MECHANISMS OF SYNAPTIC PLASTICITY IN THE RAT OLFACTORY BULB by YUAN GAO Submitted in partial fulfillment of the requirements For the degree of Doctor of Philosophy Thesis Advisor: Dr. Ben W. Strowbridge Department of Neurosciences CASE WESTERN RESERVE UNIVERSITY January, 2010 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of Yuan Gao candidate for the Ph.D degree *. (signed) Stefan Herlitze (chair of the committee) Ben W. Strowbridge Diana L. Kunze Christopher Wilson (date) Oct 2 2009 * We also certify that written approval has been obtained for any proprietary material contained therein. ii Table of Contents Table of Contents............................................................................................................. iii List of Figures.................................................................................................................... v Acknowledgements .......................................................................................................... vi List of Abbreviations ...................................................................................................... vii Abstract............................................................................................................................. ix Chapter 1 Introduction .................................................................................................... 1 Signal Transduction in Mammalian Olfactory System............................................... 3 Olfactory epithelium ........................................................................................... 3 Olfactory bulb ..................................................................................................... 4 Olfactory cortex .................................................................................................. 6 Plasticity in the Olfactory System............................................................................... 8 Olfactory system related behavioral plasticity.................................................... 8 Long-term plasticity in the olfactory structures................................................ 11 Regulation of Odor Representation in Mitral Cells .................................................. 13 Spiking pattern regulated by intrinsic properties.............................................. 13 Dendrodendritic inhibition between mitral and granule cells........................... 15 Synaptic regulation by periglomerular cells ..................................................... 20 Lateral excitation and self-excitation on mitral cells........................................ 22 Other mechanism .............................................................................................. 25 Chapter 2 Long-term Plasticity of Excitatory Inputs to Granule Cells in the Rat Olfactory Bulb................................................................................................................. 40 Abstract..................................................................................................................... 41 Results....................................................................................................................... 42 Supplementary Methods ........................................................................................... 48 Olfactory bulb brain slice and recording methods............................................ 48 2-Photon guided focal stimulation.................................................................... 49 Analysis of EPSPs in granule cell intracellular recordings .............................. 50 Analysis of cell-attached granule cell recordings ............................................. 52 Analysis of IPSPs in mitral cell intracellular recordings.................................. 52 Chapter 3 Extra-glomerular Layer Excitation of Olfactory Bulb Mitral Cells Mediated through a Carbenoxolone and NBQX-sensitive Pathway.......................... 70 Abstract..................................................................................................................... 71 Introduction............................................................................................................... 72 Materials and methods .............................................................................................. 75 Olfactory bulb brain slice preparation and recording methods......................... 75 Two-Photon imaging ........................................................................................ 76 Data acquisition and analysis............................................................................ 77 Results....................................................................................................................... 78 Discussion................................................................................................................. 84 Dye-coupling between mitral cells and unknown processes ............................ 84 Sensitivity to carbenoxolone............................................................................. 86 The pathway of signal transduction .................................................................. 87 Potential functional role of “off-beam” mitral cell excitation .......................... 90 Chapter 4 General Discussion ..................................................................................... 109 iii Overview................................................................................................................. 110 Mechanisms underlying granule cell spiking ......................................................... 115 Modulation of dendrodendritic inhibition by granule cell LTP.............................. 117 Regulation of the granule cell distal synaptic plasticity ......................................... 120 Functional relevance of STDP on the granule cell ................................................. 122 Electrical coupling in the extraglomerular regions................................................. 124 Impact of proximal and distal inhibitory input onto mitral cells ............................ 128 Significance and future direction............................................................................ 129 Bibliography.................................................................................................................. 140 iv List of Figures Figure 1-1. Zonal organization of sensory inputs from the olfactory epithelium to the olfactory bulb ................................................................................................ 28 Figure 1-2. Synaptic organization of the mammalian main olfactory bulb ...................... 30 Figure 1-3. Synchronization in the olfactory bulb and the olfactory cortex..................... 32 Figure 1-4. Depolarization evoked clusters of spiking and subthreshold oscillation in olfactory bulb mitral cells.............................................................................. 34 Figure 1-5. Reciprocal dendrodendritic synapse between mitral and granule cells ......... 36 Figure 1-6. Lateral excitation and electrical coupling between two mitral cells.............. 38 Figure 2-1. Spike timing–dependent plasticity of proximal excitatory inputs to granule cells................................................................................................................ 54 Figure 2-2. LTP evoked by TBS....................................................................................... 56 Supplementary Figure 2-1. Properties of proximal and distal EPSPs recorded in granule cells................................................................................................................ 58 Supplementary Figure 2-2. Pairing synaptic stimulation with intracellular depolarization induces long-term potentiation in a resting granule cell ............................... 60 Supplementary Figure 2-3. Proximal EPSPs recorded in granule cells were not potentiated by trains of postsynaptic action potentials or presynaptic stimuli presented separately ...................................................................................... 62 Supplementary Figure 2-4. Pairing stimulation-induced potentiation of proximal granule cell EPSPs requires NMDA receptors........................................................... 64 Supplementary Figure 2-5. Theta-burst stimulation potentates EPSPs in a P16 rat......... 66 Supplementary Figure 2-6. Theta-burst stimulation potentates EPSPs in a P30 rat......... 68 Figure 3-1. Mapping of GCL-evoked postsynaptic potentials recorded in a mitral cell .. 91 Figure 3-2. Two types of mitral cell IPSPs evoked by GCL stimulation ......................... 93 Figure 3-3. Mitral cell EPSPs evoked by GCL stimulation.............................................. 95 Figure 3-4. The lack of the glomerular layer in dissected olfactory bulb slices............... 97 Figure 3-5. Two-photon imaging of a mitral cell that intracellulary filled with lucifer yellow in dissected olfactory bulb slice ........................................................ 99 Figure 3-6. Blockade of the GCL-evoked mitral cell depolarization by NBQX and TTX in dissected olfactory bulb slices................................................................. 101 Figure 3-7. The GCL-evoked mitral cell depolarization was sensitive to carbenoxolone (CBX) in dissected olfactory bulb slices....................................................