Collège de France

About: Collège de France is a education organization based out in Paris, France. It is known for research contribution in the topics: Population & Receptor. The organization has 6541 authors who have published 11983 publications receiving 648742 citations. The organization is also known as: College de France.

The design of cationic lipids for gene delivery.

Abstract: Synthetic gene delivery vectors are gaining increasing importance in gene therapy as an alternative to recombinant viruses. Among the various types of non-viral vectors, cationic lipids are especially attractive as they can be prepared with relative ease and extensively characterised. Further, each of their constituent parts can be modified, thereby facilitating the elucidation of structure-activity relationships. In this forward-looking review, cationic lipid-mediated gene delivery will mainly be discussed in terms of the structure of the three basic constituent parts of any cationic lipid: the polar headgroup, hydrophobic moiety and linker. Particular emphasis will be placed on recent advances in the field as well as on our own original contributions. In addition to reviewing critical physicochemical features (such as headgroup hydration) of monovalent lipids, the use of headgroups with known nucleic-acid binding modes, such as linear and branched polyamines, aminoglycosides and guanidinium functions, will be comprehensively assessed. A particularly exciting innovation in linker design is the incorporation of environment-sensitive groups, the intracellular hydrolysis of which may lead to more controlled DNA delivery. Examples of pH-, redox- and enzyme-sensitive functional groups integrated into the linker are highlighted and the benefits of such degradable vectors can be evaluated in terms of transfection efficiency and cationic lipid-associated cytotoxicity. Finally, possible correlations between the length and type of hydrophobic moiety and transfection efficiency will be discussed. In conclusion it may be foreseen that in order to be successful, the future of cationic lipid-based gene delivery will probably require the development of sophisticated virus-like systems, which can be viewed as "programmed supramolecular systems" incorporating the various functions required to perform in a chronological order the different steps involved in gene transfection.

Response to stress of mesocortico-frontal dopaminergic neurones in rats after long-term isolation

Abstract: Recent studies suggest that the mesocortico-frontal dopaminergic neurones which originate in the ventral tegmental area (VTA) have an inhibitory role in locomotor activity1,2. They are also markedly activated under stress3–5. This effect was shown in rats and mice subjected to electric foot-shocks by measuring either the rate of decline of dopamine (DA) after α-methylparatyrosine treatment3 or the changes in dihydroxyphenylacetic acid (dopac) levels and the dopac/DA ratio4–6. In rats, stress-induced activation of the dopaminergic neurones was prevented by benzodiazepines4,5, and studies in BALB/c mice introduced for 2 min into an open field further established the role of dopaminergic neurones in emotional responses7. These observations led us to examine the effects of long-term isolation on the activity of the mesocortico-frontal dopaminergic neurones in rats, some of which were subjected to a stressful situation. Indeed, several groups have reported that long-term isolation in rodents induced behavioural disturbances such as increased motor activity8,9 and aggression9,10 and hyper-reactivity to a new environment or stressful stimuli10,11. As measured by the changes in dopac levels or the dopac/DA ratio, we report here that the activity of the mesocortico-frontal dopaminergic neurones was reduced after isolation. This was not the case for the dopaminergic neurones projecting to the nucleus accumbens or the striatum, the rate of DA utilisation in these structures was even enhanced in isolated rats in which the activity of the mesocortico-frontal dopaminergic neurones was markedly reduced. Finally, we will show that a 3-min electric foot-shock session is more effective in enhancing dopac levels or the dopac/DA ratio in the frontal cortex of isolated than grouped rats.

Quantum Kibble–Zurek mechanism and critical dynamics on a programmable Rydberg simulator

Abstract: Quantum phase transitions (QPTs) involve transformations between different states of matter that are driven by quantum fluctuations1. These fluctuations play a dominant part in the quantum critical region surrounding the transition point, where the dynamics is governed by the universal properties associated with the QPT. Although time-dependent phenomena associated with classical, thermally driven phase transitions have been extensively studied in systems ranging from the early Universe to Bose–Einstein condensates, understanding critical real-time dynamics in isolated, non-equilibrium quantum systems remains a challenge. Here we use a Rydberg atom quantum simulator with programmable interactions to study the quantum critical dynamics associated with several distinct QPTs. By studying the growth of spatial correlations when crossing the QPT, we experimentally verify the quantum Kibble–Zurek mechanism (QKZM) for an Ising-type QPT, explore scaling universality and observe corrections beyond QKZM predictions. This approach is subsequently used to measure the critical exponents associated with chiral clock models, providing new insights into exotic systems that were not previously understood and opening the door to precision studies of critical phenomena, simulations of lattice gauge theories and applications to quantum optimization.

Titanium oxo-clusters: precursors for a Lego-like construction of nanostructured hybrid materials.

Abstract: Titanium oxo-clusters, well-defined monodispersed nano-objects, are appropriate nano-building blocks for the preparation of organic–inorganic materials by a bottom up approach. This critical review proposes to present the different structures of titanium oxo-clusters referenced in the literature and the different strategies followed to build up hybrid materials with these versatile building units. In particular, this critical review cites and reports on the most important papers in the literature, concentrating on recent developments in the field of synthesis, characterization, and the use of titanium oxo-clusters for the construction of advanced hybrid materials (137 references).

The Peculiar History of Scientific Reason

Abstract: Science is a social field of forces, struggles, and relationships that is defined at every moment by the relations of power among the protagonists. Scientific choices are guided by taken-for-granted assumptions, interactive with practices, as to what constitutes real and important problems, valid methods, and authentic knowledge. Such choices also are shaped by the social capital controlled by various positions and stances within the field. This complex and dynamic representation thus simultaneously rejects both the absolutist-idealist conception of the immanent development of science and the historicist relativism of those who consider science as purely a conventional social construct. The strategies used in science are at once social and intellectual; for example, strategies that are founded on implicit agreement with the established scientific order are thereby in affinity with the positions of power within the field itself. In established scientific fields of high autonomy, “revolutions” no longer are necessarily at the same time political ruptures but rather are generated within the field themselves: the field becomes the site of a permanent revolution. Under certain conditions, then, strategies used in struggles for symbolic power transcend themselves as they are subjected to the crisscrossing censorship that represents the constitutive reason of the field. The necessary and sufficient condition for this critical correction is a social organization such that each participant can realize specific interest only by mobilizing all the scientific resources available for overcoming the obstacles shared by all his or her competitors. Thus, the type of analysis here illustrated does not lead to reductive bias or sociologism that would undermine its own foundations. Rather it points to a comprehensive and reflexive objectivism that opens up a liberating collective self-analysis.