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More MS news articles for December 2002

Laser leads nerve growth

Beam could help repair spine damage or wire up implants

27 November 2002
Philip Ball

A laser beam can guide nerve cells to grow in a particular direction, researchers have shown. The technique might help damaged nerves to regrow or could connect them to electronic implants, such as artificial retinas and prosthetic limbs.

Rat and mouse nerve cells growing over a glass plate take the path pointed out by a red laser, report Allen Ehrlicher, of the University of Leipzig in Germany, and colleagues1. The cells move towards the spot of laser light, travelling as if down a gentle slope, they think.

Moreover, the laser does not harm the cells, the researchers report, even if it leads them along a zigzag. Normally, cells don't like making sharp turns; forced to do so, they soon try to straighten out. Previous attempts to guide cells in channels or on adhesive tracks damaged their delicate walls.

To repair spinal-cord injuries, say, nerves on either side of a rupture must be guided to join up. Researchers have had some success, using tubular plastic channels, for example. But they haven't been able to make joins good enough to restore movement to paralysed patients. The new study hints that fibre optics might help the ends of damaged nerves to meet and merge.

Finger pointing

Nerve cells grow by extending a finger called a lamellipodium. Stiff filaments of the protein actin push the lamellipodium forwards. The filaments lengthen as new blobs of actin are added - this polymerization process prods the cell membrane like a pole pushing up the roof of a tent.

Lasers have been used to manipulate microscopic objects such as cells since the 1970s. Normally, focused laser beams are used like tweezers to trap an object and drag it.

One way to guide a nerve cell's growth would be to pinch the tip of its lamellipodium between optical tweezers and pull. But this approach could simply rip the cell. Ehrlicher's team use a laser beam too dim and unfocused to create a light trap.

They aim the spot so that it overlaps the tip of the lamellipodium. As they move the beam slowly, the cell's finger follows. They can thus alter the direction of nerve growth by angles of up to 90°. Laser guidance also makes the lamellipodium grow about five times faster than normal, the team reckons.

Ehrlicher and colleagues admit that they don't know why the laser has this effect. They suggest that light may marshal actin molecules, enhancing filament growth.

  1. Ehrlicher, A. et al. Guiding neuronal growth with light. Proceedings of the National Academy of Sciences USA, Publshed online, doi:10.1073/pnas/252631899, (2002).

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