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The Role of Type 2 Polyaxonal Amacrine Cells (PAC2) in mediating light adaptation Work conducted under advisor: Dr. David M. Berson Marjo Beltoja, Biophysics, Class of 2018 A thesis presented for the Honors in Biophysics Bachelors of Science Degree Department of Biophysics Brown University USA April, 2018 Contents 1 Abstract 4 2 Introduction 6 2.1 Anatomy of the Retina . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Amacrine Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 The Intrinsically Photosensitive Retinal Ganglion Cell . . . . . . . . . 11 3 Methods 14 3.1 Animal Model Used . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 3.2 Retinal Tissue Preparation . . . . . . . . . . . . . . . . . . . . . . . . 14 3.3 Imaging via SBEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.4 Tracing Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 4 Results 17 4.1 The Polyaxonal Amacrine Cell (PAC 2) Circuitry . . . . . . . . . . . 17 5 Discussion 25 5.1 Summary of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 5.2 Further directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 5.3 Limitations of Knossos Tracing . . . . . . . . . . . . . . . . . . . . . 26 5.4 Advantages of Knossos Tracing . . . . . . . . . . . . . . . . . . . . . 28 6 Acknowledgments 29 6.1 Appreciations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 6.2 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2 List of Figures 2.1 General overview of the retina’s location in the eye. . . . . . . . . . . 7 2.2 The different layers constituting the retina. . . . . . . . . . . . . . . . 8 2.3 A likely model of how PAC2s modulate RGCs. . . . . . . . . . . . . . 10 2.4 The M1-M3 ipRGCs displayed in numerical order starting with the M1 on the far left. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4.1 Electron micrograph of an output synapse from the PAC2. . . . . . . 18 4.2 Output synapses of the PAC 2. . . . . . . . . . . . . . . . . . . . . . 19 4.3 A.