The goals of this proposal are to determine (1) what cellular interactions are essential for pioneering the initial scaffold of axon pathways in the embryonic grasshopper central nervous system, (2) how later neurons are guided in their cell specific choices among this scaffold of axon pathways, and (3) what molecules are involved in guiding growth cones in their initial and later pathway choices. The grasshopper embryonic nervous system will be used to answer these questions. This model system is uniquely suited for these experiments because of the in vivo cellular resolution and accessibility it offers. Single identified growth cones in an identified cellular environment can be observed and manipulated in the grasshopper embryo. Specific neuron-epithelial, neuron-glial, and neuron-neuron interactions will be characterized at light and EM level and then experimental manipulations will be performed to determine the role of each interaction in growth cone guidance and pathway choice. Monoclonal antibodies will generated against this same set of epithelial, glial, and neuronal cells to find molecular correlates of the specific interactions required for growth cone guidance.