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Functional Connectivity in Cerebellar Cortex in Vivo

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Functional Connectivity in Cerebellar Cortex in Vivo PRINCIPLES OF EXCITATORY AND INHIBITORY FUNCTIONAL CONNECTIVITY IN CEREBELLAR CORTEX IN VIVO Charlotte Arlt University College London Thesis submitted for the degree of Doctor of Philosophy in Neuroscience 2017 Declaration I, Charlotte Arlt, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated. London, January 2017 2 Abstract Determining the functional impact of single interneurons on neuronal output, and how interneurons are recruited by physiological patterns of excitation, are crucial to our understanding of inhibition. In the cerebellar cortex, molecular layer interneurons and their targets, Purkinje cells, receive excitatory inputs from granule cells and climbing fibres, the latter signalling to interneurons via glutamate spillover. How these feed-forward pathways are engaged by physiological patterns of activity in vivo is insufficiently understood. Using dual patch-clamp recordings from interneurons and Purkinje cells in mice in vivo, I have probed the spatiotemporal interactions between these circuit elements. I demonstrate that single spikes in single interneurons can potently inhibit the spiking of Purkinje cells. Granule cell input activates both interneurons and the Purkinje cells they inhibit, generating local feed-forward inhibition. Climbing fibre input activates interneurons via glutamate spillover, but only rarely activates interneurons that inhibit spiking of the same Purkinje cell receiving the climbing fibre input. Rather, by activating inhibition among interneurons, climbing fibre glutamate spillover results in delayed inhibition of interneurons controlling Purkinje cell spike output, forming a disinhibitory motif. Functional climbing fibre-interneuron inhibition, inhibition among interneurons, and interneuron-Purkinje cell inhibition are vertically organised in the molecular layer, providing an anatomical substrate for this microcircuit motif. During sensory processing, these motifs account for pathway-specific recruitment of interneurons, generating fast and delayed excitatory interneuron responses via the granule cell and climbing fibre pathway, respectively. Sensory stimulation recruits granule cell input into INs and PCs near-simultaneously, resulting in rapid feed-forward inhibition. Together, these findings quantify the functional impact of single interneurons on their targets in vivo, and reveal how granule cell and climbing fibre inputs differentially recruit inhibitory microcircuits to diversify cerebellar computations. 3 Acknowledgements I would like to thank Michael Häusser for giving me the freedom to develop independently as a scientist, and for creating a diverse working environment with excellent colleagues. I am moreover grateful to Christian Wilms for taking me under his wing early on, for creating an atmosphere in which there truly are no stupid questions, and for providing conceptual and technical help on various levels along the way, also after his departure from the lab. I would also like to thank Arnd Roth and Beverley Clark, for their scientific and personal support. My thanks also belong to many brilliant lab members, postdocs, and students that I was lucky enough to get to know and learn from, and that have made this experience fun, beery and ripe of new friendships: Matt Hoddinott, Soyon Chun, Bilal Haider, Christoph Schmidt-Hieber, Adam Packer, Ingrid van Welie, Mehmet Fisek, Dimitar Kostadinov, Nick Robinson, Christina Buetfering, Eran Eldar, Jeffrey Seely, Alex Mathy, James Cottam, Sarah Rieubland, Jonathan Cornford, Yuya Kanemoto, Gabija Toleikyte, Matej Macak, Lea Götz, Noah Pettit, Lloyd Russell, Henry Dalgleish, Oli Gauld and Joanna Lau. Thank you to my family: to my dad for his unconditional enthusiasm about my work, to my siblings for listening to my complaints, and to my mother and uncle, who keep supporting me even in their absence. Finally, thank you to my best friend, for everything. 4 Table of contents DECLARATION ................................................................................................................................ 2 ABSTRACT ....................................................................................................................................... 3 ACKNOWLEDGEMENTS ............................................................................................................... 4 TABLE OF CONTENTS ................................................................................................................... 5 TABLE OF FIGURES ....................................................................................................................... 9 ABBREVIATIONS .......................................................................................................................... 11 1 INTRODUCTION ........................................................................................................................ 12 1.1 THE NEURON DOCTRINE AND RECEPTIVE FIELDS ............................................................................. 12 1.2 MODELS OF NEURAL NETWORKS ......................................................................................................... 15 1.3 INHIBITION AND ITS ROLE IN MICROCIRCUITS ................................................................................... 17 1.3.1 Ionic mechanisms of excitation and inhibition ................................................................. 17 1.3.2 Diversity of inhibitory cell types .............................................................................................. 19 1.3.3 Postsynaptic effects of inhibition depend on target location ...................................... 19 1.3.4 Inhibitory microcircuit motifs and function ....................................................................... 21 1.4 STUDYING CIRCUIT ARCHITECTURE AND ACTIVITY .......................................................................... 25 1.5 THE CEREBELLAR CORTEX .................................................................................................................... 29 1.5.1 Gross anatomical organisation and distal connectivity ................................................ 29 1.5.2 Anatomy and physiology of the cerebellar cortex ............................................................ 30 1.5.3 Plasticity in the cerebellar cortex ............................................................................................ 34 1.5.4 Theories of cerebellar function ................................................................................................ 35 1.5.5 Experimental models of cerebellar function ...................................................................... 39 1.5.6 Molecular layer inhibition and cerebellar function ........................................................ 41 1.6 AIMS OF THIS THESIS ............................................................................................................................. 43 2 MATERIALS & METHODS ...................................................................................................... 44 2.1 ANIMALS ................................................................................................................................................... 44 2.2 SURGERY FOR ELECTROPHYSIOLOGICAL RECORDINGS ..................................................................... 44 2.3 TWO-PHOTON TARGETED ELECTROPHYSIOLOGICAL RECORDINGS ............................................... 45 2.4 SENSORY STIMULATION ......................................................................................................................... 46 2.5 VIRAL INJECTIONS .................................................................................................................................. 46 2.6 TAMOXIFEN ADMINISTRATION ............................................................................................................. 47 2.7 LIGHT-ACTIVATED OPSIN STIMULATION ............................................................................................ 47 2.8 HISTOCHEMISTRY ................................................................................................................................... 47 5 2.9 CONFOCAL MICROSCOPY ........................................................................................................................ 48 2.10 DATA ANALYSIS .................................................................................................................................... 48 2.10.1 - Electrophysiology: Spontaneous and electrically induced activity - .................. 48 2.10.2 - Electrophysiology: Sensory-evoked activity - ............................................................... 49 2.10.3 - Metrics for quantifying spiking response amplitudes: The baseline- normalised binned rate versus the net spike change - .............................................................. 50 2.10.4 - Two-photon stacks of pipette positions - ........................................................................ 53 2.10.5 - Statistics - ..................................................................................................................................... 54 3 FUNCTIONAL INTERNEURON-PURKINJE CELL CONNECTIVITY ................................ 55 IN VIVO ............................................................................................................................................ 55 3.1 INTRODUCTION ......................................................................................................................................
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