PROJECT SUMMARY/ABSTRACT The long-term goal of this project is to determine the molecular mechanisms by which sex-determining genes and reproductive hormones differentially regulate olfactory sensitivity in males and females. In humans, olfactory performance is highly dependent on age and sex; women generally outperform men in smell identification, and men are more prone to olfactory impairment as they age. Similarly, in other animal species, select groups of odorant receptor neurons (ORNs), such as those important for pheromone detection, exhibit sexually dimorphic characteristics as animals reach the age of sexual maturity. However, the mechanisms underlying sexually-dimorphic neurophysiology are poorly understood.The research outlined here takes advantage of the powerful genetic toolkit of the Drosophila olfactory system to address this complex question. In this proposal, the first aim is to determine the generality of age-dependent sensitization in courtship- promoting ORNs. The hypothesis that all courtship-promoting ORNs in males undergo age-dependent sensitization will be tested using genetic, pharmacological, and functional imaging approaches. The second aim proposes a genetic analysis of downstream effector molecules that enhance olfactory sensitivity in the courtship-promoting ORNs. Finally, the third aim will test the hypothesis that a reproductive hormone promotes age-dependent sensitization through its interaction with a male-specific transcription factor. Results from these studies are expected to yield critical mechanistic insights into how sex-determining genes and reproductive hormones jointly regulate sensory neurophysiology and olfactory processing. These insights may have implications in understanding sexually dimorphic neurophysiology and sex-specific proclivities for certain neurodegenerative diseases.