Neuroplasticity in chemosensory-mediated social behaviors - Summary During development and throughout adulthood, humans display strong neuroplasticity, the capacity of adaptive changes of neurons and neural circuits in response to social environments. Plasticity in chemosensory system is essential for learning and memory, social communication and quality of life. Loss of olfactory sensing (anosmia) leads to social isolation, neurological diseases, such as schizophrenia, Alzheimer’s disease (AD) and Parkinson’s disease (PD), and social disorders such as autism. However, the role of neuroplasticity in olfactory- mediated social behaviors is unclear and understudied. We and other labs have developed genetic tools in ants, thereby providing a novel model to study olfactory neuroplasticity in social organisms, as (a) ants are highly social and display complex social behavior; (b) ants display striking neuroplasticity during development and throughout adulthood; (c) neuronal activity is likely required for proper development of olfactory neurons in ants, which is reminiscent of activity-dependent neuronal survival in mammals. The Drosophila genome contains 60 odorant receptor (Or) genes, while 300-500 Or genes have been identified in several ant genomes. In the ant Harpegnathos saltator, mutation in the gene odorant receptor co- receptor (orco), which disrupts the function of all ORs, significantly impacts ant olfaction, and mutant animals display a wide range of abnormal social behaviors. Surprisingly, and unlike other insects, such as Drosophila, this loss of OR functionality during development dramatically reduces the number of odorant receptor neurons (ORNs) and antennal lobe (AL) glomeruli where ORNs project. Further transcriptome analysis suggests that there are two types of ORNs: activity-dependent and activity-independent ORNs. We will use these features in the orco-/- ants and perform a series of molecular and cellular experiments to determine (a) the role of neuronal activity and receptor trafficking in olfactory neuronal survival, and (b) the role of gustatory and ionotropic receptors in neural development.