Laura Anne DeNardo - US grants

DESCRIPTION (provided by applicant): The mammalian neocortex is a six-layered structure that creates a representation of the world by integrating sensory information and controls behavior by generating the appropriate motor output. Each layer processes information differently, so understanding how layer-specific neuronal networks are organized will provide a foundation for understanding how different layers function within circuits. The medial prefrontal cortex (mPFC) integrates information from many brain regions and is involved in complex behaviors including social interaction and decision-making. Importantly, mPFC circuits are often disrupted in neurodevelopmental disorders such as autism, but little is known about the fine scale organization of mPFC or how mPFC layers integrate different kinds of information. The Luo lab recently developed a modified rabies-based mono-trans- synaptic tracing technique that allows for detailed analysis of local circuitry in addition to whole brain long- distance mapping. This new rabies technique can be combined with layer-specific Cre driver mouse lines to generate detailed maps of layer-specific circuits in medial prefrontal cortex (mPFC). Cre-dependent rabies tracing will also be combined with cell-type specific gene knockout, so these maps will provide a basis for studying genetic regulation of neocortical connectivity in development and disease with unprecedented precision and scope. To begin to dissect the molecular pathways involved in establishing specific mPFC connectivity, this project will focus on the role of the autism-related gene Tsc1. Recent studies showed that Tsc1 deletion increases excitatory synaptic connectivity and alters the balance of excitation and inhibition, causing hyperexcitability in hippocampal neurons. This phenotype may be related to the role of Tsc1 in Tuberous Sclerosis Complex, a disease in which patients suffer from benign tumors, epilepsy, and autism. Performing Cre-dependent rabies tracing in conditional Tsc1fl/fl mice crossed with layer-specific Cre-drivers will facilitate investigation of the cell-autonomous role o Tsc1 in the development of mPFC connectivity and layer- specific organization. As Tsc1 is a negative regulator of the mammalian target of rapamycin complex, mTORC1, the molecular mechanisms underlying the in vivo function of Tsc1 will also be investigated to elucidate how these signaling pathways regulate brain development. This work will provide a deeper understanding of the molecular and the circuit-level mechanisms that give rise to autism and epilepsy in patients with Tsc1 mutations.

PROJECT SUMMARY / ABSTRACT The long-term goal of this proposal is to establish successful independent laboratory focused on dissecting medial prefrontal cortex (mPFC) circuits underlying behaviors that become maladaptive in psychiatric disorders. mPFC plays a critical role in cognition, memory, and emotional behaviors which become maladaptive in diseases such as ADHD, dementia, and anxiety and trauma-related disorders. mPFC projects widely to cortical association areas, limbic centers, and midbrain and brainstem nuclei which are uniquely implicated in mPFC-dependent behaviors. How does mPFC coordinate its diverse projections to give rise to specific behaviors? Here I propose to use learned fear and fear extinction as entry points to elucidate classes of mPFC neurons that underlie behavior. Memories of fearful associations promote survival and can last a lifetime, but become extinguished when a stimulus no longer poser threat. Anxiety and trauma-related disorders have a lifetime prevalence of 28% and are characterized by maladaptive threat assessment that leads to inappropriate fear responses. The mPFC subregion PL is required for expression of learned fear at recent and remote time points, but, largely due to the lack of appropriate tools, the processes by which the remote trace forms in PL remains mysterious. Furthermore, it is unclear how behavioral extinction affects the memory trace in PL, and the classes of PL projections neurons underlying fearful behaviors remain unknown. The objective of this proposal is to determine 1) how the remote memory trace forms in PL, 2) which classes of PL projection neurons underlie remote memory retrieval, and 3) how extinction impacts the PL remote memory trace. The central hypothesis is that specific classes of mPFC neurons can be accessed based on their activity during behavior, and subsequently characterized based on their projection patterns and behavioral function. This hypothesis will be tested using cutting-edge neuroscience technologies in combination with TRAP2, a new mouse genetic tool for permanently accessing neurons that are transiently activated during a particular experience. Completion of the proposed studies will elucidate the behavioral function and projection patterns of PL neurons that contribute to remote memory retrieval, and determine how their function is influenced by extinction. These contributions are significant because they will reveal the functional circuit organization underlying mPFC-dependent fear behaviors that are relevant to psychiatric disorders. A team of world-renowned neuroscientists will oversee this research. Drs. Liqun Luo, Gregory Quirk, Vikaas Sohal, Marc Tessier-Lavigne, and Mark Schnitzer and will provide new training to link the organization of neural circuits to behavior and offer career advice. Together with a comprehensive training plan that includes additional coursework and numerous career development activities, completion of this proposal will provide the necessary skills for Dr. DeNardo to secure an independent faculty position at a top research institution.