Our long-range goal is to answer three basic questions concerning the regulation of axonal transport: 1) What are the changes that neuron makes in the export of materials from the cell body and their distribution in the axonal tree? 2) How are these changes elicited? 3) How do these changes to enduring changes in form and function of the neuron? Because axon regeneration and changes in the pattern of growth of the axonal tree seem to be associated with, and perhaps rely on, changes in transport, these have been good specific models with which to address these general questions and, consequently, the cellular and molecular events underlying axon growth are in themselves also concerns of this project. One approach will be to try to identify critical events at the axon endings and the cell body that cause the metabolism (probably synthesis) of a few transported proteins to change dramatically following axotomy. We will use an in vitro system of an identified giant Alpysia neuron and targets cells to try to determine which aspects of the interaction (which is interrupted by axotomy) is critical in eliciting changes in the metabolism of some of these proteins. Also we intend to examine early changes in nuclear proteins for insight into events in the cell body that modulate the metabolism of the axotomy-responsive proteins. Heavy use will be made of 2-D gel electrophoresis and we also hope to employ monoclonal antibodies in our studies. The other sets of experiments in the project employ in vitro single neuron models of differential branch growth of an axonal tree to examine cellular and molecular events that contribute to determining the final shape and extent of the tree. Three experiments will employ computer-assisted video microscopy and electron microscopy. In addressing basic questions of the cell biology of regeneration, this research program is relevant to an understanding of the consequences of spinal cord injury and to the formulation of therapies. It is also relevant to the study of diseases like amyotrophic lateral sclerosis, where compensatory sprouting of healthy axons occurs and may affect the progression of the disease.
