Research Project
10387757
PROJECT SUMMARY The overall goal of NIGMS-funded research in my lab is to understand the fundamental principles of how the brain integrates the sensory percept of food with the sensation of hunger to regulate food intake on the level of molecules, cells and circuits. We are using the genetically tractable model organism, the fly (Drosophila melanogaster) to study how food intake circuits function and are regulated in the brain. One of the main aims of this project is to capture neural activity from circuits that regulate food intake when flies are changing their metabolic states. These experiments require non-invasive imaging of the fly brain at long time scales (>6 hours). Current methods used in fly optical neurophysiology do not allow such experiments because the cuticle-open imaging preparations that are commonly used in fly neuroscience research show reliable calcium responses for a maximum of ~3-4 hours before the fly brain starts degenerating. Recently, we have developed a non-invasive, chronic functional imaging method in flies. We first showed that, in contrast to a misconception in the field, the fly head cuticle has surprisingly high transmission at wavelengths > 900 nm, and the difficulty of through-cuticle imaging is due to the air sacs and/or fat tissue underneath the head cuticle. Removing air sacs completely or relocating them out of the imaging window by non-invasive compression of the fly head allows optical access to the fly brain without dissecting away the head cuticle. Using our through-cuticle imaging method, we first imaged the mushroom body Kenyon cells and the central complex ring neurons in the fly brain through the cuticle using 2P and 3P microscopy. Our measurements showed that 2P and 3P excitation performed similarly in shallow regions of the fly brain, but 3P excitation at 1320 nm is superior for deeper brain structures. We demonstrated the functional imaging performance of through-cuticle multiphoton imaging by capturing odor evoked calcium responses from mushroom body Kenyon cells expressing GCaMP6s in short-term and in long-term as flies are being food deprived. We plan to use through-cuticle functional imaging to capture the activity of neural circuits that regulate taste perception and food intake in flies. These neural circuits are located in deeply buried regions of the fly brain below the esophagus (subesophageal zone), therefore cannot be accessed with 2P excitation (920nm) through the cuticle. Therefore, our plan is to use 3P excitation (1320nm) to image these deep neural circuits in the intact fly brain through-cuticle. 3P-microscopy will enable chronic imaging of the taste sensitive neurons and food intake circuits as flies are changing their metabolic states and will allow us to answer important questions in neuroscience, such as: How do the taste circuits change activity when animals are changing their physiological states such as hunger/thirst? How do neural circuits encode behavioral states such as hunger/thirst? This project will not only push the limits of in vivo functional imaging in flies but also answer fundamental questions in neuroscience.
