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29 Nov 2002
Experiments suggest that laser light can be used to guide neurons and repair broken links in the nervous system.
A focused spot of infrared laser light can influence the growth of nerve cells, according to a US-German research team. The finding suggests that optical techniques may one day be able to perform in-vivo repair of the nervous system.
Scientists from the University of Texas at Austin and the University of Leipzig illuminated the leading edge of mouse and rat neurons with a low-power beam from a Ti:sapphire laser. In 35 out of 44 experiments, they found that this enhanced neuron growth towards the focus of the beam. In 17 out of 20 tests, steering the beam caused the growing neuron to make guided turns.
"We can use weak optical forces to guide the direction taken by the leading edge, or growth cone, of a nerve cell," report the authors in the December 10 issue of the Proceedings of the National Academy of Sciences. "Our laser beam asymmetrically positioned to the left or the right of the leading edge of a growth cone clearly affects advancing nerves."
The cells were placed on a glass slide and illuminated with 800 nm light guided by a confocal scanning microscope. The beam power was varied between 20 and 120 mW, while the focused spot size was between 2 and 16 microns. The cell was illuminated by approximately one quarter to one half of the beam, with the remainder positioned ahead of the cell's leading edge.
The researchers admit that they do not fully understand the molecular mechanism behind the guidance effects. They speculate that it is likely to involve some kind of interaction between the optical force and proteins in the cell cytoplasm.
However, they are convinced that any heating effects caused by absorption of the laser beam do not play an important role in the observed behaviour. They say that the low power of the beam only induces a maximum temperature rise of a few degrees, while it is known that the rate of nerve cell growth is relatively insensitive to small changes in temperature.
Author
Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.
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