reduced osteoclast formation and restoration of trabecular bone formation in mice lacking Flt3L (Flt3LKO). Finally, we could identify a previously unacknowledged role for Flt3 in peripheral B-cell responses. We demonstrated that Flt3 was re-expressed on activated B-cells following LPS stimulation in vitro and on a population of germinal center B-cells in vivo. By using Flt3LKO mice we could identify an important role for Flt3L in class switch recombination (CSR) to IgG1. B-cells from Flt3LKO mice were found have reduced activation of Stat6 after IL-4 stimulation, resulting in impaired initiation of CSR to IgG1 and highly reduced formation of IgG1+ B-cells and IgG1 production. In summary this thesis shows that Flt3L has an important function in regulating DC and Treg homeostasis and function during arthritis. Furthermore, Flt3L has a regulatory role on osteoclast development and on trabecular bone formation. Finally, signaling through the Flt3 receptor on activated B-cells has an important role in the CSR process and deficiency of Flt3L leads to a skewed antibody response towards the more potent IgG subclasses IgG2b and IgG2c. Together, these results suggest that Flt3L might play a protective role during arthritis by reduction of bone destruction, induction of regulatory T-cells and regulation of antibody effector functions. The conclusion of this thesis is that signaling through the tyrosine kinase Flt3 plays an important role in modulating immune responses during experimental arthritis

Molecular-resolution images of Langmuir-Blodgett films using atomic force microscopy

THE ability to prepare thin films of amphiphilic molecules (Langmuir-Blodgett (LB) films) is valuable to many areas of research. In biology they provide models for ideal membranes; the two-dimensional behaviour and structural phase transitions are of fundamental interest in surface physics; and their tribological characteristics suggest potential engineering applications. For determining the structure of these films, the common techniques such as X-ray and neutron scattering are limited to thick (greater-than-or-similar-to 200 angstrom) multilayers. Thinner films can be studied by transmission electron microscopy and low-energy electron diffraction 1,2, but these electron-beam techniques tend to damage thin films. More recently, the scanning tunnelling microscope 3 has provided a non-destructive means of investigating the structures of LB films 4-6, but as the films are insulating, the interpretation of such images has been controversial. The atomic force microscope 7 is not plagued with these ambiguities, as it does not require a conductive sample. Here we present images, with molecular resolution, of LB films of cadmium arachidate deposited on an amorphous silicate substrate. Despite the disorder in the substrate, the films display a periodic structure over large distances (several hundreds of angstroms). This suggests that the adsorbed molecules near the interface are driven to self-assemble primarily, if not solely, by intermolecular forces rather than by dependence on substrate periodicity