Use-Dependent Adjustments to Dopamine Reception in Motivational Control - Motivational disruptions are at the center of mental illness, triggering depression, addiction, bipolar, and a variety of other disorders. Shifts in dopamine signaling often underlie these conditions, but the molecular mechanisms that trigger and sustain lasting dopaminergic changes are poorly understood. Elevations in dopamine that occur during drug use have long been known to trigger an enduring decrease in natural dopamine signaling. This homeostatic downregulation is a central factor in addiction, both because addicts require more and more drug and because non-drug related behaviors become devalued. To my knowledge, dopamine-triggered dopamine desensitization has never been linked to the motivational control of natural behavior. I present a new, genetically tractable system that links the devaluation that occurs after goal attainment to dopamine desensitization. This system brings the power of Drosophila genetics to this important and widespread phenomenon, making use of innate behavior in a well-defined system with genetic access to dopamine-releasing and dopamine-receiving neurons. I show that devaluation occurs over the course of repeated bouts of Drosophila mating behavior. We have localized this effect to the desensitization of the D2 dopamine receptor on a defined set of decision-making neurons. I propose to assemble a detailed molecular pathway that initiates and sustains desensitization to dopamine. We will integrate the results from new genes identified in a genetic screen with the knowledge obtained over decades in the GPCR inactivation and addiction fields to understand how the rewarding dopamine released during prior matings triggers a long-lasting desensitization of the D2 receptor. Our data implicate β- arrestin signaling, which inactivates the D2 receptor in mammals, another early indication of the broad relevance of our findings. Our ability to precisely label and manipulate the neurons that receive the dopamine signal gives us a unique opportunity to observe the mechanisms of dopamine desensitization and the molecular and physiological consequences. We have pioneered the use of 2-photon Fluorescence Lifetime Imaging (FLIM) in Drosophila neurobiology and have developed a preparation to monitor the devaluation of mating at the level of D2 receptor desensitization. We will use the FLIM-compatible biosensors for calcium and CaMKII that we have adapted for the fly, and will use them, together with our molecular genetic manipulations to visualize desensitization and its underlying mechanisms. These experiments will establish a new platform for rapidly identifying and understanding the genes involved in triggering and sustaining behaviorally-relevant shifts in dopamine reception. They will identify new pathways for control over changes in motivational states, generating a molecular-level understanding of motivational control and developing new hypotheses for treating the consequences of its disruption.
