The NMDA receptor has been implicated in a host of developmental and maturational processes that occur in the central nervous system. We propose to study the role of NMDA receptors in synapse stability by using a reduced system where we force presynaptic axons to choose between synaptic targets that have NMDA receptors or synaptic targets that lack the receptor. Using whole-cell voltage clamp recording we can measure the extent of innervation of each target in this situation to determine if synapses are preferentially stabilized on one target or another. We will couple the electrophysiological analysis with live imaging of neurons that are transfected with fluorescent tags coupled to pre-or postsynaptic markers. This technique will allow us to follow the behavior of individual synapses for several hours or days and will allow us to examine the turnover time of synapses that contain NMDA receptors compared to synapses that lack the receptor.