ERC FUNDED PROJECTS

"Chunking allows the brain to efficiently organize memories and actions. Although basal ganglia circuits have been implicated in action chunking, little is known about how individual elements are concatenated into a behavioral unit at the neuronal level. Using a differential reinforcement procedure where mice learn to chunk rapid action sequences, we uncovered neuronal activity encoding entire sequences as single actions in basal ganglia circuits. Besides activity signaling sequence initiation (start), we found neurons with sustained or inhibited activity throughout the execution of an entire sequence. These findings clearly show that basal ganglia circuits display neural activity related to the execution of whole action sequences, rather than unitary elements. Neurons with start, sustained and inhibited sequence-related activity were observed throughout the basal ganglia, namely in the main input (striatum), and output (substantia nigra reticulata) nuclei of the basal ganglia. However, the basal ganglia have different cell types/subcircuits linking input to output, the so called direct ves. indirect pathways. Furthermore, basal ganglia output projects to different target areas. Here we will 1) determine if these correlates of motor concatenation are differentially expressed in direct versus indirect basal ganglia pathways by optogenetic identification of cell types in the striatum and in vivo imaging, 2) test the necessity and sufficiency of these two pathways in action sequence initiation and performance, and 3) test if different basal ganglia output circuits express and mediate different aspects of action chunking. These experiments will dissect with unprecedented spatial and temporal precision the role of basal ganglia subcircuits in the initiation and performance of action chunks."

1 998 600 €

Start date: 2014-11-01, End date: 2019-10-31

Understanding how our brains extract relevant features of sensory input to select and guide appropriate actions is a fundamental goal of neuroscience. Yet even relatively simple sensorimotor reflexes can depend on activity within complex networks of neurons that are distributed across the brain, presenting a challenge for traditional neuroscience approaches. Our recent work has demonstrated the capacity to image neural activity with single cell resolution throughout the small transparent brain of behaving zebrafish. Here we will trace, from sensory input to motor output, the neural circuits that allow zebrafish to select and execute distinct swimming patterns in response to varying visual input. Through comprehensive whole-brain functional imaging in combination with optical and genetic circuit tracing, we aim to determine the principles on which these sensorimotor circuits are organised and reveal how activity dynamics unfold throughout the whole brain during behaviour. We will take a systematic approach to this problem, based on a thorough quantitative analysis of swim kinematics and the sensory stimuli that drive them. We will: 1) Use whole-brain functional imaging of genetically defined neural populations to reveal the neural circuit organization and activity dynamics during visuomotor behaviour. 2) Establish how motor commands are encoded at the single-cell and population level by brainstem reticulospinal neurons, through imaging and ablation studies and 3) Systematically map the functional organisation of retinal inputs into the brain. Taken together, these experiments will provide an unprecedented, single-cell resolution view of the organization of complete circuits that transform retinal inputs to motor outputs in the vertebrate brain.

1 694 063 €

Start date: 2018-02-01, End date: 2023-01-31

In every day life, we constantly have to select the appropriate actions to obtain specific outcomes. Actions can be selected based on their consequences, for example when we press an elevator button to get to the particular floor where we live. This goal-directed behaviour is crucial to face the ever-changing environment but demands an effortful control and monitoring of the response; one way to balance the need for flexibility and efficiency is through automatization of recurring decision processes as a habit. Habitual responses no longer need the evaluation of their consequences, and can be elicited by particular situations or stimuli, for example when we press the button for our home floor in a building that we are visiting for the first time. There is growing evidence that the neural circuits underlying intentional or goal-directed actions are different from those underlying habits; associative corticostriatal circuits have been implicated in goal-directed actions, and sensorimotor circuits in habit formation. Dopamine (DA) has been implicated in both voluntary actions and habits. However, DA neurons from the VTA and the SNc project to different cortical and striatal regions, and the specific role of VTA and SNc DA in goal-directed actions and habits has not been clarified. We propose to: 1) use cell-type and region specific genetic manipulations to test if phasic firing in VTA or SNc DA neurons is necessary for goal-directed actions or habits, respectively, 2) generate cell-type specific channelrodhopsin transgenic mice to test if phasic DA neuron firing in these areas is sufficient to produce goal-directed actions or habits, and 3) selectively manipulate striatal neurons modulated by VTA or SNc phasic DA to test if they are necessary for goal-directed actions or habits. The dissection of the molecular and circuit mechanisms underlying goal-directed and habitual responses will be critical to understand decision-making, and the origins of compulsive behaviour.

