Two research groups have turned the conventional wisdom about glial cells—that they do not form synapses with neurons—on its head, opening up new avenues of scientific exploration directed at glia. They have reported convincing evidence of synapses that directly link neurons with a type of glial cell in the corpus callosum, the white matter tracts that connect the brain’s hemispheres.
Their work is the latest chapter in a succession of unanticipated results that are challenging the long-held view of glia as the necessary but unremarkable supporting cast to the reigning star of the nervous system, the neuron. The new findings were reported in Nature Neuroscience in March by lead investigators Dwight Bergles of Johns Hopkins University, and Dirk Dietrich of the University Clinic Bonn in Germany.
“The two studies are beautifully done,” says Erik Ullian, who studies glial modulation of neuronal communication in development at University of California, San Francisco. “What is so surprising is that they’ve found these synaptic connections in the white-matter tracts.”
Bergles agrees: “The white matter has always been thought to be involved only in transmitting signals between different brain areas.” He likens the bundles of axons that make up white-matter tracts to “little highways through which you can conduct nerve signals, but there’s no off-ramp.”
“What we’ve shown is that those signals are actually communicating as they come down the axon. They’re carrying information and there are cells that are receiving that information,” Bergles says.