Dynamic changes in the molecules that form the internal skeleton of nerve cells are related to nerve cell form and function. Development of the nervous system requires that the neuronal cytoskeleton be endowed the seemingly incompatible properties of morphological stability and plasticity. Morphological stability is critical for maintenance and proper function of neuronal circuits, while plasticity is required for cell growth and remodeling of cell processes during response to environmental stimuli or injury. The assembly or disassembly kinetics of microtubules will be studied using the powerful techniques of microinjection, laser-induced photobleaching and photoactivation. Previous studies using these techniques have led to controversial results regarding the site of assembly of microtubules in neuronal processes. Novel experiments will be performed to resolve this controversy and to evaluate the potentially powerful photobleaching laser technology as applied to living nerve cells. This award will provide the PI with the laser equipment necessary for these experiments.