In the present study, the team, led by Douglas H. Smith, MD, Professor of Neurosurgery and Director of the Center for Brain Injury and Repair, placed neurons from rat dorsal root ganglia (clusters of nerves just outside the spinal cord) on nutrient- filled plastic plates. Axons sprouted from the neurons on each plate and connected with neurons on the other plate. The plates were then slowly pulled apart over a series of days, aided by a precise computer-controlled motor system. "By rapid and continuous stretching, we end up with huge bundles of axons that are visible to the eye," says Smith. The axons started at an invisible 100 microns and have been stretched to 10 centimeters in less than two weeks. Smith and colleagues report their findings in the cover story of the September 8, 2004 issue of the Journal of Neuroscience.
"This type of stretch growth of axons is really a new perspective," says Smith. Despite the extreme growth in length, the axons substantially increased in diameter as well. Using electron microscopy, they confirmed this growth by identifying a fully formed internal skeleton and a full complement of cellular structures called organelles in the stretched axons. "Surprisingly, the axon appears to be invigorated by this extreme growth," says Smith. "It doesn't disconnect, but forms a completely normal-appearing internal structure.
Contact: Karen Kreeger
University of Pennsylvania School of Medicine