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Neurotransmitters in the neuronal circuit for motion vision in Drosophila melanogaster
Neurotransmitters in the neuronal circuit for motion vision in Drosophila melanogaster
Understanding how neuronal circuits perform computations on the cellular and molecular level is a crucial step towards deciphering how brains function. Yet, the complete elucidation of mechanisms underlying simple computations such as the visual detection of movement is still missing. In this dissertation, I employ genetically accessible model organism Drosophila melanogaster to investigate the neurotransmitter systems that are used by cells in the neuronal circuit for motion vision. The contribution of this dissertation to current knowledge about the neuronal circuit for motion vision in D. melanogaster is as follows: In the publication “Neural circuit to integrate opposing motions in the visual field”, together with my colleagues, we identify two new types of neurons in the motion vision circuit termed LPi3-4 and LPi4-3 cells that receive input from the local motion detectors, the T4 and T5 neurons and provide inhibitory input to wide-field motion-selective lobula plate tangential cells. Using antibody immunostainings and single-cell transcriptome analysis, we show that the neurotransmitter used by the LPi3-4 and LPi4-3 neurons is glutamate. Glutamate released from the LPi3-4 neurons opens a chloride channel GluClα on the dendrites of the LPTCs and thus, its role at this synapse is inhibitory. In addition, we demonstrate that the LPi3-4 neurons are necessary for tuning of the lobula plate tangential cells to movement in a specific direction in naturalistic situations where competing visual stimuli moving in various directions are present. In the publication “RNA-seq transcriptome analysis of direction-selective T4/T5 neurons in Drosophila”, I provide the first genome – wide transcriptome analysis of the T4 and T5 neurons. The obtained gene expression database characterizes the expression levels of all neurotransmitter receptors in T4 and T5 neurons and thus, gives information on which neurotransmitters provide input to T4 and T5 neurons. Moreover, the transcriptome analysis reveals the co-existence of the cholinergic and GABAergic markers in D. melanogaster neurons that has not been described previously. This study also analyzes the biophysical implementation of the computations performed by the T4 and T5 neurons on the molecular level. In the publication “Transgenic line for the identification of cholinergic release sites in Drosophila melanogaster”, using the newly generated FRT-STOP-FRT-VAChT::HA allele, I show that the Mi1 and Tm3 neurons possess cholinergic release sites in their axons and thereby likely provide cholinergic input to the local motion detectors, the T4 neurons. The FRT-STOP-FRT-VAChT::HA allele described in this study is a universal tool that can serve for the identification of cholinergic cells also in other neuronal circuits in D. melanogaster.
vision, acetylcholine, GABA, motion detection, circuit neuroscience
Pankova, Katarina
2017
English
Universitätsbibliothek der Ludwig-Maximilians-Universität München
Pankova, Katarina (2017): Neurotransmitters in the neuronal circuit for motion vision in Drosophila melanogaster. Dissertation, LMU München: Graduate School of Systemic Neurosciences (GSN)
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Abstract

Understanding how neuronal circuits perform computations on the cellular and molecular level is a crucial step towards deciphering how brains function. Yet, the complete elucidation of mechanisms underlying simple computations such as the visual detection of movement is still missing. In this dissertation, I employ genetically accessible model organism Drosophila melanogaster to investigate the neurotransmitter systems that are used by cells in the neuronal circuit for motion vision. The contribution of this dissertation to current knowledge about the neuronal circuit for motion vision in D. melanogaster is as follows: In the publication “Neural circuit to integrate opposing motions in the visual field”, together with my colleagues, we identify two new types of neurons in the motion vision circuit termed LPi3-4 and LPi4-3 cells that receive input from the local motion detectors, the T4 and T5 neurons and provide inhibitory input to wide-field motion-selective lobula plate tangential cells. Using antibody immunostainings and single-cell transcriptome analysis, we show that the neurotransmitter used by the LPi3-4 and LPi4-3 neurons is glutamate. Glutamate released from the LPi3-4 neurons opens a chloride channel GluClα on the dendrites of the LPTCs and thus, its role at this synapse is inhibitory. In addition, we demonstrate that the LPi3-4 neurons are necessary for tuning of the lobula plate tangential cells to movement in a specific direction in naturalistic situations where competing visual stimuli moving in various directions are present. In the publication “RNA-seq transcriptome analysis of direction-selective T4/T5 neurons in Drosophila”, I provide the first genome – wide transcriptome analysis of the T4 and T5 neurons. The obtained gene expression database characterizes the expression levels of all neurotransmitter receptors in T4 and T5 neurons and thus, gives information on which neurotransmitters provide input to T4 and T5 neurons. Moreover, the transcriptome analysis reveals the co-existence of the cholinergic and GABAergic markers in D. melanogaster neurons that has not been described previously. This study also analyzes the biophysical implementation of the computations performed by the T4 and T5 neurons on the molecular level. In the publication “Transgenic line for the identification of cholinergic release sites in Drosophila melanogaster”, using the newly generated FRT-STOP-FRT-VAChT::HA allele, I show that the Mi1 and Tm3 neurons possess cholinergic release sites in their axons and thereby likely provide cholinergic input to the local motion detectors, the T4 neurons. The FRT-STOP-FRT-VAChT::HA allele described in this study is a universal tool that can serve for the identification of cholinergic cells also in other neuronal circuits in D. melanogaster.