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J. Neurosci. 24 (36): 7978-7983

Copyright © 2004 by the Society for Neuroscience.

BRIEF COMMUNICATION

Extreme Stretch Growth of Integrated Axons

Bryan J. Pfister,1 Akira Iwata,1 David F. Meaney,2 , and Douglas H. Smith1

Departments of 1Neurosurgery and 2Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104

Abstract: Large animals can undergo enormous growth during development, suggesting that axons in nerves and white matter tracts rapidly expand as well. Because integrated axons have no growth cones to extend from, it has been postulated that mechanical forces may stimulate axon elongation matching the growth of the animal. However, this distinct form of rapid and sustained growth of integrated axons has never been demonstrated. Here, we used a microstepper motor system to evaluate the effects of escalating rates of stretch on integrated axon tracts over days to weeks in culture. We found that axon tracts could be stretch grown at rates of 8 mm/d and reach lengths of 10 cm without disconnection. Despite dynamic and long-term elongation, stretched axons increased in caliber by 35%, while the morphology and density of cytoskeletal constituents and organelles were maintained. These data provide the first evidence that mechanical stimuli can induce extreme "stretch growth" of integrated axon tracts, far exceeding any previously observed limits of axon growth.

Key Words: axon • growth • development • stretch • elongation • cytoskeleton

Received for publication May 20, 2004. Revision received July 20, 2004. Accepted for publication July 23, 2004.

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