Feldmeyer / Lübke New Aspects of Axonal Structure and Function

1. Auflage 2010
ISBN: 978-1-4419-1676-1
Verlag: Springer-Verlag
Format: PDF
Kopierschutz: Adobe DRM (»Systemvoraussetzungen)

E-Book, Englisch, 237 Seiten

Axons are neuronal output elements and are responsible for the transfer and processing of signals from one neuron to another, even over very large distances. For a given neuronal cell type, axons are unique and display very heterogeneous patterns with respect to shape, length and target structure. Axons are the usually long process of a nerve fiber that generally conducts impulses away from the body of the nerve cell. This book is intended to summarize recent findings covering morphological, physiological, developmental, computational and pathophysiological aspects of axons. It attempts to cover new findings concerning axonal structure and functions together with their implications for signal transduction, processes implicated in the formation of axonal arbors and the transport of subcellular elements to their targets, and finally how a dysfunction in one or several of these steps could lead to axonal degeneration and ultimately to neurodegenerative diseases.

Autoren/Hrsg.

Feldmeyer, Dirk

Lübke, Joachim

Inhaltsverzeichnis

1;Foreword;5
1.1;Development ;5
1.2;Axonal Function ;6
1.3;Axons in Circuits ;7
1.4;Degeneration and Regeneration of Axons ;8
2;Preface;10
3;Contents;11
4;Contributors;13
5;Part I Axons in Development;16
5.1;1 Molecular Aspects of Commissural Axon Guidance;17
5.1.1;1.1 Basic Principles of Axonal Navigation;17
5.1.2;1.2 Commissural Neurons as a Model System to Study Axonal Pathfinding;18
5.1.2.1;1.2.1 Commissural Axon Guidance in the Vertebrate Spinal Cord;18
5.1.2.1.1;1.2.1.1 Guidance Toward the Floorplate;19
5.1.2.1.2;1.2.1.2 Guidance Across the Floorplate;20
5.1.2.1.3;1.2.1.3 Rostral Turning and Longitudinal Projection After Crossing;23
5.1.2.2;1.2.2 Commissural Axon Guidance in Drosophila melanogaster ;25
5.1.2.2.1;1.2.2.1 Guidance Toward the Midline;25
5.1.2.2.2;1.2.2.2 Guidance Across the Midline;26
5.1.2.2.3;1.2.2.3 Longitudinal Projection After Crossing;27
5.1.3;1.3 Open Questions;28
5.2;References;28
5.3;2 Subplate and the Formation of the Earliest Cerebral Cortical Circuits;33
5.3.1;2.1 Clinical Importance of the Understanding of Early Cortical Circuits;36
5.3.2;2.2 Recent Microarray Screen of Murine Subplate Neurons;38
5.3.3;2.3 Recent Studies of Subplate Neuron Integration into the Cortical and Extracortical Circuitry in Reporter Gene Expressing Mouse Models;38
5.3.4;2.4 Manipulation of the Sensory Periphery Alters Subplate Integration into the Barrel Field;39
5.3.5;2.5 Subplate Cell Populations in Mutants with Cortical Migration Defects;40
5.3.6;2.6 Summary;41
5.4;References;42
6;Part II Axonal Function;46
6.1;3 Sodium Signals and Their Significance for Axonal Function;47
6.1.1;3.1 Introduction;47
6.1.2;3.2 Sodium Signals and the Measurement of [Na+]i ;48
6.1.2.1;3.2.1 Sodium Signals in Dendrites and Glial Processes;48
