Projet ANR-10-BLAN-1411 – OpticNeuron : Dissection optique du flux d'information dans un neurone du cerveau
Programme : Sciences de la vie, de la santé et des écosystèmes :  Neurosciences (Blanc SVSE 4)
Année de financement : 2010
Coordinateur du projet : Monsieur David DiGregorio (INSTITUT PASTEUR)
Partenaires : Institut Pasteur
Montant : 481077.0 euros
Date de début : 2011
Durée : 36 mois
Résumé : Optical approach to the study of how neurons in the brain compute informationInformation processing in the brain involves the summation, integration, and propagation of electrical and chemical signals. We use optical methods to identify fundamental rules by which neurons process and/or compute such signals.
Application of novel optical methods for studying how neurons communicate via synapses.Synapses are the fundamental computation unit of neurons, but are extremely small and inaccessible by classical studies using electrodes. We have developed and characterized molecules that indicates changes in voltage and calcium be increasing their fluorescence. We expect these tools and methods to be useful for other investigators and are suitable for the study of neuronal function in models of human neurological disorders.
Application of novel optical methods for studying how neurons communicate via synapses.1. We further characterized an optical reporter of membrane voltage that we developed in the laboratory a few years previously. We demonstrated that it can be used for detecting single synaptic responses in remote parts of the cell and can be used with the advanced optical microscopy (multi-photon excitation) which enables imaging in live animals.2. Using multi-photon excitation (deep tissue imaging of single neurons) and optical activation of synapses to study, for the first time, how dendrites of cerebellar interneurons compute incoming information. 3. We are currently combining the optical sensors of voltage (see point 1) and calcium, using the deep tissue imaging methods to extend the study of dendritic computations.
Résumé de la soumission : Le cerveau contient des milliards de neurones qui communiquent entre eux au travers de contacts spécialisés que l'on nomme synapses. Les défauts de fonctionnement de ces contacts entre neurones sont responsables des déficits mnésiques associés à des désordres neuropathologiques comme la maladie d'Alzheimer. Nous proposons ici une série d'expériences développées pour identifier et caractériser les mécanismes cellulaires et physiologiques qui influencent la transmission et l'intégration synaptique au sein du cerveau sain. L'étude de ces mécanismes est difficile en raison de l'inaccessibilité de la signalétique des compartiments subcellulaires des neurones (i.e., synapse, dendrite, axone). Nous combinerons des méthodes optiques récemment développées en microscopie confocale et holographique pour réaliser de l'imagerie calcique et des mesures de potentiel transmembranaire au sein des compartiments jusqu'alors inaccessibles d'un neurone. Ces mesures seront simultanément réalisées avec des photoactivations de synapses uniques ou multiples. En montrant et manipulant la signalétique des synapses au sein de dendrites très fins, d'épines uniques, de branches dendritiques, voire dans les boutons presynaptiques, nous espérons pouvoir identifier des mécanises cellulaires fondamentaux nécessaires à une meilleur compréhension du transfert de l'information, et des capacités computationnelles, d'un neurone du cerveau.
Résultats : 1. We further characterized an optical reporter of membrane voltage that we developed in the laboratory a few years previously. We demonstrated that it can be used for detecting single synaptic responses in remote parts of the cell and can be used with the advanced optical microscopy (multi-photon excitation) which enables imaging in live animals.
2. Using multi-photon excitation (deep tissue imaging of single neurons) and optical activation of synapses to study, for the first time, how dendrites of cerebellar interneurons compute incoming information. 
3. We found that calcium ions are summated differently than the synaptic voltage, resulting in differential signaling that is capable of changing the strength or efficacy of synapses –potentially important for storing motor memories in the cerebellum.
Perspectives : While optical strategies for making such measurements hold great promise, optical sensors generally lack the speed and sensitivity necessary to record neuronal activity on a single-trial, single-neuron basis. Here we show that our voltage sensitive indicator is sufficiently fast and sensitive that we can monitor the flow of electrical signals between and within neurons within living brain tissue, and may be applicable to the study in live animals.
Interneurons are important for regulating information flow in the brain, and defects in their signaling produce runaway excitation resulting in epileptic episodes. Our findings that cerebellar interneurons serve to signal sparse patterns of electrical activity because of dendrite computations are  important for understanding how the cerebellum cortical circuit functions, and may contribute to  such behaviors as motor coordination. Finally, our findings indicate computational rule that could pervade in neurons of other brain regions.
Publications et brevets : 1. Abrahamsson, T.,  Cathala,  L., Matsui, K., Shigemoto, R., and DiGregorio, DA. Thin dendrites of cerebellar interneurons confer sublinear synaptic integration and a gradient of short-term plasticity. Neuron, 73: 1159-1172 (2012).
2. Fink AE., Bender, KJ., Trussell, LO., Otis, TS. and DiGregorio, DA. Two-photon compatibility and single-voxel, single-trial detection of subthreshold neuronal activity by a two-component optical voltage sensor. PLoS One, 7(8):e41434 (2012).