Thanks to new research by scientists at the Salk Institute for Biological Studies, we are closer to understanding how these complicated network connections are wired up during embryonic development. Salk researchers have discovered that the same chemicals (called neurotransmitters) that are responsible for nerve signals are also involved in the wiring of synapses, the network's crucial contact points between nerves, or between nerves and muscle cells.

The study, published in the May issue of the journal Neuron, showed that as the motor neurons grow from their home base in the spinal cord towards muscles throughout the body, they release two opposing chemical signals. These signals act to preserve synapses that link a motor neuron to its correct muscle cell. 'Spare' sites for potential synapses that fail to team up with a motor neuron are dismantled.

"Our study provides the first evidence in a living animal system that the neurotransmitters themselves are sculpturing the developing nervous system," said Kuo-Fen Lee, Associate Professor at the Salk, who heads the research team reporting its results in Neuron.

Using mice as a model for human biology, Lee and colleagues showed that each long, thin muscle cell in the developing embryo prepares for the arrival of its motor neurons by creating sites for many potential synapses along its length. However, three weeks after conception, all the sites have disappeared, except those that connected with a newly arrived motor neuron and formed a fully functioning synapse. The scientists wanted to know: how does the embryo 'weed out' the potential synapse sites that are not needed? The answer to this question is crucial because it might shine light on how the nervous system could make new connections
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Contact: Cathy Yarbrough
yarbrough@salk.edu
858-452-8051
Salk Institute
2-Jun-2005