6.1.2.1.1;3.2.1.1 Action Potential-Induced [Na+]i Changes;48
6.1.2.1.2;3.2.1.2 Synaptically Evoked [Na+]i Changes in Dendrites and Glia;49
6.1.3;3.3 Sodium Signals in Axons;52
6.1.3.1;3.3.1 Pathophysiological Implications of [Na+]i Changes;56
6.1.3.2;3.3.2 Possible Physiological Roles of [Na+]i Changes;58
6.1.4;3.4 Conclusions and Outlook;60
6.2;References;61
6.3;4 New Insights in Information Processing in the Axon;66
6.3.1;4.1 Introduction;66
6.3.2;4.2 Complexity of Axonal Arborization: Branch Points and Varicosities;67
6.3.3;4.3 Functional Computation in the Axon;67
6.3.3.1;4.3.1 Shaping Action Potential;67
6.3.3.1.1;4.3.1.1 Activity-Dependent Broadening of Presynaptic Action Potential;68
6.3.3.1.2;4.3.1.2 Activity-Dependent Reduction of Presynaptic Action Potential;69
6.3.3.2;4.3.2 Signal Amplification Along the Axon;70
6.3.3.3;4.3.3 Axonal Integration;70
6.3.4;4.4 Propagation Failures;73
6.3.4.1;4.4.1 Geometrical Factors: Branch Points and Swellings;73
6.3.4.2;4.4.2 Frequency-Dependent Propagation Failures;75
6.3.4.3;4.4.3 Frequency-Independent Propagation Failures;79
6.3.5;4.5 Ping-Pong Propagation: Reflection of Action Potential Propagation;80
6.3.6;4.6 Spike Timing in the Axon;82
6.3.6.1;4.6.1 Axonal Delay Imposed by Axonal Length;82
6.3.6.2;4.6.2 Extra Delays Imposed by Axonal Irregularities and Ion Channels;84
6.3.6.3;4.6.3 Ephaptic Interactions and Axonal Spike Synchronization;85
6.3.6.4;4.6.4 Electric Coupling in Axons and Fast Synchronization;85
6.3.7;4.7 Conclusion;86
6.3.7.1;4.7.1 Increased Computational Capabilities;86
6.3.7.2;4.7.2 Future Directions and Missing Pieces;86
6.4;References;88
6.5;5 Electrical Coupling of Axons;95
6.5.1;5.1 Mechanisms of Electrical Coupling;95
6.5.2;5.2 Methodological Issues;98
6.5.3;5.3 Axo-axonal Synapses;100
6.5.4;5.4 Physiological Significance of Axo-axonic Gap Junctions;105
6.6;References;107
6.7;6 To Myelinate or Not to Myelinate?;113
6.7.1;6.1 Introduction;113
6.7.2;6.2 Results;115
6.7.2.1;6.2.1 Axonal Cost with Fixed Conduction Delay;115
6.7.2.2;6.2.2 Axon with a Finite Conduction Delay Cost;117
6.7.2.3;6.2.3 Comparison with Experiments;119
6.7.3;6.3 Discussion;121
6.7.4;6.4 Conclusions;121
6.7.5;6.5 Methods;122
6.8;References;123
7;Part III Axons and Neuronal Circuits;124
7.1;7 An Axonal Perspective on Cortical Circuits;125
7.1.1;7.1 Introduction;125
7.1.2;7.2 Local Circuits;127
7.1.3;7.3 Capturing Axon Morphology;128
7.1.4;7.4 The Problem of Choice;135
7.1.5;7.5 Wiring Neurons;137
7.1.6;7.6 Improving Peters Rule;139
7.1.7;7.7 Computation in Daisy Architectures;141
7.2;References;144
7.3;8 Axons Predict Neuronal Connectivity Within and Between Cortical Columns and Serve as Primary Classifiers of Interneurons in a Cortical Column;148
7.3.1;8.1 Definition of a Cortical Column by the Geometry of Axonal Domains;150
7.3.2;8.2 Inference of Synaptic Connectivity Within a Cortical Column;151
7.3.3;8.3 Classification of Inhibitory Interneurons Based on Their Innervation Domains with Reference to Cortical Columns;153