1 526 304 €

Start date: 2009-11-01, End date: 2014-10-31

Determining how the organisation of neural circuitry gives rise to its function has been a major challenge for understanding the neural basis of perception and behaviour. In order to uncover how different regions of the neocortex process sensory information, it is necessary to understand how the pattern and properties of synaptic connections in a specific sensory circuit determine the computations it performs. I propose to establish the relationship between synaptic connectivity and neuronal function in primary visual cortex (V1) with the aim of revealing circuit-level mechanisms of sensory processing. To this end, my laboratory has developed a new method, by which visual response properties of neurons are first characterised with two-photon calcium imaging in vivo, and then synaptic connections between a subset of these neurons are assayed with multiple whole-cell recordings in slices of the same tissue. We will use this method to determine how connectivity, synaptic and intrinsic properties of different excitatory and inhibitory cell types relate to the emergence of their visual receptive fields (RFs). Specifically, we will test the dependence of connections on RF position, structure and other visual response properties, the specificity of connections between simple and complex cells, and the relative contribution of feedforward and recurrent excitation and inhibition towards shaping RFs. Morphological, physiological, connectional and functional data will be used to develop a biophysically realistic network model of this V1 circuit to examine the contribution of different circuit components to single-neuron and network function.

1 983 289 €

Start date: 2014-05-01, End date: 2019-04-30

"Repulsive guidance cues for growing axons and factors inhibiting neurite growth are increasingly recognized as key players for nerve fiber growth and plasticity in the developing and adult nervous system. The first neurite growth inhibitory factor discovered in the context of axonal regeneration in the adult central nervous system (CNS) was the membrane protein Nogo-A. Inactivation of Nogo-A, e.g. by neutralizing antibodies, after spinal cord injury, brain injury or stroke leads to improved functional recovery in parallel with long distance regeneration of injured fibers and enhanced compensatory sprouting. The molecular mechanisms of action of Nogo-A is only partially known; a key element, the Nogo-A-specific receptor has remained undefined. We have recently found a membrane protein that binds to Nogo-A with high affinity; blockers of this new receptor neutralize many of the typical Nogo-A effects in vitro. The present proposal addresses new aspects of the mechanism of action and the in vivo roles of this novel Nogo-A receptor and its interactions with the known Nogo receptor components. The new results will contribute to the molecular and physiological understanding of Nogo-A and related growth inhibitors in the nervous system. Together with the currently ongoing clinical trial to enhance recovery after spinal cord injury in patients by anti-Nogo-A antibodies, the results of the present project will form an important basis for further treatments in brain injury and stroke."

2 500 000 €

Start date: 2012-06-01, End date: 2017-05-31

To understand the molecular basis of any biological process, it is critical that one is not only able to visualize and monitor molecular events that underlie this process, but also to possess the tools to manipulate these events in a spatial and temporal fashion both in and out of the cell. The overall objective of this proposal is to apply chemical biology approaches to allow real time monitoring of protein aggregation and to dissect the role of specific disease-associated post-translational modifications, phosphorylation, nitration, and truncation on the structure, aggregation, and biochemical properties of monomeric a-syn in health and disease. To achieve these goals, we plan to use a combination of organic chemistry, molecular biology, proteomics, protein engineering, and semisynthetic strategies to facilitate site-specific introduction of post-translational modifications that can be masked and activated in a controllable manner, both inside and outside living cells. Modified synthetic ±-syn will be introduced into primary neurons and cellular models of synucleinopathies and the consequences of masking or activating specific modifications will be assessed using biochemical, immunofluorescence, and live imaging techniques (Specific Aim 1). The absence of specific molecular probes that allow in vivo monitoring and quantitative measurement of toxic misfolded and aggregation intermediates represents a major impediment to understanding the relationship among protein misfolding, post-translational modification, protein aggregation, neurodegeneration, and cell death in PD and other neurodegenerative disorders. To address this challenge, we plan to develop and characterize novel antibodies that target different species along the amyloid formation pathway of ±-syn (Specific Aim 2).

