The initial formation of the synaptic connections that enable neurons to communicate with each other is a complex process. The incoming axons of one group of neurons must be targeted to the dendrites of a receiving neuron--no easy task given that the dendritic 'tree' is also growing at the same time. These processes are intimately related, suggests a report in the March issue of Nature Neuroscience, with newly formed synapses helping to direct how a dendrite will grow.
Stephen Smith and colleagues imaged growing dendrites in living zebrafish larvae over the course of several days, while simultaneously looking for developing synapses using a protein label. They found that most synapses form first on a newly extended dendrite-like projection called a filopodium. Only a small number of these new synapses are maintained, but those that remain are able to stabilize the filopodium, which in turn matures into a bona fide dendrite. The process then continues, with new synapses leading to more dendritic branches. Such a model of coordinated synapse and dendrite development may help to explain how nerve cells are able to form highly specific connections.
Stephen J. Smith
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Washington University School of Medicine
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