USING a weak laser beam to guide nerve cells could help build artificial neural networks. These could be used for testing drugs to combat brain diseases such as Alzheimer鈥檚 and Parkinson鈥檚.
The technique also brings the prospect of regrowing damaged nerves a step closer. It could allow surgeons to reconnect nerve fibres damaged in an accident or even to reconstruct whole networks.
Regenerating nerves in patients with a severed spinal cord, for example, is fraught with difficulties. Researchers have had some success using tubular scaffolds to guide nerve growth, but no one has restored movement in paralysed patients.
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Creating artificial nerve networks on chips also means guiding nerve growth. These 鈥渂rains-on-a-chip鈥� are useful for testing drugs (快猫短视频, 19 October, p 18) and understanding brain function. To nudge the cells in the right direction, researchers etch channels onto their 鈥渃ircuit boards鈥� or lay down traces of adhesive which the nerves follow. But these bully-boy tactics can damage the delicate cells. They tend to straighten and stiffen with time which can lead to ruptures at the bends.
Allen Ehrlicher and his team at the University of Leipzig in Germany favour a lighter approach instead. When they placed a nerve cell on a glass plate and shone a weak laser beam overlapping the cell鈥檚 edge, the nerves grew towards the light (Proceedings of the National Academy of Sciences, vol 99, p 16,024). By carefully steering the beam the group could persuade the neuron to grow in any direction they wanted. The cell would even make right-angle turns. 鈥淚t also dramatically enhanced the growth speed of the neurons,鈥� says Ehrlicher. The cells grew at 60 micrometres per hour 鈥� six times faster than normal, he says.
The approach resembles another device 鈥� known as optical tweezers 鈥� which moves cells around with much more powerful and focused lasers. But rather than manhandling the cells, Ehrlicher鈥檚 method manipulates the cells鈥� own growth processes, so it is far kinder. Even after a four-hour session under the laser, the cells were unharmed.
Quite why the cells are so obedient to their laser pointer is unclear, but Ehrlicher speculates that the laser鈥檚 electromagnetic field concentrates the molecular building blocks of the scaffold protein actin at the leading edge of the cell. As these join up to form a chain they create a bulge in the cell membrane which advances in the direction of the laser.
Eventually, the technique could help repair nerves close to the skin鈥檚 surface non-invasively. Combined with surgery, it might one day even tackle deeper nerve damage, such as to the spinal cord. But some neuroscientists are sceptical. Steve Potter, a brain expert at Caltech in Pasedena, says that regrowing nerves is 鈥渏ust science fiction鈥�.
For the moment, Ehrlicher thinks the technology will be of most help in building nerve networks for testing drugs. Such networks allow you to test more subtle drug effects than is possible with single cells.