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Mechanisms of Synaptic and Intrinsic Modulation Of MECHANISMS OF SYNAPTIC AND INTRINSIC MODULATION OF GRANULE CELLS IN THE RAT OLFACTORY BULB By RICHARD TODD PRESSLER Submitted in partial fulfillment of the requirements For the degree Doctor of Philosophy Thesis Adviser: Dr. Ben W. Strowbridge Department of Neurosciences CASE WESTERN RESERVE UNIVERSITY August, 2006 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the dissertation of ______________________________________________________ candidate for the Ph.D. degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Table of contents Table of contents................................................................................................................iii List of figures......................................................................................................................iv Acknowledgements..............................................................................................................v List of Abbreviations..........................................................................................................vi Abstract..............................................................................................................................vii Chapter 1: Introduction........................................................................................................1 Basic circuit description of the olfactory bulb.........................................................2 Diversity of interneurons in the olfactory bulb......................................................10 Centrifugal input to the olfactory bulb...................................................................14 Chapter 2: Blanes cells mediate persistent feedforward inhibition onto granule cells in the olfactory bulb.....................................................................................................................30 Summary................................................................................................................31 Introduction............................................................................................................32 Results....................................................................................................................35 Discussion..............................................................................................................50 Experimental Procedures.......................................................................................61 Chapter 3: Muscarinic receptor modulation of afterpotentials and firing modes in olfactory bulb granule cells................................................................................................87 Introduction............................................................................................................88 Materials and Methods...........................................................................................92 Results....................................................................................................................94 Discussion............................................................................................................104 Chapter 4: Discussion......................................................................................................123 Enhancement of excitability by an intrinsic activity-evoked Afterdepolarization..............................................................................................125 Afterdepolarizations as a mechanism for generating persistent firing.................133 Similarities and differences between olfactory bulb circuitry and retinal circuitry.....................................................................................................136 Factors that modulate granule cell activity..........................................................138 Strategies to determine the contributions of these two inputs onto granule cells inintact and behaving animals.....................................................................144 Future Directions.................................................................................................145 Chapter 5: Bibliography...................................................................................................151 iii List of Figures Figure 1-1 The spatial map of odorant receptors onto olfactory bulb glomeruli...............24 Figure 1-2 The basic circuit of the olfactory bulb.............................................................26 Figure 1-3 Original description of the olfactory bulb Blanes cell.....................................28 Figure 2-1 Multiple Cell Types in Granule Cell Layer of the Olfactory Bulb..................66 Figure 2-2 Visualization of Blanes Cell Morphology with Two-Photon Microscopy......68 Figure 2-3 Blanes Cells Are GABAergic and Innervate Granule Cells............................70 Figure 2-4 Afterdepolarizations in Blanes Cells................................................................73 Figure 2-5 Calcium-Dependent Afterdepolarizations in Blanes Cells..............................75 Figure 2-6 Afterdepolarizations Are Blocked by ICAN Antagonists..................................77 Figure 2-7 Brief Depolarizations Trigger Persistent Firing in Blanes Cells......................79 Figure 2-8 Prolonged Hyperpolarization Stops Persistent Firing......................................82 Figure 2-9 Synaptic Stimulation Activates Blanes Cells and Evokes Long-Lasting Inhibition onto Granule Cells.................................................................................84 Figure 3-1 Carbachol reveals an afterdepolarization in granule cells..............................111 Figure 3-2 Calcium-dependent afterdepolarizations in granule cells..............................113 Figure 3-3 Pharmacology of mACh receptor activation in granule cells........................115 Figure 3-4 Increased concentrations of carbachol enhance granule cell excitability......117 Figure 3-5 Carbachol enhances granule cell output onto mitral cells..............................119 Figure 3-6 During Carbachol application, brief depolarizations in granule cells can trigger persistent firing..................................................................................121 Figure 4-1: A schematic showing the olfactory bulb circuit............................................149 iv Acknowledgements I would like to thank my thesis advisor, Dr. Ben Strowbridge, for the years of advice and painstaking instruction in electrophysiological methods, and neuroscience history. Since my days as an undergraduate in his laboratory, he has been shaping my critical thinking skills and pushing me to go the extra distance in pursuit of answering the interesting questions, and for that I will always be eternally grateful. I would also like to thank the members of my thesis committee, Dr. Hillel Chiel, Dr. Stefan Herlitze, Dr. Diana Kunze, and Dr. Iain Robinson for their assistance and helpful suggestions in my research. v List of Abbreviations ACSF: artificial cerebrospinal fluid AMPA: alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate AMPAR: AMPA receptor AP: action potential 4-AP: 4-aminopyridine, fast K channel blocker BAPTA: O,O’-Bis(2-aminophenyl)ethyleneglycol-N,N,N’,N’-tetraacetic acid tetrapotassium salt D-APV: D-2-amino-5-phosphonovalerate, NMDA receptor antagonist cAMP: cyclic adenosine monophosphate cGMP: cyclic guanosine monophosphate EGTA: O,O’-Bis(2-aminoethyl)ethyleneglycol-N,N,N’,N’-tetraacetic acid, slow Ca chelator EPL: external plexiform layer EPSC: excitatory postsynaptic current EPSP: excitatory postsynaptic potential GABA: gamma-aminobutyric acid, the neurotransmitter in granule cells GC: granule cell GCL: granule cell layer IPSC: inhibitory postsynaptic current IPSP: inhibitory postsynaptic potential LOT: lateral olfactory tract, axons of mitral cells MC: mitral cell MCL: mitral cell layer NBQX: 1,2,3,4-tetrahydro-6-nitro-2,3-dioxo-benzo[f]quinoxaline-7-sulfonamide, AMPA receptor antagonist NMDA: N-methyl D-aspartate NMDAR: NMDA receptor NMG: N-methyl D-glucamine OB: olfactory bulb TEA: tetraethylammonium TTX: tetrodotoxin, blocks voltage activated Na channels VDCC: voltage dependent Ca2+ channel vi MECHANISMS OF SYNAPTIC AND INTRINSIC MODULATION OF GRANULE CELLS IN THE RAT OLFACTORY BULB Abstract By Richard Todd Pressler Mitral cell activity during olfactory behavior varies with respect to spatial location in the olfactory bulb, and temporally evolves during olfaction (Kay and Laurent, 1999). The main inhibitory input onto mitral cells originates from granule cells, axonless interneurons in the olfactory bulb, which sculpt and pattern mitral cell output through dendrodendritic inhibitory synapses (Price and Powell, 1970b). This dendrodendritic microcircuit can mediate recurrent inhibition onto mitral cells (Jahr et al., 1980), as well as lateral inhibition between mitral cells (Isaacson and Strowbridge, 1998). Additionally, this microcircuit plays a large part in generating gamma-frequency oscillations in the olfactory bulb during olfactory behavior (Lagier et al., 2004).
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