Project Summary/Abstract Understanding how endogenously-generated adult-born neurons functionally integrate into neural circuits may inform strategies employing stem cell-derived neurons to repair damaged brain areas. Olfactory sensory neurons (OSNs), which are generated throughout life in all mammals, provide an ideal model to study functional integration in both the healthy and the regenerating olfactory system. Our long-term goal is to determine how circuit function and regeneration can be enhanced by functional integration of newborn neurons. The overall objective of this application is to determine how evoked activity during an immature developmental window influences OSN survival and integration in the healthy and the regenerating olfactory system. Our central hypothesis is that odor selective input to immature OSNs is required for their survival and functional integration in both the healthy and the regenerating olfactory system. To test this hypothesis, we propose three specific aims. First, we will define the odor selectivity of immature OSN sensory input to the OB, using in vivo 2-photon calcium imaging. Second, we will determine the role of evoked activity in immature adult-born OSNs in their survival and functional integration. We will up- and down-regulate evoked activity in OSNs during the immature developmental stage, and use immunohistochemistry, electron microscopy, optogenetics and in vivo 2-photon structural and functional imaging to assay their survival, synaptogenesis and functional integration. Finally, we will determine the role of immature OSN activity in regeneration of OSN input to the OB. For this aim, we will chemically ablate OSNs, which regenerate from olfactory epithelium stem cells, manipulate activity using naris occlusion and chemogenetic silencing during regeneration, and use in vivo 2-photon time-lapse imaging to track structural and functional regeneration of OSN input to glomeruli. We expect to find that evoked activity during immaturity plays a key role in the survival and integration of that OSN. Hence, our proposed work will have an important impact by defining how functional integration of an endogenous population of stem cell-derived neurons is regulated to maintain and regenerate brain function. This study will be highly significant in elucidating the role of activity in an endogenously-generated population of newborn neurons in regulating their functional integration, thereby providing important insight relevant to the development of stem cell-based therapeutic strategies to repair damaged neural circuits. Our proposed research is conceptually innovative in proposing that sensory input during the immature phase of development is crucial to successful functional integration of OSNs in the healthy and regenerating OB and will employ a technically innovative array of experimental approaches.