Regenerating neurons in the leech can form functional connections with their normal targets, thus restoring at the level of single cells precisely the wiring established during development. Just what steps a neuron takes as it locates and synapses with its proper targets, what roles are played by surrounding glia, neighboring neurons, and target neurons, and how the new synapses compare with the old in structure, distribution and function are the questions the proposed project addresses. The methodology will include extracellular and intracellular electrophysiological recrding and intracellular injection of markers for subsequent light- and electron microscopic examination. Complex patterns of regenerated synaptic contact between neurons will be constructed with a computer. Regeneration will be studied in culture as well as within the leech; single cells can be killed with intracellular injection of proteases.