Measurements of Optically and Chemically Stimulated Neurotransmitter Release in Drosophila

Model systems are needed in the study of neurotransmission mechanisms and in the search for treatments for diseases of the central nervous system. Drosophila melanogaster, the fruit fly, is an attractive model organism because it has a complex nervous system that has many conserved pathways with mammals and it is easy to genetically alter. To use Drosophila as a model system to study the molecular and genetic basis for neurological diseases, a comprehensive understanding of its neurotransmitter systems is necessary.
My dissertation research focuses on measurements of real-time neurotransmitter changes in Drosophila central nervous system using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. My research concentrates on developing methods in three aspects: the sensor for detection, the modeling method and the control of neurotransmitter release. Chapter 2 introduces a method to modify the microelectrode with aligned carbon nanotube forests. The aligned carbon nanotube forests greatly improved electrode sensitivity and selectivity, and facilitated faster measurement. Chapter 3 describes optogenetic control of serotonin or dopamine release with pulsed optical stimulations. A modeling method which has been well established in mammalian models was exploited to estimate dopamine and serotonin release and clearance kinetics in Drosophila larva. We found the Vmax and Km for serotonin and dopamine in Drosophila were similar to their values in mammals, but the amount of neurotransmitter released per pulse was smaller. Chapter 4 employs a chemical stimulation method to investigate the releasable and reserve dopamine pools in Drosophila larva. With ATP/P2X2 mediated stimulation, we found both synthesis and reuptake were needed to maintain the releasable dopamine pool, with synthesis playing a major part in long-term replenishment and reuptake being more important for short-term replenishment and there was no cocaine-activated reserve pool of dopamine in Drosophila. These studies overcome critical technical barriers to get a better understanding of dopamine and serotonin regulation in Drosophila, and strengthen the use of this model organism for the study of mechanisms underlying human behaviors and neurodegenerative diseases.