Ian R. Wickersham - US grants

? DESCRIPTION (provided by applicant): Genetic tools have dramatically increased the power and resolution of neuroscientific experiments, allowing monitoring and perturbation of specific neuronal populations within the brain, often in the context of complex cognitive and behavioral paradigms. However, the usefulness of these tools is limited by the available means of delivering them in circuit-specific ways, a major drawback in view of the critical importance of specific connectivity between individual neurons and between neuronal classes. The primary available means of achieving transgene expression based on neurons' synaptic connections is virus-based transsynaptic tracing, which allows identification, activity imaging, optogenetic control, and perturbation of gene expression in networks of synaptically connected neurons in vivo. The required viruses, however, are toxic within a few days, precluding longer-term experiments that are needed to address many central questions in neuroscience. We will solve this problem by engineering viral transsynaptic tracing systems with either greatly reduced or entirely eliminated toxicity, so that the role of neuronal networks of known connectivity in cognition and behavior. The result will be a set of tools that will allow optical imaging, physiological recording, and manipulation of the activity and gene expression of neuronal networks of known synaptic connectivity in the context of behavioral and other experimental paradigms lasting weeks, months, or years, in any mammalian model species. This will greatly enhance our understanding of the neural bases of normal cognition as well as neurological and mental disorders.

? DESCRIPTION (provided by applicant): Monosynaptic tracing using rabies virus has become a standard component of the systems neuroscience toolkit, allowing identification and manipulation of neurons directly presynaptic to any targeted neuronal population in the brain. However, while this retrograde monosynaptic tracing system is now well established, an anterograde counterpart, which would allow identification and manipulation of neurons directly postsynaptic to a target cell group, has never been constructed. Here we propose to meet this important outstanding need, with a multipronged and tiered strategy designed to ensure the delivery of at least one anterograde monosynaptic tracing system to the field, and possibly of several such systems, of differing levels of ease of use, power, and sophistication. Success of any of our aims will provide neuroscience with a transformative new tool for understanding and manipulating neural circuits throughout the brain, in many species including rodents and primates. Achievement of all of our aims will provide a versatile and powerful array of techniques to systems neuroscientists, allowing a broad set of new experimental designs that are likely to quickly yield major insights into the organization of neuronal circuits and the biological bases of normal cognition and behavior and the dysfunctions underlying neurological and mental disorders.

PROJECT SUMMARY Every part of the brain is composed of dense tangles of heavily-interconnected neurons of many different types, each playing completely different roles in the circuitry. Rabies viral vectors have become indispensable tools for revealing the organization of this otherwise generally indecipherable jumble, because they allow the identification of synaptically-connected networks of neurons within the tissue. They also allow monitoring and manipulation of the activity of the virally-labeled neurons by optogenetics and other techniques, so that the contributions to mental processes of identified components of neural circuitry can be revealed. Despite their usefulness, however, rabies viral vectors have drawbacks, chief among which is their toxicity to the labeled neurons, which prevents their use in longer-term physiological and behavioral experiments that would provide major insights into the biological bases of cognition. In this project, we will develop a new generation of rabies viral vectors and monosynaptic tracing systems based on them that will allow completely nontoxic fluorescent labeling, optical monitoring, and optogenetic manipulation of synaptically-connected neuronal networks.