In the January 5, 2006, issue of the journal Nature, the researchers show that a gradient of a molecule known as Wnt3 counterbalances another force provided by the EphrinB1-EphB signaling system. The balance between these two signaling systems, they show, is necessary to establish the carefully controlled pattern of nerve connections required to convey spatial information in the correct order from the eye to the brain.
"This is the first biological validation of a computational model developed in the early 1980s that suggested that two such forces would be necessary to guide axons as they establish the connections that relay spatial information from one part of the nervous system to another," said study author Yimin Zou, Ph.D., assistant professor of neurobiology at the University of Chicago.
Neurobiologists refer to this type of neuronal connection in which the spatial order of neurons of one part of the nervous system is "copied" onto another -- as "topographic mapping." The term describes the creation of a coordinated connection that allows positional information from a grid of sensors, in this case the light-sensitive cells in the retina, to be smoothly and systematically transferred to their target, the structures in the brain that interpret information from the eyes.
"Without an orderly and faithful connection," said Zou, "information from the eyes could not be properly deciphered by the brain."
"Topographic maps are a very common wiring strategy in our brains," he said. Similar systems are thought to regulate other sensory syste
Contact: John Easton
University of Chicago Medical Center