7.3.4;8.4 Local Versus Lateral Inhibitors in Neocortex;155
7.3.5;8.5 Subsequent Classification Steps;158
7.3.6;8.6 Summary;159
7.4;References;159
7.5;9 The Axon of Excitatory Neurons in the Neocortex: Projection Patterns and Target Specificity;163
7.5.1;9.1 Introduction;163
7.5.2;9.2 Highly Variable Axonal Domains of Neocortical Excitatory Neurons;164
7.5.3;9.3 Layer 2/3;165
7.5.4;9.4 Layer 4;167
7.5.4.1;9.4.1 Spiny Stellate and Star Pyramidal Neurons;167
7.5.4.2;9.4.2 Star Pyramidal Cells;169
7.5.5;9.5 Layer 5;171
7.5.5.1;9.5.1 Sublamina 5A;171
7.5.5.2;9.5.2 Sublamina 5B;172
7.5.6;9.6 Layer 6;174
7.5.6.1;9.6.1 Sublamina 6A;174
7.5.6.2;9.6.2 Sublamina 6B;176
7.5.7;9.7 Subcellular Axonal Targets;177
7.5.8;9.8 Outlook;178
7.6;References;179
8;Part IV Axons and Degeneration/Regeneration;185
8.1;10 Axon Degeneration: Mechanisms and Consequences;186
8.1.1;10.1 Introduction;186
8.1.2;10.2 The Axon as a Functionally Distinct Compartment;186
8.1.3;10.3 Axon Degeneration;189
8.1.3.1;10.3.1 Morphological Changes;189
8.1.3.2;10.3.2 Protein Expression Changes;191
8.1.3.3;10.3.3 Wlds ;192
8.1.3.4;10.3.4 Pathways Involved in Axonal Degeneration;195
8.1.3.4.1;10.3.4.1 Mitogen-Activated Protein Kinases (MAPKs);196
8.1.3.4.2;10.3.4.2 Mitochondria;197
8.1.3.4.3;10.3.4.3 Calcium/Calpains;197
8.1.3.4.4;10.3.4.4 Ubiquitin Proteasome System;198
8.1.4;10.4 Lessons from Anuclear Models of Degeneration;200
8.1.5;10.5 Cellular Responses in Axon Degeneration;201
8.1.5.1;10.5.1 Ensheathing Cells;201
8.1.5.2;10.5.2 Macrophages;202
8.1.6;10.6 Concluding Remarks;204
8.1.7;References;205
8.2;11 Regeneration After CNS Lesion: Help from the ImmuneSystem?;213
8.2.1;11.1 Introduction;213
8.2.2;11.2 Wound Healing Responses of the CNS;214
8.2.2.1;11.2.1 Inflammation in Autoimmune Neurodegeneration Versus CNS Repair After Trauma;214
8.2.2.2;11.2.2 Multi-phase Responses of the CNS After Trauma;215
8.2.3;11.3 The Adaptive Immune System in CNS Injury;220
8.2.3.1;11.3.1 T Cells in the Healthy and Injured CNS;220
8.2.3.2;11.3.2 Self-Reactive T Cells in CNS Injury;221
8.2.3.3;11.3.3 Neuronal Injury in T Cell-Deficient Mice;222
8.2.3.4;11.3.4 The Controversy About ''Protective Autoimmunity'';222
8.2.4;11.4 T-Helper Cell Subpopulations in CNS Injury and Repair?;223
8.2.4.1;11.4.1 Analysis of the Th1/Th2 Ratio;224
8.2.4.2;11.4.2 Are Subpopulations of T Cells Responsible for Neuroprotective and Pro-regenerative Effects?;225
8.2.5;11.5 CNS Injury-Induced Immunosuppression Results in a Systemic Th2 Shift;226
8.2.6;11.6 Are Beneficial T-Cell Effects Exclusively Attributable to Th2 Cells?;226
8.2.7;11.7 How May T Cells Contribute to CNS Repair?;227
8.2.7.1;11.7.1 Neurotrophin Secretion by T Cells;228
8.2.7.2;11.7.2 Modulation of Microglia Functions;228
8.2.7.3;11.7.3 Modulation of Endogenous and Exogenous Stem Cells;228
8.2.7.4;11.7.4 Anti-inflammatory T-Cell Effects;228
8.2.7.5;11.7.5 Direct Stimulation of Axon Growth by T-Cell Cytokines;229
8.2.8;11.8 Future Perspectives;229
8.2.9;References;229
9;Index;237