1 495 400 €

Start date: 2009-12-01, End date: 2014-11-30

Chemosensory systems permit organisms to perceive diverse chemicals in the environment signalling the presence of food, dangers, kin or mates. How a specific chemical stimulus is recognised and converted into neural activity that provokes the appropriate behaviour is a fundamental problem in neuroscience. I investigate this question in the olfactory system of the fruit fly, Drosophila melanogaster, which exhibits sophisticated odour-driven behaviours under the control of a simple and genetically accessible nervous system. I recently discovered a novel Drosophila olfactory receptor family, the Ionotropic Receptors (IRs). IRs are expressed in sensory neurons distinct from the previously described Odorant Receptor (OR) family. Strikingly, IRs are structurally similar to ionotropic glutamate receptors (iGluRs), a conserved family of ligand-gated ion channels present in animals, plants and bacteria. iGluRs are best characterised for their role in mediating synaptic communication in the mammalian brain as receptors for the neurotransmitter glutamate, but IRs have divergent ligand-binding domains. The proposed project investigates the function of the IRs and their sensory circuits in the recognition of, and behavioural responses to, olfactory stimuli through four specific aims. Aim 1: Defining the molecular basis of IR/odour interactions. Aim 2: Visualising the mechanisms of IR trafficking. Aim 3: Mapping IR sensory circuits in the brain. Aim 4: Exploring the behavioural responses mediated by IR olfactory pathways. By combining genetic, cell biological, electrophysiological and behavioural approaches, this project will provide an integrated understanding of the function and evolution of these novel olfactory receptors and circuits. This knowledge will be of significance to chemical detection mechanisms across diverse sensory systems in eukaryotes and prokaryotes, and of interest to chemical ecologists, neuroscientists, evolutionary biologists and biomedical researchers.

1 500 000 €

Start date: 2008-07-01, End date: 2013-06-30

I recently proposed a model that helps explain the presence of p53 mutations and genomic instability in human cancers (Nature, 2005; Nature 2006; Science 2008). The key features of this model are that oncogenes induce DNA replication stress, which in turn leads to DNA double-strand breaks, genomic instability and p53-induced senescence or apoptosis. This model is relevant for almost all cancer types and explains the spectrum of mutations being reported in thousands of human cancers by the cancer sequencing consortia. In this project, I propose to take the next logical steps that follow from my discovery. Specifically, I propose the following objectives: 1. Elucidate the mechanisms by which oncogenes induce DNA replication stress. Oncogene-induced genomic deletions map within very large actively transcribed genes. Accordingly, I hypothesize that oncogenes and transcription synergistically disrupt pre-replicative complexes resulting in large genomic regions that have a low density of replication initiation events. To test this hypothesis, I propose to introduce by site-directed homologous recombination a transcription termination sequence at the beginning of very large gene and determine whether it remains sensitive to oncogene-induced genomic instability. Genome-wide transcription and DNA replication patterns will also be examined in cells that are sensitive to oncogene-induced DNA replication stress (most somatic cells and cell lines) and cells that are resistant (induced pluripotent stem cells). 2. Identify and characterize genes necessary for proliferation of cells with oncogene-induced DNA replication stress. Using high throughput siRNA screens we will identify genes, whose depletion inhibits proliferation of cells with oncogene-induced DNA replication stress, without affecting normal cells. We will explore the function of these genes using molecular biology, structural biology and genetic approaches. Some promising candidates have already been identified.

2 499 351 €

Start date: 2012-05-01, End date: 2018-04-30

While the functions of sleep are still a matter of debate and may include memory consolidation, brain clearance, anabolism and plasticity, the neural substrates of sleep and wake states are the subject of intense study. Successive sleep-wake cycles rely on an appropriate balance between sleep-promoting nuclei of the brain located in the anterior hypothalamus and, arousal-promoting nuclei from the posterior hypothalamus and the brainstem. My laboratory identified different subsets of hypothalamic cells that controls wakefulness and rapid-eye movement (also called paradoxical) sleep using optogenetics in combination with high-density electrophysiology in freely-behaving mice. We further identified their connections with (and functional modulation of) other sleep-wake circuits throughout the brain. Although we and others have dissected important subcortical and cortical sleep-wake circuits in the brain, the precise mechanism bridging sub-cortical circuits to thalamic and cortical networks remains unclear. I hypothesizes that the thalamus represents a hub that integrates sleep-wake inputs of both subcortical and cortical origin into stable sleep-wake states, through topographically distinct sub-cortical inputs and temporally precise circuit dynamics (spiking pattern, coherence). To test this hypothesis, my experimental objectives are divided into three specific aims: 1) Identify the simultaneous cellular dynamics of thalamo-cortical network activity across sleep-wake states (Observational approach; Year 1-3) 2) Characterize the subcortical modulation of thalamic structures across sleep-wake states (Perturbational approach; Year 2-4) 3) Study the role of TRN/CMT circuits in sleep homeostasis and consciousness (Functional approach; Year 4-5) Completion of this project will provide a mechanistic perspective on sub-cortical, thalamo-cortical and cortical control of sleep-wake states, sleep homeostasis and consciousness in the mammalian brain.

1 915 000 €

Start date: 2017-06-01, End date: 2022-05-31