Investigating Through Multiple Experimental Approaches How Early Visual Circuit Functions Affect Drosophila Behaviour

Abstract Drosophila melanogaster has become a versatile model organism, with high genetic tractability and ease of manipulability, mixed with low cost and low space constraints. Genetic tools with which to modify flies in myriad ways are constantly developed and updated, whilst physical tools have also become more apt for access to various biological systems. In this thesis I have used several such tools, such as the Drosophila flight simulator, High Pressure Freezing and Transmission Electron Microscopy to test visual behaviour and synaptic function, respectively. In Drosophila’s early visual system, R1-R6 and R7/R8 information channels carry visual information to the visual brain. These channels have been thought separated on the basis of their structure and function, however it is our hypothesis that these channels can functionally inform each other and that this occurs at an early stage of the visual pathway. Here I have used the flight simulator to show that the absence of ‘chromatic’ photoreceptors adversely affects visually-driven optomotor behaviour. In conjunction with other electrophysiological data, I have helped to support the idea that this influence may result from functional connection between R1-R6 and R7/R8 photoreceptors. Similarly, I have used the flight simulator to show that Ca2+-activated K+ channel mutations in post-synaptic Large Monopolar Cells can affect visual behaviour, but that these effects are often managed by homeostatic mechanisms that serve to maintain biologically-relevant function. Additionally, I have shown that the absence of dietary Polyunsaturated Fatty Acids can influence visual behaviour. Pre- and post-synaptic information at Drosophila photoreceptor synapses has been shown to adapt in accordance with changing visual conditions. I used programmes of light- and dark-adaptation, along with High Pressure Freezing and Transmission Electron Microscopy to test how these adaptations are translated at the synapse. All of these conclusions are discussed alongside electrophysiological findings acquired from the early visual system.