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 & Dopamine. The organization has 6541 authors who have published 11983 publications receiving 648742 citations. The organization is also known as: College de France.

Crystal structure of the human RXRα ligand-binding domain bound to its natural ligand: 9-cis retinoic acid

Abstract: The pleiotropic effects of active retinoids are transduced by their cognate nuclear receptors, retinoid X receptors (RXRs) and retinoic acid receptors (RARs), which act as transcriptional regulators activated by two stereoisomers of retinoic acid (RA): 9-cis RA (9-cRA) and all-trans RA (a-tRA). Among nuclear receptors, RXR occupies a central position and plays a crucial role in many intracellular signalling pathways as a ubiquitous heterodimerization partner with numerous other members of this superfamily. Whereas RARs bind both isomers, RXRs exclusively bind 9-cRA. The crystal structure of the ligand-binding domain (LBD) of human RXRα bound to 9-cRA reveals the molecular basis of this ligand selectivity and allows a comparison of both apo and holo forms of the same nuclear receptor. In the crystal, the receptor is monomeric and exhibits a canonical agonist conformation without direct contacts between the ligand and the transactivation helix H12. Comparison with the unliganded RXRα LBD structure reveals the molecular mechanisms of ligand-induced conformational changes and allows us to describe at the atomic level how these changes generate the proper protein interface involved in nuclear receptor–coactivator interaction.

Visual-vestibular interactive responses in the macaque ventral intraparietal area (VIP).

Abstract: Self-motion detection requires the interaction of a number of sensory systems for correct perceptual interpretation of a given movement and an eventual motor response. Parietal cortical areas are thought to play an important role in this function, and we have thus studied the encoding of multimodal signals and their spatiotemporal interactions in the ventral intraparietal area of macaque monkeys. Thereby, we have identified for the first time the presence of vestibular sensory input to this area and described its interaction with somatosensory and visual signals, via extracellular single-cell recordings in awake head-fixed animals. Visual responses were driven by large field stimuli that simulated either backward or forward self-motion (contraction or expansion stimuli, respectively), or movement in the frontoparallel plane (visual increments moving simultaneously in the same direction). While the dominant sensory modality in most neurons was visual, about one third of all recorded neurons responded to horizontal rotation. These vestibular responses were typically in phase with head velocity, but in some cases they could signal acceleration or even showed integration to position. The associated visual responses were always codirectional with the vestibular on-direction, i.e. noncomplementary. Somatosensory responses were in register with the visual preferred direction, either in the same or in the opposite direction, thus signalling translation or rotation in the horizontal plane. These results, taken together with data on responses to optic flow stimuli obtained in a parallel study, strongly suggest an involvement of area VIP in the analysis and the encoding of self-motion.

Release of dopamine in vivo from cat substantia nigra

Abstract: THE central aminergic neurones present some original characteristics. By means of quantitative autoradiographic studies, it has been demonstrated that serotoninergic terminals projecting into the cerebral cortex and the locus coeruleus exhibit very few classical synaptic contacts1,2. This has also been seen with cortical noradrenergic terminals1. It has been suggested that the amines could be released not only in synapses, but also from varicosities devoid of synaptic junctions: they could thus act as neuromodulators at some distance from the release sites. It has also been proposed that dopamine could be released from dendrites of nigrostriatal dopaminergic neurones3. Indeed, a release of endogenous dopamine (Cuello, personal communication) or of labelled dopamine4,5 previously taken up in tissues, has been demonstrated using slices of the rat substantia nigra exposed to a high concentration of potassium (30 mM). This process was calcium dependent. An indication of possible dendritic release was also obtained indirectly in vivo by measuring dopamine metabolites in the rat substantia nigra6. Dihydroxyphenylacetic acid and homovanillic acid levels were increased after stimulation of the medial forebrain bundle, which contains axons of various ascending aminergic pathways including the nigrostriatal dopaminergic system. Therefore, dopamine could be released not only from nerve terminals in the striatum, but also from dendrites in the substantia nigra. If the latter mechanism was occuring in physiological states, it could have important implications for the understanding of the regulatory processes involved in the control of the activity of the dopaminergic neurones. It thus seemed necessary to demonstrate directly an in vivo release of dopamine in the substantia nigra.

Glass transitions in thin polymer films

Abstract: Freely standing polystyrene films show an anomalous drop of the glass temperature \(\) when the molecular weight is high and the thickness smaller than the coil size R0. We present here a tentative explanation for these features, where two types of motions compete: a) standard motions, controlled by the free volume, and independent of chain length, b) collective motions along the chain, which require a weaker free volume (except for the end groups). For bulk systems, the standard motion always wins because of the end group hindrance. But for films thinner than the coil size, the dominant process may be the collective motion of a “loop” which does not involve the chain ends. What matters then is not the overall polymerisation index (N), but the length g of a typical loop starting from the surface (which is a more fluid region) and reaching deep into the film. With these ingredients, some surprising aspects of \(\) may possibly be understood.