Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Extreme stretch-growth of axons

08.09.2004


Pushing neurons’ physiological limits provides researchers with new ways to repair nerve damage

Sometimes it is the extremes that point the way forward. Researchers at the University of Pennsylvania School of Medicine have induced nerve fibers – or axons – to grow at rates and lengths far exceeding what has been previously observed. To mimic extreme examples in nature and learn more about neuronal physiology, they have mechanically stretched axons at rates of eight millimeters per day, reaching lengths of up to ten centimeters without breaking. This new work has implications for spinal cord and nerve-damage therapy, since longer implantable axons are necessary for this type of repair.

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."

These extreme rates of growth are not consistent with the current understanding of the limitations of axon growth. "Proteins necessary to sustain this growth are somehow correctly brought to sites along the axon faster than conceivable rates of transport," notes Smith. The team suggests two possible mechanisms to explain this: increasing transport to a very fast rate or making the necessary proteins at the site, proximal to the growing axons. Smith believes that this form of growth commonly occurs in nature. "For example, it can be inferred that axons in a blue whale’s spine grow more than three centimeters a day and in a giraffe’s neck at two centimeters a day at peak growth."

The team also found that they had to condition the axons to grow in an extreme way. "Although they can handle enormous growth, you can’t just spring it on them," explains Bryan Pfister, PhD a post-doctoral fellow in Smith’s lab and coauthor of the study. "If we ramp up the stretch rate too fast, the axons will snap." From this the team surmises that in nature animals must grow at a metered pace, which allows for constant feedback and conditioning.

It has been well established that axons initially grow out from neurons and follow a chemical stimulus to connect with another neuron. However, once the axon has reached its target a relatively unknown form of stretch-growth must ensue as the animal grows. Mechanical changes in the growing brain, spine, and other bones are the starting point for natural stretch-growth in axons. "We know that it’s not tension on the neuron itself, but tension on the axon," says Smith. "It’s deformation, a pulling on the axon." At this point, it is unclear what receptors and cell signaling pathways are involved to get the process started, but from this and previous studies the investigators do report that the signal is from a mechanical stimulus along the length of the axon as opposed to a chemical stimulus. "The stretch is coming from the whole body growing," explains Smith. "For example, the growing spine bones in the whale likely exert mechanical forces on the axons in the spinal cord."

The researchers conclude that this is a genetic program for growth that has been conserved throughout animal species, but just hasn’t been studied in depth. By revealing the mechanisms of extreme-stretch growth, the team is currently applying this knowledge to develop nerve constructs to repair nerve and spinal cord damage. "To find that tension is actually good for your nerves for both growth and repair may not be such a long stretch," says Smith.

Karen Kreeger | EurekAlert!
Further information:
http://www.upenn.edu

More articles from Health and Medicine:

nachricht Satellites, airport visibility readings shed light on troops' exposure to air pollution
09.12.2016 | Veterans Affairs Research Communications

nachricht Oxygen can wake up dormant bacteria for antibiotic attacks
08.12.2016 | Penn State

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>